Acute exercise reduces hepatic glucose production through inhibition of the Foxo1/HNF-4alpha pathway in insulin resistant mice

m 6 A-mediated gluconeogenic enzyme PCK1 upregulation protects against hepatic ischemia-reperfusion injury

BACKGROUND AND AIMS

Ischemia-reperfusion (I/R) injury frequently occurs during liver surgery, representing a major reason for liver failure and graft dysfunction after operation. The metabolic shift from oxidative phosphorylation to glycolysis during ischemia increased glucose consumption and accelerated lactate production. We speculate that donor livers will initiate gluconeogenesis, the reverse process of glycolysis in theory, to convert noncarbohydrate carbon substrates (including lactate) to glucose to reduce the loss of hepatocellular energy and foster glycogen storage for use in the early postoperative period, thus improving post-transplant graft function.

APPROACH AND RESULTS

By analyzing human liver specimens before and after hepatic I/R injury, we found that the rate-limiting enzyme of gluconeogenesis, PCK1, was significantly induced during liver I/R injury. Mouse models with liver I/R operation and hepatocytes treated with hypoxia/reoxygenation confirmed upregulation of PCK1 during I/R stimulation. Notably, high PCK1 level in human post-I/R liver specimens was closely correlated with better outcomes of liver transplantation. However, blocking gluconeogenesis with PCK1 inhibitor aggravated hepatic I/R injury by decreasing glucose level and deepening lactate accumulation, while overexpressing PCK1 did the opposite. Further mechanistic study showed that methyltransferase 3-mediated RNA N6-methyladinosine modification contributes to PCK1 upregulation during hepatic I/R injury, and hepatic-specific knockout of methyltransferase 3 deteriorates liver I/R injury through reducing the N6-methyladinosine deposition on PCK1 transcript and decreasing PCK1 mRNA export and expression level.

CONCLUSIONS

Our study found that activation of the methyltransferase 3/N6-methyladinosine-PCK1-gluconeogenesis axis is required to protect against hepatic I/R injury, providing potential intervention approaches for alleviating hepatic I/R injury during liver surgery.

HM-Chromanone Alleviates Hyperglycemia by Activating AMPK and PI3K/AKT Pathways in Mice Fed a High-Fat Diet

OBJECTIVES

We investigated potential antihyperglycemic effects of HM-chromanone (HMC), a homoisoflavonoid isolated from Portulaca oleracea, in mice fed a high-fat diet (HFD).

METHODS

Five-week-old male C57BL/6J mice (n = 24) were divided into three groups: controls, mice fed an HFD (11 weeks), and HFD-fed mice receiving HMC supplementation (8 weeks). Various analyses assessed liver and skeletal muscle proteins, pancreatic β-cell histology, blood glucose and HbA1c levels, and homeostatic index of insulin resistance (HOMA-IR).

RESULTS

HMC supplementation significantly reduced fasting blood glucose and postprandial blood glucose levels in HFD-fed mice. HbA1c and serum insulin levels reduced significantly, and HOMA-IR improved. Compensatory β-cell hyperplasia was reduced, and pancreatic β-cell function improved. AMP-activated protein kinase (AMPK) was significantly activated in skeletal muscle and liver tissues. IRS-1tyr612 expression increased significantly. PI3K activation and Akt phosphorylation in skeletal muscles improved insulin signaling. Forkhead box protein O1 phosphorylation increased through hepatic AMPK activation. Phosphoenolpyruvate carboxykinase and glucose-6-phosphatase expression was inhibited. Glycogen synthase kinase 3β phosphorylation increased.

CONCLUSIONS

HMC supplementation alleviated hyperglycemia by activating the AMPK and PI3K/Akt pathways in skeletal muscles and the AMPK pathway in the liver of HFD-fed mice.

High-Fat Diet Modulates the Excitability of Neurons within the Brain-Liver Pathway

Stimulation of hepatic sympathetic nerves increases glucose production and glycogenolysis. Activity of pre-sympathetic neurons in the paraventricular nucleus (PVN) of the hypothalamus and in the ventrolateral and ventromedial medulla (VLM/VMM) largely influence the sympathetic output. Increased activity of the sympathetic nervous system (SNS) plays a role in the development and progression of metabolic diseases; however, despite the importance of the central circuits, the excitability of pre-sympathetic liver-related neurons remains to be determined. Here, we tested the hypothesis that the activity of liver-related neurons in the PVN and VLM/VMM is altered in diet-induced obese mice, as well as their response to insulin. Patch-clamp recordings were conducted from liver-related PVN neurons, VLM-projecting PVN neurons, and pre-sympathetic liver-related neurons in the ventral brainstem. Our data demonstrate that the excitability of liver-related PVN neurons increased in high-fat diet (HFD)-fed mice compared to mice fed with control diet. Insulin receptor expression was detected in a population of liver-related neurons, and insulin suppressed the firing activity of liver-related PVN and pre-sympathetic VLM/VMM neurons in HFD mice; however, it did not affect VLM-projecting liver-related PVN neurons. These findings further suggest that HFD alters the excitability of pre-autonomic neurons as well as their response to insulin.

Exercise and inactivity as modifiers of β cell function and type 2 diabetes risk

Exercise and regular physical activity are beneficial for the prevention and management of metabolic diseases such as obesity and type 2 diabetes, whereas exercise cessation, defined as deconditioning from regular exercise or physical activity that has lasted for a period of months to years, can lead to metabolic derangements that drive disease. Adaptations to the insulin-secreting pancreatic β-cells are an important benefit of exercise, whereas less is known about how exercise cessation affects these cells. Our aim is to review the impact that exercise and exercise cessation have on β-cell function, with a focus on the evidence from studies examining glucose-stimulated insulin secretion (GSIS) using gold-standard techniques. Potential mechanisms by which the β-cell adapts to exercise, including exerkine and incretin signaling, autonomic nervous system signaling, and changes in insulin clearance, will also be explored. We will highlight areas for future research.

