BMP-2-driven osteo-organoid formation retains key osteogenic-support features and promotes bone repair following total-body irradiation

Abstract

Irradiation stress causes persistent skeletal injury by disrupting marrow homeostasis, stromal function, and bone repair. However, the temporal remodeling of the native bone microenvironment and the capacity of a biomaterial-induced osteogenic environment to sustain regeneration under systemic irradiation remain unclear. Using 6 Gy total body irradiation (TBI), we characterized time-resolved changes in the native femur and evaluated BMP-2-loaded hyaluronic acid methacryloyl (BMP-2/HAMA)-induced osteo-organoids relative to their corresponding non-irradiated controls. TBI caused progressive femoral deterioration, including trabecular bone loss, persistent B-cell depletion, neutrophil-associated myeloid expansion, Type-H endothelial-cell decline, and accumulation of senescence-associated mesenchymal stromal cells (MSCs). Single-cell RNA sequencing further resolved mature B-cell loss and enrichment of inflammatory and mature neutrophil states. In osteo-organoids, irradiation delayed but did not abolish tissue maturation. By 6 weeks, irradiated osteo-organoids approached the tissue and cellular features of non-irradiated osteo-organoids at the mature 3-week stage, while the MSC-associated stromal compartment remained relatively stable. Osteo-organoid-derived MSCs exhibited less pronounced irradiation-associated dysfunction and retained clonogenic, osteogenic, and immunomodulatory capacities. In an irradiation-impaired femoral defect model, BMP-2/HAMA enhanced mineralized tissue formation, mechanical competence, and gait function. These findings support BMP-2/HAMA as a biomaterial-assisted strategy for functional bone regeneration under irradiation-impaired conditions.