ABCG8

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Helen H Hobbs - One of the best experts on this subject based on the ideXlab platform.

  • structural role of abcg5 ABCG8 in sterol transport
    Biophysical Journal, 2017
    Co-Authors: Jyh-yeuan Lee, Daniel M. Rosenbaum, Helen H Hobbs
    Abstract:

    ATP binding cassette (ABC) transporters play critical roles in maintaining sterol homeostasis in eukaryotic organisms, including yeast, plants and mammals. In humans, the heterodimeric ABCG5/ABCG8 (G5G8) mediates the excretion of cholesterol and dietary plant sterols into bile and into the gut lumen. Mutations inactivating either ABCG5 or ABCG8 cause sitosterolemia, a rare autosomal recessive genetic disorder characterized by plant sterol accumulation, hypercholesterolemia, and premature coronary atherosclerosis. ABCG5 and ABCG8 are half ABC transporters;each subunit consists of an N-terminal nucleotide-binding domain (NBD) and a C-terminal transmembrane domain (TMD). The NBDs dimerize to form two catalytically asymmetric nucleotide-binding sites (NBS), one that is catalytically active (NBS2) and the other inactive (NBS1). To understand the structural basis for G5G8-mediated sterol transport we developed a large-scale purification of human G5G8 by exploiting Pichia patoris yeast. We crystallized the transporter in lipid bilayers, solved its structure in a nucleotide-free state at 3.9 A resolution, and generated the first atomic model of an ABC sterol transporter. G5G8 presents a new structural configuration for the TMD of ABC transporters, which is present in a large and functionally diverse ABC2 superfamily. We discover that the TMD and the NBS are coupled through networks of interactions that differ between NBS1 and NBS2, reflecting the catalytic asymmetry of the transporter. A series of conserved polar residues in the TMD form polar networks that we proposed play a role in transmitting signals from the ATPase catalysis in the NBS to sterol transport on the TMD. Molecular dynamic simulation and long-range coevolution analysis revealed an inward-upward TMD movement that predicts a significant conformational change between the TMD subunits. Thus, the G5G8 structure provides a molecular framework that allows us to propose a mechanistic model for ABC transporter-mediated sterol transport and to analyze the disruptive effects of mutations causing sitosterolemia. The structure will serve as a structural template for homology modelling to a wide range of transport system that is regulated by ABCG transporters and by ABC2 superfamily.

  • selective sterol accumulation in abcg5 ABCG8 deficient mice
    Journal of Lipid Research, 2004
    Co-Authors: Klaus Von Bergmann, Dieter Lutjohann, Helen H Hobbs, Jonathan Cohen
    Abstract:

    The ATP binding cassette (ABC) transporters ABCG5 and ABCG8 limit intestinal absorption and promote biliary secretion of neutral sterols. Mutations in either gene cause sitosterolemia, a rare recessive disease in which plasma and tissue levels of several neutral sterols are in- creased to varying degrees. To determine why patients with sitosterolemia preferentially accumulate noncholesterol ste- rols, levels of cholesterol and the major plant sterols were compared in plasma, liver, bile, and brain of wild-type and ABCG5/ABCG8-deficient ( G5G8 � / � ) mice. The total sterol content of liver and plasma was similar in G5G8 � / � mice and wild-type animals despite an � 30-fold increase in non- cholesterol sterol levels in the knockout animals. The relative enrichment of each sterol in the plasma and liver of G5G8 � / � mice (stigmasterolsitosterolcholestanolbassicas- terolcampesterolcholesterol) reflected its relative en- richment in the bile of wild-type mice. These results indi- cate that 24-alkylated, � 22 , and 5 � -reduced sterols are preferentially secreted into bile and that preferential biliary secretion of noncholesterol sterols by ABCG5 and ABCG8 prevents the accumulation of these sterols in normal ani- mals. The mRNA levels for 13 enzymes in the cholesterol biosynthetic pathway were reduced in the livers of the G5G8 � / � mice, despite a 50% reduction in hepatic choles- terol level. Thus, the accumulation of sterols other than cholesterol is sensed by the cholesterol regulatory machin- ery. —Yu, L., K. von Bergmann, D. Lutjohann, H. H. Hobbs, and J. C. Cohen. Selective sterol accumulation in ABCG5/ ABCG8-deficient mice. J. Lipid Res. 2004. 45: 301-307.