Labeled breath tests in patients with NASH: Octanoate oxidation relates best to measures of glucose metabolism

In vivo methods to estimate human liver mitochondrial activity are lacking and this project's goal was to use a non-invasive breath test to quantify complete mitochondrial fat oxidation and determine how test results changed when liver disease state was altered over time. Patients with suspected non-alcoholic fatty liver disease (NAFLD; 9 men, 16 women, 47 ± 10 years, 113 ± 23 kg) underwent a diagnostic liver biopsy and liver tissue was histologically scored by a pathologist using the NAFLD activity score (0-8). To assess liver oxidation activity, a labeled medium chain fatty acid was consumed orally (23.4 mg ¹³C₄-octanoate) and breath samples collected over 135 min. Total CO₂ production rates were measured using breath ¹³CO₂ analysis by isotope ratio mass spectrometry. Fasting endogenous glucose production (EGP) was measured using an IV infusion of ¹³C₆-glucose. At baseline, subjects oxidized 23.4 ± 3.9% (14.9%-31.5%) of the octanoate dose and octanoate oxidation (OctOx) was negatively correlated with fasting plasma glucose (r = -0.474, p = 0.017) and EGP (r = -0.441, p = 0.028). Twenty-two subjects returned for repeat tests 10.2 ± 1.0 months later, following lifestyle treatment or standardized care. OctOx (% dose/kg) was significantly greater across all subjects (p = 0.044), negatively related to reductions in EGP (r = -0.401, p = 0.064), and tended to correlate with reduced fasting glucose (r = -0.371, p = 0.090). Subjects exhibited reductions in steatosis (p = 0.007) which tended to correlate with increased OctOx (% of dose/kg, r = -0.411, p = 0.058). Based on our findings, the use of an ¹³C-octanoate breath test may be an indicator of hepatic steatosis and glucose metabolism, but these relationships require verification through larger studies in NAFLD populations.

HIIT Ameliorates Inflammation and Lipid Metabolism by Regulating Macrophage Polarization and Mitochondrial Dynamics in the Liver of Type 2 Diabetes Mellitus Mice

High-intensity interval training (HIIT), a new type of exercise, can effectively prevent the progression of metabolic diseases. The aim of this study was to investigate the effects of HIIT on liver inflammation and metabolic disorders in type 2 diabetes mellitus (T2DM) mice induced by a high-fat diet (HFD) combined with streptozotocin (STZ) and to explore the possible mechanisms of macrophage polarization and mitochondrial dynamics. Our results showed that HIIT can increase fatty acid oxidation-related gene (PPARα, CPT1α, and ACOX1) mRNA levels and decrease adipogenesis-related gene (PPARγ) mRNA levels to improve liver metabolism in T2DM mice. The improvement of lipid metabolism disorder may occur through increasing liver mitochondrial biosynthesis-related genes (PGC-1α and TFAM) and restoring mitochondrial dynamics-related gene (MFN2 and DRP1) mRNA levels. HIIT can also reduce the mRNA levels of liver inflammatory factors (TNF-α, IL-6, and MCP-1) in T2DM mice. The reduction in liver inflammation may occur through reducing the expression of total macrophage marker (F4/80) and M1 macrophage marker (CD86) mRNA and protein and increasing the expression of M2 macrophage marker (CD163, CD206, and Arg1) mRNA and protein in the liver. HIIT can also increase the expression of insulin signaling pathway (IRS1, PI3K, and AKT) mRNA and protein in the liver of T2DM mice, which may be related to the improvements in liver inflammation and lipid metabolism. In conclusion, these results suggested that 8 weeks of HIIT can improve inflammation and lipid metabolism disorders in the liver of type 2 diabetes mellitus mice, macrophage M1/M2 polarization, and mitochondrial dynamics may be involved in this process.

Validity of the peak velocity to detect physical training improvements in athymic mice

This study comprises two complementary experiments with athymic Balb/c (Nu/Nu) mice. In experiment 1, the aim was to verify the reproducibility of the peak velocity (V_Peak) determined from the incremental test. The second experiment aimed to assess the V_Peak sensitivity to prescribe and detect modulations of the physical training in athymic nude mice. Sixteen mice were submitted to two incremental treadmill tests separated by 48-h (Experiment 1). The test consisted of an initial warm-up of 5 minutes. Subsequently, animals initiated the tests at 8 m min⁻¹ with increments of 2 m min⁻¹ every 3 minutes. The V_Peak was determined as the highest velocity attained during the protocol. In experiment 2, these animals were randomly allocated to an exercise group (EG) or a control group (CG). The training protocol consisted of 30-min of treadmill running at 70% of the V_Peak five times a week for 4 weeks. High indexes of reproducibility were obtained for V_Peak (Test = 19.7 ± 3.6 m min⁻¹; Retest = 19.2 ± 3.4 m min⁻¹; p = 0.171; effect size = 0.142; r = 0.90). Animals from the EG had a significant increase of V_Peak (Before = 18.4 ± 2.7 m min⁻¹; After = 24.2 ± 6.0 m min⁻¹; p = 0.023). Conversely, a significant decrease was observed for the CG (Before = 21.1 ± 3.9 m min⁻¹; After = 15.9 ± 2.7 m min⁻¹; p = 0.038). The V_Peak is a valid parameter for exercise prescription in studies involving athymic nude mice.

Aerobic Exercise Training Exerts Beneficial Effects Upon Oxidative Metabolism and Non-Enzymatic Antioxidant Defense in the Liver of Leptin Deficiency Mice

Non-alcoholic fatty liver disease (NAFLD) is one of the most common forms of liver disease, which is associated with several etiological factors, including stress and dysfunction in oxidative metabolism. However, studies showed that aerobic exercise training (AET) can combat the oxidative stress (OS) and improves mitochondrial functionality in the NAFLD. To test the hypothesis that AET improves oxidative metabolism and antioxidant defense in the liver of ob/ob mice. Male ob/ob mice with eight weeks old were separated into two groups: the sedentary group (S), n=7, and the trained group (T), n=7. The T mice were submitted to an 8-week protocol of AET at 60% of the maximum velocity achieved in the running capacity test. Before AET, no difference was observed in running test between the groups (S=10.4 ± 0.7 min vs. T= 13 ± 0.47 min). However, after AET, the running capacity was increased in the T group (12.8 ± 0.87 min) compared to the S group (7.2 ± 0.63 min). In skeletal muscle, the T group (26.91 ± 1.12 U/mg of protein) showed higher citrate synthase activity compared with the S group (19.28 ± 0.88 U/mg of protein) (p =0.006). In the analysis of BW evolution, significant reductions were seen in the T group as of the fourth week when compared to the S group. In addition, food intake was not significant different between the groups. Significant increases were observed in the activity of enzymes citrate synthase (p=0.004) and β-HAD (p=0.01) as well as in PGC-1α gene expression (p=0.002) in the liver of T group. The levels of TBARs and carbonyls, as well as SOD, CAT and GST were not different between the groups. However, in the nonenzymatic antioxidant system, we found that the T group had higher sulfhydryl (p = 0.02), GSH (p=0.001) and GSH/GSSG (p=0.02) activity. In conclusion, the AET improved body weight evolution and the aerobic capacity, increased the response of oxidative metabolism markers in the liver such as PGC-1α gene expression and citrate synthase and β-HAD enzyme activities in ob/ob mice. In addition, AET improved the non-enzymatic antioxidant defense and did not change the enzymatic defense.

