Association of protein tyrosine phosphatase 1B gene polymorphisms with type 2 diabetes

Protein tyrosine phosphatase 1B in metabolic diseases and drug development

Protein tyrosine phosphatase 1B (PTP1B), a non-transmembrane phosphatase, has a major role in a variety of signalling pathways, including direct negative regulation of classic insulin and leptin signalling pathways, and is implicated in the pathogenesis of several cardiometabolic diseases and cancers. As such, PTP1B has been a therapeutic target for over two decades, with PTP1B inhibitors identified either from natural sources or developed throughout the years. Some of these inhibitors have reached phase I and/or II clinical trials in humans for the treatment of type 2 diabetes mellitus, obesity and/or metastatic breast cancer. In this Review, we summarize the cellular processes and regulation of PTP1B, discuss evidence from in vivo preclinical and human studies of the association between PTP1B and different disorders, and discuss outcomes of clinical trials. We outline challenges associated with the targeting of this phosphatase (which was, until the past few years, viewed as difficult to target), the current state of the field of PTP1B inhibitors (and dual phosphatase inhibitors) and future directions for manipulating the activity of this key metabolic enzyme.

Association between PTPN1 polymorphisms and obesity-related phenotypes in European adolescents: influence of physical activity

BACKGROUND

To study the associations of Protein Tyrosine Phosphatase-N1 (PTPN1) polymorphisms with obesity-related phenotypes in European adolescents, and the influence of physical activity on these relationships.

METHODS

Five polymorphisms of PTPN1 were genotyped in 1057 European adolescents (12-18 years old). We measured several phenotypes related to obesity, such as adiposity markers, and biochemical and clinical parameters. Physical activity was objectively measured by accelerometry.

RESULTS

The T, A, T, T and G alleles of the rs6067472, rs10485614, rs2143511, rs6020608 and rs968701 polymorphisms, respectively, were associated with lower levels of obesity-related phenotypes (i.e., body mass index, body fat percentage, hip circumference, fat mass index, systolic blood pressure and leptin) in European adolescents. In addition, the TATTG haplotype was associated with lower body fat percentage and fat mass index compared to the AACCA haplotype. Finally, when physical activity levels were considered, alleles of the rs6067472, rs2143511, rs6020608 and rs968701 polymorphisms were only associated with lower adiposity in active adolescents.

CONCLUSIONS

PTPN1 polymorphisms were associated with adiposity in European adolescents. Specifically, alleles of these polymorphisms were associated with lower adiposity only in physically active adolescents. Therefore, meeting the recommendations of daily physical activity may reduce obesity risk by modulating the genetic predisposition to obesity.

IMPACT

Using gene-phenotype and gene*environment analyses, we detected associations between polymorphisms of the Protein Tyrosine Phosphatase-N1 (PTPN1) gene and obesity-related phenotypes, suggesting a mechanism that can be modulated by physical activity. This study shows that genetic variability of PTPN1 is associated with adiposity, while physical activity seems to modulate the genetic predisposition. This brings insights about the mechanisms by which physical activity positively influences obesity.

Neem and Turmeric in the management of Covid Associated Mucormycosis (CAM) derived through network pharmacology

Mucormycosis or 'Black Fungus' has been known to target immunocompromised individuals even before the emergence of COVID-19. Nevertheless, the present circumstances provide the best opening for Covid Associated Mucormycosis (CAM), as the global pandemic is engulfing a large part of human population making them immunocompromised. This drastic increase in Mucormycosis infections has to be addressed as early as possible. There is a growing tendency of relying upon herbal drugs that have minimal side effects and does not compromise our immune system. Recently, the concept of network pharmacology has grabbed the attention of modern science, especially advanced medical sciences. This is a new discipline that can use computational power to systematically catalogue the molecular interactions between botanical formulations and the human body. In this study, Neem and Turmeric was considered as the target plants and an attempt was made to reveal various aspects through which phytocompounds derived from them may effectively manage CAM menace. We have taken a step-by-step approach for identifying the target proteins and ligands associated with Mucormycosis treatment. Functional network analysis and Molecular docking approaches were applied to validate our findings. Quercetin derived from both Neem and Turmeric was found to be one of the main phytocompounds working against Mucormycosis. Along with that, Caffeic acid, Curcumin, Kaempferol, Tetrahydrocurcumin and Myricetin also play a pivotal role in fighting against Black-Fungus. A thorough analysis of our result suggested a triple-front attack on the fungal pathogens and the approaches are necrosis inhibition, iron chelation and immuno-boosting.Communicated by Ramaswamy H. Sarma.

Genotyping and Whole-Genome Resequencing of Welsh Sheep Breeds Reveal Candidate Genes and Variants for Adaptation to Local Environment and Socioeconomic Traits

Background

Advances in genetic tools applied to livestock breeding has prompted research into the previously neglected breeds adapted to harsh local environments. One such group is the Welsh mountain sheep breeds, which can be farmed at altitudes of 300 m above sea level but are considered to have a low productive value because of their poor wool quality and small carcass size. This is contrary to the lowland breeds which are more suited to wool and meat production qualities, but do not fare well on upland pasture. Herein, medium-density genotyping data from 317 individuals representing 15 Welsh sheep breeds were used alongside the whole-genome resequencing data of 14 breeds from the same set to scan for the signatures of selection and candidate genetic variants using haplotype- and SNP-based approaches.

Results

Haplotype-based selection scan performed on the genotyping data pointed to a strong selection in the regions of GBA3, PPARGC1A, APOB, and PPP1R16B genes in the upland breeds, and RNF24, PANK2, and MUC15 in the lowland breeds. SNP-based selection scan performed on the resequencing data pointed to the missense mutations under putative selection relating to a local adaptation in the upland breeds with functions such as angiogenesis (VASH1), anti-oxidation (RWDD1), cell stress (HSPA5), membrane transport (ABCA13 and SLC22A7), and insulin signaling (PTPN1 and GIGFY1). By contrast, genes containing candidate missense mutations in the lowland breeds are related to cell cycle (CDK5RAP2), cell adhesion (CDHR3), and coat color (MC1R).

Conclusion

We found new variants in genes with potentially functional consequences to the adaptation of local sheep to their environments in Wales. Knowledge of these variations is important for improving the adaptative qualities of UK and world sheep breeds through a marker-assisted selection.

A comprehensive review on the antidiabetic activity of flavonoids targeting PTP1B and DPP-4: a structure-activity relationship analysis

Type 2 diabetes (T2D) is an expanding global health problem, resulting from defects in insulin secretion and/or insulin resistance. In the past few years, both protein tyrosine phosphatase 1B (PTP1B) and dipeptidyl peptidase-4 (DPP-4), as well as their role in T2D, have attracted the attention of the scientific community. PTP1B plays an important role in insulin resistance and is currently one of the most promising targets for the treatment of T2D, since no available PTP1B inhibitors were still approved. DPP-4 inhibitors are among the most recent agents used in the treatment of T2D (although its use has been associated with possible cardiovascular adverse events). The antidiabetic properties of flavonoids are well-recognized, and include inhibitory effects on the above enzymes, although hitherto not therapeutically explored. In the present study, a comprehensive review of the literature of both synthetic and natural isolated flavonoids as inhibitors of PTP1B and DPP-4 activities is made, including their type of inhibition and experimental conditions, and structure-activity relationship, covering a total of 351 compounds. We intend to provide the most favorable chemical features of flavonoids for the inhibition of PTP1B and DPP-4, gathering information for the future development of compounds with improved potential as T2D therapeutic agents.

