P061 The macrophage-specific role of PTPN23 in Acute and Chronic Colitis

Abstract Background Single nucleotide polymorphisms within the gene locus encoding PTPN2, are associated with Crohn’s disease and ulcerative colitis. We have previously shown that, deletion of PTPN2 results in PTPN23 upregulation in intestinal epithelial cells (IEC) in vivo. PTPN23 is known to be involved in endosomal sorting and responsible for epidermal growth factor receptor (EGFR) internalization from the cell surface and thus negatively controls EGFR signalling in epithelial cells. Though PTPN23 is highly expressed in IEC and intestinal macrophages, nothing is known about its function in myeloid cells and its role in intestinal inflammation. Methods Experimental colitis was induced in PTPN23fl/flLysMCre+/- (KO) and PTPN23fl/flLysMCre-/- (WT) littermates by administration of 2% DSS in drinking water for 7 days (acute colitis) or for 4 cycles of 1.5% DSS for 7 days followed by 10 days recovery, each (chronic colitis). Immune cells were isolated from spleen and colon lamina propria from KO and WT mice and PTPN23 expression was detected by qPCR of RNA isolated after cell sorting with flow cytometry. Results The mRNA expression of PTPN23 in untreated WT mice was significantly higher in macrophages isolated from the lamina propria of the colon than in those isolated from spleen (p=0.0279). PTPN23fl/flLysMCre+/- (KO) mice were protected from DSS-induced acute colitis when compared to their WT littermates. This was apparent by a lack of DSS-induced weight loss (p=0.02); longer colon length (p=0.01), reduced endoscopic colitis scores (p=0.0016) and lower spleen weights (p=0.0063) in KO mice. In HE staining of colon tissue, the loss of crypts was less pronounced in KO mice. On mRNA level a lower expression of the pro-inflammatory cytokines interleukin 6 (IL-6) (p=0.0117) and tumour necrosis factor α (TNFα) (p=0.0024) was observed in KO compared to WT mice, supporting a reduced inflammatory response. In chronic colitis the same trends was observed, however the effects were less pronounced. WT mice lost more weight during the DSS cycles compared to KO mice, whereas no difference in weight development was detected between the genotypes in water control groups. Higher MEICSs scores were observed in WT compared to KO mice (p<0.0001) and loss of colonic crypts was more pronounced in HE stained colon samples in WT mice than KO mice. Conclusion PTPN23 deletion in myeloid cells results in protection from DSS-induced acute and chronic colitis. Additionally, a higher expression in intestinal macrophages compared to macrophages isolated from the spleen suggest a specific role in the intestinal immune system.