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Fukumoto-Inukai AK, Bermeo K, Arenas I, Rosendo-Pineda MJ, Pimentel-Cabrera JA, Garcia DE. AMPK inhibits voltage-gated calcium channel-current in rat chromaffin cells. Mol Cell Endocrinol 2024; 591:112275. [PMID: 38777212 DOI: 10.1016/j.mce.2024.112275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2024] [Revised: 05/08/2024] [Accepted: 05/18/2024] [Indexed: 05/25/2024]
Abstract
Metabolic changes are critical in the regulation of Ca2+ influx in central and peripheral neuroendocrine cells. To study the regulation of L-type Ca2+ channels by AMPK we used biochemical reagents and ATP/glucose-concentration manipulations in rat chromaffin cells. AICAR and Compound-C, at low concentration, significantly induce changes in L-type Ca2+ channel-current amplitude and voltage dependence. Remarkably, an overlasting decrease in the channel-current density can be induced by lowering the intracellular level of ATP. Accordingly, Ca2+ channel-current density gradually diminishes by decreasing the extracellular glucose concentration. By using immunofluorescence, a decrease in the expression of CaV1.2 is observed while decreasing extracellular glucose, suggesting that AMPK reduces the number of functional Ca2+ channels into the plasma membrane. Together, these results support for the first time the dependence of metabolic changes in the maintenance of Ca2+ channel-current by AMPK. They reveal a key step in Ca2+ influx in secretory cells.
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Affiliation(s)
- A K Fukumoto-Inukai
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, UNAM, Circuito Exterior S/N, Ciudad Universitaria, Coyoacán, 04510, Ciudad de México, Mexico
| | - K Bermeo
- Licenciatura en Neurociencias, Facultad de Medicina, Universidad Nacional Autónoma de México, UNAM, Circuito Exterior S/N, Ciudad Universitaria, Coyoacán, 04510, Ciudad de México, Mexico
| | - I Arenas
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, UNAM, Circuito Exterior S/N, Ciudad Universitaria, Coyoacán, 04510, Ciudad de México, Mexico
| | - M J Rosendo-Pineda
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, UNAM, Circuito Exterior S/N, Ciudad Universitaria, Coyoacán, 04510, Ciudad de México, Mexico
| | - J A Pimentel-Cabrera
- Laboratorio Nacional de Microscopía Avanzada, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
| | - D E Garcia
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, UNAM, Circuito Exterior S/N, Ciudad Universitaria, Coyoacán, 04510, Ciudad de México, Mexico.
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2
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Blandino-Rosano M, Scheys JO, Werneck-de-Castro JP, Louzada RA, Almaça J, Leibowitz G, Rüegg MA, Hall MN, Bernal-Mizrachi E. Novel roles of mTORC2 in regulation of insulin secretion by actin filament remodeling. Am J Physiol Endocrinol Metab 2022; 323:E133-E144. [PMID: 35723227 PMCID: PMC9291412 DOI: 10.1152/ajpendo.00076.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Revised: 06/08/2022] [Accepted: 06/10/2022] [Indexed: 01/23/2023]
Abstract
Mammalian target of rapamycin (mTOR) kinase is an essential hub where nutrients and growth factors converge to control cellular metabolism. mTOR interacts with different accessory proteins to form complexes 1 and 2 (mTORC), and each complex has different intracellular targets. Although mTORC1's role in β-cells has been extensively studied, less is known about mTORC2's function in β-cells. Here, we show that mice with constitutive and inducible β-cell-specific deletion of RICTOR (βRicKO and iβRicKO mice, respectively) are glucose intolerant due to impaired insulin secretion when glucose is injected intraperitoneally. Decreased insulin secretion in βRicKO islets was caused by abnormal actin polymerization. Interestingly, when glucose was administered orally, no difference in glucose homeostasis and insulin secretion were observed, suggesting that incretins are counteracting the mTORC2 deficiency. Mechanistically, glucagon-like peptide-1 (GLP-1), but not gastric inhibitory polypeptide (GIP), rescued insulin secretion in vivo and in vitro by improving actin polymerization in βRicKO islets. In conclusion, mTORC2 regulates glucose-stimulated insulin secretion by promoting actin filament remodeling.NEW & NOTEWORTHY The current studies uncover a novel mechanism linking mTORC2 signaling to glucose-stimulated insulin secretion by modulation of the actin filaments. This work also underscores the important role of GLP-1 in rescuing defects in insulin secretion by modulating actin polymerization and suggests that this effect is independent of mTORC2 signaling.
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Affiliation(s)
- Manuel Blandino-Rosano
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
| | - Joshua O Scheys
- Medical School, Division of Metabolism, Endocrinology, and Diabetes and Brehm Center for Diabetes Research, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan
| | - Joao Pedro Werneck-de-Castro
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
| | - Ruy A Louzada
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
| | - Joana Almaça
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
| | - Gil Leibowitz
- Diabetes Unit and Endocrine Service, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | | | | | - Ernesto Bernal-Mizrachi
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
- Miami VA Healthcare System, Miami, Florida
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3
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Ferri G, Pesce L, Tesi M, Marchetti P, Cardarelli F. β-Cell Pathophysiology: A Review of Advanced Optical Microscopy Applications. Int J Mol Sci 2021; 22:ijms222312820. [PMID: 34884624 PMCID: PMC8657725 DOI: 10.3390/ijms222312820] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 11/24/2021] [Accepted: 11/24/2021] [Indexed: 11/30/2022] Open
Abstract
β-cells convert glucose (input) resulting in the controlled release of insulin (output), which in turn has the role to maintain glucose homeostasis. β-cell function is regulated by a complex interplay between the metabolic processing of the input, its transformation into second-messenger signals, and final mobilization of insulin-containing granules towards secretion of the output. Failure at any level in this process marks β-cell dysfunction in diabetes, thus making β-cells obvious potential targets for therapeutic purposes. Addressing quantitatively β-cell (dys)function at the molecular level in living samples requires probing simultaneously the spatial and temporal dimensions at the proper resolution. To this aim, an increasing amount of research efforts are exploiting the potentiality of biophysical techniques. In particular, using excitation light in the visible/infrared range, a number of optical-microscopy-based approaches have been tailored to the study of β-cell-(dys)function at the molecular level, either in label-free mode (i.e., exploiting intrinsic autofluorescence of cells) or by the use of organic/genetically-encoded fluorescent probes. Here, relevant examples from the literature are reviewed and discussed. Based on this, new potential lines of development in the field are drawn.
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Affiliation(s)
- Gianmarco Ferri
- NEST Laboratory, Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy; (G.F.); (L.P.)
| | - Luca Pesce
- NEST Laboratory, Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy; (G.F.); (L.P.)
| | - Marta Tesi
- Islet Cell Laboratory, Department of Clinical and Experimental Medicine, University of Pisa, 56127 Pisa, Italy; (M.T.); (P.M.)
| | - Piero Marchetti
- Islet Cell Laboratory, Department of Clinical and Experimental Medicine, University of Pisa, 56127 Pisa, Italy; (M.T.); (P.M.)
| | - Francesco Cardarelli
- NEST Laboratory, Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy; (G.F.); (L.P.)
- Correspondence:
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Hua KF, Chao AC, Lin TY, Chen WT, Lee YC, Hsu WH, Lee SL, Wang HM, Yang DI, Ju TC. Ginsenoside compound K reduces the progression of Huntington's disease via the inhibition of oxidative stress and overactivation of the ATM/AMPK pathway. J Ginseng Res 2021; 46:572-584. [PMID: 35818427 PMCID: PMC9270658 DOI: 10.1016/j.jgr.2021.11.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2021] [Revised: 10/16/2021] [Accepted: 11/04/2021] [Indexed: 12/12/2022] Open
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Tumor Metabolic Reprogramming by Adipokines as a Critical Driver of Obesity-Associated Cancer Progression. Int J Mol Sci 2021; 22:ijms22031444. [PMID: 33535537 PMCID: PMC7867092 DOI: 10.3390/ijms22031444] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 01/28/2021] [Accepted: 01/28/2021] [Indexed: 12/11/2022] Open
Abstract
Adiposity is associated with an increased risk of various types of carcinoma. One of the plausible mechanisms underlying the tumor-promoting role of obesity is an aberrant secretion of adipokines, a group of hormones secreted from adipose tissue, which have exhibited both oncogenic and tumor-suppressing properties in an adipokine type- and context-dependent manner. Increasing evidence has indicated that these adipose tissue-derived hormones differentially modulate cancer cell-specific metabolism. Some adipokines, such as leptin, resistin, and visfatin, which are overproduced in obesity and widely implicated in different stages of cancer, promote cellular glucose and lipid metabolism. Conversely, adiponectin, an adipokine possessing potent anti-tumor activities, is linked to a more favorable metabolic phenotype. Adipokines may also play a pivotal role under the reciprocal regulation of metabolic rewiring of cancer cells in tumor microenvironment. Given the fact that metabolic reprogramming is one of the major hallmarks of cancer, understanding the modulatory effects of adipokines on alterations in cancer cell metabolism would provide insight into the crosstalk between obesity, adipokines, and tumorigenesis. In this review, we summarize recent insights into putative roles of adipokines as mediators of cellular metabolic rewiring in obesity-associated tumors, which plays a crucial role in determining the fate of tumor cells.
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Pervaiz S, Bellot GL, Lemoine A, Brenner C. Redox signaling in the pathogenesis of human disease and the regulatory role of autophagy. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2020; 352:189-214. [DOI: 10.1016/bs.ircmb.2020.03.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Ferri G, Digiacomo L, Lavagnino Z, Occhipinti M, Bugliani M, Cappello V, Caracciolo G, Marchetti P, Piston DW, Cardarelli F. Insulin secretory granules labelled with phogrin-fluorescent proteins show alterations in size, mobility and responsiveness to glucose stimulation in living β-cells. Sci Rep 2019; 9:2890. [PMID: 30814595 PMCID: PMC6393586 DOI: 10.1038/s41598-019-39329-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 01/15/2019] [Indexed: 11/13/2022] Open
Abstract
The intracellular life of insulin secretory granules (ISGs) from biogenesis to secretion depends on their structural (e.g. size) and dynamic (e.g. diffusivity, mode of motion) properties. Thus, it would be useful to have rapid and robust measurements of such parameters in living β-cells. To provide such measurements, we have developed a fast spatiotemporal fluctuation spectroscopy. We calculate an imaging-derived Mean Squared Displacement (iMSD), which simultaneously provides the size, average diffusivity, and anomalous coefficient of ISGs, without the need to extract individual trajectories. Clustering of structural and dynamic quantities in a multidimensional parametric space defines the ISGs' properties for different conditions. First, we create a reference using INS-1E cells expressing proinsulin fused to a fluorescent protein (FP) under basal culture conditions and validate our analysis by testing well-established stimuli, such as glucose intake, cytoskeleton disruption, or cholesterol overload. After, we investigate the effect of FP-tagged ISG protein markers on the structural and dynamic properties of the granule. While iMSD analysis produces similar results for most of the lumenal markers, the transmembrane marker phogrin-FP shows a clearly altered result. Phogrin overexpression induces a substantial granule enlargement and higher mobility, together with a partial de-polymerization of the actin cytoskeleton, and reduced cell responsiveness to glucose stimulation. Our data suggest a more careful interpretation of many previous ISG-based reports in living β-cells. The presented data pave the way to high-throughput cell-based screening of ISG structure and dynamics under various physiological and pathological conditions.
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Affiliation(s)
- Gianmarco Ferri
- NEST - Scuola Normale Superiore, Istituto Nanoscienze - CNR (CNR-NANO), Pisa, Italy
- Nanoscopy, Nanophysics, Istituto Italiano di Tecnologia, via Morego 30, 16163, Genoa, Italy
| | - Luca Digiacomo
- Department of Molecular Medicine, "La Sapienza" University of Rome, Rome, Italy
| | - Zeno Lavagnino
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Margherita Occhipinti
- Department of Clinical and Experimental Medicine, Islet Cell Laboratory, University of Pisa, Pisa, Italy
| | - Marco Bugliani
- Department of Clinical and Experimental Medicine, Islet Cell Laboratory, University of Pisa, Pisa, Italy
| | | | - Giulio Caracciolo
- Department of Molecular Medicine, "La Sapienza" University of Rome, Rome, Italy
| | - Piero Marchetti
- Department of Clinical and Experimental Medicine, Islet Cell Laboratory, University of Pisa, Pisa, Italy
| | - David W Piston
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Francesco Cardarelli
- NEST - Scuola Normale Superiore, Istituto Nanoscienze - CNR (CNR-NANO), Pisa, Italy.
