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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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The phospholipase A 2 superfamily as a central hub of bioactive lipids and beyond. Pharmacol Ther 2023; 244:108382. [PMID: 36918102 DOI: 10.1016/j.pharmthera.2023.108382] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Revised: 03/06/2023] [Accepted: 03/07/2023] [Indexed: 03/13/2023]
Abstract
In essence, "phospholipase A2" (PLA2) means a group of enzymes that release fatty acids and lysophospholipids by hydrolyzing the sn-2 position of glycerophospholipids. To date, more than 50 enzymes possessing PLA2 or related lipid-metabolizing activities have been identified in mammals, and these are subdivided into several families in terms of their structures, catalytic mechanisms, tissue/cellular localizations, and evolutionary relationships. From a general viewpoint, the PLA2 superfamily has mainly been implicated in signal transduction, driving the production of a wide variety of bioactive lipid mediators. However, a growing body of evidence indicates that PLA2s also contribute to phospholipid remodeling or recycling for membrane homeostasis, fatty acid β-oxidation for energy production, and barrier lipid formation on the body surface. Accordingly, PLA2 enzymes are considered one of the key regulators of a broad range of lipid metabolism, and perturbation of specific PLA2-driven lipid pathways often disrupts tissue and cellular homeostasis and may be associated with a variety of diseases. This review covers current understanding of the physiological functions of the PLA2 superfamily, focusing particularly on the two major intracellular PLA2 families (Ca2+-dependent cytosolic PLA2s and Ca2+-independent patatin-like PLA2s) as well as other PLA2 families, based on studies using gene-manipulated mice and human diseases in combination with comprehensive lipidomics.
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3
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Wong HY, Langlotz M, Gan-Schreier H, Xu W, Staffer S, Tuma-Kellner S, Liebisch G, Merle U, Chamulitrat W. Constitutive oxidants from hepatocytes of male iPLA2β-null mice increases the externalization of phosphatidylethanolamine on plasma membrane. Free Radic Res 2021; 55:625-633. [PMID: 34696671 DOI: 10.1080/10715762.2021.1987426] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
We have found that group VIA calcium-independent phospholipase A2 (iPLA2β) has specificity for hydrolysis of phosphatidylethanolamine (PE) in mouse livers. Phospholipids (PLs) are transported to plasma membrane and some PLs including PE are externalized to maintain membrane PL asymmetry. Here we demonstrated that hepatocytes of iPLA2β-null (KO) mice showed an increase in PE containing palmitate and oleate. We aimed to examine whether externalization of PE on the outer leaflets could be affected by iPLA2β deficiency and its modulation by reactive oxygen species (ROS) or apoptosis. As duramycin has high affinity to PE, we used duramycin conjugated with biotin (DLB) and streptavidin 488 as a probe for detection of externalized PE. Compared to WT, naïve KO hepatocytes showed an increase in both PE externalization and ROS generation. These events were observed in male but not in female KO mice. Hydrogen peroxide or menadione treatment enhanced PE externalization to the same extent for both male/female WT and KO hepatocytes. By indirect immunofluorescence, DLB-streptavidin staining was observed as small punctuated spots on the cell surface of menadione-treated KO hepatocytes. Unlike the reported PS externalization, CD95/FasL treatment did not lead to any increase in PE externalization, and iPLA2β deficiency-dependent PE externalization was also not correlated with apoptosis. Thus, constitutive (but not induced) ROS generation in iPLA2β-deficient hepatocytes leads to PE externalization observed only in male mice. Such PE externalization may imply detrimental effects regarding further oxidation of PE fatty acids and the binding with pathogens on the outer leaflets of hepatocyte plasma membrane.
