Role of Cholesterol 25-Hydroxylase (Ch25h) in Mediating Innate Immune Responses to Streptococcus pneumoniae Infection.

Alveolar macrophages (AM) are long-lived tissue-resident innate immune cells of the airways. AM are key effectors of recognition, initiation, and resolution of the host defense against microbes and play an essential role in mediating host responses to Streptococcus pneumoniae infection. Lipid metabolism in AM can significantly impact cellular function and biology. Dysregulated metabolism contributes to an accumulation of lipids, unfolded protein response induction, and inflammatory cytokine production. Our study was designed to investigate the impact of Ch25h on mediating innate immune responses by macrophages during S. pneumoniae infection. Using wild-type and Ch25-/- mice, we examined the role of cholesterol metabolism on inflammatory cytokine production and bacterial clearance. Our results demonstrate that Ch25h plays an important role in the initiation and intensity of cytokine and chemokine production in the lung during S. pneumoniae infection. In the absence of Ch25h, there was enhanced phagocytosis and bacterial clearance. Taken together, our findings demonstrate the important role of Ch25h in modulating host responsiveness to S. pneumoniae infection.

The Role of Glutathione Reductase in Influenza Infection.

Influenza infection induces lung epithelial cell injury via programmed cell death. Glutathione, a potent antioxidant, has been reported to be associated with influenza infection. We hypothesized that lung epithelial cell death during influenza infection is regulated by glutathione metabolism. Eight-week-old male and female BALB/c mice were infected with influenza (PR8: A/PR/8/34 [H1N1]) via intranasal instillation. Metabolomic analyses were performed on whole lung lysate after influenza infection. For in vitro analysis, Beas-2B cells were infected with influenza. RNA was extracted, and QuantiTect Primer Assay was used to assess gene expression. Glutathione concentrations were assessed by colorimetric assay. Influenza infection resulted in increased inflammation and epithelial cell injury in our murine model, leading to increased morbidity and mortality. In both our in vivo and in vitro models, influenza infection was found to induce apoptosis and necroptosis. Influenza infection led to decreased glutathione metabolism and reduced glutathione reductase activity in lung epithelial cells. Genetic inhibition of glutathione reductase suppressed apoptosis and necroptosis of lung epithelial cells. Pharmacologic inhibition of glutathione reductase reduced airway inflammation, lung injury, and cell death in our murine influenza model. Our results demonstrate that glutathione reductase activity is suppressed during influenza. Glutathione reductase inhibition prevents epithelial cell death and morbidity in our murine influenza model. Our results suggest that glutathione reductase-dependent glutathione metabolism may play an important role in the host response to viral infection by regulating lung epithelial cell death.

Antiviral Gene Expression in Young and Aged Murine Lung during H1N1 and H3N2.

Influenza is a respiratory virus that alone or in combination with secondary bacterial pathogens can contribute to the development of acute pneumonia in persons >65 years of age. Host innate immune antiviral signaling early in response to influenza is essential to inhibit early viral replication and guide the initiation of adaptive immune responses. Using young adult (3 months) and aged adult mice infected with mouse adapted H1N1 or H3N2, the results of our study illustrate dysregulated and/or diminished activation of key signaling pathways in aged lung contribute to increased lung inflammation and morbidity. Specifically, within the first seven days of infection, there were significant changes in genes associated with TLR and RIG-I signaling detected in aged murine lung in response to H1N1 or H3N2. Taken together, the results of our study expand our current understanding of age-associated changes in antiviral signaling in the lung.