BMP3b Is a Novel Antifibrotic Molecule Regulated by Meflin in Lung Fibroblasts.

Fibroblasts play a central role in the lung fibrotic process. Our recent study identified a novel subpopulation of lung fibroblasts expressing meflin (mesenchymal stromal cell- and fibroblast-expressing Linx paralogue), antifibrotic properties of which were confirmed by murine lung fibrosis model. Meflin-expressing fibroblasts were resistant to fibrogenesis induced by TGF-β (transforming growth factor-β), but its underlying mechanisms remain unknown. In this study, evaluation of a silica-nanoparticle-induced lung fibrosis model confirmed the antifibrotic effect of meflin via the regulation of TGF-β signaling. We conducted comparative gene expression profiling in lung fibroblasts, which identified growth differentiation factor 10 (<i>Gdf10</i>) encoding bone morphogenic protein 3b (BMP3b) as the most downregulated gene in meflin-deficient cells under the profibrotic condition with TGF-β. We hypothesized that BMP3b can be an effector molecule playing an antifibrotic role downstream of meflin. As suggested by single-cell transcriptomic data, restricted expressions of <i>Gdf10 (Bmp3b)</i> in stromal cells including fibroblasts were confirmed. We examined possible antifibrotic properties of BMP3b in lung fibroblasts and demonstrated that <i>Bmp3b</i>-null fibroblasts were more susceptible to TGF-β-induced fibrogenic changes. Furthermore, <i>Bmp3b</i>-null mice exhibited exaggerated lung fibrosis induced by silica-nanoparticles <i>in vivo</i>. We also demonstrated that treatment with recombinant BMP3B was effective against TGF-β-induced fibrogenesis in fibroblasts, especially in the suppression of excessive extracellular matrix production. These lines of evidence suggested that BMP3b is a novel humoral effector molecule regulated by meflin which exerts antifibrotic properties in lung fibroblasts. Supplementation of BMP3B could be a novel therapeutic strategy for fibrotic lung diseases.