Marked impairment of protein tyrosine phosphatase 1B activity in adipose tissue of obese subjects with and without type 2 diabetes mellitus

Multireceptor Analysis for Evaluating the Antidiabetic Efficacy of Karanjin: A Computational Approach

BACKGROUND

Diabetes mellitus, notably type 2, is a rising global health challenge, prompting the need for effective management strategies. Common medications such as metformin, insulin, repaglinide and sitagliptin can induce side effects like gastrointestinal disturbances, hypoglycemia, weight gain and specific organ risks. Plant-derived therapies like Karanjin from Pongamia pinnata present promising alternatives due to their historical use, holistic health benefits and potentially fewer adverse effects. This study employs in silico analysis to explore Karanjin's interactions with diabetes-associated receptors, aiming to unveil its therapeutic potential while addressing the limitations and side effects associated with conventional medications.

METHODOLOGY

The research encompassed the selection of proteins from the Protein Data Bank (PDB), followed by structural refinement processes and optimization. Ligands such as Karanjin and standard drugs were retrieved from PubChem, followed by a comprehensive analysis of their ADMET profiling and pharmacokinetic properties. Protein-ligand interactions were evaluated through molecular docking using AutoDockTools 1.5.7, followed by the analysis of structural stability using coarse-grained simulations with CABS Flex 2.0. Molecular dynamics simulations were performed using Desmond 7.2 and the OPLS4 force field to explore how Karanjin interacts with proteins over 100 nanoseconds, focusing on the dynamics and structural stability.

RESULTS

Karanjin, a phytochemical from Pongamia pinnata, shows superior drug candidate potential compared to common medications, offering advantages in efficacy and reduced side effects. It adheres to drug-likeness criteria and exhibits optimal ADMET properties, including moderate solubility, high gastrointestinal absorption and blood-brain barrier penetration. Molecular docking revealed Karanjin's highest binding energy against receptor 3L2M (Pig pancreatic alpha-amylase) at -9.1 kcal/mol, indicating strong efficacy potential. Molecular dynamics simulations confirmed stable ligand-protein complexes with minor fluctuations in RMSD and RMSF, suggesting robust interactions with receptors 3L2M.

CONCLUSION

Karanjin demonstrates potential in pharmaceutical expansion for treating metabolic disorders such as diabetes, as supported by computational analysis. Prospects for Karanjin in pharmaceutical development include structural modifications for enhanced efficacy and safety. Nanoencapsulation may improve bioavailability and targeted delivery to pancreatic cells, while combination therapies could optimize treatment outcomes in diabetes management. Clinical trials and experimental studies are crucial to validate its potential as a novel therapeutic agent.

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.

Bioinformatics Analysis of Next Generation Sequencing Data Identifies Molecular Biomarkers Associated With Type 2 Diabetes Mellitus

Background

Type 2 diabetes mellitus (T2DM) is the most common metabolic disorder. The aim of the present investigation was to identify gene signature specific to T2DM.

Methods

The next generation sequencing (NGS) dataset GSE81608 was retrieved from the gene expression omnibus (GEO) database and analyzed to identify the differentially expressed genes (DEGs) between T2DM and normal controls. Then, Gene Ontology (GO) and pathway enrichment analysis, protein-protein interaction (PPI) network, modules, miRNA (micro RNA)-hub gene regulatory network construction and TF (transcription factor)-hub gene regulatory network construction, and topological analysis were performed. Receiver operating characteristic curve (ROC) analysis was also performed to verify the prognostic value of hub genes.

Results

A total of 927 DEGs (461 were up regulated and 466 down regulated genes) were identified in T2DM. GO and REACTOME results showed that DEGs mainly enriched in protein metabolic process, establishment of localization, metabolism of proteins, and metabolism. The top centrality hub genes APP, MYH9, TCTN2, USP7, SYNPO, GRB2, HSP90AB1, UBC, HSPA5, and SQSTM1 were screened out as the critical genes. ROC analysis provides prognostic value of hub genes.

Conclusion

The potential crucial genes, especially APP, MYH9, TCTN2, USP7, SYNPO, GRB2, HSP90AB1, UBC, HSPA5, and SQSTM1, might be linked with risk of T2DM. Our study provided novel insights of T2DM into genetics, molecular pathogenesis, and novel therapeutic targets.

N-myristoylation regulates insulin-induced phosphorylation and ubiquitination of Caveolin-2 for insulin signaling

N-myristoylation is a ubiquitous protein lipidation in eukaryotes, but regulatory roles for myristoylation on proteins still remain to be explored. Here, we show that N-myristoylation of Caveolin-2 (Cav-2) controls insulin signaling. Alternative translation initiation (ATI)-yielded truncated form of non-N-myristoylable Cav-2β and various conditional Cav-2 mutants were compared to full-length form of N-myristoylable Cav-2α. Insulin induced insulin receptor (IR) tyrosine kinase-catalyzed Tyr-19 phosphorylation of N-myristoylable M14A Cav-2 and triggered activation of IR signaling cascade. In contrast, insulin induced ubiquitination of non-N-myristoylable M1A and G2A Cav-2 to facilitate protein-tyrosine phosphatase 1B interaction with IR which desensitized IR signaling through internalization. Metabolic labeling and click chemistry showed palmitoylation of M14A but not M1A and G2A Cav-2. Insulin did not induce phosphorylation of M1A and G2A Cav-2 and Cav-2β. Like Cav-2α, G2A Cav-2 and Cav-2β formed large homo-oligomers localized in lipid rafts. These findings show Cav-2 N-myristoylation plays a crucial role to coordinate its phosphorylation, palmitoylation, and ubiquitination to control insulin signaling.

Insulin Resistance-Related Proteins Are Overexpressed in Patients and Rats Treated With Olanzapine and Are Reverted by Pueraria in the Rat Model

BACKGROUND

Olanzapine, a commonly used second-generation antipsychotic, causes severe metabolic adverse effects, such as elevated blood glucose and insulin resistance (IR). Previous studies have proposed that overexpression of CD36, GGPPS, PTP-1B, GRK2, and adipose triglyceride lipase may contribute to the development of metabolic syndrome, and Pueraria could eliminate the metabolic adverse effects. The study aimed to investigate the association between olanzapine-associated IR and IR-related proteins (IRRPs) and determine the role of Pueraria in protection against the metabolic adverse effects of olanzapine.

METHODS

The expression levels of IRRPs were examined in schizophrenia patients and rat models with long-term olanzapine treatment. The efficacy of Pueraria on anti-IR by reducing the expression of IRRPs was comprehensively evaluated.

RESULTS

Our study demonstrated that in schizophrenia patients chronically treated with olanzapine, the expression levels of IRRPs in patients with a high IR index significantly increased, and these phenomena were further confirmed in a rat model. The expression levels of IRRPs were reduced significantly in Pueraria-treated IR rat models. The body weight, blood glucose, and IR index were restored to levels similar to those of normal controls.

CONCLUSIONS

The IRRPs are closely related to IR induced by olanzapine, and Pueraria could interfere with olanzapine-associated IR and revert overexpressed IRRPs. These findings suggest that IRRPs are key players in olanzapine-associated IR and that Pueraria has potential as a clinical drug to prevent the metabolic adverse effects of olanzapine, further improving compliance of schizophrenia patients.

