Chronic intoxication with manganese (Mn) is the cause of a degenerative movement disorder, termed manganism, with clinical features that resemble Parkinson's disease. Recent findings suggest that injury to this region of the brain involves perturbation of the normally supportive function of glial cells to an activated state that results in increased expression of inflammatory genes such as inducible nitric oxide synthase (NOS2), that can subsequently produce neurotoxic levels of nitric oxide (NO). Similar deleterious neuro-glial interactions occur in other degenerative disorders of the basal ganglia, such as Parkinson's and Huntington's diseases, highlighting the need to elucidate the mechanisms underlying these damaging interactions. The long-term goal of this research program is to better understand role of glial cells in the pathogenesis of diseases of the basal ganglia. The objective of this application is to identify mechanisms underlying glial-mediated neuronal injury in an experimental model of manganism. The central hypothesis is that Mn exposure results in glial activation and expression of NOS2 that contributes to age-dependent neuronal injury and debilitation of basal ganglia function through overproduction of NO. This hypothesis will be tested by pursuing two specific aims: 1) Determine the Mn-dependent signals that cause induction of NOS2 in astroglial cells. The working hypothesis for this aim is that Mn increases NF-KappaB-dependent expression of NOS2 by activating specific MAP kinases. 2) Identify the mechanisms underlying age-dependent susceptibility of the basal ganglia to manganese. It is postulated under this aim that Mn-mediated production of NO during development results in glial activation and neuronal injury that decreases the threshold for basal ganglia dysfunction upon subsequent exposures. The experimental approach proposed utilizes genetic interdiction of specific signaling molecules in the NF-KappaB pathway to identify critical upstream activators of NOS2 expression in astroglial cells. The activity of the factors identified will be quantified in relation to activity of NF-KappaB and expression of NOS2 in neonatal and adult wildtype and transgenic mice exposed to Mn. It is expected that this innovative approach will identify important early targets of Mn that promote neuronal injury by increased synthesis of NO. The proposed research is significant, because it is expected to advance understanding of the pathogenic role of glial-derived NO in disorders of the basal ganglia and, thereby, to foster the development of neuroprotective therapeutic strategies that target inflammatory signaling pathways in glial cells.
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