ELN and pulmonary emphysema: Increased levels of MMP12, which degrades elastin, are central to emphysema pathogenesis both (1) in vivo, in MMP12 knockout and overexpressed mouse models exposed to CS (Hautamaki et al., 1997; Morris et al., 2003; Shapiro et al., 2003), and (2) in clinical studies, from analyses of emphysema patients’ sputum, blood and lung tissue samples (Molet et al., 2005; Demedts et al., 2006; Elkington and Friedland, 2006; Chaudhuri et al., 2012; Ishii et al., 2014).