Looking at Marine-Derived Bioactive Molecules as Upcoming Anti-Diabetic Agents: A Special Emphasis on PTP1B Inhibitors

Diabetes mellitus (DM) is a chronic metabolic disease with high morbimortality rates. DM has two types: type 1, which is often associated with a total destruction of pancreatic beta cells, and non-insulin-dependent or type 2 diabetes mellitus (T2DM), more closely associated with obesity and old age. The main causes of T2DM are insulin resistance and/or inadequate insulin secretion. Protein-tyrosine phosphatase 1B (PTP1B) negatively regulates insulin signaling pathways and plays an important role in T2DM, as its overexpression may induce insulin resistance. Thus, since PTP1B may be a therapeutic target for both T2DM and obesity, the search for novel and promising natural inhibitors has gained much attention. Hence, several marine organisms, including macro and microalgae, sponges, marine invertebrates, sea urchins, seaweeds, soft corals, lichens, and sea grasses, have been recently evaluated as potential drug sources. This review provides an overview of the role of PTP1B in T2DM insulin signaling and treatment, and highlights the recent findings of several compounds and extracts derived from marine organisms and their relevance as upcoming PTP1B inhibitors. In this systematic literature review, more than 60 marine-derived metabolites exhibiting PTP1B inhibitory activity are listed. Their chemical classes, structural features, relative PTP1B inhibitory potency (assessed by IC50 values), and structure⁻activity relationships (SARs) that could be drawn from the available data are discussed. The upcoming challenge in the field of marine research-metabolomics-is also addressed.

Alternative translation initiation of Caveolin-2 desensitizes insulin signaling through dephosphorylation of insulin receptor by PTP1B and causes insulin resistance

Insulin resistance, defined as attenuated sensitivity responding to insulin, impairs insulin action. Direct causes and molecular mechanisms of insulin resistance have thus far remained elusive. Here we show that alternative translation initiation (ATI) of Caveolin-2 (Cav-2) regulates insulin sensitivity. Cav-2β isoform yielded by ATI desensitizes insulin receptor (IR) via dephosphorylation by protein-tyrosine phosphatase 1B (PTP1B), and subsequent endocytosis and lysosomal degradation of IR, causing insulin resistance. Blockage of Cav-2 ATI protects against insulin resistance by preventing Cav-2β-PTP1B-directed IR desensitization, thereby normalizing insulin sensitivity and glucose uptake. Our findings show that Cav-2β is a negative regulator of IR signaling, and identify a mechanism causing insulin resistance through control of insulin sensitivity via Cav-2 ATI.

Oligonol promotes glucose uptake by modulating the insulin signaling pathway in insulin-resistant HepG2 cells via inhibiting protein tyrosine phosphatase 1B

Insulin resistance and protein tyrosine phosphatase 1B (PTP1B) overexpression are strongly associated with type 2 diabetes mellitus (T2DM), which is characterized by defects in insulin signaling and glucose intolerance. In a previous study, we demonstrated oligonol inhibits PTP1B and α-glucosidase related to T2DM. In this study, we examined the molecular mechanisms underlying the anti-diabetic effects of oligonol in insulin-resistant HepG2 cells. Glucose uptake was assessed using a fluorescent glucose tracer, 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose, and the signaling pathway was investigated by western blotting. Oligonol significantly increased insulin-provoked glucose uptake and decreased PTP1B expression, followed by modulation of ERK phosphorylation. In addition, oligonol activated insulin receptor substrate 1 by reducing phosphorylation at serine 307 and increasing that at tyrosine 895, and enhanced the phosphorylations of Akt and phosphatidylinositol 3-kinase. Interestingly, it also reduced the expression of two key enzymes of gluconeogenesis (glucose 6-phosphatase and phosphoenolpyruvate carboxykinase), attenuated oxidative stress by scavenging/inhibiting peroxynitrite, and reactive oxygen species (ROS) generation, and augmented the expression of nuclear factor kappa B. These findings suggest oligonol improved the insulin sensitivity of insulin-resistant HepG2 cells by attenuating the insulin signaling blockade and modulating glucose uptake and production. Furthermore, oligonol attenuated ROS-related inflammation and prevented oxidative damage in our in vitro model of type 2 diabetes. These result indicate oligonol has promising potential as a treatment for T2DM.

Promising Inhibitory Effects of Anthraquinones, Naphthopyrone, and Naphthalene Glycosides, from Cassia obtusifolia on α-Glucosidase and Human Protein Tyrosine Phosphatases 1B

The present work aims to evaluate the anti-diabetic potentials of 16 anthraquinones, two naphthopyrone glycosides, and one naphthalene glycoside from Cassia obtusifolia via inhibition against the protein tyrosine phosphatases 1B (PTP1B) and α-glucosidase. Among them, anthraquinones emodin and alaternin exhibited the highest inhibitory activities on PTP1B and α-glucosidase, respectively. Moreover, we examined the effects of alaternin and emodin on stimulation of glucose uptake by insulin-resistant human HepG2 cells. The results showed that alaternin and emodin significantly increased the insulin-provoked glucose uptake. In addition, our kinetic study revealed that alaternin competitively inhibited PTP1B, and showed mixed-type inhibition against α-glucosidase. In order to confirm enzyme inhibition, we predicted the 3D structure of PTP1B using Autodock 4.2 to simulate the binding of alaternin. The docking simulation results demonstrated that four residues of PTP1B (Gly183, Arg221, Ile219, Gly220) interact with three hydroxyl groups of alaternin and that the binding energy was negative (−6.30 kcal/mol), indicating that the four hydrogen bonds stabilize the open form of the enzyme and potentiate tight binding of the active site of PTP1B, resulting in more effective PTP1B inhibition. The results of the present study clearly demonstrate that C. obtusifolia and its constituents have potential anti-diabetic activity and can be used as a functional food for the treatment of diabetes and associated complications.

Pancreatic Protein Tyrosine Phosphatase 1B Deficiency Exacerbates Acute Pancreatitis in Mice

Acute pancreatitis (AP) is a common and devastating gastrointestinal disorder that causes significant morbidity. The disease starts as local inflammation in the pancreas that may progress to systemic inflammation and complications. Protein tyrosine phosphatase 1B (PTP1B) is implicated in inflammatory signaling, but its significance in AP remains unclear. To investigate whether PTP1B may have a role in AP, we used pancreas PTP1B knockout (panc-PTP1B KO) mice and determined the effects of pancreatic PTP1B deficiency on cerulein- and arginine-induced acute pancreatitis. We report that PTP1B protein expression was increased in the early phase of AP in mice and rats. In addition, histological analyses of pancreas samples revealed enhanced features of AP in cerulein-treated panc-PTP1B KO mice compared with controls. Moreover, cerulein- and arginine-induced serum amylase and lipase were significantly higher in panc-PTP1B KO mice compared with controls. Similarly, pancreatic mRNA and serum concentrations of the inflammatory cytokines IL-1B, IL-6, and tumor necrosis factor-α were increased in panc-PTP1B KO mice compared with controls. Furthermore, panc-PTP1B KO mice exhibited enhanced cerulein- and arginine-induced NF-κB inflammatory response accompanied with increased mitogen-activated protein kinases activation and elevated endoplasmic reticulum stress. Notably, these effects were recapitulated in acinar cells treated with a pharmacological inhibitor of PTP1B. These findings reveal a novel role for pancreatic PTP1B in cerulein- and arginine-induced acute pancreatitis.

Recent progress in studies on the health benefits of pyrroloquinoline quinone

Pyrroloquinoline quinone (PQQ), an aromatic tricyclic o-quinone, was identified initially as a redox cofactor for bacterial dehydrogenases. Although PQQ is not biosynthesized in mammals, trace amounts of PQQ have been found in human and rat tissues because of its wide distribution in dietary sources. Importantly, nutritional studies in rodents have revealed that PQQ deficiency exhibits diverse systemic responses, including growth impairment, immune dysfunction, and abnormal reproductive performance. Although PQQ is not currently classified as a vitamin, PQQ has been implicated as an important nutrient in mammals. In recent years, PQQ has been receiving much attention owing to its physiological importance and pharmacological effects. In this article, we review the potential health benefits of PQQ with a focus on its growth-promoting activity, anti-diabetic effect, anti-oxidative action, and neuroprotective function. Additionally, we provide an update of its basic pharmacokinetics and safety information in oral ingestion.

