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The intestine is an important metabolic organ that has gained attention in recent years for the newly identified role that it plays in the pathophysiology of various metabolic diseases including obesity, insulin resistance and diabetes. Recent insights regarding the role of enteroendocrine hormones, such as GIP, GLP-1, and PYY in metabolic diseases, as well as the emerging role of the gut microbial community and gastric bypass bariatric surgeries in modulating metabolic function and dysfunction have sparked a wave of interest in understanding the mechanisms involved, in an effort to identify new therapeutics and novel regulators of metabolism. This review summarizes the current evidence that the gastrointestinal tract has a key role in the development of obesity, inflammation, insulin resistance and diabetes and discusses the possible players that can be targeted for therapeutic intervention. [ABSTRACT FROM AUTHOR]

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of insulin and tyrosine kinase growth factor signaling. We have recently demonstrated that PTP1B deficiency increases GLUT2/insulin receptor (IR) A complexes and glucose uptake in suckling, but not adult, primary hepatocytes. Herein we have investigated intrahepatic glucose utilization in 3–5 days old wild-type and PTP1B-/- mice. PTP1B deficiency decreased glycogen, lactate, and pyruvate content in the livers from suckling mice. Conversely, the activity of glucose 6-phosphate dehydrogenase (G6PD), the rate limiting enzyme of the pentose phosphate cycle (PPC) which provides substrates for DNA synthesis, was enhanced in the liver of PTP1B-/- animals. Liver weight, liver-to-body mass ratio, DNA content, and PCNA expression were increased in PTP1B-/- suckling mice compared to the wild-type controls. At the molecular level, STAT 5B phosphorylation, IGF-I mRNA, and protein levels as well as IGF-IR tyrosine phosphorylation were increased in the livers of PTP1B-deficient neonates. Unexpectedly, hepatic and serum triglycerides (TG) were increased by PTP1B deficiency, although the expression of lipogenic enzymes remained as in the wild-type controls. However, the analysis of milk composition revealed higher TG content in lactating females lacking PTP1B. The effects of PTP1B deficiency on G6PD activity, STAT 5B/IGF-I/IGF-IR axis, PCNA expression and liver growth during suckling were maintained by transferring PTP1B-/- embryos (PTP1B-/-T) to a wild-type female. Conversely, PTP1B-/-T mice did not show hepatic fat accumulation. In conclusion, the present study suggests that PTP1B plays a unique role in the control of the physiological liver development after birth. J. Cell. Physiol. 225: 214–222, 2010. © 2010 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

The contribution of the liver to glucose utilization is essential to maintain glucose homeostasis. Previous data from protein tyrosine phosphatase (PTP) 1B-deficient mice demonstrated that the liver is a major site for PTP1B action in the periphery. In this study, we have investigated the consequences of PTP1B deficiency in glucose uptake in hepatocytes from neonatal and adult mice. The lack of PTP1B increased basal glucose uptake in hepatocytes from neonatal (3-5 days old) but not adult (10-12 wk old) mice. This occurs without changes in hexokinase, glucokinase, and glucose 6-phosphatase enzymatic activities. By contrast, the glucose transporter GLUT2 was upregulated at the protein level in neonatal hepatocytes and livers from PTP1B-deficient neonates. These results were accompanied by a significant increase in the net free intrahepatic glucose levels in the livers of PTP1B-/- neonates. The association between GLUT2 and insulin receptor (IR) A isoform was increased in PTP1B-/- neonatal hepatocytes compared with the wild-type. Indeed, PTP1B deficiency in neonatal hepatocytes shifted the ratio of isoforms A and B of the IR by increasing the amount of IRA and decreasing IRB. Moreover, overexpression of IRA in PTP1B-/- neonatal hepatocytes increased the amount of IRA/GLUT2 complexes. Conversely, hepatocytes from adult mice only expressed IRB. Since IRA plays a direct role in the regulation of glucose uptake in neonatal hepatocytes through its specific association with GLUT2, we propose the increase in IRA/GLUT2 complexes due to PTP1B deficiency as the molecular mechanism of the increased glucose uptake in the neonatal stage. [ABSTRACT FROM AUTHOR]

