Crosstalk between lipid droplets and other organelles in podocytes

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ABSTRACT Research supports a role for lipid droplet (LD) accumulation in mitochondrial dysfunction (MD) and podocyte injury in the pathogenesis of glomerular diseases of metabolic and non-metabolic origin, including Alport Syndrome (AS). LDs regulate the storage and homeostasis of intracellular TGs and regulate the availability of free fatty acids (FFAs), which can be oxidized in mitochondria and used as an energy source. Proper contact of LDs with mitochondria is mediated by LD-associated proteins, such as perilipin 5 (PLIN5). PLIN5 is a protein that regulates lipolysis of TGs stored in LDs, mediates LD-mitochondrial contact formation, and serves as a substrate for chaperone-mediated autophagy (CMA). However, little is known about the function of PLIN5 in podocytes. In preliminary data, we demonstrated decreased PLIN5 expression in kidney cortices of Col4a3 KO (AS mice), in AS podocytes and in a zebrafish model of AS when compared to controls. In AS podocytes, PLIN5 deficiency is associated with increased lipolysis, FFA accumulation, and reduced LD-mitochondrial contact formation and mitochondrial membrane potential, which was restored by PLIN5 overexpression. AS podocytes also have an increased autophagosome number compared to WT podocytes, often in proximity of mitochondria, suggesting increased mitophagy may occur in AS. PLIN5 expression is restored by Ezetimibe (EZ), a compound that was initially developed to prevent cholesterol absorption via its binding to NPC1L1, suggesting an off-target effect of this compound. Our results suggest an important role for PLIN5 deficiency in lipotoxicity-induced MD and podocyte injury and renal disease progression in AS. The overall goal of this proposal is to investigate a novel mechanism linking PLIN5 deficiency to podocyte injury in AS. We hypothesize that PLIN5 deficiency contributes to the renal phenotype observed in Col4a3 knockout mice, a mouse model of AS and causes podocyte injury and in renal failure in AS. In aim 1, we will investigate the mechanism by which PLIN5 deficiency contributes to podocyte injury and by which Ezetimibe protects from podocyte injury. In aim 2, we will determine if podocyte-specific overexpression of PLIN5 in Col4a3 KO mice is sufficient to prevent renal failure in AS (aim 2). If successful, this innovative study will link PLIN5 deficiency to a novel pathway of lipotoxicity-induced podocyte injury and may reveal a new MoA of Ezetimibe.