Maintaining Cholesterol Homeostasis in Small Intestine for the Prevention of Atherosclerosis

doi:10.3881/j.issn.1000-503X.2018.01.016

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Acta Academiae Medicinae Sinicae ›› 2018, Vol. 40 ›› Issue (1) : 104-111. DOI: 10.3881/j.issn.1000-503X.2018.01.016

Review Articles

Maintaining Cholesterol Homeostasis in Small Intestine for the Prevention of Atherosclerosis

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Abstract

Cholesterol is an important lipid that significantly affects life. High blood cholesterol level can lead to the cholesterol deposition on the intima of large and middle arteries,and the formation of atherosclerotic plaques,which can trigger endothelial injury and lipid infiltration and finally induce atherosclerosis (AS). Up to now R&D of cholesterol-lowering drugs are mainly focused on the the function of liver in cholesterol synthesis. Notably,the small intestine is the major site of cholesterol metabolism and is involved in maintaining the homeostasis of cholesterol. Gut maintains the cholesterol homeostasis through a complex regulatory mechanism that involves different stages including cholesterol absorption,transformation,and excretion as well as lipoprotein synthesis. In this article we summarizes the research advances in the molecular regulation of cholesterol metabolism in small intestine and its relationship with AS,with an attempt to provide a new insight into the diagnosis and treatment of atherosclerotic disease.

Key words

small intestine / cholesterol / atherosclerosis / bile acid / lipoprotein synthesis

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Maintaining Cholesterol Homeostasis in Small Intestine for the Prevention of Atherosclerosis[J]. Acta Academiae Medicinae Sinicae. 2018, 40(1): 104-111 https://doi.org/10.3881/j.issn.1000-503X.2018.01.016

References

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The polytopic transmembrane protein, Niemann-Pick C1-Like 1 (NPC1L1), is enriched in the apical membrane of small intestine absorptive enterocytes where it mediates extracellular sterol transport across the brush border membrane. It is essential for intestinal sterol absorption and is the molecular target of ezetimibe, a potent cholesterol absorption inhibitor that lowers blood cholesterol in humans. NPC1L1 is also highly expressed in human liver. The hepatic function of NPC1L1 may be to limit excessive biliary cholesterol loss. NPC1L1-dependent sterol uptake seems to be a clathrin-mediated endocytic process and is regulated by cellular cholesterol content. Recently, NPC1L1 inhibition has been shown to have beneficial effects on components of the metabolic syndrome, such as obesity, insulin resistance, and fatty liver, in addition to atherosclerosis.

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Abstract Dietary cholesterol consumption and intestinal cholesterol absorption contribute to plasma cholesterol levels, a risk factor for coronary heart disease. The molecular mechanism of sterol uptake from the lumen of the small intestine is poorly defined. We show that Niemann-Pick C1 Like 1(NPC1L1) protein plays a critical role in the absorption of intestinal cholesterol. NPC1L1 expression is enriched in the small intestine and is in the brush border membrane of enterocytes. Although otherwise phenotypically normal, NPC1L1-deficient mice exhibit a substantial reduction in absorbed cholesterol, which is unaffected by dietary supplementation of bile acids. Ezetimibe, a drug that inhibits cholesterol absorption, had no effect in NPC1L1 knockout mice, suggesting that NPC1L1 resides in an ezetimibe-sensitive pathway responsible for intestinal cholesterol absorption.

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78 NPC1L1 mediates cholesterol absorption in small intestine and liver. 78 NPC1L1 recycles between PM and ERC in response to cholesterol levels. 78 The N-terminal domain of NPC1L1 binds cholesterol not phytosterols. 78 NPC1L1 and flotillins form cholesterol enriched membrane microdomains. 78 Cholesterol is taken up by the endocytosis of these membrane microdomains.

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Increased blood cholesterol is an independent risk factor for atherosclerotic cardiovascular disease. Cholesterol homeostasis in the body is controlled mainly by endogenous synthesis, intestinal absorption, and hepatic excretion. Niemann-Pick C1-Like 1 (NPC1L1) is a polytopic transmembrane protein localized at the apical membrane of enterocytes and the canalicular membrane of hepatocytes. It functions as a sterol transporter to mediate intestinal cholesterol absorption and counter-balances hepatobiliary cholesterol excretion. NPC1L1 is the molecular target of ezetimibe, a potent cholesterol absorption inhibitor that is widely used in treating hypercholesterolemia. Recent findings suggest that NPC1L1 deficiency or ezetimibe treatment also prevents diet-induced hepatic steatosis and obesity in addition to reducing blood cholesterol. Future studies should focus on molecular mechanisms underlying NPC1L1-dependent cholesterol transport and elucidation of how a cholesterol transporter modulates the pathogenesis of metabolic diseases.

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Niemann–Pick C1-like 1 (NPC1L1), ATP-binding cassette (ABC)G5, and ABCG8 are all involved in intestinal cholesterol absorption. It is unclear whether a high-cholesterol (HC) diet affects the expression of these transporters in rats and mice as well as humans. We examined the effects of an HC diet on their expression in small intestine and the differences between rats and mice in the responsive of this expression to an HC diet. In addition to these transporters, alterations in six representative drug and nutrient transporters (multidrug resistance-associated protein, breast cancer resistance protein, peptide transporter, sodium-glucose linked transporter, glucose transporter, and l -type amino acid transporter) and transcriptional factors such as hepatocyte nuclear factor (HNF)4α, sterol regulatory element-binding protein (SREBP)2, and liver X receptor (LXR)α were determined. In rats and mice fed an HC diet for 702days, the mRNA and protein levels of NPC1L1 in the small intestine were determined by real-time reverse transcription polymerase chain reaction and western blotting, respectively. The mRNA levels of ABCG5 and ABCG8, six representative transporters, and transcriptional factors such as HNF4α, SREBP2, and LXR were examined. Significant decreases in the expression levels of NPC1L1 were observed in mice, but not rats, fed the HC diet. The mRNA levels of ABCG5 and ABCG8 were significantly increased in HC rats but not in mice. Only minor changes in the mRNA levels of the other transporters were seen in HC rats and mice. Decreased mRNA levels of HNF4α and SREBP2 in mice could be involved in the reduction in NPC1L1 expression observed upon the introduction of an HC diet. These results indicate that the effects of an HC diet on the expression levels of NPC1L1, ABCG5, and ABCG8 differ between mice and rats.

https://doi.org/10.1007/s13318-015-0269-2

https://www.ncbi.nlm.nih.gov/pubmed/25716431

http://link.springer.com/article/10.1007/s13318-015-0269-2

Cited in this article [1]

[7]

Xie

,Li

,Chen

,et al.The small GTPase Cdc42 interacts with Niemann-Pick C1-like 1 (NPC1L1) and controls its movement from endocytic recycling compartment to plasma membrane in a cholesterol-dependent manner[J]. J Biol Chem,2011,286(41):35933-35942. DOI:10.1074/jbc.M111.270199.

Niemann-Pick C1-like 1 (NPC1L1) is a multi-transmembrane protein that mediates the absorption of dietary and biliary cholesterol through vesicular endocytosis. The subcellular localization of NPC1L1 is regulated by cholesterol. Cholesterol depletion induces the transport of NPC1L1 to plasma membrane (PM) from endocytic recycling compartment that requires MyoVb路Rab11a路Rab11-FIP2 triple complex, and cholesterol-replenishment renders the internalization of NPC1L1 together with cholesterol. Here, we find that GTP-bound Cdc42 interacts with NPC1L1. Cholesterol depletion regulates the activation of Cdc42 and enhances NPC1L1-Cdc42 interaction. Overexpression of constitutive GTP-bound Cdc42 mutant form or knockdown of Cdc42 inhibits the transport of NPC1L1 to the PM and disturbs the cholesterol-regulated binding of NPC1L1 to Rab11a, MyoVb, and actin. Knockdown of Cdc42 downstream effectors N-WASP or Arp3 also leads to the similar results. In liver-specific Cdc42 knock-out (Cdc42 LKO) mice, NPC1L1 fails to localize to bile canaliculi, and the biliary cholesterol cannot be efficiently reabsorbed. These results indicate that Cdc42 controls the cholesterol-regulated transport and localization of NPC1L1, and plays a role in cholesterol absorption.

https://doi.org/10.1074/jbc.M111.270199

https://www.ncbi.nlm.nih.gov/pubmed/21844200

http://www.jbc.org/lookup/doi/10.1074/jbc.M111.270199

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This is the first detailed analysis of the role of NPC1L1 mutations in an exceptional responder to ezetimibe. The results point to a complex set of events in which the combined mutations were shown to affect cholesterol uptake in the presence of ezetimibe. Proteomic analysis suggests that the exceptional response may also lie in the nature of interactions with cytosolic proteins.

https://doi.org/10.1016/j.atherosclerosis.2015.12.032

https://www.ncbi.nlm.nih.gov/pubmed/26761771

http://linkinghub.elsevier.com/retrieve/pii/S0021915015302616

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,Hata

,Takagi

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Purpose. Niemann-Pick C1-like 1 (NPC1L1), ATP-binding cassette (ABC)G5, and ABCG8 mediate intestinal cholesterol absorption. It is unclear whether pravastatin (PR) or ezetimibe (EZ) affect expression of these transporters. We examined the effects of PR and EZ on NPC1L1, ABCG5, and ABCG8 expression in human hepatoma HepG2 cells and the murine small intestine. We also assessed expression of the transcription factors liver X receptor (LXR)a, LXRb and sterol regulatory element-binding protein. Methods. Transporter mRNA levels were determined in murine small intestines 6 and 24 h after oral PR and EZ administration by real-time reverse-transcriptase polymerase chain reaction (RT-PCR). In PR- and EZ-treated HepG2 cells, transporter and transcription factor mRNA and protein levels were examined by RT-PCR and western blot, respectively. Results. Significant decreases in NPC1L1 , ABCG5 , and ABCG8 mRNA expression were observed in the duodenum, but not jejunum and ileum, of mice 24 h after treatment with PR, but not EZ. In HepG2 cells, PR but not EZ treatment for 24 h also significantly decreased NPC1L1 protein and ABCG5 , and ABCG8 mRNA expression, while increasing LXR a 02mRNA levels. Conclusion. PR but not EZ treatment reduced duodenal cholesterol transporter expression in mice. PR-induced increases in LXR a 02mRNA levels may be involved in attenuation of NPC1L1 expression, subsequently decreasing intestinal cholesterol absorption. 02 This article is open to POST-PUBLICATION REVIEW . Registered readers (see “For Readers”) may comment by clicking on ABSTRACT on the issue’s contents page.

https://doi.org/10.18433/J3M029

https://www.ncbi.nlm.nih.gov/pubmed/26670369

https://journals.library.ualberta.ca/jpps/index.php/JPPS/article/view/24989

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[10]

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,Zhou

,Li

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正The multiple transmembrane protein Niemann-Pick C1 like1(NPC1L1) is essential for intestinal cholesterol absorption.Ezetimibe binds to NPC1L1 and is a clinically used cholesterol absorption inhibitor.Recent studies in cultured cells have shown that NPC1L1 mediates cholesterol uptake through vesicular endocytosis that can be blocked by ezctimibe. However,how NPC1L1 and ezetimibe work in small intestine is unknown.In this study,we

https://doi.org/10.1194/jlr.M027359

https://www.ncbi.nlm.nih.gov/pubmed/22811412

http://www.jlr.org/lookup/doi/10.1194/jlr.M027359

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[11]

