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

Protein Tyrosine Phosphatase 1B (PTP1B): A Comprehensive Review of Its Role in Pathogenesis of Human Diseases

Overexpression of protein tyrosine phosphatase 1B (PTP1B) disrupts signaling pathways and results in numerous human diseases. In particular, its involvement has been well documented in the pathogenesis of metabolic disorders (diabetes mellitus type I and type II, fatty liver disease, and obesity); neurodegenerative diseases (Alzheimer's disease, Parkinson's disease); major depressive disorder; calcific aortic valve disease; as well as several cancer types. Given this multitude of therapeutic applications, shortly after identification of PTP1B and its role, the pursuit to introduce safe and selective enzyme inhibitors began. Regrettably, efforts undertaken so far have proved unsuccessful, since all proposed PTP1B inhibitors failed, or are yet to complete, clinical trials. Intending to aid introduction of the new generation of PTP1B inhibitors, this work collects and organizes the current state of the art. In particular, this review intends to elucidate intricate relations between numerous diseases associated with the overexpression of PTP1B, as we believe that it is of the utmost significance to establish and follow a brand-new holistic approach in the treatment of interconnected conditions. With this in mind, this comprehensive review aims to validate the PTP1B enzyme as a promising molecular target, and to reinforce future research in this direction.

Drugging Protein Tyrosine Phosphatases through Targeted Protein Degradation

Protein tyrosine phosphatases (PTPs) are an important class of enzymes that regulate protein tyrosine phosphorylation levels of a large variety of proteins in cells. Anomalies in protein tyrosine phosphorylation have been associated with the development of numerous human diseases, leading to a heightened interest in PTPs as promising targets for drug development. However, therapeutic targeting of PTPs has faced skepticism about their druggability. Besides the conventional small molecule inhibitors, proteolysis-targeting chimera (PROTAC) technology offers an alternative approach to target PTPs. PROTAC molecules utilize the ubiquitin-proteasome system to degrade specific proteins and have unique advantages compared with inhibitors: 1) PROTACs are highly efficient and can work at much lower concentrations than that expected based on their biophysical binding affinity; 2) PROTACs may achieve higher selectivity for the targeted protein than that dictated by their binding affinity alone; and 3) PROTACs may engage any region of the target protein in addition to the functional site. This review focuses on the latest advancement in the development of targeted PTP degraders and deliberates on the obstacles and prospective paths of harnessing this technology for therapeutic targeting of the PTPs.

Proteasome activation: A novel strategy for targeting undruggable intrinsically disordered proteins

Intrinsically disordered proteins (IDPs) are characterized by their inability to adopt well-defined tertiary structures under physiological conditions. Nonetheless, they often play pivotal roles in the progression of various diseases, including cancer, neurodegenerative disorders, and cardiovascular ailments. Owing to their inherent dynamism, conventional drug design approaches based on structural considerations encounter substantial challenges when applied to IDPs. Consequently, the pursuit of therapeutic interventions directed towards IDPs presents a complex endeavor. While there are indeed existing methodologies for targeting IDPs, they are encumbered by noteworthy constrains. Hence, there exists an imminent imperative to investigate more efficacious and universally applicable strategies for modulating IDPs. Here, we present an overview of the latest advancements in the research pertaining to IDPs, along with the indirect regulation approach involving the modulation of IDP degradation through proteasome. By comprehending these advancements in research, novel insights can be generated to facilitate the development of new drugs targeted at addressing the accumulation of IDPs in diverse pathological conditions.

Insulin granule morphology and crinosome formation in mice lacking the pancreatic β cell-specific phogrin (PTPRN2) gene

We recently reported that phogrin, also known as IA-2β or PTPRN2, forms a complex with the insulin receptor in pancreatic β cells upon glucose stimulation and stabilizes insulin receptor substrate 2. In β cells of systemic phogrin gene knockout (IA-2β-/-) mice, impaired glucose-induced insulin secretion, decreased insulin granule density, and an increase in the number and size of lysosomes have been reported. Since phogrin is expressed not only in β cells but also in various neuroendocrine cells, the precise impact of phogrin expressed in β cells on these cells remains unclear. In this study, we performed a comprehensive analysis of morphological changes in RIP-Cre+/-Phogrinflox/flox (βKO) mice with β cell-specific phogrin gene knockout. Compared to control RIP-Cre+/- Phogrin+/+ (Ctrl) mice, aged βKO mice exhibited a decreased density of insulin granules, which can be categorized into three subtypes. While no differences were observed in the density and size of lysosomes and crinosomes, organelles involved in insulin granule reduction, significant alterations in the regions of lysosomes responding positively to carbohydrate labeling were evident in young βKO mice. These alterations differed from those in Ctrl mice and continued to change with age. These electron microscopic findings suggest that phogrin expression in pancreatic β cells plays a role in insulin granule homeostasis and crinophagy during aging, potentially through insulin autocrine signaling and other mechanisms.

Exploring the Anti-Diabetic Potential of Quercetagitrin through Dual Inhibition of PTPN6 and PTPN9

Protein tyrosine phosphatases (PTPs) are pivotal contributors to the development of type 2 diabetes (T2DM). Hence, directing interventions towards PTPs emerges as a valuable therapeutic approach for managing type 2 diabetes. In particular, PTPN6 and PTPN9 are targets for anti-diabetic effects. Through high-throughput drug screening, quercetagitrin (QG) was recognized as a dual-target inhibitor of PTPN6 and PTPN9. We observed that QG suppressed the catalytic activity of PTPN6 (IC50 = 1 μM) and PTPN9 (IC50 = 1.7 μM) in vitro and enhanced glucose uptake by mature C2C12 myoblasts. Additionally, QG increased the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and insulin-dependent phosphorylation of Akt in mature C2C12 myoblasts. It further promoted the phosphorylation of Akt in the presence of palmitic acid, suggesting the attenuation of insulin resistance. In summary, our results indicate QG's role as a potent inhibitor targeting both PTPN6 and PTPN9, showcasing its potential as a promising treatment avenue for T2DM.

Targeting Protein Tyrosine Phosphatases to Improve Cancer Immunotherapies

Advances in immunotherapy have brought significant therapeutic benefits to many cancer patients. Nonetheless, many cancer types are refractory to current immunotherapeutic approaches, meaning that further targets are required to increase the number of patients who benefit from these technologies. Protein tyrosine phosphatases (PTPs) have long been recognised to play a vital role in the regulation of cancer cell biology and the immune response. In this review, we summarize the evidence for both the pro-tumorigenic and tumour-suppressor function of non-receptor PTPs in cancer cells and discuss recent data showing that several of these enzymes act as intracellular immune checkpoints that suppress effective tumour immunity. We highlight new data showing that the deletion of inhibitory PTPs is a rational approach to improve the outcomes of adoptive T cell-based cancer immunotherapies and describe recent progress in the development of PTP inhibitors as anti-cancer drugs.

BACH1 controls hepatic insulin signaling and glucose homeostasis in mice

Hepatic insulin resistance is central to the metabolic syndrome. Here we investigate the role of BTB and CNC homology 1 (BACH1) in hepatic insulin signaling. BACH1 is elevated in the hepatocytes of individuals with obesity and patients with non-alcoholic fatty liver disease (NAFLD). Hepatocyte-specific Bach1 deletion in male mice on a high-fat diet (HFD) ameliorates hyperglycemia and insulin resistance, improves glucose homeostasis, and protects against steatosis, whereas hepatic overexpression of Bach1 in male mice leads to the opposite phenotype. BACH1 directly interacts with the protein-tyrosine phosphatase 1B (PTP1B) and the insulin receptor β (IR-β), and loss of BACH1 reduces the interaction between PTP1B and IR-β upon insulin stimulation and enhances insulin signaling in hepatocytes. Inhibition of PTP1B significantly attenuates BACH1-mediated suppression of insulin signaling in HFD-fed male mice. Hepatic BACH1 knockdown ameliorates hyperglycemia and improves insulin sensitivity in diabetic male mice. These results demonstrate a critical function for hepatic BACH1 in the regulation of insulin signaling and glucose homeostasis.

