SQR mediates therapeutic effects of H2S by targeting mitochondrial electron transport to induce mitochondrial uncoupling

Recent advances in upconversion nanoparticle-based nanocomposites for gas therapy

Gas therapy has attracted wide attention for the treatment of various diseases. However, a controlled gas release is highly important for biomedical applications. Upconversion nanoparticles (UCNPs) can precisely convert the long wavelength of light to ultraviolet/visible (UV/Vis) light in gas therapy for the controlled gas release owing to their unique upconversion luminescence (UCL) ability. In this review, we mainly summarized the recent progress of UCNP-based nanocomposites in gas therapy. The gases NO, O2, H2, H2S, SO2, and CO play an essential role in the physiological and pathological processes. The UCNP-based gas therapy holds great promise in cancer therapy, bacterial therapy, anti-inflammation, neuromodulation, and so on. Furthermore, the limitations and prospects of UCNP-based nanocomposites for gas therapy are also discussed.

Dynamic Distribution of HIG2A between the Mitochondria and the Nucleus in Response to Hypoxia and Oxidative Stress

Mitochondrial respiratory supercomplex formation requires HIG2A protein, which also has been associated with cell proliferation and cell survival under hypoxia. HIG2A protein localizes in mitochondria and nucleus. DNA methylation and mRNA expression of the HIGD2A gene show significant alterations in several cancers, suggesting a role for HIG2A in cancer biology. The present work aims to understand the dynamics of the HIG2A subcellular localization under cellular stress. We found that HIG2A protein levels increase under oxidative stress. H2O2 shifts HIG2A localization to the mitochondria, while rotenone shifts it to the nucleus. HIG2A protein colocalized at a higher level in the nucleus concerning the mitochondrial network under normoxia and hypoxia (2% O2). Hypoxia (2% O2) significantly increases HIG2A nuclear colocalization in C2C12 cells. In HEK293 cells, chemical hypoxia with CoCl2 (>1% O2) and FCCP mitochondrial uncoupling, the HIG2A protein decreased its nuclear localization and shifted to the mitochondria. This suggests that the HIG2A distribution pattern between the mitochondria and the nucleus depends on stress and cell type. HIG2A protein expression levels increase under cellular stresses such as hypoxia and oxidative stress. Its dynamic distribution between mitochondria and the nucleus in response to stress factors suggests a new communication system between the mitochondria and the nucleus.

Expanding the Reactive Sulfur Metabolome: Intracellular and Efflux Measurements of Small Oxoacids of Sulfur (SOS) and H2S in Human Primary Vascular Cell Culture

Hydrogen sulfide (H2S) is an endogenous signaling molecule which is important for cardiovascular health, but its mechanism of action remains poorly understood. Here, we report measurements of H2S as well as its oxidized metabolites, termed small oxoacids of sulfur (SOS = HSOH and HOSOH), in four human primary vascular cell lines: smooth muscle and endothelial cells derived from both human arterial and coronary tissues. We use a methodology that targets small molecular weight sulfur species; mass spectrometric analysis allows for species quantification to report cellular concentrations based on an H2S calibration curve. The production of H2S and SOS is orders of magnitude higher in smooth muscle (nanomolar) as compared to endothelial cell lines (picomolar). In all the primary lines measured, the distributions of these three species were HOSOH >H2S > HSOH, with much higher SOS than seen previously in non-vascular cell lines. H2S and SOS were effluxed from smooth muscle cells in higher concentrations than endothelial cells. Aortic smooth muscle cells were used to examine changes under hypoxic growth conditions. Hypoxia caused notable increases in HSOH and ROS, which we attribute to enhanced sulfide quinone oxidase activity that results in reverse electron transport.

A redox cycle with complex II prioritizes sulfide quinone oxidoreductase-dependent H2S oxidation

The dual roles of H₂S as an endogenously synthesized respiratory substrate and as a toxin raise questions as to how it is cleared when the electron transport chain is inhibited. Sulfide quinone oxidoreductase (SQOR) catalyzes the first step in the mitochondrial H₂S oxidation pathway, using CoQ as an electron acceptor, and connects to the electron transport chain at the level of complex III. We have discovered that at high H₂S concentrations, which are known to inhibit complex IV, a new redox cycle is established between SQOR and complex II, operating in reverse. Under these conditions, the purine nucleotide cycle and the malate aspartate shuttle furnish fumarate, which supports complex II reversal and leads to succinate accumulation. Complex II knockdown in colonocytes decreases the efficiency of H₂S clearance while targeted knockout of complex II in intestinal epithelial cells significantly decreases the levels of thiosulfate, a biomarker of H₂S oxidation, to approximately one-third of the values seen in serum and urine samples from control mice. These data establish the physiological relevance of this newly discovered redox circuitry between SQOR and complex II for prioritizing H₂S oxidation and reveal the quantitatively significant contribution of intestinal epithelial cells to systemic H₂S metabolism.

