Post-Weaning Gut Microbiota Colonization Reveals Divergent Recovery of Skeletal Muscle and Peripheral Nerves

We previously demonstrated that the absence of a complex gut microbiota (CGM) impairs the postnatal development of peripheral nerves and motor targets in germ-free (GF) mice. In this study, we investigated whether establishing a complex gut microbiota after weaning could reverse these developmental alterations. To address this question, GF mice were colonized with a complex gut microbiota by co-housing with conventionally raised mice. Microbiota composition, peripheral nerve morphology and transcriptional profiles, skeletal muscle proteome, neuromuscular junction architecture and circulating metabolites were comprehensively analyzed and compared with those of GF, gnotobiotic OMM12 and CGM mice. Post-weaning colonization partially restored microbial diversity and resulted in a compositionally distinct microbial community with reduced alpha diversity and enrichment of Duncaniella muris strain B8. Despite successful microbial colonization, peripheral nerve abnormalities persisted, including axon hypermyelination, transcriptional alterations in sciatic nerves, elongated nodes of Ranvier, and dysregulated axon-glia interactions. In contrast, skeletal muscle defects were largely rescued, with restoration of muscle mass, normalization of proteomic profiles, recovery of metabolic and structural pathways, and reduced fragmentation of the postsynaptic neuromuscular junction, although presynaptic abnormalities persisted. These findings demonstrate that microbiota-dependent developmental alterations differ markedly in their reversibility across the neuromuscular system. Specifically, post-weaning colonization with a complex gut microbiota resulted in broad recovery of skeletal muscle but failed to rescue peripheral nerve abnormalities. Our findings provide a framework for future studies investigating how the timing of microbial colonization, microbiota composition, and microbiota-derived signals influence the reversibility of microbiota-dependent neuromuscular alterations.