MMP12 and chronic obstructive pulmonary disease: Mmp12 overexpression in the lungs is associated with reduced lung diffusing capacity (Molet et al., 2005; Chaudhuri et al., 2012; Ishii et al., 2014), as well as increased levels of Mmp12 in the sputum of COPD patients (Demedts et al., 2006; Elkington and Friedland, 2006).