SR-B1 Expression Research Articles

Abstract 394: Bacterial Serum Opacity Factor Rescues HDL Functionality in SR-B1 -/- Mice

Although plasma HDL-C levels negatively correlate with atherosclerotic cardiovascular disease (ACVD), attempts to reduce ACVD risk by raising plasma HDL have disappointed. Thus, hypotheses about salutary HDL effects have shifted from higher-is-better to function-is-more-important. The SR-B1 -/- mouse is an extreme model of HDL dsyfunctionality; compared to WT mice, SR-B1 -/- mice have higher plasma HDL levels and an HDL surface that is free cholesterol (FC)-rich (60 vs. 15 mol%). This would be expected to increase HDL-FC bioavailability to cytotoxic levels. HDL dysfunctionality among SR-B1 -/- mice is associated with multiple metabolic abnormalities—impaired cell membrane structure and function and atherosusceptibility, despite having high plasma HDL-C levels; moreover, female SR-B1 -/- mice are infertile. Liver-specific SR-B1 expression in SR-B1 -/- mice normalizes HDL size and FC content. Thus, the SR-B1 -/- mouse phenotype is due to lack of hepatic clearance of lipids from dysfunctional HDL. Serum opacity factor (SOF) is a bacterial protein that catalyzes the quantitative disproportionation of HDL into a cholesteryl ester-rich micro emulsion (CERM), neo HDL, and lipid-free apo AI. The CERM contains apo E and all HDL-CE. Injection of SOF (4 μg) into WT mice lowers plasma cholesterol by diverting the CERM to hepatic LDLR. Thus, we began testing whether adeno-viral delivery of SOF (AAV SOF ) to SR-B1 -/- mice rescues HDL functionality. A plasmid encoding the SOF gene was synthesized; SOF DNA was isolated by restriction enzyme digestion and cloned into a pAAV-TBG-mcs plasmid that was submitted to the PENN Vector Lab for virus production and isolation. AAV GFP plasmid (UPENN) was used as control. Good SOF production and secretion was confirmed by transfection of Huh7 hepatocytes. AAV SOF injection into SR-B1 -/- mice induced constitutive plasma SOF activity and reduced HDL-C levels to nil. Superposition of high plasma HDL levels and a high mol% FC in SR-B1 -/- is expected to increase HDL-FC bioavailablity that contributes to whole-body FC-toxicity and the observed metabolic abnormalities. Future tests will determine whether ablation of dysfunctional HDL in SR-B1 -/- mice rescues their pathological phenotype, especially atherosclerosis.

High scavenger receptor class B type I expression is related to tumor aggressiveness and poor prognosis in lung adenocarcinoma: A STROBE compliant article.

Scavenger receptor class B type I (SR-B1) is highly expressed in a variety of cancers, including prostate, breast and ovarian. However, the relationship between SR-B1 and lung adenocarcinoma is unknown. We analyzed the expression of SR-B1 in a well-characterized lung adenocarcinoma tissue microarray by immunohistochemistry, in 90 cancerous and 90 adjacent normal lung tissues. Results showed that the positive expression rate of SR-B1 in cancer tissues (86/90, 96%) was significantly higher than that of adjacent tissues (50/90, 56%) (P < .001). And SR-B1 overexpression in lung adenocarcinoma tissue was significantly higher than that of adjacent normal tissue (P < .001), accounting for 67% of cases. This elevated SR-B1 expression was associated with AJCC stage (P < .001), T stage (P = .012), N stage (P = .002), and lymph node positivity (P < .001). The Kaplan–Meier survival analysis indicated that patients with high SR-B1 expression had a shorter overall survival (P < .001). On the multivariate analysis, SR-B1 was an independent prognostic factor for outcomes after adjustment for other prognostic factors (P = .038). In conclusion, high SR-B1 expression is associated with conventional pathologic parameters that represent tumor aggressiveness and may purport a poor clinical prognosis in lung adenocarcinoma.

Transthyretin uptake in placental cells is regulated by the high-density lipoprotein receptor, scavenger receptor class B member 1.

