Activation of 5'-AMP-activated kinase is mediated through c-Src and phosphoinositide 3-kinase activity during hypoxia-reoxygenation of bovine aortic endothelial cells. Role of peroxynitrite

Isoliquiritigenin attenuates pathological cardiac hypertrophy via regulating AMPKα in vivo and in vitro

Isoliquiritigenin (ISL) is a type of flavonoid, derived from the root of the legume plant Glycyrrhiza, that has multiple pharmacological properties. However, its role in cardiac remodeling induced by pressure overload has yet to be fully elucidated. Aortic banding (AB) surgery was used to establish a cardiac hypertrophy model in male C57BL/6 mice. Mice were randomly divided into four groups (n = 20 per group) as follows: Sham + vehicle, sham + ISL, AB + vehicle and AB + ISL. ISL was administered to the mice intragastrically for 1 week after the operation. To evaluate the role of ISL in mice challenged with AB, echocardiography, histological analysis and molecular biochemistry examinations were performed. ISL treatment decreased cardiac hypertrophy and improved cardiac dysfunction induced by pressure overload. In addition, ISL decreased the cross-sectional area of cardiomyocytes. Furthermore, ISL reversed the AB-mediated increase in phosphorylated (p-)mTOR and p-ERK protein levels and further increased the protein expression of p-AMP-activated protein kinase (AMPK)α in response to AB, whereas knockout of AMPKα abolished the protective effects of ISL. The present study suggested that ISL could suppress pressure overload-induced cardiac hypertrophy through the activation of AMPKα. Therefore, ISL may serve as a therapeutic target for cardiac remodeling.

Trelagliptin ameliorates oxygen-glucose deprivation/reperfusion (OGD/R)-induced mitochondrial dysfunction and metabolic disturbance of endothelial cells

Acute myocardial infarction (AMI) is a severe cardiovascular disease with high mortality. It is reported to be closely related to the mitochondrial dysfunction and metabolic disturbance on endothelial cells under a chronic hypoxic state. Significant declined mitochondrial respiration, ATP production, and metabolic changes are the main characteristics of endothelial injury in the disease. Trelagliptin is a DPP-4 inhibitor applied for the treatment of type II diabetes and has been recently reported to exert various pharmacological properties. In this investigation, we examined whether Trelagliptin possessed a protective effect against mitochondrial dysfunction and metabolic disturbance in human aortic valvular endothelial cells (HAVECs) under oxygen-glucose deprivation/reperfusion (OGD/R) conditions. We found that both the cytotoxicity and mitochondrial oxidative stress in HAVECs induced by OGD/R stimulation were greatly alleviated by Trelagliptin. In addition, the declined mitochondrial respiration and ATP production decreased secretion of cystathionine and creatine, and the increased production of triglyceride and adiponectin in OGD/R-challenged HAVECs was dramatically reversed by Trelagliptin, accompanied by the upregulated expression level of PGC-1α and CPT-1. Lastly, the AMPK pathway was observed to be significantly activated in OGD/R-challenged HAVECs by Trelagliptin treatment. After co-administration of the inhibitor of the AMPK pathway, the effects of Trelagliptin on mitochondrial function and metabolic alterations were significantly abolished. Taken together, our data indicate that Trelagliptin ameliorated OGD/R-induced mitochondrial disturbance and metabolic changes by activating the AMPK pathway.

Metabolic reprogramming of ovarian cancer involves ACSL1-mediated metastasis stimulation through upregulated protein myristoylation

As a result of the hostile microenvironment, metabolic alterations are required to enable the malignant growth of cancer cells. To understand metabolic reprogramming during metastasis, we conducted shotgun proteomic analysis of highly metastatic (HM) and non-metastatic (NM) ovarian cancer cells. The results suggest that the genes involved in fatty-acid (FA) metabolism are upregulated, with consequent increases of phospholipids with relatively short FA chains (myristic acid, MA) in HM cells. Among the upregulated proteins, ACSL1 expression could convert the lipid profile of NM cells to that similar of HM cells and make them highly aggressive. Importantly, we demonstrated that ACSL1 activates the AMP-activated protein kinase and Src pathways via protein myristoylation and finally enhances FA beta oxidation. Patient samples and tissue microarray data also suggested that omentum metastatic tumours have higher ACSL1 expression than primary tumours and a strong association with poor clinical outcome. Overall, our data reveal that ACSL1 enhances cancer metastasis by regulating FA metabolism and myristoylation.

Depression of Mitochondrial Function in the Rat Skeletal Muscle Model of Myofascial Pain Syndrome Is Through Down-Regulation of the AMPK-PGC-1α-SIRT3 Axis

Purpose

The causative mechanisms triggering myofascial pain syndrome (MPS) are still in debate. It is becoming evident that mitochondrial dysfunction may regulate pathways controlling MPS. The aim of this study was to investigate whether AMPK-PGC-1α-SIRT3 axis is associated with depression of mitochondrial function in the rat MPS model.

Methods

A total of 32 Sprague-Dawley rats were randomly divided into control group and experimental group. The expression level of mRNA and protein of gastrocnemius medialis (GM) was analyzed by Western blot and RT-PCR. The histopathological findings were investigated through electron microscopes in GM of all groups.

Results

Our results showed that MPS induces continuous depression of mitochondrial biogenesis and function via down-regulation of PGC-1α-SIRT3 axis accompanying with ATP fuel crisis as compared to control group. However, the expression level of SIRT3 mRNA did not change. Additionally, a correlated reduction of the mRNA and protein expression level of NRF-1 and TFAM, known as the downstream target of PGC-1α, suggesting further transcription of nuclear genes encoding mitochondria functional proteins for promoting mitochondria proliferation, oxidative phosphorylation and energy production is continuously depressed. Furthermore, phosphorylation extent of AMPK is also declined following MPS, and it is negatively correlated with reduction of ATP generation, suggesting that the complex network involves different inhibition in transcription, post-translational modification and a plethora of other effectors that mediate the inhibition roles.

Conclusion

We here suggested that the down-regulation in AMPK-PGC-1α-SIRT3 axis network may be the basis for the association between mitochondrial dysfunction and MPS, where a vicious circle further aggravates the disease symptoms with ongoing ATP energy crisis.

Ouabain impairs cancer metabolism and activates AMPK-Src signaling pathway in human cancer cell lines

In addition to the well-known cardiotonic effects, cardiac glycosides (CGs) produce potent anticancer effects with various molecular mechanisms. We previously show that ouabain induces autophagic cell death in human lung cancer cells by regulating AMPK-mediated mTOR and Src-mediated ERK1/2 signaling pathways. However, whether and how AMPK and Src signaling interacts in ouabain-treated cancer cells remains unclear. Given the pivotal role of AMPK in metabolism, whether ouabain affects cancer cell metabolism remains elusive. In this study we showed that treatment with ouabain (25 nM) caused simultaneous activation of AMPK and Src signaling pathways in human lung cancer A549 cells and human breast cancer MCF7 cells. Cotreatment with AMPK inhibitor compound C or siRNA greatly abrogates ouabain-induced Src activation, whereas cotreatment with Src inhibitor PP2 has little effect on ouabain-induced AMPK activity, suggesting that AMPK served as an upstream regulator of the Src signaling pathway. On the other hand, ouabain treatment greatly depletes ATP production in A549 and MCF7 cells, and supplement of ATP (100 μM) blocked ouabain-induced AMPK activation. We further demonstrated that ouabain greatly inhibited the mitochondrial oxidative phosphorylation (OXPHOS) in the cancer cells, and exerted differential metabolic effects on glycolysis depending on cancer cell type. Taken together, this study reveals that the altered cancer cell metabolism caused by ouabain may contribute to AMPK activation, as well as its cytotoxicity towards cancer cells.

Memory T cells delay the progression of atherosclerosis via AMPK signaling pathway

Background

Memory T cells play a key role in the development of atherosclerosis (AS). This study aimed to investigate the role of AMPK signaling pathway of spleen memory T cells in the pathogenesis of AS in high-fat diet (HFD) fed mice.

Methods

Mice were divided into 5 groups: normal group, AS group, AS + solvent group, AS + Compound C (AMPK inhibitor) group and AS + A-769662 (AMPK agonist) group. HFD animals were intraperitoneally treated with Compound C at 20 mg/kg thrice weekly or A-769662 at 30 mg/kg once daily for 15 weeks. Then, the degree of AS was assessed, and the proportion of memory T cell was determined by flow cytometry.

