H2S-induced S-sulfhydration of pyruvate carboxylase contributes to gluconeogenesis in liver cells

S-Sulfhydration of ATP synthase by hydrogen sulfide stimulates mitochondrial bioenergetics

Mammalian cells can utilize hydrogen sulfide (H2S) to support mitochondrial respiration. The aim of our study was to explore the potential role of S-sulfhydration (a H2S-induced posttranslational modification, also known as S-persulfidation) of the mitochondrial inner membrane protein ATP synthase (F1F0 ATP synthase/Complex V) in the regulation of mitochondrial bioenergetics. Using a biotin switch assay, we have detected S-sulfhydration of the α subunit (ATP5A1) of ATP synthase in response to exposure to H2S in vitro. The H2S generator compound NaHS induced S-sulfhydration of ATP5A1 in HepG2 and HEK293 cell lysates in a concentration-dependent manner (50-300μM). The activity of immunocaptured mitochondrial ATP synthase enzyme isolated from HepG2 and HEK293 cells was stimulated by NaHS at low concentrations (10-100nM). Site-directed mutagenesis of ATP5A1 in HEK293 cells demonstrated that cysteine residues at positions 244 and 294 are subject to S-sulfhydration. The double mutant ATP synthase protein (C244S/C294S) showed a significantly reduced enzyme activity compared to control and the single-cysteine-mutated recombinant proteins (C244S or C294S). To determine whether endogenous H2S plays a role in the basal S-sulfhydration of ATP synthase in vivo, we compared liver tissues harvested from wild-type mice and mice deficient in cystathionine-gamma-lyase (CSE, one of the three principal mammalian H2S-producing enzymes). Significantly reduced S-sulfhydration of ATP5A1 was observed in liver homogenates of CSE-/- mice, compared to wild-type mice, suggesting a physiological role for CSE-derived endogenous H2S production in the S-sulfhydration of ATP synthase. Various forms of critical illness (including burn injury) upregulate H2S-producing enzymes and stimulate H2S biosynthesis. In liver tissues collected from mice subjected to burn injury, we detected an increased S-sulfhydration of ATP5A1 at the early time points post-burn. At later time points (when systemic H2S levels decrease) S-sulfhydration of ATP5A1 decreased as well. In conclusion, H2S induces S-sulfhydration of ATP5A1 at C244 and C294. This post-translational modification may be a physiological mechanism to maintain ATP synthase in a physiologically activated state, thereby supporting mitochondrial bioenergetics. The sulfhydration of ATP synthase may be a dynamic process, which may be regulated by endogenous H2S levels under various pathophysiological conditions.

Implications of Hydrogen Sulfide in Glucose Regulation: How H2S Can Alter Glucose Homeostasis through Metabolic Hormones

Diabetes and its comorbidities continue to be a major health problem worldwide. Understanding the precise mechanisms that control glucose homeostasis and their dysregulation during diabetes are a major research focus. Hydrogen sulfide (H₂S) has emerged as an important regulator of glucose homeostasis. This is achieved through its production and action in several metabolic and hormone producing organs including the pancreas, liver, and adipose. Of importance, H₂S production and signaling in these tissues are altered during both type 1 and type 2 diabetes mellitus. This review first examines how H₂S is produced both endogenously and by gastrointestinal microbes, with a particular focus on the altered production that occurs during obesity and diabetes. Next, the action of H₂S on the metabolic organs with key roles in glucose homeostasis, with a particular focus on insulin, is described. Recent work has also suggested that the effects of H₂S on glucose homeostasis goes beyond its role in insulin secretion. Several studies have demonstrated important roles for H₂S in hepatic glucose output and adipose glucose uptake. The mechanism of H₂S action on these metabolic organs is described. In the final part of this review, future directions examining the roles of H₂S in other metabolic and glucoregulatory hormone secreting tissues are proposed.

