Loss of estrogen receptor beta decreases mitochondrial energetic potential and increases thrombogenicity of platelets in aged female mice

Gender Differences in Atrial Fibrillation: From the Thromboembolic Risk to the Anticoagulant Treatment Response

Atrial fibrillation (AF) is the most common cardiac arrhythmia associated with an increased thromboembolic risk. The impact of the female sex as an independent risk factor for thromboembolic events in AF is still debated. Background and Objectives: The aim of this review is to evaluate the gender-related differences in cardioembolic risk and response to anticoagulants among AF patients. Materials and Methods: The PubMed database is used to review the reports about gender differences and thromboembolic risk in atrial fibrillation. Results: Non-vitamin K oral anticoagulants (NOACs) represent the gold standard for thromboembolic risk prevention in patients with non-valvular atrial fibrillation (NVAF). Despite a similar rate of stroke and systemic embolism (SE) among men and women in NOACs or vitamin K antagonists (VKAs) treatment, the use of NOACs in AF women is associated with a lower risk of intracranial bleeding, major bleeding, and all-cause mortality than in men. Conclusions: The female sex can be defined as a stroke risk modifier rather than a stroke risk factor since it mainly increases the thromboembolic risk in the presence of other risk factors. Further studies about the efficacy and safety profile of NOACs according to sex are needed to support clinicians in performing the most appropriate and tailored anticoagulant therapy, either in male or female AF patients.

Aspirin Administration Mitigates Platelet Hyperaggregability After Splenectomy in a Murine Model

INTRODUCTION

Patients who undergo splenectomy (SPLN) have an estimated 10%-35% risk of venous thromboembolic events; however, the underlying mechanism and strategy for prevention have yet to be identified. The goals of this study were to 1) investigate platelet aggregation after SPLN, 2) examine if aspirin administration could mitigate this effect, and 3) determine if concomitant hemorrhage would affect post-SPLN platelet function and response to aspirin.

METHODS

Murine models of operative SPLN and submandibular bleed (SMB) were utilized. Mice were randomized to eight groups as follows: untouched, SPLN, sham (laparotomy only), SMB, SPLN + SMB, SPLN + aspirin (ASA), SMB + ASA, and SPLN + SMB + ASA. Aspirin (50 mg/kg) was administered on postoperative days (PODs) one and two via oral gavage. Mice were euthanized on POD 3, platelet counts were obtained, and blood samples were analyzed via rotational thromboelastometry and impedance aggregometry with adenosine diphosphate (ADP) and arachidonic acid (AA) as agonists.

RESULTS

By POD 3, SPLN mice displayed a significant thrombocytosis compared to untouched, SMB, and sham SPLN mice. Clotting time and clot formation time were significantly decreased in SPLN and SPLN + SMB cohorts compared to untouched and sham controls with elevated mean clot firmness. SPLN mice also displayed a significant increase in ADP- and AA-mediated platelet aggregability compared to untouched controls, SMB, and SPLN + SMB. ASA significantly decreased platelet aggregation via both ADP and AA signaling in SPLN and SPLN + SMB cohorts without affecting viscoelastic coagulation testing.

CONCLUSIONS

Platelet hyperaggregability after SPLN is mediated by both ADP and AA signaling. Early aspirin administration may prevent increased platelet aggregation exacerbated after polytrauma.

Integrated bioinformatics analysis identifies microRNA-200a-5p as a new plasma marker in patient with venous thromboembolism

AIMS

Venous thromboembolism (VTE) is a major global health problem with high incidence and mortality. Vein endothelial cell (VEC) dysfunction is the primary cause of VTE. MicroRNAs (miRNAs) assist in the regulation of VEC functional pathways. Our objective was to identify potential miRNA target genes associated with VTE.

MATERIALS AND METHODS

To explore the association between mRNAs and miRNAs in VTE, we performed mRNA or miRNA microarray analysis and experiments in vitro. In addition, five online bioinformatics tools identified the target genes of differentially expressed miRNAs, and miRNA-gene network was constructed. As a result, hub miRNA and mRNA were confirmed. Finally, wound healing assay and transwell migration assay were performed to elucidate the effect of hub miRNA in VEC. Luciferase reporter assay and real-time quantitative polymerase chain reaction (RT-qPCR) were performed to decide the role of miRNA in the expression of hub mRNA.

RESULTS

Screening identified eight overlapping dysregulated genes in patients with VTE, three of which demonstrated significantly decreased expression of miR-200a-5p. Low expression miR-200a-5p in VTE patients is confirmed by ROC analysis (AUC=0.800, P=0.023) and binary logistic regression (OR=0.359, 95% confidence interval: 0.605-0.995). RT-qPCR results showed that miR-200a-5p level was decreased in hypoxia VEC (P=0.038). MiR-200a-5p significantly promoted the migration ability of VEC. The result of Dual-luciferase reporter assay showed that cytochrome coxidaseⅦc(COX7C) directly inhibit the miR-200a-5p expression by binding 5'UTR of miR-200a-5p (P=0.011).

