Gut microbiota disturbance disrupts osteonal organization and mechanical competence during postnatal cortical bone maturation in rabbits with local metabolic and transcriptional remodeling.

Introduction: Bone strength depends not only on bone mass and mineral density but also on cortical tissue organization and material quality. Osteons are key structural units of cortical bone, yet whether gut microbiota disturbance affects cortical bone maturation at the osteon level remains unclear. Methods: We first characterized cortical canal remodeling and osteonal organization in New Zealand rabbits at 1, 2, and 3 months of age. Antibiotic-induced microbiota disturbance (AIMD) was then applied during this early osteon-forming window, followed by assessments of gut microbiota composition, osteon morphology, cortical bone micro-CT parameters, mechanical performance, femoral metabolomics, and cortical bone transcriptomics. Results: AIMD reduced gut microbial diversity and altered microbial community structure. At 3 months of age, AIMD-treated rabbits showed impaired osteonal organization, including a reduced proportion of secondary osteons and altered osteon morphology. These osteon-level changes were accompanied by decreased maximum load and stiffness, whereas conventional micro-CT parameters of cortical geometry and mineral density remained unchanged. Multi-omics analyses further revealed local metabolic and transcriptional remodeling involving lipid-related metabolites, bone matrix regulation, osteocyte communication, and metabolic enzyme programs. Discussion: These findings suggest that early gut microbiota disturbance impairs osteon-level cortical bone maturation and reduces mechanical competence. Osteonal organization may therefore represent a sensitive layer of cortical bone quality affected by gut microbiota disturbance during postnatal skeletal development.