Sterol Regulatory Element Binding Protein-2 Activation Pathway Gene And Coronary Heart Disease Association Studies

BackgroundCoronary heart disease (CHD) is a complex disease where both genetic and environmental factors interact to produce the phenotype. Dyslipidemia, especially hypercholesterolemia, is one of established major modifiable risk factors. It has been reported that lipid- lowering treatment could significantly decrease the risk of CHD in both primary and secondary prevention. Therefore, many genes involving in lipids metabolism have been considered to be important candidate genes to elucidate the genetic basis of CHD. Sterol regulatory element binding proteins (SREBPs), as a family of membrane-bound transcription factors, play important roles in feed back regulation of cellular cholesterol and fatty acid metabolism by activating related genes. The SREBPs include SREBP-1a, SREBP-1c, and SREBP-2, of which the SREBP2 preferentially activates cholesterol metabolism by binding sterol regulatory element (SRE) of the target genes involved in cholesterol synthesis such as 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, HMG CoA synthase and uptake such as low density-lipoprotein (LDL) receptor (LDLR). The SREBPs are synthesized as inactive precursors residing in the endoplasmic reticulum (ER) membrane and activation of SREBPs require cleavage by two proteases in the Golgi apparatus. The transportation of SREBPs from ER to Golgi needs another two kinds of proteins, namely SREBP cleavage-activating protein (Scap) and insulin induced gene (Insig) proteins including Insig1 and Insig2. In present study, we conducted a case-control study in Chinese Han population to investigate the relationship between the genetic variants of the SREBPs activating pathway, involving SREBP2, SCAP, INSIG1 and INSIG2 genes, and risk of CHD.MethodsA total of 1801 unrelated subjects were included in this study. We recruited 853 patients with CHD from patients hospitalized at the Fuwai Hospital and Cardiovascular Institute (Beijing, China) between October 1997 and December 2001. Eligible patients were those who survived an acute myocardial infarction or were documented by coronary angiography to have evidence of left main coronary artery≥50% and/or at least a 70% stenosis in any major coronary artery. Patients with congenital heart disease, cardiomyopathy, valvular disease, familial hypercholesterolemia and renal or hepatic disease were excluded. A total of 948 age-matched (±2 years) and gender-matched control subjects were randomly selected from individuals residing in Beijing and participating in the InterASIA (International Collaborative Study of Cardiovascular Disease in Asia). The controls were judged to be free of ischemic changes by ECG, without symptoms of chest pain and to be free of CHD by medical history, the Rose questionnaire and clinical examination. All subjects were Chinese Han nationality. Details of medical history were obtained from all participants by standardized questionnaire, together with information of drug intake, cigarette smoking, and alcohol consumption. Blood pressure, height, weight, waistline and were measured. Concentrations of serum lipids and glucose were determined by standard protocols.Haplotype-tagging SNPs (htSNPs) were chosen for SCAP, INSIG1 and INSIG2 with Haploview 4.0 software based on the genotyped SNPs in the Han Chinese of Beijing (CHB) of the HapMap project (the PhaseⅡdatabase, Apr 2007) within each gene and located in 2kb from 5' flanking upstream and 3' flanking downstream, respectively. One nonsynonymous-coding SNP rs4822063 in SREBP2 gene was selected. All SNPs were further genotyped in all subjects by using PCR-RFLP protocols. Association analyses were done separately for each of the SNPs and followed up by haplotype analyses. The Haplo.stats approach was used to test the association of statistically inferred haplotypes with CHD. The gene-gene interaction was examined using both the Multifactor Dimensionality Reduction (MDR) program (non-parametric) and Logistic regression model (parametric).ResultsCompared with the control group, the CHD group had more male and older patients and more individuals with hypertension, diabetes, alcohol consumption. Moreover, the patients had higher mean BMI and SBP, higher levels of serum triglycerides (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and fasting glucose, and lower high density lipoprotein cholesterol (HDL-C) levels than the controls. Based on the genotyped SNPs in the Han Chinese of Beijing (CHB) of the HapMap project, we selected 3, 4, 2 htSNPs for the INSIG1, INSIG2 and SCAP genes. Our results: (1) Single polymorphism analyses on risk of CHD didn't show any association with CHD. (2) Single polymorphism analyses on plasma glucose showed that the SNP rs9769826 of the INSIG1 gene was significantly associated with plasma glucose among controls. The minor allele G carriers had higher glucose level than individuals with major AA homozygous genotype (5.74±2.03mmol/L versus 5.45±1.37mmol/L, p=0.015). (3) Single polymorphism analyses on plasma lipid levels showed that the rs4822063 of SREBP2 was associated with LDL-C in the controls. The genotype CC carriers had higher LDL-C and TC than the major allele G carriers (GG+GC) (3.44±0.90mmol/L versus 3.17±0.84mmol/L, p=0.031 for LDL-C; 5.43±1.06mmol/L versus 5.13±0.97mmol/L,p=0.040 for TC). (4) Haplotype analysis showed that haplotype Hap3 (TGA) of the INSIG1 gene had lower frequency in CHD patients compared with controls (0.162 vs 0.203, simulation p=0.0107). However, the haplotype Hap4 (TTA) had higher prevalence in the CHD patients (0.129 vs 0.085, simulation p=0.0001). The haplotype Hap4 significantly associated with an increased risk of CHD (adjusted OR=1.59, 95%CI: 1.22-2.06, p=0.0006), while the haplotype Hap3 significantly associated with a decreased risk of CHD (adjusted OR=0.74, 95%CI: 0.60-0.92,p=0.006), compared with the reference haplotype Hap1 (GGA). (5) Multi-loci interaction analyses indicated that the 2-locus model involving the rs10271719 and rs9719268 of the INSIG1 gene showed the highest level of testing accuracy (56.09%, p=0.002 on 1000 permutations) as well as the 4-locus model showed significant interaction underlying the pathgenesis of CHD by MDR and Logistic regression model.ConclusionThe present study was the first time to illustrate the relationship between genetic variants from the SREBP2 activating-related pathway and CHD. Our results demonstrated a significant association between the INSIG1 gene variation and CHD. Our study also demonstrated a significant association between the SREBP2 gene variant and plasma lipid levels; and the INSIG1 gene variant was associated with plasma glucose. Moreover, our results provided evidence of interaction between the genes from SREBP2 activating-related pathway on risk of CHD for first time. Our findings warranted further study to replicate our results in other population and to elucidate the biological mechanism.