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Ramanadham S, Turk J, Bhatnagar S. Noncanonical Regulation of cAMP-Dependent Insulin Secretion and Its Implications in Type 2 Diabetes. Compr Physiol 2023; 13:5023-5049. [PMID: 37358504 PMCID: PMC10809800 DOI: 10.1002/cphy.c220031] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/27/2023]
Abstract
Impaired glucose tolerance (IGT) and β-cell dysfunction in insulin resistance associated with obesity lead to type 2 diabetes (T2D). Glucose-stimulated insulin secretion (GSIS) from β-cells occurs via a canonical pathway that involves glucose metabolism, ATP generation, inactivation of K ATP channels, plasma membrane depolarization, and increases in cytosolic concentrations of [Ca 2+ ] c . However, optimal insulin secretion requires amplification of GSIS by increases in cyclic adenosine monophosphate (cAMP) signaling. The cAMP effectors protein kinase A (PKA) and exchange factor activated by cyclic-AMP (Epac) regulate membrane depolarization, gene expression, and trafficking and fusion of insulin granules to the plasma membrane for amplifying GSIS. The widely recognized lipid signaling generated within β-cells by the β-isoform of Ca 2+ -independent phospholipase A 2 enzyme (iPLA 2 β) participates in cAMP-stimulated insulin secretion (cSIS). Recent work has identified the role of a G-protein coupled receptor (GPCR) activated signaling by the complement 1q like-3 (C1ql3) secreted protein in inhibiting cSIS. In the IGT state, cSIS is attenuated, and the β-cell function is reduced. Interestingly, while β-cell-specific deletion of iPLA 2 β reduces cAMP-mediated amplification of GSIS, the loss of iPLA 2 β in macrophages (MØ) confers protection against the development of glucose intolerance associated with diet-induced obesity (DIO). In this article, we discuss canonical (glucose and cAMP) and novel noncanonical (iPLA 2 β and C1ql3) pathways and how they may affect β-cell (dys)function in the context of impaired glucose intolerance associated with obesity and T2D. In conclusion, we provide a perspective that in IGT states, targeting noncanonical pathways along with canonical pathways could be a more comprehensive approach for restoring β-cell function in T2D. © 2023 American Physiological Society. Compr Physiol 13:5023-5049, 2023.
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Affiliation(s)
- Sasanka Ramanadham
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Alabama, USA
- Comprehensive Diabetes Center, University of Alabama at Birmingham, Alabama, USA
| | - John Turk
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Sushant Bhatnagar
- Comprehensive Diabetes Center, University of Alabama at Birmingham, Alabama, USA
- Department of Medicine, University of Alabama at Birmingham, Alabama, USA
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2
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Effects of Arachidonic Acid and Its Metabolites on Functional Beta-Cell Mass. Metabolites 2022; 12:metabo12040342. [PMID: 35448529 PMCID: PMC9031745 DOI: 10.3390/metabo12040342] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2022] [Revised: 04/06/2022] [Accepted: 04/09/2022] [Indexed: 01/26/2023] Open
Abstract
Arachidonic acid (AA) is a polyunsaturated 20-carbon fatty acid present in phospholipids in the plasma membrane. The three primary pathways by which AA is metabolized are mediated by cyclooxygenase (COX) enzymes, lipoxygenase (LOX) enzymes, and cytochrome P450 (CYP) enzymes. These three pathways produce eicosanoids, lipid signaling molecules that play roles in biological processes such as inflammation, pain, and immune function. Eicosanoids have been demonstrated to play a role in inflammatory, renal, and cardiovascular diseases as well type 1 and type 2 diabetes. Alterations in AA release or AA concentrations have been shown to affect insulin secretion from the pancreatic beta cell, leading to interest in the role of AA and its metabolites in the regulation of beta-cell function and maintenance of beta-cell mass. In this review, we discuss the metabolism of AA by COX, LOX, and CYP, the roles of these enzymes and their metabolites in beta-cell mass and function, and the possibility of targeting these pathways as novel therapies for treating diabetes.
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3
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Hancock WD, Lei X, Clines GA, Tusing YG, Nozell SE, Ramanadham S. Ca 2+-independent phospholipase A 2β-derived PGE 2 contributes to osteogenesis. Prostaglandins Other Lipid Mediat 2022; 158:106605. [PMID: 34923151 PMCID: PMC8753754 DOI: 10.1016/j.prostaglandins.2021.106605] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2019] [Revised: 12/13/2021] [Accepted: 12/14/2021] [Indexed: 02/03/2023]
Abstract
Bone modeling can be modulated by lipid signals such as arachidonic acid (AA) and its cyclooxygenase 2 (COX2) metabolite, prostaglandin E2 (PGE2), which are recognized mediators of optimal bone formation. Hydrolysis of AA from membrane glycerophospholipids is catalyzed by phospholipases A2 (PLA2s). We reported that mice deficient in the Ca2+- independent PLA2beta (iPLA2β), encoded by Pla2g6, exhibit a low bone phenotype, but the cause for this remains to be identified. Here, we examined the mechanistic and molecular roles of iPLA2β in bone formation using bone marrow stromal cells and calvarial osteoblasts from WT and iPLA2β-deficient mice, and the MC3T3-E1 osteoblast precursor cell line. Our data reveal that transcription of osteogenic factors (Bmp2, Alpl, and Runx2) and osteogenesis are decreased with iPLA2β-deficiency. These outcomes are corroborated and recapitulated in WT cells treated with a selective inhibitor of iPLA2 β (10 μM S-BEL), and rescued in iPLA2β-deficient cells by additions of 10 μM PGE2. Further, under osteogenic conditions we find that PGE2 production is through iPLA2β activity and that this leads to induction of Runx2 and iPLA2β transcription. These findings reveal a strong link between osteogenesis and iPLA2β-derived lipids and raise the intriguing possibility that iPLA2β-derived PGE2 participates in osteogenesis and in the regulation of Runx2 and also iPLA2β.
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Affiliation(s)
- William D Hancock
- Department of Biochemistry and Molecular Biology Virginia Commonwealth University, Richmond, VA, USA
| | - Xiaoyong Lei
- Department of Cell, Developmental, and Integrative Biology, USA; Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Gregory A Clines
- Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA
| | - Ying G Tusing
- Department of Cell, Developmental, and Integrative Biology, USA; Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Susan E Nozell
- Department of Radiation Oncology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Sasanka Ramanadham
- Department of Cell, Developmental, and Integrative Biology, USA; Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL, USA.
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4
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Hernández MC, Rojas P, Carrasco F, Basfi-Fer K, Valenzuela R, Codoceo J, Inostroza J, Ruz M. Fatty acid desaturation in red blood cell membranes of patients with type 2 diabetes is improved by zinc supplementation. J Trace Elem Med Biol 2020; 62:126571. [PMID: 32534376 DOI: 10.1016/j.jtemb.2020.126571] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Revised: 05/14/2020] [Accepted: 05/26/2020] [Indexed: 12/26/2022]
Abstract
BACKGROUND/OBJECTIVE Membrane flexibility can be a determining factor in pathophysiological mechanisms of type 2 diabetes (T2D). As a cofactor of delta-5 desaturase (D5D) and delta-6 desaturase (D6D), and gene expression regulator, zinc may play a role modulating membrane flexibility by increasing membrane polyunsaturated fatty acids (PUFA) abundance. The objective of this study was to evaluate the effect of a 24-month zinc supplementation (30 mg elemental zinc) on membrane fatty acid composition in patients with T2D. SUBJECTS/METHODS Sixty patients with T2D were evaluated. Thirty were randomly assigned to the zinc supplemented group and thirty to the placebo group. Fatty acid composition in red blood cell (RBC) membranes was determined by gas chromatography. Expression of gene encoding for D5D (FADS1), and D6D (FADS2) were evaluated in peripheral blood mononuclear cells by real-time polymerase chain reaction. RESULTS After 24 months of supplementation, a greater abundance of docosapentaenoic acid (C22:5 n-3), arachidonic acid (C20:4 n-6), adrenic acid (C22:4 n-6), and total n-6 PUFA was found (p = 0.001, p = 0.007, p = 0.033, p = 0.048, respectively). The unsaturated fatty acids/saturated fatty acids ratio, and unsaturation index was increased in the zinc supplemented group at month 24 (p = 0.003 and p = 0.000, respectively). FADS1 gene was upregulated in the zinc group in relation to placebo at month 12 (p = 0.020). CONCLUSIONS Supplementation with 30 mg/d elemental zinc during 24 months in patients with T2D had an effect on the composition of RBC membranes increasing PUFA abundance and in turn, improving membrane flexibility. This effect may be mediated by induction of D5D gene expression.
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Affiliation(s)
| | - Pamela Rojas
- From the Department of Nutrition, Faculty of Medicine, University of Chile, Santiago, Chile
| | - Fernando Carrasco
- From the Department of Nutrition, Faculty of Medicine, University of Chile, Santiago, Chile
| | - Karen Basfi-Fer
- From the Department of Nutrition, Faculty of Medicine, University of Chile, Santiago, Chile
| | - Rodrigo Valenzuela
- From the Department of Nutrition, Faculty of Medicine, University of Chile, Santiago, Chile
| | - Juana Codoceo
- From the Department of Nutrition, Faculty of Medicine, University of Chile, Santiago, Chile
| | - Jorge Inostroza
- From the Department of Nutrition, Faculty of Medicine, University of Chile, Santiago, Chile
| | - Manuel Ruz
- From the Department of Nutrition, Faculty of Medicine, University of Chile, Santiago, Chile.
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5
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Metabolic Effects of Selective Deletion of Group VIA Phospholipase A 2 from Macrophages or Pancreatic Islet Beta-Cells. Biomolecules 2020; 10:biom10101455. [PMID: 33080873 PMCID: PMC7602969 DOI: 10.3390/biom10101455] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Revised: 10/08/2020] [Accepted: 10/13/2020] [Indexed: 12/11/2022] Open
Abstract
To examine the role of group VIA phospholipase A2 (iPLA2β) in specific cell lineages in insulin secretion and insulin action, we prepared mice with a selective iPLA2β deficiency in cells of myelomonocytic lineage, including macrophages (MØ-iPLA2β-KO), or in insulin-secreting β-cells (β-Cell-iPLA2β-KO), respectively. MØ-iPLA2β-KO mice exhibited normal glucose tolerance when fed standard chow and better glucose tolerance than floxed-iPLA2β control mice after consuming a high-fat diet (HFD). MØ-iPLA2β-KO mice exhibited normal glucose-stimulated insulin secretion (GSIS) in vivo and from isolated islets ex vivo compared to controls. Male MØ-iPLA2β-KO mice exhibited enhanced insulin responsivity vs. controls after a prolonged HFD. In contrast, β-cell-iPLA2β-KO mice exhibited impaired glucose tolerance when fed standard chow, and glucose tolerance deteriorated further when introduced to a HFD. β-Cell-iPLA2β-KO mice exhibited impaired GSIS in vivo and from isolated islets ex vivo vs. controls. β-Cell-iPLA2β-KO mice also exhibited an enhanced insulin responsivity compared to controls. These findings suggest that MØ iPLA2β participates in HFD-induced deterioration in glucose tolerance and that this mainly reflects an effect on insulin responsivity rather than on insulin secretion. In contrast, β-cell iPLA2β plays a role in GSIS and also appears to confer some protection against deterioration in β-cell functions induced by a HFD.
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Fernandes ACS, Soares DC, Neves RFC, Koeller CM, Heise N, Adade CM, Frases S, Meyer-Fernandes JR, Saraiva EM, Souto-Padrón T. Endocytosis and Exocytosis in Leishmania amazonensis Are Modulated by Bromoenol Lactone. Front Cell Infect Microbiol 2020; 10:39. [PMID: 32117812 PMCID: PMC7020749 DOI: 10.3389/fcimb.2020.00039] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2019] [Accepted: 01/21/2020] [Indexed: 12/15/2022] Open
Abstract
In the protozoan pathogen Leishmania, endocytosis, and exocytosis occur mainly in the small area of the flagellar pocket membrane, which makes this parasite an interesting model of strikingly polarized internalization and secretion. Moreover, little is known about vesicle recognition and fusion mechanisms, which are essential for both endo/exocytosis in this parasite. In other cell types, vesicle fusion events require the activity of phospholipase A2 (PLA2), including Ca2+-independent iPLA2 and soluble, Ca2+-dependent sPLA2. Here, we studied the role of bromoenol lactone (BEL) inhibition of endo/exocytosis in promastigotes of Leishmania amazonensis. PLA2 activities were assayed in intact parasites, in whole conditioned media, and in soluble and extracellular vesicles (EVs) conditioned media fractions. BEL did not affect the viability of promastigotes, but reduced the differentiation into metacyclic forms. Intact parasites and EVs had BEL-sensitive iPLA2 activity. BEL treatment reduced total EVs secretion, as evidenced by reduced total protein concentration, as well as its size distribution and vesicles in the flagellar pocket of treated parasites as observed by TEM. Membrane proteins, such as acid phosphatases and GP63, became concentrated in the cytoplasm, mainly in multivesicular tubules of the endocytic pathway. BEL also prevented the endocytosis of BSA, transferrin and ConA, with the accumulation of these markers in the flagellar pocket. These results suggested that the activity inhibited by BEL, which is one of the irreversible inhibitors of iPLA2, is required for both endocytosis and exocytosis in promastigotes of L. amazonensis.