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Affiliation(s)
| | - Monika Langlotz
- Center for Molecular Biology, University of Heidelberg, Heidelberg, Germany
| | | | - Weihong Xu
- Heidelberg University Hospital, Heidelberg, Germany
| | | | | | - Gerhard Liebisch
- Institute of Clinical Chemistry and Laboratory Medicine, University Regensburg, Regensburg, Germany
| | - Uta Merle
- Heidelberg University Hospital, Heidelberg, Germany
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4
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Cole LK, Agarwal P, Doucette CA, Fonseca M, Xiang B, Sparagna GC, Seshadri N, Vandel M, Dolinsky VW, Hatch GM. Tafazzin Deficiency Reduces Basal Insulin Secretion and Mitochondrial Function in Pancreatic Islets From Male Mice. Endocrinology 2021; 162:bqab102. [PMID: 34019639 PMCID: PMC8197286 DOI: 10.1210/endocr/bqab102] [Citation(s) in RCA: 7] [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] [Received: 03/10/2021] [Indexed: 12/13/2022]
Abstract
Tafazzin (TAZ) is a cardiolipin (CL) biosynthetic enzyme important for maintaining mitochondrial function. TAZ affects both the species and content of CL in the inner mitochondrial membrane, which are essential for normal cellular respiration. In pancreatic β cells, mitochondrial function is closely associated with insulin secretion. However, the role of TAZ and CL in the secretion of insulin from pancreatic islets remains unknown. Male 4-month-old doxycycline-inducible TAZ knock-down (KD) mice and wild-type littermate controls were used. Immunohistochemistry was used to assess β-cell morphology in whole pancreas sections, whereas ex vivo insulin secretion, CL content, RNA-sequencing analysis, and mitochondrial oxygen consumption were measured from isolated islet preparations. Ex vivo insulin secretion under nonstimulatory low-glucose concentrations was reduced ~52% from islets isolated from TAZ KD mice. Mitochondrial oxygen consumption under low-glucose conditions was also reduced ~58% in islets from TAZ KD animals. TAZ deficiency in pancreatic islets was associated with significant alteration in CL molecular species and elevated polyunsaturated fatty acid CL content. In addition, RNA-sequencing of isolated islets showed that TAZ KD increased expression of extracellular matrix genes, which are linked to pancreatic fibrosis, activated stellate cells, and impaired β-cell function. These data indicate a novel role for TAZ in regulating pancreatic islet function, particularly under low-glucose conditions.
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Affiliation(s)
- Laura K Cole
- Department of Pharmacology, Winnipeg, R3E3P4, Canada
- Department of Therapeutics, Winnipeg, R3E3P4, Canada
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children’s Hospital Research Institute of Manitoba, Faculty of Health Sciences, University of Manitoba, Winnipeg, R3E3P4, Canada
| | - Prasoon Agarwal
- KTH Royal Institute of Technology, School of Electrical Engineering and Computer Science, 10044 Stockholm, Sweden
- Science for Life Laboratory, 16939 Solna, Sweden
| | - Christine A Doucette
- Physiology and Pathophysiology, Winnipeg, R3E3P4, Canada
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children’s Hospital Research Institute of Manitoba, Faculty of Health Sciences, University of Manitoba, Winnipeg, R3E3P4, Canada
| | - Mario Fonseca
- Department of Pharmacology, Winnipeg, R3E3P4, Canada
- Department of Therapeutics, Winnipeg, R3E3P4, Canada
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children’s Hospital Research Institute of Manitoba, Faculty of Health Sciences, University of Manitoba, Winnipeg, R3E3P4, Canada
| | - Bo Xiang
- Department of Pharmacology, Winnipeg, R3E3P4, Canada
- Department of Therapeutics, Winnipeg, R3E3P4, Canada
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children’s Hospital Research Institute of Manitoba, Faculty of Health Sciences, University of Manitoba, Winnipeg, R3E3P4, Canada
| | - Genevieve C Sparagna
- Department of Medicine, Division of Cardiology, University of Colorado Anschutz Medical Center, Aurora, CO 80045, USA
| | - Nivedita Seshadri
- Physiology and Pathophysiology, Winnipeg, R3E3P4, Canada
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children’s Hospital Research Institute of Manitoba, Faculty of Health Sciences, University of Manitoba, Winnipeg, R3E3P4, Canada
| | - Marilyne Vandel
- Department of Pharmacology, Winnipeg, R3E3P4, Canada
- Department of Therapeutics, Winnipeg, R3E3P4, Canada
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children’s Hospital Research Institute of Manitoba, Faculty of Health Sciences, University of Manitoba, Winnipeg, R3E3P4, Canada
| | - Vernon W Dolinsky
- Department of Pharmacology, Winnipeg, R3E3P4, Canada
- Department of Therapeutics, Winnipeg, R3E3P4, Canada
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children’s Hospital Research Institute of Manitoba, Faculty of Health Sciences, University of Manitoba, Winnipeg, R3E3P4, Canada
| | - Grant M Hatch
- Department of Pharmacology, Winnipeg, R3E3P4, Canada
- Department of Therapeutics, Winnipeg, R3E3P4, Canada
- Diabetes Research Envisioned and Accomplished in Manitoba (DREAM) Theme, Children’s Hospital Research Institute of Manitoba, Faculty of Health Sciences, University of Manitoba, Winnipeg, R3E3P4, Canada
