Study of renal diseases caused by podocyte injury

为了研究足细胞损伤与肾小球硬化(慢性肾功能衰竭的标志)之间的因果关系，我们开发了一种转基因小鼠系(NEP25)，在该系中，一次注射免疫毒素(LMB2)可以诱导足细胞选择性损伤。注射LMB2后，NEP25小鼠表现为足细胞等肾小球细胞损伤，并迅速发展为肾小球硬化。利用Cre-loxP系统对足细胞谱系的标记显示，随着足细胞标志物的下调，足细胞逐渐丢失，不会转化为其他类型的细胞。用嵌合小鼠进行的研究表明，从足细胞的一部分开始的损伤被扩散到其他足细胞，从而形成一个自持性损伤的恶性循环。使用我们建立的其他转基因小鼠系，我们证明了在fvb/N遗传背景、HIV-1基因、vpr和nef的存在下，足细胞协同损伤，导致类似于HIV-1相关性肾病的FSGS崩溃。在Np25和HIV-1模型中，输尿管梗阻都能显著防止足细胞的损伤，表明持续的肾小球滤过是足细胞进行性损伤和随后的肾小球硬化发展的先决条件。我们还研究了突变的α-actinin-4，导致人类常染色体显性遗传局灶节段性肾小球硬化(FSGS)。在足细胞中表达突变α-肌动蛋白-4的转基因小鼠进展缓慢。通过将α-Actinin-4与NEP25小鼠杂交，我们证明了突变的α-Actinin-4可以减轻LMB2诱导的肾小球损伤。因此，我们证明了在肾小球滤过存在的情况下，各种因素引起的足细胞损伤会自动扩散到肾小球内的其他足细胞和细胞类型，从而导致肾小球硬化。

To investigate causal relationship between podocyte injury and glomerular sclerosis, a hallmark of chronic renal failure, we developed a transgenic mouse line (NEP25) in which podocyte-selective injury can be induced by a single injection of immunotoxin (LMB2). After LMB2 injection, NEP25 mice manifested injury of podocytes and other glomerular cells and rapidly developed glomerular sclerosis. Labeling of the podocyte-lineage utilizing the Cre-loxP system revealed that following downregulation of podocyte markers, podocytes were progressively lost, without transforming into other types of cell. Studies using chimeric mice revealed that injury initiated in a portion of podocytes was spread to other podocytes, thus forming a vicious cycle of self-perpetuating injury.Using other transgenic mouse lines that we developed, we demonstrated that in the presence of FVB/N genetic background, HIV-1 genes, vpr and nef, synergistically damage podocytes, leading to collapsing FSGS similar to HIV-1 associated nephropathy of humans.In both NEP25 and HIV-1 models, damage of podocytes was prevented remarkably by ureteral obstruction, indicating that continued glomerular filtration is a prerequisite for progressive injury of podocytes, and subsequent development of glomerular sclerosis.We also studied the role of mutant α-Actinin-4, which causes autosomal dominant focal segmental glomerular sclerosis (FSGS) in humans. Transgenic mice expressing mutant α-Actinin-4 in podocytes developed slowly progressive FSGS. By crossing α-Actinin-4 with NEP25 mice, we demonstrated that mutant α-Actinin-4 attenuated glomerular damage induced by LMB2.Thus, we demonstrated that in the presence of glomerular filtration, podocyte damage induced by various factors is automatically spread to other podocytes and types of cell within the glomerulus, which leads to glomerular sclerosis.