LEP and idiopathic pulmonary fibrosis: Leptin levels are reported to be elevated in serum and correlated with the severity of lung fibrosis, since leptin significantly promotes the epithelial–mesenchymal transition in A549 cells, decreases autophagosome formation, inhibits the lipidation of LC3I to LC3II, and up-regulates the expression of p62 by activating the PI3K/Akt/mTOR pathway [88] involved in the onset and development of IPF (Figure 3).