Sex and statin-related genetic associations at the PCSK9 gene locus: results of genome-wide association meta-analysis.

BACKGROUND: Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a key player of lipid metabolism with higher plasma levels in women throughout their life. Statin treatment affects PCSK9 levels also showing evidence of sex-differential effects. It remains unclear whether these differences can be explained by genetics. METHODS: We performed genome-wide association meta-analyses (GWAS) of PCSK9 levels stratified for sex and statin treatment in six independent studies of Europeans (8936 women/11,080 men respectively 14,825 statin-free/5191 statin-treated individuals). Loci associated in one of the strata were tested for statin- and sex-interactions considering all independent signals per locus. Independent variants at the PCSK9 gene locus were then used in a stratified Mendelian Randomization analysis (cis-MR) of PCSK9 effects on low-density lipoprotein cholesterol (LDL-C) levels to detect differences of causal effects between the subgroups. RESULTS: We identified 11 loci associated with PCSK9 in at least one stratified subgroup (p < 1.0 × 10-6), including the PCSK9 gene locus and five other lipid loci: APOB, TM6SF2, FADS1/FADS2, JMJD1C, and HP/HPR. The interaction analysis revealed eight loci with sex- and/or statin-interactions. At the PCSK9 gene locus, there were four independent signals, one with a significant sex-interaction showing stronger effects in men (rs693668). Regarding statin treatment, there were two significant interactions in PCSK9 missense mutations: rs11591147 had stronger effects in statin-free individuals, and rs11583680 had stronger effects in statin-treated individuals. Besides replicating known loci, we detected two novel genome-wide significant associations: one for statin-treated individuals at 6q11.1 (within KHDRBS2) and one for males at 12q24.22 (near KSR2/NOS1), both with significant interactions. In the MR of PCSK9 on LDL-C, we observed significant causal estimates within all subgroups, but significantly stronger causal effects in statin-free subjects compared to statin-treated individuals. CONCLUSIONS: We performed the first double-stratified GWAS of PCSK9 levels and identified multiple biologically plausible loci with genetic interaction effects. Our results indicate that the observed sexual dimorphism of PCSK9 and its statin-related interactions have a genetic basis. Significant differences in the causal relationship between PCSK9 and LDL-C suggest sex-specific dosages of PCSK9 inhibitors.

The protein "proprotein convertase subtilisin/kexin type 9" (PCSK9) regulates the levels of low-density lipoprotein cholesterol (LDL-C) in blood, and thus, contributes to the risk of cardio-vascular diseases. Women tend to have higher PCSK9 plasma levels throughout their life, although the difference is smaller in patients under LDL-C lowering medication (e.g., statins). We investigated the interplay of genetics, statin-treatment and sex, using combined data from six European studies. We detected 11 genetic regions associated with PCSK9 levels, of which one was specific for women (at SLCO1B3, a statin-transporter gene), and three were specific for men (e.g., ALOX5, encoding a protein linked to chronic inflammatory diseases such as atherosclerosis). We also tested if statin use changed the genetic effect and found five genes only associated with PCSK9 levels in untreated participants. Variants in the gene encoding PCSK9 were most strongly associated and had heterogeneous effects in dependence on statin treatment and sex: On one hand, there were genetic variants with stronger effects in men than women. Those variants are also linked to sex-differential gene expression of PCSK9. On the other hand, there were also variants with treatment-depending effects, linked to protein structure and functionality of PCSK9. This indicates that the observed sexual and treatment-related effects on PCSK9 levels have a genetic basis. In addition, we compared the causal effects of PCSK9 on LDL-C levels between men and women and found a different response to statin treatment. This highlights the need for sex-sensitive dosages of lipid-lowering medication.

Functional analysis of two PLA2G2A variants associated with secretory phospholipase A2-IIA levels.

BACKGROUND: Secretory phospholipase A2 group IIA (sPLA2-IIA) has been identified as a biomarker of atherosclerosis in observational and animal studies. The protein is encoded by the PLA2G2A gene and the aim of this study was to test the functionality of two PLA2G2A non-coding SNPs, rs11573156 C>G and rs3767221 T>G where the rare alleles have been previously associated with higher and lower sPLA2-IIA levels respectively. METHODOLOGY/PRINCIPAL FINDINGS: Luciferase assays, electrophoretic mobility shift assays (EMSA), and RNA expression by RT-PCR were used to examine allelic differences. For rs3767221 the G allele showed ∼55% lower luciferase activity compared to the T allele (T = 62.1 (95% CI 59.1 to 65.1) G = 27.8 (95% CI 25.0 to 30.6), p = 1.22×10⁻³5, and stronger EMSA binding of a nuclear protein compared to the T-allele. For rs11573156 C >G there were no luciferase or EMSA allelic differences seen. In lymphocyte cell RNA, from individuals of known rs11573156 genotype, there was no allelic RNA expression difference for exons 5 and 6, but G allele carriers (n = 7) showed a trend to lower exon 1-2 expression compared to CC individuals. To take this further, in the ASAP study (n = 223), an rs11573156 proxy (r²â€Š= 0.91) showed ∼25% higher liver expression of PLA2G2A (1.67×10⁻¹7) associated with the G allele. However, considering exon specific expression, the association was greatly reduced for exon 2 (4.5×10⁻5) compared to exons 3-6 (10⁻¹° to 10⁻²°), suggesting rs11573156 G allele-specific exon 2 skipping. CONCLUSION: Both SNPs are functional and provide useful tools for Mendelian Randomisation to determine whether the relationship between sPLA2-IIA and coronary heart disease is causal.

Variants in the coagulation factor 2 receptor (F2R) gene influence the risk of myocardial infarction in men through an interaction with interleukin 6 serum levels.

Thrombin-activated factor 2 receptor (F2R) links thrombosis to inflammation modulating interleukin (IL)6 synthesis. We have investigated the role of F2R genetic variants and their interaction with IL6 serum levels in the occurrence of myocardial infarction (MI) in the Stockholm Heart Epidemiology Program (SHEEP). Seven SNPs -1738 G/A, -506-/GGCCGCGGGAAGC (D/I), 2860 G/A, 2930 T/C, 9113 C/A, 9333 C/T and 120813 T/C within F2R locus were genotyped in the SHEEP (n=2,774). The C allele at position 2930 was associated with a slight reduction in MI risk in men. IL6 serum levels were higher in male cases carrying genotypes AA at the -1738 (p= 0.01) and GG at the 2860 loci (p= 0.03) and both alleles were found to differentially modulate IL6 serum levels in the context of selective haplotypes. High IL6 serum levels (>75(th) percentile), were independently associated with an increased risk of MI in men with an odds ratio (OR) (95% confidence interval [CI]) of 2.44 (1.72-3.46), (p=0.0016), but not in women ( OR 0.83 [95%CI 0.50-1.36], p=0.64). In the presence of high IL6 serum levels, the -1738A allele increased and the 2860A allele reduced the risk of MI (all p < or = 0.02). Consistently, the AG diplotype increased MI risk (OR 1.71 [95%CI 1.17-2.51], p=0.005). The -1738 and 2860 loci association with IL6 serum levels was replicated in men in the Stockholm Coronary Artery Risk Factor (SCARF) study (both p < or = 0.04). In the pooled data from the two populations, the A and G allele modulated the risk of MI in men with high IL6 serum levels (p < or = 0.03). Our results demonstrate that in men F2R genetic variants influence the risk of MI mainly through an interaction with IL6 serum levels.