Microglia, the principal immune effector cells of the brain, play an important role in the regulation of the immunologic microenvironment within the CNS. They lie dormant until the integrity of the CNS is challenged by injury, infection or disease processes and when chronically activated, secrete a number of inflammatory mediators including cytokines and tissue damaging free radicals as part of the pathogenic mechanism common to a variety of CNS disorders including stroke, Alzheimer's Disease, AIDS dementia and demyelinating diseases such as multiple sclerosis. A mechanistic understanding of the process of microglial activation is, therefore, crucial for devising therapeutic strategies to suppress neuroinflammation. This project tests the hypothesis that signal transduction pathways mediated by members of the mitogen-activated protein kinase (MAPK) family play a key role in microgiial activation and the induction of inflammatory responses. Primary cultures of rat brain microglia wili be used as a model to accomplish the following objectives. The activities and the roles of MAPK cascades (i.e., extracellular signal-regulated kinase or ERK, p38 MAPK and c-Jun N-terminal kinase or JNK) will be investigated in microglia activated in response to endotoxin and receptor (CD40) ligation. The effects of pharmacological inhibitors of MAPKs on the expression of microglial antigens (i.e., MHC class 11, B7 and CD40), cytokines (i.e., TNFa, IL-1, IL-6) and inducible nitric oxide synthase (iNOS) will be determined by immunochemical and RT-PCR techniques. Possible isoforrn-specific roles and down-stream targets of p38 MAPK and JNK in inducing cytokine and iNOS gene expression will be characterized in transient transfection studies using molecular mutants of the kinases along with iNOS and cytokine gene promoter constructs. The suppressive effects of the kinase inhibitors on activation-associated microglial functions; i.e., targeting of oligodendrocytes and myelin phagocytosis will be tested using in vitro models.