Edgeworthia gardneri (Wall.) Meisn. Water Extract Ameliorates Palmitate Induced Insulin Resistance by Regulating IRS1/GSK3β/FoxO1 Signaling Pathway in Human HepG2 Hepatocytes

The flower of Edgeworthia gardneri (Wall.) Meisn is commonly used in beverage products in Tibet and has potential health benefits for diabetes. However, the mechanisms underlying anti-insulin resistance (IR) action of the flower of E. gardneri are not fully understood. This study aims to investigate the effects of the water extract of the flower of E. gardneri (WEE) on IR in palmitate (PA)-exposed HepG2 hepatocytes. WEE was characterized by UPLC analysis. PA-treated HepG2 cells were selected as the IR cell model. The cell viability was determined using MTT assay. Moreover, the glucose consumption and production were measured by glucose oxidase method. The glucose uptake and glycogen content were determined by the 2-NBDG (2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl) amino]-D-glucose) glucose uptake assay and anthrone-sulfuric acid assay, respectively. The intracellular triglyceride content was detected by oxidative enzymic method. Protein levels were examined by Western blotting. Nuclear localization of FoxO1 was detected using immunofluorescence analyses and Western blotting. The expression of FoxO1 target genes was detected by quantitative real-time polymerase chain reaction (qRT-PCR). The viability of PA-treated HepG2 cells was concentration-dependently increased by incubation with WEE for 24 h. WEE treatment remarkably increased the consumption and uptake of glucose in PA-exposed HepG2 cells. Moreover, treatment with WEE significantly decreased the PA-induced over-production of glucose in HepG2 cells. After exposure of HepG2 cells with PA and WEE, the glycogen content was significantly elevated. The phosphorylation and total levels of IRβ, IRS1, and Akt were upregulated by WEE treatment in PA-exposed HepG2 cells. The phosphorylation of GSK3β was elevated after WEE treatment in PA-treated cells. WEE treatment also concentration-dependently downregulated the phosphorylated CREB, ERK, c-Jun, p38 and JNK in PA-exposed HepG2 cells. Furthermore, the nuclear protein level and nuclear translocation of FoxO1 were also suppressed by WEE. Additionally, PA-induced changes of FoxO1 targeted genes were also attenuated by WEE treatment. The GLUT2 and GLUT4 translocation were also promoted by WEE treatment in PA-treated HepG2 cells. Taken together, WEE has potential anti-IR effect in PA-exposed HepG2 cells; the underlying mechanism of this action may be associated with the regulation of IRS1/GSK3β/FoxO1 signaling pathway. This study provides a pharmacological basis for the application of WEE in the treatment of metabolic diseases such as type 2 diabetes mellitus.

Enzymatically modified isoquercitrin promotes energy metabolism through activating AMPKα in male C57BL/6 mice

Quercetin possesses various health beneficial functions, but its poor bioavailability limits these functions. Enzymatically modified isoquercitrin (EMIQ) is a quercetin glycoside with a greater bioavailability than quercetin. In this study, we investigated whether EMIQ regulates energy metabolism in mice and its underlying molecular mechanism. Male C57BL/6 mice were fed a normal diet with different doses of EMIQ or quercetin (0.02%, 0.1% and 0.5%) for two weeks. Supplementation with 0.1% EMIQ significantly decreased white adipose tissue (WAT) weight. Supplementation with 0.02% and 0.1% EMIQ promoted phosphorylation of adenosine monophosphate activated protein kinase (AMPK) in the WAT, liver, and muscle. In the WAT, 0.1% EMIQ downregulated peroxisome proliferator-activated receptor (PPAR)γ, CCAAT-enhancer-binding protein (C/EBP)α, C/EBPβ, and sterol regulatory element-binding protein 1 expression, as well as upregulated mitochondrial uncoupling protein (UCP) 2 and carnitine palmitoyltransferase-1 expression. Supplementation with 0.1% EMIQ also promoted the expression of thermogenesis-associated factors including PPARγ coactivator α (PGC-1α), UCP1, PR-domain containing protein 16, and sirtuin 1 in the WAT. In the liver, EMIQ promoted the phosphorylation of acetyl-CoA carboxylase, and increased the expression of PPARα, constitutive androstane-receptor, and farnesoid X receptor. Furthermore, supplementation with 0.02% or 0.1% EMIQ suppressed the plasma glucose level accompanied by the translocation of glucose transporter 4 to the plasma membrane of the muscle. Our results suggest that EMIQ is a potential food additive for the regulation of energy metabolism through AMPK phosphorylation.

