17beta-Estradiol induces protein S-nitrosylation in the endothelium

Estrogen: the forgotten player in metaflammation

Metaflammation is low-grade inflammation triggered by chronic metabolic imbalance and caused by dysregulated metabolites in metabolic inflammatory syndrome (MIS), which includes four diseases: obesity, type 2 diabetes mellitus (T2DM), atherosclerosis (AS), and nonalcoholic fatty liver diseases (NAFLD, recently proposed to be replaced by metabolic dysfunction-associated steatotic liver disease, MASLD). These diseases exhibit apparent sex dimorphism as regards MIS. Estrogen not only plays a crucial role in gender differences in adults but also possesses an anti-inflammatory effect on many metabolic diseases. In this study, we present a prediction of the differential proteins and signal transduction of estrogen in MIS through network pharmacology and review the validated studies on obesity, T2DM, AS, and NAFLD. Subsequently, we compared them to obtain valuable targets, identify current gaps, and provide perspectives for future research on the mechanisms of estrogen in metaflammation.

Roles of Protein S-Nitrosylation in Endothelial Homeostasis and Dysfunction

Significance: Nitric oxide (NO) plays several distinct roles in endothelial homeostasis. Except for activating the guanylyl cyclase enzyme-dependent cyclic guanosine monophosphate signaling pathway, NO can bind reactive cysteine residues in target proteins, a process known as S-nitrosylation (SNO). SNO is proposed to explain the multiple biological functions of NO in the endothelium. Investigating the targets and mechanism of protein SNO in endothelial cells (ECs) can provide new strategies for treating endothelial dysfunction-related diseases. Recent Advances: In response to different environments, proteomics has identified multiple SNO targets in ECs. Functional studies confirm that SNO regulates NO bioavailability, inflammation, permeability, oxidative stress, mitochondrial function, and insulin sensitivity in ECs. It also influences EC proliferation, migration, apoptosis, and transdifferentiation. Critical Issues: Single-cell transcriptomic analysis of ECs isolated from different mouse tissues showed heterogeneous gene signatures. However, litter research focuses on the heterogeneous properties of SNO proteins in ECs derived from different tissues. Although metabolism reprogramming plays a vital role in endothelial functions, little is known about how protein SNO regulates metabolism reprogramming in ECs. Future Directions: Precisely deciphering the effects of protein SNO in ECs isolated from different tissues under different conditions is necessary to further characterize the relationship between protein SNO and endothelial dysfunction-related diseases. In addition, identifying SNO targets that can influence endothelial metabolic reprogramming and the underlying mechanism can offer new views on the crosstalk between metabolism and post-translational protein modification. Antioxid. Redox Signal. 40, 186-205.

Post-Transcriptional and Epigenetic Regulation of Estrogen Signaling

Post-translational and epigenetic regulation are important mechanisms controlling functions of genes and proteins. Although the "classic" estrogen receptors (ERs) have been acknowledged to function in mediating estrogen effects via transcriptional mechanisms, estrogenic agents modulate the turnover of several proteins via post-transcriptional and post-translational pathways including epigenetics. For instance, the metabolic and angiogenic action of G-protein coupled estrogen receptor (GPER) in vascular endothelial cells has been recently elucidated. By interacting with GPER, 17β-estradiol and the GPER agonist G1 enhance endothelial stability of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) and capillary tube formation by increasing ubiquitin-specific peptidase 19 levels, thereby reducing PFKFB3 ubiquitination and proteasomal degradation. In addition to ligands, the functional expression and trafficking of ERs can be modulated by post-translational modification, including palmitoylation. MicroRNAs (miRNAs), the most abundant form of endogenous small RNAs in humans, regulate multiple target genes and are at the center of the multi-target regulatory network. This review also discusses the emerging evidence of how miRNAs affect glycolytic metabolism in cancer, as well as their regulation by estrogens. Restoring dysregulated miRNA expression represents a promising strategy to counteract the progression of cancer and other disease conditions. Accordingly, estrogen post-transcriptional regulatory and epigenetic mechanisms represent novel targets for pharmacological and nonpharmacological intervention for the treatment and prevention of hormone-sensitive noncommunicable diseases, including estrogen-sensitive cancers of the reproductive system in women. SIGNIFICANCE STATEMENT: The effects of estrogen are mediated by several mechanisms that are not limited to the transcriptional regulation of target genes. Slowing down the turnover of master regulators of metabolism by estrogens allows cells to rapidly adapt to environmental cues. Identification of estrogen-targeted microRNAs may lead to the development of novel RNA therapeutics that disrupt pathological angiogenesis in estrogen-dependent cancers.

Estrogen signaling as a bridge between the nucleus and mitochondria in cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide. Epidemiological studies indicate that pre-menopausal women are more protected against the development of CVDs compared to men of the same age. This effect is attributed to the action/effects of sex steroid hormones on the cardiovascular system. In this context, estrogen modulates cardiovascular function in physiological and pathological conditions, being one of the main physiological cardioprotective agents. Here we describe the common pathways and mechanisms by which estrogens modulate the retrograde and anterograde communication between the nucleus and mitochondria, highlighting the role of genomic and non-genomic pathways mediated by estrogen receptors. Additionally, we discuss the presumable role of bromodomain-containing protein 4 (BRD4) in enhancing mitochondrial biogenesis and function in different CVD models and how this protein could act as a master regulator of estrogen protective activity. Altogether, this review focuses on estrogenic control in gene expression and molecular pathways, how this activity governs nucleus-mitochondria communication, and its projection for a future generation of strategies in CVDs treatment.

