Reactive oxygen species and diabetic nephropathy

高血糖诱导的线粒体活性氧簇(ROS)的过量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到TIM23复合体的膜锚，参与了线粒体靶向前蛋白进入线粒体基质的过程。这一过程依赖于线粒体Hsp70的内膜电位(Δψ)和ATPase结构域上的三磷酸腺苷的降解。以日本血凝病毒(HVJ)为载体，经尾静脉注入链脲佐菌素(STZ)诱导的糖尿病小鼠CD-1模型，每周一次尾静脉注射日本血凝病毒(HVJ)-囊膜载体pcDNA3.1。注射后8周，基因载体可减轻蛋白尿和肾脏肥大，抑制肾细胞增殖和凋亡，抑制超氧化物生成。用人近端肾小管(HK2)细胞进行的体外实验表明，Tim44的基因传递逆转了高糖诱导的代谢和细胞异常，如ROS产生增加，ATP含量增加，内膜电位改变，细胞增殖和凋亡增加。通过siRNA和表达载体Tim44的表达，发现Tim44能促进超氧化物歧化酶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维持线粒体的功能，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.