Protein tyrosine phosphatases as emerging targets for cancer immunotherapy

Contemporary strategies in cancer immunotherapy, despite remarkable success, remain constrained by inherent limitations such as suboptimal patient responses, the emergence of drug resistance, and the manifestation of pronounced adverse effects. Consequently, the need for alternative strategies for immunotherapy becomes clear. Protein tyrosine phosphatases (PTPs) wield a pivotal regulatory influence over an array of essential cellular processes. Substantial research has underscored the potential in targeting PTPs to modulate the immune responses and/or regulate antigen presentation, thereby presenting a novel paradigm for cancer immunotherapy. In this review, we focus on recent advances in genetic and biological validation of several PTPs as emerging targets for immunotherapy. We also highlight recent development of small molecule inhibitors and degraders targeting these PTPs as novel cancer immunotherapeutic agents.

Combinational application of the natural products 1-deoxynojirimycin and morin ameliorates insulin resistance and lipid accumulation in prediabetic mice

BACKGROUND

Prediabetes, a stage characterized by chronic inflammation, obesity and insulin resistance. Morin and 1-deoxynojirimycin (DNJ) are natural flavonoids and alkaloids extracted from Morus nigra L., exhibiting anti-hyperglycemic efficacy. However, the benefits of DNJ are shadowed by the adverse events, and the mechanism of morin in anti-diabetes remains under investigation.

PURPOSE

In this study, the combinational efficacy and mechanisms of DNJ and morin in ameliorating insulin resistance and pre-diabetes were investigated.

METHODS

The mice model with prediabetes and Alpha mouse liver-12 (AML-12) cell model with insulin resistance were established. The anti-prediabetic efficacy of the drug combination was determined via analyzing the blood glucose, lipid profiles and inflammatory factors. The application of network pharmacology provided guidance for the research mechanism.

RESULTS

In our study, the intervention of morin ameliorated the insulin resistance via activating the Peroxisome proliferator-activated receptor γ (PPARγ). However, PPARγ activation leaded to the lipid accumulation in prediabetic mice. The combination of 5 mg/kg dose of DNJ and 25 mg/kg morin effectively hindered the progression of T2DM by 87.56%, which was achieved via inhibition of Suppressors of cytokine signaling 3 (SOCS3) and promotion of PPARγ as well as SOCS2 expression. Furthermore, this treatment exhibited notable capabilities in combating dyslipidemia and adipogenesis, achieved by suppressing the Cluster of differentiation 36/ Sterol-regulatory element binding proteins-1/ Fatty acid synthetase (CD36/Serbp1/Fas) signaling.

CONCLUSION

This research confirmed that the drug combination of DNJ and morin in ameliorating insulin resistance and lipid accumulation, and revealed the potential mechanisms. In summary, the combination of DNJ and morin is an underlying alternative pharmaceutical composition in T2DM prevention.

Protein tyrosine phosphatase non-receptor type 2 as the therapeutic target of atherosclerotic diseases: past, present and future

Tyrosine-protein phosphatase non-receptor type 2(PTPN2), an important member of the protein tyrosine phosphatase family, can regulate various signaling pathways and biological processes by dephosphorylating receptor protein tyrosine kinases. Accumulating evidence has demonstrated that PTPN2 is involved in the occurrence and development of atherosclerotic cardiovascular disease. Recently, it has been reported that PTPN2 exerts an anti-atherosclerotic effect by regulating vascular endothelial injury, monocyte proliferation and migration, macrophage polarization, T cell polarization, autophagy, pyroptosis, and insulin resistance. In this review, we summarize the latest findings on the role of PTPN2 in the pathogenesis of atherosclerosis to provide a rationale for better future research and therapeutic interventions.

The impact of dietary fructose on gut permeability, microbiota, abdominal adiposity, insulin signaling and reproductive function

The excessive intake of fructose in the regular human diet could be related to global increases in metabolic disorders. Sugar-sweetened soft drinks, mostly consumed by children, adolescents, and young adults, are the main source of added fructose. Dietary high-fructose can increase intestinal permeability and circulatory endotoxin by changing the gut barrier function and microbial composition. Excess fructose transports to the liver and then triggers inflammation as well as de novo lipogenesis leading to hepatic steatosis. Fructose also induces fat deposition in adipose tissue by stimulating the expression of lipogenic genes, thus causing abdominal adiposity. Activation of the inflammatory pathway by fructose in target tissues is thought to contribute to the suppression of the insulin signaling pathway producing systemic insulin resistance. Moreover, there is some evidence that high intake of fructose negatively affects both male and female reproductive systems and may lead to infertility. This review addresses dietary high-fructose-induced deteriorations that are obvious, especially in gut permeability, microbiota, abdominal fat accumulation, insulin signaling, and reproductive function. The recognition of the detrimental effects of fructose and the development of relevant new public health policies are necessary in order to prevent diet-related metabolic disorders.

Inhibition of the type 1 diabetes candidate gene PTPN2 aggravates TNF-α-induced human beta cell dysfunction and death

AIMS/HYPOTHESIS

TNF-α plays a role in pancreatic beta cell loss in type 1 diabetes mellitus. In clinical interventions, TNF-α inhibition preserves C-peptide levels in early type 1 diabetes. In this study we evaluated the crosstalk of TNF-α, as compared with type I IFNs, with the type 1 diabetes candidate gene PTPN2 (encoding protein tyrosine phosphatase non-receptor type 2 [PTPN2]) in human beta cells.

METHODS

EndoC-βH1 cells, dispersed human pancreatic islets or induced pluripotent stem cell (iPSC)-derived islet-like cells were transfected with siRNAs targeting various genes (siCTRL, siPTPN2, siJNK1, siJNK3 or siBIM). Cells were treated for 48 h with IFN-α (2000 U/ml) or TNF-α (1000 U/ml). Cell death was evaluated using Hoechst 33342 and propidium iodide staining. mRNA levels were assessed by quantitative reverse transcription PCR (qRT-PCR) and protein expression by immunoblot.

RESULTS

PTPN2 silencing sensitised beta cells to cytotoxicity induced by IFN-α and/or TNF-α by 20-50%, depending on the human cell model utilised; there was no potentiation between the cytokines. We silenced c-Jun N-terminal kinase (JNK)1 or Bcl-2-like protein 2 (BIM), and this abolished the proapoptotic effects of IFN-α, TNF-α or the combination of both after PTPN2 inhibition. We further observed that PTPN2 silencing increased TNF-α-induced JNK1 and BIM phosphorylation and that JNK3 is necessary for beta cell resistance to IFN-α cytotoxicity.

CONCLUSIONS/INTERPRETATION

We show that the type 1 diabetes candidate gene PTPN2 is a key regulator of the deleterious effects of TNF-α in human beta cells. It is conceivable that people with type 1 diabetes carrying risk-associated PTPN2 polymorphisms may particularly benefit from therapies inhibiting TNF-α.

