T-Cell Protein Tyrosine Phosphatase Attenuates STAT3 and Insulin Signaling in the Liver to Regulate Gluconeogenesis

OBJECTIVE: Insulin-induced phosphatidylinositol 3-kinase (PI3K)/Akt signaling and interleukin-6 (IL-6)-instigated JAK/STAT3-signaling pathways in the liver inhibit the expression of gluconeogenic genes to decrease hepatic glucose output. The insulin receptor (IR) and JAK1 tyrosine kinases and STAT3 can serve as direct substrates for the T-cell protein tyrosine phosphatase (TCPTP). Homozygous TCPTP-deficiency results in perinatal lethality prohibiting any informative assessment of TCPTP's role in glucose homeostasis. Here we have used Ptpn2+/- mice to investigate TCPTP's function in glucose homeostasis. RESEARCH DESIGN AND METHODS: We analyzed insulin sensitivity and gluconeogenesis in chow versus high-fat-fed (HFF) Ptpn2+/- and Ptpn2+/+ mice and insulin and IL-6 signaling and gluconeogenic gene expression in Ptpn2+/- and Ptpn2+/+ hepatocytes. RESULTS: HFF Ptpn2+/- mice exhibited lower fasted blood glucose and decreased hepatic glucose output as determined in hyperinsulinemic euglycemic clamps and by the decreased blood glucose levels in pyruvate tolerance tests. The reduced hepatic glucose output coincided with decreased expression of the gluconeogenic genes G6pc and Pck1 and enhanced hepatic STAT3 phosphorylation and PI3K/Akt signaling in the fasted state. Insulin-induced IR-beta-subunit Y1162/Y1163 phosphorylation and PI3K/Akt signaling and IL-6-induced STAT3 phosphorylation were also enhanced in isolated Ptpn2+/- hepatocytes. The increased insulin and IL-6 signaling resulted in enhanced suppression of G6pc and Pck1 mRNA. CONCLUSIONS: Liver TCPTP antagonises both insulin and STAT3 signaling pathways to regulate gluconeogenic gene expression and hepatic glucose output

Leptin and Insulin Act on POMC Neurons to Promote the Browning of White Fat

SummaryThe primary task of white adipose tissue (WAT) is the storage of lipids. However, “beige” adipocytes also exist in WAT. Beige adipocytes burn fat and dissipate the energy as heat, but their abundance is diminished in obesity. Stimulating beige adipocyte development, or WAT browning, increases energy expenditure and holds potential for combating metabolic disease and obesity. Here, we report that insulin and leptin act together on hypothalamic neurons to promote WAT browning and weight loss. Deletion of the phosphatases PTP1B and TCPTP enhanced insulin and leptin signaling in proopiomelanocortin neurons and prevented diet-induced obesity by increasing WAT browning and energy expenditure. The coinfusion of insulin plus leptin into the CNS or the activation of proopiomelanocortin neurons also increased WAT browning and decreased adiposity. Our findings identify a homeostatic mechanism for coordinating the status of energy stores, as relayed by insulin and leptin, with the central control of WAT browning

Ptpn2 and KLRG1 regulate the generation and function of tissue-resident memory CD8 + T cells in skin

Tissue-resident memory T cells (T cells) are key elements of tissue immunity. Here, we investigated the role of the regulator of T cell receptor and cytokine signaling, Ptpn2, in the formation and function of T cells in skin. Ptpn2-deficient CD8 T cells displayed a marked defect in generating CD69 CD103 T cells in response to herpes simplex virus type 1 (HSV-1) skin infection. This was accompanied by a reduction in the proportion of KLRG1 memory precursor cells and a transcriptional bias toward terminal differentiation. Of note, forced expression of KLRG1 was sufficient to impede T cell formation. Normalizing memory precursor frequencies by transferring equal numbers of KLRG1− cells restored T generation, demonstrating that Ptpn2 impacted skin seeding with precursors rather than downstream T cell differentiation. Importantly, Ptpn2-deficient T cells augmented skin autoimmunity but also afforded superior protection from HSV-1 infection. Our results emphasize that KLRG1 repression is required for optimal T cell formation in skin and reveal an important role of Ptpn2 in regulating TRM cell functionality.K. Hochheiser was supported by the German Research Council (grant HO 5417/1-1) and is a Rhian and Paul Brazis Fellow in Translational Melanoma Immunology administered by the Peter MacCallum Cancer Foundation. T. Gebhardt is a Senior Biomedical Research Fellow supported by the Sylvia and Charles Viertel Charitable Foundatio

T-cell–specific PTPN2 deficiency in NOD mice accelerates the development of type 1 diabetes and autoimmune comorbidities