Hydrogen sulfide exhibits cardioprotective effects by decreasing endoplasmic reticulum stress in a diabetic cardiomyopathy rat model

Endoplasmic reticulum (ER) stress is critical in the occurrence and development of diabetic cardiomyopathy (DC). Hydrogen sulfide (H2S) has been found to be the third gaseous signaling molecule with anti‑ER stress effects. Previous studies have shown that H2S acts as a potent inhibitor of fibrosis in the heart of diabetic rats. This study aimed to demonstrate whether H2S exhibits protective effects on the myocardium of streptozotocin (STZ)‑induced diabetic rats by suppressing ER stress. In this study, diabetic models were established by intraperitoneal (i.p.) injection of 40 mg/kg STZ. The STZ‑treated mice were divided into three groups, and subsequently treated with normal saline, 30 µmol/kg or 100 µmol/kg NaHS, i.p., respectively, for 8 weeks. The extent of myocyte hypertrophy was measured using hematoxylin and eosin‑stained sections and collagen components were investigated using immunostaining. The expression of glucose-regulated protein (Grp78), C/EBP‑homologous protein (CHOP) and caspase‑12 in the heart tissue of each group was detected by western blot analysis. It was demonstrated that H2S could improve myocardial hypertrophy and myocardial collagen deposition in diabetic rats. In addition, it could reduce the expression of Grp78, caspase-12 and CHOP. In conclusion, these findings demonstrate that H2S suppresses STZ‑induced ER stress in the hearts of rats, and it may serve as a novel cardioprotective agent for DC.

Thioredoxin 1 regulation of protein S-desulfhydration

The importance of H₂S in biology and medicine has been widely recognized in recent years, and protein S-sulfhydration is proposed to mediate the direct actions of H₂S bioactivity in the body. Thioredoxin 1 (Trx1) is an important reducing enzyme that cleaves disulfides in proteins and acts as an S-denitrosylase. The regulation of Trx1 on protein S-sulfhydration is unclear. Here we showed that Trx1 facilitates protein S-desulfhydration. Overexpression of Trx1 attenuated the basal level and H₂S-induced protein S-sulfhydration by direct interaction with S-sulfhydrated proteins, i.e., glyceraldehyde 3-phosphate dehydrogenase and pyruvate carboxylase. In contrast, knockdown of Trx1 mRNA expression by short interfering RNA or blockage of Trx1 redox activity with PX12 or 2,4-dinitrochlorobenzene enhanced protein S-sulfhydration. Mutation of cysteine-32 but not cysteine-35 in the Trp-Cys³²-Gly-Pro-Cys³⁵ motif eliminated the binding of Trx1 with S-sulfhydrated proteins and abolished the S-desulfhydrating effect of Trx1. All these data suggest that Trx1 acts as an S-desulfhydrase.

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

Spinocerebellar ataxia type 3 (SCA3) is a polyglutamine (polyQ) disorder caused by a CAG repeat expansion in the ataxin-3 (ATXN3) gene resulting in toxic protein aggregation. Inflammation and oxidative stress are considered secondary factors contributing to the progression of this neurodegenerative disease. There is no cure that halts or reverses the progressive neurodegeneration of SCA3. Here we show that overexpression of cystathionine γ-lyase, a central enzyme in cysteine metabolism, is protective in a Drosophila model for SCA3. SCA3 flies show eye degeneration, increased oxidative stress, insoluble protein aggregates, reduced levels of protein persulfidation and increased activation of the innate immune response. Overexpression of Drosophila cystathionine γ-lyase restores protein persulfidation, decreases oxidative stress, dampens the immune response and improves SCA3-associated tissue degeneration. Levels of insoluble protein aggregates are not altered; therefore, the data implicate a modifying role of cystathionine γ-lyase in ameliorating the downstream consequence of protein aggregation leading to protection against SCA3-induced tissue degeneration. The cystathionine γ-lyase expression is decreased in affected brain tissue of SCA3 patients, suggesting that enhancers of cystathionine γ-lyase expression or activity are attractive candidates for future therapies.