Characterization of the role of AMP-activated protein kinase in the regulation of glucose-activated gene expression using constitutively active and dominant negative forms of the kinase

Metabolomics reveals the protective of Dihydromyricetin on glucose homeostasis by enhancing insulin sensitivity

Dihydromyricetin (DMY), an important flavanone found in Ampelopsis grossedentata, possesses antioxidative properties that ameliorate skeletal muscle insulin sensitivity and exert a hepatoprotective effect. However, little is known about the effects of DMY in the context of high-fat diet (HFD)-induced hepatic insulin resistance. Male Sprague-Dawley(SD) rats were fed a HFD(60% fat) supplemented with DMY for 8 weeks. The administration of DMY to the rats with HFD-induced insulin resistance reduces hyperglycemia, plasma levels of insulin, and steatosis in the liver. Furthermore, DMY treatment modulated 24 metabolic pathways, including glucose metabolism, the TCA cycle. DMY significantly enhanced glucose uptake and improved the translocation of glucose transporter 1. The specificity of DMY promoted the phosphorylation of AMP-activated protein kinase (AMPK). In addition, the exposure of HepG2 cells to high glucose concentrations impaired the insulin-stimulated phosphorylation of Akt2 Ser474 and insulin receptor substrate-1 (IRS-1) Ser612, increased GSK-3β phosphorylation, and upregulated G6Pase and PEPCK expression. Collectively, DMY improved glucose-related metabolism while reducing lipid levels in the HFD-fed rats. These data suggest that DMY might be a useful drug for use in type 2 diabetes insulin resistance therapy and for the treatment of hepatic steatosis.

Protein kinase C phosphorylates AMP-activated protein kinase α1 Ser487

The key metabolic regulator, AMP-activated protein kinase (AMPK), is reported to be down-regulated in metabolic disorders, but the mechanisms are poorly characterised. Recent studies have identified phosphorylation of the AMPKα1/α2 catalytic subunit isoforms at Ser487/491, respectively, as an inhibitory regulation mechanism. Vascular endothelial growth factor (VEGF) stimulates AMPK and protein kinase B (Akt) in cultured human endothelial cells. As Akt has been demonstrated to be an AMPKα1 Ser487 kinase, the effect of VEGF on inhibitory AMPK phosphorylation in cultured primary human endothelial cells was examined. Stimulation of endothelial cells with VEGF rapidly increased AMPKα1 Ser487 phosphorylation in an Akt-independent manner, without altering AMPKα2 Ser491 phosphorylation. In contrast, VEGF-stimulated AMPKα1 Ser487 phosphorylation was sensitive to inhibitors of protein kinase C (PKC) and PKC activation using phorbol esters or overexpression of PKC-stimulated AMPKα1 Ser487 phosphorylation. Purified PKC and Akt both phosphorylated AMPKα1 Ser487 in vitro with similar efficiency. PKC activation was associated with reduced AMPK activity, as inhibition of PKC increased AMPK activity and phorbol esters inhibited AMPK, an effect lost in cells expressing mutant AMPKα1 Ser487Ala. Consistent with a pathophysiological role for this modification, AMPKα1 Ser487 phosphorylation was inversely correlated with insulin sensitivity in human muscle. These data indicate a novel regulatory role of PKC to inhibit AMPKα1 in human cells. As PKC activation is associated with insulin resistance and obesity, PKC may underlie the reduced AMPK activity reported in response to overnutrition in insulin-resistant metabolic and vascular tissues.

Dietary Fructose and GLUT5 Transporter Activity Contribute to Antipsychotic-Induced Weight Gain

Receptors for antipsychotics in the hypothalamus contribute to antipsychotics-induced weight gain; however, many of these receptors are also expressed in the intestine. The role of these intestinally-expressed receptors, and their potential modulation of nutrient absorption, have not been investigated in the context of antipsychotics-induced weight gain. Here we tested the effect of dietary fructose and intestinal fructose uptake on clozapine-induced weight gain in mice. Weight gain was determined in wild type mice and mice lacking the GLUT5 fructose transporter that were "orally-administered" 20mg/kg clozapine for 28 days. To assess the role of dietary fructose, clozapine-treated mice were fed controlled diets with different levels of fructose. Effect of clozapine treatment on intestinal fructose transport activity and expression levels of various receptors that bind clozapine, as well as several genes involved in gluconeogenesis and lipogenesis were measured using real-time RT-PCR and western blotting. Oral administration of clozapine significantly increased body weight in wild type C57BL/6 mice but not in GLUT5 null mice. The clozapine-induced weight gain was proportional to the percentage of fructose in the diet. Clozapine-treated mice increased intestinal fructose uptake without changing the intestinal expression level of GLUT5. Clozapine-treated mice expressed significantly higher levels of intestinal H1 histamine receptor in the wild type but not GLUT5 null mice. Clozapine also increased the intestinal expression of fructokinase and several genes involved in gluconeogenesis and lipogenesis. Our results suggest that increased intestinal absorption and metabolism of fructose contributes to clozapine-induced weight gain. Eliminating dietary fructose might prevent antipsychotics-induced weight gain.

Extracellular pH regulates autophagy via the AMPK-ULK1 pathway in rat cardiomyocytes

Various pathological conditions contribute to pH fluctuations and affect the functions of vital organs such as the heart. In this study, we show that in rat cardiomyocytes, acidic extracellular pH (pHe) inhibits autophagy, whereas alkaline pHe stimulates it. We also find that adenosine monophosphate-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR) and Unc-51-like kinase 1 (ULK1) are very sensitive to pHe changes. Furthermore, by interfering with AMPK, mTOR or ULK1 activity, we demonstrate that the AMPK-ULK1 pathway, but not the mTOR pathway, plays a crucial role on pHe-regulated autophagy and cardiomyocyte viability. These data provide a potential therapeutic strategy against cardiomyocyte injury triggered by pH fluctuations.

The diabetes medication Canagliflozin reduces cancer cell proliferation by inhibiting mitochondrial complex-I supported respiration

Objective

The sodium-glucose transporter 2 (SGLT2) inhibitors Canagliflozin and Dapagliflozin are recently approved medications for type 2 diabetes. Recent studies indicate that SGLT2 inhibitors may inhibit the growth of some cancer cells but the mechanism(s) remain unclear.

Methods

Cellular proliferation and clonogenic survival were used to assess the sensitivity of prostate and lung cancer cell growth to the SGLT2 inhibitors. Oxygen consumption, extracellular acidification rate, cellular ATP, glucose uptake, lipogenesis, and phosphorylation of AMP-activated protein kinase (AMPK), acetyl-CoA carboxylase, and the p70S6 kinase were assessed. Overexpression of a protein that maintains complex-I supported mitochondrial respiration (NDI1) was used to establish the importance of this pathway for mediating the anti-proliferative effects of Canagliflozin.

Results

Clinically achievable concentrations of Canagliflozin, but not Dapagliflozin, inhibit cellular proliferation and clonogenic survival of prostate and lung cancer cells alone and in combination with ionizing radiation and the chemotherapy Docetaxel. Canagliflozin reduced glucose uptake, mitochondrial complex-I supported respiration, ATP, and lipogenesis while increasing the activating phosphorylation of AMPK. The overexpression of NDI1 blocked the anti-proliferative effects of Canagliflozin indicating reductions in mitochondrial respiration are critical for anti-proliferative actions.

Conclusion

These data indicate that like the biguanide metformin, Canagliflozin not only lowers blood glucose but also inhibits complex-I supported respiration and cellular proliferation in prostate and lung cancer cells. These observations support the initiation of studies evaluating the clinical efficacy of Canagliflozin on limiting tumorigenesis in pre-clinical animal models as well epidemiological studies on cancer incidence relative to other glucose lowering therapies in clinical populations.

