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Kim N, Lee JO, Lee HJ, Lee SK, Moon JW, Kim SJ, Park SH, Kim HS. AMPKα2 translocates into the nucleus and interacts with hnRNP H: implications in metformin-mediated glucose uptake. Cell Signal 2014; 26:1800-6. [PMID: 24686086 DOI: 10.1016/j.cellsig.2014.03.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Accepted: 03/14/2014] [Indexed: 10/25/2022]
Abstract
Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a cytoplasmic protein that plays a critical role in the maintenance of energy homeostasis. However, its role in the nucleus is still largely unknown. Here, we showed that AMPKα2 translocated into the nucleus during muscle differentiation. We also showed that upon treatment with 5-aminoimidazole-4-carboxy-amide-1-d-ribofuranoside (AICAR), an AMPK activator, AMPK rapidly translocated into the nucleus in rat myoblast L6 cells. On the other hand, the AMPKα2 phosphorylation-defective mutant did not translocate into the nucleus. Knockdown of AMPKα2 suppressed the differentiation-induced expression of myogenin, a differentiation marker. A physiological AMPK activator, metformin, also induced the translocation of AMPKα2 into the nucleus. Both inhibition and knockdown of AMPKα2 suppressed metformin-mediated glucose uptake. In addition, AMPKα2 was shown to directly interact with the heterogeneous nuclear ribonucleoprotein H (hnRNP H). AICAR treatment increased the phosphorylation of hnRNP H. Metformin increased the interaction between AMPKα2 and hnRNP H in the nucleus. Knockdown of hnRNP H blocked metformin-induced glucose uptake. In summary, these results demonstrate that AMPKα2 translocates into the nucleus via phosphorylation, AMPKα2 interacts with and phosphorylates hnRNP H in the nucleus, and such a protein-protein interaction modulates metformin-mediated glucose uptake.
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Affiliation(s)
- Nami Kim
- Department of Anatomy, Korea University College of Medicine, Seoul, Republic of Korea
| | - Jung Ok Lee
- Department of Anatomy, Korea University College of Medicine, Seoul, Republic of Korea
| | - Hye Jeong Lee
- Department of Anatomy, Korea University College of Medicine, Seoul, Republic of Korea
| | - Soo Kyung Lee
- Department of Anatomy, Korea University College of Medicine, Seoul, Republic of Korea
| | - Ji Wook Moon
- Department of Anatomy, Korea University College of Medicine, Seoul, Republic of Korea
| | - Su Jin Kim
- Department of Anatomy, Korea University College of Medicine, Seoul, Republic of Korea
| | - Sun Hwa Park
- Department of Anatomy, Korea University College of Medicine, Seoul, Republic of Korea
| | - Hyeon Soo Kim
- Department of Anatomy, Korea University College of Medicine, Seoul, Republic of Korea.
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Chen S, Zhu P, Guo HM, Solis RS, Wang Y, Ma Y, Wang J, Gao J, Chen JM, Ge Y, Zhuang J, Li J. Alpha1 catalytic subunit of AMPK modulates contractile function of cardiomyocytes through phosphorylation of troponin I. Life Sci 2014; 98:75-82. [PMID: 24447627 PMCID: PMC4777330 DOI: 10.1016/j.lfs.2014.01.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2013] [Revised: 12/16/2013] [Accepted: 01/06/2014] [Indexed: 11/17/2022]
Abstract
AIMS The specific role of AMPKα1 or AMPKα2 in mediating cardiomyocyte contractile function remains elusive. The present study investigated how AMPK activation modulates the contractility of isolated cardiomyocytes. MAIN METHODS Mechanical properties and intracellular Ca(2+) properties were measured in isolated cardiomyocytes. The stress signaling was evaluated using western blot and immunoprecipitation analysis. KEY FINDINGS AMPK activator, A-769662 induced maximal velocity of shortening (+dL/dt) and relengthening (-dL/dt), peak height and peak shortening (PS) amplitude in both WT and AMPKα2 KO cardiomyocytes, but did not affect time-to-90% relengthening (TR90). AMPK KD cardiomyocytes demonstrated contractile dysfunction compared with cardiomyocytes from WT and AMPKα2 KO hearts. However, the rise of intracellular Ca(2+) levels as well as intracellular ATP levels has no significant difference among WT, AMPKα2 KO and AMPK KD groups with and without the presence of A-769662. Besides, WT, AMPKα2 KO and AMPK KD group displayed a phosphorylated AMPK and downstream acetyl-CoA carboxylase (ACC) phosphorylation. Interestingly, A-769662 also triggered troponin I (cTnI) phosphorylation at Ser(149) site which is related to contractility of cardiomyocytes. Furthermore, the immunoprecipitation analysis revealed that AMPKα1 of cardiomyocytes was phosphorylated by A-769662. SIGNIFICANCE This is the first study illustrating that activation of AMPK plays a significant role in mediating the contractile function of cardiomyocytes using transgenic animal models. AMPK activator facilitates the contractility of cardiomyocytes via activating AMPKα1 catalytic subunit. The phosphorylation of cTnI by AMPK could be a factor attributing to the regulation of contractility of cardiomyocytes.
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Affiliation(s)
- Si Chen
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University at Buffalo - State University of New York, Buffalo, NY, United States
| | - Ping Zhu
- Department of Cardiovascular Surgery, Guangdong Cardiovascular Institute, Guangdong General Hospital, Guangdong Academy of Medical Sciences, Guangzhou, China
| | - Hui-Ming Guo
- Department of Cardiovascular Surgery, Guangdong Cardiovascular Institute, Guangdong General Hospital, Guangdong Academy of Medical Sciences, Guangzhou, China
| | - Raquel Sancho Solis
- Department of Cell and Regenerative Biology, School of Medicine and Public Health, University of Wisconsin - Madison, WI, United States
| | - Yanqing Wang
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University at Buffalo - State University of New York, Buffalo, NY, United States
| | - Yina Ma
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University at Buffalo - State University of New York, Buffalo, NY, United States
| | - Jinli Wang
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University at Buffalo - State University of New York, Buffalo, NY, United States
| | - Junjie Gao
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University at Buffalo - State University of New York, Buffalo, NY, United States
| | - Ji-Mei Chen
- Department of Cardiovascular Surgery, Guangdong Cardiovascular Institute, Guangdong General Hospital, Guangdong Academy of Medical Sciences, Guangzhou, China
| | - Ying Ge
- Department of Cell and Regenerative Biology, School of Medicine and Public Health, University of Wisconsin - Madison, WI, United States
| | - Jian Zhuang
- Department of Cardiovascular Surgery, Guangdong Cardiovascular Institute, Guangdong General Hospital, Guangdong Academy of Medical Sciences, Guangzhou, China.
| | - Ji Li
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University at Buffalo - State University of New York, Buffalo, NY, United States.
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Harmel E, Grenier E, Bendjoudi Ouadda A, El Chebly M, Ziv E, Beaulieu JF, Sané A, Spahis S, Laville M, Levy E. AMPK in the small intestine in normal and pathophysiological conditions. Endocrinology 2014; 155:873-88. [PMID: 24424053 DOI: 10.1210/en.2013-1750] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The role of AMPK in regulating energy storage and depletion remains unexplored in the intestine. This study will to define its status, composition, regulation and lipid function, as well as to examine the impact of insulin resistance and type 2 diabetes on intestinal AMPK activation, insulin sensitivity, and lipid metabolism. Caco-2/15 cells and Psammomys obesus (P. obesus) animal models were experimented. We showed the predominance of AMPKα1 and the prevalence of α1/β2/γ1 heterotrimer in Caco-2/15 cells. The activation of AMPK by 5-aminoimidazole-4-carboxamide ribonucleoside and metformin resulted in increased phospho(p)-ACC. However, the down-regulation of p-AMPK by compound C and high glucose lowered p-ACC without affecting 3-hydroxy-3-methylglutaryl-coenzyme A reductase. Administration of metformin to P. obesus with insulin resistance and type 2 diabetes led to 1) an up-regulation of intestinal AMPK signaling pathway typified by ascending p-AMPKα(-Thr172); 2) a reduction in ACC activity; 3) an elevation of carnitine palmitoyltransferase 1; 4) a trend of increase in insulin sensitivity portrayed by augmentation of p-Akt and phospho-glycogen synthetase kinase 3β; 5) a reduced phosphorylation of p38-MAPK and ERK1/2; and 6) a decrease in diabetic dyslipidemia following lowering of intracellular events that govern lipoprotein assembly. These data suggest that AMPK fulfills key functions in metabolic processes in the small intestine.
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Affiliation(s)
- Elodie Harmel
- Research Center (E.H., E.G., A.B.O., M.E.C., A.S., S.S., E.L.), Sainte-Justine MUHC, Montreal, Quebec, Canada, H3T 1C5; Department of Nutrition (E.H., E.G., S.S., E.L.) and Department of Biochemistry (M.E.C.), Université de Montréal, Montreal, Quebec, Canada, H3T 1C5; Diabetes Unit (E.Z.), Division of Internal Medicine, Hadassah Ein Kerem Hospital, 120 Jerusalem, Israel-91; Canadian Institutes for Health Research Team on the Digestive Epithelium (J.F.B., E.L.), Department of Anatomy and Cellular Biology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Quebec, Canada, J1H 5N4; and CRNH Rhône-Alpes (E.H., M.L.), Université Lyon 1, Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche 1060, CENS, Centre Hospitalier Lyon-Sud, F-69310 Pierre Bénite, France
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Sinnett SE, Brenman JE. Past strategies and future directions for identifying AMP-activated protein kinase (AMPK) modulators. Pharmacol Ther 2014; 143:111-8. [PMID: 24583089 DOI: 10.1016/j.pharmthera.2014.02.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Accepted: 02/13/2014] [Indexed: 12/30/2022]
Abstract
AMP-activated protein kinase (AMPK) is a promising therapeutic target for cancer, type II diabetes, and other illnesses characterized by abnormal energy utilization. During the last decade, numerous labs have published a range of methods for identifying novel AMPK modulators. The current understanding of AMPK structure and regulation, however, has propelled a paradigm shift in which many researchers now consider ADP to be an additional regulatory nucleotide of AMPK. How can the AMPK community apply this new understanding of AMPK signaling to translational research? Recent insights into AMPK structure, regulation, and holoenzyme-sensitive signaling may provide the hindsight needed to clearly evaluate the strengths and weaknesses of past AMPK drug discovery efforts. Improving future strategies for AMPK drug discovery will require pairing the current understanding of AMPK signaling with improved experimental designs.
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Affiliation(s)
- Sarah E Sinnett
- Neurobiology Curriculum, University of North Carolina at Chapel Hill (UNC), United States
| | - Jay E Brenman
- UNC Neuroscience Center, United States; Department of Cell Biology and Physiology, UNC, United States.
