Beyond deacetylation: crosstalk mechanisms and context-dependent regulation of sirtuin non-classical enzymatic functions in disease.

The sirtuin (SIRT) family, long regarded as NAD⁺-dependent lysine deacetylases, is now recognized as a diverse superfamily of lysine deacylases with high substrate selectivity. Beyond classical deacetylation, sirtuin isoforms catalyze various non-classical enzymatic activities, including demyristoylation, desuccinylation, delactylation, and mono-ADP-ribosylation, and regulate cellular signaling via non-catalytic protein interactions. While the classification of sirtuins as a lysine deacylase superfamily is well-established, their integration into complex disease networks remains fragmented. This review synthesizes the context-dependent mechanisms of these non-classical functions across five major disease areas: metabolic syndrome, cancer, aging, neurodegeneration, and cardiovascular disease. We emphasize that the same non-classical sirtuin activity exerts context-dependent bidirectional effects, either protective or pathogenic, influenced by tissue type, cellular microenvironment, and substrate availability. We illustrate synergistic and antagonistic crosstalk among sirtuin members that supports precise metabolic regulation. We also summarize emerging therapeutic strategies targeting non-classical sirtuin activities, including small molecules, natural products, and biologics, and highlight key challenges: improving substrate selectivity, minimizing off-target effects, and promoting clinical translation. Finally, we propose three critical research directions: clarifying dynamic mechanisms of substrate selectivity, developing condition-specific targeting approaches, and advancing high-resolution detection of post-translational modifications. This review provides a paradigm shift in understanding sirtuin biology and lays the molecular foundation for precision therapies against metabolic and age-related diseases.