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Canagliflozin inhibits the proliferation and clonogenic survival of cancer cells.

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Canagliflozin enhances the anti-clonogenic effects of radiation and Docetaxel.

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Canagliflozin reduces glucose uptake and complex-I supported respiration.

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Canagliflozin decreases intracellular ATP and inhibits lipogenesis.

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Bypassing complex-1 supported respiration reversed the effects of Canagliflozin.

Up-regulation of lipolysis genes and increased production of AMP-activated protein kinase protein in the skeletal muscle of rats after resistance training

The purpose of this study was to investigate the expression of lipogenesis- and lipolysis-related genes and proteins in skeletal muscles after 12 weeks of resistance training. Sprague-Dawley rats (n=12) were randomly divided into control (resting) and resistance training groups. A tower-climbing exercise, in which rats climbed to the top of their cage with a weight applied to their tails, used for resistance training. After 12 weeks, rats from the resistance training group had lower body weights (411.66±14.71 g vs. 478.33±24.63 g in the control), there was no significant difference between the two groups in the concentrations of total cholesterol, and high or low density lipoprotein cholesterol. However, the concentration of triglyceride was lower in resistance-trained rats (59.83±14.05 μg/mL vs 93.33±33.89 μg/mL in the control). The mRNA expression levels of the lipogenesis-related genes sterol regulatory element binding protein-1c, acetyl-CoA carboxylase, and fatty acid synthase were not significantly different between the resistance-trained and control rats; however, mRNA expression of the lipolysis-related carnitine palmitoyl transferase 1 and malonyl-CoA decarboxylase increased significantly with resistance training. AMP-activated protein kinase protein levels also significantly increased in resistance training group compared with in the control group. These results suggested that resistance exercise training contributing to reduced weight gain may be in part be due to increase the lipolysis metabolism and energy expenditure in response to resistance training.

Perilipin 5 restores the formation of lipid droplets in activated hepatic stellate cells and inhibits their activation

Hepatic stellate cells (HSC) are major effectors during hepatic fibrogenesis. The activation of HSC is coupled to the loss of lipid droplets (LDs), which are specialized organelles composed of neutral lipids surrounded by perilipins. LDs have emerged as a focal point of interest in understanding the metabolic regulation of intrahepatic lipids during lipid-mediated liver fibrogenesis. Perilipin 5 (Plin5) is a newly identified LD protein in the perilipin family, which plays a key role in regulating aspects of intracellular trafficking, signaling, and cytoskeletal organization in hepatocytes. Recent work in Plin5 knockout mice suggests a role in high fat diet-induced hepatic lipotoxicity. The current report is to evaluate the impact of Plin5 on HSC activation and to elucidate the underlying mechanisms. We now show that high fat diet-induced liver fibrosis is accompanied by an approximate 75% reduction in Plin5 in HSC, and that spontaneous activation of primary HSC produces temporally coincident loss of Plin5 expression and LD depletion. As modulating lipid content in HSC is a suggested strategy for inhibition of HSC activation and treatment of hepatic fibrosis, we asked whether exogenous Plin5 expression in primary HSC would reverse the activation phenotype and promote LD formation. Recombinant lentiviral Plin5 expression in primary mouse HSC restored the formation of LDs, increased lipid content by inducing expression of pro-lipogenic genes and suppressing expression of pro-lipolytic genes, and suppressed HSC activation (~two fold reduction in expression of procollagen and α-smooth muscle actin, two unique biomarkers for activated HSC). In addition, the expression of exogenous Plin5 in HSC attenuated cellular oxidative stress by reducing cellular reactive oxygen species, elevating cellular glutathione, and inducing gene expression of glutamate-cysteine ligase. Taken together, our results indicate that expression of Plin5 plays a critical role in the formation of LDs, the elevation of lipid content in HSC, and the inhibition of the activation of HSC.

Ethanol extracts of chickpeas alter the total lipid content and expression levels of genes related to fatty acid metabolism in mouse 3T3-L1 adipocytes

Desi-type chickpeas, which have long been used as a natural treatment for diabetes, have been reported to lower visceral adiposity, dyslipidemia and insulin resistance induced by a chronic high-fat diet in rats. In this study, in order to examine the effects of chickpeas of this type in an in vitro system, we used the 3T3-L1 mouse cell line, a subclone of Swiss 3T3 cells, which can differentiate into cells with an adipocyte-like phenotype, and we used ethanol extracts of chickpeas (ECP) instead of chickpeas. Treatment of the 3T3-L1 cells with ECP led to a decrease in the lipid content in the cells. The desaturation index, defined as monounsaturated fatty acids (MUFAs)/saturated fatty acids (SFAs), was also decreased by ECP due to an increase in the cellular content of SFAs and a decrease in the content of MUFAs. The decrease in this index may reflect a decreased reaction from SFA to MUFA, which is essential for fat storage. To confirm this hypothesis, we conducted a western blot analysis, which revealed a reduction in the amount of stearoyl-CoA desaturase 1 (SCD1), a key enzyme catalyzing the reaction from SFA to MUFA. We observed simultaneous inactivations of enzymes participating in lipogenesis, i.e., liver kinase B1 (LKB1), acetyl-CoA carboxylase (ACC) and AMPK, by phosphorylation, which may lead to the suppression of reactions from acetyl-CoA to SFA via malonyl-CoA in lipogenesis. We also investigated whether lipolysis is affected by ECP. The amount of carnitine palmitoyltransferase 1 (CPT1), an enzyme important for the oxidation of fatty acids, was increased by ECP treatment. ECP also led to an increase in uncoupling protein 2 (UCP2), reported as a key protein for the oxidation of fatty acids. All of these results obtained regarding lipogenesis and fatty acid metabolism in our in vitro system are consistent with the results previously shown in rats. We also examined the effects on SCD1 and lipid contents of ethanol extracts of Kabuli-type chickpeas, which are used worldwide. The effects were similar, but of much lesser magnitude compared to those of ECP described above. Thus, Desi-type chickpeas may prove to be effective for the treatment of diabetes, as they can alter the lipid content, thus reducing fat storage.

Glucose Metabolism and AMPK Signaling Regulate Dopaminergic Cell Death Induced by Gene (α-Synuclein)-Environment (Paraquat) Interactions

While environmental exposures are not the single cause of Parkinson's disease (PD), their interaction with genetic alterations is thought to contribute to neuronal dopaminergic degeneration. However, the mechanisms involved in dopaminergic cell death induced by gene-environment interactions remain unclear. In this work, we have revealed for the first time the role of central carbon metabolism and metabolic dysfunction in dopaminergic cell death induced by the paraquat (PQ)-α-synuclein interaction. The toxicity of PQ in dopaminergic N27 cells was significantly reduced by glucose deprivation, inhibition of hexokinase with 2-deoxy-D-glucose (2-DG), or equimolar substitution of glucose with galactose, which evidenced the contribution of glucose metabolism to PQ-induced cell death. PQ also stimulated an increase in glucose uptake, and in the levels of glucose transporter type 4 (GLUT4) and Na⁺-glucose transporters isoform 1 (SGLT1) proteins, but only inhibition of GLUT-like transport with STF-31 or ascorbic acid reduced PQ-induced cell death. Importantly, while autophagy protein 5 (ATG5)/unc-51 like autophagy activating kinase 1 (ULK1)-dependent autophagy protected against PQ toxicity, the inhibitory effect of glucose deprivation on cell death progression was largely independent of autophagy or mammalian target of rapamycin (mTOR) signaling. PQ selectively induced metabolomic alterations and adenosine monophosphate-activated protein kinase (AMPK) activation in the midbrain and striatum of mice chronically treated with PQ. Inhibition of AMPK signaling led to metabolic dysfunction and an enhanced sensitivity of dopaminergic cells to PQ. In addition, activation of AMPK by PQ was prevented by inhibition of the inducible nitric oxide syntase (iNOS) with 1400W, but PQ had no effect on iNOS levels. Overexpression of wild type or A53T mutant α-synuclein stimulated glucose accumulation and PQ toxicity, and this toxic synergism was reduced by inhibition of glucose metabolism/transport and the pentose phosphate pathway (6-aminonicotinamide). These results demonstrate that glucose metabolism and AMPK regulate dopaminergic cell death induced by gene (α-synuclein)-environment (PQ) interactions.

