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Browsing by Author "Rigotti, A"

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Biliary lipid secretion, bile acid metabolism, and gallstone formation are not impaired in hepatic lipase-deficient mice
(W B SAUNDERS CO, 2003) Amigo, L; Mardones, P; Ferrada, C; Zanlungo, S; Nervi, F; Miquel, JF; Rigotti, A
Whereas hepatic lipase (HL) has been implicated in lipoprotein metabolism and atherosclerosis, its role in controlling biliary lipid physiology has not been reported. This work characterizes plasma lipoprotein cholesterol, hepatic cholesterol content, bile acid metabolism, biliary cholesterol secretion, and gallstone formation in HL-deficient mice and C57BL/6 controls fed standard chow, a cholesterol-supplemented diet, or a lithogenic diet. Compared with C57BL/6 controls, HL knockout mice exhibited increased basal plasma high-density lipoprotein (HDL) cholesterol as well as reduced cholesterol levels transported in large lipoproteins in response to cholesterol-enriched diets. Hepatic cholesterol content and biliary cholesterol secretion of chow-fed HL knockout and wild-type mice were not different and increased similarly in both strains after feeding dietary cholesterol or a lithogenic diet. There were no differences in biliary bile acid secretion, bile acid pool size and composition, or fecal bile acid excretion between HL-deficient and control mice. HL knockout mice had a similar prevalence of gallstone formation as compared with control mice when both strains were fed with a lithogenic diet. In conclusion, the deficiency of HL has no major impact on the availability of lipoprotein-derived hepatic cholesterol for biliary secretion; HL expression is not essential for diet-induced gallstone formation in mice.
Cholesterol depletion induces PKA-mediated basolateral-to-apical transcytosis of the scavenger receptor class B type I in MDCK cells
(NATL ACAD SCIENCES, 2004) Burgos, PV; Klattenhoff, C; de la Fuente, E; Rigotti, A; Gonzalez, A
Cholesterol-based membrane microdomains, or lipid rafts, are believed to play important, yet poorly defined, roles in protein trafficking and signal transduction. In polarized epithelial cells, the current view is that rafts are involved in apical but not in basolateral protein transport from the trans-Golgi network (TGN). We report here that cholesterol is required in a post-TGN mechanism of basolateral regionalization. Permanently transfected Madin-Darby canine kidney cells segregated the caveolae/raft-associated high-density lipoprotein scavenger receptor class B type I (SR-BI) predominantly to the basolateral domain where it was constitutively internalized and recycled basolaterally. Acute cholesterol depletion did not significantly alter SR-BI internalization, implying a cholesterol depletion-insensitive endocytic process but instead induced its transcytosis through a protein kinase A (PKA)- and microtubule-dependent mechanism. Forskolin also elicited SR-BI transcytosis. The basolateral distribution of endogenous epidermal growth factor receptor remained unaffected. Strikingly, cholesterol depletion induced PKA activity without increasing the cAMP levels. Thus, our results are consistent with a scenario in which cholesterol-based rafts promote internalization and basolateral recycling of internalized SR-BI whereas a PKA pool sensitive to cholesterol depletion mediates SR-BI transcytosis. Regulated transcytosis of SR-BI may provide an additional mechanism to control cholesterol homeostasis. These results disclose relationships between cholesterol-based rafts and PKA activity operating in a post-TGN mechanism of regulated apical-to-basolateral cell surface protein distribution.
