PTGER2 and idiopathic pulmonary fibrosis: Hypermethylation of specific genes not only can suppress the expression of some genes [Thy-1, COX-2, PTGER2, p14ARF, IP-10 (Zhou et al., 2020), SFRP1/4, CDKN2B (Xue et al., 2021)], but also can promote the expression of some genes [α-SMA, MeCP2, KCNMB1 (Xue et al., 2021)], which eventually leads to the development of IPF (Figure 5A).