AMP-activated kinase (AMPK) regulates activity of HER2 and EGFR in breast cancer

AMP-activated Protein Kinase (AMPK) activity retards growth of many types of cancers. Investigating effects of AMPK activation on breast cancer cell signaling and survival, we found that breast cancer cell lines with amplification and over-expression of HER2 or EGFR are 2- to 5-fold more sensitive to cytotoxic effects of AICAR, a canonical pharmacological activator of AMPK, than breast cancer cell lines lacking HER2 or EGFR overexpression. Paralleling effects on cell survival, AICAR leads to dose- and time-dependent inhibition of HER2 and EGFR in HER2-amplified breast cancer cells, with activation of AMPK and suppression of HER2/EGFR activity preceding commitment to cell death. Transfection of constitutively active AMPKα also leads to decreased HER2 and EGFR phosphorylation, reduced downstream signaling associated with these receptor tyrosine kinases (RTKs), and reduced breast cancer cell growth, confirming effects of AMPK activity on HER2/EGFR. Ensuing co-immunoprecipitation experiments demonstrated an interaction of HER2 with AMPK and an in vitro phosphorylation assay found that HER2 and EGFR contain sequences that are potential substrates for AMPK. Our results lead us to postulate that AMPK regulates HER2 and EGFR activity in HER2-amplified breast cancer cells and thus activation of AMPK might provide therapeutic benefit in such cancers.

Lessons from Nature: Sources and Strategies for Developing AMPK Activators for Cancer Chemotherapeutics

Adenosine Monophosphate-Activated Protein Kinase or AMPK is a highly-conserved master-regulator of numerous cellular processes, including: Maintaining cellular-energy homeostasis, modulation of cytoskeletaldynamics, directing cell growth-rates and influencing cell-death pathways. AMPK has recently emerged as a promising molecular target in cancer therapy. In fact, AMPK deficiencies have been shown to enhance cell growth and proliferation, which is consistent with enhancement of tumorigenesis by AMPK-loss. Conversely, activation of AMPK is associated with tumor growth suppression via inhibition of the Mammalian Target of Rapamycin Complex-1 (mTORC1) or the mTOR signal pathway. The scientific communities' recognition that AMPK-activating compounds possess an anti-neoplastic effect has contributed to a rush of discoveries and developments in AMPK-activating compounds as potential anticancer-drugs. One such example is the class of compounds known as Biguanides, which include Metformin and Phenformin. The current review will showcase natural compounds and their derivatives that activate the AMPK-complex and signaling pathway. In addition, the biology and history of AMPK-signaling and AMPK-activating compounds will be overviewed, their anticancer-roles and mechanisms-of-actions will be discussed, and potential strategies for the development of novel, selective AMPK-activators with enhanced efficacy and reduced toxicity will be proposed.

(-)-Hydroxycitric acid reduced fat deposition via regulating lipid metabolism-related gene expression in broiler chickens

BACKGROUND

Chicken as a delicious food for a long history, and it is well known that excess fat deposition in broiler chickens will not only induced metabolic diseases, but also lead to adverse effect in the consumer's health. (-)-Hydroxycitric acid (HCA), a major active ingredient of Garcinia Cambogia extracts, had shown to suppress fat accumulation in animals and humans. While, the precise physiological mechanism of HCA has not yet been full clarified, especially its action in broiler chickens. Thus, this study aimed to assess the effect of (-)-HCA on lipid metabolism in broiler chickens.

METHODS

A total of 120 1-day-old broiler chickens were randomly allocated to four groups, with each group was repeated three times with 10 birds. Birds received a commercial diet supplemented with (-)-HCA at 0, 1000, 2000 or 3000 mg/kg, respectively, for a period of 4 weeks ad libitum.

RESULTS

Body weight (BW) in the 2000 and 3000 mg/kg (-)-HCA groups was significantly decreased (P < 0.05) than that in control group. A significantly decreased of serum triglyceride (TG) and density lipoprotein-cholesterol (LDL-C) content were observed in 3000 mg/kg (-)-HCA group (P < 0.05). Broiler chickens supplmented with 2000 and 3000 mg/kg (-)-HCA had pronouncedly higher hepatic lipase (HL) activity, hepatic glycogen and non-esterified fatty acid (NEFA) contents in liver (P < 0.05). Serum free triiodothyronine (FT3) and thyroxin (T4) contents were significantly higher in 3000 mg/kg (-)-HCA group (P < 0.05) compared with the control group. Supplemental (-)-HCA markedly decreased fatty acid synthase (FAS) and sterol regulatory element binding protein-1c (SREBP-1c) (P < 0.05) mRNA levels, while the mRNA abundance of adenosine 5'-monophosphate-activated protein kinaseβ2 (AMPKβ2) (P < 0.05) was significantly increased. In addition, ATP-citrate lyase (ACLY) mRNA level (P < 0.05) was significantly decreased in broiler chickens supplemented with 3000 mg/kg (-)-HCA. No differences was observed on carnitine palmitoyl transferase-I(CPT-I), while peroxisome proliferators-activated receptor α (PPARα) mRNA level (P < 0.05) was significantly increased in broiler chickens supplemented with 2000 and 3000 mg/kg (-)-HCA.

CONCLUSIONS

Supplemental (-)-HCA inhibited lipogenesis by inhibiting ACLY, SREBP-1c and FAS expression, and accelerated lipolysis through enhancing HL activity and PPARα expression, which eventually led to the reduced abdominal fat deposition in broiler chickens. Graphical abstract Mechanism of (-)-HCA effect on hepatic lipids metabolism.

Molecular Regulation of Adipogenesis and Potential Anti-Adipogenic Bioactive Molecules

Adipogenesis is the process by which precursor stem cells differentiate into lipid laden adipocytes. Adipogenesis is regulated by a complex and highly orchestrated gene expression program. In mammalian cells, the peroxisome proliferator-activated receptor γ (PPARγ), and the CCAAT/enhancer binding proteins (C/EBPs) such as C/EBPα, β and δ are considered the key early regulators of adipogenesis, while fatty acid binding protein 4 (FABP4), adiponectin, and fatty acid synthase (FAS) are responsible for the formation of mature adipocytes. Excess accumulation of lipids in the adipose tissue leads to obesity, which is associated with cardiovascular diseases, type II diabetes and other pathologies. Thus, investigating adipose tissue development and the underlying molecular mechanisms is vital to develop therapeutic agents capable of curbing the increasing incidence of obesity and related pathologies. In this review, we address the process of adipogenic differentiation, key transcription factors and proteins involved, adipogenic regulators and potential anti-adipogenic bioactive molecules.