CONCLUSIONS

We anticipate that miR-200a-5p-COX7C pair might be involved in the progression of VTE. Moreover, miR-200a-5p might be a therapeutic target for VTE.

Estrogenic Pastures: A Source of Endocrine Disruption in Sheep Reproduction

Phytoestrogens can impact on reproductive health due to their structural similarity to estradiol. Initially identified in sheep consuming estrogenic pasture, phytoestrogens are known to influence reproductive capacity in numerous species. Estrogenic pastures continue to persist in sheep production systems, yet there has been little headway in our understanding of the underlying mechanisms that link phytoestrogens with compromised reproduction in sheep. Here we review the known and postulated actions of phytoestrogens on reproduction, with particular focus on competitive binding with nuclear and non-nuclear estrogen receptors, modifications to the epigenome, and the downstream impacts on normal physiological function. The review examines the evidence that phytoestrogens cause reproductive dysfunction in both the sexes, and that outcomes depend on the developmental period when an individual is exposed to phytoestrogen.

The peri-menopause in a woman's life: a systemic inflammatory phase that enables later neurodegenerative disease

The peri-menopause or menopausal transition—the time period that surrounds the final years of a woman’s reproductive life—is associated with profound reproductive and hormonal changes in a woman’s body and exponentially increases a woman’s risk of cerebral ischemia and Alzheimer’s disease. Although our understanding of the exact timeline or definition of peri-menopause is limited, it is clear that there are two stages to the peri-menopause. These are the early menopausal transition, where menstrual cycles are mostly regular, with relatively few interruptions, and the late transition, where amenorrhea becomes more prolonged and lasts for at least 60 days, up to the final menstrual period. Emerging evidence is showing that peri-menopause is pro-inflammatory and disrupts estrogen-regulated neurological systems. Estrogen is a master regulator that functions through a network of estrogen receptors subtypes alpha (ER-α) and beta (ER-β). Estrogen receptor-beta has been shown to regulate a key component of the innate immune response known as the inflammasome, and it also is involved in regulation of neuronal mitochondrial function. This review will present an overview of the menopausal transition as an inflammatory event, with associated systemic and central nervous system inflammation, plus regulation of the innate immune response by ER-β-mediated mechanisms.

Estrogen Signaling in Alzheimer's Disease: Molecular Insights and Therapeutic Targets for Alzheimer's Dementia

Estrogens play a crucial physiological function in the brain; however, debates exist concerning the role of estrogens in Alzheimer's disease (AD). Women during pre-, peri-, or menopause periods are more susceptible for developing AD, suggesting the connection of sex factors and a decreased estrogen signaling in AD pathogenesis. Yet, the underlying mechanism of estrogen-mediated neuroprotection is unclarified and is complicated by the existence of estrogen-related factors. Consequently, a deeper analysis of estrogen receptor (ER) expression and estrogen-metabolizing enzymes could interpret the importance of estrogen in age-linked cognitive alterations. Previous studies propose that hormone replacement therapy may attenuate AD onset in postmenopausal women, demonstrating that estrogen signaling is important for the development and progression of AD. For example, ERα exerts neuroprotection against AD by maintaining intracellular signaling cascades and study reported reduced expression of ERα in hippocampal neurons of AD patients. Similarly, reduced expression of ERβ in female AD patients has been associated with abnormal function in mitochondria and improved markers of oxidative stress. In this review, we discuss the critical interaction between estrogen signaling and AD. Moreover, we highlight the potential of targeting estrogen-related signaling for therapeutic intervention in AD.

Keratin 86 is up-regulated in the uterus during implantation, induced by oestradiol

Background

Uterine receptivity is one of the determinants of embryo implantation, which is responsible for pregnancy success. Aberrant embryo implantation due to disrupted uterine receptivity is usually found in ovarian hyperstimulation induced hyperoestrogen patients.

Results

This study identified keratin 86 (KRT86), a fibrous structural protein, which was upregulated in uterine endometrium during peri-implantation. Using a hyperoestrogen mouse model established in a previous study, we found abnormal oestradiol (E2) levels during pre-implantation could trigger high expression of Krt86 in the uterine epithelium. In an ovariectomised mouse model, combining oestrogen receptors ERα and ERβ knockout mice models, uterine Krt86 was found to be up-regulated after E2 treatment, mediated by nuclear ERα. Furthermore, we found progesterone (P4) could ameliorate Krt86 expression, induced by abnormal E2.

Conclusions

These results revealed the dynamic expression and regulation of Krt86, especially in hyperoestrogen treated mice, indicating it might act as a marker for non-receptive uterus.

