AMP-activated Protein Kinase In Tissues Research Articles

The Impact of Neonatal Curcumin Intake on Key Molecular Markers in Lipid and Glucose Metabolism

The high prevalence of obesity, resulting from the increased consumption of a fructose-rich diet, poses a serious global threat to children's public health. Obesity is linked to several metabolic disorders, including insulin resistance and type-2 diabetes. Furthermore, type-2 diabetes is characterized by impaired lipid and glucose metabolism. This study investigated the impact of neonatal curcumin intake on the expression of key molecular markers related to liver lipid metabolism [Liver kinase B-1 (LKB-1), AMP-activated protein kinase (AMPK), Carnitine palmitoyltransferase-1 (CPT-1), and Acetyl-coenzyme A carboxylase-1 (ACC-1)] and glucose metabolism [serine/threonine-protein kinase (AKT-1), Glucose transporter-2 (GLUT-2), glycogen phosphorylase (GP), and Phosphoglucomutase (PGM)]. Curcumin, a polyphenolic compound derived from turmeric, is currently under extensive research for its potential therapeutic applications in various diseases. In this study, a metabolic syndrome model was induced in Sprague Dawley rats by feeding them a high fructose diet, with curcumin administered as the treatment. Gene expression was assessed through Real-Time quantitative PCR, and protein expression was analyzed using the western blot technique. The study observed that a high fructose diet led to the upregulation of genes and proteins associated with lipid metabolism, such as AMPK, LKB-1, ACC-1, and CPT-1 in liver tissues. Curcumin treatment reversed these effects, restoring normal lipid metabolism. Additionally, the high fructose diet downregulated the expression of AKT-1 in hepatic insulin signaling, which was counteracted by curcumin. Moreover, the high fructose diet increased hepatic glucose production, as indicated by the upregulation of GP and PGM gene and protein expression, while curcumin treatment suppressed hepatic glucose production by downregulating GP and PGM expression. The findings improve our understanding of curcumin's molecular mechanisms, which are not yet fully understood. They offer further evidence of curcumin's positive effects. Thus, early neonatal consumption of curcumin could be a potential strategy to prevent high fructose diet-induced obesity and related metabolic disorders, including insulin resistance and type-2 diabetes. Lipid and Glucose Metabolism. This project was funded by the North-West University. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Glucose restriction induces ROS-AMPK-mediated CTR1 expression and increases cisplatin efficiency in NSCLC

Cisplatin is one of the principal platinum-based chemotherapeutic agents for many types of cancer, including non-small-cell lung cancer (NSCLC). Copper transporter 1 (CTR1) plays a significant role in increasing cellular cisplatin uptake and sensitivity. The current study found that glucose restriction upregulated AMPK (AMP-activated protein kinase) through reactive oxygen species (ROS) to induce CTR1 expression in NSCLC cells. Direct upregulation of ROS levels also activated AMPK expression. The changes in CTR1 expression were consistent with glucose concentrations and AMPK expression. Feeding a low-carbohydrate ketogenic diet (a glucose restriction diet) to a severe combined immune deficiency (SCID) mouse xenograft model significantly enhanced the efficacy of cisplatin. The tumor size was significantly smaller in the group treated with cisplatin plus the low-carbohydrate ketogenic diet than in the group treated with cisplatin alone. Survival was longer in mice treated with the low-carbohydrate ketogenic diet than in the controls. Mice fed the low-carbohydrate ketogenic diet showed increased expression of CTR1 and AMPK in tumor tissues. These results suggest a novel mechanism whereby glucose restriction induces ROS-AMPK-mediated CTR1 expression in NSCLC, indicating glucose restriction as an effective adjuvant NSCLC therapy.

Mice with Whole-Body Disruption of AMPK-Glycogen Binding Have Increased Adiposity, Reduced Fat Oxidation and Altered Tissue Glycogen Dynamics.