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105
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Yamada E, Bastie CC. Disruption of Fyn SH3 domain interaction with a proline-rich motif in liver kinase B1 results in activation of AMP-activated protein kinase. PLoS One 2014; 9:e89604. [PMID: 24586906 PMCID: PMC3934923 DOI: 10.1371/journal.pone.0089604] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Accepted: 01/22/2014] [Indexed: 11/19/2022] Open
Abstract
Fyn-deficient mice display increased AMP-activated Protein Kinase (AMPK) activity as a result of Fyn-dependent regulation of Liver Kinase B1 (LKB1) in skeletal muscle. Mutation of Fyn-specific tyrosine sites in LKB1 results in LKB1 export into the cytoplasm and increased AMPK activation site phosphorylation. This study characterizes the structural elements responsible for the physical interaction between Fyn and LKB1. Effects of point mutations in the Fyn SH2/SH3 domains and in the LKB1 proline-rich motif on 1) Fyn and LKB1 binding, 2) LKB1 subcellular localization and 3) AMPK phosphorylation were investigated in C2C12 muscle cells. Additionally, novel LKB1 proline-rich motif mimicking cell permeable peptides were generated to disrupt Fyn/LKB1 binding and investigate the consequences on AMPK activity in both C2C12 cells and mouse skeletal muscle. Mutation of either Fyn SH3 domain or the proline-rich motif of LKB1 resulted in the disruption of Fyn/LKB1 binding, re-localization of 70% of LKB1 signal in the cytoplasm and a 2-fold increase in AMPK phosphorylation. In vivo disruption of the Fyn/LKB1 interaction using LKB1 proline-rich motif mimicking cell permeable peptides recapitulated Fyn pharmacological inhibition. We have pinpointed the structural elements within Fyn and LKB1 that are responsible for their binding, demonstrating the functionality of this interaction in regulating AMPK activity.
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Affiliation(s)
- Eijiro Yamada
- Diabetes Research and Training Center, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Department of Medicine and Molecular Science, Gunma University Graduate School of Medicine, Gunma, Japan
| | - Claire C. Bastie
- Diabetes Research and Training Center, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Division Metabolic and Vascular Health, Warwick Medical School, University of Warwick, Coventry, United Kingdom
- * E-mail:
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106
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Buyandelger B, Mansfield C, Knöll R. Mechano-signaling in heart failure. Pflugers Arch 2014; 466:1093-9. [PMID: 24531746 PMCID: PMC4033803 DOI: 10.1007/s00424-014-1468-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Revised: 01/29/2014] [Accepted: 01/30/2014] [Indexed: 02/07/2023]
Abstract
Mechanosensation and mechanotransduction are fundamental aspects of biology, but the link between physical stimuli and biological responses remains not well understood. The perception of mechanical stimuli, their conversion into biochemical signals, and the transmission of these signals are particularly important for dynamic organs such as the heart. Various concepts have been introduced to explain mechanosensation at the molecular level, including effects on signalosomes, tensegrity, or direct activation (or inactivation) of enzymes. Striated muscles, including cardiac myocytes, differ from other cells in that they contain sarcomeres which are essential for the generation of forces and which play additional roles in mechanosensation. The majority of cardiomyopathy causing candidate genes encode structural proteins among which titin probably is the most important one. Due to its elastic elements, titin is a length sensor and also plays a role as a tension sensor (i.e., stress sensation). The recent discovery of titin mutations being a major cause of dilated cardiomyopathy (DCM) also underpins the importance of mechanosensation and mechanotransduction in the pathogenesis of heart failure. Here, we focus on sarcomere-related mechanisms, discuss recent findings, and provide a link to cardiomyopathy and associated heart failure.
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Affiliation(s)
- Byambajav Buyandelger
- Imperial College, British Heart Foundation-Centre for Research Excellence, National Heart and Lung Institute, Imperial Centre for Translational and Experimental Medicine, Hammersmith Campus, Du Cane Road, London, W12 0NN, UK
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Anil TM, Harish C, Lakshmi MN, Harsha K, Onkaramurthy M, Sathish Kumar V, Shree N, Geetha V, Balamurali GV, Gopala AS, Madhusudhan Reddy B, Govind MK, Anup MO, Moolemath Y, Venkataranganna MV, Jagannath MR, Somesh BP. CNX-012-570, a direct AMPK activator provides strong glycemic and lipid control along with significant reduction in body weight; studies from both diet-induced obese mice and db/db mice models. Cardiovasc Diabetol 2014; 13:27. [PMID: 24460834 PMCID: PMC3906767 DOI: 10.1186/1475-2840-13-27] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Accepted: 01/24/2014] [Indexed: 12/16/2022] Open
Abstract
Objectives AMP activated protein kinase (AMPK) regulates the coordination of anabolic and catabolic processes and is an attractive therapeutic target for T2DM, obesity and metabolic syndrome. We report the anti-hyperglycemic and anti-hyperlipidemic effects of CNX-012-570 is an orally bioavailable small molecule (molecular weight of 530 Daltons) that directly activates AMPK in DIO and db/db animal models of diabetes. Methods Activity and efficacy of the compound was tested in cell based as well as cell free systems in vitro. Male C57BL/6 mice fed with high fat diet (HFD) were assigned to either vehicle or CNX-012-570 (3 mg/kg, orally once a day) for 8 weeks (n = 8). Genetically diabetic db/db mice on chow diet were dosed with vehicle control or CNX-012-570 (2.5 mg/kg, orally once a day) for 6 weeks (n = 8). Results CNX-012-570 is a highly potent and orally bioavailable compound activating AMPK in both cell and cell free systems. It inhibits lipolysis (33%) and gluconeogenesis (28%) in 3T3L1 cells and rat primary hepatocytes respectively. The efficacy of the molecule was translated to both DIO and db/db animal models of diabetes. CNX-012-570 has reduced fasting blood glucose levels by 14%, body weight by 24% and fasting serum triglycerides (TG) by 24%. CNX-012-570 showed a 22% reduction in fed serum cholesterol levels and 19% increase in HDL levels. In db/db mice model, CNX-012-570 has shown 18% decrease in fed glucose and 32% decrease in fasting glucose with a 2.57% reduction in absolute HbA1c. Decrease in serum insulin and glucose AUC indicates the increased insulin sensitivity. Body weight was reduced by 13% with increased browning of adipose tissue and decreased inguinal and mesenteric fat mass. There was significant reduction in liver TG and liver total cholesterol. Conclusions CNX-012-570 has the potential to control hyperglycemia and hyperlipidemia. It also reduces body weight gain with an additional benefit of minimizing cardiovascular risks in diabetics.
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108
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Lin D, He H, Ji H, Willis J, Willard L, Jiang Y, Medeiros DM, Wark L, Han J, Liu Y, Lu B. Wolfberries potentiate mitophagy and enhance mitochondrial biogenesis leading to prevention of hepatic steatosis in obese mice: the role of AMP-activated protein kinase α2 subunit. Mol Nutr Food Res 2014; 58:1005-15. [PMID: 24449471 DOI: 10.1002/mnfr.201300186] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Revised: 11/10/2013] [Accepted: 11/14/2013] [Indexed: 01/22/2023]
Abstract
SCOPE The aim of this study is to investigate whether AMP-activated protein kinase α2 (AMPKα2) is essential for wolfberry's protective effects on mitochondrial dysfunction and subsequent hepatic steatosis in mice. METHODS AND RESULTS Six-week-old male AMPKα2 knockout mice and genetic background C57BL/6J (B6) mice were fed a control, high-fat diet (HD, 45% (kilocalorie) fat), and/or HD with 5% (kilocalarie) wolfberry diets for 18 wk. At termination, blood and liver tissues were sampled for analysis by ELISA, HPLC, microscopy, real-time PCR, and Western blot. HD lowered hepatic lutein and zeaxanthin contents, inhibited protein expression of β,β-carotene 9',10'-oxygenase 2 (BCO2) and heat shock protein 60 in mitochondria, increased reactive oxygen species level, and suppressed mitophagy and mitochondrial biogenesis as determined by accumulation of p62, inhibited phosphorylation of Unc-51-like kinase 1 on Ser555, and declined expression of peroxisome proliferator-activated receptor γ coactivator 1 α, resulting in hepatic steatosis in B6 and knockout mice. Dietary wolfberry elevated the xanthophyll concentrations and enhanced expression of BCO2 and heat shock protein 60, attenuated mitochondrial oxidative stress, activated AMPKα2, potentiated mitophagy and mitochondrial biogenesis, and enhanced lipid oxidation and secretion in the liver of B6 mice. CONCLUSION Dietary wolfberry selectively activated AMPKα2, which resulted in enhanced mitochondrial biogenesis and potentiated mitophagy, leading to the prevention of hepatic steatosis in obese mice.
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Affiliation(s)
- Dingbo Lin
- Department of Nutritional Sciences, Oklahoma State University, Stillwater, OK, USA
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109
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Hernández JS, Barreto-Torres G, Kuznetsov AV, Khuchua Z, Javadov S. Crosstalk between AMPK activation and angiotensin II-induced hypertrophy in cardiomyocytes: the role of mitochondria. J Cell Mol Med 2014; 18:709-20. [PMID: 24444314 PMCID: PMC3981893 DOI: 10.1111/jcmm.12220] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Accepted: 11/28/2013] [Indexed: 12/25/2022] Open
Abstract
AMP-kinase (AMPK) activation reduces cardiac hypertrophy, although underlying molecular mechanisms remain unclear. In this study, we elucidated the anti-hypertrophic action of metformin, specifically, the role of the AMPK/eNOS/p53 pathway. H9c2 rat cardiomyocytes were treated with angiotensin II (AngII) for 24 hrs in the presence or absence of metformin (AMPK agonist), losartan [AngII type 1 receptor (AT1R) blocker], Nω-nitro-L-arginine methyl ester (L-NAME, pan-NOS inhibitor), splitomicin (SIRT1 inhibitor) or pifithrin-α (p53 inhibitor). Results showed that treatment with metformin significantly attenuated AngII-induced cell hypertrophy and death. Metformin attenuated AngII-induced activation (cleavage) of caspase 3, Bcl-2 down-regulation and p53 up-regulation. It also reduced AngII-induced AT1R up-regulation by 30% (P < 0.05) and enhanced AMPK phosphorylation by 99% (P < 0.01) and P-eNOS levels by 3.3-fold (P < 0.01). Likewise, losartan reduced AT1R up-regulation and enhanced AMPK phosphorylation by 54% (P < 0.05). The AMPK inhibitor, compound C, prevented AT1R down-regulation, indicating that metformin mediated its effects via AMPK activation. Beneficial effects of metformin and losartan converged on mitochondria that demonstrated high membrane potential (Δψm) and low permeability transition pore opening. Thus, this study demonstrates that the anti-hypertrophic effects of metformin are associated with AMPK-induced AT1R down-regulation and prevention of mitochondrial dysfunction through the SIRT1/eNOS/p53 pathway.
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Affiliation(s)
- Jessica Soto Hernández
- Department of Physiology, School of Medicine, University of Puerto Rico, San Juan, PR, USA
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Yang W, Park IJ, Yun H, Im DU, Ock S, Kim J, Seo SM, Shin HY, Viollet B, Kang I, Choe W, Kim SS, Ha J. AMP-activated protein kinase α2 and E2F1 transcription factor mediate doxorubicin-induced cytotoxicity by forming a positive signal loop in mouse embryonic fibroblasts and non-carcinoma cells. J Biol Chem 2014; 289:4839-52. [PMID: 24398673 DOI: 10.1074/jbc.m113.496315] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Doxorubicin is one of the most widely used anti-cancer drugs, but its clinical application is compromised by severe adverse effects in different organs including cardiotoxicity. In the present study we explored mechanisms of doxorubicin-induced cytotoxicity by revealing a novel role for the AMP-activated protein kinase α2 (AMPKα2) in mouse embryonic fibroblasts (MEFs). Doxorubicin robustly induced the expression of AMPKα2 in MEFs but slightly reduced AMPKα1 expression. Our data support the previous notion that AMPKα1 harbors survival properties under doxorubicin treatment. In contrast, analyses of Ampkα2(-/-) MEFs, gene knockdown of AMPKα2 by shRNA, and inhibition of AMPKα2 activity with an AMPK inhibitor indicated that AMPKα2 functions as a pro-apoptotic molecule under doxorubicin treatment. Doxorubicin induced AMPKα2 at the transcription level via E2F1, a transcription factor that regulates apoptosis in response to DNA damage. E2F1 directly transactivated the Ampkα2 gene promoter. In turn, AMPKα2 significantly contributed to stabilization and activation of E2F1 by doxorubicin, forming a positive signal amplification loop. AMPKα2 directly interacted with and phosphorylated E2F1. This signal loop was also detected in H9c2, C2C12, and ECV (human epithelial cells) cells as well as mouse liver under doxorubicin treatment. Resveratrol, which has been suggested to attenuate doxorubicin-induced cytotoxicity, significantly blocked induction of AMPKα2 and E2F1 by doxorubicin, leading to protection of these cells. This signal loop appears to be non-carcinoma-specific because AMPKα2 was not induced by doxorubicin in five different tested cancer cell lines. These results suggest that AMPKα2 may serve as a novel target for alleviating the cytotoxicity of doxorubicin.
