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

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 (HIF1α) is a pro‐proliferative mediator and may be involved in the development of human pulmonary arterial hypertension. The estrogen metabolite 2‐methoxyestradiol (2ME2) has antiproliferative properties and is also an inhibitor of HIF1α. Here, we examine sex differences in HIF1α signaling in the rat and human pulmonary circulation and determine if 2ME2 can inhibit HIF1α in vivo and in vitro. Methods and Results: HIF1α signaling was assessed in male and female distal human pulmonary artery smooth muscle cells (hPASMCs), and the effects of 2ME2 were also studied in female hPASMCs. The in vivo effects of 2ME2 in the chronic hypoxic rat (male and female) model of pulmonary hypertension were also determined. Basal HIF1α protein expression was higher in female hPASMCs compared with male. Both factor‐inhibiting HIF and prolyl hydroxylase‐2 (hydroxylates HIF leading to proteosomal degradation) protein levels were significantly lower in female hPASMCs when compared with males. In vivo, 2ME2 ablated hypoxia‐induced pulmonary hypertension in male and female rats while decreasing protein expression of HIF1α. 2ME2 reduced proliferation in hPASMCs and reduced basal protein expression of HIF1α. Furthermore, 2ME2 caused apoptosis and significant disruption to the microtubule network. Conclusions: Higher basal HIF1α in female hPASMCs may increase susceptibility to developing pulmonary arterial hypertension. These data also demonstrate that the antiproliferative and therapeutic effects of 2ME2 in pulmonary hypertension may involve inhibition of HIF1α and/or microtubular disruption in PASMCs

Role of the aryl hydrocarbon receptor in Sugen 5416-induced experimental pulmonary hypertension

Rationale: Rats dosed with the vascular endothelial growth factor (VEGF) inhibitor Sugen 5416 (Su), placed in hypoxia then restored to normoxia has become a widely used model of pulmonary arterial hypertension (PAH). The mechanism by which Su exaccerbates pulmonary hypertension is, however, unclear. Objectives: We investigated Su-activation of the aryl hydrocarbon receptor (AhR) in patient human pulmonary arterial smooth muscle cells (hPASMCs) and patient blood outgrowth endothelial cells (BOECs). We also examined the effect of AhR on aromatase and estrogen levels in the lung. Methods, Measurements and Main Results: Protein and mRNA analysis demonstrated that CYP1A1 was very highly induced in the lungs of Su/hypoxic (Su/Hx) rats. The AhR antagonist CH223191 (8mg/kg/day) reversed the development of PAH in this model in vivo and normalized lung CYP1A1 expression. Increased lung aromatase and estrogen levels in Su/Hx rats were also normalized by CH223191 as was AhR nuclear translocator (ARNT [HIF-1β]) which is shared by HIF-1α and AhR. Su reduced HIF1α expression in hPASMCs. Su induced proliferation in BOECs and increased apoptosis in human pulmonary microvascular endothelial cells (hPMECs) and also induced translocation of AhR to the nucleus in hPASMCs. Under normoxic conditions, hPASMCs do not proliferate to Su. However when grown in hypoxia (1%) Su induced hPASMC proliferation. Conclusion: In combination with hypoxia, Su is proliferative in patient hPASMCs and patient BOECs and Su/Hx-induced PAH in rats may be facilitated by AhR-induced CYP1A1, ARNT and aromatase. Inhibition of the AhR receptor may be a novel approach to the treatment of pulmonary hypertension

Transient but not genetic loss of miR-451 attenuates the development of pulmonary arterial hypertension

<b>Rationale:</b> MicroRNAs are small non-coding RNAs involved in the regulation of gene expression and have recently been implicated in the development of pulmonary arterial hypertension (PAH). Previous work established that miR-451 is up-regulated in rodent models of PAH.<p></p> <b>Objectives:</b> The role of miR-451 in the pulmonary circulation is unknown. We therefore sought to assess the involvement of miR-451 in the development of pulmonary arterial hypertension.<p></p> <b>Methods:</b> Silencing of miR-451 was performed in vivo using miR-451 knockout mice and an antimiR targeting mature miR-451 in rats. Coupled with exposure to hypoxia, indices of pulmonary arterial hypertension were assessed. The effect of modulating miR-451 on human pulmonary artery smooth muscle cell proliferation and migration was analysed.<p></p> <b>Measurements and Main Results:</b> We observed a reduction in systolic right ventricular pressure in hypoxic rats pre-treated with antimiR-451 compared to hypoxia alone (47.7 ± 1.36mmHg and 56.0 ± 2.03mmHg respectively, p<0.01). In miR-451 knockout mice following exposure to chronic hypoxia, no significant differences were observed compared to wild type hypoxic mice. In vitro analysis demonstrated that over-expression of miR-451 in human pulmonary artery smooth muscle cells promoted migration under serum-free conditions. No effect on cellular proliferation was observed.<p></p> <b>Conclusions:</b> Transient inhibition of miR-451 attenuated the development of pulmonary arterial hypertension in hypoxia exposed rats. Genetic deletion of miR-451 had no beneficial effect on indices of pulmonary arterial hypertension, potentially due to pathway redundancy compensating for the loss of miR-451.<p></p&gt

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

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

Serotonin signaling through the 5-HT1B receptor and NADPH oxidase 1 in pulmonary arterial hypertension

Objective: Serotonin can induce human pulmonary artery smooth muscle cell (hPASMC) proliferation through reactive oxygen species (ROS), influencing the development of pulmonary arterial hypertension (PAH). We hypothesise that in PASMCs, serotonin induces oxidative stress through NADPH-oxidase-derived ROS generation and reduced Nrf-2 anti-oxidant systems, promoting vascular injury. Approach and Results: HPASMCs from controls and PAH patients, and PASMCs from Nox1-/- mice, were stimulated with serotonin in the absence/presence of inhibitors of Src kinase, the 5-HT1B receptor and NADPH oxidase 1 (Nox1). Markers of fibrosis were also determined. The pathophysiological significance of our findings was examined in vivo in serotonin transporter overexpressing (SERT+) female mice, a model of pulmonary hypertension (PH). We confirmed serotonin increased superoxide and H2O2 production in these cells. For the first time, we show that serotonin increased oxidized protein tyrosine phosphatases and peroxiredoxin-SO3H and decreased Nrf-2 and catalase activity in hPASMCs. ROS generation was exaggerated, and dependent on c-Src, 5-HT1B receptor and the serotonin transporter in PAH-hPASMCs. Proliferation and extracellular matrix remodeling were exaggerated in PAH-hPASMCs and dependent on 5-HT1B receptor signaling and Nox1, confirmed in PASMCs from Nox1-/- mice. In SERT+ mice, SB216641, a 5-HT1B receptor antagonist, prevented development of PH in a ROS-dependent manner. Conclusions: Serotonin can induce c-Src-regulated Nox1-induced ROS and Nrf-2 dysregulation, contributing to increased post-translational oxidative modification of proteins, activation of redox-sensitive signaling pathways in hPASMCs; associated with mitogenic responses. 5-HT1B receptors contribute to experimental PH by inducing lung ROS production. Our results suggest 5-HT1B receptor-dependent c-Src-Nox1-pathways contribute to vascular remodeling in PAH

Notch3 signaling and vascular remodeling 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

Dexfenfluramine and the oestrogen-metabolizing enzyme CYP1B1 in the development of pulmonary arterial hypertension

<p>Aims: Pulmonary 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.</p> <p>Methods and results: Dfen (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.</p> <p>Conclusion: CYP1B1 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.</p&gt