Results

AS was evident in the aorta of HFD mice. The areas of plaque formation in both AS + Compound C group and AS + A-769662 group reduced as compared to the AS group and AS + solvent group. After intervention of AMPK activity, the proportion of memory T cells in the spleen reduced as compared to the AS group and AS + solvent group; the pro proportion of memory T cells in HFD groups was markedly higher than in the normal group and this increase was more evident in the AS + Compound C than in the AS + A-769662 group.

Conclusions

The decreased memory T cells can improve AS, which may be related to the AMPK signaling pathway. Thus, AMPK in the memory T cells may serve as a target in the prevention and treatment of AS.

The Role of AMPK/mTOR Modulators in the Therapy of Acute Myeloid Leukemia

Differentiation therapy of acute promyelocytic leukemia with all-trans retinoic acid represents the most successful pharmacological therapy of acute myeloid leukemia (AML). Numerous studies demonstrate that drugs that inhibit mechanistic target of rapamycin (mTOR) and activate AMP-kinase (AMPK) have beneficial effects in promoting differentiation and blocking proliferation of AML. Most of these drugs are already in use for other purposes; rapalogs as immunosuppressants, biguanides as oral antidiabetics, and 5-amino-4-imidazolecarboxamide ribonucleoside (AICAr, acadesine) as an exercise mimetic. Although most of these pharmacological modulators have been widely used for decades, their mechanism of action is only partially understood. In this review, we summarize the role of AMPK and mTOR in hematological malignancies and discuss the possible role of pharmacological modulators in proliferation and differentiation of leukemia cells.

Mitochondrial glycerol 3-phosphate dehydrogenase promotes skeletal muscle regeneration

While adult mammalian skeletal muscle is stable due to its post‐mitotic nature, muscle regeneration is still essential throughout life for maintaining functional fitness. During certain diseases, such as the modern pandemics of obesity and diabetes, the regeneration process becomes impaired, which leads to the loss of muscle function and contributes to the global burden of these diseases. However, the underlying mechanisms of the impairment are not well defined. Here, we identify mGPDH as a critical regulator of skeletal muscle regeneration. Specifically, it regulates myogenic markers and myoblast differentiation by controlling mitochondrial biogenesis via CaMKKβ/AMPK. mGPDH^−/− attenuated skeletal muscle regeneration in vitro and in vivo, while mGPDH overexpression ameliorated dystrophic pathology in mdx mice. Moreover, in patients and animal models of obesity and diabetes, mGPDH expression in skeletal muscle was reduced, further suggesting a direct correlation between its abundance and muscular regeneration capability. Rescuing mGPDH expression in obese and diabetic mice led to a significant improvement in their muscle regeneration. Our study provides a potential therapeutic target for skeletal muscle regeneration impairment during obesity and diabetes.

The Photomodulation Activity of Metformin Against Oral Microbiome

Periodontitis is one of the most common inflammatory diseases of the periodontium, which results in the inflammatory destruction of supporting structures around teeth and is closely associated with the development of systemic disease. Due to a wide variety of antibiotic resistance periodontopathic bacteria, photodynamic therapy (PDT) is a non-invasive adjunctive therapeutic modality that is capable of destroying the whole range of microbes. Metformin (Metf) is an antidiabetic drug, and recent studies suggest that cancer patients who receive Metf and are exposed to radiotherapy and chemotherapy show better outcomes. Our surveys in this review introduce Metf as a potent stimulus in increasing the efficacy of PDT in the induction of destruction in microbial cells.

Selective Ah receptor ligands mediate enhanced SREBP1 proteolysis to restrict lipogenesis in sebocytes

The aryl hydrocarbon receptor (AHR) mediates 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) induced toxicity that can lead to chloracne in humans. A characteristic of chloracne, in contrast to acne vulgaris, is shrinkage or loss of sebaceous glands. Acne vulgaris, on the other hand, is often accompanied by excessive sebum production. Here, we examined the role of AHR in lipid synthesis in human sebocytes using distinct classes of AHR ligands. Modulation of AHR activity attenuated the expression of lipogenic genes and key pro-inflammatory markers in the absence of canonical DRE-driven transcription of the AHR target gene CYP1A1. Furthermore, topical treatment with TCDD, which mediates DRE-dependent activity, and SGA360, which fails to induce DRE-mediated responses, both exhibited a decrease in the size of sebaceous glands and the number of sebocytes within each gland in the skin. To elucidate the mechanism of AHR-mediated repression of lipid synthesis, we demonstrated that selective AHR modulators, SGA360 and SGA315 increased the protein turnover of the mature sterol regulatory element-binding protein (mSREBP-1), the principal transcriptional regulator of the fatty acid synthesis pathway. Interestingly, selective AHR ligand treatment significantly activated the AMPK-dependent kinase (AMPK) in sebocytes. Moreover, we demonstrated an inverse correlation between the active AMPK and the mSREBP-1 protein, which is consistent with the previously reported role of AMPK in inhibiting cleavage of SREBP-1. Overall, our findings indicate a DRE-independent function of selective AHR ligands in modulating lipid synthesis in human sebocytes, which might raise the possibility of using AHR as a therapeutic target for treatment of acne.

Role of liver sinusoidal endothelial cells in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) and its complications are an expanding health problem associated with the metabolic syndrome. Liver sinusoidal endothelial cells (LSECs) are highly specialized endothelial cells localized at the interface between the blood derived from the gut and the adipose tissue on the one side, and other liver cells on the other side. In physiological conditions, LSECs are gatekeepers of liver homeostasis. LSECs display anti-inflammatory and anti-fibrogenic properties by preventing Kupffer cell and hepatic stellate cell activation and regulating intrahepatic vascular resistance and portal pressure. This review focusses on changes occurring in LSECs in NAFLD and on their consequences on NAFLD progression and complications. Capillarization, namely the loss of LSEC fenestrae, and LSEC dysfunction, namely the loss of the ability of LSECs to generate vasodilator agents in response to increased shear stress both occur early in NAFLD. These LSEC changes favour steatosis development and set the stage for NAFLD progression. At the stage of non-alcoholic steatohepatitis, altered LSECs release inflammatory mediators and contribute to the recruitment of inflammatory cells, thus promoting liver injury and inflammation. Altered LSECs also fail to maintain hepatic stellate cell quiescence and release fibrogenic mediators, including Hedgehog signalling molecules, promoting liver fibrosis. Liver angiogenesis is increased in NAFLD and contributes to liver inflammation and fibrosis, but also to hepatocellular carcinoma development. Thus, improving LSEC health appears to be a promising approach to prevent NAFLD progression and complications.

Mechanotransduction of mitochondrial AMPK and its distinct role in flow-induced breast cancer cell migration

The biophysical microenvironment of the tumor site has significant impact on breast cancer progression and metastasis. The importance of altered mechanotransduction in cancerous tissue has been documented, yet its role in the regulation of cellular metabolism and the potential link between cellular energy and cell migration remain poorly understood. In this study, we investigated the role of mechanotransduction in AMP-activated protein kinase (AMPK) activation in breast cancer cells in response to interstitial fluid flow (IFF). Additionally, we explored the involvement of AMPK in breast cancer cell migration. IFF was applied to the 3D cell-matrix construct. The subcellular signaling activity of Src, FAK, and AMPK was visualized in real-time using fluorescent resonance energy transfer (FRET). We observed that breast cancer cells (MDA-MB-231) are more sensitive to IFF than normal epithelial cells (MCF-10A). AMPK was activated at the mitochondria of MDA-MB-231 cells by IFF, but not in other subcellular compartments (i.e., cytosol, plasma membrane, and nucleus). The inhibition of FAK or Src abolished flow-induced AMPK activation in the mitochondria of MDA-MB-231 cells. We also observed that global AMPK activation reduced MDA-MB-231 cell migration. Interestingly, specific AMPK inhibition in the mitochondria reduced cell migration and blocked flow-induced cell migration. Our results suggest the linkage of FAK/Src and mitochondria-specific AMPK in mechanotransduction and the differential role of AMPK in breast cancer cell migration depending on its subcellular compartment-specific activation.

