BHLHE40 and idiopathic pulmonary fibrosis: Herein, we aimed to explore DEC1 expression in IPF and bleomycin (BLM)-induced PF in mice and the mechanisms underlying the fibrogenic effect of DEC1 in PF in vivo and in vitro by Dec1-knockout (Dec1−/−) mice, knockdown and overexpression of DEC1 in alveolar epithelial cells (A549 cells).