Comparative effect of fish oil feeding and other dietary fatty acids on plasma lipoproteins, biliary lipids, and hepatic expression of proteins involved in reverse cholesterol transport in the rat
(KARGER, 2005) Morgado, N; Rigotti, A; Valenzuela, A
Background: While elevated plasma high-density lipoprotein (HDL) levels has been associated to a reduction in cardiovascular risk, dietary fish oils rich in omega-3 polyunsaturated fatty acids (PUFAs) may protect against this disease. The protective effect of HDL is associated to its participation in the reverse cholesterol transport pathway. On the other hand, omega-3 PUFAs decrease plasma HDL levels compared to other fatty acids, which may suggest an effect on reverse cholesterol transport. Aim: In this work, the effect of dietary fish oil on the fatty acid composition of hepatic membranes, plasma lipoprotein cholesterol profile, biliary lipids, and the expression of proteins involved in reverse cholesterol transport, was compared to other dietary oils having a different degree of fatty acid unsaturation. Methods: Male rats were fed a semi synthetic diet containing fish oil ( omega -3), sunflower oil (omega-6), olive oil (omega-9) or coconut oil (saturated). Hepatic membrane fatty acid composition, plasma cholesterol levels, lipoprotein cholesterol profile, biliary lipids, hepatic mRNA levels for lecithin cholesterol acyltransferase, hepatic lipase, apo E, and apo A-I, and hepatic protein levels of the scavenger receptor class B type I, caveolin-1, and the ATP binding cassette transporter A1 were analyzed. Plasma apo A-I and apo E protein levels were also evaluated. Results: Compared to the other diets, omega - 3 PUFAs significantly changed omega-3/omega-6 fatty acid ratio of hepatic membranes, caused a reduction of plasma total and HDL cholesterol, and selectively increased biliary cholesterol secretion. No modifi cation in the expression levels of lecithin cholesterol acyltransferase, hepatic lipase, apo A-I and apo E mRNA was observed. Hepatic scavenger receptor class B type I, caveolin-1, and the ATP binding cassette transporter A1 protein levels were also not affected. Plasma apo A-I, but not apo E, was reduced. Conclusions: These results show that dietary omega-3 PUFAs reduce plasma HDL cholesterol and increase biliary cholesterol without concomitant modifi cations in the expression of key genes and proteins involved in reverse cholesterol transport. These fi ndings suggest that functional changes in the activity of these proteins as consequence of the incorporation of omega3 PUFAs into hepatic membranes and plasma lipoproteins may underlie the effect of fi sh oil feeding on plasma and hepatic cholesterol metabolism in the rat. Copyright (c) 2005 S. Karger AG, Basel.
Down-regulation of intestinal scavenger receptor class B, type I (SR-BI) expression in rodents under conditions of deficient bile delivery to the intestine
(PORTLAND PRESS LTD, 2001) Voshol, PJ; Schwarz, M; Rigotti, A; Krieger, M; Groen, AK; Kuipers, F
Scavenger receptor class B, type I (SR-BI) is expressed in the intestines of rodents and has been suggested to be involved in the absorption of dietary cholesterol. The aim of this study was to determine whether intestinal SR-BI expression is affected in animal models with altered bile delivery to the intestine and impaired cholesterol absorption. SR-BI protein and mRNA levels were determined in proximal and distal small intestine from control, bile-duct-ligated and bile-diverted rats and from control and bile-duct-ligated mice. Two genetically altered mouse models were studied: multidrug resistance-2 P-glycoprotein-deficient [Mdr2((-/-))] mice that produce phospholipid/cholesterol-free bile, and cholesterol 7 alpha -hydroxylase-deficient [Cyp7a((-/-))] mice, which exhibit qualitative and quantitative changes in the bile-salt pool. Cholesterol-absorption efficiency was quantified using a dual-isotope ratio method. SR-BI was present at the apical membrane of enterocytes in control rats and mice and was more abundant in proximal than in distal segments of the intestine. In bile-duct-ligated animals, levels of SR-BI protein were virtually absent and mRNA levels were decreased by approximate to 50 %. Bile-diverted rats, Mdr2((-/-)) mice and Cyp7a((-/-)) mice showed decreased levels of intestinal SR-BI protein while mRNA levels were unaffected. Cholesterol absorption was reduced by > 90% in bile-duct-ligated and bile-diverted animals and in Cyp7a((-/-)) mice, whereas Mdr2((-/-)) mice showed an approximate to 50% reduction. This study shows that SR-BI is expressed at the apical membrane of enterocytes of rats and mice; mainly in the upper intestine where cholesterol absorption is greatest, and indicates that bile components play a role in post-transcriptional regulation of SR-BI expression. Factors associated with cholestasis appear to be involved in transcriptional control of intestinal SR-BI expression. The role of SR-BI in the cholesterol-absorption process remains to be defined.
