Oestrogen receptor alpha in pulmonary hypertension

Pulmonary Hypertension and Hyperglycemia-Not a Sweet Combination

Hyperglycemia and pulmonary hypertension (PH) share common pathological pathways that lead to vascular dysfunction and resultant cardiovascular complications. These shared pathologic pathways involve endothelial dysfunction, inflammation, oxidative stress, and hormonal imbalances. Individuals with hyperglycemia or pulmonary hypertension also possess shared clinical factors that contribute to increased morbidity from both diseases. This review aims to explore the relationship between PH and hyperglycemia, highlighting the mechanisms underlying their association and discussing the clinical implications. Understanding these common pathologic and clinical factors will enable early detection for those at-risk for complications from both diseases, paving the way for improved research and targeted therapeutics.

Characterization of PANoptosis-related genes and the immune landscape in moyamoya disease

Moyamoya disease (MMD) is a cerebrovascular narrowing and occlusive condition characterized by progressive stenosis of the terminal portion of the internal carotid artery and the formation of an abnormal network of dilated, fragile perforators at the base of the brain. However, the role of PANoptosis, an apoptotic mechanism associated with vascular disease, has not been elucidated in MMD. In our study, a total of 40 patients' genetic data were included, and a total of 815 MMD-related differential genes were screened, including 215 upregulated genes and 600 downregulated genes. Among them, DNAJA3, ESR1, H19, KRT18 and STK3 were five key genes. These five key genes were associated with a variety of immune cells and immune factors. Moreover, GSEA (gene set enrichment analysis) and GSVA (gene set variation analysis) showed that the different expression levels of the five key genes affected multiple signaling pathways associated with MMD. In addition, they were associated with the expression of MMD-related genes. Then, based on the five key genes, a transcription factor regulatory network was constructed. In addition, targeted therapeutic drugs against MMD-related genes were obtained by the Cmap drug prediction method: MST-312, bisacodyl, indirubin, and tropanyl-3,5-dimethylbenzoate. These results suggest that the PANoptosis-related genes may contribute to the pathogenesis of MMD through multiple mechanisms.

Pulmonary arterial hypertension: Sex matters

Pulmonary arterial hypertension (PAH) is a complex disease of multifactorial origin. While registries have demonstrated that women are more susceptible to the disease, females with PAH have superior right ventricle (RV) function and a better prognosis than their male counterparts, a phenomenon referred to as the 'estrogen paradox'. Numerous pre-clinical studies have investigated the involvement of sex hormones in PAH pathobiology, often with conflicting results. However, recent advances suggest that abnormal estrogen synthesis, metabolism and signalling underpin the sexual dimorphism of this disease. Other sex hormones, such as progesterone, testosterone and dehydroepiandrosterone may also play a role. Several non-hormonal factor including sex chromosomes and epigenetics have also been implicated. Though the underlying pathophysiological mechanisms are complex, several compounds that modulate sex hormones levels and signalling are under investigation in PAH patients. Further elucidation of the estrogen paradox will set the stage for the identification of additional therapeutic targets for this disease.

Hydroxy-Safflower Yellow A Mitigates Vascular Remodeling in Rat Pulmonary Arterial Hypertension

Purpose

The underlying causes of pulmonary arterial hypertension (PAH) often remain obscure. Addressing PAH with effective treatments presents a formidable challenge. Studies have shown that Hydroxysafflor yellow A (HSYA) has a potential role in PAH, While the mechanism underlies its protective role is still unclear. The study was conducted to investigate the potential mechanisms of the protective effects of HSYA.

Methods

Using databases such as PharmMapper and GeneCards, we identified active components of HSYA and associated PAH targets, pinpointed intersecting genes, and constructed a protein-protein interaction (PPI) network. Core targets were singled out using Cytoscape for the development of a model illustrating drug-component-target-disease interactions. Intersection targets underwent analysis for Gene Ontology (GO) functions and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment. Selected components were then modeled for target interaction using Autodock and Pymol. In vivo validation in a monocrotaline-induced PAH (MCT-PAH) animal model was utilized to substantiate the predictions made by network pharmacology.

Results

We associated HSYA with 113 targets, and PAH with 1737 targets, identifying 34 mutual targets for treatment by HSYA. HSYA predominantly affects 9 core targets. Molecular docking unveiled hydrogen bond interactions between HSYA and several PAH-related proteins such as ANXA5, EGFR, SRC, PPARG, PGR, and ESR1.

Conclusion

Utilizing network pharmacology and molecular docking approaches, we investigated potential targets and relevant human disease pathways implicating HSYA in PAH therapy, such as the chemical carcinogenesis receptor activation pathway and the cancer pathway. Our findings were corroborated by the efficacious use of HSYA in an MCT-induced rat PAH model, confirming its therapeutic potential.

Emerging pharmacotherapies for the treatment of pulmonary arterial hypertension

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a progressive and life-threatening disease. Approved treatment options currently primarily target abnormal cell signaling pathways involved in vasoconstriction and proliferation, such as those mediated by prostacyclin, cyclic guanosine monophosphate, and endothelin.

AREAS COVERED

Recent advancements have led to new applications and modes of delivery of currently approved PAH medications. At the same time, novel drugs targeting specific molecular pathways involved in PAH pathogenesis have been developed and are being investigated in clinical trials. This review summarizes investigational drug trials for PAH gathered from a comprehensive search using PubMed and ClinicalTrials.gov between 2003 and 2023. It includes both currently approved medications studied at different doses or new administration forms and experimental drugs that have not yet been approved.

EXPERT OPINION

Approved treatments for PAH target imbalances in pulmonary vasoactive pathways that work primarily on enhancing pulmonary vasodilation with less salient effects on pulmonary vascular remodeling. The advent of more locally acting inhaled medications offers additional therapeutic options that may improve the ease of drug delivery and reduce adverse systemic effects. The more recent emphasis on developing and applying therapeutics that directly impact the aberrant signaling pathways implicated in PAH appears more likely to advance the treatment of this devastating disease.

