Reversal of Sp1 transactivation and TGFβ1/SMAD1 signaling by H2S prevent nickel-induced fibroblast activation

Hydrogen sulfide and metal interaction: the pathophysiological implications

Hydrogen sulfide (H₂S), previously recognized as a toxic gas, has emerged as an important gaseous signaling molecule along with nitric oxide, carbon monoxide and also hydrogen. H₂S can be endogenously produced in the mammalian body at a very low level for various pathophysiological processes. Notably, H₂S can interact with several essential metals in the body such as iron, copper, nickel, and zinc to carry out specific functions. The interactions of H₂S with metal-binding proteins have been shown to aid in its signal transduction and cellular metabolism. In addition, H₂S is capable of providing a cytoprotective role against metal toxicity. As the research in the field of H₂S signaling in biology and medicine increases, much progresses have been developed for detecting H₂S via interaction with metals. In this review, the interaction of H₂S with metals, specifically in regard to metal-driven metabolism of H₂S, the protection against metal toxicity by H₂S and the detection of H₂S using metals will be discussed. Discovering the interactions of this gasotransmitter with metals is important for determining the mechanisms underlying the cellular functions of H₂S as well as developing novel therapeutic avenues.

H2S protects from oxidative stress-driven ACE2 expression and cardiac aging

Cystathionine gamma-lyase (CSE)-derived hydrogen sulfide (H₂S) plays an essential role in preserving cardiac functions. Angiotensin-converting enzyme 2 (ACE2) acts as the negative regulator of the renin-angiotensin system, exerting anti-oxidative stress and anti-inflammatory properties within the body. The interplays of CSE/H₂S signaling and ACE2 in cardiac aging are unclear. In this study, the regulatory roles of H₂S on ACE2 expression in mouse heart tissue and rat cardiomyocytes under different stress conditions were investigated. It was found that ACE2 protein level was lower in heart tissues from old mice (56-week-old) than young mice (8-week-old), and the knockout of CSE (CSE KO) induced moderate oxidative stress and further inhibited ACE2 protein level in mouse hearts at both young and old age. Incubation of rat cardiac cells (H9C2) with a low dose of H₂O₂ (50 µM) suppressed ACE2 protein level and induced cellular senescence, which was completely reversed by co-incubation with 30 µM NaHS (a H₂S donor). Prolonged nutrient excess is an increased risk of heart disorders by causing metabolic dysfunction and cardiac remodeling. We further found high-fat diet feeding stimulated ACE2 expression and induced severe oxidative stress in CSE KO heart in comparison with wild-type heart. Lipid overload in H9C2 cells to mimic a status of nutrient excess also enhanced the expression of ACE2 protein and induced severe oxidative stress and cell senescence, which were significantly attenuated by the supplementation of exogenous H₂S. Furthermore, the manipulation of ACE2 expression partially abolished the protective role of H₂S against cellular senescence. These results demonstrate the dynamic roles of H₂S in the maintenance of ACE2 levels under different levels of oxidative stress, pointing to the potential implications in targeting the CSE/H₂S system for the interruption of aging and diabetes-related heart disorders.

Transcriptional repression of E-cadherin in nickel-exposed lung epithelial cells mediated by loss of Sp1 binding at the promoter

