Estrogen Replacement Therapy in Ovariectomized Nonpregnant Ewes Stimulates Uterine Artery Hydrogen Sulfide Biosynthesis by Selectively Up-Regulating Cystathionine β-Synthase Expression

Therapeutic Potential of Hydrogen Sulfide in Reproductive System Disorders

Hydrogen sulfide (H2S), previously regarded as a toxic exhaust and atmospheric pollutant, has emerged as the third gaseous signaling molecule following nitric oxide (NO) and carbon monoxide (CO). Recent research has revealed significant biological effects of H2S in a variety of systems, such as the nervous, cardiovascular, and digestive systems. Additionally, H2S has been found to impact reproductive system function and may have therapeutic implications for reproductive disorders. This paper explores the relationship between H2S and male reproductive disorders, specifically erectile dysfunction, prostate cancer, male infertility, and testicular damage. Additionally, it examines the impact of H2S regulation on the pathophysiology of the female reproductive system, including improvements in preterm birth, endometriosis, pre-eclampsia, fetal growth restriction, unexplained recurrent spontaneous abortion, placental oxidative damage, embryo implantation, recovery of myometrium post-delivery, and ovulation. The study delves into the regulatory functions of H2S within the reproductive systems of both genders, including its impact on the NO/cGMP pathway, the activation of K+ channels, and the relaxation mechanism of the spongy smooth muscle through the ROCK pathway, aiming to broaden the scope of potential therapeutic strategies for treating reproductive system disorders in clinical settings.

Plasma homocysteine level, estradiol level, and brain atrophy: a Mendelian randomization study

OBJECTIVES

Observational studies link elevated plasma homocysteine (Hcy) with vascular disease. Our aim was to assess the gender difference in the association between the plasma tHcy level and brain atrophy and identify the possible influencer. We employed Mendelian randomization (MR) to explore the causal relationship between plasma tHcy level, estradiol level, and brain atrophy.

METHODS

A total of 687 patients with brain atrophy were included, and gender-specific subgroup analyses in association between tHcy and brain atrophy are conducted. From genome-wide association studies, we selected genetic variants (P < 5 × 10-8) for the plasma tHcy level and estradiol level. We investigated the degree of brain atrophy (including gray matter volume and total brain volume) in the UK biobank (n = 7,916). The inverse variance-weighted and several sensitivity MR regression analyses were carried out.

RESULTS

The plasma tHcy level was significantly associated with brain atrophy for females, but not for males. An MR study showed that there was little evidence of the causal link between elevated plasma tHcy and brain atrophy. On the other hand, we found evidence to support causality for genetically decreased estradiol with higher risk of brain atrophy. Furthermore, genetic predisposition to elevated plasma tHcy was associated with a lower estradiol level.

CONCLUSIONS

The influence of estradiol on the association between tHcy and brain atrophy deserves further investigation.

Regulatory effects of hydrogen sulfide on the female reproductive system

Hydrogen sulfide (H2S), a colorless exhaust gas, has been traditionally considered an air pollutant. However, recent studies have revealed that H2S functions as a novel gas signaling molecule, exerting diverse biological effects on various systems, including the cardiovascular, digestive, and nervous systems. Thus, H2S is involved in various pathophysiological processes. As H2S affects reproductive function, it has potential therapeutic implications in reproductive system diseases. This review examined the role of H2S in various female reproductive organs, including the ovary, fallopian tube, vagina, uterus, and placenta. Additionally, the regulatory function of H2S in the female reproductive system has been discussed to provide useful insights for developing clinical therapeutic strategies for reproductive diseases.

ICI 182,780 Attenuates Selective Upregulation of Uterine Artery Cystathionine β-Synthase Expression in Rat Pregnancy

Endogenous hydrogen sulfide (H2S) produced by cystathionine β-synthase (CBS) and cystathionine-γ lyase (CSE) has emerged as a novel uterine vasodilator contributing to pregnancy-associated increases in uterine blood flow, which safeguard pregnancy health. Uterine artery (UA) H2S production is stimulated via exogenous estrogen replacement and is associated with elevated endogenous estrogens during pregnancy through the selective upregulation of CBS without altering CSE. However, how endogenous estrogens regulate uterine artery CBS expression in pregnancy is unknown. This study was conducted to test a hypothesis that endogenous estrogens selectively stimulate UA CBS expression via specific estrogen receptors (ER). Treatment with E2β (0.01 to 100 nM) stimulated CBS but not CSE mRNA in organ cultures of fresh UA rings from both NP and P (gestational day 20, GD20) rats, with greater responses to all doses of E2β tested in P vs. NP UA. ER antagonist ICI 182,780 (ICI, 1 µM) completely attenuated E2β-stimulated CBS mRNA in both NP and P rat UA. Subcutaneous injection with ICI 182,780 (0.3 mg/rat) of GD19 P rats for 24 h significantly inhibited UA CBS but not mRNA expression, consistent with reduced endothelial and smooth muscle cell CBS (but not CSE) protein. ICI did not alter mesenteric and renal artery CBS and CSE mRNA. In addition, ICI decreased endothelial nitric oxide synthase mRNA in UA but not in mesenteric or renal arteries. Thus, pregnancy-augmented UA CBS/H2S production is mediated by the actions of endogenous estrogens via specific ER in pregnant rats.