Exercise ameliorates insulin resistance via regulating TGFβ-activated kinase 1 (TAK1)-mediated insulin signaling in liver of high-fat diet-induced obese rats

Exercise is an effective therapy for insulin resistance. However, the underlying mechanism remains to be elucidated. Previous research demonstrated that TGFβ-activated kinase 1 (TAK1)-dependent signaling plays a crucial character in hepatic insulin resistance. Hepatic ubiquitin specific protease 4 (USP4), USP18, and dual-specificity phosphatases 14 (DUSP14) can suppress TAK1 phosphorylation, besides tumor necrosis factor receptor-associated factor 3 (TRAF3) and tripartite motif 8 (TRIM8) promote its phosphorylation. In this study, we tried to verify our hypothesis that exercise improves insulin resistance in high-fat diet (HFD)-induced obese (DIO) rats via regulating the TAK1 dependent signaling and TAK1 regulators in liver. Forty male Sprague-Dawley rats were randomized into four groups (n = 10): standard diet and sedentary as normal control; fed on HFD and DIO-sedentary; fed on HFD and DIO-chronic exercise; and fed on HFD and DIO-acute exercise. HFD feeding resulted in increased body weight, visceral fat mass, serum FFAs and hepatic lipid deposition, but decreased hepatic glycogen content and insulin sensitivity. Moreover, hepatic TRAF3 and TRIM8 protein levels increased, whereas USP4, USP18, and DUSP14 protein levels were decreased under obese status, which resulted in enhanced TAK1 phosphorylation and impaired insulin signaling. Exercise training, containing chronic and acute mode, both ameliorated insulin resistance. Meanwhile, decreased TAK1, c-Jun N-terminal kinase 1 (JNK1), and insulin receptor substrate 1 (IRS1) phosphorylation enhanced Akt phosphorylation in liver. Moreover, exercise enhanced USP4 and DUSP14 protein levels, whereas decreased TRIM8 protein levels in obese rats' liver. These results showed that exercise triggered a crucial modulation in TAK1-dependent signaling and its regulators in obese rats' liver, and distinct improvement in insulin sensitivity, which provide new insights into the mechanism by which physical exercise improves insulin resistance.

HNF-4alpha Negatively Regulates Hepcidin Expression Through BMPR1A in HepG2 Cells

Hepcidin synthesis is reported to be inadequate according to the body iron store in patients with non-alcoholic fatty liver disease (NAFLD) undergoing hepatic iron overload (HIO). However, the underlying mechanisms remain unclear. We hypothesize that hepatocyte nuclear factor-4α (HNF-4α) may negatively regulate hepcidin expression and contribute to hepcidin deficiency in NAFLD patients. The effect of HNF-4α on hepcidin expression was observed by transfecting specific HNF-4α small interfering RNA (siRNA) or plasmids into HepG2 cells. Both direct and indirect mechanisms involved in the regulation of HNF-4α on hepcidin were detected by real-time PCR, Western blotting, chromatin immunoprecipitation (chIP), and reporter genes. It was found that HNF-4α suppressed hepcidin messenger RNA (mRNA) and protein expressions in HepG2 cells, and this suppressive effect was independent of the potential HNF-4α response elements. Phosphorylation of SMAD1 but not STAT3 was inactivated by HNF-4α, and the SMAD4 response element was found essential to HNF-4α-induced hepcidin reduction. Neither inhibitory SMADs, SMAD6, and SMAD7 nor BMPR ligands, BMP2, BMP4, BMP6, and BMP7 were regulated by HNF-4α in HepG2 cells. BMPR1A, but not BMPR1B, BMPR2, ActR2A, ActR2B, or HJV, was decreased by HNF-4α, and HNF4α-knockdown-induced stimulation of hepcidin could be entirely blocked when BMPR1A was interfered with at the same time. In conclusion, the present study suggests that HNF-4α has a suppressive effect on hepcidin expression by inactivating the BMP pathway, specifically via BMPR1A, in HepG2 cells.

Effect of Exercise and Calorie Restriction on Tissue Acylcarnitines, Tissue Desaturase Indices, and Fat Accumulation in Diet-Induced Obese Rats

Both exercise and calorie restriction interventions have been recommended for inducing weight-loss in obese states. However, there is conflicting evidence on their relative benefits for metabolic health and insulin sensitivity. This study seeks to evaluate the differential effects of the two interventions on fat mobilization, fat metabolism, and insulin sensitivity in diet-induced obese animal models. After 4 months of ad libitum high fat diet feeding, 35 male Fischer F344 rats were grouped (n = 7 per cohort) into sedentary control (CON), exercise once a day (EX1), exercise twice a day (EX2), 15% calorie restriction (CR1) and 30% calorie restriction (CR2) cohorts. Interventions were carried out over a 4-week period. We found elevated hepatic and muscle long chain acylcarnitines with both exercise and calorie restriction, and a positive association between hepatic long chain acylcarnitines and insulin sensitivity in the pooled cohort. Our result suggests that long chain acylcarnitines may not indicate incomplete fat oxidation in weight loss interventions. Calorie restriction was found to be more effective than exercise in reducing body weight. Exercise, on the other hand, was more effective in reducing adipose depots and muscle triglycerides, favorably altering muscle/liver desaturase activity and improving insulin sensitivity.

Gestation under chronic constant light leads to extensive gene expression changes in the fetal rat liver

Recent reports account for altered metabolism in adult offspring from pregnancy subjected to abnormal photoperiod, suggesting fetal programming of liver physiology. To generate a pipeline of subsequent mechanistic experiments addressing strong candidate genes, here we investigated the effects of constant gestational light on the fetal liver transcriptome. At 10 days of gestation, dams were randomized in two groups ( n = 7 each): constant light (LL) and normal photoperiod (12 h light/12 h dark; LD). At 18 days of gestation, RNA was isolated from the fetal liver and subjected to DNA microarray (Affymetrix platform for 28,000 genes). Selected differential mRNAs were validated by quantitative PCR (qPCR), while integrated transcriptional changes were analyzed with Ingenuity Pathway Analysis and other bioinformatics tools. Comparison of LL relative to LD fetal liver led to the following findings. Significant differential expression was found for 3,431 transcripts (1,960 upregulated and 1,471 downregulated), with 393 of them displaying ≥ 1.5-fold change. We validated 27 selected transcripts by qPCR, which displayed fold-change values highly correlated with microarray ( r2 = 0.91). Different markers of nonalcoholic fatty liver disease were either upregulated (e.g., Ndn and Pnpla3) or downregulated (e.g., Gnmt, Bhmt1/2, Sult1a1, Mpo, and Mat1a). Diverse pathways were altered, including hematopoiesis, coagulation cascade, complement system, and carbohydrate and lipid metabolism. The microRNAs 7a-1, 431, 146a, and 153 were upregulated, while the abundant hepatic miRNA 122 was downregulated. Constant gestational light induced extensive modification of the fetal liver transcriptome. A number of differentially expressed transcripts belong to fundamental functional pathways, potentially contributing to long-term liver disease.