AMP-activated Protein Kinase Suppresses Biosynthesis of Glucosylceramide by Reducing Intracellular Sugar Nucleotides

The membrane glycolipid glucosylceramide (GlcCer) plays a critical role in cellular homeostasis. Its intracellular levels are thought to be tightly regulated. How cells regulate GlcCer levels remains to be clarified. AMP-activated protein kinase (AMPK), which is a crucial cellular energy sensor, regulates glucose and lipid metabolism to maintain energy homeostasis. Here, we investigated whether AMPK affects GlcCer metabolism. AMPK activators (5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside and metformin) decreased intracellular GlcCer levels and synthase activity in mouse fibroblasts. AMPK inhibitors or AMPK siRNA reversed these effects, suggesting that GlcCer synthesis is negatively regulated by an AMPK-dependent mechanism. Although AMPK did not affect the phosphorylation or expression of GlcCer synthase, the amount of UDP-glucose, an activated form of glucose required for GlcCer synthesis, decreased under AMPK-activating conditions. Importantly, the UDP-glucose pyrophosphatase Nudt14, which degrades UDP-glucose, generating UMP and glucose 1-phosphate, was phosphorylated and activated by AMPK. On the other hand, suppression of Nudt14 by siRNA had little effect on UDP-glucose levels, indicating that mammalian cells have an alternative UDP-glucose pyrophosphatase that mainly contributes to the reduction of UDP-glucose under AMPK-activating conditions. Because AMPK activators are capable of reducing GlcCer levels in cells from Gaucher disease patients, our findings suggest that reducing GlcCer through AMPK activation may lead to a new strategy for treating diseases caused by abnormal accumulation of GlcCer.

Kazinol C from Broussonetia kazinoki activates AMP-activated protein kinase to induce antitumorigenic effects in HT-29 colon cancer cells

Kazinol C is a 1,3-diphenylpropane, obtained from Broussonetia kazinoki, that has been employed in folk medicine as an edema suppressant. It exerts beneficial effects in oxidative stress-related diseases, such as cancer. However, the molecular mechanism involved in the anticancer effects remains to be determined. AMP-activated protein kinase (AMPK) has emerged as a possible anticancer target molecule. The present study investigated the effect of kazinol C on AMPK activation as well as subsequent HT-29 colon cancer cell viability, apoptosis and migration. Kazinol C markedly induced AMPK phosphorylation and significantly attenuated HT-29 colon cancer cell growth and viability. Compound C, as a well‑known AMPK inhibitor, blocked the kazinol C-induced cell death, and stable transduction of dominant-negative (DN) AMPK in colon cancer cells also inhibited kazinol C-induced cell apoptosis. In addition, kazinol C inhibited HT-29 cell migration and anchorage-independent growth. AMPK inhibition using stable transduction with DN AMPK significantly abrogated the kazinol C-induced inhibition of cancer cell migration. Thus, AMPK is a critical and novel regulator of kazinol C-mediated cancer cell apoptosis and inhibition of migration, suggesting that AMPK is a prime cancer target.

Glucose and palmitate uncouple AMPK from autophagy in human aortic endothelial cells

Dysregulated autophagy and decreased AMP-activated protein kinase (AMPK) activity are each associated with atherogenesis. Atherogenesis is preceded by high circulating concentrations of glucose and fatty acids, yet the mechanism by which these nutrients regulate autophagy in human aortic endothelial cells (HAECs) is not known. Furthermore, whereas AMPK is recognized as an activator of autophagy in cells with few nutrients, its effects on autophagy in nutrient-rich HAECs has not been investigated. We maintained and passaged primary HAECs in media containing 25 mM glucose and incubated them subsequently with 0.4 mM palmitate. These conditions impaired basal autophagy and rendered HAECs more susceptible to apoptosis and adhesion of monocytes, outcomes attenuated by the autophagy activator rapamycin. Glucose and palmitate diminished AMPK activity and phosphorylation of the uncoordinated-51-like kinase 1 (ULK1) at Ser555, an autophagy-activating site targeted by AMPK. 5-Aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR)-mediated activation of AMPK phosphorylated acetyl-CoA carboxylase, but treatment with AICAR or other AMPK activators (A769662, phenformin) did not restore ULK1 phosphorylation or autophagosome formation. To determine whether palmitate-induced ceramide accumulation contributed to this finding, we overexpressed a ceramide-metabolizing enzyme, acid ceramidase. The increase in acid ceramidase expression ameliorated the effects of excess nutrients on ULK1 phosphorylation, without altering the effects of the AMPK activators. Thus, unlike low nutrient conditions, AMPK becomes uncoupled from autophagy in HAECs in a nutrient-rich environment, such as that found in patients with increased cardiovascular risk. These findings suggest that combinations of AMPK-independent and AMPK-dependent therapies may be more effective alternatives than either therapy alone for treating nutrient-induced cellular dysfunction.

Nonalcoholic Fatty liver disease: pathogenesis and therapeutics from a mitochondria-centric perspective

Nonalcoholic fatty liver disease (NAFLD) describes a spectrum of disorders characterized by the accumulation of triglycerides within the liver. The global prevalence of NAFLD has been increasing as the obesity epidemic shows no sign of relenting. Mitochondria play a central role in hepatic lipid metabolism and also are affected by upstream signaling pathways involved in hepatic metabolism. This review will focus on the role of mitochondria in the pathophysiology of NAFLD and touch on some of the therapeutic approaches targeting mitochondria as well as metabolically important signaling pathways. Mitochondria are able to adapt to lipid accumulation in hepatocytes by increasing rates of beta-oxidation; however increased substrate delivery to the mitochondrial electron transport chain (ETC) leads to increased reactive oxygen species (ROS) production and eventually ETC dysfunction. Decreased ETC function combined with increased rates of fatty acid beta-oxidation leads to the accumulation of incomplete products of beta-oxidation, which combined with increased levels of ROS contribute to insulin resistance. Several related signaling pathways, nuclear receptors, and transcription factors also regulate hepatic lipid metabolism, many of which are redox sensitive and regulated by ROS.

Involvement of store-operated Ca(2+) entry in activation of AMP-activated protein kinase and stimulation of glucose uptake by M3 muscarinic acetylcholine receptors in human neuroblastoma cells

Gq/11-coupled muscarinic acetylcholine receptors (mAChRs) belonging to M1, M3 and M5 subtypes have been shown to activate the metabolic sensor AMP-activated protein kinase (AMPK) through Ca(2+)/calmodulin-dependent protein kinase kinase-β (CaMKKβ)-mediated phosphorylation at Thr172. However, the source of Ca(2+) required for this response has not been yet elucidated. Here, we investigated the involvement of store-operated Ca(2+) entry (SOCE) in AMPK activation by pharmacologically defined M3 mAChRs in human SH-SY5Y neuroblastoma cells. In Ca(2+)-free medium the cholinergic agonist carbachol (CCh) caused a transient increase of phospho-Thr172 AMPK that rapidly ceased within 2min. Conversely, in the presence of extracellular Ca(2+) CCh-induced AMPK phosphorylation lasted for at least 180min. The SOCE modulator 2-aminoethoxydiphephenyl borate (2-APB), at a concentration (50μM) that suppressed CCh-induced intracellular Ca(2+) ([Ca(2+)]i) plateau, inhibited CCh-induced AMPK phosphorylation. CCh triggered the activation of the endoplasmic reticulum Ca(2+) sensor stromal interaction molecule (STIM) 1, as indicated by redistribution of STIM1 immunofluorescence into puncta, and promoted the association of STIM1 with the SOCE channel component Orai1. Cell depletion of STIM1 by siRNA treatment reduced both CCh-induced [Ca(2+)]i plateau and AMPK activation. M3 mAChRs increased glucose uptake and this response required extracellular Ca(2+) and was inhibited by 2-APB, STIM1 knockdown, CaMKKβ and AMPK inhibitors, and adenovirus infection with dominant negative AMPK. Thus, the study provides evidence that SOCE is required for sustained activation of AMPK and stimulation of downstream glucose uptake by M3 mAChRs and suggests that SOCE is a critical process connecting M3 mAChRs to the control of neuronal energy metabolism.

