Protein tyrosine phosphatases in hypothalamic insulin and leptin signaling

The hypothalamus is critical to the coordination of energy balance and glucose homeostasis. It responds to peripheral factors, such as insulin and leptin, that convey to the brain the degree of adiposity and the metabolic status of the organism. The development of leptin and insulin resistance in hypothalamic neurons appears to have a key role in the exacerbation of diet-induced obesity. In rodents, this has been attributed partly to the increased expression of the tyrosine phosphatases Protein Tyrosine Phosphatase 1B (PTP1B) and T cell protein tyrosine phosphatase (TCPTP), which attenuate leptin and insulin signaling. Deficiencies in PTP1B and TCPTP in the brain, or specific neurons, promote insulin and leptin signaling and prevent diet-induced obesity, type 2 diabetes mellitus (T2DM), and fatty liver disease. Although targeting phosphatases and hypothalamic circuits remains challenging, recent advances indicate that such hurdles might be overcome. Here, we focus on the roles of PTP1B and TCPTP in insulin and leptin signaling and explore their potential as therapeutic targets

TCPTP-deficiency in muscle does not alter insulin signalling and glucose homeostasis.

Aims/Hypothesis: Insulin activates the insulin receptor (IR) protein tyrosine kinase and downstream phosphatidylinositol-3-kinase (PI3K)/Akt signalling in muscle to promote glucose uptake. The IR can serve as a substrate for the protein tyrosine phosphatases (PTP) 1B and TCPTP, which share a striking 74% sequence identity in their catalytic domains. PTP1B is a validated therapeutic target for the alleviation of insulin resistance in type 2 diabetes. PTP1B dephosphorylates the IR in liver and muscle to regulate glucose homeostasis, whereas TCPTP regulates IR signalling and gluconeogenesis in the liver. In this study we have assessed for the first time the role of TCPTP in the regulation of IR signalling in muscle. Methods: We generated muscle-specific TCPTP-deficient (MCK-Cre;Ptpn2lox/lox) mice and assessed the impact on glucose homeostasis and muscle IR signalling in chow versus high fat fed mice. Results: Blood glucose and insulin levels, insulin and glucose tolerances and insulininduced muscle IR activation and downstream PI3K/Akt signalling remained unaltered in chow fe

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

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

Skeletal muscle NOX4 is required for adaptive responses that prevent insulin resistance

Reactive oxygen species (ROS) generated during exercise are considered integral for the health-promoting effects of exercise. However, the precise mechanisms by which exercise and ROS promote metabolic health remain unclear. Here, we demonstrate that skeletal muscle NADPH oxidase 4 (NOX4), which is induced after exercise, facilitates ROS-mediated adaptive responses that promote muscle function, maintain redox balance, and prevent the development of insulin resistance. Conversely, reductions in skeletal muscle NOX4 in aging and obesity contribute to the development of insulin resistance. NOX4 deletion in skeletal muscle compromised exercise capacity and antioxidant defense and promoted oxidative stress and insulin resistance in aging and obesity. The abrogated adaptive mechanisms, oxidative stress, and insulin resistance could be corrected by deleting the H2O2-detoxifying enzyme GPX-1 or by treating mice with an agonist of NFE2L2, the master regulator of antioxidant defense. These findings causally link NOX4-derived ROS in skeletal muscle with adaptive responses that promote muscle function and insulin sensitivity

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

PTPN2, Distinctively Expressed in GCB-Like and ABC-Like DLBCL, Is the Nuclear Phosphatase of STAT6

Abstract Gene expression profiling studies sub-classified diffuse large B-cell lymphomas (DLBCL) into two clinically distinct types: Germinal Center B cell (GCB)-like and Activated B-cell (ABC)-like tumors, characterized by long and short survival, respectively. We have recently reported distinct responsiveness of GCB-like and ABC-like DLBCL cell lines to IL-4 stimulation. In GCB-like lymphoma cells, IL-4 leads to nuclear accumulation of phosphorylated signal transducer and activator of transcription 6 (STAT6) and induction of IL-4 target genes, while in ABC-like tumor cells there is an increased nuclear dephosphorylation of pSTAT6 and no induction of IL-4 target genes (Lu et al: Blood2005;105:2924). Furthermore, GCB-like and ABC-like DLBCL tumors exhibit a different expression profile of protein tyrosine phosphatases (PTPs). Among the distinctively expressed PTPs, only 45kDa isoform of protein tyrosine phosphatase non-receptor type 2 (PTPN2, also known as T-cell PTP-TCPTP) localizes to the nucleus. Despite PTPN2–45 having an apparent exclusively nuclear localization in resting cells, specific stimuli can induce PTPN2–45 shuttling to the cytoplasm, thus gaining access to the cytoplasmic substrates, such as the epidermal growth factor (EGF) receptor, the insulin receptor, Src family kinases, adaptor protein p52 Shc and Janus protein tyrosine kinases (JAK 1 and 3), thereby regulating multiple intracellular signaling pathways. In contrast, STAT1, 5A and 5B are the only to date known PTPN2-45 nuclear substrates. Substrate identification is a crucial step in delineating the functional spectrum of PTPN2 in vivo. Herein, we demonstrate that STAT6 may serve as a physiological nuclear substrate of PTPN2-45. Over-expression of PTPN2 leads to nuclear STAT6 dephosphorylation. By using a nuclear restricted version of PTPN2 (pEGFP-PTPN2), we show that the dephosphorylation of STAT6 is independent of PTPN2 induced JAK dephosphorylation. We demonstrate interactions between endogenous PTPN2 and STAT6 and delineate the STAT6 and PTPN2 protein domains responsible for the interaction: the catalytic domain of PTPN2 and the C terminal transactivation domain of STAT6. Furthermore, we demonstrate that over-expression of PTPN2 ameliorates IL-4 induced expression of its target genes in GCB-like DLBCL tumor cells. We observe tight control of PTPN2 at different differentiation levels of B cell lymphocytes thus suggesting that distinct expression of PTPN2 in GCB-like and ABC-like DLBCL tumors stems from different cellular origin of these lymphomas. Our findings identify STAT6 as a new nuclear target of PTPN2 and suggest that distinct PTPs expression profiles may contribute to different biological characteristics of GCB-like and ABC-like DLBCL