Vibration exercise decreases insulin resistance and modulates the insulin signaling pathway in a type 2 diabetic rat model

Vibration exercise (VE) is a new type of physical training, but little is known about its effects on insulin resistance at the molecular level. A Sprague-Dawley rat model of type 2 diabetes with insulin resistance was induced with a high-fat diet and low-dose streptozotocin. Animals were then subjected to 8 wk of VE consisting of placing the rats on a vibration stand bracket (8 cm × 8 cm × 20 cm) with a maximum vertical vibration displacement of 52 mm for 15 min twice a day, 6 d each week. Various metabolic markers and the phosphorylation and expression of proteins within the PI3K/AKT insulin signaling pathway were assessed. The high-fat diet and low-dose streptozotocin increased food intake, body weight, and levels of blood glucose, triglycerides, total cholesterol, and free fatty acids, while Kitt rate, 2-deoxyglucose uptake, and glycogen levels were decreased. These effects were ameliorated in animals receiving VE. VE treatment activated the PI3K/AKT insulin-signaling pathway, and also increased the expression of GLUT4. In conclusion, VE improved the metabolic issues associated with the diabetic state by suppressing the reduction of IRS1, AKT2, and GLUT4 in the diabetic condition, indicating that VE could be used as a therapeutic intervention for insulin resistance and type 2 diabetes.

Physical training improves body weight and energy balance but does not protect against hepatic steatosis in obese mice

This study sought to determine the role of physical training (PT) on body weight (BW), energy balance, histological markers of nonalcoholic fatty liver disease (NAFLD) and metabolic gene expression in the liver of ob/ob mice. Adult male ob/ob mice were assigned into groups sedentary (S; n = 8) and trained (T; n = 9). PT consisted in running sessions of 60 min at 60% of maximal speed conducted five days per week for eight weeks. BW of S group was higher from the 4(th) to 8(th) week of PT compared to their own BW at the beginning of the experiment. PT decreased daily food intake and increased resting oxygen consumption and energy expenditure in T group. No difference was observed in respiratory exchange ratio, but the rates of carbohydrate and lipids oxidation, and maximal running capacity were greater in T than S group. Both groups showed liver steatosis but not inflammation. PT increased CPT1a and SREBP1c mRNA expression in T group, but did not change MTP, PPAR-α, PPAR-γ, and NFKB mRNA expression. In conclusion, PT prevented body weight gain in ob/ob mice by inducing negative energy balance and increased physical exercise tolerance. However, PT did not change inflammatory gene expression and failed to prevent liver steatosis possible due to an upregulation in the expression of SREBP1c transcription factor. These findings reveal that PT has positive effect on body weight control but not in the liver steatosis in a leptin deficiency condition.

Regulation of hepatic TRB3/Akt interaction induced by physical exercise and its effect on the hepatic glucose production in an insulin resistance state

To maintain euglycemia in healthy organisms, hepatic glucose production is increased during fasting and decreased during the postprandial period. This whole process is supported by insulin levels. These responses are associated with the insulin signaling pathway and the reduction in the activity of key gluconeogenic enzymes, resulting in a decrease of hepatic glucose production. On the other hand, defects in the liver insulin signaling pathway might promote inadequate suppression of gluconeogenesis, leading to hyperglycemia during fasting and after meals. The hepatocyte nuclear factor 4, the transcription cofactor PGC1-α, and the transcription factor Foxo1 have fundamental roles in regulating gluconeogenesis. The loss of insulin action is associated with the production of pro-inflammatory biomolecules in obesity conditions. Among the molecular mechanisms involved, we emphasize in this review the participation of TRB3 protein (a mammalian homolog of Drosophila tribbles), which is able to inhibit Akt activity and, thereby, maintain Foxo1 activity in the nucleus of hepatocytes, inducing hyperglycemia. In contrast, physical exercise has been shown as an important tool to reduce insulin resistance in the liver by reducing the inflammatory process, including the inhibition of TRB3 and, therefore, suppressing gluconeogenesis. The understanding of these new mechanisms by which physical exercise regulates glucose homeostasis has critical importance for the understanding and prevention of diabetes.

Chronic exercise increases plasma brain-derived neurotrophic factor levels, pancreatic islet size, and insulin tolerance in a TrkB-dependent manner

BACKGROUND

Physical exercise improves glucose metabolism and insulin sensitivity. Brain-derived neurotrophic factor (BDNF) enhances insulin activity in diabetic rodents. Because physical exercise modifies BDNF production, this study aimed to investigate the effects of chronic exercise on plasma BDNF levels and the possible effects on insulin tolerance modification in healthy rats.

METHODS

Wistar rats were divided into five groups: control (sedentary, C); moderate- intensity training (MIT); MIT plus K252A TrkB blocker (MITK); high-intensity training (HIT); and HIT plus K252a (HITK). Training comprised 8 weeks of treadmill running. Plasma BDNF levels (ELISA assay), glucose tolerance, insulin tolerance, and immunohistochemistry for insulin and the pancreatic islet area were evaluated in all groups. In addition, Bdnf mRNA expression in the skeletal muscle was measured.

PRINCIPAL FINDINGS

Chronic treadmill exercise significantly increased plasma BDNF levels and insulin tolerance, and both effects were attenuated by TrkB blocking. In the MIT and HIT groups, a significant TrkB-dependent pancreatic islet enlargement was observed. MIT rats exhibited increased liver glycogen levels following insulin administration in a TrkB-independent manner.

CONCLUSIONS/SIGNIFICANCE

Chronic physical exercise exerted remarkable effects on insulin regulation by inducing significant increases in the pancreatic islet size and insulin sensitivity in a TrkB-dependent manner. A threshold for the induction of BNDF in response to physical exercise exists in certain muscle groups. To the best of our knowledge, these are the first results to reveal a role for TrkB in the chronic exercise-mediated insulin regulation in healthy rats.

