The Association Of STK39,OXSR1,SLC12A3 With Essential Hypertension In Northeast Han Chinese

BackgroundEssential hypertension is a complex disease and affects 25% to 30% of the adult population worldwide. It contributes to morbidity and mortality related to stroke, myocardial infarction, congestive heart failure, and end-stage renal disease. Genetic and multiple environmental determinants play important roles in the etiology and pathogenesis of essential hypertension. An estimated 30% to 50% of blood pressure variation in the general population is determined by genetic factors. Therefore, identifying or establishing genetic susceptibility genes and genetic markers for hypertension can lead to a better understanding of regulatory mechanisms of blood pressure and help with prevention and therapy.Among the pathogenesis of essential hypertension, renal transporters play an important role in regulating salt/water balance. Recently, studies showed that Sterile-20 like related praline alanine rich kinase (SPAK, gene symbol:STK39) interacts with oxidative stress-responsive kinase 1 (OSR1, gene symbol:OXSR1) and phosphorylates the sodium-chloride co-transporter (NCC, gene symbol:SLC12A3), which plays a critical role in regulating the salt/water balance and blood pressure. However, it has not been studied the association of this pathway with hypertension in Han Chinese. Recently, a new hypertension susceptibility gene, STK39, was identified in an Amish population by a genome-wide association study. Given the fact that the heterogeneity in the etiology of hypertension or the confounding in genetic association studies caused by population stratification, it is necessary to estimate the association of STK39 and its downstream molecular with hypertension in Han Chinese.Hypertension is a complex multigenic disease and is affected by a number of risk factors, such as age, gender, race, obesity, diabetes, life style, and heredity. Therefore, it is important to determine "gene-gene" or "gene-other risk factors" interactions in the contribution of genetic factors to hypertension. In our study, we investigated how STK39,OXSR1, SLC12A3 (three components of the SPAK/OSR1-NCC pathway) and other major risk factors contribute to essential hypertension in Northeast Han Chinese.MethodsWe recruited Han Chinese participants from two medical centers in Shenyang and Harbin in China between January 2005 and December 2008. The standard mercury sphygmomanometers were used to measure the systolic and diastolic blood pressure (SBP and DBP, respectively) from an individual's right arm. A questionnaire was used for collecting other related information such as family history, smoking, and alcoholic intake. The inclusion criteria for the essential hypertension were SBP≥140 mmHg, and/or DBP≥90 mmHg, and/or current under antihypertensive treatment. Normotensive subjects were selected from those who had regular physical exam over the past 5 years in the two centers based on three criteria:1) SBP and DBP were never above 140 and 90 mmHg,2) no family history of hypertension was reported, and 3) one never received antihypertensive treatments. Type 2 diabetes mellitus (T2DM) was diagnosed according to 1997 American Diabetes Association criteria.In this study, we selected 11 tagging SNPs based on three criteria 1) tagging SNPs with maximum coverage; 2) functional if possible; and 3) minor allele frequency (MAF) >10% from the International HapMap project (CHB). Of selected tagging SNPs,5 were for STK39,2 for OXSR1, and 4 for SLC12A3, respectively.Genomic DNA was isolated by the proteinase K method. SNP genotyping was performed by Allelic Specific PCR and direct sequencing. We compared the differences in allele and genotype distributions between cases and controls in two populations. We also analyzed the "gene-gene" and "gene-other risk factors" interactions in this study.ResultsTwo SNPs of STK39, rs6433027 and rs3754777, were found to be associated with hypertension in population 1 (Shenyang) males (P=0.008-0.024). All other SNPs were not associated with hypertension in either gender. The association of rs6433027 and rs3754777 with male hypertension was validated by genotyping another 4598 hypertensive and healthy individuals (Harbin). The odds ratios (95% confidence interval, P value) in males were 1.269 (1.13-1.43; P=0.0001) and 1.231 (1.078-1.41; P =0.004) of rs6433027 and rs3754777, respectively. The allele T of rs6433027 presented a strong epistatic effect on the allele A of rs3754777 in hypertensive trait. The minor allele frequencies of two SNPs were not stratified by age, BMI, or diabetes, the three major risk factors for hypertension.ConclusionOur results suggest that STK39 is an independent risk factor for male hypertension and that its intragenic SNPs can interact and function in the control of blood pressure.