Association between the PTPN2 gene and Crohn's disease: dissection of potential causal variants

PTPN2 Regulates Iron Handling Protein Expression in Inflammatory Bowel Disease Patients and Prevents Iron Deficiency in Mice

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.

Association between HMGCR, CRP, and CETP gene polymorphisms and metabolic/inflammatory serum profile in healthy adolescents

BACKGROUND

The complex interplay between health, lifestyle and genetics represents a critical area of research for understanding and promoting human well-being. Importantly, genetics plays a key role in determining individual susceptibility to disease and response to lifestyle. The aim of the present study was to identify genetic factors related to the metabolic/inflammatory profile of adolescents providing new insights into the individual predisposition to the different effects of the substances from the environment.

METHODS

Association analysis of genetic variants and biochemical parameters was performed in a total of 77 healthy adolescents recruited in the context of the DIMENU study.

RESULTS

Polymorphisms of 3-hydroxy-3-methylglutaril coenzyme A reductase (HMGCR; rs142563098), C-reactive protein gene (CRP; rs1417938, rs1130864), cholesteryl ester transfer protein (CETP; rs5030708), interleukin (IL)-10 (IL-10; rs3024509) genes were significantly associated (p < 0.05) with various serum metabolic parameters. Of particular interest were also the correlations between the HMGCRpolymorphism (rs3846663) and tumor necrosis factor (TNF)-α levels, as well Fatty-acid desaturase (FADS) polymorphism (rs7481842) and IL-10 level opening a new link between lipidic metabolism genes and inflammation.

CONCLUSION

In this study, we highlighted associations between single nucleotide polymorphisms (SNPs) and serum levels of metabolic and inflammatory parameters in healthy young individuals, suggesting the importance of genetic profiling in the prevention and management of chronic disease.

The first association study of Protein Tyrosine Phosphatase, Non-Receptor Type 2 (PTPN2) gene polymorphisms in Malaysian patients with Crohn's disease

Crohn's disease (CD) is one of the sub-entities of Inflammatory Bowel Disease which causes chronic inflammation in the gastrointestinal tract. The development of CD has shown to have a strong genetic association. Therefore, the present study aimed to investigate the association between genetic polymorphisms in a susceptible locus of CD, the protein tyrosine phosphatase, non-receptor type 2 (PTPN2) gene and the development of CD in Malaysian patients. A total of 137 CD patients and 274 matched healthy controls were recruited in the present study. Genomic DNA was extracted from the venous blood of participants and five targeted single nucleotide polymorphisms (SNPs) in the PTPN2 gene were genotyped using polymerase chain reaction. Associations between the SNPs and CD were determined using Fisher's exact test and odds ratio. Findings showed that all five selected SNPs were not significantly associated with the development of CD in Malaysian patients, which was in contrast to studies among the European populations. Malaysian Chinese with rs487273 heterozygous G/T genotype was found to have a lower occurrence of CD (P-value = 0.0253; OR = 0.4396). Patients with rs2542152 homozygous T genotype were associated with stricturing behaviour (P-value = 0.0302, OR = 2.9944). The rs16939895 A/G genotype was associated with inflammation at the ileum site (P-value = 0.0387, OR = 2.2105)while homozygous G genotype was associated with colonic CD (P-value = 0.0164, OR = 2.3917). Functional studies of these SNPs are needed to evaluate their potential use as a biomarker for disease phenotypes among Asian patients.

Common polymorphisms of protein tyrosine phosphate non-receptor type 2 gene are not associated with risk of Crohn’s disease in Indian

BACKGROUND

Multiple genetic risk factors for Crohn’s disease (CD) have been identified. However, these observations are not consistent across different populations. The protein tyrosine phosphate non-receptor type 2 (PTPN2) gene plays a role in various aspects of host defense including epithelial barrier function, autophagy, and innate and adaptive immune response. Two common polymorphisms in the PTPN2 gene (rs2542151 and rs7234029) have been associated with risk of CD in Western countries.