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,Pfeffer

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NPC1L1 mediates dietary cholesterol uptake and is the target of the drug ezetimibe. Others have concluded that cholesterol uptake requires sterol-dependent internalization. The present work shows that endocytosis is not required for NPC1L1 function and the drug does not alter endocytosis. Thus NPC1L1 may deliver cholesterol directly into the bilayer. Human NPC1L1 protein mediates cholesterol absorption in the intestine and liver and is the target of the drug ezetimibe, which is used to treat hypercholesterolemia. Previous studies concluded that NPC1L1-GFP protein trafficking is regulated by cholesterol binding and that ezetimibe blocks NPC1L1-GFP function by inhibiting its endocytosis. We used cell surface biotinylation to monitor NPC1L1-GFP endocytosis and show that ezetimibe does not alter the rate of NPC1L1-GFP endocytosis in cultured rat hepatocytes grown under normal growth conditions. As expected, NPC1L1-GFP endocytosis depends in part on C-terminal, cytoplasmically oriented sequences, but endocytosis does not require cholesterol binding to NPC1L1鈥檚 N-terminal domain. In addition, two small- molecule inhibitors of general (and NPC1L1-GFP) endocytosis failed to inhibit the ezetimibe-sensitive uptake of [3H]cholesterol from taurocholate micelles. These experiments demonstrate that cholesterol uptake by NPC1L1 does not require endocytosis; moreover, ezetimibe interferes with NPC1L1鈥檚 cholesterol adsorption activity without blocking NPC1L1 internalization in RH7777 cells.

https://doi.org/10.1091/mbc.E16-03-0154

https://www.ncbi.nlm.nih.gov/pubmed/27075173

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[12]

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,Zhang

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Hypercholesterolemia, typically due to excessive cholesterol uptake, is a major risk factor for cardiovascular disease, which is responsible for 鈭50% of all deaths in developed societies. Although it has been shown that intestinal cholesterol absorption is mediated by vesicular endocytosis of the Niemann-Pick C1-like 1 (NPC1L1) protein, the mechanism of sterol-stimulated NPC1L1 internalization is still mysterious. Here, we identified an endocytic peptide signal, YVNXXF (where X stands for any amino acid), in the cytoplasmic C-terminal tail of NPC1L1. Cholesterol binding on the N-terminal domain of NPC1L1 released the YVNXXF-containing region of NPC1L1 from association with the plasma membrane and enabled Numb binding. We also found that Numb, a clathrin adaptor, specifically recognized this motif and recruited clathrin for internalization. Disrupting the NPC1L1-Numb interaction decreased cholesterol uptake. Ablation of Numb in mouse intestine significantly reduced dietary cholesterol absorption and plasma cholesterol level. Together, these data show that Numb is a pivotal protein for intestinal cholesterol absorption and may provide a therapeutic target for hypercholesterolemia.

https://doi.org/10.1038/nm.3417

https://www.ncbi.nlm.nih.gov/pubmed/24336247

http://www.nature.com/articles/nm.3417

Cited in this article [1]

[13]

Wei

,Fu

,Li

,et al.The clathrin adaptor proteins ARH,Dab2,and numb play distinct roles in Niemann-Pick C1-like 1 versus low density lipoprotein receptor-mediated cholesterol uptake[J]. J Biol Chem,2014,289(48):33689-33700. DOI:10.1074/jbc.M114.593764.

The uptake of circulating low density lipoproteins (LDL) is mediated by LDL receptor (LDLR) through clathrin-dependent endocytosis. At the early stage of this process, adaptor proteins ARH and Dab2 specifically bind the endocytic signal motif in LDLR and recruit clathrin/AP2 to initiate internalization. On the other hand, intestinal cholesterol is absorbed by Niemann-Pick C1-Like 1 (NPC1L1) through clathrin-dependent endocytosis. Another adaptor protein, Numb recognizes the endocytic motif in NPC1L1 C terminus and couples NPC1L1 to endocytic machinery. The ARH, Dab2, and Numb proteins contain a homogeneous phosphotyrosine binding (PTB) domain that directly binds endocytic motifs. Because ARH, Dab2, and Numb are all PTB domain family members, the emerging mystery is whether these adaptors act complementally in LDLR and NPC1L1 endocytosis. Here, we found that ARH and Dab2 did not bind NPC1L1 and were not required for NPC1L1 internalization. Similarly, Numb lacked the ability to interact with the LDLR C terminus and was dispensable for LDL uptake. Only the Numb isoforms with shorter PTB domain could facilitate NPC1L1 endocytosis. Besides the reported function in intestinal cholesterol absorption, Numb also mediated cholesterol reabsorption from bile in liver. We further identified a Numb variant with G595D substitution in humans of low blood LDL-cholesterol. The G595D substitution impaired NPC1L1 internalization and cholesterol reabsorption, due to attenuating affinity of Numb to clathrin/AP2. These results demonstrate that Numb specifically regulates NPC1L1-mediated cholesterol absorption both in human intestine and liver, distinct from ARH and Dab2, which selectively participate in LDLR-mediated LDL uptake.

https://doi.org/10.1074/jbc.M114.593764

https://www.ncbi.nlm.nih.gov/pubmed/25331956

http://www.jbc.org/lookup/doi/10.1074/jbc.M114.593764

Cited in this article [1]

[14]

Parikh

,Patel

,Soni

,et al.Liver X receptor:a cardinal target for atherosclerosis and beyond[J]. J Atheroscler Thromb,2014,21(6):519-531.

Abstract The nuclear receptor liver X receptor [LXR] is activated by endogenous oxidized derivatives of cholesterol. It constitutes a critical receptor in the regulation of various physiological functions related to the development of metabolic and cardiovascular diseases, such as atherosclerosis and diabetes, as well as various other disorders. Both isoforms of LXR, LXR伪 [NR1H3] and LXR尾 [NR1H2], form heterodimers with the isoforms of the retinoid X receptor [RXR], which then regulate the gene expression by binding to DNA sequences associated with target genes. LXR acts as a cholesterol sensor in response to an increased concentration of cholesterol in cells and induces the transcription of genes that protect cells from cholesterol overload. LXRs play numerous roles in controlling cholesterol homeostasis via their actions on bile acid synthesis and metabolism/excretion, reverse cholesterol transport and cholesterol absorption/excretion in the intestines. Therefore, these receptors show great potential as pharmacological targets for anti-atherosclerotic activities. Recent discoveries have also emphasized the important involvement of LXRs in the pathogenesis of diabetes, Alzheimer's disease, inflammation, adrenal steroid synthesis, skin aging and male fertility. However, LXR activation has also been shown to stimulate lipogenesis via sterol regulatory element binding protein-1c, leading to liver steatosis and hypertriglyceridemia. This review summarizes recent scientific discoveries and the biological actions of LXR with a special focus on the involvement of this type of receptor in important diseases and conditions.

https://doi.org/10.5551/jat.19778

https://www.ncbi.nlm.nih.gov/pubmed/24695022

http://www.ncbi.nlm.nih.gov/pubmed/24695022

Cited in this article [1]

[15]

Zambrano

,Saavedra

,Lanas

,et al.Efficacy of ezetimibe is not related to NPC1L1 gene polymorphisms in a pilot study of Chilean hypercholesterolemic subjects[J]. Mol Diagn Ther,2015,19(1):45-52. DOI:10.1007/s40291-014-0128-x.

Background and Objective Niemann- Pick C1 Like 1 (NPC1L1) is a multi-transmembrane transport protein highly expressed in the small intestine. It mediates sterol transfer throughout the brush border membrane of enterocytes, becoming essential for intestinal cholesterol absorption and ensuing whole-body cholesterol homeostasis. This protein is targeted by ezetimibe, a potent cholesterol absorption inhibitor. Single nucleotide polymorphisms ( SNPs ) in NPC1L1 have been associated to variation in both plasma low-density lipoprotein (LDL) cholesterol levels and lipid-lowering medication with ezetimibe. However, there are no data evaluating the impact of NPC1L1 variants on Chilean subjects medicated with ezetimibe monotherapy. Therefore, we assessed the contribution of two unexplored NPC1L1 variants on plasma lipids and response to ezetimibe in Chilean hypercholesterolemic individuals. Methods Using PCR-restriction fragment length polymorphism ( RFLP ), we analyzed the SNP distribution of two common variants; 61133A>G (rs17655652) and 1679C>G (rs2072183), and their relation with plasma lipids and lipid-lowering response to ezetimibe in 60 hypercholesterolemic Chilean subjects. Results Genotype distribution for the rs17655652 variant was AA 5702%, 4002% AG and 302% GG, whereas for the rs2072183 SNP was 5702% CC, 3502% CG and 802% GG. Minor allele frequencies (MAFs) were 0.23 and 0.26, respectively. No association was observed between NPC1L1 SNPs and baseline cholesterol. After therapy, none of the polymorphisms affected ezetimibe response in the studied cohort ( P 02>020.05). Conclusion Data obtained indicates that polymorphisms rs17655652 and rs2072183 were not related to cholesterol variability. Also, lipid-lowering response to ezetimibe is not impacted by the NPC1L1 polymorphisms studied in Chilean hypercholesterolemic subjects.

https://doi.org/10.1007/s40291-014-0128-x

https://www.ncbi.nlm.nih.gov/pubmed/2558933911

http://link.springer.com/10.1007/s40291-014-0128-x

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[16]

Sui

,Helsley

,Park

,et al.Intestinal pregnane X receptor links xenobiotic exposure and hypercholesterolemia[J]. Mol Endocrinol,2015,29(5):765-776. DOI:10.1210/me.2014-1355.

Recent studies have associated endocrine-disrupting chemical (EDC) exposure with the increased risk of cardiovascular disease in humans, but the underlying mechanisms responsible for these associations remain elusive. Many EDCs have been implicated in activation of the nuclear receptor pregnane X receptor (PXR), which acts as a xenobiotic sensor to regulate xenobiotic metabolism in the liver and intestine. Here we report an important role of intestinal PXR in linking xenobiotic exposure and hyperlipidemia. We identified tributyl citrate (TBC), one of a large group of Food and Drug Administration-approved plasticizers for pharmaceutical or food applications, as a potent and selective PXR agonist. TBC efficiently activated PXR and induced PXR target gene expression in vitro and in vivo. Interestingly, TBC activated intestinal PXR but did not affect hepatic PXR activity. Exposure to TBC increased plasma total cholesterol and atherogenic low-density lipoprotein cholesterol levels in wild-type mice, but not in PXR-deficient mice. TBC-mediated PXR activation stimulated the expression of an essential cholesterol transporter, Niemann-Pick C1-like 1 (NPC1L1), in the intestine. Promoter analysis revealed a DR-4 type of PXR response element in the human NPC1L1 promoter, and TBC promoted PXR recruitment onto the NPC1L1 promoter. Consistently, TBC treatment significantly increased lipid uptake by human and murine intestinal cells and deficiency of PXR inhibited TBC-elicited lipid uptake. These findings provide critical mechanistic insight for understanding the impact of EDC-mediated PXR activation on lipid homeostasis and demonstrate a potential role of PXR in mediating the adverse effects of EDCs on cardiovascular disease risk in humans.

https://doi.org/10.1210/me.2014-1355

https://www.ncbi.nlm.nih.gov/pubmed/25811240

https://academic.oup.com/mend/article-lookup/doi/10.1210/me.2014-1355

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[17]

Lee

,Kinch

,Borek

,et al.Crystal structure of the human sterol transporter ABCG5/ABCG8[J]. Nature,2016,533(7604):561-564. DOI:10.1038/nature17666.