The AMP-activated protein kinase (AMPK), a central regulator of cellular energy balance and metabolism, binds glycogen via its β subunit. However, the physiological effects of disrupting AMPK-glycogen interactions remain incompletely understood. To chronically disrupt AMPK-glycogen binding, AMPK β double knock-in (DKI) mice were generated with mutations in residues critical for glycogen binding in both the β1 (W100A) and β2 (W98A) subunit isoforms. We examined the effects of this DKI mutation on whole-body substrate utilization, glucose homeostasis, and tissue glycogen dynamics. Body composition, metabolic caging, glucose and insulin tolerance, serum hormone and lipid profiles, and tissue glycogen and protein content were analyzed in chow-fed male DKI and age-matched wild-type (WT) mice. DKI mice displayed increased whole-body fat mass and glucose intolerance associated with reduced fat oxidation relative to WT. DKI mice had reduced liver glycogen content in the fed state concomitant with increased utilization and no repletion of skeletal muscle glycogen in response to fasting and refeeding, respectively, despite similar glycogen-associated protein content relative to WT. DKI liver and skeletal muscle displayed reductions in AMPK protein content versus WT. These findings identify phenotypic effects of the AMPK DKI mutation on whole-body metabolism and tissue AMPK content and glycogen dynamics.

Potent PDE4 inhibitor activates AMPK and Sirt1 to induce mitochondrial biogenesis.

AMP-activated protein kinase (AMPK) is an evolutionarily conserved energy sensor. Activation of AMPK leads to a number of metabolic benefits, including improved mitochondrial function in skeletal muscle and lowering of serum glucose levels in type-2 diabetes models. However, direct activation of AMPK leads to cardiac enlargement, and an alternative strategy that activates AMPK without affecting the heart is needed. Inhibition of phosphodiesterase 4 (PDE4), which is poorly expressed in the human heart, activates AMPK in other tissues. In a screen to identify novel PDE4 inhibitors, we discovered compound CBU91, which is 5–10 fold more potent than rolipram, the best characterized PDE4 inhibitor. CBU91, like rolipram, is able to activate AMPK and Sirt1 and increase mitochondrial function in myotubes. These findings suggest that activation of AMPK in myotubes is a general property of PDE4 inhibition and that PDE4 inhibition may activate AMPK in metabolically relevant tissues without affecting the heart.

AICAR decreases acute lung injury by phosphorylating AMPK and upregulating heme oxygenase-1.

We investigated the mechanisms by which N1-(β-d-ribofuranosyl)-5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an activator of AMP-activated protein kinase (AMPK), decreases lung injury and mortality when administered to mice post exposure to bromine gas (Br2). We exposed male C57BL/6 mice and heme oxygenase-1 (HO-1)-deficient (HO-1-/-) and corresponding wild-type (WT) littermate mice to Br2 (600 ppm for 45 or 30 min, respectively) in environmental chambers and returned them to room air. AICAR was administered 6 h post exposure (10 mg·kg-1, intraperitoneal). We assessed survival, indices of lung injury, high mobility group box 1 (HMGB1) in the plasma, HO-1 levels in lung tissues and phosphorylation of AMPK and its upstream liver kinase B1 (LKB1). Rat alveolar type II epithelial (L2) cells and human club-like epithelial (H441) cells were also exposed to Br2 (100 ppm for 10 min). After 24 h we measured apoptosis and necrosis, AMPK and LKB1 phosphorylation, and HO-1 expression. There was a marked downregulation of phosphorylated AMPK and LKB1 in lung tissues and in L2 and H441 cells post exposure. AICAR increased survival in C57BL/6 but not in HO-1-/- mice. In WT mice, AICAR decreased lung injury and restored phosphorylated AMPK and phosphorylated LKB1 to control levels and increased HO-1 levels in both lung tissues and cells exposed to Br2. Treatment of L2 and H441 cells with small interfering RNAs against nuclear factor erythroid 2-related factor 2 or HO-1 abrogated the protective effects of AICAR. Our data indicate that the primary mechanism for the protective action of AICAR in toxic gas injury is the upregulation of lung HO-1 levels.

The autophagy protein Becn1 improves insulin sensitivity by promoting adiponectin secretion via exocyst binding.