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of tyrosine kinase growth factor signaling. To assess the importance of PTP1B in the balance between death and survival in the liver, we have developed immortalized neonatal hepatocyte cell lines lacking (PTP1B-/-) or overexpressing (PTP1B+/+PTP1B) PTP1B. Early activation of caspase-3 occurred in PTP1B+/+PTP1B hepatocytes but was nearly abolished in PTP1B-/- cells. At the molecular level, PTP1B overexpression/deficiency altered the balance of pro-(Bim) and anti-(Bcl-xL) apoptotic members of the Bcl-2 family upon serum withdrawal. Likewise, cytosolic cytochrome C increased rapidly in PTP1B+/+PTP1B hepatocytes whereas it was retained in the mitochondria of PTP1B-/- cells. DNA fragmentation and the increase of apoptotic cells induced by serum withdrawal in wild-type (PTP1B+/+) hepatocytes were absent in PTP1B-/- cells. Conversely, overexpression of PTP1B accelerated DNA laddering and increased the number of apoptotic cells. In serum-deprived PTP1B+/+PTP1B hepatocytes, a rapid entry of Foxo1 into the nucleus and an earlier activation of caspase-8 was observed. However, both events were suppressed in PTP1B-/- hepatocytes. Moreover, PTP1B deficiency conferred resistance to apoptosis induced by activation of Fas and constitutively active Foxo1. Rescue of PTP 1B in deficient hepatocytes recovered the phenotype of wild-type cells whereas reduction of PTP1B by siRNA suppressed apoptosis. Our results reveal a unique role for PTP1B as a mediator of the apoptotic pathways triggered by trophic factors withdrawal in hepatocytes. This novel mechanism may represent an important target in the design of therapeutic strategies for human liver regeneration after pathological damage as well as for treatment of hepatocarcinomas. J. Cell. Physiol. 212: 76–88, 2007. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Hepatic insulin resistance is considered to be a dominant component in the pathogenesis of fasting hyperglycemia in Type 2 diabetes. The role of nutrients, free fatty acids and secretory inflammatory factors released by visceral fat in the pathogenesis of liver insulin resistance requires clarification, but a number of signaling pathways and serine kinases have been implicated. These include the discovery of c-Jun N-terminal kinase, I κβ kinase, protein kinase C θ, δ and ϵ, and ribosomal protein S6 kinase 1 as critical regulators of insulin action and steatosis in liver. In this article, the causes and mechanisms involved in the development of hepatic insulin resistance, and the signaling pathways and kinases involved, will be discussed. Elucidation of the molecular mechanisms underlying regulation and specificity may prompt novel approaches to the pharmacological modulation of protein kinase activities involved in hepatic insulin resistance. This review will detail recent discoveries and highlight emerging kinase targets that hold potential to reduce hepatic insulin resistance and normalize blood glucose. [ABSTRACT FROM AUTHOR]

Protein-tyrosine phosphatase (PTP)1B is a negative regulator of insulin signaling and a therapeutic target for type 2 diabetes. In this study, we have assessed the role of PTP1B in the insulin sensitivity of skeletal muscle under physiological and insulin-resistant conditions. Immortalized myocytes have been generated from PTP1B-deficient and wild-type neonatal mice. PTP1B(-/-) myocytes showed enhanced insulin-dependent activation of insulin receptor autophosphorylation and downstream signaling (tyrosine phosphorylation of insulin receptor substrate [IRS]-1 and IRS-2, activation of phosphatidylinositol 3-kinase, and serine phosphorylation of AKT), compared with wild-type cells. Accordingly, PTP1B(-/-) myocytes displayed higher insulin-dependent stimulation of glucose uptake and GLUT4 translocation to the plasma membrane than wild-type cells. Treatment with tumor necrosis factor-alpha (TNF-alpha) induced insulin resistance on glucose uptake, impaired insulin signaling, and increased PTP1B activity in wild-type cells. Conversely, the lack of PTP1B confers protection against insulin resistance by TNF-alpha in myocyte cell lines and in adult male mice. Wild-type mice treated with TNF-alpha developed a pronounced hyperglycemia along the glucose tolerance test, accompanied by an impaired insulin signaling and increased PTP1B activity in muscle. However, mice lacking PTP1B maintained a rapid clearance of glucose and insulin sensitivity and displayed normal muscle insulin signaling regardless the presence of TNF-alpha. [ABSTRACT FROM AUTHOR]