A small molecule inhibitor of PTP1B and PTPN2 enhances T cell anti-tumor immunity

The inhibition of protein tyrosine phosphatases 1B (PTP1B) and N2 (PTPN2) has emerged as an exciting approach for bolstering T cell anti-tumor immunity. ABBV-CLS-484 is a PTP1B/PTPN2 inhibitor in clinical trials for solid tumors. Here we have explored the therapeutic potential of a related small-molecule-inhibitor, Compound-182. We demonstrate that Compound-182 is a highly potent and selective active site competitive inhibitor of PTP1B and PTPN2 that enhances T cell recruitment and activation and represses the growth of tumors in mice, without promoting overt immune-related toxicities. The enhanced anti-tumor immunity in immunogenic tumors can be ascribed to the inhibition of PTP1B/PTPN2 in T cells, whereas in cold tumors, Compound-182 elicited direct effects on both tumor cells and T cells. Importantly, treatment with Compound-182 rendered otherwise resistant tumors sensitive to α-PD-1 therapy. Our findings establish the potential for small molecule inhibitors of PTP1B and PTPN2 to enhance anti-tumor immunity and combat cancer.

A small molecule inhibitor of PTP1B and PTPN2 enhances T cell anti-tumor immunity

The inhibition of protein tyrosine phosphatases (PTPs), such as PTP1B and PTPN2 that function as intracellular checkpoints, has emerged as an exciting new approach for bolstering T cell anti-tumor immunity to combat cancer. ABBV-CLS-484 is a dual PTP1B and PTPN2 inhibitor currently in clinical trials for solid tumors. Here we have explored the therapeutic potential of targeting PTP1B and PTPN2 with a related small molecule inhibitor, Compound 182. We demonstrate that Compound 182 is a highly potent and selective active site competitive inhibitor of PTP1B and PTPN2 that enhances antigen-induced T cell activation and expansion ex vivo and represses the growth of syngeneic tumors in C57BL/6 mice without promoting overt immune-related toxicities. Compound 182 repressed the growth of immunogenic MC38 colorectal and AT3-OVA mammary tumors as well as immunologically cold AT3 mammary tumors that are largely devoid of T cells. Treatment with Compound 182 increased both the infiltration and activation of T cells, as well as the recruitment of NK cells and B cells that promote anti-tumor immunity. The enhanced anti-tumor immunity in immunogenic AT3-OVA tumors could be ascribed largely to the inhibition of PTP1B/PTPN2 in T cells, whereas in cold AT3 tumors, Compound 182 elicited both direct effects on tumor cells and T cells to facilitate T cell recruitment and thereon activation. Importantly, treatment with Compound 182 rendered otherwise resistant AT3 tumors sensitive to anti-PD1 therapy. Our findings establish the potential for small molecule active site inhibitors of PTP1B and PTPN2 to enhance anti-tumor immunity and combat cancer.

Small Molecule Degraders of Protein Tyrosine Phosphatase 1B and T-Cell Protein Tyrosine Phosphatase for Cancer Immunotherapy

Protein tyrosine phosphatase 1B (PTP1B) and T-cell protein tyrosine phosphatase (TC-PTP) play non-redundant negative regulatory roles in T-cell activation, tumor antigen presentation, insulin and leptin signaling, and are potential targets for several therapeutic applications. Here, we report the development of a highly potent and selective small molecule degrader DU-14 for both PTP1B and TC-PTP. DU-14 mediated PTP1B and TC-PTP degradation requires both target protein(s) and VHL E3 ligase engagement and is also ubiquitination- and proteasome-dependent. DU-14 enhances IFN-γ induced JAK1/2-STAT1 pathway activation and promotes MHC-I expression in tumor cells. DU-14 also activates CD8+ T-cells and augments STAT1 and STAT5 phosphorylation. Importantly, DU-14 induces PTP1B and TC-PTP degradation in vivo and suppresses MC38 syngeneic tumor growth. The results indicate that DU-14, as the first PTP1B and TC-PTP dual degrader, merits further development for treating cancer and other indications.

Protein Tyrosine Phosphatases: Mighty oaks from little acorns grow

In October 2020, we were finally able to gather for a celebration of Eddy Fischer's 100th birthday. As with many other events, COVID had disrupted and restricted preparations for the gathering, which ultimately was held via ZOOM. Nevertheless, it was a wonderful opportunity to share a day with Eddy, an exceptional scientist and true renaissance man, and to appreciate his stellar contributions to science. Eddy Fischer, together with Ed Krebs, was responsible for the discovery of reversible protein phosphorylation, which launched the entire field of signal transduction. The importance of this seminal work is now being felt throughout the biotechnology industry with the development of drugs that target protein kinases, which have transformed the treatment of a wide array of cancers. I was privileged to have worked with Eddy both as a postdoc and a junior faculty member, during which time we laid the foundations for our current understanding of the protein tyrosine phosphatase (PTP) family of enzymes and their importance as critical regulators of signal transduction. This tribute to Eddy is based upon the talk I presented at the event, giving a personal perspective on Eddy's influence on my career, our early research efforts together in this area, and how the field has developed since then.

The SWGEDWGEIW from Soybean Peptides Reduces Insulin Resistance in 3T3-L1 Adipocytes by Activating p-Akt/GLUT4 Signaling Pathway

Diabetes mellitus, a group of metabolic disorders characterized by persistent hyperglycemia, affects millions of people worldwide and is on the rise. Dietary proteins, from a wide range of food sources, are rich in bioactive peptides with anti-diabetic properties. Notably, the protective mechanism of the single peptide SWGEDWGEIW (TSP) from soybean peptides (SBPs) on insulin resistance of adipocytes in an inflammatory state was investigated by detecting the lipolysis and glucose absorption and utilization of adipocytes. The results showed that different concentrations of TSP (5, 10, 20 µg/mL) intervention can reduce 3T3-L1 adipocytes’ insulin resistance induced by inflammatory factors in a dose-dependent manner and increase glucose utilization by 34.2 ± 4.6%, 74.5 ± 5.2%, and 86.7 ± 6.1%, respectively. Thus, TSP can significantly alleviate the lipolysis of adipocytes caused by inflammatory factors. Further mechanism analysis found that inflammatory factors significantly reduced the phosphorylation (p-Akt) of Akt, two critical proteins of glucose metabolism in adipocytes, and the expression of GLUT4 protein downstream, resulting in impaired glucose utilization, while TSP intervention significantly increased the expression of these two proteins. After pretreatment of adipocytes with PI3K inhibitor (LY294002), TSP failed to reduce the inhibition of p-Akt and GLUT4 expression in adipocytes. Meanwhile, the corresponding significant decrease in glucose absorption and the increase in the fat decomposition of adipocytes indicated that TSP reduced 3T3-L1 adipocytes’ insulin resistance by specifically activating the p-Akt/GLUT4 signal pathway. Therefore, TSP has the potential to prevent obesity-induced adipose inflammation and insulin resistance.

In Vitro Exposure to Glucose Alters the Expression of Phosphorylated Proteins in Platelets

Diabetes mellitus (DM) is a pro-thrombotic state that can potentially cause serious cardiovascular complications. Platelet hyperactivation plays an important role in these pathological processes, however there is little or no information on the effect of hyperglycemia on platelet proteins. The aim of this study was to identify the molecular targets associated with platelet reactivity under hyperglycemia. Towards this goal, we examined the effects of the exposure of platelets to 1 and 2 h glucose (300 mg/dL) and control (vehicle and osmolality control using mannitol) on platelet proteins (n = 4 samples per group) using two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) combined with MALDI-TOF/TOF tandem mass spectrometry. Two-hour exposure to glucose significantly up-regulated the expression of ATP synthase subunit beta, filamin-A, and L-lactate dehydrogenase A chain in platelets. Pro-Q Diamond staining confirmed the effect of 2 h glucose on vinculin, heat shock protein HSP 90-alpha, filamin-A, and fructose-bisphosphate aldolase A (platelet phosphorylated proteins). The identified proteins are involved in various cellular processes and functions and possibly in platelet reactivity under hyperglycemic conditions.