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Chen D, Chu B, Yang X, Liu Z, Jin Y, Kon N, Rabadan R, Jiang X, Stockwell BR, Gu W. iPLA2β-mediated lipid detoxification controls p53-driven ferroptosis independent of GPX4. Nat Commun 2021; 12:3644. [PMID: 34131139 PMCID: PMC8206155 DOI: 10.1038/s41467-021-23902-6] [Citation(s) in RCA: 166] [Impact Index Per Article: 55.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 05/21/2021] [Indexed: 12/20/2022] Open
Abstract
Here, we identify iPLA2β as a critical regulator for p53-driven ferroptosis upon reactive oxygen species (ROS)-induced stress. The calcium-independent phospholipase iPLA2β is known to cleave acyl tails from the glycerol backbone of lipids and release oxidized fatty acids from phospholipids. We found that iPLA2β-mediated detoxification of peroxidized lipids is sufficient to suppress p53-driven ferroptosis upon ROS-induced stress, even in GPX4-null cells. Moreover, iPLA2β is overexpressed in human cancers; inhibition of endogenous iPLA2β sensitizes tumor cells to p53-driven ferroptosis and promotes p53-dependent tumor suppression in xenograft mouse models. These results demonstrate that iPLA2β acts as a major ferroptosis repressor in a GPX4-independent manner. Notably, unlike GPX4, loss of iPLA2β has no obvious effect on normal development or cell viability in normal tissues but iPLA2β plays an essential role in regulating ferroptosis upon ROS-induced stress. Thus, our study suggests that iPLA2β is a promising therapeutic target for activating ferroptosis-mediated tumor suppression without serious toxicity concerns.
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Affiliation(s)
- Delin Chen
- Institute for Cancer Genetics, and Department of Pathology and Cell Biology, and Herbert Irving Comprehensive Cancer Center,Vagelos College of Physicians & Surgeons, Columbia University, New York, NY, 10032, USA
| | - Bo Chu
- Institute for Cancer Genetics, and Department of Pathology and Cell Biology, and Herbert Irving Comprehensive Cancer Center,Vagelos College of Physicians & Surgeons, Columbia University, New York, NY, 10032, USA
| | - Xin Yang
- Institute for Cancer Genetics, and Department of Pathology and Cell Biology, and Herbert Irving Comprehensive Cancer Center,Vagelos College of Physicians & Surgeons, Columbia University, New York, NY, 10032, USA
| | - Zhaoqi Liu
- Program for Mathematical Genomics, Departments of Systems Biology and Biomedical Informatics, Columbia University, New York, NY, 10032, USA
| | - Ying Jin
- Institute for Cancer Genetics, and Department of Pathology and Cell Biology, and Herbert Irving Comprehensive Cancer Center,Vagelos College of Physicians & Surgeons, Columbia University, New York, NY, 10032, USA
| | - Ning Kon
- Institute for Cancer Genetics, and Department of Pathology and Cell Biology, and Herbert Irving Comprehensive Cancer Center,Vagelos College of Physicians & Surgeons, Columbia University, New York, NY, 10032, USA
| | - Raul Rabadan
- Program for Mathematical Genomics, Departments of Systems Biology and Biomedical Informatics, Columbia University, New York, NY, 10032, USA
| | - Xuejun Jiang
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY, 10065, USA
| | - Brent R Stockwell
- Department of Biological Sciences, Department of Chemistry, Columbia University, New York, NY, 10027, USA
| | - Wei Gu
- Institute for Cancer Genetics, and Department of Pathology and Cell Biology, and Herbert Irving Comprehensive Cancer Center,Vagelos College of Physicians & Surgeons, Columbia University, New York, NY, 10032, USA.
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6
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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: 6] [Impact Index Per Article: 1.5] [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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7
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Rescue of Hepatic Phospholipid Remodeling Defectin iPLA2β-Null Mice Attenuates Obese but Not Non-Obese Fatty Liver. Biomolecules 2020; 10:biom10091332. [PMID: 32957701 PMCID: PMC7565968 DOI: 10.3390/biom10091332] [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: 08/24/2020] [Revised: 09/15/2020] [Accepted: 09/15/2020] [Indexed: 12/19/2022] Open
Abstract
Polymorphisms of group VIA calcium-independent phospholipase A2 (iPLA2β or PLA2G6) are positively associated with adiposity, blood lipids, and Type-2 diabetes. The ubiquitously expressed iPLA2β catalyzes the hydrolysis of phospholipids (PLs) to generate a fatty acid and a lysoPL. We studied the role of iPLA2β on PL metabolism in non-alcoholic fatty liver disease (NAFLD). By using global deletion iPLA2β-null mice, we investigated three NAFLD mouse models; genetic Ob/Ob and long-term high-fat-diet (HFD) feeding (representing obese NAFLD) as well as feeding with methionine- and choline-deficient (MCD) diet (representing non-obese NAFLD). A decrease of hepatic PLs containing monounsaturated- and polyunsaturated fatty acids and a decrease of the ratio between PLs and cholesterol esters were observed in all three NAFLD models. iPLA2β deficiency rescued these decreases in obese, but not in non-obese, NAFLD models. iPLA2β deficiency elicited protection against fatty liver and obesity in the order of Ob/Ob › HFD » MCD. Liver inflammation was not protected in HFD NAFLD, and that liver fibrosis was even exaggerated in non-obese MCD model. Thus, the rescue of hepatic PL remodeling defect observed in iPLA2β-null mice was critical for the protection against NAFLD and obesity. However, iPLA2β deletion in specific cell types such as macrophages may render liver inflammation and fibrosis, independent of steatosis protection.