Transfer of thyroid hormone into cells is critical for normal physiology and transplacental transfer of maternal thyroid hormones is essential for normal fetal growth and development. Free thyroid hormone is known to enter cells through specific cell surface transport proteins, and for many years this uptake of unbound thyroid hormones was assumed to be the only relevant mechanism. Recently, evidence has emerged of alternate pathways for hormone entry into cells that are dependent on hormone binding proteins. In this study we identify the high-density lipoprotein receptor Scavenger Receptor class B member 1 (SR-B1) as important in the uptake and transport of transthyretin-bound thyroid hormone by placental trophoblast cells. High-density lipoprotein increases expression of SR-B1 in placental cells but also reduces uptake of transthyretin-thyroid hormone through the SR-B1 transporter. SR-B1 is expressed in many cells and this study suggests that SR-B1 may be universally important in thyroid hormone uptake. Further investigation of SR-B1-TTR interactions may fundamentally change our understanding of hormone biology and have important clinical consequences.

Expression patterns of SRB1 and other stress-related genes in Candida albicans under oxidative, hyperosmotic and thermal stress.

Candida albicans, a human fungal pathogen, is able to tolerate certain levels of environmental stresses. Its cell wall plays an important role in cellular homeostasis, responding to environmental stimuli. SRB1 gene encodes a GDP-mannose pyrophosphorylase that catalyzes the formation of the major cell wall component, mannan. The exact relationship between SRB1 and various stresses is not yet fully understood. In current study, C. albicans SC5314 cells were exposed to oxidative, hyperosmotic, and thermal stresses. The expression of SRB1 and related stress response genes, HOG1, CAP1, MKC1, and HSP90, was systematically evaluated in cells exposed to various levels of stress. In addition, the apoptosis and ultrastructural changes of the cells were examined. We found that the expression of SRB1 and related stress response genes significantly increased under oxidative, hyperosmotic, and thermal stresses, and the increased gene expression was correlated with higher percentages of apoptosis and ultrastructural changes in C. albicans cells. We propose that protein glycosylation is associated with stress response that involves SRB1 in C. albicans. Further in-depth studies of SRB1 function should aid our understanding of C. albicans pathogenesis, and provide important clues about the development of novel antifungal compounds for drug resistant C. albicans.

3-(4-Hydroxyphenyl)propionic acid, a major microbial metabolite of procyanidin A2, shows similar suppression of macrophage foam cell formation as its parent molecule.

The effect of procyanidin A2 (PCA2) and its major colonic metabolite 3-(4-hydroxyphenyl)propionic acid (HPPA) on the suppression of macrophage foam cell formation, and underlying mechanism, were investigated for the first time. The results showed that 12.5 μg mL−1 PCA2 and HPPA significantly reduced cellular lipid accumulation and inhibited foam cell formation. HPPA promoted macrophage cholesterol efflux by up-regulating mRNA expressions of ABCA1 and SR-B1, while PCA2 significantly increased SR-B1 and LXR-α mRNA expression levels. Moreover, PCA2 and HPPA significantly lowered the elevated levels of CD36 mRNA expression in ox-LDL-treated macrophage cells. Besides these, the ox-LDL-induced cellular oxidative stress and inflammation was also restricted by PCA2 and HPPA treatment via nuclear factor kappa-B pathways. In conclusion, PCA2 and its major microbial metabolite, HPPA, inhibited the conversion of macrophage into foam cells via regulating cellular lipid metabolism and suppressing cellular oxidative stress and inflammation.

Apolipoprotein A-1 mimetic peptide 4F promotes endothelial repairing and compromises reendothelialization impaired by oxidized HDL through SR-B1