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Affiliation(s)
- Wookyeom Yang
- From the Department of Biochemistry and Molecular Biology, Medical Research Center and Biomedical Science Institute, School of Medicine, Kyung Hee University, Seoul 130-701, Republic of Korea
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Saks V, Schlattner U, Tokarska-Schlattner M, Wallimann T, Bagur R, Zorman S, Pelosse M, Santos PD, Boucher F, Kaambre T, Guzun R. Systems Level Regulation of Cardiac Energy Fluxes Via Metabolic Cycles: Role of Creatine, Phosphotransfer Pathways, and AMPK Signaling. SYSTEMS BIOLOGY OF METABOLIC AND SIGNALING NETWORKS 2014. [DOI: 10.1007/978-3-642-38505-6_11] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Antineuroinflammatory effects of lycopene via activation of adenosine monophosphate-activated protein kinase-α1/heme oxygenase-1 pathways. Neurobiol Aging 2014; 35:191-202. [DOI: 10.1016/j.neurobiolaging.2013.06.020] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Revised: 05/21/2013] [Accepted: 06/30/2013] [Indexed: 12/21/2022]
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Abdulrahman RM, Boon MR, Sips HCM, Guigas B, Rensen PCN, Smit JWA, Hovens GCJ. Impact of Metformin and compound C on NIS expression and iodine uptake in vitro and in vivo: a role for CRE in AMPK modulation of thyroid function. Thyroid 2014; 24:78-87. [PMID: 23819433 DOI: 10.1089/thy.2013.0041] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
BACKGROUND Although adenosine monophosphate activated protein kinase (AMPK) plays a crucial role in energy metabolism, a direct effect of AMPK modulation on thyroid function has only recently been reported, and much of its function in the thyroid is currently unknown. The aim of this study was to investigate the mechanism of AMPK modulation in iodide uptake. Furthermore, we wanted to investigate the potential of the AMPK inhibitor compound C as an enhancer of iodide uptake by thyrocytes. METHODS The in vitro and in vivo effects of AMPK modulation on sodium-iodide symporter (NIS) protein levels and iodide uptake were examined in follicular rat thyroid cell-line cells and C57Bl6/J mice. Activation of AMPK by metformin resulted in a strong reduction of iodide uptake (up to sixfold with 5 mM metformin after 96 h) and NIS protein levels in vitro, whereas AMPK inhibition by compound C not only stimulated iodide uptake but also enhanced NIS protein levels both in vitro (up to sevenfold with 1 μM compound C after 96 h) and in vivo (1.5-fold after daily injections with 20 mg/kg for 4 days). We investigated the regulation of NIS expression by AMPK using a range of promoter constructs consisting of either the NIS promoter or isolated CRE (cAMP response element) and NF-κB elements, which are present within the NIS promoter. RESULTS Metformin reduced NIS promoter activity (0.6-fold of control), whereas compound C stimulated its activity (3.4-fold) after 4 days. This largely coincides with CRE activation (0.6- and 3.0-fold). These experiments show that AMPK exerts its effects on iodide uptake, at least partly, through the CRE element in the NIS promoter. Furthermore, we have used AMPK-alpha1 knockout mice to determine the long-term effects of AMPK inhibition without chemical compounds. These mice have a less active thyroid, as shown by reduced colloid volume and reduced responsiveness to thyrotropin. CONCLUSION NIS expression and iodine uptake in thyrocytes can be modulated by metformin and compound C. These compounds exert their effect by modulation of AMPK, which, in turn, regulates the activation of the CRE element in the NIS promoter. Overall, this suggests that the use of AMPK modulating compounds may be useful for the enhancement of iodide uptake by thyrocytes, which could be useful for the treatment of thyroid cancer patients with radioactive iodine.
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Affiliation(s)
- Randa M Abdulrahman
- 1 Department of Endocrinology and Metabolic Diseases, University Medical Center , Leiden, The Netherlands
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Ramamurthy S, Chang E, Cao Y, Zhu J, Ronnett GV. AMPK activation regulates neuronal structure in developing hippocampal neurons. Neuroscience 2013; 259:13-24. [PMID: 24295634 DOI: 10.1016/j.neuroscience.2013.11.048] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Revised: 11/21/2013] [Accepted: 11/23/2013] [Indexed: 12/25/2022]
Abstract
AMP-activated protein kinase (AMPK) is a serine/threonine kinase that functions as a cellular and whole organism energy sensor to regulate ATP-consuming (anabolic) and ATP-generating (catabolic) pathways. The heterotrimeric AMPK complex consists of a catalytic α-subunit, regulatory β-subunit, and an AMP/ATP-binding γ-subunit. Several alternate isoforms exist for each subunit (α1, α2, β1, β2, γ1, γ2 and γ3). However, little is known of the expression pattern or function of the individual catalytic complexes in regulating neuronal structure. In this study, we examined the role of AMPK subunits in differentiating hippocampal neurons. We found that during development, the expression of AMPK subunits increase and that activation of AMPK by energetic stress inhibits neuronal development at multiple stages, not only during axon outgrowth, but also during dendrite growth and arborization. The presence of a single functional AMPK catalytic complex was sufficient to mediate these inhibitory effects of energetic stress. Activation of AMPK mediates these effects by suppressing both the mTOR and Akt signaling pathways. These findings demonstrate that the energy-sensing AMPK pathway regulates neuronal structure in distinct regions of developing neurons at multiple stages of development.
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Affiliation(s)
- S Ramamurthy
- Department of Neuroscience, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA; Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA
| | - E Chang
- Department of Neuroscience, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA; Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA
| | - Y Cao
- Department of Neuroscience, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA; Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA
| | - J Zhu
- Department of Neuroscience, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA; Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA
| | - G V Ronnett
- Department of Neuroscience, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA; Department of Neurology, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA; Department of Biological Chemistry, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA; Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, 855 N Wolfe Street, Baltimore, MD 21205, USA; Daegu Gyeongbuk Institute of Science and Technology, Daegu, Republic of Korea.
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Vidal AP, Andrade BM, Vaisman F, Cazarin J, Pinto LFR, Breitenbach MMD, Corbo R, Caroli-Bottino A, Soares F, Vaisman M, Carvalho DP. AMP-activated protein kinase signaling is upregulated in papillary thyroid cancer. Eur J Endocrinol 2013; 169:521-8. [PMID: 23904275 DOI: 10.1530/eje-13-0284] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
UNLABELLED AMP-activated protein kinase (AMPK) is activated by the depletion in cellular energy levels and allows adaptive changes in cell metabolism and cell survival. Recently, our group described that AMPK plays an important role in the regulation of iodide and glucose uptake in thyroid cells. However, AMPK signaling pathway in human thyroid carcinomas has not been investigated so far. OBJECTIVE To evaluate the expression and activity of AMPK in papillary thyroid carcinomas. METHODS We examined total and phosphorylated AMPK (tAMPK and pAMPK) and phosphorylated acetyl-CoA-carboxylase (pACC) expressions through imunohistochemistry, using a tissue microarray block composed of 73 papillary thyroid carcinomas (PAP CA) or microcarcinomas (PAP MCA) and six adenoma (AD) samples from patients followed at the Federal University Hospital. The expression levels were compared with the non-neoplastic tissues from the same patient. Two different pathologists analyzed the samples and attributed scores of staining intensity and the proportion of stained cells. A total index was obtained by multiplying the values of intensity and the proportion of stained cells (INTxPROP). RESULTS tAMPK, pAMPK, and pACC showed a predominant cytoplasmic staining in papillary carcinomas, adenomas, and non-neoplastic thyroid tissues. However, the intensity and the proportion of stained cells were higher in carcinomas, so that a significant increase was found in the INTxPROP score both in PAP CA and PAP MCA, when compared with their respective controls. CONCLUSION Our results show unequivocally that AMPK pathway is highly activated in papillary thyroid carcinomas; however, more studies are necessary to understand the pathophysiological significance of AMPK activation in thyroid carcinogenesis.
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Affiliation(s)
- Ana Paula Vidal
- Serviço de Anatomia Patológica do Hospital Universitário Clementino Fraga Filho, Universidade Federal do Rio de Janeiro, Avenida Rodolpho Paulo Rocco 255, Ilha do Fundão, Rio de Janeiro, Brazil
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Localisation of AMPK γ subunits in cardiac and skeletal muscles. J Muscle Res Cell Motil 2013; 34:369-78. [PMID: 24037260 PMCID: PMC3853370 DOI: 10.1007/s10974-013-9359-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Accepted: 08/30/2013] [Indexed: 11/22/2022]
Abstract
The trimeric protein AMP-activated protein kinase (AMPK) is an important sensor of energetic status and cellular stress, and mutations in genes encoding two of the regulatory γ subunits cause inherited disorders of either cardiac or skeletal muscle. AMPKγ2 mutations cause hypertrophic cardiomyopathy with glycogen deposition and conduction abnormalities; mutations in AMPKγ3 result in increased skeletal muscle glycogen. In order to gain further insight into the roles of the different γ subunits in muscle and into possible disease mechanisms, we localised the γ2 and γ3 subunits, along with the more abundant γ1 subunit, by immunofluorescence in cardiomyocytes and skeletal muscle fibres. The predominant cardiac γ2 variant, γ2-3B, gave a striated pattern in cardiomyocytes, aligning with the Z-disk but with punctate staining similar to T-tubule (L-type Ca2+ channel) and sarcoplasmic reticulum (SERCA2) markers. In skeletal muscle fibres AMPKγ3 localises to the I band, presenting a uniform staining that flanks the Z-disk, also coinciding with the position of Ca2+ influx in these muscles. The localisation of γ2-3B- and γ3-containing AMPK suggests that these trimers may have similar functions in the different muscles. AMPK containing γ2-3B was detected in oxidative skeletal muscles which had low expression of γ3, confirming that these two regulatory subunits may be co-ordinately regulated in response to metabolic requirements. Compartmentalisation of AMPK complexes is most likely dependent on the regulatory γ subunit and this differential localisation may direct substrate selection and specify particular functional roles.
