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

急性肾损伤(AKI)本身和作为一个主要的危险因素，都会导致显著的发病率和死亡率。 慢性肾脏疾病(CKD)的发展。近端小管(PT)是AKI的主要靶点，触发 导致损伤的PT细胞代谢的深刻变化。而未受损伤的PT细胞利用脂肪酸 氧化(FAO)、TCA循环和氧化磷酸化生成ATP，在伤害中，这些过程是 严重下调，糖酵解补偿不足。粮农组织的实验性上调可以 部分挽救AKI，但这些策略到目前为止还没有转化为临床应用。此外，钥匙的丢失 粮农组织调节剂PPARa在基线时不会导致PT损伤，这表明其他重要的PT代谢 具体途径仍有待描述。支链氨基酸(支链氨基酸；缬氨酸、亮氨酸、异亮氨酸)是 经肾脏分解生成三氯乙酸循环中间体。我们最近报道了编码支链氨基酸的基因 在AKI和CKD小鼠模型中，分解代谢酶强烈下调，而在人类CKD中，很可能 由Krüppel样因子6(KLF6)转录抑制所驱动。在体外，这导致了ATP产量的下降， 而支链氨基酸分解代谢的激活增加了线粒体的呼吸。然而，它的意义在于 AKI或CKD中下调的支链氨基酸分解代谢尚未被探索。支行氨基酸缺失的潜在影响 分解代谢可能包括失去三磷酸腺苷的产生，以及有毒或有害地积累未分解的支链氨基酸。 特别是，亮氨酸是雷帕霉素(MTOR)复合体1(MTORC1)机械靶点的有效激活剂 信号，这可能下调粮农组织，但这还没有在肾脏中表现出来。这项提议将 通过测试我们的中心假设，即转录抑制PT，来解决目前该领域的这些差距 肾毒性AKI中支链氨基酸的分解代谢通过失去ATP的产生，激活mTORC1信号， 和对粮农组织的压制。这一假说将在两个特定的目标中进行检验，以：1)通过以下方式阐明机制 扰乱支链氨基酸分解代谢通过激活mTORC1改变粮农组织；以及2)确定 BCAA分解代谢与AKI的严重程度和向纤维化的过渡。这些研究将增进对 支链氨基酸在肾脏中分解代谢的意义，目前非常活跃，但尚不清楚。此外， 支链氨基酸分解代谢与mTORC1信号的关键细胞通路和FAO之间的联系，所有这些 可能是可下药的，将允许设计改进的治疗AKI的方法。长期目标是 全面确定肾毒性和非肾毒性AKI患者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.