Mapping Pregnancy-dependent Sulfhydrome Unfolds Diverse Functions of Protein Sulfhydration in Human Uterine Artery

Uterine artery (UA) hydrogen sulfide (H2S) production is augmented in pregnancy and, on stimulation by systemic/local vasodilators, contributes to pregnancy-dependent uterine vasodilation; however, how H2S exploits this role is largely unknown. S-sulfhydration converts free thiols to persulfides at reactive cysteine(s) on targeted proteins to affect the entire proteome posttranslationally, representing the main route for H2S to elicit its function. Here, we used Tag-Switch to quantify changes in sulfhydrated (SSH-) proteins (ie, sulfhydrome) in H2S-treated nonpregnant and pregnant human UA. We further used the low-pH quantitative thiol reactivity profiling platform by which paired sulfhydromes were subjected to liquid chromatography tandem mass spectrometry-based peptide sequencing to generate site (cysteine)-specific pregnancy-dependent H2S-responsive human UA sulfhydrome. Total levels of sulfhydrated proteins were significantly greater in pregnant vs nonpregnant human UA and further stimulated by treatment with sodium hydrosulfide. We identified a total of 360 and 1671 SSH-peptides from 480 and 1186 SSH-proteins in untreated and sodium hydrosulfide-treated human UA, respectively. Bioinformatics analyses identified pregnancy-dependent H2S-responsive human UA SSH peptides/proteins, which were categorized to various molecular functions, pathways, and biological processes, especially vascular smooth muscle contraction/relaxation. Pregnancy-dependent changes in these proteins were rectified by immunoblotting of the Tag-Switch labeled SSH proteins. Low-pH quantitative thiol reactivity profiling failed to identify low abundance SSH proteins such as KATP channels in human UA; however, immunoblotting of Tag-Switch-labeled SSH proteins identified pregnancy-dependent upregulation of SSH-KATP channels without altering their total proteins. Thus, comprehensive analyses of human UA sulfhydromes influenced by endogenous and exogenous H2S inform novel roles of protein sulfhydration in uterine hemodynamics regulation.

ERα/ERβ-directed CBS transcription mediates E2β-stimulated hUAEC H2S production

Elevated endogenous estrogens stimulate human uterine artery endothelial cell (hUAEC) hydrogen sulfide (H2S) production by selectively upregulating the expression of H2S synthesizing enzyme cystathionine β-synthase (CBS), but the underlying mechanisms are underdetermined. We hypothesized that CBS transcription mediates estrogen-stimulated pregnancy-dependent hUAEC H2S production. Estradiol-17β (E2β) stimulated CBS but not cystathionine γ-lyase (CSE) expression in pregnant human uterine artery ex vivo, which was attenuated by the estrogen receptor (ER) antagonist ICI 182,780. E2β stimulated CBS mRNA/protein and H2S production in primary hUAEC from nonpregnant and pregnant women, but with greater responses in pregnant state; all were blocked by ICI 182,780. Human CBS promoter contains multiple estrogen-responsive elements (EREs), including one ERE preferentially binding ERα (αERE) and three EREs preferentially binding ERβ (βERE), and one full ERE (α/βERE) and one half ERE (½α/βERE) binding both ERα and ERβ. Luciferase assays using reporter genes driven by human CBS promoter with a series of 5'-deletions identified the α/βEREs binding both ERα and ERβ (α/βERE and ½α/βERE) to be important for baseline and E2β-stimulated CBS promoter activation. E2β stimulated ERα/ERβ heterodimerization by recruiting ERα to α/βEREs and βERE, and ERβ to βERE, α/βEREs, and αERE. ERα or ERβ agonist alone trans-activated CBS promoter, stimulated CBS mRNA/protein and H2S production to levels comparable to that of E2β-stimulated, while ERα or ERβ antagonist alone abrogated E2β-stimulated responses. E2β did not change human CSE promoter activity and CSE mRNA/protein in hUAEC. Altogether, estrogen-stimulated pregnancy-dependent hUAEC H2S production occurs by selectively upregulating CBS expression via ERα/ERβ-directed gene transcription.

A comprehensive analysis of metabolomics and transcriptomics to reveal major metabolic pathways and potential biomarkers of human preeclampsia placenta

Background: The etiology of preeclampsia (PE) remains unclear. With the utilization of metabolomics, dysregulated production of several metabolic components in human plasma, such as lipids, amino acids, androgens and estrogens, was found to be important in the pathogenesis of PE. Transcriptomics adds more in-depth information, and the integration of transcriptomics and metabolomics may yield further insight into PE pathogenesis than either one alone.

Objectives: We investigated the placental metabolomics and transcriptomics of PE patients to identify affected metabolic pathways and potential biological targets for exploring the disease pathogenesis.

Methods: Integrated transcriptomics and metabolomics were used to analyze five paired human placentas from patients with severe PE and normal pregnancies. This was followed by further validation of our findings in a publicly available dataset of 173 PE vs. 157 control placentas. In addition, weighted gene coexpression network construction was performed to assess the correlation between genetic alterations and diseases.

Results: We identified 66 and 41 differentially altered metabolites in negative and positive ion modes, respectively, in the PE group compared to the control group, and found 2,560 differentially expressed genes. Several pathways were aberrantly altered in the PE placenta at both the metabolic and transcriptional levels, including steroid hormone biosynthesis, the cAMP signaling pathway, neuroactive ligand–receptor interactions, taste transduction and prion diseases. Additionally, we found 11 differential metabolites and 11 differentially expressed genes involved in the steroid hormone biosynthesis pathway, indicating impaired metabolism of steroid hormones in the PE placenta. Furthermore, we found that CYP11A1, HSD3B2, and HSD17B6 are highly correlated with diseases.

Conclusion: Our findings provide a profile of the dysregulated steroid hormone biosynthesis in PE placenta, we observed a dysregulated cortisol-to-cortisone ratio, testosterone accumulation, decreased testosterone downstream metabolites, impaired production of estrone and estriol, and aberrant hydroxylation and methylation of estradiol. Disorders of placental steroid hormone metabolism might be a consequence or a compensatory change in pathological placentation in PE, which underscores the need to investigate the physiology of steroid hormone metabolites in the etiology of PE.

Estrogen-Induced Uterine Vasodilation in Pregnancy and Preeclampsia

Normal pregnancy is associated with dramatically increased estrogen biosynthesis whose role is believed to raise uterine blood flow to facilitate the bi-directional maternal-fetal exchanges of gases (O₂ and CO₂), to deliver nutrients, and exhaust wastes to support fetal development and survival. Constrained uterine blood flow in pregnancy is a leading cause of preeclampsia with fetal growth restriction, rendering investigations of uterine hemodynamics to hold a high promise to inform pathways as targets for therapeutic interventions for preeclampsia. The mechanisms of estrogen-induced uterine vasodilation in pregnancy have long been attributed to enhanced endothelium production of nitric oxide, but clinical trials targeting this pathway that dominates uterine hemodynamics have achieved no to little success. Emerging evidence has recently shown a novel proangiogenic vasodilatory role of hydrogen sulfide in regulating uterine hemodynamics in pregnancy and preeclampsia, provoking a new field of perinatal research in searching for alternative pathways for pregnancy disorders especially preeclampsia and intrauterine growth restriction. This minireview is intended to summarize the nitric oxide pathway and to discuss the emerging hydrogen sulfide pathway in modulating estrogen-induced uterine vasodilation in pregnancy and preeclampsia.

