Variants in scavenger receptor class B type I gene are associated with HDL cholesterol levels in younger women

Influence of the rs4238001 Genetic Polymorphism of the SR-B1 Gene on Serum Lipid Levels and Response to Rosuvastatin in Myocardial Infarction Iraqi Patients

Scavenger receptor type B (SR-BI) is a receptor that binds both native and altered lipoproteins. It was revealed to facilitate utilization of high-density lipoprotein HDL and significantly affect the reverse transport of cholesterol. Therefore, the objectives were to identify the possible role of the genetic variant rs4238001 in patients with myocardial infarction (MI) on serum lipid level, and how this variant could impact the response of rosuvastatin drug. The genotyping of the rs4238001 genetic polymorphism of the SR-B1 gene was performed in 300 participants, including 150 MI patients treated with 20mg/day/4 weeks of rosuvastatin and 150 healthy control using Taq man probes (FAM and VIC) by Real-time PCR technique. The concentrations of the lipid profile were evaluated. The significance of the anthropometric data was revealed in the ejection fraction and smoking status (p < 0.05) between groups. The lipid profile shows either significant differences between control and MI patients (pre-treatment) or between pre-and post-treatment of MI patients (p < 0.05), but not HDL-c (p > 0.05). The minor allele frequency MAF% of the T allele and TT genotype were more frequent in MI patients than in controls (P = 0.173; OR = 3.62; 95% CI = 0.74-17.64). CC genotype was found to be associated with response to rosuvastatin therapy with a change of % (29.08 ± 53.2; p = 0.021). In the Iraqi population, the rs4238001 polymorphism of the SR-B1 gene is associated with variations in serum lipids, and the CC genotype of the SNP is related to higher HDL-C in the lipid-lowering rosuvastatin response.

Zebrafish as outgroup model to study evolution of scavenger receptor class B type I functions

BACKGROUND AND AIMS

Scavenger receptor class B1 (SCARB1) - also known as the high-density lipoprotein (HDL) receptor - is a multi-ligand scavenger receptor that is primarily expressed in liver and steroidogenic organs. This receptor is known for its function in reverse cholesterol transport (RCT) in mammals and hence disruption leads to a massive increase in HDL cholesterol in these species. The extracellular domain of SCARB1 - which is important for cholesterol handling - is highly conserved across multiple vertebrates, except in zebrafish.

METHODS

To examine the functional conservation of SCARB1 among vertebrates, two stable scarb1 knockout zebrafish lines, scarb1 715delA (scarb1 -1 nt) and scarb1 715_716insGG (scarb1 +2 nt), were created using CRISPR-Cas9 technology.

RESULTS

We demonstrate that, in zebrafish, SCARB1 deficiency leads to disruption of carotenoid-based pigmentation, reduced fertility, and a decreased larvae survival rate, whereas steroidogenesis was unaltered. The observed reduced fertility is driven by defects in female fertility (-50 %, p < 0.001). Importantly, these alterations were independent of changes in free (wild-type 2.4 ± 0.2 μg/μl versus scarb1^-/- 2.0 ± 0.1 μg/μl) as well as total (wild-type 4.2 ± 0.4 μg/μl versus scarb1^-/- 4.0 ± 0.3 μg/μl) plasma cholesterol levels. Uptake of HDL in the liver of scarb1^-/- zebrafish larvae was reduced (-86.7 %, p < 0.001), but this coincided with reduced perfusion of the liver. No effect was observed on lipoprotein uptake in the caudal vein. SCARB1 deficient canaries, which also lack carotenoids in their plumage, similarly as scarb1^-/- zebrafish, failed to show an increase in plasma free- and total cholesterol levels.

CONCLUSION

Our findings suggest that the specific function of SCARB1 in maintaining plasma cholesterol could be an evolutionary novelty that became prominent in mammals, while other known functions were already present earlier during vertebrate evolution.

Effects of SNVs in ABCA1, ABCG1, ABCG5, ABCG8, and SCARB1 Genes on Plasma Lipids, Lipoproteins, and Adiposity Markers in a Brazilian Population

Several proteins are involved in cholesterol homeostasis, as scavenger receptor class B type I and ATP-binding cassette (ABC) transporters including ABCA1, ABCG1, ABCG5, and ABCG8. This study aimed to determine the effects of single nucleotide variants (SNVs) rs2275543 (ABCA1), rs1893590 (ABCG1), rs6720173 (ABCG5), rs6544718 (ABCG8), and rs5888 (SCARB1) on plasma lipids, lipoproteins, and adiposity markers in an asymptomatic population and its sex-specific effects. Volunteers (n = 590) were selected and plasma lipids, lipoproteins, and adiposity markers (waist-to-hip and waist-to-height ratios, lipid accumulation product and body adiposity index) were measured. Genomic DNA was isolated from peripheral blood cells according to the method adapted from Gross-Bellard. SNVs were detected in the TaqMan® OpenArray® Real-Time polymerase chain reaction platform and data analyses were performed using the TaqMan® Genotyper Software. The rs2275543*C point to an increase of high-density lipoprotein size in females while in males very-low-density lipoprotein, cholesterol, and triglycerides were statistically lower (P value < 0.05). The rs1893590*C was statistically associated with lower apolipoprotein A-I levels and higher activities of paraoxonase-1 and cholesteryl ester transfer protein (P value < 0.05). The rs6720173 was statistically associated with an increase in cholesterol and low-density lipoprotein cholesterol in males; moreover, rs6544718*T reduced adiposity markers in females (P value < 0.05). Regarding the rs5888, a decreased adiposity marker in the total population and in females occurred (P value < 0.05). Multivariate analysis of variance showed that SNVs could influence components of high-density lipoprotein metabolism, mainly through ABCG1 (P value < 0.05). The ABCA1 and ABCG5 variants showed sex-specific effects on lipids and lipoproteins, while SCARB1 and ABCG8 variants might influence adiposity markers in females. Our data indicate a possible role of ABCG1 on HDL metabolism.

Association between a genetic variant in scavenger receptor class B type 1 and its role on codon usage bias with increased risk of developing coronary artery disease

OBJECTIVE

Coronary artery disease (CAD) as an important cause of morbidity and mortality globally. The scavenger receptor class B type 1 (SCARB1) plays an essential role in the reverse cholesterol transport. We have explored the association between a genetic variant, rs5888, in the SCARB1 gene with CAD and serum HDL-C levels.

METHODS

Patients were categorized into two groups' angiogram positive (>50% coronary stenosis) and angiogram negative (<50% coronary stenosis). Genotyping was carried out using polymerase chain reaction-amplification refractory mutation system. The association between the SNP rs5888 and serum HDL-C was analyzed using a logistic regression model.

RESULTS

The results showed that the subjects carrying a T allele was associated with a decreased serum HDL-C levels compared to the C allele in total population (p < 0.001). The risk of angiogram positivity in subjects carrying a T allele was 3.1-fold higher than for the control group (p < 0.001).

CONCLUSION

CVD patients carrying the T allele of rs5888 variant in the SCARB1 gene was associated with decreased serum level of HDL.

SR-B1, a Key Receptor Involved in the Progression of Cardiovascular Disease: A Perspective from Mice and Human Genetic Studies

High plasma level of low-density lipoprotein (LDL) is the main driver of the initiation and progression of cardiovascular disease (CVD). Nevertheless, high-density lipoprotein (HDL) is considered an anti-atherogenic lipoprotein due to its role in reverse cholesterol transport and its ability to receive cholesterol that effluxes from macrophages in the artery wall. The scavenger receptor B class type 1 (SR-B1) was identified as the high-affinity HDL receptor, which facilitates the selective uptake of cholesterol ester (CE) into the liver via HDL and is also implicated in the plasma clearance of LDL, very low-density lipoprotein (VLDL) and lipoprotein(a) (Lp(a)). Thus, SR-B1 is a multifunctional receptor that plays a main role in the metabolism of different lipoproteins. The aim of this review is to highlight the association between SR-B1 and CVD risk through mice and human genetic studies.

Sex-Specific Influence of the SCARB1 Rs5888 SNP on the Serum Lipid Response to Atorvastatin in Patients with Acute Coronary Syndrome Undergoing Percutaneous Coronary Intervention

Background

Epidemiological studies have shown that there are sex differences in blood lipid levels and lipid responses to statins. Previous studies have shown that the rs5888 single nucleotide polymorphism (SNP) in the scavenger receptor class B type 1 (SCARB1) gene is associated with serum lipid levels in a sex-specific manner. The present study was undertaken to detect the sex-specific influence of the SCARB1 rs5888 SNP on the serum lipid response to atorvastatin in patients with acute coronary syndrome (ACS) undergoing percutaneous coronary intervention (PCI).

Methods

A total of 158 unrelated ACS patients (108 males, 50 females) were enrolled, and all patients received atorvastatin 20 mg/daily after PCI. Genotyping of the rs5888 SNP was performed by polymerase chain reaction and direct sequencing. Serum lipid profiles were determined before treatment and after an average follow-up time of one year.

