Down-regulation of Wt1 activates Wnt/β-catenin signaling through modulating endocytic route of LRP6 in podocyte dysfunction in vitro

Podocyte dysfunction plays important roles in the pathogenesis of chronic kidney disease, and Wt1 has long been considered to be a marker of podocyte, whereas its roles and mechanisms in podocyte injury are still unclear though Wt1 mutations are reported to be involved in the development of glomerular disease in human and mice. Here we show that down-regulation of Wt1 could induce podocyte dysfunction and apoptosis through activating Wnt/β-catenin signaling. Podocytes treated with adriamycin demonstrated decreased expression of Wt1, coupled with activated Wnt/β-catenin signaling in vitro. Reduced expression of Wt1 in podocytes transfected with Wt1 siRNA is correlated with activated Wnt/β-catenin signaling, increased podocyte apoptosis, as well as suppressed expression of nephrin. Blockade of Wnt/β-catenin signaling with Dickkopf-1 ameliorated podocyte injury and apoptosis induced by Wt1 siRNA. We also found that membrane LRP6 was increased dramatically in podocytes transfected with Wt1 siRNA compared with control siRNA, while no significant change was found in total LRP6. Caveolin- and clathrin-dependent endocytosis were both involved in the regulation of β-catenin signaling. And we found that down-regulation of Wt1 in podocytes mediates activation of Wnt/β-catenin signaling by recruiting LRP6 to the caveolin-mediated endocytosis route, thereby sequestering it from clathrin-dependent endocytosis. As a result, we concluded that Wt1 expression levels in podocytes regulate Wnt/β-catenin signaling through modulating the endocytic fate of LRP6, and this indicates a potential target for the therapy of CKD.