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Affiliation(s)
- Anne C S Fernandes
- Centro de Ciências da Saúde, Instituto de Microbiologia Paulo de Góes, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil.,Instituto Nacional de Ciência e Tecnologia de Biologia Estrutural e Bioimagem, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Deivid C Soares
- Centro de Ciências da Saúde, Instituto de Microbiologia Paulo de Góes, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Roberta F C Neves
- Centro de Ciências da Saúde, Instituto de Microbiologia Paulo de Góes, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Carolina M Koeller
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Norton Heise
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Camila M Adade
- Centro de Ciências da Saúde, Instituto de Microbiologia Paulo de Góes, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Susana Frases
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil
| | - José R Meyer-Fernandes
- Instituto Nacional de Ciência e Tecnologia de Biologia Estrutural e Bioimagem, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil.,Centro de Ciências da Saúde, Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Elvira M Saraiva
- Centro de Ciências da Saúde, Instituto de Microbiologia Paulo de Góes, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Thaïs Souto-Padrón
- Centro de Ciências da Saúde, Instituto de Microbiologia Paulo de Góes, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil.,Instituto Nacional de Ciência e Tecnologia de Biologia Estrutural e Bioimagem, Universidade Federal Do Rio de Janeiro, Rio de Janeiro, Brazil
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7
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Nelson AJ, Stephenson DJ, Cardona CL, Lei X, Almutairi A, White TD, Tusing YG, Park MA, Barbour SE, Chalfant CE, Ramanadham S. Macrophage polarization is linked to Ca 2+-independent phospholipase A 2β-derived lipids and cross-cell signaling in mice. J Lipid Res 2019; 61:143-158. [PMID: 31818877 DOI: 10.1194/jlr.ra119000281] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 11/27/2019] [Indexed: 12/27/2022] Open
Abstract
Phospholipases A2 (PLA2s) catalyze hydrolysis of the sn-2 substituent from glycerophospholipids to yield a free fatty acid (i.e., arachidonic acid), which can be metabolized to pro- or anti-inflammatory eicosanoids. Macrophages modulate inflammatory responses and are affected by Ca2+-independent phospholipase A2 (PLA2)β (iPLA2β). Here, we assessed the link between iPLA2β-derived lipids (iDLs) and macrophage polarization. Macrophages from WT and KO (iPLA2β-/-) mice were classically M1 pro-inflammatory phenotype activated or alternatively M2 anti-inflammatory phenotype activated, and eicosanoid production was determined by ultra-performance LC ESI-MS/MS. As a genotypic control, we performed similar analyses on macrophages from RIP.iPLA2β.Tg mice with selective iPLA2β overexpression in β-cells. Compared with WT, generation of select pro-inflammatory prostaglandins (PGs) was lower in iPLA2β-/- , and that of a specialized pro-resolving lipid mediator (SPM), resolvin D2, was higher; both changes are consistent with the M2 phenotype. Conversely, macrophages from RIP.iPLA2β.Tg mice exhibited an opposite landscape, one associated with the M1 phenotype: namely, increased production of pro-inflammatory eicosanoids (6-keto PGF1α, PGE2, leukotriene B4) and decreased ability to generate resolvin D2. These changes were not linked with secretory PLA2 or cytosolic PLA2α or with leakage of the transgene. Thus, we report previously unidentified links between select iPLA2β-derived eicosanoids, an SPM, and macrophage polarization. Importantly, our findings reveal for the first time that β-cell iPLA2β-derived signaling can predispose macrophage responses. These findings suggest that iDLs play critical roles in macrophage polarization, and we posit that they could be targeted therapeutically to counter inflammation-based disorders.
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Affiliation(s)
- Alexander J Nelson
- Department of Cell, Developmental, and Integrative Biology University of Alabama at Birmingham, Birmingham, AL 35294.,Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Daniel J Stephenson
- Department of Cell Biology, Microbiology, and Molecular Biology (CMMB), University of South Florida, Tampa, FL 33620
| | - Christopher L Cardona
- Department of Cell Biology, Microbiology, and Molecular Biology (CMMB), University of South Florida, Tampa, FL 33620
| | - Xiaoyong Lei
- Department of Cell, Developmental, and Integrative Biology University of Alabama at Birmingham, Birmingham, AL 35294.,Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Abdulaziz Almutairi
- Department of Cell, Developmental, and Integrative Biology University of Alabama at Birmingham, Birmingham, AL 35294.,Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Tayleur D White
- Department of Cell, Developmental, and Integrative Biology University of Alabama at Birmingham, Birmingham, AL 35294.,Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Ying G Tusing
- Department of Cell, Developmental, and Integrative Biology University of Alabama at Birmingham, Birmingham, AL 35294.,Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Margaret A Park
- Department of Cell Biology, Microbiology, and Molecular Biology (CMMB), University of South Florida, Tampa, FL 33620
| | - Suzanne E Barbour
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602
| | - Charles E Chalfant
- Department of Cell Biology, Microbiology, and Molecular Biology (CMMB), University of South Florida, Tampa, FL 33620.,Research Service, James A. Haley Veterans Hospital, Tampa, FL 33612
| | - Sasanka Ramanadham
- Department of Cell, Developmental, and Integrative Biology University of Alabama at Birmingham, Birmingham, AL 35294 .,Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL 35294
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8
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Li J, Du H, Zhang M, Zhang Z, Teng F, Zhao Y, Zhang W, Yu Y, Feng L, Cui X, Zhang M, Lu T, Guan F, Chen L. Amorphous solid dispersion of Berberine mitigates apoptosis via iPLA 2β/Cardiolipin/Opa1 pathway in db/db mice and in Palmitate-treated MIN6 β-cells. Int J Biol Sci 2019; 15:1533-1545. [PMID: 31337982 PMCID: PMC6643135 DOI: 10.7150/ijbs.32020] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 04/12/2019] [Indexed: 01/09/2023] Open
Abstract
Aims: Berberine (BBR) improves beta-cell function in Type 2 diabetes (T2D) because of its anti-apoptotic activity, and our laboratory developed a new preparation named Huang-Gui Solid Dispersion (HGSD) to improve the oral bioavailability of BBR. However, the mechanism by which BBR inhibits beta-cell apoptosis is unclear. We hypothesized that the Group VIA Ca2+-Independent Phospholipase A2 (iPLA2β)/Cardiolipin(CL)/Opa1 signaling pathway could exert a protective role in T2D by regulating beta-cell apoptosis and that HGSD could inhibit β-cell apoptosis through iPLA2β/CL/Opa1 upregulation. Methods: We examined how iPLA2β and BBR regulated apoptosis and insulin secretion through CL/Opa1 in vivo and in vitro. In in vitro studies, we developed Palmitate(PA)-induced apoptotic cell death model in mouse insulinoma cells (MIN6). iPLA2β overexpression and silencing technology were used to examine how the iPLA2β/CL/Opa1 interaction may play an important role in BBR treatment. In in vivo studies, db/db mice were used as a diabetic animal model. The pancreatic islet function and morphology, beta-cell apoptosis and mitochondrial injury were examined to explore the effects of HGSD. The expression of iPLA2β/CL/Opa1 was measured to explore whether the signaling pathway was damaged in T2D and was involved in HGSD treatment. Results: The overexpression of iPLA2β and BBR treatment significantly attenuated Palmitate- induced mitochondrial injury and apoptotic death compared with Palmitate-treated MIN6 cell. In addition, iPLA2β silencing could simultaneously partly abolish the anti-apoptotic effect of BBR and decrease CL/Opa1 signaling in MIN6 cells. Moreover, HGSD treatment significantly decreased beta-cell apoptosis and resulted in the upregulation of iPLA2β/CL/Opa1 compared to those of the db/db mice. Conclusion: The results indicated that the regulation of iPLA2β/CL/Opa1 by HGSD may prevent beta-cell apoptosis and may improve islet beta-cell function in Type 2 diabetic mice and in palmitate-treated MIN6 cells.
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Affiliation(s)
- Junnan Li
- Department of Pharmacology, School of Basic Medical Sciences, Jilin University, Changchun 130021, China
| | - Hongwei Du
- Department of Pediatric Endocrinology, The First Clinical Hospital Affiliated to Jilin University, Changchun 130021, China
| | - Meishuang Zhang
- Department of Pharmacology, School of Basic Medical Sciences, Jilin University, Changchun 130021, China
| | - Zhi Zhang
- School of Life Sciences, Jilin University, Changchun 130012, China
| | - Fei Teng
- Department of Pharmacology, School of Basic Medical Sciences, Jilin University, Changchun 130021, China
| | - Yali Zhao
- Department of Pharmacology, School of Basic Medical Sciences, Jilin University, Changchun 130021, China
| | - Wenyou Zhang
- Department of Pharmacology, School of Basic Medical Sciences, Jilin University, Changchun 130021, China
| | - Yang Yu
- Department of Pharmacology, School of Basic Medical Sciences, Jilin University, Changchun 130021, China
| | - Linjing Feng
- Department of Pharmacology, School of Basic Medical Sciences, Jilin University, Changchun 130021, China
| | - Xinming Cui
- Key Laboratory of Pathobiology, Ministry of Education, School of Basic Medical Sciences, Jilin University, Changchun 130021, China
| | - Ming Zhang
- Department of Pharmacology, School of Basic Medical Sciences, Jilin University, Changchun 130021, China
| | - Tzongshi Lu
- Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, United States
| | - Fengying Guan
- Department of Pharmacology, School of Basic Medical Sciences, Jilin University, Changchun 130021, China.,Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, United States
| | - Li Chen
- Department of Pharmacology, School of Basic Medical Sciences, Jilin University, Changchun 130021, China
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9
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Turk J, White TD, Nelson AJ, Lei X, Ramanadham S. iPLA 2β and its role in male fertility, neurological disorders, metabolic disorders, and inflammation. Biochim Biophys Acta Mol Cell Biol Lipids 2018; 1864:846-860. [PMID: 30408523 DOI: 10.1016/j.bbalip.2018.10.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2018] [Revised: 10/26/2018] [Accepted: 10/29/2018] [Indexed: 02/06/2023]
Abstract
The Ca2+-independent phospholipases, designated as group VI iPLA2s, also referred to as PNPLAs due to their shared homology with patatin, include the β, γ, δ, ε, ζ, and η forms of the enzyme. The iPLA2s are ubiquitously expressed, share a consensus GXSXG catalytic motif, and exhibit organelle/cell-specific localization. Among the iPLA2s, iPLA2β has received wide attention as it is recognized to be involved in membrane remodeling, cell proliferation, cell death, and signal transduction. Ongoing studies implicate participation of iPLA2β in a variety of disease processes including cancer, cardiovascular abnormalities, glaucoma, and peridonditis. This review will focus on iPLA2β and its links to male fertility, neurological disorders, metabolic disorders, and inflammation.
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Affiliation(s)
- John Turk
- Department of Medicine, Washington University School of Medicine, St. Louis, MO, United States of America
| | - Tayleur D White
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, United States of America; Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL, United States of America
| | - Alexander J Nelson
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, United States of America; Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL, United States of America
| | - Xiaoyong Lei
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, United States of America; Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL, United States of America
| | - Sasanka Ramanadham
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, United States of America; Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL, United States of America.
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10
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Shridas P, Noffsinger VP, Trumbauer AC, Webb NR. The dual role of group V secretory phospholipase A 2 in pancreatic β-cells. Endocrine 2017; 58:47-58. [PMID: 28825176 PMCID: PMC5693688 DOI: 10.1007/s12020-017-1379-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Accepted: 07/21/2017] [Indexed: 10/19/2022]
Abstract
PURPOSE Group X (GX) and group V (GV) secretory phospholipase A2 (sPLA2) potently release arachidonic acid (AA) from the plasma membrane of intact cells. We previously demonstrated that GX sPLA2 negatively regulates glucose-stimulated insulin secretion (GSIS) by a prostaglandin E2 (PGE2)-dependent mechanism. In this study we investigated whether GV sPLA2 similarly regulates GSIS. METHODS GSIS and pancreatic islet-size were assessed in wild-type (WT) and GV sPLA2-knock out (GV KO) mice. GSIS was also assessed ex vivo in isolated islets and in vitro using MIN6 pancreatic beta cell lines with or without GV sPLA2 overexpression or silencing. RESULTS GSIS was significantly decreased in islets isolated from GV KO mice compared to WT mice and in MIN6 cells with siRNA-mediated GV sPLA2 suppression. MIN6 cells overexpressing GV sPLA2 (MIN6-GV) showed a significant increase in GSIS compared to control cells. Though the amount of AA released into the media by MIN6-GV cells was significantly higher, PGE2 production was not enhanced or cAMP content decreased compared to control MIN6 cells. Surprisingly, GV KO mice exhibited a significant increase in plasma insulin levels following i.p. injection of glucose compared to WT mice. This increase in GSIS in GV KO mice was associated with a significant increase in pancreatic islet size and number of proliferating cells in β-islets compared to WT mice. CONCLUSIONS Deficiency of GV sPLA2 results in diminished GSIS in isolated pancreatic beta-cells. However, the reduced GSIS in islets lacking GV sPLA2 appears to be compensated by increased islet mass in GV KO mice.
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Affiliation(s)
- Preetha Shridas
- Saha Cardiovascular Research Center, University of Kentucky Medical Center, Lexington, KY, 40536, USA.
- Departments of Internal Medicine, University of Kentucky Medical Center, Lexington, KY, 40536, USA.
| | - Victoria P Noffsinger
- Saha Cardiovascular Research Center, University of Kentucky Medical Center, Lexington, KY, 40536, USA
- Departments of Internal Medicine, University of Kentucky Medical Center, Lexington, KY, 40536, USA
| | - Andrea C Trumbauer
- Saha Cardiovascular Research Center, University of Kentucky Medical Center, Lexington, KY, 40536, USA
| | - Nancy R Webb
- Saha Cardiovascular Research Center, University of Kentucky Medical Center, Lexington, KY, 40536, USA
- Pharmacology and Nutritional Sciences, Division of Nutritional Sciences, University of Kentucky Medical Center, Lexington, KY, 40536, USA
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11
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Nadler A, Yushchenko DA, Müller R, Stein F, Feng S, Mulle C, Carta M, Schultz C. Exclusive photorelease of signalling lipids at the plasma membrane. Nat Commun 2015; 6:10056. [PMID: 26686736 PMCID: PMC4703838 DOI: 10.1038/ncomms10056] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Accepted: 10/28/2015] [Indexed: 12/17/2022] Open
Abstract
Photoactivation of caged biomolecules has become a powerful approach to study cellular signalling events. Here we report a method for anchoring and uncaging biomolecules exclusively at the outer leaflet of the plasma membrane by employing a photocleavable, sulfonated coumarin derivative. The novel caging group allows quantifying the reaction progress and efficiency of uncaging reactions in a live-cell microscopy setup, thereby greatly improving the control of uncaging experiments. We synthesized arachidonic acid derivatives bearing the new negatively charged or a neutral, membrane-permeant coumarin caging group to locally induce signalling either at the plasma membrane or on internal membranes in β-cells and brain slices derived from C57B1/6 mice. Uncaging at the plasma membrane triggers a strong enhancement of calcium oscillations in β-cells and a pronounced potentiation of synaptic transmission while uncaging inside cells blocks calcium oscillations in β-cells and causes a more transient effect on neuronal transmission, respectively. The precise subcellular site of arachidonic acid release is therefore crucial for signalling outcome in two independent systems. Caged signalling intermediates are powerful cell biological tools, however it can be challenging to precisely control where activation occurs. Nadler et al. develop a caging group that specifically targets the plasma membrane, and demonstrate spatially controlled activation of arachidonic acid signalling.
