Podocyte-specific Rap1 agonism for treatment of glomerular disease

项目概要/摘要： 蛋白尿肾病的发病率正在增加，全世界有超过5亿例病例。 在过去的二十年里，已经清楚的是，专门的肾脏细胞，称为足细胞，调节 肾过滤，并在所有形式的蛋白尿疾病中受损，而不管病因如何。尽管如此， 保护足细胞和减缓慢性肾病进展的靶向有效疗法， 完全缺乏。以前，我们报道过小GTIPRap 1调节基本的 通过在非活性GDP结合形式和活性GTP结合形式之间循环，在足细胞中进行生物学过程。 我们证明足细胞Rap 1的激活状态受许多上游因素控制， 正的和负的，其收敛以控制GTP结合形式和GDP结合形式的比率。的基本 人类家族性肾病综合征的出现强调了这些上游调节因子的作用 由这些基因中的几个突变引起，包括新发现的功能获得突变， 负Rap 1调节因子Rap 1GAP这些突变中的每一个都有一个共同点， 足细胞Rap 1-GTP耗竭。在目前的提案中，我们表明足细胞Rap 1-GTP水平 在包括糖尿病肾病（DKD）在内的人肾小球疾病中也减少。 增强足细胞Rap 1激活水平在遗传上或基因上保护足细胞， 短期伤害模型通过靶向足细胞特异性上游Rap 1调控途径， 开发新的Rap 1激动剂化合物，在足细胞中激活Rap 1，但在其他细胞类型中不激活Rap 1。 这种方法允许足细胞特异性药理学Rap 1激活，并避免了潜在的 全身毒性。目前拨款的目标是探索Rap 1的治疗潜力。 在足细胞疾病包括DKD中的激动剂。我们通过三个具体目标来实现这一目标：i）测试 增强的足细胞Rap 1激活是否会减轻慢性肾小球损伤， 诱导足细胞特异性组成型活性Rap 1转基因小鼠。ii）表征肾小球 表达双错义Rap 1GAP的新型Rap 1GAP基因敲入小鼠模型的表型 人类疾病相关变体，然后利用两种新小鼠模型来阐明特异性Rap 1 建立足细胞损伤易感性与保护的下游效应物。iii）合成 足细胞靶向的Rap 1激动剂化合物，并筛选其拯救足细胞损伤的能力。 转基因Rap 1-GTP缺陷型斑马鱼。将在小鼠中测试先导化合物的功效。 肾脏疾病模型，包括DKD。我们目前的先导化合物BT-529是Rap 1-Rap 1GAP 相互作用拮抗剂，诱导足细胞中Rap 1活化，但不诱导其他肾细胞中Rap 1活化， 显著保护培养的足细胞免受损伤。总的来说，这项工作为迫切需要的 肾脏疾病的新足细胞靶向疗法。

Project Summary/Abstract: The incidence of proteinuric kidney diseases are increasing with well over 500 million cases worldwide. Over the last two decades, it has become clear that specialized kidney cells, called podocytes, regulate kidney filtration and are injured in all forms of proteinuric diseases regardless of etiology. Despite this, targeted effective therapies that protect podocytes and slow chronic kidney disease progression are completely lacking. Previously, we reported that the small GTPase Rap1 regulates fundamental biological processes in podocytes by cycling between inactive GDP-bound and active GTP-bound forms. We demonstrate that the podocyte Rap1 activation state is controlled by many upstream factors, both positive and negative, that converge to control the ratio of GTP- and GDP-bound forms. The essential role of these upstream regulators is emphasized by the presence of human familial nephrotic syndrome caused by mutations to several of these genes, including newly identified gain of function mutations in the negative Rap1 regulator, Rap1GAP. Each of these mutations has in common that they cause relative depletion of podocyte Rap1-GTP. In the current proposal, we show that levels of podocyte Rap1-GTP are also diminished in human glomerular diseases including in diabetic kidney disease (DKD). Augmenting levels of podocyte Rap1 activation genetically or pharmacologically protects podocytes in short term injury models. By targeting podocyte-specific upstream Rap1 regulatory pathways, we are developing novel Rap1 agonist compounds that activate Rap1 in podocytes, but not in other cell types. Such an approach allows for podocyte-specific pharmacological Rap1 activation and avoids potential systemic toxicities. The goals of the current grant are to explore the therapeutic potential of Rap1 agonists in podocyte diseases including in DKD. We accomplish this via three specific aims: i) Test whether enhanced podocyte Rap1 activation will mitigate chronic glomerular injury utilizing novel inducible podocyte-specific constitutively active Rap1 transgenic mice. ii) Characterize the glomerular phenotype of a novel Rap1GAP knock-in mouse model that expresses a double missense Rap1GAP human disease-associated variant and then utilize both novel mouse models to elucidate specific Rap1 downstream effectors that establish podocyte injury susceptibility versus protection. iii) Synthesize podocyte-targeted Rap1 agonist compounds and screen their ability to rescue podocyte injury in transgenic Rap1-GTP deficient zebrafish. The efficacy of lead compounds will be tested in mouse models of kidney disease including in DKD. Our current lead compound, BT-529, a Rap1-Rap1GAP interaction antagonist, induces Rap1 activation in podocytes but not in other kidney cells and dramatically protects cultured podocytes from injury. Overall, this work sets the stage for urgently needed new podocyte-targeted therapies for kidney diseases.