Sex Differences in Pulmonary Hypertension

Pulmonary hypertension (PH) includes multiple diseases that share as common characteristic an elevated pulmonary artery pressure and right ventricular involvement. Sex differences are observed in practically all causes of PH. The most studied type is pulmonary arterial hypertension (PAH) which presents a gender bias regarding its prevalence, prognosis, and response to treatment. Although this disease is more frequent in women, once affected they present a better prognosis compared to men. Even if estrogens seem to be the key to understand these differences, animal models have shown contradictory results leading to the birth of the estrogen paradox. In this review we will summarize the evidence regarding sex differences in experimental animal models and, very specially, in patients suffering from PAH or PH from other etiologies.

Bioactivities and mechanisms of natural medicines in the management of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive and rare disease without obvious clinical symptoms that shares characteristics with pulmonary vascular remodeling. Right heart failure in the terminal phase of PAH seriously threatens the lives of patients. This review attempts to comprehensively outline the current state of knowledge on PAH its pathology, pathogenesis, natural medicines therapy, mechanisms and clinical studies to provide potential treatment strategies. Although PAH and pulmonary hypertension have similar pathological features, PAH exhibits significantly elevated pulmonary vascular resistance caused by vascular stenosis and occlusion. Currently, the pathogenesis of PAH is thought to involve multiple factors, primarily including genetic/epigenetic factors, vascular cellular dysregulation, metabolic dysfunction, even inflammation and immunization. Yet many issues regarding PAH need to be clarified, such as the "oestrogen paradox". About 25 kinds monomers derived from natural medicine have been verified to protect against to PAH via modulating BMPR2/Smad, HIF-1α, PI3K/Akt/mTOR and eNOS/NO/cGMP signalling pathways. Yet limited and single PAH animal models may not corroborate the efficacy of natural medicines, and those natural compounds how to regulate crucial genes, proteins and even microRNA and lncRNA still need to put great attention. Additionally, pharmacokinetic studies and safety evaluation of natural medicines for the treatment of PAH should be undertaken in future studies. Meanwhile, methods for validating the efficacy of natural drugs in multiple PAH animal models and precise clinical design are also urgently needed to promote advances in PAH.

Role of estrogen receptors in health and disease

Estrogen receptors (ERs) regulate multiple complex physiological processes in humans. Abnormal ER signaling may result in various disorders, including reproductive system-related disorders (endometriosis, and breast, ovarian, and prostate cancer), bone-related abnormalities, lung cancer, cardiovascular disease, gastrointestinal disease, urogenital tract disease, neurodegenerative disorders, and cutaneous melanoma. ER alpha (ERα), ER beta (ERβ), and novel G-protein-coupled estrogen receptor 1 (GPER1) have been identified as the most prominent ERs. This review provides an overview of ERα, ERβ, and GPER1, as well as their functions in health and disease. Furthermore, the potential clinical applications and challenges are discussed.

Sex and gender in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare disease characterised by pulmonary vascular remodelling and elevated pulmonary pressure, which eventually leads to right heart failure and death. Registries worldwide have noted a female predominance of the disease, spurring particular interest in hormonal involvement in the disease pathobiology. Several experimental models have shown both protective and deleterious effects of oestrogens, suggesting that complex mechanisms participate in PAH pathogenesis. In fact, oestrogen metabolites as well as receptors and enzymes implicated in oestrogen signalling pathways and associated conditions such as BMPR2 mutation contribute to PAH penetrance more specifically in women. Conversely, females have better right ventricular function, translating to a better prognosis. Along with right ventricular adaptation, women tend to respond to PAH treatment differently from men. As some young women suffer from PAH, contraception is of particular importance, considering that pregnancy in patients with PAH is strongly discouraged due to high risk of death. When contraception measures fail, pregnant women need a multidisciplinary team-based approach. This article aims to review epidemiology, mechanisms underlying the higher female predominance, but better prognosis and the intricacies in management of women affected by PAH.

"NOVEL MECHANISMS TARGETED BY DRUG TRIALS IN PULMONARY ARTERIAL HYPERTENSION"

Pulmonary arterial hypertension (PAH) is a rare disease associated with abnormally elevated pulmonary pressures and right heart failure resulting in high morbidity and mortality. While PAH prognosis has improved with the introduction of pulmonary vasodilators, disease progression remains a major problem. Given that available therapies are inadequate for preventing small vessel loss and obstruction, there is an active interest in identifying drugs capable of targeting angiogenesis and mechanisms involved in regulation of cell growth and fibrosis. Among the mechanisms linked to PAH pathogenesis, recent preclinical studies have identified promising compounds that are currently being tested in clinical trials. These drugs target seven of the major mechanisms associated with PAH pathogenesis: BMP signaling, tyrosine kinase receptors, estrogen metabolism, extracellular matrix, angiogenesis, epigenetics, and serotonin metabolism. In this review, we will discuss the preclinical studies that led to prioritization of these mechanisms and will discuss recently completed and ongoing phase 2/3 trials using novel interventions such as sotatercept, anastrozole, rodatristat ethyl, tyrosine kinase inhibitors, and endothelial progenitor cells among others. We anticipate that the next generation of compounds will build upon the success of the current standard of care and improve clinical outcomes and quality of life of patients afflicted with PAH.

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

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

Sex-dependent right ventricular hypertrophic gene changes after methamphetamine treatment in mice

Methamphetamine (MA) abuse is associated with the development of pulmonary arterial hypertension (PAH) and subsequent right ventricular failure. A recent clinical study demonstrated that female sex is a major risk factor for MA-induced PAH. The mechanisms associated with increased prevalence and severity of MA-induced PAH in females are still unclear. We hypothesized that MA may promote changes in gene expression in the right ventricle contributing to the development and/or worsening of PAH in females. Male and female C57BL/6 mice were treated with either MA or vehicle. Right and left ventricular systolic pressures (RVSP and LVSP, respectively) were assessed and tissue samples were collected for gene expression and histology. LVSP and RVSP were not affected by MA in either males or females. Right ventricular hypertrophy was significantly increased by MA in females but it was not affected by MA in males. In the female mice, MA-induced right ventricular hypertrophy was associated with increased expression of brain natriuretic peptide gene and members of the TGF-β receptor signaling pathway such as TGF-β receptor-1, smad3 and smad7. In male mice, there were no changes in right ventricular gene expression. Our results suggest that MA caused right ventricular hypertrophy in female mice, but not in males and that this was associated with an increase in hypertrophic genes. The right ventricular hypertrophy was not dependent on increased RVSP suggesting a direct effect of MA on the right ventricle. If this translates to PAH patients, it might explain the poor outcome observed in MA-associated female PAH patients.