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Affiliation(s)
- André Nadler
- European Molecular Biology Laboratory, Cell Biology and Biophysics Unit, Meyerhofstraße 1, 69117 Heidelberg, Germany.,Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstraße 108, 01307 Dresden, Germany
| | - Dmytro A Yushchenko
- European Molecular Biology Laboratory, Cell Biology and Biophysics Unit, Meyerhofstraße 1, 69117 Heidelberg, Germany.,Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610 Prague 6, Czech Republic
| | - Rainer Müller
- European Molecular Biology Laboratory, Cell Biology and Biophysics Unit, Meyerhofstraße 1, 69117 Heidelberg, Germany
| | - Frank Stein
- European Molecular Biology Laboratory, Cell Biology and Biophysics Unit, Meyerhofstraße 1, 69117 Heidelberg, Germany
| | - Suihan Feng
- European Molecular Biology Laboratory, Cell Biology and Biophysics Unit, Meyerhofstraße 1, 69117 Heidelberg, Germany
| | - Christophe Mulle
- Institut Interdisciplinaire de Neurosciences, CNRS UMR 5297 Université Bordeaux 2, 146, rue Léo-Saignat, 33077 Bordeaux, France
| | - Mario Carta
- Institut Interdisciplinaire de Neurosciences, CNRS UMR 5297 Université Bordeaux 2, 146, rue Léo-Saignat, 33077 Bordeaux, France
| | - Carsten Schultz
- European Molecular Biology Laboratory, Cell Biology and Biophysics Unit, Meyerhofstraße 1, 69117 Heidelberg, Germany
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12
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Ramanadham S, Ali T, Ashley JW, Bone RN, Hancock WD, Lei X. Calcium-independent phospholipases A2 and their roles in biological processes and diseases. J Lipid Res 2015; 56:1643-68. [PMID: 26023050 DOI: 10.1194/jlr.r058701] [Citation(s) in RCA: 135] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2015] [Indexed: 12/24/2022] Open
Abstract
Among the family of phospholipases A2 (PLA2s) are the Ca(2+)-independent PLA2s (iPLA2s) and they are designated group VI iPLA2s. In relation to secretory and cytosolic PLA2s, the iPLA2s are more recently described and details of their expression and roles in biological functions are rapidly emerging. The iPLA2s or patatin-like phospholipases (PNPLAs) are intracellular enzymes that do not require Ca(2+) for activity, and contain lipase (GXSXG) and nucleotide-binding (GXGXXG) consensus sequences. Though nine PNPLAs have been recognized, PNPLA8 (membrane-associated iPLA2γ) and PNPLA9 (cytosol-associated iPLA2β) are the most widely studied and understood. The iPLA2s manifest a variety of activities in addition to phospholipase, are ubiquitously expressed, and participate in a multitude of biological processes, including fat catabolism, cell differentiation, maintenance of mitochondrial integrity, phospholipid remodeling, cell proliferation, signal transduction, and cell death. As might be expected, increased or decreased expression of iPLA2s can have profound effects on the metabolic state, CNS function, cardiovascular performance, and cell survival; therefore, dysregulation of iPLA2s can be a critical factor in the development of many diseases. This review is aimed at providing a general framework of the current understanding of the iPLA2s and discussion of the potential mechanisms of action of the iPLA2s and related involved lipid mediators.
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Affiliation(s)
- Sasanka Ramanadham
- Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294 Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Tomader Ali
- Undergraduate Research Office, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Jason W Ashley
- Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, PA 19104
| | - Robert N Bone
- Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294 Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL 35294
| | - William D Hancock
- Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294 Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Xiaoyong Lei
- Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294 Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL 35294
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13
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Barbour SE, Nguyen PT, Park M, Emani B, Lei X, Kambalapalli M, Shultz JC, Wijesinghe D, Chalfant CE, Ramanadham S. Group VIA Phospholipase A2 (iPLA2β) Modulates Bcl-x 5'-Splice Site Selection and Suppresses Anti-apoptotic Bcl-x(L) in β-Cells. J Biol Chem 2015; 290:11021-31. [PMID: 25762722 DOI: 10.1074/jbc.m115.648956] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2015] [Indexed: 01/09/2023] Open
Abstract
Diabetes is a consequence of reduced β-cell function and mass, due to β-cell apoptosis. Endoplasmic reticulum (ER) stress is induced during β-cell apoptosis due to various stimuli, and our work indicates that group VIA phospholipase A2β (iPLA2β) participates in this process. Delineation of underlying mechanism(s) reveals that ER stress reduces the anti-apoptotic Bcl-x(L) protein in INS-1 cells. The Bcl-x pre-mRNA undergoes alternative pre-mRNA splicing to generate Bcl-x(L) or Bcl-x(S) mature mRNA. We show that both thapsigargin-induced and spontaneous ER stress are associated with reductions in the ratio of Bcl-x(L)/Bcl-x(S) mRNA in INS-1 and islet β-cells. However, chemical inactivation or knockdown of iPLA2β augments the Bcl-x(L)/Bcl-x(S) ratio. Furthermore, the ratio is lower in islets from islet-specific RIP-iPLA2β transgenic mice, whereas islets from global iPLA2β(-/-) mice exhibit the opposite phenotype. In view of our earlier reports that iPLA2β induces ceramide accumulation through neutral sphingomyelinase 2 and that ceramides shift the Bcl-x 5'-splice site (5'SS) selection in favor of Bcl-x(S), we investigated the potential link between Bcl-x splicing and the iPLA2β/ceramide axis. Exogenous C6-ceramide did not alter Bcl-x 5'SS selection in INS-1 cells, and neutral sphingomyelinase 2 inactivation only partially prevented the ER stress-induced shift in Bcl-x splicing. In contrast, 5(S)-hydroxytetraenoic acid augmented the ratio of Bcl-x(L)/Bcl-x(S) by 15.5-fold. Taken together, these data indicate that β-cell apoptosis is, in part, attributable to the modulation of 5'SS selection in the Bcl-x pre-mRNA by bioactive lipids modulated by iPLA2β.
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Affiliation(s)
- Suzanne E Barbour
- From the Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298-0614
| | - Phuong T Nguyen
- From the Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298-0614
| | - Margaret Park
- From the Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298-0614
| | - Bhargavi Emani
- From the Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298-0614
| | - Xiaoyong Lei
- the Department of Cell, Developmental, and Integrative Biology and Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, Alabama 35294
| | - Mamatha Kambalapalli
- From the Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298-0614
| | - Jacqueline C Shultz
- From the Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298-0614
| | - Dayanjan Wijesinghe
- From the Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298-0614, the Hunter Holmes McGuire Veterans Affairs Medical Center, Richmond, Virginia 23249
| | - Charles E Chalfant
- From the Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298-0614, the Hunter Holmes McGuire Veterans Affairs Medical Center, Richmond, Virginia 23249, the Massey Cancer Center, Richmond, Virginia 23298, and the Virginia Commonwealth University Reanimation Engineering Science Center, Richmond, Virginia 23298
| | - Sasanka Ramanadham
- the Department of Cell, Developmental, and Integrative Biology and Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, Alabama 35294,
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14
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Bone RN, Gai Y, Magrioti V, Kokotou MG, Ali T, Lei X, Tse HM, Kokotos G, Ramanadham S. Inhibition of Ca2+-independent phospholipase A2β (iPLA2β) ameliorates islet infiltration and incidence of diabetes in NOD mice. Diabetes 2015; 64:541-54. [PMID: 25213337 PMCID: PMC4303959 DOI: 10.2337/db14-0097] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/17/2014] [Accepted: 09/02/2014] [Indexed: 12/14/2022]
Abstract
Autoimmune β-cell death leads to type 1 diabetes, and with findings that Ca(2+)-independent phospholipase A2β (iPLA2β) activation contributes to β-cell death, we assessed the effects of iPLA2β inhibition on diabetes development. Administration of FKGK18, a reversible iPLA2β inhibitor, to NOD female mice significantly reduced diabetes incidence in association with 1) reduced insulitis, reflected by reductions in CD4(+) T cells and B cells; 2) improved glucose homeostasis; 3) higher circulating insulin; and 4) β-cell preservation. Furthermore, FKGK18 inhibited production of tumor necrosis factor-α (TNF-α) from CD4(+) T cells and antibodies from B cells, suggesting modulation of immune cell responses by iPLA2β-derived products. Consistent with this, 1) adoptive transfer of diabetes by CD4(+) T cells to immunodeficient and diabetes-resistant NOD.scid mice was mitigated by FKGK18 pretreatment and 2) TNF-α production from CD4(+) T cells was reduced by inhibitors of cyclooxygenase and 12-lipoxygenase, which metabolize arachidonic acid to generate bioactive inflammatory eicosanoids. However, adoptive transfer of diabetes was not prevented when mice were administered FKGK18-pretreated T cells or when FKGK18 administration was initiated with T-cell transfer. The present observations suggest that iPLA2β-derived lipid signals modulate immune cell responses, raising the possibility that early inhibition of iPLA2β may be beneficial in ameliorating autoimmune destruction of β-cells and mitigating type 1 diabetes development.
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Affiliation(s)
- Robert N Bone
- Department of Pathology, University of Alabama at Birmingham, Birmingham, AL Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL
| | - Ying Gai
- Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL
| | - Victoria Magrioti
- Laboratory of Organic Chemistry, Department of Chemistry, University of Athens, Athens, Greece
| | - Maroula G Kokotou
- Laboratory of Organic Chemistry, Department of Chemistry, University of Athens, Athens, Greece
| | - Tomader Ali
- Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL
| | - Xiaoyong Lei
- Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL
| | - Hubert M Tse
- Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL
| | - George Kokotos
- Laboratory of Organic Chemistry, Department of Chemistry, University of Athens, Athens, Greece
| | - Sasanka Ramanadham
- Comprehensive Diabetes Center, University of Alabama at Birmingham, Birmingham, AL Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL
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15
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Mayer O, Seidlerová J, Filipovský J, Timoracká K, Bruthans J, Vaněk J, Cerná L, Wohlfahrt P, Renata C, Trefil L. Unexpected inverse relationship between impaired glucose metabolism and lipoprotein-associated phospholipase A2 activity in patients with stable vascular disease. Eur J Intern Med 2014; 25:556-60. [PMID: 24930071 DOI: 10.1016/j.ejim.2014.05.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Revised: 04/16/2014] [Accepted: 05/20/2014] [Indexed: 11/25/2022]
Abstract
BACKGROUND Elevated lipoprotein-associated phospholipase A2 activity (aLp-PLA2) is associated with increased risk of cardiovascular events. In patients with stable atherovascular disease, we aimed to investigate whether impaired glucose metabolism might be associated with higher risk of elevated aLp-PLA2. METHODS We conducted a cross-sectional study in 825 stable patients after acute coronary syndrome, coronary revascularization or after first ischemic stroke (Czech part of EUROASPIRE III surveys). We measured aLp-PLA2 using diaDexus commercial kit. RESULTS In multiple step-wise regression analysis, the aLp-PLA2 was significantly positively associated with male gender, current smoking, LDL cholesterol and metabolic syndrome and negatively with statin treatment, body mass index and LDL/apoB ratio. After adjustment for these confounders, we observed an inverse relationship between aLp-PLA2 and fasting glycemia [β coefficient -2.18 (p<0.0001)] or glycated hemoglobin A1c (HbA1c) [β coefficient -5.89 (p<0.0001)]. Moreover, we found a positive association between aLp-PLA2 and pancreatic β cell function [β coefficient +0.10 (p<0.0001)], but not with an insulin sensitivity. CONCLUSION In present study, we cannot confirm any additive risk of impaired glucose metabolism in terms of increased activity of Lp-PLA2. On the contrary, presence of inadequately controlled diabetes mellitus was independently associated with lower risk of elevated aLp-PLA2 .
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Affiliation(s)
- Otto Mayer
- 2nd Department of Internal Medicine, Medical Faculty of Charles University and University Hospital, Pilsen, Czech Republic; Biomedical Center, Medical Faculty of Charles University, Pilsen, Czech Republic.
| | - Jitka Seidlerová
- 2nd Department of Internal Medicine, Medical Faculty of Charles University and University Hospital, Pilsen, Czech Republic; Biomedical Center, Medical Faculty of Charles University, Pilsen, Czech Republic
| | - Jan Filipovský
- 2nd Department of Internal Medicine, Medical Faculty of Charles University and University Hospital, Pilsen, Czech Republic; Biomedical Center, Medical Faculty of Charles University, Pilsen, Czech Republic
| | - Katarina Timoracká
- 2nd Department of Internal Medicine, Medical Faculty of Charles University and University Hospital, Pilsen, Czech Republic
| | - Jan Bruthans
- 2nd Department of Internal Medicine, Medical Faculty of Charles University and University Hospital, Pilsen, Czech Republic; Centre for Cardiovascular Prevention of the First Faculty of Medicine, Charles University and Thomayer Hospital, Prague, Czech Republic
| | - Jiří Vaněk
- 2nd Department of Internal Medicine, Medical Faculty of Charles University and University Hospital, Pilsen, Czech Republic
| | - Lenka Cerná
- Department of Neurology, University Hospital, Pilsen, Czech Republic
| | - Peter Wohlfahrt
- Centre for Cardiovascular Prevention of the First Faculty of Medicine, Charles University and Thomayer Hospital, Prague, Czech Republic; International Clinical Research Centre, St. Anne's University Hospital Brno, Czech Republic
| | - Cífková Renata
- Centre for Cardiovascular Prevention of the First Faculty of Medicine, Charles University and Thomayer Hospital, Prague, Czech Republic; International Clinical Research Centre, St. Anne's University Hospital Brno, Czech Republic
| | - Ladislav Trefil
- Department of Clinical Biochemistry and Hematology, University Hospital Pilsen, Czech Republic
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16
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Ali T, Kokotos G, Magrioti V, Bone RN, Mobley JA, Hancock W, Ramanadham S. Characterization of FKGK18 as inhibitor of group VIA Ca2+-independent phospholipase A2 (iPLA2β): candidate drug for preventing beta-cell apoptosis and diabetes. PLoS One 2013; 8:e71748. [PMID: 23977134 PMCID: PMC3748103 DOI: 10.1371/journal.pone.0071748] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Accepted: 06/30/2013] [Indexed: 01/27/2023] Open
Abstract
Ongoing studies suggest an important role for iPLA2β in a multitude of biological processes and it has been implicated in neurodegenerative, skeletal and vascular smooth muscle disorders, bone formation, and cardiac arrhythmias. Thus, identifying an iPLA2βinhibitor that can be reliably and safely used in vivo is warranted. Currently, the mechanism-based inhibitor bromoenol lactone (BEL) is the most widely used to discern the role of iPLA2β in biological processes. While BEL is recognized as a more potent inhibitor of iPLA2 than of cPLA2 or sPLA2, leading to its designation as a "specific" inhibitor of iPLA2, it has been shown to also inhibit non-PLA2 enzymes. A potential complication of its use is that while the S and R enantiomers of BEL exhibit preference for cytosol-associated iPLA2β and membrane-associated iPLA2γ, respectively, the selectivity is only 10-fold for both. In addition, BEL is unstable in solution, promotes irreversible inhibition, and may be cytotoxic, making BEL not amenable for in vivo use. Recently, a fluoroketone (FK)-based compound (FKGK18) was described as a potent inhibitor of iPLA2β. Here we characterized its inhibitory profile in beta-cells and find that FKGK18: (a) inhibits iPLA2β with a greater potency (100-fold) than iPLA2γ, (b) inhibition of iPLA2β is reversible, (c) is an ineffective inhibitor of α-chymotrypsin, and (d) inhibits previously described outcomes of iPLA2β activation including (i) glucose-stimulated insulin secretion, (ii) arachidonic acid hydrolysis; as reflected by PGE2 release from human islets, (iii) ER stress-induced neutral sphingomyelinase 2 expression, and (iv) ER stress-induced beta-cell apoptosis. These findings suggest that FKGK18 is similar to BEL in its ability to inhibit iPLA2β. Because, in contrast to BEL, it is reversible and not a non-specific inhibitor of proteases, it is suggested that FKGK18 is more ideal for ex vivo and in vivo assessments of iPLA2β role in biological functions.