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High glucose stimulates cell proliferation and Collagen IV production in rat mesangial cells through inhibiting AMPK-K ATP signaling. Int Urol Nephrol 2017; 49:2079-2086. [PMID: 28748494 DOI: 10.1007/s11255-017-1654-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Accepted: 07/06/2017] [Indexed: 01/22/2023]
Abstract
PURPOSE The present study investigated the putative mechanisms underlying effects of KATP channel on high glucose (HG)-induced mesangial cell proliferation and tissue inhibitors of metalloproteinases (TIMP)-2 and Collagen IV production. METHODS Rat mesangial cells were subjected to whole cell patch clamp to record the KATP channel currents under high glucose (HG, 30 mM) condition. Cell proliferation was measured using a CCK-8 assay. The production of TIMP-2 and Collagen IV and AMP-activated protein kinase (AMPK)-signaling pathway activity was assessed by ELISA and Western blotting, respectively. AMPK agonist (AICAR) was used to analyze the role of this kinase. The expression of KATP subunit (Kir6.1, Kir6.2, SUR1, SUR2A and SUR2B) was examined using quantitative real-time PCR (RT-PCR). RESULTS We found that HG was significant decreases in the expression of Kir6.1, SUB2A and SUB2B, three subunits of KATP, TIMP-2 production, KATP channel activity and AMPK activity, while it promoted the cell proliferation and Collagen IV production in rat mesangial cells. Pretreatment with KATP selective opener (diazoxide, DZX) significantly inhibited HG-induced mesangial cell proliferation, Collagen IV production and decrease in KATP channel activity in rat mesangial cells, which were reversed by pretreatment of 5-hydroxydecanoate, a selective inhibitor of KATP. Moreover, AICAR pretreatment inhibited HG-induced decrease in KATP channel activity. CONCLUSIONS Taken together, activating AMPK-KATP signaling may protect against HG-induced mesangial cell proliferation and Collagen IV production, and, thereby, provides new insights into the molecular mechanisms underlying early diabetic nephropathy (DN).
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9
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Abstract
The pancreatic β-cell secretes insulin in response to elevated plasma glucose. This review applies an external bioenergetic critique to the central processes of glucose-stimulated insulin secretion, including glycolytic and mitochondrial metabolism, the cytosolic adenine nucleotide pool, and its interaction with plasma membrane ion channels. The control mechanisms responsible for the unique responsiveness of the cell to glucose availability are discussed from bioenergetic and metabolic control standpoints. The concept of coupling factor facilitation of secretion is critiqued, and an attempt is made to unravel the bioenergetic basis of the oscillatory mechanisms controlling secretion. The need to consider the physiological constraints operating in the intact cell is emphasized throughout. The aim is to provide a coherent pathway through an extensive, complex, and sometimes bewildering literature, particularly for those unfamiliar with the field.
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Affiliation(s)
- David G Nicholls
- Buck Institute for Research on Aging, Novato, California; and Department of Clinical Sciences, Unit of Molecular Metabolism, Lund University Diabetes Centre, Malmo, Sweden
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10
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Sato Y, Tsuyama T, Sato C, Karim MF, Yoshizawa T, Inoue M, Yamagata K. Hypoxia reduces HNF4α/MODY1 protein expression in pancreatic β-cells by activating AMP-activated protein kinase. J Biol Chem 2017; 292:8716-8728. [PMID: 28364040 DOI: 10.1074/jbc.m116.767574] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Revised: 03/29/2017] [Indexed: 12/12/2022] Open
Abstract
Hypoxia plays a role in the deterioration of β-cell function. Hepatocyte nuclear factor 4α (HNF4α) has an important role in pancreatic β-cells, and mutations of the human HNF4A gene cause a type of maturity-onset diabetes of the young (MODY1). However, it remains unclear whether hypoxia affects the expression of HNF4α in β-cells. Here, we report that hypoxia reduces HNF4α protein expression in β-cells. Hypoxia-inducible factor was not involved in the down-regulation of HNF4α under hypoxic conditions. The down-regulation of HNF4α was dependent on the activation of AMP-activated protein kinase (AMPK), and the reduction of HNF4α protein expression by metformin, an AMPK activator, and hypoxia was inhibited by the overexpression of a kinase-dead (KD) form of AMPKα2. In addition, hypoxia decreased the stability of the HNF4α protein, and the down-regulation of HNF4α was sensitive to proteasome inhibitors. Adenovirus-mediated overexpression of KD-AMPKα2 improved insulin secretion in metformin-treated islets, hypoxic islets, and ob/ob mouse islets. These results suggest that down-regulation of HNF4α could be of importance in β-cell dysfunction by hypoxia.
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Affiliation(s)
- Yoshifumi Sato
- From the Department of Medical Biochemistry, Faculty of Life Sciences, Kumamoto University, Kumamoto, 1-1-1 Honjo, Chuo-ku, Kumamoto 860-8556 and
| | - Tomonori Tsuyama
- From the Department of Medical Biochemistry, Faculty of Life Sciences, Kumamoto University, Kumamoto, 1-1-1 Honjo, Chuo-ku, Kumamoto 860-8556 and
| | - Chinami Sato
- From the Department of Medical Biochemistry, Faculty of Life Sciences, Kumamoto University, Kumamoto, 1-1-1 Honjo, Chuo-ku, Kumamoto 860-8556 and
| | - Md Fazlul Karim
- From the Department of Medical Biochemistry, Faculty of Life Sciences, Kumamoto University, Kumamoto, 1-1-1 Honjo, Chuo-ku, Kumamoto 860-8556 and
| | - Tatsuya Yoshizawa
- From the Department of Medical Biochemistry, Faculty of Life Sciences, Kumamoto University, Kumamoto, 1-1-1 Honjo, Chuo-ku, Kumamoto 860-8556 and
| | - Masahiro Inoue
- the Department of Biochemistry, Osaka Medical Center for Cancer and Cardiovascular Diseases, 1-3-3 Nakamichi, Higashinari-ku, Osaka 537-8511, Japan
| | - Kazuya Yamagata
- From the Department of Medical Biochemistry, Faculty of Life Sciences, Kumamoto University, Kumamoto, 1-1-1 Honjo, Chuo-ku, Kumamoto 860-8556 and
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11
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Yavari A, Stocker CJ, Ghaffari S, Wargent ET, Steeples V, Czibik G, Pinter K, Bellahcene M, Woods A, Martínez de Morentin PB, Cansell C, Lam BYH, Chuster A, Petkevicius K, Nguyen-Tu MS, Martinez-Sanchez A, Pullen TJ, Oliver PL, Stockenhuber A, Nguyen C, Lazdam M, O'Dowd JF, Harikumar P, Tóth M, Beall C, Kyriakou T, Parnis J, Sarma D, Katritsis G, Wortmann DDJ, Harper AR, Brown LA, Willows R, Gandra S, Poncio V, de Oliveira Figueiredo MJ, Qi NR, Peirson SN, McCrimmon RJ, Gereben B, Tretter L, Fekete C, Redwood C, Yeo GSH, Heisler LK, Rutter GA, Smith MA, Withers DJ, Carling D, Sternick EB, Arch JRS, Cawthorne MA, Watkins H, Ashrafian H. Chronic Activation of γ2 AMPK Induces Obesity and Reduces β Cell Function. Cell Metab 2016; 23:821-36. [PMID: 27133129 PMCID: PMC4873618 DOI: 10.1016/j.cmet.2016.04.003] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 03/01/2016] [Accepted: 04/01/2016] [Indexed: 12/02/2022]
Abstract
Despite significant advances in our understanding of the biology determining systemic energy homeostasis, the treatment of obesity remains a medical challenge. Activation of AMP-activated protein kinase (AMPK) has been proposed as an attractive strategy for the treatment of obesity and its complications. AMPK is a conserved, ubiquitously expressed, heterotrimeric serine/threonine kinase whose short-term activation has multiple beneficial metabolic effects. Whether these translate into long-term benefits for obesity and its complications is unknown. Here, we observe that mice with chronic AMPK activation, resulting from mutation of the AMPK γ2 subunit, exhibit ghrelin signaling-dependent hyperphagia, obesity, and impaired pancreatic islet insulin secretion. Humans bearing the homologous mutation manifest a congruent phenotype. Our studies highlight that long-term AMPK activation throughout all tissues can have adverse metabolic consequences, with implications for pharmacological strategies seeking to chronically activate AMPK systemically to treat metabolic disease.
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Affiliation(s)
- Arash Yavari
- Experimental Therapeutics, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK.
| | - Claire J Stocker
- The Buckingham Institute for Translational Medicine, University of Buckingham, Buckingham MK18 1EG, UK
| | - Sahar Ghaffari
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Edward T Wargent
- The Buckingham Institute for Translational Medicine, University of Buckingham, Buckingham MK18 1EG, UK
| | - Violetta Steeples
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Gabor Czibik
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Katalin Pinter
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Mohamed Bellahcene
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Angela Woods
- Cellular Stress Group, MRC Clinical Sciences Centre, Imperial College London, London SW7 2AZ, UK
| | | | - Céline Cansell
- Rowett Institute of Nutrition and Health, University of Aberdeen, Aberdeen AB25 2ZD, UK
| | - Brian Y H Lam
- University of Cambridge Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, Cambridge CB2 0QQ, UK
| | - André Chuster
- Pos Graduação Ciências Médicas, Faculdade Ciências Médicas, Universidade Federal de Minas Gerais, Belo Horizonte-MG 31270-901, Brazil
| | - Kasparas Petkevicius
- University of Cambridge Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, Cambridge CB2 0QQ, UK
| | - Marie-Sophie Nguyen-Tu
- Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology, and Metabolism, Imperial College London, London SW7 2AZ, UK
| | - Aida Martinez-Sanchez
- Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology, and Metabolism, Imperial College London, London SW7 2AZ, UK
| | - Timothy J Pullen
- Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology, and Metabolism, Imperial College London, London SW7 2AZ, UK
| | - Peter L Oliver
- MRC Functional Genomics Unit, Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, UK
| | - Alexander Stockenhuber
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Chinh Nguyen
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Merzaka Lazdam
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK
| | - Jacqueline F O'Dowd
- The Buckingham Institute for Translational Medicine, University of Buckingham, Buckingham MK18 1EG, UK
| | - Parvathy Harikumar
- The Buckingham Institute for Translational Medicine, University of Buckingham, Buckingham MK18 1EG, UK
| | - Mónika Tóth
- Department of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest 1083, Hungary
| | - Craig Beall
- Cardiovascular and Diabetes Medicine, Medical Research Institute, University of Dundee, Dundee DD1 9SY, UK
| | - Theodosios Kyriakou
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Julia Parnis
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Dhruv Sarma
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - George Katritsis
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Diana D J Wortmann
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Andrew R Harper
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Laurence A Brown
- Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, OX3 9DU, UK
| | - Robin Willows
- Cellular Stress Group, MRC Clinical Sciences Centre, Imperial College London, London SW7 2AZ, UK
| | - Silvia Gandra
- Pos Graduação Ciências Médicas, Faculdade Ciências Médicas, Universidade Federal de Minas Gerais, Belo Horizonte-MG 31270-901, Brazil
| | - Victor Poncio
- Universidade Estadual de Campinas, Campinas-SP 13083-970, Brazil
| | | | - Nathan R Qi
- Department of Internal Medicine, Division of Metabolism, Endocrinology, and Diabetes, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Stuart N Peirson
- Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, OX3 9DU, UK
| | - Rory J McCrimmon
- Cardiovascular and Diabetes Medicine, Medical Research Institute, University of Dundee, Dundee DD1 9SY, UK
| | - Balázs Gereben
- Department of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest 1083, Hungary
| | - László Tretter
- Department of Medical Biochemistry, Semmelweis University, Budapest 1085, Hungary; MTA-SE Laboratory for Neurobiochemistry, Semmelweis University, Budapest 1085, Hungary
| | - Csaba Fekete
- Department of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest 1083, Hungary; Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, Tupper Research Institute, Tufts Medical Center, Boston, MA 02111, USA
| | - Charles Redwood
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Giles S H Yeo
- University of Cambridge Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, Cambridge CB2 0QQ, UK
| | - Lora K Heisler
- Rowett Institute of Nutrition and Health, University of Aberdeen, Aberdeen AB25 2ZD, UK
| | - Guy A Rutter
- Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology, and Metabolism, Imperial College London, London SW7 2AZ, UK
| | - Mark A Smith
- Metabolic Signalling Group, MRC Clinical Sciences Centre, Imperial College London, London W12 0NN, UK
| | - Dominic J Withers
- Metabolic Signalling Group, MRC Clinical Sciences Centre, Imperial College London, London W12 0NN, UK
| | - David Carling
- Cellular Stress Group, MRC Clinical Sciences Centre, Imperial College London, London SW7 2AZ, UK
| | - Eduardo B Sternick
- Pos Graduação Ciências Médicas, Faculdade Ciências Médicas, Universidade Federal de Minas Gerais, Belo Horizonte-MG 31270-901, Brazil
| | - Jonathan R S Arch
- The Buckingham Institute for Translational Medicine, University of Buckingham, Buckingham MK18 1EG, UK
| | - Michael A Cawthorne
- The Buckingham Institute for Translational Medicine, University of Buckingham, Buckingham MK18 1EG, UK
| | - Hugh Watkins
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
| | - Houman Ashrafian
- Experimental Therapeutics, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 9DU, UK; Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK; Experimental Therapeutics, Clinical Science Group, New Medicines, UCB Pharma S.A., Slough, Berkshire SL1 3WE, UK.
