Scavenger Receptor Class B Type I Expression Research Articles

SR-BI expression regulates the gastric cancer tumor immune microenvironment and is associated with poor prognosis

<b>Aim:</b> Scavenger receptor class B, type I (SR-BI) is an integral plasma membrane protein that has been reported to be overexpressed in various malignancies, such as renal cancer, breast cancer, and prostate cancer, and is an independent prognostic factor. However, the clinical value and expression of SR-BI in GC are unknown. Our research aimed to explore the role of SR-BI in combination with immune markers as a diagnostic and prognostic marker for gastric cancer (GC). <b>Methods:</b> GC tissues, paracancerous tissues, and clinicopathological data of 149 patients were collected. The expression level of SR-BI, Tumor-infiltrating lymphocytes (TILs), and PD-L1 were evaluated by immunohistochemistry (IHC). The associations of the SR-BI staining intensity with clinicopathological features and immune markers were determined by the chi-square test. Univariate and multivariate COX regression analyses were used to evaluate independent prognostic factors. Kaplan–Meier analyses were performed to plot the survival curve. <b>Results:</b> Our results indicated that SR-BI was expressed at higher levels in tumor tissues than in adjacent paracancerous tissues (<i>p</i> < 0.001), and patients with high levels of SR-BI expression had a worse prognosis. Univariate and multivariate analyses revealed that high SR-BI expression was an independent factor for poor prognosis. The chi-square test determined that the expression of SR-BI was negatively correlated with CD4+ T cells and CD8+ T cells (CD4+ T cells, <i>p</i> = 0.013; CD8+ T cells, <i>p</i> = 0.021), and positively correlated with PD-L1 (<i>p</i> = 0.022). Finally, survival analysis revealed that CD4+ T cells were associated with the prognosis of GC patients (<i>p</i> = 0.019), and the combined survival analysis of SR-BI and CD4+ T cells was also statistically significant (<i>p</i> = 0.030). <b>Conclusion:</b> SR-BI is highly expressed in GC tissue and associated with poor prognosis. Moreover, SR-BI can also regulate the GC tumor immune microenvironment.

Scavenger receptor class B type I genetic variants associated with disease severity in chronic hepatitis C virus infection.

Analysis of host genetic polymorphisms is an increasingly important tool for understanding and predicting pathogenesis and treatment response of viral diseases. The gene locus of scavenger receptor class B type I (SR-BI), encoding a cell entry factor and receptor for hepatitis C virus (HCV), contains several genetic polymorphisms.We applied a probe extension assay to determine the frequency of six single nucleotide polymorphisms (SNPs)within the SR-BI gene locus in 374 individuals with history of HCV infection. In addition, SR-BImessenger RNA (mRNA) levels were analyzed in liver biopsy specimens of chronically infected HCV subjects.The rs5888 variant allele T was present at a higher frequency in subjects with advanced fibrosis (χ2 , p = 0.016) and after adjusting for age, duration of infection and alcohol intake as confounding factors. Haplotype analysis of SNPfrequencies showed that a haplotype consisting of rs61932577 variant allele C and rs5888 variant allele T was associated with an increased risk of advanced liver fibrosis (defined by an Ishak score 4-6) (adjusted odds ratio 2.81; 95% confidence interval1.06-7.46. p = 0.038). Carriers of the rs5888 variant allele T displayed reduced SR-BI mRNA expression in liver biopsy specimens.In conclusion the rs5888 polymorphism variant is associated with decreased SR-BI expression and an increased risk of development of advanced fibrosis in chronic HCV infection. These findings provide further evidence for a role of SR-BI in HCV pathogenesis and provides a genetic marker for prediction of those infected individuals at greater risk of developing severe disease.

Recombinant Humanized IgG1 Antibody Promotes Reverse Cholesterol Transport through FcRn-ERK1/2-PPARα Pathway in Hepatocytes