Association of protein tyrosine phosphatase 1B gene polymorphism with the effects of weight reduction therapy on bodyweight and glycolipid profiles in obese patients

Aims/Introduction

Weight reduction therapy is the primary treatment to prevent complications of obesity, such as lifestyle diseases and cardiovascular disease; however, to date, useful methods and genetic factors for predicting the outcomes of weight reduction therapy in obese patients have not been established. Protein tyrosine phosphatase 1B (PTP1B), a negative regulator for insulin and leptin signaling, potentially modulates glucose and energy homeostasis. This study aimed to investigate the contribution of PTPN1 polymorphisms on weight reduction and diabetes in obese Japanese patients.

Materials and Methods

PTPN1‐tagged single‐nucleotide polymorphisms (SNPs) rs3787348 and rs6067484 were genotyped in 447 obese Japanese patients from the general population. In this prospective cohort study, all obese patients underwent a 3‐month weight reduction therapy with lifestyle modifications, as recommended by guidelines.

Results

In obese patients (male/female 196/251, age 50 ± 15 years, body mass index [BMI] 32 ± 6 kg/m²), the minor allele appeared at a frequency of 45.5% in rs3787348 SNP of the PTPN1 gene. The T allele of rs3787348 was significantly associated with a higher BMI (P = 0.041 in the additive model). The patients with the T allele in SNP rs3787348 of PTPN1 had significantly smaller reductions in BMI, bodyweight and waist circumference levels during weight reduction therapy (BMI G/G, −1.9 ± 0.2; G/T, −1.5 ± 0.1; T/T, −1.2 ± 0.1; P = 0.001 in the additive model).

Conclusions

Our findings show that the SNP rs3787348 in PTPN1 was associated with the effects of weight reduction therapy on BMI and waist circumference among obese Japanese patients.

A set of miRNAs predicts T2DM remission in patients with coronary heart disease: from the CORDIOPREV study

MicroRNAs (miRNAs) regulate the expression of genes associated with the development of diseases, including type 2 diabetes mellitus (T2DM). However, the use of miRNAs to predict T2DM remission has been poorly studied. Therefore, we aimed to investigate whether circulating miRNAs could be used to predict the probability of T2DM remission in patients with coronary heart disease. We included the newly diagnosed T2DM (n = 190) of the 1,002 patients from the CORDIOPREV study. Seventy-three patients reverted from T2DM after 5 years of dietary intervention with a low-fat or Mediterranean diet. Plasma levels of 56 miRNAs were measured by OpenArray. Generalized linear model, receiver operating characteristic (ROC), Cox regression, and pathway analyses were performed. ROC analysis based on clinical variables showed an area under the curve (AUC) of 0.66. After a linear regression analysis, seven miRNAs were identified as the most important variables in the group’s differentiation. The addition of these miRNAs to clinical variables showed an AUC of 0.79. Cox regression analysis using a T2DM remission score including miRNAs showed that high-score patients have a higher probability of T2DM remission (hazard ratio [HR]_{low versus high}, 4.44). Finally, 26 genes involved in 10 pathways were related to the miRNAs. We have identified miRNAs (hsa-let-7b, hsa-miR-101, hsa-miR-130b-3p, hsa-miR-27a, hsa-miR-30a-5p, hsa-miR-375, and hsa-miR-486) that contribute to the prediction of T2DM remission in patients with coronary heart disease.

Antisense Inhibition of Protein Tyrosine Phosphatase 1B With IONIS-PTP-1BRx Improves Insulin Sensitivity and Reduces Weight in Overweight Patients With Type 2 Diabetes

OBJECTIVE

To evaluate safety and efficacy of IONIS-PTP-1B_Rx, a second-generation 2'-O-methoxyethyl antisense inhibitor of protein tyrosine phosphatase 1B, as add-on therapy in overweight patients with type 2 diabetes inadequately controlled with metformin with or without sulfonylurea therapy.

RESEARCH DESIGN AND METHODS

In this phase II, double-blind, randomized, placebo-controlled, multicenter trial, overweight and obese patients (BMI ≥27 kg/m²) with type 2 diabetes (HbA_1c ≥7.5% [58 mmol/mol] and ≤10.5% [91 mmol/mol]) on a stable dose of metformin alone or with sulfonylurea were randomized 2:1 to IONIS-PTP-1B_Rx 200 mg (n = 62) or placebo (n = 30) once weekly for 26 weeks.

RESULTS

Mean baseline HbA_1c was 8.6% (70 mmol/mol) and 8.7% (72 mmol/mol) in placebo and active treatment, respectively. At week 27, IONIS-PTP-1B_Rx reduced mean HbA_1c levels by -0.44% (-4.8 mmol/mol; P = 0.074) from baseline and improved leptin (-4.4 ng/mL; P = 0.007) and adiponectin (0.99 μg/mL; P = 0.026) levels compared with placebo. By week 36, mean HbA_1c was significantly reduced (-0.69% [-7.5 mmol/mol]; P = 0.034) and accompanied by reductions in fructosamine (-33.2 μmol/L; P = 0.005) and glycated albumin (-1.6%; P = 0.031) versus placebo. Despite both treatment groups receiving similar lifestyle counseling, mean body weight significantly decreased from baseline to week 27 with IONIS-PTP-1B_Rx versus placebo (-2.6 kg; P = 0.002) independent of HbA_1c reduction (R² = 0.0020). No safety concerns were identified in the study.

CONCLUSIONS

Compared with placebo, IONIS-PTP-1B_Rx treatment for 26 weeks produced prolonged reductions in HbA_1c, improved medium-term glycemic parameters, reduced leptin and increased adiponectin levels, and resulted in a distinct body weight-reducing effect.

Blood-Based DNA Methylation Biomarkers for Type 2 Diabetes: Potential for Clinical Applications

Type 2 diabetes (T2D) is a leading cause of death and disability worldwide. It is a chronic metabolic disorder that develops due to an interplay of genetic, lifestyle, and environmental factors. The biological onset of the disease occurs long before clinical symptoms develop, thus the search for early diagnostic and prognostic biomarkers, which could facilitate intervention strategies to prevent or delay disease progression, has increased considerably in recent years. Epigenetic modifications represent important links between genetic, environmental and lifestyle cues and increasing evidence implicate altered epigenetic marks such as DNA methylation, the most characterized and widely studied epigenetic mechanism, in the pathogenesis of T2D. This review provides an update of the current status of DNA methylation as a biomarker for T2D. Four databases, Scopus, Pubmed, Cochrane Central, and Google Scholar were searched for studies investigating DNA methylation in blood. Thirty-seven studies were identified, and are summarized with respect to population characteristics, biological source, and method of DNA methylation quantification (global, candidate gene or genome-wide). We highlight that differential methylation of the TCF7L2, KCNQ1, ABCG1, TXNIP, PHOSPHO1, SREBF1, SLC30A8, and FTO genes in blood are reproducibly associated with T2D in different population groups. These genes should be prioritized and replicated in longitudinal studies across more populations in future studies. Finally, we discuss the limitations faced by DNA methylation studies, which include including interpatient variability, cellular heterogeneity, and lack of accounting for study confounders. These limitations and challenges must be overcome before the implementation of blood-based DNA methylation biomarkers into a clinical setting. We emphasize the need for longitudinal prospective studies to support the robustness of the current findings of this review.

