Reactive oxygen species and diabetic nephropathy

高血糖诱导的线粒体活性氧（ROS）过度产生已成为糖尿病血管并发症的主要因素。哺乳动物线粒体内膜转位酶44 （Tim44）在糖尿病小鼠肾脏中表达上调。Tim44作为mtHsp70 - TIM23复合物的膜锚点，参与线粒体靶向前蛋白进入线粒体基质。该过程依赖于内膜电位（Δψ）和mtHsp70的ATP酶结构域上的ATP水解。将日本血凝病毒（HVJ）包膜载体携带含有Tim44全长cDNA和对照质粒的pcDNA3.1质粒，每周从尾静脉注射到未切除的链脲霉素诱导的糖尿病CD-1小鼠体内。基因传递减轻了注射后8周的蛋白尿和肾肥大，抑制了肾细胞的增殖和凋亡，抑制了超氧化物的产生。在体外实验中，利用人近端小管（HK2）细胞，发现Tim44基因传递逆转了高糖诱导的代谢和细胞异常，如ROS生成增强、ATP含量增加、内膜电位改变、细胞增殖和凋亡增加。用siRNA和Tim44表达载体转染后发现，Tim44可促进超氧化物歧化酶（SOD）和谷胱甘肽过氧化物酶等抗氧化酶进入线粒体。因此，Tim44的基因传递似乎有利于线粒体功能的维持，是糖尿病肾病的一种新的治疗方法。

Hyperglycemia-induced overproduction of mitochondrial reactive oxygen species (ROS) has emerged as a major player in diabetic vascular complications. Mammalian translocase of inner mitochondrial membrane 44 (Tim44) was identified by up-regulation in diabetic mouse kidneys. Tim44 functions as a membrane anchor of mtHsp70 to TIM23 complex and involves in the import of mitochondria-targeted preproteins into mitochondrial matrix. The process is dependent on inner membrane potential (Δψ) and ATP hydrolysis on ATPase domain of mtHsp70. Hemagglutination virus of Japan (HVJ)-envelope vector carrying pcDNA3.1 plasmid containing the full length cDNA of Tim44 and control plasmid were weekly injected from tail vein into uninephrectomized streptozotocin-induced diabetic CD-1 mice. The gene delivery alleviated proteinuria and renal hypertrophy at 8 weeks after the injection and inhibited renal cell proliferation and apoptosis, and suppressed superoxide production. In vitro experiments, using human proximal tubular (HK2) cells, revealed that the gene delivery of Tim44 reversed high glucose induced metabolic and cellular abnormalities such as, enhanced ROS production, increased ATP contents, alterations in inner membrane potential, increased cell proliferation and apoptosis. Transfection with siRNA and expressing vector of Tim44 revealed that Tim44 facilitates import of anti-oxidative enzymes such as superoxide dismutase (SOD) and glutathione peroxidase into mitochondria. The gene delivery of Tim44 thus seems to be beneficial for the maintenance of mitochondrial function and is a novel therapeutic approach for diabetic nephropathy.