Phenotypic and functional changes in glial cells as a function of age

Both in vivo and in vitro investigations point to an important role for the immune system in the development of age-related neurodegeneration. Microglia isolated from aged female F344 rats, 18–20 months, show a higher percentage of cells with an ameboid morphology indicative of activation, whereas, astrocytes had a quiescent morphology. The ability of astrocytes and microglia to attenuate toxin-induced neuronal injury was examined. Post-natal day 1–3 pup cells optimally rescued neurons from Aβ-induced toxicity, whereas mixed glial cells from 18–20 month old rats were unable to rescue neurons from Aβ-induced toxicity. Our results suggested the appearance of a neurotoxic co-factor, therefore we investigated the basal level of nitric oxide and pro-inflammatory cytokines to determine if altered levels of immune mediators play a role in the toxicity. Mitogen-stimulated nitric oxide production increased 10 fold with age of donor, whereas, only the pup cells expressed an increase in TNF-α production. Basal levels of pro-inflammatory cytokines, as measured by RNA protection assays, increased with age. In particular, IL-1β was increased 2 fold between adult and aged glial cells. The elevated cytokine expression may contribute to enhanced susceptibility to neurodegenerative diseases.