FZD4 and chronic obstructive pulmonary disease: As depicted in Fig. 3B, compared with the control group, significant down-regulation was observed for WNT10b, WNT2, LRP6, LGR6, FZD4, CTNNB1, LEF1, and FOSL1 in AECOPD (P < 0.05), and partial WNT/β-catenin signaling components including WNT10b, FZD4, and FOSL1 were significantly down-regulated in stable COPD (P < 0.05).