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.

Objective-Pulmonary arterial hypertension is a progressive pulmonary vascular disorder with high morbidity and mortality. Compelling evidence suggests that receptor tyrosine kinases, such as platelet-derived growth factor (PDGF) are closely involved in the pathogenesis of pulmonary arterial hypertension. We investigated the effects of 2 novel PDGF inhibitors, nilotinib/AMN107 (Abl kinases/PDGF receptor inhibitor) and dasatinib/BMS-354825 (Abl kinases/PDGF receptor/Src inhibitor), on the proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs) and on the hemodynamics and pulmonary vascular remodeling in experimental pulmonary hypertension, and determined the expression and regulation of Src family kinases. Methods and Results-Human PASMCs were stimulated by PDGF alone or multiple growth factors to induce proliferation and migration in vitro. Dasatinib (0.03 mol/L), nilotinib (0.3 mol/L), and imatinib (1 mol/L) potently inhibited PDGF-induced signal transducer and activator of transcription 3 and Akt phosphorylation. All 3 inhibitors decreased PDGF-induced proliferation, cell cycle gene regulation, and migration. In contrast, only dasatinib inhibited multiple growth factor-induced PASMC proliferation, and this was associated with the inhibition of Src phosphorylation. Combination of specific Src inhibitors (phosphoprotein phosphatase 1, phosphoprotein phosphatase 2) with either imatinib or nilotinib reduced multiple growth factor-induced proliferation to a similar extent as dasatinib. Importantly, Src phosphorylation increased in pulmonary arterial hypertension PASMCs compared with control PASMCs. Finally, in vivo dasatinib (15 mg/kg per body weight) treatment caused a complete reversal of pulmonary vascular remodeling and achieved similar effectiveness as imatinib (100 mg/kg per body weight) in both monocrotaline-and hypoxia-induced pulmonary hypertension models. Conclusion-We

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal parenchymal lung disease with limited therapeutic options, with fibroblast‐to‐myofibroblast transdifferentiation and hyperproliferation playing a major role. Investigating ex vivo‐cultured (myo)fibroblasts from human IPF lungs as well as fibroblasts isolated from bleomycin‐challenged mice, Forkhead box O3 (FoxO3) transcription factor was found to be less expressed, hyperphosphorylated, and nuclear‐excluded relative to non‐diseased controls. Downregulation and/or hyperphosphorylation of FoxO3 was reproduced by exposure of normal human lung fibroblasts to various pro‐fibrotic growth factors and cytokines (FCS, PDGF, IGF1, TGF‐β1). Moreover, selective knockdown of FoxO3 in the normal human lung fibroblasts reproduced the transdifferentiation and hyperproliferation phenotype. Importantly, mice with global‐ (Foxo3 −/−) or fibroblast‐specific (Foxo3 f.b −/−) FoxO3 knockout displayed enhanced susceptibility to bleomycin challenge, with augmented fibrosis, loss of lung function, and increased mortality. Activation of FoxO3 with UCN‐01, a staurosporine derivative currently investigated in clinical cancer trials, reverted the IPF myofibroblast phenotype in vitro and blocked the bleomycin‐induced lung fibrosis in vivo. These studies implicate FoxO3 as a critical integrator of pro‐fibrotic signaling in lung fibrosis and pharmacological reconstitution of FoxO3 as a novel treatment strategy.