Résumé
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that affects both upper and lower motor neurons. As motor neurons degenerate, they lose their connection to muscle cells, leading to the onset of fasciculations and muscle atrophy. Eventually, ALS results in paralysis, with symptoms progressively worsening over time. The disease typically leads to death within 3–5 years after diagnosis. Currently, there is no definitive cure. Understanding the morphological and mechanical modifications in skeletal muscle fibers of an ALS mouse model (SOD1-G93A) could be crucial for uncovering the molecular mechanisms underlying the disease.In this study, second harmonic generation (SHG) multiphoton microscopy and atomic force microscopy (AFM) were used to evaluate sarcomere periodicity, stiffness, and orientation in gastrocnemius muscle fibers from symptomatic SOD1-G93A mice (90 days), comparing them to wild-type (WT) controls. Our results reveal a significant reduction in sarcomere periodicity in SOD1-G93A mice compared to WT controls. Furthermore, AFM data indicate the presence of two populations of muscle fibers: slower Type-I and faster Type-II fibers. Notably, SOD1-G93A tissue exhibits a dramatic softening of fast fibers, while not statistical difference was detected for slow fibers. This result could indicate that ALS, at this stage of the disease, selectively affects skeletal muscle fibers specialized for fast contraction.These alterations in mechanical properties and morphology reflect structural and molecular changes in the sarcomeres, suggesting a change in inner structure of the main structural proteins.