Abstract ATP binding cassette (ABC) transporters play critical roles in maintaining sterol balance in higher eukaryotes. The ABCG5/ABCG8 heterodimer (G5G8) mediates excretion of neutral sterols in liver and intestines. Mutations disrupting G5G8 cause sitosterolaemia, a disorder characterized by sterol accumulation and premature atherosclerosis. Here we use crystallization in lipid bilayers to determine the X-ray structure of human G5G8 in a nucleotide-free state at 3.90900090105 resolution, generating the first atomic model of an ABC sterol transporter. The structure reveals a new transmembrane fold that is present in a large and functionally diverse superfamily of ABC transporters. The transmembrane domains are coupled to the nucleotide-binding sites by networks of interactions that differ between the active and inactive ATPases, reflecting the catalytic asymmetry of the transporter. The G5G8 structure provides a mechanistic framework for understanding sterol transport and the disruptive effects of mutations causing sitosterolaemia.

https://doi.org/10.1038/nature17666

https://www.ncbi.nlm.nih.gov/pubmed/27144356

http://www.nature.com/articles/nature17666

Cited in this article [1]

[18]

Wang

,Mitsche

,Lutjohann

,et al.Relative roles of ABCG5/ABCG8 in liver and intestine[J]. J Lipid Res,2015,56(2):319-330. DOI:10.1194/jlr.M054544.

ABCG5 (G5) and ABCG8 (G8) form a sterol transporter that acts in liver and intestine to prevent accumulation of dietary sterols. Mutations in either G5 or G8 cause sitosterolemia, a recessive disorder characterized by sterol accumulation and premature coronary atherosclerosis. Hepatic G5G8 mediates cholesterol excretion into bile, but the function and relative importance of intestinal G5G8 has not been defined. To determine the role of intestinal G5G8, we developed liver-specific (L-G5G8(-/-)), intestine-specific (I-G5G8(-/-)), and total (G5G8(-/-)) KO mice. Tissue levels of sitosterol, the most abundant plant sterol, were >90-fold higher in G5G8(-/-) mice than in WT animals. Expression of G5G8 only in intestine or only in liver decreased tissue sterol levels by 90% when compared with G5G8(-/-) animals. Biliary sterol secretion was reduced in L-G5G8(-/-) and G5G8(-/-) mice, but not in I-G5G8(-/-) mice. Conversely, absorption of plant sterols was increased in I-G5G8(-/-) and G5G8(-/-) mice, but not in L-G5G8(-/-) mice. Reverse cholesterol transport, as assessed from the fraction of intravenously administered (3)H-cholesterol that appeared in feces, was reduced in G5G8(-/-), I-G5G8(-/-), and L-G5G8(-/-) mice. Thus, G5G8 expression in both the liver and intestine protects animals from sterol accumulation, and intestinal G5G8 contributes to extrahepatic cholesterol efflux in mice.

https://doi.org/10.1194/jlr.M054544

https://www.ncbi.nlm.nih.gov/pubmed/4306686

http://www.jlr.org/lookup/doi/10.1194/jlr.M054544

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[19]

Mendez-Gonzalez

,Julve

,Rotllan

,et al.ATP-binding cassette G5/G8 deficiency causes hypertriglyceridemia by affecting multiple metabolic pathways[J]. Biochim Biophys Acta,2011,1811(12):1186-1193. DOI:10.1016/j.bbalip.2011.07.019.

Mutations in ABCG5 or ABCG8 transporters are responsible for sitosterolemia, an autosomal recessive disease characterized by the accumulation of plant sterols. The aim of this study was to investigate the effects of ABCG5 and ABCG8 deficiency on TG metabolism in mice. Experiments were carried out in wild-type (G5/G8+/+) mice, mice heterozygous for ABCG5 and ABCG8 deficiency (G5/G8+/-) and ABCG5/G8-deficient (G5/G8-/-) mice fed a chow diet. Plasma TG were 2.6 and 4.3-fold higher in fasted G5/G8+/- and G5/G8-/- mice, respectively, than in G5/G8+/+ mice. Postprandial TG were 5-fold higher in G5/G8-/- mice. TG metabolism studies indicate that: first, the fractional catabolic rate was significantly lower in G5/G8+/- (1.3-fold) and G5/G8-/- mice (1.5-fold) compared to G5/G8+/+ and postheparin plasma lipoprotein lipase activities were significantly lower in G5/G8+/- (1.8-fold) and G5/G8-/- mice (5.4-fold) than in G5/G8+/+. Second, liver TG secretion was 1.3-fold higher in G5/G8+/- and G5/G8-/- than in G5/G8+/+ mice and this was associated with an increase in liver LXR, FAS, ACAC and CD36 gene expression. Third, TG intestinal secretion, determined after an oral fat gavage of glycerol tri[9,10(n)-(3)H] oleate, was 5.8-fold higher in G5/G8-/- than in G5/G8+/+ mice. Also, the HOMA index was 2.6-fold higher in G5/G8-/- than in G5/G8+/+ mice, reflecting a degree of insulin resistance. In conclusion, ABCG5/G8 deficiency in mice fed a chow diet markedly raises TG levels by impairing TG catabolism and by increasing liver and intestinal TG secretion.

https://doi.org/10.1016/j.bbalip.2011.07.019

https://www.ncbi.nlm.nih.gov/pubmed/21855652

http://linkinghub.elsevier.com/retrieve/pii/S1388198111001442

Cited in this article [1]

[20]

Zhang

,Xu

,Yang

,et al.ABCG5/G8 deficiency in mice reduces dietary triacylglycerol and cholesterol transport into the lymph[J]. Lipids,2015,50(4):371-379. DOI:10.1007/s11745-015-3995-y.

The adenosine triphosphate-binding cassette (ABC) transporter G5/G8 is critical in protecting the body from accumulating dietary plant sterols. Expressed in the liver and small intestine, it transports plant sterols into the biliary and intestinal lumens, thus promoting their excretion. The extent to which G5/G8 regulates cholesterol absorption remains unclear. G5/G8 is also implicated in reducing the absorption of dietary triacylglycerols (TAG) by unknown mechanisms. We hypothesized that G5/G8 suppresses the production of chylomicrons, and its deficiency would enhance the absorption of both dietary TAG and cholesterol. The aim of this study was to investigate the effects of G5/G8 deficiency on lipid uptake and secretion into the lymph under steady-state conditions. Surprisingly, compared with wild-type mice (WT) (n02=029), G5/G8 KO (n02=0213) lymph fistula mice given a continuous intraduodenal infusion of [3H]-TAG and [14C]-cholesterol showed a significant (P02<020.05) reduction in lymphatic transport of both [(3)H]-TAG and [(14)C]-cholesterol, concomitant with a significant (P02<020.05) increase of [(3)H]-TAG and [(14)C]-cholesterol accumulated in the intestinal lumen. There was no difference in the total amount of radiolabeled lipids retained in the intestinal mucosa between the two groups. G5/G8 KO mice given a bolus of TAG showed reduced intestinal TAG secretion compared with WT, suggesting an independent role for G5/G8 in facilitating intestinal TAG transport. Our data demonstrate that G5/G8 deficiency reduces the uptake and secretion of both dietary TAG and cholesterol by the intestine, suggesting a novel role for the sterol transporter in the formation and secretion of chylomicrons.

https://doi.org/10.1007/s11745-015-3995-y

https://www.ncbi.nlm.nih.gov/pubmed/25676339

http://doi.wiley.com/10.1007/s11745-015-3995-y

Cited in this article [1]

[21]

Dikkers

,De Boer

,Groen

,et al.Hepatic ABCG5/G8 overexpression substantially increases biliary cholesterol secretion but does not impact in vivo macrophage-to-feces RCT[J]. Atherosclerosis,2015,243(2):402-406. DOI:10.1016/j.aherosclerosis.2015.10.010.

Biliary cholesterol secretion is important for reverse cholesterol transport (RCT). ABCG5/G8 contribute most cholesterol mass secretion into bile. We investigated the impact of hepatic ABCG5/G8 on cholesterol metabolism and RCT.Biliary and fecal sterol excretion (FSE) as well as RCT were determined using wild-type controls, Abcg8 knockout mice, Abcg8 knockouts with adenovirus-mediated hepatocyte-specific Abcg8 reinstitution and hepatic Abcg5/g8 overexpression in wild-types.In Abcg8 knockouts, biliary cholesterol secretion was decreased by 75% (p<0.001), while mass FSE and RCT were unchanged. Hepatic reinstitution of Abcg8 increased biliary cholesterol secretion 5-fold (p<0.001) without changing FSE or overall RCT. Overexpression of both ABCG5/G8 elevated biliary cholesterol secretion 5-fold and doubled FSE (p<0.001) without affecting overall RCT.ABCG5/G8 mediate mass biliary cholesterol secretion but not from a RCT-relevant pool. Intervention strategies aiming at increasing hepatic Abcg5/g8 expression for enhancing RCT are not likely to be successful.

https://doi.org/10.1016/j.atherosclerosis.2015.10.010

https://www.ncbi.nlm.nih.gov/pubmed/26520893

http://linkinghub.elsevier.com/retrieve/pii/S002191501530157X

Cited in this article [1]

[22]

Altemus

,Patel

,Sehayek

.Liver-specific induction of Abcg5 and Abcg8 stimulates reverse cholesterol transport in response to ezetimibe treatment[J]. Metabolism,2014,63(10):1334-1341. DOI:10.1016/j.metabol.2014.06.014.

Previous studies have shown ezetimibe treatment results in a 2-6-fold increase in reverse cholesterol transport (RCT). However, recent sterol balance studies question the role of biliary sterol secretion in RCT, and challenge the hypothesis that ezetimibe increases RCT through decreased absorption of biliary cholesterol in the intestine. We set out to determine whether ezetimibe may increase RCT by mechanisms that are independent of its well-established inhibition of intestinal cholesterol absorption.C57BL/6J, Npc1l1-KO, and/or Abcg8-KO mice were fed a chow diet with or without ezetimibe and fecal [(14)C]-neutral and [(14)C]-acidic sterols were measured to examine macrophage-to-feces RCT. We measured the expression of RCT related genes in the liver and jejunum in these mice. To confirm our significant gene expression findings, we utilized primary human hepatocytes cultured with or without a glucuronated metabolite of ezetimibe.Our studies revealed that treatment with ezetimibe was associated with increased expression of hepatic Abcg5 and Abcg8. Ezetimibe did not directly affect expression in the liver, but this expression was due to the inhibition of intestinal cholesterol absorption. This conclusion was supported by the absence of an ABCG5/ABCG8 expression response to treatment with an ezetimibe metabolite in primary human hepatocytes. Finally, we found that the ezetimibe-dependent stimulation of RCT was attenuated in the absence of Abcg8.Our study is the first to demonstrate ezetimibe treatment cooperatively stimulated macrophage-to-feces RCT by indirectly increasing liver Abcg5/Abcg8 expression in addition to its known suppression of intestinal cholesterol absorption.

https://doi.org/10.1016/j.metabol.2014.06.014

https://www.ncbi.nlm.nih.gov/pubmed/25060694

http://linkinghub.elsevier.com/retrieve/pii/S0026049514001814

Cited in this article [1]

[23]

,Li-Hawkins

,Hammer

,et al.Overexpression of ABCG5 and ABCG8 promotes biliary cholesterol secretion and reduces fractional absorption of dietary cholesterol[J]. J Clin Invest,2002,110(5):671-680. DOI:10.1172/jci16001.

Abstract Two ATP-binding cassette (ABC) transporters, ABCG5 and ABCG8, have been proposed to limit sterol absorption and to promote biliary sterol excretion in humans. To test this hypothesis, a P1 clone containing the human ABCG5 and ABCG8 genes was used to generate transgenic mice. The transgenes were expressed primarily in the liver and small intestine, mirroring the expression pattern of the endogenous genes. Transgene expression only modestly affected plasma and liver cholesterol levels but profoundly altered cholesterol transport. The fractional absorption of dietary cholesterol was reduced by about 50%, and biliary cholesterol levels were increased more than fivefold. Fecal neutral sterol excretion was increased three- to sixfold and hepatic cholesterol synthesis increased two- to fourfold in the transgenic mice. No significant changes in the pool size, composition, and fecal excretion of bile acids were observed in the transgenic mice. Transgene expression attenuated the increase in hepatic cholesterol content induced by consumption of a high cholesterol diet. These results demonstrate that increased expression of ABCG5 and ABCG8 selectively drives biliary neutral sterol secretion and reduces intestinal cholesterol absorption, leading to a selective increase in neutral sterol excretion and a compensatory increase in cholesterol synthesis.

https://doi.org/10.1172/JCI16001

https://www.ncbi.nlm.nih.gov/pubmed/151111

http://www.jci.org/articles/view/16001

Cited in this article [1]

[24]

Wang

,Li

,Patel

,et al.Evidence that the adenosine triphosphate-binding cassette G5/G8-independent pathway plays a determinant role in cholesterol gallstone formation in mice[J]. Hepatology,2016,64(3):853-864. DOI:10.1002/hep.28570.

