Population-based study of SR-BI genetic variation and lipid profile

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-BI messenger 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 SNP frequencies 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 interval 1.06-7.46. 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.

Single nucleotide polymorphisms in the 3′ UTR of follistatin-like 4 and scavenger receptor class B member 1 are associated with Dazu black goat litter size

The untranslated regions (UTR) of genes play crucial roles in regulating gene expression at the post-transcriptional level such as affecting mRNA stabilization. In this study, 26 single nucleotide polymorphisms (SNPs) and one deletion located in UTR were genotyped from 186 Dazu black goats via SNaPshot, and the correlation between genotype and litter size was analyzed. Results indicated that two SNP loci, SNP_chr17-20182525 and SNP_chr7-65652612, which are located at the 3′UTR of scavenger receptor class B member 1 and follistatin-like 4, are significantly (p<0.05) correlated with the litter size of first parity goats. SNP_chr7-65652612 is also significantly associated with the total litter size of first and second parity offspring (p<0.05). In conclusion, SNP_chr7-65652612 and SNP_chr17-20182525 have correlation with the litter size of Dazu black goat and they are potential genetic markers for litter size breeding.

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.

Increased Risk of High Body Fat and Altered Lipid Metabolism Associated to Suboptimal Consumption of Vitamin A Is Modulated by Genetic Variants rs5888 (SCARB1), rs1800629 (UCP1) and rs659366 (UCP2)

Obesity is characterized by an excessive body fat percentage (BF%). Animal and cell studies have shown benefits of vitamin A (VA) on BF% and lipid metabolism, but it is still controversial in humans. Furthermore, although some genetic variants may explain heterogeneity in VA plasma levels, their role in VA metabolic response is still scarcely characterized. This study was designed as a combination of an observational study involving 158 male subjects followed by a study with a well-balanced genotype-phenotype protocol, including in the design an ex vivo intervention study performed on isolated peripheral blood mononuclear cells (PBMCs) of the 41 former males. This is a strategy to accurately identify the delivery of Precision Nutrition recommendations to targeted subjects. The study assesses the influence of rs5888 (SCARB1), rs659366 (UCP2), and rs1800629 (UCP1) variants on higher BF% associated with suboptimal VA consumption and underlines the cellular mechanisms involved by analyzing basal and retinoic acid (RA) response on PBMC gene expression. Data show that male carriers with the major allele combinations and following suboptimal-VA diet show higher BF% (adjusted ANOVA test p-value = 0.006). Genotype-BF% interaction is observed on oxidative/inflammatory gene expression and also influences lipid related gene expression in response to RA. Data indicate that under suboptimal consumption of VA, carriers of VA responsive variants and with high-BF% show a gene expression profile consistent with an impaired basal metabolic state. The results show the relevance of consuming VA within the required amounts, its impact on metabolism and energy balance, and consequently, on men's adiposity with a clear influence of genetic variants SCARB1, UCP2 and UCP1.

Gender-specific associations of CD36 polymorphisms with the lipid profile and susceptibility to premature multi-vessel coronary artery heart disease in the Northern Han Chinese

BACKGROUND

The aim of the present study was to detect potential gender-specific associations between some common CD36 single nucleotide polymorphisms (SNPs) and the lipid profile, as well as the susceptibility to premature multi-vessel coronary artery heart disease (CHD) in the Han population of Northern China.

METHODS

A systematic three-step study process was employed to detect associations between CD36 gene variants and blood lipid profiles, as well as premature multi-vessel CHD in a gender-specific manner.

RESULTS

The current study documented the following novel findings: (I) the full population-based association study in 329 Northern Han Chinese showed that four common CD36 polymorphisms were significantly related to extreme lipid profiles, with statistically significant effects based on gender interactions (rs1049673: P = 0.001; rs7755: P = 0.008; rs3211956: P = 0.034; and rs3173798: P = 0.004); (ii) these statistically significant effects could be decomposed into statistically significant atherogenic effects in males, but non-significant non-atherogenic effects in females; (iii) the results of logistic regression analysis indicated that current smoking status, low density lipoprotein cholesterol (LDL-C) levels, and type-2 diabetes were independent risk factors for premature multi-vessel CHD phenotype (P < 0.0001).

