Background-This study investigated the effect of the phosphodiesterase 5 inhibitor sildenafil on the pulmonary vascular response to hypoxia in humans and mice. Methods and Results-In a randomized, double-blind study, sildenafil 100 mg or placebo was given orally to 10 healthy volunteers 1 hour before breathing 11% O 2 for 30 minutes. Pulmonary artery pressure (PAP) was measured with an indwelling right heart catheter.

Pulmonary hypertension (PH) is characterized by increased proliferation and apoptosis resistance of pulmonary artery smooth muscle cells (PASMCs). Forkhead box O (FoxO) transcription factors are key regulators of cellular proliferation. Here we show that in pulmonary vessels and PASMCs of human and experimental PH lungs, FoxO1 expression is downregulated and FoxO1 is inactivated via phosphorylation and nuclear exclusion. These findings could be reproduced using ex vivo exposure of PASMCs to growth factors and inflammatory cytokines. Pharmacological inhibition and genetic ablation of FoxO1 in smooth muscle cells reproduced PH features in vitro and in vivo. Either pharmacological reconstitution of FoxO1 activity using intravenous or inhaled paclitaxel, or reconstitution of the transcriptional activity of FoxO1 by gene therapy, restored the physiologically quiescent PASMC phenotype in vitro, linked to changes in cell cycle control and bone morphogenic protein receptor type 2 (BMPR2) signaling, and reversed vascular remodeling and right-heart hypertrophy in vivo. Thus, PASMC FoxO1 is a critical integrator of multiple signaling pathways driving PH, and reconstitution of FoxO1 activity offers a potential therapeutic option for PH.

Our data demonstrate that A-17 improves heart and lung function in experimental PH by interfering with lung vascular and right ventricular remodeling. The beneficial effects may be related to the up-regulation of p21. Thus, inhibition of miR-17 may represent a novel therapeutic concept to ameliorate disease state in PH.

Previous studies have suggested a genetic component in susceptibility to hypoxia-induced pulmonary hypertension. We therefore estimated the prevalence of high-altitude pulmonary hypertension (HAPH) in a Kyrgyz population and whether the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene associates with HAPH. An electrocardiographic survey of 741 highlanders demonstrated electrocardiogram signs of cor pulmonale in 14% of subjects. Pulmonary artery hemodynamics measured in an independent group of 136 male highlanders with symptoms of dyspnea at altitude revealed established pulmonary hypertension (mean pulmonary artery pressure [MPAP] > or = 25 mm Hg) in 20%. However, 26% of the normal subjects demonstrated an exaggerated response (twofold or greater increase in MPAP) to inhalation of 11% oxygen, and were classified as hyperresponsive. Ten-year follow-up of this group revealed increases in the MPAP, but not in normal subjects. Comparison of ACE I/D genotypes in the catheterized group revealed a threefold higher frequency of the I/I genotype in highlanders with HAPH, compared with normal highlanders (chi2 = 11.59, p = 0.003). In addition, MPAP was higher in highlanders with the I/I genotype (26.9 +/- 4.0 mm Hg) compared with the I/D genotype (20.6 +/- 1.2 mm Hg) or the D/D genotype (18.3 +/- 0.9 mm Hg) (p < 0.05). We conclude that HAPH is associated with ACE I/D genotype among Kyrgyz highlanders and the development of HAPH in this population and may be predicted by hyperresponsiveness to acute hypoxia.

Pulmonary arterial hypertension (PAH) is characterised by excessive pulmonary vascular remodelling involving deregulated proliferation of cells in intima, media as well as adventitia. Pulmonary arterial endothelial cell (PAEC) hyperproliferation and survival underlies the endothelial pathobiology of the disease.The indispensable involvement of Notch1 in the arterial endothelial phenotype and angiogenesis provides intriguing prospects for its involvement in the pathogenesis of PAH.We observed an increased expression of Notch1 in lungs of idiopathic PAH (IPAH) patients and hypoxia/SU5416 (SUHx) rats compared with healthy subjects. In vitro loss- and gain-of-function studies demonstrated that Notch1 increased proliferation of human PAECs (hPAECs) via downregulation of p21 and inhibited apoptosis via Bcl-2 and Survivin. Inhibition of Notch signalling using the γ-secretase inhibitor dibenzazepine dose-dependently decreased proliferation and migration of hPAECs. Notably, Notch1 expression and transcriptional activity were increased under hypoxia in hPAECs and knockdown of Notch1 inhibited hypoxia-induced proliferation of the cells. Furthermore, in vivo treatment with a γ-secretase inhibitor (AMG2008827) significantly reduced the right ventricular systolic pressure and right heart hypertrophy in SUHx rats.Here, we conclude that Notch1 plays a critical role in PAH and Notch inhibitors may be a promising therapeutic option for PAH.

