Novel Targets for the Treatment of Diabetic Kidney Disease

 描述（由申请人提供）： 糖尿病肾病（DN）是美国终末期肾病（ESKD）最常见的原因。因此，许多努力致力于了解糖尿病肾病中促进肾小球损伤的机制。大量证据表明，肾小球足细胞在DN的发病机制中起着关键作用。足细胞数量减少是患有糖尿病肾病的动物和人类的特征。由于足细胞是具有很少增殖潜力的终末分化细胞，因此丢失的足细胞不能被有效地替代，从而导致肾小球簇的不稳定并促进疾病进展。虽然足细胞丢失的病因可能是多因素的，但细胞凋亡是糖尿病肾病的突出特征，也是DN足细胞丢失的重要原因。细胞凋亡的关键调节因子是细胞内钙。事实上，糖尿病肾病发病机制中涉及的大量信号传导途径增加了细胞内钙水平。增强的细胞内钙水平激活下游信号传导途径，包括钙激活磷酸酶钙调神经磷酸酶（CN）。我们的实验室已经发现，增加胞浆钙水平和刺激CN活性的受体系统通过CN依赖性激活NFAT（活化T细胞的核因子）介导的机制促进足细胞凋亡。CN信号传导的重要基因靶标是瞬时受体电位阳离子通道C6（TRPC 6）。这些观察结果似乎与DN相关，因为：1。TRPC 6在1型糖尿病小鼠模型（秋田小鼠）中上调，2. CN抑制剂FK 506减弱秋田小鼠足细胞凋亡，3.缺乏TRPC 6的秋田小鼠的白蛋白尿减少。基于这些观察，我们假设CN通过涉及TRPC 6上调的机制在DN中起关键作用。为了研究这一假设，提出了3个具体目标。在具体目标#1中，我们将研究NFAT同种型在培养的足细胞中的胞质溶胶和细胞核之间的动态穿梭，这取决于CN磷酸酶和NFAT激酶的相对活性。这些研究的目的是确定用于调节肾小球疾病中的CN-NFAT信号传导的新策略。在具体目标#2中，我们将确定TRPC 6的缺乏是否抑制足细胞凋亡并减少缺乏TRPC 6的秋田小鼠的肾小球损伤。在具体目标#3中，我们将确定CN的足细胞特异性缺失是否减少DN中的足细胞凋亡，并进而改善秋田小鼠的肾损伤。拟议研究的长期目标是确定治疗人类DN的新治疗靶点。

 DESCRIPTION (provided by applicant): Diabetic nephropathy (DN) is the most common cause of end stage kidney disease (ESKD) in the United States. As a result, much effort has been devoted to understanding the mechanisms that promote glomerular damage in diabetic kidney disease. A large body of evidence suggests that glomerular podocytes play a pivotal role in the pathogenesis of DN. A reduced number of podocytes is a characteristic feature of both animals and humans with diabetic kidney disease. Because podocytes are terminally differentiated cells with little potential for proliferation, podocytes that are lost cannot be effectively replaced causing instability of glomerular tuft and promoting disease progression. While the etiology of podocyte loss is likely multifactorial, apoptosis is a prominent feature of diabetic kidney disease and is an important cause of podocyte loss in DN. A key regulator of apoptosis is intracellular calcium. Indeed, a large number of signaling pathways implicated in the pathogenesis of diabetic kidney disease increase intracellular calcium levels. Enhanced intracellular calcium levels activate downstream signaling pathways including the calcium activated phosphatase calcineurin (CN). Our lab has found that receptor systems that increase cytosolic calcium levels and stimulate CN activity promote podocyte apoptosis by mechanisms that are mediated by CN-dependent activation of NFAT (nuclear factor of activated T cells). An important gene target of CN signaling is the transient receptor potential cation channel C6 (TRPC6). These observations appear relevant to DN because: 1. TRPC6 is upregulated in a mouse model of type 1 diabetes (Akita mice), 2. The CN inhibitor FK506 attenuates podocyte apoptosis in Akita mice, and 3. Albuminuria is reduced in Akita mice lacking TRPC6. Based on these observations, we hypothesized that CN plays a key role in DN through mechanisms that involve up-regulation of TRPC6. To investigate this hypothesis, 3 specific aims are proposed. In specific aim #1, we will investigate the dynamic shuttling of NFAT isoforms between the cytosol and nucleus in cultured podocytes, which is dependent on the relative activity of CN phosphatases and NFAT kinases. The goal of these studies is to identify novel strategies for modulating CN- NFAT signaling in glomerular diseases. In specific aim #2, we will determine if the absence of TRPC6 inhibits podocyte apoptosis and reduces glomerular injury in Akita mice lacking TRPC6. In specific aim #3, we will determine if podocyte specific deletion of CN decreases podocyte apoptosis in DN and, in turn, ameliorates kidney injury in Akita mice. The long-term goal of the proposed studies is to identify novel therapeutic targets for the treatment of DN in humans.