CONCLUSIONS

Four common CD36 polymorphisms (rs1049673, rs7755, rs3211956, and rs3173798) were identified to be significantly associated with extreme lipid profiles and had statistically opposite gender-specific clinical lipid profile effects. Thus, the 3'-untranslated regions (3'-UTR) CD36 SNPs could be a novel target for metabolic abnormalities in males of the Han nationality from Northern China.

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.

HDL Cholesterol Metabolism and the Risk of CHD: New Insights from Human Genetics

PURPOSE OF REVIEW

Elevated high-density lipoprotein cholesterol levels in the blood (HDL-C) represent one of the strongest epidemiological surrogates for protection against coronary heart disease (CHD), but recent human genetic and pharmacological intervention studies have raised controversy about the causality of this relationship. Here, we review recent discoveries from human genome studies using new analytic tools as well as relevant animal studies that have both addressed, and in some cases, fueled this controversy.

RECENT FINDINGS

Methodologic developments in genotyping and sequencing, such as genome-wide association studies (GWAS), exome sequencing, and exome array genotyping, have been applied to the study of HDL-C and risk of CHD in large, multi-ethnic populations. Some of these efforts focused on population-wide variation in common variants have uncovered new polymorphisms at novel loci associated with HDL-C and, in some cases, CHD risk. Other efforts have discovered loss-of-function variants for the first time in genes previously implicated in HDL metabolism through common variant studies or animal models. These studies have allowed the genetic relationship between these pathways, HDL-C and CHD to be explored in humans for the first time through analysis tools such as Mendelian randomization. We explore these discoveries for selected key HDL-C genes CETP, LCAT, LIPG, SCARB1, and novel loci implicated from GWAS including GALNT2, KLF14, and TTC39B. Recent human genetics findings have identified new nodes regulating HDL metabolism while reshaping our current understanding of known candidate genes to HDL and CHD risk through the study of critical variants across model systems. Despite their effect on HDL-C, variants in many of the reviewed genes were found to lack any association with CHD. These data collectively indicate that HDL-C concentration, which represents a static picture of a very dynamic and heterogeneous metabolic milieu, is unlikely to be itself causally protective against CHD. In this context, human genetics represent an extremely valuable tool to further explore the biological mechanisms regulating HDL metabolism and investigate what role, if any, HDL plays in the pathogenesis of CHD.

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.

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.

SCARB1 Gene Variants Are Associated With the Phenotype of Combined High High-Density Lipoprotein Cholesterol and High Lipoprotein (a)

BACKGROUND

SR-B1 (scavenger receptor class B type 1), encoded by the gene SCARB1, is a lipoprotein receptor that binds both high-density lipoprotein (HDL) and low-density lipoprotein. We reported that SR-B1 is also a receptor for lipoprotein (a) (Lp(a)), mediating cellular uptake of Lp(a) in vitro and promoting clearance of Lp(a) in vivo. Although genetic variants in SCARB1 are associated with variations in HDL level, no SCARB1 variants affecting Lp(a) have been reported.

METHODS AND RESULTS

In an index subject with high levels of HDL cholesterol and Lp(a), SCARB1 was sequenced and demonstrated a missense mutation resulting in an S129L substitution in exon 3. To follow up, 2 cohorts (GeneSTAR, the family-based Genetic Study of Atherosclerosis Risk [n=543], and CCHS, the population-based Copenhagen City Heart Study [n=5835]) were screened for combined HDL cholesterol and Lp(a) elevations. Subjects with the extreme phenotype (HDL >80 mg/dL and Lp(a) >100 nmol/L in GeneSTAR, n=8, and >100 mg/dL in CCHS, n=9) underwent sequencing of SCARB1 exons; 15 of 18 from the combined population demonstrated genetic variants, including rare or uncommon missense or splice site mutations in 9 and homozygous synonymous variants in 6. Functional studies with 4 of the SCARB1 variants (c.386C>T, c.631-14T>G, c.4G>A, and c.631-53^mC>T & c.726+55^mCG>CA) showed decreased receptor function in vitro.

CONCLUSIONS

Human SCARB1 gene variants are associated with a new lipid phenotype, characterized by high levels of both HDL cholesterol and Lp(a). SCARB1 exonic variants often result in diminished function of translated SR-B1 via reduced binding/intracellular transport of Lp(a).

