Role of Atp6ap2 in renal proximal tubule lipotoxicity

Project Summary The rising rates of obesity worldwide contribute directly to an increased prevalence of chronic kidney disease. With current methods for mitigating obesity related kidney injury incompletely effective, novel approaches to this problem are needed. In renal lipotoxicity, toxic lipid metabolites accumulate in certain kidney cell types, including proximal tubule cells. This has recently been identified as an important mechanism behind obesity related kidney disease but is also not well understood. In obesity, greater proximal tubule uptake of lipid occurs through increased luminal endocytosis of fatty acid bound to albumin, facilitated by interaction of the vacuolar H+ -ATPase and mTOR with the megalin/cubulin complex. At the same time, decreased activation of renal AMPK in obesity leads to decreased fatty acid oxidation through inactivation of PGC-1α, and CPT1A, further resulting in intracellular lipid accumulation in the proximal tubule. ATP6AP2 is an integral component of the vacuolar H+ -ATPase and has also been shown to have a role in intracellular energy signaling including inhibition of AMPK and PGC-1α as well as activation of mTOR in diabetes. Renal cortical ATP6AP2 expression increases in obesity but its role in lipotoxicity is unknown. Mice with nephron specific ATP6AP2 knockout during obesity have increased urinary excretion of albumin and fatty acid, reduced proximal tubule lipid content during diet induced obesity, decreased endoplasmic reticulum stress, a marker of lipotoxicity, and altered intrarenal lipid profile. This proposal will test the hypothesis that in obesity ATP6AP2 promotes proximal tubule lipotoxicity through endocytosis of albumin bound fatty acid as well as reduced intracellular fatty acid oxidation. Aim 1 proposes that ATP6AP2 increases fatty acid endocytosis through the H+ -ATPase/mTOR/megalin/cubulin. Aim 2 will test the hypothesis that ATP6AP2 reduces fatty acid oxidation through AMPK/PGC-1α/CPT1A.. This project will also greatly facilitate my career development toward the goal of becoming a fully independent physician scientist performing basic and translational research. The career development plan described in this application will include formal training in lipid science and lipidomics, the use of transgenic mouse models, microscopy, and scientific writing, as well as mentorship by leaders in endocrinology and lipid science including my mentors Drs. Helmy Siragy and Thurl Harris. This will take place at the University of Virginia, an excellent research training environment with state-of-the art research facilities and core laboratories as well as a superb academic environment for early career scientists. Data generated by the proposed studies will establish the basis for an independent research career, distinct from my mentors.