Disruption of endothelial monolayer integrity is the primary instigating factor for many cardiovascular diseases. High density lipoprotein (HDL) oxidized by heme enzyme myeloperoxidase (MPO) is dysfunctional in promoting endothelial repair. Apolipoprotein A-1 mimetic 4F with its pleiotropic benefits has been proven effective in many in vivo models. In this study we investigated whether 4F promotes endothelial repair and restores the impaired function of oxidized HDL (Cl/NO2-HDL) in promoting re-endothelialization. We demonstrate that 4F and Cl/NO2-HDL act on scavenger receptor type I (SR-B1) using human aorta endothelial cells (HAEC) and SR-B1 (-/-) mouse aortic endothelial cells. Wound healing, transwell migration, lamellipodia formation and single cell migration assay experiments show that 4F treatment is associated with a recovery of endothelial cell migration and associated with significantly increased endothelial nitric oxide synthase (eNOS) activity, Akt phosphorylation and SR-B1 expression. 4F increases NO generation and diminishes oxidative stress. In vivo, 4F can stimulate cell proliferation and re-endothelialization in the carotid artery after treatment with Cl/NO2-HDL in a carotid artery electric injury model but fails to do so in SR-B1(-/-) mice. These findings demonstrate that 4F promotes endothelial cell migration and has a potential therapeutic benefit against early endothelial injury in cardiovascular diseases.

Lactational exposure of polychlorinated biphenyls impair Leydig cellular steroidogenesis in F1 progeny rats

The present study was aimed to determine the effects of lactational exposure of PCBs (Aroclor 1254) on Leydig cellular steroidogenesis in F1 progeny rats. Lactating dams were orally treated by gavage with different doses of PCBs (1, 2 and 5mg/kg b.wt./day). Male progenies were sacrificed on PND60. Our results demonstrated that exposure to PCBs decreased the body weight, testis weight and anogenital distance (AGD) index in the F1 progeny rats. Importantly, PCBs exposure reduced the serum levels of LH, testosterone and estradiol. Interestingly, PCBs caused a decrease in the Leydig cell population along with decreased activities of steroidogenic enzymes 3β- and 17β-HSD. Additionally, we observed a significant decrease in LHR, SR-B1, StAR protein, Cyp11a1, 3β-HSD, Cyp17a1, 17β-HSD, 5α-reductase, Cyp19a1 and AR gene expression in the Leydig cells of progeny rats. In conclusion, our study demonstrates that lactational exposure of PCBs alters Leydig cellular steroidogenesis in the F1 progeny rats.

Scavenger receptor class B type 1 regulates neuroblastoma cell proliferation, migration and invasion

Neuroblastoma (NB) is an extra cranial pediatric embryonal tumor most prevalent in children less than 1 year of age. NB accounts for 7% of all pediatric cancers but accounts for 15% of all childhood cancer deaths. Scavenger receptor class B type 1 (SR-B1), a mediator of cellular cholesterol uptake, is overexpressed in and have been linked to the aggressiveness of many cancers. Nevertheless, no studies have so far investigated the relationship between SR-B1 and NB. Elucidation of receptors that promote NB may pave the way for discovery of new therapeutic targets. Here we show that inhibition of SR-B1 reduced cell survival, migration and invasion, and cholesterol content in NB cell lines. Additionally analysis of SR-B1 levels in NB patient biopsies using the R2: Genomics Analysis and Visualization Platform showed that high SR-B1 expression correlated with decreased overall and event-free survival.

Effects of sepsis on the metabolism of sphingomyelin and cholesterol in mice with liver dysfunction.

Sepsis is characterized by a severe inflammatory response to infection. With the spread of sepsis, various tissues, including the lungs, liver and kidney, may be damaged. This may finally develop into multiple organ dysfunction syndrome. Sphingomyelin and cholesterol are two main lipids involved in sepsis. The metabolism of sphingomyelin and cholesterol in the livers of mice with sepsis needs to be clarified. To achieve this, the present study intraperitoneally injected mice with PBS, lipopolysaccharide (LPS; 10 mg/kg) and LPS + pyrrolidine dithiocarbamate (PDTC; 30 mg/kg). Subsequently, sphingomyelin and cholesterol content were measured using kits, the sphingomyelin synthase (SMS) activity was measured using thin layer chromatography, and the expression levels of SMS1 and 2, hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), ATP binding cassette subfamily A member 1 (ABCA1), scavenger receptor class B member 1 (SR-B1) and apolipoprotein A1 (Apo A1) were determined by western blotting in the livers of mice. Results demonstrated that, in the LPS group, sphingomyelin and cholesterol content was significantly increased (P<0.001; n=6), the SMS activity significantly enhanced (P<0.001; n=6), the expression levels of SMS2, HMGCR, ABCA1 and SR-B1 were augmented (P<0.05; n=6), and the expression of Apo A1 was decreased (P<0.05; n=6), whereas SMS1 level only slightly increased with no statistical significance (P>0.05; n=6), compared to the levels in the control group. However, PDTC was able to attenuate these alterations. These results indicated that sphingomyelin and cholesterol content may increase in the liver dysfunction of sepsis by increasing the expression of SMS2, HMGCR, SR-B1 and ABCA1, and downregulating Apo A1.

