Estrogen paradox in pulmonary hypertension: current controversies and future perspectives

Age and sex mediated effects of estrogen and Β3-adrenergic receptor on cardiovascular pathophysiology

Sex differences are consistently identified in determining the prevalence, manifestation, and response to therapies in several systemic disorders, including those affecting the cardiovascular (CV), skeletal muscle, and nervous system. Interestingly, such differences are often more noticeable as we age. For example, premenopausal women experience a lower risk of CV disease than men of the same age. While at an advanced age, with menopause, the risk of cardiovascular diseases and adverse outcomes increases exponentially in women, exceeding that of men. However, this effect appears to be reversed in diseases such as pulmonary hypertension, where women are up to seven times more likely than men to develop an idiopathic form of the disease with symptoms developing ten years earlier than their male counterparts. Explaining this is a complex question. However, several factors and mechanisms have been identified in recent decades, including a role for sex hormones, particularly estrogens and their related receptors. Furthermore, an emerging role in these sex differences has also been suggested for β-adrenergic receptors (βARs), which are essential regulators of mammalian physiology. It has in fact been shown that βARs interact with estrogen receptors (ER), providing further demonstration of their involvement in determining sexual differences. Based on these premises, this review article focused on the β3AR subtype, which shows important activities in adipose tissue but with new and interesting roles in regulating the function of cardiomyocytes and vascular cells. In detail, we examined how β3AR and ER signaling are intertwined and whether there would be sex- and age-dependent specific effects of these receptor systems.

Overview of Methamphetamine-Associated Pulmonary Arterial Hypertension

TOPIC IMPORTANCE

The global surge in methamphetamine use is a critical public health concern, particularly due to its robust correlation with methamphetamine-associated pulmonary arterial hypertension (MA-PAH). This association raises urgent alarms about the potential escalation of MA-PAH incidence, posing a significant and imminent challenge to global public health.

REVIEW FINDINGS

This comprehensive review meticulously explores MA-PAH, offering insights into its epidemiology, pathophysiology, clinical presentation, diagnostic intricacies, and management strategies. The pathogenesis, yet to be fully described, involves complex molecular interactions, including alterations in serotonin signaling, reduced activity of carboxylesterase 1, oxidative stress, and dysregulation of pulmonary vasoconstrictors and vasodilators. These processes culminate in the structural remodeling of the pulmonary vasculature, resulting in pulmonary arterial hypertension. MA-PAH exhibits a more severe clinical profile in functional class and hemodynamics compared with idiopathic pulmonary arterial hypertension. Management involves a multifaceted approach, integrating pulmonary vasodilators, cessation of methamphetamine use, and implementing social and rehabilitation programs. These measures aim to enhance patient outcomes and detect potential relapses for timely intervention.

SUMMARY

This review consolidates our understanding of MA-PAH, pinpointing knowledge gaps for future studies. Addressing these gaps is crucial for advancing diagnostic accuracy, unraveling mechanisms, and optimizing treatment for MA-PAH, thereby addressing the evolving landscape of this complex health concern.

A peripheral system disease-Pulmonary hypertension

Pulmonary hypertension (PH) is a cardiovascular disorder characterized by substantial morbidity and mortality rates. It is a chronic condition characterized by intricate pathogenesis and uncontrollable factors. We summarized the pathological effects of estrogen, genetics, neuroinflammation, intestinal microbiota, metabolic reorganization, and histone modification on PH. PH is not only a pulmonary vascular disease, but also a systemic disease. The findings emphasize that the onset of PH is not exclusively confined to the pulmonary vasculature, consequently necessitating treatment approaches that extend beyond targeting pulmonary blood vessels. Hence, the research on the pathological mechanism of PH is not limited to target organs such as pulmonary vessels, but also focuses on exploring other fields (such as estrogen, genetics, neuroinflammation, intestinal microbiota, metabolic reorganization, and histone modification).

Recommendations for Women in Mountain Sports and Hypoxia Training/Conditioning

The (patho-)physiological responses to hypoxia are highly heterogeneous between individuals. In this review, we focused on the roles of sex differences, which emerge as important factors in the regulation of the body's reaction to hypoxia. Several aspects should be considered for future research on hypoxia-related sex differences, particularly altitude training and clinical applications of hypoxia, as these will affect the selection of the optimal dose regarding safety and efficiency. There are several implications, but there are no practical recommendations if/how women should behave differently from men to optimise the benefits or minimise the risks of these hypoxia-related practices. Here, we evaluate the scarce scientific evidence of distinct (patho)physiological responses and adaptations to high altitude/hypoxia, biomechanical/anatomical differences in uphill/downhill locomotion, which is highly relevant for exercising in mountainous environments, and potentially differential effects of altitude training in women. Based on these factors, we derive sex-specific recommendations for mountain sports and intermittent hypoxia conditioning: (1) Although higher vulnerabilities of women to acute mountain sickness have not been unambiguously shown, sex-dependent physiological reactions to hypoxia may contribute to an increased acute mountain sickness vulnerability in some women. Adequate acclimatisation, slow ascent speed and/or preventive medication (e.g. acetazolamide) are solutions. (2) Targeted training of the respiratory musculature could be a valuable preparation for altitude training in women. (3) Sex hormones influence hypoxia responses and hormonal-cycle and/or menstrual-cycle phases therefore may be factors in acclimatisation to altitude and efficiency of altitude training. As many of the recommendations or observations of the present work remain partly speculative, we join previous calls for further quality research on female athletes in sports to be extended to the field of altitude and hypoxia.

Women at Altitude: Sex-Related Physiological Responses to Exercise in Hypoxia

Sex differences in physiological responses to various stressors, including exercise, have been well documented. However, the specific impact of these differences on exposure to hypoxia, both at rest and during exercise, has remained underexplored. Many studies on the physiological responses to hypoxia have either excluded women or included only a limited number without analyzing sex-related differences. To address this gap, this comprehensive review conducted an extensive literature search to examine changes in physiological functions related to oxygen transport and consumption in hypoxic conditions. The review encompasses various aspects, including ventilatory responses, cardiovascular adjustments, hematological alterations, muscle metabolism shifts, and autonomic function modifications. Furthermore, it delves into the influence of sex hormones, which evolve throughout life, encompassing considerations related to the menstrual cycle and menopause. Among these physiological functions, the ventilatory response to exercise emerges as one of the most sex-sensitive factors that may modify reactions to hypoxia. While no significant sex-based differences were observed in cardiac hemodynamic changes during hypoxia, there is evidence of greater vascular reactivity in women, particularly at rest or when combined with exercise. Consequently, a diffusive mechanism appears to be implicated in sex-related variations in responses to hypoxia. Despite well-established sex disparities in hematological parameters, both acute and chronic hematological responses to hypoxia do not seem to differ significantly between sexes. However, it is important to note that these responses are sensitive to fluctuations in sex hormones, and further investigation is needed to elucidate the impact of the menstrual cycle and menopause on physiological responses to hypoxia.

Clinical differences between children and adults with idiopathic and heritable pulmonary arterial hypertension

BACKGROUND

Although previous studies have demonstrated that paediatric pulmonary arterial hypertension remains distinct from that in adults, there are limited studies evaluating a direct comparison between children and adults. The aim of this head-to-head comparison study was to compare the gender, haemodynamic parameters, and prognosis between paediatric and adult pulmonary arterial hypertension.