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Affiliation(s)
- Tomader Ali
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
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17
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Tian L, Kim HS, Kim H, Jin X, Jung HS, Park KS, Cho KW, Park S, Moon WK. Changes in metabolic markers in insulin-producing β-cells during hypoxia-induced cell death as studied by NMR metabolomics. J Proteome Res 2013; 12:3738-45. [PMID: 23795807 DOI: 10.1021/pr400315e] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
This study was designed to investigate changes in the metabolites in the intracellular fluid of the pancreatic β-cell line INS-1 to identify potential early and late biomarkers for predicting hypoxia-induced cell death. INS-1 cells were incubated under normoxic conditions (95% air, 5% CO₂) or hypoxic conditions (1% O₂, 5% CO₂, 95% N₂) for 2, 4, 6, 12, or 24 h. The biological changes indicating the process of cell death were analyzed using the MTT assay, flow cytometry, Western blotting, and immunostaining. Changes in the metabolic profiles from cell lysates were identified using ¹H nuclear magnetic resonance (¹H NMR) spectroscopy, and the spectra were analyzed by the multivariate model Orthogonal Projections to Latent Structure-Discriminant Analysis. Cell viability decreased approximately 40% after 12-24 h of hypoxia, coincident with a high level of cleaved caspase-3. A high level of HIF-1α was detected in the 12-24 h hypoxic conditions. The metabolite profiles were altered according to the degree of exposure to hypoxia. A spectral analysis showed significant differences in creatine-containing compounds at the early stage (2-6 h) and taurine-containing compounds at the late stage (12-24 h), with the detection of HIF-1α and cleaved caspase-3 in cells exposed to hypoxia compared to normoxia. Glycerophosphocholine decreased during the early stage hypoxia. The change in taurine- and creatine-containing compounds and choline species could be involved in the β-cell death process as inhibitors or activators of cell death. Our results imply that assessment by ¹H NMR spectroscopy would be a useful tool to predict the cell death process and to identify molecules regulating hypoxia-induced cell death mechanisms.
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Affiliation(s)
- Lianji Tian
- Department of Biomedical Science, College of Medicine, Medical Research Center, Seoul National University, 101 Daehangno, Jongnogu, Seoul 110-744, Korea
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18
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Lei X, Bone RN, Ali T, Wohltmann M, Gai Y, Goodwin KJ, Bohrer AE, Turk J, Ramanadham S. Genetic modulation of islet β-cell iPLA₂β expression provides evidence for its impact on β-cell apoptosis and autophagy. Islets 2013; 5:29-44. [PMID: 23411472 PMCID: PMC3662380 DOI: 10.4161/isl.23758] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
β-cell apoptosis is a significant contributor to β-cell dysfunction in diabetes and ER stress is among the factors that contributes to β-cell death. We previously identified that the Ca²⁺-independent phospholipase A₂β (iPLA₂β), which in islets is localized in β-cells, participates in ER stress-induced β-cell apoptosis. Here, direct assessment of iPLA₂β role was made using β-cell-specific iPLA₂β overexpressing (RIP-iPLA₂β-Tg) and globally iPLA₂β-deficient (iPLA₂β-KO) mice. Islets from Tg, but not KO, express higher islet iPLA₂β and neutral sphingomyelinase, decrease in sphingomyelins, and increase in ceramides, relative to WT group. ER stress induces iPLA₂β, ER stress factors, loss of mitochondrial membrane potential (∆Ψ), caspase-3 activation, and β-cell apoptosis in the WT and these are all amplified in the Tg group. Surprisingly, β-cells apoptosis while reduced in the KO is higher than in the WT group. This, however, was not accompanied by greater caspase-3 activation but with larger loss of ∆Ψ, suggesting that iPLA₂β deficiency impacts mitochondrial membrane integrity and causes apoptosis by a caspase-independent manner. Further, autophagy, as reflected by LC3-II accumulation, is increased in Tg and decreased in KO, relative to WT. Our findings suggest that (1) iPLA₂β impacts upstream (UPR) and downstream (ceramide generation and mitochondrial) pathways in β-cells and (2) both over- or under-expression of iPLA₂β is deleterious to the β-cells. Further, we present for the first time evidence for potential regulation of autophagy by iPLA₂β in islet β-cells. These findings support the hypothesis that iPLA₂β induction under stress, as in diabetes, is a key component to amplifying β-cell death processes.
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Affiliation(s)
- Xiaoyong Lei
- Department of Cell, Developmental, and Integrative Biology; University of Alabama at Birmingham; Birmingham, AL USA
| | - Robert N. Bone
- Department of Pathology; University of Alabama at Birmingham; Birmingham, AL USA
| | - Tomader Ali
- Department of Cell, Developmental, and Integrative Biology; University of Alabama at Birmingham; Birmingham, AL USA
| | - Mary Wohltmann
- Department of Medicine; Mass Spectrometry Resource; Division of Endocrinology, Metabolism and Lipid Research; Washington University School of Medicine; St. Louis, MO USA
| | - Ying Gai
- Department of Cell, Developmental, and Integrative Biology; University of Alabama at Birmingham; Birmingham, AL USA
| | - Karen J. Goodwin
- Department of Cell, Developmental, and Integrative Biology; University of Alabama at Birmingham; Birmingham, AL USA
| | - Alan E. Bohrer
- Department of Medicine; Mass Spectrometry Resource; Division of Endocrinology, Metabolism and Lipid Research; Washington University School of Medicine; St. Louis, MO USA
| | - John Turk
- Department of Medicine; Mass Spectrometry Resource; Division of Endocrinology, Metabolism and Lipid Research; Washington University School of Medicine; St. Louis, MO USA
| | - Sasanka Ramanadham
- Department of Cell, Developmental, and Integrative Biology; University of Alabama at Birmingham; Birmingham, AL USA
- Correspondence to: Sasanka Ramanadham,
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19
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Song H, Wohltmann M, Tan M, Bao S, Ladenson JH, Turk J. Group VIA PLA2 (iPLA2β) is activated upstream of p38 mitogen-activated protein kinase (MAPK) in pancreatic islet β-cell signaling. J Biol Chem 2012; 287:5528-41. [PMID: 22194610 PMCID: PMC3285329 DOI: 10.1074/jbc.m111.285114] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2011] [Revised: 12/21/2011] [Indexed: 01/09/2023] Open
Abstract
Group VIA phospholipase A(2) (iPLA(2)β) in pancreatic islet β-cells participates in glucose-stimulated insulin secretion and sarco(endo)plasmic reticulum ATPase (SERCA) inhibitor-induced apoptosis, and both are attenuated by pharmacologic or genetic reductions in iPLA(2)β activity and amplified by iPLA(2)β overexpression. While exploring signaling events that occur downstream of iPLA(2)β activation, we found that p38 MAPK is activated by phosphorylation in INS-1 insulinoma cells and mouse pancreatic islets, that this increases with iPLA(2)β expression level, and that it is stimulated by the iPLA(2)β reaction product arachidonic acid. The insulin secretagogue D-glucose also stimulates β-cell p38 MAPK phosphorylation, and this is prevented by the iPLA(2)β inhibitor bromoenol lactone. Insulin secretion induced by d-glucose and forskolin is amplified by overexpressing iPLA(2)β in INS-1 cells and in mouse islets, and the p38 MAPK inhibitor PD169316 prevents both responses. The SERCA inhibitor thapsigargin also stimulates phosphorylation of both β-cell MAPK kinase isoforms and p38 MAPK, and bromoenol lactone prevents both events. Others have reported that iPLA(2)β products activate Rho family G-proteins that promote MAPK kinase activation via a mechanism inhibited by Clostridium difficile toxin B, which we find to inhibit thapsigargin-induced β-cell p38 MAPK phosphorylation. Thapsigargin-induced β-cell apoptosis and ceramide generation are also prevented by the p38 MAPK inhibitor PD169316. These observations indicate that p38 MAPK is activated downstream of iPLA(2)β in β-cells incubated with insulin secretagogues or thapsigargin, that this requires prior iPLA(2)β activation, and that p38 MAPK is involved in the β-cell functional responses of insulin secretion and apoptosis in which iPLA(2)β participates.
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Affiliation(s)
- Haowei Song
- From the Mass Spectrometry Resource, Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, and
| | - Mary Wohltmann
- From the Mass Spectrometry Resource, Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, and
| | - Min Tan
- From the Mass Spectrometry Resource, Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, and
| | - Shunzhong Bao
- From the Mass Spectrometry Resource, Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, and
| | - Jack H. Ladenson
- the Division of Laboratory and Genomic Medicine, Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - John Turk
- From the Mass Spectrometry Resource, Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, and
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Yeung-Yam-Wah V, Lee AK, Tse A. Arachidonic acid mobilizes Ca2+ from the endoplasmic reticulum and an acidic store in rat pancreatic β cells. Cell Calcium 2011; 51:140-8. [PMID: 22197025 DOI: 10.1016/j.ceca.2011.11.012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Revised: 11/30/2011] [Accepted: 11/30/2011] [Indexed: 11/17/2022]
Abstract
In rat pancreatic β cells, arachidonic acid (AA) triggered intracellular Ca(2+) release. This effect could be mimicked by eicosatetraynoic acid, indicating that AA metabolism is not required. The AA-mediated Ca(2+) signal was not affected by inhibition of ryanodine receptors or emptying of ryanodine-sensitive store but was reduced by ∼70% following the disruption of acidic stores (treatment with bafilomycin A1 or glycyl-phenylalanyl-β-naphthylamide (GPN)). The action of AA did not involve TRPM2 channels or NAADP receptors because intracellular dialysis of adenosine diphosphoribose (ADPR; an activator of TRPM2 channels) or NAADP did not affect the AA response. In contrast, stimulation of IP(3) receptors via intracellular dialysis of adenophostin A, or exogenous application of ATP largely abolished the AA-mediated Ca(2+) signal. Intracellular dialysis of heparin abolished the ATP-mediated Ca(2+) signal but not the AA response, suggesting that the action of AA did not involve the IP(3)-binding site. Treatment with the SERCA pump inhibitor, thapsigargin, reduced the amplitude of the AA-mediated Ca(2+) signal by ∼70%. Overall, our finding suggests that AA mobilizes Ca(2+) from the endoplasmic reticulum as well as an acidic store and both stores could be depleted by IP(3) receptor agonist. The possibility of secretory granules as targets of AA is discussed.
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Arachidonic acid actions on functional integrity and attenuation of the negative effects of palmitic acid in a clonal pancreatic β-cell line. Clin Sci (Lond) 2010; 120:195-206. [PMID: 20840078 PMCID: PMC2990202 DOI: 10.1042/cs20100282] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Chronic exposure of pancreatic β-cells to saturated non-esterified fatty acids can lead to inhibition of insulin secretion and apoptosis. Several previous studies have demonstrated that saturated fatty acids such as PA (palmitic acid) are detrimental to β-cell function compared with unsaturated fatty acids. In the present study, we describe the effect of the polyunsaturated AA (arachidonic acid) on the function of the clonal pancreatic β-cell line BRIN-BD11 and demonstrate AA-dependent attenuation of PA effects. When added to β-cell incubations at 100 μM, AA can stimulate cell proliferation and chronic (24 h) basal insulin secretion. Microarray analysis and/or real-time PCR indicated significant AA-dependent up-regulation of genes involved in proliferation and fatty acid metabolism [e.g. Angptl (angiopoietin-like protein 4), Ech1 (peroxisomal Δ3,5,Δ2,4-dienoyl-CoA isomerase), Cox-1 (cyclo-oxygenase-1) and Cox-2, P<0.05]. Experiments using specific COX and LOX (lipoxygenase) inhibitors demonstrated the importance of COX-1 activity for acute (20 min) stimulation of insulin secretion, suggesting that AA metabolites may be responsible for the insulinotropic effects. Moreover, concomitant incubation of AA with PA dose-dependently attenuated the detrimental effects of the saturated fatty acid, so reducing apoptosis and decreasing parameters of oxidative stress [ROS (reactive oxygen species) and NO levels] while improving the GSH/GSSG ratio. AA decreased the protein expression of iNOS (inducible NO synthase), the p65 subunit of NF-κB (nuclear factor κB) and the p47 subunit of NADPH oxidase in PA-treated cells. These findings indicate that AA has an important regulatory and protective β-cell action, which may be beneficial to function and survival in the ‘lipotoxic’ environment commonly associated with Type 2 diabetes mellitus.
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Lei X, Zhang S, Emani B, Barbour SE, Ramanadham S. A link between endoplasmic reticulum stress-induced β-cell apoptosis and the group VIA Ca2+-independent phospholipase A2 (iPLA2β). Diabetes Obes Metab 2010; 12 Suppl 2:93-8. [PMID: 21029305 PMCID: PMC3713613 DOI: 10.1111/j.1463-1326.2010.01270.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Endoplasmic reticulum (ER) stress is becoming recognized as an important contributing factor in various diseases, including diabetes mellitus. Prolonged ER stress can cause β-cell apoptosis; however, the underlying mechanism(s) that contribute to this process are not well understood. Early reports suggested that arachidonic acid metabolites and a Ca(2+)-independent phospholipase A(2) (iPLA(2)) activity play a role in β-cell apoptosis. The PLA(2) family of enzymes catalyse the hydrolysis of the sn-2 substituent (i.e. arachidonic acid) of membrane phospholipids. In light of our findings that the pancreatic islet β-cells are enriched in arachidonate-containing phospholipids and express the group VIA iPLA(2)β, we considered the possibility that iPLA(2)β participates in ER stress-induced β-cell apoptosis. Our work revealed a novel mechanism, involving ceramide generation and triggering of mitochondrial abnormalities, by which iPLA(2)β participates in the β-cell apoptosis process. Here, we review our evidence linking ER stress, β-cell apoptosis and iPLA(2)β. Continued studies in this area will increase our understanding of the contribution of iPLA(2)β to the evolution of diabetes mellitus and will further our knowledge of factors that influence β-cell health in diabetes mellitus and identify potential targets for future therapeutic interventions to prevent β-cell death.