Sex Hormones and Lung Inflammation

Inflammation is a characteristic marker in numerous lung disorders. Several immune cells, such as macrophages, dendritic cells, eosinophils, as well as T and B lymphocytes, synthetize and release cytokines involved in the inflammatory process. Gender differences in the incidence and severity of inflammatory lung ailments including asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis (PF), lung cancer (LC), and infectious related illnesses have been reported. Moreover, the effects of sex hormones on both androgens and estrogens, such as testosterone (TES) and 17β-estradiol (E2), driving characteristic inflammatory patterns in those lung inflammatory diseases have been investigated. In general, androgens seem to display anti-inflammatory actions, whereas estrogens produce pro-inflammatory effects. For instance, androgens regulate negatively inflammation in asthma by targeting type 2 innate lymphoid cells (ILC2s) and T-helper (Th)-2 cells to attenuate interleukin (IL)-17A-mediated responses and leukotriene (LT) biosynthesis pathway. Estrogens may promote neutrophilic inflammation in subjects with asthma and COPD. Moreover, the activation of estrogen receptors might induce tumorigenesis. In this chapter, we summarize the most recent advances in the functional roles and associated signaling pathways of inflammatory cellular responses in asthma, COPD, PF, LC, and newly occurring COVID-19 disease. We also meticulously deliberate the influence of sex steroids on the development and progress of these common and severe lung diseases.

Estrogen Regulation of the Expression of Pain Factor NGF in Rat Chondrocytes

OBJECTIVE

Pain is the main symptom of osteoarthritis (OA). Nerve growth factor (NGF) plays a crucial role in the generation of OA pain. And estrogen-alone used resulted in a sustained joint pain reduction in postmenopausal women. So we aim to find whether estrogen alters chondrocytes' NGF level, affecting OA pain.

METHODS

Primary chondrocytes and cartilage explants isolated from Sprague Dawley rat knees were cultured with physiological concentrations of estrogen (17β-Estradiol ≥ 98%, E2), Estrogen Receptor α (ERα) inhibitor and stimulants. Then, chondrocytes NGF mRNA expression and protein release were analyzed by a quantitative real-time polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA) respectively. Additionally, cultures were pre-incubated with MEK-ERK inhibitor to identify the signaling pathway that estrogen alters NGF mRNA and protein levels.

RESULTS

We found that chondrocytes NGF expression and release were decreased by E2. E2 also reduced chondrocytes IL-1β-stimulated or TGF-β1-stimulated NGF expression. Phosphorylated extracellular signal-regulated kinasep1/2 (p-ERK1/2) signals were detected stronger than the control group by Western Blotting (WB). When we cultured chondrocytes with PD98059 (MEK-ERK inhibitor, PD), NGF mRNA expression was added to 1.41Ct (2.07±0.1 fold).

CONCLUSION

We showed that E2 reduces chondrocytes NGF expression significantly, even after stimulation by TGF-β1 or IL-1β. MEK-ERK signaling is involved in this process.

17β-Estradiol and estrogen receptor α protect right ventricular function in pulmonary hypertension via BMPR2 and apelin

Women with pulmonary arterial hypertension (PAH) exhibit better right ventricular (RV) function and survival than men; however, the underlying mechanisms are unknown. We hypothesized that 17β-estradiol (E2), through estrogen receptor α (ER-α), attenuates PAH-induced RV failure (RVF) by upregulating the procontractile and prosurvival peptide apelin via a BMPR2-dependent mechanism. We found that ER-α and apelin expression were decreased in RV homogenates from patients with RVF and from rats with maladaptive (but not adaptive) RV remodeling. RV cardiomyocyte apelin abundance increased in vivo or in vitro after treatment with E2 or ER-α agonist. Studies employing ER-α-null or ER-β-null mice, ER-α loss-of-function mutant rats, or siRNA demonstrated that ER-α is necessary for E2 to upregulate RV apelin. E2 and ER-α increased BMPR2 in pulmonary hypertension RVs and in isolated RV cardiomyocytes, associated with ER-α binding to the Bmpr2 promoter. BMPR2 is required for E2-mediated increases in apelin abundance, and both BMPR2 and apelin are necessary for E2 to exert RV-protective effects. E2 or ER-α agonist rescued monocrotaline pulmonary hypertension and restored RV apelin and BMPR2. We identified what we believe to be a novel cardioprotective E2/ER-α/BMPR2/apelin axis in the RV. Harnessing this axis may lead to novel RV-targeted therapies for PAH patients of either sex.

Resveratrol: Mechanistic and therapeutic perspectives in pulmonary arterial hypertension

Resveratrol, trans 3,5,4'-trihydroxystilbene, is a stilbenoid polyphenol with a wide range of properties including antioxidant, neuroprotective, cardioprotective, anti-inflammatory and anticancer activities. It is found in the skins of grape (50-100 μg/mL), red wine, peanuts, bilberries, blueberries and cranberries. The most important effects of resveratrol have been found in cardiovascular disease, with pulmonary arterial hypertension (PAH) being a major severe and progressive component. Many factors are involved in the pathogenesis of PAH, including enzymes, transcription factors, proteins, chemokines, cytokines, hypoxia, oxidative stress and others. Resveratrol treats PAH through its actions on various signaling pathways. These signaling pathways are mainly suppressed SphK1-mediated NF-κB activation, BMP/SMAD signaling pathway, miR-638 and NR4A3/cyclin D1 pathway, SIRT1 pathway, Nrf-2, HIF-1 α expression, MAPK/ERK1 and PI3K/AKT pathways, and RhoA-ROCK signaling pathway. Resveratrol efficiently inhibits the proliferation of pulmonary arterial smooth muscle cells and right ventricular remodeling, which are underlying processes leading to enhanced PAH. While supportive evidence from randomized controlled trials is yet to be available, current in vitro and in vivo studies seem to be convincing and suggest a therapeutic promise for the use of resveratrol in PAH.