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Activation of the AMP-activated protein kinase reduces inflammatory nociception. THE JOURNAL OF PAIN 2013; 14:1330-40. [PMID: 23916727 DOI: 10.1016/j.jpain.2013.05.012] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Revised: 05/28/2013] [Accepted: 05/29/2013] [Indexed: 01/07/2023]
Abstract
UNLABELLED The activation of the adenosine monophosphate (AMP)-activated kinase (AMPK) has been associated with beneficial effects such as improvement of hyperglycemic states in diabetes as well as reduction of obesity and inflammatory processes. Recent studies provide evidence for a further role of AMPK in models of acute and neuropathic pain. In this study, we investigated the impact of AMPK on inflammatory nociception. Using 5-amino-1-β-d-ribofuranosyl-imidazole-4-carboxamide (AICAR) and metformin as AMPK activators, we observed anti-inflammatory and antinociceptive effects in 2 models of inflammatory nociception. The effects were similar to those observed with the standard analgesic ibuprofen. The mechanism appears to be based on regulation of the AMPKα2 subunit of the kinase because AMPKα2 knockout mice showed increased nociceptive responses that could not be reversed by the AMPK activators. On the molecular level, antinociceptive effects are at least partially mediated by reduced activation of different MAP-kinases in the spinal cord and a subsequent decrease in pain-relevant induction of c-fos, which constitutes a reliable marker of elevated activity in spinal cord neurons following peripheral noxious stimulation. In summary, our results indicate that activation of AMPKα2 might represent a novel therapeutic option for the treatment of inflammation-associated pain, providing analgesia with fewer unwanted side effects. PERSPECTIVE AMPK activation is associated with beneficial effects on diabetes and obesity. In addition, we have shown analgesic properties of pharmacologic AMPK activation in inflammatory nociception, indicating that AMPK might serve as a novel therapeutic target in pain with fewer unwanted side effects.
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Lu DY, Huang BR, Yeh WL, Lin HY, Huang SS, Liu YS, Kuo YH. Anti-neuroinflammatory Effect of a Novel Caffeamide Derivative, KS370G, in Microglial cells. Mol Neurobiol 2013; 48:863-74. [DOI: 10.1007/s12035-013-8474-y] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Accepted: 05/07/2013] [Indexed: 11/29/2022]
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Sid B, Verrax J, Calderon PB. Role of AMPK activation in oxidative cell damage: Implications for alcohol-induced liver disease. Biochem Pharmacol 2013; 86:200-9. [PMID: 23688501 DOI: 10.1016/j.bcp.2013.05.007] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2013] [Revised: 05/03/2013] [Accepted: 05/08/2013] [Indexed: 02/08/2023]
Abstract
Chronic alcohol consumption is a well-known risk factor for liver disease. Progression of alcohol-induced liver disease (ALD) is a multifactorial process that involves a number of genetic, nutritional and environmental factors. Experimental and clinical studies increasingly show that oxidative damage induced by ethanol contributes in many ways to the pathogenesis of alcohol hepatoxicity. Oxidative stress appears to activate AMP-activated protein kinase (AMPK) signaling system, which has emerged in recent years as a kinase that controls the redox-state and mitochondrial function. This review focuses on the most recent insights concerning the activation of AMPK by reactive oxygen species (ROS), and describes recent evidences supporting the hypothesis that AMPK signaling pathways play an important role in promoting cell viability under conditions of oxidative stress, such as during alcohol exposure. We suggest that AMPK activation by ROS can promote cell survival by inducing autophagy, mitochondrial biogenesis and expression of genes involved in antioxidant defense. Hence, increased intracellular concentrations of ROS may represent a general mechanism for enhancement of AMPK-mediated cellular adaptation, including maintenance of redox homeostasis. On the other hand, AMPK inhibition in the liver by ethanol appears to play a key role in the development of steatosis induced by chronic alcohol consumption. Although more studies are needed to assess the functions of AMPK during oxidative stress, AMPK may be a possible therapeutic target in the particular case of alcohol-induced liver disease.
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Affiliation(s)
- Brice Sid
- Université Catholique de Louvain, Louvain Drug Research Institute, Toxicology and Cancer Biology Research Group GTOX, Brussels, Belgium
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120
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Iseli TJ, Turner N, Zeng XY, Cooney GJ, Kraegen EW, Yao S, Ye Y, James DE, Ye JM. Activation of AMPK by bitter melon triterpenoids involves CaMKKβ. PLoS One 2013; 8:e62309. [PMID: 23638033 PMCID: PMC3636144 DOI: 10.1371/journal.pone.0062309] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2012] [Accepted: 03/19/2013] [Indexed: 01/11/2023] Open
Abstract
We recently showed that bitter melon-derived triterpenoids (BMTs) activate AMPK and increase GLUT4 translocation to the plasma membrane in vitro, and improve glucose disposal in insulin resistant models in vivo. Here we interrogated the mechanism by which these novel compounds activate AMPK, a leading anti-diabetic drug target. BMTs did not activate AMPK directly in an allosteric manner as AMP or the Abbott compound (A-769662) does, nor did they activate AMPK by inhibiting cellular respiration like many commonly used anti-diabetic medications. BMTs increased AMPK activity in both L6 myotubes and LKB1-deficient HeLa cells by 20–35%. Incubation with the CaMKKβ inhibitor, STO-609, completely attenuated this effect suggesting a key role for CaMKKβ in this activation. Incubation of L6 myotubes with the calcium chelator EGTA-AM did not alter this activation suggesting that the BMT-dependent activation was Ca2+-independent. We therefore propose that CaMKKβ is a key upstream kinase for BMT-induced activation of AMPK.
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Affiliation(s)
- Tristan J. Iseli
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Sydney, Australia
| | - Nigel Turner
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Sydney, Australia
| | - Xiao-Yi Zeng
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Sydney, Australia
- Health Innovations Research Institute and School of Health Sciences, RMIT University, Melbourne, Australia
| | - Gregory J. Cooney
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Sydney, Australia
| | - Edward W. Kraegen
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Sydney, Australia
| | - Sheng Yao
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Yang Ye
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - David E. James
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Sydney, Australia
| | - Ji-Ming Ye
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Sydney, Australia
- Health Innovations Research Institute and School of Health Sciences, RMIT University, Melbourne, Australia
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
- * E-mail:
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121
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Bijland S, Mancini SJ, Salt IP. Role of AMP-activated protein kinase in adipose tissue metabolism and inflammation. Clin Sci (Lond) 2013; 124:491-507. [PMID: 23298225 DOI: 10.1042/cs20120536] [Citation(s) in RCA: 225] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
AMPK (AMP-activated protein kinase) is a key regulator of cellular and whole-body energy balance. AMPK phosphorylates and regulates many proteins concerned with nutrient metabolism, largely acting to suppress anabolic ATP-consuming pathways while stimulating catabolic ATP-generating pathways. This has led to considerable interest in AMPK as a therapeutic target for the metabolic dysfunction observed in obesity and insulin resistance. The role of AMPK in skeletal muscle and the liver has been extensively studied, such that AMPK has been demonstrated to inhibit synthesis of fatty acids, cholesterol and isoprenoids, hepatic gluconeogenesis and translation while increasing fatty acid oxidation, muscle glucose transport, mitochondrial biogenesis and caloric intake. The role of AMPK in the other principal metabolic and insulin-sensitive tissue, adipose, remains poorly characterized in comparison, yet increasing evidence supports an important role for AMPK in adipose tissue function. Obesity is characterized by hypertrophy of adipocytes and the development of a chronic sub-clinical pro-inflammatory environment in adipose tissue, leading to increased infiltration of immune cells. This combination of dysfunctional hypertrophic adipocytes and a pro-inflammatory environment contributes to insulin resistance and the development of Type 2 diabetes. Exciting recent studies indicate that AMPK may not only influence metabolism in adipocytes, but also act to suppress this pro-inflammatory environment, such that targeting AMPK in adipose tissue may be desirable to normalize adipose dysfunction and inflammation. In the present review, we discuss the role of AMPK in adipose tissue, focussing on the regulation of carbohydrate and lipid metabolism, adipogenesis and pro-inflammatory pathways in physiological and pathophysiological conditions.
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Affiliation(s)
- Silvia Bijland
- Institute of Cardiovascular & Medical Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK
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122
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Yu H, Wark L, Ji H, Willard L, Jaing Y, Han J, He H, Ortiz E, Zhang Y, Medeiros DM, Lin D. Dietary wolfberry upregulates carotenoid metabolic genes and enhances mitochondrial biogenesis in the retina of db/db diabetic mice. Mol Nutr Food Res 2013; 57:1158-69. [PMID: 23505020 DOI: 10.1002/mnfr.201200642] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2012] [Revised: 01/16/2013] [Accepted: 01/16/2013] [Indexed: 12/25/2022]
Abstract
SCOPE Our aim was to investigate whether dietary wolfberry altered carotenoid metabolic gene expression and enhanced mitochondrial biogenesis in the retina of diabetic mice. METHODS AND RESULTS Six-week-old male db/db and wild-type mice were fed the control or wolfberry diets for 8 weeks. At study termination, liver and retinal tissues were collected for analysis by transmission electron microscopy, real-time PCR, immunoprecipitation, Western blot, and HPLC. Wolfberry elevated zeaxanthin and lutein levels in the liver and retinal tissues and stimulated expression of retinal scavenger receptor class B type I, glutathione S-transferase Pi 1, and β,β-carotene 9',10'-oxygenase 2, and induced activation and nuclear enrichment of retinal AMP-activated protein kinase α2 (AMPK-α2). Furthermore, wolfberry attenuated hypoxia and mitochondrial stress as demonstrated by declined expression of hypoxia-inducible factor-1-α, vascular endothelial growth factor, and heat shock protein 60. Wolfberry enhanced retinal mitochondrial biogenesis in diabetic retinas as demonstrated by reversed mitochondrial dispersion in the retinal pigment epithelium, increased mitochondrial copy number, elevated citrate synthase activity, and upregulated expression of peroxisome proliferator-activated receptor γ co-activator 1α, nuclear respiratory factor 1, and mitochondrial transcription factor A. CONCLUSION Consumption of dietary wolfberry could be beneficial to retinoprotection through reversal of mitochondrial function in diabetic mice.
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Affiliation(s)
- Huifeng Yu
- Department of Human Nutrition, Kansas State University, Manhattan, KS, USA
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123
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Ceddia RB. The role of AMP-activated protein kinase in regulating white adipose tissue metabolism. Mol Cell Endocrinol 2013; 366:194-203. [PMID: 22750051 DOI: 10.1016/j.mce.2012.06.014] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Revised: 03/16/2012] [Accepted: 06/21/2012] [Indexed: 01/19/2023]
Abstract
AMP-activated protein kinase (AMPK) is a heterotrimeric enzyme that plays a major role in the maintenance of energy homeostasis in various organs and tissues. When activated, AMPK can induce substrate catabolism and shut down energy-consuming anabolic pathways to increase intracellular ATP availability. Even though most of these effects have been described in muscle and liver, several studies have provided compelling evidence that AMPK also plays an important role in the regulation of white adipose tissue (WAT) glucose and lipid metabolism. In fact, the effects of acute and chronic AMPK activation in the WAT induce profound changes in adiposity with important implications for the treatment of obesity and its related metabolic disorders. This review discusses the role of AMPK in the regulation of white adipocyte metabolism with respect to energy storage and release, gene expression, mitochondrial biogenesis, oxidative capacity, cell differentiation, and the potential impact on whole-body adiposity and energy homeostasis.
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Affiliation(s)
- R B Ceddia
- School of Kinesiology and Health Science, York University, Toronto, ON, Canada.
