Parkinson's disease (PD) is a progressive neurodegenerative disease marked by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) resulting in dopamine deficiency in the striatum and subsequent movement disorders (Dauer and Przedborski, 2003). In addition to reduced levels of dopamine, PD patients also exhibit reduced levels of the brain- derived neurotrophic factor BDNF (Mogi et al., 1999). To date, all effective treatments currently available for controlling the symptoms of PD have been shown to increase the levels of BDNF (Fumagalli et al., 2006), suggesting that the BDNF signaling cascade is the critical therapeutic target. BDNF promotes cell survival through the activation of the high affinity tyrosine receptor kinase trkB. Upon binding BDNF, trkB dimerizes and undergoes trans-autophosphorylation of critical tyrosine residues which function as docking sites to allow activation of the intracellular signaling cascades which mediate BDNF-dependent neuron survival. This proposal will test the hypothesis that delaying trkB dephosphorylation by inhibiting the trkB tyrosine phosphatase will prolonged BDNF signaling and thus increase BDNF efficacy allowing normally insufficient levels of BDNF to now support neuron survival. As a first step toward testing this hypothesis, we will conduct siRNA screening in human NT2 neurons and in gel-phosphatase assays on cell extracts to identify the tyrosine-phosphatase for trkB. Using siRNA targeting the phosphatase, the effects of reduced phosphatase activity will then be tested by examining the dose response curve for the activation of trkB and downstream signaling molecules by BDNF. Most importantly, the ability of reduced levels of BDNF to promote neuron survival will be assayed following inactivation of the trkB tyrosine phosphatase. Neurodegenerative diseases are an enormous burden on this nation both socially and economically and new targets for therapeutic intervention are necessary in order to enhance our ability to delay or inhibit the neuronal death underlying these diseases. This proposal seeks to test the feasibility of increasing neuron survival by enhancing the ability of endogenous brain-derived neurotrophic factor (BDNF) to promote cell survival. This proposal is based on the simple idea that prolonging the duration of cell signaling induced upon BDNF binding to its receptor trkB may allow the reduced levels of BDNF often associated with neurodegenerative disease such as Parkinson's disease or Alzheimer's disease to be sufficient to maintain neuron function and viability. ? ? ?
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