Hyperlipidemia-associated lipid disorders are considered the cause of atherosclerotic cardiovascular disease. Reverse cholesterol transport (RCT) is a mechanism by which excess peripheral cholesterol is transported to the liver and further converted into bile acid for excretion from the body in feces, which contributes to reducing hyperlipidemia as well as cardiovascular disease. We previously found that the recombinant humanized IgG1 antibody promotes macrophages to engulf lipids and increases cholesterol efflux to high-density lipoprotein (HDL) through ATP-binding cassette sub-family A1 (ABCA1), one of the key proteins related to RCT. In the present study, we explored other RCT related proteins expression on hepatocytes, including scavenger receptor class B type I (SR-BI), apolipoprotein A-I (ApoA-I), and apolipoprotein A-II (ApoA-II), and its modulation mechanism involved. We confirmed that the recombinant humanized IgG1 antibody selectively activated ERK1/2 to upregulate SR-BI, ApoA-I, and ApoA-II expression in mice liver and human hepatocellular carcinoma cell lines HepG2 cells. The rate-limiting enzymes of bile acid synthesis, including cholesterol 7α-hydroxylase (CYP7A1) and sterol 27-hydroxylase (CYP27A1), exhibited a significant increase when treated with the recombinant humanized IgG1 antibody, as well as increased excretion of bile acids in feces. Besides, abolishment or mutation of peroxisome proliferator-activated receptor α (PPARα)/RXR binding site on SR-BI promoter eliminated SR-BI reporter gene luciferase activity even in the presence of the recombinant humanized IgG1 antibody. Knock down the neonatal Fc receptor (FcRn) on hepatocytes impaired the effect of recombinant humanized IgG1 antibody on activation of ERK1/2, as well as upregulation of SR-BI, ApoA-I, and ApoA-II expression. In conclusion, one of the mechanisms on the recombinant humanized IgG1 antibody attenuates hyperlipidemia in ApoE-/- mice model fed with high-fat-diet might be through reinforcement of liver RCT function in an FcRn-ERK1/2-PPARα dependent manner.

The Distinct Role of the HDL Receptor SR-BI in Cholesterol Homeostasis of Human Placental Arterial and Venous Endothelial Cells.

As opposed to adults, high-density lipoprotein (HDL) is the main cholesterol carrying lipoprotein in fetal circulation. The major HDL receptor, scavenger receptor class B type I (SR-BI), contributes to local cholesterol homeostasis. Arterial endothelial cells (ECA) from human placenta are enriched with cholesterol compared to venous endothelial cells (ECV). Moreover, umbilical venous and arterial plasma cholesterol levels differ markedly. We tested the hypothesis that the uptake of HDL-cholesteryl esters differs between ECA and ECV because of the differential expression of SR-BI. We aimed to identify the key regulators underlying these differences and the functional consequences. Immunohistochemistry was used for visualization of SR-BI in situ. ECA and ECV were isolated from the chorionic plate of human placenta and used for RT-qPCR, Western Blot, and HDL uptake assays with 3H- and 125I-labeled HDL. DNA was extracted for the methylation profiling of the SR-BI promoter. SR-BI regulation was studied by exposing ECA and ECV to differential oxygen concentrations or shear stress. Our results show elevated SR-BI expression and protein abundance in ECA compared to ECV in situ and in vitro. Immunohistochemistry demonstrated that SR-BI is mainly expressed on the apical side of placental endothelial cells in situ, allowing interaction with mature HDL circulating in the fetal blood. This was functionally linked to a higher increase of selective cholesterol ester uptake from fetal HDL in ECA than in ECV, and resulted in increased cholesterol availability in ECA. SR-BI expression on ECV tended to decrease with shear stress, which, together with heterogeneous immunostaining, suggests that SR-BI expression is locally regulated in the placental vasculature. In addition, hypomethylation of several CpG sites within the SR-BI promoter region might contribute to differential expression of SR-BI between chorionic arteries and veins. Therefore, SR-BI contributes to a local cholesterol homeostasis in ECA and ECV of the human feto-placental vasculature.

HDL and Scavenger Receptor Class B Type I (SRBI).

The scavenger receptor class B type I (SR-BI) is a versatile HDL receptor protein. It is highly expressed in liver and steroidogenic tissues. SR-BI regulates selective uptake of cholesterol ester (CE) from HDL, revealing its role in mediating reverse cholesterol transport (RCT) and steroid hormone synthesis. In addition, SR-BI is involved in cholesterol transport, cellular inflammatory response, platelet reactivity, and HDL-initiated signaling in the vascular system in several mouse models. Mutations in the human SR-BI gene (SCARB1) have been found to be associated with abnormally high plasma HDL-C levels and an increased risk of atherosclerotic cardiovascular disease. At present, the key regions of SR-BI transmembrane structure and the regulatory mechanisms of SR-BI expression still need to be further studied. In this chapter, the structural, functional, and regulatory characteristics of SR-BI are reviewed, and the importance of SR-BI in related metabolic diseases was expounded.