Novel Mixed-Type Inhibitors of Protein Tyrosine Phosphatase 1B. Kinetic and Computational Studies

The Atlas of Diabetes reports 415 million diabetics in the world, a number that has surpassed in half the expected time the twenty year projection. Type 2 diabetes is the most frequent form of the disease; it is characterized by a defect in the secretion of insulin and a resistance in its target organs. In the search for new antidiabetic drugs, one of the principal strategies consists in promoting the action of insulin. In this sense, attention has been centered in the protein tyrosine phosphatase 1B (PTP1B), a protein whose overexpression or increase of its activity has been related in many studies with insulin resistance. In the present work, a chemical library of 250 compounds was evaluated to determine their inhibition capability on the protein PTP1B. Ten molecules inhibited over the 50% of the activity of the PTP1B, the three most potent molecules were selected for its characterization, reporting Ki values of 5.2, 4.2 and 41.3 µM, for compounds 1, 2, and 3, respectively. Docking and molecular dynamics studies revealed that the three inhibitors made interactions with residues at the secondary binding site to phosphate, exclusive for PTP1B. The data reported here support these compounds as hits for the design more potent and selective inhibitors against PTP1B in the search of new antidiabetic treatment.

Regulation of malonyl-CoA-acyl carrier protein transacylase network in umbilical cord blood affected by intrauterine hyperglycemia

Background

Gestational diabetes mellitus (GDM) has been shown to be associated with high risk of diabetes in offspring. However, the mechanisms involved in the insulin resistance in offspring are still unclear. Mitochondrial dysfunction is related with insulin resistance. In mitochondria, malonyl-CoA-acyl carrier protein transacylase (MCAT) is the key enzyme of mitochondrial fatty acid synthesis and is estimated to contribute to insulin resistance. In this study, we aimed to examine the role of MCAT and its network in the umbilical cord blood in GDM-induced offspring insulin resistance.

Methods

We isolated lymphocytes from umbilical cord vein blood in 6 GDM patients and 6 controls and examined the differences of RNA by RNA sequencing. qRT-PCR and western blot were used to measure mRNA and protein changes. Bisulfite genomic sequencing PCR was applied to detect DNA methylation.

Results

We found more than 400 genes were differentially regulated in the lymphocytes of umbilical cord blood from GDM patients and these genes were mainly enriched in immune system and endocrine system, which relate to mitochondrial dysfunction and insulin resistance. MCAT closely related with PTPN1 (Protein Tyrosine Phosphatase, Non-Receptor Type1) and STAT5A (Signal Transducer And Activator of Transcription 5A), which were all increased in umbilical cord blood from GDM patients. Increase in MCAT may be due to decreased MCAT DNA methylation.

Conclusion

MCAT and its network with PTPN1, STAT5A are regulated in umbilical cord blood affected by maternal intrauterine hyperglycemia.

Elevation of PTPN1 promoter methylation is a significant risk factor of type 2 diabetes in the Chinese population

The present study aimed to investigate the contribution of DNA methylation of the protein tyrosine phosphatase, non-receptor type 1 (PTPN1) gene to the susceptibility to type 2 diabetes (T2D). Peripheral blood mononuclear cells (PBMCs) were collected from 97 patients with T2D and 97 age- and gender-matched controls. DNA methylation of the PTPN1 gene promoter was evaluated by bisulfite pyrosequencing. Independent sample t-tests were used to compare the differences in the PTPN1 promoter and other phenotypes between the patients with T2D and the controls. The results indicated a significant correlation between PTPN1 promoter methylation and the risk of T2D. Additionally, a breakdown analysis by gender revealed that PTPN1 methylation was associated with an increased risk of T2D in females. Furthermore, low-density lipoprotein (r=−0.183, P=0.046) and total cholesterol (r=−0.310, P=0.001) were inversely associated with PTPN1 methylation in females. In conclusion, the results indicate that elevated PTPN1 promoter methylation is a risk factor for T2D in the female Chinese population.

A dioxidovanadium (V) complex of NNO-donor Schiff base as a selective inhibitor of protein tyrosine phosphatase 1B: Synthesis, characterization, and biological activities

A new dioxidovanadium (V) complex, VO₂(HPPCH) (1) (H₂PPCH = N'-picolinoylpyridin-1-ium-2-carbohydrazonate) has been synthesized and characterized by elemental analysis, IR, X-ray diffraction analysis and electrospray ionization mass spectra. Complex 1 crystallized in the monoclinic system with space group P2₁/c. It potently inhibited PTP1B with IC₅₀ of 0.13 μM, about 7, 15 and 125-fold stronger against PTP1B than over TCPTP, SHP-1 and SHP-2, displaying obvious selectivity against PTP1B. Western blotting analysis indicated that complex 1 effectively increased the phosphorylation of PTP1B substrates, especially the phosphorylation of IR/IGF 1R and IRS-1. It exhibited lower cytotoxicity than positive control VOSO₄. These results make complex 1 a promising candidate for novel anti-diabetic drug development.

Discovery of biaryl-4-carbonitriles as antihyperglycemic agents that may act through AMPK-p38 MAPK pathway

A series of functionalized biaryl-4-carbonitriles was synthesized in three steps and evaluated for PTP-1B inhibitory activity. Among the synthesized compounds, four biaryls 6a-d showed inhibition (IC50 58-75 μM) against in vitro PTP-1B assay possibly due to interaction with amino acid residues Lys120, Tyr46 through hydrogen bonding and aromatic-aromatic interactions, respectively. Two biaryl-4-carbonitriles 6b and 6c showed improved glucose tolerance, fasting as well as postprandial blood glucose, serum total triglycerides, and increased high-density lipoprotein-cholesterol in SLM, STZ, STZ-S and C57BL/KsJ-db/db animal models. The bioanalysis of 4'-bromo-2,3-dimethyl-5-(piperidin-1-yl)biphenyl-4-carbonitrile (6b) revealed that like insulin, it increased 2-deoxyglucose uptake in skeletal muscle cells (L6 and C2C12 myotubes). The compound 6b significantly up-regulated the genes related to the insulin signaling pathways like AMPK, MAPK including glucose transporter-4 (GLUT-4) gene in muscle tissue of C57BL/KsJ-db/db mice. Furthermore, it was observed that the compound 6b up-regulated PPARα, UCP2 and HNF4α, which are key regulator of glucose, lipid, and fatty acid metabolism. Western blot analysis of the compound 6b showed that it significantly increased the phosphorylation of AMPK and p38 MAPK and ameliorated glucose uptake in C57BL/KsJ-db/db mice through the AMPK-p38 MAPK pathway.

Genetic contributions to Type 2 diabetes: recent insights

Few Type 2 diabetes loci are considered confirmed and replicated across multiple populations. Some genes that have become accepted as contributors to diabetes risk include: calpain 10, peroxisome proliferator-activated receptor-gamma, ATP-sensitive inwardly rectifying potassium channel subunit Kir6.2, hepatocyte nuclear factor 4alpha and hepatic transcription factor 1. While numerous reports of new diabetes loci enter the literature on a regular basis, this review focuses on selected novel associations reported within the last 12 months. In particular, we highlight recent reports of associations between Type 2 diabetes and the transcription factor 7-like 2 gene, associations with micro-opioid receptor and supressor of cytokine signaling 2 genes, and expression and functional analyses of adipokines vaspin and retinol binding protein 4. These new results provide insights into possible mechanisms influencing disease susceptibility and thus new diagnostic and therapeutic opportunities for Type 2 diabetes.

Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training

Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.

