In vivo evidence that during environmental exposure to a hypoxic environment, PDGF beta receptor activation underlies both functional components of the ventilatory response as well as mechanisms responsible for hypoxic tolerance and adaptation. Based on these data, a model encompassing the signaling pathways potentially involved in PDGF beta receptor mediated cellular adaptations to hypoxia was developed. We therefore propose to test the hypothesis that differential susceptibility to apoptosis elicited by the hypoxic stimulus in central neurons is modulated by discrete differences in PDGF beta receptor or its intracellular signaling pathways. To further assess the validity of this hypothetical model, we will study the role of PDGF B-PDGF beta receptor signaling during hypoxia in neuronal cell lines with differential susceptibility to hypoxia. Such experimental approach will allow for identification of kinase systems mediating signal transduction pathway(s) that prevent hypoxia-induced apoptosis and enable adaptation to hypoxia. Four major aims will be addressed in this application, namely (1) To identify and characterize distinct neuronal cell lines that differ in their susceptibility to hypoxia-induced apoptosis. (2) To compare the apoptotic response patterns of neuronal cell lines to sustained hypoxia and intermittent hypoxia in relation to their PDGF beta receptor expression. (3) To delineate the PDGF beta receptor signal transduction pathways underlying the differential susceptibility to hypoxia-induced apoptosis and identify pathway differences between continuous and intermittent hypoxia. (4) To modify the differential susceptibility to hypoxia-induced apoptosis by performing transfection experiments of candidate kinase systems identified in Specific Aim 3. In previous experiments, we found that hypoxia elicits nuclear activation of the NF-kappaB transcription factor and activates the anti-apoptotic kinase Akt to phosphorylate and inactivate the pro-apoptotic BAD via a PDGF beta receptor-dependent pathway. In hypoxia-tolerant neurons within the rat brainstem, PDGF receptor signaling may underlie tolerance mechanisms to adverse conditions such as hypoxia. Identification of neuronal cellular model to study functional implications of PDGF B-PDGF beta receptor and downstream signaling pathways during hypoxia will allow for delineation of interventional strategies aiming to modify hypoxic neuronal vulnerability. These strategies may further help to refine approaches aiming to promote cell survival and cell specific differentiation during cell transplantation therapies of the injured CNS so as to promote graft survival.
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