Sex Differences, Estrogen Metabolism and Signaling in the Development of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a complex and devastating disease with a poor long-term prognosis. While women are at increased risk for developing PAH, they exhibit superior right heart function and higher survival rates than men. Susceptibility to disease risk in PAH has been attributed, in part, to estrogen signaling. In contrast to potential pathological influences of estrogen in patients, studies of animal models reveal estrogen demonstrates protective effects in PAH. Consistent with this latter observation, an ovariectomy in female rats appears to aggravate the condition. This discrepancy between observations from patients and animal models is often called the "estrogen paradox." Further, the tissue-specific interactions between estrogen, its metabolites and receptors in PAH and right heart function remain complex; nonetheless, these relationships are essential to characterize to better understand PAH pathophysiology and to potentially develop novel therapeutic and curative targets. In this review, we explore estrogen-mediated mechanisms that may further explain this paradox by summarizing published literature related to: (1) the synthesis and catabolism of estrogen; (2) activity and functions of the various estrogen receptors; (3) the multiple modalities of estrogen signaling in cells; and (4) the role of estrogen and its diverse metabolites on the susceptibility to, and progression of, PAH as well as their impact on right heart function.

S100a9 Protects Male Lupus-Prone NZBWF1 Mice From Disease Development

Systemic lupus erythematosus (SLE) is an autoimmune disorder disproportionally affecting women. A similar sex difference exists in the murine New Zealand Black/White hybrid model (NZBWF1) of SLE with all females, but only 30-40% of males, developing disease within the first year of life. Myeloid-derived suppressor cells (MDSCs) are prominent in NZBWF1 males and while depletion of these cells in males, but not females, promotes disease development, the mechanism of suppression remains unknown. S100a9, expressed by neutrophils and MDSCs, has previously been shown to exert immunosuppressive functions in cancer and inflammation. Here we investigated if S100a9 exerts immunosuppressive functions in NZBWF1 male and female mice. S100a9^+/+, S100a9^+/- and S100a9^-/- NZBWF1 mice were followed for disease development for up to 8 months of age. Serum autoantibody levels, splenomegaly, lymphocyte activation, glomerulonephritis and proteinuria were measured longitudinally or at the time of harvest. In accordance with an immunosuppressive function of MDSCs in male mice, S100a9-deficient male NZBWF1 mice developed accelerated autoimmunity as indicated by increased numbers of differentiated effector B and T cells, elevated serum autoantibody levels, increased immune-complex deposition and renal inflammation, and accelerated development of proteinuria. In contrast, female mice showed either no response to S100a9-deficiency or even a slight reduction in disease symptoms. Furthermore, male, but not female, S100a9^-/- NZBWF1 mice displayed an elevated type I interferon-induced gene signature, suggesting that S100a9 may dampen a pathogenic type I interferon signal in male mice. Taken together, S100a9 exerts an immunosuppressive function in male NZBWF1 mice effectively moderating lupus-like disease development via inhibition of type I interferon production, lymphocyte activation, autoantibody production and the development of renal disease.

Cardioprotective action of chia (Salvia hispanica L.) in ovariectomized rats fed a high fat diet

The reduction in estrogen levels is associated with the increased risk factors for cardiovascular disease development. The present study aimed to evaluate the effect of chia consumption in a standard diet (SD) or high fat diet (HFD) on ovariectomized (OVX) and non-ovariectomized (SHAM) rats, in relation to biometric measurements, oxidative stress, mineral content and ATPase enzymes in the heart. The study was conducted with 80 female Wistar rats, which received a SD or HFD for 18 weeks. During the first 7 weeks, the animals received the SD or HFD. Then, 40 rats were ovariectomized and 40 rats were SHAM operated. After recovery from surgery, the animals were allocated to 8 groups (n = 10) and they received one of the following diets for 8 weeks: SD, SD + chia, HFD and HFD + chia. In the OVX group, HFD increased weight gain, adiposity, cardiac hypertrophy, and nitric oxide (NO) and K concentration and decreased the Na⁺/K⁺ATPase activity. In combination with HFD, ovariectomy decreased the catalase activity, Mg, Cu and Zn concentration, total ATPase activity, and Na⁺/K⁺ATPase and Mg2 + ATPase activities; this group also presented higher NO, Ca, K, Fe and Mn concentration in the heart. The SHAM group fed chia presented a lower fat content in the heart. In the OVX group fed HFD, chia increased the activity of superoxide dismutase, decreased NO and maintained the content of minerals and ATPase enzymes. Thus, chia improved the biometric parameters of the heart, the antioxidant activity and maintained the content of minerals and ATPase enzymes, showing a cardioprotective action, but without reversing the deleterious effects of ovariectomy.

bFGF alleviates diabetes-associated endothelial impairment by downregulating inflammation via S-nitrosylation pathway

Protein S-nitrosylation is a reversible protein modification implicated in both physiological and pathophysiological regulation of protein function. However, the relationship between dysregulated S-nitrosylation homeostasis and diabetic vascular complications remains incompletely understood. Here, we demonstrate that basic fibroblast growth factor (bFGF) is a key regulatory link between S-nitrosylation homeostasis and inflammation, and alleviated endothelial dysfunction and angiogenic defects in diabetes. Subjecting human umbilical vein endothelial cells (HUVECs) to hyperglycemia and hyperlipidemia significantly decreased endogenous S-nitrosylated proteins, including S-nitrosylation of inhibitor kappa B kinase β (IKKβ^C179) and transcription factor p65 (p65^C38), which was alleviated by bFGF co-treatment. Pretreatment with carboxy-PTIO (c-PTIO), a nitric oxide scavenger, abolished bFGF-mediated S-nitrosylation increase and endothelial protection. Meanwhile, nitrosylation-resistant IKKβ^C179S and p65^C38S mutants exacerbated endothelial dysfunction in db/db mice, and in cultured HUVECs subjected to hyperglycemia and hyperlipidemia. Mechanistically, bFGF-mediated increase of S-nitrosylated IKKβ and p65 was attributed to synergistic effects of increased endothelial nitric oxide synthase (eNOS) and thioredoxin (Trx) activity. Taken together, the endothelial protective effect of bFGF under hyperglycemia and hyperlipidemia can be partially attributed to its role in suppressing inflammation via the S-nitrosylation pathway.

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.

