Role of branched-chain amino acid catabolism in the proximal tubule

急性肾损伤（阿基）本身和作为急性肾损伤的主要风险因素引起显著的发病率和死亡率。 慢性肾脏病（CKD）的发展。近端小管（PT）是阿基的主要靶点， 导致损伤的PT细胞代谢的深刻变化。虽然未受伤的PT细胞利用脂肪酸 氧化（FAO），TCA循环和氧化磷酸化产生ATP，在损伤中，这些过程是 严重下调，糖酵解补偿不足。FAO的实验性上调可以 部分挽救阿基，但这些策略迄今尚未转化为临床应用。此外，钥匙丢失 FAO调节剂PPARa在基线时不会导致PT损伤，这表明其他重要的PT代谢 路径仍有待描述。支链氨基酸（BCAA;缬氨酸，亮氨酸，异亮氨酸）是 通过肾脏分解代谢产生TCA循环中间体。我们最近报道了编码支链氨基酸的基因 在阿基和CKD的小鼠模型中，以及在人类CKD中， 由Krüppel样因子6（KLF 6）的转录抑制驱动。在体外，这导致ATP产量减少， 而BCAA催化剂的活化增加线粒体呼吸。然而， 在阿基或CKD中下调的BCAA催化剂尚未被探索。BCAA损失的潜在影响 代谢障碍可能包括ATP生产的损失，以及未分解代谢的BCAA的有毒或有害积累。 特别地，亮氨酸是雷帕霉素（mTOR）复合物1（mTORC 1）的机械靶点的有效激活剂。 信号传导，这可能下调FAO，但这尚未在肾脏中得到证实。这项建议会 通过检验我们的核心假设，即PT的转录抑制， 肾毒性阿基中的BCAA催化剂通过ATP产生的损失、mTORC 1信号传导的激活、 对粮农组织的压制。这一假设将在两个特定的目标进行测试，以：1）阐明机制， 其破坏BCAA催化剂通过mTORC 1活化改变FAO;和2）确定 BCAA会加重阿基的严重程度并转变为纤维化。这些研究将增进对 BCAA在肾脏中分解代谢的重要性，肾脏高度活跃，但目前尚未探索。此外，委员会认为， BCAA催化剂与mTORC 1信号传导和FAO的关键细胞通路之间的联系，所有这些 是潜在的药物，将允许设计改进的阿基治疗剂。长期目标是 全面定义肾毒性和非肾毒性阿基中的PT代谢改变。

Acute kidney injury (AKI) causes significant morbidity and mortality, both of itself and as a major risk factor for development of chronic kidney disease (CKD). The proximal tubule (PT) is the primary target of AKI, triggering profound changes in PT cellular metabolism that contribute to injury. Whilst uninjured PT cells utilize fatty acid oxidation (FAO), TCA cycle and oxidative phosphorylation to generate ATP, in injury, these processes are severely downregulated, with inadequate compensation from glycolysis. Experimental upregulation of FAO can partially rescue AKI, but these strategies have so far not translated to clinical use. Furthermore, loss of the key FAO regulator PPARa does not result in PT injury at baseline, suggesting that other important PT metabolic pathways remain to be described. Branched chain amino acids (BCAA; valine, leucine, isoleucine) are catabolized by the kidney to generate TCA cycle intermediates. We recently reported that genes encoding BCAA catabolic enzymes are strongly downregulated in mouse models of AKI and CKD, and in human CKD, likely driven by transcriptional repression by Krüppel-like factor 6 (KLF6). In vitro, this led to decreased ATP production, whilst activation of BCAA catabolism increased mitochondrial respiration. However, the significance of downregulated BCAA catabolism in AKI or CKD has not been explored. Potential effects of loss of BCAA catabolism may include loss of ATP production, and toxic or detrimental accumulation of uncatabolized BCAA. In particular, leucine is a potent activator of mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) signaling, which may downregulate FAO, but this has not been demonstrated in kidney. This proposal will address these current gaps in the field by testing our central hypothesis that transcriptional suppression of PT BCAA catabolism in nephrotoxic AKI is detrimental via loss of ATP production, activation of mTORC1 signaling, and suppression of FAO. This hypothesis will be tested in two specific aims, to: 1) elucidate the mechanism by which disrupted BCAA catabolism alters FAO through mTORC1 activation; and 2) determine the contribution of BCAA catabolism to the severity of AKI and transition to fibrosis. These studies will enhance understanding of the significance of BCAA catabolism in the kidney, which is highly active yet currently unexplored. Furthermore, the link between BCAA catabolism and the critical cellular pathways of mTORC1 signaling and FAO, all of which are potentially druggable, will allow design of improved therapeutics for AKI. The long-term goal is to comprehensively define PT metabolic alterations in nephrotoxic and non-nephrotoxic AKI.