Study of renal diseases caused by podocyte injury

为了研究足细胞损伤和肾小球硬化（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（NEP 25），其中足细胞选择性损伤可以通过单次注射免疫毒素（LMB 2）诱导。注射LMB 2后，NEP 25小鼠表现出足细胞和其他肾小球细胞的损伤，并迅速发展成肾小球硬化。利用Cre-loxP系统标记足细胞谱系揭示了足细胞标记物下调后，足细胞逐渐丢失，而不转化为其他类型的细胞。使用嵌合体小鼠的研究显示，在一部分足细胞中引发的损伤扩散到其他足细胞，从而形成自我持续损伤的恶性循环。使用我们开发的其他转基因小鼠品系，我们证明了在FVB/N遗传背景的存在下，HIV-1基因，vpr和nef，协同损伤足细胞，在NEP 25和HIV-1模型中，足细胞的损伤被输尿管梗阻显著阻止，表明持续的肾小球滤过是足细胞进行性损伤和随后肾小球硬化发展的先决条件。我们还研究了突变型α-辅肌动蛋白-4的作用，其引起人类常染色体显性局灶节段性肾小球硬化（FSGS）。在足细胞中表达突变型α-肌动蛋白-4的转基因小鼠发展为缓慢进行性FSGS。通过α-Actinin-4与NEP 25小鼠杂交，我们证明突变的α-Actinin-4可以减轻LMB 2诱导的肾小球损伤。因此，我们证明在肾小球滤过存在的情况下，各种因素诱导的足细胞损伤自动扩散到肾小球内的其他足细胞和其他类型的细胞，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.