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.

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.

Investigation of genetic variation in scavenger receptor class B, member 1 (SCARB1) and association with serum carotenoids

OBJECTIVE

To investigate association of scavenger receptor class B, member 1 (SCARB1) genetic variants with serum carotenoid levels of lutein (L) and zeaxanthin (Z) and macular pigment optical density (MPOD).

DESIGN

A cross-sectional study of healthy adults aged 20 to 70.

PARTICIPANTS

We recruited 302 participants after local advertisement.

METHODS

We measured MPOD by customized heterochromatic flicker photometry. Fasting blood samples were taken for serum L and Z measurement by high-performance liquid chromatography and lipoprotein analysis by spectrophotometric assay. Forty-seven single nucleotide polymorphisms (SNPs) across SCARB1 were genotyped using Sequenom technology. Association analyses were performed using PLINK to compare allele and haplotype means, with adjustment for potential confounding and correction for multiple comparisons by permutation testing. Replication analysis was performed in the TwinsUK and Carotenoids in Age-Related Eye Disease Study (CAREDS) cohorts.

MAIN OUTCOME MEASURES

Odds ratios for MPOD area, serum L and Z concentrations associated with genetic variations in SCARB1 and interactions between SCARB1 and gender.

RESULTS

After multiple regression analysis with adjustment for age, body mass index, gender, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, smoking, and dietary L and Z levels, 5 SNPs were significantly associated with serum L concentration and 1 SNP with MPOD (P<0.01). Only the association between rs11057841 and serum L withstood correction for multiple comparisons by permutation testing (P<0.01) and replicated in the TwinsUK cohort (P = 0.014). Independent replication was also observed in the CAREDS cohort with rs10846744 (P = 2×10(-4)), an SNP in high linkage disequilibrium with rs11057841 (r(2) = 0.93). No interactions by gender were found. Haplotype analysis revealed no stronger association than obtained with single SNP analyses.

CONCLUSIONS

Our study has identified association between rs11057841 and serum L concentration (24% increase per T allele) in healthy subjects, independent of potential confounding factors. Our data supports further evaluation of the role for SCARB1 in the transport of macular pigment and the possible modulation of age-related macular degeneration risk through combating the effects of oxidative stress within the retina.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosures may be found after the references.

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.

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.

Novel mutations in scavenger receptor BI associated with high HDL cholesterol in humans

The scavenger receptor class B, member 1 (SR-BI), is a key cellular receptor for high-density lipoprotein (HDL) in mice, but its relevance to human physiology has not been well established. Recently a family was reported with a mutation in the gene encoding SR-BI and high HDL cholesterol (HDL-C). Here we report two additional individuals with extremely high HDL-C (greater than the 90th percentile for age and gender) with rare mutations in the gene encoding SR-BI. These mutations segregate with high HDL-C in family members of each proband and are associated with a 37% increase in plasma HDL-C in heterozygous individuals carrying them. Both mutations occur at highly conserved positions in the large extracellular loop region of SR-BI and are predicted to impair the function of the SR-BI protein. Our findings, combined with the prior report of a single mutation in the gene encoding SR-BI, further validate that mutations in SR-BI are a rare but recurring cause of elevated HDL-C in humans.

Regulation of platelet function by class B scavenger receptors in hyperlipidemia

Platelets constitutively express class B scavenger receptors CD36 and SR-BI, 2 closely related pattern recognition receptors best known for their roles in lipoprotein and lipid metabolism. The biological role of scavenger receptors in platelets is poorly understood. However, in vitro and in vivo data suggest that class B scavenger receptors modulate platelet function and contribute significantly to thrombosis by sensing pathological or physiological ligands, inducing prothrombotic signaling, and increasing platelet reactivity. Platelet CD36 recognizes a novel family of endogenous oxidized choline phospholipids that accumulate in plasma of hyperlipidemic mice and in plasma of subjects with low high-density lipoprotein levels. This interaction leads to the activation of specific signaling pathways and promotes platelet activation and thrombosis. Platelet SR-BI, on the other hand, plays a critical role in the induction of platelet hyperreactivity and accelerated thrombosis under conditions associated with increased platelet cholesterol content. Intriguingly, oxidized high-density lipoprotein, an SR-BI ligand, can suppress platelet function. These recent findings demonstrate that platelet class B scavenger receptors play roles in thrombosis in dyslipidemia and may contribute to acute cardiovascular events in vivo in hypercholesterolemia.