Regulation of mitochondrial function as a promising target in platelet activation-related diseases

Platelets are anucleated cell elements produced by fragmentation of the cytoplasm of megakaryocytes and have a unique metabolic phenotype compared with circulating leukocytes, exhibiting a high coupling efficiency to mitochondrial adenosine triphosphate production with reduced respiratory reserve capacity. Platelet mitochondria are well suited for ex vivo analysis of different diseases. Even some diseases induce mitochondrial changes in platelets without reflecting them in other organs. During platelet activation, an integrated participation of glycolysis and oxidative phosphorylation is mediated by oxidative stress production-dependent signaling. The platelet activation-dependent procoagulant activity mediated by collagen, thrombin and hyperglycemia induce mitochondrial dysfunction to promote thrombosis in oxidative stress-associated pathological conditions. Interestingly, some compounds exhibit a protective action on platelet mitochondrial dysfunction through control of mitochondrial oxidative stress production or inhibition of respiratory complexes. They can be grouped in a) Natural source-derived compounds (e.g. Xanthohumol, Salvianoloc acid A and Sila-amide derivatives of NAC), b) TPP⁺-linked small molecules (e.g. mitoTEMPO and mitoQuinone) and c) FDA-approved drugs (e.g. metformin and statins), illustrating the wide range of molecular structures capable of effectively interacting with platelet mitochondria. The present review article aims to discuss the mechanisms of mitochondrial dysfunction and their association with platelet activation-related diseases.

Estrogen receptor profiling and activity in cardiac myocytes

Estrogen signaling appears critical in the heart. However a mechanistic understanding of the role of estrogen in the cardiac myocyte is lacking. Moreover, there are multiple cell types in the heart and multiple estrogen receptor (ER) isoforms. Therefore, we studied expression, localization, transcriptional and signaling activity of ERs in isolated cardiac myocytes. We found only ERα RNA (but no ERβ RNA) in cardiac myocytes using two independent methods. The vast majority of full-length ERα protein (ERα66) localizes to cardiac myocyte nuclei where it is competent to activate transcription. Alternate isoforms of ERα encoded by the same genomic locus (ERα46 and ERα36) have differential transcriptional activity in cardiac myocytes but also primarily localize to nuclei. In contrast to other reports, no ERα isoform is competent to activate MAPK or PI3K signaling in cardiac myocytes. Together these data support a role for ERα at the level of transcription in cardiac myocytes.

Differential co-expression analysis of venous thromboembolism based on gene expression profile data

The aim of the present study was to screen differentially co-expressed genes and the involved transcription factors (TFs) and microRNAs (miRNAs) in venous thromboembolism (VTE). Microarray data of GSE19151 were downloaded from Gene Expression Omnibus, including 70 patients with VTE and 63 healthy controls. Principal component analysis (PCA) was performed using R software. Differential co-expression analysis was performed using R, followed by screening of modules using Cytoscape. Functional annotation was performed using Database for Annotation, Visualization, and Integrated Discovery. Moreover, Fisher test was used to screen key TFs and miRNAs for the modules. PCA revealed the disease and healthy samples could not be distinguished at the gene expression level. A total of 4,796 upregulated differentially co-expressed genes (e.g. zinc finger protein 264, electron-transfer-flavoprotein, beta polypeptide and Janus kinase 2) and 3,629 downregulated differentially co-expressed genes (e.g. adenylate cyclase 7 and single-stranded DNA binding protein 2) were identified, which were further mined to obtain 17 and eight modules separately. Functional annotation revealed that the largest upregulated module was primarily associated with acetylation and the largest downregulated module was mainly involved in mitochondrion. Moreover, 48 TFs and 62 miRNA families were screened for the 17 upregulated modules, such as E2F transcription factor 4, miR-30 and miR-135 regulating the largest module. Conversely, 35 TFs and 18 miRNA families were identified for the 8 downregulated modules, including mitochondrial ribosomal protein S12 and miR-23 regulating the largest module. Differentially co-expressed genes regulated by TFs and miRNAs may jointly contribute to the abnormal acetylation and mitochondrion presentation in the progression of VTE.

Specific cell-derived microvesicles: Linking endothelial function to carotid artery intima-media thickness in low cardiovascular risk menopausal women

BACKGROUND

Decreases in endothelial function measured by reactive hyperemic index (RHI) correlated with increases in carotid intima-media thickness (CIMT) in recently menopausal women with a low risk cardiovascular profile. Factors linking this association are unknown.

OBJECTIVE

Assess, longitudinally, markers of platelet activation and cell-derived, blood-borne microvesicles (MV) in relationship to RHI and CIMT in asymptomatic, low risk menopausal women.