Integrating virtual and biochemical screening for protein tyrosine phosphatase inhibitor discovery

Protein tyrosine phosphatases (PTPs) represent an important class of enzymes that mediate signal transduction and control diverse aspects of cell behavior. The importance of their activity is exemplified by their significant contribution to disease etiology with over half of all human PTP genes implicated in at least one disease. Small molecule inhibitors targeting individual PTPs are important biological tools, and are needed to fully characterize the function of these enzymes. Moreover, potent and selective PTP inhibitors hold the promise to transform the treatment of many diseases. While numerous methods exist to develop PTP-directed small molecules, we have found that complimentary use of both virtual (in silico) and biochemical (in vitro) screening approaches expedite compound identification and drug development. Here, we summarize methods pertinent to our work and others. Focusing on specific challenges and successes we have experienced, we discuss the considerable caution that must be taken to avoid enrichment of inhibitors that function by non-selective oxidation. We also discuss the utility of using "open" PTP structures to identify active-site directed compounds, a rather unconventional choice for virtual screening. When integrated closely, virtual and biochemical screening can be used in a productive workflow to identify small molecules targeting PTPs.

PTP1B: a simple enzyme for a complex world

Our understanding of the fundamental regulatory roles that tyrosine phosphatases play within cells has advanced significantly in the last two decades. Out-dated ideas that tyrosine phosphatases acts solely as the "off" switch counterbalancing the action of tyrosine kinases has proved to be flawed. PTP1B is the most characterized of all the tyrosine phosphatases and it acts as a critical negative and positive regulator of numerous signaling cascades. PTP1B's direct regulation of the insulin and the leptin receptors makes it an ideal therapeutic target for type II diabetes and obesity. Moreover, the last decade has also seen several reports establishing PTP1B as key player in cancer serving as both tumor suppressor and tumor promoter depending on the cellular context. Despite many key advances in these fields one largely ignored area is what role PTP1B may play in the modulation of immune signaling. The important recognition that PTP1B is a major negative regulator of Janus kinase - signal transducer and activator of transcription (JAK-STAT) signaling throughout evolution places it as a key link between metabolic diseases and inflammation, as well as a unique regulator between immune response and cancer. This review looks at the emergence of PTP1B through evolution, and then explore at the cell and systemic levels how it is controlled physiologically. The second half of the review will focus on the role(s) PTP1B can play in disease and in particular its involvement in metabolic syndromes and cancer. Finally we will briefly examine several novel directions in the development of PTP1B pharmacological inhibitors.

Phytochemicals targeting genes relevant for type 2 diabetes

Nutrigenomic approaches based on ethnopharmacology and phytotherapy concepts have revealed that type 2 diabetes mellitus (T2DM) may be susceptible to dietary intervention. Interaction between bioactive food components and the genome may influence cell processes and modulate the onset and progression of the disease. T2DM, characterized by insulin resistance and beta cell dysfunction, is one of the leading causes of death and disability. Despite the great advances that have been made in the understanding and management of this complex, multifactorial disease, T2DM has become a worldwide epidemic in the 21st century. Population and family studies have revealed a strong genetic component of T2DM, and a number of candidate genes have been identified in humans. Variations in the gene sequences such as single nucleotide polymorphisms, explain the individual differences in traits like disease susceptibility and response to treatment. A clear understanding of how nutrients affect the expression of genes should facilitate the development of individualized intervention and, eventually, treatment strategies for T2DM. Review of the literature identified many phytochemicals/extracts from traditional medicinal plants that can target diabetogenic genes. This review focuses on the genetic aspects of T2DM, nutrient modification of genes relevant for diabetes, and future prospects of nutritional therapy of T2DM.

Protein tyrosine phosphatase variants in human hereditary disorders and disease susceptibilities

Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism to steer normal development and physiological functioning of multicellular organisms. Phosphotyrosine dephosphorylation is exerted by members of the super-family of protein tyrosine phosphatase (PTP) enzymes and many play such essential roles that a wide variety of hereditary disorders and disease susceptibilities in man are caused by PTP alleles. More than two decades of PTP research has resulted in a collection of PTP genetic variants with corresponding consequences at the molecular, cellular and physiological level. Here we present a comprehensive overview of these PTP gene variants that have been linked to disease states in man. Although the findings have direct bearing for disease diagnostics and for research on disease etiology, more work is necessary to translate this into therapies that alleviate the burden of these hereditary disorders and disease susceptibilities in man.

Variants of insulin-signaling inhibitor genes in type 2 diabetes and related metabolic abnormalities

Insulin resistance has a central role in the pathogenesis of several metabolic diseases, including type 2 diabetes, obesity, glucose intolerance, metabolic syndrome, atherosclerosis, and cardiovascular diseases. Insulin resistance and related traits are likely to be caused by abnormalities in the genes encoding for proteins involved in the composite network of insulin-signaling; in this review we have focused our attention on genetic variants of insulin-signaling inhibitor molecules. These proteins interfere with different steps in insulin-signaling: ENPP1/PC-1 and the phosphatases PTP1B and PTPRF/LAR inhibit the insulin receptor activation; INPPL1/SHIP-2 hydrolyzes PI3-kinase products, hampering the phosphoinositide-mediated downstream signaling; and TRIB3 binds the serine-threonine kinase Akt, reducing its phosphorylation levels. While several variants have been described over the years for all these genes, solid evidence of an association with type 2 diabetes and related diseases seems to exist only for rs1044498 of the ENPP1 gene and for rs2295490 of the TRIB3 gene. However, overall the data recapitulated in this Review article may supply useful elements to interpret the results of novel, more technically advanced genetic studies; indeed it is becoming increasingly evident that genetic information on metabolic diseases should be interpreted taking into account the complex biological pathways underlying their pathogenesis.

Protein tyrosine phosphatases and type 1 diabetes: genetic and functional implications of PTPN2 and PTPN22

Protein tyrosine phosphatases (PTPs) play a central role in modulating the transduction of cellular signals, including the cells of the immune system. Several PTPs, PTPN22, PTPN2, and UBASH3A, have been associated with risk of type 1 diabetes (T1D) by genome wide association studies. Based on the current understanding of PTPs, it is clear that these variants impact antigen receptor signaling and cytokine signaling. This impact likely contributes to the development and progression of autoimmunity through multiple mechanisms, including failures of central and peripheral tolerance and the promotion of proinflammatory T cell responses. In this review, we discuss the genetic and functional implications of two of these PTPs, PTPN22 and PTPN2, in the development of T1D. We describe the known roles of these proteins in immune function, and how the expression and function of these proteins is altered by the genetic variants associated with T1D. Yet, there are still controversies in the field that require further study and the development of new approaches to extend our understanding of these PTP variants, with the goal of using the information gained to improve our ability to predict and cure T1D.

Decrease of microRNA-122 causes hepatic insulin resistance by inducing protein tyrosine phosphatase 1B, which is reversed by licorice flavonoid

Protein tyrosine phosphatase 1B (PTP1B) inhibits hepatic insulin signaling by dephosphorylating tyrosine residues in insulin receptor (IR) and insulin receptor substrate (IRS). MicroRNAs may modulate metabolic functions. In view of the lack of understanding of the regulatory mechanism of PTP1B and its chemical inhibitors, this study investigated whether dysregulation of specific microRNA causes PTP1B-mediated hepatic insulin resistance, and if so, what the underlying basis is. In high-fat-diet-fed mice or hepatocyte models with insulin resistance, the expression of microRNA-122 (miR-122), the most abundant microRNA in the liver, was substantially down-regulated among those predicted to interact with the 3'-untranslated region of PTP1B messenger RNA (mRNA). Experiments using miR-122 mimic and its inhibitor indicated that miR-122 repression caused PTP1B induction. Overexpression of c-Jun N-terminal kinase 1 (JNK1) resulted in miR-122 down-regulation with the induction of PTP1B. A dominant-negative mutant of JNK1 had the opposite effect. JNK1 facilitated inactivating phosphorylation of hepatocyte nuclear factor 4α (HNF4α) responsible for miR-122 expression, as verified by the lack of HNF4α binding to the gene promoter. The regulatory role of JNK1 in PTP1B induction by a decrease in miR-122 level was strengthened by cell-based assays using isoliquiritigenin and liquiritigenin (components in Glycyrrhizae radix) as functional JNK inhibitors; JNK inhibition enabled cells to restore IR and IRS1/2 tyrosine phosphorylation and insulin signaling against tumor necrosis factor alpha, and prevented PTP1B induction. Moreover, treatment with each of the agents increased miR-122 levels and abrogated hepatic insulin resistance in mice fed a high-fat diet, causing a glucose-lowering effect.