E-cadherin plays a central role in the stability of epithelial tissues by facilitating cell-cell adhesion. Loss of E-cadherin expression is a hallmark of epithelial-mesenchymal transition (EMT), a major event in the pathogenesis of several lung diseases. Our earlier studies showed that nickel, a ubiquitous environmental toxicant, induced EMT by persistently downregulating E-cadherin expression in human lung epithelial cells and that the EMT remained irreversible postexposure. However, the molecular basis of persistent E-cadherin downregulation by nickel exposure is not understood. Here, our studies show that the binding of transcription factor Sp1 to the promoter of E-cadherin encoding gene, CDH1, is essential for its expression. Nickel exposure caused a loss of Sp1 binding at the CDH1 promoter, resulting in its downregulation and EMT induction. Loss of Sp1 binding at the CDH1 promoter was associated with an increase in the binding of ZEB1 adjacent to the Sp1 binding site. ZEB1, an EMT master regulator persistently upregulated by nickel exposure, is a negative regulator of CDH1. CRISPR-Cas9-mediated knockout of ZEB1 restored Sp1 binding at the CDH1 promoter. Furthermore, ZEB1 knockout rescued E-cadherin expression and re-established the epithelial phenotype. Since EMT is associated with a number of nickel-exposure-associated chronic inflammatory lung diseases including asthma, fibrosis and cancer and metastasis, our findings provide new insights into the mechanisms associated with nickel pathogenesis.

H2S signaling and extracellular matrix remodeling in cardiovascular diseases: A tale of tense relationship

Extracellular matrix (ECM) is a non-cellular three-dimensional macromolecular network that not only provides mechanical support but also transduces essential molecular signals in organ functions. ECM is constantly remodeled to control tissue homeostasis, responsible for cell adhesion, cell migration, cell-to-cell communication, and cell differentiation, etc. The dysregulation of ECM components contributes to various diseases, including cardiovascular diseases, fibrosis, cancer, and neurodegenerative diseases, etc. Aberrant ECM remodeling is initiated by various stress, such as oxidative stress, inflammation, ischemia, and mechanical stress, etc. Hydrogen sulfide (H₂S) is a gasotransmitter that exhibits a wide variety of cytoprotective and physiological functions through its anti-oxidative and anti-inflammatory actions. Amounting research shows that H₂S can attenuate aberrant ECM remodeling. In this review, we discussed the implications and mechanisms of H₂S in the regulation of ECM remodeling in cardiovascular diseases, and highlighted the potential of H₂S in the prevention and treatment of cardiovascular diseases through attenuating adverse ECM remodeling.

Acute acrylonitrile exposure inhibits endogenous H2S biosynthesis in rat brain and liver: The role of CBS/3-MPST-H2S pathway in its astrocytic toxicity

Hydrogen sulfide (H₂S) as the third gasotransmitter molecule serves various biological regulatory roles in health and disease. Acrylonitrile (AN) is a common occupational toxicant and environmental pollutant, causing brain and liver damage in mammals. The biotransformation of AN is dependent-upon reduced glutathione (GSH), cysteine and other sulfur-containing compounds. However, the effects of AN on the endogenous H₂S biosynthesis pathway have yet to be determined. Herein, we demonstrated that a single exposure to AN (at 25, 50, or 75 mg/kg for 1, 6 or 24 h) decreased the endogenous H₂S content and H₂S-producing capacity in a dose-dependent manner, both in the cerebral cortex and liver of rats in vivo. In addition, the inhibitory effects of AN (1, 2.5, 5, 10 mM for 12 h) on the H₂S content and/or the expression of H₂S-producing enzymes were also found both in primary rat astrocytes and rat liver cell line (BRL cells). Impairment in the H₂S biosynthesis pathway was also assessed in primary rat astrocytes treated with AN. It was found that inhibition of the cystathionine-β-synthase (CBS)/3-mercaptopyruvate sulfurtransferase (3-MPST)-H₂S pathway with the CBS inhibitor or 3-MPST-targeted siRNA significantly increased the AN-induced (5 mM for 12 h) cytotoxicity in astrocytes. In turn, CBS activation or 3-MPST overexpression as well as exogenous NaHS supplementation significantly attenuated AN-induced cytotoxicity. Taken together, endogenous H₂S biosynthesis pathway was disrupted in rats acutely exposed to AN, which contributes to acute AN neurotoxicity in primary rat astrocytes.