Hydrogen sulfide inhibits development of atherosclerosis through up-regulating protein S-nitrosylation

Hydrogen sulfide (H₂S) is an important gaseous signaling molecule that serves many important regulatory roles in physiological and pathophysiological conditions. H₂S exerts an anti-atherosclerotic effect through mediating the biological functions of nitric oxide (NO). However, its mechanism of action is unclear. The purpose of this study is to explore the effect mechanism of H₂S on the development of atherosclerosis with regard to protein S-nitrosylation. A total of 45 male apoE^-/- mice were randomly divided into three groups. Atherosclerosis was induced by Western diet (21% fat and 0.15% cholesterol) with/without administration of a H₂S donor (NaHS) or an endogenous cystathionine γ-lyase inhibitor (d, l-propargylglycine) for 12 weeks. After 12 weeks, plasma lipid and plasma NO levels were measured. Aortic gross lesion area and histopathological features of aortic lesion were determined. Additionally, the level of S-nitrosylated proteins in vascular smooth muscle cells (VSMCs) was detected using immunofluorescence in aorta. Rat VSMCs were performed in an in vitro experiment. Inducible nitric oxide synthase (iNOS) protein expression, NO generation, protein S-nitrosylation, and cell proliferation and migration were measured. We found that H₂S significantly reduced the aortic atherosclerotic lesion area (P=0.006) and inhibited lipid and macrophage accumulation (P=0.004, P=0.002) and VSMC proliferation (P=0.019) in apoE^-/- mice. H₂S could up-regulate levels of plasma NO and protein S-nitrosylation in aorta VSMCs. However, d, l- propargylglycine had the opposite effect, increasing the lesion area and the content of lipids and macrophages in the lesions of apoE^-/- mice and down-regulating plasma NO levels and protein S-nitrosylation in aorta VSMCs. In vitro experiments, H₂S could significantly reverse the reduction of iNOS expression and NO generation induced by oxidized low-density lipoprotein in VSMCs. Moreover, H₂S could increase the protein S-nitrosylation level of VSMCs in a dose-dependent manner, and the effect could be inhibited by iNOS inhibitors. In addition, proliferation and migration of VSMCs could be inhibited by H₂S in a dose-dependent manner, which could be blocked by an iNOS inhibitor or protein S-nitrosylation removal agent. Our data suggest that H₂S could inhibit the development of atherosclerosis by up-regulating plasma NO and protein S-nitrosylation, thereby inhibiting the proliferation and migration of VSMCs.

Vasorelaxation Effect of Estrone Derivate EA204 in Rabbit Aorta

Estrogen and its derivatives exert vascular protective effects, but the underlying mechanisms remain to be studied fully. Objective. To investigate the vasorelaxation effect and related mechanisms of an estrone derivate EA204[3-(2-piperidin-1-yl)-ethoxy-estra-1, 3, 5 (10)-trien-17-one] on isolated arterial preparation from rabbit thoracic aorta. Methods. Aortic rings from rabbit thoracic aorta were prepared and held in small organ bath filled with Krebs solution; tension change was recorded by a multichannel physiological signal collection and handling system. Results. EA204 (10(-5) to 10(-3) M) induced a concentration-dependent relaxation of aortic rings with endothelium and without endothelium. In denuded arterial preparations, EA204 had a potent relaxing effect on isolated arterial preparations contracted with phenylephrine, norepinephrine, and high-K(+) solution or BaCl2. Mechanism study indicates that EA204 relaxes aortic rings by inhibiting Ca(2+) channels (both receptor-operating Ca(2+) channels and the voltage-dependent Ca(2+) channels were involved) to decrease extracellular Ca(2+) influx and intracellular Ca(2+) release. EA204 is different from verapamil, which is a noncompetitive inhibitor of Ca(2+) channels. In addition, K(+) channels opening may contribute to this vasorelaxation effect. Conclusion. EA204 had a potent endothelium-independent relaxing effect on isolated arterial preparation by inhibiting Ca(2+) channels and opening K(+) channels. The results suggest that EA204 is a potential compound for treatment of cardiovascular diseases in postmenopausal women.

Estrogen receptor β actions in the female cardiovascular system: A systematic review of animal and human studies

Five medical databases were searched for studies that assessed the role of ERβ in the female cardiovascular system and the influence of age and menopause on ERβ functioning. Of 9472 references, 88 studies met our inclusion criteria (71 animal model experimental studies, 15 human model experimental studies and 2 population based studies). ERβ signaling was shown to possess vasodilator and antiangiogenic properties by regulating the activity of nitric oxide, altering membrane ionic permeability in vascular smooth muscle cells, inhibiting vascular smooth muscle cell migration and proliferation and by regulating adrenergic control of the arteries. Also, a possible protective effect of ERβ signaling against left ventricular hypertrophy and ischemia/reperfusion injury via genomic and non-genomic pathways was suggested in 27 studies. Moreover, 5 studies reported that the vascular effects of ERβ may be vessel specific and may differ by age and menopause status. ERβ seems to possess multiple functions in the female cardiovascular system. Further studies are needed to evaluate whether isoform-selective ERβ-ligands might contribute to cardiovascular disease prevention.

Estriol-induced fibrinolysis due to the activation of plasminogen to plasmin by nitric oxide synthesis in platelets

Estriol, an oestrogen, at 0.6 nmol/l was reported to inhibit ADP-induced platelet aggregation through nitric oxide synthesis. As nitric oxide has been reported to cause fibrinolysis due to the activation of plasminogen to plasmin, the role of estriol as a fibrinolytic agent was investigated. Also, the mechanism of estriol-induced nitric oxide synthesis in anucleated platelets was investigated. The estriol-induced lysis of platelet-rich plasma (PRP) clot was determined by photography of the clot lysis and by the assay of fibrin degradation products in the lysate and was obtained by SDS-PAGE. Nitric oxide was determined by methemoglobin method. The platelet membrane protein was isolated from the platelets by using Triton X-100 (0.05% v/v). The binding of estriol to the protein was determined by Scatchard plot by using an ELISA for estriol. Estriol at 0.6 nmol/l was found to lyse the clotted PRP due to fibrinolysis that produced fibrin degradation products in the lysate. The amino acid analysis of the platelet membrane protein, which resembles with nitric oxide synthase (NOS) activity, was activated nearly 10-fold over the control in the presence of estriol and was identified to be a human serum albumin precursor (Mr. 69 kDa) that binds to estriol with Kd1 of 6.0 × 10 mol/l and 39 ± 2 molecules of estriol bound the NOS molecule. The estriol-induced nitric oxide is capable of inducing fibrinolysis of the clotted PRP. The binding of estriol to platelet membrane NOS activated the enzyme in the absence of DNA in the platelet.