Results

The baseline serum total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and apolipoprotein (Apo)AI levels were higher in females than in males (P<0.05). After treatment with atorvastatin, serum TC, LDL-C, and ApoB were decreased, and ApoAI was increased (P<0.05). The effects of atorvastatin on serum lipid levels were different between males and females, and females had greater decreases in TC, LDL-C and ApoB levels than males (P<0.05). The genotypic frequencies of the rs5888 SNP were not different between males and females. The atorvastatin response was not associated with the rs5888 SNP in males (P > 0.05). Nonetheless, in female individuals carrying the rs5888 T-allele, we observed a greater reduction in TC, LDL-C, and ApoB levels after the use of 20 mg/day atorvastatin (P<0.05).

Conclusion

This study indicates that the SCARB1 rs5888 T-allele was associated with a greater reduction in serum TC, LDL-C, and ApoB after atorvastatin treatment in female patients with ACS undergoing PCI.

SR-BI as a target of natural products and its significance in cancer

Scavenger receptor class B type I (SR-BI) protein is an integral membrane glycoprotein. SR-BI is emerging as a multifunctional protein, which regulates autophagy, efferocytosis, cell survival and inflammation. It is well known that SR-BI plays a critical role in lipoprotein metabolism by mediating cholesteryl esters selective uptake and the bi-directional flux of free cholesterol. Recently, SR-BI has also been identified as a potential marker for cancer diagnosis, prognosis, or even a treatment target. Natural products are a promising source for the discovery of new drug leads. Multiple natural products were identified to regulate SR-BI protein expression. There are still a number of challenges in modulating SR-BI expression in cancer and in using natural products for modulation of such protein expression. In this review, our purpose is to discuss the relationship between SR-BI protein and cancer, and the molecular mechanisms regulating SR-BI expression, as well as to provide an overview of natural products that regulate SR-BI expression.

Vitamin E Metabolic Effects and Genetic Variants: A Challenge for Precision Nutrition in Obesity and Associated Disturbances

Vitamin E (VE) has a recognized leading role as a contributor to the protection of cell constituents from oxidative damage. However, evidence suggests that the health benefits of VE go far beyond that of an antioxidant acting in lipophilic environments. In humans, VE is channeled toward pathways dealing with lipoproteins and cholesterol, underlining its relevance in lipid handling and metabolism. In this context, both VE intake and status may be relevant in physiopathological conditions associated with disturbances in lipid metabolism or concomitant with oxidative stress, such as obesity. However, dietary reference values for VE in obese populations have not yet been defined, and VE supplementation trials show contradictory results. Therefore, a better understanding of the role of genetic variants in genes involved in VE metabolism may be crucial to exert dietary recommendations with a higher degree of precision. In particular, genetic variability should be taken into account in targets concerning VE bioavailability per se or concomitant with impaired lipoprotein transport. Genetic variants associated with impaired VE liver balance, and the handling/resolution of oxidative stress might also be relevant, but the core information that exists at present is insufficient to deliver precise recommendations.

Scavenger receptor B type 1: expression, molecular regulation, and cholesterol transport function

Cholesterol is required for maintenance of plasma membrane fluidity and integrity and for many cellular functions. Cellular cholesterol can be obtained from lipoproteins in a selective pathway of HDL-cholesteryl ester (CE) uptake without parallel apolipoprotein uptake. Scavenger receptor B type 1 (SR-B1) is a cell surface HDL receptor that mediates HDL-CE uptake. It is most abundantly expressed in liver, where it provides cholesterol for bile acid synthesis, and in steroidogenic tissues, where it delivers cholesterol needed for storage or steroidogenesis in rodents. SR-B1 transcription is regulated by trophic hormones in the adrenal gland, ovary, and testis; in the liver and elsewhere, SR-B1 is subject to posttranscriptional and posttranslational regulation. SR-B1 operates in several metabolic processes and contributes to pathogenesis of atherosclerosis, inflammation, hepatitis C virus infection, and other conditions. Here, we summarize characteristics of the selective uptake pathway and involvement of microvillar channels as facilitators of selective HDL-CE uptake. We also present the potential mechanisms of SR-B1-mediated selective cholesterol transport; the transcriptional, posttranscriptional, and posttranslational regulation of SR-B1; and the impact of gene variants on expression and function of human SR-B1. A better understanding of this unique pathway and SR-B1's role may yield improved therapies for a wide variety of conditions.

Meta-analysis of the association between SCARB1 polymorphism and fasting blood lipid levels

Studies have shown that the scavenger receptor class B type 1 (SCARB1) rs5888 polymorphism impacts fasting blood lipid levels differently in men and women. A meta-analysis and statistical tests was therefore performed to determine the relationship between the rs5888 polymorphism and lipid levels in men and women. Twelve studies with 12,147 subjects were selected for this study. In a dominant model, the CT+TT genotype group had lower triglyceride levels than the CC group in men (standardized mean difference (SMD): −0.11; 95% confidence interval (CI): −0.21 to −0.02; P = 0.016; I² = 51.5%). No statistical differences were detected in women. Subgroup analysis of different racial groups revealed significant correlation between the SCARB1 rs5888 polymorphism and higher high-density lipoprotein cholesterol (HDL-C) levels (SMD: 0.15; 95% CI: 0.08 to 0.21; P ≤ 0.001; I² = 0%) and lower triglyceride levels (SMD: −0.16; 95% CI: −0.26 to −0.04; P = 0.013; I² = 60.6%) in non-Asian men. No evidence of heterogeneity was observed when eliminating outlier studies, and no publication bias was detected. This meta-analysis suggests the SCARB1 rs5888 polymorphism is associated with higher HDL-C and lower triglyceride levels in non-Asian men.

Scavenger receptor class B member 1 (SCARB1) variants modulate hepatitis C virus replication cycle and viral load

BACKGROUND & AIMS

There are numerous coding and non-coding variants in the SCARB1 gene that encodes scavenger receptor class B member 1 (SR-BI), a key receptor for both high density lipoproteins and hepatitis C virus (HCV). Many have been linked to clinical phenotypes, yet their impact on the HCV replication cycle is incompletely understood. The aim of this study was to analyze the impact of these variants on the molecular biology and clinical course of HCV.

METHODS

We analyzed key coding non-synonymous as well as non-coding SCARB1 variants using virological in vitro and human genetics approaches.

RESULTS

Non-synonymous variants: S112F and T175A have greatly reduced HCV receptor function. When present on the cell surface, these variants are impaired in their ability to interact with HCV E2. Non-coding variants: The G allele in rs3782287 is associated with decreased viral load. Haplotype analysis confirmed these findings and identified haplotype rs3782287 A/rs5888 C as a risk allele associated with increased viral load. We also detected a trend towards lower hepatic SR-BI expression in individuals with the rs3782287 GG genotype associated with low viral load suggesting a potential underlying mechanism.

CONCLUSION

Coding and non-coding genetic SCARB1 variants modulate the HCV replication cycle and possibly clinical features of hepatitis C. These findings underscore the relevance of SR-BI as an HCV receptor and contribute to our understanding of inter-individual variation in HCV infection.

LAY SUMMARY

The cell surface receptor SR-BI (scavenger receptor class B member 1), is essential for hepatitis C virus (HCV) entry into hepatocytes. Variations in the gene coding this receptor influence infectivity and viral load. We analyzed these variations to gain a better understanding of inter-individual differences over the course of HCV infection.

Genetic determinants of inherited susceptibility to hypercholesterolemia - a comprehensive literature review

Hypercholesterolemia is a strong determinant of mortality and morbidity associated with cardiovascular diseases and a major contributor to the global disease burden. Mutations in four genes (LDLR, APOB, PCSK9 and LDLRAP1) account for the majority of cases with familial hypercholesterolemia. However, a substantial proportion of adults with hypercholesterolemia do not have a mutation in any of these four genes. This indicates the probability of having other genes with a causative or contributory role in the pathogenesis of hypercholesterolemia and suggests a polygenic inheritance of this condition. Here in, we review the recent evidence of association of the genetic variants with hypercholesterolemia and the three lipid traits; total cholesterol (TC), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C), their biological pathways and the associated pathogenetic mechanisms. Nearly 80 genes involved in lipid metabolism (encoding structural components of lipoproteins, lipoprotein receptors and related proteins, enzymes, lipid transporters, lipid transfer proteins, and activators or inhibitors of protein function and gene transcription) with single nucleotide variants (SNVs) that are recognized to be associated with hypercholesterolemia and serum lipid traits in genome-wide association studies and candidate gene studies were identified. In addition, genome-wide association studies in different populations have identified SNVs associated with TC, HDL-C and LDL-C in nearly 120 genes within or in the vicinity of the genes that are not known to be involved in lipid metabolism. Over 90% of the SNVs in both these groups are located outside the coding regions of the genes. These findings indicates that there might be a considerable number of unrecognized processes and mechanisms of lipid homeostasis, which when disrupted, would lead to hypercholesterolemia. Knowledge of these molecular pathways will enable the discovery of novel treatment and preventive methods as well as identify the biochemical and molecular markers for the risk prediction and early detection of this common, yet potentially debilitating condition.

