The central hypothesis of this proposal is that injury-induced perturbations of homeostasis in the central nervous system (CNS) reflect, in part, local increases in oxygen-derived free radicals. Also, that neurotrophic factors, such as the neurotrophins, ameliorate the effects of injuries on neuronal survival in part due to their effects on cellular antioxidant defenses, e.g. catalase and glutathione peroxidase, and by enhancing recovery from the depletion of glutathione and NADP+. These homeostatic failures may also reflect alterations in the levels of intercellular signals such as the nerve growth factor protein (NGF), a member of the neurotrophin family, in CNS neurons and glia, respectively. It is further proposed that a critical component of these homeostatic processes is the interaction of NGF with glucocorticoids in these target cells in terms of expression of the two NGF receptors p75NGFR and p140trk). In order to test these hypotheses, the NGF effects on glutathione and pyridine metabolism in rat pheochromocytoma PC12 cells will be characterized. Also, the extent of the response of glutathione and pyridine metabolism that have been challenged with H2O2 and the xanthine oxidase/hypoxanthine/ADP-Fe+3 free radical generating system will be examined in the presence and absence of NGF. Key enzyme activities and mRNA species, as well as the appropriate cofactor and substrate levels, that are responsible for glutathione cycling and pyridine metabolism will be determined by spectrophotometric assays, Northerns, reverse transcriptase-polymerase chain reaction (RT-PCR), and ribonuclease protection assays. Appropriate inhibitors will be applied to deplete glutathione levels and interfere with pyridine metabolism as part of these studies. In order to evaluate the roles of p75NGFR and p140trk in PC12 dependence on NGF for survival, the effects of glucocorticoids and NGF on PC12 p75NGFR and p140trk mRNA levels will be determined. Also, the requirement for p75NGFR and p140trk mRNA expression for survival will be analyzed applying the above mentioned techniques and the use of antisense oligonucleotides. Our goal is to understand the relative importance of oxidative metabolism in injured CNS and the potentials and limitations of neurotrophic effects on neuronal survival and CNS homeostatic mechanisms. A better understanding of ischemic and traumatic neural injury will result from these studies.
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