Sphingosine-1-phosphate receptor 1 transmits estrogens' effects in endothelial cells

We have previously reported that the steroid hormone estrogens stimulate activation of sphingosine kinase 1 (SphK1) and sphingosine-1-phosphate (S1P) receptors in breast cancer cells. Both estrogens and S1P are potent biological modulators of endothelial function in vasculature able to activate multiple effectors, including endothelial nitric oxide synthase (eNOS). In this study we report that treatment of endothelial cells (ECs) with 17β-estradiol (E2) resulted in a rapid, transient, and dose-dependent increase in SphK activity and increased S1P production. The effect was not reproduced by the inactive E2 analogue 17α-E2. Expression of the dominant-negative mutant SphK1(G82D) or transfection of SphK1-targeted siRNA in ECs caused not only a defect in SphK activation by E2, but also a significant inhibition of E2-induced activation of Akt/eNOS. Furthermore, E2 treatment induced internalization of plasma membrane S1P1 receptor, accompanied with an increase in the amount of cytosolic S1P1. By down-regulating S1P1 receptor expression, the S1P1-specific antisense oligonucleotides significantly inhibited E2-induced activation of Akt/eNOS in ECs. E2-induced EC migration and tube formation were also inhibited by S1P1 down-regulation. Thus, the findings indicate an important role of the SphK1/S1P1 pathway in mediating estrogen signaling and its actions in vasculature.

Light-evoked S-nitrosylation in the retina

Nitric oxide (NO) synthesis in the retina is triggered by light stimulation. NO has been shown to modulate visual signal processing at multiple sites in the vertebrate retina, via activation of the most sensitive target of NO signaling, soluble guanylate cyclase. NO can also alter protein structure and function and exert biological effects directly by binding to free thiol groups of cysteine residues in a chemical reaction called S-nitrosylation. However, in the central nervous system, including the retina, this reaction has not been considered to be significant under physiological conditions. Here we provide immunohistochemical evidence for extensive S-nitrosylation that takes place in the goldfish and mouse retinas under physiologically relevant light intensities, in an intensity-dependent manner, with a strikingly similar pattern in both species. Pretreatment with N-ethylmaleimide (NEM), which occludes S-nitrosylation, or with 1-(2-trifluromethylphenyl)imidazole (TRIM), an inhibitor of neuronal NO synthase, eliminated the light-evoked increase in S-nitrosylated protein immunofluorescence (SNI) in the retinas of both species. Similarly, light did not increase SNI, above basal levels, in retinas of transgenic mice lacking neuronal NO synthase. Qualitative analysis of the light-adapted mouse retina with mass spectrometry revealed more than 300 proteins that were S-nitrosylated upon illumination, many of which are known to participate directly in retinal signal processing. Our data strongly suggest that in the retina light-evoked NO production leads to extensive S-nitrosylation and that this process is a significant posttranslational modification affecting a wide range of proteins under physiological conditions.

Hypercysteinemia promotes atherosclerosis by reducing protein S-nitrosylation

Protein S-nitrosylation plays important role in the regulation of cardiovascular functions in nitric oxide (NO) Pathway. Hypercysteinemia (HHcy) is an independently risk factor for atherosclerosis. We hypothesized that HHcy promotes atherosclerosis by reducing level of vascular protein S-nitrosylation. The aim of present study is to investigate effect of HHcy on vascular protein S-nitrosylation. A total of 45 male apoE-/- mice were randomly divided into three groups. The control group was fed a Western-type diet. The HHcy group was fed a diet containing 4.4% L-methionine, and the HHcy+NONOate group was fed a diet containing 4.4% L-methionine and administrated NONOate (ip). Human umbilical vein endothelial cells were performed for in vitro experiment. Plasma lipids were measured every 4 weeks. After 12 weeks, aortic atherosclerotic lesion areas were detected as well as cellular components. The levels of plasma homocysteine (Hcy) and NO were measured. S-nitrosylation was detected using immunofluorescence, and further confirmed by biotin switch method. We found that compared with the control group, Hcy levels, and atherosclerotic plaque, and content of vascular smooth muscle cells and macrophages in lesions significantly increased, and levels of NO significantly decreased in the HHcy group. However, NONOate reverses this effect. In addition, Hcy significantly reduced protein S-nitrosylation in human umbilical vein endothelial cells. This reduction of protein S-nitrosylation was accompanied by reduced levels of NO. Our results suggested that Hcy promoted atherosclerosis by inhibiting vascular protein S-nitrosylation.

Efficacy of female rat models in translational cardiovascular aging research

Cardiovascular disease is the leading cause of death in women in the United States. Aging is a primary risk factor for the development of cardiovascular disease as well as cardiovascular-related morbidity and mortality. Aging is a universal process that all humans undergo; however, research in aging is limited by cost and time constraints. Therefore, most research in aging has been done in primates and rodents; however it is unknown how well the effects of aging in rat models translate into humans. To compound the complication of aging gender has also been indicated as a risk factor for various cardiovascular diseases. This review addresses the systemic pathophysiology of the cardiovascular system associated with aging and gender for aging research with regard to the applicability of rat derived data for translational application to human aging.

Effects of biological sex on the pathophysiology of the heart

Cardiovascular diseases are the leading causes of death in men and women in industrialized countries. While the effects of biological sex on cardiovascular pathophysiology have long been known, the sex-specific mechanisms mediating these processes have been further elucidated over recent years. This review aims at analysing the sex-based differences in cardiac structure and function in adult mammals, and the sex-based differences in the main molecular mechanisms involved in the response of the heart to pathological situations. It emerged from this review that the sex-based difference is a variable that should be dealt with, not only in basic science or clinical research, but also with regards to therapeutic approaches.

