Protein Tyrosine Phosphatase 1B Knockout Research Articles

Oleanolic acid derivative alleviates cardiac fibrosis through inhibiting PTP1B activity and regulating AMPK/TGF-β/Smads pathway

Cardiac fibrosis (CF) in response to persistent exogenous stimuli or myocardial injury results in cardiovascular diseases (CVDs). Protein tyrosine phosphatase 1B (PTP1B) can promote collagen deposition through regulating AMPK/TGF-β/Smads signaling pathway, and PTP1B knockout improves cardiac dysfunction against overload-induced heart failure. Oleanolic acid (OA) has been proven to be an inhibitor of PTP1B, and its anti-cardiac remodeling effects have been validated in different mouse models. To improve the bioactivity of OA and to clarify whether OA derivatives with stronger inhibition of PTP1B activity have greater prevention of cardiac remodeling than OA, four new OA derivatives were synthesized and among them, we found that compound B had better effects than OA in inhibiting cardiac fibrosis both in vivo in the isoproterenol (ISO)-induced mouse cardiac fibrosis and in vitro in the TGF-β/ISO-induced 3T3 cells. Combining with the results of molecular docking, surface plasmon resonance and PTP1B activity assay, we reported that OA and compound B directly bound to PTP1B and inhibited its activity, and that compound B showed comparable binding capability but stronger inhibitory effect on PTP1B activity than OA. Moreover, compound B presented much greater effects on AMPK activation and TGF-β/Smads inhibition than OA. Taken together, OA derivative compound B more significantly alleviated cardiac fibrosis than OA through much greater inhibition of PTP1B activity and thus much stronger regulation of AMPK/TGF-β/Smads signaling pathway.

Hypothalamic JNK1-hepatic fatty acid synthase axis mediates a metabolic rewiring that prevents hepatic steatosis in male mice treated with olanzapine via intraperitoneal: Additional effects of PTP1B inhibition

Olanzapine (OLA), a widely used second-generation antipsychotic (SGA), causes weight gain and metabolic alterations when administered orally to patients. Recently, we demonstrated that, contrarily to the oral treatment which induces weight gain, OLA administered via intraperitoneal (i.p.) in male mice resulted in body weight loss. This protection was due to an increase in energy expenditure (EE) through a mechanism involving the modulation of hypothalamic AMPK activation by higher OLA levels reaching this brain region compared to those of the oral treatment. Since clinical studies have shown hepatic steatosis upon chronic treatment with OLA, herein we further investigated the role of the hypothalamus-liver interactome upon OLA administration in wild-type (WT) and protein tyrosine phosphatase 1B knockout (PTP1B–KO) mice, a preclinical model protected against metabolic syndrome. WT and PTP1B–KO male mice were fed an OLA-supplemented diet or treated via i.p. Mechanistically, we found that OLA i.p. treatment induces mild oxidative stress and inflammation in the hypothalamus in a JNK1-independent and dependent manner, respectively, without features of cell dead. Hypothalamic JNK activation up-regulated lipogenic gene expression in the liver though the vagus nerve. This effect concurred with an unexpected metabolic rewiring in the liver in which ATP depletion resulted in increased AMPK/ACC phosphorylation. This starvation-like signature prevented steatosis. By contrast, intrahepatic lipid accumulation was observed in WT mice treated orally with OLA; this effect being absent in PTP1B–KO mice. We also demonstrated an additional benefit of PTP1B inhibition against hypothalamic JNK activation, oxidative stress and inflammation induced by chronic OLA i.p. treatment, thereby preventing hepatic lipogenesis. The protection conferred by PTP1B deficiency against hepatic steatosis in the oral OLA treatment or against oxidative stress and neuroinflammation in the i.p. treatment strongly suggests that targeting PTP1B might be also a therapeutic strategy to prevent metabolic comorbidities in patients under OLA treatment in a personalized manner.

