LMO7 drives profibrotic fibroblast polarization and pulmonary fibrosis in mice through TGF-β signalling

Idiopathic pulmonary fibrosis (IPF) is a progressive lethal disease. Profibrotic fibroblast polarization during wound healing is one of the main causes of IPF, and the molecular mechanisms involved have yet to be fully determined. LIM domain-only protein 7 (LMO7), which acts as an E3 ubiquitin ligase, is highly expressed in the lung, brain and heart and plays important roles in embryonic development, cancer progression, inflammatory bowel disease and Dreifuss muscular dystrophy (EDMD). In this study, we investigated the role of LMO7 in pulmonary fibrosis. Bleomycin (BLM)-induced lung fibrosis was established in mice. For AAV-mediated gene therapy, AAV-Lmo7 shRNA (AAV-Lmo7 shRNA) was intratracheally administered 6 days before BLM injection. Through transcriptome analysis, we found that the expression of LMO7 was significantly upregulated in the fibroblasts of IPF patients and BLM-induced mice. Knockdown of LMO7 impaired the profibrotic phenotype of fibroblasts in BLM-treated mice and in primary lung fibroblasts stimulated with TGF-β in vitro. We observed that LMO7 binds to SMAD7, mediating its degradation by polyubiquitination of lysine 70 and increasing the stability of TGF-β receptor 1 (TGFβR1). Finally, intratracheal administration of adeno-associated virus (AAV)-mediated Lmo7 shRNA significantly ameliorated the progression of BLM-induced lung fibrosis. Our results suggest that LMO7 is a promising target for blocking profibrotic fibroblast polarization for the treatment of fibrotic lung disease. A model for the role of LMO7 in TGF-β/SMAD signaling during pulmonary fibrosis. During pulmonary fibrosis, ubiquitin E3 ligase LMO7 is up-regulated, and binds with. SMAD7. LMO7 mediates the ubiquitination of SMAD7 on Lysine 70, leading to its degradation, and further enhances the stability of transforming growth factor-beta receptor 1 (TGFβR1).