CONCLUSION

Decreased levels of miR-122 as a consequence of HNF4α phosphorylation by JNK1 lead to hepatic insulin resistance through PTP1B induction, which may be overcome by chemical inhibition of JNK.

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.

PTP1B and TCPTP--nonredundant phosphatases in insulin signaling and glucose homeostasis

Insulin resistance is a key pathological feature of type 2 diabetes and is characterized by defects in signaling by the insulin receptor (IR) protein tyrosine kinase. The inhibition of protein tyrosine phosphatases (PTPs) that antagonize IR signaling may provide a means for enhancing the insulin response and alleviating insulin resistance. The prototypic phosphotyrosine-specific phosphatase PTP1B dephosphorylates the IR and attenuates insulin signaling in muscle and liver. Mice that are deficient for PTP1B exhibit improved glucose homeostasis in diet and genetic models of insulin resistance and type 2 diabetes. The phosphatase TCPTP shares 72% catalytic domain sequence identity with PTP1B and has also been implicated in IR regulation. Despite their high degree of similarity, PTP1B and TCPTP act together in vitro and in vivo to regulate insulin signaling and glucose homeostasis. This review highlights their capacity to act specifically and nonredundantly in cellular signaling, describes their roles in IR regulation and glucose homeostasis, and discusses their potential as drug targets for the enhancement of IR phosphorylation and insulin sensitivity in type 2 diabetes.

Improved glucose-stimulated insulin secretion by intra-islet inhibition of protein-tyrosine phosphatase 1B expression in rats fed a high-fat diet

BACKGROUND

Insulin resistance of pancreatic β-cell itself may be a potential link between systemic insulin resistance and impaired insulin secretion in Type 2 diabetes. Protein tyrosine phosphatase 1B (PTP1B) dephosphorylates tyrosine residues in insulin receptors (IR) and IR substrate (IRS) proteins, and thereby inhibits insulin signaling. Thus the impact of PTP1B expression on β-cell insulin pathway may affect insulin secretory function.

AIM

The aim of the present study was to investigate the effects of intra-islet inhibition of PTP1B expression on glucose-stimulated insulin secretion and potential mechanisms in rats fed a high-fat diet (HFD).

MATERIALS AND METHODS

Twenty 10-week-old Sprague Dawley rats were randomly assigned to a regular diet (RD) or a HFD for 8 weeks. At the end of the 8th week, fasting glucose, fasting insulin concentration and lipid profile were measured and an oral glucose tolerance test was done after 12-h fast. Then islet isolation was performed for static incubation and perifusion. Recombinant adenoviruses containing siPTP1B (Ad-siPTP1B), or siControl (Ad-siControl) sequences were constructed using AdEasy™ system. Islets were transfected and then assigned to the Ad-siPTP1B group, the Ad-siControl group, and mock control group. Real-time RT-PCR and Western blot were used to evaluate the expression level of PTP1B. Western blot of glucose transporter 2 (GLUT-2) and glucokinsase were also done to investigate the β-cell glucose-sensing apparatus. Islets were incubated with Krebs-Ringer bicarbonate containing 2.8 mmol/l glucose then 16.7 mmol/l glucose to evaluate glucose-stimulated insulin secretion (GSIS). Islet perifusion was also performed to evaluate kinetics of insulin release in vitro.

RESULTS

HFD rats manifested modest glucose intolerance compared with RD group. And PTP1B expression in isolated islets of rats in the HFD group was higher than that of the RD group. GSIS was impaired in islets of HFD rats (2.3±0.5-fold as basal for HFD vs 8.1±1.3-fold for RD; p<0.05). Ad-siPTP1B treatment resulted in 73% decrease in PTP1B mRNA levels and 61% decrease in PTP1B protein compared with islets treated with Ad-siControl (p<0.05). Simultaneously, PTP1B inhibition resulted in 4.7±0.8-fold increase of GSIS from basal (vs 1.9±0.1-fold for Ad-siControl, p<0.05). Perifusion showed notable improvement of first-phase insulin secretion by AdsiPTP1B treatment. Significant decrease of both GLUT-2 (by 49.8%) and glucokinase (GCK, by 43.7%) were found in the HFD group when compared with the RD group, while up-regulation of both GLUT-2 (by 98%) and GCK (by 62%) was achieved after PTP1B inhibiton by Ad-siPTP1B.

CONCLUSIONS

Intra-islet PTP1B is an important physiological regulator of glucose-induced insulin release and the characteristics of PTP1B inhibitors in insulin secretion could make it a potential novel therapeutics for protection of β-cell secretory function in Type 2 diabetes.

The Genetics of PTPN1 and Obesity: Insights from Mouse Models of Tissue-Specific PTP1B Deficiency

The protein tyrosine phosphatase PTP1B is a negative regulator of both insulin and leptin signaling and is involved in the control of glucose homeostasis and energy expenditure. Due to its prominent role in regulating metabolism, PTP1B is a promising therapeutic target for the treatment of human obesity and type 2 diabetes. The PTP1B protein is encoded by the PTPN1 gene on human chromosome 20q13, a region that shows linkage with insulin resistance, type 2 diabetes, and obesity in human populations. In this paper, we summarize the genetics of the PTPN1 locus and associations with metabolic disease. In addition, we discuss the tissue-specific functions of PTP1B as gleaned from genetic mouse models.

PTP1B deficiency exacerbates inflammation and accelerates leukocyte trafficking in vivo

It is reported that PTP1B limits cytokine signaling in vitro. However, PTP1B's function during inflammation in vivo is not known. In this report, we determined whether PTP1B deficiency affects allergic inflammation in vivo. Briefly, lungs of OVA-challenged PTP1B(-/-) mice had elevated numbers of eosinophils and eosinophil progenitors at 6 h after one OVA challenge and at 24 h after a third OVA challenge as compared with OVA-challenged wild-type mice. There was also an increase in numbers of CD11b(+)SiglecF(+)CD34(+)IL-5Rα(+) eosinophil progenitors in the bone marrow, peripheral blood, and spleens of OVA-challenged PTP1B(-/-) mice. Intravital microscopy revealed that, in OVA-challenged PTP1B(-/-) mice, blood leukocytes rapidly bound to endothelium (5-30 min), whereas, in wild-type mice, blood leukocytes bound to endothelium at the expected 6-18 h. Consistent with early recruitment of leukocytes, lung eotaxin and Th2 cytokine levels were elevated early in the PTP1B(-/-) mice. Interestingly, spleen leukocytes from PTP1B(-/-) mice exhibited an increased chemotaxis, chemokinesis, and transendothelial migration in vitro. In summary, PTP1B functions as a critical negative regulator to limit allergic responses.