  • ABCG5 and ABCG8 Are Obligate Heterodimers for Protein Trafficking and Biliary Cholesterol Excretion
    Journal of Biological Chemistry, 2003
    Co-Authors: Gregory A Graf, Robert Gerard, Pamela L Tuma, Wei-ping Li, Jonathan C Cohen, Liqing Yu, Helen H Hobbs
    Abstract:

    ABCG5 (G5) and ABCG8 (G8) are ATP-binding cassette (ABC) transporters that limit intestinal absorption and promote biliary excretion of neutral sterols. Mutations in either ABCG5 or ABCG8 result in an identical clinical phenotype, suggesting that these two half-transporters function as heterodimers. Expression of both G5 and G8 is required for either protein to be transported to the plasma membrane of cultured cells. In this paper we used immunofluorescence microscopy to confirm, in vivo, that G5 is localized to the apical membranes of mouse enterocytes and hepatocytes. Other ABC half-transporters function as homodimers or as heterodimers with other subfamily members. To determine whether G5 or G8 complex with other ABCG half-transporters, we co-expressed G1, G2, and G4 with either G5 or G8 in cultured cells. G1, G2, and G4 co-immunoprecipitated with G5, and G4 co-immunoprecipitated with G8, but the putative dimers were retained in the endoplasmic reticulum (ER). Adenovirus-mediated expression of either G5 or G8 in the liver of G5G8 null mice resulted in ER retention of the expressed proteins and no increase in biliary cholesterol. In contrast, co-expression of G5 and G8 resulted in transit of the proteins out of the ER and a 10-fold increase in biliary cholesterol concentration. Finally, adenoviral expression of G2 in the presence or absence of G5 or G8 failed to promote sterol excretion into bile. These experiments indicate that G5 and G8 function as obligate heterodimers to promote sterol excretion into bile.

  • Disruption of Abcg5 and ABCG8 in mice reveals their crucial role in biliary cholesterol secretion
    Proceedings of the National Academy of Sciences of the United States of America, 2002
    Co-Authors: Robert E Hammer, Jia Li-hawkins, Dieter Lutjohann, Jonathan Cohen, Klaus Von Bergmann, Helen H Hobbs
    Abstract:

    Cholesterol and other sterols exit the body primarily by secretion into bile. In patients with sitosterolemia, mutations in either of two ATP-binding cassette (ABC) half-transporters, ABCG5 or ABCG8, lead to reduced secretion of sterols into bile, implicating these transporters in this process. To elucidate the roles of ABCG5 and ABCG8 in the trafficking of sterols, we disrupted Abcg5 and ABCG8 in mice (G5G8−/−). The G5G8−/− mice had a 2- to 3-fold increase in the fractional absorption of dietary plant sterols, which was associated with an ≈30-fold increase in plasma sitosterol. Biliary cholesterol concentrations were extremely low in the G5G8−/− mice when compared with wild-type animals (mean = 0.4 vs. 5.5 μmol/ml) and increased only modestly with cholesterol feeding. Plasma and liver cholesterol levels were reduced by 50% in the chow-fed G5G8−/− mice and increased 2.4- and 18-fold, respectively, after cholesterol feeding. These data indicate that ABCG5 and ABCG8 are required for efficient secretion of cholesterol into bile and that disruption of these genes increases dramatically the responsiveness of plasma and hepatic cholesterol levels to changes in dietary cholesterol content.

  • coexpression of atp binding cassette proteins abcg5 and ABCG8 permits their transport to the apical surface
    Journal of Clinical Investigation, 2002
    Co-Authors: Gregory A Graf, Jonathan Cohen, Robert D Gerard, Ingrid Gelissen, Ann L White, Helen H Hobbs
    Abstract:

    Mutations in either ATP-binding cassette (ABC) G5 or ABCG8 cause sitosterolemia, an autosomal recessive disorder of sterol trafficking. To determine the site of action of ABCG5 and ABCG8, we expressed recombinant, epitope-tagged mouse ABCG5 and ABCG8 in cultured cells. Both ABCG5 and ABCG8 underwent N-linked glycosylation. When either protein was expressed individually in cells, the N-linked sugars remained sensitive to Endoglycosidase H (Endo H). When ABCG5 and ABCG8 were coexpressed, the attached sugars were Endo H–resistant and neuraminidase-sensitive, indicating that the proteins were transported to the trans-Golgi complex. The mature, glycosylated forms of ABCG5 and ABCG8 coimmunoprecipitated, consistent with heterodimerization of these two proteins. The Endo H–sensitive forms of ABCG5 and ABCG8 were confined to the endoplasmic reticulum (ER), whereas the mature forms were present in non-ER fractions in cultured hepatocytes. Immunoelectron microscopy revealed ABCG5 and ABCG8 on the plasma membrane of these cells. In polarized WIF-B cells, recombinant ABCG5 localized to the apical (canalicular) membrane when coexpressed with ABCG8, but not when expressed alone. To our knowledge this is the first direct demonstration that trafficking of an ABC half-transporter to the cell surface requires the presence of its dimerization partner.

