Project Summary/Abstract Ischemic acute kidney injury (AKI) is a common and often a life-threatening consequence of reduced blood flow to this critical organ causes major morbidity and mortality, and lacks an effective treatment. For the first time, we have detected identical biochemical events in both ischemic murine and human kidneys that mediate renal cell death leading to AKI. In this proposal, we study the role of nucleophosmin (NPM), a protein present in all mammalian cells that is converted from “friend” to a “foe” during ischemic stress. During renal ischemia, NPM undergoes biochemical changes that promote its toxicity in renal epithelial cells, a major contributor to organ failure during AKI. These steps include: NPM translocation from the nuclear to the cytosolic compartment, NPM de-oligomerization, interaction with Bax, a major cause of outer mitochondrial membrane injury, and renal cell death by both apoptosis and necrosis, the two forms of cell death consistently detected in ischemic human kidneys. Preliminary data using mass spectroscopy have identified 5 phosphorylation changes in murine and human proximal tubule cells, kidney tissue, and urine that regulate NPM toxicity during renal ischemia. In three AIMS, we will link post-translational phosphorylation events with NPM toxicity, identify the role of NPM in human renal disease using banked kidney biopsy tissue, test NPM phospho-mutant proteins that replicate toxic modifications, and develop novel peptide reagents for ameliorating NPM toxicity. Once identified in vitro, we will test the most effective peptides and pharmaceuticals to treat ischemic AKI in vivo. This in vitro testing minimizes the number of animals required to perform our proposed studies that will examine the biologic effects of gender in AKI diagnosis and treatment. We have developed a novel urinary NPM assay that will be used to as an early AKI biomarker and also for measuring the therapeutic efficacy of our treatment. Assessment of total and site-specific phosphorylated NPM in urine and tissue will trigger early treatment, and may ultimately permit us to predict the severity of AKI and its recovery. Detection of NPM in human kidney biopsy tissue will identify potential AKI causes (e.g., ischemia or nephrotoxin-induced AKI) that are amenable to anti-NPM therapeutics. Since NPM is identically regulated during ischemia in mice and humans, it is likely that effective interventions in mice will translate to human clinical trials.