A Case for Hydrogen Sulfide Metabolism as an Oxygen Sensing Mechanism

The ability to detect oxygen availability is a ubiquitous attribute of aerobic organisms. However, the mechanism(s) that transduce oxygen concentration or availability into appropriate physiological responses is less clear and often controversial. This review will make the case for oxygen-dependent metabolism of hydrogen sulfide (H₂S) and polysulfides, collectively referred to as reactive sulfur species (RSS) as a physiologically relevant O₂ sensing mechanism. This hypothesis is based on observations that H₂S and RSS metabolism is inversely correlated with O₂ tension, exogenous H₂S elicits physiological responses identical to those produced by hypoxia, factors that affect H₂S production or catabolism also affect tissue responses to hypoxia, and that RSS efficiently regulate downstream effectors of the hypoxic response in a manner consistent with a decrease in O₂. H₂S-mediated O₂ sensing is then compared to the more generally accepted reactive oxygen species (ROS) mediated O₂ sensing mechanism and a number of reasons are offered to resolve some of the confusion between the two.

Hydrogen Sulfide Attenuates Angiotensin II-Induced Cardiac Fibroblast Proliferation and Transverse Aortic Constriction-Induced Myocardial Fibrosis through Oxidative Stress Inhibition via Sirtuin 3

Sirtuin 3 (SIRT3) is critical in mitochondrial function and oxidative stress. Our present study investigates whether hydrogen sulfide (H₂S) attenuated myocardial fibrosis and explores the possible role of SIRT3 on the protective effects. Neonatal rat cardiac fibroblasts were pretreated with NaHS followed by angiotensin II (Ang II) stimulation. SIRT3 was knocked down with siRNA technology. SIRT3 promoter activity and expression, as well as mitochondrial function, were measured. Male wild-type (WT) and SIRT3 knockout (KO) mice were intraperitoneally injected with NaHS followed by transverse aortic constriction (TAC). Myocardium sections were stained with Sirius red. Hydroxyproline content, collagen I and collagen III, α-smooth muscle actin (α-SMA), and dynamin-related protein 1 (DRP1) expression were measured both in vitro and in vivo. We found that NaHS enhanced SIRT3 promoter activity and increased SIRT3 mRNA expression. NaHS inhibited cell proliferation and hydroxyproline secretion, decreased collagen I, collagen III, α-SMA, and DRP1 expression, alleviated oxidative stress, and improved mitochondrial respiration function and membrane potential in Ang II-stimulated cardiac fibroblasts, which were unavailable after SIRT3 was silenced. In vivo, NaHS reduced hydroxyproline content, ameliorated perivascular and interstitial collagen deposition, and inhibited collagen I, collagen III, and DRP1 expression in the myocardium of WT mice but not SIRT3 KO mice with TAC. Altogether, NaHS attenuated myocardial fibrosis through oxidative stress inhibition via a SIRT3-dependent manner.

AMPK S-sulfuration contributes to H2S donors-induced AMPK phosphorylation and autophagy activation in dopaminergic cells

Hydrogen sulfide (H₂S) serves as a neuromodulator and regulator of neuroinflammation. It is reported to be therapeutic for Parkinson's disease (PD) animal and cellular models. However, whether it affects α-synuclein accumulation in dopaminergic cells, the key pathological feature in PD, is poorly understood. In this study we reported that exogenous H₂S donors NaHS and GYY4137 (GYY) enhanced the autophagy activity, as indicated by the increases of autophagy marker LC3-II expression and LC3 dots formation even during lysosome inhibition in dopaminergic cell lines and HEK293 cells. The enhancement of H₂S donors on autophagic flux was mediated by adenosine 5'-monophosphate-activated protein kinase (AMPK)-dependent mammalian target of rapamycin (mTOR) inhibition, as H₂S donors activated AMPK but reduced the mTOR activity and H₂S donors-induced LC3-II increase was diminished by mTOR activator. Moreover, point mutation of Cys302 into alanine (C302A) in AMPKα2 subunit abolished the AMPK activation and mTOR inhibition, as well as autophagic flux increase elicited by NaHS. Interestingly, NaHS triggered AMPK S-sulfuration, which was not observed in AMPK C302A-transfected cells. Further, NaHS was able to attenuate α-synuclein accumulation in a cellular model induced by dopamine oxidized metabolite 3, 4-dihydroxyphenylacetaldehyde (DOPAL), and this effect was interfered by autophagy inhibitor wortmannin and also eliminated in AMPK Cys302A-transfected cells. In sum, the findings identified a role of Cys302 S-sulfuration in AMPK activation induced by exogenous H₂S and demonstrated that H₂S donors could enhance the autophagic flux via AMPK-mTOR signaling and thus reduce α-synuclein accumulation in vitro.

