A new pathogenic mechanism for diabetic retinopathy

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PROJECT SUMMARY/ABSTRACT Diabetes-induced oxidative stress and chronic inflammation in the retina play a key pathogenic role in diabetic retinopathy (DR). Mitochondrial dysfunction and impairment have been identified as the major cause of oxidative stress and inflammation in DR. Peroxisome Proliferator-Activated Receptor α (PPARα) is a hormone- activated receptor and transcription factor. It is known to regulate lipid metabolism, and thus, PPARα agonists are used clinically to treat hyperlipidemia. Recently, two independent, prospective clinical studies reported a surprising finding that oral administration of fenofibrate, a PPARα agonist, has robust therapeutic effects on DR in type 2 diabetic patients. In the prior grant period, we have successfully demonstrated that the therapeutic effect of fenofibrate on DR is through a PPARα-dependent mechanism. We have shown that PPARα is down- regulated in the retinas of diabetic humans and diabetic animal models, and PPARα has protective effects against DR. We have shown that PPARα knockout (KO) exacerbated, while activation of PPARα by fenofibrate alleviated retinal oxidative stress and retinal inflammation in DR models. This proposal will extend these studies and elucidate the mechanism responsible for the protective effects of PPARα. Our preliminary studies showed that fenofibrate treatment decreased diabetes-induced acellular capillary formation and pericyte loss in the retina. Further, Seahorse analysis showed that PPARα KO resulted in mitochondrial dysfunction in the retina and primary pericytes. Further, PPARα-/- retina showed decreased mitochondrial DNA (mtDNA) copy numbers, suggesting impaired mitochondrial biogenesis and/or DNA repair. This project will address a novel hypothesis that diabetes-induced down-regulation of PPARα expression is responsible for, at least in part, for diabetes-induced mitochondrial dysfunction, which leads to retinal oxidative stress and inflammation in DR. We will determine if PPARα KO exacerbates, while PPARα over-expression alleviates, mitochondrial dysfunction (basal OCR, maximal OCR and ATP production) and mtDNA damage as well as retinal oxidative stress, leukostasis, vascular leakage, acellular capillary formation and pericyte dropout in the retina of diabetic mice. We will also determine the impacts of PPARα deficiency in pericytes on diabetes-induced mitochondrial damage, oxidative stress and pericyte apoptosis using pericyte-specific conditional PPARα KO mice and primary PPARα-/- pericytes. We will also investigate if PPARα regulates mitochondrial biogenesis and function through the SIRT1/PGC-1α pathway using pericyte-specific SIRT1 KO mice and primary SIRT1-/- pericytes. These studies will elucidate a novel pathogenic mechanism responsible for mitochondrial damage and oxidative stress in DR and reveal a new therapeutic strategy for DR. These studies will also contribute to the understanding of the mechanism underlying therapeutic effects of fenofibrate on retinal inflammation and pericyte loss in DR.