METHODS

RHI by digital pulse tonometry (n = 93), CIMT by ultrasound (n = 113), measures of platelet activation and specific cell-derived, blood-borne MV were evaluated in women throughout the Kronos Early Estrogen Prevention Study (KEEPS) at Mayo Clinic.

RESULTS

CIMT, but not RHI, increased significantly over 4 years. The average change in CIMT correlated significantly with the average follow-up values of MV positive for common leukocyte antigen [CD45; ρ = 0.285 (P = 0.002)] and VCAM-1 [ρ = 0.270 (P = 0.0040)]. Using principal components analysis (PC) on the aggregate set of average follow-up measures, the first derived PC representing numbers of MV positive for markers of vascular endothelium, inflammatory cells (leukocyte and monocytes), pro-coagulant (tissue factor), and cell adhesion molecules (ICAM-1 and VCAM-1) associated with changes in RHI and CIMT. Changes in RHI associated with another PC defined by measures of platelet activation (dense granular ATP secretion, surface expression of P-selectin and fibrinogen receptors).

CONCLUSIONS

MV derived from activated endothelial and inflammatory cells, and those expressing cell adhesion and pro-coagulant molecules may reflect early vascular dysfunction in low risk menopausal women. Assays of MV as non-conventional measures to assess cardiovascular risk in asymptomatic women remain to be developed.

Estrogenic Impact on Cardiac Ischemic/Reperfusion Injury

The increase in cardiovascular disease and metabolic syndrome incidence following the onset of menopause has highlighted the role of estrogen as a cardiometabolic protective agent. Specifically regarding the heart, estrogen induced an improvement in cardiac function, preserved calcium homeostasis, and inhibited the mitochondrial apoptotic pathway. The beneficial effects of estrogen in relation to cardiac ischemia/reperfusion (I/R) injury, such as reduced infarction and ameliorated post-ischemic recovery, have also been shown. Nevertheless, controversial findings exist and estrogen therapy is reported to be related to a higher rate of thromboembolic events and atrial fibrillation in post-menopausal women. Therefore, greater clarification is needed to evaluate the exact potential of estrogen use in cases of cardiac I/R injury. This article reviews the effects of estrogen, in both acute and chronic treatment, and collates the studies with regard to their in vivo, in vitro, or clinical trial settings in cases of cardiac I/R injury and myocardial infarction.

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.

Age-related changes in platelet function are more profound in women than in men

Age is a risk factor for cardiovascular disease (CVD), however the effect of age on platelet function remains unclear. Ideally, platelet function should be assayed under flow and shear conditions that occur in vivo. Our study aimed to characterise the effect of age on platelet translocation behaviour using a novel flow-based assay that measures platelet function in less than 200 μl of blood under conditions of arterial shear. Blood from males (n = 53) and females (n = 56), ranging in age from 19–82 and 21–70 respectively were perfused through custom-made parallel plate flow chambers coated with immobilised human von Willebrand Factor (VWF) under arterial shear (1,500s⁻¹). Platelet translocation behaviour on VWF was recorded by digital-image microscopy and analysed. The study showed that aging resulted in a significant decrease in the number of platelet tracks, translocating platelets and unstable platelet interactions with VWF. These age related changes in platelet function were more profound in women than in men indicating that age and gender significantly impacts on platelet interactions with VWF.

Age- and sex-specific differences in blood-borne microvesicles from apparently healthy humans

Background

Sex differences in incidence of cardiovascular disease may reflect age-associated intravascular cellular activation resulting in shedding of cell membrane-derived bioactive microvesicles (MV or microparticles) into the blood. Concentrations of cell-specific MV in blood have the potential to be a diagnostic/prognostic marker of pathology, but ranges of MV must first be established in healthy individuals. This study identified cellular origin of blood-borne MV >0.2 μm in blood of apparently healthy women and men aged from 20–70 years.

Methods

Venous blood from apparently healthy participants in the Mayo Clinic Biobank was collected into tubes containing protease inhibitors as the anticoagulant. MV were isolated by standardized differential centrifugation and characterized by digital flow cytometer. Each cellular origin of MV was verified by two different antibodies with strong correlation between the two distinct antibodies (e.g., for platelet-derived MV, r² = 0.97).

Results

MV derived from platelets were the most abundant type of MV in blood from women and men in all age groups. Total numbers of phosphatidylserine, P-selectin, and platelet- and endothelium-derived MV were significantly (P < 0.05) greater in women than men. Numbers of MV from erythrocytes and stem/progenitor cells were significantly lower in premenopausal women than age-matched men. Number of tissue factor pathway inhibitor positive MV were significantly (P < 0.05) lower whereas erythrocyte-derived MV were significantly higher in postmenopausal women compared to premenopausal women. In women, there was a positive relationship between age and erythrocyte-derived MV (ρ = 0.28; P = 0.009), while in men adipocyte-derived MV increased with age (ρ = 0.33; P = 0.01).