SUMMARYAutophagy dysregulation is implicated in metabolic diseases, including type 2 diabetes. However, the mechanism by which the autophagy machinery regulates metabolism is largely unknown. Autophagy is generally considered a degradation process via lysosomes. Here, we unveil a metabolically important non-cell-autonomous, non-degradative mechanism regulated by the essential autophagy protein Becn1 in adipose tissue. Upon high-fat diet challenge, autophagy-hyperactive Becn1F121A mice show systemically improved insulin sensitivity and enhanced activation of AMP-activated protein kinase (AMPK), a central regulator of energy homeostasis, via a non-cell-autonomous mechanism mediated by adiponectin, an adipose-derived metabolic hormone. Adipose-specific Becn1F121A expression is sufficient to activate AMPK in non-adipose tissues and improve systemic insulin sensitivity by increasing adiponectin secretion. Further, Becn1 enhances adiponectin secretion by interacting with components of the exocyst complex via the coiled-coil domain. Together, our study demonstrates that Becn1 improves insulin sensitivity by facilitating adiponectin secretion through binding the exocyst in adipose tissue.

Mechanisms underlying the attenuation of chronic inflammatory diseases by aged garlic extract: Involvement of the activation of AMP-activated protein kinase.

AMP-activated protein kinase (AMPK) is an ubiquitously expressed serine/threonine kinase and an important regulator of energy metabolism. The decreased activity of AMPK induced by low-grade chronic inflammation has been implicated in several diseases, including type 2 diabetes and atherosclerosis. However, the activation of AMPK by natural and synthetic products can ameliorate these diseases through the inhibition of inflammation. For example, aged garlic extract (AGE) has been shown to enhance the phosphorylation of Thr172 of the α-subunit of AMPK in several tissues of disease model animals. In addition, AGE has been reported to suppress the progression of atherosclerotic plaque formation in an animal model of atherosclerosis. Moreover, AGE has been found to decrease the level of plasma glycated albumin and to improve hyperglycemia in an animal model of type 2 diabetes. These inhibitory effects of AGE are induced by the suppression of the inflammatory response. In the present review, we discuss the mechanisms through which AGE activates AMPK, as well as the mechanisms through which the activation of AMPK by AGE modulates the inflammatory response in disease models.

Adipose tissue-specific knockout of AMPKα1/α2 results in normal AICAR tolerance and glucose metabolism

AMP-activated protein kinase (AMPK) is a member of Ser/Thr kinases that has been shown to regulate energy balance. Although recent studies have demonstrated the function of AMPK in adipose tissue using different fat-specific AMPK knockout mouse models, the results were somewhat inconsistent. For this study, we tested the hypothesis that AMPK in adipose tissue regulates whole body glucose metabolism. To determine the role of adipose tissue AMPK in vivo, we generated fat-specific AMPKα1/α2 knockout mice (AMPKFKO) using the Cre-loxP system. Body weights of AMPKFKO mice were not different between 8 and 27 weeks of age. Furthermore, tissue weights (liver, kidney, muscle, heart and white and brown adipose tissue) were similar to wild type littermates and DEXA scan analysis revealed no differences in percentages of body fat and lean mass. Knockout of AMPKα1/α2 in adipose tissue abolished basal and AICAR-stimulated phosphorylation of AMPK and Acetyl-CoA Carboxylase, a downstream of AMPK. Despite of the ablation of AICAR-stimulated AMPK phosphorylation, the blood glucose-lowering effect of AICAR injection (i.p.) was normal in AMPKFKO mice. In addition, AMPKFKO displayed normal fasting blood glucose concentration, glucose tolerance, insulin tolerance, and insulin signaling, indicating normal whole body glucose metabolism. These data demonstrate that adipose tissue AMPK plays a minimum role in whole body glucose metabolism on a chow diet.

Emerging Role of AMPK in Brown and Beige Adipose Tissue (BAT): Implications for Obesity, Insulin Resistance, and Type 2 Diabetes.