Abstract P3058: Cardiac-specific Deletion Of Ptp1b Induces A Global Metabolic And Lean Phenotype

About 13% of US adults have diabetes, and more than half of them exhibitcardiac hypertrophy and fibrosis, resulting in cardiac diastolic dysfunction,systolic dysfunction and heart failure. Obesity is the leading risk factor for type2 diabetes. The Global Burden of Disease 2019 listed the high BMI as the fifthrisk of preterm deaths for females, and the sixth for males worldwide. Thecurrent treatments for these diseases are ineffective providing an urgent needof new therapeutic targets. Protein tyrosine phosphatase 1B (PTP1B) is themaster regulator of insulin signaling and its expression in brain, heart, liver andadipose tissues are elevated in obese mice and humans. It has been reportedthat neuronal deletion of PTP1B decreased food intake, increased energyexpenditure and protected mice from diet-induced obesity. However, whetherPTP1B in peripheral tissues would also contribute to diet-induced obesityremains unclear. To test if cardiac-PTP1B plays roles in the development ofobesity, we generated cardiomyocyte-specific PTP1B knockout mice (PTP1BCM-KO mice) and fed them with high-fat diets. Our preliminary datademonstrated that, compared to control mice, the PTP1B CM-KO mice hadreduced body weight and improved glucose homeostasis. Further analysisrevealed that deletion of PTP1B in cardiomyocytes increased energyexpenditure but didn’t affect the food intake. Metabolomics data suggested fattyacid oxidation is elevated in PTP1B CM-KO mice heart, whereas the glycolysispathway is suppressed, the amount of AMP (Adenosine Monophosphate) inPTP1B CM-KO mice is elevated 86 times than control mice on HFD. Thesefindings were further verified by qPCR analysis and ELISA. PTP1B knockoutupregulated not only NAD+ (nicotinamide adenine dinucleotide) but alsoNADPH in the heart. Nicotinamide phosphoribosyltransferase (Nampt) is therate-limiting enzyme of the NAD + salvage pathway and exists in an intracellular(iNampt) and an extracellular (eNampt) form. iNampt plays a regulatory role inNAD + biosynthesis and affects energy homeostasis. eNampt has been reportedto act as a cytokine and associated with obesity and diabetes. In the PTP1BCM-KO mice, we observed a higher level of both iNampt and eNampt,suggesting a mechanism through iNampt locally and/or through eNamptsystematically. Based on these observations, we hypothesize that the deficiency of PTP1B in cardiomyocytes increases energy expenditure,protects mice from diet-induced obesity and attenuates cardiacmalfunction induced by obesity, and cardiac-PTP1B governs whole bodyenergy homeostasis through Nampt and NAD + . We will test our hypothesisin the following specific Aims: Aim1: To elucidate the role of PTP1B in cardiac function and glucosehomeostasis.Aim2: To determine if and how the deletion of cardiac-PTP1B affectenergy balance and metabolic status through iNampt locally and/oreNampt systemically.

Deletion of PTP1B From Brain Neurons Partly Protects Mice From Diet-Induced Obesity and Minimally Improves Fertility.

Reproductive dysfunction in women has been linked to high caloric diet (HCD)-feeding and obesity. Central resistance to leptin and insulin have been shown to accompany diet-induced infertility in rodent studies, and we have previously shown that deleting suppressor of cytokine signaling 3, which is a negative regulator of leptin signaling, from all forebrain neurons partially protects mice from HCD-induced infertility. In this study, we were interested in exploring the role of protein tyrosine phosphatase 1B (PTP1B), which is a negative regulator of both leptin and insulin signaling, in the pathophysiology of HCD-induced obesity and infertility. To this end, we generated male and female neuron-specific PTP1B knockout mice and compared their body weight gain, food intake, glucose tolerance, and fertility relative to control littermates under both normal calorie diet and HCD feeding conditions. Both male and female mice with neuronal PTP1B deletion exhibited slower body weight gain in response to HCD feeding, yet only male knockout mice exhibited improved glucose tolerance compared with controls. Neuronal PTP1B deletion improved the time to first litter in HCD-fed mice but did not protect female mice from eventual HCD-induced infertility. While the mice fed a normal caloric diet remained fertile throughout the 150-day period of assessment, HCD-fed females became infertile after producing only a single litter, regardless of their genotype. These data show that neuronal PTP1B deletion is able to partially protect mice from HCD-induced obesity but is not a critical mediator of HCD-induced infertility.

Regulation of Phosphoinositide Levels in the Retina by Protein Tyrosine Phosphatase 1B and Growth Factor Receptor-Bound Protein 14.