NDRG2 overexpression enhances glucose deprivation-mediated apoptosis in breast cancer cells via inhibition of the LKB1-AMPK pathway

The newly identified tumor suppressor, N-myc downstream-regulated gene 2 (NDRG2), has been studied in various cancers because of its anticancer and antimetastasis effects. In this study, we examined the effect of NDRG2 expression on cell viability in MDA-MB-231 human breast cancer cells under conditions that are similar to the microenvironment of solid tumors, which include glucose deprivation. NDRG2 overexpression enhanced the pro-apoptotic effects of glucose deprivation. Glucose deprivation also induced the activation of AMP-activated protein kinase (AMPK), which plays a role in protecting tumor cells from metabolic stresses. NDRG2 overexpression strongly reduced glucose deprivation-induced AMPK phosphorylation and increased the cleavage of poly (ADP-ribose) polymerase (PARP), which indicated the induction of apoptosis. The expression of a constitutively active form of AMPK effectively blocked glucose deprivation-induced apoptosis in NDRG2-overexpressing MDA-MB-231 cells. Moreover, NDRG2 overexpression also enhanced the pro-apoptotic effects of 2-deoxyglucose (2-DG) or hypoxia, an inducer of metabolic stresses. Finally, we showed that LKB1 is an upstream kinase of AMPK that is involved in the inhibition of glucose deprivation-induced AMPK activity in NDRG2-overexpressing cells. Our findings collectively suggest that NDRG2 is a negative regulator of AMPK activity and functions as a sensitizer of glucose deprivation.

Luteolin alleviates alcoholic liver disease induced by chronic and binge ethanol feeding in mice

Ethanol consumption can lead to hepatic steatosis that contributes to late-stage liver diseases such as cirrhosis and hepatocellular carcinoma. In this study, we investigated the potential protective effect of a flavonoid, luteolin, on ethanol-induced fatty liver development and liver injury. Six-wk-old male C57BL/6 mice were divided into 3 groups: a control group; a group exposed to alcohol by using a chronic and binge ethanol feeding protocol (EtOH); and a group that was administered daily 50 mg/kg of luteolin in addition to ethanol exposure (EtOH + Lut). A chronic and binge ethanol feeding protocol was used, including chronic ethanol consumption (1%, 2%, and 4% for 3 d, and 5% for 9 d) and a binge (30% ethanol) on the last day. Compared with the control group, the EtOH group had a significant elevation in serum concentrations of alanine aminotransferase (ALT) (561%), triglyceride (TG) (47%), and LDL cholesterol (95%), together with lipid accumulation in the liver. Compared with the EtOH group, the EtOH + Lut group had significant reductions in serum concentrations of ALT (43%), TG (22%), LDL cholesterol (52%), and lipid accumulation in the liver. Ethanol elevated liver expression of lipogenic genes including sterol regulatory element-binding protein 1c (Srebp1c) (560%), fatty acid synthase (Fasn) (190%), acetyl-CoA carboxylase (Acc) (48%), and stearoyl-CoA desaturase 1 (Scd1) (286%). Luteolin reduced ethanol-induced expression of these genes in the liver: Srebp1c (79%), Fasn (80%), Acc (60%), and Scd1 (89%). In cultured hepatocytes, luteolin prevented alcohol-induced lipid accumulation and increase in the expression of lipogenic genes. The transcriptional activity of the master regulator of lipid synthesis, sterol regulatory element-binding protein (SREBP), was enhanced by ethanol treatment (160%) and reduced by luteolin administration (67%). In addition, ethanol-induced reduction of AMP-activated protein kinase and SREBP-1c phosphorylation was abrogated by luteolin. Collectively, our study indicates that luteolin is effective in ameliorating ethanol-induced hepatic steatosis and injury.

Expression levels of the hypothalamic AMPK gene determines the responsiveness of the rats to electroacupuncture-induced analgesia

BACKGROUND

Although electroacupuncture (EA) relieves various types of pain, individual differences in the sensitivity to EA analgesia have been reported, causing experimental and clinical difficulties. Our functional genomic study using cDNA microarray identified that 5'-AMP-activated protein kinase (AMPK), a well-known factor in the regulation of energy homeostasis, is the most highly expressed gene in the hypothalamus of the rats that were sensitive to EA analgesia ("responder"), as compared to the rats that were insensitive to EA analgesia ("non-responder"). In this study, we investigated the causal relationship between the hypothalamic AMPK and the individual variation in EA analgesia.

METHODS

Sprague-Dawley (SD) rats were divided into the responder and the non-responder groups, based on EA-induced analgesic effects in the tail flick latency (TFL) test, which measures the latency of the tail flick response elicited by radiant heat applied to the tail. Real-time reverse transcription-polymerase chain reaction (RT-PCR) was performed to quantify the expression levels of AMPK mRNA in the hypothalamus of the responder and non-responder rats. Further, we examined whether viral manipulation of the AMPK expression in the hypothalamus modulates EA analgesia in rats.

RESULTS

The real-time RT-PCR analysis showed that mRNA expression levels of AMPK in the hypothalamus of the responder rats are significantly higher than those of the non-responder rats, validating the previous microarray results. Microinjection of dominant negative (DN) AMPK adenovirus, which inhibits AMPK activity, into the rat hypothalamus significantly attenuates EA analgesia (p < 0.05), whereas wild type (WT) AMPK virus did not affect EA analgesia (p > 0.05).

CONCLUSIONS

The present results demonstrated that levels of AMPK gene expression in the rat hypothalamus determine the individual differences in the sensitivity to EA analgesia. Thus, our findings provide a clinically useful evidence for the application of acupuncture or EA for analgesia.

Folliculin (Flcn) inactivation leads to murine cardiac hypertrophy through mTORC1 deregulation

Cardiac hypertrophy, an adaptive process that responds to increased wall stress, is characterized by the enlargement of cardiomyocytes and structural remodeling. It is stimulated by various growth signals, of which the mTORC1 pathway is a well-recognized source. Here, we show that loss of Flcn, a novel AMPK-mTOR interacting molecule, causes severe cardiac hypertrophy with deregulated energy homeostasis leading to dilated cardiomyopathy in mice. We found that mTORC1 activity was upregulated in Flcn-deficient hearts, and that rapamycin treatment significantly reduced heart mass and ameliorated cardiac dysfunction. Phospho-AMP-activated protein kinase (AMPK)-alpha (T172) was reduced in Flcn-deficient hearts and nonresponsive to various stimulations including metformin and AICAR (5-amino-1-β-D-ribofuranosyl-imidazole-4-carboxamide). ATP levels were elevated and mitochondrial function was increased in Flcn-deficient hearts, suggesting that excess energy resulting from up-regulated mitochondrial metabolism under Flcn deficiency might attenuate AMPK activation. Expression of Ppargc1a, a central molecule for mitochondrial metabolism, was increased in Flcn-deficient hearts and indeed, inactivation of Ppargc1a in Flcn-deficient hearts significantly reduced heart mass and prolonged survival. Ppargc1a inactivation restored phospho-AMPK-alpha levels and suppressed mTORC1 activity in Flcn-deficient hearts, suggesting that up-regulated Ppargc1a confers increased mitochondrial metabolism and excess energy, leading to inactivation of AMPK and activation of mTORC1. Rapamycin treatment did not affect the heart size of Flcn/Ppargc1a doubly inactivated hearts, further supporting the idea that Ppargc1a is the critical element leading to deregulation of the AMPK-mTOR-axis and resulting in cardiac hypertrophy under Flcn deficiency. These data support an important role for Flcn in cardiac homeostasis in the murine model.