Transcriptional Induction of Cystathionine γ-Lyase, a Reactive Sulfur-Producing Enzyme, by Copper Diethyldithiocarbamate in Cultured Vascular Endothelial Cells

As toxic substances can enter the circulating blood and cross endothelial monolayers to reach parenchymal cells in organs, vascular endothelial cells are an important target compartment for such substances. Reactive sulfur species protect cells against oxidative stress and toxic substances, including heavy metals. Reactive sulfur species are produced by enzymes, such as cystathionine γ-lyase (CSE), cystathionine β-synthase, 3-mercaptopyruvate sulfurtransferase, and cysteinyl-tRNA synthetase. However, little is known about the regulatory mechanisms underlying the expression of these enzymes in vascular endothelial cells. Bio-organometallics is a research field that analyzes biological systems using organic-inorganic hybrid molecules (organometallic compounds and metal coordinating compounds) as molecular probes. In the present study, we analyzed intracellular signaling pathways that mediate the expression of reactive sulfur species-producing enzymes in cultured bovine aortic endothelial cells, using copper diethyldithiocarbamate (Cu10). Cu10 selectively upregulated CSE gene expression in vascular endothelial cells independent of cell density. This transcriptional induction of endothelial CSE required both the diethyldithiocarbamate scaffold and the coordinated copper ion. Additionally, the present study revealed that ERK1/2, p38 MAPK, and hypoxia-inducible factor (HIF)-1α/HIF-1β pathways mediate transcriptional induction of endothelial CSE by Cu10. The transcription factors NF-κB, Sp1, and ATF4 were suggested to act in constitutive CSE expression, although the possibility that they are involved in the CSE induction by Cu10 cannot be excluded. The present study used a copper complex as a molecular probe to reveal that the transcription of CSE is regulated by multiple pathways in vascular endothelial cells, including ERK1/2, p38 MAPK, and HIF-1α/HIF-1β. Bio-organometallics appears to be an effective strategy for analyzing the functions of intracellular signaling pathways in vascular endothelial cells.

Hydrogen sulfide signaling in regulation of cell behaviors

Recent advances in the biomedical importance of H₂S have help us understand various cellular functions and pathophysiological processes from a new aspect. Specially, H₂S has been demonstrated to play multiple roles in regulating cell behaviors, including cell survival, cell differentiation, cell senescence, cell hypertrophy, cell atrophy, cell metaplasia, and cell death, etc. H₂S contributes to cell behavior changes via various mechanisms, such as histone modification, DNA methylation, non-coding RNA changes, DNA damage repair, transcription factor activity, and post-translational modification of proteins by S-sulfhydration, etc. In this review, we summarized the recent research progress on H₂S signaling in control of cell behaviors and discussed the ways of H₂S regulation of gene expressions. Given the key roles of H₂S in both health and diseases, a better understanding of the regulation of H₂S on cell behavior change and the underlying molecular mechanisms will help us to develop novel and more effective strategies for clinical therapy.

Nuclear-mitochondrial communication involving miR-181c plays an important role in cardiac dysfunction during obesity

AIMS

In cardiomyocytes, there is microRNA (miR) in the mitochondria that originates from the nuclear genome and matures in the cytoplasm before translocating into the mitochondria. Overexpression of one such miR, miR-181c, can lead to heart failure by stimulating reactive oxygen species (ROS) production and increasing mitochondrial calcium level ([Ca²⁺]_m). Mitochondrial calcium uptake 1 protein (MICU1), a regulatory protein in the mitochondrial calcium uniporter complex, plays an important role in regulating [Ca²⁺]_m. Obesity results in miR-181c overexpression and a decrease in MICU1. We hypothesize that lowering miR-181c would protect against obesity-induced cardiac dysfunction.