Influence of SCARB1 gene SNPs on serum lipid levels and susceptibility to coronary heart disease and cerebral infarction in a Chinese population

The SCARB1 gene encodes human scavenger receptor class B type I (SR-BI), the primary receptor for high-density lipoprotein (HDL)- cholesteryl ester uptake, and polymorphisms in this gene may influence SR-BI protein expression and serum lipid levels, modulating susceptibility to coronary heart disease (CHD) and cerebral infarction (CI). Therefore, we investigated the association between singlenucleotide polymorphisms (SNPs) in the SCARB1 gene and serum lipid levels as well as risk of CHD and CI in the Chinese Han population. Genotypes in 295 CHD patients, 302 CI patients and 312 healthy controls matched for age and gender were determined by high-resolution melting (HRM). Among the 5 SNPs investigated in this study, rs10846744 and rs2278986 were significantly associated with CHD risk. The frequency of the C allele for rs10846744 and that of the T allele for rs2278986 appeared to be significantly increased in the CHD group (OR: 1.416, 95%CI: 1.128-1.778, P=0.0058 and OR: 1.681, 95%CI: 1.327-2.130, P<0.0001, respectively). CHD patients with genotypes CC and CG for rs10846744 had a higher HDL-c level than those with genotype GG, and CHD patients with genotypes CC and CT for the rs2278986 SNP had a higher HDL-c level compared to those with the TT allele. The other 3 SNPs, rs5888, rs10744182 and rs838893, showed no significant association with serum lipid levels and CHD or CI risk in the Chinese population. The CCCTT and CCTTC haplotypes of rs5888, rs10846744, rs10744182, rs2278986 and rs838893 appear to significantly increase CHD risk, whereas the CGTTC, CCTCT and TGCTC haplotypes appear to significantly reduce risk. Overall, the CCTTC and TGTTC haplotypes acted as a significant risk for CI, with the CGCTC and CCCCT haplotypes conferring significantly reduced risk. These results suggest that SCARB1 gene polymorphisms may contribute to genetic susceptibility to CHD; in particular, the C allele of rs10846744 and the C allele of rs2278986 may serve as risk and protective factors for CHD, respectively.

Polymorphisms of lipid metabolism enzyme-coding genes in patients with diabetic dyslipidemia

Objective:

The polymorphisms/mutations of genes encoding proteins and enzymes involved in lipoprotein metabolism play important roles in the development of diabetic dyslipidemia. The aim of our study was to investigate the effects of LPL (rs320), LIPC (rs2070895), SCARB1 (rs5888), LCAT (rs2292318), CETP (rs708272), ADIPOQ (rs1501299), RETN (rs3745367), PON1 (rs662), and MNSOD (rs4880) gene polymorphisms on lipid metabolism and diabetic dyslipidemia.

Methods:

This case-control study included 217 patients with diabetic dyslipidemia and 212 healthy age- and gender-matched individuals. Genomic DNA isolation was performed from blood samples, and genotype analysis was performed using melting curve analysis on a LightCycler^® 480 Instrument. The chi-square test was used to compare genotype distribution and allele frequencies between the groups.

Results:

Significant associations were observed between LPL (rs320) (p<0.001), LIPC (rs2070895) (p<0.001), SCARB1 (rs5888) (p<0.001), LCAT (rs2292318) (p<0.001), CETP (rs708272) (p<0.001), ADIPOQ (rs1501299) (p=0.01), RETN (rs3745367) (p<0.001), and MNSOD (rs4880) (p<0.001) polymorphisms and diabetic dyslipidemia. However, no association was observed between PON1 (rs662) polymorphisms and diabetic dyslipidemia (p=0.611).

Conclusion:

LPL (rs320), LIPC (rs2070895), SCARB1 (rs5888), LCAT (rs2292318), CETP (rs708272), ADIPOQ (rs1501299), RETN (rs3745367), and MNSOD (rs4880) polymorphisms play an important role in basic molecular metabolism in diabetic dyslipidemia. Therefore, these polymorphisms may be used as a predictive marker for diabetic dyslipidemia in high-risk patients. (Anatol J Cardiol 2017; 17: 313-21)

Association of SCARB1 Gene Polymorphisms with Virological Response in Chronic Hepatitis C Patients Receiving Pegylated Interferon plus Ribavirin Therapy

The scavenger receptor type B class I(SR-BI) is a receptor for high-density lipoproteins(HDL) and one of entry factors for hepatitis C virus(HCV). We examined the association of single nucleotide polymorphisms(SNPs) of the SCARB1 gene, which encodes SR-BI, with virologic responses to pegylated interferon-based treatment in Asian chronic hepatitis C(CHC) patients. Human genomic and clinical data were collected from 156 consecutive Taiwanese HCV genotype 1 or 2 patients who received pegylated interferon plus ribavirin therapy and 153 non-HCV healthy subjects. Three SNPs(rs10846744, rs5888, and rs3782287) of the SCARB1 gene that have been linked to humans diseases were investigated. rs10846744 rather than rs5888 or rs3782287 was associated with serum HCV RNA level and sustained virologic response(SVR) to pegylated interferon plus ribavirin therapy in CHC patients(GG vs. non-GG genotype, Adjusted Odds Ratio, 95% CI: 0.32, 0.11–0.95, P = 0.039). Among patients with IL28B rs8099917 non-TT genotypes, those with rs10846744 non-GG genotype had a higher SVR rate than those with GG genotypes. In addition, patients with GG genotype had a higher fasting blood glucose level than those with CC genotype. In conclusion, SCARB1 gene polymorphisms may serve as a potential predictor of treatment responses in CHC patients receiving interferon-based therapy. (ClinicalTrials.gov number, NCT02714712).

The rs5888 single nucleotide polymorphism in scavenger receptor class B type 1 (SCARB1) gene and the risk of premature coronary artery disease: a case-control study

Background

Several single nucleotide polymorphisms (SNPs) in lipid transport genes have been shown to be associated with premature coronary artery disease (PCAD). The scavenger receptor BI (SCARB1) is a key component of the reverse cholesterol transport and lipid metabolism. We aimed to examine the relationship between the rs5888 SNP within SCARB1and the risk of angiographically determined PCAD.

Methods

We used an age cut-off of 55 years for women and 45 years for men to define PCAD. Five-hundred and five patients with newly diagnosed angiographically documented PCAD (≥50 % luminal stenosis of any coronary vessel) as case group compared with 546 controls (subjects with no luminal stenosis at coronary arteries). The severity of CAD was determined by vessel score as well as Gensini score. A real-time polymerase chain reaction (PCR) and High Resolution Melting (HRM) analysis was used to distinguish between genotypes.

Results

T allele as compared to C allele was associated with increased odds of PCAD in total population (adjusted OR = 1.3, 95 % CI = 1.0 to 1.5; p = 0.020), and in women (adjusted OR = 1.3, 95 % CI = 1.0 to 1.8; p = 0.037), but not in men (adjusted OR = 1.2, 95 % CI = 0.9 to 1.5; p = 0.311). There was also no significant association between the examined polymorphism and the severity of CAD in whole or in men or women subgroups.

Conclusions

Our findings suggest that the SNP (rs5888) within SCARB1 is independently associated with PCAD in a sex-dependent manner.

Genetic contribution of SCARB1 variants to lipid traits in African Blacks: a candidate gene association study

Background

High-density lipoprotein cholesterol (HDL-C) exerts many anti-atherogenic properties including its role in reverse cholesterol transport (RCT). Scavenger receptor class B member 1 (SCARB1) plays a key role in RCT by selective uptake of HDL cholesteryl esters. We aimed to explore the genetic contribution of SCARB1 to affecting lipid levels in African Blacks from Nigeria.

Methods

We resequenced 13 exons and exon-intron boundaries of SCARB1 in 95 individuals with extreme HDL-C levels using Sanger method. Then, we genotyped 147 selected variants (78 sequence variants, 69 HapMap tagSNPs, and 2 previously reported relevant variants) in the entire sample of 788 African Blacks using either the iPLEX Gold or TaqMan methods. A total of 137 successfully genotyped variants were further evaluated for association with major lipid traits.

Results

The initial gene-based analysis demonstrated evidence of association with HDL-C and apolipoprotein A-I (ApoA-I). The follow-up single-site analysis revealed nominal evidence of novel associations of nine common variants with HDL-C and/or ApoA-I (P < 0.05). The strongest association was between rs11057851 and HDL-C (P = 0.0043), which remained significant after controlling for multiple testing using false discovery rate. Rare variant association testing revealed a group of 23 rare variants (frequencies ≤1 %) associated with HDL-C (P = 0.0478). Haplotype analysis identified four SCARB1 regions associated with HDL-C (global P < 0.05).

Conclusions

To our knowledge, this is the first report of a comprehensive association study of SCARB1 variations with lipid traits in an African Black population. Our results showed the consistent association of SCARB1 variants with HDL-C across various association analyses, supporting the role of SCARB1 in lipoprotein-lipid regulatory mechanism.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-015-0250-6) contains supplementary material, which is available to authorized users.

