Roles of Glia‐Derived Cytokines on Neuronal Degeneration and Regeneration

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Abstract
Accumulation of activated microglia and reactive astrocytes is observed around degenerating neurons in various inflammatory or degenerative disorders in the central nervous system. These reactive glial cells may play either neurotoxic or neuroprotective roles. In this study, we examined the effects of glia-derived cytokines on neuronal degeneration and regeneration. Neuron-rich cultures were stimulated with supernatant of microglia and astrocytes stimulated with LPS, or a various concentrations of recombinant cytokines. Neurotoxicity was evaluated by an MTS assay. Neuronal damage was also evaluated by a frequency of dendritic beading, which was found to be an early feature of neuronal damage toward cell death. Effects of the cytokines on production of neurotrophic factors by astrocytes were also examined by RT-PCR for the expression of mRNA. Supernatant of LPS-stimulated microglia induced neuronal cell death. However, all the recombinant cytokines examined did not induce cell death, while IFNgamma and TNFalpha induced dendrite beading, an early feature of neuronal damage. IL-1beta and TNFalpha enhanced the production of neurotrophic factors by astrocytes. These observations suggest that glial cell-derived cytokines may synergistically function in neuronal degeneration with other toxic factors produced by activated microglia, and that some of them may also function in regeneration by inducing neurotrophic factors.