Hydrogen sulfide (H ₂ S) metabolism in mitochondria and its regulatory role in energy production

Abstract

Although many types of ancient bacteria and archea rely on hydrogen sulfide (H 2 S) for their energy production, eukaryotes generate ATP in an oxygen-dependent fashion. We hypothesize that endogenous H 2 S remains a regulator of energy production in mammalian cells under stress conditions, which enables the body to cope with energy demand when oxygen supply is insufficient. Cystathionine γ-lyase (CSE) is a major H 2 S-producing enzyme in the cardiovascular system that uses cysteine as the main substrate. Here we show that CSE is localized only in the cytosol, not in mitochondria, of vascular smooth-muscle cells (SMCs) under resting conditions, revealed by Western blot analysis and confocal microscopy of SMCs transfected with GFP-tagged CSE plasmid. After SMCs were exposed to A23187, thapsigargin, or tunicamycin, intracellular calcium level was increased, and CSE translocated from the cytosol to mitochondria. CSE was coimmunoprecipitated with translocase of the outer membrane 20 (Tom20) in mitochondrial membrane. Tom20 siRNA significantly inhibited mitochondrial translocation of CSE and mitochondrial H 2 S production. The cysteine level inside mitochondria is approximately three times that in the cytosol. Translocation of CSE to mitochondria metabolized cysteine, produced H 2 S inside mitochondria, and increased ATP production. Inhibition of CSE activity reversed A23187-stimulated mitochondrial ATP production. H 2 S improved mitochondrial ATP production in SMCs with hypoxia, which alone decreased ATP production. These results suggest that translocation of CSE to mitochondria on specific stress stimulations is a unique mechanism to promote H 2 S production inside mitochondria, which subsequently sustains mitochondrial ATP production under hypoxic conditions. mitochondrion | oxygen sensing | evolution | sulfur metabolism | phenylephrine M any photoautotrophic and chemoautotrophic bacteria and certain animals, such as the lugworm Arenicola marina, use sulfide as an energetic substrate. Mitochondria are the powerhouse of eukaryotic cells, where ATP is produced via oxidative phosphorylation. Considering mitochondria as the evolutionary trait of bacteria in eukaryotes, the metabolism of hydrogen sulfide (H 2 S) in mitochondria may serve as a means for energy supplementation. It has been demonstrated that H 2 S can drastically reduce metabolic demand (1). Similar to nitric oxide, H 2 S exerts protective effects on mitochondrial function and respiration (2). However, a conventional belief is that H 2 S is produced in the cytoplasm resulting from the cytosol localization of H 2 Sgenerating enzymes and is consumed through oxidation in mitochondria (3). It was recently demonstrated that mitochondria of human colon adenocarcinoma cells use sulfide as an energetic substrate at low micromolar concentrations, well below toxic levels (4). The foregoing observations call for reevaluation of the metabolism of H 2 S and its role in mitochondrial energization of eukaryotes. In the present study, we explored whether H 2 S can be prod...

Roles for ROS and hydrogen sulfide in the longevity response to germline loss in Caenorhabditis elegans

“…To learn more about KRI-1's role in ROS generation, we asked whether the DHE/ROS signal we observed, which was cytoplasmic, might have a mitochondrial origin. This notion seemed plausible, because mitochondria are major sites of ROS production, and H 2 S also can be produced in mitochondria (36,46). In addition, DHE can be oxidized by mitochondrial superoxide.…”

Hydrogen sulfide as an oxygen sensor

“…CBS, CSE, and CAT/3-MST are cytosolic enzymes, whereas CAT and 3-MST are also present in mitochondria (71). 3-MST is especially abundant in the mitochondrial matrix (103), presumably enabling access to a threefold higher cysteine concentration here than in the cytosol (42). Hypoxia appears to increase CBS in the mitochondria (164) and stress-related stimuli can translocate CSE to the mitochondria, although this may take hours (42); additional details are provided in sections ''CBS Translocation to Mitochondria'' and ''CSE Translocation to Mitochondria.''…”

“…3-MST is especially abundant in the mitochondrial matrix (103), presumably enabling access to a threefold higher cysteine concentration here than in the cytosol (42). Hypoxia appears to increase CBS in the mitochondria (164) and stress-related stimuli can translocate CSE to the mitochondria, although this may take hours (42); additional details are provided in sections ''CBS Translocation to Mitochondria'' and ''CSE Translocation to Mitochondria.'' Initially, it was believed that CBS was predominantly found in the brain and CSE was found in the cardiovascular system [reviewed in Kimura (73)], although a broader distribution is now becoming apparent (6,73,129).…”

“…CSE translocation to mitochondria: Hypoxia stimulates CSE translocation from the cytosol to the mitochondria in vascular smooth muscle cells to take advantage of a threefold increase in cysteine concentration and presumably generate ATP from H 2 S, supposedly providing some protection from hypoxia (42). However, there are several problems with this theory: First, anaerobic metabolism is sufficient for energy production in vascular smooth muscle, even during hypoxia (35), and second, electron transport cannot continue in the absence of O 2 .…”

Overexpression of Cystathionine γ-Lyase Suppresses Detrimental Effects of Spinocerebellar Ataxia Type 3

“…H 2 S also confers cytoprotection via suppression of inflammation (17) and by protecting mitochondrial function and integrity (17,18). Decreased levels of H 2 S in brain tissue are associated with neurodegenerative age-related diseases such as Parkinson's (19), and administration of H 2 S has been shown protective in experimental models for this disease (20)(21)(22).…”