The global prevalence of type 2 diabetes (T2D) is escalating at alarming rates, demanding the development of additional classes of therapeutics to further reduce the burden of disease. Recent studies have indicated that increasing the metabolic activity of brown and beige adipose tissue may represent a novel means to reduce circulating glucose and lipids in people with T2D. The AMP-activated protein kinase (AMPK) is a cellular energy sensor that has recently been demonstrated to be important in potentially regulating the metabolic activity of brown and beige adipose tissue. The goal of this review is to summarize recent work describing the role of AMPK in brown and beige adipose tissue, focusing on its role in adipogenesis and non-shivering thermogenesis. Ablation of AMPK in mouse adipocytes results in cold intolerance, a reduction in non-shivering thermogenesis in brown adipose tissue (BAT), and the development of non-alcoholic fatty liver disease (NAFLD) and insulin resistance; effects associated with a defect in mitochondrial specific autophagy (mitophagy) within BAT. The effects of a β3-adrenergic agonist on the induction of BAT thermogenesis and the browning of white adipose tissue (WAT) are also blunted in mice lacking adipose tissue AMPK. A specific AMPK activator, A-769662, also results in the activation of BAT and the browning of WAT, effects which may involve demethylation of the PR domain containing 16 (Prdm16) promoter region, which is important for BAT development. AMPK plays an important role in the development and maintenance of brown and beige adipose tissue. Adipose tissue AMPK is reduced in people with insulin resistance, consistent with findings that mice lacking adipocyte AMPK develop greater NAFLD and insulin resistance. These data suggest that pharmacologically targeting adipose tissue AMPK may represent a promising strategy to enhance energy expenditure and reduce circulating glucose and lipids, which may be effective for the treatment of NAFLD and T2D.

Salidroside and Curcumin Formula Prevents Liver Injury in Nonalcoholic Fatty Liver Disease in Rats

Introduction and aim. Salidroside and curcumin (SC) formula could alleviate lipid deposition in high fat diet-induced nonalcoholic fatty liver disease (NAFLD). However, the mechanisms are still unknown, and the magnitude of potential therapeutic benefit remains understudied. Material and methods. The rats were treated with high fat diet for 14 weeks to induce NAFLD. The experiment was divided into control, model (NAFLD), SC formula and rosiglitazone groups (n = 7 in each group). Hematoxylin-eosin (H&E) staining was applied to detect liver morphological changes. Biochemical, metabolic indices and inflammation factors in liver tissue and serum were detected. Additionally, the activities of related enzymes were detected by enzyme-linked immunosorbent assay. Results. In the established rat model, typical lipid deposition and liver steatosis were observed. Liver triglyceride, free fatty acids, sera alanine aminotransferase, aspartate aminotransferase, gamma-glutamyl transferase, fasting insulin, fasting blood glucose and homeostasis model assessment of insulin resistance were elevated in model group. Liver malondialdehyde was significantly elevated, while superoxide dismutase was significantly decreased in model group, compared with control. Moreover, tumor necrosis factor-α and Interleukin-1 were significantly produced in model group, compared with control. As a mechanism, high fat diet decreased tissue AMP-activated protein kinase (AMPK), phosphorylated AMPK, carnitine palmitoyltransferase 1 and increased inacetyl-CoA carboxylase (ACCase), phosphorylated ACCase. Importantly, these abnormal changes caused by high fat diet were reduced by SC formula administration. Conclusion. SC formula could ameliorate the injury caused by high fat diet. The effect was likely mediated via its influence on insulin resistance, lipid peroxidation injury and AMPK signaling pathway.

Desmoplasia suppression by metformin-mediated AMPK activation inhibits pancreatic cancer progression

Emerging evidence suggests that metformin, an activator of AMP-activated protein kinase (AMPK), may be useful in preventing and treating pancreatic ductal adenocarcinoma (PDAC). However, whether metformin has an effect on the stromal reaction of PDAC remains unknown. In this study, we first evaluated the expression of AMPK and phosphorylated-AMPK (P-AMPK) in normal and PDAC tissues, our data indicate that reduced P-AMPK expression is a frequent event in PDAC and correlated with poor prognosis and the dense stromal reaction. We then determined the efficacy of metformin on PDAC growth in vitro and in vivo. We reveal that metformin reduces the production of fibrogenic cytokines from pancreatic cancer cells (PCs) and inhibits paracrine-mediated pancreatic stellate cells (PSCs) activation under PCsPSCs co-culture conditions. By using a xenograft PDAC mouse model, we show that metformin intervention prevents tumor growth and enhances the antitumor effect of gemcitabine via suppression of desmoplastic reaction. Taken together, these results suggest that induction of AMPK activation by metformin represents a novel therapeutic approach for treating advanced PDAC through reducing the desmoplastic reaction in PDAC.

