Necroptosis Signaling Promotes Inflammation, Airway Remodeling, and Emphysema in Chronic Obstructive Pulmonary Disease.

Abstract

<b>Rationale:</b> Necroptosis, mediated by RIPK3 (receptor-interacting protein kinase 3) and MLKL (mixed lineage kinase domain-like), is a form of regulated necrosis that can drive tissue inflammation and destruction; however, its contribution to chronic obstructive pulmonary disease (COPD) pathogenesis is poorly understood. <b>Objectives:</b> To determine the role of necroptosis in COPD. <b>Methods:</b> Total and active (phosphorylated) RIPK3 and MLKL were measured in the lung tissue of patients with COPD and control subjects without COPD. Necroptosis-related mRNA and proteins as well as cell death were examined in lungs and pulmonary macrophages of mice with cigarette smoke (CS)-induced experimental COPD. The responses of <i>Ripk3</i>^-/- and <i>Mlkl</i>^-/- mice to acute and chronic CS exposure were compared with those of wild-type mice. The combined inhibition of apoptosis (with the pan-caspase inhibitor quinoline-Val-Asp-difluorophenoxymethylketone [qVD-OPh]) and necroptosis (with deletion of <i>Mlkl</i> in mice) was assessed. <b>Measurements and Main Results:</b> The total MLKL protein in the epithelium and macrophages and the pRIPK3 and pMLKL in lung tissue were increased in patients with severe COPD compared with never-smokers or smoker control subjects without COPD. Necroptosis-related mRNA and protein levels were increased in the lungs and macrophages in CS-exposed mice and experimental COPD. <i>Ripk3</i> or <i>Mlkl</i> deletion prevented airway inflammation upon acute CS exposure. <i>Ripk3</i> deficiency reduced airway inflammation and remodeling as well as the development of emphysematous pathology after chronic CS exposure. <i>Mlkl</i> deletion and qVD-OPh treatment reduced chronic CS-induced airway inflammation, but only <i>Mlkl</i> deletion prevented airway remodeling and emphysema. <i>Ripk3</i> or <i>Mlkl</i> deletion and qVD-OPh treatment reduced CS-induced lung-cell death. <b>Conclusions:</b> Necroptosis is induced by CS exposure and is increased in the lungs of patients with COPD and in experimental COPD. Inhibiting necroptosis attenuates CS-induced airway inflammation, airway remodeling, and emphysema. Targeted inhibition of necroptosis is a potential therapeutic strategy in COPD.