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Affiliation(s)
- X Lei
- Department of Medicine, Mass Spectrometry Resource and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St Louis, MO 63110, USA
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Mancuso DJ, Sims HF, Yang K, Kiebish MA, Su X, Jenkins CM, Guan S, Moon SH, Pietka T, Nassir F, Schappe T, Moore K, Han X, Abumrad NA, Gross RW. Genetic ablation of calcium-independent phospholipase A2gamma prevents obesity and insulin resistance during high fat feeding by mitochondrial uncoupling and increased adipocyte fatty acid oxidation. J Biol Chem 2010; 285:36495-510. [PMID: 20817734 DOI: 10.1074/jbc.m110.115766] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Phospholipases are critical enzyme mediators participating in many aspects of cellular function through modulating the generation of lipid 2nd messengers, membrane physical properties, and cellular bioenergetics. Here, we demonstrate that mice null for calcium-independent phospholipase A(2)γ (iPLA(2)γ(-/-)) are completely resistant to high fat diet-induced weight gain, adipocyte hypertrophy, hyperinsulinemia, and insulin resistance, which occur in iPLA(2)γ(+/+) mice after high fat feeding. Notably, iPLA(2)γ(-/-) mice were lean, demonstrated abdominal lipodystrophy, and remained insulin-sensitive despite having a marked impairment in glucose-stimulated insulin secretion after high fat feeding. Respirometry of adipocyte explants from iPLA(2)γ(-/-) mice identified increased rates of oxidation of multiple different substrates in comparison with adipocyte explants from wild-type littermates. Shotgun lipidomics of adipose tissue from wild-type mice demonstrated the anticipated 2-fold increase in triglyceride content after high fat feeding. In sharp contrast, the adipocyte triglyceride content was identical in iPLA(2)γ(-/-) mice fed either a standard diet or a high fat diet. Respirometry of skeletal muscle mitochondria from iPLA(2)γ(-/-) mice demonstrated marked decreases in state 3 respiration using multiple substrates whose metabolism was uncoupled from ATP production. Shotgun lipidomics of skeletal muscle revealed a decreased content of cardiolipin with an altered molecular species composition thereby identifying the mechanism underlying mitochondrial uncoupling in the iPLA(2)γ(-/-) mouse. Collectively, these results identify iPLA(2)γ as an obligatory upstream enzyme that is necessary for efficient electron transport chain coupling and energy production through its participation in the alterations of cellular bioenergetics that promote the development of the metabolic syndrome.
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Affiliation(s)
- David J Mancuso
- Division of Bioorganic Chemistry and Molecular Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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24
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Song H, Bao S, Lei X, Jin C, Zhang S, Turk J, Ramanadham S. Evidence for proteolytic processing and stimulated organelle redistribution of iPLA(2)beta. BIOCHIMICA ET BIOPHYSICA ACTA 2010; 1801:547-58. [PMID: 20132906 PMCID: PMC2848069 DOI: 10.1016/j.bbalip.2010.01.006] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2009] [Revised: 12/24/2009] [Accepted: 01/19/2010] [Indexed: 12/31/2022]
Abstract
Over the past decade, important roles for the 84-88kDa Group VIA Ca(2+)-independent phospholipase A(2) (iPLA(2)beta) in various organs have been described. We demonstrated that iPLA(2)beta participates in insulin secretion, insulinoma cells and native pancreatic islets express full-length and truncated isoforms of iPLA(2)beta, and certain stimuli promote perinuclear localization of iPLA(2)beta. To gain a better understanding of its mobilization, iPLA(2)beta was expressed in INS-1 cells as a fusion protein with EGFP, enabling detection of subcellular localization of iPLA(2)beta by monitoring EGFP fluorescence. Cells stably-transfected with fusion protein expressed nearly 5-fold higher catalytic iPLA(2)beta activity than control cells transfected with EGFP cDNA alone, indicating that co-expression of EGFP does not interfere with manifestation of iPLA(2)beta activity. Dual fluorescence monitoring of EGFP and organelle Trackers combined with immunoblotting analyses revealed expression of truncated iPLA(2)beta isoforms in separate subcellular organelles. Exposure to secretagogues and induction of ER stress are known to activate iPLA(2)beta in beta-cells and we find here that these stimuli promote differential localization of iPLA(2)beta in subcellular organelles. Further, mass spectrometric analyses identified iPLA(2)beta variants from which N-terminal residues were removed. Collectively, these findings provide evidence for endogenous proteolytic processing of iPLA(2)beta and redistribution of iPLA(2)beta variants in subcellular compartments. It might be proposed that in vivo processing of iPLA(2)beta facilitates its participation in multiple biological processes.
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Affiliation(s)
- Haowei Song
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - Shunzhong Bao
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - Xiaoyong Lei
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - Chun Jin
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - Sheng Zhang
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - John Turk
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - Sasanka Ramanadham
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
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Lei X, Barbour SE, Ramanadham S. Group VIA Ca2+-independent phospholipase A2 (iPLA2beta) and its role in beta-cell programmed cell death. Biochimie 2010; 92:627-37. [PMID: 20083151 DOI: 10.1016/j.biochi.2010.01.005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Accepted: 01/11/2010] [Indexed: 01/09/2023]
Abstract
Activation of phospholipases A(2) (PLA(2)s) leads to the generation of biologically active lipid mediators that can affect numerous cellular events. The Group VIA Ca(2+)-independent PLA(2), designated iPLA(2)beta, is active in the absence of Ca(2+), activated by ATP, and inhibited by the bromoenol lactone suicide inhibitor (BEL). Over the past 10-15 years, studies using BEL have demonstrated that iPLA(2)beta participates in various biological processes and the recent availability of mice in which iPLA(2)beta expression levels have been genetically-modified are extending these findings. Work in our laboratory suggests that iPLA(2)beta activates a unique signaling cascade that promotes beta-cell apoptosis. This pathway involves iPLA(2)beta dependent induction of neutral sphingomyelinase, production of ceramide, and activation of the intrinsic pathway of apoptosis. There is a growing body of literature supporting beta-cell apoptosis as a major contributor to the loss of beta-cell mass associated with the onset and progression of Type 1 and Type 2 diabetes mellitus. This underscores a need to gain a better understanding of the molecular mechanisms underlying beta-cell apoptosis so that improved treatments can be developed to prevent or delay the onset and progression of diabetes mellitus. Herein, we offer a general review of Group VIA Ca(2+)-independent PLA(2) (iPLA(2)beta) followed by a more focused discussion of its participation in beta-cell apoptosis. We suggest that iPLA(2)beta-derived products trigger pathways which can lead to beta-cell apoptosis during the development of diabetes.
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Affiliation(s)
- Xiaoyong Lei
- Department of Medicine, Mass Spectrometry Resource and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, MO 63110, USA
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Yeung-Yam-Wah V, Lee AK, Tse FW, Tse A. Arachidonic acid stimulates extracellular Ca(2+) entry in rat pancreatic beta cells via activation of the noncapacitative arachidonate-regulated Ca(2+) (ARC) channels. Cell Calcium 2009; 47:77-83. [PMID: 20018371 DOI: 10.1016/j.ceca.2009.11.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2009] [Revised: 11/05/2009] [Accepted: 11/17/2009] [Indexed: 11/15/2022]
Abstract
Arachidonic acid (AA) is generated in the pancreatic islets during glucose stimulation. We investigated whether AA activated extracellular Ca(2+) entry in rat pancreatic beta cells via a pathway that was independent of the activation of voltage-gated Ca(2+) channels. The AA triggered [Ca(2+)](i) rise did not involve activation of GPR40 receptors or AA metabolism. When cells were voltage clamped at -70mV, the AA-mediated intracellular Ca(2+) release was accompanied by extracellular Ca(2+) entry. AA accelerated the rate of Mn(2+) quench of indo-1 fluorescence (near the Ca(2+)-independent wavelength of indo-1), reflecting the activation of a Ca(2+)-permeable pathway. The AA-mediated acceleration of Mn(2+) quench was inhibited by La(3+) but not by 2-APB (a blocker of capacitative Ca(2+) entry), suggesting the involvement of arachidonate-regulated Ca(2+) (ARC) channels. Consistent with this, intracellular application of the charged membrane-impermeant analog of AA, arachidonyl-coenzyme A (ACoA) triggered extracellular Ca(2+) entry, as well as the activation of a La(3+)-sensitive small inward current (1.7pA/pF) at -70mV. Our results indicate that the activation of ARC channels by intracellular AA triggers extracellular Ca(2+) entry. This action may contribute to the effects of AA on Ca(2+) signals and insulin secretion in rat beta cells.
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Lei X, Zhang S, Bohrer A, Ramanadham S. Calcium-independent phospholipase A2 (iPLA2 beta)-mediated ceramide generation plays a key role in the cross-talk between the endoplasmic reticulum (ER) and mitochondria during ER stress-induced insulin-secreting cell apoptosis. J Biol Chem 2008; 283:34819-32. [PMID: 18936091 PMCID: PMC2596401 DOI: 10.1074/jbc.m807409200] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Revised: 10/15/2008] [Indexed: 01/09/2023] Open
Abstract
Endoplasmic reticulum (ER) stress induces INS-1 cell apoptosis by a pathway involving Ca(2+)-independent phospholipase A(2) (iPLA(2)beta)-mediated ceramide generation, but the mechanism by which iPLA(2)beta and ceramides contribute to apoptosis is not well understood. We report here that both caspase-12 and caspase-3 are activated in INS-1 cells following induction of ER stress with thapsigargin, but only caspase-3 cleavage is amplified in iPLA(2)beta overexpressing INS-1 cells (OE), relative to empty vector-transfected cells, and is suppressed by iPLA(2)beta inhibition. ER stress also led to the release of cytochrome c and Smac and, unexpectedly, their accumulation in the cytosol is amplified in OE cells. These findings raise the likelihood that iPLA(2)beta participates in ER stress-induced apoptosis by activating the intrinsic apoptotic pathway. Consistent with this possibility, we find that ER stress promotes iPLA(2)beta accumulation in the mitochondria, opening of mitochondrial permeability transition pore, and loss in mitochondrial membrane potential (Delta Psi) in INS-1 cells and that these changes are amplified in OE cells. ER stress also led to greater ceramide generation in ER and mitochondria fractions of OE cells. Exposure to ceramide alone induces loss in Delta Psi and apoptosis and these are suppressed by forskolin. ER stress-induced mitochondrial dysfunction and apoptosis are also inhibited by forskolin, as well as by inactivation of iPLA(2)beta or NSMase, suggesting that iPLA(2)beta-mediated generation of ceramides via sphingomyelin hydrolysis during ER stress affect the mitochondria. In support, inhibition of iPLA(2)beta or NSMase prevents cytochrome c release. Collectively, our findings indicate that the iPLA(2)beta-ceramide axis plays a critical role in activating the mitochondrial apoptotic pathway in insulin-secreting cells during ER stress.
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Affiliation(s)
| | | | | | - Sasanka Ramanadham
- Department of Medicine, Mass Spectrometry Resource and Division of
Endocrinology, Metabolism, and Lipid Research, Washington University School of
Medicine, St. Louis, Missouri 63110
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Saturated and unsaturated (including arachidonic acid) non-esterified fatty acid modulation of insulin secretion from pancreatic beta-cells. Biochem Soc Trans 2008; 36:955-8. [PMID: 18793168 DOI: 10.1042/bst0360955] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Both stimulatory and detrimental effects of NEFAs (non-esterified fatty acids) on pancreatic beta-cells have been recognized. Acute exposure of the pancreatic beta-cell to high glucose concentrations and/or saturated NEFAs results in a substantial increase in insulin release, whereas chronic exposure results in desensitization and suppression of secretion followed by induction of apoptosis. Some unsaturated NEFAs also promote insulin release acutely, but they are less toxic to beta-cells during chronic exposure and can even exert positive protective effects. In the present review, we focus on exogenous and endogenous effects of NEFAs, including the polyunsaturated fatty acid, arachidonic acid (or its metabolites generated from cyclo-oxygenase activity), on beta-cell metabolism, and have explored the outcomes with respect to beta-cell insulin secretion.
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Bao S, Jacobson DA, Wohltmann M, Bohrer A, Jin W, Philipson LH, Turk J. Glucose homeostasis, insulin secretion, and islet phospholipids in mice that overexpress iPLA2beta in pancreatic beta-cells and in iPLA2beta-null mice. Am J Physiol Endocrinol Metab 2008; 294:E217-29. [PMID: 17895289 PMCID: PMC2268609 DOI: 10.1152/ajpendo.00474.2007] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Studies with genetically modified insulinoma cells suggest that group VIA phospholipase A(2) (iPLA(2)beta) participates in amplifying glucose-induced insulin secretion. INS-1 insulinoma cells that overexpress iPLA(2)beta, for example, exhibit amplified insulin-secretory responses to glucose and cAMP-elevating agents. To determine whether similar effects occur in whole animals, we prepared transgenic (TG) mice in which the rat insulin 1 promoter (RIP) drives iPLA(2)beta overexpression, and two characterized TG mouse lines exhibit similar phenotypes. Their pancreatic islet iPLA(2)beta expression is increased severalfold, as reflected by quantitative PCR of iPLA(2)beta mRNA, immunoblotting of iPLA(2)beta protein, and iPLA(2)beta enzymatic activity. Immunofluorescence microscopic studies of pancreatic sections confirm iPLA(2)beta overexpression in RIP-iPLA(2)beta-TG islet beta-cells without obviously perturbed islet morphology. Male RIP-iPLA(2)beta-TG mice exhibit lower blood glucose and higher plasma insulin concentrations than wild-type (WT) mice when fasting and develop lower blood glucose levels in glucose tolerance tests, but WT and TG blood glucose levels do not differ in insulin tolerance tests. Islets from male RIP-iPLA(2)beta-TG mice exhibit greater amplification of glucose-induced insulin secretion by a cAMP-elevating agent than WT islets. In contrast, islets from male iPLA(2)beta-null mice exhibit blunted insulin secretion, and those mice have impaired glucose tolerance. Arachidonate incorporation into and the phospholipid composition of RIP-iPLA(2)beta-TG islets are normal, but they exhibit reduced Kv2.1 delayed rectifier current and prolonged glucose-induced action potentials and elevations of cytosolic Ca(2+) concentration that suggest a molecular mechanism for the physiological role of iPLA(2)beta to amplify insulin secretion.