Regulation of the redox metabolome and thiol proteome by hydrogen sulfide

Overproduction of reactive oxygen species and compromised antioxidant defenses perturb intracellular redox homeostasis and is associated with a myriad of human diseases as well as with the natural process of aging. Hydrogen sulfide (H₂S), which is biosynthesized by organisms ranging from bacteria to man, influences a broad range of physiological functions. A highly touted molecular mechanism by which H₂S exerts its cellular effects is via post-translational modification of the thiol redox proteome, converting cysteine thiols to persulfides, in a process referred to as protein persulfidation. The physiological relevance of this modification in the context of specific signal transmission pathways remains to be rigorously established, while a general protective role for protein persulfidation against hyper-oxidation of the cysteine proteome is better supported. A second mechanism by which H₂S modulates redox homeostasis is via remodeling the redox metabolome, targeting the electron transfer chain and perturbing the major redox nodes i.e. CoQ/CoQH₂, NAD⁺/NADH and FAD/FADH₂. The metabolic changes that result from H₂S-induced redox changes fan out from the mitochondrion to other compartments. In this review, we discuss recent developments in elucidating the roles of H₂S and its oxidation products on redox homeostasis and its role in protecting the thiol proteome.

A Novel BODIPY Quaternary Ammonium Salt-Based Fluorescent Probe: Synthesis, Physical Properties, and Live-Cell Imaging

The development of biological fluorescent probes is of great significance to the field of cancer bio-imaging. However, most current probes within the bulky hydrophobic group have limited application in aqueous medium and restricted imaging under physiological conditions. Herein, we proposed two efficient molecules to study their physical properties and imaging work, and the absorption and fluorescence intensity were collected with varying ions attending in aqueous medium. We enhance the water solubility through the quaternization reaction and form a balance between hydrophilic and hydrophobicity with dipyrrome-theneboron difluoride (BODIPY) fluorophore. We introduced pyridine and dimethylaminopyridine (DMAP) by quaternization and connected the BODIPY fluorophore by ethylenediamine. The final synthesized probes have achieved ideal affinity with HeLa cells (human cervical carcinoma cell line) in live-cell imaging which could be observed by Confocal Microscope. The probes also have a good affinity with subcutaneous tumor cells in mice in in vivo imaging, which may make them candidates as oncology imaging probes.

Hydrogen Sulfide, an Endogenous Stimulator of Mitochondrial Function in Cancer Cells

Hydrogen sulfide (H₂S) has a long history as toxic gas and environmental hazard; inhibition of cytochrome c oxidase (mitochondrial Complex IV) is viewed as a primary mode of its cytotoxic action. However, studies conducted over the last two decades unveiled multiple biological regulatory roles of H₂S as an endogenously produced mammalian gaseous transmitter. Cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST) are currently viewed as the principal mammalian H₂S-generating enzymes. In contrast to its inhibitory (toxicological) mitochondrial effects, at lower (physiological) concentrations, H₂S serves as a stimulator of electron transport in mammalian mitochondria, by acting as an electron donor—with sulfide:quinone oxidoreductase (SQR) being the immediate electron acceptor. The mitochondrial roles of H₂S are significant in various cancer cells, many of which exhibit high expression and partial mitochondrial localization of various H₂S producing enzymes. In addition to the stimulation of mitochondrial ATP production, the roles of endogenous H₂S in cancer cells include the maintenance of mitochondrial organization (protection against mitochondrial fission) and the maintenance of mitochondrial DNA repair (via the stimulation of the assembly of mitochondrial DNA repair complexes). The current article overviews the state-of-the-art knowledge regarding the mitochondrial functions of endogenously produced H₂S in cancer cells.