Fumosorinone, a novel PTP1B inhibitor, activates insulin signaling in insulin-resistance HepG2 cells and shows anti-diabetic effect in diabetic KKAy mice

Insulin resistance is a characteristic feature of type 2 diabetes mellitus (T2DM) and is characterized by defects in insulin signaling. Protein tyrosine phosphatase 1B (PTP1B) is a key negative regulator of the insulin signaling pathways, and its increased activity and expression are implicated in the pathogenesis of insulin resistance. Therefore, the inhibition of PTP1B is anticipated to become a potential therapeutic strategy to treat T2DM. Fumosorinone (FU), a new natural product isolated from insect fungi Isaria fumosorosea, was found to inhibit PTP1B activity in our previous study. Herein, the effects of FU on insulin resistance and mechanism in vitro and in vivo were investigated. FU increased the insulin-provoked glucose uptake in insulin-resistant HepG2 cells, and also reduced blood glucose and lipid levels of type 2 diabetic KKAy mice. FU decreased the expression of PTP1B both in insulin-resistant HepG2 cells and in liver tissues of diabetic KKAy mice. Furthermore, FU increased the phosphorylation of IRβ, IRS-2, Akt, GSK3β and Erk1/2 in insulin-resistant HepG2 cells, as well as the phosphorylation of IRβ, IRS-2, Akt in liver tissues of diabetic KKAy mice. These results showed that FU increased glucose uptake and improved insulin resistance by down-regulating the expression of PTP1B and activating the insulin signaling pathway, suggesting that it may possess antidiabetic properties.

Sustained high protein-tyrosine phosphatase 1B activity in the sperm of obese males impairs the sperm acrosome reaction

Evidence of a causal link between male obesity and subfertility or infertility has been demonstrated previously. However, the mechanism underlying this link is incompletely understood. Here, we report that sustained high protein-tyrosine phosphatase 1B (PTP1B) activity in sperm of obese donors plays an essential role in coupling male obesity and subfertility or infertility. First, PTP1B level and activity were significantly higher in sperm from ob/ob mice than in wild-type littermates. High PTP1B level and activity in sperm was also observed in obese patients compared with non-obese donors. The enhanced sperm PTP1B level and activity in ob/ob mice and obese patients correlated with a defect of the sperm acrosome reaction (AR). Second, treating sperm from male ob/ob mice or obese men with a specific PTP1B inhibitor largely restored the sperm AR. Finally, blockade of sperm AR by enhanced PTP1B activity in male ob/ob mice or obese men was due to prolonged dephosphorylation of N-ethylmaleimide-sensitive factor by PTP1B, leading to the inability to reassemble the trans-SNARE complexes, which is a critical step in sperm acrosomal exocytosis. In summary, our study demonstrates for the first time that a sustained high PTP1B level or activity in the sperm of obese donors causes a defect of sperm AR and that PTP1B is a novel potential therapeutic target for male infertility treatment.

Leptin signaling in skeletal muscle after bed rest in healthy humans

PURPOSE

This study aimed at determining the effects of bed rest on the skeletal muscle leptin signaling system.

METHODS

Deltoid and vastus lateralis muscle biopsies and blood samples were obtained from 12 healthy young men (mean ± SD, BMI 22.8 ± 2.7 kg/m(2)) before and after 7 days of bed rest. Leptin receptor isoforms (OB-Rs), suppressor of cytokine signaling 3 (SOCS3) and protein tyrosine phosphatase 1B (PTP1B) protein expression and signal transducer and activator of transcription 3 (STAT3) phosphorylation were analyzed by Western blot.

RESULTS

After bed rest basal insulin concentration was increased by 53% (P < 0.05), the homeostasis model assessment (HOMA) by 40% (P < 0.05), and serum leptin concentration by 35% (P < 0.05) with no changes in body fat mass. Although the soluble isoform of the leptin receptor (s-OBR) remained unchanged, the molar excess of leptin over sOB-R was increased by 1.4-fold after bed rest (P < 0.05). OB-Rs and SOCS3 protein expression, and STAT3 phosphorylation level remained unaffected in deltoid and vastus lateralis by bed rest, as PTP1B in the deltoid. PTP1B was increased by 90% with bed rest in the vastus lateralis (P < 0.05). There was a linear relationship between the increase in vastus lateralis PTP1B and the increase in both basal insulin concentrations (r = 0.66, P < 0.05) and HOMA (r = 0.68, P < 0.05) with bed rest.

CONCLUSIONS

One week of bed rest is associated with increased leptin levels without augmenting STAT3 phosphorylation indicating some degree of leptin resistance in skeletal muscle, which can be explained, at least in part, by an elevation of PTP1B protein content in the vastus lateralis muscle.

Protein tyrosine phosphatase 1B inhibits adipocyte differentiation and mediates TNFα action in obesity

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of systemic glucose and insulin homeostasis; however, its exact role in adipocytes is poorly understood. This study was to elucidate the role of PTP1B in adipocyte differentiation and its implication in obesity. During differentiation of 3T3-L1 white preadipocytes, PTP1B decreased progressively with adipocyte maturation. Lentivirus-mediated PTP1B overexpression in preadipocytes delayed adipocyte differentiation, shown as lack of mature adipocytes, low level of lipid accumulation, and down-regulation of main markers (PPARγ2, SREBP-1c, FAS and LPL). In contrast, lentivirus-mediated PTP1B knockdown accelerated adipocyte differentiation, demonstrated as full of mature adipocytes, high level of lipid accumulation, and up-regulation of main markers. Dominant-negative inhibition on endogenous PTP1B by lentivirus-mediated overexpression of PTP1B double mutant in Tyr-46 and Asp-181 residues (LV-D/A-Y/F) also stimulated adipogenesis, more efficient than PTP1B knockdown. Diet-induced obesity mice exhibited an up-regulation of PTP1B and TNFα accompanied by a down-regulation of PPARγ2 in white adipose tissue. TNFα recombinant protein impeded PTP1B reduction and inhibited adipocyte differentiation in vitro; this inhibitory effect was prevented by LV-D/A-Y/F. Moreover, PTP1B inhibitor treatment improved adipogenesis and suppressed TNFα in adipose tissue of obese mice. All together, PTP1B negatively regulates adipocyte development and may mediate TNFα action to impair adipocyte differentiation in obesity. Our study provides novel evidence for the importance of PTP1B in obesity and for the potential application of PTP1B inhibitors.

Protein Tyrosine Phosphatase 1B Variant Associated with Fat Distribution and Insulin Metabolism

Protein tyrosine phosphatase 1B (PTPN1) affects the regulation of insulin signaling and energy metabolism. We studied whether polymorphisms in the PTPN1 gene impact body fat distribution in the HERITAGE Family Study cohort in 502 white and 276 black subjects. Insulin sensitivity index, glucose disappearance index, acute insulin response to glucose (AIR(glucose)), and the disposition index (DI) were obtained from the frequently sampled intravenous glucose tolerance test. White subjects with the G82G at the PTPN1 IVS6+G82A polymorphism had higher body fat levels (p = 0.031) and sum of eight skinfolds (p = 0.003) and highest subcutaneous fat on the limbs (p = 0.002). G82A subjects had the lowest AIR(glucose) (p = 0.005) and disposition index (p = 0.040). Interaction effects between PTPN1 and leptin receptor gene variants influenced insulin sensitivity index and AIR(glucose) (p from 0.006 to 0.010). The variant PTPN1 Pro387Leu was associated with lower fasting insulin level (p = 0.035) and glucose disappearance index (p = 0.038). In summary, PTPN1 IVS6+G82G homozygotes showed higher levels of all measures of adiposity. G82 allele heterozygotes are potentially at higher risk for type 2 diabetes. Gene-gene interactions between the PTPN1 and leptin receptor genes contributed to the phenotypic variability of insulin sensitivity. The PTPN1 Pro387Leu variant was associated with lower glucose tolerance.