Uteroplacental Circulation in Normal Pregnancy and Preeclampsia: Functional Adaptation and Maladaptation

Uteroplacental blood flow increases as pregnancy advances. Adequate supply of nutrients and oxygen carried by uteroplacental blood flow is essential for the well-being of the mother and growth/development of the fetus. The uteroplacental hemodynamic change is accomplished primarily through uterine vascular adaptation, involving hormonal regulation of myogenic tone, vasoreactivity, release of vasoactive factors and others, in addition to the remodeling of spiral arteries. In preeclampsia, hormonal and angiogenic imbalance, proinflammatory cytokines and autoantibodies cause dysfunction of both endothelium and vascular smooth muscle cells of the uteroplacental vasculature. Consequently, the vascular dysfunction leads to increased vascular resistance and reduced blood flow in the uteroplacental circulation. In this article, the (mal)adaptation of uteroplacental vascular function in normal pregnancy and preeclampsia and underlying mechanisms are reviewed.

Quantitative chemoproteomics reveals O-GlcNAcylation of cystathionine γ-lyase (CSE) represses trophoblast syncytialization

Emerging evidence indicates the involvement of O-GlcNAc modification in placental development and pregnant health through mechanisms that are not well understood. Herein, by applying the quantitative O-GlcNAc proteomics, we established a database of O-GlcNAcylated proteins in human placental trophoblasts. Hundreds of proteins that were dynamically O-GlcNAcylated during trophoblast differentiation were identified, among which cystathionine γ-lyase (CSE) exhibited the most significant change. Site-specific analysis by mass spectrometry revealed Ser¹³⁸ as the core O-GlcNAc site in CSE, and its O-GlcNAcylation promoted the enzymatic activity to produce H₂S, which in turn repressed trophoblast differentiation via inhibiting androgen receptor dimerization. Consistently, in preeclamptic placentas, remarkably enhanced CSE O-GlcNAcylation and H₂S production were associated with restricted trophoblast differentiation. The findings establish a resource of O-GlcNAc dynamics in human placenta, and provide a deeper insight into the biological significance of O-GlcNAcylation in placental development as well as potential therapeutic targets for the relevant pregnant complications.

Estrogen Regulates Local Cysteine Metabolism in Mouse Myometrium

Sulfur amino acid metabolism influences reproductive physiology, and transsulfuration in particular may be critical for normal cellular function. The sex hormone estrogen (E2) modulates gene expression and redox balance in some tissues by inducing the transsulfuration enzymes cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). The role of sex hormones in sulfur amino acid metabolism by uterine smooth muscle is not known. Here, we show that CBS and CSE proteins increase in the mouse myometrium during estrus and diestrus, respectively, suggesting that E2 reciprocally regulates myometrial CBS and CSE expression. In ovariectomized mice, exogenous E2 upregulates CBS and downregulates CSE levels. E2 promotes CBS mRNA and protein expression but attenuates CSE protein expression without affecting CSE mRNA. This pattern of E2-stimulated changes in transsulfuration enzyme expression is specific to the uterine smooth muscle. E2 does not change vaginal or cervical expression of CBS or CSE significantly, and E2 decreases expression of CSE in the liver without affecting CBS. E2 also downregulates myometrial cysteinesulfinic acid decarboxylase (CSAD) and decreases myometrial biochemical synthesis of the gaso-transmitter hydrogen sulfide (H2S). These findings suggest that myometrial sulfur amino acid metabolism may regulate uterine redox homeostasis, with implications for the source and metabolism of myometrial cysteine in high E2 states such as estrus and pregnancy.

Cystathionine γ-lyase promotes estrogen-stimulated uterine artery blood flow via glutathione homeostasis

During pregnancy, estrogen (E₂) stimulates uterine artery blood flow (UBF) by enhancing nitric oxide (NO)-dependent vasodilation. Cystathionine γ-lyase (CSE) promotes vascular NO signaling by producing hydrogen sulfide (H₂S) and by maintaining the ratio of reduced-to-oxidized intracellular glutathione (GSH/GSSG) through l-cysteine production. Because redox homeostasis can influence NO signaling, we hypothesized that CSE mediates E₂ stimulation of UBF by modulating local intracellular cysteine metabolism and GSH/GSSG levels to promote redox homeostasis. Using non-pregnant ovariectomized WT and CSE-null (CSE KO) mice, we performed micro-ultrasound of mouse uterine and renal arteries to assess changes in blood flow upon exogenous E₂ stimulation. We quantified serum and uterine artery NO metabolites (NO_x), serum amino acids, and uterine and renal artery GSH/GSSG. WT and CSE KO mice exhibited similar baseline uterine and renal blood flow. Unlike WT, CSE KO mice did not exhibit expected E₂ stimulation of UBF. Renal blood flow was E₂-insensitive for both genotypes. While serum and uterine artery NO_x were similar between genotypes at baseline, E₂ decreased NO_x in CSE KO serum. Cysteine was also lower in CSE KO serum, while citrulline and homocysteine levels were elevated. E₂ and CSE deletion additively decreased GSH/GSSG in uterine arteries. In contrast, renal artery GSH/GSSG was insensitive to E₂ or CSE deletion. Together, these findings suggest that CSE maintenance of uterine artery GSH/GSSG facilitates nitrergic signaling in uterine arteries and is required for normal E₂ stimulation of UBF. These data have implications for pregnancy pathophysiology and the selective hormone responses of specific vascular beds.

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CSE-null mice exhibit abnormal estrogen augmentation of uterine artery blood flow.

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Estrogen lowers uterine artery nitric oxide metabolites in CSE null mice.

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CSE loss and estrogen additively impair uterine artery glutathione homeostasis.

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Neither CSE loss nor estrogen influences renal artery blood flow or glutathione.