Effect of physical training on liver expression of activin A and follistatin in a nonalcoholic fatty liver disease model in rats

Nonalcoholic fatty liver disease (NAFLD) is characterized by fat accumulation in the liver and is associated with obesity and insulin resistance. Activin A is a member of the transforming growth factor beta (TGF)-β superfamily and inhibits hepatocyte growth. Follistatin antagonizes the biological actions of activin. Exercise is an important therapeutic strategy to reduce the metabolic effects of obesity. We evaluated the pattern of activin A and follistatin liver expression in obese rats subjected to swimming exercise. Control rats (C) and high-fat (HF) diet-fed rats were randomly assigned to a swimming training group (C-Swim and HF-Swim) or a sedentary group (C-Sed and HF-Sed). Activin βA subunit mRNA expression was significantly higher in HF-Swim than in HF-Sed rats. Follistatin mRNA expression was significantly lower in C-Swim and HF-Swim than in either C-Sed or HF-Sed animals. There was no evidence of steatosis or inflammation in C rats. In contrast, in HF animals the severity of steatosis ranged from grade 1 to grade 3. The extent of liver parenchyma damage was less in HF-Swim animals, with the severity of steatosis ranging from grade 0 to grade 1. These data showed that exercise may reduce the deleterious effects of a high-fat diet on the liver, suggesting that the local expression of activin-follistatin may be involved.

Resveratrol reduces chronic inflammation and improves insulin action in the myocardium of high-fat diet-induced obeserats

OBJECTIVE: To evaluate the effects of resveratrol on insulin signaling and inflammation pathway in the myocardium of high-fat diet-induced obese rats. METHODS: Thirty Wistar rats were divided into a control group (n=10, standard diet), obese group (n=10, high-fat diet), and obese supplemented with resveratrol group (n=10, 20 mg/kg/day) for eight weeks. An insulin tolerance test was performed at the end of the study period "0" (without insulin), 5, 10, 15, 20, 25, and 30 minutes after an intraperitoneal injection of insulin (2 U/kg). Body and epididymal adipose tissue were weighed. Fragments of the myocardium were extracted for Western blot analyses of insulin pathway and proinflammatory molecules. RESULTS: Resveratrol increased the rate of glucose disappearance, phosphorylation of the insulin receptor, insulin receptor substrate 1, and protein kinase B; and reduced expression of tumor necrosis factor alpha and of the molecules involved in proinflammatory signal transduction, namely Ikappa B kinase and nuclear factor kappa B complex. The results also suggest that higher insulin sensitivity and lower levels of proinflammatory molecules occurred regardless of weight and epididymal adipose tissue loss. CONCLUSION: Resveratrol increases insulin action and reduces inflammatory molecules in the myocardium.

Exercise training decreases mitogen-activated protein kinase phosphatase-3 expression and suppresses hepatic gluconeogenesis in obese mice

Insulin plays an important role in the control of hepatic glucose production. Insulin resistant states are commonly associated with excessive hepatic glucose production, which contributes to both fasting hyperglycaemia and exaggerated postprandial hyperglycaemia. In this regard, increased activity of phosphatases may contribute to the dysregulation of gluconeogenesis. Mitogen-activated protein kinase phosphatase-3 (MKP-3) is a key protein involved in the control of gluconeogenesis. MKP-3-mediated dephosphorylation activates FoxO1 (a member of the forkhead family of transcription factors) and subsequently promotes its nuclear translocation and binding to the promoters of gluconeogenic genes such as phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase). In this study, we investigated the effects of exercise training on the expression of MKP-3 and its interaction with FoxO1 in the livers of obese animals. We found that exercised obese mice had a lower expression of MKP-3 and FoxO1/MKP-3 association in the liver. Further, the exercise training decreased FoxO1 phosphorylation and protein levels of Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and gluconeogenic enzymes (PEPCK and G6Pase). These molecular results were accompanied by physiological changes, including increased insulin sensitivity and reduced hyperglycaemia, which were not caused by reductions in total body mass. Similar results were also observed with oligonucleotide antisense (ASO) treatment. However, our results showed that only exercise training could reduce an obesity-induced increase in HNF-4α protein levels while ASO treatment alone had no effect. These findings could explain, at least in part, why additive effects of exercise training treatment and ASO treatment were not observed. Finally, the suppressive effects of exercise training on MKP-3 protein levels appear to be related, at least in part, to the reduced phosphorylation of Extracellular signal-regulated kinases (ERK) in the livers of obese mice.

Hypothalamic AMPK activation blocks lipopolysaccharide inhibition of glucose production in mice liver

Endotoxic hypoglycaemia has an important role in the survival rates of septic patients. Previous studies have demonstrated that hypothalamic AMP-activated protein kinase (hyp-AMPK) activity is sufficient to modulate glucose homeostasis. However, the role of hyp-AMPK in hypoglycaemia associated with endotoxemia is unknown. The aims of this study were to examine hyp-AMPK dephosphorylation in lipopolysaccharide (LPS)-treated mice and to determine whether pharmacological hyp-AMPK activation could reduce the effects of endotoxemia on blood glucose levels. LPS-treated mice showed reduced food intake, diminished basal glycemia, increased serum TNF-α and IL-1β levels and increased hypothalamic p-TAK and TLR4/MyD88 association. These effects were accompanied by hyp-AMPK/ACC dephosphorylation. LPS-treated mice also showed diminished liver expression of PEPCK/G6Pase, reduction in p-FOXO1, p-AMPK, p-STAT3 and p-JNK level and glucose production. Pharmacological hyp-AMPK activation blocked the effects of LPS on the hyp-AMPK phosphorylation, liver PEPCK expression and glucose production. Furthermore, the effects of LPS were TLR4-dependent because hyp-AMPK phosphorylation, liver PEPCK expression and fasting glycemia were not affected in TLR4-mutant mice. These results suggest that hyp-AMPK activity may be an important pharmacological target to control glucose homeostasis during endotoxemia.

Experimental evidence for the use of CCR2 antagonists in the treatment of type 2 diabetes

OBJECTIVE

CCR2 inhibition has produced promising experimental and clinical anti-hyperglycemic effects. These results support the thesis that insulin resistance and Type 2 diabetes (T2D) are associated with chronic unresolved inflammation. The aim of this study was to provide a broad analysis of the various physiological changes occurring in mouse models of T2D in connection with pharmacological CCR2 inhibition.

MATERIALS/METHODS

A mouse-active chemical analogue of the clinical candidate CCX140-B was tested in diet-induced obese (DIO) mice and db/db mice. Measurements included: adipose tissue inflammatory macrophage counts; peripheral blood glucose levels at steady-state and after glucose and insulin challenges; peripheral blood insulin and adiponectin levels; 24-h urine output and urinary glucose levels; pancreatic islet number and size; hepatic triglyceride and glycogen content; and hepatic glucose-6-phosphatase levels.