Effects of Caloric Restriction and Aerobic Exercise on Adipose Tissue AMP-activated Protein Kinase Gene Expression in Obese Older Women

AMP-activated protein kinase (AMPK) plays a key role as a master regulator of cellular energy homeostasis. In adipose tissue, AMPK activation results in fatty acid oxidation and lowers chronic inflammation. PURPOSE: To investigate the effect of caloric restriction and caloric restriction plus aerobic exercise at different intensities on adipose tissue AMPK gene expression in obese older women. METHODS: Twenty nine overweight or obese, postmenopausal women were assigned to one of three 20-week intervention groups: caloric restriction (CR only, n=9), CR plus moderate-intensity aerobic exercise (CR+moderate-intensity, n=12), or CR plus vigorous-intensity aerobic exercise (CR+vigorous-intensity, n=8). Total calorie deficit was adjusted to approximately 2800 kcal/week, and the exercise involved treadmill walking at an intensity of 45-50% (moderate-intensity) or 70-75% (vigorous-intensity) of heart rate reserve. Subcutaneous abdominal adipose tissue samples were collected before and after the interventions. Adipose tissue AMPK mRNA levels were determined by real-time reverse transcription polymerase chain reaction. RESULTS: The average weight loss was 12.8±3.9 kg (14.6±5.2%) and it was not different among the three intervention groups. At baseline, adipose tissue AMPK mRNA levels did not differ among the three intervention groups. Compared to pre-intervention, CR increased adipose tissue AMPK mRNA levels (0.12±0.05 vs. 0.17±0.06, expressed as AMPK/β-actin mRNA ratio, P<0.05); however, CR+moderate-intensity and CR+vigorous-intensity did not alter adipose tissue AMPK mRNA levels (0.13±0.05 vs. 0.12±0.03 and 0.13±0.05 vs. 0.12±0.04, respectively). Moreover, change in AMPK mRNA levels in the CR group was significantly different from those in the CR+moderate-intensity and CR+vigorous-intensity groups (both P<0.05) CONCLUSION: Caloric restriction, but not caloric restriction plus aerobic exercise, increased abdominal adipose tissue AMPK gene expression in obese older women. The role of adipose tissue AMPK gene expression in regulating energy metabolism and inflammatory reactions during weight loss needs further investigation. (Supported by NIH R01-AG/DK20583, P30-AG21332, and M01-RR07122)

Prognostic significance of AMPK activation in advanced stage colorectal cancer treated with chemotherapy plus bevacizumab.

Background:AMP-activated protein kinase (AMPK) has a central role in cellular energy sensing and is activated in preclinical tumour models following anti-vascular endothelial growth factor (VEGF) therapy. The possible predictive or prognostic role of AMPK status in cancer patients treated with anti-VEGF drugs has not been investigated so far.Methods:Expression of components of the AMPK pathway including phosphorylated AMPK (pAMPK), phosphorylated acetyl-Coa carboxylase (pACC) and liver kinase B1 (LKB1) was investigated by immunohistochemistry in 48 colorectal cancers treated with FOLFIRI plus bevacizumab. Correlation between pAMPK and pACC and associations between the AMPK pathway scores and clinico-pathological characteristics were assessed. Overall survival (OS) was estimated through Kaplan–Meier method, whereas hazard ratios were computed to identify prognostic factors.Results:Fourteen patients (29.2%) were included in the pAMPK-negative group (score ⩽5), whereas 34 patients (70.8%) were included in the pAMPK-positive group (score >5). The Spearman's coefficient for the correlation between pAMPK and pACC scores in primary tumour samples was 0.514 (P=0.0002). Low pAMPK levels were associated with worse OS (P-value 0.0002) but not with PFS, whereas low pACC levels were associated both with worse OS and PFS (P-value 0.0007 and 0.01, respectively).Conclusions:Our findings suggest that high tissue AMPK activation is a prognostic biomarker in this cohort of metastatic colorectal cancer patients.