METHODS AND RESULTS

We used an in vivo mouse model of high-fat diet (HFD) for 18 weeks and induced high lipid load in H9c2 cells with oleate-conjugated bovine serum albumin in vitro. We tested the cardioprotective role of lowering miR-181c by using miR-181c/d^-/- mice (in vivo) and AntagomiR against miR-181c (in vitro). HFD significantly upregulated heart levels of miR-181c and led to cardiac hypertrophy in wild-type mice, but not in miR-181c/d^-/- mice. HFD also increased ROS production and pyruvate dehydrogenase activity (a surrogate for [Ca²⁺]_m), but the increases were alleviated in miR-181c/d^-/- mice. Moreover, miR-181c/d^-/- mice fed a HFD had higher levels of MICU1 than did wild-type mice fed a HFD, attenuating the rise in [Ca²⁺]_m. Overexpression of miR-181c in neonatal ventricular cardiomyocytes (NMVM) caused increased ROS production, which oxidized transcription factor Sp1 and led to a loss of Sp1, thereby slowing MICU1 transcription. Hence, miR-181c increases [Ca²⁺]_m through Sp1 oxidation and downregulation of MICU1, suggesting that the cardioprotective effect of miR-181c/d^-/- results from inhibition of Sp1 oxidation.

CONCLUSION

This study has identified a unique nuclear-mitochondrial communication mechanism in the heart orchestrated by miR-181c. Obesity-induced overexpression of miR-181c increases [Ca²⁺]_m via downregulation of MICU1 and leads to cardiac injury. A strategy to inhibit miR-181c in cardiomyocytes can preserve cardiac function during obesity by improving mitochondrial function. Altering miR-181c expression may provide a pharmacologic approach to improve cardiomyopathy in individuals with obesity/type 2 diabetes.

Hydrogen Sulfide as a Potential Alternative for the Treatment of Myocardial Fibrosis

Harmful, stressful conditions or events in the cardiovascular system result in cellular damage, inflammation, and fibrosis. Currently, there is no targeted therapy for myocardial fibrosis, which is highly associated with a large number of cardiovascular diseases and can lead to fatal heart failure. Hydrogen sulfide (H₂S) is an endogenous gasotransmitter similar to nitric oxide and carbon monoxide. H₂S is involved in the suppression of oxidative stress, inflammation, and cellular death in the cardiovascular system. The level of H₂S in the body can be boosted by stimulating its synthesis or supplying it exogenously with a simple H₂S donor with a rapid- or slow-releasing mode, an organosulfur compound, or a hybrid with known drugs (e.g., aspirin). Hypertension, myocardial infarction, and inflammation are exaggerated when H₂S is reduced. In addition, the exogenous delivery of H₂S mitigates myocardial fibrosis caused by various pathological conditions, such as a myocardial infarct, hypertension, diabetes, or excessive β-adrenergic stimulation, via its involvement in a variety of signaling pathways. Numerous experimental findings suggest that H₂S may work as a potential alternative for the management of myocardial fibrosis. In this review, the antifibrosis role of H₂S is briefly addressed in order to gain insight into the development of novel strategies for the treatment of myocardial fibrosis.

Induction of cystathionine gamma-lyase expression and metallothionein-1 S-sulfhydration alleviate cadmium-induced cell death in myoblast cells

Hydrogen sulfide (H₂S), a multifunctional gasotransmitter, participates in a wide range of cellular signal transduction and pathophysiological processes. Cystathionine gamma-lyase (CSE) acts as a major H₂S-generating enzyme in peripheral organs and tissues. As a cysteine-rich and heavy metal-binding protein, metallothionein-1 (MT-1) is known to protect cells from various environmental stresses. Here we demonstrated that exposure of cadmium (Cd) induced oxidative stress, depleted intracellular thiols, and stimulated apoptotic cell death in mouse myoblast cells. CSE expression and H₂S production were significantly enhanced by Cd treatment. NaHS, a well-known H₂S donor, at physiologically relevant concentration significantly alleviated Cd-induced damage in both myoblasts and mouse skeletal muscles. In contrast, down-regulation of CSE/H₂S system deteriorated Cd-stimulated oxidative stress and cell death. Exposure of the cells to Cd lead to increased expressions of metal regulatory transcription factor 1 and MT-1, while siRNA-mediated MT-1 knockdown alleviated Cd-induced CSE expression and caused more oxidative stress and cell death. In addition, H₂S post-translationally modified MT-1 by S-sulfhydration and stabilized zinc-protein complex. Taken together, these data suggest that CSE/H₂S system would protect myoblasts and skeletal muscles from Cd-induced damage by S-sufhydrating MT-1.