Protein tyrosine kinases and protein phosphatases play a critical role in cellular regulation. The length of a cellular response depends on the interplay between activating protein kinases and deactivating protein phosphatases. Protein tyrosine phosphatase 1B (PTP1B) and growth factor receptor-bound protein 14 (Grb14) are negative regulators of receptor tyrosine kinases. However, in the retina, we have previously shown that PTP1B inactivates insulin receptor signaling, whereas phosphorylated Grb14 inhibits PTP1B activity. In silico docking of phosphorylated Grb14 and PTP1B indicate critical residues in PTP1B that may mediate the interaction. Phosphoinositides (PIPs) are acidic lipids and minor constituents in the cell that play an important role in cellular processes. Their levels are regulated by growth factor signaling. Using phosphoinositide binding protein probes, we observed increased levels of PI(3)P, PI(4)P, PI(3,4)P2, PI(4,5)P2, and PI(3,4,5)P3 in PTP1B knockout mouse retina and decreased levels of these PIPs in Grb14 knockout mouse retina. These observations suggest that the interplay between PTP1B and Grb14 can regulate PIP metabolism.

Deletion of protein tyrosine phosphatase 1B obliterates endoplasmic reticulum stress-induced myocardial dysfunction through regulation of autophagy

Endoplasmic reticulum (ER) stress has been demonstrated to prompt various cardiovascular risks although the underlying mechanism remains elusive. Protein tyrosine phosphatase-1B (PTP1B) serves as an essential negative regulator for insulin signaling. This study examined the role of PTP1B in ER stress-induced myocardial anomalies and underlying mechanism involved with a focus on autophagy. WT and PTP1B knockout mice were subjected to the ER stress inducer tunicamycin (1mg/kg). Cardiac function was evaluated with echocardiography and an Ion-Optix MyoCam system. Western blot analysis was used to monitor the levels of ER stress, autophagy and insulin signaling including insulin receptor substrate (IRS), tribbles homolog 3 (TRIB3), Atg5/7, p62 and LC3-II. Our results showed that ER stress resulted in compromised echocardiographic and cardiomyocyte contractile function, intracellular Ca2+ mishandling, ER stress, O2− production, apoptosis, the effects of which (with the exception of ER stress) were significantly attenuated or negated by PTP1B ablation. Levels of serine phosphorylation of IRS-1, TRIB3, Atg5/7, LC3B and the autophagy adaptor p62 were significantly upregulated while IRS-1 tyrosine phosphorylation was reduced by tunicamycin, the effect of which were obliterated by PTP1B ablation. In vitro study revealed that the autophagy inducer rapamycin and TRIB3 overexpression cancelled PTP1B ablation-offered beneficial effects on cardiomyocyte function or O2− production in murine cardiomyocytes or H9C2 myoblasts. Antioxidant or gene silencing of TRIB3 mimicked PTP1B ablation-induced protective effects. These findings collectively suggested that PTP1B ablation protects against ER stress-induced cardiac anomalies through regulation of autophagy.

Myeloid protein tyrosine phosphatase 1B (PTP1B) deficiency protects against atherosclerotic plaque formation in the ApoE−/− mouse model of atherosclerosis with alterations in IL10/AMPKα pathway

ObjectiveCardiovascular disease (CVD) is the most prevalent cause of mortality among patients with Type 1 or Type 2 diabetes, due to accelerated atherosclerosis. Recent evidence suggests a strong link between atherosclerosis and insulin resistance due to impaired insulin receptor (IR) signaling. Moreover, inflammatory cells, in particular macrophages, play a key role in pathogenesis of atherosclerosis and insulin resistance in humans. We hypothesized that inhibiting the activity of protein tyrosine phosphatase 1B (PTP1B), the major negative regulator of the IR, specifically in macrophages, would have beneficial anti-inflammatory effects and lead to protection against atherosclerosis and CVD. MethodsWe generated novel macrophage-specific PTP1B knockout mice on atherogenic background (ApoE−/−/LysM-PTP1B). Mice were fed standard or pro-atherogenic diet, and body weight, adiposity (echoMRI), glucose homeostasis, atherosclerotic plaque development, and molecular, biochemical and targeted lipidomic eicosanoid analyses were performed. ResultsMyeloid-PTP1B knockout mice on atherogenic background (ApoE−/−/LysM-PTP1B) exhibited a striking improvement in glucose homeostasis, decreased circulating lipids and decreased atherosclerotic plaque lesions, in the absence of body weight/adiposity differences. This was associated with enhanced phosphorylation of aortic Akt, AMPKα and increased secretion of circulating anti-inflammatory cytokine interleukin-10 (IL-10) and prostaglandin E2 (PGE2), without measurable alterations in IR phosphorylation, suggesting a direct beneficial effect of myeloid-PTP1B targeting. ConclusionsHere we demonstrate that inhibiting the activity of PTP1B specifically in myeloid lineage cells protects against atherosclerotic plaque formation, under atherogenic conditions, in an ApoE−/− mouse model of atherosclerosis. Our findings suggest for the first time that macrophage PTP1B targeting could be a therapeutic target for atherosclerosis treatment and reduction of CVD risk.