Metformin Ameliorates Hepatic Steatosis and Inflammation without Altering Adipose Phenotype in Diet-Induced Obesity

Non-alcoholic fatty liver disease (NAFLD) is closely associated with obesity and insulin resistance. To better understand the pathophysiology of obesity-associated NAFLD, the present study examined the involvement of liver and adipose tissues in metformin actions on reducing hepatic steatosis and inflammation during obesity. C57BL/6J mice were fed a high-fat diet (HFD) for 12 weeks to induce obesity-associated NAFLD and treated with metformin (150 mg/kg/d) orally for the last four weeks of HFD feeding. Compared with HFD-fed control mice, metformin-treated mice showed improvement in both glucose tolerance and insulin sensitivity. Also, metformin treatment caused a significant decrease in liver weight, but not adiposity. As indicated by histological changes, metformin treatment decreased hepatic steatosis, but not the size of adipocytes. In addition, metformin treatment caused an increase in the phosphorylation of liver AMP-activated protein kinase (AMPK), which was accompanied by an increase in the phosphorylation of liver acetyl-CoA carboxylase and decreases in the phosphorylation of liver c-Jun N-terminal kinase 1 (JNK1) and in the mRNA levels of lipogenic enzymes and proinflammatory cytokines. However, metformin treatment did not significantly alter adipose tissue AMPK phosphorylation and inflammatory responses. In cultured hepatocytes, metformin treatment increased AMPK phosphorylation and decreased fat deposition and inflammatory responses. Additionally, in bone marrow-derived macrophages, metformin treatment partially blunted the effects of lipopolysaccharide on inducing the phosphorylation of JNK1 and nuclear factor kappa B (NF-κB) p65 and on increasing the mRNA levels of proinflammatory cytokines. Taken together, these results suggest that metformin protects against obesity-associated NAFLD largely through direct effects on decreasing hepatocyte fat deposition and on inhibiting inflammatory responses in both hepatocytes and macrophages.

Citrus junosTanaka Peel Extract Exerts Antidiabetic Effects via AMPK and PPAR-γbothIn VitroandIn Vivoin Mice Fed a High-Fat Diet

The antidiabetic effect of the Citrus junos Tanaka (also known as yuja or yuzu) was examined. Ethanol extract of yuja peel (YPEE) significantly stimulated 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG) uptake in C2C12 myotubes. However, ethanol extract of yuja pulp (YpEE) and water extract of yuja peel (YPWE) or pulp (YpWE) did not stimulate glucose uptake. In addition, peroxisome proliferator-activated receptor gamma (PPAR-γ) and AMP-activated protein kinase (AMPK) activities were increased by YPEE in a dose-dependent manner. Pretreatment of AMPK inhibitor decreased the glucose uptake stimulated by YPEE in C2C12 myotubes. We confirmed the anti-diabetic effect of YPEE in mice fed a high fat-diet (HFD). Compared with control mice on a normal diet (ND), these mice showed increased body weight, liver fat, insulin resistance, triacylglycerol (TG), and total cholesterol content. Addition of 5% YPEE significantly reduced the weight gain and rise in liver fat content, serum triacylglycerol (TG), total cholesterol, and insulin resistance found in mice fed a high-fat diet (HFD). Moreover, YPEE reduced the secretion of HFD-induced adipocytokines such as leptin and resistin. YPEE also resulted in increased phosphorylation of AMPK in muscle tissues. These results suggest that ethanol extract of yuja peel exerts anti-diabetic effects via AMPK and PPAR-γ in both cell culture and mouse models.

