Overexpression of bone morphogenetic protein receptor type 2 suppresses transforming growth factor β-induced profibrotic responses in lung fibroblasts

Purpose of the study: Idiopathic pulmonary fibrosis (IPF) is a progressive disease with a poor prognosis. As the efficacy of currently available antifibrotics is limited, development of new therapies is warranted. Transforming growth factor (TGF)-β plays a central role in the pathogenesis of IPF through mechanisms such as promoting the production of extracellular matrix by fibroblasts. Conversely, bone morphogenetic proteins (BMPs) are known to be antifibrotic and may counterbalance TGF-β signaling via BMP receptor type 2 (BMPR2). However, little is known about the expression status of BMPR2 and its function in pulmonary fibrosis, and manipulation of BMPR2 expression has never been attempted. In this study, we aimed at evaluating the effectiveness of BMPR2 upregulation for modulating the imbalance of the TGF-β/BMP axis and reduce the profibrotic changes in lung fibroblasts. Materials and Methods: We investigated BMPR2 expression in pulmonary fibrosis and TGF-β/BMP signaling in lung fibroblasts. Then we evaluated the impact of BMPR2 upregulation using adenoviral transduction on TGF-β-induced Smad2/3 phosphorylation and fibronectin production in lung fibroblasts. Results: BMPR2 was distributed in airway epithelium and alveolar walls in rat lungs. BMPR2 expression was decreased in fibrotic lesions in the lungs of rats with bleomycin-induced pulmonary fibrosis and in human lung fibroblasts (HLFs) stimulated with TGF-β. Although Smad2/3 phosphorylation and fibronectin production were not suppressed solely by BMPs, phosphorylated Smad2/3 was decreased in BMPR2-transduced cells even without BMP stimulation. Fibronectin was decreased only when BMPR2-transduced HLFs were stimulated with BMP7 (but not BMP4). Similar results were also observed in IPF patient HLFs and rat lung fibroblasts. Conclusions: BMPR2 expression was reduced in fibrotic lungs and lung fibroblasts stimulated with TGF-β. BMPR2 transduction to lung fibroblasts reduced Smad2/3 phosphorylation, and reduced fibronectin production when treated with BMP7. Upregulation of BMPR2 may be a possible strategy for treating pulmonary fibrosis.