Conclusions

This study provides ranges for cellular origin of blood-borne MV in age-matched, apparently healthy women and men from which to compare diagnostic and prognostic uses of blood-borne MV in larger studies and patient population. In addition, sex- and age-specific differences in phosphatidylserine, platelet-, endothelium-, erythrocyte-, and adipocyte-derived blood-borne MV may contribute to differential progression of cardiovascular disease in women compared to men.

Hyperaggregability and impaired nitric oxide production in platelets from postmenopausal women

OBJECTIVE

Cardiovascular mortality increases after menopause in women. Nitric oxide is essential for proper platelet function inhibiting its aggregation and maintaining vascular haemostasis. Here, we investigated whether platelet function and intraplatelet l-arginine-nitric oxide pathway are impaired in postmenopausal women.

STUDY DESIGN

Cross-sectional.

MAIN OUTCOMES MEASURES

Blood was collected from 16 premenopausal and 12 postmenopausal women without any additional risk factor for cardiovascular disease. Platelet reactivity was measured by light transmission aggregometry. l-Arginine-nitric oxide pathway was assessed measuring transmembrane l-[(3)H]-arginine transport, nitric oxide synthase activity by the citrulline assay, and arginase activity by the conversion of l-[(14)C]arginine to l-[(14)C]-urea. The activity of antioxidant enzymes was measured by spectrophotometric assays. Protein expression was determined by Western blotting.

RESULTS

Platelet aggregation was increased in postmenopausal compared to premenopausal women. Postmenopausal women demonstrated reduced plasma levels of l-arginine, a lower nitric oxide synthase activity, similar endothelial and inducible nitric oxide synthase expression, and a compensatory increase in l-arginine transmembrane transport. Arginase expression and activity did not differ between groups. In regard to oxidative stress, no differences between groups were observed NAPDH oxidase subunits expression and protein carbonylation. However, the activity of the antioxidant enzyme superoxide dismutase and catalase protein levels in platelets were higher in postmenopausal women.

CONCLUSION

Postmenopausal women present increased platelet reactivity, which may be due to a reduction in intraplatelet nitric oxide synthesis. Platelet hyperaggregability is known to be associated with arterial and venous thromboembolic event; therefore, it may contribute to the heightened risk of cardiovascular adverse events in this population.

Estrogen-provided cardiac protection following burn trauma is mediated through a reduction in mitochondria-derived DAMPs

Mitochondria-derived danger-associated molecular patterns (DAMPs) play important roles in sterile inflammation after acute injuries. This study was designed to test the hypothesis that 17β-estradiol protects the heart via suppressing myocardial mitochondrial DAMPs after burn injury using an animal model. Sprague-Dawley rats were given a third-degree scald burn comprising 40% total body surface area (TBSA). 17β-Estradiol, 0.5 mg/kg, or control vehicle was administered subcutaneously 15 min following burn. The heart was harvested 24 h postburn. Estradiol showed significant inhibition on the productivity of H2O2 and oxidation of lipid molecules in the mitochondria. Estradiol increased mitochondrial antioxidant defense via enhancing the activities and expression of superoxide dismutase (SOD) and glutathione peroxidase (GPx). Estradiol also protected mitochondrial respiratory function and structural integrity. In parallel, estradiol remarkably decreased burn-induced release of mitochondrial cytochrome c and mitochondrial DNA (mtDNA) into cytoplasm. Further, estradiol inhibited myocardial apoptosis, shown by its suppression on DNA laddering and downregulation of caspase 1 and caspase 3. Estradiol's anti-inflammatory effect was demonstrated by reduction in systemic and cardiac cytokines (TNF-α, IL-1β, and IL-6), decrease in NF-κB activation, and attenuation of the expression of inflammasome component ASC in the heart of burned rats. Estradiol-provided cardiac protection was shown by reduction in myocardial injury marker troponin-I, amendment of heart morphology, and improvement of cardiac contractility after burn injury. Together, these data suggest that postburn administration of 17β-estradiol protects the heart via an effective control over the generation of mitochondrial DAMPs (mtROS, cytochrome c, and mtDNA) that incite cardiac apoptosis and inflammation.

Female sex as an independent risk factor for stroke in atrial fibrillation: possible mechanisms

Atrial fibrillation (AF) is an independent risk factor for thromboembolism and stroke. Women with AF are at a higher overall risk for thromboembolic stroke when compared to men with AF. Recent evidence suggests that female sex, after adjusting for stroke risk profile and sex differences in utilisation of anticoagulation, is an independent stroke risk factor in AF. The inclusion of female sex has improved the accuracy of the CHADS2 stroke risk stratification schema (Congestive heart failure, Hypertension, Age 75 years or greater, Diabetes mellitus, and prior Stroke or TIA). The newly revised and validated schema, CHA2DS2-VASc, dichotomises age and incorporates female sex and vascular disease history. The pathophysiological mechanisms to explain this increased risk in women are not well understood. According to Virchow's triad, thrombosis that leads to stroke in AF should arise from three co-existing phenomena: structural abnormalities, blood stasis, and a hypercoagulable state. Herein, we explore the sex differences in the biological processes that lead to thrombus formation as applied to Virchow's Triad. The objective of this review is to describe the potential mechanisms behind the increased risk of stroke in AF associated with female sex.