METHODS AND RESULTS

We retrospectively assessed the clinical differences in 40 childhood-onset (under 20 years old) patients and 40 adult-onset patients with idiopathic and heritable pulmonary arterial hypertension who were followed up at two centres. There was no female predominance among patients with childhood-onset pulmonary arterial hypertension (child female: 42.5%, adult female: 80%). The percent of New York Heart Association functional class IV in adult-onset pulmonary arterial hypertension tended to be higher than those in childhood-onset pulmonary arterial hypertension (22.5 and 10%, respectively), although children had worse haemodynamic parameters at diagnosis (mean pulmonary artery pressure (children versus adults); median 65 mmHg versus 49 mmHg, p < 0.001). There was no significant difference in the event-free survival rate between the two groups (95% vs. 85%) during the follow-up period (median, 96 months; range, 1-120 months).

CONCLUSIONS

Although paediatric pulmonary arterial hypertension patients had worse haemodynamic parameters at diagnosis than adults, children survived as long as adults with appropriate therapeutic strategies.

The Role of G Protein-Coupled Estrogen Receptor (GPER) in Vascular Pathology and Physiology

OBJECTIVE

Estrogen is indispensable in health and disease and mainly functions through its receptors. The protection of the cardiovascular system by estrogen and its receptors has been recognized for decades. Numerous studies with a focus on estrogen and its receptor system have been conducted to elucidate the underlying mechanism. Although nuclear estrogen receptors, including estrogen receptor-α and estrogen receptor-β, have been shown to be classical receptors that mediate genomic effects, studies now show that GPER mainly mediates rapid signaling events as well as transcriptional regulation via binding to estrogen as a membrane receptor. With the discovery of selective synthetic ligands for GPER and the utilization of GPER knockout mice, significant progress has been made in understanding the function of GPER. In this review, the tissue and cellular localizations, endogenous and exogenous ligands, and signaling pathways of GPER are systematically summarized in diverse physiological and diseased conditions. This article further emphasizes the role of GPER in vascular pathology and physiology, focusing on the latest research progress and evidence of GPER as a promising therapeutic target in hypertension, pulmonary hypertension, and atherosclerosis. Thus, selective regulation of GPER by its agonists and antagonists have the potential to be used in clinical practice for treating such diseases.

Endothelial FIS1 DeSUMOylation Protects Against Hypoxic Pulmonary Hypertension

BACKGROUND

Hypoxia is a major cause and promoter of pulmonary hypertension (PH), a representative vascular remodeling disease with poor prognosis and high mortality. However, the mechanism underlying how pulmonary arterial system responds to hypoxic stress during PH remains unclear. Endothelial mitochondria are considered signaling organelles on oxygen tension. Results from previous clinical research and our studies suggested a potential role of posttranslational SUMOylation (small ubiquitin-like modifier modification) in endothelial mitochondria in hypoxia-related vasculopathy.

METHODS

Chronic hypoxia mouse model and Sugen/hypoxia rat model were employed as PH animal models. Mitochondrial morphology and subcellular structure were determined by transmission electron and immunofluorescent microscopies. Mitochondrial metabolism was determined by mitochondrial oxygen consumption rate and extracellular acidification rate. SUMOylation and protein interaction were determined by immunoprecipitation.

RESULTS

The involvement of SENP1 (sentrin-specific protease 1)-mediated SUMOylation in mitochondrial remodeling in the pulmonary endothelium was identified in clinical specimens of hypoxia-related PH and was verified in human pulmonary artery endothelial cells under hypoxia. Further analyses in clinical specimens, hypoxic rat and mouse PH models, and human pulmonary artery endothelial cells and human embryonic stem cell-derived endothelial cells revealed that short-term hypoxia-induced SENP1 translocation to endothelial mitochondria to regulate deSUMOylation (the reversible process of SUMOylation) of mitochondrial fission protein FIS1 (mitochondrial fission 1), which facilitated FIS1 assembling with fusion protein MFN2 (mitofusin 2) and mitochondrial gatekeeper VDAC1 (voltage-dependent anion channel 1), and the membrane tethering activity of MFN2 by enhancing its oligomerization. Consequently, FIS1 deSUMOylation maintained the mitochondrial integrity and endoplasmic reticulum-mitochondria calcium communication across mitochondrial-associated membranes, subsequently preserving pulmonary endothelial function and vascular homeostasis. In contrast, prolonged hypoxia disabled the FIS1 deSUMOylation by diminishing the availability of SENP1 in mitochondria via inducing miR (micro RNA)-138 and consequently resulted in mitochondrial dysfunction and metabolic reprogramming in pulmonary endothelium. Functionally, introduction of viral-packaged deSUMOylated FIS1 within pulmonary endothelium in mice improved pulmonary endothelial dysfunction and hypoxic PH development, while knock-in of SUMO (small ubiquitin-like modifier)-conjugated FIS1 in mice exaggerated the diseased cellular and tissue phenotypes.

CONCLUSIONS

By maintaining endothelial mitochondrial homeostasis, deSUMOylation of FIS1 adaptively preserves pulmonary endothelial function against hypoxic stress and consequently protects against PH. The FIS1 deSUMOylation-SUMOylation transition in pulmonary endothelium is an intrinsic pathogenesis of hypoxic PH.

Estrogen-mediated mechanisms in hypertension and other cardiovascular diseases

Cardiovascular disease (CVD) is the leading cause of death globally for men and women. Premenopausal women have a lower incidence of hypertension and other cardiovascular events than men of the same age, but diminished sex differences after menopause implicates 17-beta-estradiol (E2) as a protective agent. The cardioprotective effects of E2 are mediated by nuclear estrogen receptors (ERα and ERβ) and a G protein-coupled estrogen receptor (GPER). This review summarizes both established as well as emerging estrogen-mediated mechanisms that underlie sex differences in the vasculature during hypertension and CVD. In addition, remaining knowledge gaps inherent in the association of sex differences and E2 are identified, which may guide future clinical trials and experimental studies in this field.

Repetitive schistosoma exposure causes perivascular lung fibrosis and persistent pulmonary hypertension

BACKGROUND

Pulmonary hypertension (PH) can occur as a complication of schistosomiasis. In humans, schistosomiasis-PH persists despite antihelminthic therapy and parasite eradication. We hypothesized that persistent disease arises as a consequence of exposure repetition.

METHODS

Following intraperitoneal sensitization, mice were experimentally exposed to Schistosoma eggs by intravenous injection, either once or three times repeatedly. The phenotype was characterized by right heart catheterization and tissue analysis.

RESULTS

Following intraperitoneal sensitization, a single intravenous Schistosoma egg exposure resulted in a PH phenotype that peaked at 7-14 days, followed by spontaneous resolution. Three sequential exposures resulted in a persistent PH phenotype. Inflammatory cytokines were not significantly different between mice exposed to one or three egg doses, but there was an increase in perivascular fibrosis in those who received three egg doses. Significant perivascular fibrosis was also observed in autopsy specimens from patients who died of this condition.

CONCLUSIONS

Repeatedly exposing mice to schistosomiasis causes a persistent PH phenotype, accompanied by perivascular fibrosis. Perivascular fibrosis may contribute to the persistent schistosomiasis-PH observed in humans with this disease.

MED1 Regulates BMP/TGF-β in Endothelium: Implication for Pulmonary Hypertension

BACKGROUND

Dysregulated BMP (bone morphogenetic protein) or TGF-β (transforming growth factor beta) signaling pathways are imperative in idiopathic and familial pulmonary arterial hypertension (PAH) as well as experimental pulmonary hypertension (PH) in rodent models. MED1 (mediator complex subunit 1) is a key transcriptional co-activator and KLF4 (Krüppel-like factor 4) is a master transcription factor in endothelium. However, MED1 and KLF4 epigenetic and transcriptional regulations of the BMP/TGF-β axes in pulmonary endothelium and their dysregulations leading to PAH remain elusive. We investigate the MED1/KLF4 co-regulation of the BMP/TGF-β axes in endothelium by studying the epigenetic regulation of BMPR2 (BMP receptor type II), ETS-related gene (ERG), and TGFBR2 (TGF-β receptor 2) and their involvement in the PH.

