Sidekick-1 Upregulation in Podocytes Induces FSGS by Disrupting MAGI-1 Function

描述（由申请人提供）：局灶性节段性肾小球硬化（FSGS）是全球肾病综合征和终末期肾病的主要原因。尽管对这一重要疾病的发病机制知之甚少，但很明显肾小球足细胞在疾病发病机制中起着核心作用。在目前的建议中，我们证明了在啮齿动物模型和人类肾脏活检样品中，FSGS中的足细胞中的嗜同性粘附分子sidekick-1（sdk-1）显著上调。我们发现sdk-1与狭缝隔膜连接蛋白MAGI-1强烈相互作用，MAGI-1已知与几种关键的足细胞蛋白相互作用，包括synaptopodin，α-辅肌动蛋白-4，nephrin，JAM 4和<$-catenin。此外，足细胞特异性过表达sdk-1的转基因小鼠发生渐进性蛋白尿、肾病和FSGS。类似地，MAGI-1缺陷型小鼠也逐渐发展为进行性蛋白尿和FSGS。这两种新型小鼠模型的表型之间的相似性以及两种相关蛋白质直接相互作用的事实表明，两种模型中可能涉及相似的致病因素。我们推测，FSGS足细胞中sdk-1的过表达破坏了MAGI-1稳定足细胞结构的能力，随着时间的推移，这导致肾小球硬化的发展。为了证实和鉴定所涉及的机制，我们提出了三个具体目标：1）确定sdk-1的过表达如何影响MAGI-1与其他关键足细胞蛋白的结合。2)表征MAGI-1缺失小鼠的肾脏表型，并将其与足细胞特异性sdk-1过表达模型的表型进行比较。3)检测sdk-1基因敲除小鼠对足细胞损伤和FSGS发生的易感性。通过这种方式，我们将证明sdk-1上调是FSGS发病机制的重要因素，并可能代表一种新的治疗靶点。公共卫生相关性：局灶性节段性肾小球硬化是美国特发性肾病综合征的主要原因，也是全球原发性肾小球疾病引起终末期肾病的最常见原因。在这个项目中，我们确定了一个新的机制，大大有助于这一重要疾病的发病机制，并可能导致新的潜在治疗靶点的确定。

DESCRIPTION (provided by applicant): Focal and segmental glomerulosclerosis (FSGS) is a leading cause of nephrotic syndrome and end-stage renal disease worldwide. Although the mechanisms underlying this important disease are poorly understood, it is clear that the glomerular podocyte plays a central role in disease pathogenesis. In the current proposal, we demonstrate that the homophilic adhesion molecule sidekick-1 (sdk-1) is dramatically upregulated in podocytes in FSGS both in rodent models and in human kidney biopsy samples. We show that sdk-1 strongly interacts with the slit diaphragm linker protein MAGI-1, which is already known to interact with several critical podocyte proteins including synaptopodin, a-actinin-4, nephrin, JAM4, and ¿-catenin. Furthermore, transgenic mice with podocyte-specific overexpression of sdk-1 develop gradual proteinuria, nephrosis, and FSGS. Similarly, MAGI-1 deficient mice also develop gradually progressive proteinuria and FSGS. The similarities between the phenotypes of these two novel mouse models and the fact that the two involved proteins directly interact suggest that similar pathogenic factors may be involved in both models. We hypothesize that the overexpression of sdk-1 in podocytes in FSGS disrupts the ability of MAGI-1 to stabilize podocyte architecture and that over time this leads to the development of glomerular sclerosis. To confirm and identify the involved mechanisms, we propose three specific aims: 1) To determine how the overexpression of sdk-1 affects the binding of MAGI-1 to other critical podocyte proteins. 2) To characterize the renal phenotype of MAGI-1 null mice and to compare it to the phenotype of the podocyte-specific sdk-1 overexpression model. 3) To test the susceptibility of sdk-1 knockout mice to podocyte injury and to the development of FSGS. In this way, we will demonstrate that sdk-1 upregulation is an important factor contributing to the pathogenesis of FSGS and could represent a novel therapeutic target. PUBLIC HEALTH RELEVANCE: Focal and segmental glomerulosclerosis is the leading cause of idiopathic nephrotic syndrome in the United States and the most common cause of end stage renal disease caused by primary glomerular disease worldwide. In this project, we identify a novel mechanism that contributes greatly to the pathogenesis of this important disease and may lead to the identification of novel potential therapeutic targets.