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12
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Pancreatic β-cell identity, glucose sensing and the control of insulin secretion. Biochem J 2015; 466:203-18. [PMID: 25697093 DOI: 10.1042/bj20141384] [Citation(s) in RCA: 251] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Insulin release from pancreatic β-cells is required to maintain normal glucose homoeostasis in man and many other animals. Defective insulin secretion underlies all forms of diabetes mellitus, a disease currently reaching epidemic proportions worldwide. Although the destruction of β-cells is responsible for Type 1 diabetes (T1D), both lowered β-cell mass and loss of secretory function are implicated in Type 2 diabetes (T2D). Emerging results suggest that a functional deficiency, involving de-differentiation of the mature β-cell towards a more progenitor-like state, may be an important driver for impaired secretion in T2D. Conversely, at least in rodents, reprogramming of islet non-β to β-cells appears to occur spontaneously in models of T1D, and may occur in man. In the present paper, we summarize the biochemical properties which define the 'identity' of the mature β-cell as a glucose sensor par excellence. In particular, we discuss the importance of suppressing a group of 11 'disallowed' housekeeping genes, including Ldha and the monocarboxylate transporter Mct1 (Slc16a1), for normal nutrient sensing. We then survey the changes in the expression and/or activity of β-cell-enriched transcription factors, including FOXO1, PDX1, NKX6.1, MAFA and RFX6, as well as non-coding RNAs, which may contribute to β-cell de-differentiation and functional impairment in T2D. The relevance of these observations for the development of new approaches to treat T1D and T2D is considered.
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13
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HAP1 helps to regulate actin-based transport of insulin-containing granules in pancreatic β cells. Histochem Cell Biol 2015; 144:39-48. [PMID: 25744490 DOI: 10.1007/s00418-015-1311-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/14/2015] [Indexed: 10/23/2022]
Abstract
Huntingtin-associated protein 1 (HAP1) is enriched in neurons and binds to polyglutamine-expanded huntingtin. It consists of two alternatively spliced isoforms, HAP1A and HAP1B, which differ only in their short C-terminal sequences. Both HAP1A and HAP1B have been also detected in pancreatic β cells, where the loss of HAP1 impairs glucose-stimulated insulin secretion. Here, we use time-lapse laser scanning confocal microscopy to provide direct evidence that HAP1A, but not HAP1B, co-localizes and co-migrates with insulin-containing vesicles and actin-based myosin Va motor protein in the INS-1 pancreatic β cell line. Knocking down HAP1 expression using small interfering RNA significantly inhibited actin-based transport of insulin vesicles following glucose stimulation. Co-immunoprecipitation experiments demonstrated interaction between HAP1A, myosin Va, and phogrin, a transmembrane protein in insulin-containing vesicles. Stimulating INS-1 cells with glucose increased the association of HAP1A with myosin Va, while silencing HAP1 expression reduced the association of myosin Va with phogrin after glucose stimulation, without affecting levels of myosin Va or actin. Our results provide real-time evidence in living cells that HAP1 may help regulate transport of insulin-containing secretory granules along cortical actin filaments. This also raises the possibility that HAP1 may play an important role in actin-based secretory vesicle trafficking in neurons.
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14
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Heaslip AT, Nelson SR, Lombardo AT, Beck Previs S, Armstrong J, Warshaw DM. Cytoskeletal dependence of insulin granule movement dynamics in INS-1 beta-cells in response to glucose. PLoS One 2014; 9:e109082. [PMID: 25310693 PMCID: PMC4195697 DOI: 10.1371/journal.pone.0109082] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Accepted: 09/01/2014] [Indexed: 02/03/2023] Open
Abstract
For pancreatic β-cells to secrete insulin in response to elevated blood glucose, insulin granules retained within the subplasmalemmal space must be transported to sites of secretion on the plasma membrane. Using a combination of super-resolution STORM imaging and live cell TIRF microscopy we investigate how the organization and dynamics of the actin and microtubule cytoskeletons in INS-1 β-cells contribute to this process. GFP-labeled insulin granules display 3 different modes of motion (stationary, diffusive-like, and directed). Diffusive-like motion dominates in basal, low glucose conditions. Upon glucose stimulation no gross rearrangement of the actin cytoskeleton is observed but there are increases in the 1) rate of microtubule polymerization; 2) rate of diffusive-like motion; and 3) proportion of granules undergoing microtubule-based directed motion. By pharmacologically perturbing the actin and microtubule cytoskeletons, we determine that microtubule-dependent granule transport occurs within the subplasmalemmal space and that the actin cytoskeleton limits this transport in basal conditions, when insulin secretion needs to be inhibited.
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Affiliation(s)
- Aoife T. Heaslip
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
| | - Shane R. Nelson
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
| | - Andrew T. Lombardo
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
| | - Samantha Beck Previs
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
| | - Jessica Armstrong
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
| | - David M. Warshaw
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
- * E-mail:
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15
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Interactome analysis of AMP-activated protein kinase (AMPK)-α1 and -β1 in INS-1 pancreatic beta-cells by affinity purification-mass spectrometry. Sci Rep 2014; 4:4376. [PMID: 24625528 PMCID: PMC3953747 DOI: 10.1038/srep04376] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Accepted: 02/26/2014] [Indexed: 12/23/2022] Open
Abstract
The heterotrimeric enzyme AMP-activated protein kinase (AMPK) is a major metabolic factor that regulates the homeostasis of cellular energy. In particular, AMPK mediates the insulin resistance that is associated with type 2 diabetes. Generally, cellular processes require tight regulation of protein kinases, which is effected through their formation of complex with other proteins and substrates. Despite their critical function in regulation and pathogenesis, there are limited data on the interaction of protein kinases. To identify proteins that interact with AMPK, we performed large-scale affinity purification (AP)-mass spectrometry (MS) of the AMPK-α1 and -β1 subunits. Through a comprehensive analysis, using a combination of immunoprecipitaion and ion trap mass spectrometry, we identified 381 unique proteins in the AMPKα/β interactomes: 325 partners of AMPK-α1 and 243 for AMPK-β1. Further, we identified 196 novel protein-protein interactions with AMPK-α1 and AMPK-β1. Notably, in our bioinformatics analysis, the novel interaction partners mediated functions that are related to the regulation of actin organization. Specifically, several such proteins were linked to pancreatic beta-cell functions, including glucose-stimulated insulin secretion, beta-cell development, beta-cell differentiation, and cell-cell communication.
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16
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Deng R, Nie A, Jian F, Liu Y, Tang H, Zhang J, Zhang Y, Shao L, Li F, Zhou L, Wang X, Ning G. Acute exposure of beta-cells to troglitazone decreases insulin hypersecretion via activating AMPK. Biochim Biophys Acta Gen Subj 2014; 1840:577-85. [DOI: 10.1016/j.bbagen.2013.10.021] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2013] [Revised: 10/05/2013] [Accepted: 10/13/2013] [Indexed: 11/16/2022]
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17
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Role of the mammalian target of rapamycin (mTOR) complexes in pancreatic β-cell mass regulation. VITAMINS AND HORMONES 2014; 95:425-69. [PMID: 24559928 DOI: 10.1016/b978-0-12-800174-5.00017-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Exquisite regulation of insulin secretion by pancreatic β-cells is essential to maintain metabolic homeostasis. β-Cell mass must be accordingly adapted to metabolic needs and can be largely modified under different situations. The mammalian target of rapamycin (mTOR) complexes has been consistently identified as key modulators of β-cell mass. mTOR can be found into two different complexes, mTORC1 and mTORC2. Under systemic insulin resistance, mTORC1/mTORC2 signaling in β-cells is needed to increase β-cell mass and insulin secretion. However, type 2 diabetes arises when these compensatory mechanisms fail, being the role of mTOR complexes still obscure in β-cell failure. In this chapter, we introduce the protein composition and regulation of mTOR complexes and their role in pancreatic β-cells. Furthermore, we describe their main signaling effectors through the review of numerous animal models, which indicate the essential role of mTORC1/mTORC2 in pancreatic β-cell mass regulation.
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18
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Dehydroepiandrosterone-sulfate (DHEAS) promotes MIN6 cells insulin secretion via inhibition of AMP-activated protein kinase. Biochem Biophys Res Commun 2013; 440:756-61. [PMID: 24120945 DOI: 10.1016/j.bbrc.2013.10.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Accepted: 10/01/2013] [Indexed: 01/17/2023]
Abstract
Derived from adrenal cortical, dehydroepiandrosterone-sulfate (DHEAS) is a precursor to androgens and estrogens, with various bioactivities. Although it has the property of anti-diabetes, the long-term effect of DHEAS on insulin secretion in beta-cells is still unclear. In this study, the effect of DHEAS on the insulin secretion activity in MIN6 cell lines in vitro was assessed. Insulin biosynthesis and secretion were stimulated by DHEAS for 24h. DHEAS inhibited the AMPK activation and upregulated the expression of ACC-1. These findings indicate that DHEAS may exert prominent stimulatory effects on insulin secretion partly via AMPK inhibition and ACC-1 upregulation.
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19
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Beall C, Watterson KR, McCrimmon RJ, Ashford MLJ. AMPK modulates glucose-sensing in insulin-secreting cells by altered phosphotransfer to KATP channels. J Bioenerg Biomembr 2013; 45:229-41. [PMID: 23575945 DOI: 10.1007/s10863-013-9509-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Accepted: 03/22/2013] [Indexed: 10/27/2022]
Abstract
Glucose-sensing (GS) behaviour in pancreatic β-cells is dependent on ATP-sensitive K(+) channel (KATP) activity, which is controlled by the relative levels of the KATP ligands ATP and ADP, responsible for closing and opening KATP, respectively. However, the mechanism by which β-cells transfer energy status from mitochondria to KATP, and hence to altered electrical excitability and insulin secretion, is presently unclear. Recent work has demonstrated a critical role for AMP-activated protein kinase (AMPK) in GS behaviour of cells. Electrophysiological recordings, coupled with measurements of gene and protein expression were made from rat insulinoma cells to investigate whether AMPK activity regulates this energy transfer process. Using the whole-cell recording configuration with sufficient intracellular ATP to keep KATP closed, raised AMPK activity induced GS electrical behaviour. This effect was prevented by the AMPK inhibitor, compound C and required a phosphotransfer process. Indeed, high levels of intracellular phosphocreatine or the presence of the adenylate kinase (AK) inhibitor AP5A blocked this action of AMPK. Using conditions that maximised AMPK-induced KATP opening, there was a significant increase in AK1, AK2 and UCP2 mRNA expression. Thus we propose that KATP opening in response to lowered glucose concentration requires AMPK activity, perhaps in concert with increased AK and UCP2 to enable mitochondrial-derived ADP signals to be transferred to plasma membrane KATP by phosphotransfer cascades.