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MESH Headings
- Animals
- Arachidonic Acid/metabolism
- Blood Glucose/metabolism
- Blood Glucose/physiology
- Blotting, Western
- Calcium/physiology
- Cell Line, Tumor
- DNA, Complementary/biosynthesis
- DNA, Complementary/genetics
- Fasting/metabolism
- Gene Expression Regulation, Enzymologic/physiology
- Genotype
- Glucose Tolerance Test
- Group IV Phospholipases A2/biosynthesis
- Group IV Phospholipases A2/genetics
- Homeodomain Proteins/genetics
- Homeostasis/physiology
- Insulin/blood
- Insulin/metabolism
- Insulin Secretion
- Insulin-Secreting Cells/metabolism
- Insulinoma/metabolism
- Islets of Langerhans/metabolism
- Kv1.2 Potassium Channel/metabolism
- Mice
- Mice, Knockout
- Mice, Transgenic
- Microscopy, Fluorescence
- Pancreatic Neoplasms/metabolism
- Patch-Clamp Techniques
- Phospholipids/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Spectrometry, Mass, Electrospray Ionization
- Trans-Activators/genetics
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Affiliation(s)
- Shunzhong Bao
- Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
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Poitout V. Phospholipid hydrolysis and insulin secretion: a step toward solving the Rubik's cube. Am J Physiol Endocrinol Metab 2008; 294:E214-6. [PMID: 17925452 PMCID: PMC3167821 DOI: 10.1152/ajpendo.00638.2007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Vincent Poitout
- Montreal Diabetes Research Center, CR-CHUM, Technopole Angus, 2901 Rachel Est, Montreal, Quebec, Canada.
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31
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Bacová Z, Orecná M, Hafko R, Strbák V. Cell swelling-induced signaling for insulin secretion bypasses steps involving G proteins and PLA2 and is N-ethylmaleimide insensitive. Cell Physiol Biochem 2007; 20:387-96. [PMID: 17762166 DOI: 10.1159/000107523] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/19/2007] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND This study was undertaken to examine putative mechanisms of calcium independent signal transduction pathway of cell swelling-induced insulin secretion. METHODS The role of phospholipase A(2), G proteins, and soluble N-ethylmaleimide-sensitive-factor attachment protein receptor (SNARE) in insulin secretion induced by 30% hypotonic medium was studied using isolated rat pancreatic islets. RESULTS In contrast to glucose stimulation, osmotically induced insulin secretion from pancreatic islets was not inhibited by 10 micromol/l bromoenol lactone, an iPLA(2) (Ca(2+) independent phospholipase) inhibitor. Similarly, preincubation of islets for 20 hours with 25 microg/ml mycophenolic acid to inhibit GTP synthesis fully abolished glucose-induced insulin secretion but was without effect on hypotonicity stimulated insulin release. Glucose-induced insulin secretion was prevented by preincubation with 20 nmol/l tetanus toxin (TeTx), a metalloprotease inactivating soluble SNARE. Cell swelling-induced insulin secretion was inhibited by TeTx in the presence of calcium ions but not in calcium depleted medium. The presence of N-ethylmaleimide (NEM, 5 mmol/l, another inhibitor of SNARE proteins) in the medium resulted in high basal insulin secretion and lacking response to glucose stimulation. In contrast, high basal insulin secretion from NEM treated islets further increased after hypotonic stimulation. CONCLUSION G proteins and iPLA(2) - putative mediators of Ca(2+) independent signaling pathway participate in glucose but not in hypotonicity-induced insulin secretion. Hypotonicity-induced insulin secretion is sensitive to clostridial neurotoxin TeTx but is resistant to NEM.
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Affiliation(s)
- Zuzana Bacová
- Institute of Experimental Endocrinology, Slovak Academy of Sciences, Bratislava, Slovakia
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32
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Lei XY, Zhang S, Bohrer A, Bao S, Song H, Ramanadham S. The group VIA calcium-independent phospholipase A2 participates in ER stress-induced INS-1 insulinoma cell apoptosis by promoting ceramide generation via hydrolysis of sphingomyelins by neutral sphingomyelinase. Biochemistry 2007; 46:10170-85. [PMID: 17685585 PMCID: PMC2530898 DOI: 10.1021/bi700017z] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Beta-cell mass is regulated by a balance between beta-cell growth and beta-cell death, due to apoptosis. We previously reported that apoptosis of INS-1 insulinoma cells due to thapsigargin-induced ER stress was suppressed by inhibition of the group VIA Ca2+-independent phospholipase A2 (iPLA2beta), associated with an increased level of ceramide generation, and that the effects of ER stress were amplified in INS-1 cells in which iPLA2beta was overexpressed (OE INS-1 cells). These findings suggested that iPLA2beta and ceramides participate in ER stress-induced INS-1 cell apoptosis. Here, we address this possibility and also the source of the ceramides by examining the effects of ER stress in empty vector (V)-transfected and iPLA2beta-OE INS-1 cells using apoptosis assays and immunoblotting, quantitative PCR, and mass spectrometry analyses. ER stress induced expression of ER stress factors GRP78 and CHOP, cleavage of apoptotic factor PARP, and apoptosis in V and OE INS-1 cells. Accumulation of ceramide during ER stress was not associated with changes in mRNA levels of serine palmitoyltransferase (SPT), the rate-limiting enzyme in de novo synthesis of ceramides, but both message and protein levels of neutral sphingomyelinase (NSMase), which hydrolyzes sphingomyelins to generate ceramides, were temporally increased in the INS-1 cells. The increases in the level of NSMase expression in the ER-stressed INS-1 cells were associated with corresponding temporal elevations in ER-associated iPLA2beta protein and catalytic activity. Pretreatment with BEL inactivated iPLA2beta and prevented induction of NSMase message and protein in ER-stressed INS-1 cells. Relative to that in V INS-1 cells, the effects of ER stress were accelerated and/or amplified in the OE INS-1 cells. However, inhibition of iPLA2beta or NSMase (chemically or with siRNA) suppressed induction of NSMase message, ceramide generation, sphingomyelin hydrolysis, and apoptosis in both V and OE INS-1 cells during ER stress. In contrast, inhibition of SPT did not suppress ceramide generation or apoptosis in either V or OE INS-1 cells. These findings indicate that iPLA2beta activation participates in ER stress-induced INS-1 cell apoptosis by promoting ceramide generation via NSMase-catalyzed hydrolysis of sphingomyelins, raising the possibility that this pathway contributes to beta-cell apoptosis due to ER stress.
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Affiliation(s)
| | | | | | | | | | - Sasanka Ramanadham
- *Address correspondence to: Sasanka Ramanadham, Dept. Medicine, Washington University School of Medicine, Campus Box 8127, 660 S. Euclid Ave., St. Louis, MO 63110; telephone 314-362-8194; FAX 314-362-7641; E-mail:
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Larsson-Nyrén G, Grapengiesser E, Hellman B. Phospholipase A2 is important for glucose induction of rhythmic Ca2+ signals in pancreatic beta cells. Pancreas 2007; 35:173-9. [PMID: 17632325 DOI: 10.1097/mpa.0b013e318053e022] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Abstract
OBJECTIVES Pancreatic beta cells respond to glucose stimulation with pulses of insulin release generated by oscillatory rises of the cytoplasmic Ca2+ concentration ([Ca2+]i). The observation that exposure to external ATP and other activators of cytoplasmic phospholipase A2 (cPLA2) rapidly induces rises of [Ca2+]i similar to ordinary oscillations made it important to analyze whether suppression of the cPLA2 activity affects glucose-induced [Ca2+]i rhythmicity in pancreatic beta cells. METHODS Ratiometric fura-2 technique was used for measuring [Ca2+]i in single beta cells and small aggregates prepared from ob/ob mouse islets. RESULTS Testing the effects of different inhibitors of cPLA2 in the presence of 20 mM glucose, it was found that N-(p-amylcinnamoyl)anthranilic acid (ACA) removed the oscillations at a concentration of 25 microM, arachidonyl trifluoromethyl ketone (AACOCF3) at 10 microM, and bromoenol lactone (BEL) at 10 to 15 microM. Withdrawal of ACA and BEL resulted in reappearance of the oscillations. Suppression of the arachidonic acid production by addition of 5 microM of the diacylglycerol lipase inhibitor 1,6-bis-(cyclohexyloximinocarbonylamino)-hexane (RHC 80267) effectively removed the [Ca2+]i oscillations, an effect reversed by removal of the inhibitor or addition of 100 microM tolbutamide. Suppression of the arachidonic acid production had a restrictive influence also on the transients of [Ca2+]i supposed to synchronize the beta-cell rhythmicity. Although less sensitive than the oscillations, most transients disappeared during exposure to 50 microM ACA or 35 microM RHC 80267. CONCLUSIONS The results support the idea that cyclic variations of cPLA2 activity are important for the generation and synchronization of the beta-cell [Ca2+]i oscillations responsible for pulsatile release of insulin.
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Affiliation(s)
- Gerd Larsson-Nyrén
- Department of Integrative Medical Biology, Section for Histology and Cell Biology, University of Umeå University, Umeå, Sweden.
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Jacobson DA, Weber CR, Bao S, Turk J, Philipson LH. Modulation of the pancreatic islet beta-cell-delayed rectifier potassium channel Kv2.1 by the polyunsaturated fatty acid arachidonate. J Biol Chem 2007; 282:7442-9. [PMID: 17197450 PMCID: PMC2044499 DOI: 10.1074/jbc.m607858200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucose stimulates both insulin secretion and hydrolysis of arachidonic acid (AA) esterified in membrane phospholipids of pancreatic islet beta-cells, and these processes are amplified by muscarinic agonists. Here we demonstrate that nonesterified AA regulates the biophysical activity of the pancreatic islet beta-cell-delayed rectifier channel, Kv2.1. Recordings of Kv2.1 currents from INS-1 insulinoma cells incubated with AA (5 mum) and subjected to graded degrees of depolarization exhibit a significantly shorter time-to-peak current interval than do control cells. AA causes a rapid decay and reduced peak conductance of delayed rectifier currents from INS-1 cells and from primary beta-cells isolated from mouse, rat, and human pancreatic islets. Stimulating mouse islets with AA results in a significant increase in the frequency of glucose-induced [Ca(2+)] oscillations, which is an expected effect of Kv2.1 channel blockade. Stimulation with concentrations of glucose and carbachol that accelerate hydrolysis of endogenous AA from islet phosphoplipids also results in accelerated Kv2.1 inactivation and a shorter time-to-peak current interval. Group VIA phospholipase A(2) (iPLA(2)beta) hydrolyzes beta-cell membrane phospholipids to release nonesterified fatty acids, including AA, and inhibiting iPLA(2)beta prevents the muscarinic agonist-induced accelerated Kv2.1 inactivation. Furthermore, glucose and carbachol do not significantly affect Kv2.1 inactivation in beta-cells from iPLA(2)beta(-/-) mice. Stably transfected INS-1 cells that overexpress iPLA(2)beta hydrolyze phospholipids more rapidly than control INS-1 cells and also exhibit an increase in the inactivation rate of the delayed rectifier currents. These results suggest that Kv2.1 currents could be dynamically modulated in the pancreatic islet beta-cell by phospholipase-catalyzed hydrolysis of membrane phospholipids to yield non-esterified fatty acids, such as AA, that facilitate Ca(2+) entry and insulin secretion.
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Affiliation(s)
- David A. Jacobson
- Department of Medicine, University of Chicago, Chicago, Illinois 60637
| | | | - Shunzhong Bao
- Medicine Department Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - John Turk
- Medicine Department Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
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Nolan CJ, Madiraju MSR, Delghingaro-Augusto V, Peyot ML, Prentki M. Fatty acid signaling in the beta-cell and insulin secretion. Diabetes 2006; 55 Suppl 2:S16-23. [PMID: 17130640 DOI: 10.2337/db06-s003] [Citation(s) in RCA: 303] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Fatty acids (FAs) and other lipid molecules are important for many cellular functions, including vesicle exocytosis. For the pancreatic beta-cell, while the presence of some FAs is essential for glucose-stimulated insulin secretion, FAs have enormous capacity to amplify glucose-stimulated insulin secretion, which is particularly operative in situations of beta-cell compensation for insulin resistance. In this review, we propose that FAs do this via three interdependent processes, which we have assigned to a "trident model" of beta-cell lipid signaling. The first two arms of the model implicate intracellular metabolism of FAs, whereas the third is related to membrane free fatty acid receptor (FFAR) activation. The first arm involves the AMP-activated protein kinase/malonyl-CoA/long-chain acyl-CoA (LC-CoA) signaling network in which glucose, together with other anaplerotic fuels, increases cytosolic malonyl-CoA, which inhibits FA partitioning into oxidation, thus increasing the availability of LC-CoA for signaling purposes. The second involves glucose-responsive triglyceride (TG)/free fatty acid (FFA) cycling. In this pathway, glucose promotes LC-CoA esterification to complex lipids such as TG and diacylglycerol, concomitant with glucose stimulation of lipolysis of the esterification products, with renewal of the intracellular FFA pool for reactivation to LC-CoA. The third arm involves FFA stimulation of the G-protein-coupled receptor GPR40/FFAR1, which results in enhancement of glucose-stimulated accumulation of cytosolic Ca2+ and consequently insulin secretion. It is possible that FFA released by the lipolysis arm of TG/FFA cycling is partly "secreted" and, via an autocrine/paracrine mechanism, is additive to exogenous FFAs in activating the FFAR1 pathway. Glucose-stimulated release of arachidonic acid from phospholipids by calcium-independent phospholipase A2 and/or from TG/FFA cycling may also be involved. Improved knowledge of lipid signaling in the beta-cell will allow a better understanding of the mechanisms of beta-cell compensation and failure in diabetes.
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Bao S, Song H, Wohltmann M, Ramanadham S, Jin W, Bohrer A, Turk J. Insulin secretory responses and phospholipid composition of pancreatic islets from mice that do not express Group VIA phospholipase A2 and effects of metabolic stress on glucose homeostasis. J Biol Chem 2006; 281:20958-20973. [PMID: 16732058 PMCID: PMC2044498 DOI: 10.1074/jbc.m600075200] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Studies involving pharmacologic or molecular biologic manipulation of Group VIA phospholipase A(2) (iPLA(2)beta) activity in pancreatic islets and insulinoma cells suggest that iPLA(2)beta participates in insulin secretion. It has also been suggested that iPLA(2)beta is a housekeeping enzyme that regulates cell 2-lysophosphatidylcholine (LPC) levels and arachidonate incorporation into phosphatidylcholine (PC). We have generated iPLA(2)beta-null mice by homologous recombination and have reported that they exhibit reduced male fertility and defective motility of spermatozoa. Here we report that pancreatic islets from iPLA(2)beta-null mice have impaired insulin secretory responses to D-glucose and forskolin. Electrospray ionization mass spectrometric analyses indicate that the abundance of arachidonate-containing PC species of islets, brain, and other tissues from iPLA(2)beta-null mice is virtually identical to that of wild-type mice, and no iPLA(2)beta mRNA was observed in any tissue from iPLA(2)beta-null mice at any age. Despite the insulin secretory abnormalities of isolated islets, fasting and fed blood glucose concentrations of iPLA(2)beta-null and wild-type mice are essentially identical under normal circumstances, but iPLA(2)beta-null mice develop more severe hyperglycemia than wild-type mice after administration of multiple low doses of the beta-cell toxin streptozotocin, suggesting an impaired islet secretory reserve. A high fat diet also induces more severe glucose intolerance in iPLA(2)beta-null mice than in wild-type mice, but PLA(2)beta-null mice have greater responsiveness to exogenous insulin than do wild-type mice fed a high fat diet. These and previous findings thus indicate that iPLA(2)beta-null mice exhibit phenotypic abnormalities in pancreatic islets in addition to testes and macrophages.