Metabolism of vascular smooth muscle cells in vascular diseases

Vascular smooth muscle cells (VSMCs) are the fundamental component of the medial layer of arteries and are essential for arterial physiology and pathology. It is becoming increasingly clear that VSMCs can alter their metabolism to fulfill the bioenergetic and biosynthetic requirements. During vascular injury, VSMCs switch from a quiescent "contractile" phenotype to a highly migratory and proliferative "synthetic" phenotype. Recent studies have found that the phenotype switching of VSMCs is driven by a metabolic switch. Metabolic pathways, including aerobic glycolysis, fatty acid oxidation, and amino acid metabolism, have distinct, indispensable roles in normal and dysfunctional vasculature. VSMCs metabolism is also related to the metabolism of endothelial cells. In the present review, we present a brief overview of VSMCs metabolism and how it regulates the progression of several vascular diseases, including atherosclerosis, systemic hypertension, diabetes, pulmonary hypertension, vascular calcification, and aneurysms, and the effect of the risk factors for vascular disease (aging, cigarette smoking, and excessive alcohol drinking) on VSMC metabolism to clarify the role of VSMCs metabolism in the key pathological process.

Obesity, estrogens and adipose tissue dysfunction - implications for pulmonary arterial hypertension

Obesity is a prevalent global public health issue characterized by excess body fat. Adipose tissue is now recognized as an important endocrine organ releasing an abundance of bioactive adipokines including, but not limited to, leptin, adiponectin and resistin. Obesity is a common comorbidity amongst pulmonary arterial hypertension patients, with 30% to 40% reported as obese, independent of other comorbidities associated with pulmonary arterial hypertension (e.g. obstructive sleep apnoea). An 'obesity paradox' has been observed, where obesity has been associated with subclinical right ventricular dysfunction but paradoxically may confer a protective effect on right ventricular function once pulmonary hypertension develops. Obesity and pulmonary arterial hypertension share multiple pathophysiological mechanisms including inflammation, oxidative stress, elevated leptin (proinflammatory) and reduced adiponectin (anti-inflammatory). The female prevalence of pulmonary arterial hypertension has instigated the hypothesis that estrogens may play a causative role in its development. Adipose tissue, a major site for storage and metabolism of sex steroids, is the primary source of estrogens and circulating estrogens levels which are elevated in postmenopausal women and men with pulmonary arterial hypertension. This review discusses the functions of adipose tissue in both health and obesity and the links between obesity and pulmonary arterial hypertension. Shared pathophysiological mechanisms and the contribution of specific fat depots, metabolic and sex-dependent differences are discussed.

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.

Notch3 signalling and vascular remodelling in pulmonary arterial hypertension

Notch signalling is critically involved in vascular morphogenesis and function. Four Notch isoforms (Notch1–4) regulating diverse cellular processes have been identified. Of these, Notch3 is expressed almost exclusively in vascular smooth muscle cells (VSMCs), where it is critically involved in vascular development and differentiation. Under pathological conditions, Notch3 regulates VSMC switching between the contractile and synthetic phenotypes. Abnormal Notch3 signalling plays an important role in vascular remodelling, a hallmark of several cardiovascular diseases, including pulmonary arterial hypertension (PAH). Because of the importance of Notch3 in VSMC (de)differentiation, Notch3 has been implicated in the pathophysiology of pulmonary vascular remodelling in PAH. Here we review the current literature on the role of Notch in VSMC function with a focus on Notch3 signalling in pulmonary artery VSMCs, and discuss potential implications in pulmonary artery remodelling in PAH.

Estrogen metabolites in a small cohort of patients with idiopathic pulmonary arterial hypertension

Increased risk and severity of idiopathic pulmonary arterial hypertension (iPAH) is associated with elevated estradiol in men and postmenopausal women. Pulmonary arteries synthesise estradiol via aromatase and metabolise it via CYP1B1 to mitogenic metabolites; SNPs in aromatase and CYP1B1 have been associated with PAH. This suggests that estradiol metabolism could be altered in iPAH. This proof-of-concept study profiles estradiol and several metabolites of estradiol simultaneously in serum from iPAH patients and controls. We show that the estradiol and metabolite profile is altered in iPAH and that 16-hydroxyestrone and 16-hydroxyestradiol accumulate in iPAH patients with 16-hydroxyestrone levels relating to disease severity.

Differential effects of integrin-linked kinase inhibitor Cpd22 on severe pulmonary hypertension in male and female rats

Pulmonary arterial hypertension (PAH) is a progressive fatal disease with no cure. Inhibition of integrin-linked kinase (ILK) reverses experimental pulmonary hypertension (PH) in male mice, but its effect on severe experimental PH in either male or female animals is unknown. We examined effects of ILK inhibitor Cpd22 on rats with SU5416/hypoxia-induced PH; treatment was performed at six to eight weeks after PH initiation. Five weeks after PH initiation, male and female rats developed similar levels of PH. Eight weeks after PH induction, vehicle-treated male rats had more severe PH than females. Cpd22-treated males, but not females, showed complete suppression of phospho-Akt in small pulmonary arteries (PAs), significantly lower PA medial thickness and percentage of fully occluded arteries, decreased systolic right ventricle (RV) pressure, PA pressure, RV hypertrophy, RV end-diastolic pressure, and improved RV contractility index compared to vehicle-treated group. Cpd22 suppressed proliferation of human male and female PAH pulmonary artery vascular smooth muscle cell (PAVSMC). 17β-estradiol had no effect as a single agent but significantly attenuated Cpd22-dependent inhibition of proliferation in female, but not male, PAH PAVSMC. Taken together, these data demonstrate that male rats develop more severe PH than females but respond better to Cpd22 treatment by reducing pulmonary vascular remodeling, PH, and RV hypertrophy and improving RV functional outcomes. 17β-estradiol diminishes anti-proliferative effect of Cpd22 in female, but not male, human PAH PAVSMC. These findings suggest potential attractiveness of ILK inhibition to reduce established PH in males and suggest that the combination with estrogen-lowering drugs could be considered to maximize anti-proliferative and anti-remodeling effects of ILK inhibitors in females.

