Hypercapnia Increases Influenza A Virus Infection of Bronchial Epithelial Cells by Augmenting Cellular Cholesterol via mTOR and Akt.

Hypercapnia, the elevation of CO2 in blood and tissue, is a risk factor for mortality in patients with severe lung disease and pulmonary infections. We previously showed that hypercapnia increases viral replication and mortality in mice infected with influenza A virus (IAV). Elevated CO2 also augmented cholesterol content and pseudo-SARS-CoV-2 entry in bronchial epithelial cells. Interestingly, cellular cholesterol facilitates IAV uptake, replication, assembly, and egress from cells. Here, we report that hypercapnia increases viral protein expression in airway epithelium of mice infected with IAV. Elevated CO2 also enhanced IAV adhesion and internalization, viral protein expression, and viral replication in bronchial epithelial cells. Hypercapnia increased the expression and activation of the transcription factor sterol-regulatory element binding protein 2 (SREBP2), resulting in elevated expression of cholesterol synthesis enzymes, decreased expression of a cholesterol efflux transporter, and augmented cellular cholesterol. Moreover, reducing cellular cholesterol with an SREBP2 inhibitor or statins blocked hypercapnia-induced increases in viral adhesion and internalization, viral protein expression, and IAV replication. Inhibitors of mTOR and Akt also blocked the effect of hypercapnia on viral growth. Our findings suggest that targeting cholesterol synthesis and/or mTOR/Akt signaling may hold promise for reducing susceptibility to influenza infection in patients with advanced lung disease and hypercapnia.