Hypoxia induces unique proliferative response in adventitial fibroblasts by activating PDGFβ receptor-JNK1 signalling

Pulmonary hypertension (PH) is a devastating condition for which no disease-modifying therapies exist. PH is recognized as proliferative disease of the pulmonary artery (PA). In the experimental newborn calf model of hypoxia-induced PH, adventitial fibroblasts in the PA wall exhibit a heightened replication index. Because elevated platelet-derived growth factor receptor (PDGF-R) signalling is associated with PH, we tested the hypothesis that the activation of PDGF-R contributes to fibroblast proliferation and adventitial remodelling in PH. Newborn calves were exposed to either ambient air (P-B 640 mmHg) (Neo-C) or high altitude (P-B 445 mm Hg) (Neo-PH) for 2 weeks. PDGF-R phosphorylation was markedly elevated in PA adventitia of Neo-PH calves as well as in cultured PA fibroblasts isolated from Neo-PH animals. PDGF-R activation with PDGF-BB stimulated higher replication in Neo-PH cells compared with that of control fibroblasts. PDGF-BB-induced proliferation was dependent on reactive oxygen species generation and extracellular signal-regulated kinase1/2 activation in both cell populations; however, only Neo-PH cell division via PDGF-R activation displayed a unique dependence on c-Jun N-terminal kinase1 (JNK1) stimulation as the blockade of JNK1 with SP600125, a pharmacological antagonist of the JNK pathway, and JNK1-targeted siRNA selectively blunted Neo-PH cell proliferation. Our data strongly suggest that hypoxia-induced modified cells engage the PDGF-R-JNK1 axis to confer distinctively heightened proliferation and adventitial remodelling in PH.