Scavenger receptor BI modulates platelet reactivity and thrombosis in dyslipidemia

Hypercholesterolemia is associated with increased platelet sensitivity to agonists and a prothrombotic phenotype. Mechanisms of platelet hypersensitivity are poorly understood; however, increased platelet cholesterol levels associated with hypercholesterolemia were proposed as leading to hypersensitivity. Scavenger receptor class B type I (SR-BI) in the liver controls plasma high-density lipoprotein (HDL) levels, and SR-BI-deficient mice display a profound dyslipoproteinemia. SR-BI is also expressed on platelets, and recent studies have suggested a role for SR-BI in platelet function; however, its role in hemostasis is unknown. Our present studies demonstrated that non-bone marrow-derived SR-BI deficiency and the dyslipidemia associated with it lead to platelet hyperreactivity that was mechanistically linked to increased platelet cholesterol content. Platelet-specific deficiency of SR-BI, on the other hand, was associated with resistance to hyperreactivity induced by increased platelet cholesterol content. Intravital thrombosis studies demonstrated that platelet SR-BI deficiency protected mice from prothrombotic phenotype in 2 types of dyslipidemia associated with increased platelet cholesterol content. These novel findings demonstrate that SR-BI plays dual roles in thrombosis and may contribute to acute cardiovascular events in vivo in hypercholesterolemia.

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.

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.

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-mediated uptake of serum cholesterol is essential for optimal adrenal glucocorticoid production

Impaired scavenger receptor class B type I (SR-BI)-mediated uptake of HDL-cholesterol esters (HDL-CE) induces adrenal insufficiency in mice. Humans contain an alternative route of HDL-CE clearance, namely through the transfer by cholesteryl ester transfer protein (CETP) to apolipoprotein B lipoproteins for subsequent uptake via the LDL receptor. In this study, we determined whether CETP can compensate for loss of adrenal SR-BI. Transgenic expression of human CETP (CETP Tg) in SR-BI knockout (KO) mice increased adrenal HDL-CE clearance from 33-58% of the control value. SR-BI KO/CETP Tg and SR-BI KO mice displayed adrenal hypertrophy due to equally high plasma adrenocorticotropic hormone levels. Adrenal cholesterol levels and plasma corticosterone levels were 38-52% decreased in SR-BI KO mice with and without CETP expression. SR-BI KO/CETP Tg mice also failed to increase their corticosterone level after lipopolysaccharide challenge, leading to an identical >4-fold increased tumor necrosis factor-alpha response compared with controls. These data indicate that uptake of CE via other routes than SR-BI is not sufficient to generate the cholesterol pool needed for optimal adrenal steroidogenesis. In conclusion, we have shown that CETP-mediated transfer of HDL-CE is not able to reverse adrenal insufficiency in SR-BI knockout mice. Thus, SR-BI-mediated uptake of serum cholesterol is essential for optimal adrenal function.

Genetic-epidemiological evidence on genes associated with HDL cholesterol levels: a systematic in-depth review

High-density lipoprotein (HDL) particles exhibit multiple antiatherogenic effects. They are key players in the reverse cholesterol transport which shuttles cholesterol from peripheral cells (e.g. macrophages) to the liver or other tissues. This complex process is thought to represent the basis for the antiatherogenic properties of HDL particles. The amount of cholesterol transported in HDL particles is measured as HDL cholesterol (HDLC) and is inversely correlated with the risk for coronary artery disease: an increase of 1mg/dL of HDLC levels is associated with a 2% and 3% decrease of the risk for coronary artery disease in men and women, respectively. Genetically determined conditions with high HDLC levels (e.g. familial hyperalphalipoproteinemia) often coexist with longevity, and higher HDLC levels were found among healthy elderly individuals. HDLC levels are under considerable genetic control with heritability estimates of up to 80%. The identification and characterization of genetic variants associated with HDLC concentrations can provide new insights into the background of longevity. This review provides an extended overview on the current genetic-epidemiological evidence from association studies on genes involved in HDLC metabolism. It provides a path through the jungle of association studies which are sometimes confusing due to the varying and sometimes erroneous names of genetic variants, positions and directions of associations. Furthermore, it reviews the recent findings from genome-wide association studies which have identified new genes influencing HDLC levels. The yet identified genes together explain only a small amount of less than 10% of the HDLC variance, which leaves an enormous room for further yet to be identified genetic variants. This might be accomplished by large population-based genome-wide meta-analyses and by deep-sequencing approaches on the identified genes. The resulting findings will probably result in a re-drawing and extension of the involved metabolic pathways of HDLC metabolism.

