Rho GTPases and Actin Cytoskeletal Function in Renal Ischemia

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DESCRIPTION (provided by applicant): The persistence of ischemic acute renal failure as a major cause of morbidity and mortality in hospitalized patients and the relative lack of improvement in outcomes for these patients challenges us the better understand the cellular mechanisms underlying this injury. Disruption of the actin cytoskeletal organization that normally underpins the structure and function of proximal tubule epithelial cells is well-established as an early and critical aspect of injury, with direct consequences for renal function and cell survival. In the previous years of this award we have shown that Rho GTPases play critical roles that may mediate the cytoskeletal alterations observed with ischemia. Moreover, we showed that activities of RhoA, Rac1 and Cdc42 are sensitive to ATP depletion, but that the activity of each protein is differentially affected by depletion. We proposed that alterations in Rho GTPase activity and consequent cytoskeletal disruption are the result of signaling through the AMPK-TSC1/2 pathway resulting in inactivation of the type II (rapamycin insensitive) mTor complex 2, which has recently been shown to regulate the cytoskeleton through Rho GTPases or via novel mTOR independent pathways downstream of TSC1/2. We propose studies to test and elucidate our proposed mechanism using complementary studies in cell culture and in animal models of renal ischemia. We propose four specific aims to address our central hypothesis: 1) Investigate the activation of AMPK by ATP depletion in vitro and ischemia in vivo; 2) Investigate the role of TSC1/2 and Rheb GTPase signaling on Rho GTPase activity and cytoskeletal organization in vitro and in vivo; 3) Determine the effect of AMPK activation on the type II mTOR complex; 4) Determine the effect of altered AMPK, TSC1/2, Rheb and mTOR signaling on actin cytoskeletal organization and proximal tubule cell function in animal models of ischemic renal injury. These studies will determine the key mechanism linking energy depletion to cytoskeletal alterations, and afford an opportunity to identify targets for novel therapies. Narrative Ischemia (loss of blood flow) is a major cause of acute kidney failure. Currently there is a poor understanding of the way that kidney cells respond to ischemia, which makes it difficult to design therapies or drugs. The studies proposed will test a possible mechanism leading to cell injury that could be a target for drug therapy.