Albert K Groen - One of the best experts on this subject based on the ideXlab platform.

  • hepatic abcg5 g8 overexpression substantially increases biliary cholesterol secretion but does not impact in vivo macrophage to feces rct
    Atherosclerosis, 2015
    Co-Authors: Arne Dikkers, Jan Freark De Boer, Albert K Groen, Uwe J. F. Tietge
    Abstract:

    Abstract Background and aims 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. Methods 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. Results In ABCG8 knockouts, biliary cholesterol secretion was decreased by 75% (p  Conclusions 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.

  • the sterol transporting heterodimer abcg5 ABCG8 requires bile salts to mediate cholesterol efflux
    FEBS Letters, 2007
    Co-Authors: Carlos L J Vrins, Edwin Vink, Kristin E. Vandenberghe, Raoul J. J. M. Frijters, Jurgen Seppen, Albert K Groen
    Abstract:

    The ATP binding cassette transporters ABCG5 and ABCG8 are indispensable for hepatobiliary cholesterol transport. In this study, we investigated the specificity of the heterodimer for cholesterol acceptors. Dog gallbladder epithelial cells were mono- or double-transfected with lentiviral mouse Abcg5 and ABCG8 vectors. Double-transfected cells showed increased efflux to different bile salt (BS) species, while mono-transfected cells did not show enhanced efflux. The efflux was initiated at micellar concentrations and addition of phosphatidylcholine increased efflux. Cholesterol secretion was highly BS dependent, whereas other cholesterol acceptors such as ApoAI, HDL or methyl-β-cyclodextrin did not elicit Abcg5/g8 dependent cholesterol secretion.

  • the mechanism of abcg5 ABCG8 in biliary cholesterol secretion in mice
    Journal of Lipid Research, 2006
    Co-Authors: Astrid Kosters, Cindy Kunne, Ronald Oude P J Elferink, Norbert Looije, Albert K Groen
    Abstract:

    The main player in biliary cholesterol secretion is the heterodimeric transporter complex, ABCG5/ABCG8, the function of which is necessary for the majority of sterols secreted into bile. It is not clear whether the primary step in this process is flopping of cholesterol from the inner to the outer leaflet of the canalicular membrane, with desorption by mixed micelles, or decreasing of the activation energy required for cholesterol desorption from the outer membrane leaflet. In this study, we investigated these mechanisms by infusing ABCG8+/+, ABCG8+/−, and ABCG8−/− mice with hydrophilic and hydrophobic bile salts. In ABCG8−/− mice, this failed to substantially stimulate biliary cholesterol secretion. Infusion of the hydrophobic bile salt taurodeoxycholate also resulted in cholestasis, which was induced in ABCG8−/− mice at a much lower infusion rate compared with Abc8−/− and ABCG8+/− mice, suggesting a reduced cholesterol content in the outer leaflet of the canalicular membrane. Indeed, isolation of canalicular membranes revealed a reduction of 45% in cholesterol content under these conditions in ABCG8−/− mice. Our data support the model that ABCG5/ABCG8 primarily play a role in flopping cholesterol (and sterols) from the inner leaflet to the outer leaflet of the canalicular membrane.—Kosters, A., C. Kunne, N. Looije, S. B. Patel, R. P. J. Oude Elferink, and A. K. Groen. The mechanism of ABCG5/ABCG8 in biliary cholesterol secretion in mice.

  • down regulation of hepatic and intestinal abcg5 and ABCG8 expression associated with altered sterol fluxes in rats with streptozotocin induced diabetes
    Diabetologia, 2004
    Co-Authors: Vincent W Bloks, Albert K Groen, Edwin Vink, W Bakkervan M Waarde, Henkjan J Verkade, Ido P Kema, Henk Wolters, Folkert Kuipers
    Abstract:

    Aim/hypothesis Type I diabetes is associated with altered hepatic bile formation and increased intestinal cholesterol absorption. The aim of this study was to evaluate whether altered expression of the ATP-Binding Cassette half-transporters Abcg5 and ABCG8, recently implicated in control of both hepatobiliary cholesterol secretion and intestinal cholesterol absorption, contributes to changed cholesterol metabolism in experimental diabetes.