Skeletal muscle protein tyrosine phosphatase 1B regulates insulin sensitivity in African Americans

Protein tyrosine phosphatase 1B (PTP1B) is postulated to modulate insulin action by dephosphorylating the insulin receptor signaling proteins and attenuating insulin signaling. We sought to determine the relationship of skeletal muscle PTP1B to whole-body insulin sensitivity. We studied 17 African Americans with type 2 diabetes mellitus (T2DM) and 16 without diabetes. PTP1B gene expression and protein abundance were determined in the biopsied skeletal muscles at the baseline of a hyperinsulinemic-euglycemic clamp. PTP1B gene expression was significantly higher in subjects with T2DM versus control (P < 0.0001) and remained significantly different after adjusting for age and insulin sensitivity (P = 0.05). PTP1B gene expression was positively related to protein abundance (r(s) = 0.39; P = 0.03; adjusted for age and insulin sensitivity) and negatively related to insulin sensitivity (r(s) = -0.52; P = 0.002; adjusted for age). Overexpression and interference RNA of PTP1B were performed in primary human skeletal muscle culture. PTP1B overexpression resulted in reduction of Akt phosphorylation in the control subjects. Moreover, interference RNA transfection downregulated PTP1B expression and enhanced Akt phosphorylation in subjects with T2DM. These data show that skeletal muscle PTP1B gene expression is increased in African American subjects with T2DM, is negatively associated with whole-body insulin sensitivity, and contributes to modulation of insulin signaling.

Adipose-specific deletion of Src homology phosphatase 2 does not significantly alter systemic glucose homeostasis

The SH2 domain-containing protein-tyrosine phosphatase Src homology phosphatase 2 (Shp2) has been implicated in a variety of growth factor signaling pathways, but its metabolic role in some peripheral insulin-responsive tissues remains unknown. To address the metabolic function of Shp2 in adipose tissue, we generated mice with adipose-specific Shp2 deletion using adiponectin-Cre transgenic mice. We then analyzed insulin sensitivity, glucose tolerance, and body mass in adipose-specific Shp2-deficient and control mice on regular chow and high-fat diet (HFD). Control mice on HFD exhibited increased Shp2 expression in various adipose depots compared with those on regular chow. Adiponectin-Cre mice enabled efficient and specific deletion of Shp2 in adipose tissue. However, adipose Shp2 deletion did not significantly alter body mass in mice on chow or HFD. In addition, mice with adipose Shp2 deletion exhibited comparable insulin sensitivity and glucose tolerance compared with controls. Consistent with this, basal and insulin-stimulated Erk and Akt phosphorylations were comparable in adipose tissue of Shp2-deficient and control mice. Our findings indicate that adipose-specific Shp2 deletion does not significantly alter systemic insulin sensitivity and glucose homeostasis.

Glucose regulates RMI1 expression through the E2F pathways in adipose cells

RecQ-mediated genome instability 1 (RMI1) has been identified as a novel energy homeostasis-related molecule. While recent studies have suggested that change in RMI1 expression levels in adipose tissue may affect the body's energy balance, no reports have identified the mechanism behind this expression regulation. In the present study, we found that RMI1 expression increased on differentiation of 3T3-L1 fibroblasts to adipocytes. In addition, glucose stimulation induced RMI1 expression to approximately eight times the baseline level. Further, knockdown of either E2F5 or E2F8 mRNA using siRNA suppressed this glucose-induced up-regulation of RMI1 expression. These results suggest that RMI1 expression may be regulated by glucose, at least in part, via E2F expression.

Pharmacological profiles of a novel protein tyrosine phosphatase 1B inhibitor, JTT-551

AIM

Protein tyrosine phosphatase 1B (PTP1B), a negative regulator of insulin signalling, is a novel therapeutic target for type 2 diabetes mellitus. We evaluated in vitro and in vivo the pharmacological profiles of a new PTP1B inhibitor, JTT-551: monosodium ({[5-(1,1-dimethylethyl)thiazol-2-yl]methyl} {[(4-{4-[4-(1-propylbutyl)phenoxy]methyl}phenyl)thiazol-2-yl]methyl}amino)acetate.

METHODS

PTP1B inhibitory activity and the inhibition mode were assayed with p-nitrophenyl phosphate as a substrate, and the selectivity of JTT-551 against other PTPs, including T-cell protein tyrosine phosphatase (TCPTP), CD45 protein tyrosine phosphatase (CD45) and leucocyte common antigen-related protein tyrosine phosphatase (LAR), was evaluated. Glucose uptake with JTT-551 treatment was evaluated in L6 rat skeletal myoblasts (L6 cells). In the in vivo study, we investigated the effects on insulin receptor (IR) phosphorylation and blood chemical parameters with JTT-551 administration in ob/ob mice and db/db mice.

RESULTS

JTT-551 showed an inhibitory effect on PTP1B with a Ki value of 0.22 microM, and a mixed-type inhibition mode. Ki values of TCPTP, CD45 and LAR were 9.3, 30 or higher and 30 or higher microM, respectively, and JTT-551 exhibited clear selectivity against the other PTPs. Moreover, JTT-551 increased the insulin-stimulated glucose uptake in L6 cells. A single administration of JTT-551 in ob/ob mice enhanced the IR phosphorylation of liver and reduced the glucose level. In db/db mice, chronic administration showed a hypoglycaemic effect without an acceleration of body weight gain.

CONCLUSIONS

JTT-551, a newly developed PTP1B inhibitor, improves glucose metabolism by enhancement of insulin signalling and could be useful in the treatment of type 2 diabetes mellitus.

Leptin receptor 170 kDa (OB-R170) protein expression is reduced in obese human skeletal muscle: a potential mechanism of leptin resistance

To examine whether obesity-associated leptin resistance could be due to down-regulation of leptin receptors (OB-Rs) and/or up-regulation of suppressor of cytokine signalling 3 (SOCS3) and protein tyrosine phosphatase 1B (PTP1B) in skeletal muscle, which blunt janus kinase 2-dependent leptin signalling and signal transducer and activator of transcription 3 (STAT3) phosphorylation and reduce AMP-activated protein kinase (AMPK) and acetyl-coenzyme A carboxylase (ACC) phosphorylation. Deltoid and vastus lateralis muscle biopsies were obtained from 20 men: 10 non-obese control subjects (mean +/- s.d. age, 31 +/- 5 years; height, 184 +/- 9 cm; weight, 91 +/- 13 kg; and percentage body fat, 24.8 +/- 5.8%) and 10 obese (age, 30 +/- 7 years; height, 184 +/- 8 cm; weight, 115 +/- 8 kg; and percentage body fat, 34.9 +/- 5.1%). Skeletal muscle OB-R170 (OB-R long isoform) protein expression was 28 and 25% lower (both P < 0.05) in arm and leg muscles, respectively, of obese men compared with control subjects. In normal-weight subjects, SOCS3 protein expression, and STAT3, AMPKalpha and ACCbeta phosphorylation, were similar in the deltoid and vastus lateralis muscles. In obese subjects, the deltoid muscle had a greater amount of leptin receptors than the vastus lateralis, whilst SOCS3 protein expression was increased and basal STAT3, AMPKalpha and ACCbeta phosphorylation levels were reduced in the vastus lateralis compared with the deltoid muscle (all P < 0.05). In summary, skeletal muscle leptin receptors and leptin signalling are reduced in obesity, particularly in the leg muscles.

Identification of pongamol and karanjin as lead compounds with antihyperglycemic activity from Pongamia pinnata fruits

AIM OF THE STUDY

To identify pongamol and karanjin as lead compounds with antihyperglycemic activity from Pongamia pinnata fruits.

MATERIAL AND METHODS

Streptozotocin-induced diabetic rats and hyperglycemic, hyperlipidemic and hyperinsulinemic db/db mice were used to investigate the antihyperglycemic activity of pongamol and karangin isolated from the fruits of Pongamia pinnata.