Abstract The ATP-binding cassette sterol transporter Abcg5/g8 is Lith9 in mice and two gallstone-associated variants in ABCG5/G8 have been identified in humans. Although ABCG5/G8 plays a critical role in determining hepatic sterol secretion, cholesterol is still secreted to bile in sitosterolemic patients with a defect in either ABCG5 or ABCG8 and in either Abcg5/g8 double or single knockout mice. We hypothesize that in the defect of ABCG5/G8, an ABCG5/G8-independent pathway is essential for regulating hepatic secretion of biliary sterols, which is independent of the lithogenic mechanism of the ABCG5/G8 pathway. To elucidate the effect of the ABCG5/G8-independent pathway on cholelithogenesis, we investigated the biliary and gallstone characteristics in male wild-type, ABCG5(-/-)/G8(-/-), and ABCG8 (-/-) mice fed a lithogenic diet or varying amounts of cholesterol, treated with an LXR agonist, or injected intravenously with [(3) H]sitostanol- and [(14) C]cholesterol-labeled HDL. We found that ABCG5(-/-)/G8(-/-) and ABCG8 (-/-) mice displayed the same biliary and gallstone phenotypes. Although both groups of knockout mice showed a significant reduction in hepatic cholesterol output compared to wild-type mice, they still formed gallstones. The LXR agonist significantly increased biliary cholesterol secretion and gallstones in wild-type, but not ABCG5(-/-)/G8(-/-) or ABCG8 (-/-) mice. The 6-hour recovery of [(14) C]cholesterol in hepatic bile was significantly lower in both groups of knockout mice than in wild-type mice and [(3) H]sitostanol was detected in wild-type, but not ABCG5(-/-)/G8(-/-) or ABCG8 (-/-) mice. We conclude that the ABCG5/G8-independent pathway plays an important role in regulating biliary cholesterol secretion, the transport of HDL-derived cholesterol from plasma to bile, and gallstone formation, which works independently of the ABCG5/G8 pathway. Further studies are needed to observe if this pathway is also operational in humans. This article is protected by copyright. All rights reserved.

https://doi.org/10.1002/hep.28570

https://www.ncbi.nlm.nih.gov/pubmed/27014967

http://doi.wiley.com/10.1002/hep.v64.3

Cited in this article [1]

[25]

,Leow

,Yang

,et al.Functional characterization of two single nucleotide polymorphisms of acyl-coenzyme A:cholesterol acyltransferase 2[J]. Gene,2015,566(2):236-241. DOI:10.1016/j.gene.2015.04.061.

Acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) plays a critical role in the formation of cholesteryl esters from cholesterol and fatty acids, and is a potential target for treating hypercholesterolemia. We recently reported the significant effects of two human ACAT2 gene polymorphisms, 41A>G (Glu(14)Gly, rs9658625) and 734C>T (Thr(254)Ile, rs2272296), on plasma lipid levels and coronary artery disease susceptibility in a case-control association study. In the present study, we evaluated the possible biological influence of the two polymorphism using two approaches.In the first approach, the functional impact of the two polymorphisms was predicted in-silico using available web-based software, and in the second approach, the varying functions of the two polymorphisms were characterized in in vitro experiments, using ACAT2-deficient AC-29 cells.Our results show that the enzymatic activity of mutant Glu(14)Gly is approximately two times higher than wildtype, and that this increase is primarily due to the increased expression and/or stability of the mutant ACAT2 protein.These results suggest that the genetic variation at Glu(14)Gly is functionally important and may contribute to ACAT2 protein expression and stability.

https://doi.org/10.1016/j.gene.2015.04.061

https://www.ncbi.nlm.nih.gov/pubmed/25917363

http://linkinghub.elsevier.com/retrieve/pii/S0378111915004886

Cited in this article [1]

[26]

Ohshiro

,Ohtawa

,Nagamitsu

,et al.New pyripyropene A derivatives,highly SOAT2-selective inhibitors,improve hypercholesterolemia and atherosclerosis in atherogenic mouse models[J]. J Pharmacol Exp Ther,2015,355(2):299-307. DOI:10.1124/jpet.115.227348.

Sterol O-acyltransferase 2 (SOAT2; also known as ACAT2) is considered as a new therapeutic target for the treatment or prevention of hypercholesterolemia and atherosclerosis. Fungal pyripyropene A (PPPA: 1,7,11-triacyl type), the first SOAT2-selective inhibitor, proved orally active in vivo using atherogenic mouse models. The purpose of the present study was to demonstrate that the PPPA derivatives (PRDs) prove more effective in the mouse models than PPPA. Among 196 semisynthetic PPPA derivatives, potent, SOAT2-selective, and stable PRDs were selected. In vivo antiatherosclerotic activity of selected PRDs was tested in apolipoprotein E knockout (Apoe(-/-)) mice or low-density lipoprotein receptor knockout (Ldlr(-/-)) mice fed a cholesterol-enriched diet (0.2% cholesterol and 21% fat) for 12 weeks. During the PRD treatments, no detrimental side effects were observed. Among three PRDs, Apoe(-/-) mice treated with PRD125 (1-,11-O-benzylidene type) at 1 mg/kg/day had significantly lower total plasma cholesterol concentration by 57.9 卤 9.3%; further, the ratio of cholesteryl oleate to cholesteryl linoleate in low-density lipoprotein was lower by 55.6 卤 7.5%, respectively. The hepatic cholesteryl ester levels and SOAT2 activity in the small intestines and livers of the PRD-treated mice were selectively lowered. The atherosclerotic lesion areas in the aortae of PRD125-treated mice were significantly lower at 62.2 卤 13.1%, respectively. Furthermore, both PRDs were also orally active in atherogenic Ldlr(-/-) mice. Among the PRDs tested, PRD125 was the most potent in both mouse models. These results suggest that SOAT2-selective inhibitors such as PRD125 have a high potential as poststatin agents for treatment and/or prevention in patients with atherosclerosis and hypercholesterolemia.

https://doi.org/10.1124/jpet.115.227348

https://www.ncbi.nlm.nih.gov/pubmed/26338984

http://jpet.aspetjournals.org/cgi/doi/10.1124/jpet.115.227348

Cited in this article [1]

[27]

Zhang

,Kelley

,Marshall

,et al.Tissue-specific knockouts of ACAT2 reveal that intestinal depletion is sufficient to prevent diet-induced cholesterol accumulation in the liver and blood[J]. J Lipid Res,2012,53(6):1144-1152. DOI:10.1194/jlr.M024356.

Abstract Acyl-CoA:cholesterol acyltransferase 2 (ACAT2) generates cholesterol esters (CE) for packaging into newly synthesized lipoproteins and thus is a major determinant of blood cholesterol levels. ACAT2 is expressed exclusively in the small intestine and liver, but the relative contributions of ACAT2 expression in these tissues to systemic cholesterol metabolism is unknown. We investigated whether CE derived from the intestine or liver would differentially affect hepatic and plasma cholesterol homeostasis. We generated liver-specific (ACAT2(L-/L-)) and intestine-specific (ACAT2(SI-/SI-)) ACAT2 knockout mice and studied dietary cholesterol-induced hepatic lipid accumulation and hypercholesterolemia. ACAT2(SI-/SI-) mice, in contrast to ACAT2(L-/L-) mice, had blunted cholesterol absorption. However, specific deletion of ACAT2 in the intestine generated essentially a phenocopy of the conditional knockout of ACAT2 in the liver, with reduced levels of plasma very low-density lipoprotein and hepatic CE, yet hepatic-free cholesterol does not build up after high cholesterol intake. ACAT2(L-/L-) and ACAT2(SI-/SI-) mice were equally protected from diet-induced hepatic CE accumulation and hypercholesterolemia. These results suggest that inhibition of intestinal or hepatic ACAT2 improves atherogenic hyperlipidemia and limits hepatic CE accumulation in mice and that depletion of intestinal ACAT2 is sufficient for most of the beneficial effects on cholesterol metabolism. Inhibitors of ACAT2 targeting either tissue likely would be beneficial for atheroprotection.

https://doi.org/10.1194/jlr.M024356

https://www.ncbi.nlm.nih.gov/pubmed/22460046

http://www.jlr.org/lookup/doi/10.1194/jlr.M024356

Cited in this article [1]

[28]

Lehner

,Lian

,Quiroga

.Lumenal lipid metabolism:implications for lipoprotein assembly[J]. Arterioscler Thromb Vasc Biol,2012,32(5):1087-1093. DOI:10.1161/atvbaha.111.241497.

Abstract Overproduction of apolipoprotein B (apoB)-containing lipoproteins by the liver and the intestine is 1 of the hallmarks of insulin resistance and type 2 diabetes and a well-established risk factor of cardiovascular disease. The assembly of apoB lipoproteins is regulated by the availability of lipids that form the neutral lipid core (triacylglycerol and cholesteryl ester) and the limiting lipoprotein monolayer (phospholipids and cholesterol). Although tremendous advances have been made over the past decade toward understanding neutral lipid and phospholipid biosynthesis and neutral lipid storage in cytosolic lipid droplets (LDs), little is known about the mechanisms that govern the transfer of lipids to the lumen of the endoplasmic reticulum for apoB lipidation. ApoB-synthesizing organs can deposit synthesized neutral lipids into at least 3 different types of LDs, each decorated with a subset of specific proteins: perilipin-decorated cytosolic LDs, and 2 types of LDs formed in the lumen of the endoplasmic reticulum, the secretion-destined LDs containing apoB, and resident lumenal LDs coated with microsomal triglyceride transfer protein and exchangeable apolipoproteins. This brief review will address the current knowledge of lumenal lipid metabolism in the context of apoB assembly and lipid storage.

https://doi.org/10.1161/ATVBAHA.111.241497

https://www.ncbi.nlm.nih.gov/pubmed/22517367

http://atvb.ahajournals.org/cgi/doi/10.1161/ATVBAHA.111.241497

Cited in this article [2]

[29]

Suzuki

,Swift

.Discovery of novel splice variants and regulatory mechanisms for microsomal triglyceride transfer protein in human tissues[J]. Sci Rep,2016,6:27308.DOI:10.1038/srep27308.

Microsomal triglyceride transfer protein (MTP) is a unique lipid transfer protein essential for the assembly of triglyceride-rich lipoproteins by the liver and intestine. Previous studies in mice identified a splice variant of MTP with an alternate first exon. Splice variants of human MTP have not been reported. Using PCR approaches we have identified two splice variants in human tissues, which we have named MTP-B and MTP-C. MTP-B has a unique first exon (Ex1B) located 10.5 kb upstream of the first exon (Ex1A) for canonical MTP (MTP-A); MTP-C contains both first exons for MTP-A and MTP-B. MTP-B was found in a number of tissues, whereas MTP-C was prominent in brain and testis. MTP-B does not encode a protein; MTP-C encodes the same protein encoded by MTP-A, although MTP-C translation is strongly inhibited by regulatory elements within its 5 -UTR. Using luciferase assays, we demonstrate that the promoter region upstream of exon 1B is quite adequate to drive expression of MTP. We conclude that alternate splicing plays a key role in regulating cellular MTP levels by introducing distinct promoter regions and unique 5鈥-UTRs, which contain elements that alter translation efficiency, enabling the cell to optimize MTP activity.

https://doi.org/10.1038/srep27308

https://www.ncbi.nlm.nih.gov/pubmed/27256115

http://www.nature.com/articles/srep27308

Cited in this article [1]

[30]

Iqbal

,Boutjdir

,Rudel

,et al.Intestine-specific MTP and global ACAT2 deficiency lowers acute cholesterol absorption with chylomicrons and HDLs[J]. J Lipid Res,2014,55(11):2261-2275. DOI:10.1194/jlr.M047951.