METHODS

High-throughput screening involving data from RNA-seq, MED1 ChIP-seq, H3K27ac ChIP-seq, ATAC-seq, and high-throughput chromosome conformation capture together with in silico computations were used to explore the epigenetic and transcriptional regulation of BMPR2, ERG, and TGFBR2 by MED1 and KLF4. In vitro experiments with cultured pulmonary arterial endothelial cells (ECs) and bulk assays were used to validate results from these in silico analyses. Lung tissue from patients with idiopathic PAH, animals with experimental PH, and mice with endothelial ablation of MED1 (EC-MED1^-/-) were used to study the PH-protective effect of MED1.

RESULTS

Levels of MED1 were decreased in lung tissue or pulmonary arterial endothelial cells from idiopathic PAH patients and rodent PH models. Mechanistically, MED1 acted synergistically with KLF4 to transactivate BMPR2, ERG, and TGFBR2 via chromatin remodeling and enhancer-promoter interactions. EC-MED1^-/- mice showed PH susceptibility. In contrast, MED1 overexpression mitigated the PH phenotype in rodents.

CONCLUSIONS

A homeostatic regulation of BMPR2, ERG, and TGFBR2 in ECs by MED1 synergistic with KLF4 is essential for the normal function of the pulmonary endothelium. Dysregulation of MED1 and the resulting impairment of the BMP/TGF-β signaling is implicated in the disease progression of PAH in humans and PH in rodent models.

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.

Integrating epigenetics and metabolomics to advance treatments for pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating vascular disease with multiple etiologies. Emerging evidence supports a fundamental role for epigenetic machinery and metabolism in the initiation and progression of PAH. Here, we summarize emerging epigenetic mechanisms that have been identified as contributors to PAH evolution, specifically, DNA methylation, histone modifications, and microRNAs. Furthermore, the interplay between epigenetics with metabolism is explored while new crosstalk targets to be investigated in PAH are proposed that highlight multi-omics strategies including integrated epigenomics and metabolomics. Therapeutic opportunities and challenges associated with epigenetics and metabolomics in PAH are examined, highlighting the role that epigenetics and metabolomics have in facilitating early detection, personalized dietary plans, and advanced drug therapy for PAH.

Pregnancy Considerations in the Multidisciplinary Care of Patients with Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a vasoconstrictive disease of the distal pulmonary vasculature resulting in adverse right heart remodeling. Pregnancy in PAH patients is associated with high maternal morbidity and mortality as well as neonatal and fetal complications. Pregnancy-associated changes in the cardiovascular, pulmonary, hormonal, and thrombotic systems challenge the complex PAH physiology. Due to the high risks, patients with PAH are currently counseled against pregnancy based on international consensus guidelines, but there are promising signs of improving outcomes, particularly for patients with mild disease. For patients who become pregnant, multidisciplinary care at a PAH specialist center is needed for peripartum monitoring, medication management, delivery, postpartum care, and complication management. Patients with PAH also require disease-specific counseling on contraception and breastfeeding. In this review, we detail the considerations for reproductive planning, pregnancy, and delivery for the multidisciplinary care of a patient with PAH.

The Impact of Sex Chromosomes in the Sexual Dimorphism of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a sex-biased disease with a poorly understood female prevalence. Emerging research suggests that nonhormonal factors, such as the XX or XY sex chromosome complement and sex bias in gene expression, may also lead to sex-based differences in PAH incidence, penetrance, and progression. Typically, one of females' two X chromosomes is epigenetically silenced to offer a gender-balanced gene expression. Recent data demonstrate that the long noncoding RNA X-inactive specific transcript, essential for X chromosome inactivation and dosage compensation of X-linked gene expression, shows elevated levels in female PAH lung specimens compared with controls. This molecular event leads to incomplete inactivation of the females' second X chromosome, abnormal expression of X-linked gene(s) involved in PAH pathophysiology, and a pulmonary artery endothelial cell (PAEC) proliferative phenotype. Moreover, the pathogenic proliferative p38 mitogen-activated protein kinase/ETS transcription factor ELK1 (Elk1)/cFos signaling is mechanistically linked to the sexually dimorphic proliferative response of PAECs in PAH. Apprehending the complicated relationship between long noncoding RNA X-inactive specific transcript and X-linked genes and how this relationship integrates into a sexually dimorphic proliferation of PAECs and PAH sex paradox remain challenging. We highlight herein new findings related to how the sex chromosome complement and sex-differentiated epigenetic mechanisms to control gene expression are decisive players in the sexual dimorphism of PAH. Pharmacologic interventions in the light of the newly elucidated mechanisms are discussed.

In search of pulmonary hypertension treatments: Effect of 17β-estradiol on PGI2 pathway in human pulmonary artery

INTRODUCTION

Prostacyclin (PGI₂) is synthetized by PGI₂ synthase (PGIS) and induces vasorelaxation via activation of cyclic AMP (cAMP) generating IP-receptor. Several components of the PGI₂ signaling pathway are reduced in patients with pulmonary hypertension (PH).

AIM

To study the effect of 17β-estradiol (E2) on the PGI₂ signaling pathway in human pulmonary arteries (HPA) and in their smooth muscle cells (hPASMC) derived from Group-3 PH and non-PH patients.

METHODS

Following E2-treatments of isolated HPA and cultured hPASMC, we measured: 6-keto-Prostaglandin F_1α (PGI₂ stable metabolite) by ELISA, PGIS and IP protein levels by Western blot and HPA vasorelaxations with an organ bath system.

RESULTS

Incubation with E2 (24/48 h, doses ≥ 10 nM) significantly increased the expression of PGIS in hPASMC derived from both PH (65-98%) and non-PH (21-33%) patients, whereas incubation with E2 (2 h, 0.1 and 1 µM) increased 6-keto-PGF_1α production in HPA from Group-3 PH patients only, and did not affect 6-keto-PGF_1α production in hPASMC from either non-PH or Group-3 PH patients. Increases in IP receptor expression were observed following 10 mM E2-treatment of hPASMC from non-PH (33% after 48 h) and Group-3 PH (23% after 24 h) patient lungs. Finally, preincubation with 100 nM E2 significantly increased arachidonic acid-induced vasorelaxation of HPA from non-PH patient lungs but not of HPA from Group-3 PH patient lungs.

CONCLUSION

E2-treatment may help to restore the PGI₂-pathway in Group-3 PH.

The Evolution of Risk Assessment in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a chronic debilitating disease that carries an unacceptably high morbidity and mortality rate despite improved survival with modern therapies. The combination of several modifiable and nonmodifiable variables yields a robust risk assessment across various available clinical calculators. The role of risk calculation is integral to managing PAH and aids in the timely referral to expert centers and potentially lung transplantation. Studies are ongoing to determine the role of risk calculators in the framework of clinical trials and to elucidate novel markers of high risk in PAH.

Pulmonary Hypertension Complicating Pregnancy

Purpose of review

This study aims to describe the pathophysiology of pregnancy in pulmonary hypertension (PH) and review recent literature on maternal and fetal outcomes.