RESULTS

In streptozotocin-induced diabetic rats, single dose treatment of pongamol and karanjin lowered the blood glucose level by 12.8% (p<0.05) and 11.7% (p<0.05) at 50mg /kg dose and 22.0% (p<0.01) and 20.7% (p<0.01) at 100mg/kg dose, respectively after 6h post-oral administration. The compounds also significantly lowered blood glucose level in db/db mice with percent activity of 35.7 (p<0.01) and 30.6 (p<0.01), respectively at 100mg/kg dose after consecutive treatment for 10 days. The compounds were observed to exert a significant inhibitory effect on enzyme protein tyrosine phosphatase-1B (EC 3.1.3.48).

CONCLUSION

The results showed that pongamol and karangin isolated from the fruits of Pongamia pinnata possesses significant antihyperglycemic activity in Streptozotocin-induced diabetic rats and type 2 diabetic db/db mice and protein tyrosine phosphatase-1B may be the possible target for their activity.

Association of protein tyrosine phosphatases (PTPs)-1B with c-Met receptor and modulation of corneal epithelial wound healing

PURPOSE

The purpose of this study was to investigate the expression and activity of protein tyrosine phosphatases (PTPs) in epithelium during corneal wound healing and to investigate how PTPs regulate activation of the c-Met receptor and the receptor's proximal signaling.

METHODS

Rabbit corneas were injured by gentle scraping of the surface, leaving the limbal epithelium intact, and epithelium was collected at 1, 2, 3, and 7 days after injury. In organ culture models, epithelium was removed and corneas were incubated with hepatocyte growth factor (HGF), with or without the PTP inhibitor bpV(phen), and the PI-3K inhibitors wortmannin and LY294002. Human corneal epithelial (HCE) cells were stimulated with HGF with or without bpV(phen). Total cell lysates and cytosolic and membrane fractions were analyzed by Western blot. PTP activities were measured with specific substrates. PTP1B and SHP-2 genes were knocked down by interference RNA (siRNA).

RESULTS

PTP activity and expression increased during wound healing. The most abundant were SHP-2, PTP1B, and PTEN. HGF activated the c-Met receptor in HCE cells up to 30 minutes and was downregulated by 2 hours. Inhibition of PTPs increased HGF-promoted wound healing, HGF-activated phosphorylation of c-Met, and its downstream signal PI-3K/Akt, but not ERK1/2 or p70S6K. PTP1B and SHP-2 were bound to the c-Met. Part of the c-Met was colocalized in the endoplasmic reticulum with PTP1B. PTP1B phosphorylation increased when the c-Met receptor was deactivated, and gene knockdown of PTP1B increased c-Met activation. SHP-2 phosphorylation and binding to c-Met was higher during receptor activation, and SHP-2 gene silencing decreased receptor phosphorylation.

CONCLUSIONS

Inhibition of PTP activity mimics the effect of HGF by activating the PI-3K/Akt signal involved in wound healing. PTP1B and SHP-2 are bound to the c-Met receptor to control its activity. Although the binding of PTP1B increases when there is a decrease in c-Met activation and acts as a negative regulator of the receptor, the increased binding and phosphorylation of SHP-2 coincide with maximal stimulation of c-Met, acting as a positive regulator.

Central and peripheral neuroendocrine peptides and signalling in appetite regulation: considerations for obesity pharmacotherapy

Appetite and satiety are mediated by complex neuroendocrine signalling pathways involving over 40 hormones, neuropeptides, enzymes, other chemical messengers and their receptors. Research efforts continue to expand understanding of the role of signalling molecules between central hypothalamic nuclei and peripheral enteroendocrine cells; and discoveries of novel networks and messengers provide new biological insights on how to manipulate appetite-satiety pathways. Despite the vast array of peptides that are potentially useful for anti-obesity drug development, only four classes of agents are approved: (i) catecholamine stimulants; (ii) serotonin and noradrenaline reuptake inhibitors; (iii) lipase inhibitors; and (iv) more recently cannabinoid-1 receptor antagonists. Clinical effects of these drugs confer modest improvements, and side effects negatively impact long-term treatment course. This paper suggests single target pharmacological interventions are possibly hampered by the myriad of alternate orexigenic peptidic signals that drive hyperphagia, hence a multiple target model or combination treatment approach is proposed to offer greater therapeutic potential in modulating appetite and managing weight.

Protein-tyrosine phosphatase 1B expression is induced by inflammation in vivo

Protein-tyrosine phosphatase 1B (PTP1B) is a major negative regulator of insulin and leptin sensitivity. PTP1B overexpression in adipose tissue and skeletal muscle of humans and rodents may contribute to insulin resistance and obesity. The mechanisms mediating PTP1B overexpression in obese and diabetic states have been unclear. We find that adipose tissue inflammation and the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha) regulate PTP1B expression in vivo. High fat feeding of mice increased PTP1B expression 1.5- to 7-fold in adipose tissue, liver, skeletal muscle, and arcuate nucleus of hypothalamus. PTP1B overexpression in high fat-fed mice coincided with increased adipose tissue expression of the macrophage marker CD68 and TNFalpha, which is implicated in causing obesity-induced insulin resistance. TNFalpha increased PTP1B mRNA and protein levels by 2- to 5-fold in a dose- and time-dependent manner in adipocyte and hepatocyte cell lines. TNFalpha administration in mice increased PTP1B mRNA 1.4- to 4-fold in adipose tissue, liver, skeletal muscle, and hypothalamic arcuate nucleus and PTP1B protein 2-fold in liver. Actinomycin D treatment blocked, and high dose salicylate treatment inhibited by 80%, TNFalpha-induced PTP1B expression in adipocyte cell lines, suggesting TNFalpha may induce PTP1B transcription via nuclear factor kappaB (NFkappaB) activation. Chromatin immunoprecipitation from adipocyte cell lines and liver of mice demonstrated TNFalpha-induced recruitment of NFkappaB subunit p65 to the PTP1B promoter in vitro and in vivo. In mice with diet-induced obesity, TNFalpha deficiency also partly blocked PTP1B overexpression in adipose tissue. Our data suggest that PTP1B overexpression in multiple tissues in obesity is regulated by inflammation and that PTP1B may be a target of anti-inflammatory therapies.

Modulation of protein tyrosine phosphatase 1B by erythropoietin in UT-7 cell line

BACKGROUND/AIMS

Since the reversible phosphorylation of tyrosyl residues is a critical event in cellular signaling pathways activated by erythropoietin (Epo), attention has been focused on protein tyrosine phosphatases (PTPs) and their coordinated action with protein tyrosine kinases. The prototypic member of the PTP family is PTP1B, a widely expressed non-receptor PTP located both in cytosol and intracellular membranes via its hydrophobic C-terminal targeting sequence. PTP1B has been implicated in the regulation of signaling pathways involving tyrosine phosphorylation induced by growth factors, cytokines, and hormones, such as the downregulation of erythropoietin and insulin receptors. However, little is known about which factor modulates the activity of this enzyme.

METHODS

The effect of Epo on PTP1B expression was studied in the UT-7 Epo-dependent cell line. PTP1B expression was analyzed under different conditions by Real-Time PCR and Western blot, while PTP1B phosphatase activity was determined by a p-nitrophenylphosphate hydrolysis assay.

RESULTS

Epo rapidly induced an increased expression of PTP1B which was associated with higher PTP1B tyrosine phosphorylation and phosphatase activity. The action of Epo on PTP1B induction involved Janus Kinase 2 (JAK2) and Phosphatidylinositol-3 kinase (PI3K).

CONCLUSION

The results allow us to suggest for the first time that, besides modulating Epo/Epo receptor signaling, PTP1B undergoes feedback regulation by Epo.

PTP1B and TC-PTP: novel roles in immune-cell signaling

It has recently been demonstrated that the protein tyrosine phosphatase (PTP) PTP1B and the T-cell PTP (TC-PTP) target several substrates involved in immune cell signaling. Recent data have furthered the view of these 2 PTP members as key regulators of the immune response. This review will focus on the substrate specificities of PTP1B and TC-PTP and their roles in immune cell signaling, and will discuss some new data implicating PTP1B and TC-PTP in myeloid development.

