A Novel Intervention for Cerebral Ischemia

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Project Summary/Abstract Stroke is the leading cause of long-term disability in adults in the United States, and no therapy is available to prevent stroke-induced neurological deficits. Neurogenesis is one of the important endogenous mechanisms for neuronal replacement, repair and functional recovery after stroke. However, the majority of newly generated neurons in the brain die soon after stroke. Among the mechanisms that could foster viable neuronal replacement, a favorable neurovascular niche with proper angiogenesis and neovascularization is the most crucial one. Therefore, strategies to enhance both neurogenesis and angiogenesis would greatly improve neuronal replacement and neurological recovery after stroke. Nicotinamide phosphoribosyltransferase (NAMPT) has been proven to be neuroprotective against ischemic brain injury. NAMPT markedly promotes cell proliferation, migration and capillary-like tube formation in human umbilical vein endothelial cell cultures. However, the effect of NAMPT on angiogenesis in the context of cerebral ischemia is under-explored. Furthermore, whether NAMPT increases neurogenesis remains unknown. We have recently found that besides acute neuroprotection, NAMPT also promotes brain repair and neurovascular remodeling. Strikingly, we found that NAMPT recombinant protein can cross the blood brain barrier (BBB) and also improve long-term functional outcomes against cerebral ischemia. Therefore, the objective of this project is to test the novel neuroprotective/ neurorestorative function of NAMPT in the context of cerebral ischemia with a long-term aim to develop NAMPT as a novel, clinically relevant therapeutic agent for ischemic stroke. The hypothesis to be tested is that NAMPT protects against ischemic brain injury and improves long-term neurological outcomes by enhancing angiogenesis and neurogenesis. Focal ischemia will be induced in mice by middle cerebral artery occlusion (MCAO) to mimic the pathophysiological changes in the brain after clinical ischemic stroke. The following specific aims are proposed: Aim 1: Test the hypothesis that NAMPT reduces brain damage and improves long-term neurological outcomes after focal cerebral ischemia. The neuroprotective effect of NAMPT on ischemic brain injury will be first tested in transgenic mice that overexpress NAMPT specifically in the brain, and then its translational potential for the treatment of ischemic stroke will be further tested using recombinant NAMPT protein. The endpoints for assessment include infarct size and functional outcomes. Aim 2: Test the hypothesis that NAMPT treatment enhances cerebral neurovascular remodeling, including augmented angiogenesis and neurogenesis after cerebral ischemia. The effect of recombinant NAMPT protein on post-stroke neovascularization in peri-infarct brain areas will be quantitatively analyzed. The effect of NAMPT on neural stem cell proliferation, migration, differentiation and neuronal replacement following ischemic stroke will also be examined. Relevance of the proposed work to the VA patient care mission Approximately 11,000 veterans are hospitalized annually with new strokes and up to 80,000 veterans are stroke survivors. The population with post-stroke physical disability continues to grow due to the lack of effective therapies to restrict and/or repair devastating neuronal damage after stroke. The proposed study will develop NAMPT as a novel, clinically feasible therapeutic strategy to offer acute neuroprotection as well as long-term neurological recovery after stroke. The success of this study will enhance post-stroke rehabilitation and improve quality of life for veterans suffering from stroke.