Impact of the group IV protein tyrosine kinase, Fer, on intestinal inflammation and neutrophil function

Fer kinase is a protein tyrosine kinase (PTK) belonging to the group IV family of cytoplasmic enzymes which consists of one other family member, Fps/Fes, and a truncated form of Fer (FerT). An important role for Fer has been proposed in modulating innate immune responses driven by bacterial antigen such as lipopolysaccharide (LPS). For example, data generated in vivo has shown LPS-induced epithelial barrier dysfunction is exacerbated in the absence of Fer kinase activity in mice. Increased damage was associated with enhanced neutrophil recruitment suggesting Fer may modulate neutrophil recruitment and/or function in the gut. Interestingly, both animal models and clinical studies have demonstrated a strong link between bacterial antigens and chronic inflammatory conditions such as inflammatory bowel disease (IBD). Therefore, we hypothesized that group IV PTK such as Fer could regulate intestinal inflammation by modulating neutrophil recruitment and/or function. In this thesis, we examined the role of Fer in two models of colitis using Fer null mutant mice (FerDR/DR). First, in a chemically-induced model of colitis (2, 4, 6-trinitrobenzene sulphonic acid (TNBS)) we demonstrate that FerDR/DR mice develop an exacerbated and prolonged colitis compared to WT mice, which was associated with enhanced neutrophil recruitment to the gut. Next we generated double mutant mice to examine the role of Fer in a spontaneous chronic model of IBD- interleukin 10 deficient (IL-10 --) model. A significant increase in macroscopic and histological inflammatory parameters was observed in IL-10--Fer DR/DR double deficient compared to single mutants. Using the under-agarose chemotaxis assay, we showed evidence for a stimulus specific role for Fer in restraining neutrophil chemotaxis. Enhanced chemotaxis was observed toward end target chemoattractants fMLP-like peptide (WKYMVm) and C5a. Next the intracellular signalling pathways (PI3K and p38MAPK) used in chemotaxis to WKYMVm were examined. The PI3K pathway in neutrophils was shown to have prolonged activation after WKYMVm stimulation in the absence of Fer kinase. Finally, we demonstrated a role for Fer in modulating the rate of superoxide production using the cytochrome c reduction assay but show no role in neutrophil intracellular bacterial killing or apoptosis assays. Our studies indicate that Fer kinase regulates intestinal inflammation responses potentially through its ability to control neutrophil recruitment and superoxide production in response to bacterial peptide.