Scavenger receptor BI facilitates the metabolism of VLDL lipoproteins in vivo

Scavenger receptor class B type I (SR-BI) functions as an HDL receptor that promotes the selective uptake of cholesteryl esters (CEs). The physiological role of SR-BI in VLDL metabolism, however, is largely unknown. SR-BI deficiency resulted in elevated VLDL cholesterol levels, both on chow diet and upon challenge with high-cholesterol diets. To specifically elucidate the role of SR-BI in VLDL metabolism, the plasma clearance and hepatic uptake of (125)I-beta-VLDL were studied in SR-BI(+/+) and SR-BI(-/-) mice. At 20 min after injection, 66 +/- 2% of the injected dose was taken up by the liver in SR-BI(+/+) mice, as compared with only 22 +/- 4% (P = 0.0007) in SR-BI(-/-) mice. In vitro studies established that the B(max) of (125)I-beta-VLDL binding was reduced from 469 +/- 30 ng/mg in SR-BI(+/+) hepatocytes to 305 +/- 20 ng/mg (P = 0.01) in SR-BI(-/-) hepatocytes. Both in vivo and in vitro, limited to no selective uptake of CEs from beta-VLDL was found. Interestingly, HDL effectively competed for the association of beta-VLDL in the presence as well as in the absence of SR-BI, indicating a second common recognition site. In conclusion, SR-BI plays an important physiological role in the metabolism of VLDL (remnants).

Scavenger receptor class B type I polymorphisms and peripheral arterial disease

Genetic variations of the scavenger receptor class B type I (SR-BI) have been demonstrated to be associated with plasma lipid parameters, anthropomorphic parameters, and coronary artery disease. We determined the frequency of 3 single-nucleotide polymorphisms within the SR-BI gene (SCARB1) in 354 patients with peripheral arterial disease (PAD) and 354 controls matched for age, sex, and diabetes and related to lipids and disease state, that is, PAD. SCARB1 combined genotype exon 1/intron 5/exon 8 were found to be associated with plasma total and low-density lipoprotein cholesterol levels, respectively. In terms of disease, a significant risk for PAD was observed in female subjects carrying the common allele of exon 8 (odds ratio, 2.623; 95% confidence interval, 1.321-5.208; P=.003). The variant allele of intron 5 was found to be a risk factor for PAD in men (odds ratio, 2.182; 95% confidence interval, 1.288-3.698; P=.005). Furthermore, the SCARB1 combined genotype intron 5/exon 8 proved predictive for PAD in the whole population (P=.006), which remained significant after correction for traditional risk factors. In conclusion, in the present study population, SCARB1 polymorphisms not only show associations with plasma levels of total and low-density lipoprotein cholesterol, respectively, but also with the risk for PAD.

Genetic determinants of HDL: monogenic disorders and contributions to variation

PURPOSE OF REVIEW

This review focuses on recent progress towards the characterization of genetic variations that contribute to interindividual variation in plasma high-density lipoprotein cholesterol levels in the general population.

RECENT FINDINGS

Many of the genes that harbor rare mutations leading to extreme high-density lipoprotein cholesterol levels contain common variation that influences plasma high-density lipoprotein cholesterol in several study populations. Candidate gene association studies provide evidence that some of these variations have an effect on high-density lipoprotein cholesterol, dependent on epistatic interactions or environmental context. Both rare and common variations contribute to interindividual high-density lipoprotein cholesterol variation. Recent comparisons of candidate gene sequences between individuals in the tails of the high-density lipoprotein cholesterol distributions (the upper or lower 1-5%) of several study populations indicate that as many as 20% of individuals with low high-density lipoprotein cholesterol harbor a rare mutation in an investigated gene. For example, the ABCA1 gene region harbors rare mutations and common variants that contribute to interindividual high-density lipoprotein cholesterol variation in the general population.

