Cellular Pathophysiology of Acute Renal Failure

最近，由于对线粒体通透性转变机制的新见解和对线粒体细胞色素c释放在细胞凋亡中的作用的认识，线粒体功能障碍作为多种形式细胞损伤的介质重新引起了人们的兴趣。近端小管是缺血性和中毒性急性肾功能衰竭的主要损伤部位，其ATP的产生对线粒体功能障碍特别敏感，因为根据不同的节段，近端小管细胞在体内没有糖酵解或糖酵解很少。在当前资助期的研究中，我们已经发现了一种线粒体损伤，其特征是复合物I中与基质凝聚和部分失电相关的电子传递受到抑制，这是新分离的兔近端小管缺氧/再氧化过程中线粒体损伤的一种重要功能形式，在整体细胞恢复中起着关键作用。病变：a)先于线粒体通透性转变和细胞色素c释放；B)长期抑制小管的能量功能；c)非常容易被特定的柠檬酸循环代谢物预防和逆转，这些代谢物促进线粒体内ATP产生和电子传递的厌氧途径，或者在有氧条件下绕过复合物I阻断。线粒体病变既表现在缺氧/再氧作用下新鲜分离的小管中，也表现在体内缺血/再灌注过程中柠檬酸循环代谢物的超微结构变化和修饰上。我们的一般假设是，这种形式的线粒体功能障碍在肾缺血性损伤的结果中起着关键作用，并且线粒体功能障碍的改善将有利于这些损伤后细胞和组织的恢复。为了验证这一假设，并进一步研究其对理解和治疗缺血性急性肾功能衰竭的意义，我们提出了以下研究：1)表征在长时间缺氧/再氧化过程中能量不足的演变，以及在这些条件下保护底物改善能量不足的作用。2)更好地界定线粒体内膜异常的机制及其对能量缺陷的相对贡献。3)评估肾脏缺血/再灌注时病变表达及保护性代谢物在体内的作用。

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.