Impact of genetic variants in human scavenger receptor class B type I (SCARB1) on plasma lipid traits

BACKGROUND

Scavenger receptor class B type 1 (SCARB1) plays an important role in high-density lipoprotein cholesterol (HDL-C) metabolism in selective cholesteryl ester uptake and in free cholesterol cellular efflux.

METHODS AND RESULTS

This study aims to identify common (minor allele frequency ≥5%) and low-frequency/rare (minor allele frequency <5%) variants, using resequencing all 13 exons and exon-intron boundaries of SCARB1 in 95 individuals with extreme HDL-C levels selected from a population-based sample of 623 US non-Hispanic whites. The sequencing step identified 44 variants, of which 11 were novel with minor allele frequency <1%. Seventy-six variants (40 sequence variants, 32 common HapMap tag single nucleotide polymorphisms, and 4 relevant variants) were selected for genotyping in the total sample of 623 subjects followed by association analyses with lipid traits. Seven variants were nominally associated with apolipoprotein B (apoB; n=4) or HDL-C (n=3; P<0.05). Three variants associated with apoB remained significant after controlling false discovery rate. The most significant association was observed between rs4765615 and apoB (P=0.0059), while rs11057844 showed the strongest association with HDL-C (P=0.0035). A set of 17 rare variants (minor allele frequency ≤1%) showed significant association with apoB (P=0.0284). Haplotype analysis revealed 4 regions significantly associated with either apoB or HDL-C.

CONCLUSIONS

Our findings provide new information about the genetic role of SCARB1 in affecting plasma apoB levels in addition to its established role in HDL-C metabolism.

Hepatic scavenger receptor BI protects against polymicrobial-induced sepsis through promoting LPS clearance in mice

Recent studies revealed that scavenger receptor BI (SR-BI or Scarb1) plays a critical protective role in sepsis. However, the mechanisms underlying this protection remain largely unknown. In this study, using Scarb1(I179N) mice, a mouse model specifically deficient in hepatic SR-BI, we report that hepatic SR-BI protects against cecal ligation and puncture (CLP)-induced sepsis as shown by 75% fatality in Scarb1(I179N) mice, but only 21% fatality in C57BL/6J control mice. The increase in fatality in Scarb1(I179N) mice was associated with an exacerbated inflammatory cytokine production. Further study demonstrated that hepatic SR-BI exerts its protection against sepsis through its role in promoting LPS clearance without affecting the inflammatory response in macrophages, the glucocorticoid production in adrenal glands, the leukocyte recruitment to peritoneum or the bacterial clearance in liver. Our findings reveal hepatic SR-BI as a critical protective factor in sepsis and point out that promoting hepatic SR-BI-mediated LPS clearance may provide a therapeutic approach for sepsis.

Gene-gene combination effect and interactions among ABCA1, APOA1, SR-B1, and CETP polymorphisms for serum high-density lipoprotein-cholesterol in the Japanese population

Background/Objective

Gene-gene interactions in the reverse cholesterol transport system for high-density lipoprotein-cholesterol (HDL-C) are poorly understood. The present study observed gene-gene combination effect and interactions between single nucleotide polymorphisms (SNPs) in ABCA1, APOA1, SR-B1, and CETP in serum HDL-C from a cross-sectional study in the Japanese population.

Methods

The study population comprised 1,535 men and 1,515 women aged 35–69 years who were enrolled in the Japan Multi-Institutional Collaborative Cohort (J-MICC) Study. We selected 13 SNPs in the ABCA1, APOA1, CETP, and SR-B1 genes in the reverse cholesterol transport system. The effects of genetic and environmental factors were assessed using general linear and logistic regression models after adjusting for age, sex, and region.

Principal Findings

Alcohol consumption and daily activity were positively associated with HDL-C levels, whereas smoking had a negative relationship. The T allele of CETP, rs3764261, was correlated with higher HDL-C levels and had the highest coefficient (2.93 mg/dL/allele) among the 13 SNPs, which was statistically significant after applying the Bonferroni correction (p<0.001). Gene-gene combination analysis revealed that CETP rs3764261 was associated with high HDL-C levels with any combination of SNPs from ABCA1, APOA1, and SR-B1, although no gene-gene interaction was apparent. An increasing trend for serum HDL-C was also observed with an increasing number of alleles (p<0.001).

Conclusions

The present study identified a multiplier effect from a polymorphism in CETP with ABCA1, APOA1, and SR-B1, as well as a dose-dependence according to the number of alleles present.

Association between APOE, SCARB1, PPARα polymorphisms and serum lipids in a population of Lithuanian adults

Background

Dyslipidemia is one of several known risk factors for coronary heart disease, a leading cause of death in Lithuania. Blood lipid levels are influenced by multiple genetic and environmental factors. Epidemiological studies demonstrated the impact of nutrition on lipid levels within the Lithuanian population although the role of genetic factors for dyslipidemias has not yet been studied. The objective of this study was to assess the distribution of the APOE, SCARB1, PPARα genotypes in the Lithuanian adult population and to determine the relationship of these genotypes with dyslipidemia.

Methods

A cross-sectional health survey was carried out in a representative random sample of the Lithuanian population aged 25–64 (n=1030). A variety of single-nucleotide polymorphisms (SNPs) of the APOE (rs429358 and rs7412), SCARB1 (rs5888) and PPARα (rs1800206) genes were assessed using real-time polymerase chain reaction. Serum lipids were determined using enzymatic methods.

Results/Principal findings

Men and women with the APOE2 genotype had the lowest level of total and low-density lipoprotein cholesterol (LDL-C). Men with the APOE2 genotype had significantly higher levels of triglycerides (TG) than those with the APOE3 genotype. In men, the carriers of the APOE4 genotype had higher odds ratios (OR) of reduced (<1.0 mmol/L) high density lipoprotein cholesterol (HDL-C) levels versus APOE3 carriers (OR=1.98; 95% CI=1.05-3.74). The odds of having elevated (>1.7 mmol/L) TG levels was significantly lower in SCARB1 genotype CT carriers compared to men with the SCARB1 genotype CC (OR=0.50; 95% CI=0.31-0.79). In men, carriers of the PPARα genotype CG had higher OR of elevated TG levels versus carriers of PPARα genotype CC (OR=2.67; 95% CI=1.15-6.16). The odds of having high LDL-C levels were lower in women with the APOE2 genotype as compared to APOE3 genotype carriers (OR=0.35; 95% CI=0.22-0.57).

Conclusions/Significance

Our data suggest a gender difference in the associations between APOE, SCARB1, PPARα genotypes and lipid levels. In men, the APOE4 genotype and PPARα genotype CG were correlated with an atherogenic lipid profile while the SCARB1 genotype CT had an atheroprotective effect. In women, APOE2 carriers had the lowest odds of high LDL-C.

Functional genomics of the human high-density lipoprotein receptor scavenger receptor BI: an old dog with new tricks

PURPOSE OF REVIEW

The athero-protective role of scavenger receptor BI (SR-BI) is primarily attributed to its ability to selectively transfer cholesteryl esters from high-density lipoproteins (HDLs) to the liver during reverse cholesterol transport (RCT). In this review, we highlight recent findings that reveal the impact of SR-BI on lipid levels and cardiovascular disease in humans. Moreover, additional responsibilities of SR-BI in modulating adrenal and platelet function, as well as female fertility in humans, are discussed.

RECENT FINDINGS

Heterozygote carriers of P297S, S112F and T175A-mutant SR-BI receptors were identified in patients with high HDL-cholesterol levels. HDL from P297S-SR-BI carriers was unable to mediate macrophage cholesterol efflux, whereas hepatocytes expressing P297S-SR-BI were unable to mediate the selective uptake of HDL-cholesteryl esters. S112F and T175A-mutant receptors exhibited similar impaired cholesterol transport functions in vitro. Reduced SR-BI function in P297S carriers was also associated with decreased steroidogenesis and altered platelet function. Further, human population studies identified SCARB1 variants associated with female infertility.

SUMMARY

Identification of SR-BI variants confirms the key role of this receptor in influencing lipid levels and RCT in humans. A deeper understanding of the contributions of SR-BI to steroidogenesis, platelet function and fertility is required in light of exploration of HDL-raising therapies aimed at reducing cardiovascular risk.

SCARB1 single nucleotide polymorphism (rs5888) is associated with serum lipid profile and myocardial infarction in an age- and gender-dependent manner

Background

Mutation in SCARB1 gene, exon 8 rs5888, has been associated with altered lipid levels and cardiovascular risk in humans though the results have been inconsistent. We analysed the impact of SCARB1 single nucleotide polymorphism (SNP) rs5888 with plasma lipid profile and association with coronary artery disease (CAD) in a Lithuanian population characterized by high morbidity and mortality from CAD and high prevalence of hypercholesterolemia.

Methods

The study included 1976 subjects from a random sample (reference group) and an myocardial infarction (MI) group of 463 patients. Genotyping of SCARB1 (rs5888) was carried out using the real-time polymerase chain reaction method.