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Affiliation(s)
- Craig Beall
- Division of Cardiovascular and Diabetes Medicine, Medical Research Institute, Ninewells Hospital and Medical School, University of Dundee, Dundee, Scotland, UK
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20
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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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21
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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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22
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Iglesias J, Barg S, Vallois D, Lahiri S, Roger C, Yessoufou A, Pradevand S, McDonald A, Bonal C, Reimann F, Gribble F, Debril MB, Metzger D, Chambon P, Herrera P, Rutter GA, Prentki M, Thorens B, Wahli W. PPARβ/δ affects pancreatic β cell mass and insulin secretion in mice. J Clin Invest 2012; 122:4105-17. [PMID: 23093780 DOI: 10.1172/jci42127] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2012] [Accepted: 07/19/2012] [Indexed: 12/30/2022] Open
Abstract
PPARβ/δ protects against obesity by reducing dyslipidemia and insulin resistance via effects in muscle, adipose tissue, and liver. However, its function in pancreas remains ill defined. To gain insight into its hypothesized role in β cell function, we specifically deleted Pparb/d in the epithelial compartment of the mouse pancreas. Mutant animals presented increased numbers of islets and, more importantly, enhanced insulin secretion, causing hyperinsulinemia. Gene expression profiling of pancreatic β cells indicated a broad repressive function of PPARβ/δ affecting the vesicular and granular compartment as well as the actin cytoskeleton. Analyses of insulin release from isolated PPARβ/δ-deficient islets revealed an accelerated second phase of glucose-stimulated insulin secretion. These effects in PPARβ/δ-deficient islets correlated with increased filamentous actin (F-actin) disassembly and an elevation in protein kinase D activity that altered Golgi organization. Taken together, these results provide evidence for a repressive role for PPARβ/δ in β cell mass and insulin exocytosis, and shed a new light on PPARβ/δ metabolic action.
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Affiliation(s)
- José Iglesias
- Center for Integrative Genomics, National Research Center Frontiers in Genetics, University of Lausanne, Lausanne, Switzerland
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23
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Tarasov AI, Semplici F, Ravier MA, Bellomo EA, Pullen TJ, Gilon P, Sekler I, Rizzuto R, Rutter GA. The mitochondrial Ca2+ uniporter MCU is essential for glucose-induced ATP increases in pancreatic β-cells. PLoS One 2012; 7:e39722. [PMID: 22829870 PMCID: PMC3400633 DOI: 10.1371/journal.pone.0039722] [Citation(s) in RCA: 139] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Accepted: 05/25/2012] [Indexed: 01/09/2023] Open
Abstract
Glucose induces insulin release from pancreatic β-cells by stimulating ATP synthesis, membrane depolarisation and Ca2+ influx. As well as activating ATP-consuming processes, cytosolic Ca2+ increases may also potentiate mitochondrial ATP synthesis. Until recently, the ability to study the role of mitochondrial Ca2+ transport in glucose-stimulated insulin secretion has been hindered by the absence of suitable approaches either to suppress Ca2+ uptake into these organelles, or to examine the impact on β-cell excitability. Here, we have combined patch-clamp electrophysiology with simultaneous real-time imaging of compartmentalised changes in Ca2+ and ATP/ADP ratio in single primary mouse β-cells, using recombinant targeted (Pericam or Perceval, respectively) as well as entrapped intracellular (Fura-Red), probes. Through shRNA-mediated silencing we show that the recently-identified mitochondrial Ca2+ uniporter, MCU, is required for depolarisation-induced mitochondrial Ca2+ increases, and for a sustained increase in cytosolic ATP/ADP ratio. By contrast, silencing of the mitochondrial Na+-Ca2+ exchanger NCLX affected the kinetics of glucose-induced changes in, but not steady state values of, cytosolic ATP/ADP. Exposure to gluco-lipotoxic conditions delayed both mitochondrial Ca2+ uptake and cytosolic ATP/ADP ratio increases without affecting the expression of either gene. Mitochondrial Ca2+ accumulation, mediated by MCU and modulated by NCLX, is thus required for normal glucose sensing by pancreatic β-cells, and becomes defective in conditions mimicking the diabetic milieu.
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Affiliation(s)
- Andrei I. Tarasov
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Francesca Semplici
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Magalie A. Ravier
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
- Institut de Génomique Fonctionnelle, INSERM U661, CNRS UMR5203, Université Montpellier I et II, Montpellier, France
| | - Elisa A. Bellomo
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Timothy J. Pullen
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Patrick Gilon
- Pole of Endocrinology, Diabetes and Nutrition, Faculty of Medicine, Université Catholique de Louvain, Brussels, Belgium
| | - Israel Sekler
- Department of Physiology, Faculty of Health Sciences, Ben Gurion University, Beer-Sheva, Israel
| | - Rosario Rizzuto
- Department of Biomedical Sciences, University of Padua, Padua, Italy
| | - Guy A. Rutter
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
- * E-mail:
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24
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Chen XY, Gu XT, Saiyin H, Wan B, Zhang YJ, Li J, Wang YL, Gao R, Wang YF, Dong WP, Najjar SM, Zhang CY, Ding HF, Liu JO, Yu L. Brain-selective kinase 2 (BRSK2) phosphorylation on PCTAIRE1 negatively regulates glucose-stimulated insulin secretion in pancreatic β-cells. J Biol Chem 2012; 287:30368-75. [PMID: 22798068 DOI: 10.1074/jbc.m112.375618] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Brain-selective kinase 2 (BRSK2) has been shown to play an essential role in neuronal polarization. In the present study, we show that BRSK2 is also abundantly expressed in pancreatic islets and MIN6 β-cell line. Yeast two-hybrid screening, GST fusion protein pull-down, and co-immunoprecipitation assays reveal that BRSK2 interacts with CDK-related protein kinase PCTAIRE1, a kinase involved in neurite outgrowth and neurotransmitter release. In MIN6 cells, BRSK2 co-localizes with PCTAIRE1 in the cytoplasm and phosphorylates one of its serine residues, Ser-12. Phosphorylation of PCTAIRE1 by BRSK2 reduces glucose-stimulated insulin secretion (GSIS) in MIN6 cells. Conversely, knockdown of BRSK2 by siRNA increases serum insulin levels in mice. Our results reveal a novel function of BRSK2 in the regulation of GSIS in β-cells via a PCTAIRE1-dependent mechanism and suggest that BRSK2 is an attractive target for developing novel diabetic drugs.
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Affiliation(s)
- Xin-Ya Chen
- State Key Laboratory of Genetic Engineering, School of Life Science, Institutes of Biomedical Sciences, Fudan University, Shanghai, 200433, China
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25
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Saha AK, Xu XJ, Balon TW, Brandon A, Kraegen EW, Ruderman NB. Insulin resistance due to nutrient excess: is it a consequence of AMPK downregulation? Cell Cycle 2012; 10:3447-51. [PMID: 22067655 DOI: 10.4161/cc.10.20.17886] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
It has long been known that excesses of glucose and branched chain amino acids, such as leucine, lead to insulin resistance in skeletal muscle. A recent study in incubated rat muscle suggests that both molecules may do so by virtue of their ability to downregulate the fuel sensing and signaling enzyme AMP-activated protein kinase (AMPK) and activate mTOR/p70S6 kinase (p70S6K) signaling. The results also demonstrated that inhibition of mTOR/p70S6K with rapamycin prevented the development of insulin resistance but had no effect on AMPK activity (Thr172 phosphorylation of its catalytic subunit). In contrast, activation of AMPK by both AICAR and α-lipoic acid led to the phosphorylation of specific molecules that diminished both mTOR/p70S6K signaling and insulin resistance. These findings suggest that downregulation of AMPK precedes mTOR/p70S6K activation in mediating glucose and leucine-induced insulin resistance, although the mechanism by which it does so remains to be determined. Also requiring study is how an excess of the two nutrients leads to AMPK downregulation.
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Affiliation(s)
- Asish K Saha
- Diabetes Research Unit, Section of Endocrinology, Department of Medicine, Boston University Medical Center, Boston, MA, USA.
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26
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Langelueddecke C, Jakab M, Ketterl N, Lehner L, Hufnagl C, Schmidt S, Geibel JP, Fuerst J, Ritter M. Effect of the AMP-kinase modulators AICAR, metformin and compound C on insulin secretion of INS-1E rat insulinoma cells under standard cell culture conditions. Cell Physiol Biochem 2012; 29:75-86. [PMID: 22415077 DOI: 10.1159/000337589] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/19/2011] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND/AIMS The function of β-cells is regulated by nutrient uptake and metabolism. The cells' metabolic state can be expressed as concentration ratios of AMP, ADP and ATP. Relative changes in these ratios regulate insulin release. An increase in the intracellular ATP concentration causes closure of K(ATP) channels and cell membrane depolarization, which triggers stimulus-secretion coupling (SSC). In addition to K(ATP) channels, the AMP-dependent protein kinase (AMPK), a major cellular fuel sensor in a variety of cells and tissues, also affects insulin secretion and β-cell survival. In a previous study we found that the widely used AMPK inhibitor compound C retards proliferation and induces apoptosis in the rat β-cell line INS-1E. We therefore tested the effects of AMPK activators (AICAR and metformin), and compound C on AMPK phosphorylation, insulin secretion, K(ATP) channel currents, cell membrane potential, intracellular calcium concentration, apoptosis and cell cycle distribution of INS-1E cells under standard cell culture conditions (11 mM glucose). METHODS Western blotting, ELISA, patch-clamp, calcium imaging and flow cytometry. RESULTS We found that basal AMPK phosphorylation is enhanced by AICAR (1 mM) and metformin (1 mM) but remained unaffected by compound C (10 μM). Both AICAR and compound C stimulated basal insulin secretion whereas metformin had no effect. Pre-incubation with AICAR (1 mM) caused an inhibition of K(ATP) currents but did not significantly alter the average cell membrane potential (Vm) or the threshold potential of electrical activity. Acute administration of AICAR (300 μM) led to a depolarization of Vm, which was not due to an inhibition of the basal- or glucose-induced chloride conductance, and was not accompanied by elevations of intracellular calcium (Ca(i)). AICAR had no additive blocking effect on K(ATP) currents when applied together with tolbutamide. Compound C applied over 24 hours induced an increase in the percentage of cells positive for caspase activity, whereas AICAR (1 mM) applied for 48 hours was without effect. Medium glucose concentration <3 mM caused cell cycle arrest, caspase activation and an increase of cell granularity. CONCLUSION We conclude that under standard cell culture conditions the AMPK modulators AICAR and compound C, but not metformin, stimulate insulin secretion by AMPK-independent mechanisms.
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Scott KEN, Wheeler FB, Davis AL, Thomas MJ, Ntambi JM, Seals DF, Kridel SJ. Metabolic regulation of invadopodia and invasion by acetyl-CoA carboxylase 1 and de novo lipogenesis. PLoS One 2012; 7:e29761. [PMID: 22238651 PMCID: PMC3253107 DOI: 10.1371/journal.pone.0029761] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2011] [Accepted: 12/04/2011] [Indexed: 01/04/2023] Open
Abstract
Invadopodia are membrane protrusions that facilitate matrix degradation and cellular invasion. Although lipids have been implicated in several aspects of invadopodia formation, the contributions of de novo fatty acid synthesis and lipogenesis have not been defined. Inhibition of acetyl-CoA carboxylase 1 (ACC1), the committed step of fatty acid synthesis, reduced invadopodia formation in Src-transformed 3T3 (3T3-Src) cells, and also decreased the ability to degrade gelatin. Inhibition of fatty acid synthesis through AMP-activated kinase (AMPK) activation and ACC phosphorylation also decreased invadopodia incidence. The addition of exogenous 16∶0 and 18∶1 fatty acid, products of de novo fatty acid synthesis, restored invadopodia and gelatin degradation to cells with decreased ACC1 activity. Pharmacological inhibition of ACC also altered the phospholipid profile of 3T3-Src cells, with the majority of changes occurring in the phosphatidylcholine (PC) species. Exogenous supplementation with the most abundant PC species, 34∶1 PC, restored invadopodia incidence, the ability to degrade gelatin and the ability to invade through matrigel to cells deficient in ACC1 activity. On the other hand, 30∶0 PC did not restore invadopodia and 36∶2 PC only restored invadopodia incidence and gelatin degradation, but not cellular invasion through matrigel. Pharmacological inhibition of ACC also reduced the ability of MDA-MB-231 breast, Snb19 glioblastoma, and PC-3 prostate cancer cells to invade through matrigel. Invasion of PC-3 cells through matrigel was also restored by 34∶1 PC supplementation. Collectively, the data elucidate the novel metabolic regulation of invadopodia and the invasive process by de novo fatty acid synthesis and lipogenesis.