Effects of hepatic expression of the high-density lipoprotein receptor SR-BI on lipoprotein metabolism and female fertility
(ENDOCRINE SOC, 2006) Yesilaltay, A; Morales, MG; Amigo, L; Zanlungo, S; Rigotti, A; Karackattu, SL; Donahee, MH; Kozarsky, KF; Krieger, M
The etiology of human female infertility is often uncertain. The sterility of high-density lipoprotein (HDL) receptor-negative (SR-BI-/-) female mice suggests a link between female infertility and abnormal lipoprotein metabolism. SR-BI-/- mice exhibit elevated plasma total cholesterol [ with normalsized and abnormally large HDL and high unesterified to total plasma cholesterol (UC:TC) ratio]. We explored the influence of hepatic SR-BI on female fertility by inducing hepatic SR-BI expression in SR-BI-/- animals by adenovirus transduction or stable transgenesis. For transgenes, we used both wild-type SR-BI and a double-point mutant, Q402R/Q418R (SR-BI-RR), which is unable to bind to and mediate lipid transfer from wild-type HDL normally, but retains virtually normal lipid transport activities with low-density lipoprotein. Essentially wild-type levels of hepatic SR-BI expression in SR-BI-/- mice restored to nearly normal the HDL size distribution and plasma UC: TC ratio, whereas approximately 7- to 40- fold overexpression dramatically lowered plasma TC and increased biliary cholesterol secretion. In contrast, SR-BI-RR overexpression had little effect on SR-BI-/- mice, but in SR-BI-/- mice, it substantially reduced levels of abnormally large HDL and normalized the UC: TC ratio. In all cases, hepatic transgenic expression restored female fertility. Overexpression in SR-BI-/- mice of lecithin: cholesterol acyl transferase, which esterifies plasma HDL cholesterol, did not normalize the UC: TC ratio, probably because the abnormal HDL was a poor substrate, and did not restore fertility. Thus, hepatic SR- BImediated lipoprotein metabolism influences murine female fertility, raising the possibility that dyslipidemia might contribute to human female infertility and that targeting lipoprotein metabolism might complement current assisted reproductive technologies.
Enrichment of canalicular membrane with cholesterol and sphingomyelin prevents bile salt-induced hepatic damage
(AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, 1999) Amigo, L; Mendoza, H; Zanlungo, S; Miquel, JF; Rigotti, A; Gonzalez, S; Nervi, F
These studies were undertaken to characterize the role of plasma membrane cholesterol in canalicular secretory functions and hepatocyte integrity against intravenous taurocholate administration. Cholesterol and sphingomyelin concentrations and cholesterol/phospholipid ratios were significantly increased in canalicular membranes of diosgenin-fed rats, suggesting a more resistant structure against solubilization by taurocholate. During taurocholate infusion, control rats had significantly decreased bile flow, whereas diosgenin-fed animals maintained bile flow, Maximal cholesterol output increased by 176% in diosgenin-fed rats, suggesting an increased precursor pool of biliary cholesterol in these animals. Maximal phospholipid output only increased by 43% in diosgenin-fed rats, whereas bile salt output remained at control levels. The kinetics of glutamic oxalacetic: transaminase, lactic dehydrogenase, and alkaline phosphatase activities in bile showed a significantly faster release in control than in diosgenin-fed rats, After 30 min of hp travenous taurocholate infusion, necrotic hepatocytes were significantly increased in control animals.jlr Preservation of bile secretory functions and hepatocellular cytoprotection by diosgenin against the intravenous infusion of toxic doses of taurocholate was associated with an increased concentration of cholesterol and sphingomyelin in the canalicular membrane. The increase of biliary cholesterol output induced by diosgenin was correlated to the enhanced concentration of cholesterol in the canalicular membrane.
Expression and regulation of scavenger receptor class B type I (SR-BI) in gall bladder epithelium
(BMJ PUBLISHING GROUP, 2003) Miquel, JF; Moreno, M; Amigo, L; Molina, H; Mardones, P; Wistuba, II; Rigotti, A
Background and aims: Biliary lipid absorption by the gall bladder mucosa and the cholesterol content of the gall bladder wall appear to play a role in cholesterol gall stone formation. As the scavenger receptor class B type I (SR-BI) regulates cellular cholesterol uptake, we studied its expression in human and murine gall bladders, its regulation by increased biliary lipid content, and its role in gall stone formation.