Mechanisms of estrogen effects on the endothelium: an overview

In this review, we aim to provide an overview of the recent advances in understanding estrogen effects on the vascular endothelium. Epidemiological studies suggest the female sex hormone estrogen mediates the relative protection of premenopausal women against cardiovascular disease, compared with age-matched men. However, results from clinical trials of exogenous estrogen supplementation in postmenopausal women have been disappointing, generating much controversy about the role of estrogen and demonstrating the need for further research in this field. Here we have discussed the roles of different estrogen receptors (ERs) such as ERα, ERβ, and G-protein coupled receptor 30; the complex genomic and nongenomic signalling pathways downstream to ER activation and the factors such as age, menopause, pregnancy, and diabetes that might alter estrogen responses. The common themes of this discussion are the complexity and diversity of endothelial estrogen responses and their modulation by 1 or more coexisting factors. Finally, we summarize the emerging therapeutic options including improved targeting of individual ERs and signalling pathways that might maximize the therapeutic potential of estrogenic compounds while minimizing their harmful side effects.

Methods for detection and characterization of protein S-nitrosylation

Reversible protein S-nitrosylation, defined as the covalent addition of a nitroso moiety to the reactive thiol group on a cysteine residue, has received increasing recognition as a critical post-translational modification that exerts ubiquitous influence in a wide range of cellular pathways and physiological processes. Due to the lability of the S-NO bond, which is a dynamic modification, and the low abundance of endogenously S-nitrosylated proteins in vivo, unambiguous identification of S-nitrosylated proteins and S-nitrosylation sites remains methodologically challenging. In this review, we summarize recent advancements and the use of state-of-art approaches for the enrichment, systematic identification and quantitation of S-nitrosylation protein targets and their modification sites at the S-nitrosoproteome scale. These advancements have facilitated the global identification of >3000 S-nitrosylated proteins that are associated with wide range of human diseases. These strategies hold promise to site-specifically unravel potential molecular targets and to change S-nitrosylation-based pathophysiology, which may further the understanding of the potential role of S-nitrosylation in diseases.

Testosterone and β-oestradiol prevent inward remodelling of rat small mesenteric arteries: role of NO and transglutaminase

Increasing evidence shows that sex hormones exert a protective effect on the vasculature, especially in the regulation of the active vasomotor responses. However, whether sex hormones affect vascular remodelling is currently unclear. In the present study, we tested the hypothesis that testosterone in males and β-oestradiol in females prevent inward remodelling, possibly through inhibition of cross-linking activity induced by enzymes of the TG (transglutaminase) family. Small mesenteric arteries were isolated from male and female Wistar rats. Dose-dependent relaxation to testosterone and β-oestradiol was inhibited by the NO synthase inhibitor L-NAME (NG-nitro-L-arginine methyl ester), confirming that these hormones induce NO release. When arteries were cannulated, pressurized and kept in organ culture with ET-1 (endothelin-1) for 3 days we observed strong vasoconstriction and inward remodelling. Remodelling was significantly inhibited by testosterone in males, and by β-oestradiol in females. This preventive effect of sex hormones was not observed in the presence of L-NAME. Inward remodelling was also reduced by the inhibitor of TG L682.777, both in males and females. In arteries from female rats, ET-1 increased TG activity, and this effect was prevented by β-oestradiol. L-NAME induced a significant increase in TG activity in the presence of sex hormones in arteries from both genders. We conclude that testosterone and β-oestradiol prevent constriction-induced inward remodelling. Inward remodelling, both in males and females, depends on NO and TG activity. In females, inhibition of inward remodelling could be mediated by NO-mediated inhibition of TG activity.

Ischemic injury promotes Keap1 nitration and disturbance of antioxidative responses in endothelial cells: a potential vasoprotective effect of melatonin

Clinical epidemiology has indicated that the endothelial injury is a potential contributor to the pathogenesis of ischemic neurovascular damage. In this report, we assessed S-nitrosylation and nitration of Keap1 to identify downstream nitric oxide redox signaling targets into endothelial cells during ischemia. Here, oxygen-glucose deprivation (OGD) exposure initiates the nuclear import of Keap1 in endothelial cells, which interacted with nuclear-localized Nrf2, as demonstrated through co-immunoprecipitation and immunocytochemical assay. Paralleling the ischemia-induced nuclear import of Keap1, increased nitrotyrosine immunoreactivity in endothelial cells was also observed. Consistently, the addition of peroxynitrite provoked nuclear import of Keap1 and a concomitant Nrf2 nuclear import in the endothelial cells. Importantly, pharmacological inhibition of nitrosative stress by melatonin partially inhibited the OGD-induced constitutive nuclear import of Keap1 and subsequently disturbance of Nrf2/Keap1 signaling. Moreover, the effect of melatonin on nitration and S-nitrosylation of keap1 was examined in endothelial cells with 6 hr OGD exposure. Here, we demonstrated that OGD induced tyrosine nitration of Keap1, which was blocked by melatonin treatment, while there were no significant changes in S-nitrosylation of Keap1. The specific amino acid residues of Keap1 involved in tyrosine nitration were identified as Y473 by mass spectrometry. Moreover, the protective role of melatonin against damage to endothelial tight junction integrity was addressed by ZO-1 expression, paralleled with the restored heme oxygenase-1 levels during OGD. Together, our results emphasize that upon nitrosative stress, the protective effect of melatonin on endothelial cells is likely mediated at least in part by inhibition of ischemia-evoked protein nitration of Keap1, hence contributing to relieve the disturbance of Nrf2/Keap1 antioxidative signaling.