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

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

Antiobesity Effect of SA37 in High‐Fat Diet‐induced Obese C57BL/6J Mice

SA37 inhibits protein tyrosine phosphatase 1B (PTP1B) with a medium potency, and inhibits IκB kinase β (IKKβ) at a submicromolar half‐maximal inhibitory concentration. In animal study, SA37 reduced diet‐induced weight gain in mice, without significantly ameliorating glucose tolerance and lipid parameters. These observations coincide partly with PTP1B knockout but are inconsistent with IKKβ depletion in mice. The effect of SA37 on high‐fat diet (HFD)‐induced obese mice was compared with previous results obtained by the authors’ group on a series of SA compounds that exhibited different inhibitory potencies toward IKKβ and PTP1B.

Pancreatic protein tyrosine phosphatase 1B deficiency exacerbates acute pancreatitis in mice

Acute pancreatitis (AP) is one of the most common gastrointestinal disorders and causes significant morbidity. The disease starts as local inflammation in the pancreas that may progress to systemic inflammation and complications. Protein tyrosine phosphatase 1B (PTP1B) is implicated in inflammatory signaling but its significance in AP remains unclear. To investigate whether PTP1B may have a role in AP we utilized pancreas PTP1B knockout (panc‐PTP1B KO) mice to determine the effects of pancreatic PTP1B deficiency on cerulein‐ and arginine‐induced pancreatitis. PTP1B protein expression was increased in the early phase of AP in mice and rats. In addition, histological analyses of pancreas samples revealed enhanced features of AP in cerulein‐treated panc‐PTP1B KO mice compared with controls. Moreover, cerulein‐ and arginine‐induced serum amylase and lipase were higher in panc‐PTP1B KO mice compared with controls. Similarly, pancreatic mRNA and serum concentrations of the inflammatory cytokines IL‐1β, IL‐6 and TNFα were increased in panc‐PTP1B KO mice. Moreover, panc‐PTP1B KO mice exhibited enhanced cerulein‐ and arginine‐induced NF‐κB inflammatory response accompanied by increased MAPKs activation and elevated ER stress. These findings revealed a novel role for pancreatic PTP1B in cerulein‐ and arginine‐induced acute pancreatitis.

Role of sodium tungstate as a potential antiplatelet agent

PurposePlatelet inhibition is a key strategy in the management of atherothrombosis. However, the large variability in response to current strategies leads to the search for alternative inhibitors. The antiplatelet effect of the inorganic salt sodium tungstate (Na2O4W), a protein tyrosine phosphatase 1B (PTP1B) inhibitor, has been investigated in this study.MethodsWild-type (WT) and PTP1B knockout (PTP1B−/−) mice were treated for 1 week with Na2O4W to study platelet function with the platelet function analyzer PFA-100, a cone-and-plate analyzer, a flat perfusion chamber, and thrombus formation in vivo. Human blood aliquots were incubated with Na2O4W for 1 hour to measure platelet function using the PFA-100 and the annular perfusion chamber. Aggregometry and thromboelastometry were also performed.ResultsIn WT mice, Na2O4W treatment prolonged closure times in the PFA-100 and decreased the surface covered (%SC) by platelets on collagen. Thrombi formed in a thrombosis mice model were smaller in animals treated with Na2O4W (4.6±0.7 mg vs 8.9±0.7 mg; P<0.001). Results with Na2O4W were similar to those in untreated PTP1B−/− mice (5.0±0.3 mg). Treatment of the PTP1B−/− mice with Na2O4W modified only slightly this response. In human blood, a dose-dependent effect was observed. At 200 μM, closure times in the PFA-100 were prolonged. On denuded vessels, %SC and thrombi formation (%T) decreased with Na2O4W. Neither the aggregating response nor the viscoelastic clot properties were affected.ConclusionNa2O4W decreases consistently the hemostatic capacity of platelets, inhibiting their adhesive and cohesive properties under flow conditions in mice and in human blood, resulting in smaller thrombi. Although Na2O4W may be acting on platelet PTP1B, other potential targets should not be disregarded.

Protein tyrosine phosphatase 1B impairs diabetic wound healing through vascular endothelial growth factor receptor 2 dephosphorylation.