Serine and threonine kinases may contribute to insulin resistance and the development of type 2 diabetes. To test the potential for members of the mitogen-activated protein (MAP) kinase family to contribute to type 2 diabetes, we examined basal and insulin-stimulated Erk 1/2, JNK, and p38 phosphorylation in adipocytes isolated from healthy and type 2 diabetic individuals. Maximal insulin stimulation increased the phosphorylation of Erk 1/2 and JNK in healthy control subjects but not type 2 diabetic patients. Insulin stimulation did not increase p38 phosphorylation in either healthy control subjects or type 2 diabetic patients. In type 2 diabetic adipocytes, the basal phosphorylation status of these MAP kinases was significantly elevated and was associated with decreased IRS-1 and GLUT4 in these fat cells. To determine whether MAP kinases were involved in the downregulation of IRS-1 and GLUT4 protein levels, selective inhibitors were used to inhibit these MAP kinases in 3T3-L1 adipocytes treated chronically with insulin. Inhibition of Erk 1/2, JNK, or p38 had no effect on insulin-stimulated reduction of IRS-1 protein levels. However, inhibition of the p38 pathway prevented the insulin-stimulated decrease in GLUT4 protein levels. In summary, type 2 diabetes is associated with an increased basal activation of the MAP kinase family. Furthermore, upregulation of the p38 pathway might contribute to the loss of GLUT4 expression observed in adipose tissue from type 2 diabetic patients. [ABSTRACT FROM AUTHOR]

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of insulin receptor (IR) signal transduction and a drug target for treatment of type 2 diabetes. Using PTP1B antisense oligonucleotides (ASOs), effects of decreased PTP1B levels on insulin signaling in diabetic ob/ob mice were examined. Insulin stimulation, prior to sacrifice, resulted in no significant activation of insulin signaling pathways in livers from ob/ob mice. However, in PTP1B ASO-treated mice, in which PTP1B protein was decreased by 60% in liver, similar stimulation with insulin resulted in increased tyrosine phosphorylation of the IR and IR substrate (IRS)-1 and -2 by threefold, fourfold, and threefold, respectively. IRS-2-associated phosphatidylinositol 3-kinase activity was also increased threefold. Protein kinase B (PKB) serine phosphorylation was increased sevenfold in liver of PTP1B ASO-treated mice upon insulin stimulation, while phosphorylation of PKB substrates, glycogen synthase kinase (GSK)-3alpha and -3beta, was increased more than twofold. Peripheral insulin signaling was increased by PTP1B ASO, as evidenced by increased phosphorylation of PKB in muscle of insulin-stimulated PTP1B ASO-treated animals despite the lack of measurable effects on muscle PTP1B protein. These results indicate that reduction of PTP1B is sufficient to increase insulin-dependent metabolic signaling and improve insulin sensitivity in a diabetic animal model. [ABSTRACT FROM AUTHOR]

Protein tyrosine phosphatase 1B (PTP1B) has been implicated as a negative regulator of insulin action. Overexpression of PTP1B protein has been observed in insulin-resistant states associated with obesity. Mice lacking a functional PTP1B gene exhibit increased insulin sensitivity and are resistant to weight gain. To investigate the role of PTP1B in adipose tissue from obese animals, hyperglycemic obese (ob/ob) mice were treated with PTP1B antisense oligonucleotide (ISIS-113715). A significant reduction in adiposity correlated with a decrease of PTP1B protein levels in fat. Antisense treatment also influenced the triglyceride content in adipocytes, correlating with a downregulation of genes encoding proteins involved in lipogenesis, such as sterol regulatory element-binding protein 1 and their downstream targets spot14 and fatty acid synthase, as well as other adipogenic genes, lipoprotein lipase, and peroxisome proliferator-activated receptor gamma. In addition, an increase in insulin receptor substrate-2 protein and a differential regulation of the phosphatidylinositol 3-kinase regulatory subunit (p85alpha) isoforms expression were found in fat from antisense-treated animals, although increased insulin sensitivity measured by protein kinase B phosphorylation was not observed. These results demonstrate that PTP1B antisense treatment can modulate fat storage and lipogenesis in adipose tissue and might implicate PTP1B in the enlargement of adipocyte energy stores and development of obesity. [ABSTRACT FROM AUTHOR]