The Role of Oxidative Inactivation of Phosphatase PTEN and TCPTP in Fatty Liver Disease

Alcoholic liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD) are becoming increasingly prevalent worldwide. Despite the different etiologies, their spectra and histological feature are similar, from simple steatosis to more advanced stages such as steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Studies including peroxiredoxin knockout models revealed that oxidative stress is crucial in these diseases, which present as consequences of redox imbalance. Protein tyrosine phosphatases (PTPs) are a superfamily of enzymes that are major targets of reactive oxygen species (ROS) because of an oxidation-susceptible nucleophilic cysteine in their active site. Herein, we review the oxidative inactivation of two tumor suppressor PTPs, phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and T-cell protein tyrosine phosphatase (TCPTP), and their contribution to the pathogenicity of ALD and NAFLD, respectively. This review might provide a better understanding of the pathogenic mechanisms of these diseases and help develop new therapeutic strategies to treat fatty liver disease.

Macromolecular crowding amplifies allosteric regulation of T-cell protein tyrosine phosphatase

T-cell protein tyrosine phosphatase (TC-PTP) is a negative regulator of T-cell receptor and oncogenic receptor tyrosine kinase signaling and implicated in cancer and autoimmune disease. TC-PTP activity is modulated by an intrinsically disordered C-terminal region (IDR) and suppressed in cells under basal conditions. In vitro structural studies have shown that the dynamic reorganization of IDR around the catalytic domain, driven by electrostatic interactions, can lead to TC-PTP activity inhibition; however, the process has not been studied in cells. Here, by assessing a mutant (³⁷⁸KRKRPR³⁸³ mutated into ³⁷⁸EAAAPE³⁸³, called TC45^E/A) with impaired tail-PTP domain interaction, we obtained evidence that the downmodulation of TC-PTP enzymatic activity by the IDR occurs in cells. However, we found that the regulation of TC-PTP by the IDR is only recapitulated in vitro when crowding polymers that mimic the intracellular environment are present in kinetic assays using a physiological phosphopeptide. Our FRET-based assays in vitro and in cells confirmed that the effect of the mutant correlates with an impairment of the intramolecular inhibitory remodeling of TC-PTP by the IDR. This work presents an early example of the allosteric regulation of a protein tyrosine phosphatase being controlled by the cellular environment and provides a framework for future studies and targeting of TC-PTP function.

Phosphatase protector alpha4 (α4) is involved in adipocyte maintenance and mitochondrial homeostasis through regulation of insulin signaling

Insulin signaling is mediated via a network of protein phosphorylation. Dysregulation of this network is central to obesity, type 2 diabetes and metabolic syndrome. Here we investigate the role of phosphatase binding protein Alpha4 (α4) that is essential for the serine/threonine protein phosphatase 2A (PP2A) in insulin action/resistance in adipocytes. Unexpectedly, adipocyte-specific inactivation of α4 impairs insulin-induced Akt-mediated serine/threonine phosphorylation despite a decrease in the protein phosphatase 2A (PP2A) levels. Interestingly, loss of α4 also reduces insulin-induced insulin receptor tyrosine phosphorylation. This occurs through decreased association of α4 with Y-box protein 1, resulting in the enhancement of the tyrosine phosphatase protein tyrosine phosphatase 1B (PTP1B) expression. Moreover, adipocyte-specific knockout of α4 in male mice results in impaired adipogenesis and altered mitochondrial oxidation leading to increased inflammation, systemic insulin resistance, hepatosteatosis, islet hyperplasia, and impaired thermogenesis. Thus, the α4 /Y-box protein 1(YBX1)-mediated pathway of insulin receptor signaling is involved in maintaining insulin sensitivity, normal adipose tissue homeostasis and systemic metabolism.

Structural insights into the pSer/pThr dependent regulation of the SHP2 tyrosine phosphatase in insulin and CD28 signaling

Serine/threonine phosphorylation of insulin receptor substrate (IRS) proteins is well known to modulate insulin signaling. However, the molecular details of this process have mostly been elusive. While exploring the role of phosphoserines, we have detected a direct link between Tyr-flanking Ser/Thr phosphorylation sites and regulation of specific phosphotyrosine phosphatases. Here we present a concise structural study on how the activity of SHP2 phosphatase is controlled by an asymmetric, dual phosphorylation of its substrates. The structure of SHP2 has been determined with three different substrate peptides, unveiling the versatile and highly dynamic nature of substrate recruitment. What is more, the relatively stable pre-catalytic state of SHP2 could potentially be useful for inhibitor design. Our findings not only show an unusual dependence of SHP2 catalytic activity on Ser/Thr phosphorylation sites in IRS1 and CD28, but also suggest a negative regulatory mechanism that may also apply to other tyrosine kinase pathways as well.

SHP2 is an important human tyrosine phosphatase with key roles in cancer, immune responses and insulin signaling. Here, the authors explore its substrate recognition mechanism in molecular detail and uncover a complex regulatory mechanism for this enzyme that marks specific target sites for dephosphorylation.

circMAP3K4 regulates insulin resistance in trophoblast cells during gestational diabetes mellitus by modulating the miR-6795-5p/PTPN1 axis

Background

Insulin resistance (IR) during gestational diabetes mellitus (GDM) has been linked to dysregulated insulin-PI3K/Akt pathway. A defective insulin-PI3K/Akt pathway and dysregulated circular RNA (circRNA) levels have been observed in the placentas of patients with GDM; however, the mechanisms underlying this association remain unclear.

Methods

circRNAs potentially associated with GDM were selected through bioinformatics analysis and initially identified by quantitative real-time PCR (qPCR) in 9 GDM patients and 9 healthy controls, of which circMAP3K4 was further validated in additional 84 samples by qPCR. circMAP3K4 identity and localization were verified. Pearson correlation analysis was applied to evaluate the correlation between circMAP3K4 expression in the placental tissues of GDM patients and IR-related indicators. An IR model of trophoblasts was constructed using glucosamine. Interactions between miR-6795-5p and circMAP3K4 or PTPN1 were confirmed using a dual-luciferase reporter assay. The circMAP3K4/miR-6795-5p/PTPN1 axis and key markers in the insulin-PI3K/Akt pathway in placentas and trophoblasts were evaluated through qRT-PCR, immunofluorescence, and western blotting. The role of circMAP3K4 in glucose metabolism and cell growth in trophoblasts was determined using the glucose uptake and CCK8 assay, respectively.

Results

circMAP3K4 was highly expressed in the placentas of patients with GDM and the IR trophoblast model; this was associated with a dysregulated insulin-PI3K/Akt pathway. circMAP3K4 in the placentas of GDM patients was positively correlated with weight gain during pregnancy and time-glucose area under the curve of OGTT. circMAP3K4 and PTPN1 could both bind to miR-6795-5p. miR-6795-5p and PTPN1 were downregulated and upregulated, respectively, in the placentas of GDM patients and the IR trophoblast model. circMAP3K4 silencing or miR-6795-5p overexpression partially reversed the decrease in glucose uptake, inhibition in cell growth, and downregulated IRS1 and Akt phosphorylation in IR-trophoblasts; this restoration was reversed upon co-transfection with an miR-6795-5p inhibitor or PTPN1.