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124
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O'Neill HM, Holloway GP, Steinberg GR. AMPK regulation of fatty acid metabolism and mitochondrial biogenesis: implications for obesity. Mol Cell Endocrinol 2013; 366:135-51. [PMID: 22750049 DOI: 10.1016/j.mce.2012.06.019] [Citation(s) in RCA: 241] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/10/2011] [Revised: 03/13/2012] [Accepted: 06/21/2012] [Indexed: 12/25/2022]
Abstract
Skeletal muscle plays an important role in regulating whole-body energy expenditure given it is a major site for glucose and lipid oxidation. Obesity and type 2 diabetes are causally linked through their association with skeletal muscle insulin resistance, while conversely exercise is known to improve whole body glucose homeostasis simultaneously with muscle insulin sensitivity. Exercise activates skeletal muscle AMP-activated protein kinase (AMPK). AMPK plays a role in regulating exercise capacity, skeletal muscle mitochondrial content and contraction-stimulated glucose uptake. Skeletal muscle AMPK is also thought to be important for regulating fatty acid metabolism; however, direct genetic evidence in this area is currently lacking. This review will discuss the current paradigms regarding the influence of AMPK in regulating skeletal muscle fatty acid metabolism and mitochondrial biogenesis at rest and during exercise, and highlight the potential implications in the development of insulin resistance.
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Affiliation(s)
- Hayley M O'Neill
- University of Melbourne, Department of Medicine, St. Vincent's Institute of Medical Research, Melbourne, Victoria, Australia.
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125
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Fu A, Eberhard CE, Screaton RA. Role of AMPK in pancreatic beta cell function. Mol Cell Endocrinol 2013; 366:127-34. [PMID: 22766107 DOI: 10.1016/j.mce.2012.06.020] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Revised: 05/08/2012] [Accepted: 06/21/2012] [Indexed: 10/28/2022]
Abstract
Pharmacological activation of AMP activated kinase (AMPK) by metformin has proven to be a beneficial therapeutic approach for the treatment of type II diabetes. Despite improved glucose regulation achieved by administration of small molecule activators of AMPK, the potential negative impact of enhanced AMPK activity on insulin secretion by the pancreatic beta cell is an important consideration. In this review, we discuss our current understanding of the role of AMPK in central functions of the pancreatic beta cell, including glucose-stimulated insulin secretion (GSIS), proliferation, and survival. In addition we discuss the controversy surrounding the role of AMPK in insulin secretion, underscoring the merits and caveats of methods used to date.
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Affiliation(s)
- Accalia Fu
- Children's Hospital of Eastern Ontario Research Institute, Ottawa, Canada
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126
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Ríos M, Foretz M, Viollet B, Prieto A, Fraga M, Costoya JA, Señarís R. AMPK activation by oncogenesis is required to maintain cancer cell proliferation in astrocytic tumors. Cancer Res 2013; 73:2628-38. [PMID: 23370326 DOI: 10.1158/0008-5472.can-12-0861] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
5'-AMP-activated protein kinase (AMPK) is an energy sensor that controls cell metabolism, and it has been related to apoptosis and cell-cycle arrest. Although its role in metabolic homeostasis is well documented, its function in cancer is much less clear. In this study, we examined the role of AMPK in a mouse model of astrocytoma driven by oncogenic H-Ras(V12) and/or with PTEN deletion based on the common constitutive activation of the Raf/MEK/ERK and PI3K/AKT cascades in human astrocytomas. We also evaluated the activity and role of AMPK in human glioblastoma cells and xenografts. AMPK was constitutively activated in astrocytes expressing oncogenic H-Ras(V12) in parallel with high cell division rates. Genetic deletion of AMPK or attenuation of its activity in these cells was sufficient to reduce cell proliferation. The levels of pAMK were always related to the levels of phosphorylated retinoblastoma (Rb) at Ser804, which may indicate an AMPK-mediated phosphorylation of Rb. We confirmed this AMPK-Rb relationship in human glioblastoma cell lines and xenografts. In clinical specimens of human glioblastoma, elevated levels of activated AMPK appeared especially in areas of high proliferation surrounding the blood vessels. Together, our findings indicate that the initiation and progression of astrocytic tumors relies upon AMPK-dependent control of the cell cycle, thereby identifying AMPK as a candidate therapeutic target in this setting.
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Affiliation(s)
- Marcos Ríos
- Departamento de Fisioloxía, CIMUS, Facultade de Medicina, Universidade de Santiago de Compostela, Santiago de Compostela, Spain
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Ju TC, Lin YS, Chern Y. Energy dysfunction in Huntington's disease: insights from PGC-1α, AMPK, and CKB. Cell Mol Life Sci 2012; 69:4107-20. [PMID: 22627493 PMCID: PMC11115139 DOI: 10.1007/s00018-012-1025-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2012] [Revised: 04/16/2012] [Accepted: 05/02/2012] [Indexed: 12/23/2022]
Abstract
Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by a CAG trinucleotide expansion in the Huntingtin (Htt) gene. When the number of CAG repeats exceeds 36, the translated polyglutamine-expanded Htt protein interferes with the normal functions of many types of cellular machinery and causes cytotoxicity. Clinical symptoms include progressive involuntary movement disorders, psychiatric signs, cognitive decline, dementia, and a shortened lifespan. The most severe brain atrophy is observed in the striatum and cortex. Besides the well-characterized neuronal defects, recent studies showed that the functions of mitochondria and several key players in energy homeostasis are abnormally regulated during HD progression. Energy dysregulation thus is now recognized as an important pathogenic pathway of HD. This review focuses on the importance of three key molecular determinants (peroxisome proliferator-activated receptor-γ coactivator-1α, AMP-activated protein kinase, and creatine kinase B) of cellular energy homeostasis and their possible involvement in HD pathogenesis.
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Affiliation(s)
- Tz-Chuen Ju
- Division of Neuroscience, Institute of Biomedical Sciences, Academia Sinica, Nankang, Taipei, 11529 Taiwan
| | - Yow-Sien Lin
- Division of Neuroscience, Institute of Biomedical Sciences, Academia Sinica, Nankang, Taipei, 11529 Taiwan
| | - Yijuang Chern
- Division of Neuroscience, Institute of Biomedical Sciences, Academia Sinica, Nankang, Taipei, 11529 Taiwan
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Abstract
AMP-activated protein kinase (AMPK) is a stress-activated kinase that functions as a cellular fuel gauge and master metabolic regulator. Recent investigation has elucidated novel molecular mechanisms of AMPK regulation and important biological actions of the AMPK pathway that are highly relevant to cardiovascular disease. Activation of the intrinsic AMPK pathway plays an important role in the myocardial response to ischemia, pressure overload, and heart failure. Pharmacological activation of AMPK shows promise as a therapeutic strategy in the treatment of heart disease. The purpose of this review is to assess how recent discoveries have extended and in some cases challenged existing paradigms, providing new insights into the regulation of AMPK, its diverse biological actions, and therapeutic potential in the heart.
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Affiliation(s)
- Vlad G Zaha
- Department of Internal Medicine, Yale Cardiovascular Research Center, Section of Cardiovascular Medicine, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
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Merrill JF, Thomson DM, Hardman SE, Hepworth SD, Willie S, Hancock CR. Iron deficiency causes a shift in AMP-activated protein kinase (AMPK) subunit composition in rat skeletal muscle. Nutr Metab (Lond) 2012; 9:104. [PMID: 23171474 PMCID: PMC3575277 DOI: 10.1186/1743-7075-9-104] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Accepted: 11/16/2012] [Indexed: 11/29/2022] Open
Abstract
Background As a cellular energy sensor, the 5’AMP-activated protein kinase (AMPK) is activated in response to energy stresses such as hypoxia and muscle contraction. To determine effects of iron deficiency on AMPK activation and signaling, as well as the AMPK subunit composition in skeletal muscle, rats were fed a control (C=50-58 mg/kg Fe) or iron deficient (ID=2-6 mg/kg Fe) diet for 6–8 wks. Results Their respective hematocrits were 47.5% ± 1.0 and 16.5% ± 0.6. Iron deficiency resulted in 28.3% greater muscle fatigue (p<0.01) in response to 10 min of stimulation (1 twitch/sec) and was associated with a greater reduction in phosphocreatine (C: Resting 24.1 ± 0.9 μmol/g, Stim 13.1 ± 1.5 μmol/g; ID: Resting 22.7 ± 1.0 μmol/g, Stim 3.2 ± 0.7 μmol/g; p<0.01) and ATP levels (C: Resting 5.89 ± 0.48 μmol/g, Stim 6.03 ± 0.35 μmol/g; ID: Resting 5.51 ± 0.20 μmol/g, Stim 4.19 ± 0.47 μmol/g; p<0.05). AMPK activation increased with stimulation in muscles of C and ID animals. A reduction in Cytochrome c and other iron-dependent mitochondrial proteins was observed in ID animals (p<0.01). The AMPK catalytic subunit (α) was examined because both isoforms are known to play different roles in responding to energy challenges. In ID animals, AMPKα2 subunit protein content was reduced to 71.6% of C (p<0.05), however this did not result in a significant difference in resting AMPKα2 activity. AMPKα1 protein was unchanged, however an overall increase in AMPKα1 activity was observed (C: 0.91 pmol/mg/min; ID: 1.63 pmol/mg/min; p<0.05). Resting phospho Acetyl CoA Carboxylase (pACC) was unchanged. In addition, we observed significant reductions in the β2 and γ3 subunits of AMPK in response to iron deficiency. Conclusions This study indicates that chronic iron deficiency causes a shift in the expression of AMPKα, β, and γ subunit composition. Iron deficiency also causes chronic activation of AMPK as well as an increase in AMPKα1 activity in exercised skeletal muscle.
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Affiliation(s)
- John F Merrill
- Department of Nutrition, Dietetics, and Food Science, Brigham Young University, Provo, Utah, USA.
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130
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Hardie DG, Ross FA, Hawley SA. AMP-activated protein kinase: a target for drugs both ancient and modern. CHEMISTRY & BIOLOGY 2012; 19:1222-36. [PMID: 23102217 PMCID: PMC5722193 DOI: 10.1016/j.chembiol.2012.08.019] [Citation(s) in RCA: 281] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/09/2012] [Revised: 08/28/2012] [Accepted: 08/31/2012] [Indexed: 02/07/2023]
Abstract
The AMP-activated protein kinase (AMPK) is a sensor of cellular energy status. It is activated, by a mechanism requiring the tumor suppressor LKB1, by metabolic stresses that increase cellular ADP:ATP and/or AMP:ATP ratios. Once activated, it switches on catabolic pathways that generate ATP, while switching off biosynthetic pathways and cell-cycle progress. These effects suggest that AMPK activators might be useful for treatment and/or prevention of type 2 diabetes and cancer. Indeed, AMPK is activated by the drugs metformin and salicylate, the latter being the major breakdown product of aspirin. Metformin is widely used to treat diabetes, while there is epidemiological evidence that both metformin and aspirin provide protection against cancer. We review the mechanisms of AMPK activation by these and other drugs, and by natural products derived from traditional herbal medicines.
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Affiliation(s)
- D Grahame Hardie
- Division of Cell Signalling & Immunology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, Scotland, UK.
