To determine the role of mechanosensitive MDM4 in lung fibrosis resolution in aged mice, we generated Mdm4 conditional KO mice (Col1α2-CreERT2;Mdm4fl/fl), in which tamoxifen-induced expression of Cre recombinase under the control of mouse type I collagen α2 promoter/enhancer–driven specific deletion of Mdm4 in collagen I–producing cells. Here, COL1A2 is linked to pulmonary fibrosis.