Results/principal findings

Analysis of rs5888 C/T gene polymorphism in the reference group revealed that male TT genotype carriers (25–74 years) had significantly higher total cholesterol and triglyceride concentrations (5.70 mmol/l vs. 5.49 mmol/l; p = 0.036, and 1.70 mmol/l vs. 1.40 mmol/l, p = 0.023, respectively) than CT carriers and the oldest males (65–74 years) TT carriers had significantly higher high density lipoprotein cholesterol concentrations in comparison to heterozygous (1.52 mmol/l vs. 1.36 mmol/l, p = 0.033). The youngest female (25–44 years) TT genotype carriers had significantly lower low density lipoprotein cholesterol concentrations in comparison to C homozygous (2.59 mmol/l vs. 2.92 mmol/l, p = 0.023). The frequency of the SCARB1 TT genotype in the oldest male MI group (65–74 years) was significantly lower than in the corresponding reference group subjects (9.4% vs. 22.3%, p = 0.006). SCARB1 TT genotype was associated with decreased odds of MI in males aged 65–75 years (OR = 0.24, 95% CI 0.10-0.56, p = 0.001).

Conclusions/significance

SCARB1 polymorphism is associated with lipid metabolism and CAD in an age- and gender- dependent manner. Analysis of SCARB1 SNP rs5888 C/T genotypes revealed an atheroprotective phenotype of lipid profile in older men and in young women TT genotype carriers in the reference group. SCARB1 TT genotype was associated with decreased odds of MI in aged men.

Scavenger receptor class B type 1 gene rs5888 single nucleotide polymorphism and the risk of coronary artery disease and ischemic stroke: a case-control study

BACKGROUND

Our previous studies have showed that the rs5888 single nucleotide polymorphism (SNP) in Scavenger receptor class B type 1 (SCARB1) gene is associated with serum lipid levels in the general Chinese populations. The present study was undertaken to detect the associations between rs5888 SNP and the risk of coronary artery disease (CAD) and ischemic stroke (IS).

METHODS

A total of 1,716 unrelated subjects (CAD, 601; IS, 533; and healthy controls, 582) were included in this study. Genotyping of the rs5888 SNP were determined by polymerase chain reaction and restriction fragment length polymorphism.

RESULTS

The genotypic frequencies of SCARB1 rs5888 SNP were different between CAD patients and controls, the subjects with TT genotype had high risk of CAD (OR = 1.76, P = 0.038 for TT vs. CC; and OR = 1.75, P = 0.036 for TT vs. CC/CT). There was no significant association between genotypes and the risk of IS. Further analysis showed that the subjects with TT genotype in the total population had lower levels of high-density lipoprotein cholesterol than the subjects with CC/CT genotypes (P < 0.05), the subjects with TT genotype in controls but not in CAD or IS patients had higher levels of serum LDL-C and ApoB than those with CC genotype (P < 0.05 for each).

CONCLUSIONS

The present study suggests that the SCARB1 rs5888 SNP influences serum lipid levels, and is associated with the risk of CAD.

Association of three polymorphisms of scavenger receptor class BI gene (exon8, exon1, intron5) with coronary stenosis in a coronary Tunisian population

BACKGROUND

The potential role of scavenger receptor class BI (gene name SCARB1) in the regulation of lipoproteins metabolism and atherosclerosis has attracted considerable interest. We tested the relationship of SCARB1 polymorphisms with significant coronary stenosis (SCS) and lipid profile in a coronary Tunisian population.

METHODS

Three SCARB1 polymorphisms (exon8 (C/T), exon1 (G/A), intron5 (C/T)) were studied in 316 Tunisian patients undergoing coronary angiography. SCS was defined as a luminal narrowing of ≥ 50% in at least one major coronary artery. Lipid profile was measured. Genotyping was performed using PCR-RFLP.

RESULTS

Individuals with TT genotypes of exon8 were associated with higher concentrations of plasma HDL-C and ApoAI in the group without SCS. Carriers of T allele of exon8 were associated with 41% lower risk of SCS. This protective effect seemed to be particularly significant in women, nondiabetics and nonsmokers. Subjects homozygous for the variant allele of intron5 were significantly associated with an increased risk of SCS, particularly in smokers. AA genotype of exon1 was associated with an increased risk of SCS in diabetics and in patients with metabolic syndrome. The (CAT) haplotype was associated with increase in the risk of SCS compared to the wild haplotype and had a 4-fold greater risk of SCS than patients with haplotype (TGC) which seems to be the most protective against SCS.

CONCLUSION

Carriers of T allele of exon8 in SCARB1 seemed to increase HDL-C and ApoAI concentrations and reduce the risk of SCS. The intron5, exon1 and (CAT) haplotype seemed to have an atherogenic effect.

Association of rs5888 SNP in the scavenger receptor class B type 1 gene and serum lipid levels

Background

Bai Ku Yao is a special subgroup of the Yao minority in China. The present study was undertaken to detect the association of rs5888 single nucleotide polymorphism (SNP) in the scavenger receptor class B type 1 (SCARB1) gene and several environmental factors with serum lipid levels in the Guangxi Bai Ku Yao and Han populations.

Methods

A total of 598 subjects of Bai Ku Yao and 585 subjects of Han Chinese were randomly selected from our stratified randomized cluster samples. Genotypes of the SCARB1 rs5888 SNP were determined by polymerase chain reaction and restriction fragment length polymorphism combined with gel electrophoresis, and then confirmed by direct sequencing.

Results

The levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), apolipoprotein (Apo) AI were lower but ApoB was higher in Bai Ku Yao than in Han (P < 0.05-0.001). The frequencies of C and T alleles were 78.3% and 21.7% in Bai Ku Yao, and 73.7% and 26.3% in Han (P < 0.01); respectively. The frequencies of CC, CT and TT genotypes were 60.0%, 36.6% and 3.4% in Bai Ku Yao, and 54.2%, 39.0% and 6.8% in Han (P < 0.01); respectively. The subjects with TT genotype in both ethnic groups had lower HDL-C and ApoAI levels than the subjects with CC or CT genotype (P < 0.05 for all). Subgroup analyses showed that the subjects with TT genotype in Bai Ku Yao had lower HDL-C and ApoAI levels in males than the subjects with CC or CT genotype (P < 0.05 for all), and the T allele carriers had higher TC, LDL-C and ApoB levels in females than the T allele noncarriers (P < 0.05 for all). The participants with TT genotype in Han also had a lower tendency of HDL-C and ApoAI levels in males than the participants with CC or CT genotype, but the difference did not reach statistically significant (P = 0.063 and P = 0.086; respectively). The association of serum HDL-C and ApoAI levels and genotypes was confirmed by the multiple linear regression analysis in both ethnic groups. Serum lipid parameters were also correlated with several environmental factors.

Conclusions

The differences in serum lipid levels between the two ethnic groups might partially attribute to the differences in the SCARB1 rs5888 SNP and several environmental factors.

Association of SCARB1 variants with subclinical atherosclerosis and incident cardiovascular disease: the multi-ethnic study of atherosclerosis

OBJECTIVE

We previously reported a statistically significant association of SCARB1 intronic single nucleotide polymorphism (SNP) rs10846744 with common carotid intimal-medial artery thickness in each of the 4 Multi-Ethnic Study of Atherosclerosis racial/ethnic groups (white, Chinese, black, and Hispanic).

METHODS AND RESULTS

Using an expanded sample of 7936 Multi-Ethnic Study of Atherosclerosis participants, phenotyped for measures of subclinical atherosclerosis, incident myocardial infarction, and cardiovascular disease, and genotyped through the SNP Health Association Resource project, we have now examined the genetic association of these phenotypes with 126 genotyped and imputed SCARB1 SNPs. We also performed stratified analyses to examine whether SCARB1 SNP effects differed by sex. Our analysis of the full Multi-Ethnic Study of Atherosclerosis cohort provides strong evidence for the association of rs10846744 with common carotid intimal-medial thickness (P=1.04E-4 in combined analysis of all 4 Multi-Ethnic Study of Atherosclerosis racial/ethnic groups). In sex-stratified analysis, we observed statistically significant association of rs10846744 with incident cardiovascular disease events in males (P=0.01). Examining analytical results from the Myocardial Infarction Genetics Consortium for replication, we observed further support for the association of rs10846744 with myocardial infarction.

CONCLUSIONS

The SCARB1 SNP, rs10846744, exerts a major effect on subclinical atherosclerosis and incident cardiovascular disease in humans.

Scavenger receptor class B type 1 gene polymorphisms and female fertility

PURPOSE OF REVIEW

Multiple studies have demonstrated a role for scavenger receptor class B type 1 (SR-B1) in female fertility. Recent studies have implicated specific SR-B1 gene polymorphisms in decreased progesterone production and suboptimal fertility outcomes.