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131
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Nakagawa K, Uehata Y, Natsuizaka M, Kohara T, Darmanin S, Asaka M, Takeda H, Kobayashi M. The nuclear protein Artemis promotes AMPK activation by stabilizing the LKB1-AMPK complex. Biochem Biophys Res Commun 2012; 427:790-5. [PMID: 23044421 DOI: 10.1016/j.bbrc.2012.09.140] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2012] [Accepted: 09/23/2012] [Indexed: 01/03/2023]
Abstract
AMP-activated protein kinase (AMPK) is a hetero-trimeric Ser/Thr kinase composed of a catalytic α subunit and regulatory β and γ subunits; it functions as an energy sensor that controls cellular energy homeostasis. In response to an increased cellular AMP/ATP ratio, AMPK is activated by phosphorylation at Thr172 in the α-subunit by upstream AMPK kinases (AMPKKs), including tumor suppressor liver kinase B1 (LKB1). To elucidate more precise molecular mechanisms of AMPK activation, we performed yeast two-hybrid screening and isolated the complementary DNA (cDNA) encoding the nuclear protein Artemis/DNA cross-link repair 1C (DCLRE1C) as an AMPKα2-binding protein. Artemis was found to co-immunoprecipitate with AMPKα2, and the co-localization of Artemis with AMPKα2 in the nucleus was confirmed by immunofluorescence staining in U2OS cells. Moreover, over-expression of Artemis enhanced the phosphorylation of AMPKα2 and the AMPK substrate acetyl-CoA carboxylase (ACC). Conversely, RNAi-mediated knockdown of Artemis reduced AMPK and ACC phosphorylation. In addition, Artemis markedly increased the physical association between AMPKα2 and LKB1. Taken together, these results suggest that Artemis functions as a positive regulator of AMPK signaling by stabilizing the LKB1-AMPK complex.
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Affiliation(s)
- Koji Nakagawa
- Department of Pathophysiology and Therapeutics, Division of Pharmascience, Faculty of Pharmaceutical Sciences, Hokkaido University, N12 W6, Kita-ku, Sapporo, Hokkaido 060-0812, Japan.
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132
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Yan H, Zhang D, Zhang Q, Wang P, Huang Y. The activation of AMPK in cardiomyocytes at the very early stage of hypoxia relies on an adenine nucleotide-independent mechanism. INTERNATIONAL JOURNAL OF CLINICAL AND EXPERIMENTAL PATHOLOGY 2012; 5:770-776. [PMID: 23071859 PMCID: PMC3466980] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 07/22/2012] [Accepted: 08/29/2012] [Indexed: 06/01/2023]
Abstract
The energy status of a cell plays a key role in its survival, and the exposure of eukaryotic cells to the hypoxia that accompanies the depletion of intracellular ATP triggers specific systemic adaptive responses. AMP-activated protein kinase (AMPK) has emerged as a key regulator of energy metabolism in the heart and plays a critical role in inducing these responses. However, the specific mechanism responsible for AMPK activation in cardiomyocytes at very early stages of hypoxia remain unclear. The goals of this study were to assess the relative contribution to AMPK activation of phosphorylation by AMPK kinase (AMPKK) and of positive allosterism due to AMP:ATP ratios in the early stages of hypoxia. Our results demonstrated that, compared with normoxic controls, neither intracellular AMP concentrations nor AMP:ATP ratios significantly increased within 1h of hypoxia onset. In contrast, a SAMS peptide phosphorylation assay and an immunoblot analysis revealed significant increases in both AMPK activity and ACC phosphorylation within 5min of hypoxic treatment. Furthermore, exposure of cardiomyocytes to hypoxia significantly increased AMPK phosphorylation within 5min, by 3- to 4-fold compared with controls (P<0.01), while overall levels of AMPKα protein did not differ between aerobic and anoxic cardiomyocytes. We also observed increased AMPKK activity in anoxic cardiomyocytes, through use of an α(312) substrate. Taken together, our findings demonstrate that in the early stage of hypoxia in cardiomyocytes, increases in AMPK activity occur prior to and independently of increases in AMP concentration or in the AMP:ATP ratio. Instead, under these circumstances, AMPK is primarily activated by phosphorylation of the conserved Thr-172 residue in its activation loop by its upstream kinase AMPKK.
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Affiliation(s)
- Hong Yan
- Institute of Burn Research, State Key Laboratory of Trauma, Burn and Combined Injury, Southwest Hospital, Third Military Medical University Chongqing, China.
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133
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Shugrue CA, Alexandre M, de Villalvilla AD, Kolodecik TR, Young LH, Gorelick FS, Thrower EC. Cerulein hyperstimulation decreases AMP-activated protein kinase levels at the site of maximal zymogen activation. Am J Physiol Gastrointest Liver Physiol 2012; 303:G723-32. [PMID: 22821946 PMCID: PMC3468535 DOI: 10.1152/ajpgi.00082.2012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The premature activation of digestive enzyme zymogens in the pancreatic acinar cell is an important initiating event in acute pancreatitis. We have previously demonstrated that vacuolar ATPase (vATPase) activity is required for zymogen activation. Adenosine monophosphate-activated protein kinase (AMPK) regulates vATPase function in kidney and epididymal clear cells. To determine whether AMPK could affect pancreatitis responses, its effects were first examined in a cellular model of pancreatitis, cerulein-hyperstimulated (100 nM) pancreatic acini. This treatment caused a prominent increase in trypsin and chymotrypsin activities. Pretreatment with AICAR or metformin (AMPK activators) or compound C (an AMPK inhibitor) reduced or increased cerulein-induced zymogen activation, respectively. The association of the vATPase E subunit with membranes, a marker of its activation, tended to be inversely related to AMPK activity (assessed by AICAR and compound C treatments). Cerulein treatment did not change AMPK (α and β) levels but did lead to an increase in its activation (phosphorylation of Thr172) and induced the time-dependent translocation of the enzyme to a Triton-insoluble compartment. Basal in vivo studies showed that AMPK was widely distributed between membrane and soluble fractions generated by differential centrifugation. After cerulein hyperstimulation, AMPK levels selectively decreased in fractions containing the highest levels of active zymogens. These studies suggest that AMPK activity has a protective role in the pancreatic acinar cell that inhibits zymogen activation in the basal state, and this AMPK effect is reduced during pancreatitis. Therapies that prevent the selective reduction of AMPK in compartments that support zymogen activation could reduce injury during pancreatitis.
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Affiliation(s)
- Christine A. Shugrue
- Departments of 1Internal Medicine, Section of Digestive Diseases, and ,4Veterans Administration Connecticut Healthcare, West Haven, Connecticut
| | - Martine Alexandre
- Departments of 1Internal Medicine, Section of Digestive Diseases, and ,4Veterans Administration Connecticut Healthcare, West Haven, Connecticut
| | - Alexander Diaz de Villalvilla
- Departments of 1Internal Medicine, Section of Digestive Diseases, and ,4Veterans Administration Connecticut Healthcare, West Haven, Connecticut
| | - Thomas R. Kolodecik
- Departments of 1Internal Medicine, Section of Digestive Diseases, and ,4Veterans Administration Connecticut Healthcare, West Haven, Connecticut
| | - Lawrence H. Young
- 3Section of Cardiovascular Medicine, Yale University School of Medicine, New Haven, Connecticut;
| | - Fred S. Gorelick
- Departments of 1Internal Medicine, Section of Digestive Diseases, and ,2Cell Biology, and ,4Veterans Administration Connecticut Healthcare, West Haven, Connecticut
| | - Edwin C. Thrower
- Departments of 1Internal Medicine, Section of Digestive Diseases, and ,4Veterans Administration Connecticut Healthcare, West Haven, Connecticut
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Abstract
SIGNIFICANCE The Atg1/ULK1 (uncoordinated-51 like kinase 1) protein complex plays an essential role regulating autophagy in mammalian cells. As autophagy is implicated in normal cellular homeostasis and multiple diseases, better mechanistic insight drives development of novel therapeutic approaches. RECENT ADVANCES Multiple independent laboratories have contributed important new insights into the ULK-signalling pathway. ULK1/2 function is regulated by mTOR complex 1 and AMPK through a network of phosphorylation events. ULK signalling controls autophagosome formation in conjunction with other key regulatory factors such as Beclin1 and Atg9. CRITICAL ISSUES From recent work, we have gained a better understanding of ULK proteins and their functional roles but details still need to be resolved. A combination of approaches has been used to better elucidate the sub-classes of autophagy that are differentially dependent upon ULK family members. Roles of ULK members in autophagy-independent trafficking and signalling pathways have also been better defined, highlighting the diversity of functions coordinated by this protein family. FUTURE DIRECTIONS As mechanisms and in vivo functions become clarified for the different ULK members, more robust strategies for targeting these essential autophagy kinases can be developed.
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Affiliation(s)
- Edmond Y Chan
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, Scotland, United Kingdom.
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135
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Phoenix KN, Devarakonda CV, Fox MM, Stevens LE, Claffey KP. AMPKα2 Suppresses Murine Embryonic Fibroblast Transformation and Tumorigenesis. Genes Cancer 2012; 3:51-62. [PMID: 22893790 DOI: 10.1177/1947601912452883] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2011] [Revised: 06/06/2012] [Accepted: 06/03/2012] [Indexed: 01/13/2023] Open
Abstract
AMP-activated kinase (AMPK) is a key metabolic sensor and stress signaling kinase. AMPK activity is known to suppress anabolic processes such as protein and lipid biosynthesis and promote energy-producing pathways including fatty acid oxidation, resulting in increased cellular energy. In addition, AMPK localizes to centrosomes during cell division, plays a role in cellular polarization, and directly targets p53, affecting apoptosis. Two distinct catalytic AMPKα isoforms exist: α1 and α2. Multiple reports indicate that both common and distinct functions exist for each of the 2 α isoforms. AMPK activation has been shown to repress tumor growth, and it has been suggested that AMPK may function as a metabolic tumor suppressor. To evaluate the potential role of each of the AMPKα isoforms in modulating cellular transformation, susceptibility to Ras-induced transformation was evaluated in normal murine embryonic fibroblasts (MEFs) obtained from genetically deleted AMPKα1- or AMPKα2-null mice. This study demonstrated that while AMPKα1 is the dominant AMPK isoform expressed in MEFs, only the AMPKα2-null MEFs displayed increased susceptibility to H-RasV12 transformation in vitro and tumorigenesis in vivo. Conversely, AMPKα1-null MEFs, which demonstrated compensation with increased expression of AMPKα2, displayed minimal transformation susceptibility, decreased cell survival, decreased cell proliferation, and increased apoptosis. Finally, this study demonstrates that AMPKα2 was selectively responsible for targeting p53, thus contributing to the suppression of transformation and tumorigenic mechanisms.
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Affiliation(s)
- Kathryn N Phoenix
- Department of Cell Biology, Center for Vascular Biology, University of Connecticut Health Center, Farmington, CT, USA
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136
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Abstract
The hydrolysis of ATP drives virtually all of the energy-requiring processes in living cells. A prerequisite of living cells is that the concentration of ATP needs to be maintained at sufficiently high levels to sustain essential cellular functions. In eukaryotic cells, the AMPK (AMP-activated protein kinase) cascade is one of the systems that have evolved to ensure that energy homoeostasis is maintained. AMPK is activated in response to a fall in ATP, and recent studies have suggested that ADP plays an important role in regulating AMPK. Once activated, AMPK phosphorylates a broad range of downstream targets, resulting in the overall effect of increasing ATP-producing pathways whilst decreasing ATP-utilizing pathways. Disturbances in energy homoeostasis underlie a number of disease states in humans, e.g. Type 2 diabetes, obesity and cancer. Reflecting its key role in energy metabolism, AMPK has emerged as a potential therapeutic target. In the present review we examine the recent progress aimed at understanding the regulation of AMPK and discuss some of the latest developments that have emerged in key areas of human physiology where AMPK is thought to play an important role.
