The Effects Of Gene-smoking Interactions And Calcium Channel-related Genes On Blood Pressure In The Han Population

Part 1:Genome-wide Gene-Smoking Interaction analyses on Blood PressureBackground and objectiveHypertension is the leading cause of cardiovascular disease and the largest contributor to global disease burden among all disease risk factors.More than 200 genetic loci have been identified by genome-wide association studies(GWAS),but these loci totally explain less than 4%of the estimated heritability of blood pressure(BP).Among the factors hypothesized to contribute to this "missing heritability" are interactions between genes and other risk factors known to influence BP.Genome-wide envirornmental interaction studies(GWEIS)can be used for the detection of novel loci associated with BP and smoking may play a role in modifying the influence of genetic variants on BP,Thus,the aim of this study was using GWEIS strategy to identify BP susceptibility loci which was also interacted with smoking.Subjects and MethodsOur study consisted of 2 stages.The first stage of this study involved 3,998 participants which were derived from the International Collaborative Study of Cardiovascular Disease in Asia(Inter ASIA).The Inter ASIA subjects were genotyped using the Affymetrix AxiomTM Genome-Wide CHB 1 Array Plate,including 657,124 single nucleotide polymorphisms(SNPs).MaCH software was used to impute the genotypes of the InterAsia participants with haplotypes derived from samples of East Asian ancestry in the 1000 Genome Project.After quality control,approximately 5.7 million SNPs were involved in the analysis.Both 1 df interaction test and 2 df joint test were explored for single marker SNP-smoking interaction analysis.Versatile gene-based association study(VEGAS)method was used for the gene-based analysis with P values derived from the single marker interaction analysis.SNPs and genes with a P value of less than 1.0×10-4 in the first stage were replicated in the Beijing Atherosclerosis Study(BAS).The 466 participants from BAS were genotyped using Affymetrix GeneChip(?)Human Mapping 500K Array Set.ProbAbel,VEGAS2,Metal,Plink and R software were used for statistical analyses.ResultsIn the first stage,a total of 49,59,62 and 38 independent SNPs were identified to be interacted with smoking and associated with systolic BP(SBP),diastolic BP(DBP),mean artery pressure(MAP)and pulse pressure(PP)by using 1df interaction analysis,respectively.A total of 69,65,77 and 55 independent SNPs were identified to be interacted with smoking and associated with SBP,DBP,MAP and PP by using 2df joint interaction analysis,respectively.Through meta-analysis of the two stages,suggestive associations of three loci(P<1×10-6)were determined by using 1df interaction analysis,including LOC105378753 rs2716127(P1dfinteraction = 7.70×107)and EBF3 rs4751139(P1dfinteraction = 1.58×10-7)with diastolic BP,LOC105378150 rs2036086(P1df interaction =6.16×10-7)with mean arterial BP.The 2df joint interaction analysis identified significant association for ADRB2 rs1465405(P2df interaction = 4.3×10-8)with pulse pressure.The ADRB2 variant rs2400643(P2d finteraction= 5.33×10-7)was suggestively associated with systolic BP through 2df joint interaction analysis.SNP rs4751139(P2df interaction =5.00×10-7)was also identifled to be suggestively associated with diastolic BP by using the 2df joint interaction analysis.In the subgroup analysis of smokers and nonsmokers,the effects of the above loci on BP were different.For instance,the rs2716127 T allele was associated with increased diastolic BP(1.91 mmHg)in smokers but decreased diastolic BP(0.73 mmHg)in nonsmokers in the InterAsia population.Similar effects were observed in the BAS population.Seven SNPs within 7 gene regions identified through GWAS in East Asian population were replicated(after Bonferroni correction)in our single marker interaction analysis,including CACNA1D,FGF5,ARL3,CYP17A1,CNNM2.NT5C2 and ATP2B1.The variance of SBP,DBP,MAP and PP explained by the 7 SNPs were 1.79%,2.28%,2.24%and 0.52%,respectively.After including the SNP-smoking interaction effects in the model,the variance explained increased to 2.11%,2.46%,2.49%and 0.85%,respectively.Genome-wide gene-based analysis identified ZBTB2,ZNF180 and CNNM2 were associated with at least one BP phenotype.LOC105378753,EBF3,LOC105378150,ZBTB2 