Therapeutic strategies in Friedreich's ataxia

First established as a diagnosis by Nikolaus Friedreich in 1863, Friedreich's ataxia (FA) is an autosomal recessive progressive neurodegenerative disorder cause by a trinucleotide repeat expansion. FA begins with the functional absence of the FXN gene product frataxin, a protein whose exact function still remains unknown. This absence results in impaired intracellular antioxidant defenses, dysregulation of iron-sulfur cluster proteins, depression of aerobic electron transport chain respiration, massive mitochondrial dysfunction, and ultimately cell death in the brain, spinal cord and heart. Herein, we review the molecular and cellular pathogenesis leading to widespread organ system dysfunction, as well as current therapeutic research aimed at preventing the debilitating effects of frataxin loss and preventing the signs and symptoms associated of FA. We also discuss the ongoing treatment strategies employed by our laboratory to prevent mitochondrial damage using synergistic effects of 17β-estradiol and methylene blue, previously shown by our group and others to have protective effects in human FA fibroblasts. This article is part of a Special Issue entitled Hormone Therapy.

Periodic 17β-estradiol pretreatment protects rat brain from cerebral ischemic damage via estrogen receptor-β

Although chronic 17β-estradiol (E2) has been shown to be a cognition-preserving and neuroprotective agent in animal brain injury models, concern regarding its safety was raised by the failed translation of this phenomenon to the clinic. Previously, we demonstrated that a single bolus of E2 48 hr prior to ischemia protected the hippocampus from damage in ovariectomized rats via phosphorylation of cyclic-AMP response element binding protein, which requires activation of estrogen receptor subtype beta (ER-β). The current study tests the hypothesis that long-term periodic E2-treatment improves cognition and reduces post-ischemic hippocampal injury by means of ER-β activation. Ovariectomized rats were given ten injections of E2 at 48 hr intervals for 21 days. Hippocampal-dependent learning, memory and ischemic neuronal loss were monitored. Results demonstrated that periodic E2 treatments improved spatial learning, memory and ischemic neuronal survival in ovariectomized rats. Additionally, periodic ER-β agonist treatments every 48 hr improved post-ischemic cognition. Silencing of hippocampal ER-β attenuated E2-mediated ischemic protection suggesting that ER-β plays a key role in mediating the beneficial effects of periodic E2 treatments. This study emphasizes the need to investigate a periodic estrogen replacement regimen to reduce cognitive decline and cerebral ischemia incidents/impact in post-menopausal women.

G protein-coupled estrogen receptor in energy homeostasis and obesity pathogenesis

Obesity and its related metabolic diseases have reached a pandemic level worldwide. There are sex differences in the prevalence of obesity and its related metabolic diseases, with men being more vulnerable than women; however, the prevalence of these disorders increases dramatically in women after menopause, suggesting that sex steroid hormone estrogens play key protective roles against development of obesity and metabolic diseases. Estrogens are important regulators of several aspects of metabolism, including body weight and body fat, caloric intake and energy expenditure, and glucose and lipid metabolism in both males and females. Estrogens act in complex ways on their nuclear estrogen receptors (ERs) ERα and ERβ and transmembrane ERs such as G protein-coupled estrogen receptor. Genetic tools, such as different lines of knockout mouse models, and pharmacological agents, such as selective agonists and antagonists, are available to study function and signaling mechanisms of ERs. We provide an overview of the evidence for the physiological and cellular actions of ERs in estrogen-dependent processes in the context of energy homeostasis and body fat regulation and discuss its pathology that leads to obesity and related metabolic states.

Position paper: The membrane estrogen receptor GPER--Clues and questions

Rapid signaling of estrogen involves membrane estrogen receptors (ERs), including membrane subpopulations of ERα and ERβ. In the mid-1990s, several laboratories independently reported the cloning of an orphan G protein-coupled receptor from vascular and cancer cells that was named GPR30. Research published between 2000 and 2005 provided evidence that GPR30 binds and signals via estrogen indicating that this intracellular receptor is involved in rapid, non-genomic estrogen signaling. The receptor has since been designated as the G protein-coupled estrogen receptor (GPER) by the International Union of Pharmacology. The availability of genetic tools such as different lines of GPER knock-out mice, as well as GPER-selective agonists and antagonists has advanced our understanding, but also added some confusion about the new function of this receptor. GPER not only binds estrogens but also other substances, including SERMs, SERDs, and environmental ER activators (endocrine disruptors; xenoestrogens) and also interacts with other proteins. This article represents a summary of a lecture given at the 7(th) International Meeting on Rapid Responses to Steroid Hormones in September 2011 in Axos, Crete, and reviews the current knowledge and questions about GPER-dependent signaling and function. Controversies that have complicated our understanding of GPER, including interactions with human ERα-36 and aldosterone as a potential ligand, will also be discussed.