Daidzein supplementation enhances embryo survival by improving hormones, antioxidant capacity, and metabolic profiles of amniotic fluid in sows

Daidzein (DAI) is a kind of natural isoflavonic phytoestrogen with estrogenic activity. However, little is known about its influence on early fetal growth in mammalian animals. The current study aimed to explore the characteristics of amniotic fluid exposure to dietary DAI using ¹H NMR-based metabolomics and biochemical analysis. Here, we found that DAI supplementation at a dose of 200 mg kg^-1 significantly enhanced the number of viable embryos at the early gestation stage (P < 0.05). DAI significantly elevated the concentrations of estrogen (E) and insulin-like growth factor-I (IGF-I) in the amniotic fluid (P < 0.05). Moreover, DAI tended to increase the concentration of progesterone, but decrease the concentration of tumor necrosis factor α (TNF-α) in the amniotic fluid (0.05 < P < 0.10). Interestingly, the activity of glutathione peroxidase (GSH-Px) was higher in the DAI group than in the CON group (P < 0.05). An ¹H NMR-based metabolomics analysis identified and quantified more than 30 compounds in the amniotic fluid, and some critical metabolites such as arginine, creatine, and citrate were found to be significantly elevated upon DAI supplementation (P < 0.05). Importantly, the metabolic pathways involved in arginine and proline metabolisms were found to be significantly affected by DAI. Collectively, dietary DAI may improve embryo survival by improving hormones, antioxidant capacity, and metabolic profiles in the maternal amniotic fluid.

Hydrogen Sulfide Relaxes Human Uterine Artery via Activating Smooth Muscle BKCa Channels

Opening of large conductance calcium-activated and voltage-dependent potassium (BK_Ca) channels hyperpolarizes plasma membranes of smooth muscle (SM) to cause vasodilation, underling a key mechanism for mediating uterine artery (UA) dilation in pregnancy. Hydrogen sulfide (H₂S) has been recently identified as a new UA vasodilator, yet the mechanism underlying H₂S-induced UA dilation is unknown. Here, we tested whether H₂S activated BK_Ca channels in human UA smooth muscle cells (hUASMC) to mediate UA relaxation. Multiple BK_Ca subunits were found in human UA in vitro and hUASMC in vitro, and high β1 and γ1 proteins were localized in SM cells in human UA. Baseline outward currents, recorded by whole-cell and single-channel patch clamps, were significantly inhibited by specific BK_Ca blockers iberiotoxin (IBTX) or tetraethylammonium, showing specific BK_Ca activity in hUASMC. H₂S dose (NaHS, 1–1000 µM)-dependently potentiated BK_Ca currents and open probability. Co-incubation with a Ca²⁺ blocker nifedipine (5 µM) or a chelator (ethylene glycol-bis (β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), 5 mM) did not alter H₂S-potentiated BK_Ca currents and open probability. NaHS also dose-dependently relaxed phenylephrine pre-constricted freshly prepared human UA rings, which was inhibited by IBTX. Thus, H₂S stimulated human UA relaxation at least partially via activating SM BK_Ca channels independent of extracellular Ca²⁺.

Enhanced Stromal Cell CBS-H2S Production Promotes Estrogen-Stimulated Human Endometrial Angiogenesis

Angiogenesis is a physiological process for endometrial regeneration in the menstrual cycle and remodeling during pregnancy. Endogenous hydrogen sulfide (H2S), produced by cystathionine-β synthase (CBS) and cystathionine-γ lyase (CSE), is a potent proangiogenic factor; yet, whether the H2S system is expressed in the endometrium and whether H2S plays a role in endometrial angiogenesis are unknown. This study was to test whether estrogens stimulate endometrial H2S biosynthesis to promote endometrial microvascular endothelial cell (EMEC) angiogenesis. CBS messenger RNA/protein and H2S production significantly differed among endometria from postmenopausal (POM), premenopausal secretory (sPRM), and proliferative (pPRM) nonpregnant (NP) and pregnant (Preg) women (P < .05) in a rank order of POM approximately equal to sPRM is less than pPRM is less than Preg, positively correlating with angiogenesis indices and endogenous estrogens and with no difference in CSE expression. CBS and CSE proteins were localized to stroma, glands, and vessels in endometrium, and greater stromal CBS protein was observed in the pPRM and Preg states. Estradiol-17β (E2) (but not progesterone) stimulated CBS (but not CSE) expression and H2S production in pPRM endometrial stromal cells (ESCs) in vitro, which were attenuated by ICI 182 780. The H2S donor sodium hydrosulfide promoted in vitro EMEC angiogenesis. Co-culture with sPRM, pPRM, and Preg ESCs all stimulated EMEC migration with a rank order of sPRM less than pPRM approximately equal to Preg. CBS (but not CSE) inhibition attenuated ESC-stimulated EMEC migration. E2 did not affect EMEC migration but potentiated ESC-stimulated EMEC migration. Altogether, estrogens stimulate specific receptor-dependent stromal CBS-H2S production to promote endometrial EMEC angiogenesis in women.

Ovine uterine artery hydrogen sulfide biosynthesis in vivo: effects of ovarian cycle and pregnancy†

Uterine vasodilation dramatically increases during the follicular phase of the estrous cycle and pregnancy, which are estrogen-dominant physiological states. Uterine vasodilation is believed to be mainly controlled by local uterine artery (UA) production of vasodilators and angiogenic factors. The extremely potent vasodilator and proangiogenic hydrogen sulfide (H2S) is synthesized via metabolizing L-cysteine by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CTH). This study was designed to determine if UA H2S production increases with augmented expression and/or activity of CBS and/or CTH during the ovarian cycle and pregnancy in sheep. Uterine arteries from intact nonpregnant (NP) luteal and follicular phase and late (130-135 days, term ≈ 145 days) pregnant (P) ewes were collected; endothelium-enriched proteins (UAendo) and endothelium-denuded smooth muscle (UAvsm) were mechanically prepared for accessing CBS and CTH proteins by immunoblotting; their cellular localization was determined by semi-quantitative immunofluorescence microscopy. H2S production was measured by the methylene blue assay. Immunoblotting revealed that CBS but not CTH protein was greater in P > > > NP follicular > luteal UAendo and UAvsm (P < 0.001). H2S production was greater in P > > > NP UAendo and UAvsm (P < 0.01). Pregnancy-augmented UAendo and UAvsm H2S production was inhibited by the specific CBS but not CTH inhibitor. CBS and CTH proteins were localized to both endothelium and smooth muscle; however, only CBS protein was significantly greater in P vs NP UA endothelium and smooth muscle. Thus, ovine UA H2S production is significantly augmented via selectively upregulating endothelium and smooth muscle CBS during the follicular phase and pregnancy in vivo.

