Abstract
Urokinase plasminogen activator receptor (uPAR) is upregulated in podocytes of glomerular diseases and crucially mediates podocyte injury through integrin β3 (ITGB3). We previously showed that the miR-30 family maintains podocyte structure and function by inhibiting injurious calcineurin signaling through nuclear factor of activated T cells C (NFATC). Here, we tested whether the miR-30-calcineurin-NFATC and uPAR-ITGB3 pathways, two of the major pathways leading to podocyte injury, could interact. We found that podocyte-specific miR-30 knockdown in mice induced uPAR upregulation and ITGB3 activation, accompanied by proteinuria and podocyte injury. These effects of miR-30 knockdown were reduced using inhibitors of ITGB3, calcineurin, and NFATC, respectively, which are known to be antiproteinuric. These results indicate that miR-30 deficiency leads to calcineurin-NFATC signaling activation, which in turn activates the uPAR-ITGB3 pathway. In cultured podocytes, miR-30 knockdown also activated uPAR-ITGB3 signaling, leading to Rho GTPase activation, synaptopodin downregulation and podocyte injury. To explore uPAR-ITGB3 signaling regulation by miR-30 in podocytopathy development, we treated mice with lipopolysaccharide (LPS) and found that miR-30 was downregulated in podocytes, accompanied by uPAR upregulation and ITGB3 activation. We obtained the same results in cultured podocytes treated with LPS. Podocyte-specific transgenic miR-30 abolished uPAR-ITGB3 signaling and ameliorated podocyte injury and proteinuria in mice. Taken together, these experiments show that uPAR-ITGB3 signaling is negatively regulated by miR-30 through calcineurin-NFATC pathway, a novel mechanism underlying podocyte injury in glomerular diseases. Our study has elucidated the relationship among the crucial players governing podocyte pathophysiology and the antiproteinuric actions of drugs commonly used for podocytopathies.