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Affiliation(s)
- Shunzhong Bao
- Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Haowei Song
- Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Mary Wohltmann
- Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Sasanka Ramanadham
- Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Wu Jin
- Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Alan Bohrer
- Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - John Turk
- Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110.
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Jenkins CM, Yan W, Mancuso DJ, Gross RW. Highly selective hydrolysis of fatty acyl-CoAs by calcium-independent phospholipase A2beta. Enzyme autoacylation and acyl-CoA-mediated reversal of calmodulin inhibition of phospholipase A2 activity. J Biol Chem 2006; 281:15615-24. [PMID: 16595686 DOI: 10.1074/jbc.m511623200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calcium-independent phospholipase A2beta (iPLA2beta) participates in numerous diverse cellular processes, such as arachidonic acid release, insulin secretion, calcium signaling, and apoptosis. Herein, we demonstrate the highly selective iPLA2beta-catalyzed hydrolysis of saturated long-chain fatty acyl-CoAs (palmitoyl-CoA approximately myristoyl-CoA >> stearoyl-CoA >> oleoyl-CoA approximately = arachidonoyl-CoA) present either as monomers in solution or guests in host membrane bilayers. Site-directed mutagenesis of the iPLA2beta catalytic serine (S465A) completely abolished acyl-CoA thioesterase activity, demonstrating that Ser-465 catalyzes both phospholipid and acyl-CoA hydrolysis. Remarkably, incubation of iPLA2beta with oleoyl-CoA, but not other long-chain acyl-CoAs, resulted in robust stoichiometric covalent acylation of the enzyme. Moreover, S465A mutagenesis or pretreatment of wild-type iPLA2beta with (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one unexpectedly increased acylation of the enzyme, indicating the presence of a second reactive nucleophilic residue that participates in the formation of the fatty acyl-iPLA2beta adduct. Radiolabeling of intact Sf9 cells expressing iPLA2beta with [3H]oleic acid demonstrated oleoylation of the membrane-associated enzyme. Partial trypsinolysis of oleoylated iPLA2beta and matrix-assisted laser desorption ionization mass spectrometry analysis localized the acylation site to a hydrophobic 25-kDa fragment (residues approximately 400-600) spanning the active site to the calmodulin binding domain. Intriguingly, calmodulin-Ca2+ blocked acylation of iPLA2beta by oleoyl-CoA. Remarkably, the addition of low micromolar concentrations (5 microM) of oleoyl-CoA resulted in reversal of calmodulin-mediated inhibition of iPLA2 beta phospholipase A2 activity. These results collectively identify the molecular species-specific acyl-CoA thioesterase activity of iPLA2beta, demonstrate the presence of a second active site that mediates iPLA2beta autoacylation, and identify long-chain acyl-CoAs as potential candidates mediating calcium influx factor activity.
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Affiliation(s)
- Christopher M Jenkins
- Division of Bioorganic Chemistry and Molecular Pharmacology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Bao S, Bohrer A, Ramanadham S, Jin W, Zhang S, Turk J. Effects of stable suppression of Group VIA phospholipase A2 expression on phospholipid content and composition, insulin secretion, and proliferation of INS-1 insulinoma cells. J Biol Chem 2006; 281:187-98. [PMID: 16286468 PMCID: PMC2156593 DOI: 10.1074/jbc.m509105200] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Studies involving pharmacologic inhibition or transient reduction of Group VIA phospholipase A2 (iPLA2beta) expression have suggested that it is a housekeeping enzyme that regulates cell 2-lysophosphatidylcholine (LPC) levels, rates of arachidonate incorporation into phospholipids, and degradation of excess phosphatidylcholine (PC). In insulin-secreting islet beta-cells and some other cells, in contrast, iPLA2beta signaling functions have been proposed. Using retroviral vectors, we prepared clonal INS-1 beta-cell lines in which iPLA2beta expression is stably suppressed by small interfering RNA. Two such iPLA2beta knockdown (iPLA2beta-KD) cell lines express less than 20% of the iPLA2beta of control INS-1 cell lines. The iPLA2beta-KD INS-1 cells exhibit impaired insulin secretory responses and reduced proliferation rates. Electrospray ionization mass spectrometric analyses of PC and LPC species that accumulate in INS-1 cells cultured with arachidonic acid suggest that 18:0/20:4-glycerophosphocholine (GPC) synthesis involves sn-2 remodeling to yield 16:0/20:4-GPC and then sn-1 remodeling via a 1-lyso/20:4-GPC intermediate. Electrospray ionization mass spectrometric analyses also indicate that the PC and LPC content and composition of iPLA2beta-KD and control INS-1 cells are nearly identical, as are the rates of arachidonate incorporation into PC and the composition and remodeling of other phospholipid classes. These findings indicate that iPLA2beta plays signaling or effector roles in beta-cell secretion and proliferation but that stable suppression of its expression does not affect beta-cell GPC lipid content or composition even under conditions in which LPC is being actively consumed by conversion to PC. This calls into question the generality of proposed housekeeping functions for iPLA2beta in PC homeostasis and remodeling.
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Affiliation(s)
- Shunzhong Bao
- Medicine Department Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Alan Bohrer
- Medicine Department Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Sasanka Ramanadham
- Medicine Department Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Wu Jin
- Medicine Department Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Sheng Zhang
- Medicine Department Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - John Turk
- Medicine Department Mass Spectrometry Facility and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
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Mancuso DJ, Jenkins CM, Sims HF, Cohen JM, Yang J, Gross RW. Complex transcriptional and translational regulation of iPLAgamma resulting in multiple gene products containing dual competing sites for mitochondrial or peroxisomal localization. ACTA ACUST UNITED AC 2005; 271:4709-24. [PMID: 15606758 DOI: 10.1111/j.1432-1033.2004.04435.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Membrane-associated calcium-independent phospholipase A2gamma (iPLA2gamma) contains four potential in-frame methionine start sites (Mancuso, D.J. Jenkins, C.M. & Gross, R.W. (2000) J. Biol. Chem.275, 9937-9945), but the mechanisms regulating the types, amount and subcellular localization of iPLA2gamma in cells are incompletely understood. We now: (a) demonstrate the dramatic transcriptional repression of mRNA synthesis encoding iPLA2gamma by a nucleotide sequence nested in the coding sequence itself; (b) localize the site of transcriptional repression to the most 5' sequence encoding the iPLA2gamma holoprotein; (c) identify the presence of nuclear protein constituents which bind to the repressor region by gel shift analysis; (d) demonstrate the translational regulation of distinct iPLA2gamma isoforms; (e) identify multiple novel exons, promoters, and alternative splice variants of human iPLA2gamma; (f) document the presence of dual-competing subcellular localization signals in discrete isoforms of iPLA2gamma; and (g) demonstrate the functional integrity of an N-terminal mitochondrial localization signal by fluorescence imaging and the presence of iPLA2gamma in the mitochondrial compartment of rat myocardium. The intricacy of the regulatory mechanisms of iPLA2gamma biosynthesis in rat myocardium is underscored by the identification of seven distinct protein products that utilize multiple mechanisms (transcription, translation and proteolysis) to produce discrete iPLA2gamma polypeptides containing either single or dual subcellular localization signals. This unanticipated complex interplay between peroxisomes and mitochondria mediated by competition for uptake of the nascent iPLA2gamma polypeptide identifies a new level of phospholipase-mediated metabolic regulation. Because uncoupling protein function is regulated by free fatty acids in mitochondria, these results suggest that iPLA2gamma processing contributes to integrating respiration and thermogenesis in mitochondria.
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Affiliation(s)
- David J Mancuso
- Division of Bioorganic Chemistry and Molecular Pharmacology, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA
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Turk J, Ramanadham S. The expression and function of a group VIA calcium-independent phospholipase A2 (iPLA2beta) in beta-cells. Can J Physiol Pharmacol 2005; 82:824-32. [PMID: 15573142 DOI: 10.1139/y04-064] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Many cells express a Group VIA phospholipase A2, designated iPLA2beta, that does not require calcium for activation, is stimulated by ATP, and is sensitive to inhibition by a bromoenol lactone suicide substrate (BEL). Studies in various cell systems have led to the suggestion that iPLA2beta has a role in phospholipid remodeling, signal transduction, cell proliferation, and apoptosis. We have found that pancreatic islets, beta-cells, and glucose-responsive insulinoma cells express an iPLA2beta that participates in glucose-stimulated insulin secretion but is not involved in membrane phospholipid remodeling. Additionally, recent studies reveal that iPLA2beta is involved in pathways that contribute to beta-cell proliferation and apoptosis, and that various phospholipid-derived mediators are involved in these processes. Detailed characterization of the enzyme suggests that the beta-cells express multiple isoforms of iPLA2beta, and we hypothesize that these participate in different cellular functions.
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Affiliation(s)
- John Turk
- Mass Spectometry Resource, Division of Endocrinology, Metabolism and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA
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Wang Z, Ramanadham S, Ma ZA, Bao S, Mancuso DJ, Gross RW, Turk J. Group VIA phospholipase A2 forms a signaling complex with the calcium/calmodulin-dependent protein kinase IIbeta expressed in pancreatic islet beta-cells. J Biol Chem 2005; 280:6840-9. [PMID: 15576376 PMCID: PMC3716912 DOI: 10.1074/jbc.m405287200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin-secreting pancreatic islet beta-cells express a Group VIA Ca(2+)-independent phospholipase A(2) (iPLA(2)beta) that contains a calmodulin binding site and protein interaction domains. We identified Ca(2+)/calmodulin-dependent protein kinase IIbeta (CaMKIIbeta) as a potential iPLA(2)beta-interacting protein by yeast two-hybrid screening of a cDNA library using iPLA(2)beta cDNA as bait. Cloning CaMKIIbeta cDNA from a rat islet library revealed that one dominant CaMKIIbeta isoform mRNA is expressed by adult islets and is not observed in brain or neonatal islets and that there is high conservation of the isoform expressed by rat and human beta-cells. Binary two-hybrid assays using DNA encoding this isoform as bait and iPLA(2)beta DNA as prey confirmed interaction of the enzymes, as did assays with CaMKIIbeta as prey and iPLA(2)beta bait. His-tagged CaMKIIbeta immobilized on metal affinity matrices bound iPLA(2)beta, and this did not require exogenous calmodulin and was not prevented by a calmodulin antagonist or the Ca(2+) chelator EGTA. Activities of both enzymes increased upon their association, and iPLA(2)beta reaction products reduced CaMKIIbeta activity. Both the iPLA(2)beta inhibitor bromoenol lactone and the CaMKIIbeta inhibitor KN93 reduced arachidonate release from INS-1 insulinoma cells, and both inhibit insulin secretion. CaMKIIbeta and iPLA(2)beta can be coimmunoprecipitated from INS-1 cells, and forskolin, which amplifies glucose-induced insulin secretion, increases the abundance of the immunoprecipitatable complex. These findings suggest that iPLA(2)beta and CaMKIIbeta form a signaling complex in beta-cells, consistent with reports that both enzymes participate in insulin secretion and that their expression is coinduced upon differentiation of pancreatic progenitor to endocrine progenitor cells.
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Affiliation(s)
- Zhepeng Wang
- Mass Spectrometry Resource, Washington University School of Medicine, St. Louis, Missouri 63110
- Divisions of Endocrinology, Diabetes, and Metabolism, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Sasanka Ramanadham
- Mass Spectrometry Resource, Washington University School of Medicine, St. Louis, Missouri 63110
- Divisions of Endocrinology, Diabetes, and Metabolism, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Zhongmin Alex Ma
- Division of Experimental Diabetes and Aging, Mount Sinai School of Medicine, New York, New York 10029
| | - Shunzhong Bao
- Mass Spectrometry Resource, Washington University School of Medicine, St. Louis, Missouri 63110
- Divisions of Endocrinology, Diabetes, and Metabolism, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
| | - David J. Mancuso
- Bioorganic Chemistry and Molecular Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Chemistry, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Richard W. Gross
- Bioorganic Chemistry and Molecular Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Chemistry, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - John Turk
- Mass Spectrometry Resource, Washington University School of Medicine, St. Louis, Missouri 63110
- Divisions of Endocrinology, Diabetes, and Metabolism, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
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Song K, Zhang X, Zhao C, Ang NT, Ma ZA. Inhibition of Ca2+-independent phospholipase A2 results in insufficient insulin secretion and impaired glucose tolerance. Mol Endocrinol 2004; 19:504-15. [PMID: 15471944 PMCID: PMC2917620 DOI: 10.1210/me.2004-0169] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Islet Ca2+-independent phospholipase A2 (iPLA2) is postulated to mediate insulin secretion by releasing arachidonic acid in response to insulin secretagogues. However, the significance of iPLA2 signaling in insulin secretion in vivo remains unexplored. Here we investigated the physiological role of iPLA2 in beta-cell lines, isolated islets, and mice. We showed that small interfering RNA-specific silencing of iPLA2 expression in INS-1 cells significantly reduced insulin-secretory responses of INS-1 cells to glucose. Immunohistochemical analysis revealed that mouse islet cells expressed significantly higher levels of iPLA2 than pancreatic exocrine acinar cells. Bromoenol lactone (BEL), a selective inhibitor of iPLA2, inhibited glucose-stimulated insulin secretion from isolated mouse islets; this inhibition was overcome by exogenous arachidonic acid. We also showed that iv BEL administration to mice resulted in sustained hyperglycemia and reduced insulin levels during glucose tolerance tests. Clamp experiments demonstrated that the impaired glucose tolerance was due to insufficient insulin secretion rather than decreased insulin sensitivity. Short-term administration of BEL to mice had no effect on fasting glucose levels and caused no apparent pathological changes of islets in pancreas sections. These results unambiguously demonstrate that iPLA2 signaling plays an important role in glucose-stimulated insulin secretion under physiological conditions.
