Inhibition of DLK1 regulates AT2 differentiation and alleviates established pulmonary fibrosis by upregulating...

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.

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.

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.

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.