Roles of KIM-1 in Renal Injury and Repair

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The applicant proposes a program of research to prepare him for a career in the academic medicine. The research will be conducted in the laboratory of Dr. Joseph Bonventre at the Massachusetts General Hospital. Dr. Bonventre is an established senior investigator with an interest in acute renal failure who has successfully trained research fellows with a variety of interests. The long-term objective of the applicant is to independently investigate mechanisms of acute renal failure and improve the therapy and outcome of patients with this disease. The proximal tubule is particularly sensitive to ischemic injury and the surviving cells in this segment undergo an active process of dedifferentiation and proliferation after ischemia ultimately resulting in the reconstitution of a well differentiated polarized morphology. However the mechanisms by which the tubular epithelial cells are restored are not fully understand. Kidney Injury Molecule-1 (KIM-1) is a type 1 transmembrane protein and an epithelial cell adhesion molecule, which expresses predominantly in the injured kidney. After ischemia/reperfusion KIM-1 is coexpressed with vimentin, a marker of epithelial cell dedifferentiation. KIM-1 is also expressed in renal cell carcinoma, which state is associated with a dedifferentiated epithelial cell phenotype. The cleaved ectodomain of KIM-1 can be detected in the urine of patients with ischemic acute renal failure. In pilot experiments, we have found that tumor necrosis factor-alpha (TNF-alpha) enhanced the shedding of KIM-1 and, meanwhile, inhibitors of MEK-1, secretory phospholipase A2, and cyclooxygenase diminished the TNF-alpha induced shedding of KIM-1 in 769-P cells, which express abundant level of endogenous KIM-I under normal culture condition and constitively shed into culture media. This project's broad objectives are to define the functional role of KIM-1 and specific signaling mechanisms controlling cytokine mediated-shedding of KIM-1 in renal epithelial cells. The studies proposed in this application will provide important new insights regarding understanding functional role of KIM-1 in injury and repair of the renal tubular epithelium and may lead to new therapeutic approaches in acute diseases affecting the kidney.
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