Constitutive Ptpn2‐Loss in Mice Decreases Number and Compromises Function of Intestinal Goblet and Paneth cells

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Among the ~200 susceptibility loci associated with Inflammatory Bowel Disease (IBD), are loss‐of‐function single nucleotide polymorphisms (SNPs) in the locus (18p11) containing the Protein Tyrosine Phosphatase non‐receptor Type 2 (PTPN2) gene. PTPN2 encodes the T Cell Protein Tyrosine Phosphatase (TCPTP) that functions as a negative regulator of diverse intracellular pathways repressing inflammatory signals. In Ptpn2‐deficient mice, we observed altered intestinal homeostasis in the form of intestinal epithelial barrier defects and altered intestinal microbiome composition. Intestinal epithelial homeostasis is maintained by active‐cycling and slow cycling stem cells confined within the crypt‐based niche and subsequent differentiation into secretory and absorptive epithelial lineages as cells migrate up the crypt‐villus axis. The goal of this study was to determine whether Ptpn2‐loss affects intestinal epithelial cell populations and function that could contribute to altered host‐bacterial interactions.MethodsIntestinal tissues (ileum, cecum, proximal and distal colon) from 21 day old wild type (WT), heterozygous (HET) and constitutive Ptpn2 knockout (KO) Balb/C mice were harvested and processed for imaging to detect proliferation (Ki‐67), apoptosis (TUNEL), Paneth cell (lysozyme), and goblet cell (periodic‐acid Shiff) numbers via staining of specific markers. cDNA was generated by reverse transcriptase, and mRNA expression of key genes associated with Paneth and goblet cells function were measured by PCR.ResultsProximal and distal colon of Ptpn2‐KO mice showed clusters of apoptotic cells at the crypt base in comparison to wildtype. In addition, the number of proliferative cells was higher in the crypts of proximal and distal colon of Ptpn2‐KO mice compared to WT (p=0.0032 and p=0.0005 respectively; n=3). Lysozyme‐positive Paneth cells were significantly reduced in HET mice (p=0.0452 vs. WT; n=2–5) and further reduced in KO mice (p=0.0040; n=4). Moreover, KO mice were almost completely devoid of both lysozyme positive and negative Paneth cells, the latter characterized by large cytosolic granules at the crypt base. mRNA expression of the Paneth cell antimicrobial peptide, Lyz1, was reduced in Ptpn2‐KO mice compared to WT (p=0.017; n=2), whereas expression of antimicrobial peptides Defa5 and Defa6 were not altered. Goblet cell number was slightly reduced in the ileum and distal colon of KO mice (n=2). There was also a preliminary trend towards reduced expression of goblet cell secreted mucin proteins, Muc2, a major mucus layer constituent, and Muc3, a mucin protein homologous to MUC17 in humans shown to be protective against enteroinvasive E. coli, in the cecum of Ptpn2‐KO mice compared to wildtype (n=2).ConclusionPtpn2‐deficiency compromises intestinal epithelial cell differentiation leading to altered numbers and function of Paneth and goblet cells consistent with increased susceptibility to bacterial infection.Support or Funding InformationSupported by NIH 2R01DK091281 (DFM), the Crohn's and Colitis Foundation (DFM), and Science Without Borders Fellowship (VC)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.