Recent findings

There is an increasing number of pregnant women with PH. Maternal mortality in pulmonary arterial hypertension (PAH) ranges from 9 to 25%, most commonly from heart failure and arrythmias. The highest risk of death is peri-partum and post-partum. Fetal/neonatal morbidity and mortality are also substantial. There are high rates of prematurity, intrauterine growth retardation, and preeclampsia. Women should be referred to expert centers for management. Combination PAH therapy with parenteral prostacyclin and a phosphodiesterase type V inhibitor is recommended. Induced vaginal delivery is preferred, except in cases of severe heart failure or obstetric indications for cesarean section.

Summary

Despite advances in management, pregnancy in PAH remains a high-risk condition and should be prevented.

Newer insights into the pathobiological and pharmacological basis of the sex disparity in patients with pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) affects more women than men, although affected females tend to survive longer than affected males. This sex disparity in PAH is postulated to stem from the diverse roles of sex hormones in disease etiology. In animal models, estrogens appear to be implicated not only in pathologic remodeling of pulmonary arteries, but also in protection against right ventricular (RV) hypertrophy. In contrast, the male sex hormone testosterone is associated with reduced survival in male animals, where it is associated with increased RV mass, volume, and fibrosis. However, it also has a vasodilatory effect on pulmonary arteries. Furthermore, patients of both sexes show varying degrees of response to current therapies for PAH. As such, there are many gaps and contradictions regarding PAH development, progression, and therapeutic interventions in male versus female patients. Many of these questions remain unanswered, which may be due in part to lack of effective experimental models that can consistently reproduce PAH pulmonary microenvironments in their sex-specific forms. This review article summarizes the roles of estrogens and related sex hormones, immunological and genetical differences, and the benefits and limitations of existing experimental tools to fill in gaps in our understanding of the sex-based variation in PAH development and progression. Finally, we highlight the potential of a new tissue chip-based model mimicking PAH-afflicted male and female pulmonary arteries to study the sex-based differences in PAH and to develop personalized therapies based on patient sex and responsiveness to existing and new drugs.

Sex Differences in Portopulmonary Hypertension

BACKGROUND

Portopulmonary hypertension (POPH), pulmonary arterial hypertension that develops in the setting of portal hypertension, can lead to right-sided heart failure and death. Being female is a known risk factor for POPH, but little is known about the effect of sex on clinical manifestations, hemodynamics, treatment response, and survival.

RESEARCH QUESTION

We sought to characterize sex differences in clinical characteristics, pulmonary hemodynamics, treatment response, and survival in patients with POPH.

STUDY DESIGN AND METHODS

We performed a retrospective cohort study of adult candidates for liver transplant (LT) who had POPH within the Organ Procurement and Transplantation Network database. Females and males were compared. Multivariate regression was performed to assess the association between sex and pulmonary vascular resistance (PVR) and survival. Patients were also stratified by age (50 years) to determine how age modifies the relationship between sex and hemodynamics and survival.

RESULTS

We included 190 adults (103 male, 87 female). Compared with men, women had a lower model for end-stage liver disease (MELD) score (12.1± 4.2 vs 13.8 ± 4.9; P = .01) and were more likely to have autoimmune liver disease. Women had a higher baseline PVR (610.6 ± 366.6 vs 461.0 ± 185.3 dynes-s-cm^-5; P < .001) and posttreatment PVR (244.6 ± 119.5 vs 202.0 ± 87.7 dynes-s-cm^-5; P = .008) and a greater treatment response (ΔPVR) (-359.3 ± 381.9 vs -260.2 ± 177.3 dynes-s-cm^-5; P = .03). In multivariate analysis, female sex (or gender) remained associated with a higher baseline PVR (P = .008). Women and men had overall similar survival (P > .05). When patients were stratified by age, being female was independently associated with worse waiting list survival after adjusting for MELD and PVR in younger patients (HR, 6.61; 95% CI, 1.25-35.08; P = .03) but not in older patients.

INTERPRETATION

Compared with male candidates, female candidates for LT who had POPH had a higher PVR and lower MELD score and were more likely to have autoimmune liver disease. Women and men had similar overall survival, but female sex (or gender) was associated with worse survival in younger patients.

Beyond the genome: challenges and potential for epigenetics-driven therapeutic approaches in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease of the cardiopulmonary system caused by the narrowing of the pulmonary arteries, leading to increased vascular resistance and pressure. This leads to right ventricle remodeling, dysfunction, and eventually, death. While conventional therapies have largely focused on targeting vasodilation, other pathological features of PAH including aberrant inflammation, mitochondrial dynamics, cell proliferation, and migration have not been well explored. Thus, despite some recent improvements in PAH treatment, the life expectancy and quality of life for patients with PAH remains poor. Showing many similarities to cancers, PAH is characterized by increased pulmonary arterial smooth muscle cell proliferation, decreased apoptotic signaling pathways, and changes in metabolism. The recent successes of therapies targeting epigenetic modifiers for the treatment of cancer has prompted epigenetic research in PAH, revealing many new potential therapeutic targets. In this minireview we discuss the emergence of epigenetic dysregulation in PAH and highlight epigenetic-targeting compounds that may be effective for the treatment of PAH.

The Role of Estrogen Receptors in Cardiovascular Disease

Cardiovascular Diseases (CVDs) are the leading cause of death globally. More than 17 million people die worldwide from CVD per year. There is considerable evidence suggesting that estrogen modulates cardiovascular physiology and function in both health and disease, and that it could potentially serve as a cardioprotective agent. The effects of estrogen on cardiovascular function are mediated by nuclear and membrane estrogen receptors (ERs), including estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and G-protein-coupled ER (GPR30 or GPER). Receptor binding in turn confers pleiotropic effects through both genomic and non-genomic signaling to maintain cardiovascular homeostasis. Each ER has been implicated in multiple pre-clinical cardiovascular disease models. This review will discuss current reports on the underlying molecular mechanisms of the ERs in regulating vascular pathology, with a special emphasis on hypertension, pulmonary hypertension, and atherosclerosis, as well as in regulating cardiac pathology, with a particular emphasis on ischemia/reperfusion injury, heart failure with reduced ejection fraction, and heart failure with preserved ejection fraction.

Sex-specific stress response and HMGB1 release in pulmonary endothelial cells

Women are known to be associated with a higher susceptibility to pulmonary arterial hypertension (PAH). In contrast, male PAH patients have a worse survival prognosis. In this study, we investigated whether the contribution of sex goes beyond the effects of sex hormones by comparing the ability of isolated male and female pulmonary endothelial cells to respire, proliferate and tolerate the stress. Mouse lung endothelial cells (MLEC) were isolated from the lungs of male and female 3-week old mice. Male MLEC showed an increased basal mitochondrial respiration rate, elevated maximal respiration, a significantly greater level of mitochondrial polarization, and a higher rate of proliferation. Exposure of cells to hypoxia (2% of O₂ for 24 hours) induced a strong apoptotic response in female but not male MLEC. In contrast, treatment with mitochondrial respiratory Complex III inhibitor Antimycin A (AA, 50μM) mediated severe necrosis specifically in male MLEC, while female cells again responded primarily by apoptosis. The same effect with female cells responding to the stress by apoptosis and male cells responding by necrosis was confirmed in starved pulmonary endothelial cells isolated from human donors. Elevated necrosis seen in male cells was associated with a significant release of damage-associated alarmin, HMGB1. No stimuli induced a significant elevation of HMGB1 secretion in females. We conclude that male cells appear to be protected against mild stress conditions, such as hypoxia, possibly due to increased mitochondrial respiration. In contrast, they are more sensitive to impaired mitochondrial function, to which they respond by necrotic death. Necrosis in male vascular cells releases a significant amount of HMGB1 that could contribute to the pro-inflammatory phenotype known to be associated with the male gender.