H19 lncRNA Promotes Skeletal Muscle Insulin Sensitivity in Part by Targeting AMPK

Skeletal muscle plays a pivotal role in regulating systemic glucose homeostasis in part through the conserved cellular energy sensor AMPK. AMPK activation increases glucose uptake, lipid oxidation, and mitochondrial biogenesis, leading to enhanced muscle insulin sensitivity and whole-body energy metabolism. Here we show that the muscle-enriched H19 long noncoding RNA (lncRNA) acts to enhance muscle insulin sensitivity, at least in part, by activating AMPK. We identify the atypical dual-specificity phosphatase DUSP27/DUPD1 as a potentially important downstream effector of H19. We show that DUSP27, which is highly expressed in muscle with previously unknown physiological function, interacts with and activates AMPK in muscle cells. Consistent with decreased H19 expression in the muscle of insulin-resistant human subjects and rodents, mice with genetic H19 ablation exhibit muscle insulin resistance. Furthermore, a high-fat diet downregulates muscle H19 via both posttranscriptional and epigenetic mechanisms. Our results uncover an evolutionarily conserved, highly expressed lncRNA as an important regulator of muscle insulin sensitivity.

Sugar or fat: The metabolic choice of the trained heart

Mammals respond to muscular exercise by increasing cardiac output to meet the increased demand for oxygen in the working muscles and it is well-established that regular bouts of exercise results in myocardial remodeling. Depending on exercise type, intensity and duration, these cardiac adaptations lead to changes in the energetic substrates required to sustain cardiac contractility. In contrast to the failing heart, fatty acids are the preferred substrate in the trained heart, though glucose metabolism is also enhanced to support oxidative phosphorylation. The participation of AMPK/eNOS and PPARα/PGC-1α pathways in the regulation of cardiac metabolism is well known but other players also contribute including sirtuins and integrins-mediated outside-in activation of FAK and other kinases. These regulatory players act by up-regulating fatty acid uptake, transport to mitochondria and oxidation, and glucose uptake via GLUT4. This exercise-induced increase in mitochondria metabolic flexibility is important to sustain the energetic demand associated with cardiomyocyte hypertrophy and hyperplasia promoted by IGF-1 and neuregulin-1-induced PI3K/Akt signaling. So, the timeless advice of Hippocrates "walking is the best medicine" seems to be justified by the promotion of mitochondrial health and, consequently, the beneficial metabolic remodeling of the heart.

Nummularic acid, a triterpenoid, from the medicinal plant Fraxinus xanthoxyloides, induces energy crisis to suppress growth of prostate cancer cells

We recently identified and characterized nummularic acid (NA) as a major chemical constituent of Fraxinus xanthoxyloides, a medicinal plant used for over hundred years in traditional medicine. In this study, we describe its potential anti-cancer activity using prostate cancer (PCa) cells as a model. We found that NA treatment (5-60 μM) significantly reduced the proliferation and colony formation capabilities of PCa DU145 and C4-2 cells in a time and dose dependent manner, reduced the migratory and invasive properties and increased apoptotic cell population. Mechanistically, we found that NA treatment to PCa cells resulted in a sustained activation of adenosine monophosphate-activated protein kinase (AMPK). NA simultaneously increased acetyl CoA carboxylase phosphorylation and decreased pS6 phosphorylation, the two major substrates of AMPK. Further, NA treatment significantly elevated the cellular ADP/ATP ratio and altered glycolytic rate. We further observed a reversible decrease in oxygen consumption rate in NA treated cells when compared to the control. Finally, we performed global untargeted metabolomics which showed that NA treatment alters PCa cell metabolism at multiple sites including glycolysis, tricarboxylic acid, and glutamine metabolism which supported our observation of a possible AMPK activation. In summary, we report NA as a novel small molecule activator of AMPK that alters cellular metabolism to induce energy crisis and ultimately cancer cell death. Because of its unique mechanism NA could be potentially applicable against other cancer types.

Reactive Oxygen Species in Metabolic and Inflammatory Signaling

Reactive oxygen species (ROS) are well known for their role in mediating both physiological and pathophysiological signal transduction. Enzymes and subcellular compartments that typically produce ROS are associated with metabolic regulation, and diseases associated with metabolic dysfunction may be influenced by changes in redox balance. In this review, we summarize the current literature surrounding ROS and their role in metabolic and inflammatory regulation, focusing on ROS signal transduction and its relationship to disease progression. In particular, we examine ROS production in compartments such as the cytoplasm, mitochondria, peroxisome, and endoplasmic reticulum and discuss how ROS influence metabolic processes such as proteasome function, autophagy, and general inflammatory signaling. We also summarize and highlight the role of ROS in the regulation metabolic/inflammatory diseases including atherosclerosis, diabetes mellitus, and stroke. In order to develop therapies that target oxidative signaling, it is vital to understand the balance ROS signaling plays in both physiology and pathophysiology, and how manipulation of this balance and the identity of the ROS may influence cellular and tissue homeostasis. An increased understanding of specific sources of ROS production and an appreciation for how ROS influence cellular metabolism may help guide us in the effort to treat cardiovascular diseases.

5-LO inhibition ameliorates palmitic acid-induced ER stress, oxidative stress and insulin resistance via AMPK activation in murine myotubes

Leukotriene B4 (LTB4) production via the 5-lipoxygenase (5-LO) pathway contributes to the development of insulin resistance in adipose and hepatic tissues, but the role of LTB4 in skeletal muscle is relatively unknown. Here, the authors investigated the role of LTB4 in C2C12 myotubes in palmitic acid (PA)-induced ER stress, inflammation and insulin resistance. PA (750 μM) evoked lipotoxicity (ER stress, oxidative stress, inflammation and insulin resistance) in association with LTB4 production. 5-LO inhibition reduced all the lipotoxic effects induced by PA. On the other hand, PA did not induce cysteinyl leukotrienes (CysLTs), which themselves had no effect on ER stress and inflammation. The beneficial effects of 5-LO suppression from PA-induced lipotoxicity were related with AMPK activation. In ob/ob mice, once daily oral administration of zileuton (50, 100 mg/kg) for 5 weeks improved insulin resistance, increased AMPK phosphorylation, and reduced LTB4 and ER stress marker expression in skeletal muscle. These results show that 5-LO inhibition by either zileuton or 5-LO siRNA protects C2C12 myotubes from PA-induced lipotoxicity, at least partly via AMPK activation, and suggest that the in vivo insulin-sensitizing effects of zileuton are in part attributable to its direct action on skeletal muscle via LTB4 downregulation followed by AMPK activation.

Dimethylarginine Dimethylaminohydrolase 1 Protects Against High-Fat Diet-Induced Hepatic Steatosis and Insulin Resistance in Mice

AIMS

High plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, are associated with hepatic dysfunction in patients with nonalcoholic fatty liver disease (NAFLD). However, it is unknown whether ADMA is involved in the pathogenesis of NAFLD. Dimethylarginine dimethylaminohydrolase 1 (DDAH1) is an enzyme that degrades ADMA. In this study, we used Ddah1^-/- mice to investigate the effects of the ADMA/DDAH1 pathway on high-fat diet (HFD)-induced hepatic steatosis.

RESULTS

After HFD feeding for 20 weeks, Ddah1^-/- mice were more obese and had developed more severe hepatic steatosis and worse insulin resistance compared with wild-type (WT) mice. In the livers of HFD-fed mice, loss of DDAH1 resulted in higher levels of lipogenic genes, lower expression of β-oxidation genes, and greater induction of oxidative stress, endoplasmic reticulum stress, and inflammation than in the WT livers. Furthermore, ADMA treatment in HepG2 cells led to oxidative stress and steatosis, whereas overexpression of DDAH1 attenuated palmitic acid-induced steatosis, oxidative stress, and inflammation. Innovation and Conclusion: Our results provide the first direct evidence that the ADMA/DDAH1 pathway has a marked effect on hepatic lipogenesis and steatosis induced by HFD feeding. Our findings suggest that strategies to increase DDAH1 activity in hepatocytes may provide a novel approach to attenuate NAFLD development. Antioxid. Redox Signal. 26, 598-609.