Deficiency of PTP1B in POMC neurons leads to alterations in energy balance and homeostatic response to cold exposure

The adipose tissue-derived hormone leptin regulates energy balance through catabolic effects on central circuits, including proopiomelanocortin (POMC) neurons. Leptin activation of POMC neurons increases thermogenesis and locomotor activity. Protein tyrosine phosphatase 1B (PTP1B) is an important negative regulator of leptin signaling. POMC neuron-specific deletion of PTP1B in mice results in reduced high-fat diet-induced body weight and adiposity gain due to increased energy expenditure and greater leptin sensitivity. Mice lacking the leptin gene (ob/ob mice) are hypothermic and cold intolerant, whereas leptin delivery to ob/ob mice induces thermogenesis via increased sympathetic activity to brown adipose tissue (BAT). Here, we examined whether POMC PTP1B mediates the thermoregulatory response of CNS leptin signaling by evaluating food intake, body weight, core temperature (T(C)), and spontaneous physical activity (SPA) in response to either exogenous leptin or 4-day cold exposure (4°C) in male POMC-Ptp1b-deficient mice compared with wild-type controls. POMC-Ptp1b(-/-) mice were hypersensitive to leptin-induced food intake and body weight suppression compared with wild types, yet they displayed similar leptin-induced increases in T(C). Interestingly, POMC-Ptp1b(-/-) mice had increased BAT weight and elevated plasma triiodothyronine (T(3)) levels in response to a 4-day cold challenge, as well as reduced SPA 24 h after cold exposure, relative to controls. These data show that PTP1B in POMC neurons plays a role in short-term cold-induced reduction of SPA and may influence cold-induced thermogenesis via enhanced activation of the thyroid axis.

Tissue specificity on insulin action and resistance: past to recent mechanisms

Insulin resistance is the most important pathophysiological feature in many pre-diabetic states. Type 2 diabetes mellitus is a complex metabolic disease and its pathogenesis involves abnormalities in both peripheral insulin action and insulin secretion by pancreatic β-cells. The creation of monogenic or polygenic genetically manipulated mice models in a tissue-specific manner was of great help to elucidate the tissue specificity of insulin action and its contribution to the overall insulin resistance. However, a complete understanding of the molecular bases of insulin action and resistance requires the identification of intracellular pathways that regulate insulin-stimulated proliferation, differentiation and metabolism. Accordingly, cell lines derived from insulin target tissues such as brown adipose tissue, liver and beta islets lacking insulin resistance or sensitive candidate genes such as IRS-1, IRS-2, IRS-3, IR and PTP1B have been developed. Indeed, these cell lines have also been very useful to understand the tissue specificity of insulin action and inaction. Obesity is a risk factor for several components of the metabolic syndromes such as type 2 diabetes, dyslipidaemia and systolic hypertension, because white and brown adipose tissues as endocrine organs express and secrete a variety of adipocytokines that can act at both local and systemic levels, modulating the insulin sensitivity. Recent studies revealed that the subjects with the highest transcription rates of genes encoding TNF-α and IL-6 were prone to develop obesity, insulin resistance and type 2 diabetes. Accordingly, we specifically focus in this review on the impact of those adipocytokines on the modulation of insulin action in skeletal muscle.

Neurobiology of overeating and obesity: the role of melanocortins and beyond

The alarming increase in the incidence of obesity and obesity-associated disorders makes the etiology of obesity a widely studied topic today. As opposed to 'homeostatic feeding', where food intake is restricted to satisfy one's biological needs, the term 'non-homeostatic' feeding refers to eating for pleasure or the trend to over-consume (palatable) food. Overconsumption is considered a crucial factor in the development of obesity. Exaggerated consumption of (palatable) food, coupled to a loss of control over food intake despite awareness of its negative consequences, suggests that overeating may be a form of addiction. At a molecular level, insulin and leptin resistance are hallmarks of obesity. In this review, we specifically address the question how leptin resistance contributes to enhanced craving for (palatable) food. Since dopamine is a key player in the motivation for food, the interconnection between dopamine, leptin and neuropeptides related to feeding will be discussed. Understanding the mechanisms by which these neuropeptidergic systems hijack the homeostatic feeding mechanisms, thus leading to overeating and obesity is the primary aim of this review. The melanocortin system, one of the crucial neuropeptidergic systems modulating feeding behavior will be extensively discussed. The inter-relationship between neuronal populations in the arcuate nucleus and other areas regulating energy homeostasis (lateral hypothalamus, paraventricular nucleus, ventromedial hypothalamus etc.) and reward circuitry (the ventral tegmental area and nucleus accumbens) will be evaluated and scrutinized.

Berberine Moderates Glucose and Lipid Metabolism through Multipathway Mechanism

Berberine is known to improve glucose and lipid metabolism disorders, but the mechanism is still under investigation. In this paper, we explored the effects of berberine on the weight, glucose levels, lipid metabolism, and serum insulin of KKAy mice and investigated its possible glucose and lipid-regulating mechanism. We randomly divided KKAy mice into two groups: berberine group (treated with 250 mg/kg/d berberine) and control group. Fasting blood glucose (FBG), weight, total cholesterol (TC), triglyceride (TG), high-density lipoprotein-cholesterol (HDL-c), low-density lipoprotein-cholesterol (LDL-c), and fasting serum insulin were measured in both groups. The oral glucose tolerance test (OGTT) was performed. RT² PCR array gene expression analysis was performed using skeletal muscle of KKAy mice. Our data demonstrated that berberine significantly decreased FBG, area under the curve (AUC), fasting serum insulin (FINS), homeostasis model assessment insulin resistance (HOMA-IR) index, TC, and TG, compared with those of control group. RT² profiler PCR array analysis showed that berberine upregulated the expression of glucose transporter 4 (GLUT4), mitogen-activated protein kinase 14 (MAPK14), MAPK8(c-jun N-terminal kinase, JNK), peroxisome proliferator-activated receptor α (PPARα), uncoupling protein 2 (UCP2), and hepatic nuclear factor 4α(HNF4α), whereas it downregulated the expression of PPARγ, CCAAT/enhancer-binding protein (CEBP), PPARγ coactivator 1α(PGC 1α), and resistin. These results suggest that berberine moderates glucose and lipid metabolism through a multipathway mechanism that includes AMP-activated protein kinase-(AMPK-) p38 MAPK-GLUT4, JNK pathway, and PPARα pathway.

Expression-based network biology identifies alteration in key regulatory pathways of type 2 diabetes and associated risk/complications

Type 2 diabetes mellitus (T2D) is a multifactorial and genetically heterogeneous disease which leads to impaired glucose homeostasis and insulin resistance. The advanced form of disease causes acute cardiovascular, renal, neurological and microvascular complications. Thus there is a constant need to discover new and efficient treatment against the disease by seeking to uncover various novel alternate signalling mechanisms that can lead to diabetes and its associated complications. The present study allows detection of molecular targets by unravelling their role in altered biological pathways during diabetes and its associated risk factors and complications. We have used an integrated functional networks concept by merging co-expression network and interaction network to detect the transcriptionally altered pathways and regulations involved in the disease. Our analysis reports four novel significant networks which could lead to the development of diabetes and other associated dysfunctions. (a) The first network illustrates the up regulation of TGFBRII facilitating oxidative stress and causing the expression of early transcription genes via MAPK pathway leading to cardiovascular and kidney related complications. (b) The second network demonstrates novel interactions between GAPDH and inflammatory and proliferation candidate genes i.e., SUMO4 and EGFR indicating a new link between obesity and diabetes. (c) The third network portrays unique interactions PTPN1 with EGFR and CAV1 which could lead to an impaired vascular function in diabetic nephropathy condition. (d) Lastly, from our fourth network we have inferred that the interaction of β-catenin with CDH5 and TGFBR1 through Smad molecules could contribute to endothelial dysfunction. A probability of emergence of kidney complication might be suggested in T2D condition. An experimental investigation on this aspect may further provide more decisive observation in drug target identification and better understanding of the pathophysiology of T2D and its complications.

