Rationale: The incidence of pulmonary arterial hypertension is greater in women, suggesting estrogens may play a role in the disease pathogenesis. Experimentally, in males, exogenously administered estrogen can protect against pulmonary hypertension (PH). However, in models that display female susceptibility, estrogens may play a causative role.Objectives: To clarify the influence of endogenous estrogen and sex in PH and assess the therapeutic potential of a clinically available aromatase inhibitor. Methods:We interrogated the effect of reduced endogenous estrogen in males and females using the aromatase inhibitor, anastrozole, in two models of PH: the hypoxic mouse and Sugen 5416/hypoxic rat. We also determined the effects of sex on pulmonary expression of aromatase in these models and in lungs from patients with pulmonary arterial hypertension.Measurements and Main Results: Anastrozole attenuated PH in both models studied, but only in females. To verify this effect was caused by reduced estrogenic activity we confirmed that in hypoxic mice inhibition of estrogen receptor a also has a therapeutic effect specifically in females. Female rodent lung displays increased aromatase and decreased bone morphogenetic protein receptor 2 and Id1 expression compared with male. Anastrozole treatment reversed the impaired bone morphogenetic protein receptor 2 pathway in females. Increased aromatase expression was also detected in female human pulmonary artery smooth muscle cells compared with male.Conclusions: The unique phenotype of female pulmonary arteries facilitates the therapeutic effects of anastrozole in experimental PH confirming a role for endogenous estrogen in the disease pathogenesis in females and suggests aromatase inhibitors may have therapeutic potential.Keywords: pulmonary hypertension; estrogen; sex At a Glance CommentaryScientific Knowledge on the Subject: Females develop pulmonary arterial hypertension (PAH) more frequently than males. The role of estrogen in this female susceptibility is poorly understood.What This Study Adds to the Field: Our research shows that inhibition of endogenous estrogen synthesis using an aromatase inhibitor or inhibition of estrogen receptor a has therapeutic effects and restores bone morphogenetic protein receptor 2 expression in female but not male models of PAH. These findings suggest estrogen plays a pathogenic role in the pathology of PAH specifically in females.

17β oestradiol is critical to the development of PAH and severe hypoxia-induced PAH in female SERT+ mice. In hPASMCs, 17β oestradiol-induced proliferation is dependant on de novo serotonin synthesis and stimulation of the 5-HT(1B) receptor. These interactions between the serotonin system and 17β oestradiol may contribute to the increased risk of PAH associated with female gender.

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. LINKED ARTICLESThis article is part of a themed section on Biological Sex and Cardiovascular Pharmacology. To view the other articles in this section visit http://dx.doi.org/10. 1111/bph.2014.171.issue-3 Abbreviations AR, androgen receptor; BMPR2, bone morphogenetic protein receptor 2; CYP19A1, aromatase; CYP1B1, cytochrome P450 1B1; DHEA, dehydroepiandosterone; DHT, dihydrotestosterone; ER, oestrogen receptor; ERα, oestrogen receptor alpha; ERβ, oestrogen receptor beta; ET-1, endothelin-1; GPER, G protein-coupled oestrogen receptor; PAH, pulmonary arterial hypertension; PASMC, pulmonary artery smooth muscle cell; SERT, serotonin transporter; Su-Hx, SUGEN hypoxic; Tph1, tryptophan hydroxylase 1 Pulmonary arterial hypertension (PAH) is a progressive disease leading to right heart failure. Recent epidemiological data reports an increased incidence of PAH among females compared to males. For example, in the UK/Ireland and the USA, the percentage of female patients is 70 and 80% respectively (Badesch et al., 2010;Ling et al., 2012). There is mounting evidence to suggest that oestrogen and its metabolites may influence the pathogenesis of PAH. Here, we will examine the pathology, current therapies and the basis for gender differences in PAH, considering evidence gathered from both patient data and animal studies. Pulmonary arterial hypertensionPAH is defined by vascular remodelling and complex vascular lesion formation arising from the accelerated proliferation of pulmonary endothelial, smooth muscle and fibroblast cells (Rabinovitch, 2008). Clinically, the disease is defined as a mean pulmonary artery pressure of >25 mmHg at rest or >30 mmHg during exercise. Symptoms are often non-specific, including fatigue, exertional dyspnoea, oedema and syncope and as a result diagnosis is frequently delayed until the disease is well established.The main genetic defect associated with PAH is a mutation in the gene encoding bone morphogenetic protein receptor 2 (BMPR2). Ge...