  • relation between hepatic expression of atp binding cassette transporters g5 and g8 and biliary cholesterol secretion in mice
    Journal of Hepatology, 2003
    Co-Authors: Astrid Kosters, Edwin Vink, Roelof Ottenhoff, Raoul J. J. M. Frijters, Frank G Schaap, Torsten Plosch, M Jirsa, Iris M De Cuyper, Folkert Kuipers, Albert K Groen
    Abstract:

    Abstract Background/Aim : Mutations in genes encoding the ATP-binding cassette (ABC)-transporters ABCG5 and ABCG8 underlie sitosterolemia, which is characterized by elevated plasma levels of phytosterols due to increased intestinal absorption and impaired biliary secretion of sterols. The aim of our study was to correlate the expression levels of Abcg5 and ABCG8 to biliary cholesterol secretion in various (genetically-modified) mouse models. Methods : Bile was collected from genetically-modified mice fed a chow diet, or from mice fed either a chow diet, or chow supplemented with either 1% diosgenin, 0.1% simvastatin, or a synthetic liver X receptor agonist, for determination of biliary lipids. Livers and small intestines were harvested and expression levels of Abcg5 , ABCG8 and Abcb4 were determined by real-time polymerase chain reaction. Results : Intestinal expression of Abcg5 and ABCG8 did not show much variation between the various models. In contrast, a linear correlation between hepatic expression levels of Abcg5 and ABCG8 and biliary cholesterol secretion rates was found. This relation was independent of Abcb4-mediated phospholipid secretion. However, in diosgenin-fed mice showing cholesterol hypersecretion, hepatic Abcg5 and ABCG8 expression levels remained unchanged. Conclusions : Our results strongly support a role for Abcg5 and ABCG8 in regulation of biliary cholesterol secretion, but also indicate the existence of a largely independent route of cholesterol secretion.

Dieter Lutjohann - One of the best experts on this subject based on the ideXlab platform.

  • systematic haplotype analysis resolves a complex plasma plant sterol locus on the micronesian island of kosrae
    Proceedings of the National Academy of Sciences of the United States of America, 2009
    Co-Authors: Eimear E Kenny, Dieter Lutjohann, Alexander Gusev, Kaitlin Riegel, Jennifer K Lowe, Jacqueline Salit, Julian Maller, Markus Stoffel, Mark J Daly, David Altshuler
    Abstract:

    Pinpointing culprit causal variants along signal peaks of genome-wide association studies (GWAS) is challenging. To overcome confounding effects of multiple independent variants at such a locus and narrow the interval for causal allele capture, we developed an approach that maps local shared haplotypes harboring a putative causal variant. We demonstrate our method in an extreme isolate founder population, the pacific Island of Kosrae. We analyzed plasma plant sterol (PPS) levels, a surrogate measure of cholesterol absorption from the intestine, where previous studies have implicated 2p21 mutations in the ATP binding cassette subfamily G members 5 or 8 (ABCG5 or ABCG8) genes. We have previously reported that 11.1% of the islanders are carriers of a frameshift ABCG8 mutation increasing PPS levels in carriers by 50%. GWAS adjusted for this mutation revealed genomewide significant signals along 11 Mb around it. To fine-map this signal, we detected pairwise identity-by-descent haplotypes using our tool GERMLINE and implemented a clustering algorithm to identify haplotypes shared across multiple samples with their unique shared boundaries. A single 526-kb haplotype mapped strongly to PPS levels, dramatically refining the mapped interval. This haplotype spans the ABCG5/ABCG8 genes, is carried by 1.8% of the islanders, and results in a striking 100% increase of PPS in carriers. Resequencing of ABCG5 in these carriers found a D450H missense mutation along the associated haplotype. These findings exemplify the power of haplotype analysis for mapping mutations in isolated populations and specifically for dissecting effects of multiple variants of the same locus.

  • atp binding cassette transporters g1 and g4 mediate cholesterol and desmosterol efflux to hdl and regulate sterol accumulation in the brain
    The FASEB Journal, 2008
    Co-Authors: Nan Wang, Laurent Yvancharvet, Tim Vanmierlo, Dieter Lutjohann, Monique Mulder, Taewan Kim
    Abstract:

    Transporters in the ABCG family appear to be involved in the cellular excretion of cholesterol and other sterols in a cell- and tissue-specific fashion. Overexpression of ATP-binding cassette transporters G1 (Abcg1) and G4 (Abcg4) can promote cellular cholesterol efflux to high-density lipoprotein (HDL), but the in vivo functions of Abcg4 are poorly understood. We used mice with knockouts of Abcg1 or Abcg4 singly or together to further elucidate the function of these transporters. Abcg1 and Abcg4 are highly expressed in the brain and are found in both astrocytes and neurons. Whereas Abcg1−/− or Abcg4−/− mice showed essentially normal levels of brain sterols, in Abcg1−/−/Abcg4−/− mice, levels of several sterol intermediates in the cholesterol biosynthetic pathway, namely desmosterol, lathosterol, and lanosterol, as well as 27-OH cholesterol, were increased 2- to 3-fold. Overexpression of Abcg1 or Abcg4 promoted efflux of desmosterol and cholesterol from cells to HDL, and combined deficiency of these transp...

