Excessive exposure to manganese (Mn) results in basal ganglia pathology and enhanced production of inflammatory mediators (cytokines, nitric oxide, prostaglandins) by activated glia in vitro. In preliminary in vivo studies we have shown that Mn exposure potentiates production of inflammatory molecules in brain and in circulation. We have also shown that this potentiation by Mn (i) is at the level of transcription, (ii) is accompanied by increased expression of early growth response factor 1 (Egr1), (iii) in vitro effects of Mn are dependent upon intracellular kinases and NADPH oxidase, and (iv) the enhancement of inflammation by Mn is independent of the nature of the activating inflammatory stimulus as increased cytokine production was observed when microglial cells were activated with different toll-like receptor (TLR) ligands. Finally, using biophotonic imaging, we also demonstrated that intrapallidal administration of Mn and an inflammagen leads to marked and sustained astrocyte activation. At present, there are no in vivo studies describing the nature of the interaction between Mn and an inflammagen nor are there studies describing the regional specificity and extent of the neuropathology associated with such an interaction. Moreover, there are no studies investigating the role of microglia vs. astrocytes in Mn neurotoxicity within the context on inflammation. We hypothesize that exposure to Mn will potentiate inflammation in mice challenged peripherally with an inflammagen in a brain region-specific manner, resulting in persistent neuroinflammation and selective neuronal loss in the basal ganglia. We also hypothesize that both astrocytes and microglia will contribute to the neuroinflammation, with microglia playing a dominant role earlier in the process. The project has the following Specific Aims: 1) determine, in a time-, brain region (striatum, globus pallidus, thalamus, substantia nigra)-, concentration-, and route of exposure- dependent fashion, the molecular alterations caused by peripheral Mn exposure alone or in combination with an inflammagen challenge;2) determine in vivo the role that the three major kinases (p38, JNK, and ERK), Egr1, and NADPH oxidase play in the potentiation of brain inflammation following exposure to Mn and an in- flammagen;3) determine the time-course, the degree of microglia and astrocyte activation, as well as cell- specific alterations in inflammatory molecules caused by exposure to Mn and an inflammagen. The proposed investigations will delineate the molecular mechanisms of the interaction between Mn and inflammagens in the induction of neurodegeneration and the role of microglia vs. astrocytes in the process.
The research proposed in this application is significant because it underscores the importance of assessing the contribution of peripheral inflammation to the neurotoxicity of Mn, thus allowing the identification of segments of the society who may at a greater potential risk when exposed to Mn. Namely, individuals with underlying inflammatory response at the time of exposure to Mn or individuals with increased body burdens of Mn, who are exposed to strong inflammatory stimuli.