Intestinal cholesterol absorption involves the chylomicron and HDL pathways and is dependent on microsomal triglyceride transfer protein (MTP) and ABCA1, respectively. Chylomicrons transport free and esterified cholesterol, whereas HDLs transport free cholesterol. ACAT2 esterifies cholesterol for secretion with chylomicrons. We hypothesized that free cholesterol accumulated during ACAT2 deficiency may be secreted with HDLs when chylomicron assembly is blocked. To test this, we studied cholesterol absorption in mice deficient in intestinal MTP, global ACAT2, and both intestinal MTP and global ACAT2. Intestinal MTP ablation significantly increased intestinal triglyceride and cholesterol levels and reduced their transport with chylomicrons. In contrast, global ACAT2 deficiency had no effect on triglyceride absorption but significantly reduced cholesterol absorption with chylomicrons and increased cellular free cholesterol. Their combined deficiency reduced cholesterol secretion with both chylomicrons and HDLs. Thus, contrary to our hypothesis, free cholesterol accumulated in the absence of MTP and ACAT2 is unavailable for secretion with HDLs. Global ACAT2 deficiency causes mild hypertriglyceridemia and reduces hepatosteatosis in mice fed high cholesterol diets by increasing hepatic lipoprotein production by unknown mechanisms. We show that this phenotype is preserved in the absence of intestinal MTP in global ACAT2-deficient mice fed a Western diet. Further, we observed increases in hepatic MTP activity in these mice. Thus, ACAT2 deficiency might increase MTP expression to avoid hepatosteatosis in cholesterol-fed animals. Therefore, ACAT2 inhibition might avert hepatosteatosis associated with high cholesterol diets by increasing hepatic MTP expression and lipoprotein production.

https://doi.org/10.1194/jlr.M047951

https://www.ncbi.nlm.nih.gov/pubmed/25030663

http://www.jlr.org/lookup/doi/10.1194/jlr.M047951

Cited in this article [1]

[31]

Ryder

,Walker

,Goosen

,et al.Insights into the novel hydrolytic mechanism of a diethyl 2-phenyl-2-(2-arylacetoxy)methyl malonate ester-based microsomal triglyceride transfer protein (MTP) inhibitor[J]. Chem Res Toxicol,2012,25(10):2138-2152. DOI:10.1021/tx300243v.

Inhibition of intestinal and hepatic microsomal triglyceride transfer protein (MTP) is a potential strategy for the treatment of dyslipidemia and related metabolic disorders. Inhibition of hepatic MTP, however, results in elevated liver transaminases and increased hepatic fat deposition consistent with hepatic steatosis. Diethyl 2-((2-(3-(dimethylcarbamoyl)-4-(4'-(trifluoromethyl)-[1,1'-biphenyl]-2-ylcarboxamido)phenyl)acetoxy)methyl)-2-phenylmalonate (JTT-130) is an intestine-specific inhibitor of MTP and does not cause increases in transaminases in short-term clinical trials in patients with dyslipidemia. Selective inhibition of intestinal MTP is achieved via rapid hydrolysis of its ester linkage by liver-specific carboxylesterase(s), resulting in the formation of an inactive carboxylic acid metabolite 1. In the course of discovery efforts around tissue-specific inhibitors of MTP, the mechanism of JTT-130 hydrolysis was examined in detail. Lack of 0160O incorporation in 1 following the incubation of JTT-130 in human liver microsomes in the presence of H600160O suggested that hydrolysis did not occur via a simple cleavage of the ester linkage. The characterization of atropic acid (2-phenylacrylic acid) as a metabolite was consistent with a hydrolytic pathway involving initial hydrolysis of one of the pendant malonate ethyl ester groups followed by decarboxylative fragmentation to 1 and the concomitant liberation of the potentially electrophilic acrylate species. Glutathione conjugates of atropic acid and its ethyl ester were also observed in microsomal incubations of JTT-130 that were supplemented with the thiol nucleophile. Additional support for the hydrolysis mechanism was obtained from analogous studies on diethyl 2-(2-(2-(3-(dimethylcarbamoyl)-4-(4'-trifluoromethyl)-[1,1'-biphenyl]-2-ylcarboxamido)phenyl)acetoxy)ethyl)-2-phenylmalonate (3), which cannot participate in hydrolysis via the fragmentation pathway because of the additional methylene group. Unlike the case with JTT-130, 0160O was readily incorporated into 1 during the enzymatic hydrolysis of 3, suggestive of a mechanism involving direct hydrolytic cleavage of the ester group in 3. Finally, 3-(ethylamino)-2-(ethylcarbamoyl)-3-oxo-2-phenylpropyl 2-(3-(dimethylcarbamoyl)-4-(4'-(trifluoromethyl)-[1,1'-biphenyl]-2-ylcarboxamido)phenyl)acetate (4), which possessed an N,N-diethyl-2-phenylmalonamide substituent (in lieu of the diethyl-2-phenylmalonate motif in JTT-130) proved to be resistant to the hydrolytic cleavage/decarboxylative fragmentation pathway that yielded 1, a phenomenon that further confirmed our hypothesis. From a toxicological standpoint, it is noteworthy to point out that the liberation of the electrophilic acrylic acid species as a byproduct of JTT-130 hydrolysis is similar to the bioactivation mechanism established for felbamate, an anticonvulsant agent associated with idiosyncratic aplastic anemia and hepatotoxicity.

https://doi.org/10.1021/tx300243v

https://www.ncbi.nlm.nih.gov/pubmed/22989032

http://pubs.acs.org/doi/10.1021/tx300243v

Cited in this article [1]

[32]

Dai

,Khatun

,Hussain

.NR2F1 and IRE1beta suppress microsomal triglyceride transfer protein expression and lipoprotein assembly in undifferentiated intestinal epithelial cells[J]. Arterioscler Thromb Vasc Biol,2010,30(3):568-574. DOI:10.1161/atvbaha.109.198135.

OBJECTIVE: Our aim was to elucidate mechanisms involved in the acquisition of lipid transport properties during enterocyte differentiation. METHODS AND RESULTS: We show that lipid mobilization via apolipoprotein B lipoproteins is dependent on the expression of microsomal triglyceride transfer protein (MTP) during differentiation of Caco-2 cells into enterocyte-like cells. Mechanistic studies showed that binding of the nuclear receptor family 2 group F member 1 (NR2F1) to the DR1 element in the MTTP promoter suppresses MTTP expression in undifferentiated cells. During cellular differentiation, NR2F1 expression and its binding to MTTP promoter decline and MTP induction ensues. Moreover, undifferentiated cells express inositol-requiring enzyme 1beta (IRE1beta), a protein that posttranscriptionally degrades MTP mRNA, and its expression substantially decreases during differentiation, contributing to MTP induction. Immunohistochemical studies revealed a significant negative relationship between the expressions of MTP and NR2F1/IRE1beta in undifferentiated and differentiated Caco-2 cells, as well as in crypt-villus and jejunum-colon axes of mouse intestine. CONCLUSIONS: We propose that transcriptional and posttranscriptional mechanisms involving NR2F1 and IRE1beta ensure low MTP expression in undifferentiated intestinal cells and avoid apolipoprotein B lipoprotein biosynthesis.

https://doi.org/10.1161/ATVBAHA.109.198135

https://www.ncbi.nlm.nih.gov/pubmed/20007910

http://atvb.ahajournals.org/cgi/doi/10.1161/ATVBAHA.109.198135

Cited in this article [1]

[33]

Mera

,Hata

,Ishii

,et al.JTT-130,a novel intestine-specific inhibitor of microsomal triglyceride transfer protein,reduces food preference for fat[J].J Diabetes Res,2014,2014:583752.DOI:10.1155/2014/583752.

Microsomal triglyceride transfer protein (MTP) is involved in the assembly and secretion of triglyceride-rich lipoproteins from enterocytes and hepatocytes. JTT-130 is a novel intestine-specific MTP inhibitor, which has been shown to be useful in the prevention and treatment of dyslipidemia, obesity, and diabetes. JTT-130 has also been shown to suppress food intake in a dietary fat-dependent manner in rats. However, whether JTT-130 enables changes in food preference and nutrient consumption remains to be determined. Therefore, the aim of the present study was to investigate the effects of JTT-130 on food preference in rat under free access to two different diets containing 3.3% fat (low-fat diet, LF diet) and 35% fat (high-fat diet, HF diet). JTT-130 decreased HF diet intake and increased LF diet intake, resulting in a change in ratio of caloric intake from LF and HF diets to total caloric intake. In addition, macronutrient analysis revealed that JTT-130 did not affect carbohydrate consumption but significantly decreased fat consumption (P<0.01). These findings suggest that JTT-130 not only inhibits fat absorption, but also suppresses food intake and specifically reduces food preference for fat. Therefore, JTT-130 is expected to provide a new option for the prevention and treatment of obesity and obesity-related metabolic disorders.

https://doi.org/10.1155/2014/583752

https://www.ncbi.nlm.nih.gov/pubmed/4052484

http://pubmedcentralcanada.ca/pmcc/articles/PMC4052484/

Cited in this article [1]

[34]

Huang

,Liu

,Ou

,et al.Octreotide promotes weight loss via suppression of intestinal MTP and apoB48 expression in diet-induced obesity rats[J]. Nutrition,2013,29(10):1259-1265. DOI:10.1016/j.nut.2013.01.013.

The goal of this study was to investigate the effect of octreotide on the expression of intestinal fat absorption-associated apolipoproteinB48 (apoB48), microsomal triglyceride transfer protein (MTP) and apolipoproteinAIV (apoAIV) in a high-fat diet-induced obesity rat model.Sprague-Dawley rats were placed into a control or high-fat diet group. Obese rats from the high-fat diet group were further divided into an obese group and an octreotide-treated group. Rats in the octreotide-treated group were subcutaneously injected with octreotide (40 g/kg body weight) twice daily for 8 d. Body weight, fasting plasma glucose (FPG), fasting serum insulin, triglyceride (TG), total cholesterol (TC), and high density lipoprotein-cholesterol (HDL-C) were measured. Intestinal MTP, apoB48, and apoAIV expression levels were determined by real-time polymerase chain reaction, Western blot, or enzyme-linked immunosorbent assay analysis.We found high-fat diet-induced obesity rats express more apoB, MTP, and apoAIV mRNA as well as apoB48 and MTP protein in the intestine than normal chow-fed rats. This observation occurred along with increased body weight, FPG, TG, TC, fasting serum insulin, and Homeostatic Model Assessment value. Octreotide intervention significantly decreased body weight and blood parameters, and down-regulated expression of apoB mRNA and apoB48 protein, as well as MTP mRNA and proteins. However, apoAIV mRNA was not significantly different between obese and octreotide-treated rats although it was decreased by 47%.High-fat diet-induced obesity is associated with increased expression of apoB48, MTP, and apoAIV in the intestine. Octreotide intervention inhibited the overexpression of apoB48 and MTP, and consequently brought about reduced fat absorption and weight loss.

https://doi.org/10.1016/j.nut.2013.01.013

https://www.ncbi.nlm.nih.gov/pubmed/23911221

http://linkinghub.elsevier.com/retrieve/pii/S0899900713000555

Cited in this article [1]

[35]

Dikkers

,Annema

,De Boer

,et al.Differential impact of hepatic deficiency and total body inhibition of MTP on cholesterol metabolism and RCT in mice[J]. J Lipid Res,2014,55(5):816-825. DOI:10.1194/jlr.M042986.