AMP-activated protein kinase mediates the effects of lipoprotein-associated phospholipase A2 on endothelial dysfunction in atherosclerosis

The present study aimed to investigate the effects of lipoprotein-associated phospholipase A2 (Lp-PLA2) on endothelial dysfunction in an in vitro cell model of atherosclerosis, and to determine whether AMP-activated protein kinase (AMPK) mediates the effects of Lp-PLA2 on endothelial dysfunction. A total of 392 patients with coronary artery disease (CAD), including various sub-conditions, were recruited, and the plasma concentrations of Lp-PLA2 were evaluated. In addition, an in vitro model of atherosclerosis was established by exposing human umbilical vein endothelial cells (HUVECs) to oxidized low-density lipoprotein (oxLDL). SB-435495 was used to inhibit Lp-PLA2, and compound C was used to suppress AMPK expression. Lp-PLA2, AMPKα and phosphorylated-AMPKα (T172) expression in HUVECs were evaluated using western blot analysis. The concentrations of nitric oxide (NO), endothelin 1 (ET-1), intercellular adhesion molecule 1 (ICAM-1) and platelet/endothelial cell adhesion molecule 1 (PECAM-1) in cell culture supernatant were determined using commercially available ELISA kits. MTT assays were employed to indicate changes in cell viability. The current study found the plasma Lp-PLA2 levels were elevated in the CAD patients with stable angina pectoris, unstable angina pectoris, acute coronary syndromes and acute myocardial infarction, compared with a healthy control population. In addition, the in vitro results showed that Lp-PLA2 expression levels were elevated in oxLDL-exposed HUVECs. Lp-PLA2 suppression could increase cell viability, induce the production of NO and decrease the secretion of ET-1, in addition to suppressing the expression of cell adhesion molecules, including ICAM-1 and PECAM-1 in oxLDL-exposed HUVECs. The expression of AMPKα and phosphorylated-AMPKα (T172) was regulated by Lp-PLA2, and AMPK suppression was able to reverse the effects of Lp-PLA2 with regard to cell viability, endothelial vasorelaxation capacity and the secretion of adhesion molecules in oxLDL-exposed HUVECs. In conclusion, the present study provides initial evidence that Lp-PLA2 is able to cause endothelial dysfunction in an in vitro model of atherosclerosis, and the effects of Lp-PLA2 on endothelial dysfunction was at least partially a result of the downregulation of AMPKα, thus contributing to the progression of atherosclerosis.

Estrogen Activates AMP-Activated Protein Kinase in Human Endothelial Cells via ERβ/Ca(2+)/Calmodulin-Dependent Protein Kinase Kinase β Pathway

Our previous studies suggested that Estrogen inhibits cytokine-induced expression of VCAM-1 and ICAM-1 in cultured human endothelial cells via AMP-activated protein kinase (AMPK) activation. Here, we sought to delineate the mechanisms underlying estrogen activation of AMPK. AMPK can be considered a 'fuel gauge' of cellular energy status in response to metabolic stress. It is controlled by upstream kinases such as Ca(2+)/calmodulin-dependent protein kinase kinase β (CaMKKβ) or LKB1. The present study of human endothelial cells demonstrates that AMPK is activated by estradiol (E2) through a Ca(2+)-dependent mechanism involving the estrogen receptor-β (ERβ) activation. Inhibition of CaMKK with STO-609, a specific inhibitor of CaMKKα and CaMKKβ, attenuated E2-induced AMPK activation, suggesting that CaMKKβ was the responsible AMPK kinase. Conversely, down-regulation of LKB1 did not affect E2-induced AMPK activation. E2 stimulation caused phosphorylation of acetyl coenzyme A carboxylase (ACC) and endothelial nitric oxide synthase (eNOS), two main targets of AMPK. Inhibition or down-regulation of CaMKKβ eliminated phosphorylation of ACC and eNOS in response to E2. Together, our data highlight the role of Ca(2+) as a regulator of AMPK activation in response to E2 stimulation. We demonstrate that E2 activates AMPK via an ERβ/Ca(2+)/CaMKKβ-dependent pathway in endothelial cells.

Deletion of PRKAA triggers mitochondrial fission by inhibiting the autophagy-dependent degradation of DNM1L

PRKAA (protein kinase, AMP-activated, α catalytic subunit) regulates mitochondrial biogenesis, function, and turnover. However, the molecular mechanisms by which PRKAA regulates mitochondrial dynamics remain poorly characterized. Here, we report that PRKAA regulated mitochondrial fission via the autophagy-dependent degradation of DNM1L (dynamin 1-like). Deletion of Prkaa1/AMPKα1 or Prkaa2/AMPKα2 resulted in defective autophagy, DNM1L accumulation, and aberrant mitochondrial fragmentation in the mouse aortic endothelium. Furthermore, autophagy inhibition by chloroquine treatment or ATG7 small interfering RNA (siRNA) transfection, upregulated DNM1L expression and triggered DNM1L-mediated mitochondrial fragmentation. In contrast, autophagy activation by overexpression of ATG7 or chronic administration of rapamycin, the MTOR inhibitor, promoted DNM1L degradation and attenuated mitochondrial fragmentation in Prkaa2-deficient (prkaa2^-/-) mice, suggesting that defective autophagy contributes to enhanced DNM1L expression and mitochondrial fragmentation. Additionally, the autophagic receptor protein SQSTM1/p62, which bound to DNM1L and led to its translocation into the autophagosome, was involved in DNM1L degradation by the autophagy-lysosome pathway. Gene silencing of SQSTM1 markedly reduced the association between SQSTM1 and DNM1L, impaired the degradation of DNM1L, and enhanced mitochondrial fragmentation in PRKAA-deficient endothelial cells. Finally, the genetic (DNM1L siRNA) or pharmacological (mdivi-1) inhibition of DNMA1L ablated mitochondrial fragmentation in the mouse aortic endothelium and prevented the acetylcholine-induced relaxation of isolated mouse aortas. This suggests that aberrant DNM1L is responsible for enhanced mitochondrial fragmentation and endothelial dysfunction in prkaa knockout mice. Overall, our results show that PRKAA deletion promoted mitochondrial fragmentation in vascular endothelial cells by inhibiting the autophagy-dependent degradation of DNM1L.

The pentacyclic triterpenoid, plectranthoic acid, a novel activator of AMPK induces apoptotic death in prostate cancer cells

Epidemiologic studies indicated that diabetics treated with metformin had a lower incidence of cancer than those taking other anti-diabetes drugs. This led to a surge in the efforts for identification of safer and more effective metformin mimetic compounds. The plant Ficus microcarpa is widely used for the treatment of type 2 diabetes in traditional medicine in South Asia. We obtained extracts from this plant and identified a small molecule, plectranthoic acid (PA), with potent 5′AMP-activated kinase (AMPK) activating properties far superior than metformin. AMPK is the central hub of metabolic regulation and a well-studied therapeutic target for metabolic syndrome, type-2 diabetes and cancer. We observed that treatment of prostate cancer (PCa) cells with PA inhibited proliferation and induced G0/G1 phase cell cycle arrest that was associated with up-regulation of cyclin kinase inhibitors p21/CIP1 and p27/KIP1. PA treatment suppressed mTOR/S6K signaling and induced apoptosis in PCa cells in an AMPK-dependent manner. Interestingly, PA-induced autophagy in PCa cells was found to be independent of AMPK activation. Combination studies of PA and metformin demonstrated that metformin had an inhibitory effect on PA-induced AMPK activation and suppressed PA-mediated apoptosis. Given the anti-proliferative role of PA in cancer and its potent anti-hyperglycemic activity, we suggest that PA should be explored further as a novel activator of AMPK for its ultimate use for the prevention of cancers and treatment of type 2 diabetes.

GFRA1 promotes cisplatin-induced chemoresistance in osteosarcoma by inducing autophagy

Recent progress in chemotherapy has significantly increased its efficacy, yet the development of chemoresistance remains a major drawback. In this study, we show that GFRA1/GFRα1 (GDNF family receptor α 1), contributes to cisplatin-induced chemoresistance by regulating autophagy in osteosarcoma. We demonstrate that cisplatin treatment induced GFRA1 expression in human osteosarcoma cells. Induction of GFRA1 expression reduced cisplatin-induced apoptotic cell death and it significantly increased osteosarcoma cell survival via autophagy. GFRA1 regulates AMPK-dependent autophagy by promoting SRC phosphorylation independent of proto-oncogene RET kinase. Cisplatin-resistant osteosarcoma cells showed NFKB1/NFκB-mediated GFRA1 expression. GFRA1 expression promoted tumor formation and growth in mouse xenograft models and inhibition of autophagy in a GFRA1-expressing xenograft mouse model during cisplatin treatment effectively reduced tumor growth and increased survival. In cisplatin-treated patients, treatment period and metastatic status were associated with GFRA1-mediated autophagy. These findings suggest that GFRA1-mediated autophagy is a promising novel target for overcoming cisplatin resistance in osteosarcoma.

