Cellular Pathophysiology of Acute Renal Failure

最近，随着对线粒体通透性转换机制的新认识和对线粒体细胞色素c释放在细胞凋亡中作用的认识，人们对线粒体功能障碍作为不同形式细胞损伤的中介重新产生了兴趣。近端肾小管是急性肾功能衰竭的主要损伤部位，近端肾小管上皮细胞产生的ATP对线粒体功能障碍特别敏感，因为根据节段的不同，体内近端肾小管细胞中不存在或仅有极少量的糖酵解。在本资助期间的研究中，我们发现了一种线粒体损伤，其特征是与基质凝结和部分失能相关的复合体I中的电子传递受阻，是新鲜分离的兔近端小管缺氧/复氧过程中线粒体损伤的一种重要形式，该损伤在整体细胞恢复中发挥重要作用。损伤：a)先于线粒体通透性转换和细胞色素c的释放；b)持续抑制本可存活的小管的能量功能；c)特定的柠檬酸循环代谢物高度易于预防和逆转，这些代谢物促进线粒体内ATP产生和电子传递的无氧途径，或在有氧条件下绕过复杂的I阻滞剂。线粒体损伤既表达于新鲜分离的缺氧/复氧肾小管，也表达于体内缺血/再灌流过程中的超微结构变化和柠檬酸循环代谢产物的修饰。我们的一般假设是，这种形式的线粒体功能障碍在肾脏缺血损伤的结局中起着关键作用，其改善将有益于细胞和组织从这些损伤中恢复。为了验证这一假说，并进一步研究其对认识和治疗缺血性急性肾功能衰竭的意义，我们建议进行以下研究：1)表征在长时间缺氧/复氧过程中能量缺乏的特征，以及保护性底物在这些条件下改善能量缺乏的效果。2)更好地确定损伤过程中线粒体内膜异常的机制及其对能量缺乏的相对贡献。3)评价肾缺血再灌流损伤的表达及保护性代谢产物的保护作用。

Recently there has been a renewal of interest in mitochondrial dysfunction as a mediator of diverse forms of cell injury as a result of new insights into the mechanism for the mitochondrial permeability transition and recognition of the role of mitochondrial cytochrome c release in apoptosis. ATP production in the proximal tubule, a major site of injury during ischemic and toxic forms of acute renal failure, is especially sensitive to mitochondrial dysfunction because, depending on the segment, glcolysis is absent or minimal in proximal tubule cells in vivo. In studies during the present funding period, we have identified a mitochondrial lesion characterized by inhibition of electron transport in complex I associated with matrix condensation and partial deenergization as a functionally important form of mitochondrial injury during hypoxia/reoxygenation of freshly isolated rabbit proximal tubules that play a pivtal role in overall cellular recovery. The lesion: a) precedes the mitochondrial permeability transition and cytochrome c release; b) depresses energetic function of otherwise viable tubules for sustained periods; and c) is highly amenable to prevention and reversal by specific citric acid cycle metabolites that promote anaerobic pathways of intramitochondrial ATP production and electron transport or, under aerobic conditions, bypass the complex I block. The mitochondrial lesion is expressed both in freshly isolated tubules subjected to hypoxia/reoxygeation, and based on ultrastructural changes and modification by citric acid cycle metabolites, during ischemia/reperfusion in vivo. Our general hypothesis is that this form of mitochondrial dysfunction plays a critical role in the outcome of ischemic insults to the kidney and that its amelioration will beneficially impact on cell and tissue recovery from these insults. To test this hypothesis and further investigate its implications for understanding and treating ischemic acute renal failure we propose studies to: 1) Characterize the energetic deficit as it evolves during extended durations of hypoxia/reoxygenation and the effects of protective substrates to ameliorate it under those conditions. 2) Better define the mechanisms for the mitochondrial inner membrane abnormalities during the insult and their relative contributions to the energetic deficit. 3) Assess expression of the lesion and test efficacy of protective metabolites during ischemia/reperfusion of the kidney in vivo.