G-protein coupled receptor 30 (GPR30): a novel regulator of endothelial inflammation

Estrogen, the female sex hormone, is known to exert anti-inflammatory and anti-atherogenic effects. Traditionally, estrogen effects were believed to be largely mediated through the classical estrogen receptors (ERs). However, there is increasing evidence that G-protein coupled receptor 30 (GPR30), a novel estrogen receptor, can mediate many estrogenic effects on the vasculature. Despite this, the localization and functional significance of GPR30 in the human vascular endothelium remains poorly understood. Given this background, we examined the subcellular location and potential anti-inflammatory roles of GPR30 using human umbilical vein endothelial cells as a model system. Inflammatory changes were induced by treatment with tumor necrosis factor (TNF), a pro-inflammatory cytokine involved in atherogenesis and many other inflammatory conditions. We found that GPR30 was located predominantly in the endothelial cell nuclei. Treatment with the selective GPR30 agonist G-1 partially attenuated the TNF induced upregulation of pro-inflammatory proteins such as intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). This effect was completely abolished by the selective GPR30 antagonist G-15, suggesting that it was indeed mediated in a GPR30 dependent manner. Interestingly, estrogen alone had no effects on TNF-treated endothelium. Concomitant activation of the classical ERs blocked the anti-inflammatory effects of G-1, indicating opposing effects of GPR30 and the classical ERs. Our findings demonstrate that endothelial GPR30 is a novel regulator of the inflammatory response which could be a potential therapeutic target against atherosclerosis and other inflammatory diseases.

C-reactive protein reduces protein S-nitrosylation in endothelial cells

C-reactive protein (CRP) emerges as an important mediator of cardiovascular lesions. In this study, we aimed to assess the role of CRP in the S-nitrosylation of proteins in endothelial cells and elucidate the potential mechanisms. Our results showed that CRP reduced protein S-nitrosylation in human umbilical vein endothelial cells (HUVECs). NO donor S-nitrosoglutathione antagonized CRP-mediated reduction of protein S-nitrosylation. Neutralizing antibody to Fcγ receptor II remarkably attenuated these changes. In addition, CRP increased NF-κB activation via the reduction of S-nitrosylation of p65, but not p50 in HUVECs, and induced the upregulation of NF-kB target gene vascular cell adhesion molecule-1. Furthermore, we confirmed that CRP reduced S-nitrosylated proteins in the rat aorta. Taken together, these data suggest that CRP-induced decline of protein S-nitrosylation by activating NF-κB via reduction of S-nitrosylation of p65, which may contribute to the endothelial dysfunction.

17β-estradiol induces vasorelaxation by stimulating endothelial hydrogen sulfide release

Estrogen exerts vascular protective effects, but the underlying mechanisms remain to be understood fully. In recent years, hydrogen sulfide (H(2)S) has increasingly been recognized as an important signaling molecule in the cardiovascular system. Vascular H(2)S is produced from L-cysteine, catalyzed by cystathionine γ-lyase (CSE). In our study, apolipoprotein E (ApoE)-deficient mice were ovariectomized and implanted with placebo (OVX mice) or 17β-estradiol (E(2)) pellets (OVX + E(2) mice). Compared with OVX mice, OVX + E(2) mice showed increased plasma H(2)S levels (P = 0.012) and decreased aortic lesion area (P = 0.028). These effects were largely reversed when supplementing with the irreversible CSE inhibitor DL-propargylglycine (PPG) in the OVX + E(2) + PPG mice. Meanwhile, the nitric oxide and prostacyclin-resistant responses to cumulative application of acetylcholine (ACh) were studied among all the three groups of femoral arteries. Compared with the arteries in the OVX group, the vasodilator sensitivity of arteries to ACh was increased in the OVX + E(2) group and attenuated in the OVX + E(2) + PPG group. E(2) and estrogen receptor (ER) α agonist 4',4″,4'″-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol rapidly increased H(2)S release in human endothelial cells, but not partially selective ERβ agonist 2,3-bis-(4-hydroxyphenyl)-propionitrile. These effects were inhibited by ER antagonist ICI 182780 or by protein kinase G (PKG) inhibitor KT5823. Furthermore, endothelial PKG activity was increased by E(2) (P = 0.003) and E(2)-induced vasodilation was inhibited by KT5823 (P = 0.009). In conclusion, the endothelial CSE/H(2)S pathway is activated by E(2) through PKG, which leads to vasodilation. These actions may be relevant to estrogen's anti-atherogenic effect.

Angiotensin II-aldosterone interaction in human coronary microarteries involves GPR30, EGFR, and endothelial NO synthase

AIMS

The aim of this study was to investigate the aldosterone-angiotensin (Ang) II interaction in human coronary microarteries (HCMAs).

METHODS AND RESULTS

HCMAs, obtained from 75 heart-beating organ donors, were mounted in myographs and exposed to Ang II, either directly or following a 30-min pre-incubation with aldosterone, 17β-oestradiol, hydrocortisone, the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580, the extracellular regulated kinase 1/2 (ERK1/2) inhibitor PD98059, the GPR30 antagonist G15, or the epidermal growth factor receptor (EGFR) antagonist AG1478. Ang II constricted HCMAs in a concentration-dependent manner. All steroids, at nanomolar levels, potentiated Ang II and G15 prevented this effect. The potentiation disappeared or was reversed into Ang II antagonism at micromolar steroid levels. NO synthase (NOS) inhibition prevented the latter antagonism in the case of 17β-oestradiol, whereas both aldosterone and 17β-oestradiol at micro- (but not nano-) molar levels induced endothelial NOS phosphorylation in human umbilical vein endothelial cells. AG1478, but not SB203580 or PD98059, abolished the Ang II-induced contraction in the presence of aldosterone or 17β-oestradiol, and none of these drugs affected Ang II alone.

CONCLUSION

Steroids including aldosterone affect Ang II-induced vasoconstriction in a biphasic manner. Potentiation occurs at nanomolar steroid levels and depends on GPR30 and EGFR transactivation. At micromolar steroid levels, this potentiation either disappears (aldosterone and hydrocortisone) or is reversed into an inhibition (17β-oestradiol), and this is due to the endothelial NOS activation that occurs at such concentrations.