Osthole Enhances Glucose Uptake through Activation of AMP-Activated Protein Kinase in Skeletal Muscle Cells

AMP-activated protein kinase (AMPK) is an energy sensor that regulates cellular metabolism. Activation of AMPK in skeletal muscles, the liver, and adipose tissues results in a favorable metabolic milieu for preventing and treating type 2 diabetes, i.e., decreased levels of circulating glucose, plasma lipids, and ectopic fat accumulation and enhanced insulin sensitivity. Osthole was extracted from a Chinese herbal medicine, and we found that it had glucose lowering activity in our previous study. However, the detailed glucose lowering mechanisms of osthole are still unclear. In this study, we used skeletal muscle cells to examine the underlying molecular mechanisms of osthole's glucose lowering activity. A Western blot analysis revealed that osthole significantly induced phosphorylation of AMPK and acetyl-CoA carboxylase (ACC). Next, we found that osthole significantly increased the level of translocation of glucose transporter 4 (GLUT4) to plasma membranes and glucose uptake in a dose-dependent manner. Osthole-induced glucose uptake was reversed by treatment with Compound C, an AMPK inhibitor, suggesting that osthole-induced glucose uptake was mediated in an AMPK-dependent manner. The increase in the AMP:ATP ratio was involved in osthole's activation of AMPK. Finally, we found that osthole counteracted hyperglycemia in mice with streptozotocin-induced diabetes. These results suggest that the increase in the AMP:ATP ratio by osthole triggered activation of the AMPK signaling pathway and led to increases in plasma membrane GLUT4 content and glucose uptake level. Therefore, osthole might have potential as an antidiabetic agent for treating diabetes.

AMP-activated protein kinase is activated in adipose tissue of individuals with type 2 diabetes treated with metformin: a randomised glycaemia-controlled crossover study.

The hypoglycaemic actions of metformin have been proposed to be mediated by hepatic AMP-activated protein kinase (AMPK). As the effects of metformin and the role of AMPK in adipose tissue remain poorly characterised, we examined the effect of metformin on AMPK activity in adipose tissue of individuals with type 2 diabetes in a randomised glycaemia-controlled crossover study. Twenty men with type 2 diabetes (aged 50-70 years) treated with diet, metformin or sulfonylurea alone were recruited from North Glasgow University National Health Service Trusts' diabetes clinics and randomised to either metformin or gliclazide for 10 weeks. Randomisation codes, generated by computer, were put into sealed envelopes and stored by the hospital pharmacist. Medication bottles were numbered, and allocation was done in sequence. The participants and investigators were blinded to group assignment. At the end of each phase of therapy adipose biopsy, AMPK activity (primary endpoint) and levels of lipid metabolism and signalling proteins were assessed. In parallel, the effect of metformin on AMPK and insulin-signalling pathways was investigated in 3T3-L1 adipocytes. Ten participants were initially randomised to metformin and subsequently crossed over to gliclazide, while ten participants were initially randomised to gliclazide and subsequently crossed over to metformin. No participants discontinued the intervention and the adipose tissue AMPK activity was analysed in all 20 participants. There were no adverse events or side effects in the study group. Adipose AMPK activity was increased following metformin compared with gliclazide therapy (0.057 ± 0.007 vs 0.030 ± 0.005 [mean ± SEM] nmol min(-1) [mg lysate](-1); p < 0.005), independent of AMPK level, glycaemia or plasma adiponectin concentrations. The increase was associated with reduced levels of acetyl-CoA carboxylase (ACC) protein and increased ACC Ser80 phosphorylation. In 3T3-L1 adipocytes, metformin reduced levels of ACC protein and stimulated phosphorylation of AMPK Thr172 and hormone-sensitive lipase Ser565. These results provide the first evidence that metformin activates AMPK and reduces ACC protein levels in human adipose tissue in vivo. Future studies are required to assess the role of adipose AMPK activation in the pharmacological effects of metformin. ISRCTN51336867.

Decreased AMP-activated protein kinase activity is associated with increased inflammation in visceral adipose tissue and with whole-body insulin resistance in morbidly obese humans