Involvement of the small protein tyrosine phosphatases TC-PTP and PTP1B in signal transduction and diseases: from diabetes, obesity to cell cycle, and cancer

As in other fields of biomedical research, the use of gene-targeted mice by homologous recombination in embryonic stem cells has provided important findings on the function of several members of the protein tyrosine phosphatase (PTP) family. For instance, the phenotypic characterization of knockout mice has been critical in understanding the sites of action of the related PTPs protein tyrosine phosphatase 1B (PTP1B) and T-cell-PTP (TC-PTP). By their increased insulin sensitivity and insulin receptor hyperphosphorylation, PTP1B null mice demonstrated a clear function for this enzyme as a negative regulator of insulin signaling. As well, TC-PTP has also been recently involved in insulin signaling in vitro. Importantly, the high identity in their amino acid sequences suggests that they must be examined simultaneously as targets of drug development. Indeed, they possess different as well as overlapping substrates, which suggest complementary and overlapping roles of both TC-PTP and PTP1B. Here, we review the function of PTP1B and TC-PTP in diabetes, obesity, and processes related to cancer.

Cytoplasmic protein tyrosine phosphatases, regulation and function: the roles of PTP1B and TC-PTP

PTP1B and TC-PTP are closely related protein tyrosine phosphatases, sharing 74% homology in their catalytic domain. However, their cellular localization, function, and regulation are found to be different. Their substrate specificity has implicated these enzymes in various signaling pathways, regulating metabolism, proliferation and cytokine signaling. For instance, PTP1B has been shown to regulate the activation of cytokine receptors through the dephosphorylation of specific members of the JAK family, namely JAK2 and TYK2, whereas TC-PTP is involved in the modulation of cytokine signaling via JAK1 and JAK3 molecules. Gene-targeting approaches will help us to unravel the physiological functions of these enzymes.

Role of insulin-induced reactive oxygen species in the insulin signaling pathway

Oxidants, including hydrogen peroxide (H2O2), have been recognized for years to mimic insulin action on glucose transport in adipose cells. Early studies also demonstrated the complementary finding that H2O2 was elaborated during treatment of cells with insulin, suggesting that cellular H2O2 generation was integral to insulin signaling. Recently, reactive oxygen species elicited by various hormones and growth factors have been shown to affect signal transduction pathways in various cell types. We recently reported that insulin-stimulated H2O2 modulates proximal and distal insulin signaling, at least in part through the oxidative inhibition of protein tyrosine phosphatases (PTPases) that negatively regulate the insulin action pathway. Nox4, a homologue in the family of NADPH oxidase catalytic subunits, was found to be prominently expressed in insulin-sensitive cells. By various molecular approaches, Nox4 was shown to mediate insulin-stimulated H2O2 generation and impact the insulin signaling cascade. Overexpression of Nox4 also significantly reversed the inhibition of insulin-stimulated receptor tyrosine phosphorylation by PTP1B, a widely expressed PTPase implicated in the negative regulation of insulin signaling, by inhibiting its catalytic activity. These recent studies have provided insight into Nox4 as a novel molecular link between insulin-stimulated reactive oxygen species and mechanisms involved in their modulation of insulin signal transduction.

The Pro387Leu variant of protein tyrosine phosphatase-1B is not associated with diabetes mellitus type 2 in a German population

OBJECTIVES

Diabetes mellitus type 2 (DM-2) is a complex disorder with a strong genetic background. Protein tyrosine phosphatase-1B (PTP-1B) dephosphorylates various receptor protein kinases in vitro, including the beta subunit of the insulin receptor, therefore representing a potential candidate to be involved in the polygenic pathogenesis of DM-2. Recently a Pro387Leu variant of the PTP-1B gene has been associated with an increased risk of DM-2 in a Danish population. Reports from China and Finland failed to confirm this association.

DESIGN, SETTING AND SUBJECTS

The purpose of the present study was to examine the possible association between the presence of DM-2 and the Pro387Leu polymorphism in a German Caucasian population. A total of 836 subjects (age 20-92 years) participated in the study. The presence of the Pro387Leu variant of the PTP-1B gene was investigated using polymerase chain reaction (PCR) restriction fragment-length polymorphism in 402 subjects with DM-2 (231 men, 171 women, age 63.1 +/- 10.8 years, BMI 28.7 +/- 5.1 kg m(-2)) and in 434 normoglycemic age- and sex-matched control subjects (248 men, 186 women, age 64.4 +/- 6.5 years, BMI 26.5 +/- 3.7 kg m(-2)).

RESULTS

Nine subjects in the control group and nine in the diabetic group (allelic frequency 0.99% in both groups) carried the Pro387Leu polymorphism. A meta-analysis on published data of >3000 subjects including our own data did not find an association between the polymorphism and DM-2. In addition, the polymorphism had no significant influence on the presence of atherosclerotic disease, whilst the influence of other known cardiovascular risk factors was confirmed. Furthermore, the impact of the mutation on metabolic and anthropometric parameters in both groups was examined. Amongst the controls there were no significant differences in BMI, HDL and LDL cholesterol or blood pressure between the two groups with or without the Pro387Leu polymorphism. The same was true for the diabetic group. Interestingly, in both diabetics and controls, Pro387Leu carriers had significantly higher triglycerides. In a logistic regression model only BMI and family history but not polymorphism were predictors of DM-2.

CONCLUSIONS

In conclusion, the present data suggest that in a German Caucasian population the Pro387Leu polymorphism of the PTP-1B gene is not associated with DM-2 but may play a role in other metabolic phenotypes.

Antidiabetic effects of extracts from Psidium guajava

During a screening of medicinal plants for inhibition of protein tyrosine phosphatase1B (PTP1B), an extract from Psidium guajava (Myrtaceae) leaves exhibited significant inhibitory effect on PTP1B. Thus, its antidiabetic effect on Lepr(db)/Lepr(db) mice was evaluated. Significant blood glucose lowering effects of the extract were observed after intraperitoneal injection of the extract at a dose of 10mg/kg in both 1- and 3-month-old Lepr(db)/Lepr(db) mice. In addition, histological analysis of the liver from the butanol-soluble fraction treated Lepr(db)/Lepr(db) mice revealed a significant decrease in the number of lipid droplets compared to the control mice. Taken together, it was suggested that the extract from Psidium guajava leaves possesses antidiabetic effect in type 2 diabetic mice model and these effect is, at least in part, mediated via the inhibition of PTP1B.

Metformin (Glucophage) inhibits tyrosine phosphatase activity to stimulate the insulin receptor tyrosine kinase

Metformin is a commonly used anti-diabetic but whether its mechanism involves action on the insulin receptor or on downstream events is still controversial. With a time course that was slow compared with insulin action, metformin increased tyrosine phosphorylation of the regulatory domain of the insulin receptor (specifically, tyrosine residues 1150 and 1151). In a direct action, therapeutic levels of metformin stimulated the tyrosine kinase activity of the soluble intracellular portion of the beta subunit of the human insulin receptor toward a substrate derived from the insulin receptor regulatory domain. However, metformin did not alter the order of substrate phosphorylation by the insulin receptor kinase. Using a Xenopus oocyte preparation, we simultaneously recorded tyrosine kinase and phosphatase activities that regulate the insulin receptor by measuring the tyrosine phosphorylation and dephosphorylation of peptides derived from the regulatory domain of the human insulin receptor. In an indirect stimulation of the insulin receptor, metformin inhibited endogenous tyrosine phosphatases and purified human protein tyrosine phosphatase 1B that dephosphorylate and inhibit the insulin receptor kinase. Thus, there was evidence that metformin acted directly upon the insulin receptor and indirectly through inhibition of tyrosine phosphatases.