Fibrates down-regulate hepatic scavenger receptor class B type I protein expression in mice
(AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, 2003) Mardones, P; Pilon, A; Bouly, M; Duran, D; Nishimoto, T; Arai, H; Kozarsky, KF; Altayo, M; Miquel, JF; Luc, G; Clavey, V; Staels, B; Rigotti, A
Fibrates are normolipidemic drugs used in atherogenic dyslipidemia because of their ability to raise high density lipoprotein (HDL) and decrease triglyceride levels. They exert multiple effects on lipid metabolism by activating the peroxisome proliferator-activated receptor-a (PPAR-alpha), which controls the transcriptional regulation of genes involved in hepatic fatty acid, cholesterol, and lipoprotein metabolism. The hepatic expression of the scavenger receptor class B type I (SR-BI) plays a critical role in lipoprotein metabolism, mainly due to its ability to mediate selective cholesterol uptake. Because fibrates and PPAR-alpha agonists upregulate SR-BI expression in human and murine macrophages, we tested whether fibrates raised a similar regulatory response on hepatic SR-BI expression in mice. Surprisingly, fibrate treatment suppressed SR-BI protein expression in the liver without changing steady state SR-BI mRNA levels. Decreased hepatic SR-BI protein expression correlated with enlarged HDL particle size. This effect was concomitant with down-regulation of CLAMP, a putative SR-BI-stabilizing protein found in the hepatic plasma membrane, which was also not associated to changes in CLAMP mRNA levels. The posttranscriptional regulatory effect of fibrates over hepatic SR-BI protein levels was dependent on PPAR-alpha expression, because it was absent in PPAR-alpha-deficient mice. Restoring hepatic SR-BI expression in fibrate-treated mice by recombinant adenoviral gene transfer abolished fibrate-mediated HDL particle size enlargement. This study describes a novel effect of fibrates on hepatic SR-BI expression providing an alternative mechanism by which this drug family modulates HDL metabolism in vivo.
Fibrates induce mdr2 gene expression and biliary phospholipid secretion in the mouse
(PORTLAND PRESS LTD, 1996) Chianale, J; Vollrath, V; Wielandt, AM; Amigo, L; Rigotti, A; Nervi, F; Gonzalez, S; Andrade, L; Pizarro, M; Accatino, L
Disruption of the murine mdr2 gene leads to the complete absence of biliary phospholipids. We tested the hypothesis that the increase in biliary phospholipid output induced by fibrates is mediated via induction of the hepatic mdr2 gene and its encoded product, the P-glycoprotein canalicular flippase. Increased levels of mdr2 mRNA were observed in the liver of mice treated with different fibrates: ciprofibrate, 660+/-155% (as compared with control group); clofibrate, 611+/-77 %; bezafibrate, 410+/-47 %; fenofibrate, 310+/-52 %; gemfibrozil, 190+/-25 % (P < 0.05 compared with control group). Induction of expression of the mdr gene family was specific to the mdr2 gene. Two- to three-fold increases in P-glycoprotein immunodetection were evident on the canalicular plasma-membrane domain of clofibrate- and ciprofibrate-treated mice. Biliary phospholipid output increased from 4.2+/-1.2 nmol/min per g of liver in the control group to 8.5+/-0.6, 7.1+/-2.9 and 5.8+/-2.5 in ciprofibrate-, clofibrate- and bezafibrate-treated mice respectively (P < 0.05 compared with control group). Moreover, a significant correlation between biliary phospholipid output and the relative levels of mdr2 mRNA was found (r = 0.86; P < 0.05). In treated animals, bile flow as well as cholesterol and bile acid outputs remained unchanged. Our findings constitute the first evidence that pharmacological modulation of biliary lipid secretion mediated by fibrates can be related to the overexpression of a specific liver gene product, the mdr2 P-glycoprotein, and are consistent with the hypothesis that the mdr2 P-glycoprotein isoform plays a crucial role in the secretion of biliary phospholipid.