Abstract Because apoB-containing lipoproteins are pro-atherogenic and their secretion by liver and intestine largely depends on microsomal triglyceride transfer protein (MTP) activity, MTP inhibition strategies are actively pursued. How decreasing the secretion of apoB-containing lipoproteins affects intracellular rerouting of cholesterol is unclear. Therefore, the aim of the present study was to determine the effects of reducing either systemic or liver-specific MTP activity on cholesterol metabolism and reverse cholesterol transport (RCT) using a pharmacological MTP inhibitor or a genetic model, respectively. Plasma total cholesterol and triglyceride levels were decreased in both MTP inhibitor-treated and liver-specific MTP knockout (L-Mttp(-/-)) mice (each P < 0.001). With both inhibition approaches, hepatic cholesterol as well as triglyceride content was consistently increased (each P < 0.001), while biliary cholesterol and bile acid secretion remained unchanged. A small but significant decrease in fecal bile acid excretion was observed in inhibitor-treated mice (P < 0.05), whereas fecal neutral sterol excretion was substantially increased by 75% (P < 0.001), conceivably due to decreased intestinal absorption. In contrast, in L-Mttp(-/-) mice both fecal neutral sterol and bile acid excretion remained unchanged. However, while total RCT increased in inhibitor-treated mice (P < 0.01), it surprisingly decreased in L-Mttp(-/-) mice (P < 0.05). These data demonstrate that: i) pharmacological MTP inhibition increases RCT, an effect that might provide additional clinical benefit of MTP inhibitors; and ii) decreasing hepatic MTP decreases RCT, pointing toward a potential contribution of hepatocyte-derived VLDLs to RCT.

https://doi.org/10.1194/jlr.M042986

https://www.ncbi.nlm.nih.gov/pubmed/3995460

http://www.jlr.org/lookup/doi/10.1194/jlr.M042986

Cited in this article [1]

[36]

Demina

,Miroshnikova

,Schwarzman

.Role of the ABC transporters A1 and G1,key reverse cholesterol transport proteins,in atherosclerosis[J]. Mol Biol (Mosk),2016,50(2):223-230. DOI:10.7868/s002689841602004x.

Atherosclerosis is one of the most common causes of death worldwide. Epidemiology studies firmly established an inverse relationship between atherogenesis and distorted lipid metabolism, in particular, higher levels of total cholesterol, an accumulation of CH-laden macrophages (foam cells), and lower plasma levels of antiatherogenic high density lipoprotein (HDL). It is believed that the reverse cholesterol transport, a process that removes excess cholesterol from peripheral tissues/cells including macrophages to circulating HDL, is one of the main mechanisms responsible for anti-atherogenic properties of HDL. The key proteins of reverse cholesterol transport—ATP-binding cassette transporters A1 (ABCA1) and G1 (ABCG1)—mediate the cholesterol efflux from macrophages and prevent their transformation into foam cells. This review focuses on the role of ABC transporters A1 and G1 in the pathogenesis of atherosclerosis.

https://doi.org/10.7868/S002689841602004X

https://www.ncbi.nlm.nih.gov/pubmed/27239842

http://link.springer.com/article/10.1134/S0026893316020047

Cited in this article [1]

[37]

Joyce

,Amar

,Lambert

,et al.The ATP binding cassette transporter A1 (ABCA1) modulates the development of aortic atherosclerosis in C57BL/6 and apoE-knockout mice[J]. Proc Natl Acad Sci USA,2002,99(1):407-412. DOI:10.1073/pnas.012587699.

Identification of mutations in the ABCA1 transporter (ABCA1) as the genetic defect in Tangier disease has generated interest in modulating atherogenic risk by enhancing ABCA1 gene expression. To investigate the role of ABCA1 in atherogenesis, we analyzed diet-induced atherosclerosis in transgenic mice overexpressing human ABCA1 (hABCA1-Tg) and spontaneous lesion formation in hABCA1-Tg x apoE-knockout (KO) mice. Overexpression of hABCA1 in C57BL/6 mice resulted in a unique anti-atherogenic profile characterized by decreased plasma cholesterol (63%), cholesteryl ester (63%), free cholesterol (67%), non-high density lipoprotein (HDL)-cholesterol (53%), and apolipoprotein (apo) B (64%) but markedly increased HDL-cholesterol (2.8-fold), apoA-I (2.2-fold), and apoE (2.8-fold) levels. These beneficial changes in the lipid profile led to significantly lower (65%) aortic atherosclerosis in hABCA1-Tg mice. In marked contrast, ABCA1 overexpression had a minimal effect on the plasma lipid profile of apoE-KO mice and resulted in a 2- to 2.6-fold increase in aortic lesion area. These combined results indicate that overexpression of ABCA1 in C57BL/6 mice on a high cholesterol diet results in an atheroprotective lipoprotein profile and decreased atherosclerosis, and thus provide previously undocumented in vivo evidence of an anti-atherogenic role for the ABCA1 transporter. In contrast, overexpression of ABCA1 in an apoE-KO background led to increased atherosclerosis, further substantiating the important role of apoE in macrophage cholesterol metabolism and atherogenesis. In summary, these results establish that, in the presence of apoE, overexpression of ABCA1 modulates HDL as well as apoB-containing lipoprotein metabolism and reduces atherosclerosis in vivo, and indicate that pharmacological agents that will increase ABCA1 expression may reduce atherogenic risk in humans.

https://doi.org/10.1073/pnas.012587699

https://www.ncbi.nlm.nih.gov/pubmed/11752403

http://www.pnas.org/cgi/doi/10.1073/pnas.012587699

Cited in this article [1]

[38]

Nomura

,Endo-Umeda

,Makishima

,et al.Development of tetrachlorophthalimides as liver X receptor beta (LXRbeta)-selective agonists[J]. Chem Med Chem,2016,11(20):2347-2360. DOI:10.1002/cmdc.201600305.

Abstract Liver61X receptor (LXR) agonists are candidates for the treatment of atherosclerosis via induction of ABCA1 (ATP-binding cassette61A1) gene expression, which contributes to reverse cholesterol transport (RCT) and to cholesterol efflux from the liver and intestine. However, LXR agonists also induce genes involved in lipogenesis, such as SREBP-1c (sterol regulatory binding element protein611c) and FAS (fatty acid synthase), thereby causing an undesirable increase in plasma and hepatic triglyceride (TG) levels. Recent studies indicate that LXRα contributes to lipogenesis in liver, and selective LXRβ activation improves RCT in mice. Therefore, LXRβ-selective agonists are promising candidates to improve atherosclerosis without increasing plasma or hepatic TG levels. However, the ligand-binding domains in the two LXR isoforms α/β share high sequence identity, and few LXR ligands show subtype selectivity. In this study we identified a tetrachlorophthalimide analogue as an LXRβ-selective agonist. Structural development led to ( E )-4,5,6,7-tetrachloro-2-(2-styrylphenyl)isoindoline-1,3-dione (2465a), which shows potent and selective LXRβ agonistic activity in reporter gene assays. In binding assays, compound 2465a bound to LXRβ preferentially over LXRα. It also induced the expression of ABCA1 mRNA but not SREBP-1c mRNA in cells. Compound 2465a appears to be a promising lead compound for therapeutic agents to treat atherosclerosis without the side effects induced by LXRα/β dual agonists.

https://doi.org/10.1002/cmdc.201600305

https://www.ncbi.nlm.nih.gov/pubmed/27690261

http://doi.wiley.com/10.1002/cmdc.v11.20

Cited in this article [1]

[39]

Kannisto

,Gafvels

,Jiang

,et al.LXR driven induction of HDL-cholesterol is independent of intestinal cholesterol absorption and ABCA1 protein expression[J]. Lipids,2014,49(1):71-83. DOI:10.1007/s11745-013-3853-8.

We investigated whether: (1) liver X receptor (LXR)-driven induction of high-density lipoprotein cholesterol (HDL-C) and other LXR-mediated effects on cholesterol metabolism depend on intestinal cholesterol absorption; and (2) combined treatment with the LXR agonist GW3965 and the cholesterol absorption inhibitor ezetimibe results in synergistic effects on cholesterol metabolism that could be beneficial for treatment of atherosclerosis. Mice were fed 0.2% cholesterol and treated with GW3965+ezetimibe, GW3965 or ezetimibe. GW3965+ezetimibe treatment elevated serum HDL-C and Apolipoprotein (Apo) AI, effectively reduced the intestinal cholesterol absorption and increased the excretion of faecal neutral sterols. No changes in intestinal ATP-binding cassette (ABC) A1 or ABCG5 protein expression were observed, despite increased mRNA expression, while hepatic ABCA1 was slightly reduced. The combined treatment caused a pronounced down-regulation of intestinal Niemann-Pick C1-like 1 (NPC1L1) and reduced hepatic and intestinal cholesterol levels. GW3965 did not affect the intestinal cholesterol absorption, but increased serum HDL-C and ApoAI levels. GW3965 also increased Apoa1 mRNA levels in primary mouse hepatocytes and HEPA1-6 cells. Ezetimibe reduced the intestinal cholesterol absorption, ABCA1 and ABCG5, but did not affect the serum HDL-C or ApoAI levels. Thus, the LXR-driven induction of HDL-C and ApoAI was independent of the intestinal cholesterol absorption and increased expression of intestinal or hepatic ABCA1 was not required. Inhibited influx of cholesterol via NPC1L1 and/or low levels of intracellular cholesterol prevented post-transcriptional expression of intestinal ABCA1 and ABCG5, despite increased mRNA levels. Combined LXR activation and blocked intestinal cholesterol absorption induced effective faecal elimination of cholesterol.

https://doi.org/10.1007/s11745-013-3853-8

https://www.ncbi.nlm.nih.gov/pubmed/24163219

http://doi.wiley.com/10.1007/s11745-013-3853-8

Cited in this article [1]

[40]

,Xiao

,Tang

,et al.Advanced oxidation protein products exacerbates lipid accumulation and atherosclerosis through downregulation of ATP-binding cassette transporter A1 and G1 expression in apolipoprotein E knockout mice[J]. Circ J,2014,78(11):2760-2770. DOI:10.1253/circj.CJ-14-0193.

https://doi.org/10.1253/circj.CJ-14-0193

http://jlc.jst.go.jp/DN/JST.JSTAGE/circj/CJ-14-0193?lang=en&from=CrossRef&type=abstract

Cited in this article [1]

[41]

Gui

,Yan

,Gao

,et al.Betulin attenuates atherosclerosis in apoE-/-mice by up-regulating ABCA1 and ABCG1[J]. Acta Pharmacol Sin,2016,37(10):1337-1348. DOI:10.1038/aps.2016.46.