Impaired wound healing is a major complication of diabetes mellitus. The mechanisms that govern wound healing, however, are complex and incompletely understood. In the present study, we determined the inhibitory role of protein tyrosine phosphatase 1B (PTP1B) in the process of diabetic wound healing. First, by comparing the wound healing process in PTP1B knockout (PTP1B(-/-)) mice, ob/ob mice and their wild-type littermates in the presence or absence of streptozotocin treatment, we showed that the inhibition of mouse wound healing in streptozotocin-induced diabetic conditions is because of the upregulation and activation of PTP1B. Second, the impaired wound healing in ob/ob mice and streptozotocin-treated wild-type mice was rescued by a PTP1B inhibitor. Third, PTP1B, which is upregulated under hyperglycemic condition, inhibited the tube formation, proliferation, and migration of human microvascular endothelial cells induced by vascular endothelial growth factor, whereas this inhibition was largely abolished by the PTP1B inhibitor. Finally, mechanism study further indicated that PTP1B likely suppressed the proliferation, migration, and tube formation of vascular endothelial cells through dephosphorylation of vascular endothelial growth factor receptor 2. Our study demonstrated that PTP1B negatively modulated the diabetic wound healing process by dephosphorylating the endothelial cell vascular endothelial growth factor receptor 2 and that the specific inhibitor of PTP1B might serve as a potential novel therapeutic tool for diabetic wound healing.

Effects of hepatic protein tyrosine phosphatase 1B and methionine restriction on hepatic and whole-body glucose and lipid metabolism in mice

AimsMethionine restriction (MR) and hepatic protein tyrosine phosphatase 1B (PTP1B) knockdown both improve hepatic insulin sensitivity by targeting different proteins within the insulin signaling pathway, as well as diminishing hepatic triglyceride content through decreasing hepatic lipogenesis. We hypothesized that a combined approach of hepatic PTP1B inhibition and methionine restriction could lead to a synergistic effect on improvements in glucose homeostasis and lipid metabolism. MethodsMale and female hepatic PTP1B knockout (Alb-Ptp1b-/-) and control wild-type (Ptp1bfl/fl) mice were maintained on control diet (0.86% methionine) or MR diet (0.172% methionine) for 8weeks. Body weight and food intake were recorded and physiological tests for whole-body glucose homeostasis were performed. Serum and tissues were analyzed biochemically. ResultsMR decreased body weight and increased food intake in Ptp1bfl/fl mice as expected, without changing PTP1B protein expression levels or activity. In females, MR treatment alone improved glucose tolerance in Ptp1bfl/fl mice, which was further amplified with hepatic PTP1B deficiency. However, other markers of glucose homeostasis were similar between MR-fed groups. In males, MR improved glucose homeostasis in both, Alb-Ptp1b-/- and wild-type Ptp1bfl/fl mice to a similar extent. Hepatic PTP1B inhibition in combination with MR could not further enhance insulin-stimulated hepatic protein kinase B/Akt phosphorylation compared to MR treatment alone and therefore led to no further increase in hepatic insulin signaling. The combined treatment did not further improve lipid metabolism relative to MR diet alone. ConclusionsMethionine restriction improves glucose and lipid homeostasis; however, adding hepatic PTP1B inhibition to MR is unlikely to yield any additional protective effects.

Complement-mediated glomerular injury is reduced by inhibition of protein-tyrosine phosphatase 1B.

The unfolded protein response and endoplasmic reticulum-associated degradation (ERAD) contribute to injury in renal glomerular diseases, including those mediated by complement C5b-9. In the present study, we address the role of protein-tyrosine phosphatase 1B (PTP1B) in complement-mediated glomerular injury and ERAD. In glomerular epithelial cells (GECs)/podocytes and PTP1B-deficient mouse embryonic fibroblasts exposed to complement, inhibition/deletion of PTP1B reduced ERAD, as monitored by the ERAD reporter CD3δ. Overexpression of PTP1B produced an effect similar to PTP1B deficiency on ERAD in complement-treated GECs. Complement-mediated cytotoxicity was reduced after PTP1B overexpression and tended to be reduced after PTP1B inhibition. PTP1B enhanced the induction of certain ERAD components via the inositol-requiring-1α branch of the unfolded protein response. PTP1B knockout mice with anti-glomerular basement membrane glomerulonephritis had decreased proteinuria and showed less podocyte loss and endoplasmic reticulum dysfunction compared with wild-type littermates. These results imply that endogenous levels of PTP1B are tightly regulated and that both overexpression and inhibition can affect ERAD. The cytoprotective effects of PTP1B deletion in cultured cells and in anti-glomerular basement membrane nephritis suggest that PTP1B may potentially be a therapeutic target in complement-mediated diseases.

