The mechanisms by which macrophages regulate intestinal epithelial cell (IEC) barrier properties are poorly understood. Protein tyrosine phosphatase non-receptor type 2 (PTPN2) protects the IEC barrier from inflammation-induced disruption and regulates macrophage functions. We investigated whether PTPN2 controls interactions between IECs and macrophages to maintain intestinal barrier function.
Human IEC (Caco-2BBe/HT-29.cl19a cells) and mouse enteroid monolayers were co-cultured with human macrophages (THP-1, U937, primary monocyte-derived macrophages from patients with inflammatory bowel disease [IBD]) or mouse macrophages, respectively. We assessed barrier function (transepithelial electrical resistance [TEER] and permeability to 4 kDa fluorescently labeled dextran [FD4] or rhodamine B-dextran 70 kDa) and macrophage polarization. We analyzed intestinal tissues from mice with myeloid cell-specific deletion of PTPN2 (Ptpn2-LysMCre mice) and mice without disruption of Ptpn2 (controls); some mice were given injections of a neutralizing antibody against interleukin 6 (IL6). Proteins were knocked down in macrophages and/or IECs with small hairpin RNAs.
Knockdown of PTPN2 in either macrophages and/or IECs increased the permeability of IEC monolayers, had a synergistic effect when knocked down from both cell types, and increased development of inflammatory macrophages in macrophage-IEC co-cultures. Colon lamina propria from Ptpn2-LysMCre mice had significant increases in inflammatory macrophages; these mice had increased in vivo and ex vivo colon permeability to FD4 and reduced ex vivo colon TEER. Nanostring analysis revealed significant increases in expression of IL6 in colon macrophages from Ptpn2-LysMCre mice. An IL6 blocking antibody reversed the effects of PTPN2-deficient macrophages, reducing permeability of IEC monolayers in culture and in Ptpn2-LysMCre mice. Macrophages from patients with IBD carrying a single-nucleotide polymorphism associated with the disease (PTPN2 rs1893217) had the same features of PTPN2-deficient macrophages from mice, including reduced TEER and increased permeability in co-cultures with human IEC or mouse enteroid monolayers, which were restored by anti-IL6.
PTPN2 is required for interactions between macrophages and IECs; loss of PTPN2 from either cell type results in intestinal barrier defects, and loss from both cell types has a synergistic effect. We provide a mechanism by which PTPN2 gene variants compromise intestinal epithelial barrier function and increase risk of inflammatory disorders such as IBD.
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