Hydrogen Sulfide: From a Toxic Molecule to a Key Molecule of Cell Life

Hydrogen sulfide (H2S) has always been considered toxic, but a huge number of articles published more recently showed the beneficial biochemical properties of its endogenous production throughout all regna. In this review, the participation of H2S in many physiological and pathological processes in animals is described, and its importance as a signaling molecule in plant systems is underlined from an evolutionary point of view. H2S quantification methods are summarized and persulfidation is described as the underlying mechanism of action in plants, animals and bacteria. This review aims to highlight the importance of its crosstalk with other signaling molecules and its fine regulation for the proper function of the cell and its survival.

Estrogen Receptors and Estrogen-Induced Uterine Vasodilation in Pregnancy

Normal pregnancy is associated with dramatic increases in uterine blood flow to facilitate the bidirectional maternal–fetal exchanges of respiratory gases and to provide sole nutrient support for fetal growth and survival. The mechanism(s) underlying pregnancy-associated uterine vasodilation remain incompletely understood, but this is associated with elevated estrogens, which stimulate specific estrogen receptor (ER)-dependent vasodilator production in the uterine artery (UA). The classical ERs (ERα and ERβ) and the plasma-bound G protein-coupled ER (GPR30/GPER) are expressed in UA endothelial cells and smooth muscle cells, mediating the vasodilatory effects of estrogens through genomic and/or nongenomic pathways that are likely epigenetically modified. The activation of these three ERs by estrogens enhances the endothelial production of nitric oxide (NO), which has been shown to play a key role in uterine vasodilation during pregnancy. However, the local blockade of NO biosynthesis only partially attenuates estrogen-induced and pregnancy-associated uterine vasodilation, suggesting that mechanisms other than NO exist to mediate uterine vasodilation. In this review, we summarize the literature on the role of NO in ER-mediated mechanisms controlling estrogen-induced and pregnancy-associated uterine vasodilation and our recent work on a “new” UA vasodilator hydrogen sulfide (H₂S) that has dramatically changed our view of how estrogens regulate uterine vasodilation in pregnancy.

Plasticity of the Maternal Vasculature During Pregnancy

Maternal cardiovascular changes during pregnancy include an expansion of plasma volume, increased cardiac output, decreased peripheral resistance, and increased uteroplacental blood flow. These adaptations facilitate the progressive increase in uteroplacental perfusion that is required for normal fetal growth and development, prevent the development of hypertension, and provide a reserve of blood in anticipation of the significant blood loss associated with parturition. Each woman's genotype and phenotype determine her ability to adapt in response to molecular signals that emanate from the fetoplacental unit. Here, we provide an overview of the major hemodynamic and cardiac changes and then consider regional changes in the splanchnic, renal, cerebral, and uterine circulations in terms of endothelial and vascular smooth muscle cell plasticity. Although consideration of gestational disease is beyond the scope of this review, aberrant signaling and/or maternal responsiveness contribute to the etiology of several common gestational diseases such as preeclampsia, intrauterine growth restriction, and gestational diabetes.

E2β stimulates ovine uterine artery endothelial cell H2S production in vitro by estrogen receptor-dependent upregulation of cystathionine β-synthase and cystathionine γ-lyase expression†

Endogenous hydrogen sulfide (H2S) is a potent vasodilator and proangiogenic second messenger synthesized from L-cysteine by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CTH). Estrogens are potent vasodilators that stimulate H2S biosynthesis in uterine arteries (UA) in vivo; however, the underlying mechanisms are unknown. We hypothesized that estrogens stimulate H2S biosynthesis in UA endothelial cells (UAEC) via specific estrogen receptor (ER)-dependent mechanisms. In cultured primary UAEC, treatment with estradiol-17β (E2β) stimulated CBS and CTH mRNAs and proteins in a time- and concentration-dependent fashion. As little as 0.1 nM E2β was effective in increasing CBS and CTH expressions and these stimulatory effects maximized with 10-100 nM E2β at 48-72 h. E2β also activated CBS and CTH promoters in UAEC, leading to CBS and CTH expression. Treatment with E2β stimulated H2S production, which was blocked by specific inhibitors of either CBS or CTH and their combination and the ER antagonist ICI 182780. Treatment with either specific agonist of ERα or ERβ stimulated both CBS and CTH mRNA and protein expressions and H2S production to levels similar to that of E2β. Specific antagonist of either ERα or ERβ blocked E2β-stimulated CBS and CTH mRNA and protein expressions and H2S production. Combinations of either ERα or ERβ agonists or their antagonists had no additive effects. Thus, E2β stimulates H2S production by upregulating CBS and CTH mRNA and protein expressions through specific ERα or ERβ-dependent CBS and CTH transcription in UAEC in vitro.

Hydrogen sulfide-mediated endothelial function and the interaction with eNOS and PDE5A activity in human internal mammary arteries

Objective

To investigate the role of hydrogen sulfide (H₂S) in human internal mammary arteries (IMA) and its interaction with endothelial nitric oxide synthase (eNOS) and phosphodiesterase (PDE)5A activity.

Methods

Human IMA segments from patients undergoing coronary artery bypass grafting (CABG) were studied by myography for acetylcholine and sodium hydrosulfide (NaHS)-induced relaxation. Locations of 3-mercaptopyruvate sulfurtransferase (3-MPST) and cysteine aminotransferase (CAT) were examined immunohistochemically. Levels of H₂S, eNOS, phosphorylated-eNOS^ser1177, and PDE5A were measured.