RECENT FINDINGS

The lipoprotein receptor SR-B1 has been known to mediate selective uptake of lipids into steroidogenic tissues such as the ovaries. SR-B1 plays a major role in the ability of the corpus luteum to produce progesterone, which is known to play a key role in sustaining early pregnancy. Animal studies have demonstrated that deficiency in SR-B1 results in subfertility that can be restored with addition of SR-B1 function. Single-nucleotide polymorphisms in SCARB1, the gene encoding SR-B1, have been associated with human lipid levels. Women undergoing infertility treatment with low SR-B1 expression in granulosa cells were noted to have plasma estradiol levels half the normal levels and a significantly lower number of retrieved oocytes. In vitro, deficiency of SR-B1 is associated with lower progesterone secretion in human granulosa cells. Certain SR-B1 polymorphisms have been associated with lower follicular progesterone levels and a significantly lower clinical pregnancy rate.

SUMMARY

Deficiency of SR-B1, particularly due to single-nucleotide polymorphisms, could explain some features of female human infertility.

The SCARB1 rs5888 SNP and serum lipid levels in the Guangxi Mulao and Han populations

BACKGROUND

The associations of scavenger receptor class B type 1 (SCARB1) rs5888 single nucleotide polymorphism (SNP) and serum lipid levels are inconsistant among diverse ethnic populations. The present study was undertaken to detect the association of rs5888 SNP and serum lipid levels in the Guangxi Mulao and Han populations.

METHODS

Genotypes of the SCARB1 rs5888 SNP in 801 subjects of Mulao and 807 subjects of Han Chinese were determined by polymerase chain reaction and restriction fragment length polymorphism combined with gel electrophoresis, and then confirmed by direct sequencing.

RESULTS

Serum apolipoprotein (Apo) B levels and the T allelic frequency were higher in Mulao than in Han. Serum high-density lipoprotein cholesterol (HDL-C) levels in Mulao were different among the genotypes, the subjects with TT genotype had lower HDL-C levels than the subjects with CC or CT genotype in female (P < 0.05). For the Han population, serum triglyceride (TG), HDL-C, ApoAI, ApoB levels and the ratio of ApoAI to ApoB in males were different among the genotypes, the T allele carriers had lower serum HDL-C, ApoAI levels and ApoAI/ApoB ratio and higher serum ApoB levels than the T allele noncarriers (P < 0.05 for all), the subjects with TT genotype had higher serum TG levels than the subjects with CC or CT genotype. Serum HDL-C levels in Mulao females and serum HDL-C, ApoAI, ApoB levels and the ApoAI/ApoB ratio in Han males were correlated with genotypes by the multiple linear regression analysis. Serum lipid parameters were also influenced by genotype-environmental interactions in Han but not in Mulao populations.

CONCLUSIONS

These results suggest that the rs5888 SNP is associated with serum HDL-C levels in Mulao females, and TG, HDL-C, ApoAI, ApoB levels and the ApoAI/ApoB ratio in Han males. The differences in serum ApoB levels between the two ethnic groups might partially attribute to different SCARB1 genotype-environmental interactions.

CYP4A11 variant is associated with high-density lipoprotein cholesterol in women

The ω-hydroxylase CYP4A11 catalyzes the transformation of epoxyeicosatrienoic acids to omega-hydroxylated-epoxyeicosatrienoic acids, endogenous peroxisome proliferator-activated receptor α (PPARα) agonists. PPARα activation increases high-density lipoprotein-cholesterol (HDL-C). A cytosine-for-thymidine (T8590C) variant of CYP4A11 encodes for a ω-hydroxylase with reduced activity. This study examined the relationship between CYP4A11 T8590C genotype and metabolic parameters in the Framingham Offspring Study and in a clinical practice-based biobank, BioVU. In women in the Framingham Offspring Study, the CYP4A11 8590C allele was associated with reduced HDL-C concentrations (54.2±0.9 mg/dL in CYP4A11 CC or CT genotype women versus 56.7±0.5 mg/dL in TT women, p=0.02), and with an increased prevalence of low HDL-C, defined categorically as ≤50mg/dL [odds ratio 1.39 (95% CI 1.02-1.90), p=0.04]. In the BioVU cohort, the CYP4A11 8590C allele was also associated with low HDL-C in women [odds ratio 1.69 (95% CI 1.03-2.77, p=0.04)]. There was no relationship between genotype and HDL-C in men in either cohort.

Pathway-Wide Association Study Implicates Multiple Sterol Transport and Metabolism Genes in HDL Cholesterol Regulation

Pathway-based association methods have been proposed to be an effective approach in identifying disease genes, when single-marker association tests do not have sufficient power. The analysis of quantitative traits may be benefited from these approaches, by sampling from two extreme tails of the distribution. Here we tested a pathway association approach on a small genome-wide association study (GWAS) on 653 subjects with extremely high high-density lipoprotein cholesterol (HDL-C) levels and 784 subjects with low HDL-C levels. We identified 102 genes in the sterol transport and metabolism pathways that collectively associate with HDL-C levels, and replicated these association signals in an independent GWAS. Interestingly, the pathways include 18 genes implicated in previous GWAS on lipid traits, suggesting that genuine HDL-C genes are highly enriched in these pathways. Additionally, multiple biologically relevant loci in the pathways were not detected by previous GWAS, including genes implicated in previous candidate gene association studies (such as LEPR, APOA2, HDLBP, SOAT2), genes that cause Mendelian forms of lipid disorders (such as DHCR24), and genes expressing dyslipidemia phenotypes in knockout mice (such as SOAT1, PON1). Our study suggests that sampling from two extreme tails of a quantitative trait and examining genetic pathways may yield biological insights from smaller samples than are generally required using single-marker analysis in large-scale GWAS. Our results also implicate that functionally related genes work together to regulate complex quantitative traits, and that future large-scale studies may benefit from pathway-association approaches to identify novel pathways regulating HDL-C levels.

Clinical impact of scavenger receptor class B type I gene polymorphisms on human female fertility

BACKGROUND

The goal of this study was to evaluate the association of SCARB1 single nucleotide polymorphisms (SNPs) and fertility outcomes in women undergoing IVF.

METHODS

Between November 2007 and March 2010, granulosa cells and follicular fluid were collected from women undergoing IVF. Five SCARB1 SNPs were sequenced and progesterone levels were measured in the follicular fluid. Fertility measurements were defined as the presence of gestational sac(s) and fetal heartbeat(s).

RESULTS

The study group consisted of 274 women (mean age of 36.4 ± 4.6 years). The racial/ethnic composition was 55% Caucasian (n = 152), 25% African-American (n = 68), 12% Asian (n = 34), 5% Hispanic, (n = 14) and 2% other (n = 6). There was a significant difference in the genotype frequencies of the SCARB1 SNPs across the groups. Subjects who were homozygous for the minor allele in the rs5888 SNP had higher follicular progesterone levels than those who were homozygous for the major allele (P = 0.03). In the Caucasian group, carriers of the minor A allele of the rs4238001 SNP had lower follicular progesterone levels compared with homozygous carriers of the major G allele (P = 0.04). In this group, follicular progesterone levels were highly predictive of the rs4238001 SNP (P = 0.03). In the entire cohort, minor allele carriers of rs4238001 did not have any viable fetuses at Day 42 following embryo transfers (P = 0.04). In the African-American group in particular, there was also an association between rs10846744 and gestational sac(s) (P = 0.006), and fetal heartbeat(s) (P = 0.005).

CONCLUSIONS

In part, SCARB1 rs4238001 and rs10846744 SNPs may contribute to human female infertility.

Influence of polymorphisms and cholesterol-lowering treatment on SCARB1 mRNA expression

AIM

This study evaluated the influence of polymorphisms and cholesterol-lowering treatments on SCARB1 mRNA expression in peripheral blood mononuclear cells and in HepG2 and Caco-2 cells.

METHODS

Blood samples were drawn from normolipidemic (NL, n = 166) and hypercholesterolemic (HC, n = 123) individuals to extract DNA and total RNA and to analyze the lipid profile. After a 4-week washout period, 98 HC individuals were treated with atorvastatin (10 mg/day/4 weeks) whereas 25 were treated with ezetimibe (10 mg/day/4 weeks), followed by simvastatin (10 mg/day/8 weeks) and simvastatin plus ezetimibe (10 mg each/day/4 weeks). HepG2 and Caco-2 cells were treated with atorvastatin, simvastatin and ezetimibe at various concentrations for 12 and 24 h and collected for RNA extraction. SCARB1 mRNA expression was measured by TaqMan® assay and SCARB1 c.4G> A, c.726 + 54C> T and c.1080C> T polymorphisms were detected by PCR-RFLP.

RESULTS

High LDL cholesterol (> 160 mg/dL) values were associated with low baseline SCARB1 mRNA expression in PBMC. Allele T carriers for SCARB1 c.726+54C> T had lower basal SCARB1 transcription in PBMC (p < 0.05). Simvastatin, atorvastatin and ezetimibe treatments did not modify the SCARB1 mRNA level in PBMC from HC patients. Similarly, these cholesterol-lowering drugs did not modulate the SCARB1 expression in HepG2 and Caco-2 cells in spite of the concentration and time of exposure (p > 0.05).