Impact of liver damage on blood-borne variables and pulmonary hemodynamic responses to hypoxia and hyperoxia in anesthetized rats

BACKGROUND

Liver disorders may be associated with normal pulmonary hemodynamic, hepatopulmonary syndrome (HPS), or portopulmonary hypertension (POPH). In this study, we aimed to investigate the effect of the severity of liver dysfunctions on blood-borne variables, and pulmonary hemodynamic during repeated ventilation with hyperoxic and hypoxic gases.

METHODS

Female Sprague Dawley rats were assigned into four groups of Sham (n = 7), portal vein ligation (PPVL, n = 7), common bile duct ligation (CBDL, n = 7), and combination of them (CBDL+ PPVL, n = 7). Twenty-eight days later, right ventricular systolic pressure (RVSP) and systemic blood pressure were recorded in anesthetized animals subjected to repeated maneuvers of hyperoxia (O₂ 50%) and hypoxia (O₂ 10%). Besides, we assessed blood parameters and liver histology.

RESULTS

Liver histology score, liver enzymes, WBC and plasma malondialdehyde in the CBDL+PPVL group were higher than those in the CBDL group. Also, the plasma platelet level in the CBDL+PPVL group was lower than those in the other groups. On the other hand, the serum estradiol in the CBDL group was higher than that in the CBDL+PPVL group. All the above parameters in the PPVL group were similar to those in the Sham group. During ventilation with hyperoxia gas, RVSP in the CBDL+PPVL group was higher than the ones in the other groups, and in the CBDL group, it was more than those in the PPVL and Sham groups. Hypoxic pulmonary vasoconstriction (HPV) was not detected in both CBDL+PPVL and CBDL groups, whereas, it retained in the PPVL group.

CONCLUSION

Severe liver damage increases RVSP in the CBDL+PPVL group linked to the high level of ROS, low levels of serum estradiol and platelets or a combination of them. Furthermore, the high RVSP at the noted group could present a reliable animal model for POPH in female rats.

Discovery of Distinct Immune Phenotypes Using Machine Learning in Pulmonary Arterial Hypertension

RATIONALE

Accumulating evidence implicates inflammation in pulmonary arterial hypertension (PAH) and therapies targeting immunity are under investigation, although it remains unknown if distinct immune phenotypes exist.

OBJECTIVE

Identify PAH immune phenotypes based on unsupervised analysis of blood proteomic profiles.

METHODS AND RESULTS

In a prospective observational study of group 1 PAH patients evaluated at Stanford University (discovery cohort; n=281) and University of Sheffield (validation cohort; n=104) between 2008 and 2014, we measured a circulating proteomic panel of 48 cytokines, chemokines, and factors using multiplex immunoassay. Unsupervised machine learning (consensus clustering) was applied in both cohorts independently to classify patients into proteomic immune clusters, without guidance from clinical features. To identify central proteins in each cluster, we performed partial correlation network analysis. Clinical characteristics and outcomes were subsequently compared across clusters. Four PAH clusters with distinct proteomic immune profiles were identified in the discovery cohort. Cluster 2 (n=109) had low cytokine levels similar to controls. Other clusters had unique sets of upregulated proteins central to immune networks-cluster 1 (n=58; TRAIL [tumor necrosis factor-related apoptosis-inducing ligand], CCL5 [C-C motif chemokine ligand 5], CCL7, CCL4, MIF [macrophage migration inhibitory factor]), cluster 3 (n=77; IL [interleukin]-12, IL-17, IL-10, IL-7, VEGF [vascular endothelial growth factor]), and cluster 4 (n=37; IL-8, IL-4, PDGF-β [platelet-derived growth factor beta], IL-6, CCL11). Demographics, PAH clinical subtypes, comorbidities, and medications were similar across clusters. Noninvasive and hemodynamic surrogates of clinical risk identified cluster 1 as high-risk and cluster 3 as low-risk groups. Five-year transplant-free survival rates were unfavorable for cluster 1 (47.6%; 95% CI, 35.4%-64.1%) and favorable for cluster 3 (82.4%; 95% CI, 72.0%-94.3%; across-cluster P<0.001). Findings were replicated in the validation cohort, where machine learning classified 4 immune clusters with comparable proteomic, clinical, and prognostic features.

CONCLUSIONS

Blood cytokine profiles distinguish PAH immune phenotypes with differing clinical risk that are independent of World Health Organization group 1 subtypes. These phenotypes could inform mechanistic studies of disease pathobiology and provide a framework to examine patient responses to emerging therapies targeting immunity.

Gender Difference in Damage-Mediated Signaling Contributes to Pulmonary Arterial Hypertension

Aims: Pulmonary arterial hypertension (PAH) is a progressive lethal disease with a known gender dimorphism. Female patients are more susceptible to PAH, whereas male patients have a lower survival rate. Initial pulmonary vascular damage plays an important role in PAH pathogenesis. Therefore, this study aimed at investigating the role of gender in activation of apoptosis/necrosis-mediated signaling pathways in PAH. Results: The media collected from pulmonary artery endothelial cells (PAECs) that died by necrosis or apoptosis were used to treat naive PAECs. Necrotic cell death stimulated phosphorylation of toll-like receptor 4, accumulation of interleukin 1 beta, and expression of E-selectin in a redox-dependent manner; apoptosis did not induce any of these effects. In the animal model of severe PAH, the necrotic marker, high mobility group box 1 (HMGB1), was visualized in the pulmonary vascular wall of male but not female rats. This vascular necrosis was associated with male-specific redox changes in plasma, activation of the same inflammatory signaling pathway seen in response to necrosis in vitro, and an increased endothelial-leukocyte adhesion in small pulmonary arteries. In PAH patients, gender-specific changes in redox homeostasis correlated with the prognostic marker, B-type natriuretic peptide. Males had also shown elevated circulating levels of HMGB1 and pro-inflammatory changes. Innovation: This study discovered the role of gender in the initiation of damage-associated signaling in PAH and highlights the importance of the gender-specific approach in PAH therapy. Conclusion: In PAH, the necrotic cell death is augmented in male patients compared with female patients. Factors released from necrotic cells could alter redox homeostasis and stimulate inflammatory signaling pathways.

Current strategies for quantification of estrogens in clinical research

Estrogens and their bioactive metabolites play key roles in regulating diverse processes in health and disease. In particular, estrogens and estrogenic metabolites have shown both protective and non-protective effects on disease pathobiology, implicating the importance of this steroid pathway in disease diagnostics and monitoring. All estrogens circulate in a wide range of concentrations, which in some patient cohorts can be extremely low. However, elevated levels of estradiol are reported in disease. For example, in pulmonary arterial hypertension (PAH) elevated levels have been reported in men and postmenopausal women. Conventional immunoassay techniques have come under scrutiny, with their selectivity, accuracy and precision coming into question. Analytical methodologies such as gas and liquid chromatography coupled to single and tandem mass spectrometric approaches (GC-MS, GC-MS/MS, LC-MS and LC-MS/MS) have been developed to quantify endogenous estrogens and in some cases their bioactive metabolites in biological fluids such as urine, serum, plasma and saliva. Liquid-liquid or solid-phase extraction approaches are favoured with derivatization remaining a necessity for detection in lower volumes of sample. The limits of quantitation of individual assays vary but are commonly in the range of 0.5-5 pg/mL for estrone and estradiol, with limits for their bioactive metabolites being higher. This review provides an overview of current approaches for measurement of unconjugated estrogens in biological matrices by MS, highlighting the advances in this field and the challenges remaining for routine use in the clinical and research environment.