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Affiliation(s)
- Keying Song
- Division of Experimental Diabetes and Aging, Department of Geriatrics and Adult Development, Mount Sinai School of Medicine, New York, New York 10029, USA
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Ramanadham S, Hsu FF, Zhang S, Jin C, Bohrer A, Song H, Bao S, Ma Z, Turk J. Apoptosis of insulin-secreting cells induced by endoplasmic reticulum stress is amplified by overexpression of group VIA calcium-independent phospholipase A2 (iPLA2 beta) and suppressed by inhibition of iPLA2 beta. Biochemistry 2004; 43:918-30. [PMID: 14744135 PMCID: PMC3732319 DOI: 10.1021/bi035536m] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The death of insulin-secreting beta-cells that causes type I diabetes mellitus (DM) occurs in part by apoptosis, and apoptosis also contributes to progressive beta-cell dysfunction in type II DM. Recent reports indicate that ER stress-induced apoptosis contributes to beta-cell loss in diabetes. Agents that deplete ER calcium levels induce beta-cell apoptosis by a process that is independent of increases in [Ca(2+)](i). Here we report that the SERCA inhibitor thapsigargin induces apoptosis in INS-1 insulinoma cells and that this is inhibited by a bromoenol lactone (BEL) inhibitor of group VIA calcium-independent phospholipase A(2) (iPLA(2)beta). Overexpression of iPLA(2)beta amplifies thapsigargin-induced apoptosis of INS-1 cells, and this is also suppressed by BEL. The magnitude of thapsigargin-induced INS-1 cell apoptosis correlates with the level of iPLA(2)beta expression in various cell lines, and apoptosis is associated with stimulation of iPLA(2)beta activity, perinuclear accumulation of iPLA(2)beta protein and activity, and caspase-3-catalyzed cleavage of full-length 84 kDa iPLA(2)beta to a 62 kDa product that associates with nuclei. Thapsigargin also induces ceramide accumulation in INS-1 cells, and this response is amplified in cells that overexpress iPLA(2)beta. These findings indicate that iPLA(2)beta participates in ER stress-induced apoptosis, a pathway that promotes beta-cell death in diabetes.
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Affiliation(s)
- Sasanka Ramanadham
- Mass Spectrometry Resource, Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Washington University School of Medicine, Box 8127, 660 South Euclid Avenue, St. Louis, Missouri 63110, USA.
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Ramanadham S, Song H, Hsu FF, Zhang S, Crankshaw M, Grant GA, Newgard CB, Bao S, Ma Z, Turk J. Pancreatic islets and insulinoma cells express a novel isoform of group VIA phospholipase A2 (iPLA2 beta) that participates in glucose-stimulated insulin secretion and is not produced by alternate splicing of the iPLA2 beta transcript. Biochemistry 2004; 42:13929-40. [PMID: 14636061 PMCID: PMC3716001 DOI: 10.1021/bi034843p] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Many cells express a group VIA 84 kDa phospholipase A(2) (iPLA(2)beta) that is sensitive to inhibition by a bromoenol lactone (BEL) suicide substrate. Inhibition of iPLA(2)beta in pancreatic islets and insulinoma cells suppresses, and overexpression of iPLA(2)beta in INS-1 insulinoma cells amplifies, glucose-stimulated insulin secretion, suggesting that iPLA(2)beta participates in secretion. Western blotting analyses reveal that glucose-responsive 832/13 INS-1 cells express essentially no 84 kDa iPLA(2)beta-immunoreactive protein but predominantly express a previously unrecognized immunoreactive iPLA(2)beta protein in the 70 kDa region that is not generated by a mechanism of alternate splicing of the iPLA(2)beta transcript. To determine if the 70 kDa-immunoreactive protein is a short isoform of iPLA(2)beta, protein from the 70 kDa region was digested with trypsin and analyzed by mass spectrometry. Such analyses reveal several peptides with masses and amino acid sequences that exactly match iPLA(2)beta tryptic peptides. Peptide sequences identified in the 70 kDa tryptic digest include iPLA(2)beta residues 7-53, suggesting that the N-terminus is preserved. We also report here that the 832/13 INS-1 cells express iPLA(2)beta catalytic activity and that BEL inhibits secretagogue-stimulated insulin secretion from these cells but not the incorporation of arachidonic acid into membrane PC pools of these cells. These observations suggest that the catalytic iPLA(2)beta activity expressed in 832/13 INS-1 cells is attributable to a short isoform of iPLA(2)beta and that this isoform participates in insulin secretory but not in membrane phospholipid remodeling pathways. Further, the finding that pancreatic islets also express predominantly a 70 kDa iPLA(2)beta-immunoreactive protein suggests that a signal transduction role of iPLA(2)beta in the native beta-cell might be attributable to a 70 kDa isoform of iPLA(2)beta.
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Affiliation(s)
- Sasanka Ramanadham
- Mass Spectrometry Resource, Division of Endocrinology, Diabetes, and Metabolism, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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Tay HK, Melendez AJ. Fcgamma RI-triggered generation of arachidonic acid and eicosanoids requires iPLA2 but not cPLA2 in human monocytic cells. J Biol Chem 2004; 279:22505-13. [PMID: 15007079 DOI: 10.1074/jbc.m308788200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Aggregation of receptors for immunoglobulin G (FcgammaRs) on myeloid cells activates a series of events that are key in the inflammatory response and that can ultimately lead to targeted cell killing by antibody-directed cellular cytotoxicity. Generation of lipid-derived proinflammatory mediators is an important component of the integrated cellular response mediated by receptors for the constant region of immunoglobulins (Fc). We have demonstrated previously that, in interferon-gamma-primed U937 cells, the high affinity receptor for IgG, FcgammaRI, is coupled to a novel intracellular signaling pathway that involves the sequential activation of phospholipase D, sphingosine kinase, calcium transients, and protein kinase C isoforms, leading to the activation of the NADPH-oxidative burst. Here, we investigate the nature of the phospholipase that regulates arachidonic acid and eicosanoid production. Our data show that FcgammaRI couples to iPLA(2)beta for the release of arachidonic acid and the generation of leukotriene B(4) and prostaglandin E(2). Activation of iPLA(2)beta was protein kinase C-dependent; on the other hand, platelet-activating factor triggered cPLA(2)alpha by means of the mitogen-activated protein kinase pathway. These studies demonstrate that intracellular PLA(2)s can be selectively regulated by different stimuli and suggest a critical role for iPLA(2)beta in the intracellular signaling cascades initiated by FcgammaRI and its functional role in the generation of key inflammatory mediators.
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Affiliation(s)
- Hwee Kee Tay
- Department of Physiology, Faculty of Medicine, National University of Singapore, Singapore 117597
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Ramanadham S, Song H, Bao S, Hsu FF, Zhang S, Ma Z, Jin C, Turk J. Islet complex lipids: involvement in the actions of group VIA calcium-independent phospholipase A(2) in beta-cells. Diabetes 2004; 53 Suppl 1:S179-85. [PMID: 14749285 PMCID: PMC3713612 DOI: 10.2337/diabetes.53.2007.s179] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The beta-isoform of group VIA calcium-independent phospholipase A(2) (iPLA(2)beta) does not require calcium for activation, is stimulated by ATP, and is sensitive to inhibition by a bromoenol lactone suicide substrate. Several potential functions have been proposed for iPLA(2)beta. Our studies indicate that iPLA(2)beta is expressed in beta-cells and participates in glucose-stimulated insulin secretion but is not involved in membrane phospholipid remodeling. If iPLA(2)beta plays a signaling role in glucose-stimulated insulin secretion, then conditions that impair iPLA(2)beta functions might contribute to the diminished capacity of beta-cells to secrete insulin in response to glucose, which is a prominent characteristic of type 2 diabetes. Our recent studies suggest that iPLA(2)beta might also participate in beta-cell proliferation and apoptosis and that various phospholipid-derived mediators are involved in these processes. Detailed characterization of the iPLA(2)beta protein level reveals that beta-cells express multiple isoforms of the enzyme, and our studies involve the hypothesis that different isoforms have different functions.
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Affiliation(s)
- Sasanka Ramanadham
- Department of Medicine, Washington University School of Medicine, St Louis, Missouri 63110,
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Abstract
Mammalian cells have developed specific pathways for the incorporation, remodeling, and release of arachidonic acid. Acyltransferase and transacylase pathways function to regulate the levels of esterified arachidonic acid in specific phospholipid pools. There are several distinct, differentially regulated phospholipases A2in cells that mediate agonist-induced release of arachidonic acid. These pathways are important in controlling cellular levels of free arachidonic acid. Both arachidonic acid and its oxygenated metabolites are potent bioactive mediators that regulate a myriad of physiological and pathophysiological processes.Key words: phospholipase A2, arachidonic acid, eicosanoid, phospholipid.
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Affiliation(s)
- Christina C Leslie
- Department of Pediatrics, National Jewish Medical and Research Center, Denver, CO 80206, USA.
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48
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Jones PM, Burns CJ, Belin VD, Roderigo-Milne HM, Persaud SJ. The role of cytosolic phospholipase A(2) in insulin secretion. Diabetes 2004; 53 Suppl 1:S172-8. [PMID: 14749284 DOI: 10.2337/diabetes.53.2007.s172] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Cytosolic phospholipase A(2) (cPLA(2)) comprises a widely expressed family of enzymes, some members of which have the properties required of signal transduction elements in electrically excitable cells. Thus, alpha- and beta-isoforms of cPLA(2) are activated by the increases in intracellular Ca(2+) concentration ([Ca(2+)](i)) achieved in depolarized cells. Activation is associated with a redistribution of the enzyme within the cell; activation of cPLA(2) generates arachidonic acid (AA), a biologically active unsaturated fatty acid that can be further metabolized to generate a plethora of biologically active molecules. Studies using relatively nonselective pharmacological inhibitors have implicated cPLA(2) in insulin secretory responses to stimuli that elevate beta-cell [Ca(2+)](i); therefore, we have investigated the role of cPLA(2) in beta-cell function by generating beta-cell lines that under- or overexpress the alpha-isoform of cPLA(2). The functional phenotype of the modified cells was assessed by observation of cellular ultrastructure, by measuring insulin gene expression and insulin protein content, and by measuring the effects of insulin secretagogues on cPLA(2) distribution, on changes in [Ca(2+)](i), and on the rate and pattern of insulin secretion. Our results suggest that cPLA(2) is not required for the initiation of insulin secretion from beta-cells, but that it plays an important role in the maintenance of beta-cell insulin stores. Our data also demonstrate that excessive production of, or exposure to, AA is deleterious to normal beta-cell secretory function through metabolic dysfunction.
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Affiliation(s)
- Peter M Jones
- Centre for Reproduction, Endocrinology and Diabetes, GKT School of Biomedical Sciences, King's College London, London, UK.
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Juhl K, Høy M, Olsen HL, Bokvist K, Efanov AM, Hoffmann EK, Gromada J. cPLA2alpha-evoked formation of arachidonic acid and lysophospholipids is required for exocytosis in mouse pancreatic beta-cells. Am J Physiol Endocrinol Metab 2003; 285:E73-81. [PMID: 12644445 DOI: 10.1152/ajpendo.00086.2003] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Using capacitance measurements, we investigated the effects of intracellularly applied recombinant human cytosolic phospholipase A2 (cPLA2alpha) and its lipolytic products arachidonic acid and lysophosphatidylcholine on Ca2+-dependent exocytosis in single mouse pancreatic beta-cells. cPLA2alpha dose dependently (EC50 = 86 nM) stimulated depolarization-evoked exocytosis by 450% without affecting the whole cell Ca2+ current or cytoplasmic Ca2+ levels. The stimulatory effect involved priming of secretory granules as reflected by an increase in the size of the readily releasable pool of granules from 70-80 to 280-300. cPLA2alpha-stimulated exocytosis was antagonized by the specific cPLA2 inhibitor AACOCF3. Ca2+-evoked exocytosis was reduced by 40% in cells treated with AACOCF3 or an antisense oligonucleotide against cPLA2alpha. The action of cPLA2alpha was mimicked by a combination of arachidonic acid and lysophosphatidylcholine (470% stimulation) in which each compound alone doubled the exocytotic response. Priming of insulin-containing secretory granules has been reported to involve Cl- uptake through ClC-3 Cl- channels. Accordingly, the stimulatory action of cPLA2alpha was inhibited by the Cl- channel inhibitor DIDS and in cells pretreated with ClC-3 Cl- channel antisense oligonucleotides. We propose that cPLA2alpha has an important role in controlling the rate of exocytosis in beta-cells. This effect of cPLA2alpha reflects an enhanced transgranular Cl- flux, leading to an increase in the number of granules available for release, and requires the combined actions of arachidonic acid and lysophosphatidylcholine.
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Affiliation(s)
- Kirstine Juhl
- Laboratory of Islet Cell Physiology, Novo Nordisk, Bagsvaerd, Denmark
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Koster JC, Remedi MS, Qiu H, Nichols CG, Hruz PW. HIV protease inhibitors acutely impair glucose-stimulated insulin release. Diabetes 2003; 52:1695-1700. [PMID: 12829635 PMCID: PMC1403824 DOI: 10.2337/diabetes.52.7.1695] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
HIV protease inhibitors (PIs) acutely and reversibly inhibit the insulin-responsive glucose transporter Glut 4, leading to peripheral insulin resistance and impaired glucose tolerance. Minimal modeling analysis of glucose tolerance tests on PI-treated patients has revealed an impaired insulin secretory response, suggesting additional pancreatic beta-cell dysfunction. To determine whether beta-cell function is acutely affected by PIs, we assayed glucose-stimulated insulin secretion in rodent islets and the insulinoma cell line MIN6. Insulin release from MIN6 cells and rodent islets was significantly inhibited by the PI indinavir with IC(50) values of 1.1 and 2.1 micro mol/l, respectively. The uptake of 2-deoxyglucose in MIN6 cells was similarly inhibited (IC(50) of 2.0 micro mol/l), whereas glucokinase activity was unaffected at drug levels as high as 1 mmol/l. Glucose utilization was also impaired at comparable drug levels. Insulin secretogogues acting downstream of glucose transport mostly reversed the indinavir-mediated inhibition of insulin release in MIN6 cells. Intravenous infusion of indinavir during hyperglycemic clamps on rats significantly suppressed the first-phase insulin response. These data suggest that therapeutic levels of PIs are sufficient to impair glucose sensing by beta-cells. Thus, together with peripheral insulin resistance, beta-cell dysfunction likely contributes to altered glucose homeostasis associated with highly active antiretroviral therapy.
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Affiliation(s)
- Joseph C Koster
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
| | - Maria S Remedi
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
| | - Haijun Qiu
- Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri
| | - Colin G Nichols
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
| | - Paul W Hruz
- Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri
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