AIM

To evaluate the association of PTPN2 gene polymorphisms with risk of CD in Indian population.

METHODS

We conducted a prospective case-control study. Patients with CD were recruited, and their clinical and investigation details were noted. Controls were patients without organic gastrointestinal disease or other comorbid illnesses. Two common polymorphisms in the PTPN2 gene (rs2542151 and rs7234029) were assessed. DNA was extracted from peripheral blood samples of cases and controls and target DNA was amplified using specific sets of primers. The amplified fragments were digested with restriction enzymes and the presence of polymorphism was detected by restriction fragment length polymorphism. The frequency of alleles was determined. The frequencies of genotypes and alleles were compared between cases and controls to look for significant differences.

RESULTS

A total of 108 patients with CD (mean age 37.5 ± 12.7 years, females 42.6%) and 100 controls (mean age 39.9 ± 13.5 years, females 37%) were recruited. For the single nucleotide polymorphism (SNP) rs7234029, the overall frequency of G variant genotype (AG or GG) was noted to be significantly lower in the cases compared to controls (35.2% vs 50%, P = 0.05). For the SNP rs2542151, the overall frequency of G variant genotype (GT or GG) was noted to be similar in cases compared to controls (43.6% vs 47%, P = 0.73). There were no significant differences in minor allele (G) frequency for both polymorphisms between the cases and controls. Both the SNPs had no significant association with age of onset of illness, gender, disease location, disease behaviour, perianal disease, or extraintestinal manifestations of CD.

CONCLUSION

Unlike observation form the West, polymorphisms in the PTPN2 gene (rs7234029 and rs2542151) are not associated with an increased risk of developing CD in Indian patients.

Targeting protein phosphatases for the treatment of inflammation-related diseases: From signaling to therapy

Inflammation is the common pathological basis of autoimmune diseases, metabolic diseases, malignant tumors, and other major chronic diseases. Inflammation plays an important role in tissue homeostasis. On one hand, inflammation can sense changes in the tissue environment, induce imbalance of tissue homeostasis, and cause tissue damage. On the other hand, inflammation can also initiate tissue damage repair and maintain normal tissue function by resolving injury and restoring homeostasis. These opposing functions emphasize the significance of accurate regulation of inflammatory homeostasis to ameliorate inflammation-related diseases. Potential mechanisms involve protein phosphorylation modifications by kinases and phosphatases, which have a crucial role in inflammatory homeostasis. The mechanisms by which many kinases resolve inflammation have been well reviewed, whereas a systematic summary of the functions of protein phosphatases in regulating inflammatory homeostasis is lacking. The molecular knowledge of protein phosphatases, and especially the unique biochemical traits of each family member, will be of critical importance for developing drugs that target phosphatases. Here, we provide a comprehensive summary of the structure, the "double-edged sword" function, and the extensive signaling pathways of all protein phosphatases in inflammation-related diseases, as well as their potential inhibitors or activators that can be used in therapeutic interventions in preclinical or clinical trials. We provide an integrated perspective on the current understanding of all the protein phosphatases associated with inflammation-related diseases, with the aim of facilitating the development of drugs that target protein phosphatases for the treatment of inflammation-related diseases.

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.

T Cell Protein Tyrosine Phosphatase in Osteoimmunology

Osteoimmunology highlights the two-way communication between bone and immune cells. T cell protein tyrosine phosphatase (TCPTP), also known as protein-tyrosine phosphatase non-receptor 2 (PTPN2), is an intracellular protein tyrosine phosphatase (PTP) essential in regulating immune responses and bone metabolism via dephosphorylating target proteins. Tcptp knockout in systemic or specific immune cells can seriously damage the immune function, resulting in bone metabolism disorders. This review provided fresh insights into the potential role of TCPTP in osteoimmunology. Overall, the regulation of osteoimmunology by TCPTP is extremely complicated. TCPTP negatively regulates macrophages activation and inflammatory factors secretion to inhibit bone resorption. TCPTP regulates T lymphocytes differentiation and T lymphocytes-related cytokines signaling to maintain bone homeostasis. TCPTP is also expected to regulate bone metabolism by targeting B lymphocytes under certain time and conditions. This review offers a comprehensive update on the roles of TCPTP in osteoimmunology, which can be a promising target for the prevention and treatment of inflammatory bone loss.

