Phosphorylation-driven regulation of SIRT1 in muscle senescence: Insights from molecular dynamics simulation and...

Sirtuin 1 (SIRT1) is a key regulator of mitochondrial function and inflammatory responses, both of which are critical in the progression of muscle aging and sarcopenia. While SIRT1's activity is known to be regulated by post-translational modifications, the specific role of Ser46 phosphorylation has not been fully elucidated. In this study, we explored the effects of Ser46 phosphorylation on SIRT1's structural stability, subcellular localization, and downstream signaling in the context of muscle cell senescence. Using a combination of molecular dynamics (MD) simulations and in vitro assays with C2C12 myoblasts, we demonstrated that phosphorylation at Ser46 enhances SIRT1's structural stability by reducing flexibility in its nuclear localization signal (NLS) and catalytic domains. This modification promotes nuclear translocation of SIRT1 and is associated with a reduction in PGC-1α expression and mitochondrial membrane potential. Additionally, Ser46 phosphorylation activates NF-κB-mediated inflammatory pathways and is associated with increased p53 expression and SA-β-gal activity, hallmarks of cellular senescence. JC-1 staining further revealed that Ser46 phosphorylation compromises mitochondrial membrane potential. These findings reveal a previously unrecognized mechanism by which Ser46 phosphorylation shifts SIRT1's function toward promoting inflammation and muscle senescence, providing a potential target for therapeutic interventions in age-related muscle degeneration.