Activation of AMPK α2 inhibits airway smooth muscle cells proliferation

The aims of the present study were to examine the effect of adenosine monophosphate-activated protein kinase (AMPK) activation on airway smooth muscle cells (ASMCs) proliferation and to address its potential mechanisms. Platelet derived growth factor (PDGF) activated phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway, and this in turn up-regulated S-phase kinase-associated protein 2 (Skp2) and consequently reduced cyclin dependent kinase inhibitor 1B (p27) leading to ASMCs proliferation. Pre-incubation of cells with metformin, an AMPK activator, blocked PDGF-induced activation of mTOR and its downstream targets changes of Skp2 and p27 without changing Akt phosphorylation and inhibited ASMCs proliferation. Transfection of ASMCs with AMPK α2-specific small interfering RNA (siRNA) reversed the effect of metformin on mTOR phosphorylation, Skp2 and p27 protein expression and cell proliferation. Our study suggests that activation of AMPK, particularly AMPK α2, negatively regulates mTOR activity to suppress ASMCs proliferation and therefore has a potential value in the prevention and treatment of asthma by negatively modulating airway remodeling.

Oleanolic, Ursolic, and Betulinic Acids as Food Supplements or Pharmaceutical Agents for Type 2 Diabetes: Promise or Illusion?

Oleanolic (OA), ursolic (UA), and betulinic (BA) acids are three triterpenic acids (TAs) with potential effects for treatment of type 2 diabetes (T2DM). Mechanistic studies showed that these TAs act as hypoglycemic and antiobesity agents mainly through (i) reducing the absorption of glucose; (ii) decreasing endogenous glucose production; (iii) increasing insulin sensitivity; (iv) improving lipid homeostasis; and (v) promoting body weight regulation. Besides these promising beneficial effects, it is believed that OA, UA, and BA protect against diabetes-related comorbidities due to their antiatherogenic, anti-inflammatory, and antioxidant properties. We also highlight the protective effect of OA, UA, and BA against oxidative damage, which may be very relevant for the treatment and/or prevention of T2DM. In the present review, we provide an integrative description of the antidiabetic properties of OA, UA, and BA, evaluating the potential use of these TAs as food supplements or pharmaceutical agents to prevent and/or treat T2DM.

Activation of AMPK inhibits PDGF-induced pulmonary arterial smooth muscle cells proliferation and its potential mechanisms

The aims of the present study were to examine signaling mechanisms for PDGF-induced pulmonary arterial smooth muscle cells (PASMC) proliferation and to determine the effect of AMPK activation on PDGF-induced PASMC proliferation and its underlying mechanisms. PDGF activated PI3K/Akt/mTOR signaling pathway, and this in turn up-regulated Skp2 and consequently reduced p27 leading to PASMC proliferation. Prior incubation of PASMC with metformin induced a dramatic AMPK activation and significantly blocked PDGF-induced cell proliferation. PASMC lacking AMPKα2 were resistant to the inhibitory effect of metformin on PDGF-induced cell proliferation. Metformin did not affect Akt activation but blocked mTOR phosphorylation in response to PDGF; these were accompanied by the reversion of Skp2 up-regulation and p27 reduction. Our study suggests that the activation of AMPK negatively regulates mTOR activity to suppress PASMC proliferation and therefore has a potential value in the prevention and treatment of pulmonary hypertension by negatively modulating pulmonary vascular remodeling.

AMPK-mediated energy homeostasis and associated metabolic effects on cancer cell response and resistance to cetuximab

We previously reported that cetuximab, an EGFR-blocking antibody, inhibits cancer metabolism via downregulation of HIF-1α and reverses the Warburg effect in cancer cells. Here, we report that inhibition of HIF-1 transcriptional activity by cetuximab does not necessarily lead to successful inhibition of cell proliferation. In several head and neck squamous cell carcinoma (HNSCC) cell lines, we observed a pattern of oscillating decrease and increase of intracellular ATP level after cetuximab treatment, and the magnitude and kinetics of which varied by cell line and appeared to be linked to the extent of cellular response to cetuximab. In HNSCC cells with low basal level of AMPK activity and that responded to cetuximab-induced growth inhibition, there was a transient, LKB1-dependent activation of AMPK. In contrast, HNSCC cells that had a high basal level of AMPK activity were less sensitive to cetuximab-induced growth inhibition despite effective inhibition of EGFR downstream signaling by cetuximab. Knockdown or inhibition of AMPK markedly enhanced response to cetuximab via induction of apoptosis. These findings indicate that a transient activation of AMPK is an early metabolic marker of cellular response to cetuximab and that high and sustained AMPK activity is an important mechanism by which cancer cells survive cetuximab treatment.

Evolving Lessons on the Complex Role of AMPK in Normal Physiology and Cancer

AMP kinase (AMPK) is an evolutionarily conserved enzyme required for adaptive responses to various physiological and pathological conditions. AMPK executes numerous cellular functions, some of which are often perceived at odds with each other. While AMPK is essential for embryonic growth and development, its full impact in adult tissues is revealed under stressful situations that organisms face in the real world. Conflicting reports about its cellular functions, particularly in cancer, are intriguing and a growing number of AMPK activators are being developed to treat human diseases such as cancer and diabetes. Whether these drugs will have only context-specific benefits or detrimental effects in the treatment of human cancer will be a subject of intense research. Here we review the current state of AMPK research with an emphasis on cancer and discuss the yet unresolved context-dependent functions of AMPK in human cancer.

Neutrophil-Derived MMP-8 Drives AMPK-Dependent Matrix Destruction in Human Pulmonary Tuberculosis

Pulmonary cavities, the hallmark of tuberculosis (TB), are characterized by high mycobacterial load and perpetuate the spread of M. tuberculosis. The mechanism of matrix destruction resulting in cavitation is not well defined. Neutrophils are emerging as key mediators of TB immunopathology and their influx are associated with poor outcomes. We investigated neutrophil-dependent mechanisms involved in TB-associated matrix destruction using a cellular model, a cohort of 108 patients, and in separate patient lung biopsies. Neutrophil-derived NF-kB-dependent matrix metalloproteinase-8 (MMP-8) secretion was up-regulated in TB and caused matrix destruction both in vitro and in respiratory samples of TB patients. Collagen destruction induced by TB infection was abolished by doxycycline, a licensed MMP inhibitor. Neutrophil extracellular traps (NETs) contain MMP-8 and are increased in samples from TB patients. Neutrophils lined the circumference of human pulmonary TB cavities and sputum MMP-8 concentrations reflected TB radiological and clinical disease severity. AMPK, a central regulator of catabolism, drove neutrophil MMP-8 secretion and neutrophils from AMPK-deficient patients secrete lower MMP-8 concentrations. AMPK-expressing neutrophils are present in human TB lung biopsies with phospho-AMPK detected in nuclei. These data demonstrate that neutrophil-derived MMP-8 has a key role in the immunopathology of TB and is a potential target for host-directed therapy in this infectious disease.

X-3, a mangiferin derivative, stimulates AMP-activated protein kinase and reduces hyperglycemia and obesity in db/db mice

Diabetes mellitus is a major health concern, affecting nearly 10% of the population. Here we describe a potential novel therapeutic agent for this disease, X-3, a derivative of mangiferin. Therapeutic administration of X-3 significantly and dose-dependently reduced plasma glucose and triglycerides in db/db mice following 8 week-treatments. Treatment with X-3 dose-dependently increased the number of insulin-positive β-cell mass. Importantly, X-3 did not cause any death or signs of toxicity in acute toxicity studies. Study of mechanism of action revealed that X-3 increased glucose uptake in parallel with increased phosphorylation of AMP-activated protein kinase (AMPK) in 3T3-L1 cells. It activates AMPK in both LKB1-dependent and -independent manner. Furthermore, administration of X-3 resulted in activation of AMPK and its downstream target, acetyl-CoA carboxylase (ACC) in the hypothalamus, liver, muscle and adipose tissues of C57BL/6 mice. An 80 mg/kg X-3 was more potent than metformin at 500 mg/kg in the hypothalamus, and interscapular fat tissues, potent than MF at the same dose in the liver. Thus, we conclude that X-3 is a promising new class of AMPK activating drug, and can potentially be used in the treatment of type 2 diabetes.

