Mammary Fibroblasts Secrete Damage Associated Molecular Patterns Through Extracellular Vesicles in Response to Ionizing Radiation

ABSTRACT Ionizing radiation (IR) is an integral component of cancer therapy. Cellular exposure to IR typically leads to major biological consequences including cell death and senescence. Furthermore, tissue injury is known to involve the release of damage‐associated molecular patterns (DAMPs) into the extracellular space, which trigger inflammation and wound healing. However, DAMP release in the context of radiation injury remains to be fully characterized. Evidence suggests that extracellular vesicle (EV) secretion and associated cargo components are part of the cellular response to IR, but the relationship between cellular damage and EV secretion post‐IR remains unclear. In this study, we show that acute radiation damage in mammary fibroblasts is associated with a senescence‐like phenotype and substantially increased EV secretion. Quantitative proteomic analysis revealed that IR‐induced EVs are enriched with extracellular and intracellular DAMPs, along with other pro‐inflammatory mediators. We show that knockdown of the GTPase Rab27a abrogates IR‐induced EV secretion and inhibits the enrichment of key DAMPs in EVs. We also show that EVs from irradiated fibroblasts promote an inflammatory response in macrophages. By examining the co‐occurrence of cellular damage and senescence‐like features with the release of inflammatory signals, this study elucidates a potentially critical role for EV‐associated proteins in the radiation response.