Interaction between Flavonoids and Carotenoids on Ameliorating Oxidative Stress and Cellular Uptake in Different Cells.

Flavonoids (quercetin, luteolin) and carotenoids (lycopene, lutein) were combined at different molecular ratios in a total concentration of 8 μM to investigate their antioxidant interactions. Cellular uptake of carotenoids, the expression of carotenoid transporters, the ROS scavenging ability, and antioxidant enzymes activities were compared in HUVEC, Caco-2, and L-02 cells. Combinations with flavonoids in the majority showed stronger antioxidant activity. Lycopene combined with quercetin at ratio 1:5 showed stronger ROS scavenging activities, increased 18, 12, and 12 Cellular antioxidant activity (CAA) units in HUVEC, Caco-2, and L-02 cells, respectively, and promoted SOD and CAT activities than individual component. The cell uptake of carotenoids was enhanced by flavonoids in antioxidant synergistic groups, while dampened by flavonoids in antagonistic groups in HUVEC cells. The synergistic group (lycopene:quercetin = 1:5) increased lycopene uptake by 271%, while antagonistic group (lutein:quercetin = 5:1) decreased lutein uptake by 17%. Flavonoids modulated the effects of carotenoids on the expression of active transporters scavenger receptor class B type I (SR-BI) or Niemann-Pick C1-like 1 (NPC1L1). The synergistic group (lycopene:quercetin = 1:5) increased the expression of SR-BI compared to individual lycopene treatment in HUVEC and Caco-2 cells. Thus, a diet rich in both flavonoids and lycopene possesses a great antioxidant activity, especially if a higher amount of flavonoids is included.

Insulin Rescued MCP-1-Suppressed Cholesterol Efflux to Large HDL2 Particles via ABCA1, ABCG1, SR-BI and PI3K/Akt Activation in Adipocytes

PurposeIntracellular cholesterol imbalance plays an important role in adipocyte dysfunction of obesity. However, it is unclear whether obesity induced monocyte chemoattractant protein-1 (MCP-1) causes the adipocyte cholesterol imbalance. In this study, we hypothesize that MCP-1 impairs cholesterol efflux of adipocytes to HDL2 and insulin rescues this process.MethodsWe recruited coronary artery disease (CAD) patients with obesity and overweight to analyze the association between MCP-1 and HDL2-C by Pearson correlation coefficients. We performed [3H]-cholesterol efflux assay to demonstrate the effect of MCP-1 and insulin on cholesterol efflux from 3T3-L1 adipocytes to large HDL2 particles. Western blot, RT-qPCR, cell-surface protein assay, and confocal microscopy were performed to determine the regulatory mechanism.ResultsPlasma MCP-1 concentrations were negatively correlated with HDL2-C in CAD patients with obesity and overweight (r = −0.60, p < 0.001). In differentiated 3T3-L1 adipocytes, MCP-1 reduced cholesterol efflux to large HDL2 particles by 55.4% via decreasing ATP-binding cassette A1 (ABCA1), ABCG1, and scavenger receptor class B type I (SR-BI) expression. Intriguingly, insulin rescued MCP-1 mediated-inhibition of cholesterol efflux to HDL2 in an Akt phosphorylation-dependent manner. The rescue efficacy of insulin was 138.2% for HDL2. Moreover, insulin increased mRNA and protein expression of ABCA1, ABCG1, and SR-BI at both transcriptional and translational levels via the PI3K/Akt activation.ConclusionsThese findings indicate that MCP-1 impairs cholesterol efflux to large HDL2 particles in adipocytes, which is reversed by insulin via the upregulation of ABCA1, ABCG1, and SR-BI. Therefore, insulin might improve cholesterol imbalance by an anti-inflammatory effect in adipocytes. Clinical trial registration number: ChiCTR2000033297; Date of registration: 2020/05/ 27; Retrospectively registered.

