Extended hypoxia-mediated H 2 S production provides for long-term oxygen sensing.

Aim: Numerous studies have shown that H ₂ S serves as an acute oxygen sensor in a variety of cells. We hypothesize that H ₂ S also serves in extended oxygen sensing.
Methods: Here, we compare the effects of extended exposure (24-48 hours) to varying O ₂ tensions on H ₂ S and polysulphide metabolism in human embryonic kidney (HEK 293), human adenocarcinomic alveolar basal epithelial (A549), human colon cancer (HTC116), bovine pulmonary artery smooth muscle, human umbilical-derived mesenchymal stromal (stem) cells and porcine tracheal epithelium (PTE) using sulphur-specific fluorophores and fluorometry or confocal microscopy.
Results: All cells continuously produced H ₂ S in 21% O ₂ and H ₂ S production was increased at lower O ₂ tensions. Decreasing O ₂ from 21% to 10%, 5% and 1% O ₂ progressively increased H ₂ S production in HEK293 cells and this was partially inhibited by a combination of inhibitors of H ₂ S biosynthesis, aminooxyacetate, propargyl glycine and compound 3. Mitochondria appeared to be the source of much of this increase in HEK 293 cells. H ₂ S production in all other cells and PTE increased when O ₂ was lowered from 21% to 5% except for HTC116 cells where 1% O ₂ was necessary to increase H ₂ S, presumably reflecting the hypoxic environment in vivo. Polysulphides (H ₂ S _n , where n = 2-7), the key signalling metabolite of H ₂ S also appeared to increase in many cells although this was often masked by high endogenous polysulphide concentrations.
Conclusion: These results show that cellular H ₂ S is increased during extended hypoxia and they suggest this is a continuously active O ₂ -sensing mechanism in a variety of cells.
(© 2019 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.)