Role of the Aryl Hydrocarbon Receptor/ARNT/Cytochrome P450 System in Pulmonary Vascular Diseases

RATIONALE

CYPs (cytochrome p450) are critically involved in the metabolism of xenobiotics and toxins. Given that pulmonary hypertension is strongly associated with environmental exposure, we hypothesize that CYPs play a role in the development and maintenance of pathological vascular remodeling.

OBJECTIVE

We sought to identify key CYPs that could link drug or hormone metabolism to the development of pulmonary hypertension.

METHODS AND RESULTS

We searched in Medline (PubMed) database, as well as http://www.clinicaltrials.gov, for CYPs associated with many key aspects of pulmonary arterial hypertension including, but not limited to, severe pulmonary hypertension, estrogen metabolism, inflammation mechanisms, quasi-malignant cell growth, drug susceptibility, and metabolism of the pulmonary arterial hypertension-specific drugs.

CONCLUSIONS

We postulate a hypothesis where the AhR (aryl hydrocarbon receptor) mediates aberrant cell growth via expression of different CYPs associated with estrogen metabolism and inflammation.

The Role of Sex in the Pathophysiology of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterised by increased pulmonary vascular resistance and pulmonary artery remodelling as result of increased vascular tone and vascular cell proliferation, respectively. Eventually, this leads to right heart failure. Heritable PAH is caused by a mutation in the bone morphogenetic protein receptor-II (BMPR-II). Female susceptibility to PAH has been known for some time, and most recent figures show a female-to-male ratio of 4:1. Variations in the female sex hormone estrogen and estrogen metabolism modify FPAH risk, and penetrance of the disease in BMPR-II mutation carriers is increased in females. Several lines of evidence point towards estrogen being pathogenic in the pulmonary circulation, and thus increasing the risk of females developing PAH. Recent studies have also suggested that estrogen metabolism may be crucial in the development and progression of PAH with studies indicating that downstream metabolites such as 16α-hydroxyestrone are upregulated in several forms of experimental pulmonary hypertension (PH) and can cause pulmonary artery smooth muscle cell proliferation and subsequent vascular remodelling. Conversely, other estrogen metabolites such as 2-methoxyestradiol have been shown to be protective in the context of PAH. Estrogen may also upregulate the signalling pathways of other key mediators of PAH such as serotonin.

Important role of endothelium-dependent hyperpolarization in the pulmonary microcirculation in male mice: implications for hypoxia-induced pulmonary hypertension

Endothelium-dependent hyperpolarization (EDH) plays important roles in the systemic circulation, whereas its role in the pulmonary circulation remains largely unknown. Furthermore, the underlying mechanisms of pulmonary hypertension (PH) also remain to be elucidated. We thus aimed to elucidate the role of EDH in pulmonary circulation in general and in PH in particular. In isolated perfused lung and using male wild-type mice, endothelium-dependent relaxation to bradykinin (BK) was significantly reduced in the presence of Nω-nitro-l-arginine by ~50% compared with those in the presence of indomethacin, and the combination of apamin plus charybdotoxin abolished the residual relaxation, showing the comparable contributions of nitric oxide (NO) and EDH in the pulmonary microcirculation under physiological conditions. Catalase markedly inhibited EDH-mediated relaxation, indicating the predominant contribution of endothelium-derived H2O2. BK-mediated relaxation was significantly reduced at day 1 of hypoxia, whereas it thereafter remained unchanged until day 28. EDH-mediated relaxation was diminished at day 2 of hypoxia, indicating a transition from EDH to NO in BK-mediated relaxation before the development of hypoxia-induced PH. Mechanistically, chronic hypoxia enhanced endothelial NO synthase expression and activity associated with downregulation of caveolin-1. Nitrotyrosine levels were significantly higher in vascular smooth muscle of pulmonary microvessels under chronic hypoxia than under normoxia. A similar transition of the mediators in BK-mediated relaxation was also noted in the Sugen hypoxia mouse model. These results indicate that EDH plays important roles in the pulmonary microcirculation in addition to NO under normoxic conditions and that impaired EDH-mediated relaxation and subsequent nitrosative stress may be potential triggers of the onset of PH.

NEW & NOTEWORTHY This study provides novel evidence that both endothelium-dependent hyperpolarization and nitric oxide play important roles in endothelium-dependent relaxation in the pulmonary microcirculation under physiological conditions in mice and that hypoxia first impairs endothelium-dependent hyperpolarization-mediated relaxation, with compensatory upregulation of nitric oxide, before the development of hypoxia-induced pulmonary hypertension.

Smooth Muscle-Specific BCL6+/- Knockout Abrogates Sex Bias in Chronic Hypoxia-Induced Pulmonary Arterial Hypertension in Mice

The "estrogen paradox" in pulmonary arterial hypertension (PAH) refers to observations that while there is a higher incidence of idiopathic PAH in women, rodent models of PAH show male dominance and estrogens are protective. To explain these differences, we previously proposed the neuroendocrine-STAT5-BCL6 hypothesis anchored in the sex-biased and species-specific patterns of growth hormone (GH) secretion by the pituitary, the targeting of the hypothalamus by estrogens to feminize GH secretion patterns, and the role of the transcription factors STAT5a/b and BCL6 as downstream mediators of this patterned GH-driven sex bias. As a test of this hypothesis, we previously reported that vascular smooth muscle cell- (SMC-) specific deletion of the STAT5a/b locus abrogated the male-dominant sex bias in the chronic hypoxia model of PAH in mice. In the present study, we confirmed reduced BCL6 expression in pulmonary arterial (PA) segments in both male and female SMC:STAT5a/b-/- mice. In order to test the proposed contribution of BCL6 to sex bias in PAH, we developed mice with SMC-specific deletion of BCL6+/- by crossing SM22α-Cre mice with BCL6-floxed mice and investigated sex bias in these mutant mice in the chronic hypoxia model of PAH. We observed that the male-bias observed in wild-type- (wt-) SM22α-Cre-positive mice was abrogated in the SMC:BCL6+/- knockouts-both males and females showed equivalent enhancement of indices of PAH. The new data confirm BCL6 as a contributor to the sex-bias phenotype observed in hypoxic PAH in mice and support the neuroendocrine-STAT5-BCL6 hypothesis of sex bias in this experimental model of vascular disease.

Pulmonary Arterial Hypertension in Women

Pulmonary arterial hypertension (PAH) is characterized by pathological hemodynamic elevation in pulmonary artery pressure. Development of international registries over the last decade has raised awareness about the disease, leading to the development of new and improved therapies. Paradigm shifts such as these warrant review of existing literature regarding PAH, especially in females, as the disease continues to affect women more than males. The aim of this review is to provide an update on the classification, pathophysiology, diagnosis, and treatment of PAH while focusing specifically on its impact on women.

Mouse Genome-Wide Association Study of Preclinical Group II Pulmonary Hypertension Identifies Epidermal Growth Factor Receptor

Pulmonary hypertension (PH) is associated with features of obesity and metabolic syndrome that translate to the induction of PH by chronic high-fat diet (HFD) in some inbred mouse strains. We conducted a genome-wide association study (GWAS) to identify candidate genes associated with susceptibility to HFD-induced PH. Mice from 36 inbred and wild-derived strains were fed with regular diet or HFD for 20 weeks beginning at 6-12 weeks of age, after which right ventricular (RV) and left ventricular (LV) end-systolic pressure (ESP) and maximum pressure (MaxP) were measured by cardiac catheterization. We tested for association of RV MaxP and RV ESP and identified genomic regions enriched with nominal associations to both of these phenotypes. We excluded genomic regions if they were also associated with LV MaxP, LV ESP, or body weight. Genes within significant regions were scored based on the shortest-path betweenness centrality, a measure of network connectivity, of their human orthologs in a gene interaction network of human PH-related genes. WSB/EiJ, NON/ShiLtJ, and AKR/J mice had the largest increases in RV MaxP after high-fat feeding. Network-based scoring of GWAS candidates identified epidermal growth factor receptor (Egfr) as having the highest shortest-path betweenness centrality of GWAS candidates. Expression studies of lung homogenate showed that EGFR expression is increased in the AKR/J strain, which developed a significant increase in RV MaxP after high-fat feeding as compared with C57BL/6J, which did not. Our combined GWAS and network-based approach adds evidence for a role for Egfr in murine PH.

