NEUROINFLAMMATION AND THE AGED DOPINERGIC SYSTEM

Medical University Of South Carolina, Charleston SC

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Abstract

Neuroinflammation in association with oxidative stress resulting from glial cell (i.e., microglia and astrocytes) activation has been recognized to play a significant role in age-related vulnerability of specific populations of neurons. The dopaminergic (DA) system of the substantia nigra (SN) in particular, may be targeted by cytokines and reactive oxygen species (ROS) derived from activated microglia. Although normally astrocytes protect neurons through their production of growth and trophic molecules, "aging" astrocytes, because of their expression of pro-oxidant enzymes such as MAO-B and a high content of free iron, can promote enzymatic and non-enzymatic oxidation of dopamine, generating toxic levels of ROS. Additionally, any lack of adequate trophic support (growth factor deficiency) and/or exposure to environmental toxins would further exacerbate the situation, resulting in compromised DA function. In Project 0003, we will test the hypothesis that activation of glia and their production of toxic mediators and cytokines represent a major factor in age-related vulnerability of the DA system under conditions of growth factor (i.e., GDNF and BDNF) deficiency and exposure, in early life, to environmental toxins represented by endotoxin (lipopolysaccharide, LPS) and methamphetamine (METH). In Specific Aim #1, the extent of age-related glial cell activation in growth factor deficient (GDNF/BDNF heterozygous) mice and in mice exposed to METH and endotoxin will be determined using specific markers of glial activation. The expression of inflammatory/toxic mediators including cytokines and the eicosanoids will be determined by ELISA, RT-PCR and/or RIA and the expression of proinflammatory/pro-oxidant enzymes including nitric oxide synthase, NADPH oxidase, MAO-B and COX2 will be determined by biochemical and immunochemical assays. In Specific Aim #2, the neuroprotective use of minocycline, an antibiotic that primarily acts by suppressing microglia-mediated neuroinflammation, will be investigated in the two dual-hit models i.e., GDNF+/- animals acutely injected with LPS and METH.