Androgens are effective bronchodilators with anti-inflammatory properties: A potential alternative for asthma therapy

Changes in plasma androgen levels in asthmatic men may be linked to asthma severity, seemingly acting through nongenomic and genomic effects. Nongenomic effects include rapid relaxation of carbachol or antigenic challenge pre-contracted guinea pig airway smooth muscle (ASM) in vitro: testosterone (TES) blocks l-type voltage dependent Ca²⁺ channels, stored operated Ca²⁺ channels, inositol 1,4,5-trisphosphate receptors and promotes prostaglandin E₂ biosynthesis. In ASM at rest, TES lowers basal intracellular Ca²⁺ concentration and tension, maintaining a proper airway patency keeping steady smooth muscle tension and basal intracellular Ca²⁺ concentration at rest. Moreover, the bronchospasm in sensitized guinea-pigs was ablated by dehydroepiandrosterone (DHEA), a precursor of steroids, TES and its metabolites 5α- and 5β-dihydrotestosterone (DHT). On the other hand, genomic effects related to androgens' anti-inflammatory properties in asthma have been recently studied. Briefly, TES negatively regulates type 2 immune response sustained by CD4+ Th2 and group 2 innate lymphoid cells, diminishing allergic airway inflammation in males. Also, novel findings establish that TES decreases interleukin (IL)-17A protein expression produced by CD4+ Th17 cells and therefore neutrophilic airway inflammation. Clearly, DHEA, TES or its 5β-reduced metabolite that possesses minimal androgenic effect, might have potential therapeutic capacities in the treatment of severe asthma via mechanisms distinct from corticosteroid treatment.

Sex, Gender, and Sex Hormones in Pulmonary Hypertension and Right Ventricular Failure

Pulmonary hypertension (PH) encompasses a syndrome of diseases that are characterized by elevated pulmonary artery pressure and pulmonary vascular remodeling and that frequently lead to right ventricular (RV) failure and death. Several types of PH exhibit sexually dimorphic features in disease penetrance, presentation, and progression. Most sexually dimorphic features in PH have been described in pulmonary arterial hypertension (PAH), a devastating and progressive pulmonary vasculopathy with a 3-year survival rate <60%. While patient registries show that women are more susceptible to development of PAH, female PAH patients display better RV function and increased survival compared to their male counterparts, a phenomenon referred to as the "estrogen paradox" or "estrogen puzzle" of PAH. Recent advances in the field have demonstrated that multiple sex hormones, receptors, and metabolites play a role in the estrogen puzzle and that the effects of hormone signaling may be time and compartment specific. While the underlying physiological mechanisms are complex, unraveling the estrogen puzzle may reveal novel therapeutic strategies to treat and reverse the effects of PAH/PH. In this article, we (i) review PH classification and pathophysiology; (ii) discuss sex/gender differences observed in patients and animal models; (iii) review sex hormone synthesis and metabolism; (iv) review in detail the scientific literature of sex hormone signaling in PAH/PH, particularly estrogen-, testosterone-, progesterone-, and dehydroepiandrosterone (DHEA)-mediated effects in the pulmonary vasculature and RV; (v) discuss hormone-independent variables contributing to sexually dimorphic disease presentation; and (vi) identify knowledge gaps and pathways forward. © 2020 American Physiological Society. Compr Physiol 10:125-170, 2020.

Hypoxia Upregulates Estrogen Receptor β in Pulmonary Artery Endothelial Cells in a HIF-1α-Dependent Manner

17β-Estradiol (E2) attenuates hypoxia-induced pulmonary hypertension (HPH) through estrogen receptor (ER)-dependent effects, including inhibition of hypoxia-induced endothelial cell proliferation; however, the mechanisms responsible for this remain unknown. We hypothesized that the protective effects of E2 in HPH are mediated through hypoxia-inducible factor 1α (HIF-1α)-dependent increases in ERβ expression. Sprague-Dawley rats and ERα or ERβ knockout mice were exposed to hypobaric hypoxia for 2-3 weeks. The effects of hypoxia were also studied in primary rat or human pulmonary artery endothelial cells (PAECs). Hypoxia increased expression of ERβ, but not ERα, in lungs from HPH rats as well as in rat and human PAECs. ERβ mRNA time dependently increased in PAECs exposed to hypoxia. Normoxic HIF-1α/HIF-2α stabilization increased PAEC ERβ, whereas HIF-1α knockdown decreased ERβ abundance in hypoxic PAECs. In turn, ERβ knockdown in hypoxic PAECs increased HIF-2α expression, suggesting a hypoxia-sensitive feedback mechanism. ERβ knockdown in hypoxic PAECs also decreased expression of the HIF inhibitor prolyl hydroxylase 2 (PHD2), whereas ERβ activation increased PHD2 and decreased both HIF-1α and HIF-2α, suggesting that ERβ regulates the PHD2/HIF-1α/HIF-2α axis during hypoxia. Whereas hypoxic wild-type or ERα knockout mice treated with E2 demonstrated less pulmonary vascular remodeling and decreased HIF-1α after hypoxia compared with untreated hypoxic mice, ERβ knockout mice exhibited increased HIF-2α and an attenuated response to E2 during hypoxia. Taken together, our results demonstrate a novel and potentially therapeutically targetable mechanism whereby hypoxia, via HIF-1α, increases ERβ expression and the E2-ERβ axis targets PHD2, HIF-1α, and HIF-2α to attenuate HPH development.

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.

