TRPV1-mediated induction of a protective heat shock response after stroke

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DESCRIPTION (provided by applicant): Ischemic stroke is among the leading causes of death and disability in the United States; however, current treatment options are very limited. We recently demonstrated significant neuroprotection following stroke by promoting therapeutic hypothermia (Tc=33� C) through selective pharmacological agonism of TRPV1 channels in conscious mice. We extend these findings in the present proposal by demonstrating that a significant portion of the neuroprotection derived from TRPV1 agonism is actually independent of the hypothermic effect. While seeking the mechanism of this novel hypothermia- independent effect, we discovered that TRPV1 agonists promote a protective heat shock response (HSR) in the brain. TRPV1 is a Ca2+-permeable non-selective cation channel found within heat- sensitive sensory fibers of the thermoregulatory system as well as multiple other cell types in the brain. The HSR is an endogenous cellular response that involves rapid transcriptional activation of heat shock proteins (Hsps) which contribute to the prevention or reversal of cellular damage. This cytoprotective mechanism contributes to the body's survival response to a variety of insults and injuries, including stroke. In the brain, Hsp27 and Hsp70 appear to play critical roles in neurorecovery from stroke. The overall aim of this project is to demonstrate TRPV1 channel agonism as an effective therapeutic strategy to promote HSR activation and sustained neuroprotection following ischemic stroke. Specifically, we will 1) determine the mechanism and cell specificity of TRPV1-mediated HSR induction in the uninjured and stroke brain and 2) determine if TRPV1-mediated HSR induction provides sustained neuroprotection following stroke. Initial studies will be performed with cultured brain astrocytes and neurons to test proposed mechanisms of TRPV1-mediated induction of Hsp27 and Hsp70, using pharmacological modulators and cultures established from mechanism-specific knockout (KO) mice. These studies will be followed by whole animal studies to determine the in vivo dose- response, time course, and cell specificity of HSR induction by TRPV1 agonism in the uninjured brain and the brain following focal ischemic stroke in wild type and mechanism-specific KO mice. Lastly, studies will be performed with stroke mice to determine if TRPV1-mediated HSR induction provides sustained neuroprotection through 28 days of reperfusion. Neuroprotection will be evaluated by histological/immunofluorescence methods to determine cell specific survival, BBB integrity, and apoptosis and by behavior testing to demonstrate ultimate functional recovery. The specific roles of Hsp27 and Hsp70 in neuroprotection will be determined with respective KO mice. It is expected that these studies will demonstrate novel neuroprotective mechanisms of TRPV1 agonism in the brain and lay the groundwork for improved treatment strategies for stroke and other neurodegenerative diseases.