Regulation of Apoptosis in Renal Ischemia

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DESCRIPTION (provided by applicant): Inhibition of apoptosis protects against ischemic renal injury (IRI). Recent reports demonstrate that inhibition of the transcription factor p53 prevents apoptosis and improves renal function following IRI; however, the signaling pathways by which p53 induces apoptosis are yet to be elucidated. We identified two pro-apoptotic p53 transcriptional targets Siva and PERP (p53 apoptosis effector related to PMP-22) to be specifically activated in IRI. Inhibition of Siva prevented apoptosis and offered functional protection from IRI in mice. Over expression of Siva led to apoptotic cell death of renal proximal tubular cells (PTC) in vitro by caspase-dependent and independent mechanisms. Our long term research goal is to elucidate the cellular signaling pathways that regulate PTC apoptotic cell death, in order to identify strategies to intervene in those pathways to treat acute kidney injury (AKI). The objective of the proposed work is to delineate the mechanisms by which Siva and PERP integrate their signals to induce apoptosis in renal PTC and intervene in their signaling pathways to treat IRI. The central hypothesis is that activation of Siva and PERP stimulate the extrinsic apoptotic pathway via the TNF-receptor, CD27, induce mitochondrial permeability to release apoptogenic factors and translocate to the nucleus to recruit apoptosis inducing factor (AIF) to trigger PTC apoptosis post-IRI. The validity of the hypothesis will be tested by pursuing three specific aims that are aimed at determining the mechanisms by which Siva-CD27 and Siva- PERP interactions elicit caspase-dependent and independent apoptosis and determine the in vivo functional significance of their signaling in inducing apoptosis and impairing renal function in mouse model of renal ischemia. The significance of the studies includes the identification of a novel pathway that may initiate PTC apoptosis that may provide new opportunities for intervention with important clinical implications, both for prognosis and management of AKI. PUBLIC HEALTH RELEVANCE: Acute kidney injury is a devastating clinical syndrome with a 50% mortality rate affecting 5-7% of all hospitalized patients. Currently, there are no accepted therapies available to treat this condition. Interfering with p53-mediated apoptotic programs may allow the development of novel therapeutic strategies to reduce the mortality and morbidity. The latter outcome could have a dramatic impact on the quality of life and reducing the health care cost associated with acute kidney injury.