Inhibition of DLK1 regulates AT2 differentiation and alleviates established pulmonary fibrosis by upregulating TTF-1/CLDN6.

BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is a devastating age-related disease with unknown causes and limited effective treatment. Dysregulation of Alveolar Type 2 (AT2) cells facilitates the initiation of IPF. While differentiation of AT2 into AT1 is necessary for restoring alveolar epithelium. Delta-like non-canonical Notch ligand 1 (DLK1) is a paternally imprinted gene that controls stem cell differentiation. However, the role of DLK1 on AT2 during lung fibrosis remains unclear. METHODS: Lung specimens from 11 patients with IPF or contemporaneous non-IPF controls were collected to determine DLK1 expression. The murine model of bleomycin (BLM) -induced pulmonary fibrosis and cell models of transforming growth factor-beta (TGF-β)-treated A549, MRC5 or primary lung fibroblasts (PLFs) were established. Epithelial DLK1 knockdown mice were constructed by an alveolar epithelial -specific adeno-associated virus (AAV) 6 vector system. Besides, primary AT2 cells were isolated from SPC-EGFP mice and cultured in 2D and 3D organoids. RESULTS: In the present study, we found that DLK1, predominantly expressed in AT2 cells, was upregulated in both IPF lungs and the murine fibrotic lung induced by BLM. AAV-mediated epithelial-specific knockdown of DLK1 promoted the proliferation and differentiation of AT2 into AT1 and alleviated the established lung fibrosis in murine BLM-induced models. In addition, recombinant DLK1 inhibited the renewal of AT2 and aggravated TGF-β-induced fibrosis in vitro, which can be rescued by si-DLK1 intervention. Mechanically, conditional knockdown of DLK1 upregulated TTF-1, a transcriptional factor that controls AT2 differentiation via CLDN6. CONCLUSION: DLK1 inhibition regulates AT2 differentiation and contributes to the mitigation of established fibrosis via TTF-1/CLDN6 pathway, which suggests that DLK1 may be a therapeutic target for IPF.