Associations between PTPN2 gene polymorphisms and psoriasis in Northeastern China

Psoriasis is a chronic immune-mediated disease with a complex etiology involving various genetic and immunological factors as well as environmental factors. Psoriasis is thought to be mediated by T-cells polarized to a Th17 fate. PTPN2 encodes the T-cell protein tyrosine phosphatase, which acts as a negative regulator of the JAK/STAT signaling pathways downstream of cytokines and plays a prominent role in T-cell activation, signaling and/or effector function. To evaluate the association between PTPN2 gene polymorphisms and psoriasis in the Northeastern Chinese population. A case-control study was conducted, and 398 patients with psoriasis and 397 healthy controls were genotyped for thirteen genetic polymorphisms in PTPN2. Allele analysis revealed that rs2847297, rs657555 and rs482160 polymorphisms were significantly associated with psoriasis (p = 0.0018, p = 0.0017 and p = 0.0086, respectively). Genotype analysis also revealed that these polymorphisms were significantly associated with psoriasis under different models (codominant, dominant and recessive models) (p < 0.05). In this study, three haplotypes (H1, H7 and H11) were also found to be associated with psoriasis (p = 0.0015, p = 0.0094, and p = 0.0124, respectively). These results indicate that PTPN2 genetic polymorphisms are associated with psoriasis in the Northeastern Chinese population.

Association of genetic variations in PTPN2 and CD122 with ocular Behcet's disease

BACKGROUND

Protein tyrosine phosphatases (PTPs) play critical roles in human autoimmunity. Previous studies found that PTPN2 may be the key regulatory factor in the T-cell-mediated immune response. PTPN2 regulates the Janus kinase/signal transducers and activators of transcription pathway by inhibiting signalling via the interleukin (IL)-2 receptor (CD122). An association between genetic variations in PTPN2 and CD122 with ocular Behcet's disease (BD) has not yet been addressed and was therefore the purpose of this study.

METHODS

A two-stage case-control study was performed in 906 patients with ocular BD and 2178 healthy controls. Genotyping analysis of 11 single nucleotide polymorphisms was carried out. The expression of PTPN2 in peripheral blood mononuclear cells (PBMCs) was quantified by real-time PCR and cytokine production was measured by ELISA.

RESULTS

The frequency of the GG genotype of PTPN2-rs7234029 was significantly lower in patients with ocular BD (p=1.94×10^-5, p_c=8.34×10^-4, OR=0.466). Stratification according to gender showed that rs7234029 was significantly associated with BD in men. A stratified analysis according to the main clinical features showed that rs7234029 was significantly associated with genital ulcers, skin lesions and a positive pathergy test. No association could be detected between BD and CD122 gene polymorphisms. Functional studies showed that rs7234029 GG genotype carriers had a higher PNPT2 mRNA expression level than those which carrying the AA or AG genotype, and a decreased secretion of IL-17 and tumour necrosis factor-alpha was seen by PBMCs from GG carriers. No significant difference could be detected concerning IL-1β or IL-6 production by stimulated PBMCs between the different genotype groups.

CONCLUSIONS

This study shows that a PTPN2-rs7234029 polymorphism is associated with ocular BD and is strongly influenced by gender. In addition, our results suggest that the genetic association with PTPN2 may involve the regulation of PTPN2 mRNA expression and cytokine secretion.