Cancer cell metabolism and the modulating effects of nitric oxide

Altered metabolic phenotype has been recognized as a hallmark of tumor cells for many years, but this aspect of the cancer phenotype has come into greater focus in recent years. NOS2 (inducible nitric oxide synthase of iNOS) has been implicated as a component in many aggressive tumor phenotypes, including melanoma, glioblastoma, and breast cancer. Nitric oxide has been well established as a modulator of cellular bioenergetics pathways, in many ways similar to the alteration of cellular metabolism observed in aggressive tumors. In this review we attempt to bring these concepts together with the general hypothesis that one function of NOS2 and NO in cancer is to modulate metabolic processes to facilitate increased tumor aggression. There are many mechanisms by which NO can modulate tumor metabolism, including direct inhibition of respiration, alterations in mitochondrial mass, oxidative inhibition of bioenergetic enzymes, and the stimulation of secondary signaling pathways. Here we review metabolic alterations in the context of cancer cells and discuss the role of NO as a potential mediator of these changes.

Activation of AMPK inhibits pulmonary arterial smooth muscle cells proliferation

The aims of the present study were to examine the effect of AMPK activation on pulmonary arterial smooth muscle cells (PASMCs) proliferation and to address its potential mechanisms. ET-1 dose and time-dependently induced PASMCs proliferation, and this effect was suppressed by a selective AMPK activator metformin. The results of the study further indicated that the proliferation of PASMCs stimulated by ET-1 was associated with the increase of Skp2 and decrease of p27, and metformin reversed ET-1-induced Skp2 elevation and raised p27 protein level. Our study suggests that activation of AMPK suppresses PASMCs proliferation and has potential value in negatively modulating pulmonary vascular remodeling and therefore could prevent or treat the development of pulmonary arterial hypertension (PAH).

Activation of AMP-activated protein kinase by metformin protects human coronary artery endothelial cells against diabetic lipoapoptosis

Background

The prevalence of type 2 diabetes (T2D) among adults worldwide is rapidly increasing, and in patients with diabetes the major cause of death is macrovascular disease. Endothelial cells play an important role in maintaining vascular homeostasis. Free fatty acids, which are elevated in T2D, have previously been shown to induce endothelial dysfunction and apoptosis of endothelial cells, which is considered as an important and early factor in the onset of atherosclerosis and cardiovascular disease. Metformin, which is used as first line treatment of T2D patients, is believed to exert its pharmacological effects through activation of AMP-activated protein kinase, which has emerged as a new potential target in reversing endothelial dysfunction.

Methods

Here we studied the protective effect of metformin against free fatty acid-induced apoptosis of human coronary artery endothelial cells (HCAECs) by assessing DNA fragmentation and cleaved caspase 3 levels. We also attempted to elucidate the underlying mechanisms by investigating the involvement of AMP-activated protein kinase, p38 MAPK and eNOS. Generation of reactive oxygen species by free fatty acid exposure was also examined.

Results

Our results suggest that metformin protects HCAECs from lipoapoptosis, an effect that involves eNOS and p38 MAPK, downstream of AMPK signaling, but not as previously suggested through suppression of reactive oxygen species.

Conclusion

The protective effect of metformin against free fatty acid induced apoptosis is potentially clinically relevant as metformin is first line treatment for patients with T2D, a patient group which is rapidly increasing and carries a high burden of cardiovascular disease.

Role of nitric oxide in skeletal muscle glucose uptake during exercise

Nitric oxide is produced within skeletal muscle fibres and has various functions in skeletal muscle. There is evidence that NO may be essential for normal increases in skeletal muscle glucose uptake during contraction/exercise. Although there have been some discrepant results, it has been consistently demonstrated that inhibition of NO synthase (NOS) attenuates the increase in skeletal muscle glucose uptake during contraction in mouse and rat muscle ex vivo, during in situ contraction in rats and during exercise in humans. The NO-mediated increase in skeletal muscle glucose uptake during contraction/exercise is probably due to the modulation of intramuscular signalling that ultimately increases glucose transporter 4 (GLUT4) translocation and is, surprisingly, independent of blood flow. In this review, we discuss the evidence for and against a role of NO in regulating skeletal muscle glucose uptake during contraction/exercise and outline the possible mechanism(s) involved. Emerging findings regarding the role of neuronal NOS mu (nNOSμ) in this process are also discussed.

Blood-brain barrier Na transporters in ischemic stroke

Blood-brain barrier (BBB) endothelial cells form a barrier that is highly restrictive to passage of solutes between blood and brain. Many BBB transport mechanisms have been described that mediate transcellular movement of solutes across the barrier either into or out of the brain. One class of BBB transporters that is all too often overlooked is that of the ion transporters. The BBB has a rich array of ion transporters and channels that carry Na, K, Cl, HCO3, Ca, and other ions. Many of these are asymmetrically distributed between the luminal and abluminal membranes, giving BBB endothelial cells the ability to perform vectorial transport of ions across the barrier between blood and brain. In this manner, the BBB performs the important function of regulating the volume and composition of brain interstitial fluid. Through functional coupling of luminal and abluminal transporters and channels, the BBB carries Na, Cl, and other ions from blood into brain, producing up to 30% of brain interstitial fluid in healthy brain. During ischemic stroke cerebral edema forms by processes involving increased activity of BBB luminal Na transporters, resulting in "hypersecretion" of Na, Cl, and water into the brain interstitium. This review discusses the roles of luminal BBB Na transporters in edema formation in stroke, with an emphasis on Na-K-Cl cotransport and Na/H exchange. Evidence that these transporters provide effective therapeutic targets for reduction of edema in stroke is also discussed, as are recent findings regarding signaling pathways responsible for ischemia stimulation of the BBB Na transporters.

Regulation of the pentose phosphate pathway in cancer

Energy metabolism is significantly reprogrammed in many human cancers, and these alterations confer many advantages to cancer cells, including the promotion of biosynthesis, ATP generation, detoxification and support of rapid proliferation. The pentose phosphate pathway (PPP) is a major pathway for glucose catabolism. The PPP directs glucose flux to its oxidative branch and produces a reduced form of nicotinamide adenine dinucleotide phosphate (NADPH), an essential reductant in anabolic processes. It has become clear that the PPP plays a critical role in regulating cancer cell growth by supplying cells with not only ribose-5-phosphate but also NADPH for detoxification of intracellular reactive oxygen species, reductive biosynthesis and ribose biogenesis. Thus, alteration of the PPP contributes directly to cell proliferation, survival and senescence. Furthermore, recent studies have shown that the PPP is regulated oncogenically and/or metabolically by numerous factors, including tumor suppressors, oncoproteins and intracellular metabolites. Dysregulation of PPP flux dramatically impacts cancer growth and survival. Therefore, a better understanding of how the PPP is reprogrammed and the mechanism underlying the balance between glycolysis and PPP flux in cancer will be valuable in developing therapeutic strategies targeting this pathway.

Redox regulation of endothelial cell fate

Endothelial cells (ECs) are present throughout blood vessels and have variable roles in both physiological and pathological settings. EC fate is altered and regulated by several key factors in physiological or pathological conditions. Reactive nitrogen species and reactive oxygen species derived from NAD(P)H oxidases, mitochondria, or nitric oxide-producing enzymes are not only cytotoxic but also compose a signaling network in the redox system. The formation, actions, key molecular interactions, and physiological and pathological relevance of redox signals in ECs remain unclear. We review the identities, sources, and biological actions of oxidants and reductants produced during EC function or dysfunction. Further, we discuss how ECs shape key redox sensors and examine the biological functions, transcriptional responses, and post-translational modifications evoked by the redox system in ECs. We summarize recent findings regarding the mechanisms by which redox signals regulate the fate of ECs and address the outcome of altered EC fate in health and disease. Future studies will examine if the redox biology of ECs can be targeted in pathophysiological conditions.

