LEP and pulmonary fibrosis: In particular, the crucial role of DDIT3/CHOP expression in the negative regulation of two neurotrophic cytokines, leptin and insulin-like growth factor-1, has been reported (51), whereas other mechanistic studies showed that CHOP regulates the production of pro-inflammatory (M2) macrophages and subsequent TGF-β signaling involved in idiopathic pulmonary fibrosis (IPF) (52).