Transgenic overexpression of protein-tyrosine phosphatase 1B in muscle causes insulin resistance, but overexpression with leukocyte antigen-related phosphatase does not additively impair insulin action

Previous studies implicate protein-tyrosine phosphatase 1B (PTP1B) and leukocyte antigen-related phosphatase (LAR) as negative regulators of insulin signaling. The expression and/or activity of PTP1B and LAR are increased in muscle of insulin-resistant rodents and humans. Overexpression of LAR selectively in muscle of transgenic mice causes whole body insulin resistance. To determine whether overexpression of PTP1B also causes insulin resistance, we generated transgenic mice overexpressing human PTP1B selectively in muscle at levels similar to those observed in insulin-resistant humans. Insulin-stimulated insulin receptor (IR) tyrosyl phosphorylation and phosphatidylinositol 3'-kinase activity were impaired by 35% and 40-60% in muscle of PTP1B-overexpressing mice compared with controls. Insulin stimulation of protein kinase C (PKC)lambda/zeta activity, which is required for glucose transport, was impaired in muscle of PTP1B-overexpressing mice compared with controls, showing that PTP1B overexpression impairs activation of these PKC isoforms. Furthermore, hyperinsulinemic-euglycemic clamp studies revealed that whole body glucose disposal and muscle glucose uptake were decreased by 40-50% in PTP1B-overexpressing mice. Overexpression of PTP1B or LAR alone in muscle caused similar impairments in insulin action; however, compound overexpression achieved by crossing PTP1B- and LAR-overexpressing mice was not additive. Antibodies against specific IR phosphotyrosines indicated overlapping sites of action of PTP1B and LAR. Thus, overexpression of PTP1B in vivo impairs insulin sensitivity, suggesting that overexpression of PTP1B in muscle of obese humans and rodents may contribute to their insulin resistance. Lack of additive impairment of insulin signaling by PTP1B and LAR suggests that these PTPs have overlapping actions in causing insulin resistance in vivo.

Prolongation of insulin-induced activation of mitogen-activated protein kinases ERK 1/2 and phosphatidylinositol 3-kinase by vanadyl sulfate, a protein tyrosine phosphatase inhibitor

Vanadium salts such as vanadyl sulfate (VS), potent inhibitors of protein tyrosine phosphatases, have been shown to mimic, augment, and prolong insulin's action. However, the molecular mechanism of responses to these salts is not clear. In the present studies, we examined if VS-induced effects on insulin action are associated with enhancement or augmentation in the activation state of key components of the insulin signaling pathway. Treatment of insulin receptor-overexpressing cells with insulin or VS resulted in a time-dependent transient increase in phosphorylation and activation of extracellular signal-regulated kinases 1 and 2 (ERK 1/2) that peaked at about 5 min, then declined rapidly to about baseline within 30 min. However, when the cells were treated with VS before stimulation with insulin, sustained ERK 1/2 phosphorylation and activation were observed well beyond 60 min. VS treatment also prolonged the insulin-stimulated activation of phosphatidylinositol 3-kinase (PI3-K), which was associated with sustained interaction between insulin receptor substrate-1 (IRS-1) and the p(85 alpha) subunit of phosphatidylinositol 3-kinase (PI3-K) in response to insulin. These data indicate that prolongation of insulin-stimulated ERK 1/2 and PI3-K activation by VS is due to a more stable complex formation of IRS-1 with the p(85 alpha) subunit which may, in turn, be responsible for its ability to enhance and extend the biological effects of insulin.

Protein tyrosine phosphatase 1B inhibitors for diabetes

Increased incidence of type 2 diabetes mellitus and obesity has elevated the medical need for new agents to treat these disease states. Resistance to the hormones insulin and leptin are hallmarks of both type 2 diabetes and obesity. Drugs that can ameliorate this resistance should be effective in treating type 2 diabetes and possibly obesity. Protein tyrosine phosphatase 1B (PTP1B) is thought to function as a negative regulator of insulin and leptin signal transduction. This article reviews PTP1B as a novel target for type 2 diabetes, and looks at the challenges in developing small-molecule inhibitors of this phosphatase.

Troglitazone ameliorates abnormal activity of protein tyrosine phosphatase in adipose tissues of Otsuka Long-Evans Tokushima Fatty rats

Protein tyrosine phosphatases (PTPases) play an essential role in the regulation of steady-state phosphorylation of the insulin receptor and other proteins in the insulin signaling pathway. To determine the role of PTPases in adipose tissue in the development into an insulin-resistant state, we examined PTPase activities and protein levels of three major candidate PTPases in adipose tissues of 26-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Particulate PTPase activities in visceral and epididymal adipose tissues of OLETF rats were increased compared to those in Long-Evans Tokushima Otsuka (LETO) rats, non-insulin-resistant controls. Cytosolic PTPase activities in these tissues were conversely decreased in OLETF rats. In subcutaneous adipose tissues, those changes were not observed. Western blot analysis showed that the amounts of leukocyte antigen-related PTPase (LAR), PTPase 1B (PTP1B), and src homology 2-containing PTPase (SH-PTP2) were increased in particulate fractions of visceral and epididymal fat of OLETF rats. On the other hand, those in the cytosolic fractions were slightly decreased. Troglitazone was administered to OLETF rats to examine the effect of the drug on the changes in PTPase activity and distribution. Troglitazone treatment restored those alterations in PTPase activity in the particulate fraction and the amounts of LAR, PTP1B and SH-PTP2 in both fractions of visceral and epididymal adipose tissues of OLETF rats. Although it remains unknown whether such effects of troglitazone are mediated by peroxisome proliferator-activated receptor y, these data provide useful information for understanding the significance of PTPase in insulin-resistant rats and the molecular mechanism of troglitazone action.

Protein tyrosine phosphatase 1B: a new target for the treatment of obesity and associated co-morbidities

Impaired insulin action is important in the pathophysiology of multiple metabolic abnormalities such as obesity and type 2 diabetes. Protein tyrosine phosphatase 1B (PTP1B) is considered a negative regulator of insulin signalling. This is best evidenced by studies on knockout mice showing that lack of PTP1B is associated with increased insulin sensitivity as well as resistance to obesity and in vitro studies whilst studies in animals and humans have given contradictory results. However, several studies support the notion that insulin signalling can be enhanced by the inhibition of PTP1B providing an attractive target for therapy against type 2 diabetes and obesity. In addition, recent genetic studies support the association between PTP1B with insulin resistance. The development of PTP1B inhibitors has already begun although it has become clear that is not easy to find both a selective, safe and effective PTP1B inhibitor. The objective of this paper is to review the current evidence of PTP1B in the pathophysiology of obesity, type 2 diabetes and cancer as well as in the treatment of these disorders.

A P387L variant in protein tyrosine phosphatase-1B (PTP-1B) is associated with type 2 diabetes and impaired serine phosphorylation of PTP-1B in vitro

In the present study, we tested the hypothesis that variability in the protein tyrosine phosphatase-1B (PTP-1B) gene is associated with type 2 diabetes. Using single-strand conformational polymorphism analysis, we examined cDNA of PTP-1B from 56 insulin-resistant patients with type 2 diabetes as well as cDNA from 56 obese patients. Four silent variants, (NT CGA-->CGG) R199R, (NT CCC-->CCT) P303P, 3'UTR+104insG, and 3'UTR+86T-->G, and one missense variant, P387L, were found. Subsequent analysis on genomic DNA revealed two intron variants, IVS9+57C-->T and IVS9+58G-->A, and two missense variants, G381S and T420M. The G381S and 3'UTR+104insG insertion variants were not associated with type 2 diabetes. In an association study, the P387L variant was found in 14 of 527 type 2 diabetic subjects (allelic frequency 1.4%, 0.4-2.4 CI) and in 5 of 542 glucose-tolerant control subjects (allelic frequency 0.5%, CI 0.1-1.1), showing a significant association to type 2 diabetes (P = 0.036). In vitro, p34 cell division cycle (p34(cdc2)) kinase-directed incorporation of [gamma-(32)P]ATP was reduced in a mutant peptide compared with native peptide (387P: 100% vs. 387L: 28.4 +/- 5.8%; P = 0.0012). In summary, a rare P387L variant of the PTP-1B gene is associated with a 3.7 (CI 1.26-10.93, P = 0.02) genotype relative risk of type 2 diabetes in the examined population of Danish Caucasian subjects and results in impaired in vitro serine phosphorylation of the PTP-1B peptide.

