Clinical, Molecular Biochemical And Genetic Analysis Of Essential Hypertension And The Target Organ Damage

Objectives:Essential hypertension has become a common condition in 21 century,with the improvement of living standard and acceleration of working pace.It has been a major research focus in China for high mortality and misdiagnosis rate in Chinese.Meta-analysis found "susceptible genes+environmental factors=essential hypertension".Otherwise,Target organ damages were key problems affecting the prognosis of essential hypertensives.Of the damages,left ventricular hypertension was found in 30-50%hypertensives.Herein,there was particular significant to study the risk factors of essential hypertension complicated with left ventricular hypertrophy.Although in recent 10 years,some progress has been made upon the pathogenesis of hypertension.However, previous studies separately analyzed hereditary and environmental factors;and separatedly investigated hyperlipidemia,atherosclerosis,diabetes and metabolic syndrome which were not consistent to the pathogenesis of the suffering. Moreover,the main objects of previous projects were the role of nuclear genes in European,African-American and Caucasians.The role of mitochondria (energy plant)in Chinese hypertensives was overlooked.To find the hereditary and clinical markers of essential hypertension and left ventricular hypertrophy, to build a new theoretical basis of diagnosing and treating hypertensives,990 Beijing residents who were out-patients or in-patients at the General Hospital of Chinese PLA were recruited.MethodsMultiple-disciplines including clinicians,geneticists,statisticians, mathematicians,molecular biochemists and specialists in computer collaborated in our study.990 cohort members attended the examination from January 2006 to January 2007 with informed consent.Firstly,thorough clinical data was obtained from questionnaires;Secondly,4ml venous blood was drawn after 12-hour fast to test biochemical assays including fasting blood sugar,total cholesterol, triglyceride,high density lipoprotein,low density lipoprotein,blood urea nitrogen, urea acid and creatinine by automatic biochemistry analyzer(Hitach 7600DDP, Japan),using Roche biochemical reaction kits.Thirdly,Echocardiograms were performed using M-mode and color-flow Doppler capabilities(GE Vingmed, System five,USA).Fourthly,with candidate gene approach and entire mitochondrial genome sequencing,we performed a systematic and extensive screening of mitochondrial genes in 3 regions,including tRNA^Leu(UUR),tRNA^Lys and tRNA^Ileat the Institute of Geriatric Cardiology,Chinese PLA General Hospital and Cincinnati Children's Hospital Medical Center.Fifthly,multivariate analyses were performed by stepwise linear regression analysis with using Mallows'Cp for model selection.The dependent variables were systolic and diastolic blood pressure.Covariates included 16 clinical variables(sex,age,heart rate,family history,age-on-set,coronary heart disease,cerebrovascular disease, sleep apnea,renal diseases,diabetes,treatment,alcohol,smoking,fasting blood glucose,blood creatinine and body surface area)and 31 mitochondrial point mutations(amino acid changes and RNAs mutations with mutation frequency≥3). By using Mallows'Cp for model selection,we obtain a measure of the goodness of fit of a model and protect against model over-fitting.All the statistical analysis was performed using the software Stata 7.0(StataCorp,College Station,TX)and SAS 9.1(SAS Institiute,Carey,NC).Lastly,the probands harboring point mutations of particular importance were detailed investigated.The pedigrees were selected and lymphoblastoid cell lines were immortalized by transformation with the Epstein-Barr virus,then mitochondrial functions were analyzed using oxygen consumption measurements and northern blotting.Results: 1.There were 6 mutations within 7 hypertensives located in mitochondrial tRNA^Ile.4277,4295 and 4316 were highly conserved from bacteria to mouse, bovine,Xenopus laevis and human being.Particulary,A4263G and T4277C were novel mutations without reporting previously.These mutations affected the stable structure of tRNA^Ile,changed the process of tRNA-aminoacylation and decreased the synthesis of protein.However,none of mutations were detected in the controls.2.Multivariate analyses showed systolic blood pressure was related to sex (β=3.52±1.27,P=0.01),mitochondrial point mutations A8343G(β=-22.99±9.00,P=0.01)and T8603C(β=26.39±10.39,P=0.01).Diastolic blood pressure was associated with heart rate(β=0.13±0.03,P=0.01),family history(β= 1.80±0.78,P=0.02),age(β=-0.34±0.03,P＜0.01),age-on-set(β=-0.08±0.03,P=0.01),fasting blood glucose(β=-1.96±0.80,P=0.01),mutation A8343G(β=-16.31±5.44,P=0.01).3.Sequence analysis of mitochondrial DNA in one Chinese pedigree identified a novel A-G transition at position 4401(14401G)at the junction of tRNA^Metand tRNA^Gln.The non-coding region mutation appeared to affect the processing of precursors in these mitochondrial tRNAs.The reduction in the rate of respiration and marked decreases in the steady-state levels of tRNA^Metand tRNA^Glnwere detected in the cells carrying this mutation.The novel mutation was absent in 270 Chinese control subjects.4.Multivariate analysis showed left ventricular mass index(LVMI)was not associated with mitochondrial mutations but was strongly associated with environmental factors including coronary heart disease(β=7.33±2.06,P＜0.0001), gender(β=-12.40±2.59,P＜0.0001),renal diseases(β=5.83±2.41,P=0.0006), body surface area(β=-15.83±6.83,P=0.0042),family history(β=-5.01±2.15, P=0.0038),age-of-onset(β=-0.32±0.07,P=0.0042),systolic(β=0.23±0.06, P＜0.0001)and diastolic blood pressure(β=-0.39±0.09,P=0.0107).Conclusion: 1.The role of mitochondrial DNA mutations in tRNA^Ilein the pathogenesis of essential hypertension can not be overlooked.It may be the new target for diagnosing and treating essential hypertension in clinical work.2.Multigenic changes(mitochondrial mutations A8343G and T8603C) together with environmental factors(gender,age and family history)may affect blood pressure in Chinese hypertensives.3.The non-coding region(A4401G)mutation may be involved in the pathogenesis of left ventricular hypertrophy in Chinese hypertensives.4.In Chinese hypertensives,while the role of mitochondrial variants in the pathogenesis and progression of LVH was not prominent,hemodynamic factors (such as blood pressure)and nonhemodynamic factors including gender, age-of-onset,family history and specific complications may serve as predictors of LVH and affect the course of LVH.5.Some novel mutations located in specific positions may affect the precursors of protein synthesis and participate in the pathogenesis of left ventricular hypertrophy in Chinese hypertensives and deserve further investigation.