Conclusion

circMAP3K4 could suppress the insulin-PI3K/Akt signaling pathway via miR-6795-5p/PTPN1 axis, probably contributing to GDM-related IR.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03386-8.

[CD36 gene deletion reduces muscle insulin sensitivity in mice by up-regulating PTP1B expression]

OBJECTIVE

To investigate the effect CD36 deficiency on muscle insulin signaling in mice fed a normal-fat diet and explore the possible mechanism.

METHODS

Wild-type (WT) mice and systemic CD36 knockout (CD36^-/-) mice with normal feeding for 14 weeks (n=12) were subjected to insulin tolerance test (ITT) after intraperitoneal injection with insulin (1 U/kg). Real-time PCR was used to detect the mRNA expressions of insulin receptor (IR), insulin receptor substrate 1/2 (IRS1/2) and protein tyrosine phosphatase 1B (PTP1B), and Western blotting was performed to detect the protein expressions of AKT, IR, IRS1/2 and PTP1B in the muscle tissues of the mice. Tyrosine phosphorylation of IR and IRS1 and histone acetylation of PTP1B promoter in muscle tissues were detected using co-immunoprecipitation (Co-IP) and chromatin immunoprecipitation (ChIP), respectively.

RESULTS

CD36^-/- mice showed significantly lowered insulin sensitivity with obviously decreased area under the insulin tolerance curve in comparison with the WT mice (P < 0.05). CD36^-/- mice also had significantly higher serum insulin concentration and HOMA-IR than WT mice (P < 0.05). Western blotting showed that the p-AKT/AKT ratio in the muscle tissues was significantly decreased in CD36^-/- mice as compared with the WT mice (P < 0.01). No significant differences were found in mRNA and protein levels of IR, IRS1 and IRS2 in the muscle tissues between WT and CD36^-/- mice (P>0.05). In the muscle tissue of CD36^-/- mice, tyrosine phosphorylation levels of IR and IRS1 were significantly decreased (P < 0.05), and the mRNA and protein levels of PTP1B (P < 0.05) and histone acetylation level of PTP1B promoters (P < 0.01) were significantly increased as compared with those in the WT mice. Intraperitoneal injection of claramine, a PTP1B inhibitor, effectively improved the impairment of insulin sensitivity in CD36^-/- mice.

CONCLUSION

CD36 is essential for maintaining muscle insulin sensitivity under physiological conditions, and CD36 gene deletion in mice causes impaired insulin sensitivity by up-regulating muscle PTP1B expression, which results in detyrosine phosphorylation of IR and IRS1.

The Use of Berberine in Diabetes and Metabolic Syndrome: Two Sides of the Same Coin. A Bibliometric Analysis

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The increased prevalence of obesity, metabolic syndrome and type 2 diabetes has prompted scientists to look for new active and safe molecules that may help the prevention of metabolic disorders: hyperglycemia, insulin-resistance and dyslipidemia. Berberine is an alkaloid compound derived from plants, and it is largely used in traditional Chinese medicine. The aim of this study is to investigate in SCOPUS and Web of Science (WOS) databases how the scientists focused on the use of berberine against metabolic disorders, in human subjects. We carried A bibliometric analysis of scientific literature and performed 2 searches: 1) “Berberine” AND “Diabetes” AND “Diabetes Type 2”, 2) “Berberine” AND “Metabolic Syndrome”, both in ARTICLE (Title/Abstract/Keyword) with a time limitation of 1st January, 2000 through 31st December, 2018, with the filter on “HUMAN” AND/OR “HUMANS”. The research sorted out 500 papers, finding about 300 (60 %) in the first search definition and 200 (40 %) in the second. The refined research sorted out 46 papers regarding the use of berberine in diabetes, and 40 articles on the use of the alkaloid compound in metabolic syndrome. For both topics, we found increasing interest between 2008 and 2009, with citation trends in a constant crescendo in the overall period studied. These findings underlined that berberine is a safe and interesting botanical compound, especially against chronic-metabolic disorder that affects billions of people globally, and emphasized that scientists are interested in searching for long-term therapies that show no major adverse effects.

A Comprehensive Review on Therapeutic Perspectives of Phytosterols in Insulin Resistance: A Mechanistic Approach

Natural products in the form of functional foods have become increasingly popular due to their protective effects against life-threatening diseases, low risk of adverse effects, affordability, and accessibility. Plant components such as phytosterol, in particular, have drawn a lot of press recently due to a link between their consumption and a modest incidence of global problems, such as Type 2 Diabetes mellitus (T2DM), cancer, and cardiovascular disease. In the management of diet-related metabolic diseases, such as T2DM and cardiovascular disorders, these plant-based functional foods and nutritional supplements have unquestionably led the market in terms of cost-effectiveness, therapeutic efficacy, and safety. Diabetes mellitus is a metabolic disorder categoriszed by high blood sugar and insulin resistance, which influence major metabolic organs, such as the liver, adipose tissue, and skeletal muscle. These chronic hyperglycemia fallouts result in decreased glucose consumption by body cells, increased fat mobilisation from fat storage cells, and protein depletion in human tissues, keeping the tissues in a state of crisis. In addition, functional foods such as phytosterols improve the body’s healing process from these crises by promoting a proper physiological metabolism and cellular activities. They are plant-derived steroid molecules having structure and function similar to cholesterol, which is found in vegetables, grains, nuts, olive oil, wood pulp, legumes, cereals, and leaves, and are abundant in nature, along with phytosterol derivatives. The most copious phytosterols seen in the human diet are sitosterol, stigmasterol, and campesterol, which can be found in free form, as fatty acid/cinnamic acid esters or as glycosides processed by pancreatic enzymes. Accumulating evidence reveals that phytosterols and diets enriched with them can control glucose and lipid metabolism, as well as insulin resistance. Despite this, few studies on the advantages of sterol control in diabetes care have been published. As a basis, the primary objective of this review is to convey extensive updated information on the possibility of managing diabetes and associated complications with sterol-rich foods in molecular aspects.

Analysis of Three Architectures for Controlling PTP1B with Light

Photosensory domains are powerful tools for placing proteins under optical control, but their integration into light-sensitive chimeras is often challenging. Many designs require structural iterations, and direct comparisons of alternative approaches are rare. This study uses protein tyrosine phosphatase 1B (PTP1B), an influential regulatory enzyme, to compare three architectures for controlling PTPs with light: a protein fusion, an insertion chimera, and a split construct. All three designs permitted optical control of PTP1B activity in vitro (i.e., kinetic assays of purified enzyme) and in mammalian cells; photoresponses measured under both conditions, while different in magnitude, were linearly correlated. The fusion- and insertion-based architectures exhibited the highest dynamic range and maintained native localization patterns in mammalian cells. A single insertion architecture enabled optical control of both PTP1B and TCPTP, but not SHP2, where the analogous chimera was active but not photoswitchable. Findings suggest that PTPs are highly tolerant of domain insertions and support the use of in vitro screens to evaluate different optogenetic designs.