H2S Protects against Cardiac Cell Hypertrophy through Regulation of Selenoproteins

Cardiac hypertrophy is defined as the enlargement of the cardiac myocytes, leading to improper nourishment and oxygen supply due to the increased functional demand. This increased stress on the cardiac system commonly leads to myocardial infarction, contributing to 85% of all cardiac-related deaths. Cystathionine gamma-lyase- (CSE-) derived H₂S is a novel gasotransmitter and plays a critical role in the preservation of cardiac functions. Selenocysteine lyase (SCLY) has been identified to produce H₂Se, the selenium homologue of H₂S. Deficiency of selenium is often found in Keshan disease, a congestive cardiomyopathy. The interaction of H₂S and H₂Se in cardiac cell hypertrophy has not been explored. In this study, cell viability was evaluated with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Oxidative stress and cell size were observed through immunostaining. The expression of genes was determined by real-time PCR and western blot. Here, we demonstrated that incubation of rat cardiac cells (H9C2) with H₂O₂ lead to increased oxidative stress and cell surface area, which were significantly attenuated by pretreatment of either H₂S or H₂Se. H₂S incubation induced SCLY/H₂Se signaling, which next caused higher expressions and activities of selenoproteins, including glutathione peroxidase and thioredoxin reductase. Furthermore, deficiency of CSE inhibited the expressions of SCLY and selenoprotein P in mouse heart tissues. We also found that both H₂S and H₂Se stimulated Nrf2-targeted downstream genes. These data suggests that H₂S protects against cardiac hypertrophy through enhancement of a group of antioxidant proteins.

The long non-coding RNA H19 induces hypoxia/reoxygenation injury by up-regulating autophagy in the hepatoma carcinoma cells

BACKGROUND

Long non-coding RNA H19 (H19) plays an important role by regulating protein expression in different tissues and organs of the body. However, whether H19 induces hypoxia/reoxygenation (h/R) injury via increase of autophagy in the hepatoma carcinoma cells is unknown.

RESULTS

H19 was expressed in the hepatoma carcinoma cells (Hep G2 and HCCLM3 cells) and its expression was most in 8 h/24R. The knockdown of H19 and 3-MA (an autophagy inhibitor) protected against h/R-induced apoptosis, cell damage, the expression of cleaved caspase-3 and cleaved caspase-9, the release of cytochrome c (Cyt c). The knockdown of H19 and 3-MA also decreased the autophagic vesicles (AVs) and the expression of Beclin-1 and the ration of LC3-II/LC3-I, and increased cell viability, the expression of Bcl-2 and P62 and the phosphorylation of PI3K, Akt and mTOR. In addition, chloroquine (CQ, an inhibitor of autophagy flux) markedly decreased formation of autophagy flux (the ration of LC3-II/LC3-I). The results of the knockdown of H19 group were similar to those of the 3-MA (or CQ) group. Rapamycin (a mTOR inhibitor, an autophagy activator) further down-regulated h/R-induced decrease of the phosphorylated PI3K, Akt and mTOR. The knockdown of H19 cancelled the effect of rapamycin. The overexpression of H19 further expanded h/R-induced increase of the ration of LC3-II/LC3-I and decrease of the phosphorylated PI3K, Akt and mTOR.

CONCLUSIONS

Our results suggest that the long non-coding RNA H19 induces h/R injury by up-regulation of autophagy via activation of PI3K-Akt-mTOR pathway in the hepatoma carcinoma cells.