Vascular smooth muscle cell-derived SO₂ sulphenylated interferon regulatory factor 1 to inhibit VSMC senescence

BACKGROUND: Vascular smooth muscle cell (VSMC) senescence is a critical driver of vascular aging and various age-related cardiovascular diseases. Endogenous sulfur dioxide (SO₂), a newly identified key cardiovascular gaseous signaling mediator, accelerates collagen deposition and vascular remodeling in VSMCs when downregulated. However, its effects on VSMC senescence remain unclear. OBJECTIVE: This study focused on exploring the role of endogenous SO₂ in VSMC senescence and its associated molecular pathways. METHODS: Aged mice (24 months old), VSMC-specific aspartate aminotransferase 1 (AAT1) knockout (VSMC-AAT1-KO) mice, D-galactose (D-gal)-treated aorta rings and rat VSMC line A7r5 were used in the experiments. AAT1 expression was detected by Western blot and single-cell RNA sequencing. Senescence markers Tp53, p21Cip/Waf, interleukin 1β (IL-1β) and IL6 expression were detected by Western blot and real-time quantitative PCR. Senescence-associated β-galactosidase (SA-β-gal) activity was detected using SA-β-gal staining kit. Sulphenylation of interferon regulatory factor 1 (IRF1) was detected using a biotin switch assay. The plasmid for mutant IRF1 (mutation of cysteine 83 to serine, C83S) were constructed by site-directed mutagenesis. RESULTS: The expression of AAT1, a key enzyme for SO₂ production, was reduced in the aortic tissue of aged mice in comparison to young mice. VSMC-AAT1-KO mice exhibited elevated protein expression of senescence markers Tp53, p21Cip/Waf and γ-H2AX in the aortic tissue. AAT1 knockdown in VSMCs elevated expression of Tp53, p21Cip/Waf, IL-1β and IL-6, and enhanced SA-β-gal activity. While SO₂ donor supplementation rescued VSMC senescence caused by AAT1 knockdown and blocked aortic ring aging induced by D-gal. Mechanistically, SO₂ promoted IRF1 sulphenylation, inhibited IRF1 nuclear translocation, which in turn downregulated the expression of senescence markers and the activity of SA-β-gal. Furthermore, mutation of C83 in IRF1 abolished SO₂-mediated IRF1 sulphenylation and blocked the inhibitory effect of SO₂ on VSMC senescence. CONCLUSION: Reduction of the endogenous SO₂/AAT1 pathway played a crucial role in driving VSMC senescence. Endogenous SO₂ counteracted VSMC senescence and vascular aging via the sulphenylation of IRF1 at C83.