Recent advances in understanding the role of protein-tyrosine phosphatases in development and disease

Protein-tyrosine phosphatases (PTPs) remove phosphate groups from tyrosine residues, and thereby propagate or inhibit signal transduction, and hence influence cellular processes such as cell proliferation and differentiation. The importance of tightly controlled PTP activity is reflected by the numerous mechanisms employed by the cell to control PTP activity, including a variety of post-translational modifications, and restricted subcellular localization. This review highlights the strides made in the last decade and discusses the important role of PTPs in key aspects of embryonic development: the regulation of stem cell self-renewal and differentiation, gastrulation and somitogenesis during early embryonic development, osteogenesis, and angiogenesis. The tentative importance of PTPs in these processes is highlighted by the diseases that present upon aberrant activity.

T cell protein tyrosine phosphatase prevents STAT1 induction of claudin-2 expression in intestinal epithelial cells

T cell protein tyrosine phosphatase (TCPTP) dephosphorylates a number of substrates, including JAK-STAT (signal transducer and activator of transcription) signaling proteins, which are activated by interferon (IFN)-γ, a major proinflammatory cytokine involved in conditions such as inflammatory bowel disease. A critical function of the intestinal epithelium is formation of a selective barrier to luminal contents. The structural units of the epithelium that regulate barrier function are the tight junctions (TJs), and the protein composition of the TJ determines the tightness of the barrier. Claudin-2 is a TJ protein that increases permeability to cations and reduces transepithelial electrical resistance (TER). We previously showed that transient knockdown (KD) of TCPTP permits increased expression of claudin-2 by IFN-γ. Here, we demonstrate that the decreased TER in TCPTP-deficient epithelial cells is alleviated by STAT1 KD. Moreover, increased claudin-2 in TCPTP-deficient cells requires enhanced STAT1 activation and STAT1 binding to the CLDN2 promoter. We also show that mutation of this STAT-binding site prevents elevated CLDN2 promoter activity in TCPTP-deficient epithelial cells. In summary, we demonstrate that TCPTP protects the intestinal epithelial barrier by restricting STAT-induced claudin-2 expression. This is a potential mechanism by which loss-of-function mutations in the gene encoding TCPTP may contribute to barrier defects in chronic intestinal inflammatory disease.

Role of protein tyrosine phosphatases in regulating the immune system: implications for chronic intestinal inflammation

Current hypothesis suggests that genetic, immunological, and bacterial factors contribute essentially to the pathogenesis of inflammatory bowel disease. Variations within the gene loci encoding protein tyrosine phosphatases (PTPs) have been associated with the onset of inflammatory bowel disease. PTPs modulate the activity of their substrates by dephosphorylation of tyrosine residues and are critical for the regulation of fundamental cellular signaling processes. Evidence emerges that expression levels of PTPN2, PTPN11, and PTPN22 are altered in actively inflamed intestinal tissue. PTPN2 seems to be critical for protecting intestinal epithelial barrier function, regulating innate and adaptive immune responses and finally for maintaining intestinal homeostasis. These observations have been confirmed in PTPN2 knockout mice in vivo. Those animals are clearly more susceptible to intestinal and systemic inflammation and feature alterations in innate and adaptive immune responses. PTPN22 controls inflammatory signaling in lymphocytes and mononuclear cells resulting in aberrant cytokine secretion pattern and autophagosome formation. PTPN22 deficiency in vivo results in more severe colitis demonstrating the relevance of PTPN22 for intestinal homeostasis in vivo. Of note, loss of PTPN22 promotes mitogen-activated protein kinase-induced cytokine secretion but limits secretion of nuclear factor κB-associated cytokines and autophagy in mononuclear cells. Loss of PTPN11 is also associated with increased colitis severity in vivo. In summary, dysfunction of those PTPs results in aberrant and uncontrolled immune responses that result in chronic inflammatory conditions. This way, it becomes more and more evident that dysfunction of PTPs displays an important factor in the pathogenesis of chronic intestinal inflammation, in particular inflammatory bowel disease.