Insulin signaling regulating genes: effect on T2DM and cardiovascular risk

Type 2 diabetes mellitus (T2DM) is a complex disorder that has a heterogeneous genetic and environmental background. In this Review, we discuss the role of relatively infrequent polymorphisms of genes that regulate insulin signaling (including the K121Q polymorphism of ENPP1, the G972R polymorphism of IRS1 and the Q84R polymorphism of TRIB3) in T2DM and other conditions related to insulin resistance. The biological relevance of these three polymorphisms has been very thoroughly characterized both in vitro and in vivo and the available data indicate that they all affect insulin signaling and action as well as insulin secretion. They also affect insulin-mediated regulation of endothelial cell function. In addition, several reports indicate that the effects of all three polymorphisms on the risk of T2DM and cardiovascular diseases related to insulin resistance depend on the clinical features of the individual, including their body weight and age at disease onset. Thus, these polymorphisms might be used to demonstrate how difficult it is to ascertain the contribution of relatively infrequent genetic variants with heterogeneous effects on disease susceptibility. Unraveling the role of such variants might be facilitated by improving disease definition and focusing on specific subsets of patients.

Molecular mechanisms involved in obesity-associated insulin resistance: therapeutical approach

Insulin resistance is an important contributor to the pathogenesis of T2D and obesity is a risk factor for its development. It has been demonstrated that these obesity-related metabolic disorders are associated with a state of chronic low-intensity inflammation. Several mediators released from adipocytes and macrophages, such as the pro-inflammatory cytokines TNF-alpha and IL-6, have been suggested to impair insulin action in peripheral tissues, including fat and skeletal muscle. Such insulin resistance can initially be compensated by increased insulin secretion, but the prolonged presence of the hormone is detrimental for insulin sensitivity. Stress and pro-inflammatory kinases as well as more recent players, phosphatases, seem to be involved in the molecular mechanisms by which pro-inflammatory cytokines and hyperinsulinemia disrupt insulin signalling at the level of IRSs. Pharmacological approaches, such as treatment with PPAR and LXR agonists, overcome such insulin resistance, exerting anti-inflammatory properties as well as controlling the expression of cytokines with tissular specificity.

Evidence for sex-specific associations between variation in acid phosphatase locus 1 (ACP1) and insulin sensitivity in Mexican-Americans

CONTEXT

Acid phosphatase locus 1 (ACP1) is a low molecular weight tyrosine phosphatase that has been shown to be an important regulator of insulin receptor signaling.

OBJECTIVE

We tested whether variation in ACP1 is associated with type 2 diabetes-related traits in 1035 individuals in 339 Mexican-American families of probands with or without a previous diagnosis of gestational diabetes mellitus (GDM).

DESIGN

Study participants were phenotyped by oral glucose tolerance test (for glucose and insulin level) and iv glucose tolerance test (for insulin sensitivity and acute insulin response) and had dual-energy x-ray absorptiometry scans to assess body composition. Six tag single nucleotide polymorphisms (SNPs) were identified from among 15 SNPs genotyped across the ACP1 region. SNPs were tested for association with phenotypes using a likelihood ratio test under a variance components framework.

RESULTS

After Bonferroni correction, none of the SNPs were associated with type 2 diabetes mellitus-related phenotypes. However, we observed a significant sex-specific effect of rs3828329. Among males, rs3828329 was significantly associated with fasting insulin (Bonferroni P = 0.007) and insulin sensitivity (Bonferroni P = 0.019) and marginally associated with 2-h insulin (Bonferroni P = 0.058) and percentage body fat (Bonferroni P = 0.09).

CONCLUSIONS

There were no significant associations in females. We conclude that variation in ACP1 is associated with fasting insulin and insulin sensitivity in a sex-specific manner.

Structure-based optimization of benzoic acids as inhibitors of protein tyrosine phosphatase 1B and low molecular weight protein tyrosine phosphatase

We have optimized previously discovered benzoic acids 1, which are active as inhibitors of PTP1B and LMW-PTP, two protein tyrosine phosphatases that have emerged as attractive targets for the development of novel therapeutic agents for the treatment of diabetes, obesity, and cancer. Our efforts led to the identification of new and more potent analogues with appreciable selectivity toward human PTP1B and the IF1 isoform of human LMW-PTP.

Protein tyrosine phosphatases PTP-1B and TC-PTP play nonredundant roles in macrophage development and IFN-gamma signaling

The control of tyrosine phosphorylation depends on the fine balance between kinase and phosphatase activities. Protein tyrosine phosphatase 1B (PTP-1B) and T cell protein tyrosine phosphatase (TC-PTP) are 2 closely related phosphatases known to control cytokine signaling. We studied the functional redundancy of PTP-1B and TC-PTP by deleting 1 or both copies of these genes by interbreeding TC-PTP and PTP-1B parental lines. Our results indicate that the double mutant (tcptp(-/-)ptp1b(-/-)) is lethal at day E9.5-10.5 of embryonic development with constitutive phosphorylation of Stat1. Mice heterozygous for TC-PTP on a PTP-1B-deficient background (tcptp(+/-)ptp1b(-/-)) developed signs of inflammation. Macrophages from these animals were highly sensitive to IFN-gamma, as demonstrated by increased Stat1 phosphorylation and nitric oxide production. In addition, splenic T cells demonstrated increased IFN-gamma secretion capacity. Mice with deletions of single copies of TC-PTP and PTP-1B (tcptp(+/-)ptp1b(+/-)) exhibited normal development, confirming that these genes are not interchangeable. Together, these data indicate a nonredundant role for PTP-1B and TC-PTP in the regulation of IFN signaling.

Heterogeneity in gene loci associated with type 2 diabetes on human chromosome 20q13.1

Human chromosome 20q12-q13.1 has been linked to type 2 diabetes mellitus (T2DM) in multiple studies. We screened a 5.795-Mb region for diabetes-related susceptibility genes in a Caucasian cohort of 310 controls and 300 cases with T2DM and end-stage renal disease (ESRD), testing 390 SNPs for association with T2DM-ESRD. The most significant SNPs were found in the perigenic regions: HNF4A (hepatocyte nuclear factor 4alpha), SLC12A5 (potassium-chloride cotransporter member 5), CDH22 (cadherin-like 22), ELMO2 (engulfment and cell motility 2), SLC13A3 (sodium-dependent dicarboxylate transporter member 3), and PREX1 (phosphatidylinositol 3,4,5-triphosphate-dependent RAC exchanger 1). Haplotype analysis found six haplotype blocks globally associated with disease (p<0.05). We replicated the PREX1 SNP association in an independent case-control T2DM population and inferred replication of CDH22, ELMO2, SLC13A3, SLC12A5, and PREX1 using in silico perigenic analysis of two T2DM Genome-Wide Association Study data sets. We found substantial heterogeneity between study results.

