MMP12 and pulmonary emphysema: At 8 weeks after birth, which is the period when surviving Ltbp2/S DKO mice develop advanced-stage emphysema, Eln expression approached the normal level, and expression of other elastogenic genes, including Fn1, Fbn1, Fbn2, Fbln4, Fbln5, and Lox was dramatically decreased, whereas the expression level of Mmp12 (macrophage elastase) was increased nearly 3-fold (Supplementary Fig. S4c).