Cth Gene In Northern Chinese Han Population, Hmox1 Gene And Hmox2 Gene And Essential Hypertension Association Studies

Section 1: Association study of the heme oxygenase genes with essential hypertension in northern Chinese Han populationBackgroundHeme oxygenase (HO) catalyzes the conversion of heme to biliverdin, with release of free iron and carbon monoxide (CO). HO exists as three isoenzymes, HO-1, HO-2, and HO-3, each encoded by a different gene. HO-1 is an inducible isoform that may be induced through the use of various pharmaceutical agents. HO-2 is constitutively expressed in blood vessels, endothelium, testis and most other tissues and its levels are relatively unaffected by factors inducing HO-1. HO-3 is constitutively expressed at low levels and is not active in heme metabolism. HO-1 and HO-2 are both viewed as playing a major role in the heme breakdown and are alike in terms of mechanism of heme oxidation, cofactor, and substrate specificities.Renal abnormalities leading to hypertension consist of reduced excertion of sodium and water, decreased renal blood flow, and decreased glomerular filtration. Such abnormalities can be corrected by inducing HO-1 activity. HO-1 induction has also been shown to exert a protective effect on renal function in animal models of rhabdomyolysis, cisplatin nephrotoxicity, and nephrotoxic nephritis. In another study, Ang II infusion decreased glomerular filtration rate (GFR), which led to hypertension. HO-1 upregulation naturally followed and provided a cytoprotective effect. Once again, the evidence suggests that HO-1 has a protective effect against the development of hypertension.Oxidative stress is a state in which excess reactive oxygen species overwhelm endogenous antioxidant systems and it plays an important role in the development of hypertension through the disturbance of the delicate balance of endothelium-derived Vasoactive factors caused by these reactions. Induction of HO-1 in vivo can suppress NADPH oxidase-derived oxidative stress. It had also been reported that the induction of HO-1 may lower blood pressure (BP) and superoxide production in the renal medulla of angiotensin II hypertensive mice. Recently, Basuroy et al. reported that the HO-2 provided endogenous protection against oxidative stress. Therefore, we presume that the HO-1 and HO-2 may act as regulator of oxidative stress and play a part in the pathogenesis of hypertension.The HO-1 and HO-2 were encoded by the heme oxygenase gene-1 (HMOX1) and the heme oxygenase gene-2 (HMOX2) respectively. This study aimed to assess the effect of these two genes on EH in northern Chinese Han population.MethodsAll the DNA samples and clinical data of the studied subjects were selected from the International collaborative study of cardiovascular disease in Asia (InterASIA in China). To maximize the potential genetic differences and statistical power for the association analysis, we selected 993 subjects as a subsample containing 503 hypertensive patients (systolic blood pressure (SBP)≥160mmHg and/or diastolic blood pressure (DBP)≥100mmHg, or self-reported current treatment for hypertension with antihypertensive medications) and 490 age-, gender- and area-matched normotensive controls (SBP<140mm Hg and DBP<90mmHg) from the main study population. With the whole gene-based tagging single nucleotide polymorphism (SNP) approach, three SNPs of the HMOX1 gene and two SNPs of the HMOX2 gene were selected as the tagSNPs by the Haploview Tagger program. These tagSNPs were genotyped in 503 cases and 490 controls. The differences in clinical characteristics between cases and controls were assessed by a t-test for quantitative variables and chi-square test for qualitative ones. The frequencies of the alleles and genotypes between cases and controls were compared by the chi-square test. To test the association between genotypes and EH, a stepwise logistic regression was also conducted to adjust for covariates including age, gender, body mass index (BMI), glucose (Glu), TG, TC, HDL-C, creatinine (Cr), smoking and drinking status. Hardy-Weinberg equilibrium (HWE) was assessed by Fisher's exact test using the program HWE. The program Haplo.stats was used to investigate the relationship between the haplotypes and EH. The program of multifactor-dimensionality reduction (MDR) was used to test for potential gene-gene interactions. ResultsThree SNPs, rs8140669, rs9607267 and rs2071749, of the HMOX1 gene and two SNPs, rs4786500 and rs9921781 of the HMOX2 gene were selected as the tagging SNPs. None of these five SNPs deviated significantly from the HWE in the case or control group. Single SNP analyses indicated that the frequency of rs9607267 of HMOX1 gene in case group was higher than that in control group. Subjects with rs9607267 CC genotype had the higher EH risk than subjects with TT or TC genotype (adjusted OR=1.41, 95%CI: 1.02-1.95, P=0.040). In addition, the CC genotype of rs9607267 was associated with