Mechanical overload induces skeletal muscle hypertrophy through coordinated fiber remodeling, neuromuscular junction (NMJ) adaptation, and transcriptional changes. The objective of this study was to determine whether acute inhibition of microRNA (miRNA) activity impairs these adaptations. We hypothesized that blocking miRNA function during hypertrophy would disrupt molecular and structural remodeling required for effective muscle growth. We developed an inducible, muscle-specific mouse model (HSA-T6B) in which doxycycline triggers expression of the T6B peptide to inhibit miRNA function without altering miRNA abundance. Adult male mice underwent 10 days of mechanical overload (MOV) of the plantaris muscle. Muscle mass, fiber cross-sectional area (CSA), fiber-type composition, NMJ markers, and transcriptomic profiles were assessed using histology, immunostaining, RNA sequencing, and co-expression network analysis. Control mice exhibited robust hypertrophy after MOV, with increased normalized muscle weight, total RNA content, whole-muscle CSA, and fiber number. In HSA-T6B mice, muscle weight and RNA content increased similarly to controls, but whole-muscle CSA, mean fiber CSA, and fiber number were largely blunted. NCAM-positive fibers, particularly Type IIa, increased in control mice but not in T6B-expressing muscles, indicating impaired NMJ adaptation. Transcriptomic analysis revealed that MOV induced 1,876 differentially expressed genes (DEGs) in controls and 3,171 DEGs in HSA-T6B mice. Direct comparison of MOV-treated Dox+ versus Dox– muscles identified 833 DEGs enriched for synaptic signaling, membrane potential regulation, and NMJ-associated processes. Weighted gene co-expression network analysis showed that miRNA inhibition selectively blunted or reversed the normal upregulation of NMJ- and synapse-related gene modules. Integration with CLIP-seq dataset highlighted miRNA targets regulating sarcomeric integrity, cytoskeletal organization, and extracellular interactions. Despite these molecular and structural perturbations, endplate potentials were preserved, suggesting compensatory mechanisms maintain NMJ transmission in the short term. These findings demonstrate that miRNA activity is essential for coordinating fiber remodeling, NMJ plasticity, and transcriptional adaptation during mechanical overload. Acute suppression of miRNA function disrupts structural and neuromuscular remodeling, revealing a critical role for miRNA-dependent regulation in skeletal muscle hypertrophy. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Vechetti et al. (Fri,) studied this question.