MMP1 and pulmonary emphysema: Animal models suggest a role for MMP-1 [11], -9 and -12 [12] in emphysema development while human studies demonstrate increased expression of MMP-1 [13–15], - 2 [15], -3 [15], -8 [14–16], -9 [13–19], -10 [15] and -12 [13, 20, 21] in the airways of COPD subjects.