Ceramides as Novel Mediators of Tubular Metabolic Dysfunction Driving Kidney Injury

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PROJECT SUMMARY/ABSTRACT. Acute kidney injury (AKI) is a prevalent condition which elicits an enormous burden on patient mortality and healthcare spending. A significant unmet need exists to elucidate kidney-specific insults driving the onset and progression of kidney injury in order to develop novel therapeutic strategies capable of directly targeting renal pathology. Compelling evidence has suggested that altered metabolism within the kidney proximal tubule is implicated in AKI. The work proposed in this fellowship application will critically evaluate the role of a class of lipotoxic lipid species, termed ceramides, as drivers of mitochondrial dysfunction, oxidative stress, and lipid accumulation characteristic of multiple kidney pathologies. Human correlational data suggest that altered tubular ceramide metabolism correlates with clinical kidney disease endpoints, such as kidney fibrosis and estimated glomerular filtration rate. Previous reports indicate that renal ceramides are elevated in pre-clinical models following kidney injury or in the setting of chronic disease, and preliminary data presented herein demonstrate that whole-body depletion of ceramides successfully prevents acute kidney injury and histopathology following renal ischemia reperfusion or obstructive injury. This application intends to address the remaining gap in knowledge regarding whether local kidney ceramides play a role in disease mechanisms and in which cell types. Specifically, the proposed project will determine if ceramides are candidate mediators of metabolic dysfunction in tubular epithelial cells. In Aim One, we will probe for protection from kidney injury incurred in novel mouse lines with genetic depletion of ceramides in the kidney tubular epithelium. Furthermore, animals with genetic gain-of-ceramide within kidney tubules will be assessed for development of kidney dysfunction and histopathology. Studies proposed in Aim Two will employ in vitro and ex vivo methods to characterize novel mechanisms of ceramides driving impairment of mitochondrial bioenergetics and lipid accumulation in kidney tubules and primary cells. Preliminary findings demonstrate that accumulation of ceramides impairs mitochondrial respiration and ATP production in cultured immortalized proximal tubular epithelial cells. This work will be the first investigation to directly assess if tubule-derived ceramides are implicated in the metabolic perturbations preceding tubular injury and histopathology and will provide valuable insight into the therapeutic potential of ceramide-lowering interventions for dominant causes of acute kidney injury. Furthermore, completion of the proposed studies will greatly enrich the applicant’s pre-doctoral training, mastery of technical skills (e.g., implementation and evaluation of kidney injury and disease models, evaluation of mitochondrial metabolism and substrate utilization, and mass spectrometry-based analysis of ceramide levels), and development as a young scientist pursuing an independent research career.