Regulation of soluble guanylyl cyclase redox state by hydrogen sulfide

Soluble guanylate cyclase (sGC) is a receptor for nitric oxide (NO). Binding of NO to ferrous (Fe²⁺) heme increases its catalytic activity, leading to the production of cGMP from GTP. Hydrogen sulfide (H₂S) is a signaling molecule that exerts both direct and indirect anti-oxidant effects. In the present, study we aimed to determine whether H₂S could regulate sGC redox state and affect its responsiveness to NO-releasing agents and sGC activators. Using cultured rat aortic smooth muscle cells, we observed that treatment with H₂S augmented the response to the NO donor DEA/NO, while attenuating the response to the heme-independent activator BAY58-2667 that targets oxidized sGC. Similarly, overexpression of H₂S-synthesizing enzyme cystathionine-γ lyase reduced the ability of BAY58-2667 to promote cGMP accumulation. In experiments with phenylephrine-constricted mouse aortic rings, treatment with rotenone (a compound that increases ROS production), caused a rightward shift of the DEA/NO concentration-response curve, an effect partially restored by H₂S. When rings were pre-treated with H₂S, the concentration-response curve to BAY 58-2667 shifted to the right. Using purified recombinant human sGC, we observed that treatment with H₂S converted ferric to ferrous sGC enhancing NO-donor-stimulated sGC activity and reducing BAY 58-2667-triggered cGMP formation. The present study identified an additional mechanism of cross-talk between the NO and H₂S pathways at the level of redox regulation of sGC. Our results provide evidence that H₂S reduces sGC heme Fe, thus, facilitating NO-mediated cellular signaling events.