The Role of Eicosanoid-PPAR axis in Exacerbating Post-Influenza Staphylococcus aureus Super-infection

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PROJECT SUMMARY/ABSTRACT Secondary bacterial infection following influenza (super-infection) can lead to cytokine storm (an overexuberant immune response) that often leads to pneumonia and death in patients. Our work focuses on the molecular mechanisms by which the immune system returns to homeostasis after microbial infections. Taking a holistic, systems approach, we investigated the inflammatory responses during a single (influenza or Staphylococcus aureus) and super-infection (influenza/S. aureus). We conducted transcriptional and lipidomic analyses in samples from a mouse super-infection model. Our lipidomic analysis was focused on eicosanoids because they play critical roles in inducing and resolving inflammation. When compared to single infections, we discovered an overproduction of a subset of eicosanoids during super-infection. These lipids (anti-inflammatory CYP450 lipid mediators, primarily DHET) can activate the nuclear receptors and transcription factors PPARa and PPARg. During influenza single infection, moderate induction of CYP lipids (primarily EET) during the resolution phase allows for appropriate anti-inflammatory responses to promote the return to homeostasis. We hypothesize that while EET promotes the physiological resolution of inflammation after microbial infections, DHET produced at an aberrant level during super-infection leads to the alteration in macrophage polarization and inhibition of bacterial clearance. The failure to control the bacterial pathogen amplifies the immune signals to recruit additional immune cells which eventually cause irreversible tissue damage. We will take the following approaches during single and super-infection to investigate the effects of the eicosanoid-PPAR axis on the inflammatory response. First, we will determine the effects of perturbing the eicosanoid-PPAR axis on the resolution or amplification of inflammation during single and super-infection. We will use chemical inhibitors in combination with genetic models to determine whether the animals will be protected from or succumb to disease during single and super- infection. We will determine the lipidomic profiles to assess the specific effects of the inhibitors have on the eicosanoid metabolism networks. We will also determine the bacterial/viral loads, cellularity, pathohistology, and targeted transcriptional profiling of macrophages. Second, we will determine the mechanism by which eicosanoid-activated PPARα/γ modulates immune signaling, macrophage polarization and immune metabolism in vitro. Macrophage polarization (classically or alternative activated) can amplify or resolve inflammatory responses. We will determine the potency of different CYP450 metabolites to activate PPARα/γ within mouse and primary human macrophages. We will determine how eicosanoids (CYP450 metabolites) affect the immune signaling, macrophage polarization, and lipid metabolism. Interestingly, While the induction of inflammation has been the subject of active investigation, the mechanisms underlying the resolution of inflammation have been elusive. By gaining insights into the resolution of inflammation during single and super-infection, we will develop novel therapeutic targets for infection- and immune-related human diseases.