Myeloid-specific genetic ablation of ATP-binding cassette transporter ABCA1 is protective against cancer.

Increased circulating levels of apolipoprotein A-I (apoA-I), the major protein of high-density lipoprotein (HDL), by genetic manipulation or infusion, protects against melanoma growth and metastasis. Herein, we explored potential roles in melanoma tumorigenesis for host scavenger receptor class B, type 1 (SR-B1), and ATP-binding cassette transporters A1 (ABCA1) and G1 (ABCG1), all mediators of apoA-I and HDL sterol and lipid transport function. In a syngeneic murine melanoma tumor model, B16F10, mice with global deletion of SR-B1 expression exhibited increased plasma HDL cholesterol (HDLc) levels and decreased tumor volume, indicating host SR-B1 does not directly contribute to HDL-associated anti-tumor activity. In mice with myeloid-specific loss of ABCA1 (Abca1−M/−M; A1−M/−M), tumor growth was inhibited by ∼4.8-fold relative to wild type (WT) animals. Abcg1−M/−M (G1−M/−M) animals were also protected by 2.5-fold relative to WT, with no further inhibition of tumor growth in Abca1/Abcg1 myeloid-specific double knockout animals (DKO). Analyses of tumor-infiltrating immune cells revealed a correlation between tumor protection and decreased presence of the immune suppressive myeloid-derived suppressor cell (MDSC) subsets, Ly-6G+Ly-6CLo and Ly-6GnegLy-6CHi cells. The growth of the syngeneic MB49 murine bladder cancer cells was also inhibited in A1−M/−M mice. Collectively, our studies provide further evidence for an immune modulatory role for cholesterol homeostasis pathways in cancer.

SR-B1 and PGRMC1 Expression in Canine Uterine Macrophages

SR-B1 and PGRMC1 Expression in Canine Uterine Macrophages

High-density lipoprotein from subjects with coronary artery disease promotes macrophage foam cell formation: role of scavenger receptor CD36 and ERK/MAPK signaling.

Although high-density lipoprotein is atheroprotective, it can become dysfunctional in chronic inflammatory conditions and increase cardiovascular risk. We previously demonstrated that HDL from subjects with documented coronary artery disease is dysfunctional and is pro-oxidant/proinflammatory in macrophages. Here we examined the influence of dysfunctional/proinflammatory HDL (piHDL) on lipid accumulation in human macrophages, in comparison to functional HDL (nHDL). Exposure of macrophages to piHDL, in contrast to nHDL, resulted in oxidative stress and marked uptake of lipids from piHDL, leading to the formation of foam cell phenotype as noted by oil red O staining with concomitant increase in total cellular cholesterol content. Using western blotting, we identified that piHDL profoundly upregulated the expression of scavenger receptor CD36 and suppressed the expression of ABCG1 and SRB1 in macrophages, thereby facilitating cholesterol influx capacity of macrophages. We then identified that CD36 did not act alone, indeed it was activated in macrophages along with ERK/MAPK, in response to piHDL, which in turn led to lipid accumulation as well as proinflammatory response via activation of NFkB and subsequent release of proinflammatory markers-TNF-ά and MMP-9. These effects were confirmed using pharmacological inhibitors for either CD36 or ERK/MAPK. Furthermore, piHDL treatment moderately activated PPAR-γ and Nrf2, the known regulators of CD36 in macrophages, suggesting that the two forms of HDL differentially regulate CD36 expression. Taken together, the results demonstrate that a novel CD36-ERK/MAPK-dependent mechanism is involved in macrophage lipid accumulation by piHDL, there by revealing the importance of functional deficiency in HDL and its potential link to atherogenesis.