Inflammation and infiltration of immune cells in white adipose tissue have been implicated in the development of obesity-associated insulin resistance. Likewise, dysregulation of the fuel-sensing enzyme AMP-activated protein kinase (AMPK) has been proposed as a pathogenetic factor for these abnormalities based on both its links to insulin action and its anti-inflammatory effects. In this study, we examined the relationships between AMPK activity, the expression of multiple inflammatory markers in visceral (mesenteric and omental) and abdominal subcutaneous adipose tissue, and whole-body insulin sensitivity in morbidly obese patients (BMI 48±1.9kg/m2) undergoing gastric bypass surgery. AMPK activity was assessed by Western-blots (P-AMPK/T-AMPK) and mRNA levels of various markers of inflammation by qRT-PCR. Patients were stratified as insulin sensitive obese or insulin-resistant obese according to their HOMA-IR values. The results indicate that AMPK activity is lower in visceral than in subcutaneous abdominal adipose tissue of these patients and that this is associated with an increased expression of multiple inflammatory genes. They also revealed that AMPK activity is lower in adipose tissue of obese patients who are insulin resistant (HOMA-IR>2.3) than in BMI-matched insulin sensitive subjects. Furthermore, this difference was evident in all three fat depots. In conclusion, the data suggest that there are close links between reduced AMPK activity and inflammation in white adipose tissue, and whole-body insulin resistance in obese humans. Whether adipose tissue AMPK dysregulation is a causal factor for the development of the inflammation and insulin resistance remains to be determined.

Whole Body Deletion of AMP-activated Protein Kinase β2 Reduces Muscle AMPK Activity and Exercise Capacity

AMP-activated protein kinase (AMPK) β subunits (β1 and β2) provide scaffolds for binding α and γ subunits and contain a carbohydrate-binding module important for regulating enzyme activity. We generated C57Bl/6 mice with germline deletion of AMPK β2 (β2 KO) and examined AMPK expression and activity, exercise capacity, metabolic control during muscle contractions, aminoimidazole carboxamide ribonucleotide (AICAR) sensitivity, and susceptibility to obesity-induced insulin resistance. We find that β2 KO mice are viable and breed normally. β2 KO mice had a reduction in skeletal muscle AMPK α1 and α2 expression despite up-regulation of the β1 isoform. Heart AMPK α2 expression was also reduced but this did not affect resting AMPK α1 or α2 activities. AMPK α1 and α2 activities were not changed in liver, fat, or hypothalamus. AICAR-stimulated glucose uptake but not fatty acid oxidation was impaired in β2 KO mice. During treadmill running β2 KO mice had reduced maximal and endurance exercise capacity, which was associated with lower muscle and heart AMPK activity and reduced levels of muscle and liver glycogen. Reductions in exercise capacity of β2 KO mice were not due to lower muscle mitochondrial content or defects in contraction-stimulated glucose uptake or fatty acid oxidation. When challenged with a high-fat diet β2 KO mice gained more weight and were more susceptible to the development of hyperinsulinemia and glucose intolerance. In summary these data show that deletion of AMPK β2 reduces AMPK activity in skeletal muscle resulting in impaired exercise capacity and the worsening of diet-induced obesity and glucose intolerance.

Tissue‐specific activation of AMP‐activated protein kinase by heat stress in the lobster, Homarus americanus

We investigated AMP‐activated protein kinase (AMPK) as a cellular signal during temperature stress in invertebrates. AMPK acts as a “fuel gauge” and since high temperatures lead to an increased energy demand, we hypothesized that AMPK is activated by heat stress in Homarus americanus. Lobsters were exposed to an acute temperature increase (6ºC/h). The temperature induced switch to anaerobic metabolism occurred at 30, 28 or 32ºC in heart, liver or muscle, respectively, indicated by significant lactate accumulation. HSP70 levels remained low in all tissues at all temperatures. AMPK activity followed a tissue‐specific pattern: in the heart, a linear increase between 14 and 22ºC, and constant until 32ºC (2.3±0.3 fold), in liver, no change below 26ºC, then a linear increase to 32ºC (1.9±1.1 fold); in muscle, no change between 14 and 32ºC. AMPK mRNA expression also showed a tissue specific pattern: compared to neural tissue AMPK expression at 14ºC was higher in heart (10.2±16.4), liver (1.4±0.8 fold) and muscle (9.3±8.9). These data indicate that in the lobster AMPK is activated by heat stress earlier than HSP70, suggesting that AMPK is a more sensitive indicator of thermal stress. The tissue‐specific differences in AMPK activity and mRNA expression indicate the differential energetic demand of the tissues and the respective role of AMPK during heat stress. Supported by NSF‐0640478 to MF and an APS summer fellowship to SP.