Gut microbiota depletion alters functional recovery and bone healing following fracture in mice.

Bone fracture pain evolves dynamically with tissue repair, yet current analgesic strategies are limited by adverse effects and concerns regarding impaired healing. The gut microbiome is an established regulator of pain and inflammation; however, its contribution to post-fracture recovery remains unclear. We tested whether antibiotic-induced microbiota depletion alters functional recovery and behavior after femoral fractures. Young female C57BL/6J mice received a broad-spectrum oral antibiotic cocktail or control water for two weeks prior to femoral fracture and were assessed longitudinally over 28 days after fracture. Microbiota depletion was associated with prolonged deficits in hindlimb loading and zone clearance performance, and continuous home-cage monitoring revealed decreased vertical rearing activity and voluntary wheel-running, collectively indicating sustained functional and motivational impairment. Despite a hypoinflammatory systemic and intestinal phenotype, microbiota-depleted mice exhibited elevated ipsilateral lumbar DRG expression of Ngf and Cxcl1 at Day 7 post-fracture alongside suppressed DRG Il10. NGF immunoreactivity was also elevated in the ipsilateral lumbar DRG of microbiota-depleted mice at the same timepoint. Microarchitectural analysis of fracture callus were suggestive of delayed secondary fracture healing. Together, these findings indicate that antibiotic-induced microbiota depletion was associated with altered inflammatory, behavioral, and skeletal responses after fracture. These results identify the gut microbiome as a potential contributor to the integrated pain-healing response to skeletal injury.