Cellular cholesterol and podocyte function in diabetic kidney disease

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ABSTRACT Podocyte injury is a key feature of DKD and renal accumulation of lipid correlates with the development of glomerulosclerosis. Decreased expression of ATP-binding cassette transporter 1 (ABCA1) occurs in glomerular transcripts from patients DKD and is associated with the presence of podocyte lipid droplets in kidney biopsies. Fibroblasts from patients with Tangier disease carrying ABCA1 loss of function mutations are characterized by cardiolipin accumulation, a mitochondrial specific phospholipid. While increases in hepatic cholesterol and cardiolipin content are observed in association with mitochondrial dysfunction in patients with non-alcoholic steatohepatitis (NASH), h yperglycemia induced excess mitochondrial superoxide production has been considered the primary driver of mitochondrial dysfunction in DKD. These observations led us to hypothesize that ABCA1 deficiency renders podocytes susceptible to DKD-mediated injury via cardiolipin dependent mitochondrial dysfunction. Our preliminary data suggest that ABCA1 deficiency leads to changes in the mitochondrial membrane lipid composition and CL accumulation in association with mitochondrial dysfunction and oxidative stress in vitro rendering podocyte susceptible to injury. In vivo, we demonstrate that podocyte specific Abca1 deficiency (pABCA1) is associated with accumulation of esterified cholesterol in kidney cortex but is not sufficient to cause proteinuria. However, Abca1 deficient podocytes cultured in diabetic milieu are more susceptible to DKD-related injury and pABCA1 diabetic mice have worsened DKD progression and accumulation of docosahexaenoic acid (DHA)-rich cardiolipin, a cardiolipin species especially susceptible to reactive oxygen species (ROS). The phenotype of these mice can be partially rescued by inhibition of cardiolipin peroxidation with Elamipretide, an inhibitor of CL peroxidation. We propose three specific aims to test several hypotheses. In specific aim 1, we will determine if ABCA1 deficiency and hyperglycemia contribute differently to mitochondrial (dys)function. In specific aim 2, we will investigate the effect of ABCA1 deficiency on the lipid composition and fluidity of mitochondrial membranes and in specific aim 3, we will determine if inhibition of cardiolipin peroxidation can rescue ABCA1 dependent mitochondrial dysfunction. This innovative study is aimed at deciphering the role of ABCA1-mediated lipid compartmentalization and CL accumulation in mitochondrial dysfunction and podocyte injury. If successful, this study will have high impact as it elucidates a new pathway important in podocyte injury and may lead to the identification of new drug targets for the treatment of patients with DKD.