Novel approaches to stimulating neurotrophin signaling for stroke recovery

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Project Summary/Abstract Stroke is a leading cause of adult neurologic disability with survivors often left with permanent deficits due to neuronal loss resulting from ischemia-induced brain injury. There are currently no successful treatments to restore normal function to stroke patients once brain damage has occurred, with the exception of rehabilitation therapy, which is limited in its ability to promote full recovery. In preclinical studies, treatments that stimulate the replacement of damaged pathways with new neuroanatomical connections from uninjured neural tissue, a process known as neuroplasticity, have proven to be promising strategies for improving recovery of function after injury. Our laboratory has used antibody therapy directed at blocking the neurite inhibitory protein Nogo- A to promote neuroplasticity and significantly improve the functional outcome of animals affected by experimental stroke. However, the cellular and molecular mechanisms responsible for anti-Nogo-A antibody- mediated recovery remain largely unknown. We have previously demonstrated that Nogo-A alters nerve growth factor (NGF)-dependent neurotrophin signaling to negatively influence neuronal survival and neurite outgrowth. The goal of this proposal is to verify that disruption of TrkA signaling is a consequence of stroke- induced Nogo-A expression, and to validate approaches designed to re-establish plasticity-promoting neurotrophin signaling by NGF receptors (TrkA and p75NTR). Our central hypothesis is that treatments that circumvent or block Nogo-A inhibition of TrkA to stimulate TrkA-mediated neurotrophin signaling pathways will enhance neuroplasticity and improve recovery following ischemic stroke. In Aim 1 we will use primary neurons in culture to examine TrkA and p75NTR neurotrophin signaling mechanisms affected by Nogo-A and test strategies designed to circumvent or block the inhibitory effect of Nogo-A on TrkA signaling. In Aim 2 we will determine the role of Nogo-A on TrkA-mediated neurotrophin signaling following ischemic stroke in vivo using neuron-specific Nogo-A knockout mice. Biochemical and immunohistochemical techniques will be used to assess the effect of stroke on NGF receptors, their downstream effectors and the association of these receptors with Nogo-A in wild type and knockout mice. In Aim 3 we will evaluate therapeutic interventions that circumvent or block the inhibitory action of Nogo-A on the TrkA receptor to enhance recovery after stroke. We will use our well-studied in vivo stroke model to determine the extent to which treatment with anti-Nogo-A antibody or the novel selective TrkA agonist gambogic amide affects NGF signaling and stroke recovery. Together, the results from this proposal will increase our understanding of underlying neurotrophin-mediated signaling mechanisms altered as a result of stroke injury. Thus, the proposed work will provide a foundation for novel and promising therapies for stroke rehabilitation, which is critically important for the design and successful outcome of future clinical trials.