Estrogen-responsive nitroso-proteome in uterine artery endothelial cells: role of endothelial nitric oxide synthase and estrogen receptor-β

Covalent adduction of a NO moiety to cysteines (S-nitrosylation or SNO) is a major route for NO to directly regulate protein functions. In uterine artery endothelial cells (UAEC), estradiol-17β (E2) rapidly stimulated protein SNO that maximized within 10-30 min post-E2 exposure. E2-bovine serum albumin stimulated protein SNO similarly. Stimulation of SNO by both was blocked by ICI 182, 780, implicating mechanisms linked to specific estrogen receptors (ERs) localized on the plasma membrane. E2-induced protein SNO was attenuated by selective ERβ, but not ERα, antagonists. A specific ERβ but not ERα agonist was able to induce protein SNO. Overexpression of ERβ, but not ERα, significantly enhanced E2-induced SNO. Overexpression of both ERs increased basal SNO, but did not further enhance E2-stimulated SNO. E2-induced SNO was inhibited by N-nitro-L-arginine-methylester and specific endothelial NO synthase (eNOS) siRNA. Thus, estrogen-induced SNO is mediated by endogenous NO via eNOS and mainly ERβ in UAEC. We further analyzed the nitroso-proteomes by CyDye switch technique combined with two-dimensional (2D) fluorescence difference gel electrophoresis. Numerous nitrosoprotein (spots) were visible on the 2D gel. Sixty spots were chosen and subjected to matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Among the 54 identified, nine were novel SNO-proteins, 32 were increased, eight were decreased, and the rest were unchanged by E2. Tandom MS identified Cys139 as a specific site for SNO in GAPDH. Pathway analysis of basal and estrogen-responsive nitroso-proteomes suggested that SNO regulates diverse protein functions, directly implicating SNO as a novel mechanism for estrogen to regulate uterine endothelial function and thus uterine vasodilatation.

Role of neuronal nitric-oxide synthase in estrogen-induced relaxation in rat resistance arteries

Estrogen has antihypertensive and vasorelaxing properties, partly via activation of endothelial nitric-oxide synthase (eNOS). Recently, neuronal nitric-oxide synthase (nNOS) has been detected in vascular cells, although the significance of this is unclear. Estrogen was found to stimulate nNOS in certain cultured cells. We hypothesized that estrogen regulates vascular tone partly via endothelium-derived nNOS. Human umbilical vein endothelial cells were used to test whether acute (5 min) stimulation with 17β-estradiol (E2) at 1 or 10 nM affected nNOS activity. Small mesenteric arteries from Sprague-Dawley rats were examined for relaxation to E2 (0.001-10 μM) in the absence or presence of selective nNOS inhibitor [N-propyl-L-arginine (L-NPA); 2 μM] or pan-NOS inhibitor [Nω-nitro-L-arginine methyl ester (L-NAME); 100 μM] using a wire myograph. Immunostaining was used to visualize nNOS in rat mesenteric artery cross-sections. Western blotting measured total and phospho-nNOS in endothelial cell lysates and thoracic aorta homogenates. E2 rapidly increased (p < 0.001) activating phosphorylation of nNOS and nitric oxide (NO) production (as measured by 4-amino-5-methylamino-2,7-difluorofluorescein fluorescence) in endothelial cells. Likewise, E2 caused dose-dependent relaxation of arteries from female rats, which was blunted by both l-NPA and l-NAME (p < 0.001). In contrast, E2 response was modest in male animals and unaffected by NOS inhibition. It is noteworthy that there was a greater baseline presence of phospho-nNOS in male relative to female aortas. Although eNOS is believed to be the main source of NO in the vascular endothelium, we confirmed nNOS expression in endothelial cells. Endothelial nNOS mediated E2 relaxation in isolated arteries from female animals. Altogether, these data suggest vascular nNOS as a novel mechanism in E2 signaling.

Estrogen signaling and cardiovascular disease

Estrogen has pleiotropic effects on the cardiovascular system. The mechanisms by which estrogen confers these pleiotropic effects are undergoing active investigation. Until a decade ago, all estrogen signaling was thought to occur by estrogen binding to nuclear estrogen receptors (estrogen receptor-α and estrogen receptor-β), which bind to DNA and function as ligand-activated transcription factors. Estrogen binding to the receptor alters gene expression, thereby altering cell function. Estrogen also binds to nuclear estrogen receptors that are tethered to the plasma membrane, resulting in acute activation of signaling kinases such as PI3K. An orphan G-protein-coupled receptor, G-protein-coupled receptor 30, can also bind estrogen and activate acute signaling pathways. Thus, estrogen can alter cell function by binding to different estrogen receptors. This article reviews the different estrogen receptors and their signaling mechanisms, discusses mechanisms that regulate estrogen receptor levels and locations, and considers the cardiovascular effects of estrogen signaling.

S-nitrosylation of proteins: a new insight into endothelial cell function regulated by eNOS-derived NO

Nitric oxide (NO) is a messenger molecule that is highly diffusible and short-lived. Despite these two characteristics, seemingly unsuitable for intracellular reactions, NO modulates a variety of cellular processes via the mechanism of S-nitrosylation. An important factor that determines the specificity of S-nitrosylation as a signaling mechanism is the compartmentalization of nitric oxide synthase (NOS) with its target proteins. Endothelial NOS (eNOS) is unique among the NOS family members by being localized mainly near specific intracellular membrane domains including the cytoplasmic face of the Golgi apparatus and plasma membrane caveolae. Nitric oxide produced by eNOS localized on the Golgi apparatus can react with thiol groups on nearby Golgi proteins via a redox mechanism resulting in S-nitrosylation of these proteins. This modification influences their function as regulators of cellular processes such as protein trafficking (e.g., exocytosis and endocytosis), redox state, and cell cycle. Thus, eNOS-derived NO regulates a wide range of endothelial cell functions, such as inflammation, apoptosis, permeability, migration, and cell growth.