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Affiliation(s)
- Kristen E. N. Scott
- Department of Cancer Biology, Wake Forest School of Medicine, Winston Salem, North Carolina, United States of America
| | - Frances B. Wheeler
- Department of Cancer Biology, Wake Forest School of Medicine, Winston Salem, North Carolina, United States of America
| | - Amanda L. Davis
- Department of Cancer Biology, Wake Forest School of Medicine, Winston Salem, North Carolina, United States of America
| | - Michael J. Thomas
- Department of Biochemistry, Wake Forest School of Medicine, Winston Salem, North Carolina, United States of America
- Comprehensive Cancer Center, Wake Forest School of Medicine, Winston Salem, North Carolina, United States of America
| | - James M. Ntambi
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Darren F. Seals
- Department of Cancer Biology, Wake Forest School of Medicine, Winston Salem, North Carolina, United States of America
- Comprehensive Cancer Center, Wake Forest School of Medicine, Winston Salem, North Carolina, United States of America
| | - Steven J. Kridel
- Department of Cancer Biology, Wake Forest School of Medicine, Winston Salem, North Carolina, United States of America
- Comprehensive Cancer Center, Wake Forest School of Medicine, Winston Salem, North Carolina, United States of America
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Rondas D, Tomas A, Soto-Ribeiro M, Wehrle-Haller B, Halban PA. Novel mechanistic link between focal adhesion remodeling and glucose-stimulated insulin secretion. J Biol Chem 2011; 287:2423-36. [PMID: 22139838 DOI: 10.1074/jbc.m111.279885] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Actin cytoskeleton remodeling is well known to be positively involved in glucose-stimulated pancreatic β cell insulin secretion. We have observed glucose-stimulated focal adhesion remodeling at the β cell surface and have shown this to be crucial for glucose-stimulated insulin secretion. However, the mechanistic link between such remodeling and the insulin secretory machinery remained unknown and was the major aim of this study. MIN6B1 cells, a previously validated model of primary β cell function, were used for all experiments. Total internal reflection fluorescence microscopy revealed the glucose-responsive co-localization of focal adhesion kinase (FAK) and paxillin with integrin β1 at the basal cell surface after short term stimulation. In addition, blockade of the interaction between β1 integrins and the extracellular matrix with an anti-β1 integrin antibody (Ha2/5) inhibited short term glucose-induced phosphorylation of FAK (Tyr-397), paxillin (Tyr-118), and ERK1/2 (Thr-202/Tyr-204). Pharmacological inhibition of FAK activity blocked glucose-induced actin cytoskeleton remodeling and glucose-induced disruption of the F-actin/SNAP-25 association at the plasma membrane as well as the distribution of insulin granules to regions in close proximity to the plasma membrane. Furthermore, FAK inhibition also completely blocked short term glucose-induced activation of the Akt/AS160 signaling pathway. In conclusion, these results indicate 1) that glucose-induced activation of FAK, paxillin, and ERK1/2 is mediated by β1 integrin intracellular signaling, 2) a mechanism whereby FAK mediates glucose-induced actin cytoskeleton remodeling, hence allowing docking and fusion of insulin granules to the plasma membrane, and 3) a possible functional role for the Akt/AS160 signaling pathway in the FAK-mediated regulation of glucose-stimulated insulin secretion.
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Affiliation(s)
- Dieter Rondas
- Department of Genetic Medicine and Development, University of Geneva, CH-1211 Geneva 4, Switzerland.
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Ju TC, Chen HM, Lin JT, Chang CP, Chang WC, Kang JJ, Sun CP, Tao MH, Tu PH, Chang C, Dickson DW, Chern Y. Nuclear translocation of AMPK-alpha1 potentiates striatal neurodegeneration in Huntington's disease. ACTA ACUST UNITED AC 2011; 194:209-27. [PMID: 21768291 PMCID: PMC3144412 DOI: 10.1083/jcb.201105010] [Citation(s) in RCA: 151] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Adenosine monophosphate-activated protein kinase (AMPK) is a major energy sensor that maintains cellular energy homeostasis. Huntington's disease (HD) is a neurodegenerative disorder caused by the expansion of CAG repeats in the huntingtin (Htt) gene. In this paper, we report that activation of the α1 isoform of AMPK (AMPK-α1) occurred in striatal neurons of humans and mice with HD. Overactivation of AMPK in the striatum caused brain atrophy, facilitated neuronal loss, and increased formation of Htt aggregates in a transgenic mouse model (R6/2) of HD. Such nuclear accumulation of AMPK-α1 was activity dependent. Prevention of nuclear translocation or inactivation of AMPK-α1 ameliorated cell death and down-regulation of Bcl2 caused by mutant Htt (mHtt). Conversely, enhanced expression of Bcl2 protected striatal cells from the toxicity evoked by mHtt and AMPK overactivation. These data demonstrate that aberrant activation of AMPK-α1 in the nuclei of striatal cells represents a new toxic pathway induced by mHtt.
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Affiliation(s)
- Tz-Chuen Ju
- Institute of Neuroscience and 2 Institute of Biochemistry and Molecular Biology, School of Life Sciences, National Yang Ming University, Taipei 112, Taiwan
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MacDonald PE, Rorsman P. Per-arnt-sim (PAS) domain kinase (PASK) as a regulator of glucagon secretion. Diabetologia 2011; 54:719-21. [PMID: 21327866 DOI: 10.1007/s00125-011-2072-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Accepted: 01/19/2011] [Indexed: 12/21/2022]
Abstract
The physiological and pathophysiological regulation of glucagon secretion from pancreatic alpha cells remains a hotly debated topic. The mechanism(s) contributing to the glucose sensitivity of glucagon release and its impaired regulation in diabetes remain unclear. A paper in the current issue of Diabetologia by da Silva Xavier and colleagues (doi: 10.1007/s00125-010-2010-7 ) provides intriguing new insight into a metabolic sensing pathway mediated by the per-arnt-sim (PAS) domain kinase (PASK) that may contribute to both the paracrine and the intrinsic glucose regulation of alpha cells. Importantly, the authors show that PASK is decreased in islets from patients with type 2 diabetes, providing a potential mechanism for impaired suppression of glucagon by hyperglycaemia in this disease. Much work remains to be done to determine the exact role and mechanism of PASK in alpha and beta cells. Nevertheless, the present work introduces a new player in the metabolic regulation of glucagon secretion.
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Affiliation(s)
- P E MacDonald
- Department of Pharmacology, University of Alberta, Edmonton, AB, Canada.
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da Silva Xavier G, Farhan H, Kim H, Caxaria S, Johnson P, Hughes S, Bugliani M, Marselli L, Marchetti P, Birzele F, Sun G, Scharfmann R, Rutter J, Siniakowicz K, Weir G, Parker H, Reimann F, Gribble FM, Rutter GA. Per-arnt-sim (PAS) domain-containing protein kinase is downregulated in human islets in type 2 diabetes and regulates glucagon secretion. Diabetologia 2011; 54:819-27. [PMID: 21181396 PMCID: PMC3052475 DOI: 10.1007/s00125-010-2010-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2010] [Accepted: 11/12/2010] [Indexed: 10/27/2022]
Abstract
AIMS/HYPOTHESIS We assessed whether per-arnt-sim (PAS) domain-containing protein kinase (PASK) is involved in the regulation of glucagon secretion. METHODS mRNA levels were measured in islets by quantitative PCR and in pancreatic beta cells obtained by laser capture microdissection. Glucose tolerance, plasma hormone levels and islet hormone secretion were analysed in C57BL/6 Pask homozygote knockout mice (Pask-/-) and control littermates. Alpha-TC1-9 cells, human islets or cultured E13.5 rat pancreatic epithelia were transduced with anti-Pask or control small interfering RNAs, or with adenoviruses encoding enhanced green fluorescent protein or PASK. RESULTS PASK expression was significantly lower in islets from human type 2 diabetic than control participants. PASK mRNA was present in alpha and beta cells from mouse islets. In Pask-/- mice, fasted blood glucose and plasma glucagon levels were 25 ± 5% and 50 ± 8% (mean ± SE) higher, respectively, than in control mice. At inhibitory glucose concentrations (10 mmol/l), islets from Pask-/- mice secreted 2.04 ± 0.2-fold (p < 0.01) more glucagon and 2.63 ± 0.3-fold (p < 0.01) less insulin than wild-type islets. Glucose failed to inhibit glucagon secretion from PASK-depleted alpha-TC1-9 cells, whereas PASK overexpression inhibited glucagon secretion from these cells and human islets. Extracellular insulin (20 nmol/l) inhibited glucagon secretion from control and PASK-deficient alpha-TC1-9 cells. PASK-depleted alpha-TC1-9 cells and pancreatic embryonic explants displayed increased expression of the preproglucagon (Gcg) and AMP-activated protein kinase (AMPK)-alpha2 (Prkaa2) genes, implying a possible role for AMPK-alpha2 downstream of PASK in the control of glucagon gene expression and release. CONCLUSIONS/INTERPRETATION PASK is involved in the regulation of glucagon secretion by glucose and may be a useful target for the treatment of type 2 diabetes.
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Affiliation(s)
- G. da Silva Xavier
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ UK
| | - H. Farhan
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ UK
| | - H. Kim
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ UK
| | - S. Caxaria
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ UK
| | - P. Johnson
- Nuffield Department of Surgical Sciences, Oxford University, Oxford, UK
| | - S. Hughes
- Nuffield Department of Surgical Sciences, Oxford University, Oxford, UK
| | - M. Bugliani
- Dipartimento di Endocrinologia e Metabolismo, Unità Metabolica, Università di Pisa, Pisa, Italy
| | - L. Marselli
- Dipartimento di Endocrinologia e Metabolismo, Unità Metabolica, Università di Pisa, Pisa, Italy
| | - P. Marchetti
- Dipartimento di Endocrinologia e Metabolismo, Unità Metabolica, Università di Pisa, Pisa, Italy
| | - F. Birzele
- Boehringer Ingelheim Pharma, Target Discovery Research, Ingelheim, Germany
| | - G. Sun
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ UK
| | - R. Scharfmann
- INSERM U845, Centre de Recherche Croissance et Signalisation, Université Paris Descartes, Faculté de Médecine, Hôpital Necker, Paris, France
| | - J. Rutter
- Division of Endocrinology, University of Utah School of Medicine, Salt Lake, UT USA
| | - K. Siniakowicz
- Section on Islet Transplantation and Cell Biology, Research Division, Joslin Diabetes Center and the Department of Medicine, Harvard Medical School, Boston, MA USA
| | - G. Weir
- Section on Islet Transplantation and Cell Biology, Research Division, Joslin Diabetes Center and the Department of Medicine, Harvard Medical School, Boston, MA USA
| | - H. Parker
- Cambridge Institute for Medical Research and Department of Clinical Biochemistry, Addenbrooke’s Hospital, Cambridge, UK
| | - F. Reimann
- Cambridge Institute for Medical Research and Department of Clinical Biochemistry, Addenbrooke’s Hospital, Cambridge, UK
| | - F. M. Gribble
- Cambridge Institute for Medical Research and Department of Clinical Biochemistry, Addenbrooke’s Hospital, Cambridge, UK
| | - G. A. Rutter
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ UK
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Rondas D, Tomas A, Halban PA. Focal adhesion remodeling is crucial for glucose-stimulated insulin secretion and involves activation of focal adhesion kinase and paxillin. Diabetes 2011; 60:1146-57. [PMID: 21357465 PMCID: PMC3064088 DOI: 10.2337/db10-0946] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
OBJECTIVE Actin cytoskeleton remodeling is known to be involved in glucose-stimulated insulin secretion (GSIS). We have observed glucose-stimulated changes at the β-cell basal membrane similar to focal adhesion remodeling in cell migration. This led us to study the role of two key focal adhesion proteins, focal adhesion kinase (FAK) and paxillin, in GSIS. RESEARCH DESIGN AND METHODS All studies were performed using rat primary β-cells or isolated islets. Protein phosphorylation and subcellular localization were determined by Western blotting and confocal immunofluorescence, respectively. Insulin was measured by radioimmunoassay. Both siRNA and pharmacological approaches were used to assess the role of FAK and paxillin in glucose-stimulated focal adhesion remodeling and insulin secretion. RESULTS Glucose stimulation of β-cells in monolayer significantly increased phosphorylation of FAK and paxillin as well as cell surface area. This coincided with the appearance at the basal membrane of numerous shorter actin filopodial extensions, containing not only phosphorylated paxillin, FAK, and extracellular signal-related kinase 1/2 but also two SNARE proteins, synaptosomal-associated protein 25 and syntaxin 1, indicating involvement in exocytosis. SR7037 completely inhibited this sequence of events, indicating the requirement of increased cytosolic Ca²(+). Furthermore, knockdown of paxillin significantly decreased GSIS, as did inhibition of glucose-induced FAK phosphorylation by compound Y15. Key findings were confirmed in β-cells within the natural setting of islets. CONCLUSIONS Glucose-stimulated remodeling of focal adhesions and phosphorylation of FAK and paxillin are involved in full development of GSIS, indicating a previously unknown role for focal adhesion remodeling in pancreatic β-cell function.