Insulin receptor substrate (IRS)-1 protein expression is markedly reduced in many insulin-resistant states, although the mechanism for this downregulation is unclear. In this study, we have investigated the early events in the insulin pathway that trigger the degradation of IRS-1. Incubation of the adipocytes with insulin induced a fast electrophoretic mobility shift of IRS-1 and a subsequent degradation of the protein. Wortmannin and rapamycin blocked this mobility shift of IRS-1, maintained the insulin-induced tyrosine phosphorylation of IRS-1, and blocked its degradation. In contrast, a glycogen synthase kinase 3 inhibitor, a mitogen-activated protein kinase/extracellular-regulated kinase inhibitor, and various protein kinase C inhibitors had no effect. Incubation with okadaic acid increased the serine/threonine phosphorylation of IRS-1 and its degradation, mimicking insulin, and its effect was prevented by the proteasome inhibitor lactacystin, as well as by rapamycin. Treatment of the cells with the tyrosine phosphatase inhibitor orthovanadate in the presence of insulin or okadaic acid partially inhibited the degradation of IRS-1. We propose that a rapamycin-dependent pathway participates as a negative regulator of IRS-1, increasing its serine/threonine phosphorylation, which triggers degradation. Thus, regulation of serine/threonine versus tyrosine phosphorylation may modulate IRS-1 degradation, affecting insulin sensitivity. [ABSTRACT FROM AUTHOR]

In a serum-free medium addition of insulin-like growth factor-1 (IGF-1) consistently enhanced lymphocyte proliferation response to PHA in a dose-dependent fashion. This effect was produced by an acceleration in the expression of clone expansion and not in the number of proliferating cells. This was documented by kinetics data obtained from the first proliferation round of PHA-stimulated lymphocytes, in which addition of IGE-1 reduced G₁-phase length, without changing Gophase, S-phase or cloned size. The data were confirmed in 10-day culture of stimulated lymphocytes where IGF-1 only accelerated cell proliferation without modifying the area enclosed by the proliferation curve. As IGF-1 is under the control of growth hormone, our results suggest that some of the immunoregulation effects ascribed to growth hormone in vivo could be produced by IGF-I. [ABSTRACT FROM AUTHOR]

Summary Ghrelin, an appetite-stimulatory hormone secreted by the stomach, was discovered as a ligand for the growth hormone secretagogue receptor (GHSR). Through GHSR, ghrelin stimulates growth hormone (GH) secretion, a function that evolved to protect against starvation-induced hypoglycemia. Though the biology mediated by ghrelin has been described in great detail, regulation of ghrelin action is poorly understood. Here, we report the discovery of liver-expressed antimicrobial peptide 2 (LEAP2) as an endogenous antagonist of GHSR. LEAP2 is produced in the liver and small intestine, and its secretion is suppressed by fasting. LEAP2 fully inhibits GHSR activation by ghrelin and blocks the major effects of ghrelin in vivo , including food intake, GH release, and maintenance of viable glucose levels during chronic caloric restriction. In contrast, neutralizing antibodies that block endogenous LEAP2 function enhance ghrelin action in vivo . Our findings reveal a mechanism for fine-tuning ghrelin action in response to changing environmental conditions. [ABSTRACT FROM AUTHOR]

Abstract: A new series of 4-anilinopyrimidines has been synthesized and evaluated as JNK1 inhibitors. SAR studies led to the discovery of potent JNK1 inhibitors with good enzymatic activity as well as cellular potency represented by compound 2b. Kinase selectivity profile and the crystal structure of 2b are also described. [Copyright &y& Elsevier]