Adiponectin signaling in the liver

High glucose production contributes to fed and fasted hyperglycemia in Type 1 Diabetes (T1D) and Type 2 Diabetes (T2D). The breakdown of the adiponectin signaling pathway in T1D and the reduction of circulating adiponectin in T2D contribute to this abnormal increase in glucose production. Sufficient amounts of insulin could compensate for the loss of adiponectin signaling in T1D and T2D and reduce hyperglycemia. However, the combination of low adiponectin signaling and high insulin resembles an insulin resistance state associated with cardiovascular disease, fatty liver disease and decreased life expectancy. The future development of "adiponectin sensitizers", medications that correct the deficiency in adiponectin signaling, could restore the metabolic balance in T1D and T2D and reduce the need for insulin. This article reviews the adiponectin signaling pathway in the liver through T-cadherin, AdipoR1, AdipoR2, AMPK, ceramidase activity, APPL1 and the recently discovered Suppressor Of Glucose from Autophagy (SOGA).

Cardiotrophin-1 eliminates hepatic steatosis in obese mice by mechanisms involving AMPK activation

BACKGROUND & AIMS

Cardiotrophin-1 (CT-1) is a hepatoprotective cytokine that modulates fat and glucose metabolism in muscle and adipose tissue. Here we analyzed the changes in hepatic fat stores induced by recombinant CT-1 (rCT-1) and its therapeutic potential in non-alcoholic fatty liver disease (NAFLD).

METHODS

rCT-1 was administered to two murine NAFLD models: ob/ob and high fat diet-fed mice. Livers were analyzed for lipid composition and expression of genes involved in fat metabolism. We studied the effects of rCT-1 on lipogenesis and fatty acid (FA) oxidation in liver cells and the ability of dominant negative inhibitor of AMP-activated protein kinase (AMPK) to block these effects.

RESULTS

CT-1 was found to be upregulated in human and murine steatotic livers. In two NAFLD mouse models, treatment with rCT-1 for 10days induced a marked decrease in liver triglyceride content with augmented proportion of poly-unsaturated FA and reduction of monounsaturated species. These changes were accompanied by attenuation of inflammation and improved insulin signaling. Chronic administration of rCT-1 caused downregulation of lipogenic genes and genes involved in FA import to hepatocytes together with amelioration of ER stress, elevation of NAD(+)/NADH ratio, phosphorylation of LKB1 and AMPK, increased expression and activity of sirtuin1 (SIRT1) and upregulation of genes mediating FA oxidation. rCT-1 potently inhibited de novo lipogenesis and stimulated FA oxidation in liver cells both in vitro and in vivo. In vitro studies showed that these effects are mediated by activated AMPK.

CONCLUSIONS

rCT-1 resolves hepatic steatosis in obese mice by mechanisms involving AMPK activation. rCT-1 deserves consideration as a potential therapy for NAFLD.

Enzogenol improves diabetes-related metabolic change in C57BL/KsJ-db/db mice, a model of type 2 diabetes mellitus

Objectives

Dietary use of pine bark extract has been associated with reduced risk of inflammation and diabetes. In this study, we investigated the antidiabetic effects of enzogenol, proanthocyanidins-rich bioflavonoid extract derived from the pine bark of New Zealand Pinus radiata trees, using C57BL/KsJ-db/db mice.

Methods

After 1-week acclimation period, the db/db mice were divided into vehicle-treated, Enzogenol-treated (12.5, 25 and 50 mg/kg; EZ) and positive control (tea polyphenol 50 mg/kg; TPP) groups.

Key findings

The administration of EZ improved the glucose tolerance and lowered the glycosylated haemoglobin (HbA1C), insulin and glucagon levels in blood. Interestingly, EZ and TPP treatments resulted in reduced hepatic free fatty acid, cholesterol and triglyceride levels in db/db mice. EZ and TPP treatments significantly elevated hepatic AMPK activity, and the expression of proteins related to glucose homeostasis and lipid metabolism, such as glucokinase, peroxisome proliferator-activated receptor (PPAR)α and long-chain acyl-CoA dehydrogenase protein level with a simultaneous reduction of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase protein expression. In addition, the EZ administration groups had an increased hepatic glycogen synthase expression in db/db mice.

Conclusions

These results suggest that EZ may be beneficial in improving insulin resistance and hyperglycaemia in type 2 diabetic mice by enhancing the glucose and lipids metabolism.

The Chinese herbal medicine FTZ attenuates insulin resistance via IRS1 and PI3K in vitro and in rats with metabolic syndrome

BACKGROUND

Insulin resistance plays an important role in the development of metabolic syndrome (MS). Fu Fang Zhen Zhu Tiao Zhi formula (FTZ), a Chinese medicinal decoction, has been used to relieve hyperlipidemia, atherosclerosis and other symptoms associated with metabolic disorders in the clinic.

METHODS

To evaluate the effect of FTZ on insulin resistance, HepG2 cells were induced with high insulin as a model of insulin resistance and treated with FTZ at one of three dosages. Next, the levels of glucose content, insulin receptor substrate1 (IRS1) protein expression and phosphatidylinositol 3-kinase (PI3K) subunit p85 mRNA expression were measured. Alternatively, MS was induced in rats via gavage feeding of a high-fat diet for four consecutive weeks followed by administration of FTZ for eight consecutive weeks. Body weight and the plasma levels of lipids, insulin and glucose were evaluated. Finally, the expression of PI3K p85 mRNA in adipose tissue of rats was measured.

RESULTS

Our results revealed that FTZ attenuated glucose content and up-regulated the expression of PI3K p85 mRNA and IRS1 protein in insulin-resistant HepG2 cells in vitro. Moreover, FTZ reduced body weight and the plasma concentrations of triacylglycerol, cholesterol, fasting glucose and insulin in insulin resistant MS rats. FTZ also elevated the expression of PI3K p85 mRNA in the adipose tissues of MS rats.

CONCLUSION

FTZ attenuated MS symptoms by decreasing the plasma levels of glucose and lipids. The underlying mechanism was attenuation of the reduced expression of PI3K p85 mRNA and IRS1 protein in both insulin-resistant HepG2 cells and MS rats.

Adiponectin and leptin molecular actions and clinical significance in breast cancer

Obesity is an important public health problem and major risk factor for postmenopausal breast cancer. Adipose tissue is the major component involved in the control of the metabolism through energy homeostasis, adipocyte differentiation, insulin sensitivity and the activation of anti-inflammatory metabolic and immune pathways. Leptin and Adiponectin pathways are involved in proliferation process in breast cancer. Current review describes potential relationship between the molecular actions and clinical significance of leptin and adiponectin in breast cancer.

(ADP-ribose) polymerase 1 and AMP-activated protein kinase mediate progressive dopaminergic neuronal degeneration in a mouse model of Parkinson's disease

Genetic and epidemiologic evidence suggests that cellular energy homeostasis is critically associated with Parkinson's disease (PD) pathogenesis. Here we demonstrated that genetic deletion of Poly (ADP-ribose) polymerase 1 completely blocked 6-hydroxydopamine-induced dopaminergic neurodegeneration and related PD-like symptoms. Hyperactivation of PARP-1 depleted ATP pools in dopaminergic (DA) neurons, thereby activating AMP-activated protein kinase (AMPK). Further, blockade of AMPK activation by viral infection with dominant-negative AMPK strongly inhibited DA neuronal atrophy with moderate suppression of nuclear translocation of apoptosis-inhibiting factor (AIF), whereas overactivation of AMPK conversely strengthened the 6-OHDA-induced DA neuronal degeneration. Collectively, these results suggest that manipulation of PARP-1 and AMPK signaling is an effective therapeutic approach to prevent PD-related DA neurodegeneration.

