MMP9 and pulmonary emphysema: Since cigarette smoke-induced emphysema results in tissue remodeling and disrupted expression of ECM proteins, we further tested the expression of matrix metalloproteinases (MMP9 and MMP12), tissue plasmin regulators (PAI-1), and ECM glycoprotein (FN-1) on 30 days CS-exposed young and old p16-3MR mice.