MMP13 and pulmonary fibrosis: The gelatinases (MMP-2 and -9) and, in particular, MMP-7, have already been suggested to play a role in human and experimental lung fibrosis, thus underscoring the dynamic regulation of the ECM and of remodeling processes in the lung [11], MMP-1 is lacking in rodents, and, hence, MMP-13 (also known as collagenase-3) is the principal interstitial collagenase in this species and has a high specificity for degrading insoluble fibrillar collagens, especially type II and I collagens [12,13].