AimsPulmonary arterial hypertension (PAH) occurs more frequently in women than men. Oestrogen and the oestrogen-metabolising enzyme cytochrome P450 1B1 (CYP1B1) play a role in the development of PAH. Anorectic drugs such as dexfenfluramine (Dfen) have been associated with the development of PAH. Dfen mediates PAH via a serotonergic mechanism and we have shown serotonin to up-regulate expression of CYP1B1 in human pulmonary artery smooth muscle cells (PASMCs). Thus here we assess the role of CYP1B1 in the development of Dfen-induced PAH.Methods and resultsDfen (5 mg kg−1 day−1 PO for 28 days) increased right ventricular pressure and pulmonary vascular remodelling in female mice only. Mice dosed with Dfen showed increased whole lung expression of CYP1B1 and Dfen-induced PAH was ablated in CYP1B1−/− mice. In line with this, Dfen up-regulated expression of CYP1B1 in PASMCs from PAH patients (PAH-PASMCs) and Dfen-mediated proliferation of PAH-PASMCs was ablated by pharmacological inhibition of CYP1B1. Dfen increased expression of tryptophan hydroxylase 1 (Tph1; the rate-limiting enzyme in the synthesis of serotonin) in PAH-PASMCs and both Dfen-induced proliferation and Dfen-induced up-regulation of CYP1B1 were ablated by inhibition of Tph1. 17β-Oestradiol increased expression of both Tph1 and CYP1B1 in PAH-PASMCs, and Dfen and 17β-oestradiol had synergistic effects on proliferation of PAH-PASMCs. Finally, ovariectomy protected against Dfen-induced PAH in female mice.ConclusionCYP1B1 is critical in the development of Dfen-induced PAH in mice in vivo and proliferation of PAH-PASMCs in vitro. CYP1B1 may provide a novel therapeutic target for PAH.

AimsPulmonary arterial hypertension (PAH) occurs more frequently in women with mutations in bone morphogenetic protein receptor type 2 (BMPR2) and dysfunctional BMPR2 signalling underpinning heritable PAH. We have previously shown that serotonin can uncover a pulmonary hypertensive phenotype in BMPR2+/− mice and that oestrogen can increase serotinergic signalling in human pulmonary arterial smooth muscle cells (hPASMCs). Hence, here we wished to characterize the expression of oestrogen receptors (ERs) in male and female human pulmonary arteries and have examined the influence of oestrogen and serotonin on BMPR2 and ERα expression.Methods and resultsBy immunohistochemistry, we showed that ERα, ERβ, and G-protein-coupled receptors are expressed in human pulmonary arteries localizing mainly to the smooth muscle layer which also expresses the serotonin transporter (SERT). Protein expression of ERα protein was higher in female PAH patient hPASMCs compared with male and serotonin also increased the expression of ERα. 17β-estradiol induced proliferation of hPASMCs via ERα activation and this engaged mitogen-activated protein kinase and Akt signalling. Female mice over-expressing SERT (SERT+ mice) develop PH and the ERα antagonist MPP attenuated the development of PH in normoxic and hypoxic female SERT+ mice. The therapeutic effects of MPP were accompanied by increased expression of BMPR2 in mouse lung.ConclusionERα is highly expressed in female hPASMCs from PAH patients and mediates oestrogen-induced proliferation of hPASMCs via mitogen-activated protein kinase and Akt signalling. Serotonin can increase ERα expression in hPASMCs and antagonism of ERα reverses serotonin-dependent PH in the mouse and increases BMPR2 expression.