Respiratory syncytial virus (RSV) infection is a common cause of lower respiratory tract illness in infants and children. RSV is a negative-sense, single-strand RNA (ssRNA) virus that mainly infects airway epithelial cells. Accumulating evidence indicates that reactive oxygen species (ROS) production is a major factor for pulmonary inflammation and tissue damage of RSV disease. We investigated immune-responsive gene-1 (IRG1) expression during RSV infection, since IRG1 has been shown to mediate innate immune response to intracellular bacterial pathogens by modulating ROS and itaconic acid production. We found that RSV infection induced IRG1 expression in human A549 cells and in the lung tissues of RSV-infected mice. RSV infection or IRG1 overexpression promoted ROS production. Accordingly, knockdown of IRG1 induction blocked RSV-induced ROS production and proinflammatory cytokine gene expression. Finally, we showed that suppression of IRG1 induction reduced immune cell infiltration and prevented lung injury in RSV-infected mice. These results therefore link IRG1 induction to ROS production and immune lung injury after RSV infection. IMPORTANCE RSV infection is among the most common causes of childhood diseases. Recent studies identify ROS production as a factor contributing to RSV disease. We investigated the cause of ROS production and identified IRG1 as a critical factor linking ROS production to immune lung injury after RSV infection. We found that IRG1 was induced in A549 alveolar epithelial cells and in mouse lungs after RSV infection. Importantly, suppression of IRG1 induction reduced inflammatory cell infiltration and lung injury in mice. This study links IRG1 induction to oxidative damage and RSV disease. It also uncovers a potential therapeutic target in reducing RSV-caused lung injury.

Circular non-coding RNAs are found to play important roles in biology but are still relatively unexplored as a structural motif for chemically regulating gene function. Here, we investigated whether small interfering RNA (siRNA) with a circular structure can circumvent off-target gene silencing, a problem often observed with standard linear duplex siRNA. In the present work, we, for the first time, synthesized a series of circular siRNAs by cyclizing two ends of a single-stranded RNA (sense or antisense strand) to construct circular siRNAs that were more resistant to enzymatic degradation. Gene silencing of GFP and luciferase was successfully achieved using these circular siRNAs with circular sense strand RNAs and their complementary linear antisense strand RNAs. The off-target effect of sense strand RNAs was evaluated and no cross off-target effects were observed. In addition, we successfully achieved longer gene-silencing efficiency in mice with circular siRNAs than with linear siRNAs. These results indicate the promise of circular siRNAs for overcoming off-target effects of siRNAs and enhancing the possible long-term effect of siRNA gene silencing in basic research and drug development.