[Microglia in neurodegenerative disorders and neuroinflammation]

Microglia often accumulate around degenerating neurons. These macrophage-like immune cells produce a variety of neurotoxic and neuroprotective factors. Thus, the accumulation of glia in various neurologic disorders does not reflect only gliosis, but likely results in an active contribution to neuroinflammation, neural degeneration, and cell regeneration. We previously showed that glutamate is the most neurotoxic factor released by activated microglia, and suppressing glutamate release from microglia can inhibit disease progression in various animal models of neurodegenerative disorders. On the other hand, when exposed to harmful stimuli, neurons also produce and release various factors that serve as "help-me" signals. For example, the CX3C chemokine fractalkine, interleukin-34, and fibroblast growth factor-2 are secreted from damaged neurons; these help-me signals induce various microglial activities to rescue neurons, including upregulated phagocytosis of toxicants and damaged debris, and production of antioxidant enzymes and other neurotrophic factors. Elucidating the interactions between neurons and microglia will help uncover the mechanisms underlying chronic neuroinflammatory conditions, and may provide insights into new therapeutic strategies for neurodegenerative disorders.