Novel small-molecule AMPK activator orally exerts beneficial effects on diabetic db/db mice

AMP-activated protein kinase (AMPK), which is a pivotal guardian of whole-body energy metabolism, has become an attractive therapeutic target for metabolic syndrome. Previously, using a homogeneous scintillation proximity assay, we identified the small-molecule AMPK activator C24 from an optimization based on the original allosteric activator PT1. In this paper, the AMPK activation mechanism of C24 and its potential beneficial effects on glucose and lipid metabolism on db/db mice were investigated. C24 allosterically stimulated inactive AMPK α subunit truncations and activated AMPK heterotrimers by antagonizing autoinhibition. In primary hepatocytes, C24 increased the phosphorylation of AMPK downstream target acetyl-CoA carboxylase dose-dependently without changing intracellular AMP/ATP ratio, indicating its allosteric activation in cells. Through activating AMPK, C24 decreased glucose output by down-regulating mRNA levels of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) in primary hepatocytes. C24 also decreased the triglyceride and cholesterol contents in HepG2 cells. Due to its improved bioavailability, chronic oral treatment with multiple doses of C24 significantly reduced blood glucose and lipid levels in plasma, and improved the glucose tolerance of diabetic db/db mice. The hepatic transcriptional levels of PEPCK and G6Pase were reduced. These results demonstrate that this orally effective activator of AMPK represents a novel approach to the treatment of metabolic syndrome.

In vivo activating transcription factor 3 silencing ameliorates the AMPK compensatory effects for ER stress-mediated β-cell dysfunction during the progression of type-2 diabetes

In obese Zucker diabetic fatty (ZDF) rats, ER stress is associated with insulin resistance and pancreatic β-cell dysfunction; however the exact mechanisms by which ER stress drives type-2 diabetes remain uncertain. Here, we investigated the role of ATF3 on the preventive regulation of AMPK against ER stress-mediated β-cell dysfunction during the end-stage progression of hyperglycemia in ZDF rats. The impaired glucose metabolism and β-cell dysfunction were significantly increased in late-diabetic phase 19-week-old ZDF rats. Although AMPK phosphorylation reduced in 6- and 12-week-old ZDF rats was remarkably increased at 19weeks, the increases of lipogenice genes, ATF3, and ER stress or ROS-mediated β-cell dysfunction were still remained, which were attenuated by in vivo-injection of chemical chaperon tauroursodeoxycholate (TUDCA), chronic AICAR, or antioxidants. ATF3 did not directly affect AMPK phosphorylation, but counteracts the preventive effects of AMPK for high glucose-induced β-cell dysfunction. Moreover, knockdown of ATF3 by delivery of in vivo-jetPEI ATF3 siRNA attenuated ER stress-mediated β-cell dysfunction and enhanced the beneficial effect of AICAR. Our data suggest that ATF3 may play as a counteracting regulator of AMPK and thus promote β-cell dysfunction and the development of type-2 diabetes and could be a potential therapeutic target in treating type-2 diabetes.

Neuroprotective Effects of AMP-Activated Protein Kinase on Scopolamine Induced Memory Impairment

AMP-activated protein kinase (AMPK), an important regulator of energy metabolism, is activated in response to cellular stress when intracellular levels of AMP increase. We investigated the neuroprotective effects of AMPK against scopolamine-induced memory impairment in vivo and glutamate-induced cytotoxicity in vitro. An adenovirus expressing AMPK wild type alpha subunit (WT) or a dominant negative form (DN) was injected into the hippocampus of rats using a stereotaxic apparatus. The AMPK WT-injected rats showed significant reversal of the scopolamine induced cognitive deficit as evaluated by escape latency in the Morris water maze. In addition, they showed enhanced acetylcholinesterase (AChE)-reactive neurons in the hippocampus, implying increased cholinergic activity in response to AMPK. We also studied the cellular mechanism by which AMPK protects against glutamate-induced cell death in primary cultured rat hippocampal neurons. We further demonstrated that AMPK WT-infected cells increased cell viability and reduced Annexin V positive hippocampal neurons. Western blot analysis indicated that AMPK WT-infected cells reduced the expression of Bax and had no effects on Bcl-2, which resulted in a decreased Bax/Bcl-2 ratio. These data suggest that AMPK is a useful cognitive impairment treatment target, and that its beneficial effects are mediated via the protective capacity of hippocampal neurons.

Metformin blocks melanoma invasion and metastasis development in AMPK/p53-dependent manner

Metformin was reported to inhibit the proliferation of many cancer cells, including melanoma cells. In this report, we investigated the effect of metformin on melanoma invasion and metastasis development. Using different in vitro approaches, we found that metformin inhibits cell invasion without affecting cell migration and independently of antiproliferation action. This inhibition is correlated with modulation of expression of proteins involved in epithelial-mesenchymal transition such as Slug, Snail, SPARC, fibronectin, and N-cadherin and with inhibition of MMP-2 and MMP-9 activation. Furthermore, our data indicate that this process is dependent on activation of AMPK and tumor suppressor protein p53. Finally, we showed that metformin inhibits melanoma metastasis development in mice using extravasation and metastasis models. The presented data reinforce the fact that metformin might be a good candidate for clinical trial in melanoma treatment.

Advances in the development of AMPK-activating compounds

BACKGROUND

AMP-activated protein kinase (AMPK) is an energy sensing enzyme that controls glucose and lipid metabolism.

OBJECTIVE

This review summarizes the present data on AMPK as a pharmacologic target for the treatment of metabolic disorders.

METHODS

The mechanisms governing AMPK activity and how this enzyme controls different metabolic pathways are reviewed briefly, and details about the effect that AMPK activators have on glucose metabolism are provided.

CONCLUSION

Evidence obtained using the AMPK-activating compound 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) suggests that AMPK promotes glucose transport into skeletal muscles and that this enzyme inhibits hepatic glucose production. AICAR also induces fatty acid oxidation in muscle and inhibits cholesterol synthesis in the liver. The metabolic effects of AICAR on glucose and lipid metabolism indicate that AMPK may be a good pharmacologic target for the treatment of type 2 diabetes and hypercholesterolemia. Novel AMPK-specific compounds are allowing researchers to examine whether this enzyme is a useful pharmacologic target for the treatment of human disease and whether chronic activation of AMPK will be safe.

AMPK phosphorylates GBF1 for mitotic Golgi disassembly

In mammalian cells, the Golgi apparatus undergoes extensive fragmentation during mitosis; this is required not only for the partitioning of the complex but also for the process of mitosis. However, the molecular mechanism underlying the mitotic fragmentation of the Golgi is far from clear. Here, we show that AMP-activated protein kinase (AMPK) is phosphorylated and activated when cells enter mitosis. Activated AMPK phosphorylates GBF1, a guanine nucleotide exchange factor (GEF) for Arf-GTPases, disassociating GBF1 from the Golgi membrane and abolishing the action of GBF1 as an Arf1-GEF. We further demonstrate that the phosphorylation of AMPK and GBF1 is essential for Golgi disassembly and subsequent mitosis entry. These data suggest that AMPK-GBF1-Arf1 signaling is involved in the regulation of Golgi fragmentation during mitosis.

What is the role of adiponectin in obesity related non-alcoholic fatty liver disease?