Insulin resistance associated to obesity: the link TNF-alpha

Adipose tissue secretes proteins which may influence insulin sensitivity. Among them, tumour necrosis factor (TNF)-alpha has been proposed as a link between obesity and insulin resistance because TNF-alpha is overexpressed in adipose tissue from obese animals and humans, and obese mice lacking either TNF-alpha or its receptor show protection against developing insulin resistance. The activation of proinflammatory pathways after exposure to TNF-alpha induces a state of insulin resistance in terms of glucose uptake in myocytes and adipocytes that impair insulin signalling at the level of the insulin receptor substrate (IRS) proteins. The mechanism found in brown adipocytes involves Ser phosphorylation of IRS-2 mediated by TNF-alpha activation of MAPKs. The Ser307 residue in IRS-1 has been identified as a site for the inhibitory effects of TNF-alpha in myotubes, with p38 mitogen-activated protein kinase (MAPK) and inhibitor kB kinase being involved in the phosphorylation of this residue. Moreover, up-regulation of protein-tyrosine phosphatase (PTP)1B expression was recently found in cells and animals treated with TNF-alpha. PTP1B acts as a physiological negative regulator of insulin signalling by dephosphorylating the phosphotyrosine residues of the insulin receptor and IRS-1, and PTP1B expression is increased in peripheral tissues from obese and diabetic humans and rodents. Accordingly, down-regulation of PTP1B activity by treatment with pharmacological agonists of nuclear receptors restores insulin sensitivity in the presence of TNF-alpha. Furthermore, mice and cells deficient in PTP1B are protected against insulin resistance induced by this cytokine. In conclusion, the absence or inhibition of PTP1B in insulin-target tissues could confer protection against insulin resistance induced by cytokines.

Lessons learned from the initial sequencing of the pig genome: comparative analysis of an 8 Mb region of pig chromosome 17

The sequencing, annotation and comparative analysis of an 8Mb region of pig chromosome 17 allows the coverage and quality of the pig genome sequencing project to be assessed

Background

We describe here the sequencing, annotation and comparative analysis of an 8 Mb region of pig chromosome 17, which provides a useful test region to assess coverage and quality for the pig genome sequencing project. We report our findings comparing the annotation of draft sequence assembled at different depths of coverage.

Results

Within this region we annotated 71 loci, of which 53 are orthologous to human known coding genes. When compared to the syntenic regions in human (20q13.13-q13.33) and mouse (chromosome 2, 167.5 Mb-178.3 Mb), this region was found to be highly conserved with respect to gene order. The most notable difference between the three species is the presence of a large expansion of zinc finger coding genes and pseudogenes on mouse chromosome 2 between Edn3 and Phactr3 that is absent from pig and human. All of our annotation has been made publicly available in the Vertebrate Genome Annotation browser, VEGA. We assessed the impact of coverage on sequence assembly across this region and found, as expected, that increased sequence depth resulted in fewer, longer contigs. One-third of our annotated loci could not be fully re-aligned back to the low coverage version of the sequence, principally because the transcripts are fragmented over several contigs.

Conclusion

We have demonstrated the considerable advantages of sequencing at increased read depths and discuss the implications that lower coverage sequence may have on subsequent comparative and functional studies, particularly those involving complex loci such as GNAS.

Inhibition of the protein tyrosine phosphatase PTP1B: potential therapy for obesity, insulin resistance and type-2 diabetes mellitus

The global epidemic of obesity and type-2 diabetes mellitus (T2DM) has highlighted the need for new therapeutic approaches. The association of insulin resistance with these disorders and the knowledge that insulin receptor signaling is mediated by tyrosine (Tyr) phosphorylation have generated great interest in the regulation of the balance between Tyr phosphorylation and dephosphorylation. Several protein Tyr phosphatases (PTPs) have been implicated in the regulation of insulin action, with the most convincing data for PTP1B. Murine models targeting PTP1B, PTP1B(-/-)mice, demonstrate enhanced insulin sensitivity without the weight gain seen with other insulin sensitizers such as peroxisome proliferator-activated receptor gamma (PPARgamma) agonists, probably due to a second action of PTP1B as a negative regulator of leptin signaling. Despite intensive efforts and recent progress, a safe, selective and efficacious PTP1B inhibitor has yet to be identified.

Insulin resistance induced by tumor necrosis factor-alpha in myocytes and brown adipocytes

Insulin resistance is an important contributor to the pathogenesis of type 2 diabetes, and obesity is a risk factor for its development, in part because adipose tissue secretes proteins, called adipokines, that may influence insulin sensitivity. Among these molecules, tumor necrosis factor (TNF)-alpha has been proposed as a link between obesity and insulin resistance because TNF-alpha is overexpressed in adipose tissues of obese animals and humans, and obese mice lacking either TNF-alpha or its receptor show protection against developing insulin resistance. Direct exposure to TNF-alpha induces a state of insulin resistance in terms of glucose uptake in myocytes and brown adipocytes because of the activation of proinflammatory pathways that impair insulin signaling at the level of the insulin receptor substrate (IRS) proteins. In this regard, the Ser(307) residue in IRS-1 has been identified as a site for the inhibitory effects of TNF-alpha in myotubes, with p38 mitogen-activated protein kinase and inhibitor kB kinase being involved in the phosphorylation of this residue. Conversely, Ser phosphorylation of IRS-2 mediated by TNF-alpha activation of mitogen-activated protein kinase was the mechanism found in brown adipocytes. Protein-Tyr phosphatase (PTP)1B acts as a physiological, negative regulator of insulin signaling by dephosphorylating the phosphotyrosine residues of the insulin receptor and IRS-1, and PTP1B expression is increased in muscle and white adipose tissue of obese and diabetic humans and rodents. Moreover, up-regulation of PTP1B expression was recently found in cells treated with TNF-alpha Accordingly, myocytes and primary brown adipocytes deficient in PTP1B are protected against insulin resistance induced by this cytokine. Furthermore, down-regulation of PTP1B activity is possible by the use of pharmacological agonists of nuclear receptors that restore insulin sensitivity in the presence of TNF-alpha. In conclusion, the lack of PTP1B in muscle and brown adipocytes increases insulin sensitivity and glucose uptake and could confer protection against insulin resistance induced by adipokines.

Polymorphisms within the Protein Tyrosine Phosphatase 1B (PTPN1) Gene Promoter: Functional Characterization and Association with Type 2 Diabetes and Related Metabolic Traits

Background: Protein tyrosine phosphatase 1B (PTPN1) dephosphorylates insulin receptors and attenuates insulin signaling. Polymorphisms in the coding sequence of PTPN1 have been variably associated with type 2 diabetes (T2D). We hypothesized that variations within the PTPN1 promoter might contribute to the development of T2D and related metabolic traits.

Methods: We screened 2.0 kb of PTPN1 promoter in 174 T2D patients and 412 controls using PCR and denaturing HPLC. Association analysis was performed between diabetes and related traits and single-nucleotide polymorphism genotypes. We functionally tested 2 variants (−1023C&gt;A and −51delA) by measuring their influence on luciferase activity in HepG2 cells and performing the electrophoretic mobility shift assay (EMSA).

Results: One common (−1023C&gt;A) and 6 rare (−51delA, −451A&gt;G, −467T&gt;C, −1045G&gt;A, −1286-3bp-del, and −1291-9bp-del) variants were identified in the PTPN1 promoter. The −1023(C) allele had significant association with T2D that disappeared after we adjusted for established diabetes risk factors. The alleles of −1023C&gt;A and −51delA variants did not show significant effects on the biochemical markers after adjustment for established diabetes risk factors in the nondiabetic and diabetic groups separately. The −51delA variant decreased luciferase gene expression in HepG2 cells by 2-fold. EMSA revealed a weaker binding of −51delA to specific protein family proteins compared with the A allele. The −1023C&gt;A variant had no influence in either experiment.

Conclusions: The PTPN1 promoter variants −1023C&gt;A and −51delA (which appears to be functional) were not associated with T2D or related traits in this study but must be investigated in a larger population to reveal any potential metabolic association.