Role of HDL and Scavenger Receptor Class B Type I (SR-BI) Expression in LNCaP and PC-3 Prostate Cancer Cell Lines. Growth Patterns in the Chick Chorioallantoic Membrane Model

Cholesterol metabolism is a key pathway affecting androgen synthesis and prostate cancer cell proliferation. Major receptors and transporters involved in cellular cholesterol homeostasis and cholesterol fluxes are ATP-binding cassette protein A1 (ABCA1), LDL receptor (LDLR) and the HDL receptor scavenger receptor class B type I (SR-BI). Especially SR-BI deserves more and more attention because it has been shown to be overexpressed by the majority of malignant tumours, promoting their proliferation and metastasis. PC-3 and LNCaP are two of the commonly used cell lines for in vitro prostate cancer studies. A comparative overview of the expression of receptors involved in cholesterol uptake and their activities in these two cell lines was missing; therefore we reviewed the current knowledge on this topic. We investigated the expression of SR-BI in these two cell lines and the uptake of labelled HDL. In order to study and compare tumour development, we assessed the growth of both cell lines in the chick chorioallantoic membrane (CAM) model. Although microtumours successfully developed, size increase was limited as confirmed by the analysis of the proliferation marker Ki67. Interestingly prostate-specific antigen (PSA) secreted by LNCaP tumours could be determined in the chick embryo blood. SR-BI is a promising therapeutic target either by its direct inhibition or more importantly as an agent for drug delivery.

Citrus Flavanones Enhance β-Carotene Uptake in Vitro Experiment Using Caco-2 Cell: Structure-Activity Relationship and Molecular Mechanisms.

Flavonoids can interfere with the absorption of carotenoids. In this study, the inherent mechanisms of 12 citrus flavanones for β-carotene (Bc) cellular uptake and the structure-activity relationship were investigated. The results showed that multiple hydroxyl groups had the lowest promoting effect. O-Glycosylation at C7 of the A ring led to the greatest promoting effect on Bc absorption. O-Glycosylation at C7 exhibited a strong affinity with the cell membrane and subsequently fluidized the cell membrane. Aglycon molecules significantly induced transient increases of paracellular permeability by decreasing tight junction proteins (ZO-1, claudin-1) expression. In addition, citrus flavanones might enhance scavenger receptor class B type I (SR-BI) expression via their actions as agonists of peroxisome proliferator-activated receptor-gamma (PPARγ). Catechol structure in the B-ring attenuated the activate action of SR-BI expression. The structure-dependent membrane permeability and activation of specific membrane proteins are mechanistically associated with the promoting effect on Bc cellular uptake by citrus flavanones.

Hepatocyte-Specific SR-BI Gene Transfer Corrects Cardiac Dysfunction in Scarb1-Deficient Mice and Improves Pressure Overload-Induced Cardiomyopathy.

Objective- We investigated the hypothesis that HDL (high-density lipoprotein) dysfunction in Scarb1-/- mice negatively affects cardiac function both in the absence and in the presence of pressure overload. Second, we evaluated whether normalization of HDL metabolism in Scarb1-/- mice by hepatocyte-specific SR-BI (scavenger receptor class B, type I) expression after E1E3E4-deleted adenoviral AdSR-BI (E1E3E4-deleted adenoviral vector expressing SR-BI protein in hepatocytes) transfer abrogates the effects of total body SR-BI deficiency on cardiac structure and function. Approach and Results- Transverse aortic constriction (TAC) or sham operation was performed at the age of 14 weeks, 2 weeks after saline injection or after gene transfer with AdSR-BI or with the control vector Adnull. Mortality rate in Scarb1-/- TAC mice was significantly increased compared with wild-type TAC mice during 8 weeks of follow-up (hazard ratio, 2.02; 95% CI, 1.14-3.61). Hepatocyte-specific SR-BI gene transfer performed 2 weeks before induction of pressure overload by TAC potently reduced mortality in Scarb1-/- mice (hazard ratio, 0.329; 95% CI, 0.180-0.600). Hepatocyte-specific SR-BI expression abrogated increased cardiac hypertrophy and lung congestion and counteracted increased myocardial apoptosis and interstitial and perivascular fibrosis in Scarb1-/- TAC mice. Scarb1-/- sham mice were, notwithstanding the absence of detectable structural heart disease, characterized by systolic and diastolic dysfunction and hypotension, which were completely counteracted by AdSR-BI transfer. Furthermore, AdSR-BI transfer abrogated increased end-diastolic pressure and diastolic dysfunction in Scarb1-/- TAC mice. Increased oxidative stress and reduced antioxidant defense systems in Scarb1-/- mice were rescued by AdSR-BI transfer. Conclusions- The detrimental effects of SR-BI deficiency on cardiac structure and function are nullified by hepatocyte-specific SR-BI transfer, which restores HDL metabolism.

