Podocyte‐parietal epithelial cell cross‐talk: a role for paracrine KLF4‐STAT3 signaling in parietal epithelial cell proliferation in proliferative glomerulopathies

Abstract

Podocyte injury contributing to parietal epithelial cell (PEC) proliferation is a dominant histologic feature in both rapidly progressive glomerulonephritis (RPGN) and subtypes of focal segmental glomerulosclerosis (FSGS). Activation of Signal Transducer and Activator of Transcription 3 (STAT3) signaling is critical to the progression of both. We recently showed that podocyte‐specific loss of Krüppel‐Like Factor 4 (KLF4), a zinc‐finger transcription factor, activates STAT3 signaling leading to mitotic catastrophe in podocytes and eventual FSGS, while triggering PEC proliferation.To determine the mechanism by which podocyte‐specific knockdown of KLF4 leads to podocyte loss and triggers PEC proliferation with dysregulated STAT3 signaling, we generated cultured human podocytes with KLF4 knockdown (KLF4‐shRNA) and screened several pharmacological STAT3‐specific inhibitors to determine that S3I‐201 prevented podocyte loss to a higher degree than other STAT3 inhibitors or DMSO‐treated KLF4‐shRNA podocytes. Furthermore, we demonstrated that S3I‐201‐treated PodCre‐KLF4fl/fl mice exhibited less proteinuria and improved renal function as compared to DMSO‐treated PodCre‐KLF4fl/fl mice. We further validated the reno‐protective effects of S3I‐201 in HIV‐1 transgenic mice, a known model of podocyte‐specific Klf4 loss and STAT3 activation, by demonstrating reduced albuminuria, podocyte loss, FSGS lesions, and parietal epithelial cell activation, with improved renal function.We previously demonstrated that supernatant harvested from KLF4‐shRNA podocytes induces PEC proliferation. To elucidate the mechanism by which loss of KLF4 specifically in podocytes triggers PEC activation and proliferation, we performed unbiased quantitative proteomics on the supernatant of KLF4‐shRNA podocytes as compared to EV‐shRNA podocytes. We subsequently cross‐matched proteins upregulated in supernatant of KLF4‐shRNA podocytes with differentially expressed transcripts from RNA‐sequencing of isolated glomeruli from PodCre‐KLF4fl/fl mice as compared to wildtype KLF4fl/fl mice. Enrichment analysis of these differentially expressed targets revealed activation of STAT‐dependent and independent pathways involved in inflammation, extracellular matrix organization, and proliferation. Interestingly, the highest expressed STAT3 downstream targets were Plasminogen Activator Inhibitor 1 (PAI‐1) and Galectin‐1 (LGALS1), which are key mediators of epithelial cell migration and proliferation.Collectively, these findings demonstrate the role of dysregulated KLF4‐STAT3 signaling in proliferative glomerulopathies and identify potential paracrine mediators of podocyte‐PEC cross‐talk.Support or Funding InformationNIH/NIDDK, SBU URECAThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.