Mechanistic reprogramming of the mtDNA-cGAS-STING axis in cellular senescence: from mitochondrial homeostatic disruption to inflammatory and immune outcomes.

In addition to cell cycle arrest, cellular senescence is characterized by disrupted mitochondrial homeostasis, development of the senescence-associated secretory phenotype (SASP), and alterations in the immune microenvironment. Mitochondrial membrane damage, disrupted mitochondrial dynamics, and impaired mitochondrial quality control (MQC) can occur during cellular senescence. These changes may cause mitochondrial DNA (mtDNA) to leak abnormally into the cytosol. Cytosolic mtDNA can then activate cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling. Unlike the acute innate immune response elicited by pathogen-derived DNA, cGAS-STING signaling in senescent cells is mainly activated by the aberrant cytosolic accumulation of endogenous DNA. This signaling activates the TANK-binding kinase 1 (TBK1)-interferon regulatory factor 3 (IRF3) axis and induces a type I interferon response. It also promotes nuclear factor kappaB (NF-κB)-mediated inflammatory transcription, sustains the SASP, and modulates paracrine signaling and immune cell function. This review focuses on mitochondrial structural damage, mtDNA release, and impaired MQC. It summarizes the mechanisms that activate the mtDNA-cGAS-STING axis during cellular senescence and examines its functional changes. It also discusses the potential development of senescence-associated biomarkers. Current evidence suggests that this signaling axis mainly contributes to the maintenance and amplification of the inflammatory senescence phenotype. It is unlikely to independently determine the onset of cellular senescence. Its effects are highly dependent on cell type and pathological context, while assay standards, causal relationships, and therapeutic windows require further clarification.