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

局灶性和节段性肾小球硬化（FSGS）是世界范围内肾病综合征和终末期肾病的主要原因。虽然这种重要疾病的发病机制尚不清楚，但肾小球足细胞在疾病发病机制中起着核心作用是明确的。在目前的提案中，我们证明了在啮齿类动物模型和人类肾脏活检样本中，FSGS足细胞中亲同性粘附分子sidekick-1 （sdk-1）显著上调。我们发现sdk-1与裂隙隔膜连接蛋白MAGI-1有强烈的相互作用，而MAGI-1已知与几个关键的足细胞蛋白相互作用，包括synaptopodin、a-actin -4、nephrin、JAM4和¿-catenin。此外，足细胞特异性过表达sdk-1的转基因小鼠会出现逐渐的蛋白尿、肾病和FSGS。同样，MAGI-1缺陷小鼠也会出现逐渐进行性蛋白尿和FSGS。这两种新型小鼠模型表型的相似性以及两种相关蛋白直接相互作用的事实表明，两种模型可能涉及相似的致病因素。我们假设FSGS足细胞中sdk-1的过度表达破坏了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。为了确认和确定相关机制，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基因敲除小鼠足细胞损伤及FSGS发生的易感性。通过这种方式，我们将证明sdk-1上调是FSGS发病机制的一个重要因素，并可能代表一个新的治疗靶点。公共卫生相关性：局灶性和节段性肾小球硬化是美国特发性肾病综合征的主要原因，也是世界范围内由原发性肾小球疾病引起的终末期肾脏疾病的最常见原因。在这个项目中，我们确定了一种新的机制，它对这种重要疾病的发病机制有很大的贡献，并可能导致发现新的潜在治疗靶点。

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.