Inhibitory effect of PCSK9 on Abca1 protein expression and cholesterol efflux in macrophages

Background and aimsProprotein convertase subtilisin/kexin type 9 (PCSK9) may have extra-hepatic effects on cholesterol homeostasis of vascular macrophages. In this study, we aimed to investigate PCSK9 role on the anti-atherogenic process of ATP binding cassette transporter A1 (Abca1)-mediated cholesterol efflux. MethodsAbca1-mediated cholesterol efflux was evaluated by a radioisotopic technique in mouse peritoneal macrophages (MPM) from wild-type (WT) or LDL receptor knock-out (Ldlr−/−) mice exposed to human recombinant PCSK9, in the presence of liver X receptor/retinoid X receptor (LXR/RXR) ligands or acetylated LDL (AcLDL) to stimulate Abca1 expression. Protein and gene expression was evaluated by Western blot and quantitative real time PCR, respectively. ResultsPCSK9 inhibited Abca1-mediated cholesterol efflux induced by LXR/RXR agonists in WT MPM (−55%, p < 0.05) but not in Ldlr−/− MPM. This effect was fully abrogated by the co-incubation with an anti-PCSK9 antibody. The inhibition of Abca1-dependent efflux induced by PCSK9 was associated with a reduction of Abca1 protein expression only in WT cells. Abca1 gene expression was significantly downregulated by PCSK9 in WT macrophages (−64%, p < 0.001) and, to a lesser extent, in MPM lacking Ldlr (−35%, p < 0.001). The inhibitory effect on Abca1-mediated efflux was also confirmed in AcLDL-treated macrophages. PCSK9 had a marginal or no effect on the expression of the lipid transporters Sr-b1 and Abcg1. ConclusionsPCSK9 plays a direct role on Abca1-mediated cholesterol efflux through a downregulation of Abca1 gene and Abca1 protein expression. This extrahepatic effect may influence relevant steps in the pathogenesis of atherosclerosis, such as foam cell formation.

Neo High-Density Lipoprotein Produced by the Streptococcal Serum Opacity Factor Activity against Human High-Density Lipoproteins Is Hepatically Removed via Dual Mechanisms

Injection of streptococcal serum opacity factor (SOF) into mice reduces the plasma cholesterol level by ∼40%. In vitro, SOF converts high-density lipoproteins (HDLs) into multiple products, including a small HDL, neo HDL. In vitro, neo HDL accounts for ∼60% of the protein mass of the SOF reaction products; in vivo, the accumulated mass of neo HDL is <1% of that observed in vitro. To identify the underlying cause of this difference, we determined the fate of neo HDL in plasma in vitro and in vivo. Following incubation with HDL, neo HDL-PC rapidly transfers to HDL, giving a small remnant, which fuses with HDL. An increased level of SR-B1 expression in Huh7 hepatoma cells and a reduced level of LDLR expression in CHO cells had little effect on neo HDL-[3H]CE uptake. Thus, the dominant receptors for neo HDL uptake are not LDLR or SR-B1. The in vivo metabolic fates of neo HDL-[3H]CE and HDL-[3H]CE were different. Thirty minutes after the injection of neo HDL-[3H]CE and HDL-[3H]CE into mice, plasma [3H]CE counts were 40 and 53%, respectively, of injected counts, with 10 times more [3H]CE appearing in the livers of neo HDL-[3H]CE-injected than in those of HDL-[3H]CE-injected mice. These data support a model of neo HDL-[3H]CE clearance by two parallel pathways. At early post-neo HDL-[3H]CE injection times, some neo HDL is directly removed by the liver; the remainder transfers its PC to HDL, leaving a remnant that fuses with HDL, which is also hepatically removed more slowly. Given that SR-B1 and SOF both remove CE from HDL, this novel mechanism may also underlie the metabolism of remnants released by hepatocytes following selective SR-B1-mediated uptake of HDL-CE.