Severe pulmonary hypertension in aging female apolipoprotein E-deficient mice is rescued by estrogen replacement therapy

Background

Apolipoprotein E (ApoE) is a multifunctional protein, and its deficiency leads to the development of atherosclerosis in mice. Patients with pulmonary hypertension (PH) have reduced expression of ApoE in lung tissue. ApoE is known to inhibit endothelial and smooth muscle cell proliferation and has anti-inflammatory and anti-platelet aggregation properties. Young ApoE-deficient mice have been shown to develop PH on high fat diet. The combined role of female sex and aging in the development of PH has not been investigated before. Here, we investigated the development of PH in young and middle-aged (MA) female ApoE-deficient mice and explored the role of exogenous estrogen (E2) replacement therapy for the aging females.

Methods

Wild type (WT) and ApoE-deficient female mice (Young and MA) were injected with a single intraperitoneal dose of monocrotaline (MCT, 60 mg/kg). Some ApoE-deficient MA female mice that received MCT were also treated with subcutaneous E2 pellets (0.03 mg/kg/day) from day 21 to 30 after MCT injection. Direct cardiac catheterization was performed terminally to record right ventricular systolic pressure (RVSP). Right ventricular (RV), left ventricular (LV), and interventricular septum (IVS) were dissected and weighed. Lung sections were examined using trichrome and immunofluorescence staining. Western blot analyses of lung and RV lysates were performed.

Results

In WT female mice, the severity of PH was similar between young and MA mice as RVSP was not significantly different (RVSP = 38.2 ± 1.2 in young vs. 40.5 ± 8.3 mmHg in MA, p < 0.05). In ApoE-deficient mice, MA females developed significantly severe PH (RVSP = 63 ± 10 mmHg) compared to young females (RVSP; 36 ± 3 mmHg, p < 0.05 vs. MA female). ApoE-deficient MA females also developed more severe RV hypertrophy compared to young females (RV hypertrophy index (RV/[LV + IVS]) = 0.53 ± 0.06 vs. 0.33 ± 0.01, p < 0.05). ApoE-deficient MA female mice manifested increased peripheral pulmonary artery muscularization and pulmonary fibrosis. E2 treatment of MA female ApoE-deficient mice resulted in a significant decrease in RVSP, reversal of pulmonary vascular remodeling, and RV hypertrophy. In MA female ApoE-deficient mice with PH, only the expression of ERβ in the lungs, but not in RV, was significantly downregulated, and it was restored by E2 treatment. The expression of ERα was not affected in either lungs or RV by PH. GPR30 was only detected in the RV, and it was not affected by PH in MA female ApoE-deficient mice.

Conclusions

Our results suggest that only aging female ApoE-deficient but not WT mice develop severe PH compared to younger females. Exogenous estrogen therapy rescued PH and RV hypertrophy in aging female ApoE-deficient mice possibly through restoration of lung ERβ.

EET-dependent potentiation of pulmonary arterial pressure: sex-different regulation of soluble epoxide hydrolase

We tested the hypothesis that suppression of epoxyeicosatrienoic acid (EET) metabolism via genetic knockout of the gene for soluble epoxide hydrolase (sEH-KO), or female-specific downregulation of sEH expression, plays a role in the potentiation of pulmonary hypertension. We used male (M) and female (F) wild-type (WT) and sEH-KO mice; the latter have high pulmonary EETs. Right ventricular systolic pressure (RVSP) and mean arterial blood pressure (MABP) in control and in response to in vivo administration of U46619 (thromboxane analog), 14,15-EET, and 14,15-EEZE [14,15-epoxyeicosa-5(z)-enoic acid; antagonist of EETs] were recorded. Basal RVSP was comparable among all groups of mice, whereas MABP was significantly lower in F-WT than M-WT mice and further reduced predominantly in F-KO compared with M-KO mice. U46619 dose dependently increased RVSP and MABP in all groups of mice. The increase in RVSP was significantly greater and coincided with smaller increases in MABP in M-KO and F-WT mice compared with M-WT mice. In F-KO mice, the elevation of RVSP by U46619 was even higher than in M-KO and F-WT mice, associated with the least increase in MABP. 14,15-EEZE prevented the augmentation of U46619-induced elevation of RVSP in sEH-KO mice, whereas 14,15-EET-induced pulmonary vasoconstriction was comparable in all groups of mice. sEH expression in the lungs was reduced, paralleled with higher levels of EETs in F-WT compared with M-WT mice. In summary, EETs initiate pulmonary vasoconstriction but act as vasodilators systemically. High pulmonary EETs, as a function of downregulation or deletion of sEH, potentiate U46619-induced increases in RVSP in a female-susceptible manner.

Hypothesis: Neuroendocrine Mechanisms (Hypothalamus-Growth Hormone-STAT5 Axis) Contribute to Sex Bias in Pulmonary Hypertension

Pulmonary hypertension (PH) is a disease with high morbidity and mortality. The prevalence of idiopathic pulmonary arterial hypertension (IPAH) and hereditary pulmonary arterial hypertension (HPAH) is approximately two- to four-fold higher in women than in men. Paradoxically, there is an opposite male bias in typical rodent models of PH (chronic hypoxia or monocrotaline); in these models, administration of estrogenic compounds (for example, estradiol-17β [E2]) is protective. Further complexities are observed in humans ingesting anorexigens (female bias) and in rodent models, such as after hypoxia plus SU5416/Sugen (little sex bias) or involving serotonin transporter overexpression or dexfenfluramine administration (female bias). These complexities in sex bias in PH remain incompletely understood. We recently discovered that conditional deletion of signal transducer and activator of transcription 5a/b (STAT5a/b) in vascular smooth muscle cells abrogated the male bias in PH in hypoxic mice and that late-stage obliterative lesions in patients of both sexes with IPAH and HPAH showed reduced STAT5a/b, reduced Tyr-P-STAT5 and reduced B-cell lymphoma 6 protein (BCL6). In trying to understand the significance of these observations, we realized that there existed a well-characterized E2-sensitive central neuroendocrine mechanism of sex bias, studied over the last 40 years, that, at its peripheral end, culminated in species-specific male ("pulsatile") versus female ("more continuous") temporal patterns of circulating growth hormone (GH) levels leading to male versus female patterned activation of STAT5a/b in peripheral tissues and thus sex-biased expression of hundreds of genes. In this report, we consider the contribution of this neuroendocrine mechanism (hypothalamus-GH-STAT5) in the generation of sex bias in different PH situations.