Functions and physiological roles of two types of estrogen receptors, ERα and ERβ, identified by estrogen receptor knockout mouse

Estrogens, a class of steroid hormones, regulate the growth, development, and physiology of the human reproductive system. Estrogens also involve in the neuroendocrine, skeletal, adipogenesis, and cardiovascular systems. Estrogen signaling pathways are selectively stimulated or inhibited depending on a balance between the activities of estrogen receptor (ER) α or ERβ in target organs. ERs belong to the steroid hormone superfamily of nuclear receptors, which act as transcription factors after binding to estrogen. The gene expression regulation by ERs is to modulate biological activities, such as reproductive organ development, bone modeling, cardiovascular system functioning, metabolism, and behavior in both females and males. Understanding of the general physiological roles of ERs has been gained when estrogen levels were ablated by ovariectomy and then replenished by treatment with exogenous estrogen. This technique is not sufficient to fully determine the exact function of estrogen signaling in general processes in living tissues. However, a transgenic mouse model has been useful to study gene-specific functions. ERα and ERβ have different biological functions, and knockout and transgenic animal models have distinct phenotypes. Analysis of ERα and ERβ function using knockout mouse models has identified the roles of estrogen signaling in general physiologic processes. Although transgenic mouse models do not always produce consistent results, they are the useful for studying the functions of these genes under specific pathological conditions.

Microvesicles at the crossroads between infection and cardiovascular diseases

Observational and experimental studies continue to support the association of infection and infection-stimulated inflammation with development of cardiovascular disease (CVD) including atherosclerosis and thrombosis. Microvesicles (MV) are heterogeneous populations of sealed membrane-derived vesicles shed into circulation by activated mammalian cells and/or pathogenic microbes that may represent an interface between bacterial/microbial infection and increased risk of CVD. This review evaluates how MV act to modulate and intersect immunological and inflammatory responses to infection with particular attention to progression of CVD. Although infection-related stimuli provoke release of MV from blood and vascular cells, MV express phosphatidylserine and other procoagulant factors on their surface, which initiate and amplify blood coagulation. In addition, MV mediate cell-cell adhesion, which may stimulate production of pro-inflammatory cytokines in vascular cells, which in turn aggravate progression of CVD and propagate atherothrombosis. MV transfer membrane receptors, RNA and proteins among cells, and present auto-antigens from their cells of origin to proximal or remote target cells. Because MV harbor cell surface proteins and contain cytoplasmic components of the parent cell, they mediate biological messages and play a pivotal role in the crossroad between infection-stimulated inflammation and CVDs.

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.

Leukocyte- and platelet-derived microvesicle interactions following in vitro and in vivo activation of toll-like receptor 4 by lipopolysaccharide

Background

Pro-coagulant membrane microvesicles (MV) derived from platelets and leukocytes are shed into the circulation following receptor-mediated activation, cell-cell interaction, and apoptosis. Platelets are sentinel markers of toll-like receptor 4 (TLR4) activation. Experiments were designed to evaluate the time course and mechanism of direct interactions between platelets and leukocytes following acute activation of TLR4 by bacterial lipopolysaccharide (LPS).

Methodology/Principal Findings

Blood from age-matched male and female wild type (WT) and TLR4 gene deleted (dTLR4) mice was incubated with ultra-pure E. coli LPS (500 ng/ml) for up to one hour. At designated periods, leukocyte antigen positive platelets, platelet antigen positive leukocytes and cell-derived MV were quantified by flow cytometry. Numbers of platelet- or leukocyte-derived MV did not increase within one hour following in vitro exposure of blood to LPS. However, with LPS stimulation numbers of platelets staining positive for both platelet- and leukocyte-specific antigens increased in blood derived from WT but not dTLR4 mice. This effect was blocked by inhibition of TLR4 signaling mediated by My88 and TRIF. Seven days after a single intravenous injection of LPS (500 ng/mouse or 20 ng/gm body wt) to WT mice, none of the platelets stained for leukocyte antigen. However, granulocytes, monocytes and apoptotic bodies stained positive for platelet antigens.

Conclusions/Significance

Within one hour of exposure to LPS, leukocytes exchange surface antigens with platelets through TLR4 activation. In vivo, leukocyte expression of platelet antigen is retained after a single exposure to LPS following turn over of the platelet pool. Acute expression of leukocyte antigen on platelets within one hour of exposure to LPS and the sustained expression of platelet antigen on leukocytes following a single acute exposure to LPS in vivo explains, in part, associations of platelets and leukocytes in response to bacterial infection and changes in thrombotic propensity of the blood.

