| Hypertension is one of the most common cardiovascular diseases, associated with coronary heart disease, stroke, heart failure and kidney disease, et al. It is one of the main risk factors associated with cardiovascular death, affecting approximately 1 billion individuals worldly and 130 million in China and the morbidity of essential hypertension (EHT) is still increasing. Mitochondrial diseases are caused by accumulation of mtDNA mutation, which lead to impaired OXPHOS (oxidative phosphorylation) process and disorder of cell function. More recently, mitochondrial tRNA has been the highlight in this field. In the previous study, we found that hypertension presented family aggregation, some of them had maternally inherited characteristic. In addition, more mitochondrial diseases complicated with high blood pressure, which implicated that mtDNA mutation was associated with hypertension.We did sequence analysis on approximately 2,000 patients with EHT and found a Chinese Han family with typical maternally inherited EHT. We collected 5 generations, including 104 individuals with 27 maternal members. Then we did statistic analyses on the clinical data and genetic characteristics of the family. Clinical examination showed the morbidity of hypertension on the maternal lineage was up to 55.6%, while that on the non-maternal lineage was only 15.6% (P<0.01). The onset age of hypertension tended to be earlier (from 62.0±6.2 y to 23.3±2.9 y); the blood pressure of the individuals on the maternal lineage was associated with age, cigarettets, alcohol and excess sodium intaking (P<0.05). And the biochemical test showed that blood glucose, total cholesterol and serum sodium of maternal lineage were significantly higher than those of non-maternal lineage (P<0.05), while the results of echocardiogram had no difference between two groups. Biochemical study revealed A4263G mutation in the tRNAIle gene, which was extraordinarily conserved base in every sequenced isoleucine tRNA from bacteria to human mitochondrial and could influence the combination of amino acids with tRNA.To study on the mechanism of the effect of tRNAIle A4263G mutation on high blood pressure, we established lymphoblastoid cell lines from 3 symptomatic and 1 aymptomatic individuals in this family carrying A4263G mutation when compared with 3 control cell lines. We compared the average value in doubling time in these cell lines and investigated the mechanism of mitochondrial voltage-dependent anion channel (VDAC) on the high blood pressure associated with tRNAIle A4263G mutation. The result revealed that the average value of doubling time of cell lines from individuals carrying tRNAIle A4263G mutation increased significantly compared with control cell lines; the expression of VDAC and Bax in individuals carrying tRNAIle A4263G mutation increased compared with control group, while the expression of small conductance calcium dependant potassium (sKCa) had no change; flow cytometry showed mitochondrial potential (Δψm) of individuals carrying tRNAIle A4263G mutation decreased compared with control and this difference was attenuated by Cyclosporin A (CsA), which was blocker of VDAC; the confocal images showed mitoVDAC was combined with Bax in individuals carrying tRNAIle A4263G mutation, while the combination was not seen on control group.To investigate the mechanism of mitochondrial voltage-dependent anion channel (VDAC) on mitochondrial calcium cycle, we established lymphoblastoid cell lines as described previously. The result of confocal imagines showed the average Rhod-2 fluorescence andΔψm of individuals carrying tRNAIle A4263G mutation was lower than that of control group; the baseline of Rhod-2 fluorescence of the control group increased after exposure to atractyloside (5μM), but no significant change was tested on cell line from A4263G mutation. TheΔψm decreased subsequently for both cell lines after exposure to atractyloside, while this effect of atractyloside were inhibited by VDAC blocker CsA (2μM).This study gave the direct evidence that mtDNA tRNAIle A4263G mutation, which was extraordinarily conserved base in every sequenced isoleucine tRNA from bacteria to human mitochondrial, was associated with hypertension. We investigated the expression and effect of mitochondrial VDAC on the apoptosis, mitochondrial potential and mitochondrial calcium cycle. And the result suggested that mitochondrial VDAC was the key point on the mechanism of maternally inherited hypertension associated with mtDNA tRNAIle A4263G mutation.
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