AgRP/NPY and POMC neurons in the arcuate nucleus and their potential role in treatment of obesity

Obesity is a major health crisis affecting over a third of the global population. This multifactorial disease is regulated via interoceptive neural circuits in the brain, whose alteration results in excessive body weight. Certain central neuronal populations in the brain are recognised as crucial nodes in energy homeostasis; in particular, the hypothalamic arcuate nucleus (ARC) region contains two peptide microcircuits that control energy balance with antagonistic functions: agouti-related peptide/neuropeptide-Y (AgRP/NPY) signals hunger and stimulates food intake; and pro-opiomelanocortin (POMC) signals satiety and reduces food intake. These neuronal peptides levels react to energy status and integrate signals from peripheral ghrelin, leptin, and insulin to regulate feeding and energy expenditure. To manage obesity comprehensively, it is crucial to understand cellular and molecular mechanisms of information processing in ARC neurons, since these regulate energy homeostasis. Importantly, a specific strategy focusing on ARC circuits needs to be devised to assist in treating obese patients and maintaining weight loss with minimal or no side effects. The aim of this review is to elucidate the recent developments in the study of AgRP-, NPY- and POMC-producing neurons, specific to their role in controlling metabolism. The impact of ghrelin, leptin, and insulin signalling via action of these neurons is also surveyed, since they also impact energy balance through this route. Lastly, we present key proteins, targeted genes, compounds, drugs, and therapies that actively work via these neurons and could potentially be used as therapeutic targets for treating obesity conditions.

The role of protein tyrosine phosphatase 1B (PTP1B) in the pathogenesis of type 2 diabetes mellitus and its complications

Insulin resistance, the most important characteristic of the type 2 diabetes mellitus (T2DM), is mostly caused by impairment in the insulin receptor (IR) signal transduction pathway. Protein tyrosine phosphatase 1B (PTP1B), one of the main negative regulators of the IR signaling pathway, is broadly expressed in various cells and tissues. PTP1B decreases the phosphorylation of the IR resulting in insulin resistance in various tissues. The evidence for the physiological role of PTP1B in regulation of metabolic pathways came from whole-body PTP1B-knockout mice. Whole-body and tissue-specific PTP1B-knockout mice showed improvement in adiposity, insulin resistance, and glucose tolerance. In addition, the key role of PTP1B in the pathogenesis of T2DM and its complications was further investigated in mice models of PTP1B deficient/overexpression. In recent years, targeting PTP1B using PTP1B inhibitors is being considered an attractive target to treat T2DM. PTP1B inhibitors improve the sensitivity of the insulin receptor and have the ability to cure insulin resistance-related diseases. We herein summarized the biological functions of PTP1B in different tissues in vivo and in vitro. We also describe the effectiveness of potent PTP1B inhibitors as pharmaceutical agents to treat T2DM.

Protein Tyrosine Phosphatases in Neuroblastoma: Emerging Roles as Biomarkers and Therapeutic Targets

Neuroblastoma is a type of cancer intimately related with early development and differentiation of neuroendocrine cells, and constitutes one of the pediatric cancers with higher incidence and mortality. Protein tyrosine phosphatases (PTPs) are key regulators of cell growth and differentiation by their direct effect on tyrosine dephosphorylation of specific protein substrates, exerting major functions in the modulation of intracellular signaling during neuron development in response to external cues driving cell proliferation, survival, and differentiation. We review here the current knowledge on the role of PTPs in neuroblastoma cell growth, survival, and differentiation. The potential of PTPs as biomarkers and molecular targets for inhibition in neuroblastoma therapies is discussed.

Germacrane sesquiterpenes from leaves of Eupatorium chinense inhibit protein tyrosine phosphatase

Three new germacrane-type sesquiterpene lactones (1-3) were isolated alongside seven known related congeners (4-10) from the leaves of Eupatorium chinense L. (Compositae). The planar structures of 1-3 were elucidated by their spectroscopic data, including 1D and 2D NMR spectra. The relative and absolute configurations of 1-3 were determined using NOESY experiments and electronic circular dichroism analyses. Compounds 1, 4, 5, and 7 inhibited protein tyrosine phosphatase (PTP) 1B activity with IC₅₀ values of 25, 11, 28, and 24 μM, respectively. Among these, compound 4 exhibited an inhibitory effect on T-cell PTP (TCPTP) with an IC₅₀ value of 25 μM. To our knowledge, this is the first study demonstrating the PTP inhibitory activity of the germacrane sesquiterpenes. The results show that compound 4 acts as an inhibitor of both PTP1B and TCPTP.

PTP61F Mediates Cell Competition and Mitigates Tumorigenesis

Tissue homeostasis via the elimination of aberrant cells is fundamental for organism survival. Cell competition is a key homeostatic mechanism, contributing to the recognition and elimination of aberrant cells, preventing their malignant progression and the development of tumors. Here, using Drosophila as a model organism, we have defined a role for protein tyrosine phosphatase 61F (PTP61F) (orthologue of mammalian PTP1B and TCPTP) in the initiation and progression of epithelial cancers. We demonstrate that a Ptp61F null mutation confers cells with a competitive advantage relative to neighbouring wild-type cells, while elevating PTP61F levels has the opposite effect. Furthermore, we show that knockdown of Ptp61F affects the survival of clones with impaired cell polarity, and that this occurs through regulation of the JAK-STAT signalling pathway. Importantly, PTP61F plays a robust non-cell-autonomous role in influencing the elimination of adjacent polarity-impaired mutant cells. Moreover, in a neoplastic RAS-driven polarity-impaired tumor model, we show that PTP61F levels determine the aggressiveness of tumors, with Ptp61F knockdown or overexpression, respectively, increasing or reducing tumor size. These effects correlate with the regulation of the RAS-MAPK and JAK-STAT signalling by PTP61F. Thus, PTP61F acts as a tumor suppressor that can function in an autonomous and non-cell-autonomous manner to ensure cellular fitness and attenuate tumorigenesis.

PTP1B is an intracellular checkpoint that limits T cell and CAR T cell anti-tumor immunity

Immunotherapies aimed at alleviating the inhibitory constraints on Tcells have revolutionised cancer management. To date, these have focused on the blockade of cell surface checkpoints such as PD-1. Herein we identify protein-tyrosine-phosphatase-1B (PTP1B) as an intracellular checkpoint that is upregulated in T cells in tumors. We show that the increased PTP1B limits T cell expansion and cytotoxicity to contribute to tumor growth. T cell-specific PTP1B deletion increased STAT-5 signaling and this enhanced the antigen-induced expansion and cytotoxicity of CD8+ T cells to suppress tumor growth. The pharmacological inhibition of PTP1B recapitulated the T cell-mediated repression of tumor growth and enhanced the response to PD-1 blockade. Furthermore, the deletion or inhibition of PTP1B enhanced the efficacy of adoptively-transferred chimeric-antigen-receptor (CAR) T cells against solid tumors. Our findings identify PTP1B as an intracellular checkpoint whose inhibition can alleviate the inhibitory constraints on T cells and CAR T cells to combat cancer.

Peptide probes containing a non-hydrolyzable phosphotyrosine-mimetic residue for enrichment of protein tyrosine phosphatases

We developed peptide probes containing a non-hydrolyzable phosphotyrosine mimetic, 4-[difluoro(phosphono)methyl]-L-phenylalanine (F₂ Pmp) for enrichment of protein tyrosine phosphatases (PTPs). We found that different F₂ Pmp probes can enrich different PTPs, depending on the probe sequence. Furthermore, proteins containing a Src homology 2 (SH2) domain were enriched together. Importantly, probes containing phosphotyrosine instead of F₂ Pmp failed to enrich PTPs due to dephosphorylation during the pulldown step. This enrichment approach using peptides containing F₂ Pmp could be a generic tool for tyrosine phosphatome analysis without the use of antibodies. This article is protected by copyright. All rights reserved.