5-Aminoimidazole-4-carboxamide ribonucleoside induces differentiation of acute myeloid leukemia cells

Adenosine monophosphate (AMP)-activated kinase (AMPK) modulators have been shown to exert cytotoxic activity in hematological malignancies, but their role in the differentiation of acute myeloid leukemia (AML) is less explored. In this study, the effects of AMPK agonists on all-trans retinoic acid (ATRA)-mediated differentiation of acute promyelocytic leukemia (APL) and non-APL AML cell lines were investigated. The results show that AMPK agonists inhibit the growth of myeloblastic HL-60, promyelocytic NB4 and monocytic U937 cells. 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR), an AMPK activator, enhances ATRA-mediated differentiation of NB4 cells. In U937 cells, AICAR alone induces the expression of cell surface markers associated with mature monocytes and macrophages. In both cell lines, AICAR increases the activity of mitogen-activated protein kinase (MAPK), and the presence of a MAPK inhibitor reduces the expression of differentiation markers. These results reveal beneficial effects of AICAR in AML, including differentiation of non-APL AML cells.

Prolonged AMP-activated protein kinase induction impairs vascular functions

AMP-activated protein kinase (AMPK) is a regulator of cellular metabolism and is involved in the pathogenesis of several diseases, including type 2 diabetes and cardiovascular diseases. Data showing the effects of AMPK on vasculature are controversial. Therefore, the aim of this study was to determine the impact of prolonged AMPK activation on vascular functions. For this purpose we have examined the role of AMPK in endothelium-dependent and -independent relaxation and vascular contractions. For this, we incubated thoracic aortic rings, from rats, with AMPK activator 5-aminoimidazole-4-carboxamide-1-4-ribofuranoside (AICAR, 500 μmol/L or 2 mmol/L) in the presence or absence of AMPK inhibitor compound C (10 μmol/L). Next, cumulative dose–response curves to acetylcholine (ACh) (10−9−10−4 mol/L), nitroglycerine (NG) (10−9–3 × 10−5 mol/L), and noradrenaline (NA) (10−9−10−4 mol/L) were obtained. Endothelial nitric oxide synthase (eNOS) protein expression was determined. Our results show that endothelium-dependent relaxation was inhibited after AICAR treatment, and that this effect was reversed by AMPK inhibition. Moreover, AICAR enhanced the contractile response to NA and caused a decrease in eNOS protein expression. In conclusion, prolonged AMPK induction causes endothelial impairment, possibly via increased degradation and (or) reduced expression of eNOS.

The role of nitric oxide signaling in food intake; insights from the inner mitochondrial membrane peptidase 2 mutant mice

Reactive oxygen species have been implicated in feeding control through involvement in brain lipid sensing, and regulating NPY/AgRP and pro-opiomelanocortin (POMC) neurons, although the underlying mechanisms are unclear. Nitric oxide is a signaling molecule in neurons and it stimulates feeding in many species. Whether reactive oxygen species affect feeding through interaction with nitric oxide is unclear. We previously reported that Immp2l mutation in mice causes excessive mitochondrial superoxide generation, which causes infertility and early signs of aging. In our present study, reduced food intake in mutant mice resulted in significantly reduced body weight and fat composition while energy expenditure remained unchanged. Lysate from mutant brain showed a significant decrease in cGMP levels, suggesting insufficient nitric oxide signaling. Thus, our data suggests that reactive oxygen species may regulate food intake through modulating the bioavailability of nitric oxide.

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Mature adult Immp2l mutant mice have reduced body weight and fat composition.

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Reduced body weight and fat composition is caused by reduced food intake.

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Energy expenditure is not affected in mutant mice.

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Brain cGMP level is lower in mutant mice.

Natural antioxidant-isoliquiritigenin ameliorates contractile dysfunction of hypoxic cardiomyocytes via AMPK signaling pathway

Isoliquiritigenin (ISL), a simple chalcone-type flavonoid, is derived from licorice compounds and is mainly present in foods, beverages, and tobacco. Reactive oxygen species (ROS) is a critical factor involved in modulating cardiac stress response signaling during ischemia and reperfusion. We hypothesize that ISL as a natural antioxidant may protect heart against ischemic injury via modulating cellular redox status and regulating cardioprotective signaling pathways. The fluorescent probe H2DCFDA was used to measure the level of intracellular ROS. The glucose uptake was determined by 2-deoxy-D-glucose-(3)H accumulation. The IonOptix System measured the contractile function of isolated cardiomyocytes. The results demonstrated that ISL treatment markedly ameliorated cardiomyocytes contractile dysfunction caused by hypoxia. ISL significantly stimulated cardioprotective signaling, AMP-activated protein kinase (AMPK), and extracellular signal-regulated kinase (ERK) signaling pathways. The ROS fluorescent probe H2DCFDA determination indicated that ISL significantly reduced cardiac ROS level during hypoxia/reoxygenation. Moreover, ISL reduced the mitochondrial potential (Δψ) of isolated mouse cardiomyocytes. Taken together, ISL as a natural antioxidant demonstrated the cardioprotection against ischemic injury that may attribute to the activation of AMPK and ERK signaling pathways and balance of cellular redox status.

Propionyl-L-carnitine induces eNOS activation and nitric oxide synthesis in endothelial cells via PI3 and Akt kinases

Propionyl-l-carnitine (PLC) is a natural short-chain derivative of l-carnitine (LC), a natural amino acid that plays an important role in fatty acid metabolism. Recent studies suggest that PLC has vascular protective effects. Because of the importance of endothelial nitric oxide synthase (eNOS) and its product, antiatherogenic molecule nitric oxide (NO), in vascular endothelial function, we sought to elucidate that if PLC would stimulate eNOS and its upstream activators Akt and phosphatidylinositol 3-kinase (PI3 Kinase) in cultured human aortic endothelial cells (HAEC). PLC caused eNOS phosphorylation at Ser-1177, and dominant negative Akt and a novel Akt-selective inhibitor MK-2206 inhibited both PLC-mediated phosphorylation and activation of the enzyme. PI3 kinase inhibition also blocked the phosphorylation and activation of eNOS by PLC. Studies with specific drug inhibitors PD173955 and PP2 showed that the non-receptor tyrosine kinase, src, is an upstream stimulator of the PI3 kinase-Akt pathway in this pathway. In addition, PLC significantly decreased intracellular ATP/ADP ratio and activate AMPK, subsequently leading to Src activation. Finally, we demonstrated that the effects of PLC to augment eNOS activity were associated with a net increase in NO release from endothelial cells. NO production following incubation with PLC was abolished in endothelial cells coincubated with L-NAME, PD173955, LY294002, MK-2206 and compound C. In conclusion, PLC, via AMPK/Src-mediated signaling that leads to activation of PI3 kinase and Akt, stimulates eNOS, leading to increased production of NO.

Characterization of the effects of metformin on porcine oocyte meiosis and on AMP-activated protein kinase activation in oocytes and cumulus cells

The adenosine monophosphate-activated protein kinase (AMPK) activators 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside (AICAR) and metformin (MET) inhibit resumption of meiosis in porcine cumulus-enclosed oocytes. The objective of this study was to characterize the inhibitory effect of MET on porcine oocyte meiosis by: (1) determining the effects of an AMPK inhibitor and of inhibitors of signalling pathways involved in MET-induced AMPK activation in other cell types on MET-mediated meiotic arrest in porcine cumulus-enclosed oocytes; (2) determining whether MET and AICAR treatments lead to increased activation of porcine oocyte and/or cumulus cell AMPK as measured by phosphorylation of its substrate acetyl-CoA carboxylase; and (3) determining the effects of inhibition of the AMPK kinase, Ca2+/calmodulin-dependent protein kinase kinase (CaMKK), and Ca2+ chelation on oocyte meiotic maturation and AMPK activation in porcine oocytes and cumulus cells. The AMPK inhibitor compound C (CC; 1 μM) did not reverse the inhibitory effect of AICAR (1 mM) and MET (2 mM) on porcine oocyte meiosis. Additionally, CC had a significant inhibitory effect on its own. eNOS, c-Src and PI-3 kinase pathway inhibitors did not reverse the effect of metformin on porcine oocyte meiosis. The level of acetyl-CoA carboxylase (ACC) phosphorylation in oocytes and cumulus cells did not change in response to culture in the presence of MET, AICAR, CC, the CaMKK inhibitor STO-609 or the Ca2+ chelator BAPTA-AM for 3 h, but STO-609 increased the percentage of porcine cumulus-enclosed oocytes (CEO) that remained at the germinal vesicle (GV) stage after 24 h of culture. These results indicate that the inhibitory effect of MET and AICAR on porcine oocyte meiosis was probably not mediated through activation of AMPK.