Results

In IMA segments from 47 patients, acetylcholine-induced relaxation (resistant to N^G-nitro-L-arginine and indomethacin) was significantly attenuated by aminooxyacetic acid or L-aspartate (CAT inhibitors), iberiotoxin (large-conductance calcium-activated K⁺ channel blocker), TRAM-34 plus apamin (intermediate- and small-conductance Ca²⁺-activated K⁺ channel blockers) or glibenclamide (ATP-sensitive K⁺ channel blocker). 3-MPST and mitochondrial CAT were found in endothelial and smooth muscle cells while cytosolic CAT was located only in endothelial cells. Acetylcholine significantly increased the H₂S levels. The H₂S donor, NaHS, increased eNOS phosphorylation and down-regulated PDE5A.

Conclusions

Human conduit artery endothelium releases H₂S under basal and stimulated conditions, involving the 3-MPST/CAT pathway, eNOS phosphorylation, PDE5A activity, and potassium channels. These findings may provide new therapeutic targets for treating vasospasm in CABG grafts and facilitate the development of new vasodilator drugs.

Elevated plasma homocysteine and cysteine are associated with endothelial dysfunction across menopausal stages in healthy women

Hyperhomocysteinemia is associated with endothelial dysfunction and increased cardiovascular disease (CVD). We determined whether elevated homocysteine (Hcy) and markers of Hcy metabolism were associated with the previously reported endothelial dysfunction across stages of the menopause transition. Brachial artery flow-mediated dilation (FMD) and plasma concentrations of Hcy, cysteine, and methionine were measured in healthy women (n = 128) 22-70 yr of age categorized as premenopausal (n = 35), perimenopausal (early: n = 16; late: n = 21), and postmenopausal (early: n = 21; late: n = 35). Dietary intake of micronutrients involved in Hcy metabolism (e.g., vitamins B6, B12, folate) was assessed in a subpopulation of women. Hcy and cysteine concentrations were progressively higher, and methionine was progressively lower across menopausal stages (all P < 0.005). The higher Hcy and cysteine concentrations correlated with lower circulating estradiol levels (r = -0.49 and -0.50, respectively, both P < 0.001). FMD was inversely correlated with Hcy (r = -0.25, P = 0.004) and cysteine (r = -0.39, P < 0.001) and positively correlated with methionine concentrations (r = 0.25, P = 0.005). Dietary intake of vitamins B6 and B12 (both P < 0.05) were lower in postmenopausal women. Vitamin B12 intake correlated with FMD (r = 0.22, P = 0.006). These data suggest that declines in estradiol across stages of the menopause transition may lead to elevations in Hcy and cysteine that may contribute to endothelial dysfunction in postmenopausal women. Future studies should examine whether targeting Hcy metabolism during the perimenopausal to early postmenopausal period with interventions, including diet, attenuates or reverses the decline in endothelial function in women. NEW & NOTEWORTHY Declines in circulating estradiol across the stages of the menopausal transition may lead to elevations in Hcy and cysteine concentrations that may contribute to endothelial dysfunction. Abnormalities in the Hcy metabolic pathways, possibly related to dietary deficiencies of vitamins B12 and B6 and folate, may contribute to elevations in Hcy and cysteine concentrations. Findings also suggest that higher cysteine levels may be more damaging to the vascular endothelium than Hcy.

Analysis of Vascular Hydrogen Sulfide Biosynthesis

With potent vasodilatory and pro-angiogenic properties, hydrogen sulfide (H₂S) is now accepted as the third gasotransmitter after nitric oxide (NO) and carbon monoxide. Endogenous H₂S is mainly synthesized by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). Akin to previous studies showing hormonal regulation of NO biosynthesis, we first reported that uterine and systemic artery H₂S biosynthesis is regulated by exogenous estrogens in an ovariectomized sheep model of estrogen replacement therapy, specifically stimulating CBS, but not CSE, expression, in uterine (UA) and mesenteric (MA), but not carotid (CA), arteries in ovariectomized nonpregnant sheep. We have found significantly elevated H₂S biosynthesis due to CBS upregulation under estrogen-dominant physiological states, the proliferative phase of menstrual cycle and pregnancy in primary human UAs. Our studies have pioneered the role of H₂S biology in uterine hemodynamics regulation although there is still much that needs to be learned before a thorough elucidation of a role that H₂S plays in normal physiology of uterine hemodynamics and its dysregulation under pregnancy complications can be determined. In this chapter we describe a series of methods that we have optimized for analyzing vascular H₂S biosynthesis, including (1) real-time quantitative PCR (qPCR) for assessing tissue and cellular levels of CBS and CSE mRNAs, (2) immunoblotting for assessing CBS and CSE proteins, (3) semiquantitative immunofluorescence microscopy to specifically localize CBS and CSE proteins on vascular wall and to quantify their cellular expression levels, and (4) methylene blue assay for assessing H₂S production in the presence of selective CBS and CSE inhibitors.

SEXUAL DIMORPHISM IN SELENIUM METABOLISM AND SELENOPROTEINS

Sexual dimorphism, the condition in which males and females in a species differ beyond the morphology of sex organs, delineates critical aspects of the biology of higher eukaryotes, including selenium metabolism. While sex differences in selenium biology have been described by several laboratories, delineation of the effects of sex in selenium function and regulation of selenoprotein expression is still in its infancy. This review encompasses the available information on sex-dependent parameters of selenium metabolism, as well as the effects of selenium on sex hormones. Gaps in the current knowledge of selenium and sex are identified and discussed.

Estradiol-17β stimulates H2 S biosynthesis by ER-dependent CBS and CSE transcription in uterine artery smooth muscle cells in vitro

Endogenous hydrogen sulfide (H₂ S), synthesized by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE), is a potent vasodilator that can be stimulated by estradiol-17β (E ₂ β) in uterine artery (UA) smooth muscle (UASMC) in vivo; however, the underlying mechanisms are unknown. This study tested a hypothesis that E ₂ β stimulates H ₂ S biosynthesis by upregulating CBS expression via specific estrogen receptor (ER). Treatment with E ₂ β stimulated time- and concentration- dependent CBS and CSE messenger RNA (mRNA) and protein expressions, and H ₂ S production in cultured primary UASMC isolated from late pregnant ewes, which were blocked by ICI 182,780. Treatment with specific ERα or ERβ agonist mimicked these E ₂ β-stimulated responses, which were blocked by specific ERα or ERβ antagonist. Moreover, E ₂ β activated both CBS and CSE promoters and ICI 182,780 blocked the E ₂ β-stimulated responses. Thus, E ₂ β stimulates H ₂ S production by upregulating CBS and CSE expression via specific ER-dependent transcription in UASMC in vitro.