Prenatal caffeine ingestion induces long-term alterations in scavenger receptor class B type I expression and glucocorticoid synthesis in adult male offspring rat adrenals

Caffeine is contained within many drinks and food that are consumed daily. Prenatal caffeine ingestion (PCI) is a risk factor for intrauterine growth retardation (IUGR). We previously observed that PCI inhibits scavenger receptor class B type I (SR-BI)-mediated cholesterol uptake in fetal adrenals, subsequently decreasing glucocorticoid synthesis and inducing IUGR. In the present study, we aimed to investigate the long-term effects of PCI on adrenal glucocorticoid synthesis in adult male offspring rats. After establishing the PCI-induced IUGR, adult male offspring was injected intraperitoneally with 5 mg/kg·d lipopolysaccharide (LPS) for 2 days to induce acute stress. We observed persistent inhibition of SR-BI expression in PCI adrenals before and after stress. Compared with the controls, the PCI offspring had higher corticosterone concentrations after stress. The serum cholesterol concentration was stable without intergroup differences before and after stress. The cholesterol concentration in PCI adrenals showed a higher decrease rate than that of the control after stress. In summary, PCI induced long-term alterations in SR-BI expression and glucocorticoid synthesis in adult male offspring rat adrenals. Cholesterol has to be over-consumed in PCI adrenals against acute stress. This study provides an experimental basis to explain the susceptibility of IUGR offspring to metabolic diseases in adults.

Scavenger receptor BI attenuates IL-17-dependent neutrophilic inflammation in asthma.

Abstract Asthma impacts over 24 million people and costs about $56 billion annually in the United States. Airway neutrophil accumulation and high levels of IL-17 are characteristic of severe asthma. However, mechanisms underlying IL-17/neutrophilic inflammation in severe asthma remain poorly defined. Scavenger receptor class B type I (SR-BI) is a multi-recognition receptor that regulates cholesterol trafficking. We previously reported SR-BI dampens pulmonary innate immune responses during bacterial pneumonia, but the role of SR-BI in asthma is unknown. We hypothesize pulmonary SR-BI expression is protective against house dust mite (HDM)-induced IL-17-dependent neutrophilic asthma. SR-BI+/+ and SR-BI−/− mice were sensitized with 10 μg HDM by oropharyngeal aspiration on day 0 and 7, and challenged with 2 μg HDM on day 14, 15, 16. Airway inflammation and cytokine production were quantified on day 17. SR-BI−/− mice had increased neutrophils but decreased eosinophils in bronchoalveolar lavage (BAL) after HDM challenge compared to SR-BI+/+ mice. BAL levels of neutrophil chemoattractants CXCL1, CXCL2 and CXCL5 were not significantly different between SR-BI+/+ and SR-BI−/− mice. SR-BI−/− mice had increased pulmonary IL-17A and GM-CSF production and decreased IL-5 production. To identify cellular sources of airspace IL-17, single cells isolated from lung were labeled with antibodies for flow cytometry. IL-17A increased in neutrophils (CD45+Ly6G+) and macrophages (CD45+CD64+CD11b−CD11c+) but not T cells (CD45+CD4+) of asthmatic SR-BI−/− mice suggesting myeloid cells rather than Th17 cells as sources of IL-17. Overall, SR-BI expression in the lung suppresses neutrophilic inflammation and IL-17 production in HDM-induced asthma model.

MicroRNA-24 aggravates atherosclerosis by inhibiting selective lipid uptake from HDL cholesterol via the post-transcriptional repression of scavenger receptor class B type I

