SFRP2 and chronic obstructive pulmonary disease: Interestingly, among these 4 inhibitors, SFRP2 showed significant gene expression change between healthy smokers and healthy nonsmokers, with SFRP2 up-regulation 4.3-fold in healthy smokers and 4.9-fold in smokers with COPD compared with healthy nonsmokers (p<0.0001, Figure 3).