Background The hallmark of podocytopathies, such as FSGS, is podocyte injury resulting in proteinuria. Transient receptor potential channel C6 (TRPC6) is a calcium-conducting ion channel expressed at the slit diaphragm. TRPC6 gain-of-function mutations and glomerular TRPC6 overexpression are associated with proteinuria. However, the pathways linking TRPC6 to podocyte injury, which is characterized by loss of the slit diaphragm protein nephrin, activation of several intracellular pathways (including calcineurin-NFAT signaling), and cytoskeletal rearrangement, remain elusive.

Methods We tested whether the calcium-dependent protease calpain-1 mediates TRPC6-dependent podocyte injury in human and experimental FSGS and cultured podocytes.

Results Compared with kidneys of healthy controls, kidneys of patients with FSGS had increased TRPC6 expression, increased calpain and calcineurin activity, and reduced expression of the calpain target Talin-1, which links the actin cytoskeleton to integrins and is critical for podocyte cytoskeletal stability. In a rat model of human FSGS, increased glomerular and urinary calpain activity associated with reduced Talin-1 abundance, enhanced calcineurin activity, and increased proteinuria. Treatment with the calpain inhibitor calpeptin prevented these effects. In cultured podocytes, pharmacologic stimulation of TRPC6-dependent calcium influx increased calpain-1 and calcineurin activity and reduced Talin-1 expression, and knockdown of TRPC6 or calpain-1 prevented these effects.

Conclusions We elucidated a novel mechanism that links TRPC6 activity to calpain-1 activation and through Talin-1 loss and possibly, calcineurin activation, the podocyte injury characterizing FSGS. Therefore, calpain-1 and/or TRPC6 inhibition could be future therapeutic options to treat patients with FSGS or other podocytopathies.

背景足细胞病变（例如FSGS）的标志是足细胞损伤导致蛋白尿。瞬态受体电位通道C6（TRPC6）是在缝隙隔膜处表达的钙传导离子通道。TRPC6功能获得性突变和肾小球TRPC6过表达与蛋白尿有关。然而，将TRPC6与足细胞损伤相关的途径（其特征是缝隙隔膜蛋白nephrin的丢失，几种细胞内途径的激活（包括钙调神经磷酸酶-NFAT信号传导）以及细胞骨架重排）仍然难以捉摸。

方法我们测试了钙依赖性蛋白酶calpain-1是否在人和实验性FSGS和培养的足细胞中介导了TRPC6依赖性足细胞损伤。

结果与健康对照者的肾脏相比，FSGS患者的肾脏具有增加的TRPC6表达，增加的钙蛋白酶和钙调神经磷酸酶活性，并降低了钙蛋白酶靶蛋白Talin-1的表达，后者将肌动蛋白细胞骨架与整联蛋白联系在一起，对足细胞的细胞骨架稳定性至关重要。在人类FSGS大鼠模型中，肾小球和尿钙蛋白酶活性增加与Talin-1丰度降低，钙调神经磷酸酶活性增加和蛋白尿增加有关。用钙蛋白酶抑制剂钙肽蛋白治疗可预防这些作用。在培养的足细胞中，药理刺激TRPC6依赖性钙内流会增加calpain-1和钙调神经磷酸酶的活性并降低Talin-1的表达，而敲低TRPC6或calpain-1可以阻止这些作用。

结论我们阐明了一种新的机制，该机制将TRPC6活性与calpain-1激活相关联，并通过Talin-1的丢失和可能的钙调神经磷酸酶激活（表征FSGS的足细胞损伤）联系起来。因此，抑制钙蛋白酶1和/或TRPC6可能是治疗FSGS或其他足细胞病患者的未来治疗选择。