CONCLUSION

LDL cholesterol levels and SCARB1 c.726 + 54C> T are associated with low mRNA expression in mononuclear cells. Cholesterol-lowering drugs do not modulate SCARB1 expression in PBMC from HC subjects or in HepG2 and Caco-2 cells.

An integrative review of the current knowledge of cardiovascular disease and associated risk factors in the Old Order Amish

PURPOSE

To review the uniqueness of the Amish culture and evaluate the published research on cardiovascular disease and associated risk factors in the Amish.

METHOD

A computerized database search from January 1999 to January 2009 was conducted using the search terms Amish and cardiovascular.

RESULTS

The majority of published research is based on the Amish in Lancaster County, Pennsylvania; is genetically based; and did not make recommendations for health care practices in the Amish.

CONCLUSIONS

Studies that focus on cardiovascular disease in the Amish outside Lancaster County, Pennsylvania, and that study cardiovascular health care practices of the Amish are needed to develop culturally specific educational interventions.

Genome-wide association study of Lp-PLA(2) activity and mass in the Framingham Heart Study

Lipoprotein-associated phospholipase A₂ (Lp-PLA₂) is an emerging risk factor and therapeutic target for cardiovascular disease. The activity and mass of this enzyme are heritable traits, but major genetic determinants have not been explored in a systematic, genome-wide fashion. We carried out a genome-wide association study of Lp-PLA₂ activity and mass in 6,668 Caucasian subjects from the population-based Framingham Heart Study. Clinical data and genotypes from the Affymetrix 550K SNP array were obtained from the open-access Framingham SHARe project. Each polymorphism that passed quality control was tested for associations with Lp-PLA₂ activity and mass using linear mixed models implemented in the R statistical package, accounting for familial correlations, and controlling for age, sex, smoking, lipid-lowering-medication use, and cohort. For Lp-PLA₂ activity, polymorphisms at four independent loci reached genome-wide significance, including the APOE/APOC1 region on chromosome 19 (p = 6×10⁻²⁴); CELSR2/PSRC1 on chromosome 1 (p = 3×10⁻¹⁵); SCARB1 on chromosome 12 (p = 1×10⁻⁸) and ZNF259/BUD13 in the APOA5/APOA1 gene region on chromosome 11 (p = 4×10⁻⁸). All of these remained significant after accounting for associations with LDL cholesterol, HDL cholesterol, or triglycerides. For Lp-PLA₂ mass, 12 SNPs achieved genome-wide significance, all clustering in a region on chromosome 6p12.3 near the PLA2G7 gene. Our analyses demonstrate that genetic polymorphisms may contribute to inter-individual variation in Lp-PLA₂ activity and mass.

Blood levels of lipoprotein-associated phospholipase A₂ (Lp-PLA₂) show a strong association with atherosclerosis in humans. This enzyme is made by certain cells of the immune system, associates with lipoproteins (HDL and LDL), and is thought to be involved in inflammation. Studies have shown that Lp-PLA₂ is a good predictor of cardiovascular disease, independent of HDL and LDL cholesterol levels. This has led to the development of drugs aimed at inhibiting Lp-PLA₂ as a way to treat or prevent cardiovascular disease. The activity and mass of Lp-PLA₂ are heritable traits, but major genetic determinants have not been explored in a systematic fashion. We examined genetic variants across the human genome to identify genes influencing Lp-PLA₂ activity and mass. We studied 6,668 Caucasian subjects from the population-based Framingham Heart Study. Clinical data and genetic data on 550,000 genetic variants were available for association analysis. There was no overlap in the most significantly associated SNPs for activity and mass. We identified four distinct gene regions showing highly significant associations with Lp-PLA₂ activity, all of which are known to include genes involved in cholesterol metabolism. The only locus associated with Lp-PLA₂ mass was a region harboring PLA2G7, the gene that encodes lipoprotein-associated phospholipase A2.

Impact of gene variants on sex-specific regulation of human Scavenger receptor class B type 1 (SR-BI) expression in liver and association with lipid levels in a population-based study

BACKGROUND

Several studies have noted that genetic variants of SCARB1, a lipoprotein receptor involved in reverse cholesterol transport, are associated with serum lipid levels in a sex-dependent fashion. However, the mechanism underlying this gene by sex interaction has not been explored.

METHODS

We utilized both epidemiological and molecular methods to study how estrogen and gene variants interact to influence SCARB1 expression and lipid levels. Interaction between 35 SCARB1 haplotype-tagged polymorphisms and endogenous estradiol levels was assessed in 498 postmenopausal Caucasian women from the population-based Rancho Bernardo Study. We further examined associated variants with overall and SCARB1 splice variant (SR-BI and SR-BII) expression in 91 human liver tissues using quantitative real-time PCR.

RESULTS

Several variants on a haplotype block spanning intron 11 to intron 12 of SCARB1 showed significant gene by estradiol interaction affecting serum lipid levels, the strongest for rs838895 with HDL-cholesterol (p=9.2x10(-4)) and triglycerides (p=1.3x10(-3)) and the triglyceride:HDL cholesterol ratio (p=2.7x10(-4)). These same variants were associated with expression of the SR-BI isoform in a sex-specific fashion, with the strongest association found among liver tissue from 52 young women<45 years old (p=0.002).

CONCLUSIONS

Estrogen and SCARB1 genotype may act synergistically to regulate expression of SCARB1 isoforms and impact serum levels of HDL cholesterol and triglycerides. This work highlights the importance of considering sex-dependent effects of gene variants on serum lipid levels.

Influence of SCARB1 polymorphisms on serum lipids of hypercholesterolemic individuals treated with atorvastatin

BACKGROUND

The SR-BI is a key component on the cholesterol metabolism. Polymorphisms in the SR-BI gene (SCARB1) were related with variations on plasma lipoprotein profile and other risk factors for cardiovascular disease. We tested the relationship of 3 SCARB1 single nucleotide polymorphisms (SNPs) with hypercholesterolemia in a Brazilian population and whether these variants can influence lipid-lowering response to atorvastatin.

METHODS

c.4G>A, c.726+54C>T and c.1050C>T SNPs and serum concentrations of lipid and apolipoproteins were evaluated in 147 hypercholesterolemic (HC) and 185 normolipidemic (NL) unrelated Brazilian subjects. HC patients were treated with atorvastatin (10 mg/day/4 weeks).

RESULTS

Frequencies of SCARB1 polymorphisms were similar between the HC and NL groups (p>0.05). The T allele for c.726+54C>T was associated with higher LDL-c in NL and with higher apoB and apoB/apoAI in HC (p<0.05). HC individuals carrying c.1050C allele carriers (CC and CT genotypes) had lower change of total cholesterol, LDL-c, apoB and apoB/apoAI ratio (p<0.05) than the TT genotype carriers in response to atorvastatin.

CONCLUSION

The SCARB1 polymorphisms are related with variations in serum lipids in the Brazilian population and c.1050C>T SNP is associated with lipid-lowering atorvastatin response.

Association of scavenger receptor class B type I polymorphisms with subclinical atherosclerosis: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Little is known about the association of scavenger receptor class B type I (SCARB1) single-nucleotide polymorphisms (SNPs) and subclinical atherosclerosis, particularly in subjects of different racial/ethnic backgrounds. We examined this relationship in the Multi-Ethnic Study of Atherosclerosis.

METHODS AND RESULTS

Forty-three SCARB1-tagging SNPs were genotyped. Baseline examinations included fasting lipids and subclinical atherosclerosis phenotypes (coronary artery calcification, common carotid intimal-medial artery thickness [CCIMT], and internal carotid intimal-medial artery thickness). Examining SNP associations with different subclinical atherosclerosis phenotypes across multiple racial/ethnic groups with adjustment for multiple covariates, we found that the C allele of SNP rs10846744 was associated with higher CCIMT in African American (P=0.03), Chinese (P=0.02), European American (P=0.05), and Hispanic participants (P=0.03) and was strongly associated in pooled analyses (P=0.0002). The results also showed that the association of this SNP with CCIMT was independent of lipids and other well-established cardiovascular risk factors. Stratifying by sex, there seemed to be a strong association of rs10846744 with CCIMT in women, but no genotype-sex interactions were observed.

CONCLUSIONS

Variation in SCARB1 at rs10846744 was significantly associated with CCIMT across racial/ethnic groups in Multi-Ethnic Study of Atherosclerosis.

A synonymous variant in scavenger receptor, class B, type I gene is associated with lower SR-BI protein expression and function

OBJECTIVE

A synonymous variant within scavenger receptor class B type I gene (SCARB1), exon 8 rs5888, has been associated with altered lipid levels and cardiovascular risk in humans. The objective was to determine if rs5888 decreased SR-BI protein expression and function in vitro.

METHODS

SR-BI RNA secondary structure, turnover, polysomal distribution and protein expression were examined in COS cells transfected with wild-type or rs5888-SR-BI plasmids by selective 2'-hydroxyl acylation and primer extension assays, actinomycin D inhibition, polysomal profiling, and western blotting. SR-BI function in murine macrophages stably expressing wild-type or rs5888-SR-BI was assessed by measuring the specific cell association of (125)I,(3)H-cholesteryl ester (CE) radiolabeled HDL.