high blood pressure level. After adjusted for covariates, systolic blood pressure and diastolic blood pressure in CC genotype carrier were higher than that in TT or TC genotype (increased by 4.7 mmHg and 2.8 mmHg, respectively). In haplotype analysis, we found the Hap3 (T-C-G) of the HMOX1 gene which carried the rs9607267 C allele was associated with blood pressure level and might increase the risk of EH (adjusted OR=1.44, 95%CI: 1.04-2.01, P=0.029). No association was observed between the HMOX2 gene and EH. The multifactor-dimensionality reduction (MDR) analysis results did not show any interaction between the HMOX1 gene and HMOX2 gene underlying the development of hypertension.ConclusionThe genetic variants of the HMOX1 gene might contribute to the risk of the EH in north Chinese Han population and other studies with large sample size and function study were needed to confirm the association between the HMOX genes and EH. Section 2: Relationship between cystathionineγ-lyase gene polymorphisms and essential hypertension in Northern Chinese Han populationBackgroundHypertension is an important worldwide public health challenge and it affects approximately 25% of the adult population worldwide. There is a direct relationship between the risks of stroke, heart attack, heart failure, kidney disease and the severity of hypertension. It is widely believed that essential hypertension (EH) is a complex disease influenced by multiple factors. Although numerous physiological alterations have been studied in hypertensive individuals, the etiopathogenisis of hypertension is still not well elucidated.The endogenous production of hydrogen sulfide (H2S) and its physiological functions, including membrane hyperpolarization and smooth muscle cell relaxation, place this gas in the family of gas transmitters, together with nitric oxide (NO) and carbon monoxide (CO). Two enzymes, cystathionineβ-synthase (CBS) and cystathionineγ-lyase (CSE), are responsible for the endogenous production of H₂S in mammalian tissues. The CBS is a predominant H2S-generating enzyme in the brain and nervous system, and the CSE is mainly expressed in liver, kidney, and vascular smooth muscles. The gene expression and the activity of the CSE in thoracic aorta were suppressed in hypertension rats, and the expression of the CSE mRNA was down-regulated in the pulmonary hypertension rats. Therefore, it is possible that the CSE, which is encoded by CTH gene, may participate in the regulation of BP and even in the development of EH. In addition, the polymorphism of rs1021737 in CTH gene was associated with variation in plasma homocysteine level, which plays a role in the pathogenesis of essential hypertension. However, no study to date has assessed the relationship between the CTH gene variations and hypertension.In this study, we performed a case-control study to investigate whether the CTH gene was associated with the EH in a northern Chinese Han population.Methods All the DNA samples and clinical data of the studied subjects were selected from the International collaborative study of cardiovascular disease in Asia (InterASIA in China). To maximize the potential genetic differences and statistical power for the association analysis, we selected 993 subjects as a subsample containing 503 hypertensive patients (systolic blood pressure (SBP)≥160mmHg and/or diastolic blood pressure (DBP)≥100mmHg, or self-reported current treatment for hypertension with antihypertensive medications) and 490 age-, gender- and area-matched normotensive controls (SBP< 140mm Hg and DBP<90mm Hg) from the main study population. Based on the FASTSNP, a web server to identify putative functional single nucleotide polymorphisms (SNPs) of genes, we selected two SNPs (rs482843 and rs1021737) in the CTH gene for genotyping. Genotyping was performed by the polymerase chain reaction and restriction fragment length polymorphism method (PCR-RFLP). The frequencies of the alleles and genotypes between cases and controls were compared by the chi-square test. The program Haplo.stats was used to investigate the relationship between the haplotypes and EH.ResultsThese two SNPs were in Hardy-Weinberg Equilibrium in both cases and controls. Genotype distributions and allele frequencies of them did not significantly differ between cases and controls (all P>0.05). In the stepwise logistic regression analysis, we did not observe their association with hypertension either. In addition, none of the four estimated haplotypes or diplotypes significantly increased or decreased the risk of hypertension before or after adjustment for several known risk factors.ConclusionThis present study suggested that the SNPs rs482843 and rsl021737 of the CTH gene were not associated with essential hypertension in Northern Chinese Han population. However, replications in other populations and further functional studies are still necessary to clarify the role of the CTH gene in the pathogenesis of EH.