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 PPARa/¿ 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 PPARa/¿ 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.