  • selective sterol accumulation in abcg5 ABCG8 deficient mice
    Journal of Lipid Research, 2004
    Co-Authors: Klaus Von Bergmann, Dieter Lutjohann, Helen H Hobbs, Jonathan Cohen
    Abstract:

    The ATP binding cassette (ABC) transporters ABCG5 and ABCG8 limit intestinal absorption and promote biliary secretion of neutral sterols. Mutations in either gene cause sitosterolemia, a rare recessive disease in which plasma and tissue levels of several neutral sterols are in- creased to varying degrees. To determine why patients with sitosterolemia preferentially accumulate noncholesterol ste- rols, levels of cholesterol and the major plant sterols were compared in plasma, liver, bile, and brain of wild-type and ABCG5/ABCG8-deficient ( G5G8 � / � ) mice. The total sterol content of liver and plasma was similar in G5G8 � / � mice and wild-type animals despite an � 30-fold increase in non- cholesterol sterol levels in the knockout animals. The relative enrichment of each sterol in the plasma and liver of G5G8 � / � mice (stigmasterolsitosterolcholestanolbassicas- terolcampesterolcholesterol) reflected its relative en- richment in the bile of wild-type mice. These results indi- cate that 24-alkylated, � 22 , and 5 � -reduced sterols are preferentially secreted into bile and that preferential biliary secretion of noncholesterol sterols by ABCG5 and ABCG8 prevents the accumulation of these sterols in normal ani- mals. The mRNA levels for 13 enzymes in the cholesterol biosynthetic pathway were reduced in the livers of the G5G8 � / � mice, despite a 50% reduction in hepatic choles- terol level. Thus, the accumulation of sterols other than cholesterol is sensed by the cholesterol regulatory machin- ery. —Yu, L., K. von Bergmann, D. Lutjohann, H. H. Hobbs, and J. C. Cohen. Selective sterol accumulation in ABCG5/ ABCG8-deficient mice. J. Lipid Res. 2004. 45: 301-307.

  • loci on chromosomes 14 and 2 distinct from abcg5 ABCG8 regulate plasma plant sterol levels in a c57bl 6j x casa rk intercross
    Proceedings of the National Academy of Sciences of the United States of America, 2002
    Co-Authors: Ephraim Sehayek, Dieter Lutjohann, Gerald Salen, Klaus Von Bergmann, Elizabeth M Duncan, Jennie G Ono, Ashok K Batta, Jan L Breslow
    Abstract:

    Plasma plant sterol levels differ among humans due to genetic and dietary factors. A disease characterized by high plasma plant sterol levels, β-sitosterolemia, was recently found to be due to mutations at the ABCG5/ABCG8 locus. To detect variants at this and other loci, a genetic cross was carried out between two laboratory mouse strains. Parental C57BL/6J had almost twice the campesterol and sitosterol levels compared with parental CASA/Rk mice, and F1 mice had levels halfway between the parentals. An intercross between F1s was performed and plasma plant sterol levels measured in 102 male and 99 female F2 mice. Plasma plant sterols in F2s displayed a unimodal distribution, suggesting the effects of several rather a single major gene. In the F2 mice, a full genome scan revealed significant linkages on chromosomes 14 and 2. With regard to chromosome 14, analysis showed a single peak for linkage at 17 cM with a logarithm of odds (LOD) score of 9.9, designated plasma plant sterol 14 (Plast14). With regard to chromosome 2, analysis showed two significant peaks for linkage at 18 and 65 cMs with LOD scores of 4.1 and 3.65, respectively, designated Plast2a and Plast2b, respectively. Four interactions between loci, predominantly of an additive nature, were also demonstrated, the most significant between Plast14 and Plast2b (LOD 16.44). No significant linkage or gene interaction was detected for the ABCG5/ABCG8 locus on chromosome 17. Therefore, other genes besides ABCG5/ABCG8 influence plasma plant sterol levels and now become candidates to explain differences in plasma plant sterol levels between humans.

  • Disruption of Abcg5 and ABCG8 in mice reveals their crucial role in biliary cholesterol secretion
    Proceedings of the National Academy of Sciences of the United States of America, 2002
    Co-Authors: Robert E Hammer, Jia Li-hawkins, Dieter Lutjohann, Jonathan Cohen, Klaus Von Bergmann, Helen H Hobbs
    Abstract:

    Cholesterol and other sterols exit the body primarily by secretion into bile. In patients with sitosterolemia, mutations in either of two ATP-binding cassette (ABC) half-transporters, ABCG5 or ABCG8, lead to reduced secretion of sterols into bile, implicating these transporters in this process. To elucidate the roles of ABCG5 and ABCG8 in the trafficking of sterols, we disrupted Abcg5 and ABCG8 in mice (G5G8−/−). The G5G8−/− mice had a 2- to 3-fold increase in the fractional absorption of dietary plant sterols, which was associated with an ≈30-fold increase in plasma sitosterol. Biliary cholesterol concentrations were extremely low in the G5G8−/− mice when compared with wild-type animals (mean = 0.4 vs. 5.5 μmol/ml) and increased only modestly with cholesterol feeding. Plasma and liver cholesterol levels were reduced by 50% in the chow-fed G5G8−/− mice and increased 2.4- and 18-fold, respectively, after cholesterol feeding. These data indicate that ABCG5 and ABCG8 are required for efficient secretion of cholesterol into bile and that disruption of these genes increases dramatically the responsiveness of plasma and hepatic cholesterol levels to changes in dietary cholesterol content.

Folkert Kuipers - One of the best experts on this subject based on the ideXlab platform.

  • stimulation of murine biliary cholesterol secretion by thyroid hormone is dependent on a functional abcg5 g8 complex
    Hepatology, 2012
    Co-Authors: Ylva Bonde, Torsten Plosch, Folkert Kuipers, Bo Angelin, Mats Rudling
    Abstract:

    Secretion of cholesterol into bile is important for the elimination of cholesterol from the body. Thyroid hormone (TH) increases biliary cholesterol secretion and hepatic gene expression of adenosine triphosphate (ATP)-binding cassette, subfamily G (WHITE), member 5 (ABCG5) and ATP-binding cassette, subfamily G (WHITE), member 8 (ABCG8), two half-transporters that act as a heterodimeric complex promoting sterol secretion. In addition, nuclear liver x receptor-alpha (LXRa), also regulated by TH, induces gene expression of ABCG5/G8. We here investigated if the TH-induced stimulation of biliary cholesterol secretion is mediated by the ABCG5/G8 complex in vivo, and if so, whether LXRa is involved. Mice homozygous for disruption of Abcg5 (Abcg5−/−) or Lxra (Lxra−/−) and their wild-type counterparts were treated with triiodothyronine (T3) for 14 days and compared to untreated mice of corresponding genetic backgrounds. Bile was collected by gallbladder cannulation, and liver samples were analyzed for gene expression levels. Basal biliary cholesterol secretion in Abcg5−/− mice was 72% lower than in Abcg5+/+ mice. T3 treatment increased cholesterol secretion 3.1-fold in Abcg5+/+ mice, whereas this response was severely blunted in Abcg5−/− mice. In contrast, biliary cholesterol secretion in T3-treated Lxra+/+ and Lxra−/− mice was increased 3.5- and 2.6-fold, respectively, and did not differ significantly. Conclusions: TH-induced secretion of cholesterol into bile is largely dependent on an intact ABCG5/G8 transporter complex, whereas LXRa is not critical for this effect. (HEPATOLOGY 2012;56:1828–1837)

  • abcg5 ABCG8 independent pathways contribute to hepatobiliary cholesterol secretion in mice
    American Journal of Physiology-gastrointestinal and Liver Physiology, 2006
    Co-Authors: Torsten Plosch, Jelske N Van Der Veen, Rick Havinga, Nicolette C A Huijkman, Vincent W Bloks, Folkert Kuipers
    Abstract:

    The ATP-binding cassette (ABC) half-transporters ABCG5 and ABCG8 heterodimerize into a functional complex that mediates the secretion of plant sterols and cholesterol by hepatocytes into bile and t...

  • reduction of cholesterol absorption by dietary plant sterols and stanols in mice is independent of the abcg5 8 transporter
    Journal of Nutrition, 2006
    Co-Authors: Torsten Plosch, Rick Havinga, Nicolette C A Huijkman, Vincent W Bloks, Janine K Kruit, Guus S M J E Duchateau, Yuguang Lin, Folkert Kuipers
    Abstract:

    Dietary supplementation with plant sterols, stanols, and their esters reduces intestinal cholesterol absorption, thus lowering plasma LDL cholesterol concentration in humans. It was suggested that these beneficial effects are attributable in part to induction of genes involved in intestinal cholesterol transport, e.g., Abcg5 and ABCG8, via the liver X receptor (LXR), but direct proof is lacking. Male C57BL/6J mice were fed a purified diet (control), diets containing cholesterol (0.12 g/100 g) only, or in combination with either plant sterols or stanols (0.5 g/100 g) for 4 wk. Plant sterols and stanols dramatically increased neutral fecal sterol excretion (2.2 and 1.4-fold, respectively, compared with cholesterol-fed mice; P , 0.05). Cholesterol and cholesterol ester concentrations were higher in livers of mice fed cholesterol compared with controls (1135% and 1925%; P , 0.05). Plant sterols and stanols completely prevented cholesterol accumulation as well as induction of LXR target genes in liver. Feeding plant sterols and stanols did not alter intestinal expression of Abcg5, ABCG8, or other LXR target genes nor of Npc1l1. Fractional cholesterol absorption in Abcg5 2/2 mice was reduced to the same extent by dietary plant sterols (49%) as in wild-type littermates (44%). Plant sterol and stanol-induced reduction of cholesterol absorption in mice is not associated with upregulation of intestinal LXR target genes nor is it influenced by Abcg5-deficiency. Our data indicate that dietary plant sterols and stanols inhibit cholesterol absorption within the intestinal lumen independently of LXR. J. Nutr. 136: 2135‐2140, 2006.