Impact of sex hormone metabolism on the vascular effects of menopausal hormone therapy in cardiovascular disease

Epidemiological studies have shown that cardiovascular disease (CVD) is less common in pre-menopausal women (Pre-MW) compared to men of the same age or post-menopausal women (Post-MW), suggesting cardiovascular benefits of estrogen. Estrogen receptors (ERs) have been identified in the vasculature, and experimental studies have demonstrated vasodilator effects of estrogen/ER on the endothelium, vascular smooth muscle (VSM) and extracellular matrix. Several natural and synthetic estrogenic preparations have been developed for relief of menopausal vasomotor symptoms. However, whether menopausal hormone therapy (MHT) is beneficial in postmenopausal CVD remains controversial. Despite reports of vascular benefits of MHT from observational and experimental studies, randomized clinical trials (RCTs), such as the Heart and Estrogen/progestin Replacement Study (HERS) and the Women's Health Initiative (WHI), have suggested that, contrary to expectations, MHT may increase the risk of CVD. These discrepancies could be due to agerelated changes in sex hormone synthesis and metabolism, which would influence the effective dose of MHT and the sex hormone environment in Post-MW. Age-related changes in the vascular ER subtype, structure, expression, distribution, and post-ER signaling pathways in the endothelium and VSM, along with factors related to the design of RCTs, preexisting CVD condition, and structural changes in the blood vessels architecture have also been suggested as possible causes of MHT failure in CVD. Careful examination of these factors should help in identifying the causes of the changes in the vascular effects of estrogen with age. The sex hormone metabolic pathways, the active versus inactive estrogen metabolites, and their effects on vascular function, the mitochondria, the inflammatory process and angiogenesis should be further examined. Also, the genomic and non-genomic effects of estrogenic compounds should be viewed as integrated rather than discrete responses. The complex interactions between these factors highlight the importance of careful design of MHT RCTs, and the need of a more customized approach for each individual patient in order to enhance the vascular benefits of MHT in postmenopausal CVD.

Beta-estradiol attenuates hypoxic pulmonary hypertension by stabilizing the expression of p27kip1 in rats

BACKGROUND

Pulmonary vascular structure remodeling (PVSR) is a hallmark of pulmonary hypertension. P27(kip1), one of critical cyclin-dependent kinase inhibitors, has been shown to mediate anti-proliferation effects on various vascular cells. Beta-estradiol (β-E2) has numerous biological protective effects including attenuation of hypoxic pulmonary hypertension (HPH). In the present study, we employed β-E2 to investigate the roles of p27(kip1) and its closely-related kinase (Skp-2) in the progression of PVSR and HPH.

METHODS

Sprague-Dawley rats treated with or without β-E2 were challenged by intermittent chronic hypoxia exposure for 4 weeks to establish hypoxic pulmonary hypertension models, which resemble moderate severity of hypoxia-induced PH in humans. Subsequently, hemodynamic and pulmonary pathomorphology data were gathered. Additionally, pulmonary artery smooth muscle cells (PASMCs) were cultured to determine the anti-proliferation effect of β-E2 under hypoxia exposure. Western blotting or reverse transcriptional polymerase chain reaction (RT-PCR) were adopted to test p27(kip1), Skp-2 and Akt-P changes in rat lung tissue and cultured PASMCs.

RESULTS

Chronic hypoxia significantly increased right ventricular systolic pressures (RVSP), weight of right ventricle/left ventricle plus septum (RV/LV+S) ratio, medial width of pulmonary arterioles, accompanied with decreased expression of p27(kip1) in rats. Whereas, β-E2 treatment repressed the elevation of RVSP, RV/LV+S, attenuated the PVSR of pulmonary arterioles induced by chronic hypoxia, and stabilized the expression of p27(kip1). Study also showed that β-E2 application suppressed the proliferation of PASMCs and elevated the expression of p27(kip1) under hypoxia exposure. In addition, experiments both in vivo and in vitro consistently indicated an escalation of Skp-2 and phosphorylated Akt under hypoxia condition. Besides, all these changes were alleviated in the presence of β-E2.

CONCLUSIONS

Our results suggest that β-E2 can effectively attenuate PVSR and HPH. The underlying mechanism may partially be through the increased p27(kip1) by inhibiting Skp-2 through Akt signal pathway. Therefore, targeting up-regulation of p27(kip1) or down-regulation of Skp-2 might provide new strategies for treatment of HPH.

Estradiol-17beta stimulates specific receptor and endogenous nitric oxide-dependent dynamic endothelial protein S-nitrosylation: analysis of endothelial nitrosyl-proteome

Covalent adduction of a nitrosyl group to cysteines [S-nitrosylation (S-NO)] is emerging as a key route for nitric oxide (NO) to directly modulate protein functions. Here, we studied the effects of estrogens on endothelial protein S-NO and analyzed the nitrosyl-proteomes by biotin/CyDye switch technique combined with two-dimensional fluorescence difference gel electrophoresis and identified nitrosoproteins by matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Estradiol-17beta (E2) rapidly stimulated protein S-NO in human umbilical vein endothelial cells, maximizing within 10- to 30-min post-E2 (10 nm) exposure. E2-BSA also rapidly stimulated protein S-NO. Both E2 and E2-BSA-induced protein S-NO was blocked by ICI 182,780 and N-nitro-l-arginine-methylester. Human umbilical vein endothelial cells expressed estrogen receptor (ER)alpha and ERbeta; both seemed to be required for E2 stimulation of protein S-NO because: 1) neither ERalpha or ERbeta agonist alone, but their combination, stimulated protein S-NO; and 2) either ERalpha or ERbeta antagonist blocked E2-induced protein S-NO. Numerous nitrosoproteins (spots) were observed on two-dimensional fluorescence difference gel. One hundred spots of interest were picked up; 58 were identified and, of which 15 were novel nitrosoproteins, 28 were up-regulated, 11 were decreased, and the rest were unchanged by E2. Pathway analysis suggested that nitrosoproteins are involved in regulating various endothelial functions, including apoptosis, cell structure and metabolism, redox homeostasis, etc. Thus, estrogens stimulate dynamic endothelial protein S-NO via mechanisms linked to specific ERs possibly on the plasma membrane and endogenous NO. These findings signify a critical next step for the understanding of the biological targets of enhanced NO production by estrogens.