We propose to examine the relationship between substrate oxidation, lipotoxicity and proximal tubule cell death. We have shown that activation of PPARalpha using a ligand, or by increased expression of PPARalpha in the proximal tubule using transgenic mice ameliorates kidney function in the ischemia reperfusion injury (IRI), and cisplatin model of nephrotoxicity. Our preliminary studies demonstrate a significant reduction in proximal tubule cell death and reduced interstitial fibrosis in PPARalpha Tg mice subjected to both unilateral ischemia and Unilateral Ureteral Obstruction (UUO), when compared to wild type mice. Our central hypothesis predicts that increased expression and activity of proximal tubule and pericyte PPARalpha interdict tubulo-interstitial inflammation and renal fibrosis, a hallmark of the progression from Acute to Chronic Kidney Disease (CKD).
Specific Aim 1. To determine whether increased proximal tubule (PT)-PPARalpha interdicts with tubulo-interstitial fibrosis. We hypothesize that increased expression of proximal tubule PPARalpha attenuates renal fibrosis. We will use wild type, genetically deficient PPARalpha mice, and PPARalpha transgenic mice and two animal models of renal fibrosis to determine if increased fatty acid oxidation, lipoprotein lipase activity, and increased autophagy contribute to reduced lipotoxicity and prevent proximal tubule cell death in models of renal fibrosis.
Specific Aim 2. To examine the mechanisms by which increased proximal tubule (PT)-PPARalpha reduces renal fibrosis. We will address several independent mechanisms by which PPARalpha expression could reduce renal fibrosis: 1) by changing macrophage phenotype in UUO mice 2) by increasing structural repair after reversal of UUO and 3) by reducing myofibroblast proliferation in renal interstitium.
Specific Aim 3. To determine cellular mechanisms by which PPARalpha reduces renal fibrosis in mouse kidney pericytes. Our preliminary studies show that PPARalpha expression as well as expression of fatty acid oxidation genes are significantly reduced in pericytes isolated from UUO mice. We propose to isolate and culture mouse kidney pericytes from wild type mice 1) to determine the effects of PPARalpha overexpression on pericyte to myofibroblasts transition in vitro, 2) to determine whether PPARalpha mediated increase in fatty acid oxidation, reduced neutral lipid accumulation, and changes on adipogenesis contribute to the transition from pericytes to myofibroblasts in vitro, 3) to determine the role of increased cellular autophagy on pericyte to myofibroblasts transition, and 4) to determine the role of PPARalpha deficiency on primary pericytes transition to myofibroblasts. Altogether these studies will further advance our knowledge of pericyte metabolism and function and should provide additional therapeutic targets to manage chronic kidney disease.
This project will establish potential mechanisms by which PPARa expression in the proximal tubule and pericytes reduces renal fibrosis and increases renal repair. By understanding the cellular mechanisms by which PPARalpha reduces interstitial fibrosis we could begin to formulate novel therapeutic strategies that we can apply to prevent progression from acute to chronic kidney disease.
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