The autoimmune susceptibility gene, PTPN2, restricts expansion of a novel mouse adherent-invasive E. coli

Intestinal Epithelial Creatine Transporter SLC6A8 Dysregulation in Inflammation and in Response to Adherent Invasive E. coli Infection

Creatine transporter (CrT1) mediates cellular uptake of creatine (Cr), a nutrient pivotal in maintaining energy homeostasis in various tissues including intestinal epithelial cells (IECs). The impact of CrT1 deficiency on the pathogenesis of various psychiatric and neurological disorders has been extensively investigated. However, there are no studies on its regulation in IECs in health and disease. Current studies have determined differential expression of CrT1 along the length of the mammalian intestine and its dysregulation in inflammatory bowel disease (IBD)-associated inflammation and Adherent Invasive E. coli (AIEC) infection. CrT1 mRNA and protein levels in normal intestines and their alterations in inflammation and following AIEC infection were determined in vitro in model IECs (Caco-2/IEC-6) and in vivo in SAMP1/YitFc mice, a model of spontaneous ileitis resembling human IBD. CrT1 is differentially expressed in different regions of mammalian intestines with its highest expression in jejunum. In vitro, CrT1 function (Na+-dependent 14C-Cr uptake), expression and promoter activity significantly decreased following TNFα/IL1β treatments and AIEC infection. SAMP1 mice and ileal organoids generated from SAMP1 mice also showed decreased CrT1 mRNA and protein compared to AKR controls. Our studies suggest that Cr deficiency in IECs secondary to CrT1 dysregulation could be a key factor contributing to IBD pathogenesis.

Immunotherapeutic implications of negative regulation by protein tyrosine phosphatases in T cells: the emerging cases of PTP1B and TCPTP

In the context of inflammation, T cell activation occurs by the concerted signals of the T cell receptor (TCR), co-stimulatory receptors ligation, and a pro-inflammatory cytokine microenvironment. Fine-tuning these signals is crucial to maintain T cell homeostasis and prevent self-reactivity while offering protection against infectious diseases and cancer. Recent developments in understanding the complex crosstalk between the molecular events controlling T cell activation and the balancing regulatory cues offer novel approaches for the development of T cell-based immunotherapies. Among the complex regulatory processes, the balance between protein tyrosine kinases (PTK) and the protein tyrosine phosphatases (PTPs) controls the transcriptional and metabolic programs that determine T cell function, fate decision, and activation. In those, PTPs are de facto regulators of signaling in T cells acting for the most part as negative regulators of the canonical TCR pathway, costimulatory molecules such as CD28, and cytokine signaling. In this review, we examine the function of two close PTP homologs, PTP1B (PTPN1) and T-cell PTP (TCPTP; PTPN2), which have been recently identified as promising candidates for novel T-cell immunotherapeutic approaches. Herein, we focus on recent studies that examine the known contributions of these PTPs to T-cell development, homeostasis, and T-cell-mediated immunity. Additionally, we describe the signaling networks that underscored the ability of TCPTP and PTP1B, either individually and notably in combination, to attenuate TCR and JAK/STAT signals affecting T cell responses. Thus, we anticipate that uncovering the role of these two PTPs in T-cell biology may lead to new treatment strategies in the field of cancer immunotherapy. This review concludes by exploring the impacts and risks that pharmacological inhibition of these PTP enzymes offers as a therapeutic approach in T-cell-based immunotherapies.

Interactions of pathogenic Escherichia coli with CEACAMs

The pathogenic Escherichia coli can be parsed into specific variants (pathovars) depending on their phenotypic behavior and/or expression of specific virulence factors. These pathogens are built around chromosomally-encoded core attributes and through acquisition of specific virulence genes that direct their interaction with the host. Engagement of E. coli pathovars with CEACAMs is determined both by core elements common to all E. coli as well as extrachromosomally-encoded pathovar-specific virulence traits, which target amino terminal immunoglobulin variable-like (IgV) regions of CEACAMs. Emerging data suggests that engagement of CEACAMs does not unilaterally benefit the pathogen and that these interactions may also provide an avenue for pathogen elimination.

Role of adherent invasive Escherichia coli in pathogenesis of inflammatory bowel disease

Gut microbiota imbalances play an important role in inflammatory bowel disease (IBD), but no single pathogenic microorganism critical to IBD that is specific to the IBD terminal ileum mucosa or can invade intestinal epithelial cells has been found. Invasive Escherichia coli (E. coli) adhesion to macrophages is considered to be closely related to the pathogenesis of inflammatory bowel disease. Further study of the specific biological characteristics of adherent invasive E. coli (AIEC) may contribute to a further understanding of IBD pathogenesis. This review explores the relationship between AIEC and the intestinal immune system, discusses the prevalence and relevance of AIEC in Crohn's disease and ulcerative colitis patients, and describes the relationship between AIEC and the disease site, activity, and postoperative recurrence. Finally, we highlight potential therapeutic strategies to attenuate AIEC colonization in the intestinal mucosa, including the use of phage therapy, antibiotics, and anti-adhesion molecules. These strategies may open up new avenues for the prevention and treatment of IBD in the future.