PTPN2 and NF-κB single nucleotide polymorphisms associated with susceptibility to ulcerative colitis

Ulcerative colitis (UC) is a form of chronic and recurrent bowel disease with unknown etiology. Pieces of evidence suggest that UC should be evolved as a result of inappropriate and ongoing activation of the mucosal immune system driven by the luminal commensal microflora in a genetically susceptible host. Protein tyrosine phosphatase non-receptor type 2 (PTPN2) and nuclear factor-kappa B (NF-κB) play important roles not only in inflammatory pathways, but also in the development of UC. In recent years, association of PTPN2 and NF-κB gene polymorphisms with susceptibility to UC has become a research focus in Western counties, but the studies are controversial in southern China. This paper reviews the PTPN2 and NF-κB gene single nucleotide poly-morphisms (SNPs) associated with susceptibility to UC.

IBD candidate genes and intestinal barrier regulation

Technological advances in the large scale analysis of human genetics have generated profound insights into possible genetic contributions to chronic diseases including the inflammatory bowel diseases (IBDs), Crohn's disease and ulcerative colitis. To date, 163 distinct genetic risk loci have been associated with either Crohn's disease or ulcerative colitis, with a substantial degree of genetic overlap between these 2 conditions. Although many risk variants show a reproducible correlation with disease, individual gene associations only affect a subset of patients, and the functional contribution(s) of these risk variants to the onset of IBD is largely undetermined. Although studies in twins have demonstrated that the development of IBD is not mediated solely by genetic risk, it is nevertheless important to elucidate the functional consequences of risk variants for gene function in relevant cell types known to regulate key physiological processes that are compromised in IBD. This article will discuss IBD candidate genes that are known to be, or are suspected of being, involved in regulating the intestinal epithelial barrier and several of the physiological processes presided over by this dynamic and versatile layer of cells. This will include assembly and regulation of tight junctions, cell adhesion and polarity, mucus and glycoprotein regulation, bacterial sensing, membrane transport, epithelial differentiation, and restitution.

Associations between PTPN2 polymorphisms and susceptibility to ulcerative colitis and Crohn's disease: a meta-analysis

OBJECTIVE

Ulcerative colitis (UC) and Crohn's disease (CD) result from an interaction between genetic and environmental factors. Though several polymorphisms have been identified in PTPN2, their roles in the incidence of UC and CD are conflicting. This meta-analysis was aimed to clarify the impact of these polymorphisms on UC and CD risk.

METHOD

PubMed, EMBASE, Cochrane Library and CBM were searched until 23 July 2013 for eligible studies on three PTPN2 polymorphisms: rs2542151, rs1893217 and rs7234029. Data were extracted, and pooled odd ratios (ORs) as well as 95 % confidence intervals (95 % CIs) were calculated.

CONCLUSION

The meta-analysis indicated that rs2542151, rs1893217 and rs1893217 were associated with increased CD risk, while the former was associated with increased UC risk. The differences in age of onset and ethnic groups may influence the associations. Gene-gene and gene-environment interactions should be investigated in the future.

RESULTS

Seventeen studies with 18,308 cases and 20,406 controls were included. Significant associations were found between rs2542151 polymorphism and CD susceptibility (OR = 1.22, 95 % CI, 1.15-1.30, I (2) = 32 %), as well as between rs2542151 and UC susceptibility (OR = 1.16, 95 % CI, 1.07-1.25, I (2) = 39 %). A similar result was found in Caucasians, but not in Asians. Moreover, a significant increase in CD risk for all carriers of the minor allele of rs1893217 (OR = 1.45, 95 % CI, 1.23-1.70, I (2) = 0 %) and rs7234029 (OR = 1.36, 95 % CI, 1.16-1.59, I (2) = 0 %) were found. For children, the rs1893217 polymorphism appeared to confer susceptibility to CD (OR = 1.56, 95 % CI, 1.28-1.89, I (2) = 0 %).