Sterol Regulatory Element Binding Protein (Srb1) Is Required for Hypoxic Adaptation and Virulence in the Dimorphic Fungus Histoplasma capsulatum.

The Histoplasma capsulatum sterol regulatory element binding protein (SREBP), Srb1 is a member of the basic helix-loop-helix (bHLH), leucine zipper DNA binding protein family of transcription factors that possess a unique tyrosine (Y) residue instead of an arginine (R) residue in the bHLH region. We have determined that Srb1 message levels increase in a time dependent manner during growth under oxygen deprivation (hypoxia). To further understand the role of Srb1 during infection and hypoxia, we silenced the gene encoding Srb1 using RNA interference (RNAi); characterized the resulting phenotype, determined its response to hypoxia, and its ability to cause disease within an infected host. Silencing of Srb1 resulted in a strain of H. capsulatum that is incapable of surviving in vitro hypoxia. We found that without complete Srb1 expression, H. capsulatum is killed by murine macrophages and avirulent in mice given a lethal dose of yeasts. Additionally, silencing Srb1 inhibited the hypoxic upregulation of other known H. capsulatum hypoxia-responsive genes (HRG), and genes that encode ergosterol biosynthetic enzymes. Consistent with these regulatory functions, Srb1 silenced H. capsulatum cells were hypersensitive to the antifungal azole drug itraconazole. These data support the theory that the H. capsulatum SREBP is critical for hypoxic adaptation and is required for H. capsulatum virulence.

Shear stress regulates endothelial cell function through SRB1‐eNOS signaling pathway

The aim of this study was to explore whether transmembrane flow shear stress could regulate eNOS expression and mediate endothelial cell function via SR-B1 signaling transduction. Parallel-plate flow chamber was used to impose laminar shear stress and evaluate the effect of shear stress upon human umbilical vein endothelial cells (HUVECs). The expression of SR-B1 and eNOS at both RNA and protein levels was detected under different dynamic conditions. RNA interference and gene transfection were performed to overexpress and knock down the SRB1 to confirm the role of SR-B1-eNOS signaling pathway. The expression levels of SR-B1 and eNOS were downregulated when HUVECs were treated with 4.2dyne/cm(2) shear stress compared with those of the control group. However, the expression of SR-B1 and eNOS was upregulated as HUVECs exposed to 8.4 and 15dyne/cm(2) shear stress. When exposed to 8.4dyne/cm(2) , SR-B1 and eNOS expression was significantly higher compared with those of the other groups. When SR-B1 was knocked down through RNAi technique, the expression of eNOS was significantly downregulated than those of the other groups. While overexpression of SR-B1 could upregulate eNOS significantly. Shear stress regulates endothelial cell function through SR-B1-eNOS signaling pathway. SR-B1 may play a pivotal role in the process of anti-atherosclerosis.

Intestinal CREBH overexpression prevents high-cholesterol diet-induced hypercholesterolemia by reducing Npc1l1 expression

ObjectiveThe transcription factor cyclic AMP-responsive element-binding protein H (CREBH, encoded by Creb3l3) is highly expressed in the liver and small intestine. Hepatic CREBH contributes to glucose and triglyceride metabolism by regulating fibroblast growth factor 21 (Fgf21) expression. However, the intestinal CREBH function remains unknown. MethodsTo investigate the influence of intestinal CREBH on cholesterol metabolism, we compared plasma, bile, fecal, and tissue cholesterol levels between wild-type (WT) mice and mice overexpressing active human CREBH mainly in the small intestine (CREBH Tg mice) under different dietary conditions. ResultsPlasma cholesterol, hepatic lipid, and cholesterol crystal formation in the gallbladder were lower in CREBH Tg mice fed a lithogenic diet (LD) than in LD-fed WTs, while fecal cholesterol output was higher in the former. These results suggest that intestinal CREBH overexpression suppresses cholesterol absorption, leading to reduced plasma cholesterol, limited hepatic supply, and greater excretion. The expression of Niemann–Pick C1-like 1 (Npc1l1), a rate-limiting transporter mediating intestinal cholesterol absorption, was reduced in the small intestine of CREBH Tg mice. Adenosine triphosphate-binding cassette transporter A1 (Abca1), Abcg5/8, and scavenger receptor class B, member 1 (Srb1) expression levels were also reduced in CREBH Tg mice. Promoter assays revealed that CREBH directly regulates Npc1l1 expression. Conversely, CREBH null mice exhibited higher intestinal Npc1l1 expression, elevated plasma and hepatic cholesterol, and lower fecal output. ConclusionIntestinal CREBH regulates dietary cholesterol flow from the small intestine by controlling the expression of multiple intestinal transporters. We propose that intestinal CREBH could be a therapeutic target for hypercholesterolemia.