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Affiliation(s)
- Dieter Rondas
- Department of Genetic Medicine and Development, University Medical Center, University of Geneva, Geneva, Switzerland.
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Riboulet-Chavey A, Diraison F, Siew LK, Wong FS, Rutter GA. AMP-activated protein kinase regulates glucagon secretion from mouse pancreatic alpha cells. Diabetologia 2011; 54:125-34. [PMID: 20938634 PMCID: PMC6101198 DOI: 10.1007/s00125-010-1929-z] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/11/2010] [Accepted: 09/01/2010] [Indexed: 10/19/2022]
Abstract
AIM/HYPOTHESIS AMP-activated protein kinase (AMPK), encoded by Prkaa genes, is emerging as a key regulator of overall energy homeostasis and the control of insulin secretion and action. We sought here to investigate the role of AMPK in controlling glucagon secretion from pancreatic islet alpha cells. METHODS AMPK activity was modulated in vitro in clonal alphaTC1-9 cells and isolated mouse pancreatic islets using pharmacological agents and adenoviruses encoding constitutively active or dominant negative forms of AMPK. Glucagon secretion was measured during static incubation by radioimmunoassay. AMPK activity was assessed by both direct phosphotransfer assay and by western (immuno-)blotting of the phosphorylated AMPK α subunits and the downstream target acetyl-CoA carboxylase 1. Intracellular free [Ca²(+)] was measured using Fura-Red. RESULTS Increasing glucose concentrations strongly inhibited AMPK activity in clonal pancreatic alpha cells. Forced increases in AMPK activity in alphaTC1-9 cells, achieved through the use of pharmacological agents including metformin, phenformin and A-769662, or via adenoviral transduction, resulted in stimulation of glucagon secretion at both low and high glucose concentrations, whereas AMPK inactivation inhibited both [Ca²(+)](i) increases and glucagon secretion at low glucose. Transduction of isolated mouse islets with an adenovirus encoding AMPK-CA under the control of the preproglucagon promoter increased glucagon secretion selectively at elevated glucose concentrations. CONCLUSIONS/INTERPRETATION AMPK is strongly regulated by glucose in pancreatic alpha cells, and increases in AMPK activity are sufficient and necessary for the stimulation of glucagon release in vitro. Modulation of AMPK activity in alpha cells may therefore provide a novel approach to controlling blood glucose concentrations.
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Affiliation(s)
- Audrey Riboulet-Chavey
- Department of Cell Biology, Division of Medicine, Sir Alexander Fleming Building, Imperial College, London, Exhibition Road, London SW7 2AZ, UK
| | - Frédérique Diraison
- Department of Cell Biology, Division of Medicine, Sir Alexander Fleming Building, Imperial College, London, Exhibition Road, London SW7 2AZ, UK
| | - L. Khai Siew
- Dept. of Cellular & Molecular Medicine, University of Bristol, School of Medical Sciences, Bristol, BS8 1TD, UK
| | - F. Susan Wong
- Dept. of Cellular & Molecular Medicine, University of Bristol, School of Medical Sciences, Bristol, BS8 1TD, UK
| | - Guy A. Rutter
- Department of Cell Biology, Division of Medicine, Sir Alexander Fleming Building, Imperial College, London, Exhibition Road, London SW7 2AZ, UK
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Garcia-Haro L, Garcia-Gimeno MA, Neumann D, Beullens M, Bollen M, Sanz P. The PP1‐R6 protein phosphatase holoenzyme is involved in the glucose‐induced dephosphorylation and inactivation of AMP‐activated protein kinase, a key regulator of insulin secretion, in MIN6 β cells. FASEB J 2010. [DOI: 10.1096/fj.10.166306] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Luisa Garcia-Haro
- Instituto de Biomedicina de Valencia, Consejo Superior de Investigaciones Cientificas and Centro de Investigación en Red de Enfermecedes Raras Valencia Spain
| | - Maria Adelaida Garcia-Gimeno
- Instituto de Biomedicina de Valencia, Consejo Superior de Investigaciones Cientificas and Centro de Investigación en Red de Enfermecedes Raras Valencia Spain
| | | | - Monique Beullens
- Laboratory of Biosignaling and TherapeuticsDepartment of Molecular Cell BiologyUniversity of Leuven Leuven Belgium
| | - Mathieu Bollen
- Laboratory of Biosignaling and TherapeuticsDepartment of Molecular Cell BiologyUniversity of Leuven Leuven Belgium
| | - Pascual Sanz
- Instituto de Biomedicina de Valencia, Consejo Superior de Investigaciones Cientificas and Centro de Investigación en Red de Enfermecedes Raras Valencia Spain
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McKiney JM, Irwin N, Flatt PR, Bailey CJ, McClenaghan NH. Acute and long-term effects of metformin on the function and insulin secretory responsiveness of clonal β-cells. Biol Chem 2010; 391:1451-9. [DOI: 10.1515/bc.2010.139] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
Functional effects of acute and prolonged (48 h) exposure to the biguanide drug metformin were examined in the clonal pancreatic β-cell line, BRIN-BD11. Effects of metformin on prolonged exposure to excessive increased concentrations of glucose and palmitic acid were also assessed. In acute 20-min incubations, 12.5–50 μm metformin did not alter basal (1.1 mm glucose) or glucose-stimulated (16.7 mm glucose) insulin secretion. However, higher concentrations of metformin (100–1000 μm) increased (1.3–1.5-fold; p<0.001) insulin release at basal glucose concentrations, but had no effect on glucose-stimulated insulin secretion. There were no apparent acute effects of metformin on intracellular Ca2+ concentrations, but metformin enhanced (p<0.05 to p<0.01) the acute insulinotropic actions of GIP and GLP-1. Exposure for 48 h to 200 μm metformin improved aspects of β-cell insulin secretory function, whereas these benefits were lost at 1 mm metformin. Prolonged glucotoxic and lipotoxic conditions impaired β-cell viability and insulin release in response to glucose and to a broad range of insulin secretagogues. Concomitant culture with 200 μm metformin partially reversed many of the adverse effects of prolonged glucotoxic conditions. However, there were no beneficial effects of metformin under prolonged culture with elevated concentrations of palmitic acid. The results suggest that metformin exerts direct effects on β-cell viability, function and survival that could contribute to the use of this agent in the treatment of type 2 diabetes.
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Garcia-Haro L, Garcia-Gimeno MA, Neumann D, Beullens M, Bollen M, Sanz P. The PP1-R6 protein phosphatase holoenzyme is involved in the glucose-induced dephosphorylation and inactivation of AMP-activated protein kinase, a key regulator of insulin secretion, in MIN6 beta cells. FASEB J 2010; 24:5080-91. [PMID: 20724523 DOI: 10.1096/fj.10-166306] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Mammalian AMP-activated protein kinase (AMPK) is a serine/threonine protein kinase that acts as a sensor of cellular energy status. It is activated by phosphorylation of the catalytic subunit on Thr172. The main objective of this study was the identification of a phosphatase involved in the regulation of AMPK activity. Mouse MIN6 β cells were used to study the glucose-induced regulation of the phosphorylation of AMPK. Small interfering RNA (siRNA) technology was used to deplete putative phosphatase candidate genes that could affect AMPK regulation. The effect of the siRNAs used in the study was compared with the effect observed using a negative control siRNA. A protein phosphatase complex composed of the catalytic subunit of protein phosphatase-1 (PP1) and the regulatory subunit R6 participates in the glucose-induced dephosphorylation of AMPK. R6 interacts physically with the β-subunit of the AMPK complex and recruits PP1 to dephosphorylate the catalytic α-subunit on Thr172. siRNA depletion of R6 decreases glucose-induced insulin secretion due to the presence of a constitutively active AMPK complex. The characterization of the PP1-R6 complex identifies this holoenzyme as a possible target for therapeutic intervention with the aim of regulating the activity of AMPK in pancreatic β cells.
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Affiliation(s)
- Luisa Garcia-Haro
- Instituto de Biomedicina de Valencia, Consejo Superior de Investigaciones Cientificas and Centro de Investigación en Red de Enfermecedes Raras, Valencia, Spain
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Mourad NI, Nenquin M, Henquin JC. Metabolic amplifying pathway increases both phases of insulin secretion independently of β-cell actin microfilaments. Am J Physiol Cell Physiol 2010; 299:C389-98. [DOI: 10.1152/ajpcell.00138.2010] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Two pathways control glucose-induced insulin secretion (IS) by β-cells. The triggering pathway involves ATP-sensitive potassium (KATP) channel-dependent depolarization, Ca2+ influx, and a rise in the cytosolic Ca2+ concentration ([Ca2+]c), which triggers exocytosis of insulin granules. The metabolic amplifying pathway augments IS without further increasing [Ca2+]c. The underlying mechanisms are unknown. Here, we tested the hypothesis that amplification implicates actin microfilaments. Mouse islets were treated with latrunculin B and cytochalasin B to depolymerize actin or jasplakinolide to polymerize actin. They were then perifused to measure [Ca2+]c and IS. Metabolic amplification was studied during imposed steady elevation of [Ca2+]c by tolbutamide or KCl or by comparing the magnitude of [Ca2+]c and IS changes produced by glucose and tolbutamide. Both actin polymerization and depolymerization augmented IS triggered by all stimuli without increasing (sometimes decreasing) [Ca2+]c, which indicates a predominantly inhibitory function of microfilaments in exocytosis at a step distal to [Ca2+]c increase. When [Ca2+]c was elevated and controlled by KCl or tolbutamide, the amplifying action of glucose was facilitated by actin depolymerization and unaffected by polymerization. Both phases of IS were larger in response to high-glucose than to tolbutamide in low-glucose, although triggering [Ca2+]c was lower. This difference in IS, due to amplification, persisted when the IS rate was doubled by actin depolymerization or polymerization. In conclusion, metabolic amplification is rapid and influences the first as well as the second phase of IS. It is a late step of stimulus-secretion coupling, which does not require functional actin microfilaments and could correspond to acceleration of the priming process conferring release competence to insulin granules.
