Role of mTORC1 pathway for podocyte injury in diabetic nephropathy

描述（由申请人提供）：糖尿病肾病（DN）是1型和2型糖尿病最致命的并发症之一。DN的破坏性作用首先表现为肾小球病的主要形式，并进展为肾小球硬化，最终导致终末期肾病（ESRD）。近年来的研究表明足细胞的损伤在DN的发生发展中起着重要作用。我们已经确定了在糖尿病足细胞中雷帕霉素复合物1（mTORC 1）的哺乳动物靶蛋白的异常激活是足细胞损伤和DN发展的关键决定因素。mTORC1激酶复合物的功能是感知营养物质的可用性。然而，糖尿病足细胞中mTORC1异常激活的分子机制仍然难以捉摸。我们发现脑酸可溶性蛋白1（BASP 1）是一种有效的mTORC 1激活剂。先前的研究已经报道了BASP1在足细胞中的表达和在糖尿病患者的肾脏中的升高。重要的是，我们发现BASP 1的表达在1型和2型糖尿病动物的足细胞中特异性增强。此外，我们的生化数据表明，BASP 1过表达显着增强mTORC 1活性，而BASP 1敲低显着减弱mTORC 1活性在多个细胞系，包括足细胞。有趣的是，BASP 1敲低主要抑制营养素诱导的mTORC 1激活，但不抑制生长因子诱导的mTORC 1激活，表明BASP 1作为一种特异性mTORC 1激活剂响应营养素，并在糖尿病足细胞中的mTORC 1激活中发挥关键作用。为了更详细地探索这种可能性，我们建议阐明糖尿病条件下足细胞中BASP 1表达增强的机制，并确定BASP 1如何支持营养诱导的mTORC 1激活。最后，我们将使用小鼠模型评估BASP 1和营养介导的mTORC 1激活在DN发展中的作用，其中BASP 1和mTORC 1介导的营养感应途径分别通过足细胞特异性消融BASP 1和p18基因而被阻断。这项研究的完成有望揭示糖尿病足细胞中mTORC1异常激活的新分子机制，并为未来减弱糖尿病足细胞中mTORC1信号传导和DN进展的治疗提供潜在的药理学靶点。

DESCRIPTION (provided by applicant): Diabetic nephropathy (DN) is among the most lethal complications of type 1 and type 2 diabetes. The devastating effect of DN presents itself first as a major form of glomerulopathy and progresses to glomerulosclerosis, and ultimately leads to end-stage renal disease (ESRD). Recent investigations have revealed that injuries to podocytes play a critical role in the development of DN. We have identified aberrant activation of mammalian target of rapamycin complex 1 (mTORC1) in diabetic podocytes as a critical determinant for podocyte injury and the development of DN. The mTORC1 kinase complex functions to sense nutrient availability. However, the molecular mechanisms underlying the aberrant activation of mTORC1 in diabetic podocytes remain elusive. We discovered brain acid soluble protein1 (BASP1) as a potent mTORC1 activator. Previous studies have reported BASP1 expression in podocytes and elevated in the kidneys of diabetic patients. Importantly, we found that BASP1 expression is specifically enhanced in the podocytes of both type 1 and type 2 diabetic animals. Further, our biochemical data showed that BASP1 overexpression dramatically enhanced mTORC1 activity, while BASP1 knockdown significantly attenuated mTORC1 activity in multiple cell lines including podocytes. Interestingly, BASP1 knockdown dominantly inhibits nutrient- but not growth factor-induced mTORC1 activation, suggesting that BASP1 functions as a specific mTORC1 activator in response to nutrients and plays a key role in the activation of mTORC1 in diabetic podocytes. To explore this possibility in greater detail, we propose to elucidate the mechanisms by which BASP1 expression is enhanced in podocytes under diabetic conditions and determine how BASP1 supports nutrient-induced mTORC1 activation. Finally, we will evaluate the roles of BASP1 and nutrient-mediated mTORC1 activation in the development of DN using mouse models where BASP1 and the mTORC1- mediated nutrient sensing pathway are blocked through the podocyte-specific ablation of the BASP1 and p18 genes, respectively. Completion of this study promises to reveal novel molecular mechanisms underlying aberrant activation of mTORC1 in diabetic podocytes and provide potential pharmacologic targets for future therapies that attenuate mTORC1 signaling in diabetic podocytes and in the progression of DN.