Autocrine and paracrine podocyte signals decrease glomerular function/health in aged kidneys

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PROJECT SUMMARY/ABSTRACT The overall scope of the problem is that as the US population lives longer, kidney disease becomes more abundant. In particular, elderly patients face worse disease outcomes, and they are now the largest group to undergo first-time dialysis. The goal of this proposal is to prove that aged podocytes are central to the many glomerular changes with aging. Changes to and loss of podocytes remain the best predictors of age-related glomerulosclerosis and reduced GFR. Major unmet needs are understanding the mechanisms of podocyte aging and the crosstalk between aged podocytes and neighboring parietal epithelial cells (PECs). To close these knowledge gaps, we performed a transcriptome analysis comparing podocytes from aged vs. young mice. Much to our surprise, transcripts for immune response processes such as inflammasome components, inflammatory factors (e.g. TNFα, interferons, interleukins and chemokines) and SASPs were significantly enriched. Importantly, similar changes were confirmed in human kidney biopsies. Based on these preliminary data, we propose a novel paradigm that aged podocytes secrete inflammatory signals and SASPs that in autocrine loops directly impact podocytes themselves. Specific Aim #1 will prove that this newly discovered inflammatory aged podocyte phenotype directly shortens the podocyte's lifespan and reduces their health-span. We will test the hypotheses that in aged podocytes: (1) Inflammasome-induced de novo intracellular inflammation reduces podocyte lifespan; (2) The PD1 signaling pathway acts downstream of the NLRP3 inflammasome; (3) A specific subset of secreted inflammatory mediators accelerates the podocyte aging phenotype through autocrine loops. We also propose a second novel paradigm in which aged podocytes play a paracrine role in accelerating PEC aging. This is based on the facts that (i) podocyte aging temporally precedes PEC aging; (ii) PEC aging is typically only present in individual glomeruli in which podocytes exhibit an aged phenotype; (iii) inhibition of the inflammasome or PD1 pathways in aged podocytes reduces PEC aging. In Specific Aim #2 we propose that SASPs and inflammatory cytokines derived from aged podocytes accelerate the PEC aging phenotype through paracrine loops. We will test the hypotheses that: (1) The inflammatory podocyte phenotypes in aged mice precedes and accelerates PEC aging. (2) A distinct subset of SASPs and inflammatory cytokines derived from aged podocytes accelerates the PEC aging phenotype. These studies are based on many innovative experimental approaches including aging studies in transgenic mice, primary human podocytes and PECs, Design-of-Experiment methodology and novel co-culture models. Finally, the focus of our study is significant for its short-term translational impact by intersecting our mouse data with a large transcriptomic data set on aged human kidneys and its long-term impact in developing therapeutic strategies that will counter the age-dependent demise of kidney function.