Background and aimsLiver scavenger receptor class B type I (SR-BI) exerts atheroprotective effects through selective lipid uptake (SLU) from high-density lipoprotein cholesterol (HDL-C). Low hepatic SR-BI expression leads to high HDL-C levels in the circulation and an increased risk of atherosclerosis. Furthermore, macrophage SR-BI mediates bidirectional cholesterol flux and may protect against atherogenesis. Previous studies have revealed that miR-24 is closely related to cardiovascular disease (CVD) progression. We aimed to investigate the molecular mechanisms by which miR-24 participates in SR-BI-mediated selective HDL cholesteryl ester (HDL-CE) uptake and further atherogenesis in apoE−/− mice. MethodsBioinformatic predictions and luciferase reporter assays were utilized to detect the association between miR-24 and the SR-BI 3′ untranslated region (3′ UTR), and RT-PCR and western blotting were used to evaluate SR-BI mRNA and protein expression, respectively. The effects of miR-24 on Dil-HDL uptake were determined by flow cytometry assay. Double-radiolabeled HDL (125I-TC-/[3H] CEt-HDL) was utilized to measure the effects of miR-24 on HDL and CE binding and SLU in HepG2 and PMA-treated THP-1 cells. In addition, total cholesterol (TC) levels in HepG2 cells were analyzed using enzymatic methods, and macrophage lipid content was evaluated by high-performance liquid chromatography (HPLC) assay. Small interfering RNA (siRNA) and pcDNA3.1(−)-hSR-BI plasmid transfection procedures were utilized to confirm the role of SR-BI in the effects of miR-24 on Dil-HDL uptake, SLU and cholesterol levels in both cell types. Hepatic SR-BI level in apoE−/− mice was measured by western blotting. Liver TC, FC and CE levels and plasma triglycerides (TG), TC and HDL-C levels were evaluated enzymatically using commercial test kits. Atherosclerotic lesion sizes were measured using Oil Red O and hematoxylin-eosin staining. ResultsmiR-24 directly repressed SR-BI expression by targeting its 3′UTR. In addition, miR-24 decreased Dil-HDL uptake and SLU in HepG2 and THP-1 macrophages. In the presence of HDL, miR-24 decreased TC levels in HepG2 cells and TC, free cholesterol (FC) and CE levels in macrophages. Overexpression and down-regulation assays showed that SR-BI mediated the effects of miR-24 on Dil-HDL uptake, SLU and cholesterol levels. Lastly, miR-24 administration decreased hepatic SR-BI expression and promoted atheromatous plaque formation in apoE−/− mice, findings in line with those of our in vitro studies. ConclusionsThese findings indicate that miR-24 accelerates atherogenesis by repressing SR-BI-mediated SLU from HDL-C.

Low scavenger receptor class B type I expression is associated with gastric adenocarcinoma tumor aggressiveness.

Scavenger receptor class B type I (SR-BI), a well-documented high-density lipoprotein receptor, has been implicated in the development and progression of human cancer. However, little is known regarding the expression profile and clinical value of SR-BI in gastric adenocarcinoma. In the present study immunohistochemistry analysis was performed on a well-annotated gastric adenocarcinoma tissue microarray to investigate the association between SR-BI expression and clinicopathological parameters or patient outcome. The results revealed that SR-BI expression was detected in 69% of the 84 gastric adenocarcinomas. Moreover, a significant association was observed between low SR-BI expression and poor histological grade, higher Tumor-Node-Metastasis T stage, higher N stage and diffuse type carcinoma. Low SR-BI expression was also significantly associated with a shorter overall survival time in patients with gastric adenocarcinoma, although it was not an independent prognostic factor. Overall, the results of the present study demonstrated that SR-BI was possibly involved in gastric carcinogenesis and could be used as a biomarker to predict malignancy of gastric adenocarcinoma.

Quercetin induces the selective uptake of HDL-cholesterol via promoting SR-BI expression and the activation of the PPARγ/LXRα pathway.

Reverse cholesterol transport (RCT) is the process to deliver cholesterol to the liver for further excretion and involves scavenger receptor class B type I (SR-BI)-mediated selective lipid uptake (SLU) from high-density lipoprotein cholesterol (HDL-C). The up-regulation of hepatic SR-BI expression accelerates HDL-C clearance in circulation and impedes the development of atherosclerosis (AS). In the present study, we explored the modulation of hepatic SR-BI expression and SR-BI-mediated SLU by quercetin, a natural flavonoid compound in the diet with a favorable role in cardiovascular disorders. We found that quercetin significantly increased the expression level of SR-BI in HepG2 cells in a concentration- and time-dependent manner. Besides, quercetin had stimulatory effects on the binding of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil)-labeled HDL to hepatocytes and 125I/3H-CE-HDL association. Treatment with small interfering RNA (siRNA) or SR-BI specific inhibitor, BLT-1, inhibited quercetin-induced Dil-HDL binding and selective HDL-C uptake. Treatment with quercetin increased both proliferator-activated receptor γ (PPARγ) and liver X receptor α (LXRα) levels. Additionally, the quercetin-induced expression of SR-BI, Dil-HDL binding and the selective uptake of HDL-C were significantly attenuated by treatment with PPARγ siRNA, LXRα siRNA, and their antagonists, respectively. In C57BL/6 mice, quercetin administration potently increased SR-BI, PPARγ and LXRα levels and lipid accumulation in the liver. Altogether, our results suggest that quercetin-induced up-regulation of SR-BI and subsequent lipid uptake in hepatocytes might contribute to its beneficial effects on cholesterol homeostasis and atherogenesis.