Deletion of protein tyrosine phosphatase 1B rescues against myocardial anomalies in high fat diet-induced obesity: Role of AMPK-dependent autophagy

Obesity-induced cardiomyopathy may be mediated by alterations in multiple signaling cascades involved in glucose and lipid metabolism. Protein tyrosine phosphatase-1B (PTP1B) is an important negative regulator of insulin signaling. This study was designed to evaluate the role of PTP1B in high fat diet-induced cardiac contractile anomalies. Wild-type and PTP1B knockout mice were fed normal (10%) or high (45%) fat diet for 5months prior to evaluation of cardiac function. Myocardial function was assessed using echocardiography and an Ion-Optix MyoCam system. Western blot analysis was employed to evaluate levels of AMPK, mTOR, raptor, Beclin-1, p62 and LC3-II. RT-PCR technique was employed to assess genes involved in hypertrophy and lipid metabolism. Our data revealed increased LV thickness and LV chamber size as well as decreased fractional shortening following high fat diet intake, the effect was nullified by PTP1B knockout. High fat diet intake compromised cardiomyocyte contractile function as evidenced by decreased peak shortening, maximal velocity of shortening/relengthening, intracellular Ca2+ release as well as prolonged duration of relengthening and intracellular Ca2+ decay, the effects of which were alleviated by PTP1B knockout. High fat diet resulted in enlarged cardiomyocyte area and increased lipid accumulation, which were attenuated by PTP1B knockout. High fat diet intake dampened myocardial autophagy as evidenced by decreased LC3-II conversion and Beclin-1, increased p62 levels as well as decreased phosphorylation of AMPK and raptor, the effects of which were significantly alleviated by PTP1B knockout. Pharmacological inhibition of AMPK using compound C disengaged PTP1B knockout-conferred protection against fatty acid-induced cardiomyocyte contractile anomalies. Taken together, our results suggest that PTP1B knockout offers cardioprotection against high fat diet intake through activation of AMPK. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Protein Tyrosine Phosphatase 1B Inhibition Protects against Podocyte Injury and Proteinuria

Protein tyrosine phosphatase 1B (PTP1B) is a ubiquitously expressed nonreceptor protein-tyrosine phosphatase that regulates various cellular functions, including migration. Recent studies suggest that an increased migratory phenotype of podocytes may be responsible for proteinuria and foot process effacement. The current study addresses the role of PTP1B in podocyte injury and proteinuria. PTP1B was markedly up-regulated in the glomerulus, notably in podocytes, in three rodent models of podocyte injury. Podocyte-specific ablation of the PTP1B gene ameliorated proteinuria induced by lipopolysaccharide and Adriamycin (doxorubicin). The use of a specific PTP1B inhibitor also protected against lipopolysaccharide-induced proteinuria. In contrast, podocyte-specific PTP1B transgenic male mice developed spontaneous proteinuria and foot process effacement. In cultured mouse podocytes, PTP1B knockdown and/or pretreatment with the PTP1B inhibitor blunted lipopolysaccharide-induced cell migration, activation of Src-family kinases (SFKs), and phosphorylation of focal adhesion kinase at Y397 (pFAK(Y397)), the latter being crucial for cell migration. Lipopolysaccharide-injected mice showed increased glomerular expression of active SFKs and pFAK(Y397), both of which were inhibited by podocyte-specific PTP1B knockout and the PTP1B inhibitor. Moreover, podocyte-specific PTP1B transgenic mice showed increased glomerular expression of active SFKs and pFAK(Y397). In summary, PTP1B up-regulation in podocytes induces a migratory response by activating SFKs and FAK, leading to foot process effacement and proteinuria. Pharmacological inhibition of PTP1B may have therapeutic potential in the treatment of proteinuric diseases.