Hepatic cholesterol and bile acid metabolism and intestinal cholesterol absorption in scavenger receptor class B type I-deficient mice
(LIPID RESEARCH INC, 2001) Mardones, P; Quinones, V; Amigo, L; Moreno, M; Miquel, JF; Schwarz, M; Miettinen, HE; Trigatti, B; Krieger, M; VanPatten, S; Cohen, DE; Rigotti, A
The scavenger receptor class B type I (SR-BI), which is expressed in the liver and intestine, plays a critical role in cholesterol metabolism in rodents. While hepatic SR-BI expression controls high density lipoprotein (HDL) cholesterol metabolism, intestinal SR-BI has been proposed to facilitate cholesterol absorption. To evaluate further the relevance of SR-BI in the enterohepatic circulation of cholesterol and bile salts, we studied biliary lipid secretion, hepatic sterol content and synthesis, bile acid metabolism, fecal neutral sterol excretion, and intestinal cholesterol absorption in SR-BI knockout mice. SR-BI deficiency selectively impaired biliary cholesterol secretion, without concomitant changes in either biliary bile acid or phospholipid secretion. Hepatic total and unesterified cholesterol contents were slightly increased in SR-BI-deficient mice, while sterol synthesis was not significantly changed, Bile acid pool size and composition, as well as fecal bile acid excretion, were not altered in SR-BI knockout mice. Intestinal cholesterol absorption was somewhat increased and fecal sterol excretion was slightly decreased in SR-BI knockout mice relative to controls. These findings establish the critical role of hepatic SR-BI expression in selectively controlling the utilization of HDL cholesterol for biliary secretion. In contrast, SR-BI expression is not essential for intestinal cholesterol absorption.
Hepatic overexpression of caveolins increases bile salt secretion in mice
(WILEY, 2003) Moreno, M; Molina, H; Amigo, L; Zanlungo, S; Arrese, M; Rigotti, A; Miquel, JF
Caveolins are cholesterol-binding proteins involved in the regulation of several intracellular processes, including cholesterol transport. Because hepatocytes express caveolin-1 and caveolin-2, these proteins might modulate hepatic lipid metabolism and biliary lipid secretion. Our aim was to investigate the potential physiologic role of caveolins in hepatic cholesterol and bile salt (BS) metabolism and transport using adenoviral gene transfer. C57BL/6 mice were infected with recombinant human caveolin-1 and caveolin-2 adenoviruses. Mice infected with adenovirus lacking the transgene were used as controls. Hepatic caveolin expression was evaluated by immunochemical methods. Reverse-transcription polymerase chain reaction (RT-PCR) and immunoblotting were used to assess messenger RNA (mRNA) levels and protein mass of BS transporters (sodium taurocholate cotransporting polypeptide [Ntcp] and bile salt export pump [Bsep]). Serum, liver, biliary, and fecal biochemical determinations and BS maximal secretory rate (SRm) were performed by standard methods. Ad.Cav-1- and Ad.Cav-2-infected mice exhibited a 10- and 7-fold increase in hepatic caveolin-1 and caveolin-2 protein expression, respectively. Caveolin-1-overexpressing mice had a significant increase in plasma high-density lipoprotein (HDL) cholesterol and hepatic free cholesterol content, whereas total plasma cholesterol and triglyceride levels remained unchanged. Hepatic caveolin-1 and/or caveolin-2 overexpression significantly increased bile flow and secretion of all biliary lipids. Caveolin-1-overexpressing mice showed a 2.5-fold increase in taurocholate (TC) SRm, indicating increased canalicular BS transport capacity. BS pool size and fecal BS excretion remained within the normal range in mice with Cav-1 overexpression. No changes were seen in the protein mass of BS transporters NtcP and Bsep. In conclusion, our findings indicate that caveolins may play an important role in regulating hepatic BS and cholesterol metabolism.
