Muscle Fiber- and Cell Type-Specificity of Training Adaptation in Male Mice

Abstract

Skeletal muscle exhibits extraordinary structural and functional plasticity in response to contractile activity. As a syncytium within a complex microenvironment, its adaptation relies on the coordinated response of specialized myonuclear populations and diverse mononucleated cells. Here, we present a high-resolution single-nucleus RNA-sequencing atlas of 550000 nuclei, capturing the longitudinal transcriptional dynamics of 17 myonuclear and 21 mononuclear populations following exhaustive exercise. We demonstrate that training status reshapes these cellular programs into divergent adaptive trajectories. While mononucleated cells serve as the primary mediators of intercellular communication during recovery, a subset of oxidative myonuclei enters a delayed regenerative state, reflecting a bifurcated response to the metabolic demands of endurance exercise. This is accompanied by signatures of impaired innervation and transient neuromuscular junction (NMJ) remodeling. Notably, prior training accelerates homeostatic recovery by preserving neuromuscular integrity and shielding oxidative nuclei from damage-associated signatures. Together, this atlas reveals that muscle plasticity emerges from a highly coordinated interplay of multicellular remodeling and provides a foundational resource for understanding the mechanisms of exercise adaptation.