Role of Microglia in Neurological Disorders and Their Potentials as a Therapeutic Target

Microglia are resident macrophage-like immune cells in the central nervous system (CNS) and play a vital role in both physiological and pathological conditions, including restoring the integrity of the CNS and promoting the progression of neurodegenerative disorders. Upon stimulation, microglia typically convert from a surveillant to an activated phenotype. The major function of microglia is to maintain homeostasis and normal function of the CNS, both during development and in response to CNS injury. Microglia regulate multiple aspects of inflammation, such as repair, cytotoxicity, regeneration, and immunosuppression due to their different kind of activation states or phenotypes. Although microglia are involved in almost all neurodegenerative disorders, the mechanisms for microglial activation and their potential contributions to neuronal degeneration remain a matter of intense debate. In inflammatory process of the CNS, polarized M1 microglia can produce proinflammatory cytokines, neurotoxic molecules, which contribute to dysfunction of neural network and promoting inflammation reaction, whereas polarized M2 microglia secrete antiinflammatory mediators and neurotrophic factors that are involved in restoring homeostasis. Modulation of microglial activation for therapeutic purposes might be realized via suppressing the deleterious effects of these cells, while simultaneously retaining their protective functions. Here, we summarize the functions of microglia and discuss dual role of microglia in neurodegenerative diseases as well as multiple sclerosis.