Dual High-Resolution α-Glucosidase and PTP1B Inhibition Profiling Combined with HPLC-PDA-HRMS-SPE-NMR Analysis for the Identification of Potentially Antidiabetic Chromene Meroterpenoids from Rhododendron capitatum

Thirteen previously undescribed chromene meroterpenoids, capitachromenic acids A-M (3-6, 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b, and 11b), were identified from an ethyl acetate extract of Rhododendron capitatum, using dual high-resolution α-glucosidase and PTP1B inhibition profiling in combination with HPLC-PDA-HRMS-SPE-NMR. In addition, one known chromene meroterpenoid, daurichromenic acid (15), and its biosynthetic precursor, grifolic acid (12), two C-methylated flavanones, (2S)-5,7,4'-trihydroxy-8-methylflavanone (1) and farrerol (2), and two triterpenoids, oleanolic acid (14a) and ursolic acid (14b), were identified. New structures were elucidated by extensive 1D and 2D NMR analysis, and absolute configurations of new chromene meroterpenoids were assigned by analysis of their ECD spectra on the basis of the empirical chromane helicity rule and from Rh₂(OCOCF₃)₄-induced ECD spectra by applying the bulkiness rule. Compounds 5, 9a, 9b, 12, and 15 showed α-glucosidase inhibitory activity with IC₅₀ values ranging from 8.0 to 93.5 μM, while compounds 3, 5, 8b, 9a, 9b, 10b, 11b, 12, and 15 showed PTP1B inhibitory activity with IC₅₀ values ranging from 2.5 to 68.1 μM.

Exploration of marine natural resources in Indonesia and development of efficient strategies for the production of microbial halogenated metabolites

Nature is a prolific source of organic products with diverse scaffolds and biological activities. The process of natural product discovery has gradually become more challenging, and advances in novel strategic approaches are essential to evolve natural product chemistry. Our focus has been on surveying untouched marine resources and fermentation to enhance microbial productive performance. The first topic is the screening of marine natural products isolated from Indonesian marine organisms for new types of bioactive compounds, such as antineoplastics, antimycobacterium substances, and inhibitors of protein tyrosine phosphatase 1B, sterol O-acyl-transferase, and bone morphogenetic protein-induced osteoblastic differentiation. The unique biological properties of marine organohalides are discussed herein and attempts to efficiently produce fungal halogenated metabolites are documented. This review presents an overview of our recent work accomplishments based on the MONOTORI study.

Insulin action at a molecular level - 100 years of progress

The discovery of insulin 100 years ago and its application to the treatment of human disease in the years since have marked a major turning point in the history of medicine. The availability of purified insulin allowed for the establishment of its physiological role in the regulation of blood glucose and ketones, the determination of its amino acid sequence, and the solving of its structure. Over the last 50 years, the function of insulin has been applied into the discovery of the insulin receptor and its signaling cascade to reveal the role of impaired insulin signaling-or resistance-in the progression of type 2 diabetes. It has also become clear that insulin signaling can impact not only classical insulin-sensitive tissues, but all tissues of the body, and that in many of these tissues the insulin signaling cascade regulates unexpected physiological functions. Despite these remarkable advances, much remains to be learned about both insulin signaling and how to use this molecular knowledge to advance the treatment of type 2 diabetes and other insulin-resistant states.

T Cell Protein Tyrosine Phosphatase in Glucose Metabolism

T cell protein tyrosine phosphatase (TCPTP), a vital regulator in glucose metabolism, inflammatory responses, and tumor processes, is increasingly considered a promising target for disease treatments and illness control. This review discusses the structure, substrates and main biological functions of TCPTP, as well as its regulatory effect in glucose metabolism, as an attempt to be referenced for formulating treatment strategies of metabolic disorders. Given the complicated regulation functions in different tissues and organs of TCPTP, the development of drugs inhibiting TCPTP with a higher specificity and a better biocompatibility is recognized as a promising therapeutic strategy for diabetes or obesity. Besides, treatments targeting TCPTP in a specific tissue or organ are suggested to be considerably promising.

Microbially Guided Discovery and Biosynthesis of Biologically Active Natural Products

The design of small molecules that inhibit disease-relevant proteins represents a longstanding challenge of medicinal chemistry. Here, we describe an approach for encoding this challenge-the inhibition of a human drug target-into a microbial host and using it to guide the discovery and biosynthesis of targeted, biologically active natural products. This approach identified two previously unknown terpenoid inhibitors of protein tyrosine phosphatase 1B (PTP1B), an elusive therapeutic target for the treatment of diabetes and cancer. Both inhibitors appear to target an allosteric site, which confers selectivity, and can inhibit PTP1B in living cells. A screen of 24 uncharacterized terpene synthases from a pool of 4464 genes uncovered additional hits, demonstrating a scalable discovery approach, and the incorporation of different PTPs into the microbial host yielded alternative PTP-specific detection systems. Findings illustrate the potential for using microbes to discover and build natural products that exhibit precisely defined biochemical activities yet possess unanticipated structures and/or binding sites.

Short-Term Strength Exercise Reduces Hepatic Insulin Resistance in Obese Mice by Reducing PTP1B Content, Regardless of Changes in Body Weight

Obesity is closely related to insulin resistance and type 2 diabetes genesis. The liver is a key organ to glucose homeostasis since insulin resistance in this organ increases hepatic glucose production (HGP) and fasting hyperglycemia. The protein-tyrosine phosphatase 1B (PTP1B) may dephosphorylate the IR and IRS, contributing to insulin resistance in this organ. Aerobic exercise is a great strategy to increase insulin action in the liver by reducing the PTP1B content. In contrast, no study has shown the direct effects of strength training on the hepatic metabolism of PTP1B. Therefore, this study aims to investigate the effects of short-term strength exercise (STSE) on hepatic insulin sensitivity and PTP1B content in obese mice, regardless of body weight change. To achieve this goal, obese Swiss mice were submitted to a strength exercise protocol lasting 15 days. The results showed that STSE increased Akt phosphorylation in the liver and enhanced the control of HGP during the pyruvate tolerance test. Furthermore, sedentary obese animals increased PTP1B content and decreased IRS-1/2 tyrosine phosphorylation; however, STSE was able to reverse this scenario. Therefore, we conclude that STSE is an important strategy to improve the hepatic insulin sensitivity and HGP by reducing the PTP1B content in the liver of obese mice, regardless of changes in body weight.

Role of Receptor Protein Tyrosine Phosphatases (RPTPs) in Insulin Signaling and Secretion

Changes in lifestyle in developed countries have triggered the prevalence of obesity and type 2 diabetes mellitus (T2DM) in the latest years. Consequently, these metabolic diseases associated to insulin resistance, and the morbidity associated with them, accounts for enormous costs for the health systems. The best way to face this problem is to identify potential therapeutic targets and/or early biomarkers to help in the treatment and in the early detection. In the insulin receptor signaling cascade, the activities of protein tyrosine kinases and phosphatases are coordinated, thus, protein tyrosine kinases amplify the insulin signaling response, whereas phosphatases are required for the regulation of the rate and duration of that response. The focus of this review is to summarize the impact of transmembrane receptor protein tyrosine phosphatase (RPTPs) in the insulin signaling cascade and secretion, and their implication in metabolic diseases such as obesity and T2DM.