International Union of Basic and Clinical Pharmacology. CII: Pharmacological Modulation of H2S Levels: H2S Donors and H2S Biosynthesis Inhibitors

Over the last decade, hydrogen sulfide (H₂S) has emerged as an important endogenous gasotransmitter in mammalian cells and tissues. Similar to the previously characterized gasotransmitters nitric oxide and carbon monoxide, H₂S is produced by various enzymatic reactions and regulates a host of physiologic and pathophysiological processes in various cells and tissues. H₂S levels are decreased in a number of conditions (e.g., diabetes mellitus, ischemia, and aging) and are increased in other states (e.g., inflammation, critical illness, and cancer). Over the last decades, multiple approaches have been identified for the therapeutic exploitation of H₂S, either based on H₂S donation or inhibition of H₂S biosynthesis. H₂S donation can be achieved through the inhalation of H₂S gas and/or the parenteral or enteral administration of so-called fast-releasing H₂S donors (salts of H₂S such as NaHS and Na₂S) or slow-releasing H₂S donors (GYY4137 being the prototypical compound used in hundreds of studies in vitro and in vivo). Recent work also identifies various donors with regulated H₂S release profiles, including oxidant-triggered donors, pH-dependent donors, esterase-activated donors, and organelle-targeted (e.g., mitochondrial) compounds. There are also approaches where existing, clinically approved drugs of various classes (e.g., nonsteroidal anti-inflammatories) are coupled with H₂S-donating groups (the most advanced compound in clinical trials is ATB-346, an H₂S-donating derivative of the non-steroidal anti-inflammatory compound naproxen). For pharmacological inhibition of H₂S synthesis, there are now several small molecule compounds targeting each of the three H₂S-producing enzymes cystathionine-β-synthase (CBS), cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase. Although many of these compounds have their limitations (potency, selectivity), these molecules, especially in combination with genetic approaches, can be instrumental for the delineation of the biologic processes involving endogenous H₂S production. Moreover, some of these compounds (e.g., cell-permeable prodrugs of the CBS inhibitor aminooxyacetate, or benserazide, a potentially repurposable CBS inhibitor) may serve as starting points for future clinical translation. The present article overviews the currently known H₂S donors and H₂S biosynthesis inhibitors, delineates their mode of action, and offers examples for their biologic effects and potential therapeutic utility.

Augmented H2S production via cystathionine-beta-synthase upregulation plays a role in pregnancy-associated uterine vasodilation

Endogenous hydrogen sulfide (H2S) synthesized via metabolizing L-cysteine by cystathionine-beta-synthase (CBS) and cystathionine-gamma-lyase (CSE) is a potent vasodilator and angiogenic factor. The objectives of this study were to determine if human uterine artery (UA) H2S production increases with augmented expression and/or activity of CBS and/or CSE during the menstrual cycle and pregnancy and whether exogenous H2S dilates UA. Uterine arteries from nonpregnant (NP) premenopausal proliferative (pPRM) and secretory (sPRM) phases of the menstrual cycle and pregnant (P) women were studied. H2S production was measured by the methylene blue assay. CBS and CSE mRNAs were assessed by quantitative real-time PCR, and proteins were assessed by immunoblotting and semiquantitative immunofluorescence microscopy. Effects of H2S on rat UA relaxation were determined by wire myography ex vivo. H2S production was greater in NP pPRM and P than NP sPRM UAs and inhibited by the specific CBS but not CSE inhibitor. CBS but not CSE mRNA and protein were greater in NP pPRM and P than NP sPRM UAs. CBS protein was localized to endothelium and smooth muscle and its levels were in a quantitative order of P >NP UAs of pPRM>sPRM. CSE protein was localized in UA endothelium and smooth muscle with no difference among groups. A H2S donor relaxed P > NP UAs but not mesentery artery. Thus, human UA H2S production is augmented with endothelium and smooth muscle CBS upregulation, contributing to UA vasodilation in the estrogen-dominant physiological states in the proliferative phase of the menstrual cycle and pregnancy.

The Role of the Hydrogen Sulfide Pathway in Male and Female Urogenital System in Health and Disease

SIGNIFICANCE

The endogenous hydrogen sulfide (H₂S) pathway produces an array of biological effects that vary depending on the bodily region. In addition, the H₂S pathway's relevance often changes depending on a healthy or disease state. There is abundant evidence pointing to a key role for this pathway in male and female genito-urinary diseases, suggesting it as a possible target for new therapeutic approaches. Recent Advances: The tissue-specific localization of the H₂S enzymes in the genito-urinary tract has allowed for a better understanding of its role in the body's pathophysiology. Indeed, in humans, cystathionine-γ-lyase (CSE) plays a major role in corpus cavernosum whereas cystathionine-β-synthase (CBS) plays a role in bladder functioning. The prostate epithelium expresses CBS and CSE, but stromal CSE only. In the uterus, up- or downregulation of CBS and CSE varies strongly depending on the female's hormonal cycle or pregnancy.

CRITICAL ISSUES

There is still the need to better define the male and female's sexual hormonal roles in regulating the H₂S pathway, particularly in human pathological conditions. The lack of a correlation between human and animal data should be carefully considered when planning preclinical studies. The unmet need for selective enzymatic inhibitors and the different methodologies for H₂S measurements still represent a critical issue in this research field.

FUTURE DIRECTIONS

It is feasible that the L-cysteine/H₂S pathway can represent an alternative therapeutic target in genito-urinary tract disorders. The research should focus on erectile dysfunction and preeclampsia, characterized by vascular defect, as well as on bladder disorders where the urothelium is compromised. Antioxid. Redox Signal. 27, 654-668.