Influence of 2-Methoxyestradiol and Sex on Hypoxia-Induced Pulmonary Hypertension and Hypoxia-Inducible Factor-1-α

Background Women are at greater risk of developing pulmonary arterial hypertension, with estrogen and its downstream metabolites playing a potential role in the pathogenesis of the disease. Hypoxia-inducible factor-1-α (HIF 1α) is a pro-proliferative mediator and may be involved in the development of human pulmonary arterial hypertension . The estrogen metabolite 2-methoxyestradiol (2 ME 2) has antiproliferative properties and is also an inhibitor of HIF 1α. Here, we examine sex differences in  HIF 1α signaling in the rat and human pulmonary circulation and determine if 2 ME 2 can inhibit HIF 1α in vivo and in vitro. Methods and Results HIF 1α signaling was assessed in male and female distal human pulmonary artery smooth muscle cells ( hPASMC s), and the effects of 2 ME 2 were also studied in female hPASMC s. The in vivo effects of 2 ME 2 in the chronic hypoxic rat (male and female) model of pulmonary hypertension were also determined. Basal HIF 1α protein expression was higher in female hPASMC s compared with male. Both factor-inhibiting HIF and prolyl hydroxylase-2 (hydroxylates HIF leading to proteosomal degradation) protein levels were significantly lower in female hPASMC s when compared with males. In vivo, 2 ME 2 ablated hypoxia-induced pulmonary hypertension in male and female rats while decreasing protein expression of HIF 1α. 2 ME 2 reduced proliferation in hPASMC s and reduced basal protein expression of HIF 1α. Furthermore, 2 ME 2 caused apoptosis and significant disruption to the microtubule network. Conclusions Higher basal HIF 1α in female hPASMC s may increase susceptibility to developing pulmonary arterial hypertension . These data also demonstrate that the antiproliferative and therapeutic effects of 2 ME 2 in pulmonary hypertension may involve inhibition of HIF 1α and/or microtubular disruption in PASMC s.

Drug repositioning in pulmonary arterial hypertension: challenges and opportunities

Despite many advances in medical therapy for pulmonary arterial hypertension (PAH) over the past 20 years, long-term survival is still poor. Novel therapies which target the underlying pathology of PAH and which could be added to current vasodilatory therapies to halt disease progression and potentially reverse pulmonary vascular remodeling are highly sought after. Given the high attrition rates, substantial costs, and slow pace of new drug development, repositioning of “old” drugs is increasingly becoming an attractive path to identify novel treatment options, especially for a rare disease such as PAH.

We here summarize the limitations of current PAH therapy, the general concept of repurposing and repositioning, success stories of approved repositioned drugs in PAH as well as novel repositioned drugs that show promise in preclinical models of pulmonary hypertension (PH) and are currently tested in clinical trials. We furthermore discuss various data-driven as well as experimental approaches currently used to identify repurposed drug candidates and review challenges for the “repositioning community” with regards to funding and patent and regulatory considerations, and to illustrate opportunities for collaborative solutions for drug repositioning relevant to PAH.

A pro-con debate: current controversies in PAH pathogenesis at the American Thoracic Society International Conference in 2017

The following review summarizes the pro-con debate about current controversies regarding the pathogenesis of pulmonary arterial hypertension (PAH) that took place at the American Thoracic Society Conference in May 2017. Leaders in the field of PAH research discussed the importance of the immune system, the role of hemodynamic stress and endothelial apoptosis, as well as bone morphogenetic protein receptor-2 signaling in PAH pathogenesis. Whereas this summary does not intend to resolve obvious conflicts in opinion, we hope that the presented arguments entice further discussions and draw a new generation of enthusiastic researchers into this vibrant field of science to bridge existing gaps for a better understanding and therapy of this fatal disease.

Predominant Role of Nuclear Versus Membrane Estrogen Receptor α in Arterial Protection: Implications for Estrogen Receptor α Modulation in Cardiovascular Prevention/Safety

BACKGROUND

Although estrogen receptor α (ERα) acts primarily as a transcription factor, it can also elicit membrane-initiated steroid signaling. Pharmacological tools and transgenic mouse models previously highlighted the key role of ERα membrane-initiated steroid signaling in 2 actions of estrogens in the endothelium: increase in NO production and acceleration of reendothelialization.

METHODS AND RESULTS

Using mice with ERα mutated at cysteine 451 (ERaC451A), recognized as the key palmitoylation site required for ERα plasma membrane location, and mice with disruption of nuclear actions because of inactivation of activation function 2 (ERaAF20 = ERaAF2°), we sought to fully characterize the respective roles of nuclear versus membrane-initiated steroid signaling in the arterial protection conferred by ERα. ERaC451A mice were fully responsive to estrogens to prevent atheroma and angiotensin II-induced hypertension as well as to allow flow-mediated arteriolar remodeling. By contrast, ERαAF20 mice were unresponsive to estrogens for these beneficial vascular effects. Accordingly, selective activation of nuclear ERα with estetrol was able to prevent hypertension and to restore flow-mediated arteriolar remodeling.

CONCLUSIONS

Altogether, these results reveal an unexpected prominent role of nuclear ERα in the vasculoprotective action of estrogens with major implications in medicine, particularly for selective nuclear ERα agonist, such as estetrol, which is currently under development as a new oral contraceptive and for hormone replacement therapy in menopausal women.

Pulmonary Arterial Hypertension and the Sex Hormone Paradox

PURPOSE OF REVIEW

Prevalence and outcome differences between women and men with pulmonary arterial hypertension (PAH) raise questions about the role of sex hormones in disease pathobiology. This review will summarize the current understanding of sex and sex hormone pathways and their influence on heart-lung function in health and in disease.

RECENT FINDINGS

Female sex has been shown to be a risk factor for the development of PAH, but women have improved survival compared to men with PAH. These paradoxical observations are likely driven in part by complex sex hormone signaling and processing pathways and their interaction with the pulmonary vasculature and the right ventricle. These relationships may vary depending on an individual's underlying sex, age, and/or genetic substrate. The study of the connections between sex, sex hormones, the pulmonary circulation, and the right ventricle may improve our understanding of disease epidemiology and outcomes and lead to new treatment strategies for PAH.

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.

Anastrozole in Pulmonary Arterial Hypertension. A Randomized, Double-Blind, Placebo-controlled Trial

RATIONALE

The aromatase inhibitor anastrozole blocks the conversion of androgens to estrogen and blunts pulmonary hypertension in animals, but its efficacy in treating patients with pulmonary arterial hypertension (PAH) is unknown.