Effects of adenovirus-mediated liver-selective overexpression of protein tyrosine phosphatase-1b on insulin sensitivity in vivo

AIM

Protein tyrosine phosphatase-1B (PTP-1B) is an intracellular PTP known to dephosphorylate and inactivate upstream tyrosine phosphoproteins in the insulin signalling cascade. We and others reported increased abundance of catalytically impaired PTP-1B in tissue lysates from obese human subjects with and without type 2 diabetes, while genetic knockout of PTP-1B improves insulin sensitivity and prevents nutritionally mediated insulin resistance and obesity. The aim of the present work was to further elucidate the role of PTP-1B in glucose metabolism in vivo.

METHODS

We used adenoviral constructs incorporating cDNAs for either wild-type (W/T) or a catalytically inactive C(215)S (C/S) mutant PTP-1B to achieve liver-selective PTP-1B overexpression in young Sprague-Dawley rats using tail vein injection, based on the high degree of hepatotropism of adenovirus 5 (Ad5). An Ad5-lacZ construct encoding beta-galactosidase was used as a control for viral effects alone. A hyperinsulinaemic euglycaemic clamp was used to study whole body glucose disposal and endogenous glucose production rates.

RESULTS

Control studies in HIRcB cells confirmed catalytic activity and inactivity of W/T and C/S respectively. Mean PTP-1B abundance was 2.24 +/- 0.02- and 2.33 +/- 0.04-fold of saline-treated control in liver lysates of W/T and C/S rats respectively. Liver selective overexpression was confirmed by analysis of tissue lysates from liver, fat and muscle tissues. Ad5 treatment did not result in a statistically or clinically significant liver injury, as determined by serum alanine aminotransferase and histological examination. Seven days post injection, no significant difference in rate of weight gain, fasting blood glucose or insulin levels were seen in any group. Similarly, under steady-state glucose clamp conditions, glucose disposal rate (R(d)), endogenous glucose production rate (EGP) and serum insulin levels were similar in all groups.

CONCLUSION

We conclude that moderate medium-term overabundance, to a degree resembling that seen in insulin-resistant states, of PTP-1B in liver tissue does not alter insulin action on glucose metabolism and that the major site of action of PTP-1B is presumably at insulin-responsive target tissue or tissues other than the liver.

Insulin-stimulated hydrogen peroxide reversibly inhibits protein-tyrosine phosphatase 1b in vivo and enhances the early insulin action cascade

The insulin signaling pathway is activated by tyrosine phosphorylation of the insulin receptor and key post-receptor substrate proteins and balanced by the action of specific protein-tyrosine phosphatases (PTPases). PTPase activity, in turn, is highly regulated in vivo by oxidation/reduction reactions involving the cysteine thiol moiety required for catalysis. Here we show that insulin stimulation generates a burst of intracellular H(2)O(2) in insulin-sensitive hepatoma and adipose cells that is associated with reversible oxidative inhibition of up to 62% of overall cellular PTPase activity, as measured by a novel method using strictly anaerobic conditions. The specific activity of immunoprecipitated PTP1B, a PTPase homolog implicated in the regulation of insulin signaling, was also strongly inhibited by up to 88% following insulin stimulation. Catalase pretreatment abolished the insulin-stimulated production of H(2)O(2) as well as the inhibition of cellular PTPases, including PTP1B, and was associated with reduced insulin-stimulated tyrosine phosphorylation of its receptor and high M(r) insulin receptor substrate (IRS) proteins. These data provide compelling new evidence for a redox signal that enhances the early insulin-stimulated cascade of tyrosine phosphorylation by oxidative inactivation of PTP1B and possibly other tyrosine phosphatases.

Insulin resistance with aging: effects of diet and exercise

Insulin resistance, a reduction in the rate of glucose disposal elicited by a given insulin concentration, is present in individuals who are obese, and those with diabetes mellitus, and may develop with aging. Methods which are utilised to measure insulin sensitivity include the hyperinsulinaemic-euglycaemic and hyperglycaemic clamps and the intravenous glucose tolerance tests. Several hormones and regulatory factors affect insulin action and may contribute to the insulin resistance observed in obesity. In addition, abnormal free fatty acid metabolism plays an important role in insulin resistance and the abnormal carbohydrate metabolism seen in individuals who are obese or diabetic. Thus, the mechanisms underlying the development of insulin resistance are multifactorial, and also involve alterations of the insulin signalling pathway. Aging is associated with an increase in bodyweight and fat mass. Not only is abdominal fat associated with hyperinsulinaemia but visceral adiposity is correlated with insulin resistance as well. Modifications of the changes in body composition with aging by diet and exercise training could delay the onset of insulin resistance. Weight loss and aerobic and resistive exercise training result in losses of total body fat and abdominal fat. Several studies report that bodyweight loss increases insulin sensitivity and improves glucose tolerance. In addition, the insulin resistance observed in aged persons can be modified by physical training. Longitudinal studies indicate significant improvements in glucose metabolism with aerobic exercise training in middle-aged and older men and women. Moreover, the improvements in insulin sensitivity with resistive training are similar in magnitude to those achieved with aerobic exercise. The improvements in glucose metabolism after bodyweight loss and exercise training may in some cases be partially attributed to changes in body composition, including reductions in total and central body fat. Yet, additional changes in skeletal muscle, blood flow and other mechanisms likely interact to modify insulin resistance with exercise training. Lifestyle modifications including bodyweight loss and physical activity provide health benefits and functional gains and should be promoted to increase insulin sensitivity and prevent glucose intolerance and type 2 diabetes mellitus in older adults.

Protein tyrosine phosphatase-1B in diabetes

A role for protein tyrosine phosphatases in the negative regulation of insulin signaling and a putative involvement in the insulin resistance associated with type 2 diabetes have been postulated since their discovery. The recent demonstration that mice lacking the protein tyrosine phosphatase-1B (PTP-1B) have enhanced insulin sensitivity validates this. Furthermore, when fed a high fat diet, these mice maintained insulin sensitivity and were resistant to obesity, suggesting that inhibition of PTP-1B activity could be a novel way of treating type 2 diabetes and obesity. This commentary reviews our current knowledge of PTP-1B in insulin signaling and its role in diabetes and discusses the development of potent and selective PTP-1B inhibitors.

Increased energy expenditure, decreased adiposity, and tissue-specific insulin sensitivity in protein-tyrosine phosphatase 1B-deficient mice

Protein-tyrosine phosphatase 1B (PTP-1B) is a major protein-tyrosine phosphatase that has been implicated in the regulation of insulin action, as well as in other signal transduction pathways. To investigate the role of PTP-1B in vivo, we generated homozygotic PTP-1B-null mice by targeted gene disruption. PTP-1B-deficient mice have remarkably low adiposity and are protected from diet-induced obesity. Decreased adiposity is due to a marked reduction in fat cell mass without a decrease in adipocyte number. Leanness in PTP-1B-deficient mice is accompanied by increased basal metabolic rate and total energy expenditure, without marked alteration of uncoupling protein mRNA expression. In addition, insulin-stimulated whole-body glucose disposal is enhanced significantly in PTP-1B-deficient animals, as shown by hyperinsulinemic-euglycemic clamp studies. Remarkably, increased insulin sensitivity in PTP-1B-deficient mice is tissue specific, as insulin-stimulated glucose uptake is elevated in skeletal muscle, whereas adipose tissue is unaffected. Our results identify PTP-1B as a major regulator of energy balance, insulin sensitivity, and body fat stores in vivo.