MMP12 and pulmonary emphysema: To validate the pathogenetic relevance of MMP12 in emphysema formation in βENaC-Tg mice, the temporal relationship between elevated MMP12 expression and structural lung damage was investigated by several independent approaches including (i) MMP12-specific FRET reporters to localize its activity in the lung [11], (ii) genetic deletion of MMP12, and (iii) pharmacological inhibition of MMP activity in βENaC-Tg mice [52].