Inhibitory Role Of BMP4 On The PDGF‐Induced Proliferation And Collagen Synthesis In PASMCs

Abstract

Pulmonary arterial hypertension (PAH) is a severe lung disease characterized by remodeling of pulmonary vascular walls due to the abnormal vascular smooth muscle cell (VSMC) proliferation and accumulation of extracellular matrix proteins such as collagen. Our recent work shows that platelet‐derived growth factor‐BB (PDGF‐BB) induces cell proliferation and collagen synthesis in pulmonary artery SMC (PASMCs) via extracellular signal–regulated kinases (ERK)‐dependent calpain activation in PAH. The aim of the present study to determine the effect of bone morphogenetic protein 4 (BMP4) on PDGF‐stimulated calpain‐Transforming growth factor beta 1 (TGFβ1) signaling in PASMCs. PASMCs from normal and PAH patients were incubated with PDGF‐BB in the presence and absence of BMP4 for 0.5 to 24 h after which protein levels of collagen‐I, p‐Smad2/3, p‐Smad1/5, p‐ERK and intracellular active TGFβ1, calpain activity and cell proliferation were measured. We found that BMP4 augmented the protein levels of p‐Smad1/5 but did not influence the protein contents of collagen‐I, p‐Smad2/3, p‐ERK, active TGFβ1, and calpain activity in normal PASMCs. However, BMP4 attenuated the PDGF‐induced increases in calpain activity, cell proliferation and protein levels of collagen‐I, p‐Smad2/3, and active TGFβ1 in control cells. The results also showed that BMP4 did not alter the PDGF‐induced increases in p‐ERK or p‐Src. In addition, downregulation of Smad1/5 did not prevent the negative effects of BMP4 on the PDGF‐activated signal pathway. Furthermore, BMP4 increased the PKA activity and blocked the PDGF‐induced decrease in calpain‐2 phosphorylation at Ser369 in normal PASMCs. Inhibition of PKA prevented the inhibitory effects of BMP4 on calpain activation and dephosphorylation of Ser369 induced by PDGF. In addition, PKA activator forskolin recapitulated the inhibitory effect of BMP4 on PDGF‐stimulated calpain activation in normal PASMCs. In contrast, the suppressive effects of BMP4 on PDGF‐induced cell proliferation and collagen synthesis were abrogated in PASMCs from PAH patients. BMP4‐evoked PKA activation was diminished in PASMCs from PAH patients and BMP4 was not able to prevent the PDGF‐induced reduction in S369 phosphorylation and activation of calpain. Collectively, these data demonstrate that BMP4 inhibits PDGF‐induced cell proliferation and collagen synthesis via PKA‐mediated inhibition of calpain‐2 in normal PASMCs. Impairment of the BMP4‐PKA signaling may contribute to elevated calpain activation and pulmonary vascular remodeling in PAH.Support or Funding InformationSupported by FAMRI CIA140083 (YS), Department of Veterans Affairs BX002035 (YS) and AHA 16POST27730023 (LK).