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Affiliation(s)
- Nizar I. Mourad
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
| | - Myriam Nenquin
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
| | - Jean-Claude Henquin
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
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Jung SR, Hille B, Nguyen TD, Koh DS. Cyclic AMP potentiates Ca2+-dependent exocytosis in pancreatic duct epithelial cells. ACTA ACUST UNITED AC 2010; 135:527-43. [PMID: 20421376 PMCID: PMC2860593 DOI: 10.1085/jgp.200910355] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Exocytosis is evoked by intracellular signals, including Ca2+ and protein kinases. We determined how such signals interact to promote exocytosis in exocrine pancreatic duct epithelial cells (PDECs). Exocytosis, detected using carbon-fiber microamperometry, was stimulated by [Ca2+]i increases induced either through Ca2+ influx using ionomycin or by activation of P2Y2 or protease-activated receptor 2 receptors. In each case, the exocytosis was strongly potentiated when cyclic AMP (cAMP) was elevated either by activating adenylyl cyclase with forskolin or by activating the endogenous vasoactive intestinal peptide receptor. This potentiation was completely inhibited by H-89 and partially blocked by Rp-8-Br-cAMPS, inhibitors of protein kinase A. Optical monitoring of fluorescently labeled secretory granules showed slow migration toward the plasma membrane during Ca2+ elevations. Neither this Ca2+-dependent granule movement nor the number of granules found near the plasma membrane were detectably changed by raising cAMP, suggesting that cAMP potentiates Ca2+-dependent exocytosis at a later stage. A kinetic model was made of the exocytosis stimulated by UTP, trypsin, and Ca2+ ionophores with and without cAMP increase. In the model, without a cAMP rise, receptor activation stimulates exocytosis both by Ca2+ elevation and by the action of another messenger(s). With cAMP elevation the docking/priming step for secretory granules was accelerated, augmenting the releasable granule pool size, and the Ca2+ sensitivity of the final fusion step was increased, augmenting the rate of exocytosis. Presumably both cAMP actions require cAMP-dependent phosphorylation of target proteins. cAMP-dependent potentiation of Ca2+-induced exocytosis has physiological implications for mucin secretion and, possibly, for membrane protein insertion in the pancreatic duct. In addition, mechanisms underlying this potentiation of slow exocytosis may also exist in other cell systems.
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Affiliation(s)
- Seung-Ryoung Jung
- Department of Physiology and Biophysics and 2 Department of Medicine, University of Washington, Seattle, Washington 98195, USA
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Luo Z, Zang M, Guo W. AMPK as a metabolic tumor suppressor: control of metabolism and cell growth. Future Oncol 2010; 6:457-70. [PMID: 20222801 DOI: 10.2217/fon.09.174] [Citation(s) in RCA: 297] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
AMPK is an evolutionarily conserved fuel-sensing enzyme that is activated in shortage of energy and suppressed in its surfeit. AMPK activation stimulates fatty acid oxidation, enhances insulin sensitivity, alleviates hyperglycemia and hyperlipidemia, and inhibits proinflammatory changes. Thus, AMPK is a well-received therapeutic target for metabolic syndrome and Type 2 diabetes. Recent studies indicate that AMPK plays a role in linking metabolic syndrome and cancer. AMPK is an essential mediator of the tumor suppressor LKB1 and could be suppressed in cancer cells containing loss-of-function mutations of LKB1 or containing active mutations of B-Raf, or in cancers associated with metabolic syndrome. The activation of AMPK reprograms cellular metabolism and enforces metabolic checkpoints by acting on mTORC1, p53, fatty acid synthase and other molecules for regulating cell growth and metabolism. In keeping with in vitro studies, recent epidemiological studies indicate that the incidence of cancer is reduced in Type 2 diabetes treated with metformin, an AMPK activator. Thus, AMPK is emerging as an interesting metabolic tumor suppressor and a promising target for cancer prevention and therapy.
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Affiliation(s)
- Zhijun Luo
- Department of Biochemistry, Boston University School of Medicine, MA 02118, USA.
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Sun G, Tarasov A, McGinty J, McDonald A, da Silva Xavier G, Gorman T, Marley A, French PM, Parker H, Gribble F, Reimann F, Prendiville O, Carzaniga R, Viollet B, Leclerc I, Rutter G. Ablation of AMP-activated protein kinase alpha1 and alpha2 from mouse pancreatic beta cells and RIP2.Cre neurons suppresses insulin release in vivo. Diabetologia 2010; 53:924-36. [PMID: 20221584 PMCID: PMC4306708 DOI: 10.1007/s00125-010-1692-1] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/19/2009] [Accepted: 02/01/2010] [Indexed: 10/19/2022]
Abstract
AIMS/HYPOTHESIS AMP-activated protein kinase (AMPK) is an evolutionarily conserved enzyme and a target of glucose-lowering agents, including metformin. However, the precise role or roles of the enzyme in controlling insulin secretion remain uncertain. METHODS The catalytic alpha1 and alpha2 subunits of AMPK were ablated selectively in mouse pancreatic beta cells and hypothalamic neurons by breeding Ampkalpha1 [also known as Prkaa1]-knockout mice, bearing floxed Ampkalpha2 [also known as Prkaa2] alleles (Ampkalpha1 ( -/- ),alpha2( fl/fl ),), with mice expressing Cre recombinase under the rat insulin promoter (RIP2). RIP2 was used to express constitutively activated AMPK selectively in beta cells in transgenic mice. Food intake, body weight and urinary catecholamines were measured using metabolic cages. Glucose and insulin tolerance were determined after intraperitoneal injection. Beta cell mass and morphology were analysed by optical projection tomography and confocal immunofluorescence microscopy, respectively. Granule docking, insulin secretion, membrane potential and intracellular free Ca(2+) were measured with standard techniques. RESULTS Trigenic Ampkalpha1 ( -/- ),alpha2( fl/fl ) expressing Cre recombinase and lacking both AMPKalpha subunits in the beta cell, displayed normal body weight and increased insulin sensitivity, but were profoundly insulin-deficient. Secreted catecholamine levels were unchanged. Total beta cell mass was unaltered, while mean islet and beta cell volume were reduced. AMPK-deficient beta cells displayed normal glucose-induced changes in membrane potential and intracellular free Ca(2+), while granule docking and insulin secretion were enhanced. Conversely, betaAMPK transgenic mice were glucose-intolerant and displayed defective insulin secretion. CONCLUSIONS/INTERPRETATION Inhibition of AMPK activity within the beta cell is necessary, but not sufficient for stimulation of insulin secretion by glucose to occur. AMPK activation in extrapancreatic RIP2.Cre-expressing cells might also influence insulin secretion in vivo.
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Affiliation(s)
- G. Sun
- Section of Cell Biology, Division of Endocrinology and Metabolism, Department of Medicine, Imperial College London
| | - A.I. Tarasov
- Section of Cell Biology, Division of Endocrinology and Metabolism, Department of Medicine, Imperial College London
| | - J. McGinty
- Photonics Group, Department of Physics, Imperial College London
| | - A. McDonald
- Section of Cell Biology, Division of Endocrinology and Metabolism, Department of Medicine, Imperial College London
| | - G. da Silva Xavier
- Section of Cell Biology, Division of Endocrinology and Metabolism, Department of Medicine, Imperial College London
| | - T. Gorman
- AstraZeneca, Alderley Edge, Cheshire
| | - A. Marley
- AstraZeneca, Alderley Edge, Cheshire
| | - P. M. French
- Photonics Group, Department of Physics, Imperial College London
| | - H. Parker
- Cambridge Institute of Medical Research, Cambridge, U.K
| | - F. Gribble
- Cambridge Institute of Medical Research, Cambridge, U.K
| | - F. Reimann
- Cambridge Institute of Medical Research, Cambridge, U.K
| | | | - R. Carzaniga
- Electron Microscopy Centre, Imperial College London
| | - B. Viollet
- Institut Cochin, Université Paris Descartes, CNRS (UMR 8104)
- Inserm, U1067, Paris, France
| | - I. Leclerc
- Section of Endocrinology and Metabolic Medicine, Division of Endocrinology and Metabolism, Department of Medicine, Imperial College London
| | - G.A. Rutter
- Section of Cell Biology, Division of Endocrinology and Metabolism, Department of Medicine, Imperial College London
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Cell-wide analysis of secretory granule dynamics in three dimensions in living pancreatic beta-cells: evidence against a role for AMPK-dependent phosphorylation of KLC1 at Ser517/Ser520 in glucose-stimulated insulin granule movement. Biochem Soc Trans 2010; 38:205-8. [PMID: 20074060 DOI: 10.1042/bst0380205] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Glucose-stimulated insulin secretion from pancreatic beta-cells requires the kinesin-1/Kif5B-mediated transport of insulin granules along microtubules. 5'-AMPK (5'-AMP-activated protein kinase) is a heterotrimeric serine/threonine kinase which is activated in beta-cells at low glucose concentrations, but inhibited as glucose levels increase. Active AMPK blocks glucose-stimulated insulin secretion and the recruitment of insulin granules to the cell surface, suggesting motor proteins may be targets for this kinase. While both kinesin-1/Kif5B and KLC1 (kinesin light chain-1) contain consensus AMPK phosphorylation sites (Thr(693) and Ser(520), respectively) only recombinant GST (glutathione transferase)-KLC1 was phosphorylated by purified AMPK in vitro. To test the hypothesis that phosphorylation at this site may modulate kinesin-1-mediated granule movement, we developed an approach to study the dynamics of all the resolvable granules within a cell in three dimensions. This cell-wide approach revealed that the number of longer excursions (>10 mum) increased significantly in response to elevated glucose concentration (30 versus 3 mM) in control MIN6 beta-cells. However, similar changes were seen in cells overexpressing wild-type KLC1, phosphomimetic (S517D/S520D) or non-phosphorylatable (S517A/S520A) mutants of KLC1. Thus, changes in the phosphorylation state of KLC1 at Ser(517)/Ser(520) seem unlikely to affect motor function.
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Affiliation(s)
- Joohun Ha
- Department of Biochemistry and Molecular Biology, College of Medicine, Kyung Hee University, Korea
| | - Sooho Lee
- Department of Biochemistry and Molecular Biology, College of Medicine, Kyung Hee University, Korea
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Wang Z, Thurmond DC. Differential phosphorylation of RhoGDI mediates the distinct cycling of Cdc42 and Rac1 to regulate second-phase insulin secretion. J Biol Chem 2009; 285:6186-97. [PMID: 20028975 DOI: 10.1074/jbc.m109.072421] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Cdc42 cycling through GTP/GDP states is critical for its function in the second/granule mobilization phase of insulin granule exocytosis in pancreatic islet beta cells, although the identities of the Cdc42 cycling proteins involved remain incomplete. Using a tandem affinity purification-based mass spectrometry screen for Cdc42 cycling factors in beta cells, RhoGDI was identified. RNA interference-mediated depletion of RhoGDI from isolated islets selectively amplified the second phase of insulin release, consistent with the role of RhoGDI as a Cdc42 cycling factor. Replenishment of RhoGDI to RNA interference-depleted cells normalized secretion, confirming the action of RhoGDI to be that of a negative regulator of Cdc42 activation. Given that RhoGDI also regulates Rac1 activation in beta cells, and that Rac1 activation occurs in a Cdc42-dependent manner, the question as to how the beta cell utilized RhoGDI for differential Cdc42 and Rac1 cycling was explored. Co-immunoprecipitation was used to determine that RhoGDI-Cdc42 complexes dissociated upon stimulation of beta cells with glucose for 3 min, correlating with the timing of glucose-induced Cdc42 activation and the onset of RhoGDI tyrosine phosphorylation. Glucose-induced disruption of RhoGDI-Rac1 complexes occurred subsequent to this, coincident with Rac1 activation, which followed the onset of RhoGDI serine phosphorylation. RhoGDI-Cdc42 complex dissociation was blocked by mutation of RhoGDI residue Tyr-156, whereas RhoGDI-Rac1 dissociation was blocked by RhoGDI mutations Y156F and S101A/S174A. Finally, expression of a triple Y156F/S101A/S174A-RhoGDI mutant specifically inhibited only the second/granule mobilization phase of glucose-stimulated insulin secretion, overall supporting the integration of RhoGDI into the activation cycling mechanism of glucose-responsive small GTPases.