Autoimmune susceptibility gene PTPN2 is required for clearance of adherent-invasive Escherichia coli by integrating bacterial uptake and lysosomal defence

OBJECTIVES

Alterations in the intestinal microbiota are linked with a wide range of autoimmune and inflammatory conditions, including inflammatory bowel diseases (IBD), where pathobionts penetrate the intestinal barrier and promote inflammatory reactions. In patients with IBD, the ability of intestinal macrophages to efficiently clear invading pathogens is compromised resulting in increased bacterial translocation and excessive immune reactions. Here, we investigated how an IBD-associated loss-of-function variant in the protein tyrosine phosphatase non-receptor type 2 (PTPN2) gene, or loss of PTPN2 expression affected the ability of macrophages to respond to invading bacteria.

DESIGN

IBD patient-derived macrophages with wild-type (WT) PTPN2 or carrying the IBD-associated PTPN2 SNP, peritoneal macrophages from WT and constitutive PTPN2-knockout mice, as well as mice specifically lacking PTPN2 in macrophages were infected with non-invasive K12 Escherichia coli, the human adherent-invasive E. coli (AIEC) LF82, or a novel mouse AIEC (mAIEC) strain.

RESULTS

Loss of PTPN2 severely compromises the ability of macrophages to clear invading bacteria. Specifically, loss of functional PTPN2 promoted pathobiont invasion/uptake into macrophages and intracellular survival/proliferation by three distinct mechanisms: Increased bacterial uptake was mediated by enhanced expression of carcinoembryonic antigen cellular adhesion molecule (CEACAM)1 and CEACAM6 in PTPN2-deficient cells, while reduced bacterial clearance resulted from defects in autophagy coupled with compromised lysosomal acidification. In vivo, mice lacking PTPN2 in macrophages were more susceptible to mAIEC infection and mAIEC-induced disease.

CONCLUSIONS

Our findings reveal a tripartite regulatory mechanism by which PTPN2 preserves macrophage antibacterial function, thus crucially contributing to host defence against invading bacteria.

Gut Dysbiosis and Intestinal Barrier Dysfunction: Potential Explanation for Early-Onset Colorectal Cancer

Colorectal cancer (CRC) is a heterogeneous disease that commonly affects individuals aged more than 50 years old globally. Regular colorectal screening, which is recommended for individuals aged 50 and above, has decreased the number of cancer death toll over the years. However, CRC incidence has increased among younger population (below 50 years old). Environmental factors, such as smoking, dietary factor, urbanization, sedentary lifestyle, and obesity, may contribute to the rising trend of early-onset colorectal cancer (EOCRC) because of the lack of genetic susceptibility. Research has focused on the role of gut microbiota and its interaction with epithelial barrier genes in sporadic CRC. Population with increased consumption of grain and vegetables showed high abundance of Prevotella, which reduces the risk of CRC. Microbes, such as Fusobacterium nucleatum, Bacteroides fragilis and Escherichia coli deteriorate in the intestinal barrier, which leads to the infiltration of inflammatory mediators and chemokines. Gut dysbiosis may also occur following inflammation as clearly observed in animal model. Both gut dysbiosis pre- or post-inflammatory process may cause major alteration in the morphology and functional properties of the gut tissue and explain the pathological outcome of EOCRC. The precise mechanism of disease progression from an early stage until cancer establishment is not fully understood. We hypothesized that gut dysbiosis, which may be influenced by environmental factors, may induce changes in the genome, metabolome, and immunome that could destruct the intestinal barrier function. Also, the possible underlying inflammation may give impact microbial community leading to disruption of physical and functional role of intestinal barrier. This review explains the potential role of the interaction among host factors, gut microenvironment, and gut microbiota, which may provide an answer to EOCRC.

Loss of PTPN22 Promotes Intestinal Inflammation by Compromising Granulocyte-mediated Antibacterial Defence

BACKGROUND AND AIMS

A single nucleotide polymorphism in protein tyrosine phosphatase non-receptor type 22 [PTPN22] has been associated with the onset of autoimmune disorders, but protects from Crohn's disease. PTPN22 deficiency in mice promotes intestinal inflammation by modulating lymphocyte function. However, the impact of myeloid PTPN22 in colitis development remains unclear. The aim of this study was to investigate the role of PTPN2 in the IL-10 and the T cell transfer colitis models.

METHODS

PTPN22-deficient mice were crossed with IL-10-/- and RAG2-/- mice. Naïve T cells were injected in RAG-/- mice to induce T-cell transfer colitis. Spontaneous colitis in IL-10-/- mice was monitored for up to 200 days.

