Hydrogen Sulfide (H2S) Metabolism, Iron Overload, and Apoptosis–Autophagy Equilibrium in Vascular Smooth Muscle Cells

Iron overload contributes to proliferative vascular diseases, yet its interplay with hydrogen sulfide (H₂S) in vascular smooth muscle cell (VSMC) proliferation remains poorly understood. This study elucidates H₂S's role in mitigating iron-overload-induced oxidative stress and cellular damage. Using aortic VSMCs from wildtype (WT) and cystathionine γ-lyase-knockout (CSE-KO) mice treated with ferric ammonium citrate (FAC) at concentrations equivalent to serum levels of iron and citrate, we demonstrate that FAC triggers the integrated stress response (ISR) in WT cells, upregulating CSE to enhance H₂S production. The ISR mediator ATF4 activates caspases but simultaneously induces CSE, which inhibits caspase activity and promotes autophagy via AMPK signaling. In CSE-KO cells, iron overload leads to diminished Ferritin upregulation, unchecked Caspase activation, and impaired autophagy compared to WT cells. Exogenous H₂S restored iron homeostasis by enhancing Ferritin expression, activating NRF2 antioxidant pathways, and restoring apoptosis-autophagy equilibrium in both WT and KO cells. These findings establish H₂S as a critical regulator of iron-induced VSMC dysfunction, highlighting its therapeutic potential in managing vascular pathologies linked to iron dysregulation.