Role of mTORC1 pathway for podocyte injury in diabetic nephropathy

描述(申请人提供)：糖尿病肾病是1型和2型糖尿病最致命的并发症之一。糖尿病肾病的破坏性影响首先表现为肾小球病变的一种主要形式，然后发展为肾小球硬化，最终导致终末期肾病(ESRD)。最近的研究表明，足细胞的损伤在糖尿病肾病的发展中起着至关重要的作用。我们发现糖尿病足细胞中哺乳动物雷帕霉素复合体靶点1(MTORC1)的异常激活是糖尿病足细胞损伤和糖尿病肾病发生的关键决定因素。MTORC1激酶复合体的功能是感知营养的可用性。然而，糖尿病足细胞中mTORC1异常激活的分子机制仍然不清楚。我们发现脑酸溶蛋白1(BASP1)是一种有效的mTORC1激活剂。以前的研究已经报道了BASP1在足细胞中的表达，并在糖尿病患者的肾脏中升高。重要的是，我们发现BASP1在1型和2型糖尿病动物的足细胞中的表达都特异性地增强。此外，我们的生化数据显示，在包括足细胞在内的多个细胞系中，BASP1的过表达显著增强了mTORC1的活性，而BASP1的敲除显著降低了mTORC1的活性。有趣的是，BASP1基因敲除主要抑制营养诱导的mTORC1激活，但不抑制生长因子诱导的mTORC1激活，这表明BASP1作为营养反应的特异性mTORC1激活因子，在糖尿病足细胞mTORC1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BASP1在足细胞中表达增强的机制，并确定BASP1如何支持营养诱导的mTORC1激活。最后，我们将使用小鼠模型评估BASP1和营养介导的mTORC1激活在糖尿病肾病发展中的作用。在小鼠模型中，BASP1和mTORC1介导的营养传感通路分别通过足细胞特异性的BASP1和p18基因的去除而被阻断。这项研究的完成有望揭示糖尿病足细胞mTORC1异常激活的新的分子机制，并为未来减弱糖尿病足细胞中的mTORC1信号和糖尿病肾病的进展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.