Respiratory Syncytial Virus-Induced Oxidative Stress Leads to an Increase in Labile Zinc Pools in Lung Epithelial Cells

Zinc supplementation in cell culture has been shown to inhibit various viruses, like herpes simplex virus, rotavirus, severe acute respiratory syndrome (SARS) coronavirus, rhinovirus, and respiratory syncytial virus (RSV). However, whether zinc plays a direct antiviral role in viral infections and whether viruses have adopted strategies to modulate zinc homeostasis have not been investigated. Results from clinical trials of zinc supplementation in infections indicate that zinc supplementation may be beneficial in a pathogen- or disease-specific manner, further underscoring the importance of understanding the interaction between zinc homeostasis and virus infections at the molecular level. We investigated the effect of RSV infection on zinc homeostasis and show that RSV infection in lung epithelial cells leads to modulation of zinc homeostasis. The intracellular labile zinc pool increases upon RSV infection in a multiplicity of infection (MOI)-dependent fashion. Small interfering RNA (siRNA)-mediated knockdown of the ubiquitous zinc uptake transporter ZIP1 suggests that labile zinc levels are increased due to the increased uptake by RSV-infected cells as an antiviral response. Adding zinc to culture medium after RSV infection led to significant inhibition of RSV titers, whereas depletion of zinc by a zinc chelator, N,N,N′,N′-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN) led to an increase in RSV titers. The inhibitory effect of zinc was specific, as other divalent cations had no effect on RSV titers. Both RSV infection and zinc chelation by TPEN led to reactive oxygen species (ROS) induction, whereas addition of zinc blocked ROS induction. These results suggest a molecular link between RSV infection, zinc homeostasis, and oxidative-stress pathways and provide new insights for developing strategies to counter RSV infection. IMPORTANCE Zinc deficiency rates in developing countries range from 20 to 30%, and zinc supplementation trials have been shown to correct clinical manifestations attributed to zinc deficiency, but the outcomes in the case of respiratory infections have been inconsistent. We aimed at understanding the role of zinc homeostasis in respiratory syncytial virus (RSV) infection. Infection of lung epithelial cell lines or primary small-airway epithelial cells led to an increase in labile zinc pools, which was due to increased uptake of zinc. Zinc supplementation inhibited RSV replication, whereas zinc chelation had an opposing effect, leading to increases in RSV titers. Increases in labile zinc in RSV-infected cells coincided with induction of reactive oxygen species (ROS). Both zinc depletion and addition of exogenous ROS led to enhanced RSV infection, whereas addition of the antioxidant inhibited RSV, suggesting that zinc is part of an interplay between RSV-induced oxidative stress and the host response to maintain redox balance.