Among these factors, Serpin Peptidase Inhibitor, Clade E Member 1 (SERPINE1) is a protease inhibitor that has been shown to be upregulated in the sputum of patients with severe COPD or during hypoxia [65], exposure to LPS, cigarette smoke [66], and oxidative stress [67]. Here, SERPINE1 is linked to chronic obstructive pulmonary disease.