Identification of a novel upregulator of ABCA1 and SRB1 expression with the action of regulating cholesterol metabolism in vitro and in vivo

Objectives: The efflux of excess cellular cholesterol from peripheral tissues and its return to liver for excretion in bile and faeces occur by a process referred to reverse colesterol transport(RCT). ABCA1 and SRBI are key proteins or receptors in RCT. This research aim is discovery of novel anti-atherosclerotic agents targeting RCT with the action of regulating cholesterol metabolism in vitro and in vivo.

Osteopontin Deficiency Alters Biliary Homeostasis and Protects against Gallstone Formation.

The precipitation of excess biliary cholesterol as solid crystals is a prerequisite for cholesterol gallstone formation, which occurs due to disturbed biliary homeostasis. Biliary homeostasis is regulated by an elaborate network of genes in hepatocytes. If unmanaged, the cholesterol crystals will aggregate, fuse and form gallstones. We have previously observed that the levels of osteopontin (OPN) in bile and gallbladder were reduced in gallstone patients. However, the role and mechanism for hepatic OPN in cholesterol gallstone formation is undetermined. In this study, we found that the expression of hepatic OPN was increased in gallstone patients compared with gallstone-free counterparts. Then, we observed that OPN-deficient mice were less vulnerable to cholesterol gallstone formation than wild type mice. Further mechanistic studies revealed that this protective effect was associated with alterations of bile composition and was caused by the increased hepatic CYP7A1 expression and the reduced expression of hepatic SHP, ATP8B1, SR-B1 and SREBP-2. Finally, the correlations between the expression of hepatic OPN and the expression of these hepatic genes were validated in gallstone patients. Taken together, our findings reveal that hepatic OPN contributes to cholesterol gallstone formation by regulating biliary metabolism and might be developed as a therapeutic target for gallstone treatments.

Impaired reverse cholesterol transport and hepatic steatosis contribute to pathogenesis of high fat dietinduced hyperlipidemia in murine models

Purpose: To investigate the pathogenesis of high fat diet (HFD)-induced hyperlipidemia (HLP) in mice, rats and hamsters and to comparatively evaluate their sensitivity to HFD. Methods: Mice, rats and hamsters were fed with high-fat diet formulation (HFD, n = 8) or a control diet (control, n = 8) for 4 weeks. Changes in body weight, relative liver weight, serum lipid profile, expressions of hepatic marker gene of lipid metabolism and liver morphology were observed in three hyperlipidemic models. Results: Elevated total cholesterol (TC), triglyceride, low density lipoprotein-cholesterol (LDL-C) and high density lipoprotein-cholesterol (HDL-C) levels and body weight were observed in all hyperlipidemic animals (p < 0.05), while hepatic steatosis was manifested in rat and hamster HLP models, and increased hepatic TC level was only seen (p < 0.05) in hamster HLP model. Suppression of HMG-CoA reductase and up-regulation of lipoproteinlipase were observed in all HFD groups. Hepatic gene expression of LDLR, CYP7A1, LCAT, SR-B1, and ApoA I, which are a response to reverse cholesterol transport (RCT), were inhibited by HFD in the three models. Among these models, simultaneous suppression of HMG-CR, LCAT, LDLR and SR-BI and elevated LPL were features of the hamster model. Conclusion: As the results show, impaired RCT and excessive fat accumulation are major contributors to pathogenesis of HFD-induced murine HLP. Thus, the hamster model is more appropriate for hyperlipidemia research.