RESULTS

In DIO mice, the CCR2 antagonist completely blocked the recruitment of inflammatory macrophages to visceral adipose tissue. The mice exhibited reduced hyperglycemia and insulinemia, improved insulin sensitivity, increased circulating adiponectin levels, decreased pancreatic islet size and increased islet number. It also reduced urine output, glucose excretion, hepatic glycogen and triglyceride content and glucose 6-phosphatase levels. Similar effects were observed in the db/db diabetic mice.

CONCLUSIONS

These data indicate that pharmacological inhibition of CCR2 in models of T2D can reduce inflammation in adipose tissue, alter hepatic metabolism and ameliorate multiple diabetic parameters. These mechanisms may contribute to the promising anti-diabetic effects seen in humans with at least one CCR2 antagonist.

Areias MF, Weissmann L, Quaresma PG, Katashima CK, Saad MJ, Prada PO. Diet-induced obesity induces endoplasmic reticulum stress and insulin resistance in the amygdala of rats

Insulin acts in the hypothalamus, decreasing food intake (FI) by the IR/PI3K/Akt pathway. This pathway is impaired in obese animals and endoplasmic reticulum (ER) stress and low-grade inflammation are possible mechanisms involved in this impairment. Here, we highlighted the amygdala as an important brain region for FI regulation in response to insulin. This regulation was dependent on PI3K/AKT pathway similar to the hypothalamus. Insulin was able to decrease neuropeptide Y (NPY) and increase oxytocin mRNA levels in the amygdala via PI3K, which may contribute to hypophagia. Additionally, obese rats did not reduce FI in response to insulin and AKT phosphorylation was decreased in the amygdala, suggesting insulin resistance. Insulin resistance was associated with ER stress and low-grade inflammation in this brain region. The inhibition of ER stress with PBA reverses insulin action/signaling, decreases NPY and increases oxytocin mRNA levels in the amygdala from obese rats, suggesting that ER stress is probably one of the mechanisms that induce insulin resistance in the amygdala.

Critical role of AKT protein in myeloma-induced osteoclast formation and osteolysis

Abnormal osteoclast formation and osteolysis are the hallmarks of multiple myeloma (MM) bone disease, yet the underlying molecular mechanisms are incompletely understood. Here, we show that the AKT pathway was up-regulated in primary bone marrow monocytes (BMM) from patients with MM, which resulted in sustained high expression of the receptor activator of NF-κB (RANK) in osteoclast precursors. The up-regulation of RANK expression and osteoclast formation in the MM BMM cultures was blocked by AKT inhibition. Conditioned media from MM cell cultures activated AKT and increased RANK expression and osteoclast formation in BMM cultures. Inhibiting AKT in cultured MM cells decreased their growth and ability to promote osteoclast formation. Of clinical significance, systemic administration of the AKT inhibitor LY294002 blocked the formation of tumor tissues in the bone marrow cavity and essentially abolished the MM-induced osteoclast formation and osteolysis in SCID mice. The level of activating transcription factor 4 (ATF4) protein was up-regulated in the BMM cultures from multiple myeloma patients. Adenoviral overexpression of ATF4 activated RANK expression in osteoclast precursors. These results demonstrate a new role of AKT in the MM promotion of osteoclast formation and bone osteolysis through, at least in part, the ATF4-dependent up-regulation of RANK expression in osteoclast precursors.

Peroxisome proliferator-activated receptors-alpha and gamma are targets to treat offspring from maternal diet-induced obesity in mice

AIM

The aim of the present study was to evaluate whether activation of peroxisome proliferator-activated receptor (PPAR)alpha and PPARgamma by Bezafibrate (BZ) could attenuate hepatic and white adipose tissue (WAT) abnormalities in male offspring from diet-induced obese dams.

MATERIALS AND METHODS

C57BL/6 female mice were fed a standard chow (SC; 10% lipids) diet or a high-fat (HF; 49% lipids) diet for 8 weeks before mating and during gestation and lactation periods. Male offspring received SC diet at weaning and were subdivided into four groups: SC, SC/BZ, HF and HF/BZ. Treatment with BZ (100 mg/Kg diet) started at 12 weeks of age and was maintained for three weeks.

RESULTS

The HF diet resulted in an overweight phenotype and an increase in oral glucose intolerance and fasting glucose of dams. The HF offspring showed increased body mass, higher levels of plasmatic and hepatic triglycerides, higher levels of pro-inflammatory and lower levels of anti-inflammatory adipokines, impairment of glucose metabolism, abnormal fat pad mass distribution, higher number of larger adipocytes, hepatic steatosis, higher expression of lipogenic proteins concomitant to decreased expression of PPARalpha and carnitine palmitoyltransferase I (CPT-1) in liver, and diminished expression of PPARgamma and adiponectin in WAT. Treatment with BZ ameliorated the hepatic and WAT abnormalities generated by diet-induced maternal obesity, with improvements observed in the structural, biochemical and molecular characteristics of the animals' livers and epididymal fat.

CONCLUSION

Diet-induced maternal obesity lead to alterations in metabolism, hepatic lipotoxicity and adverse liver and WAT remodeling in the offspring. Targeting PPAR with Bezafibrate has beneficial effects reducing the alterations, mainly through reduction of WAT inflammatory state through PPARgamma activation and enhanced hepatic beta-oxidation due to increased PPARalpha/PPARgamma ratio in liver.