RESULTS

Rs5888 changed RNA secondary structure and led to marked differences in the polysomal profiles compared with wild-type transcript (p<0.02). As compared to wild-type cells, COS cells expressing rs5888 had significantly lower SR-BI protein expression (p<0.04), but no difference in total RNA transcript levels. There were no differences in SR-BI RNA turnover in murine macrophages, whereas specific cell association of (125)I (p<0.0001) or (3)H-CE (p<0.00001) was significantly lower in rs5888 cells.

CONCLUSIONS

The rs5888 variant affected SR-BI RNA secondary structure, protein translation, and was significantly associated with reduced SR-BI protein expression and function in vitro.

Increased HDL cholesterol and apoA-I in humans and mice treated with a novel SR-BI inhibitor

OBJECTIVE

Increasing HDL levels is a potential strategy for the treatment of atherosclerosis.

METHODS AND RESULTS

ITX5061, a molecule initially characterized as a p38 MAPK inhibitor, increased HDL-C levels by 20% in a human population of hypertriglyceridemic subjects with low HDL levels. ITX5061 also moderately increased apoA-I but did not affect VLDL/LDL cholesterol or plasma triglyceride concentrations. ITX5061 increased HDL-C in WT and human apoA-I transgenic mice, and kinetic experiments showed that ITX5061 decreased the fractional catabolic rate of HDL-CE and reduced its hepatic uptake. In transfected cells, ITX5061 inhibited SR-BI-dependent uptake of HDL-CE. Moreover, ITX5061 failed to increase HDL-C levels in SR-BI(-/-) mice. To assess effects on atherosclerosis, ITX5061 was given to atherogenic diet-fed Ldlr(+/-) mice with or without CETP expression for 18 weeks. In both the control and CETP-expressing groups, ITX5061-treated mice displayed reductions of early atherosclerotic lesions in the aortic arch -40%, P<0.05), and a nonsignificant trend to reduced lesion area in the proximal aorta.

CONCLUSIONS

Our data indicate that ITX5061 increases HDL-C levels by inhibition of SR-BI activity. This suggests that pharmacological inhibition of SR-BI has the potential to raise HDL-C and apoA-I levels without adverse effects on VLDL/LDL cholesterol levels in humans.

rs5888 variant of SCARB1 gene is a possible susceptibility factor for age-related macular degeneration

Major genetic factors for age-related macular degeneration (AMD) have recently been identified as susceptibility risk factors, including variants in the CFH gene and the ARMS2 LOC387715/HTRA1locus. Our purpose was to perform a case-control study in two populations among individuals who did not carry risk variants for CFHY402H and LOC387715 A69S (ARMS2), called “study” individuals, in order to identify new genetic risk factors. Based on a candidate gene approach, we analyzed SNP rs5888 of the SCARB1 gene, coding for SRBI, which is involved in the lipid and lutein pathways. This study was conducted in a French series of 1241 AMD patients and 297 controls, and in a North American series of 1257 patients with advanced AMD and 1732 controls. Among these individuals, we identified 61 French patients, 77 French controls, 85 North American patients and 338 North American controls who did not carry the CFH nor ARMS2 polymorphisms. An association between AMD and the SCARB1 gene was seen among the study subjects. The genotypic distribution of the rs5888 polymorphism was significantly different between cases and controls in the French population (p<0.006). Heterozygosity at the rs5888 SNP increased risk of AMD compared to the CC genotypes in the French study population (odds ratio (OR) = 3.5, CI95%: 1.4–8.9, p<0.01) and after pooling the 2 populations (OR = 2.9, 95% CI: 1.6–5.3, p<0.002). Subgroup analysis in exudative forms of AMD revealed a pooled OR of 3.6 for individuals heterozygous for rs5888 (95% CI: 1.7–7.6, p<0.0015). These results suggest the possible contribution of SCARB1, a new genetic factor in AMD, and implicate a role for cholesterol and antioxidant micronutrient (lutein and vitamin E) metabolism in AMD.

Disparities in allele frequencies and population differentiation for 101 disease-associated single nucleotide polymorphisms between Puerto Ricans and non-Hispanic whites

Background

Variations in gene allele frequencies can contribute to differences in the prevalence of some common complex diseases among populations. Natural selection modulates the balance in allele frequencies across populations. Population differentiation (F_ST) can evidence environmental selection pressures. Such genetic information is limited in Puerto Ricans, the second largest Hispanic ethnic group in the US, and a group with high prevalence of chronic disease. We determined allele frequencies and population differentiation for 101 single nucleotide polymorphisms (SNPs) in 30 genes involved in major metabolic and disease-relevant pathways in Puerto Ricans (n = 969, ages 45–75 years) and compared them to similarly aged non-Hispanic whites (NHW) (n = 597).

Results

Minor allele frequency (MAF) distributions for 45.5% of the SNPs assessed in Puerto Ricans were significantly different from those of NHW. Puerto Ricans carried risk alleles in higher frequency and protective alleles in lower frequency than NHW. Patterns of population differentiation showed that Puerto Ricans had SNPs with exceptional F_ST values in intronic, non-synonymous and promoter regions. NHW had exceptional F_ST values in intronic and promoter region SNPs only.

Conclusion

These observations may serve to explain and broaden studies on the impact of gene polymorphisms on chronic diseases affecting Puerto Ricans.

Polymorphisms of the scavenger receptor class B member 1 are associated with insulin resistance with evidence of gene by sex interaction

BACKGROUND

Genetic variation in diabetes-associated genes cumulatively explain little of the overall heritability of this trait. We sought to determine whether polymorphisms of the scavenger receptor class B, member I (SCARB1), an estrogen-regulated chromosome 12q24 positional candidate diabetes gene, were associated with type 2 diabetes or insulin resistance in a sex-specific fashion.

METHODS

We evaluated 34 haplotype-tagged single-nucleotide polymorphisms (SNPs) of SCARB1 for their association with type 2 diabetes and measures of insulin resistance in two populations: a clinic-based sample of 444 Mexican-American women from Proyecto SALSA and a community-based sample of 830 white women from the Rancho Bernardo Study.

RESULTS

We identified significant associations between a tagged SNP in intron 9, rs9919713, and fasting glucose in the SALSA population (P = 2.3 x 10(-4)). In the Rancho Bernardo Study, the same SNP also showed significant association with the related traits homeostasis model assessment for insulin resistance (P = 3.0 x 10(-4)), fasting glucose (P = 1.1 x 10(-3)), and type 2 diabetes (P = 9.0 x 10(-3)). In men from the Rancho Bernardo population, the opposite effect was found (genotype by sex interaction in the Rancho Bernardo population P < 10(-3) for insulin resistance).

CONCLUSIONS

Our data support an association between SCARB1 variants and insulin resistance, especially in women, with evidence of significant gene by sex interaction. These findings warrant further investigation in additional populations and prompt exploration of a role for SR-BI in the development of insulin resistance.

Scavenger receptor class B type I protein as an independent predictor of high-density lipoprotein cholesterol levels in subjects with hyperalphalipoproteinemia

CONTEXT

In mice, scavenger receptor class B, type I (SR-BI) receptor protein deficiency is associated with elevated high-density lipoprotein (HDL)-cholesterol (HDL-C) levels.

OBJECTIVE

Our objective was to determine the relationship between SR-BI protein and HDL-C levels in humans.

DESIGN

This was a prospective study of adults with hyperalphalipoproteinemia. Fasting blood was obtained for lipid and lipoprotein measurement, genomic DNA, and monocyte-derived macrophages. SR-BI protein levels were measured by Western blots, and SR-BI activity was measured by cholesteryl ester (CE) uptake of each donor's radiolabeled HDL with their monocyte-derived macrophages, or by degradation and specific cell association of dual-labeled HDL in vitro.

SETTING

The study was performed in a tertiary university teaching hospital.

RESULTS

The mean age was 57.2 +/- 10.9 yr (n = 65). SR-BI protein levels were inversely associated with HDL-C levels (P < 0.002), HDL particle size (P < 0.05), and positively associated with CE uptake (P < 0.004); there was no association with plasma apolipoprotein levels. SR-BI protein levels (P = 0.01) were independent predictors of HDL-C levels. Subjects who were carriers of the A allele for the rs4238001 (glycine to serine at position 2) polymorphism [single nucleotide polymorphism (SNP)] had lower SR-BI protein levels (P = 0.01), whereas carriers of the C allele for the rs2278986 SNP also had lower SR-BI protein levels (P = 0.02). Body mass index (P = 0.05), rs4238001 (P = 0.01), and rs2278986 (P = 0.01) SNPs were independent predictors of SR-BI protein levels. In vitro studies of murine macrophages stably expressing the glycine to serine at position 2 SNP showed less degradation (P < 0.0004) and specific cell association (P < 0.0004) of [(125)I, (3)H]-CE-labeled HDL.

CONCLUSIONS

SR-BI protein has an independent effect on HDL-C levels in women with hyperalphalipoproteinemia. Two SNPs were significantly associated with lower SR-BI protein levels.