Inflammatory bowel disease (IBD) is a progressive disease that includes Crohn's diseases and ulcerative colitis. Over one third of IBD patients have secondary organ pathologies and pulmonary manifestations are common. The platelet activating factor receptor (PAFR) plays a critical role in regulating inflammation and it is expressed on epithelial cells and neutrophils in both colon and lung. Having identified increased expression of PAFR in both the gastrointestinal (GI) tract and lungs of mice with dextran sulfate sodium (DSS) colitis, we hypothesised that PAFR was a mediator of the pulmonary inflammation associated with colitis. We aimed to elucidate the role of PAFR in gutâlung inflammatory crossâtalk using of the DSSâinduced experimental model of colitis (7 days). DSS mice were treated with PAFR antagonist CV6209 both intranasally and intravenously and lung, colon and blood were assessed for inflammatory cells and mediators by qPCR, immunoblot, immunohistochemistry and flow cytometry. We demonstrated that DSSâinduced colitis resulted in inflammation in mouse bronchoalveolar lavage fluid (BALF) and lungs, as well as increased PAFR protein levels in lungs and colons. Pulmonary neutrophils in DSS animals showed increased PAFR staining. Bacterial 16S mRNA expression were also increased in mouse lungs after 7 days DSS challenge. Both intravenous and intranasal inhibition of PAFR by CV6209 reduced colitisâinduced numbers of neutrophils, but not macrophages, in mouse lungs. Inhibition of PAFR also reduced levels of TNF and ILâ1b proteins and bacterial 16S expression in mouse lungs. Importantly, intravenous administration of CV6209 reduced colitis pathology, TNF and ILâ1b protein levels in mouse colons after 7 days DSS challenge. In the DSS model, increased PAFR protein expression was associated with inflammasome activation, characterized by increased NLRP3 and mature caspaseâ1 proteins, however inhibition of PAFR by CV6209 reduced NLRP3 and caspaseâ1 levels after DSS challenge in mouse lungs. In vitro, NLRP3, activated caspaseâ1 and secreted ILâ1b protein levels were increased in human alveolar epithelial cell culture (A549) after 24h LPS stimulation, and this was inhibited by treatment with CV6209. These data suggest that PAFR regulates colitisâinduced lung inflammation by ILâ1b protein activation via the NLRP3 inflammasome signalling pathway. PAFR may act as an inflammasomeâactivating pattern recognition receptor during mucosal inflammation thus is a potential therapeutic target for lung inflammation associated with colitis and bacteraemia.
Support or Funding Information
This study was supported by a grant from National Health Medical Research Council (NHMRC) Australia
This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.