Unrepaired DNA damage in macrophages causes elevation of particulate matter-induced airway inflammatory response

The inflammatory cascade can be initiated with the recognition of damaged DNA. Macrophages play an essential role in particulate matter (PM)-induced airway inflammation. In this study, we aim to explore the PM induced DNA damage response of macrophages and its function in airway inflammation. The DNA damage response and inflammatory response were assessed using bone marrow-derived macrophages following PM treatment and mouse model instilled intratracheally with PM. We found that PM induced significant DNA damage both in vitro and in vivo and simultaneously triggered a rapid DNA damage response, represented by nuclear RPA, 53BP1 and gamma H2AX foci formation. Genetic ablation or chemical inhibition of the DNA damage response sensor amplified the production of cytokines including Cxcl1, Cxcl2 and Ifn-gamma after PM stimulation in bone marrow-derived macrophages. Similar to that seen in vitro, mice with myeloid-specific deletion of RAD50 showed higher levels of airway inflammation in response to the PM challenge, suggesting a protective role of DNA damage sensor during inflammation. These data demonstrate that PM exposure induces DNA damage and activation of DNA damage response sensor MRN complex in macrophages. Disruption of MRN complex lead to persistent, unrepaired DNA damage that causes elevated inflammatory response.