Galectin-9^high Neutrophils Exacerbate Radiation-Induced Frailty

Local radiation injury-induced frailty seriously impacts the quality of life of patients undergoing radiotherapy or nuclear accident casualties and causes a significant medical and economic burden. However, the underlying mechanisms of the frailty remain unknown. In this study, a unique population of hyperactive GAL-9^high neutrophils is identified with characteristics of elevated ROS, NETs, and IFN-γ, prolonged lifespan, etc. These neutrophils infiltrate into multiple organs to induce injuries, also disrupt the bone marrow microenvironment, drive sustained bone marrow myeloid-biased differentiation, and resist clearance by bone marrow macrophages, serving as a crucial factor to exacerbate frailty. GAL-9 protein is demonstrated to play a vital role in the regulation of neutrophil hyperactivity. EccDNA shedding after skin radiation injury is shown to activate the JAK1/2-STAT1 pathway in splenic GMP cells, which is a potential origin of GAL-9^high neutrophils. In summary, our results highlight the significance of the previously unrecognized hyperactive GAL-9^high neutrophils to exacerbate frailty through a 'skin-spleen-bone marrow-multiple organs' axis after local radiation injury.