  • down regulation of hepatic and intestinal abcg5 and ABCG8 expression associated with altered sterol fluxes in rats with streptozotocin induced diabetes
    Diabetologia, 2004
    Co-Authors: Vincent W Bloks, Albert K Groen, Edwin Vink, W Bakkervan M Waarde, Henkjan J Verkade, Ido P Kema, Henk Wolters, Folkert Kuipers
    Abstract:

    Aim/hypothesis Type I diabetes is associated with altered hepatic bile formation and increased intestinal cholesterol absorption. The aim of this study was to evaluate whether altered expression of the ATP-Binding Cassette half-transporters Abcg5 and ABCG8, recently implicated in control of both hepatobiliary cholesterol secretion and intestinal cholesterol absorption, contributes to changed cholesterol metabolism in experimental diabetes.

  • relation between hepatic expression of atp binding cassette transporters g5 and g8 and biliary cholesterol secretion in mice
    Journal of Hepatology, 2003
    Co-Authors: Astrid Kosters, Edwin Vink, Roelof Ottenhoff, Raoul J. J. M. Frijters, Frank G Schaap, Torsten Plosch, M Jirsa, Iris M De Cuyper, Folkert Kuipers, Albert K Groen
    Abstract:

    Abstract Background/Aim : Mutations in genes encoding the ATP-binding cassette (ABC)-transporters ABCG5 and ABCG8 underlie sitosterolemia, which is characterized by elevated plasma levels of phytosterols due to increased intestinal absorption and impaired biliary secretion of sterols. The aim of our study was to correlate the expression levels of Abcg5 and ABCG8 to biliary cholesterol secretion in various (genetically-modified) mouse models. Methods : Bile was collected from genetically-modified mice fed a chow diet, or from mice fed either a chow diet, or chow supplemented with either 1% diosgenin, 0.1% simvastatin, or a synthetic liver X receptor agonist, for determination of biliary lipids. Livers and small intestines were harvested and expression levels of Abcg5 , ABCG8 and Abcb4 were determined by real-time polymerase chain reaction. Results : Intestinal expression of Abcg5 and ABCG8 did not show much variation between the various models. In contrast, a linear correlation between hepatic expression levels of Abcg5 and ABCG8 and biliary cholesterol secretion rates was found. This relation was independent of Abcb4-mediated phospholipid secretion. However, in diosgenin-fed mice showing cholesterol hypersecretion, hepatic Abcg5 and ABCG8 expression levels remained unchanged. Conclusions : Our results strongly support a role for Abcg5 and ABCG8 in regulation of biliary cholesterol secretion, but also indicate the existence of a largely independent route of cholesterol secretion.

Edwin Vink - One of the best experts on this subject based on the ideXlab platform.

  • the sterol transporting heterodimer abcg5 ABCG8 requires bile salts to mediate cholesterol efflux
    FEBS Letters, 2007
    Co-Authors: Carlos L J Vrins, Edwin Vink, Kristin E. Vandenberghe, Raoul J. J. M. Frijters, Jurgen Seppen, Albert K Groen
    Abstract:

    The ATP binding cassette transporters ABCG5 and ABCG8 are indispensable for hepatobiliary cholesterol transport. In this study, we investigated the specificity of the heterodimer for cholesterol acceptors. Dog gallbladder epithelial cells were mono- or double-transfected with lentiviral mouse Abcg5 and ABCG8 vectors. Double-transfected cells showed increased efflux to different bile salt (BS) species, while mono-transfected cells did not show enhanced efflux. The efflux was initiated at micellar concentrations and addition of phosphatidylcholine increased efflux. Cholesterol secretion was highly BS dependent, whereas other cholesterol acceptors such as ApoAI, HDL or methyl-β-cyclodextrin did not elicit Abcg5/g8 dependent cholesterol secretion.

