β-Nicotinamide Mononucleotide Inhibits Cellular Senescence in Mouse C2C12 Skeletal Muscle Cells

β-Nicotinamide mononucleotide (NMN), as the precursor of nicotinamide adenine dinucleotide (NAD⁺), has remarkable therapeutic potential in aging-associated diseases. Skeletal muscle exhibits not only reduced mass but also impaired strength and function during aging. However, the protective effects of NMN against skeletal muscle cell senescence remain to be fully elucidated. In this study, we used D-galactose (D-gal) to establish a senescence model in C2C12 cells. Our results demonstrate that aging C2C12 cells displayed a significant impairment in differentiation capacity, an effect that was ameliorated by NMN treatment, as indicated by an increase in myotube formation and elevated myosin heavy chain (MHC) expression. NMN significantly decreased reactive oxygen species (ROS) levels in both aged C2C12 myoblasts and myotubes. NMN treatment downregulated the mRNA expression of aging-associated markers, including tumor protein p53 (Trp53), poly (ADP-ribose) polymerases (PARPs), and interleukin-1α (IL-1α) in aged C2C12 myotubes. Immunofluorescence staining revealed that the expressions of p53 and interleukin-1β (IL-1β) were significantly upregulated in aged C2C12 myotubes, while NMN treatment significantly attenuated this elevation. Collectively, the present study demonstrates that NMN treatment attenuates D-gal-induced ROS accumulation, enhances myotube formation, and downregulates several senescence-associated molecules. Therefore, our findings suggest that NMN represents a promising therapeutic agent for mitigating skeletal muscle cell aging.