Suplementação de ácidos graxos poli-insaturados ômega-3 reduz marcadores inflamatórios e melhora a ação da insulina em fígado de camundongos

OBJETIVO: Avaliar os efeitos da suplementação do ácido graxo poliinsaturado ômega-3 (n3) sobre a sinalização da insulina e via próinflamatória no tecido hepático de camundongos. MÉTODOS: Camundongos Swiss foram divididos em seis grupos que receberam, por gavagem esofágica, diferentes doses de óleo de peixe contendo ômega-3 (1mg, 5mg, 10mg e 50mg). O grupo-controle recebeu água. Para determinar os efeitos do ômega-3 dependentes de dose e tempo, a glicemia de jejum foi avaliada nos dias 0 (sem suplementação), 14 e 21 (após suplementação). Como o grupo n-3-21dias (21 dias de suplementação) apresentou menor nível de glicemia, esse intervalo de tempo foi selecionado para as análises moleculares. Após jejum de 8 horas, amostras do tecido hepático foram obtidas do grupo-controle, e n-3-21dias e análises das vias de sinalização da insulina e próinflamatória foram realizadas por western blot. RESULTADOS: Os resultados mostraram que a dose de 10mg induziu maior redução na glicemia no 14° e no 21° dias quando comparada às demais doses. Dessa forma, essa foi a dose utilizada nos experimentos de análises moleculares e foi a que diminuiu de forma significativa a fosforilação da c-Jun n-terminal quinase e quinase e níveis proteicos do fator de transcrição Kappa B. Em paralelo, foi observado aumento na fosforilação do receptor da insulina, substrato do receptor de insulina 1 e proteína quinase B. CONCLUSÃO: O presente estudo sugere que o ômega-3 induza melhora na via de sinalização da insulina no fígado de camundongos, pelo menos em parte, por reduzir inflamação. Esses resultados podem explicar menores níveis de glicose de jejum.

Can healthy lifestyle modify risk factors for dementia? Findings from a pilot community-based survey in Chennai (India) and Newcastle (UK)

BACKGROUND

Currently there are no effective treatments available for dementia. Attention has turned to defining preventive strategies and identifying modifying effects of lifestyle, including physical activity, diet, alcohol intake and smoking, in reducing cognitive decline and overt memory problems in the elderly.

METHODS

In this study, we addressed the modifying aspects of various components of lifestyle in two ageing samples and explored the possible effects that exercise, diet and spiritual and religious beliefs have upon physical and mental health. A total of 251 subjects (128 in Chennai, India, and 123 in Newcastle, UK) filled in a questionnaire regarding their lifestyle habits. Data were analysed with χ² analysis.

RESULTS

Our findings highlight that spiritual and religious beliefs promoted good physical and mental health and were negatively associated with risk factors for dementia, such as high blood pressure, high cholesterol level and diabetes. Lifelong diet and physical activity also contributed to better overall well-being in both samples.

CONCLUSIONS

Our study suggests substantial lifestyle variations between two urban populations in Chennai, India, and Newcastle-upon-Tyne, UK. Further detailed work is required to identify the lifestyle components that have the greatest impact on modifying the known risk factors for dementia.

Endurance training stimulates growth and survival pathways and the redox balance in rat pancreatic islets

Endurance training has been shown to increase pancreatic β-cell function and mass. However, whether exercise modulates β-cell growth and survival pathways signaling is not completely understood. This study investigated the effects of exercise on growth and apoptotic markers levels in rat pancreatic islets. Male Wistar rats were randomly assigned to 8-wk endurance training or to a sedentary control group. After that, pancreatic islets were isolated; gene expression and the total content and phosphorylation of several proteins related to growth and apoptotic pathways as well as the main antioxidant enzymes were determined by real-time polymerase chain reaction and Western blot analysis, respectively. Reactive oxygen species (ROS) production was measured by fluorescence. Endurance training increased the time to reach fatigue by 50%. Endurance training resulted in increased protein phosphorylation content of AKT (75%), AKT substrate (AS160; 100%), mTOR (60%), p70s6k (90%), and ERK1/2 (50%), compared with islets from control group. Catalase protein content was 50% higher, whereas ROS production was 49 and 77% lower in islets from trained rats under basal and stimulating glucose conditions, respectively. Bcl-2 mRNA and protein levels increased by 46 and 100%, respectively. Bax and cleaved caspase-3 protein contents were reduced by 25 and 50% in islets from trained rats, respectively. In conclusion, these results demonstrate that endurance training favors the β-cell growth and survival by activating AKT and ERK1/2 pathways, enhancing antioxidant capacity, and reducing ROS production and apoptotic proteins content.

The intensity of IUGR-induced transcriptome deregulations is inversely correlated with the onset of organ function in a rat model

A low-protein diet applied during pregnancy in the rat results in intrauterine growth restricted (IUGR) fetuses. In humans, IUGR is associated with increased perinatal morbidity, higher incidence of neuro-developmental defects and increased risk of adult metabolic anomalies, such as diabetes and cardiovascular disease. Development and function of many organs are affected by environmental conditions such as those inducing fetal and early postnatal growth restriction. This phenomenon, termed "fetal programming" has been studied unconnectedly in some organs, but very few studies (if any) have investigated at the same time several organs, on a more comparative basis. However, it is quite probable that IUGR affects differentially most organ systems, with possible persistent changes in gene expression. In this study we address transcriptional alterations induced by IUGR in a multi-organ perspective, by systematic analysis of 20-days rat fetuses. We show that (1) expressional alterations are apparently stronger in organs functioning late in foetal or postnatal life than in organs that are functioning early (2) hierarchical classification of the deregulations put together kidney and placenta in one cluster, liver, lungs and heart in another; (3) the epigenetic machinery is set up especially in the placenta, while its alterations are rather mild in other organs; (4) the genes appear deregulated in chromosome clusters; (5) the altered expression cascades varies from organ to organ, with noticeably a very significant modification of the complement and coagulation cascades in the kidney; (6) we found a significant increase in TF binding site for HNF4 proteins specifically for liver genes that are down-regulated in IUGR, suggesting that this decrease is achieved through the action of HNF transcription factors, that are themselves transcriptionnally induced in the liver by IUGR (x 1.84 fold). Altogether, our study suggests that a combination of tissue-specific mechanisms contributes to bring about tissue-driven modifications of gene cascades. The question of these cascades being activated to adapt the organ to harsh environmental condition, or as an endpoint consequence is still raised.

Does physical inactivity cause nonalcoholic fatty liver disease?

While physical activity represents a key element in the prevention and management of many chronic diseases, we and others believe that physical inactivity is a primary cause of obesity and associated metabolic disorders. Unfortunately, accumulating evidence suggests that we have engineered physical activity out of our normal daily living activity. One such consequence of our sedentary and excessive lifestyle is nonalcoholic fatty liver disease (NAFLD), which is now considered the most common cause of chronic liver disease in Westernized societies. In this review, we will present evidence that physical inactivity, low aerobic fitness, and overnutrition, either separately or in combination, are an underlying cause of NAFLD.