SUMMARY

The genetic control of high-density lipoprotein cholesterol level is complex. Maximizing the utility of genetic knowledge for predicting an individual's high-density lipoprotein cholesterol level or response to intervention will require a better understanding of the action of combinations of genetic variants and environmental exposures.

Effects of amino acid substitutions at glycine 420 on SR-BI cholesterol transport function

Scavenger receptor class B type I (SR-BI) facilitates the uptake of HDL cholesteryl esters (CEs) in a two-step process involving binding of HDL to its extracellular domain and transfer of HDL core CEs to a metabolically active membrane pool, where they are subsequently hydrolyzed by a neutral CE hydrolase. Recently, we characterized a mutant, G420H, which replaced glycine 420 in the extracellular domain of SR-BI with a histidine residue and had a profound effect on SR-BI function. The G420H mutant receptor exhibited a reduced ability to mediate selective HDL CE uptake and was unable to deliver HDL CE for hydrolysis, despite the fact that it retained the ability to bind HDL. This did not hold true if glycine 420 was replaced with an alanine residue; G420A maintained wild-type HDL binding and cholesterol transport activity. To further understand the role that glycine 420 plays in SR-BI function and why there was a disparity between replacing glycine 420 with a histidine versus an alanine, we generated a battery of point mutants by substituting glycine 420 with amino acids possessing side chains that were charged, hydrophobic, polar, or bulky and tested the resulting mutants for their ability to support HDL binding, HDL cholesterol transport, and delivery for hydrolysis. The results indicated that substitution with a negatively charged residue or a proline impaired cell surface expression of SR-BI or its interaction with HDL, respectively. Furthermore, substitution of glycine 420 with a positively charged residue reduced HDL CE uptake as well as its subsequent hydrolysis.

Scavenger receptor class B type I (SCARB1) c.1119C>T polymorphism affects postprandial triglyceride metabolism in men

The scavenger receptor class B type I (SCARB1) is a cell surface glycoprotein that plays a key role in reverse cholesterol transport. A polymorphism in exon 8 (c.1119C>T) has been associated with fasting HDL- and LDL- cholesterol concentrations in Caucasian populations. This study evaluated whether this variant is associated with postprandial lipemia in 59 normolipidemic males. After an overnight fast, the subjects were given a single fat load comprising 60% of energy as fat, 15% as protein, and 25% as carbohydrate. Blood was drawn every hour from baseline to 6 h, then every 2.5 h until h 11. We measured plasma lipid concentrations including triglycerides (TG) in large and small triglyceride rich lipoprotein particles (TRL). Changes in postprandial small TRL TG differed among groups over time (Pgeno x time = 0.034) whereby TT and CT subjects maintained lower concentrations throughout most of the postprandial period compared with CC subjects. Significant differences occurred at h 1, 2, 4, and 5 (P < 0.05). Postprandial changes in large TRL TG (Pgeno x time = 0.923) or total TG (Pgeno x time = 0.529) did not differ by genotype. These results suggest that the c.1119C>T polymorphism is associated with a lower postprandial TG response in the smaller, partially catabolized lipoprotein fraction.

Association of lower plasma estradiol levels and low expression of scavenger receptor class B, type I in infertile women

OBJECTIVE

To determine the expression of the scavenger receptor, class B, type I (SR-BI) in human granulosa cells.

DESIGN

Prospective cohort analysis.

SETTING

Tertiary academic university hospital.

PATIENT(S)

Women undergoing IVF treatment.

INTERVENTION(S)

Granulosa cells were isolated from oocyte retrievals.

MAIN OUTCOME MEASURE(S)

Total RNA and cell lysates were isolated from the granulosa cells, and SR-BI RNA and protein expression were quantified by real-time polymerase chain reaction and western blotting, respectively. Baseline and peak E2 levels were drawn before IVF treatment and before hCG stimulation.

