Background: Inhibitors of the serine/threonine kinase mechanistic target of rapamycin (mTOR) have been shown to induce inflammatory lung disease in mice. Here, we examined the impact of sirolimus (rapamycin) treatment on the lung pathology associated with acute influenza A virus (IAV) infection.
Methods: BALB/c mice were inoculated intranasally with 10 ÁL IAV [A/PR/8/34] of 108.1 TCID50. The mice were also injected intraperitoneally with either sirolimus (2.5 mg/g) or DMSO (about 5 ÁL), given daily beginning on the day of inoculation. The mice were sacrificed on days 2 and 4 post-inoculation. Mouse weight, lung and thymus histology, lung cytosolic cytochrome c expression (using rabbit anti-cytochrome c antibody), lung and thymus tissues intracellular caspase activity (using the caspase-3 substrate Ac-DEVD), lung and thymus cellular GSH (using monobromobimane labeling), and lung viral copies (using RT-PCR) were measured to assess the impact of sirolimus on the course of IAV infection.
Results: Mice treated with sirolimus alone exhibited poor body weight gain (Fig.1) associated with adverse events in the lung (pulmonary inflammation, Fig.2) and thymus (effaced thymus peripheral cortex, decreased caspase activity, and increased glutathione). In addition, IAV-infected mice treated with sirolimus exhibited significantly increased weight loss (p=0.029) as compared to controls (Fig.1). Histopathology following IAV infection revealed increased pulmonary inflammation in mice administered sirolimus as compared to controls (Fig. 2). Cellular glutathione was also increased in mice administered sirolimus as compared to controls. Despite the increased disease, sirolimus administration had no impact on viral replication. In contrast, cytosolic cytochrome c staining in inflammatory cells was less prominent in IAV-infected mice that were administered sirolimus as compared to mice received either IAV or sirolimus alone (Fig. 2). Similarly, intracellular caspase activity was reduced in IAV-infected mice treated with sirolimus as compared to controls.
Conclusion: Thus, mTOR plays a critical role in modulating pulmonary inflammation and inflammatory cell apoptosis, both of which influence the relative severity of IAV infection.
S. Varga, None