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137
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Blagih J, Krawczyk CM, Jones RG. LKB1 and AMPK: central regulators of lymphocyte metabolism and function. Immunol Rev 2012; 249:59-71. [DOI: 10.1111/j.1600-065x.2012.01157.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
| | - Connie M. Krawczyk
- Department of Microbiology and Immunology; McGill University; Montreal; Quebec
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138
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Salt IP, Palmer TM. Exploiting the anti-inflammatory effects of AMP-activated protein kinase activation. Expert Opin Investig Drugs 2012; 21:1155-67. [PMID: 22694351 DOI: 10.1517/13543784.2012.696609] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
INTRODUCTION AMP-activated protein kinase (AMPK) is the downstream component of a serine/threonine protein kinase cascade involved in the regulation of metabolism. Many studies have also revealed that AMPK activation can exert significant anti-inflammatory and immunosuppressive effects in a variety of cell types and models of inflammatory/autoimmune disease. Because metformin, an AMPK activator that is a favored first-line therapeutic option for type 2 diabetes, may confer benefits in chronic inflammatory diseases and cancers independent of its ability to normalize blood glucose, there is now considerable interest in identifying and exploiting AMPK's anti-inflammatory effects. AREAS COVERED The authors provide a background to AMPK signaling and describe the pro-inflammatory signaling pathways and processes shown to be regulated by AMPK activation. EXPERT OPINION Identification of AMPK subunits responsible for specific anti-inflammatory effects, and a molecular understanding of the mechanisms involved, will be necessary to exploit AMPK pathway activation in acute and chronic inflammatory disease settings while minimizing adverse reactions due to deregulation of AMPK's wide-ranging effects on metabolism.
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Affiliation(s)
- Ian P Salt
- University of Glasgow, Institute of Cardiovascular & Medical Sciences, College of Medical, Veterinary & Life Sciences, Glasgow G12 8QQ, Scotland, UK
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139
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Abstract
Current concepts of mechanosensation are general and applicable to almost every cell type. However, striated muscle cells are distinguished by their ability to generate strong forces via actin/myosin interaction, and this process is fine-tuned for optimum contractility. This aspect, unique for actively contracting cells, may be defined as "sensing of the magnitude and dynamics of contractility," as opposed to the well-known concepts of the "perception of extracellular mechanical stimuli." The acto/myosin interaction, by producing changes in ATP, ADP, Pi, and force on a millisecond timescale, may be regarded as a novel and previously unappreciated mechanosensory mechanism. In addition, sarcomeric mechanosensory structures, such as the Z-disc, are directly linked to autophagy, survival, and cell death-related pathways. One emerging example is telethonin and its ability to interfere with p53 metabolism and hence apoptosis (mechanoptosis). In this article, we introduce contractility per se as an important mechanosensory mechanism, and we differentiate extracellular from intracellular mechanosensory effects.
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Affiliation(s)
- Ralph Knöll
- Heart Science Section, National Heart & Lung Institute, Imperial College, London W12 0NN, UK.
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140
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AMP-activated protein kinase-α1 as an activating kinase of TGF-β-activated kinase 1 has a key role in inflammatory signals. Cell Death Dis 2012; 3:e357. [PMID: 22833096 PMCID: PMC3406594 DOI: 10.1038/cddis.2012.95] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Although previous studies have proposed plausible mechanisms of the activation of transforming growth factor-β-activated kinase 1 (TAK1) in inflammatory signals, including Toll-like receptors (TLRs), its activating kinase still remains to be unclear. In the present study, we have provided evidences that AMP-activated protein kinase (AMPK)-α1 has a pivotal role for activating TAK1, and thereby regulate NF-κB-dependent gene expressions in inflammatory signaling mediated by TLR4 and TNF-α stimulation. AMPK-α1 specifically interacts with TAK1 and reciprocally regulates their kinase activities. Upon the stimulation of lipopolysaccharide, AMPK-α1-knockdown (AMPK-α1(KD)) or TAK1-knockdown human monocytic THP-1 cells exhibit a dramatic reduction in the TAK1 or AMPK-α1 kinase activity, respectively, and subsequent suppressions of its downstream signaling cascades, which further leads to inhibitions of NF-κB and thereby productions of proinflammatory cytokines, such as TNF-α, IL-1β, and IL-6. Importantly, the microarray analysis of AMPK-α1(KD) cells revealed a dramatic reduction in the NF-κB-dependent genes induced by TLR4 and TNF-α stimulation, and the observation was in significant correlation with the results of quantitative real-time PCR. Moreover, AMPK-α1(KD) cells are highly sensitive to the TNF-α-induced apoptosis, which is accompanied with dramatic reductions in the NF-κB-dependent and anti-apoptotic genes. As a result, our data demonstrate that AMPK-α1 as an activating kinase of TAK1 has a key role in mediating inflammatory signals triggered by TLR4 and TNF-α.
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141
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Song P, Zou MH. Regulation of NAD(P)H oxidases by AMPK in cardiovascular systems. Free Radic Biol Med 2012; 52:1607-19. [PMID: 22357101 PMCID: PMC3341493 DOI: 10.1016/j.freeradbiomed.2012.01.025] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/22/2011] [Revised: 01/25/2012] [Accepted: 01/27/2012] [Indexed: 02/07/2023]
Abstract
Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are ubiquitously produced in cardiovascular systems. Under physiological conditions, ROS/RNS function as signaling molecules that are essential in maintaining cardiovascular function. Aberrant concentrations of ROS/RNS have been demonstrated in cardiovascular diseases owing to increased production or decreased scavenging, which have been considered common pathways for the initiation and progression of cardiovascular diseases such as atherosclerosis, hypertension, (re)stenosis, and congestive heart failure. NAD(P)H oxidases are primary sources of ROS and can be induced or activated by all known cardiovascular risk factors. Stresses, hormones, vasoactive agents, and cytokines via different signaling cascades control the expression and activity of these enzymes and of their regulatory subunits. But the molecular mechanisms by which NAD(P)H oxidase is regulated in cardiovascular systems remain poorly characterized. Investigations by us and others suggest that adenosine monophosphate-activated protein kinase (AMPK), as an energy sensor and modulator, is highly sensitive to ROS/RNS. We have also obtained convincing evidence that AMPK is a physiological suppressor of NAD(P)H oxidase in multiple cardiovascular cell systems. In this review, we summarize our current understanding of how AMPK functions as a physiological repressor of NAD(P)H oxidase.
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Affiliation(s)
| | - Ming-Hui Zou
- To whom correspondence should be addressed: Ming-Hui Zou, M.D., Ph.D., Department of Medicine, University of Oklahoma Health Science Center, 941 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA, Phone: 405-271-3974, Fax: 405-271-3973,
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142
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Abstract
AMPK (AMP-activated protein kinase) is one of the key players in maintaining intracellular homoeostasis. AMPK is well known as an energy sensor and can be activated by increased intracellular AMP levels. Generally, the activation of AMPK turns on catabolic pathways that generate ATP, while inhibiting cell proliferation and biosynthetic processes that consume ATP. In recent years, intensive investigations on the regulation and the function of AMPK indicates that AMPK not only functions as an intracellular energy sensor and regulator, but is also a general stress sensor that is important in maintaining intracellular homoeostasis during many kinds of stress challenges. In the present paper, we will review recent literature showing that AMPK functions far beyond its proposed energy sensor and regulator function. AMPK regulates ROS (reactive oxygen species)/redox balance, autophagy, cell proliferation, cell apoptosis, cellular polarity, mitochondrial function and genotoxic response, either directly or indirectly via numerous downstream pathways under physiological and pathological conditions.
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143
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Klaus A, Polge C, Zorman S, Auchli Y, Brunisholz R, Schlattner U. A two-dimensional screen for AMPK substrates identifies tumor suppressor fumarate hydratase as a preferential AMPKα2 substrate. J Proteomics 2012; 75:3304-13. [PMID: 22507198 DOI: 10.1016/j.jprot.2012.03.040] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2011] [Revised: 02/26/2012] [Accepted: 03/25/2012] [Indexed: 12/17/2022]
Abstract
AMP-activated protein kinase (AMPK) is emerging as a central cellular signaling hub involved in energy homeostasis and proliferation. The kinase is considered as a suitable target for pharmacological intervention in several energy-related pathologies like diabetes type II and cancer, although its signaling network is still incompletely understood. Here we apply an original two-dimensional in vitro screening approach for AMPK substrates that combines biophysical interaction based on surface plasmon resonance with in vitro phosphorylation. By enriching for proteins that interact with a specific AMPK isoform, we aimed to identify substrates that are also preferentially phosphorylated by this specific AMPK isoform. Application of this screen to full-length AMPK α2β2γ1 and soluble rat liver proteins identified the tumor suppressor fumarate hydratase (FH). FH was confirmed to interact with and to be preferentially phosphorylated by the AMPKα2 isoform by using yeast-two-hybrid and in vitro phosphorylation assays. AMPK-mediated phosphorylation of FH significantly increased enzyme activity in vitro and in vivo, suggesting that it is a bona fide AMPK substrate. In vivo, AMPKα2 is supposed to target the cytosolic/nuclear pools of FH, whose tumor suppressor function relies on DNA damage repair and inhibition of HIF-1α-signaling.
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Affiliation(s)
- Anna Klaus
- Laboratory of Fundamental and Applied Bioenergetics, University Joseph Fourier, Grenoble Cedex 9, France
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144
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Pinter K, Jefferson A, Czibik G, Watkins H, Redwood C. Subunit composition of AMPK trimers present in the cytokinetic apparatus: Implications for drug target identification. Cell Cycle 2012; 11:917-21. [PMID: 22333580 DOI: 10.4161/cc.11.5.19412] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
AMP-activated protein kinase has been shown to be a key regulator of energy homeostasis; it has also been identified as a tumor suppressor and is required for correct cell division and chromosome segregation during mitosis. The enzyme is a heterotrimer, with each subunit having more than one isoform, each encoded by a separate gene (two α, two β and three γ isoforms). In human endothelial cells, the activated kinase subunit of AMPK in the cytokinetic apparatus is α2, the minority α subunit, which co-localizes with β2 and γ2. This is the first demonstration of a trimeric complex of AMPK containing the γ2 regulatory subunit becoming selectively activated and being linked to mitotic processes. We also show that α1 and γ1, the predominant AMPK subunits, are almost exclusively localized in the cytoskeleton, while α2 and γ2 are present in all subcellular fractions, including the nuclei. These data suggest that pharmacological interventions targeted to specific AMPK subunit isoforms have the potential to modify selective functions of AMPK.
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Affiliation(s)
- Katalin Pinter
- Department of Cardiovascular Medicine, University of Oxford, West Wing Level 6, John Radcliffe Hospital, Oxford, United Kingdom
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145
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Tsai AYL, Gazzarrini S. AKIN10 and FUSCA3 interact to control lateral organ development and phase transitions in Arabidopsis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2012; 69:809-21. [PMID: 22026387 DOI: 10.1111/j.1365-313x.2011.04832.x] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The Snf1 (sucrose non-fermenting-1)/AMPK (AMP-activated protein kinase)/SnRK1 (Snf1-related protein kinase 1) kinases act as sensors of energy status in eukaryotes. Despite the important role of these kinases in regulation of cellular responses to metabolic stress, only a few SnRK1 substrates have been identified. Using yeast two-hybrid screens, we isolated AKIN10 as an interactor of the B3-domain transcription factor FUSCA3 (FUS3), an essential regulator of seed maturation in Arabidopsis. Pull-down and bi-molecular fluorescence complementation (BiFC) assays confirm the interaction in vitro and in planta, respectively. In-gel kinase assays show that AKIN10 phosphorylates FUS3 and that the N-terminal domain of FUS3 is required for AKIN10 phosphorylation. Mutations of three serines (fus3(S55A/S56A/S57A) ) within a partial SnRK1 consensus sequence in the N-terminal region of FUS3 reduce greatly FUS3 phosphorylation by AKIN10, which indicates that these serines are the predominant AKIN10 target sites. In a cell-free system, AKIN10 positively regulates FUS3 stability, as overexpression of AKIN10 delayed the degradation of the recombinant FUS3. Plants over-expressing AKIN10 show delayed seed germination, vegetative growth and flowering time, indicating that AKIN10 antagonizes the embryonic-to-vegetative and vegetative-to-reproductive phase transitions. Furthermore, overexpression of AKIN10 alters cotyledon, silique and floral organ development, suggesting that AKIN10 regulates lateral organ development. Genetic interaction studies show that the fus3-3 mutation partially rescues the phase transition and organ development defects caused by AKIN10 overexpression. Taken together, these findings indicate that FUS3 and AKIN10 interact physically and share overlapping pathways to regulate developmental phase transitions and organogenesis in Arabidopsis.
