SIRT1 in Senescence: Mitochondria and Immune Crosstalk.

Cellular senescence is one of the hallmarks of aging. These growth-arrested cells actively secrete inflammatory mediators that reshape the tissue microenvironment and fuel age-related pathology. Sirtuin 1 (SIRT1) is an NAD+-dependent deacetylase that regulates senescence largely through its control over mitochondrial integrity and inflammatory signaling. SIRT1 levels and activity fall with age, and this decline directly promotes senescence. SIRT1 maintains mitochondrial function through three interconnected pathways: PGC-1α-driven mitochondria biogenesis, FOXO-dependent antioxidant defense, and mitophagic clearance of damaged organelles. When SIRT1 activity is in an unsteady state, mitochondria become unhealthy. This leads to excessive ROS generation and the leakage of mitochondrial DNA (mtDNA) into the cytosol, which activates the innate immune pathway, consequently resulting in the production of inflammatory cytokines that further inhibit SIRT1. This self-amplifying loop drives cells to irreversible senescence. In this study, we integrate the current understanding of the SIRT1-mitochondria-immune axis within the framework of senescence by examining the biological roles of SIRT1 and the mechanisms that lead to its reduction with aging, while also exploring the interrelated mitochondrial pathways and inflammatory signaling. Furthermore, we assess possible therapeutic strategies targeting this axis and highlight essential questions that necessitate additional research.