Genome-wide association studies have identified PTPN2 as an important non-major histocompatibility complex gene for autoimmunity. Single nucleotide polymorphisms that reduce PTPN2 expression have been linked with the development of varied autoimmune disorders, including type 1 diabetes. The tyrosine-phosphatase PTPN2 attenuates T cell receptor and cytokine signalling in T cells to maintain peripheral tolerance, but the extent to which PTPN2-deficiency in T cells might influence type 1 diabetes onset remains unclear. Non-Obese Diabetic (NOD) mice develop spontaneous autoimmune type 1 diabetes, similar to that seen in humans. T cell PTPN2-deficiency in NOD mice markedly accelerated the onset and increased the incidence of type 1 diabetes, as well as that of other disorders, including colitis and Sjogren’s syndrome. Although PTPN2-deficiency in CD8+ T cells alone was able to drive the destruction of pancreatic β cells and onset of diabetes, T cell-specific PTPN2-deficiency was also accompanied by increased CD4+ T-helper type 1 differentiation and T follicular helper cell polarisation and an increased abundance of B cells in pancreatic islets as seen in human type 1 diabetes. These findings causally link PTPN2-deficiency in T cells with the development of type 1 diabetes and associated autoimmune co-morbidities

T cell receptor reversed polarity recognition of a self-antigen major histocompatibility complex

Central to adaptive immunity is the interaction between the αβ T cell receptor (TCR) and peptide presented by the major histocompatibility complex (MHC) molecule. Presumably reflecting TCR-MHC bias and T cell signaling constraints, the TCR universally adopts a canonical polarity atop the MHC. We report the structures of two TCRs, derived from human induced T regulatory (iTreg) cells, complexed to an MHC class II molecule presenting a proinsulin-derived peptide. The ternary complexes revealed a 180° polarity reversal compared to all other TCR-peptide-MHC complex structures. Namely, the iTreg TCR α-chain and β-chain are overlaid with the α-chain and β-chain of MHC class II, respectively. Nevertheless, this TCR interaction elicited a peptide-reactive, MHC-restricted T cell signal. Thus TCRs are not 'hardwired' to interact with MHC molecules in a stereotypic manner to elicit a T cell signal, a finding that fundamentally challenges our understanding of TCR recognition

Reversed T cell receptor docking on a major histocompatibility class I complex limits involvement in the immune response

The anti-viral T cell response is drawn from the naive T cell repertoire. During influenza infection, the CD8+ T cell response to an H-2Db-restricted nucleoprotein epitope (NP366) is characterized by preferential expansion of T cells bearing TRBV13+ T cell receptors (TCRs) and avoidance of TRBV17+ T cells, despite the latter dominating the naive precursor repertoire. We found two TRBV17+ TCRs that bound H-2Db-NP366 with a 180° reversed polarity compared to the canonical TCR-pMHC-I docking. The TRBV17 β-chain dominated the interaction and, whereas the complementarity determining region-3 (CDR3) loops exclusively mediated contacts with the MHC-I, peptide specificity was attributable to germline-encoded recognition. Nevertheless, the TRBV17+ TCR exhibited moderate affinity toward H-2Db-NP366 and was capable of signal transduction. Thus, the naive CD8+ T cell pool can comprise TCRs adopting reversed pMHC-I docking modes that limit their involvement in the immune response

Strain-Dependent Differences in Bone Development, Myeloid Hyperplasia, Morbidity and Mortality in Ptpn2-Deficient Mice

Single nucleotide polymorphisms in the gene encoding the protein tyrosine phosphatase TCPTP (encoded by PTPN2) have been linked with the development of autoimmunity. Here we have used Cre/LoxP recombination to generate Ptpn2ex2−/ex2− mice with a global deficiency in TCPTP on a C57BL/6 background and compared the phenotype of these mice to Ptpn2−/− mice (BALB/c-129SJ) generated previously by homologous recombination and backcrossed onto the BALB/c background. Ptpn2ex2−/ex2− mice exhibited growth retardation and a median survival of 32 days, as compared to 21 days for Ptpn2−/− (BALB/c) mice, but the overt signs of morbidity (hunched posture, piloerection, decreased mobility and diarrhoea) evident in Ptpn2−/− (BALB/c) mice were not detected in Ptpn2ex2−/ex2− mice. At 14 days of age, bone development was delayed in Ptpn2−/− (BALB/c) mice. This was associated with increased trabecular bone mass and decreased bone remodeling, a phenotype that was not evident in Ptpn2ex2−/ex2− mice. Ptpn2ex2−/ex2− mice had defects in erythropoiesis and B cell development as evident in Ptpn2−/− (BALB/c) mice, but not splenomegaly and did not exhibit an accumulation of myeloid cells in the spleen as seen in Ptpn2−/− (BALB/c) mice. Moreover, thymic atrophy, another feature of Ptpn2−/− (BALB/c) mice, was delayed in Ptpn2ex2−/ex2− mice and preceded by an increase in thymocyte positive selection and a concomitant increase in lymph node T cells. Backcrossing Ptpn2−/− (BALB/c) mice onto the C57BL/6 background largely recapitulated the phenotype of Ptpn2ex2−/ex2− mice. Taken together these results reaffirm TCPTP's important role in lymphocyte development and indicate that the effects on morbidity, mortality, bone development and the myeloid compartment are strain-dependent