Hepatic overexpression of sterol carrier protein-2 inhibits VLDL production and reciprocally enhances biliary lipid secretion
(AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, 2003) Amigo, L; Zanlungo, S; Miquel, JF; Glick, JM; Hyogo, H; Cohen, DE; Rigotti, A; Nervi, F
We examined in vivo a role for sterol carrier protein-2 (SCP-2) in the regulation of lipid secretion across the hepatic sinusoidal and canalicular membranes. Recombinant adenovirus Ad.rSCP2 was used to overexpress SCP-2 in livers of mice. We determined plasma, hepatic, and biliary lipid concentrations; hepatic fatty acid (FA) and cholesterol synthesis; hepatic and biliary phosphatidylcholine (PC) molecular species; and VLDL triglyceride production. In Ad.rSCP2 mice, there was marked inhibition of hepatic fatty acids and cholesterol synthesis to <62% of control mice. Hepatic triglyceride contents were decreased, while cholesterol and phospholipids concentrations were elevated in Ad.rSCP2 mice. Hepatic VLDL triglyceride production fell in Ad.rSCP2 mice to 39% of control values. As expected, biliary cholesterol, phospholipids, bile acids outputs, and biliary PC hydrophobic index were significantly increased in Ad.rSCP2 mice. These studies indicate that SCP-2 overexpression in the liver markedly inhibits lipid synthesis as well as VLDL production, and alters hepatic lipid contents. In contrast, SCP-2 increased biliary lipid secretion and the proportion of hydrophobic PC molecular species in bile. These effects suggest a key regulatory role for SCP-2 in hepatic lipid metabolism and the existence of a reciprocal relationship between the fluxes of lipids across the sinusoidal and canalicular membranes.
Influence of the high density lipoprotein receptor SR-BI on reproductive and cardiovascular pathophysiology
(NATL ACAD SCIENCES, 1999) Trigatti, B; Rayburn, H; Vinals, M; Braun, A; Miettinen, H; Penman, M; Hertz, M; Schrenzel, M; Amigo, L; Rigotti, A; Krieger, M
The high density lipoprotein (HDL) receptor SR-BI (scavenger receptor class B type I) mediates the selective uptake of plasma HDL cholesterol by the liver and steroidogenic tissues. As a consequence, SR-BI can influence plasma HDL cholesterol levels, HDL structure, biliary cholesterol concentrations, and the uptake, storage, and utilization of cholesterol by steroid hormone-producing cells. Here we used homozygous null SR-BI knockout mice to show that SR-BI is required for maintaining normal biliary cholesterol levels, oocyte development, and female fertility. We also used SR-BI/apolipoprotein E double homozygous knockout mice to show that SR-BI can protect against early-onset atherosclerosis. Although the mechanisms underlying the effects of SR-BI loss on reproduction and atherosclerosis have not been established, potential causes include changes in (i) plasma lipoprotein levels and/or structure, (ii) cholesterol flux into or out of peripheral tissues (ovary, aortic wall), and (iii) reverse cholesterol transport, as indicated by the significant reduction of gallbladder bile cholesterol levels in SR-BI and SR-BI/apolipoprotein E double knockout mice relative to controls. If SR-BI has similar activities in humans, it may become an attractive target for therapeutic intervention in a variety of diseases.
NPC2 is expressed in human and murine liver and secreted into bile: Potential implications for body cholesterol homeostasis
(WILEY, 2006) Klein, A; Amigo, L; Retamal, MJ; Morales, MG; Miquel, JF; Rigotti, A; Zanlungo, S
The liver plays a critical role in the metabolism of lipoprotein cholesterol and in controlling its elimination through the bile. Niemann-Pick type C 2 (NPC2), a cholesterol-binding protein, is key for normal intracellular trafficking of lipoprotein cholesterol, allowing its exit from the endolysosomal pathway into the metabolically active pool of the cell. In addition, NPC2 is a secretory protein from astrocytes and epididymal cells. Although NPC2 mRNA is detected in the liver, plasma and biliary NPC2 protein levels and function have not been reported. This study demonstrates that NPC2 is present in murine and human plasma and bile. In addition, hepatic NPC2 protein expression was dramatically increased in NPC1-deficient mice but not regulated by cholesterol feeding or pharmacological modulation of various nuclear receptors involved in cholesterol and bile acid metabolism. Interestingly, biliary NPC2 levels were 3-fold increased in gallstone-susceptible C57BL6/J versus gallstone-resistant BALB/c mice. Furthermore, NPC2 was exclusively found in the cholesterol pro-nucleating ConA-binding fraction of human bile. In conclusion, NPC2 is secreted from the liver into bile and plasma, where it may have a functional role in cholesterol transport in normal and disease conditions.