  • A mouse model of sitosterolemia: absence of ABCG8/sterolin-2 results in failure to secrete biliary cholesterol
    BMC Medicine, 2004
    Co-Authors: Eric Klett, Sarah Shefer, Hongwei Yu, Kangmo Lu, Ashok Batta, Astrid Kosters, Edwin Vink, Michael Altenburg, Jianliang Chen, Richard Klein
    Abstract:

    Background Mutations in either of two genes comprising the STSL locus, ATP-binding cassette (ABC)-transporters ABCG5 (encoding sterolin-1) and ABCG8 (encoding sterolin-2), result in sitosterolemia, a rare autosomal recessive disorder of sterol trafficking characterized by increased plasma plant sterol levels. Based upon the genetics of sitosterolemia, ABCG5/sterolin-1 and ABCG8/sterolin-2 are hypothesized to function as obligate heterodimers. No phenotypic difference has yet been described in humans with complete defects in either ABCG5 or ABCG8. These proteins, based upon the defects in humans, are responsible for regulating dietary sterol entry and biliary sterol secretion. Methods In order to mimic the human disease, we created, by a targeted disruption, a mouse model of sitosterolemia resulting in ABCG8/sterolin-2 deficiency alone. Homozygous knockout mice are viable and exhibit sitosterolemia. Results Mice deficient in ABCG8 have significantly increased plasma and tissue plant sterol levels (sitosterol and campesterol) consistent with sitosterolemia. Interestingly, Abcg5/sterolin-1 was expressed in both liver and intestine in ABCG8/sterolin-2 deficient mice and continued to show an apical expression. Remarkably, ABCG8 deficient mice had an impaired ability to secrete cholesterol into bile, but still maintained the ability to secrete sitosterol. We also report an intermediate phenotype in the heterozygous ABCG8 +/- mice that are not sitosterolemic, but have a decreased level of biliary sterol secretion relative to wild-type mice. Conclusion These data indicate that ABCG8/sterolin-2 is necessary for biliary sterol secretion and that loss of ABCG8/sterolin-2 has a more profound effect upon biliary cholesterol secretion than sitosterol. Since biliary sitosterol secretion is preserved, although not elevated in the sitosterolemic mice, this observation suggests that mechanisms other than by ABCG8/sterolin-2 may be responsible for its secretion into bile.

  • down regulation of hepatic and intestinal abcg5 and ABCG8 expression associated with altered sterol fluxes in rats with streptozotocin induced diabetes
    Diabetologia, 2004
    Co-Authors: Vincent W Bloks, Albert K Groen, Edwin Vink, W Bakkervan M Waarde, Henkjan J Verkade, Ido P Kema, Henk Wolters, Folkert Kuipers
    Abstract:

    Aim/hypothesis Type I diabetes is associated with altered hepatic bile formation and increased intestinal cholesterol absorption. The aim of this study was to evaluate whether altered expression of the ATP-Binding Cassette half-transporters Abcg5 and ABCG8, recently implicated in control of both hepatobiliary cholesterol secretion and intestinal cholesterol absorption, contributes to changed cholesterol metabolism in experimental diabetes.

  • relation between hepatic expression of atp binding cassette transporters g5 and g8 and biliary cholesterol secretion in mice
    Journal of Hepatology, 2003
    Co-Authors: Astrid Kosters, Edwin Vink, Roelof Ottenhoff, Raoul J. J. M. Frijters, Frank G Schaap, Torsten Plosch, M Jirsa, Iris M De Cuyper, Folkert Kuipers, Albert K Groen
    Abstract:

    Abstract Background/Aim : Mutations in genes encoding the ATP-binding cassette (ABC)-transporters ABCG5 and ABCG8 underlie sitosterolemia, which is characterized by elevated plasma levels of phytosterols due to increased intestinal absorption and impaired biliary secretion of sterols. The aim of our study was to correlate the expression levels of Abcg5 and ABCG8 to biliary cholesterol secretion in various (genetically-modified) mouse models. Methods : Bile was collected from genetically-modified mice fed a chow diet, or from mice fed either a chow diet, or chow supplemented with either 1% diosgenin, 0.1% simvastatin, or a synthetic liver X receptor agonist, for determination of biliary lipids. Livers and small intestines were harvested and expression levels of Abcg5 , ABCG8 and Abcb4 were determined by real-time polymerase chain reaction. Results : Intestinal expression of Abcg5 and ABCG8 did not show much variation between the various models. In contrast, a linear correlation between hepatic expression levels of Abcg5 and ABCG8 and biliary cholesterol secretion rates was found. This relation was independent of Abcb4-mediated phospholipid secretion. However, in diosgenin-fed mice showing cholesterol hypersecretion, hepatic Abcg5 and ABCG8 expression levels remained unchanged. Conclusions : Our results strongly support a role for Abcg5 and ABCG8 in regulation of biliary cholesterol secretion, but also indicate the existence of a largely independent route of cholesterol secretion.