Non-alcoholic fatty liver disease (NAFLD) is recognized as the most common type of chronic liver disease in Western countries. Insulin resistance is a key factor in the pathogenesis of NAFLD, the latter being considered as the hepatic component of insulin resistance or obesity. Adiponectin is the most abundant adipose-specific adipokine. There is evidence that adiponectin decreases hepatic and systematic insulin resistance, and attenuates liver inflammation and fibrosis. Adiponectin generally predicts steatosis grade and the severity of NAFLD; however, to what extent this is a direct effect or related to the presence of more severe insulin resistance or obesity remains to be addressed. Although there is no proven pharmacotherapy for the treatment of NAFLD, recent therapeutic strategies have focused on the indirect upregulation of adiponectin through the administration of various therapeutic agents and/or lifestyle modifications. In this adiponectin-focused review, the pathogenetic role and the potential therapeutic benefits of adiponectin in NAFLD are analyzed systematically.

Adiponectin receptors in energy homeostasis and obesity pathogenesis

Adipokines, that is factors secreted by adipose tissue, act through a network of autocrine, paracrine, and endocrine pathways to regulate several aspects of physiology, including glucose and lipid metabolism, neuroendocrine function, reproduction, and cardiovascular function. In particular, adiponectin, a 30-kDa protein, is associated with the regulation of insulin sensitivity, and its levels in serum are affected by altered metabolic homeostasis. Adiponectin effects are mediated by adiponectin receptors, which occur as two isoforms (AdipoR1 and AdipoR2). Transcriptional regulation of adiponectin is by the peroxisome proliferator-activated receptor-gamma (PPAR-γ). However, acting through AdipoR1 and AdipoR2, adiponectin enhances 5' adenosine monophosphate-activated protein kinase (AMPK) and the PPARα-mediated pathways in the liver and skeletal muscles. Adiponectin receptors mediate a wide spectrum of metabolic reactions, including gluconeogenesis and fatty-acid oxidation. Altogether, adiponectin deficiency and/or decreased adiponectin receptor-mediated activity possibly contribute to insulin resistance in metabolic syndromes, coronary heart disease, and liver disease.

Adenosine monophosphate-activated protein kinase overactivation leads to accumulation of α-synuclein oligomers and decrease of neurites

Neuronal inclusions of α-synuclein (α-syn), termed Lewy bodies, are a hallmark of Parkinson disease (PD). Increased α-syn levels can occur in brains of aging human and neurotoxin-treated mice. Because previous studies have shown increased brain lactate levels in aging brains, in PD affected subjects when compared with age-matched controls, and in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP), we tested the effects of lactate exposure on α-syn in a cell-based study. We demonstrated that (1) lactate treatment led to α-syn accumulation and oligomerization in a time- and concentration-dependent manner; (2) such alterations were mediated via adenosine monophosphate-activated protein kinase (AMPK) and associated with increasing cytoplasmic phosphorylated AMPK levels; (3) AMPK activation facilitated α-syn accumulation and phosphorylation; (4) lactate treatment or overexpression of the active form of AMPK decreased α-syn turnover and neurite outgrowth; and (5) Lewy body-bearing neurons displayed abnormal cytoplasmic distribution of phosphorylated AMPK, which normally is located in nuclei. Together, our results suggest that chronic neuronal accumulation of α-syn induced by lactate-triggered AMPK activation in aging brains might be a novel mechanism underlying α-synucleinopathies in PD and related disorders.

Negative regulation of AMP-activated protein kinase (AMPK) activity by macrophage migration inhibitory factor (MIF) family members in non-small cell lung carcinomas

AMP-activated protein kinase (AMPK) is a nutrient- and metabolic stress-sensing enzyme activated by the tumor suppressor kinase, LKB1. Because macrophage migration inhibitory factor (MIF) and its functional homolog, d-dopachrome tautomerase (d-DT), have protumorigenic functions in non-small cell lung carcinomas (NSCLCs) but have AMPK-activating properties in nonmalignant cell types, we set out to investigate this apparent paradox. Our data now suggest that, in contrast to MIF and d-DTs AMPK-activating properties in nontransformed cells, MIF and d-DT act cooperatively to inhibit steady-state phosphorylation and activation of AMPK in LKB1 wild type and LKB1 mutant human NSCLC cell lines. Our data further indicate that MIF and d-DT, acting through their shared cell surface receptor, CD74, antagonize NSCLC AMPK activation by maintaining glucose uptake, ATP production, and redox balance, resulting in reduced Ca(2+)/calmodulin-dependent kinase kinase β-dependent AMPK activation. Combined, these studies indicate that MIF and d-DT cooperate to inhibit AMPK activation in an LKB1-independent manner.

The hypotriglyceridemic effect of biotin supplementation involves increased levels of cGMP and AMPK activation

In addition to its role as a carboxylase cofactor, biotin modifies gene expression and has manifold effects on systemic processes. Several studies have shown that biotin supplementation reduces hypertriglyceridemia. We have previously reported that this effect is related to decreased expression of lipogenic genes. In the present work, we analyzed signaling pathways and posttranscriptional mechanisms involved in the hypotriglyceridemic effects of biotin. Male BALB/cAnN Hsd mice were fed a control or a biotin-supplemented diet (1.76 or 97.7 mg of free biotin/kg diet, respectively for 8 weeks after weaning. The abundance of mature sterol regulatory element-binding protein (SREBP-1c), fatty-acid synthase (FAS), total acetyl-CoA carboxylase-1 (ACC-1) and its phosphorylated form, and AMP-activated protein kinase (AMPK) were evaluated in the liver. We also determined the serum triglyceride concentrations and the hepatic levels of triglycerides and cyclic GMP (cGMP). Compared to the control group, biotin-supplemented mice had lower serum and hepatic triglyceride concentrations. Biotin supplementation increased the levels of cGMP and the phosphorylated forms of AMPK and ACC-1 and decreased the abundance of the mature form of SREBP-1c and FAS. These data provide evidence that the mechanisms by which biotin supplementation reduces lipogenesis involve increased cGMP content and AMPK activation. In turn, these changes lead to augmented ACC-1 phosphorylation and decreased expression of both the mature form of SREBP-1c and FAS. Our results demonstrate for the first time that AMPK is involved in the effects of biotin supplementation and offer new insights into the mechanisms of biotin-mediated hypotriglyceridemic effects.

Berberine inhibits human colon cancer cell migration via AMP-activated protein kinase-mediated downregulation of integrin β1 signaling

Colon cancer is associated with a poor prognosis, motivating strategies to prevent its development. An encouraging preventative strategy is the use of nutraceuticals; however, scientific verification of therapeutic functions and mechanisms of biological activity are necessary for the acceptance of dietary supplements in cancer treatment. Berberine is a benzylisoquinoline alkaloid extracted from many kinds of medicinal plants that has been extensively used as a Chinese traditional medicine. Recently, berberine has been reported to possess antitumoral activities. Among the various cellular targets of berberine is AMP-activated protein kinase (AMPK), which regulates tumor progression and metastasis. However, the specific role of berberine-induced AMPK activation and its effects on the metastatic potential of colon cancer remain largely unknown. The present study investigated berberine-induced activation of AMPK and its effects on colon cancer cell migration. Berberine decreased the migration of SW480 and HCT116 cells. We found that berberine activated AMPK in human colon cancer cell lines. Notably, berberine-induced activation of AMPK reduced the integrin β1 protein levels and decreased the phosphorylation of integrin β1 signaling targets. Knockdown of AMPKα1 subunits using small interfering RNA significantly attenuated berberine-induced downregulation of integrin β1 and inhibition of tumor cell migration. Collectively, our results suggest that berberine-induced AMPK activation inhibits the metastatic potential of colon cancer cells by decreasing integrin β1 protein levels and downstream signaling.