Scavenger receptor class B type I (SR-BI) and high-density lipoprotein metabolism: Recent lessons from genetically manipulated mice
(BIOSCIENCE EDIPRINT INC, 2000) Trigatti, B; Rigotti, A
The scavenger receptor BI is a cell surface lipoprotein receptor for selective high-density lipoprotein (HDL) cholesterol uptake in the liver and steroidogenic tissues. Studies of genetically manipulated strains of mice have revealed that SR-BI plays a key role in regulating HDL metabolism, cholesterol transport to steroidogenic tissues and bile cholesterol secretion. Furthermore, SR-BI protects against the development of atherosclerosis and is required for normal female fertility: If SR-BI has similar functions in lipoprotein metabolism and atherosclerosis in humans, it may represent a new target for the prevention and/or treatment of atherosclerotic cardiovascular disease.
Sterol carrier protein 2 gene transfer changes lipid metabolism and enterohepatic sterol circulation in mice
(W B SAUNDERS CO, 2000) Zanlungo, S; Amigo, L; Mendoza, H; Miquel, JF; Vio, C; Glick, JM; Rodriguez, A; Kozarsky, K; Quinones, V; Rigotti, A; Nervi, F
Background & Aims: Sterol carrier protein 2 (SCP-2) enhances sterol cycling and facilitates cholesterol translocation between intracellular organelles and plasma membrane in cultured cells, including hepatocytes. We examined the role of SCP-2 in hepatic cholesterol and lipid trafficking through the sinusoidal and canalicular secretory pathways of the liver in vivo. Methods: Recombinant adenovirus-mediated SCP-2 gene transfer was used to obtain hepatic overexpression of SCP-2 in C57BL/6 mice. Results: SCP-2 overexpression in the mouse liver resulted in an 8-fold increase of SCP-2 protein levels and determined various effects on lipid metabolism. It decreased high-density lipoprotein cholesterol and increased low-density lipoprotein (LDL) cholesterol concentrations. The expressions of hepatic LDL receptor, apolipoprotein (apo) A-I, apoB, and apoE were decreased. SCP-2 overexpression also increased hepatic cholesterol concentration, associated with decreased cholesterol neosynthesis. Increased biliary cholesterol and bile acid secretion, bile acid pool size, and intestinal cholesterol absorption were also observed. Conclusions: These results indicate that modulation of SCP-2 expression in the liver determines important modifications on lipoprotein metabolism, hepatic cholesterol synthesis and storage, biliary lipid secretion, bile acid metabolism and intestinal cholesterol absorption.
Targeted disruption of the PDZK1 gene in mice causes tissue-specific depletion of the high density lipoprotein receptor scavenger receptor class B type I and altered lipoprotein metabolism
(AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, 2003) Kocher, O; Yesilaltay, A; Cirovic, C; Pal, R; Rigotti, A; Krieger, M
PDZK1, a multi-PDZ domain containing adaptor protein, interacts with various membrane proteins, including the high density lipoprotein (HDL) receptor scavenger receptor class B type I (SR-BI). Here we show that PDZK1 controls in a tissue-specific and post-transcriptional fashion the expression of SR-BI in vivo. SR-BI protein expression in PDZK1 knock-out (KO) mice was reduced by 95% in the liver, 50% in the proximal intestine, and not affected in steroidogenic organs (adrenal, ovary, and testis). Thus, PDZK1 joins a growing list of adaptors that control tissue-specific activity of cell surface receptors. Hepatic expression of SR-BII, a minor splice variant with an alternative C-terminal cytoplasmic domain, was not affected in PDZK1 KO mice, suggesting that binding of PDZK1 to SR-BI is required for controlling hepatic SR-BI expression. The loss of hepatic SR-BI was the likely cause of the elevation in plasma total and HDL cholesterol and the increase in HDL particle size in PDZK1 KO mice, phenotypes similar to those observed in SR-BI KO mice. PDZK1 KO mice differed from SR-BI KO mice in that the ratio of unesterified to total plasma cholesterol was normal, females were fertile, and cholesteryl ester stores in steroidogenic organs were essentially unaffected. These differences may be due to nearly normal extrahepatic expression of SR-BI in PDZK1 KO mice. The PDZK1-dependent regulation of hepatic SR-BI and, thus, lipoprotein metabolism supports the proposal that this adaptor may represent a new target for therapeutic intervention in cardiovascular disease.

Browsing by Author "Rigotti, A"

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