Association And Functional Characterization Of β1-Adrenoceptor Gene Haplotypes With Essential Hypertension

Theβ1-adrenergic receptor (β1-AR) is a member of G-protein-coupled receptor(GPCR) superfamilies and plays an important role in blood pressure regulation.Recently, two common functional coding-region single nucleotidepolymorphisms(cSNPs), 49S>G(145A/G) and 389R>G(1165C/G), have been studiedisolation, but the results were inconsistent. To date, there have been no reports aboutthe association ofβ1-AR haplotypes with essential hypertension. The present studyaimed to determine the association ofβ1-AR haplotypes (combinations of 49S>G and389R>G) rather than a single SNP behavior with essential hypertension (EH) and theeffect of different haplotypes on receptor activities.Materials and methodsAll study subjects, including 391 unrelated patients with hypertension andunrelated healthy control subjects were from the Zhangwu County, Liaoning Province.We carried out case-control study to analyze the relationship of ?l-AR haplotypeswith hypertension. Furthermore, we constructed haplotype expression vectorpcDNA3．1((＋)-β1-AR and stably transfected into COS7 cells. The intracellular cAMP,rennin and Ca²⁺ were measured to assay haplotype receptor activity by stimulatingcells withβ1-AR stimulator isoprenaline(ISO), norepinephrine(NE) andβ-blockermetoprolol. 1．The baseline characteristics of the case-control population showed that patientswith hypertension had significantly higher body mass index (BMI), triglyceride (TG),total cholesterol (T-chol), low-density lipoprotein (LDL) and lower high-densitylipoprotein (HDL) than the controls(p<0．05) , suggesting BMI, TG, T-chol and LDLwere risk factors of hypertension ,while HDL was protective factor of hypertension inour study subjects.2．Linkage disequilibrium analysis with ARLEQUIN software displayed 49S>Gand 389R>G were in linkage disequilibrium (D'=0．843, r² =0．262, p<0．0001) . In thestudy population, the most common haplotype is SG haplotype(51．4%), while GGhaplotype is the least (2．0%).3．GG haplotype was independent predictors for hypertension in the population(OR=3．843,p=0．027) , and there was significantly positive correlation of GG haplotypewith DBP (92．94±3．55 vs.84．31±0．54mmHg, p=0．022) .4．The basal intracellular cAMP was GR>GG>SR>SG (GR 33．44±1．18, GG27．98±1．17, SR 25．12±0．94, SG 20．08±1．19pmol/mg protein) in rank order. Meanwhile,our data indicated that regardless of the substitution at position 49, haplotypes carrying389R had significantly increased maximal isoprenaline-stimulated rise in intracellularcAMP (SR 159．48%±21．35%, GR 99．86%±11．33% vs. SG 61．98%±1．54% and GG44．03%±4．99%, p<0．01) , and greater metoprolol-induced reduction (SR 84．51±8．94%,GR 78．51±8．36% vs. SG 42．83±4．15% and GG 3．87±2．63%, p<0．05) , and in the fourhaplotypes, GG haplotype was the least sensitive to stimuli.5．After sustained NE stimulation, receptors containing SG haplotype showedmuch faster and more complete desensitization than GG substitution (96．87%±0．89%vs. 75．86%±2．96%,p<0．001) .6．Our data revealed that GG haplotype had the highest basal renin activity,whereas SG haplotype the lowest (GG 9．37±0．32, GR 6．89±0．21, SR 6．62±0．26, andSG 4．93±0．20 pg/μg). Moreover, the substitution of 389G with R in either the 49S or 锘?9G containing haplotypes mediated stronger responses to stimuli (p<0．01) , and in thefour haplotypes, GG haplotype was the least sensitive to stimuli, which were similar toabove analysis about cAMP.鈽?. We also found that permanent ISO (1渭M for 20hr)-evoked intracellularcalcium were higher in cells expressing GG haplotype (372．29卤24．33 vs.286．51卤1．33nmol/L,p=0．017) than cells expressing SG haplotype.鈽匔onclusion鈽?. In the study population, 49S>G and 389R>G were in linkage disequilibrium(D'=0．843, r²=0．262, p<0．0001) . The most common haplotype is SG (51．4%) and theleast is GG (2．0%).鈽?. It seemed that the effect of 389R>G polymorphism on receptor activity wasmore predominant over the 49S>G polymorphism.鈽?. In the four haplotype, the activity of GG haplotype receptor was the least, andwith poor desensitization, the least sensitivity toå°¾1-AR agonist and blocker. While, theactivities of 389R haplotype carriers were higher and more sensitive to stimuli than389G haplotype carriers.鈽?. Individuals with GG haplotype will be at increased risk to developehypertension.