RESULT(S)

The expression of SR-BI RNA and protein were positively correlated. The prevalence of low SR-BI RNA expression (defined as below 25th percentile) was 26%, whereas the prevalence of high SR-BI expression (defined as above 75th percentile) was 24%. Expression of SR-BI RNA was not correlated with body mass index, age, race or ethnicity, primary diagnosis of infertility, or pregnancy outcomes. However, baseline and peak E2 levels were significantly lower in subjects with low SR-BI RNA expression as compared with subjects with high SR-BI expression (P<.04). There was a positive correlation between the number of retrieved (P<.02) and fertilized oocytes (P<.002) and SR-BI RNA levels.

CONCLUSION(S)

Scavenger receptor-BI is expressed in human granulosa cells. Subjects with low SR-BI expression had lower baseline and peak E2 levels and lower number of retrieved and fertilized oocytes.

Gene by sex interaction in the etiology of coronary heart disease and the preceding metabolic syndrome

BACKGROUND

Despite decades of research, the genetic basis of coronary heart disease and its metabolic risk factors is poorly understood. Few studies consider that sex may modify the effect of gene variants on disease. Investigation of gene by sex interaction may help to elucidate underlying genetic susceptibilities and explain the sexual dimorphism of these complex traits.

AIMS

The aim of this review is to summarize evidence for gene by sex interaction in the etiology of coronary heart disease and the metabolic syndrome.

DATA SYNTHESIS

Published literature was examined in the areas of familial aggregation of coronary heart disease; heritability of body mass, insulin resistance, hypertension and dyslipidemia; genome-wide linkage analysis in humans and rodents; and large-scale genetic association studies. Possible mechanisms of gene by sex interaction are discussed including X-linked inheritance, confounding by risk factors and the effect of sex hormones.

CONCLUSIONS

The strongest evidence for gene by sex interaction in relation to coronary heart disease and the metabolic syndrome is in the etiology of body mass, insulin resistance and possibly dyslipidemia. Genetic studies of these traits would benefit from taking sex differences into account. Alternative mechanisms underlying gene by sex interaction, besides obvious sex hormone differences, should be considered.

Estrogen regulation of the scavenger receptor class B gene: Anti-atherogenic or steroidogenic, is there a priority?

High density lipoprotein (HDL) participates in reverse cholesterol transport and in the delivery of cholesterol to the liver and steroidogenic tissues by a mechanism called "selective lipid uptake" which is mediated by the HDL receptor, scavenger receptor B type I (SR-BI). Overexpression of SR-BI suppresses atherosclerosis by increasing reverse cholesterol transport. In contrast, genetic ablation of SR-BI has a negative effect on cardiovascular physiology in both males and females and a gender specific negative impact on female fertility. Cholesterol is essential for mammalian embryonic development as a necessary component of cell membranes and as a substrate for steroidogenesis. The SR-BI receptor is highly expressed in the human placenta allowing the growing fetus to obtain a considerable portion of cholesterol from maternal lipoproteins. Estrogen, which plays an important role in maintaining pregnancy, has been shown to enhance plasma HDL levels and promote reverse cholesterol transport. Since SR-BI is the major determinant of serum HDL levels, direct regulation of the SR-BI gene by estrogen is theorized. The objective of this manuscript is to summarize the current information related to estrogen regulation of the gene that codes for the SR-BI receptor.

Hepatic high-density lipoprotein receptors: roles in lipoprotein metabolism and potential for therapeutic modulation

High-density lipoprotein (HDL) plays an important role in protection against atherosclerosis. A major part of HDL's antiatherogenic role is through mediating reverse cholesterol transport from peripheral cells, such as macrophages and other cells in the artery wall, to the liver. Hepatic HDL receptors should, therefore, play an important role in either mediating or modulating HDL-dependent reverse cholesterol transport. The scavenger receptor class B type I (SR-BI) was first identified as a hepatic HDL receptor almost 10 years ago and is well characterized at the molecular level. This review highlights recent studies that provide insight into the cellular pathways involved in SR-BI-mediated lipid transfer between bound lipoproteins and cells, supports a role for this receptor in reverse cholesterol transport and protection against experimental atherosclerosis in mice, and explores the consequences of sequence variations in the gene encoding SR-BI in humans.