Regulation of growth hormone induced JAK2 and mTOR signalling by hepatic protein tyrosine phosphatase 1B

Protein tyrosine phosphatase 1B (PTP1B) regulates various signalling pathways including insulin, leptin, IGF-1 and growth hormone (GH) signalling. Transmission of the GH signal depends on Janus kinase 2 (JAK2), which is how PTP1B is thought to modulate GH signalling in the liver, based on studies utilising global PTP1B knockout mice (Ptp1b−/−). Here, we investigated the liver-specific role of PTP1B in GH signalling, using liver-specific Ptp1b−/− mice (alb-crePtp1b−/−), under physiological (chow) or insulin resistant (high-fat diet [HFD]) feeding conditions. Body weight and adiposity were comparable between female alb-crePtp1b−/− and Ptp1bfl/fl control mice. On chow diet, under 48-hour fasting GH-resistant conditions, GH stimulation in vivo led to a robust stimulation of the JAK-STAT signalling pathway. Alb-crePtp1b−/− mice exhibited significantly higher GH-induced JAK2 phosphorylation and SOCS3 gene expression post-GH stimulation. However, STAT3, STAT5 and ERK1/2 phosphorylation and SOCS2 gene expression were similar between groups. Interestingly, GH-induced mTOR phosphorylation was significantly higher in alb-crePtp1b−/− mice 5-min post-GH stimulation compared to controls, revealing this part of the pathway under direct control of PTP1B. Under ad lib HFD-fed conditions, GH-induced STAT5 phosphorylation significantly increased in alb-crePtp1b−/− mice only, with no alterations in the controls. Overall, our data demonstrate that liver-specific PTP1B deletion leads to significant alterations in GH signalling with increased JAK2, STAT5 and mTOR phosphorylation and SOCS3 gene expression.

Protein Tyrosine Phosphatase-1B Modulates Pancreatic β-cell Mass

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of the insulin signalling pathway. It has been demonstrated that PTP1B deletion protects against the development of obesity and Type 2 Diabetes, mainly through its action on peripheral tissues. However, little attention has been paid to the role of PTP1B in β-cells. Therefore, our aim was to study the role of PTP1B in pancreatic β-cells. Silencing of PTP1B expression in a pancreatic β-cell line (MIN6 cells) reveals the significance of this endoplasmic reticulum bound phosphatase in the regulation of cell proliferation and apoptosis. Furthermore, the ablation of PTP1B is able to regulate key proteins involved in the proliferation and/or apoptosis pathways, such as STAT3, AKT, ERK1/2 and p53 in isolated islets from PTP1B knockout (PTP1B −/−) mice. Morphometric analysis of pancreatic islets from PTP1B −/− mice showed a higher β-cell area, concomitantly with higher β-cell proliferation and a lower β-cell apoptosis when compared to islets from their respective wild type (WT) littermates. At a functional level, isolated islets from 8 weeks old PTP1B −/− mice exhibit enhanced glucose-stimulated insulin secretion. Moreover, PTP1B −/− mice were able to partially reverse streptozotocin-induced β-cell loss. Together, our data highlight for the first time the involvement of PTP1B in β-cell physiology, reinforcing the potential of this phosphatase as a therapeutical target for the treatment of β-cell failure, a central aspect in the pathogenesis of Type 2 Diabetes.

Relationship status update for PTP1B and LepR: It׳s complicated.