OBJECTIVES

We aimed to determine the safety and efficacy of anastrozole in PAH.

METHODS

We performed a randomized, double-blind, placebo-controlled trial of anastrozole in patients with PAH who received background therapy at two centers.

MEASUREMENTS AND MAIN RESULTS

A total of 18 patients with PAH were randomized to anastrozole 1 mg or matching placebo in a 2:1 ratio. The two co-primary outcomes were percent change from baseline in 17β-estradiol levels (E2) and tricuspid annular plane systolic excursion (TAPSE) at 3 months. Anastrozole significantly reduced E2 levels compared with placebo (percent change: -40%; interquartile range [IQR], -61 to -26% vs. -4%; IQR, -14 to +4%; P = 0.003), but there was no difference in TAPSE. Anastrozole significantly increased the 6-minute-walk distance (median change = +26 m) compared with placebo (median change = -12 m) (median percent change: anastrozole group, 8%; IQR, 2 to 17% vs. placebo -2%; IQR, -7 to +1%; P = 0.042). Anastrozole had no effect on circulating biomarkers, functional class, or health-related quality of life. There was no difference in adverse events.

CONCLUSIONS

Anastrozole significantly reduced E2 levels in patients with PAH but had no effect on TAPSE. Anastrozole was safe, well tolerated, and improved 6-minute-walk distance in this small "proof-of-principle" study. Larger and longer phase II clinical trials of anastrozole may be warranted in patients with PAH. Clinical trial registered with www.clinicaltrials.gov (NCT 1545336).

Steps forward in the treatment of pulmonary arterial hypertension: latest developments and clinical opportunities

Pulmonary arterial hypertension (PAH) is a chronic disease that results in narrowing of the small pre-capillary pulmonary arteries leading to elevation of pulmonary artery pressure and pulmonary vascular resistance, subsequent right ventricular failure, and if unchecked, death. Advances in the treatment of PAH over the last two decades have markedly improved survival. These improvements reflect a combination of changes in treatments, improved patient care strategies, and varying disease phenotypes in the PAH population. Currently approved therapies for PAH are directed at the recognized abnormalities within the pulmonary vasculature and include endothelin receptor antagonists, phosphodiesterase-5 inhibitors, soluble guanylate cyclase stimulators, and prostacyclin pathway agents. Most of these drugs have been approved on the basis of short-term trials that mainly demonstrated improvements in exercise capacity. More recently, long-term, event-driven trials of novel drugs have been performed, demonstrating new efficacy parameters. There have also been exciting advances in the understanding of right heart failure pathophysiology in PAH that have the potential to inspire the development of right ventricular targeted therapy and continued discoveries in the heterogeneity of disease and response to treatment has great potential for developing more 'personalized' therapeutic options. In this article, we review the current available data regarding the management of PAH, with an emphasis on the pharmacologic therapies and discussion of novel therapeutic directions for the treatment of this fatal disease.

Activation of GPER ameliorates experimental pulmonary hypertension in male rats

RATIONALE

Pulmonary hypertension (PH) is characterized by pulmonary vascular remodeling that leads to pulmonary congestion, uncompensated right-ventricle (RV) failure, and premature death. Preclinical studies have demonstrated that the G protein-coupled estrogen receptor (GPER) is cardioprotective in male rats and that its activation elicits vascular relaxation in rats of either sex.

OBJECTIVES

To study the effects of GPER on the cardiopulmonary system by the administration of its selective agonist G1 in male rats with monocrotaline (MCT)-induced PH.

METHODS

Rats received a single intraperitoneal injection of MCT (60mg/kg) for PH induction. Experimental groups were as follows: control, MCT+vehicle, and MCT+G1 (400μg/kg/daysubcutaneous). Animals (n=5pergroup) were treated with vehicle or G1 for 14days after disease onset.

MEASUREMENTS AND MAIN RESULTS

Activation of GPER attenuated exercise intolerance and reduced RV overload in PH rats. Rats with PH exhibited echocardiographic alterations, such as reduced pulmonary flow, RV hypertrophy, and left-ventricle dysfunction, by the end of protocol. G1 treatment reversed these PH-related abnormalities of cardiopulmonary function and structure, in part by promoting pulmonary endothelial nitric oxide synthesis, Ca²⁺ handling regulation and reduction of inflammation in cardiomyocytes, and a decrease of collagen deposition by acting in pulmonary and cardiac fibroblasts.

CONCLUSIONS

G1 was effective to reverse PH-induced RV dysfunction and exercise intolerance in male rats, a finding that have important implications for ongoing clinical evaluation of new cardioprotective and vasodilator drugs for the treatment of the disease.

Novel signaling pathways in pulmonary arterial hypertension (2015 Grover Conference Series)

The proliferative endothelial and smooth muscle cell phenotype, inflammation, and pulmonary vascular remodeling are prominent features of pulmonary arterial hypertension (PAH). Mutations in bone morphogenetic protein type 2 receptor (BMPR2) have been identified as the most common genetic cause of PAH and females with BMPR2 mutations are 2.5 times as likely to develop heritable forms of PAH than males. Higher levels of estrogen have also been observed in males with PAH, implicating sex hormones in PAH pathogenesis. Recently, the estrogen metabolite 16α-OHE1 (hydroxyestrone) was implicated in the regulation of miR29, a microRNA involved in modulating energy metabolism. In females, decreased miR96 enhances serotonin's effect by upregulating the 5-hydroxytryptamine 1B (5HT1B) receptor. Because PAH is characterized as a quasi-malignant disease, likely due to BMPR2 loss of function, altered signaling pathways that sustain this cancer-like phenotype are being explored. Extracellular signal-regulated kinases 1 and 2 and p38 mitogen-activated protein kinases (MAPKs) play a critical role in proliferation and cell motility, and dysregulated MAPK signaling is observed in various experimental models of PAH. Wnt signaling pathways preserve pulmonary vascular homeostasis, and dysregulation of this pathway could contribute to limited vascular regeneration in response to injury. In this review, we take a closer look at sex, sex hormones, and the interplay between sex hormones and microRNA regulation. We also focus on MAPK and Wnt signaling pathways in the emergence of a proproliferative, antiapoptotic endothelial phenotype, which then orchestrates an angioproliferative process of vascular remodeling, with the hope of developing novel therapies that could reverse the phenotype.