Effect of Chronic Administration of Estradiol on Responsiveness of Isolated Systemic and Pulmonary Blood Vessels from Ovariectomized Wistar Rats with Hypoxic Pulmonary Hypertension

The long-term (4 weeks) administration of estradiol (15 μg/kg/day) to ovariectomized female Wistar rats induced hypoxic pulmonary hypertension and significantly (p<0.05) diminished relaxation of perfused serotonin-preconstricted isolated vascular segments of the pulmonary artery in response to estradiol (10(-6) M). At the same time, the isolated segments of systemic popliteal artery demonstrated a diminished response to serotonin and increased relaxation induced by acetylcholine (10(-5) M) or estradiol (10(-5) M) in comparison with preconstricted control vessels. Moderation of responsiveness to estradiol in pulmonary circulation can be one of the factors underlying the pro-hypertensive action of estradiol in female rats with hypoxic pulmonary hypertension.

STAT5a/b contribute to sex bias in vascular disease: A neuroendocrine perspective

Previous studies have elucidated a neuroendocrine mechanism consisting of the hypothalamus (growth hormone releasing hormone, GHRH) - pituitary (growth hormone, GH) - STAT5a/b axis that underlies sex-biased gene expression in the liver. It is now established that male vs female patterned secretion of GHRH, and thus of circulating GH levels ("pulsatile" vs "more continuous" respectively), leading to differently patterned activation of PY-STAT5a/b in hepatocytes results in sex-biased gene expression of cohorts of hundreds of downstream genes. This review outlines new data in support of a STAT5a/b-based mechanism of sex bias in the vascular disease pulmonary hypertension (PH). Puzzling observations in PH include its 2-4-fold higher prevalence in women but a male-dominance in many rodent models, and, paradoxically, inhibition of PH development by estrogens in such models. We observed that conditional deletion of STAT5a/b in vascular smooth muscle cells (SMC) in mice converted the male-dominant model of chronic hypoxia-induced PH into a female-dominant phenotype. In human idiopathic PH, there was reduced STAT5a/b and PY-STAT5 in cells in late-stage obliterative pulmonary arterial lesions in both men and women. A juxtaposition of the prior liver data with the newer PH-related data drew attention to the hypothalamus-GH-STAT5 axis, which is the major target of estrogens at the level of the hypothalamus. This hypothesis explains many of the puzzling aspects of sex bias in PH in humans and rodent models. The extension of STAT5-anchored mechanisms of sex bias to vascular disease emphasizes the contribution of central neuroendocrine processes in generating sexual dimorphism in different tissues and cell types.

Deletion of STAT5a/b in vascular smooth muscle abrogates the male bias in hypoxic pulmonary hypertension in mice: implications in the human disease

Chronic hypoxia typically elicits pulmonary hypertension (PH) in mice with a male-dominant phenotype. There is an opposite-sex bias in human PH, with a higher prevalence in women, but greater survival (the "estrogen paradox"). We investigated the involvement of the STAT5a/b species, previously established to mediate sexual dimorphism in other contexts, in the sex bias in PH. Mice with heterozygous or homozygous deletions of the STAT5a/b locus in vascular smooth muscle cells (SMCs) were generated in crosses between STAT5a/b(fl/fl) and transgelin (SM22α)-Cre(+/+) parents. Wild-type (wt) males subjected to chronic hypoxia showed significant PH and pulmonary arterial remodeling, with wt females showing minimal changes (a male-dominant phenotype). However, in conditional STAT5(+/-) or STAT5(-/-) mice, hypoxic females showed the severest manifestations of PH (a female-dominant phenotype). Immunofluorescence studies on human lung sections showed that obliterative pulmonary arterial lesions in patients with idiopathic pulmonary arterial hypertension (IPAH) or hereditary pulmonary arterial hypertension (HPAH), both male and female, overall had reduced STAT5a/b, reduced PY-STAT5 and reduced endoplasmic reticulum (ER) GTPase atlastin-3 (ATL3). Studies of SMCs and endothelial cell (EC) lines derived from vessels isolated from lungs of male and female IPAH patients and controls revealed instances of coordinate reductions in STAT5a, STAT5b and ATL3 in IPAH-derived cells, including SMCs and ECs from the same patient. Taken together, these data provide the first definitive evidence for a contribution of STAT5a/b to the sex bias in PH in the hypoxic mouse and implicate reduced STAT5 in the pathogenesis of the human disease.

Sex steroid signaling: implications for lung diseases

There is increasing recognition that sex hormones (estrogen, progesterone, and testosterone) have biological and pathophysiological actions in peripheral, non-reproductive organs, including the lung. Clinically, sex differences in the incidence, morbidity and mortality of lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, lung cancer and pulmonary hypertension have been noted, although intrinsic sex differences vs. the roles of sex steroids are still not well-understood. Accordingly, it becomes important to ask the following questions: 1) Which sex steroids are involved? 2) How do they affect different components of the lung under normal circumstances? 3) How does sex steroid signaling change in or contribute to lung disease, and in this regard, are sex steroids detrimental or beneficial? As our understanding of sex steroid signaling in the lung improves, it is important to consider whether such information can be used to develop new therapeutic strategies to target lung diseases, perhaps in both sexes or in a sex-specific manner. In this review, we focus on the basics of sex steroid signaling, and the current state of knowledge regarding how they influence structure and function of specific lung components across the life span and in the context of some important lung diseases. We then summarize the potential for sex steroids as useful biomarkers and therapeutic targets in these lung diseases as a basis for future translational research in the area of gender and individualized medicine.

Pulmonary arterial hypertension: basis of sex differences in incidence and treatment response

Pulmonary arterial hypertension (PAH) is a complex disease characterized by elevated pulmonary arterial pressure, pulmonary vascular remodelling and occlusive pulmonary vascular lesions, leading to right heart failure. Evidence from recent epidemiological studies suggests the influence of gender on the development of PAH with an approximate female to male ratio of 4:1, depending on the underlying disease pathology. Overall, the therapeutic strategy for PAH remains suboptimal with poor survival rates observed in both genders. Endogenous sex hormones, in particular 17β oestradiol and its metabolites, have been implicated in the development of the disease; however, the influence of sex hormones on the underlying pathobiology remains controversial. Further understanding of the influence of sex hormones on the normal and diseased pulmonary circulation will be critical to our understanding the pathology of PAH and future therapeutic strategies. In this review, we will discuss the influence of sex hormones on the development of PAH and address recent controversies.

Pulmonary arterial hypertension: the clinical syndrome

Pulmonary arterial hypertension is a progressive disorder in which endothelial dysfunction and vascular remodeling obstruct small pulmonary arteries, resulting in increased pulmonary vascular resistance and pulmonary pressures. This leads to reduced cardiac output, right heart failure, and ultimately death. In this review, we attempt to answer some important questions commonly asked by patients diagnosed with pulmonary arterial hypertension pertaining to the disease, and aim to provide an explanation in terms of classification, diagnosis, pathophysiology, genetic causes, demographics, and prognostic factors. Furthermore, important molecular pathways that are central to the pathogenesis of pulmonary arterial hypertension are reviewed, including nitric oxide, prostacyclin, endothelin-1, reactive oxygen species, and endothelial and smooth muscle proliferation.

The immune system in menopause: pros and cons of hormone therapy

With aging, a general decline in immune function is observed leading to immune-senescence. Several of these changes are gender specific affecting postmenopausal women. Menopause is a normal part of a woman's lifecycle and consists of a series of body changes that can last from one to ten years. It is known that loss of sex hormones due to aging results in a reduction of immune functions. However, there remains a major gap in our understanding regarding the loss of immune functions particularly in the female reproductive tract (FRT) following menopause and the role of menopausal hormone therapy (MHT) in protecting against immune senescence. The current review presents an overview of changes in the immune system due to aging, focusing on genital tract immunity in menopausal women and the risks and benefits of using MHT. This article is part of a Special Issue entitled 'Menopause'.