高血压相关的线粒体新突变tRNA-Ala 5655T>C的致病机理研究

Hypertension is a major public health problem. However, the etiology of hypertension is not well understood beacause it is often a multi-factorial condition. Mitochondrial dysfunction has been potentially implicated in both human and experimental hypertension. In particular, maternal transimission of hypertension has been implicated in some pedigrees,suggesting that mutations in mitochondrial DNA (mtDNA) is one of the molecular bases for this disorder. However,the role of mitochondrial dysfunction in hypertension remains poorly underdtood. To understand a role of mitochondrial genomes in the pathogenesis of hypertension in the Chinese population, we have initiated a systematic and extended mutational screening of mtDNA in a large cohort of hypertension subjects. As a result, we have identified a novel mitochondrial tRNA-Ala 5655T>C mutation in a large Chinese pedigree with maternal transmission of hypertension. This mutation localizes at the processing site for the tRNA-Ala 5'end precursor, which is catalyzed by the RNase P. It is anticiapted that an inefficiency of RNA processing by this mutation causes a failure in tRNA metabolism. It is also hypotheseized that aletered tRNA metabolism leads to an impairement of mitochondrial translation and deficient respiration and increasing production of reactive oxygen species. To test this hypothesis, we will generate the cell lines derived from affected matrileal relatives and control subjects. These cell lines will be examined for the steady-state levels and aminoacylation capacities of mitochondrial tRNAs including tRNAAla . These cell lines will be further assessed for the effects of the 5655T>C mutation on mitochondrial protein synthesis, endogenous respiration and substrate-dependent respiration as well as the production of reactive oxygen species. Furthermore, we will investigate whether the overexpression of human mitochondrial alanyl-tRNA synthetase in the cytoplasmic hybrid cells carrying the 5655T>C mutation corrects the mitochondrial dysfunctions. The success of this study may provide new insights into pathophysiology of maternally transmitted hypertension and intervention target of this disorder.

高血压是一种复杂性疾病，由遗传、环境因素或两者相互作用所致，但其致病机制仍不清楚。线粒体DNA突变引起的线粒体功能障碍是导致高血压病的重要原因之一，但一些重要位点突变导致线粒体功能障碍的机制尚未阐明。本课题在前期一母系遗传的汉族高血压家系中筛查、鉴定了一个新的有意义位点tRNA-Ala 5655T>C.该位点位于mtRNA-Ala 5'端，是RNase P剪切位点。为此我们假设该突变影响线粒体内RNase P剪切效率而降低了稳态tRNA水平，致线粒体蛋白合成缺陷，呼吸链OXPHOS水平下降，最终致线粒体功能障碍。为验证这一假说，我们拟在细胞水平上从遗传、分子和生化多方面阐述新突变T5655C的功能及分子机制，并以提高稳态tRNA-Ala 水平为目标，探讨AARS2对线粒体功能障碍的补偿作用。本课题将进一步完善高血压发生发展的致病机制，并为母系遗传高血压的防治提供新思路。

高血压是一种复杂疾病，由遗传、环境或两者相互作用所致。线粒体DNA突变引起的线粒体功能障碍是导致高血压的重要原因之一，但一些重要位点突变导致线粒体功能障碍的分子机制尚未阐明。本课题在前期一个母系汉族高血压家系中筛查到一个新的，有意义位点tRNAAla 5655T>C。经扩大样本筛查，我们又在另2个家系中验证了此位点，在2000例患者中该位点发生频率为0.14%，却未在正常人群中检测到。三个家系的高血压患者均呈现母系遗传特征，说明线粒体5655T>C突变与母系遗传性高血压相关。通过构建患者来源的转线粒体细胞及细胞功能分析，我们发现突变改变了RNaseP对线粒体tRNAAla 前体的剪切效率，进而突变细胞线粒体内氨酰化tRNAAla 水平下降，稳态tRNAAla 水平降低，线粒体蛋白合成中含Ala密码子多的ND1和ATP6蛋白下降显著，最终导致线粒体功能障碍，具体表现为呼吸链功能、复合物I酶活和ATP合成下降，而胞内ROS增加。同时我们也发现高表达mtAlaRs对线粒体功能有一定修复作用。研究结果进一步完善高血压发生发展的致病机制，并为母系遗传性高血压的防治提供新思路。