Hydrogen sulfide perturbs mitochondrial bioenergetics and triggers metabolic reprogramming in colon cells

Unlike most other tissues, the colon epithelium is exposed to high levels of H₂S derived from gut microbial metabolism. H₂S is a signaling molecule that modulates various physiological effects. It is also a respiratory toxin that inhibits complex IV in the electron transfer chain (ETC). Colon epithelial cells are adapted to high environmental H₂S exposure as they harbor an efficient mitochondrial H₂S oxidation pathway, which is dedicated to its disposal. Herein, we report that the sulfide oxidation pathway enzymes are apically localized in human colonic crypts at the host-microbiome interface, but that the normal apical-to-crypt gradient is lost in colorectal cancer epithelium. We found that sulfide quinone oxidoreductase (SQR), which catalyzes the committing step in the mitochondrial sulfide oxidation pathway and couples to complex III, is a critical respiratory shield against H₂S poisoning. H₂S at concentrations ≤20 μm stimulated the oxygen consumption rate in colon epithelial cells, but, when SQR expression was ablated, H₂S concentrations as low as 5 μm poisoned cells. Mitochondrial H₂S oxidation altered cellular bioenergetics, inducing a reductive shift in the NAD⁺/NADH redox couple. The consequent electron acceptor insufficiency caused uridine and aspartate deficiency and enhanced glutamine-dependent reductive carboxylation. The metabolomic signature of this H₂S-induced stress response mapped, in part, to redox-sensitive nodes in central carbon metabolism. Colorectal cancer tissues and cell lines appeared to counter the growth-restricting effects of H₂S by overexpressing sulfide oxidation pathway enzymes. Our findings reveal an alternative mechanism for H₂S signaling, arising from alterations in mitochondrial bioenergetics that drive metabolic reprogramming.