Ferulic acid combined with skeletal stem cells to repair irradiated bone defect

The reconstruction of irradiated bone defects after settlement of skeletal tumors remains a significant challenge in clinical applications. In this study, we explored radiation-induced skeletal stem cell (SSC) stemness impairments and rescuing effects of ferulic acid (FA) on SSCs in vitro and in vivo . The immunophenotype, cell renewal, cell proliferation, and differentiation of SSCs in vitro after irradiation were investigated. Mechanistically, the changes in tissue regeneration-associated gene expression and MAPK pathway activation in irradiated SSCs were evaluated. The regenerative capacity of SSCs in the presence of FA in an irradiated bone defect mouse model was also investigated. We found that irradiation reduced CD140a- and CD105-positive cells in skeletal tissues and mouse-derived SSCs. Additionally, irradiation suppressed cell proliferation, colony formation, and osteogenic differentiation of SSCs. The RNA-Seq results showed that tissue regeneration-associated gene expression decreased, and the western blotting results demonstrated the suppression of phosphorylated p38/MAPK and ERK/MAPK in irradiated SSCs. Notably, FA significantly rescued the radiation-induced impairment of SSCs by activating the p38/MAPK and ERK/MAPK pathways. Moreover, the results of imaging and pathological analyses demonstrated that FA enhanced the bone repair effects of SSCs in an irradiated bone defect mouse model substantially. Importantly, inhibition of the p38/MAPK and ERK/MAPK pathways in SSCs by specific chemical inhibitors partially abolished the promotive effect of FA on SSC-mediated bone regeneration. In summary, our findings reveal a novel function of FA in repairing irradiated bone defects by maintaining SSC stemness and suggest that the p38/MAPK and ERK/MAPK pathways contribute to SSC-mediated tissue regeneration post-radiation. Significance Statement Radiotherapy combined with surgery for the settlement of skeletal tumors usually leads to large bone defects and hampers wound healing. Skeletal stem cells (SSCs) have been defined as tissue-specific stem cells in skeletons and are highlighted in bone development and regeneration. Ferulic acid is a phytochemical with a wide range of therapeutic effects, including alleviation of radiation-induced oxidative stress and promotion of tissue regeneration. In the current study, promising data based on an in vitro cell model and an in vivo animal model demonstrates that ferulic acid alleviates radiation-induced impairment of SSCs and promotes SSC-mediated bone regeneration post-radiation. ### Competing Interest Statement The authors have declared no competing interest.