Anemia is the most common extraintestinal manifestation of inflammatory bowel disease (IBD). Iron deficiency is the most frequent cause of anemia in IBD; however, the mechanisms involved are still poorly understood. Here, we investigated the role of the IBD risk gene, protein tyrosine phosphatase non-receptor type 2 (PTPN2), in regulating iron homeostasis. Proteomic analyses were performed on serum from IBD patients genotyped for the IBD-associated loss-of-function rs1893217 PTPN2 variant. Constitutive Ptpn2 wild type (WT), heterozygous (Het), and knockout (KO) mice were analyzed for iron content, blood parameters, and expression of iron handling proteins. Iron absorption was assessed through radiotracer assays. Serum proteomic analyses revealed that the “iron homeostasis signaling pathway” was the main pathway downregulated in Crohn’s disease (CD) patients carrying the PTPN2 risk allele, independent of disease activity. Ptpn2-KO mice showed characteristics of anemia, including reduced hemoglobin concentrations along with serum and tissue iron deficiency and elevated serum hepcidin levels vs. Ptpn2-WT and Het mice. ⁵⁵Fe absorption via oral gavage was significantly impaired in Ptpn2-KO mice. Correspondingly, Ptpn2-KO mice showed reduced apical membrane expression of the iron transporter DMT1. CD patients with the PTPN2 loss-of-function rs1893217 variant display alterations in serum iron handling proteins. Loss of Ptpn2 in mice caused features of anemia, including iron deficiency associated with reduced apical membrane expression of DMT1. These findings identify an important role for PTPN2 in regulating systemic iron homeostasis.

Loss of activity of the inflammatory bowel disease (IBD) susceptibility gene, protein tyrosine phosphatase non-receptor type 2 (PTPN2), is associated with altered microbiome composition in both human subjects and mice. Furthermore, expansion of the bacterial pathobiont, adherent-invasive E. coli (AIEC), is strongly linked to IBD pathogenesis. The mechanism by which intestinal epithelial cells (IEC) maintain equilibrium between commensal microbiota and immune cells to restrict invading pathobionts is poorly understood. Here, we investigated the role of IEC-specific PTPN2 in regulating AIEC colonization. Tamoxifen-inducible, intestinal epithelial cell-specific Ptpn2 knockout mice (Ptpn2^∆IEC) and control Ptpn2^fl/fl mice were infected with either noninvasive E. coli K12, or fluorescent-tagged mAIEC (mAIEC^red) for four consecutive days or administered PBS. Subsequently, bacterial colonization in mouse tissues was quantified. mRNA and protein expression were assayed in intestinal epithelial cells (IECs) or whole tissue lysates by PCR and Western blot. Tissue cytokine expression was determined by ELISA. Intestinal barrier function was determined by in vivo administration of 4 kDa FITC-dextran (FD4) or 70kDa Rhodamine-B dextran (RD70) fluorescent probes. Confocal microscopy was used to determine the localization of tight-junction proteins. Ptpn2^∆IEC mice exhibited increased mAIEC^red - but not K12 - bacterial load in the distal colon compared to infected Ptpn2^fl/fl mice. The higher susceptibility to mAIEC^red infection was associated with altered levels of antimicrobial peptide (AMPs). Ileal RNA expression of the alpha-defensin AMPs, Defa5, and Defa6, as well as MMP7, was significantly lower in Ptpn2^∆IEC vs. Ptpn2^fl/fl mice, after mAIEC^red but not K12 infection. Furthermore, we observed an increased tight junction-regulated permeability determined by elevated in vivo FD4 but not RD70 permeability in Ptpn2^∆IEC-K12 mice compared to their respective controls. This effect was further exacerbated in Ptpn2^∆IEC mAIEC-infected mice. Further, Ptpn2^∆IEC mice displayed lower IL-22, IL-6, IL-17A cytokine expression post mAIEC infection compared to Ptpn2^fl/fl controls. Recombinant IL-22 reversed the FD4 permeability defect and reduced bacterial burden in Ptpn2^∆IEC mice post mAIEC challenge. Our findings highlight that the intestinal epithelial PTPN2 is crucial for mucosal immunity and gut homeostasis by promoting anti-bacterial defense mechanisms involving coordinated epithelial-immune responses to restrict pathobiont colonization.