PTPN2-deficiency exacerbates T follicular helper cell and B cell responses and promotes the development of autoimmunity

Non-coding single nucleotide polymorphisms that repress PTPN2 expression have been linked with the development of type 1 diabetes, rheumatoid arthritis and Crohn's disease. PTPN2 attenuates CD8þ T cell responses to self and prevents overt autoreactivity in the context of T cell homeostasis and antigen crosspresentation. The role of PTPN2 in other immune subsets in the development of autoimmunity remains unclear. Here we show that the inducible deletion of PTPN2 in hematopoietic compartment of adult nonautoimmune prone mice results in systemic inflammation and autoimmunity. PTPN2-deficient mice had increased inflammatory monocytes, B cells and effector T cells in lymphoid and non-lymphoid tissues and exhibited symptoms of dermatitis, glomerulonephritis, pancreatitis and overt liver disease. Autoimmunity was characterised by the formation of germinal centers in the spleen and associated with markedly increased germinal center B cells and T follicular helper (Tfh) cells and circulating anti-nuclear antibodies, inflammatory cytokines and immunoglobulins. CD8þ T cell proliferative responses were enhanced, and interleukin-21-induced STAT-3 signalling in Tfh cells and B cells was increased and accompanied by enhanced B cell proliferation ex vivo. These results indicate that deficiencies in PTPN2 across multiple immune lineages, including naive T cells, Tfh cells and B cells, contribute to the development of autoimmunityThis work was supported by the National Health and Medical Research Council (NHMRC) of Australia (1047055); T.T. is a NHMRC Principal Research Fellow (1103037)

Induction of novel cytokines and chemokines by advanced glycation endproducts determined with a cytometric bead array

Advanced glycation endproducts (AGEs) accumulate on long-lived protein deposits, e.g. those composed of β2-microglobulin (in dialysis-related amyloidosis) or β-amyloid peptide (in Alzheimer's disease). When AGEs bind to the "receptor for advanced glycation endproducts", they activate redox-sensitive transcription factors such as NF-κB, and subsequently induce the expression of pro-inflammatory cytokines such as IL-1, IL-6 and TNF-α. Using a cytokine bead array, we have further analyzed the Bovine Serum Albumin (BSA)-AGE induced expression of selected cytokines/chemokines in two murine cell lines, RAW 264.7 macrophages and N-11 microglia. Our study showed that monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor (TNF-α) were both released in a time-dependent manner from both RAW 264.7 macrophages and N-11 microglia upon stimulation with BSA-AGE or lipopolysaccharide (LPS), which was used as a positive control. Interestingly, MCP-1 was also constitutively expressed by unstimulated cells, although at a lower levels. Much higher levels of IL-6 were secreted by RAW 264.7 macrophages than by N-11 microglia in response to both stimuli. IL-12p70, interferon-γ and the anti-inflammatory cytokine IL-10 were not induced by either LPS or BSA-AGE. Our results indicate a very similar pattern of chemokine and cytokine expression induced by such different ligands as AGEs and LPS indicating similar or convergent downstream signaling pathways

TNF but not Fas ligand provides protective anti-L. major immunity in C57BL/6 mice

The pro-inflammatory cytokine TNF is essential for a protective immune response to some but not all strains of Leishmania major. TNF-deficient mice of a resistant genetic background succumbed rapidly to an infection with L. major BNI. Another member of the TNF superfamily, Fas ligand (FasL), has also been reported to be critical for the immune response to L. major. To test the relative importance of TNF versus FasL for the control of L. major BNI, we infected wildtype C57BL/6 (B6.WT), B6.TNF–/–, B6.gld and C57BL/6.gld x TNF–/– (B6.gld.TNF–/–) double-negative mice. Visceral, fatal disease was only observed in B6.TNF–/– mice, but not in B6 gld mice. The course of infection and the immune response of B6.gld.TNF–/– mice were similar to those of B6.TNF–/– mice. B6.gld.TNF–/– mice had a high tissue parasite burden and expressed prominent amounts of inducible nitric oxide synthase (iNOS) in the skin, the lymph nodes (LN) and the spleen as previously reported for B6.TNF–/– mice, whereas the tissue parasite load and the iNOS expression of B6.gld mice resembled that of B6.WT controls. Neither the TNF- nor the FasL-deficiency exerted a detectable intrinsic effect on the proliferation of T cells. Thus, TNF, but not FasL is essential for the control of L. major BNI. The discrepancy between these and other published data are most likely due to the use of different strains of the pathogen