Betulin is a pentacyclic triterpenoid isolated from the bark of yellow and white birch trees with anti-cancer and anti-malaria activities. In this study we examined the effects of betulin on atherosclerosis in apoE61/61mice and the underlying mechanisms. Murine macrophage RAW264.7 cells and human monocyte-derived THP-1 cells were tested. Foam cell formation was detected with Oil Red O staining. Cholesterol efflux was assessed using [3H]-cholesterol efflux assay. The expression of ATP-binding cassette transporter A1 and G1 (ABCA1 and ABCG1) was examined using RT-PCR and Western-blotting. The ABCA1 promoter activity was evaluated using luciferase activity assay. Male apoE61/61mice fed on a high-fat-diet (HFD), and received betulin (20 and 40 mg·kg611·d611, ig) for 12 weeks. The macrophage content and ABCA1 expression in the aortic sinuses were evaluated with immunofluorescence staining. The hepatic, intestinal and fecal cholesterol were also analyzed in the mice. In RAW264.7 cells, betulin (0.1–2.5 μg/mL) dose-dependently ameliorated oxLDL-induced cholesterol accumulation and enhanced cholesterol efflux. In both RAW264.7 and THP-1 cells, betulin increased the expression of ABCA1 and ABCG1 via suppressing the transcriptional repressors sterol-responsive element-binding proteins (SREBPs) that bound to E-box motifs in ABCA1 promoter, whereas E-box binding site mutation markedly attenuated betulin-induced ABCA1 promoter activity. In HFD-fed apoE61/61mice, betulin administration significantly reduced lesions in en face aortas and aortic sinuses. Furthermore, betulin administration significantly increased ABCA1 expression and suppressed macrophage positive areas in the aortic sinuses. Moreover, betulin administration improved plasma lipid profiles and enhanced fecal cholesterol excretion in the mice. Betulin attenuates atherosclerosis in apoE61/61mice by promoting cholesterol efflux in macrophages.

https://doi.org/10.1038/aps.2016.46

https://www.ncbi.nlm.nih.gov/pubmed/27374487

http://www.nature.com/articles/aps201646

Cited in this article [1]

[42]

Temel

,Brown

.A new model of reverse cholesterol transport:enTICEing strategies to stimulate intestinal cholesterol excretion[J]. Trends Pharmacol Sci,2015,36(7):440-451. DOI:10.1016/j.tips.2015.04.002.

Cardiovascular disease (CVD) remains the largest cause of mortality in most developed countries. Although recent failed clinical trials and Mendelian randomization studies have called into question the high-density lipoprotein (HDL) hypothesis, it remains well accepted that stimulating the process of reverse cholesterol transport (RCT) can prevent or even regress atherosclerosis. The prevailing model for RCT is that cholesterol from the artery wall must be delivered to the liver where it is secreted into bile before leaving the body through fecal excretion. However, many studies have demonstrated that RCT can proceed through a non-biliary pathway known as transintestinal cholesterol excretion (TICE). The goal of this review is to discuss the current state of knowledge of the TICE pathway, with emphasis on points of therapeutic intervention.

https://doi.org/10.1016/j.tips.2015.04.002

https://www.ncbi.nlm.nih.gov/pubmed/4485953

http://linkinghub.elsevier.com/retrieve/pii/S0165614715000747

Cited in this article [1]

[43]

Nakano

,Inoue

,Takenaka

,et al.Ezetimibe promotes brush border membrane-to-lumen cholesterol efflux in the small intestine[J]. PLoS One,2016,11(3):e0152207. DOI:10.1371/journal.pone.0152207.

Abstract Ezetimibe inhibits Niemann-Pick C1-like 1 (NPC1L1), an apical membrane cholesterol transporter of enterocytes, thereby reduces intestinal cholesterol absorption. This treatment also increases extrahepatic reverse cholesterol transport via an undefined mechanism. To explore this, we employed a trans-intestinal cholesterol efflux (TICE) assay, which directly detects circulation-to-intestinal lumen 3H-cholesterol transit in a cannulated jejunal segment, and found an increase of TICE by 45%. To examine whether such increase in efflux occurs at the intestinal brush border membrane(BBM)-level, we performed luminal perfusion assays, similar to TICE but the jejunal wall was labelled with orally-given 3H-cholesterol, and determined elevated BBM-to-lumen cholesterol efflux by 3.5-fold with ezetimibe. Such increased efflux probably promotes circulation-to-lumen cholesterol transit eventually; thus increases TICE. Next, we wondered how inhibition of NPC1L1, an influx transporter, resulted in increased efflux. When we traced orally-given 3H-cholesterol in mice, we found that lumen-to-BBM 3H-cholesterol transit was rapid and less sensitive to ezetimibe treatment. Comparison of the efflux and fractional cholesterol absorption revealed an inverse correlation, indicating the efflux as an opposite-regulatory factor for cholesterol absorption efficiency and counteracting to the naturally-occurring rapid cholesterol influx to the BBM. These suggest that the ezetimibe-stimulated increased efflux is crucial in reducing cholesterol absorption. Ezetimibe-induced increase in cholesterol efflux was approximately 2.5-fold greater in mice having endogenous ATP-binding cassette G5/G8 heterodimer, the major sterol efflux transporter of enterocytes, than the knockout counterparts, suggesting that the heterodimer confers additional rapid BBM-to-lumen cholesterol efflux in response to NPC1L1 inhibition. The observed framework for intestinal cholesterol fluxes may provide ways to modulate the flux to dispose of endogenous cholesterol efficiently for therapeutic purposes.

https://doi.org/10.1371/journal.pone.0152207

https://www.ncbi.nlm.nih.gov/pubmed/4811413

http://dx.plos.org/10.1371/journal.pone.0152207

Cited in this article [1]

[44]

Kockx

,Jessup

,Kritharides

.Getting to the ‘guts’ of the matter:intestinal control of lipid metabolism[J]. Curr Opin Lipidol,2013,24(1):105-106. DOI:10.1097/MOL.0b013e32835c7b5f.

https://doi.org/10.1097/MOL.0b013e32835c7b5f

https://insights.ovid.com/crossref?an=00041433-201302000-00018

Cited in this article [1]

[45]

Praslickova

,Torchia

,Sugiyama

,et al.The ileal lipid binding protein is required for efficient absorption and transport of bile acids in the distal portion of the murine small intestine[J]. PLoS One,2012,7(12):e50810. DOI:10.1371/journal.pone.0050810.

The ileal lipid binding protein (ilbp) is a cytoplasmic protein that binds bile acids with high affinity. However evidence demonstrating the role of this protein in bile acid transport and homeostasis is missing. We created a mouse strain lacking ilbp (Fabp6(-/-) mice) and assessed the impact of ilbp deficiency on bile acid homeostasis and transport in vivo. Elimination of ilbp increased fecal bile acid excretion (54.2%, P<0.05) in female but not male Fabp6(-/-) mice. The activity of cholesterol 7伪-hydroxylase (cyp7a1), the rate-controlling enzyme of the classical bile acid biosynthetic pathway, was significantly increased in female (63.5%, P<0.05) but not in male Fabp6(-/-) mice. The amount of [(3)H]taurocholic acid (TCA) excreted by 24 h after oral administration was 102% (P<0.025) higher for female Fabp6(-/-) mice whereas it was 57.3% (P<0.01) lower for male Fabp6(-/-) mice, compared to wild-type mice. The retained fraction of the [(3)H]TCA localized in the small and large intestines was increased by 22% (P<0.02) and decreased by 62.7% (P<0.01), respectively, in male Fabp6(-/-) mice relative wild-type mice, whereas no changes were seen in female Fabp6(-/-) mice. Mucosal to serosal bile acid transport using everted distal gut sacs was decreased by 74% (P<0.03) in both sexes of Fabp6(-/-) mice as compared to wild-type mice. The results demonstrate that ilbp is involved in the apical to basolateral transport of bile acids in ileal enterocytes, and is vital for the maintenance of bile acid homeostasis in the enterohepatic circulation (EHC) in mice.

https://doi.org/10.1371/journal.pone.0050810

https://www.ncbi.nlm.nih.gov/pubmed/3519535

http://dx.plos.org/10.1371/journal.pone.0050810

Cited in this article [1]

[46]

Lan

,Haywood

,Dawson

.Inhibition of ileal apical but not basolateral bile acid transport reduces atherosclerosis in apoE(-)/(-) mice[J]. Atherosclerosis,2013,229(2):374-380. DOI:10.1016/j.atherosclerosis.2013.05.017.

Decreases in ileal FGF15, with subsequent increases in hepatic Cyp7a1 expression and bile acid synthesis appear to be necessary for the plasma cholesterol-lowering and atheroprotective effects associated with blocking intestinal bile acid absorption.

https://doi.org/10.1016/j.atherosclerosis.2013.05.017

https://www.ncbi.nlm.nih.gov/pubmed/23880190

http://linkinghub.elsevier.com/retrieve/pii/S0021915013003225

Cited in this article [4]

[47]

Moscovitz

,Kong

,Buckley

,et al.Restoration of enterohepatic bile acid pathways in pregnant mice following short term activation of Fxr by GW4064[J]. Toxicol Appl Pharmacol,2016,310:60-67. DOI:10.1016/j.taap.2016.08.021.

The farnesoid X receptor (Fxr) controls bile acid homeostasis by coordinately regulating the expression of synthesizing enzymes (Cyp7a1, Cyp8b1), conjugating enzymes (Bal, Baat) and transporters in the ileum (Asbt, Ost / ) and liver (Ntcp, Bsep, Ost ). Transcriptional regulation by Fxr can be direct, or through the ileal Fgf15/FGF19 and hepatic Shp pathways. Circulating bile acids are increased during pregnancy due to hormone-mediated disruption of Fxr signaling. While this adaptation enhances lipid absorption, elevated bile acids may predispose women to develop maternal cholestasis. The objective of this study was to determine whether short-term treatment of pregnant mice with GW4064 (a potent FXR agonist) restores Fxr signaling to the level observed in virgin mice. Plasma, liver and ilea were collected from virgin and pregnant mice administered vehicle or GW4064 by oral gavage. Treatment of pregnant mice with GW4064 induced ileal Fgf15, Shp and Ost / mRNAs, and restored hepatic Shp, Bal, Ntcp, and Bsep back to vehicle-treated virgin levels. Pregnant mice exhibited 2.5-fold increase in Cyp7a1 mRNA compared to virgin controls, which was reduced by GW4064. Similarly treatment of mouse primary hepatocytes with plasma isolated from pregnant mice induced Cyp7a1 mRNA by nearly 3-fold as compared to virgin plasma, which could be attenuated by co-treatment with either GW4064 or recombinant FGF19 protein. Collectively, these data reveal that repressed activity of intestinal and hepatic Fxr in pregnancy, as previously demonstrated, may be restored by pharmacological activation. This study provides the basis for a novel approach to restore bile acid homeostasis in patients with maternal cholestasis.

https://doi.org/10.1016/j.taap.2016.08.021

https://www.ncbi.nlm.nih.gov/pubmed/27609522

http://linkinghub.elsevier.com/retrieve/pii/S0041008X16302447

Cited in this article [2]

[48]

Dawson

.Impact of inhibiting ileal apical versus basolateral bile acid transport on cholesterol metabolism and atherosclerosis in mice[J]. Dig Dis,2015,33(3):382-387. DOI:10.1159/000371691.

Bile acid sequestrants have been used for many years to treat hypercholesterolemia by increasing hepatic conversion of cholesterol to bile acids, thereby inducing hepatic LDL receptor expression and clearance of apoB-containing particles. In order to further understand the underlying molecular mechanisms linking gut-liver signaling and cholesterol homeostasis, mouse models defective in ileal apical membrane bile acid transport (Asbt-null) and ileal basolateral membrane bile acid transport (Ost伪-null) were studied under basal and hypercholesterolemic conditions. Hepatic conversion of cholesterol to bile acids is the major pathway for cholesterol catabolism and a major mechanism for cholesterol elimination. Blocking ileal apical membrane bile acid transport (Asbt-null mice) increases fecal bile acid excretion, hepatic Cyp7a1 expression, and the relative proportion of taurocholate in the bile acid pool, but decreases ileal FGF15 expression, bile acid pool size, and hepatic cholesterol content. In contrast, blocking ileal basolateral membrane bile acid transport (Ost -null mice) increases ileal FGF15 expression, reduces hepatic Cyp7a1 expression, and increases the proportion of tauro- -muricholic acid in the bile acid pool. In the hypercholesterolemic apoE-null background, plasma cholesterol levels and measurements of atherosclerosis were reduced in Asbt/apoE-null mice, but not in Ost /apoE-null mice. Blocking the intestinal absorption of bile acids at the apical versus basolateral membrane differentially affects bile acid and cholesterol metabolism, including the development of hypercholesterolemia-associated atherosclerosis. The molecular mechanism likely involves an altered regulation of ileal FGF15 expression.

https://doi.org/10.1159/000371691

https://www.ncbi.nlm.nih.gov/pubmed/26045273

https://www.karger.com/Article/FullText/371691

Cited in this article [1]

[49]

Ferrebee

,Dawson

.Metabolic effects of intestinal absorption and enterohepatic cycling of bile acids[J]. Acta Pharm Sin B,2015,5(2):129-134. DOI:10.1016/j.apsb.2015.01.001.

