PPAR-γ in Macrophages Limits Pulmonary Inflammation and Promotes Host Recovery following Respiratory Viral Infection

Alveolar macrophages (AM) play pivotal roles in modulating host defense, pulmonary inflammation, and tissue injury following respiratory viral infections. However, the transcriptional regulation of AM function during respiratory viral infections is still largely undefined. Here we have screened the expression of 84 transcription factors in AM in response to influenza A virus (IAV) infection. We found that the transcription factor PPAR-gamma was downregulated following IAV infection in AM through type I interferon (IFN)-dependent signaling. PPAR-gamma expression in AM was critical for the suppression of exaggerated antiviral and inflammatory responses of AM following IAV and respiratory syncytial virus (RSV) infections. Myeloid PPAR-gamma deficiency resulted in enhanced host morbidity and increased pulmonary inflammation following both IAV and RSV infections, suggesting that macrophage PPAR-gamma is vital for restricting severe host disease development. Using approaches to selectively deplete recruiting monocytes, we demonstrate that PPAR-gamma expression in resident AM is likely important in regulating host disease development. Furthermore, we show that PPAR-gamma was critical for the expression of wound healing genes in AM. As such, myeloid PPAR-gamma deficiency resulted in impaired inflammation resolution and defective tissue repair following IAV infection. Our data suggest a critical role of PPAR-gamma expression in lung macrophages in the modulation of pulmonary inflammation, the development of acute host diseases, and the proper restoration of tissue homeostasis following respiratory viral infections. IMPORTANCE Respiratory viral infections, like IAV and respiratory syncytial virus (RSV) infections, impose great challenges to public health. Alveolar macrophages (AM) are lung-resident immune cells that play important roles in protecting the host against IAV and RSV infections. However, the underlying molecular mechanisms by which AM modulate host inflammation, disease development, and tissue recovery are not very well understood. Here we identify that PPAR-gamma expression in AM is crucial to suppress pulmonary inflammation and diseases and to promote fast host recovery from IAV and RSV infections. Our data suggest that targeting macrophage PPAR-gamma may be a promising therapeutic option in the future to suppress acute inflammation and simultaneously promote recovery from severe diseases associated with respiratory viral infections.