Human microglial responses to DNA damage are mediated by the cytosolic sensor cGAS

Abstract

Abstract Genomic instability is a key driving force for cancer development and age-related disease. While DNA damage responses are known to regulate genome integrity and cell fates, there is mounting evidence that genomic instability can trigger inflammatory and/or antitumor responses via pattern recognition receptors (PRRs) located in the cytosol. One such PRR, cyclic GMP-AMP synthase (cGAS), canonically detects foreign viral or bacterial DNA resulting from infection, initiating a signaling cascade resulting in the production and secretion of type I interferons and inflammatory cytokines. However, we hypothesize that cGAS contributes to the initiation of innate immune responses following DNA damage in the central nervous system (CNS) outside of its canonical role of viral/microbial cytosolic DNA recognition. In the present study, we induced DNA damage using ionizing radiation or oxidative stress in a human microglial cell line, and assessed the effect of cGAS knock-down on the immune responses of these cells to these insults. DNA damage following exposure to radiation or oxidative stress was verified by fluorescent microscopy for the formation of micronuclei and expression of γH2AX. Wild-type microglia showed robust production and secretion of IL-6 and IL-8 following DNA damage as assessed specific-capture ELISA. Importantly, these inflammatory responses at 24 hours following DNA damage were significantly attenuated in human microglia-like cells following cGAS knock-down. Taken together, these data support the contention that cGAS plays a significant role in the initiation of potentially detrimental proinflammatory immune responses by human CNS cells following DNA damage outside of its canonical role in antiviral immunity. Supported by a grant from NINDS (NS111260)