Masutakeside I from Styrax japonicus improves mitochondrial function to promote myogenesis in skeletal muscle cells

Purpose: Skeletal muscle, accounting for approximately 40% of the total body mass, plays a critical role in movement, postural support, and metabolic homeostasis.Muscle mass is determined by the balance between protein synthesis and degradation, which is closely regulated by the mitochondrial function.Mitochondrial dysfunctions contribute to muscle loss by promoting oxidative stress and cellular damage.This study examined the effects of masutakeside I, a lignan glycoside derived from Styrax japonicus, on the mitochondrial function and muscle differentiation in C2C12 myoblasts.Methods: C2C12 myoblasts differentiated into myotubes in the presence of masutakeside I (0-10 ng/mL).Myogenic differentiation was assessed by myosin heavy chain (MHC) immunofluorescence, and multinucleated myotubes and relative diameters were quantified.The mitochondrial function was evaluated by measuring the mitochondrial reactive oxygen species (ROS), mitochondrial mass, and mitochondrial membrane potential using MitoSOX, MitoTracker Green, and JC-1 staining, respectively.Gene expression related to muscle differentiation, protein degradation, and the mitochondrial life cycle was analyzed using quantitative reverse transcription polymerase chain reaction.Results: Masutakeside I significantly increased the number of multinucleated (≥ 5 nuclei) MHC-positive myotubes and relative myotube diameter compared to the control.In addition, masutakeside I upregulated the myogenic markers, including phosphoinositide 3-kinase and MHC isoforms (Myh2, Myh4, and Myh7), while significantly downregulating