Human trophoblast-derived hydrogen sulfide stimulates placental artery endothelial cell angiogenesis

Endogenous hydrogen sulfide (H2S), mainly synthesized by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CTH), has been implicated in regulating placental angiogenesis; however, the underlying mechanisms are unknown. This study was to test a hypothesis that trophoblasts synthesize H2S to promote placental angiogenesis. Human choriocarcinoma-derived BeWo cells expressed both CBS and CTH proteins, while the first trimester villous trophoblast-originated HTR-8/SVneo cells expressed CTH protein only. The H2S producing ability of BeWo cells was significantly inhibited by either inhibitors of CBS (carboxymethyl hydroxylamine hemihydrochloride, CHH) or CTH (β-cyano-L-alanine, BCA) and that in HTR-8/SVneo cells was inhibited by CHH only. H2S donors stimulated cell proliferation, migration, and tube formation in ovine placental artery endothelial cells (oFPAECs) as effectively as vascular endothelial growth factor. Co-culture with BeWo and HTR-8/SVneo cells stimulated oFPAEC migration, which was inhibited by CHH or BCA in BeWo but CHH only in HTR-8/SVneo cells. Primary human villous trophoblasts (HVT) were more potent than trophoblast cell lines in stimulating oFPAEC migration that was inhibited by CHH and CHH/BCA combination in accordance with its H2S synthesizing activity linked to CBS and CTH expression patterns. H2S donors activated endothelial nitric oxide synthase (NOS3), v-AKT murine thymoma viral oncogene homolog 1 (AKT1), and extracellular signal-activated kinase 1/2 (mitogen-activated protein kinase 3/1, MAPK3/1) in oFPAECs. H2S donor-induced NOS3 activation was blocked by AKT1 but not MAPK3/1 inhibition. In keeping with our previous studies showing a crucial role of AKT1, MAPK3/1, and NOS3/NO in placental angiogenesis, these data show that trophoblast-derived endogenous H2S stimulates placental angiogenesis, involving activation of AKT1, NOS3/NO, and MAPK3/1.

Pregnancy Augments VEGF-Stimulated In Vitro Angiogenesis and Vasodilator (NO and H2S) Production in Human Uterine Artery Endothelial Cells

CONTEXT

Augmented uterine artery (UA) production of vasodilators, including nitric oxide (NO) and hydrogen sulfide (H2S), has been implicated in pregnancy-associated and agonist-stimulated rise in uterine blood flow that is rate-limiting to pregnancy health.

OBJECTIVE

Developing a human UA endothelial cell (hUAEC) culture model from main UAs of nonpregnant (NP) and pregnant (P) women for testing a hypothesis that pregnancy augments endothelial NO and H2S production and endothelial reactivity to vascular endothelial growth factor (VEGF).

DESIGN

Main UAs from NP and P women were used for developing hUAEC culture models. Comparisons were made between NP- and P-hUAECs in in vitro angiogenesis, activation of cell signaling, expression of endothelial NO synthase (eNOS) and H2S-producing enzymes cystathionine β-synthase (CBS) and cystathionine γ-lyase, and NO/H2S production upon VEGF stimulation.

RESULTS

NP- and P-hUAECs displayed a typical cobblestone-like shape in culture and acetylated low-density lipoprotein uptake, stained positively for endothelial and negatively for smooth muscle markers, maintained key signaling proteins during passage, and had statistically significant greater eNOS and CBS proteins in P- vs NP-hUAECs. Treatment with VEGF stimulated in vitro angiogenesis and eNOS protein and NO production only in P-hUEACs and more robust cell signaling in P- vs NP-hUAECs. VEGF stimulated CBS protein expression, accounting for VEGF-stimulated H2S production in hUAECs.

CONCLUSION

Comparisons between NP- and P-hUAECs reveal that pregnancy augments VEGF-stimulated in vitro angiogenesis and NO/H2S production in hUAECs, showing that the newly established hUAEC model provides a critical in vitro tool for understanding human uterine hemodynamics.

Testosterone Represses Estrogen Signaling by Upregulating miR-22

Preeclampsia, a multisystem syndrome occurring during mid- to late gestation in humans, is a leading cause of maternal and perinatal morbidity and mortality. Patients usually present with high circulating testosterone and reduced estradiol production, but the mechanisms remain unclear. Revealing the mechanism that modulating the imbalance of testosterone and estradiol in preeclampsia is of great value in understanding the cause of the disease. The placenta is the predominant source of steroid hormone production during gestation, and we observed markedly increased 17β-HSD3 (17β-hydroxysteroid dehydrogenase 3) levels and downregulated aromatase expression, the key enzymes responsible for synthesis of testosterone and estradiol, respectively, in preeclamptic placentas compared with controls. Furthermore, we found a significant upregulation of microRNA (miR)-22 in preeclamptic placentas. In a trophoblast cell line, JEG-3 cells, testosterone repressed the expression of aromatase and estrogen receptor α and the production of estradiol while promoting miR-22 expression. miR-22 directly targeted and inhibited estrogen receptor α expression while indirectly decreasing aromatase expression and estradiol production by interfering with estrogen receptor α signaling. Furthermore, inhibition of miR-22 expression significantly reversed the inhibitory effect of testosterone on de novo estradiol synthesis in human trophoblastic cells. The findings reveal a mechanism underlying the balanced production of androgen and estrogen modulated by miR-22 in the human placenta and provide new insights into the pathogenesis of preeclampsia from the aspect of endocrine regulation.

H2S biosynthesis and catabolism: new insights from molecular studies

Hydrogen sulfide (H₂S) has profound biological effects within living organisms and is now increasingly being considered alongside other gaseous signalling molecules, such as nitric oxide (NO) and carbon monoxide (CO). Conventional use of pharmacological and molecular approaches has spawned a rapidly growing research field that has identified H₂S as playing a functional role in cell-signalling and post-translational modifications. Recently, a number of laboratories have reported the use of siRNA methodologies and genetic mouse models to mimic the loss of function of genes involved in the biosynthesis and degradation of H₂S within tissues. Studies utilising these systems are revealing new insights into the biology of H₂S within the cardiovascular system, inflammatory disease, and in cell signalling. In light of this work, the current review will describe recent advances in H₂S research made possible by the use of molecular approaches and genetic mouse models with perturbed capacities to generate or detoxify physiological levels of H₂S gas within tissues.