Estrogen protection in Friedreich's ataxia skin fibroblasts

Estrogens have been shown to have protective effects on a wide range of cell types and animal models for many neurodegenerative diseases. The present study demonstrates the cytoprotective effects of 17β-estradiol (E2) and estrogen-like compounds in an in vitro model of Friedreich's ataxia (FRDA) using human donor FRDA skin fibroblasts. FRDA fibroblasts are extremely sensitive to free radical damage and oxidative stress, produced here using l-buthionine (S,R)-sulfoximine to inhibit de novo glutathione synthesis. We have shown that the protective effect of E2 in the face of l-buthionine (S,R)-sulfoximine -induced oxidative stress is independent of estrogen receptor-α, estrogen receptor-β or G protein-coupled receptor 30 as shown by the inability of either ICI 182,780 or G15 to inhibit the E2-mediated protection. These cytoprotective effects appear to be dependent on antioxidant properties and the phenolic structure of estradiol as demonstrated by the observation that all phenolic compounds tested were protective, whereas all nonphenolic compounds were inactive, and the observation that the phenolic compounds reduced the levels of reactive oxygen species, whereas the nonphenolic compounds did not. These data show for the first time that phenolic E2-like compounds are potent protectors against oxidative stress-induced cell death in FRDA fibroblasts and are possible candidate drugs for the treatment and prevention of FRDA symptoms.

Tamoxifen increases nuclear respiratory factor 1 transcription by activating estrogen receptor beta and AP-1 recruitment to adjacent promoter binding sites

Little is known about endogenous estrogen receptor β (ERβ) gene targets in human breast cancer. We reported that estradiol (E(2)) induces nuclear respiratory factor-1 (NRF-1) transcription through ERα in MCF-7 breast cancer cells. Here we report that 4-hydroxytamoxifen (4-OHT), with an EC(50) of ~1.7 nM, increases NRF-1 expression by recruiting ERβ, cJun, cFos, CBP, and RNA polymerase II to and dismissing NCoR from the NRF1 promoter. Promoter deletion and transient transfection studies showed that the estrogen response element (ERE) is essential and that an adjacent AP-1 site contributes to maximal 4-OHT-induced NRF-1 transcription. siRNA knockdown of ERβ revealed that ERβ inhibits basal NRF-1 expression and is required for 4-OHT-induced NRF-1 transcription. An AP-1 inhibitor blocked 4-OHT-induced NRF-1 expression. The 4-OHT-induced increase in NRF-1 resulted in increased transcription of NRF-1 target CAPNS1 but not CYC1, CYC2, or TFAM despite increased NRF-1 coactivator PGC-1α protein. The absence of TFAM induction corresponds to a lack of Akt-dependent phosphorylation of NRF-1 with 4-OHT treatment. Overexpression of NRF-1 inhibited 4-OHT-induced apoptosis and siRNA knockdown of NRF-1 increased apoptosis, indicating an antiapoptotic role for NRF-1. Overall, NRF-1 expression and activity is regulated by 4-OHT via endogenous ERβ in MCF-7 cells.

Atherosclerosis and sex hormones: current concepts

CVD (cardiovascular disease) is the leading cause of death for women. Considerable progress has been made in both our understanding of the complexities governing menopausal hormone therapy and our understanding of the cellular and molecular mechanisms underlying hormone and hormone receptor function. Understanding the interplay of atherosclerosis and sex steroid hormones and their cognate receptors at the level of the vessel wall has important ramifications for clinical practice. In the present review, we discuss the epidemiology of CVD in men and women, the clinical impact of sex hormones on CVD, and summarize our current understanding of the pathogenesis of atherosclerosis with a focus on gender differences in CVD, its clinical presentation and course, and pathobiology. The critical animal and human data that pertain to the role of oestrogens, androgens and progestins on the vessel wall is also reviewed, with particular attention to the actions of sex hormones on each of the three key cell types involved in atherogenesis: the endothelium, smooth muscle cells and macrophages. Where relevant, the systemic (metabolic) effects of sex hormones that influence atherogenesis, such as those involving vascular reactivity, inflammation and lipoprotein metabolism, are discussed. In addition, four key current concepts in the field are explored: (i) total hormone exposure time and coronary heart disease risk; (ii) the importance of tissue specificity of sex steroid hormones, critical timing and the stage of atherosclerosis in hormone action; (iii) biomarkers for atherosclerosis with regard to hormone therapy; and (iv) the complex role of sex steroids in inflammation. Future studies in this field will contribute to guiding clinical treatment recommendations for women and help define research priorities.