AMP-activated protein kinase as regulator of P2Y(6) receptor-induced insulin secretion in mouse pancreatic β-cells

5'-AMP-activated protein kinase (AMPK) and its pharmacological modulators have been targeted for treating type 2 diabetes. Extracellular uridine 5'-diphosphate (UDP) activates P2Y6 receptors (P2Y6Rs) in pancreatic β-cells to release insulin and reduce apoptosis, which would benefit diabetes. Here, we studied the role of P2Y6R in activation of AMPK in MIN6 mouse pancreatic β-cells and insulin secretion. Treatment with a potent P2Y6R dinucleotide agonist MRS2957 (500nM) activated AMPK, which was blocked by P2Y6R-selective antagonist MRS2578. Also, MRS2957 induced phosphorylation of acetyl-coenzyme A carboxylase (ACC), a marker of AMPK activity. Calcium chelator BAPTA-AM, calmodulin-dependent protein kinase kinase (CaMKK) inhibitor STO-069 and IP3 receptor antagonist 2-APB attenuated P2Y6R-mediated AMPK phosphorylation revealing involvement of intracellular Ca(2+) pathways. P2Y6R agonist induced insulin secretion at high glucose, which was reduced by AMPK siRNA. Thus, P2Y6R has a crucial role in β-cell function, suggesting its potential as a therapeutic target in diabetes.

Inhibition of ATP citrate lyase induces an anticancer effect via reactive oxygen species: AMPK as a predictive biomarker for therapeutic impact

De novo lipogenesis is activated in most cancers. Inhibition of ATP citrate lyase (ACLY), the enzyme that catalyzes the first step of de novo lipogenesis, leads to growth suppression and apoptosis in a subset of human cancer cells. Herein, we found that ACLY depletion increases the level of intracellular reactive oxygen species (ROS), whereas addition of an antioxidant reduced ROS and attenuated the anticancer effect. ACLY depletion or exogenous hydrogen peroxide induces phosphorylation of AMP-activated protein kinase (p-AMPK), a crucial regulator of lipid metabolism, independently of energy status. Analysis of various cancer cell lines revealed that cancer cells with a higher susceptibility to ACLY depletion have lower levels of basal ROS and p-AMPK. Mitochondrial-deficient ρ(0) cells retained high levels of ROS and p-AMPK and were resistant to ACLY depletion, whereas the replenishment of normal mitochondrial DNA reduced the levels of ROS and p-AMPK and restored the sensitivity to ACLY depletion, indicating that low basal levels of mitochondrial ROS are critical for the anticancer effect of ACLY depletion. Finally, p-AMPK levels were significantly correlated to the levels of oxidative DNA damage in colon cancer tissues, suggesting that p-AMPK reflects cellular ROS levels in vitro and in vivo. Together, these data suggest that ACLY inhibition exerts an anticancer effect via increased ROS, and p-AMPK could be a predictive biomarker for its therapeutic outcome.

Mitochondrial reactive oxygen species enhance AMP-activated protein kinase activation in the endothelium of patients with coronary artery disease and diabetes

The aim of the present study was to determine whether the endothelial dysfunction associated with CAD (coronary artery disease) and T2D (Type 2 diabetes mellitus) is concomitant with elevated mtROS (mitochondrial reactive oxygen species) production in the endothelium and establish if this, in turn, regulates the activity of endothelial AMPK (AMP-activated protein kinase). We investigated endothelial function, mtROS production and AMPK activation in saphenous veins from patients with advanced CAD. Endothelium-dependent vasodilation was impaired in patients with CAD and T2D relative to those with CAD alone. Levels of mitochondrial H(2)O(2) and activity of AMPK were significantly elevated in primary HSVECs (human saphenous vein endothelial cells) from patients with CAD and T2D compared with those from patients with CAD alone. Incubation with the mitochondria-targeted antioxidant, MitoQ(10) significantly reduced AMPK activity in HSVECs from patients with CAD and T2D but not in cells from patients with CAD alone. Elevated mtROS production in the endothelium of patients with CAD and T2D increases AMPK activation, supporting a role for the kinase in defence against oxidative stress. Further investigation is required to determine whether pharmacological activators of AMPK will prove beneficial in the attenuation of endothelial dysfunction in patients with CAD and T2D.

Inhibition of AMP-activated protein kinase accentuates lipopolysaccharide-induced lung endothelial barrier dysfunction and lung injury in vivo

The aim of this study was to determine the role of AMP-activated protein kinase (AMPK) in lipopolysaccharide (LPS)-induced lung endothelial barrier dysfunction and lung injury in vivo. Both cultured human pulmonary artery endothelial cells (HPAECs) and experimental animals [AMPK subunit α-deficient mice and wild-type (WT) control mice (C57BL/6J)] were used. In cultured HPAECs, LPS increased endothelial permeability in parallel with a decrease in AMPK activity. Consistent with this observation, AMPK activation with the potent AMPK activator 5-aminoimidazole-4-carboxamide-1-d-ribofuranoside (AICAR) attenuated LPS-induced endothelial hyperpermeability in vitro. Intratracheal administration of LPS (1 mg/kg) in WT mice reduced AMPK phosphorylation at Thr172 in lung tissue extracts, increased protein content and cell count in bronchial alveolar lavage fluid, and increased Evans Blue dye infiltration into the lung. These same attributes were similarly enhanced in AMPKα-knockout mice, compared with WT mice. Pretreatment with AICAR reduced these lung injury indicators in LPS-treated WT mice. AMPK activation with AICAR attenuated LPS-induced endothelial hyperpermeability by activating the Rac/Cdc42/PAK pathway, with concomitant inhibition of the Rho pathway, and decreased VE-cadherin phosphorylation at Tyr658. We conclude that AMPK activity supports normal endothelial barrier function and that LPS exposure inhibits AMPK, thereby contributing to endothelial barrier dysfunction and lung injury.

Astragalus polysaccharide stimulates glucose uptake in L6 myotubes through AMPK activation and AS160/TBC1D4 phosphorylation

AIM

To establish the mechanism responsible for the stimulation of glucose uptake by Astragalus polysaccharide (APS), extracted from Astragalus membranaceus Bunge, in L6 myotubes in vitro.

METHODS

APS-stimulated glucose uptake in L6 myotubes was measured using the 2-deoxy-[(3)H]-D-glucose method. The adenine nucleotide contents in the cells were measured by HPLC. The phosphorylation of AMP-activated protein kinase (AMPK) and Akt substrate of 160 kDa (AS160) was examined using Western blot analysis. The cells transfected with 4P mutant AS160 (AS160-4P) were constructed using gene transfer approach.

RESULTS

Treatment of L6 myotubes with APS (100-1600 μg/mL) significantly increased glucose uptake in time- and concentration-dependent manners. The maximal glucose uptake was reached in the cells treated with APS (400 μg/mL) for 36 h. The APS-stimulated glucose uptake was significantly attenuated by pretreatment with Compound C, a selective AMPK inhibitor or in the cells overexpressing AS160-4P. Treatment of L6 myotubes with APS strongly promoted the activation of AMPK. We further demonstrated that either Ca(2+)/calmodulin-dependent protein kinase kinase β (CaMKKβ) or liver kinase B1 (LKB1) mediated APS-induced activation of AMPK in L6 myotubes, and the increased cellular AMP: ATP ratio was also involved. Treatment of L6 myotubes with APS robustly enhanced the phosphorylation of AS160, which was significantly attenuated by pretreatment with Compound C.

CONCLUSION

Our results demonstrate that APS stimulates glucose uptake in L6 myotubes through the AMP-AMPK-AS160 pathway, which may contribute to its hypoglycemic effect.