-Hydrogen sulfide (HS), generated by cystathionine γ lyase (CSE), is an important endogenous regulator of vascular function. The aim of the present study was to investigate the control and consequences of CSE activity in endothelial cells under physiological and pro-atherogenic conditions. -Endothelial cell CSE knock out mice were generated and lung endothelial cells were studied (gene expression, protein sulfhydration and monocyte adhesion). Mice were crossed onto the ApoE background and atherogenesis (partial carotid artery ligation) was monitored over 21 days. CSE expression, HS bioavailability and amino acid profiling were also performed using human material. -The endothelial cell-specific deletion of CSE selectively increased the expression of CD62E and elevated monocyte adherence in the absence of an inflammatory stimulus. Mechanistically, CD62E mRNA was more stable in endothelial cells from CSE-deficient mice, an effect attributed to the attenuated sulfhydration and dimerization of the RNA-binding protein HuR. CSE expression was upregulated in mice following partial carotid artery ligation as well as in atheromas from human subjects. Despite the increase in CSE protein, circulating and intra-plaque HS levels were reduced, a phenomenon that could be attributed to the serine phosphorylation (on Ser377) and inhibition of the enzyme, most likely due to increased IL-1β. Consistent with the loss of HS, HuR sulfhydration was attenuated in atherosclerosis, and resulted in the stabilization of HuR-target mRNAs e.g. CD62E and cathepsin S, both of which are linked with endothelial cell activation and atherosclerosis. The deletion of CSE from endothelial cells was associated with the accelerated development of endothelial dysfunction and atherosclerosis, effects that were reversed upon treatment with a HS donor. Finally, in mice and humans, plasma levels of the CSE substrate; L-cystathionine, negatively correlated with vascular reactivity and HS levels indicating its potential use as a biomarker for vascular disease. -The constitutive S-sulfhydration of HuR (on Cys13) by CSE-derived HS prevents its homo-dimerization and activity which attenuates the expression of target proteins such as CD62E and cathepsin S. However, as a consequence of vascular inflammation the beneficial actions of CSE-derived HS are lost due to the phosphorylation and inhibition of the enzyme.

Pulmonary arterial hypertension (PAH) is a devastating disease with poor prognosis and limited therapeutic options. We screened for pathways that may be responsible for the abnormal phenotype of pulmonary arterial smooth muscle cells (PASMCs), a major contributor of PAH pathobiology, and identified cyclin-dependent kinases (CDKs) as overactivated kinases in specimens derived from patients with idiopathic PAH. This increased CDK activity is confirmed at the level of mRNA and protein expression in human and experimental PAH, respectively. Specific CDK inhibition by dinaciclib and palbociclib decreases PASMC proliferation via cell cycle arrest and interference with the downstream CDK-Rb (retinoblastoma protein)-E2F signaling pathway. In two experimental models of PAH (i.e., monocrotaline and Su5416/hypoxia treated rats) palbociclib reverses the elevated right ventricular systolic pressure, reduces right heart hypertrophy, restores the cardiac index, and reduces pulmonary vascular remodeling. These results demonstrate that inhibition of CDKs by palbociclib may be a therapeutic strategy in PAH.

Although p38 mitogen-activated protein kinase (MAPK) is known to have a role in ischemic heart disease and many other diseases, its contribution to the pathobiology of right ventricular (RV) hypertrophy and failure is unclear. Therefore, we sought to investigate the role of p38 MAPK in the pathophysiology of pressure overload-induced RV hypertrophy and failure. The effects of the p38 MAPK inhibitor PH797804 were investigated in mice with RV hypertrophy/failure caused by exposure to hypoxia or pulmonary artery banding. In addition, the effects of p38 MAPK inhibition or depletion (by small interfering RNA) were studied in isolated mouse RV fibroblasts. Echocardiography, invasive hemodynamic measurements, immunohistochemistry, collagen assays, immunofluorescence staining, and Western blotting were performed. Expression of phosphorylated p38 MAPK was markedly increased in mouse and human hypertrophied/failed RVs. In mice, PH797804 improved RV function and inhibited cardiac fibrosis compared with placebo. In isolated RV fibroblasts, p38 MAPK inhibition reduced transforming growth factor (TGF)-β-induced collagen production as well as stress fiber formation. Moreover, p38 MAPK inhibition/depletion suppressed TGF-β-induced SMAD2/3 phosphorylation and myocardin-related transcription factor A (MRTF-A) nuclear translocation, and prevented TGF-β-induced cardiac fibroblast transdifferentiation. Moreover, p38 MAPK inhibition in mice exposed to pulmonary artery banding led to diminished nuclear levels of MRTF-A and phosphorylated SMAD3 in RV fibroblasts. Together, our data indicate that p38 MAPK inhibition significantly improves RV function and inhibits RV fibrosis. Inhibition of p38 MAPK in RV cardiac fibroblasts, resulting in coordinated attenuation of MRTF-A cytoplasmic-nuclear translocation and SMAD3 deactivation, indicates that p38 MAPK signaling contributes to distinct disease-causing mechanisms.