Inhibition of the NLRP3 inflammasome attenuates foam cell formation of THP-1 macrophages by suppressing ox-LDL uptake and promoting cholesterol efflux

The NOD-like receptor family, pyrin domain–containing protein 3 (NLRP3) inflammasome plays an important role in the development of atherosclerosis. The activated NLRP3 inflammasome has been reported to promote macrophage foam cell formation, but not all studies have obtained the same result, and how NLRP3 inflammasome is involved in the formation of foam cells remains elusive. We used selective NLRP3 inflammasome inhibitors and NLRP3-deficient THP-1 cells to assess the effect of NLRP3 inflammasome inhibition on macrophage foam cell formation, oxidized low-density lipoprotein (ox-LDL) uptake, esterification, and cholesterol efflux, as well as the expression of associated proteins. Inhibition of the NLRP3 inflammasome attenuated foam cell formation, diminished ox-LDL uptake, and promoted cholesterol efflux from THP-1 macrophages. Moreover, it downregulated CD36, acyl coenzyme A: cholesterol acyltransferase-1 and neutral cholesterol ester hydrolase expression; upregulated ATP-binding cassette transporter A1 (ABCA1) and scavenger receptor class B type I (SR-BI) expression; but had no effect on the expression of scavenger receptor class A and ATP-binding cassette transporter G1. Collectively, our findings show that inhibition of the NLRP3 inflammasome decreases foam cell formation of THP-1 macrophages via suppression of ox-LDL uptake and enhancement of cholesterol efflux, which may be due to downregulation of CD36 expression and upregulation of ABCA1 and SR-BI expression, respectively.

Urolithin A shows anti-atherosclerotic activity via activation of class B scavenger receptor and activation of Nef2 signaling pathway.

This study investigates the therapeutic potential of urothelin A in attenuating atherosclerotic lesion in wistar rat models and explore the role of Scavenger receptor-class B type I (SR-BI) and activation of Nrf-2 singling pathway. Wistar rats (n=48) were feed with high cholesterol diet supplemented with Vitamin D3 and subjected to balloon injury of the aorta. Three days prior to the aortal injury, rats (n=16) were administered urothelin A (3mg/kg/d; po). Positive control were rats receiving high cholesterol diet and balloon injury of the aorta (n=16). The sham group (n=16) consisted of rats fed on basal diet. After twelve weeks blood was collected from all animals for estimation of lipid and angiotensin II (Ang II) levels along, subsequently all animals were sacrificed and morphologic analysis of the aorta was performed. Expression of SR-BI and phosphorylated extracellular signal regulated kinase 1/2 (p-ERK1/2) protein were evaluated by Western blot. After twelve weeks of treatment with urolithin A, there was a significant decrease in the plasma lipid and Ang II levels and improvement of aortic lesion compared with the sham group. There was an increased expression of SR-BI and inhibition of p-ERK1/2 (p<0.05). The expression of SR-BI was inversely correlated with levels of Ang II. From the results it can be safely concluded that administration of urolithin A attenuates atherosclerosis via upregulation of SR-BI expression and inhibition of p-ERK1/2 levels.

Abstract 187: Genetic Targeting at Apolipoprotein E Locus to Knockdown Scavenger Receptor Class B Type I in Mice: Characterization of a Novel Mouse Model of Coronary Heart Disease