The PTP1B mutant PTP1B∆2-4 is a positive regulator of the JAK/STAT signalling pathway in Hodgkin lymphoma

The neoplastic Hodgkin/Reed-Sternberg (HRS) cells of classical Hodgkin lymphoma (cHL) depend on chronic activation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signalling pathways to maintain survival and proliferation. Accumulating reports highlight the importance of the inactivation or reduced expression of negative JAK/STAT regulators such as the protein-tyrosine phosphatase 1B (PTP1B/PTPN1) in this process. Various PTPN1 mRNA variants as well as truncated PTP1B proteins were identified in cHL cell lines and primary cHL tumour samples. These PTPN1 mRNA variants lack either one or several exon sequences and therefore render these PTP1B variants catalytically inactive. Here, we show that one of these mutants, PTP1B∆2-4, is not only a catalytically inactive variant, but also augmented the IL-4-induced JAK/STAT activity similar to the recently reported PTP1B∆6 splice variant. Moreover, while PTP1B∆6 diminished the activity and protein levels of PTP1BWT, PTP1BWT remained unaffected by PTP1B∆2-4, arguing for different molecular mechanisms of JAK/STAT modulation by PTP1B∆6 and PTP1B∆2-4. Collectively, these data indicate that PTPN1 variants missing one or more exon sequences originated either from alternative splicing or from gene mutation, create PTP1B gain-of-function variants with oncogenic potential by augmenting JAK/STAT signalling in cHL.

Activation of Insulin Signaling by Botanical Products

Type 2 diabetes (T2D) is a worldwide health problem, ranked as one of the leading causes for severe morbidity and premature mortality in modern society. Management of blood glucose is of major importance in order to limit the severe outcomes of the disease. However, despite the impressive success in the development of new antidiabetic drugs, almost no progress has been achieved with regard to the development of novel insulin-sensitizing agents. As insulin resistance is the most eminent factor in the patho-etiology of T2D, it is not surprising that an alarming number of patients still fail to meet glycemic goals. Owing to its wealth of chemical structures, the plant kingdom is considered as an inventory of compounds exerting various bioactivities, which might be used as a basis for the development of novel medications for various pathologies. Antidiabetic activity is found in over 400 plant species, and is attributable to varying mechanisms of action. Nevertheless, relatively limited evidence exists regarding phytochemicals directly activating insulin signaling, which is the focus of this review. Here, we will list plants and phytochemicals that have been found to improve insulin sensitivity by activation of the insulin signaling cascade, and will describe the active constituents and their mechanism of action.

Intranasal Targeting of Hypothalamic PTP1B and TCPTP Reinstates Leptin and Insulin Sensitivity and Promotes Weight Loss in Obesity

The importance of hypothalamic leptin and insulin resistance in the development and maintenance of obesity remains unclear. The tyrosine phosphatases protein tyrosine phosphatase 1B (PTP1B) and T cell protein tyrosine phosphatase (TCPTP) attenuate leptin and insulin signaling and are elevated in the hypothalami of obese mice. We report that elevated PTP1B and TCPTP antagonize hypothalamic leptin and insulin signaling and contribute to the maintenance of obesity. Deletion of PTP1B and TCPTP in the hypothalami of obese mice enhances CNS leptin and insulin sensitivity, represses feeding, and increases browning, to decrease adiposity and improve glucose metabolism. The daily intranasal administration of a PTP1B inhibitor, plus the glucocorticoid antagonist RU486 that decreases TCPTP expression, represses feeding, increases browning, promotes weight loss, and improves glucose metabolism in obese mice. Our findings causally link heightened hypothalamic PTP1B and TCPTP with leptin and insulin resistance and the maintenance of obesity and define a viable pharmacological approach by which to promote weight loss in obesity.

POMC Neurons Dysfunction in Diet-induced Metabolic Disease: Hallmark or Mechanism of Disease?

One important lesson from the last decade of studies in the field of systemic energy metabolism is that obesity is first and foremost a brain disease. Hypothalamic neurons dysfunction observed in response to chronic metabolic stress is a key pathogenic node linking consumption of hypercaloric diets with body weight gain and associated metabolic sequelae. A key hypothalamic neuronal population expressing the neuropeptide Pro-opio-melanocortin (POMC) displays altered electrical activity and dysregulated neuropeptides production capacity after long-term feeding with hypercaloric diets. However, whether such neuronal dysfunction represents a consequence or a mechanism of disease, remains a subject of debate. Here, we will review and highlight emerging pathogenic mechanisms that explain why POMC neurons undergo dysfunctional activity in response to caloric overload, and critically address whether these mechanisms may be causally implicated in the physiopathology of obesity and of its associated co-morbidities.

The Role of Protein Tyrosine Phosphatase (PTP)-1B in Cardiovascular Disease and Its Interplay with Insulin Resistance

Endothelial dysfunction is a key feature of cardiovascular disorders associated with obesity and diabetes. Several studies identified protein tyrosine phosphatase (PTP)-1B, a member of the PTP superfamily, as a major negative regulator for insulin receptor signaling and a novel molecular player in endothelial dysfunction and cardiovascular disease. Unlike other anti-diabetic approaches, genetic deletion or pharmacological inhibition of PTP1B was found to improve glucose homeostasis and insulin signaling without causing lipid buildup in the liver, which represents an advantage over existing therapies. Furthermore, PTP1B was reported to contribute to cardiovascular disturbances, at various molecular levels, which places this enzyme as a unique single therapeutic target for both diabetes and cardiovascular disorders. Synthesizing selective small molecule inhibitors for PTP1B is faced with multiple challenges linked to its similarity of sequence with other PTPs; however, overcoming these challenges would pave the way for novel approaches to treat diabetes and its concurrent cardiovascular complications. In this review article, we summarized the major roles of PTP1B in cardiovascular disease with special emphasis on endothelial dysfunction and its interplay with insulin resistance. Furthermore, we discussed some of the major challenges hindering the synthesis of selective inhibitors for PTP1B.

Therapeutic Mechanisms of Herbal Medicines Against Insulin Resistance: A Review

Insulin resistance is a condition in which insulin sensitivity is reduced and the insulin signaling pathway is impaired. Although often expressed as an increase in insulin concentration, the disease is characterized by a decrease in insulin action. This increased workload of the pancreas and the consequent decompensation are not only the main mechanisms for the development of type 2 diabetes (T2D), but also exacerbate the damage of metabolic diseases, including obesity, nonalcoholic fatty liver disease, polycystic ovary syndrome, metabolic syndrome, and others. Many clinical trials have suggested the potential role of herbs in the treatment of insulin resistance, although most of the clinical trials included in this review have certain flaws and bias risks in their methodological design, including the generation of randomization, the concealment of allocation, blinding, and inadequate reporting of sample size estimates. These studies involve not only the single-flavored herbs, but also herbal formulas, extracts, and active ingredients. Numerous of in vitro and in vivo studies have pointed out that the role of herbal medicine in improving insulin resistance is related to interventions in various aspects of the insulin signaling pathway. The targets involved in these studies include insulin receptor substrate, phosphatidylinositol 3-kinase, glucose transporter, AMP-activated protein kinase, glycogen synthase kinase 3, mitogen-activated protein kinases, c-Jun-N-terminal kinase, nuclear factor-kappaB, protein tyrosine phosphatase 1B, nuclear factor-E2-related factor 2, and peroxisome proliferator-activated receptors. Improved insulin sensitivity upon treatment with herbal medicine provides considerable prospects for treating insulin resistance. This article reviews studies of the target mechanisms of herbal treatments for insulin resistance.