Toll-Interacting Protein Down-Regulation by Cigarette Smoke Exposure Impairs Human Lung Defense against Influenza A Virus Infection.

Cigarette smoking is a primary cause of chronic obstructive pulmonary disease (COPD). Smokers have a higher risk of influenza-related mortality, but the underlying mechanisms remain unclear. Toll-interacting protein (TOLLIP), an immune regulator, inhibits influenza A virus (IAV) infection, but its regulation in COPD has not been well understood. This study was designed to determine whether cigarette smoke (CS) exposure down-regulated TOLLIP expression via epigenetic mechanisms, including histone methylation. TOLLIP and histone-methylating enzymes enhancer of zeste homolog 1/2 (EZH1/2) were measured in healthy and COPD human lungs, human airway epithelial cells cultured under submerged and air-liquid interface conditions, and precision-cut lung slices (PCLSs) exposed to CS with or without IAV infection. EZH1/2 siRNA and inhibitors were used to investigate their effects on TOLLIP expression. In patients with COPD, TOLLIP levels decreased, whereas EZH1 and EZH2 expression increased. Repeated CS exposure decreased TOLLIP and increased EZH1, EZH2, trimethylation of histone H3 at lysine 27 (H3K27me3), and IAV levels in human airway epithelial cells and PCLSs. EZH1/2 siRNA or their pharmacologic inhibitor valemetostat tosylate, in part, restored TOLLIP and reduced IAV levels in CS-exposed airway epithelial cells and PCLSs. These findings suggest that repeated CS exposure during viral infection reduced TOLLIP levels and increased viral load in part through EZH1/EZH2-H3K27me3-mediated epigenetic mechanisms. Targeting EZH1 and EZH2 may serve as one of the potential therapeutic strategies to restore TOLLIP expression and host defense against viral infections in patients with COPD.