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Affiliation(s)
- Zhanxiang Wang
- Herman B Wells Center for Pediatric Research, Basic Diabetes Research Group, Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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Lim A, Park SH, Sohn JW, Jeon JH, Park JH, Song DK, Lee SH, Ho WK. Glucose deprivation regulates KATP channel trafficking via AMP-activated protein kinase in pancreatic beta-cells. Diabetes 2009; 58:2813-9. [PMID: 19720793 PMCID: PMC2780861 DOI: 10.2337/db09-0600] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
OBJECTIVE AMP-activated protein kinase (AMPK) and the ATP-sensitive K(+) (K(ATP)) channel are metabolic sensors that become activated during metabolic stress. AMPK is an important regulator of metabolism, whereas the K(ATP) channel is a regulator of cellular excitability. Cross talk between these systems is poorly understood. RESEARCH DESIGN AND METHODS Rat pancreatic beta-cells or INS-1 cells were pretreated for 2 h at various concentrations of glucose. Maximum K(ATP) conductance (G(max)) was monitored by whole-cell measurements after intracellular ATP washout using ATP-free internal solutions. K(ATP) channel activity (NPo) was monitored by inside-out patch recordings in the presence of diazoxide. Distributions of K(ATP) channel proteins (Kir6.2 and SUR1) were examined using immunofluorescence imaging and surface biotinylation studies. Insulin secretion from rat pancreatic islets was measured using an enzyme immunoassay. RESULTS G(max) and NPo in cells pretreated with glucose-free or 3 mmol/l glucose solutions were significantly higher than in cells pretreated in 11.1 mmol/l glucose solutions. Immunofluorescence imaging and biotinylation studies revealed that glucose deprivation induced an increase in the surface level of Kir6.2 without affecting the total cellular amount. Increases in G(max) and the surface level of Kir6.2 were inhibited by compound C, an AMPK inhibitor, and siAMPK transfection. The effects of glucose deprivation on K(ATP) channels were mimicked by an AMPK activator. Glucose deprivation reduced insulin secretion, but this response was attenuated by compound C. CONCLUSIONS K(ATP) channel trafficking is regulated by energy status via AMPK, and this mechanism may play a key role in inhibiting insulin secretion under low energy status.
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Affiliation(s)
- Ajin Lim
- National Research Laboratory for Cell Physiology, Seoul National University College of Medicine, Seoul, Korea
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
| | - Sun-Hyun Park
- National Research Laboratory for Cell Physiology, Seoul National University College of Medicine, Seoul, Korea
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
| | - Jong-Woo Sohn
- National Research Laboratory for Cell Physiology, Seoul National University College of Medicine, Seoul, Korea
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
| | - Ju-Hong Jeon
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
| | - Jae-Hyung Park
- Department of Physiology and Chronic Disease Research Center, Keimyung University School of Medicine, Daegu, Korea
| | - Dae-Kyu Song
- Department of Physiology and Chronic Disease Research Center, Keimyung University School of Medicine, Daegu, Korea
| | - Suk-Ho Lee
- National Research Laboratory for Cell Physiology, Seoul National University College of Medicine, Seoul, Korea
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
| | - Won-Kyung Ho
- National Research Laboratory for Cell Physiology, Seoul National University College of Medicine, Seoul, Korea
- Department of Physiology, Seoul National University College of Medicine, Seoul, Korea
- Corresponding author: Won-Kyung Ho,
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Lin P, Chen L, Li D, Liu J, Yang N, Sun Y, Xu Y, Fu Y, Hou X. Adiponectin reduces glucotoxicity-induced apoptosis of INS-1 rat insulin-secreting cells on a microfluidic chip. TOHOKU J EXP MED 2009; 217:59-65. [PMID: 19155609 DOI: 10.1620/tjem.217.59] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Diabetes mellitus is a metabolic disorder characterized by elevated blood sugar and progressive failure of insulin-producing beta-cells. Persistent hyperglycemia and blood sugar fluctuation are two general phenomena in diabetic patients, and both of them can result in an increased frequency of beta-cell apoptosis. Therefore, rescuing pancreatic beta-cells from glucotoxicity-induced beta-cell apoptosis is increasing viewed as a promising means for curing. The aim of this study was to investigate whether adiponectin, an important cytokine expressed in adipose tissue, has a potential for the application as the antiapoptotic strategy. INS-1 rat insulin-secreting cell line was used in this study as a model of pancreatic beta-cells, because INS-1 cells show the susceptibility to glucotoxicity, as seen in beta-cells. INS-1 cells were cultured on a novel microfluidic chip with persistent perfusion and subsequently exposed to sustained high glucose (SHG) (25 mmol/l) or intermittent high glucose (IHG) (11.1 and 25 mmol/l glucose alternating every 12 h) in the absence or presence of adiponectin for 72 h. Using this device, we showed that IHG induced more serious impairment in INS-1 cells than did SHG, and adiponectin partially rescued INS-1 cells from glucotoxicity-induced apoptosis, dysfunction and reduction of insulin gene expression. Simultaneously, the mRNA expression of AMP-activated protein kinase (AMPK), which is a signaling protein that acts to modulate glucose uptake in skeletal muscle, was restored in the presence of adiponectin. Based on the above evidence, we suggest that adiponectin could reduce glucotoxicity-induced apoptosis of beta-cells, at least in part, by transiently activating AMPK signaling pathway.
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Affiliation(s)
- Peng Lin
- Department of Endocrine, Qilu Hospital, Shandong University, Ji'nan, Shandong, PR China.
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When hypothermia meets hypotension and hyperglycemia: the diverse effects of adenosine 5'-monophosphate on cerebral ischemia in rats. J Cereb Blood Flow Metab 2009; 29:1022-34. [PMID: 19319149 PMCID: PMC2726621 DOI: 10.1038/jcbfm.2009.28] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Mild hypothermia renders potent neuroprotection against acute brain injury. Recent reports show that adenosine 5'-monophosphate (AMP) plays a role in thermoregulation and induces hypothermia in mice. Therefore, this study sought to determine whether AMP induces hypothermia in rats and to study its collective effects on cerebral ischemia induced by 2-h middle cerebral artery occlusion. An intraperitoneal injection of AMP induced hypothermia dose-dependently. At the dose of 4 mmol/kg, AMP induced promising mild hypothermia for 2.5 h. Unexpectedly, the AMP-induced hypothermia failed to reduce infarct volume after brain ischemia; instead, it exaggerated the ischemic damage, indicated by an increased infarct volume, as well as increased incidences of hemorrhagic transformation, seizure, and animal death. Physiologic parameter monitoring revealed that AMP causes profound hypotension, leading to cerebral hypoperfusion. Furthermore, AMP administration resulted in severe hyperglycemia, metabolic acidosis, and hypocalcemia. In addition, western blots showed early dephosphorylation and degradation of AMP-activated kinase in the ischemic cortex in AMP-treated rats. Taken together, our findings suggest that AMP induces hypothermia in rats, probably by limiting cellular access to glucose. However, the potential neuroprotection of AMP-mediated hypothermia against ischemia was overwhelmed by the detrimental effects of hypotension and hyperglycemia, thus making AMP an unlikely agent for inducing hypothermia to protect the brain against ischemic injury.
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Zhang J, Luo R, Wu H, Wei S, Han W, Li G. Role of type Ialpha phosphatidylinositol-4-phosphate 5-kinase in insulin secretion, glucose metabolism, and membrane potential in INS-1 beta-cells. Endocrinology 2009; 150:2127-35. [PMID: 19116346 DOI: 10.1210/en.2008-0516] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Insulin secretion from beta-cells is regulated by a complex signaling network. Our earlier study has reported that Rac1 participates in glucose- and cAMP-induced insulin secretion probably via maintaining a functional actin structure for recruitment of insulin granules. Type Ialpha phosphatidylinositol-4-phosphate 5-kinase (PIP5K-Ialpha) is a downstream effector of Rac1 and a critical enzyme for synthesis of phosphatidylinositol-4,5-bisphosphate (PIP(2)). By using an RNA interference technique, PIP5K-Ialpha in INS-1 beta-cells could be specifically knocked down by 70-75%. PIP5K-Ialpha knockdown disrupted filamentous actin structure and caused changes in cell morphology. In addition, PIP(2) content in the plasma membrane was reduced and the glucose effect on PIP(2) was abolished but without affecting glucose-induced formation of inositol 1,4,5-trisphosphate. At basal conditions (2.8 mM glucose), PIP5K-Ialpha knockdown doubled insulin secretion, elevated glucose metabolic rate, depolarized resting membrane potential, and raised cytoplasmic free Ca(2+) levels ([Ca(2+)](i)). The total insulin release at high glucose was increased upon PIP5K-Ialpha knockdown. However, the percent increment of insulin secretion by high glucose and forskolin over the basal release was significantly reduced, an effect more apparent on the late phase of insulin secretion. Metabolism and [Ca(2+)](i) rises at high glucose were also attenuated in cells after PIP5K-Ialpha knockdown. In contrast, PIP5K-Ialpha knockdown had no effect on cell growth and viability. Taken together, our data suggest that PIP5K-Ialpha may play an important role in both the proximal and distal steps of signaling cascade for insulin secretion in beta-cells.
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Affiliation(s)
- Jiping Zhang
- Cardiovascular Research Institute, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597
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Griffiths EJ, Rutter GA. Mitochondrial calcium as a key regulator of mitochondrial ATP production in mammalian cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:1324-33. [PMID: 19366607 DOI: 10.1016/j.bbabio.2009.01.019] [Citation(s) in RCA: 272] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2008] [Revised: 01/23/2009] [Accepted: 01/27/2009] [Indexed: 12/30/2022]
Abstract
Mitochondrial Ca(2+) transport was initially considered important only in buffering of cytosolic Ca(2+) by acting as a "sink" under conditions of Ca(2+) overload. The main regulator of ATP production was considered to be the relative concentrations of high energy phosphates. However, work by Denton and McCormack in the 1970s and 1980s showed that free intramitochondrial Ca(2+) ([Ca(2+)](m)) activated dehydrogenase enzymes in mitochondria, leading to increased NADH and hence ATP production. This leads them to propose a scheme, subsequently termed a "parallel activation model" whereby increases in energy demand, such as hormonal stimulation or increased workload in muscle, produced an increase in cytosolic [Ca(2+)] that was relayed by the mitochondrial Ca(2+) transporters into the matrix to give an increase in [Ca(2+)](m). This then stimulated energy production to meet the increased energy demand. With the development of methods for measuring [Ca(2+)](m) in living cells that proved [Ca(2+)](m) changed over a dynamic physiological range rather than simply soaking up excess cytosolic [Ca(2+)], this model has now gained widespread acceptance. However, work by ourselves and others using targeted probes to measure changes in both [Ca(2+)] and [ATP] in different cell compartments has revealed variations in the interrelationships between these two in different tissues, suggesting that metabolic regulation by Ca(2+) is finely tuned to the demands and function of the individual organ.
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Affiliation(s)
- Elinor J Griffiths
- Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
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Lage R, Diéguez C, Vidal-Puig A, López M. AMPK: a metabolic gauge regulating whole-body energy homeostasis. Trends Mol Med 2008; 14:539-49. [DOI: 10.1016/j.molmed.2008.09.007] [Citation(s) in RCA: 359] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2008] [Revised: 09/26/2008] [Accepted: 09/29/2008] [Indexed: 12/19/2022]
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Hanna ST, Pigeau GM, Galvanovskis J, Clark A, Rorsman P, MacDonald PE. Kiss-and-run exocytosis and fusion pores of secretory vesicles in human beta-cells. Pflugers Arch 2008; 457:1343-50. [PMID: 18795319 DOI: 10.1007/s00424-008-0588-0] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2008] [Revised: 08/27/2008] [Accepted: 09/01/2008] [Indexed: 01/18/2023]
Abstract
Exocytosis of secretory vesicles results in the release of insulin from pancreatic beta-cells, although little is known about this process in humans. We examined the exocytosis of single secretory vesicles and their associated fusion pores in human beta-cells by cell-attached capacitance and conductance measurement. Unitary capacitance steps were observed, consistent with the exocytosis of single secretory vesicles. These were often coincident with increases in patch conductance representing the presence of a stable fusion pore. In some events, the fusion pore closed, mediating kiss-and-run, which contributed 20% of the exocytotic events. The cAMP-raising agent forskolin (5 microM) doubled the relative contribution of kiss-and-run. This effect was confirmed visually in MIN6 cells expressing a fluorescent granule probe. Thus, we demonstrate the unitary capacitance steps and fusion pores during single vesicle exocytosis in human beta-cells. Furthermore, these secretory vesicles can undergo rapid recycling by kiss-and-run, and this process is up-regulated by cAMP.
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Affiliation(s)
- Salma T Hanna
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, HRIF East, Rm 6-126, Edmonton, AB T6G 2E1, Canada
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