Abstract
The accumulation of senescent cells in aged tissues has been implicated in a variety of age-related diseases, including cancer and neurodegenerative disorders. Recent studies have demonstrated a link between age-associated increase of senescent glial cells in the brain and the pathogenesis of Alzheimer's disease (AD). However, there is a lack of in vitro cellular models of senescent human microglia, which significantly limits our approaches to study AD pathogenesis. Here, we show for the first time that ionizing radiation (IR) dose-dependently induces premature senescence in HMC3 human microglial cells. Senescence-associated β-galactosidase activity, a well-characterized marker of cellular senescence, was substantially increased in irradiated HMC3 cells compared with control cells. Furthermore, we found that phosphorylated p53 levels and p21 expression levels were markedly higher in IR-induced senescent microglia than in control cells. Senescent human microglia exhibited the senescence-associated secretory phenotype (SASP), as evidenced by the increased secretion of pro-inflammatory cytokine interleukin-6 (IL-6). Treatment with an NF-κB inhibitor, BAY 11-7082, inhibits the secretion of IL-6 by senescent HMC3 cells. Collectively, our studies have established an in vitro cellular model of human microglial senescence and suggest that the NF-κB pathway may play a critical role in regulating the SASP of senescent HMC3 cells.