The classical functions of bile acids include acting as detergents to facilitate the digestion and absorption of nutrients in the gut. In addition, bile acids also act as signaling molecules to regulate glucose homeostasis, lipid metabolism and energy expenditure. The signaling potential of bile acids in compartments such as the systemic circulation is regulated in part by an efficient enterohepatic circulation that functions to conserve and channel the pool of bile acids within the intestinal and hepatobiliary compartments. Changes in hepatobiliary and intestinal bile acid transport can alter the composition, size, and distribution of the bile acid pool. These alterations in turn can have significant effects on bile acid signaling and their downstream metabolic targets. This review discusses recent advances in our understanding of the inter-relationship between the enterohepatic cycling of bile acids and the metabolic consequences of signaling via bile acid-activated receptors, such as farnesoid X nuclear receptor (FXR) and the G-protein-coupled bile acid receptor (TGR5).

https://doi.org/10.1016/j.apsb.2015.01.001

https://www.ncbi.nlm.nih.gov/pubmed/4629214

http://linkinghub.elsevier.com/retrieve/pii/S2211383515000039

Cited in this article [1]

[50]

,Li

,Zalzala

,et al.Farnesoid X receptor activation increases reverse cholesterol transport by modulating bile acid composition and cholesterol absorption in mice[J]. Hepatology,2016,64(4):1072-1085. DOI:10.1002/hep.28712.

Activation of farnesoid X receptor (FXR) markedly attenuates development of atherosclerosis in animal models. However, the underlying mechanism is not well elucidated. Here, we show that the FXR agonist, obeticholic acid (OCA), increases fecal cholesterol excretion and macrophage reverse cholesterol transport (RCT) dependent on activation of hepatic FXR. OCA does not increase biliary cholesterol secretion, but inhibits intestinal cholesterol absorption. OCA markedly inhibits hepatic cholesterol 7 -hydroxylase (Cyp7a1) and sterol 12 -hydroxylase (Cyp8b1) partly through inducing small heterodimer partner, leading to reduced bile acid pool size and altered bile acid composition, with the / -muricholic acid proportion in bile increased by 2.6-fold and taurocholic acid (TCA) level reduced by 71%. Overexpression of Cyp8b1 or concurrent overexpression of Cyp7a1 and Cyp8b1 normalizes TCA level, bile acid composition, and intestinal cholesterol absorption. Activation of FXR inhibits intestinal cholesterol absorption by modulation of bile acid pool size and composition, thus leading to increased RCT. Targeting hepatic FXR and/or bile acids may be useful for boosting RCT and preventing the development of atherosclerosis. (Hepatology 2016;64:1072-1085).

https://doi.org/10.1002/hep.28712

https://www.ncbi.nlm.nih.gov/pubmed/27359351

http://doi.wiley.com/10.1002/hep.28712

Cited in this article [1]

[51]

de Boer

,Schonewille

,Boesjes

,et al. Intestinal farnesoid X receptor controls transintestinal cholesterol excretion in mice[J].Gastroenterology,2017,152(5):1126-1138.DOI:10.1053/j.gastro.2016.12.037.

BACKGROUND & AIMS: The role of the intestine in the maintenance of cholesterol homeostasis is increasingly recognized. Fecal excretion of cholesterol is the last step in the atheroprotective reverse cholesterol transport pathway, to which biliary and transintestinal cholesterol excretion (TICE) contribute. The mechanisms controlling the flux of cholesterol through the TICE pathway are, however, poorly understood. We aimed to identify mechanisms that regulate and stimulate TICE. METHODS: We performed studies with C57Bl/6J mice, as well as mice with intestine-specific knockout of the farnesoid X receptor (FXR), mice that express an FXR transgene specifically in the intestine, and ABCG8-knockout mice. Mice were fed a control diet or a diet supplemented with the FXR agonist PX20606, with or without the cholesterol absorption inhibitor ezetimibe. Some mice with intestine-specific knockout of FXR were given daily injections of fibroblast growth factor (FGF)19. To determine fractional cholesterol absorption, mice were given intravenous injections of cholesterol-D5 and oral cholesterol-D7. Mice were given (13)C-acetate in drinking water for measurement of cholesterol synthesis. Bile cannulations were performed and biliary cholesterol secretion rates were assessed. In a separate set of experiments, bile ducts of male Wistar rats were exteriorized, allowing replacement of endogenous bile by a model bile. RESULTS: In mice, we found TICE to be regulated by intestinal FXR, via induction of its target gene Fgf15 (in mouse; FGF19 in rat and human). Stimulation of this pathway caused mice to excrete up to 60% of their total cholesterol content each day. PX20606 and FGF19 each increased the ratio of muricholate:cholate in bile, inducing a more hydrophilic bile salt pool. The altered bile salt pool stimulated robust secretion of cholesterol into the intestinal lumen via the sterol-exporting heterodimer ATP binding cassette subfamily G member 5/8 (ABCG5/G8). Of note, the increase in TICE induced by PX20206 was independent of changes in cholesterol absorption. CONCLUSIONS: Hydrophilicity of the bile salt pool, controlled by FXR and FGF15/19, is an important determinant of cholesterol removal via TICE. Strategies that alter bile salt pool composition might be developed for prevention of cardiovascular disease.

https://doi.org/10.1053/j.gastro.2016.12.037

https://www.ncbi.nlm.nih.gov/pubmed/28065787

http://linkinghub.elsevier.com/retrieve/pii/S0016508517300057

Cited in this article [1]

[52]

Xiao

,Dash

,Morgantini

,et al.New and emerging regulators of intestinal lipoprotein secretion[J]. Atherosclerosis,2014,233(2):608-615. DOI:10.1016/j.atherosclerosis.2013.12.047.

Abstract Overproduction of hepatic apoB100-containing VLDL particles has been well documented in animal models and in humans with insulin resistance such as the metabolic syndrome and type 2 diabetes, and contributes to the typical dyslipidemia of these conditions. In addition, postprandial hyperlipidemia and elevated plasma concentrations of intestinal apoB48-containing chylomicron and chylomicron remnant particles have been demonstrated in insulin resistant states. Intestinal lipoprotein production is primarily determined by the amount of fat ingested and absorbed. Until approximately 10 years ago, however, relatively little attention was paid to the role of the intestine itself in regulating the production of triglyceride-rich lipoproteins (TRL) and its dysregulation in pathological states such as insulin resistance. We and others have shown that insulin resistant animal models and humans are characterized by overproduction of intestinal apoB48-containing lipoproteins. Whereas various factors are known to regulate hepatic lipoprotein particle production, less is known about factors that regulate the production of intestinal lipoprotein particles. Monosacharides, plasma free fatty acids (FFA), resveratrol, intestinal peptides (e.g. GLP-1 and GLP-2), and pancreatic hormones (e.g. insulin) have recently been shown to be important regulators of intestinal lipoprotein secretion. Available evidence in humans and animal models strongly supports the concept that the small intestine is not merely an absorptive organ but rather plays an active role in regulating the rate of production of chylomicrons in fed and fasting states. Metabolic signals in insulin resistance and type 2 diabetes and in some cases an aberrant intestinal response to these factors contribute to the enhanced formation and secretion of TRL. Understanding the regulation of intestinal lipoprotein production is imperative for the development of new therapeutic strategies for the prevention and treatment of dyslipidemia. Here we review recent developments in this field and present evidence that intestinal lipoprotein production is a process with metabolic plasticity and that modulation of intestinal lipoprotein secretion may be a feasible therapeutic strategy in the treatment of dyslipidemia and possibly prevention of atherosclerosis. Copyright 2014 Elsevier Ireland Ltd. All rights reserved.

https://doi.org/10.1016/j.atherosclerosis.2013.12.047

https://www.ncbi.nlm.nih.gov/pubmed/24534456

http://linkinghub.elsevier.com/retrieve/pii/S0021915014000239

Cited in this article [3]

[53]

Levy

.Insights from human congenital disorders of intestinal lipid metabolism[J]. J Lipid Res,2015,56(5):945-962. DOI:10.1194/jlr.R052415.

The intestine must challenge the profuse daily flux of dietary fat that serves as a vital source of energy and as an essential component of cell membranes. The fat absorption process takes place in a series of orderly and interrelated steps, including the uptake and translocation of lipolytic products from the brush border membrane to the endoplasmic reticulum, lipid esterification, Apo synthesis, and ultimately the packaging of lipid and Apo components into chylomicrons (CMs). Deciphering inherited disorders of intracellular CM elaboration afforded new insight into the key functions of crucial intracellular proteins, such as Apo B, microsomal TG transfer protein, and Sar1b GTPase, the defects of which lead to hypobetalipoproteinemia, abetalipoproteinemia, and CM retention disease, respectively. These "experiments of nature" are characterized by fat malabsorption, steatorrhea, failure to thrive, low plasma levels of TGs and cholesterol, and deficiency of liposoluble vitamins and essential FAs. After summarizing and discussing the functions and regulation of these proteins for reader's comprehension, the current review focuses on their specific roles in malabsorptions and dyslipidemia-related intestinal fat hyperabsorption while dissecting the spectrum of clinical manifestations and managements. The influence of newly discovered proteins (proprotein convertase subtilisin/kexin type 9 and angiopoietin-like 3 protein) on fat absorption has also been provided. Finally, it is stressed how the overexpression or polymorphism status of the critical intracellular proteins promotes dyslipidemia and cardiometabolic disorders.

https://doi.org/10.1194/jlr.R052415

https://www.ncbi.nlm.nih.gov/pubmed/25387865

http://www.jlr.org/lookup/doi/10.1194/jlr.R052415

Cited in this article [1]

[54]

Dash

,Xiao

,Morgantini

,et al.New Insights into the Regulation of Chylomicron Production[J]. Annu Rev Nutr,2015,35:265-294. DOI:10.1146/annurev-nutr-071714-034338.

Abstract Dietary lipids are efficiently absorbed by the small intestine, incorporated into triglyceride-rich lipoproteins (chylomicrons), and transported in the circulation to various tissues. Intestinal lipid absorption and mobilization and chylomicron synthesis and secretion are highly regulated processes. Elevated chylomicron production rate contributes to the dyslipidemia seen in common metabolic disorders such as insulin-resistant states and type 2 diabetes and likely increases the risk for atherosclerosis seen in these conditions. An in-depth understanding of the regulation of chylomicron production may provide leads for the development of drugs that could be of therapeutic utility in the prevention of dyslipidemia and atherosclerosis. Chylomicron secretion is subject to regulation by various factors, including diet, body weight, genetic variants, hormones, nutraceuticals, medications, and emerging interventions such as bariatric surgical procedures. In this review we discuss the regulation of chylomicron production, mechanisms that underlie chylomicron dysregulation, and potential avenues for future research.

https://doi.org/10.1146/annurev-nutr-071714-034338

https://www.ncbi.nlm.nih.gov/pubmed/25974693

http://www.annualreviews.org/doi/10.1146/annurev-nutr-071714-034338

Cited in this article [2]