Nicotinamide Adenine Dinucleotide Phosphate Oxidase-Mediated Redox Signaling and Vascular Remodeling by 16α-Hydroxyestrone in Human Pulmonary Artery Cells: Implications in Pulmonary Arterial Hypertension

Estrogen and oxidative stress have been implicated in pulmonary arterial hypertension (PAH). Mechanisms linking these systems are elusive. We hypothesized that estrogen metabolite, 16α-hydroxyestrone (16αOHE1), stimulates nicotinamide adenine dinucleotide phosphate oxidase (Nox)-induced reactive oxygen species (ROS) generation and proliferative responses in human pulmonary artery smooth muscle cells (hPASMCs) and that in PAH aberrant growth signaling promotes vascular remodeling. The pathophysiological significance of estrogen-Nox-dependent processes was studied in female Nox1(-/-) and Nox4(-/-) mice with PAH. PASMCs from control subjects (control hPASMCs) and PAH patients (PAH-hPASMCs) were exposed to estrogen and 16αOHE1 in the presence/absence of inhibitors of Nox, cytochrome P450 1B1, and estrogen receptors. Estrogen, through estrogen receptor-α, increased Nox-derived ROS and redox-sensitive growth in hPASMCs, with greater effects in PAH-hPASMCs versus control hPASMCs. Estrogen effects were inhibited by cytochrome P450 1B1 blockade. 16αOHE1 stimulated transient ROS production in hPASMCs, with sustained responses in PAH-hPASMCs. Basal expression of Nox1/Nox4 was potentiated in PAH-hPASMCs. In hPASMCs, 16αOHE1 increased Nox1 expression, stimulated irreversible oxidation of protein tyrosine phosphatases, decreased nuclear factor erythroid-related factor 2 activity and expression of nuclear factor erythroid-related factor 2-regulated antioxidant genes, and promoted proliferation. This was further amplified in PAH-hPASMCs. Nox1(-/-) but not Nox4(-/-) mice were protected against PAH and vascular remodeling. Our findings demonstrate that in PAH-hPASMCs, 16αOHE1 stimulates redox-sensitive cell growth primarily through Nox1. Supporting this, in vivo studies exhibited protection against pulmonary hypertension and remodeling in Nox1(-/-) mice. This study provides new insights through Nox1/ROS and nuclear factor erythroid-related factor 2 whereby 16αOHE1 influences hPASMC function, which when upregulated may contribute to vascular injury in PAH, particularly important in women.

Metformin Reverses Development of Pulmonary Hypertension via Aromatase Inhibition

Females are more susceptible to pulmonary arterial hypertension than males, although the reasons remain unclear. The hypoglycemic drug, metformin, is reported to have multiple actions, including the inhibition of aromatase and stimulation of AMP-activated protein kinase. Inhibition of aromatase using anastrazole is protective in experimental pulmonary hypertension but whether metformin attenuates pulmonary hypertension through this mechanism remains unknown. We investigated whether metformin affected aromatase activity and if it could reduce the development of pulmonary hypertension in the sugen 5416/hypoxic rat model. We also investigated its influence on proliferation in human pulmonary arterial smooth muscle cells. Metformin reversed right ventricular systolic pressure, right ventricular hypertrophy, and decreased pulmonary vascular remodeling in the rat. Furthermore, metformin increased rat lung AMP-activated protein kinase signaling, decreased lung and circulating estrogen levels, levels of aromatase, the estrogen metabolizing enzyme; cytochrome P450 1B1 and its transcription factor; the aryl hydrocarbon receptor. In human pulmonary arterial smooth muscle cells, metformin decreased proliferation and decreased estrogen synthesis by decreasing aromatase activity through the PII promoter site of Cyp19a1 . Thus, we report for the first time that metformin can reverse pulmonary hypertension through inhibition of aromatase and estrogen synthesis in a manner likely to be mediated by AMP-activated protein kinase.

The serotonin transporter promotes a pathological estrogen metabolic pathway in pulmonary hypertension via cytochrome P450 1B1

Pulmonary arterial hypertension (PAH) is a devastating vasculopathy that predominates in women and has been associated with dysregulated estrogen and serotonin signaling. Overexpression of the serotonin transporter (SERT(+)) in mice results in an estrogen-dependent development of pulmonary hypertension (PH). Estrogen metabolism by cytochrome P450 1B1 (CYP1B1) contributes to the pathogenesis of PAH, and serotonin can increase CYP1B1 expression in human pulmonary arterial smooth muscle cells (hPASMCs). We hypothesized that an increase in intracellular serotonin via increased SERT expression may dysregulate estrogen metabolism via CYP1B1 to facilitate PAH. Consistent with this hypothesis, we found elevated lung CYP1B1 protein expression in female SERT(+) mice accompanied by PH, which was attenuated by the CYP1B1 inhibitor 2,3',4,5'-tetramethoxystilbene (TMS). Lungs from female SERT(+) mice demonstrated an increase in oxidative stress that was marked by the expression of 8-hydroxyguanosine; however, this was unaffected by CYP1B1 inhibition. SERT expression was increased in monocrotaline-induced PH in female rats; however, TMS did not reverse PH in monocrotaline-treated rats but prolonged survival. Stimulation of hPASMCs with the CYP1B1 metabolite 16α-hydroxyestrone increased cellular proliferation, which was attenuated by an inhibitor (MPP) of estrogen receptor alpha (ERα) and a specific ERα antibody. Thus, increased intracellular serotonin caused by increased SERT expression may contribute to PAH pathobiology by dysregulation of estrogen metabolic pathways via increased CYP1B1 activity. This promotes PASMC proliferation by the formation of pathogenic metabolites of estrogen that mediate their effects via ERα. Our studies indicate that targeting this pathway in PAH may provide a promising antiproliferative therapeutic strategy.

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.

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.