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Affiliation(s)
- Allen Yi-Lun Tsai
- Department of Biological Sciences and Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
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Absence of RIP140 reveals a pathway regulating glut4-dependent glucose uptake in oxidative skeletal muscle through UCP1-mediated activation of AMPK. PLoS One 2012; 7:e32520. [PMID: 22389706 PMCID: PMC3289711 DOI: 10.1371/journal.pone.0032520] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2011] [Accepted: 01/31/2012] [Indexed: 01/08/2023] Open
Abstract
Skeletal muscle constitutes the major site of glucose uptake leading to increased removal of glucose from the circulation in response to insulin. Type 2 diabetes and obesity are often associated with insulin resistance that can be counteracted by exercise or the use of drugs increasing the relative proportion of oxidative fibers. RIP140 is a transcriptional coregulator with a central role in metabolic tissues and we tested the effect of modulating its level of expression on muscle glucose and lipid metabolism in two mice models. Here, we show that although RIP140 protein is expressed at the same level in both oxidative and glycolytic muscles, it inhibits both fatty acid and glucose utilization in a fiber-type dependent manner. In RIP140-null mice, fatty acid utilization increases in the extensor digitorum longus and this is associated with elevated expression of genes implicated in fatty acid binding and transport. In the RIP140-null soleus, depletion of RIP140 leads to increased GLUT4 trafficking and glucose uptake with no change in Akt activity. AMPK phosphorylation/activity is inhibited in the soleus of RIP140 transgenic mice and increased in RIP140-null soleus. This is associated with increased UCP1 expression and mitochondrial uncoupling revealing the existence of a signaling pathway controlling insulin-independent glucose uptake in the soleus of RIP140-null mice. In conclusion, our findings reinforce the participation of RIP140 in the maintenance of energy homeostasis by acting as an inhibitor of energy production and particularly point to RIP140 as a promising therapeutic target in the treatment of insulin resistance.
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147
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Sanli T, Linher-Melville K, Tsakiridis T, Singh G. Sestrin2 modulates AMPK subunit expression and its response to ionizing radiation in breast cancer cells. PLoS One 2012; 7:e32035. [PMID: 22363791 PMCID: PMC3282792 DOI: 10.1371/journal.pone.0032035] [Citation(s) in RCA: 103] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2011] [Accepted: 01/18/2012] [Indexed: 12/20/2022] Open
Abstract
Background The sestrin family of stress-responsive genes (SESN1-3) are suggested to be involved in regulation of metabolism and aging through modulation of the AMPK-mTOR pathway. AMP-activated protein kinase (AMPK) is an effector of the tumour suppressor LKB1, which regulates energy homeostasis, cell polarity, and the cell cycle. SESN1/2 can interact directly with AMPK in response to stress to maintain genomic integrity and suppress tumorigenesis. Ionizing radiation (IR), a widely used cancer therapy, is known to increase sestrin expression, and acutely activate AMPK. However, the regulation of AMPK expression by sestrins in response to IR has not been studied in depth. Methods and Findings Through immunoprecipitation we observed that SESN2 directly interacted with the AMPKα1β1γ1 trimer and its upstream regulator LKB1 in MCF7 breast cancer cells. SESN2 overexpression was achieved using a Flag-tagged SESN2 expression vector or a stably-integrated tetracycline-inducible system, which also increased AMPKα1 and AMPKβ1 subunit phosphorylation, and co-localized with phosphorylated AMPKα-Thr127 in the cytoplasm. Furthermore, enhanced SESN2 expression increased protein levels of LKB1 and AMPKα1β1γ1, as well as mRNA levels of LKB1, AMPKα1, and AMPKβ1. Treatment of MCF7 cells with IR elevated AMPK expression and activity, but this effect was attenuated in the presence of SESN2 siRNA. In addition, elevated SESN2 inhibited IR-induced mTOR signalling and sensitized MCF7 cells to IR through an AMPK-dependent mechanism. Conclusions Our results suggest that in breast cancer cells SESN2 is associated with AMPK, it is involved in regulation of basal and IR-induced expression and activation of this enzyme, and it mediates sensitization of cancer cells to IR.
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Affiliation(s)
- Toran Sanli
- Research Department, Juravinski Cancer Center, Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Katja Linher-Melville
- Research Department, Juravinski Cancer Center, Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
| | | | - Gurmit Singh
- Research Department, Juravinski Cancer Center, Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
- * E-mail:
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148
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Kim M, Shen M, Ngoy S, Karamanlidis G, Liao R, Tian R. AMPK isoform expression in the normal and failing hearts. J Mol Cell Cardiol 2012; 52:1066-73. [PMID: 22314372 DOI: 10.1016/j.yjmcc.2012.01.016] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2011] [Revised: 01/20/2012] [Accepted: 01/23/2012] [Indexed: 12/27/2022]
Abstract
AMP-activated protein kinase (AMPK) is a master metabolic switch that plays an important role in energy homeostasis at the cellular and whole body level, hence a promising drug target. AMPK is a heterotrimeric complex composed of catalytic α-subunit and regulatory β- and γ-subunits with multiple isoforms for each subunit. It has been shown that AMPK activity is increased in cardiac hypertrophy and failure but it is unknown whether changes in subunit composition of AMPK contribute to the altered AMPK activity. In this study, we determined the protein expression pattern of AMPK subunit isoforms during cardiac development as well as during cardiac hypertrophy and heart failure in mouse heart. We also compared the findings in failing mouse heart to that of the human failing hearts in order to determine whether the mouse heart is a good model of AMPK in human diseases. In mouse developmental hearts, AMPK was highly expressed in the fetal stages and fell back to the adult level after birth. In the failing mouse heart, there was a significant increase in α2, β2, and γ2 subunits both at the mRNA and protein levels. In contrary, we found significant increases in the protein level of α1, β1 and γ2c subunits in human failing hearts with no change in the mRNA level. We also compared isoform-specific AMPK activity in the mouse and human failing hearts. Consistent with the literature, in the failing mouse heart, the α2 complexes accounted for ~2/3 of total AMPK activity while the α1 complexes accounted for the remaining 30-35%. In the human hearts, however, the contribution of α1-AMPK activity was significantly higher (>40%) in the non-failing hearts, and it further increased to 50% in the failing hearts. Thus, the human hearts have a greater amount of α1-AMPK activity compared to the rodent hearts. In summary, the protein level and the isoform distribution of AMPK in the heart change significantly during normal development as well as in heart failure. These observations provide a basis for future development of therapeutic strategies for targeting AMPK.
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Affiliation(s)
- Maengjo Kim
- Mitochondria and Metabolism Center, Department of Anesthesiology and Pain Medicine, University of Washington, Seattle, WA 98109, USA
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149
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Interscapular brown adipose tissue metabolic reprogramming during cold acclimation: Interplay of HIF-1α and AMPKα. Biochim Biophys Acta Gen Subj 2011; 1810:1252-61. [DOI: 10.1016/j.bbagen.2011.09.007] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Revised: 08/25/2011] [Accepted: 09/09/2011] [Indexed: 11/16/2022]
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150
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Stephenne X, Foretz M, Taleux N, van der Zon GC, Sokal E, Hue L, Viollet B, Guigas B. Metformin activates AMP-activated protein kinase in primary human hepatocytes by decreasing cellular energy status. Diabetologia 2011; 54:3101-10. [PMID: 21947382 PMCID: PMC3210354 DOI: 10.1007/s00125-011-2311-5] [Citation(s) in RCA: 199] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2011] [Accepted: 08/18/2011] [Indexed: 01/27/2023]
Abstract
AIM/HYPOTHESIS The glucose-lowering drug metformin has been shown to activate hepatic AMP-activated protein kinase (AMPK), a master kinase regulating cellular energy homeostasis. However, the underlying mechanisms remain controversial and have never been investigated in primary human hepatocytes. METHODS Hepatocytes isolated from rat, mouse and human livers were treated with various concentrations of metformin. Isoform-specific AMPKα abundance and activity, as well as intracellular adenine nucleotide levels and mitochondrial oxygen consumption rates were determined at different time points. RESULTS Metformin dose- and time-dependently increased AMPK activity in rat and human hepatocytes, an effect associated with a significant rise in cellular AMP:ATP ratio. Surprisingly, we found that AMPKα2 activity was undetectable in human compared with rat hepatocytes, while AMPKα1 activities were comparable. Accordingly, metformin only increased AMPKα1 activity in human hepatocytes, although both AMPKα isoforms were activated in rat hepatocytes. Analysis of mRNA expression and protein levels confirmed that only AMPKα1 is present in human hepatocytes; it also showed that the distribution of β and γ regulatory subunits differed between species. Finally, we demonstrated that the increase in AMP:ATP ratio in hepatocytes from liver-specific Ampkα1/2 (also known as Prkaa1/2) knockout mice and humans is due to a similar and specific inhibition of the mitochondrial respiratory-chain complex 1 by metformin. CONCLUSIONS/INTERPRETATION Activation of hepatic AMPK by metformin results from a decrease in cellular energy status owing to metformin's AMPK-independent inhibition of the mitochondrial respiratory-chain complex 1. The unique profile of AMPK subunits found in human hepatocytes should be considered when developing new pharmacological agents to target the kinase.
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Affiliation(s)
- X. Stephenne
- Laboratory of Paediatric Hepatology and Cell Therapy, Université catholique de Louvain and Cliniques St Luc, Brussels, Belgium
| | - M. Foretz
- Inserm, U1016, Institut Cochin, Paris, France
- CNRS, UMR8104, Paris, France
- Université Paris Descartes, Paris, France
| | - N. Taleux
- Hormone and Metabolic Research Unit, Université catholique de Louvain and de Duve Institute, Brussels, Belgium
- Bioénergétique Fondamentale et Appliquée Inserm-U884, Université J. Fourier, Grenoble, France
| | - G. C. van der Zon
- Department of Molecular Cell Biology, Leiden University Medical Center, Postzone S1-P, Postbus 9600, 2300 RC Leiden, the Netherlands
| | - E. Sokal
- Laboratory of Paediatric Hepatology and Cell Therapy, Université catholique de Louvain and Cliniques St Luc, Brussels, Belgium
| | - L. Hue
- Hormone and Metabolic Research Unit, Université catholique de Louvain and de Duve Institute, Brussels, Belgium
| | - B. Viollet
- Inserm, U1016, Institut Cochin, Paris, France
- CNRS, UMR8104, Paris, France
- Université Paris Descartes, Paris, France
| | - B. Guigas
- Hormone and Metabolic Research Unit, Université catholique de Louvain and de Duve Institute, Brussels, Belgium
- Department of Molecular Cell Biology, Leiden University Medical Center, Postzone S1-P, Postbus 9600, 2300 RC Leiden, the Netherlands
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