The adipocyte-derived hormone leptin is an important regulator of systemic energy metabolism. Transported via the circulation to the brain in proportion to fat mass, leptin promotes its biological action through activation of the long form of the leptin receptor (LepRb). Accordingly, binding of leptin to the extracellular domain of LepRb promotes transphosphorylation of the LepRb-associated Janus kinase 2 (JAK2), which in turn phosphorylates other tyrosine residues (Tyr985, Tyr1077, Tyr1138) along the intracellular tail of LepRb in order to facilitate downstream signaling [1]. The protein tyrosine phosphatase 1B (PTP1B) is an important negative regulator of leptin action due to its ability to directly inhibit LepRb-Jak2 signaling (Figure 1). The relevance of PTP1B to regulate energy metabolism was first shown in mice with global PTP1B deletion [2] and was later confirmed in a series of other studies. These whole body PTP1B deficient mice show decreased body weight, food intake and adiposity, leading to resistance to diet-induced obesity (DIO) and improved leptin sensitivity and glucose metabolism when exposed to a high-fat diet (HFD) [2]. Of appreciable note, mice with specific deletion of PTP1B in muscle, liver or adipose tissue show no overt changes in body weight, adiposity or glucose tolerance [3–5]. However, deletion of PTP1B specifically in the central nervous system (CNS) [6], in LepRb-expressing cells [7] and POMC neurons [8,9] mimics the results observed in the global PTP1B deficient mice. These studies strongly support the relevance of central PTP1B signaling in regulating energy metabolism. It remains unclear, however, whether and to what extent the metabolic benefits arising from central PTP1B deficiency depend on PTP1B׳s action within the hypothalamus and whether the observed effects on metabolism are mediated via hypothalamic leptin receptor signaling. An elegant step in solving these questions has now been taken by the group of Kendra Bence from the University of Pennsylvania [10]. In the current issue of Molecular Metabolism, Tsou and colleagues used mice with hypothalamus-specific expression of Cre recombinase (Nkx2.1 cre) to specifically delete PTP1B in the hypothalamus. Compared to wildtype control mice, these hypothalamus-specific PTP1B deficient mice (Nkx2.1 PTP1B−/−) show decreased body weight, adiposity and food intake under chronic HFD exposure. These data corroborate previous reports about the relevance of central PTP1B signaling in the regulation of systems metabolism. Moreover, they show for the first time that the hypothalamus plays a key role in mediating PTP1B׳s action on metabolism and that hypothalamic selective PTP1B deletion mimics the phenotype of the whole body, whole brain, LepRb-expressing cell and POMC neuronal PTP1B knockout mice [6–9]. To further assess whether the metabolic benefits observed in the hypothalamus-specific PTP1B−/− mice depend on hypothalamic leptin receptor signaling, the authors generated mice with concomitant deletion of PTP1B and the leptin receptor in the hypothalamus (Nkx2.1 PTP1B−/−: LepRb−/−). Interestingly, when comparing these double mutant mice with hypothalamus-specific LepRb deficient mice, the metabolic benefits of PTP1B deletion vanished. No difference in body weight, food intake, adiposity or glucose tolerance was observed when double mutant mice were compared to mice that lack only the leptin receptor, but not PTP1B, in the hypothalamus. Together, the data indicate that the improved body weight and adiposity that is observed upon hypothalamic PTP1B deletion is mediated via interaction of PTP1B and the leptin receptor in the hypothalamus and that the metabolic benefits arising from PTP1B deficiency thus depend on a functional leptin receptor in the hypothalamus. These results underscore the importance of hypothalamic leptin receptor signaling for the regulation of energy and glucose metabolism and highlight the role of PTP1B in systems metabolism. In summary, the recent data by Tsou et al., combined with a series of previous studies, make PTP1B an interesting target for studies aiming to improve leptin sensitivity in states of pathologically increased body weight. Figure 1 Schematic of how PTP1B affects intracellular leptin receptor signaling. Binding of leptin to the extracellular domain of LepRb leads to autophosphorylation of the Janus kinase 2 (JAK2). JAK2 in turn phosphorylates three LepRb tyrosine residues (Tyr985 ...

Myeloid-Cell Protein Tyrosine Phosphatase-1B Deficiency in Mice Protects Against High-Fat Diet and Lipopolysaccharide-Induced Inflammation, Hyperinsulinemia, and Endotoxemia Through an IL-10 STAT3-Dependent Mechanism

Protein tyrosine phosphatase-1B (PTP1B) negatively regulates insulin and leptin signaling, rendering it an attractive drug target for treatment of obesity-induced insulin resistance. However, some studies suggest caution when targeting macrophage PTP1B, due to its potential anti-inflammatory role. We assessed the role of macrophage PTP1B in inflammation and whole-body metabolism using myeloid-cell (LysM) PTP1B knockout mice (LysM PTP1B). LysM PTP1B mice were protected against lipopolysaccharide (LPS)-induced endotoxemia and hepatic damage associated with decreased proinflammatory cytokine secretion in vivo. In vitro, LPS-treated LysM PTP1B bone marrow-derived macrophages (BMDMs) displayed increased interleukin (IL)-10 mRNA expression, with a concomitant decrease in TNF-α mRNA levels. These anti-inflammatory effects were associated with increased LPS- and IL-10-induced STAT3 phosphorylation in LysM PTP1B BMDMs. Chronic inflammation induced by high-fat (HF) feeding led to equally beneficial effects of macrophage PTP1B deficiency; LysM PTP1B mice exhibited improved glucose and insulin tolerance, protection against LPS-induced hyperinsulinemia, decreased macrophage infiltration into adipose tissue, and decreased liver damage. HF-fed LysM PTP1B mice had increased basal and LPS-induced IL-10 levels, associated with elevated STAT3 phosphorylation in splenic cells, IL-10 mRNA expression, and expansion of cells expressing myeloid markers. These increased IL-10 levels negatively correlated with circulating insulin and alanine transferase levels. Our studies implicate myeloid PTP1B in negative regulation of STAT3/IL-10-mediated signaling, highlighting its inhibition as a potential anti-inflammatory and antidiabetic target in obesity.