Abstract
Hydrogen sulfide (H(2)S) is a gasotransmitter and a potential therapeutic agent. However, molecular targets relevant to its therapeutic actions remain enigmatic. Sulfide-quinone oxidoreductase (SQR) irreversibly oxidizes H(2)S. Therefore, SQR is assumed to inhibit H(2)S signaling. We now report that SQR-mediated oxidation of H(2)S drives reverse electron transport (RET) at mitochondrial complex I, which, in turn, repurposes mitochondrial function to superoxide production. Unexpectedly, complex I RET, a process dependent on high mitochondrial membrane potential, induces superoxide-dependent mitochondrial uncoupling and downstream activation of adenosine monophosphate-activated protein kinase (AMPK). SQR-induced mitochondrial uncoupling is separated from the inhibition of mitochondrial complex IV by H(2)S. Moreover, deletion of SQR, complex I, or AMPK abolishes therapeutic effects of H(2)S following intracerebral hemorrhage. To conclude, SQR mediates H(2)S signaling and therapeutic effects by targeting mitochondrial electron transport to induce mitochondrial uncoupling. Moreover, SQR is a previously unrecognized target for developing non-protonophore uncouplers with broad clinical implications.