RESULTS

Here, we demonstrate that PTPN22 in non-lymphoid immune cells is required to protect against T cell transfer-mediated and IL-10 knock-out colitis. Analysis of the intestinal immune landscape demonstrated a marked reduction of granulocyte influx into the inflamed colon in PTPN22-deficient mice. On a molecular level, granulocytes were not only reduced by numbers, but also revealed a defective function. In particular, granulocyte activation and granulocyte-mediated bacteria killing was impaired upon loss of PTPN22, resulting in elevated bacterial burden and translocation beyond the intestinal epithelial barrier in PTPN22-deficient mice. Consistently, antibiotic-induced depletion of bacteria reverted the increased colitis susceptibility in PTPN22-deficient mice, whereas granulocyte depletion induced acolitis phenotype in wild-type mice similar to that observed in PTPN22-deficient mice.

CONCLUSIONS

In conclusion, our data demonstrate that PTPN22 is essential for adequate granulocyte activation and antimicrobial defence to protect the inflamed intestine from bacterial invasion and exacerbated colitis.

T cell protein tyrosine phosphatase protects intestinal barrier function by restricting epithelial tight junction remodeling

Genome-wide association studies revealed that loss-of-function mutations in protein tyrosine phosphatase non-receptor type 2 (PTPN2) increase the risk of developing chronic immune diseases, such as inflammatory bowel disease (IBD) and celiac disease. These conditions are associated with increased intestinal permeability as an early etiological event. The aim of this study was to examine the consequences of deficient activity of the PTPN2 gene product, T cell protein tyrosine phosphatase (TCPTP), on intestinal barrier function and tight junction organization in vivo and in vitro. Here, we demonstrate that TCPTP protected against intestinal barrier dysfunction induced by the inflammatory cytokine IFN-γ by 2 mechanisms: it maintained localization of zonula occludens 1 and occludin at apical tight junctions and restricted both expression and insertion of the cation pore-forming transmembrane protein, claudin-2, at tight junctions through upregulation of the inhibitory cysteine protease, matriptase. We also confirmed that the loss-of-function PTPN2 rs1893217 SNP was associated with increased intestinal claudin-2 expression in patients with IBD. Moreover, elevated claudin-2 levels and paracellular electrolyte flux in TCPTP-deficient intestinal epithelial cells were normalized by recombinant matriptase. Our findings uncover distinct and critical roles for epithelial TCPTP in preserving intestinal barrier integrity, thereby proposing a mechanism by which PTPN2 mutations contribute to IBD.

The JAK Inhibitor Tofacitinib Rescues Intestinal Barrier Defects Caused by Disrupted Epithelial-macrophage Interactions

BACKGROUND AND AIMS

Loss-of-function variants in protein tyrosine phosphatase non-receptor type-2 [PTPN2] promote susceptibility to inflammatory bowel diseases [IBD]. PTPN2 regulates Janus-kinase [JAK] and signal transducer and activator of transcription [STAT] signalling, while protecting the intestinal epithelium from inflammation-induced barrier disruption. The pan-JAK inhibitor tofacitinib is approved to treat ulcerative colitis, but its effects on intestinal epithelial cell-macrophage interactions and on barrier properties are unknown. We aimed to determine if tofacitinib can rescue disrupted epithelial-macrophage interaction and barrier function upon loss of PTPN2.

METHODS

Human Caco-2BBe intestinal epithelial cells [IECs] and THP-1 macrophages expressing control or PTPN2-specific shRNA were co-cultured with tofacitinib or vehicle. Transepithelial electrical resistance and 4 kDa fluorescein-dextran flux were measured to assess barrier function. Ptpn2fl/fl and Ptpn2-LysMCre mice, which lack Ptpn2 in myeloid cells, were treated orally with tofacitinib citrate twice daily to assess the in vivo effect on the intestinal epithelial barrier. Colitis was induced via administration of 1.5% dextran sulphate sodium [DSS] in drinking water.

RESULTS

Tofacitinib corrected compromised barrier function upon PTPN2 loss in macrophages and/or IECs via normalisation of: [i] tight junction protein expression; [ii] excessive STAT3 signalling; and [iii] IL-6 and IL-22 secretion. In Ptpn2-LysMCre mice, tofacitinib reduced colonic pro-inflammatory macrophages, corrected underlying permeability defects, and prevented the increased susceptibility to DSS colitis.

CONCLUSIONS

PTPN2 loss in IECs or macrophages compromises IEC-macrophage interactions and reduces epithelial barrier integrity. Both of these events were corrected by tofacitinib in vitro and in vivo. Tofacitinib may have greater therapeutic efficacy in IBD patients harbouring PTPN2 loss-of-function mutations.