Background: Scavenger Receptor Class B Type I (SRBI) is the key player mediating HDL-dependent reverse cholesterol transport (RCT) in hepatocyte, and SRBI mutation causes coronary heart disease (CHD) in humans. Mice lacking SRBI and apolipoprotein E (apoE), fed on chow diet, develop cardinal features of CHD and succumb to premature death. However, the application of this model is limited due to the short lifespan, early onset of CHD symptom, the difficulty to maintain genetic mutations at two different loci, and infertility. The latter may be related to adrenal SRBI deficiency. Methods and Results: A genetic mouse model, named as SRBI KD ApoE -/- was produced by using CRISPR/Cas9 technique, in which an SRBI knock-down cassette (at both mRNA and proteins levels) is inserted downstream of the indogenous apoE promoter, thus abolishing apoE expression. Real-time PCR and Western blot characterization showed that SRBI expression in liver was significantly reduced (33% vs. 100% by RT-PCR, 0.5% vs. 100% by WB, P&lt;0.001), but no significant difference was found in other examined tissues. SRBI KD ApoE -/- mice are fertile and do not exhibit pre-mature cardiovascular death on chow diet up to 10 months. Compared to ApoE -/- mice, SRBI KD ApoE -/- mice showed significant increase in serum HDL-C (3.11 vs 1.70 mmol/L, P&lt;0.01), whereas serum triglyceride or LDL-C was similar (triglyceride: 0.87 vs. 0.9 mmol/L; LDL-C: 8.35 vs. 7.74 mmol/L). When treated with high-fat diet (HFD: 21% fat, 0.2% cholesterol in weight, n=6/group) for 8 weeks (starting at 8-week old), SRBI KD ApoE -/- mice gained significantly more weight than ApoE -/- mice(P&lt;0.05 for females), and exhibited higher weight ratio of heart to body than that of ApoE -/- mice (females: 6.51% vs. 5.16%, P=0.051; males: 6.54% vs. 4.64%, P&lt;0.01). Splenomegaly was observed more frequently in these mice than in ApoE -/- mice (females: 17.7% vs. 5.99%, P&lt;0.001; males: 6.12% vs. 3.99%, P&lt;0.01).

Regulation of lipid metabolism by obeticholic acid in hyperlipidemic hamsters

The farnesoid X receptor (FXR) plays critical roles in plasma cholesterol metabolism, in particular HDL-cholesterol (HDL-C) homeostasis. Obeticholic acid (OCA) is a FXR agonist being developed for treating various chronic liver diseases. Previous studies reported inconsistent effects of OCA on regulating plasma cholesterol levels in different animal models and in different patient populations. The mechanisms underlying its divergent effects have not yet been thoroughly investigated. The scavenger receptor class B type I (SR-BI) is a FXR-modulated gene and the major receptor for HDL-C. We investigated the effects of OCA on hepatic SR-BI expression and correlated such effects with plasma HDL-C levels and hepatic cholesterol efflux in hyperlipidemic hamsters. We demonstrated that OCA induced a time-dependent reduction in serum HDL-C levels after 14 days of treatment, which was accompanied by a significant reduction of liver cholesterol content and increases in fecal cholesterol in OCA-treated hamsters. Importantly, hepatic SR-BI mRNA and protein levels in hamsters were increased to 1.9- and 1.8-fold of control by OCA treatment. Further investigations in normolipidemic hamsters did not reveal OCA-induced changes in serum HDL-C levels or hepatic SR-BI expression. We conclude that OCA reduces plasma HDL-C levels and promotes transhepatic cholesterol efflux in hyperlipidemic hamsters via a mechanism involving upregulation of hepatic SR-BI.

Baicalin promotes cholesterol efflux by regulating the expression of SR-BI in macrophages.

Intake of a high dosage of baicalin has previously been shown to attenuate hyperlipidemia induced by a high-fat diet. Baicalin functions as an activator of peroxisome proliferator-activated receptor-γ (PPAR-γ), which is the key regulator of reverse cholesterol transport (RCT). The present study aimed to test the hypothesis that baicalin could promote cholesterol efflux in macrophages through activating PPAR-γ. Phorbol 12-myristate 13-acetate-stimulated THP-1 cells were treated with oxidized low-density lipoprotein and (3H)-cholesterol for 24 h, and the effects of baicalin on cholesterol efflux were evaluated in the presence of apolipoprotein A-1 (ApoA-1), or high-density lipoprotein subfraction 2 (HDL2) or subfraction 3 (HDL3). The expression levels of scavenger receptor class B type I (SR-BI), PPAR-γ and liver X receptor-α (LXRα) were detected and specific inhibitors or activators of SR-BI, PPAR-γ and LXRα were applied to investigate the mechanism. Treatment of THP-1 macrophages with baicalin significantly accelerated HDL-mediated, but not ApoA-1-mediated cholesterol efflux. However, baicalin treatment increased the expression of SR-BI at the mRNA and protein levels in a dose- and time-dependent manner, and pre-treatment with the SR-BI inhibitor BLT-1 and SR-BI small interfering RNA significantly inhibited baicalin-induced cholesterol efflux. Furthermore, baicalin increased the expression of PPAR-γ and LXRα, and the application of specific agonists and inhibitors of PPAR-γ and LXRα changed the expression of SR-BI, as well as cholesterol efflux. It may be concluded that baicalin induced cholesterol efflux from THP-1 macrophages via the PPAR-γ/LXRα/SR-BI pathway.