and ZNF180 were reported to be associated with BP for the first time.ConclusionIn conclusion,we provide the first evidence of genome-wide gene-smoking interaction effects on BP in Chinese population.ADRB2 rs1465405 was significantly associated with BP,EBF3 rs4751139,LOC105378150 rs2716127 and LOC105378150 rs2036086 were suggestively associated with BP.The gene-based analysis identified ZBTB2,ZNF180 and CNNM2 genes to be associated with at least one BP trait.Using genome-wide gene-smoking interaction analysis strategy we are able to identify novel loci with a relatively small sample size and explain more varianceof BP.Further studies are warranted to confirm these associations in different populations and elucidate the underlying biological mechanisms of these loci.Part 2:Associations of Variants in the CACNA1A and CACNA1C Genes With Longitudinal Blood Pressure Changes:the GenSalt StudyBackground and objectiveHypertension is the leading risk factor for morbidity worldwide.Althouth GWAS had already identified numerous BP associated loci,but the exact genomic mechanisms of blood pressure regulation remain largely unknown.Base on the key known BP susceptibility genes,one can effectively identify new BP susceptibility genes and will help to explain BP regulation mechanism.Voltage-dependent calcium channels(VDCCs)are involved in a variety of physiological processes,including vascular smooth muscle contraction,which is crucial in BP regulation.It is reported that polymorphisms in the VDCCs genes were associated with cross-sectional BP and hypertension.However,the associations of VDCCs genes with longitudinal BP changes and hypertension incidence were not clear.We aimed to examine single marker and aggregate associations of VDCCs genes with BP changes and hypertension incidence in a longitudinal family study.Subjects and MethodsA total of 1,768 Han Chinese participants from 633 families in the Genetic Epidemiology Network of Salt Sensitivity(GenSalt)study were eligible for the current study.The GenSalt baseline study was conducted from 2003-2005,and the two GenSalt follow-up studies were conducted from 2008 to 2009 and 2011 to 2012.Mean systolic BP and diastolic BP were calculated using nine BP measurements,which were obtained at baseline and each follow-up visit using a random-zero sphygmomanometer.After quality control,total of 219 SNPs within 9 VDCCs genes were selected for our analysis.Mixed-effect models were used to assess additive associations of 219 SNPs with longitudinal BP changes and hypertension incidence.The truncated product method(TPM)was used for gene-based analysis.Bonferroni correction was used for the adjustment of multiple testing.ResultsA total of 1,768 GenSalt participants were involved,52.3%of them were male.On average,participants were 39.0 years of age,had a mean body mass index(BMI)of 23.4 kg/m2,and mean baseline SBP and DBP of 116.9 mmHg and 73.8 mmHg,respectively.During an average of 7.2 years of follow-up,mean SBP and mean DBP increased to 129.1 mmHg and 82.2 mmHg respectively,and 512(32.1%)participants developed hypertension.CACNA1A SNP rs8182538 was significantly associated with longitudinal DBP change after Bonferroni correction(Pintersaction= 9.9×10-5),with mean DBP increases of 0.85,1.03,and 1.19 mmHg per year for participants with genotypes C/C,C/T and T/T,respectively.A similar trend was also observed for the association of rs8182538 with SBP change.In the gene-based analyses,CACNA1A and CACNA1C were found to be associated with DBP and SBP changes over time after Bonferroni correction,respectively(P = 2.0×10-5 for CACNA1A,and P = 1.4×10-4 for CACNA1C).Sensitivity analyses removing the most significant SNP within each gene also identified significant associations of CACNA1A and CACNA1C with DBP and SBP changes,respectively(P = 3.5×10-4 for CACNA1A,and P = 7.1 × 104 for CACNA 1C).ConclusionOur study found a significant association of CACNA1A marker rs8182538 with DBP change over time among Han Chinese population.In addition,the gene-based analysis revealed substantial overall effects of SNPs in the CACNA 1A and CACNA 1C genes on DBP and SBP changes,respectively.Future replication and functional studies are required to confirm these findings and extend the understanding of the underlying mechanisms of CACNA1A and CACA1C genes on BP regulation.