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8
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Zhu X, Gan-Schreier H, Otto AC, Cheng Y, Staffer S, Tuma-Kellner S, Ganzha A, Liebisch G, Chamulitrat W. iPla2β deficiency in mice fed with MCD diet does not correct the defect of phospholipid remodeling but attenuates hepatocellular injury via an inhibition of lipid uptake genes. Biochim Biophys Acta Mol Cell Biol Lipids 2019; 1864:677-687. [PMID: 30735854 DOI: 10.1016/j.bbalip.2019.02.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 02/01/2019] [Accepted: 02/03/2019] [Indexed: 12/19/2022]
Abstract
Group VIA calcium-independent phospholipase A2 (iPla2β) is among modifier genes of non-alcoholic fatty liver disease which leads to non-alcoholic steatohepatitis (NASH). Consistently, iPla2β deletion protects hepatic steatosis and obesity in genetic ob/ob and obese mice chronically fed with high-fat diet by replenishing the loss of hepatic phospholipids (PL). As mouse feeding with methionine- and choline-deficient (MCD) diet is a model of lean NASH, we tested whether iPla2β-null mice could still be protected since PL syntheses are disturbed. MCD-diet feeding of female wild-type for 5 weeks induced hepatic steatosis with a severe reduction of body and visceral fat weights concomitant with a decrease of hepatic phosphatidylcholine. These parameters were not altered in MCD-fed iPla2β-null mice. However, iPla2β deficiency attenuated MCD-induced elevation of serum transaminase activities and hepatic expression of fatty-acid translocase Cd36, fatty-acid binding protein-4, peroxisome-proliferator activated receptorγ, and HDL-uptake scavenger receptor B type 1. The reduction of lipid uptake genes was consistent with a decrease of hepatic esterified and unesterified fatty acids and cholesterol esters. On the contrary, iPla2β deficiency under MCD did not have any effects on inflammasomes and pro-inflammatory markers but exacerbated hepatic expression of myofibroblast α-smooth muscle actin and vimentin. Thus, without any rescue of PL loss, iPla2β inactivation attenuated hepatocellular injury in MCD-induced NASH with a novel mechanism of lipid uptake inhibition. Taken together, we have shown that iPla2β mediates hepatic steatosis and lipotoxicity in hepatocytes in both obese and lean NASH, but elicits exacerbated liver fibrosis in lean NASH likely by affecting other cell types.
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Affiliation(s)
- Xingya Zhu
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Hongying Gan-Schreier
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Ann-Christin Otto
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Yuting Cheng
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Simone Staffer
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Sabine Tuma-Kellner
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Alexandra Ganzha
- Institute of Clinical Chemistry and Laboratory Medicine, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany
| | - Gerhard Liebisch
- Institute of Clinical Chemistry and Laboratory Medicine, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany
| | - Walee Chamulitrat
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany.
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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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Yin R, Kyle J, Burnum-Johnson K, Bloodsworth KJ, Sussel L, Ansong C, Laskin J. High Spatial Resolution Imaging of Mouse Pancreatic Islets Using Nanospray Desorption Electrospray Ionization Mass Spectrometry. Anal Chem 2018; 90:6548-6555. [PMID: 29718662 PMCID: PMC5990474 DOI: 10.1021/acs.analchem.8b00161] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Nanospray Desorption Electrospray Ionization mass spectrometry imaging (nano-DESI MSI) enables ambient imaging of biological samples with high sensitivity and minimal sample pretreatment. Recently, we developed an approach for constant-distance mode MSI using shear force microscopy to precisely control the distance between the sample and the nano-DESI probe. Herein, we demonstrate the power of this approach for robust imaging of pancreatic islets with high spatial resolution of ∼11 μm. Pancreatic islets are difficult to characterize using traditional mass spectrometry approaches due to their small size (∼100 μm) and molecular heterogeneity. Nano-DESI MSI was used to examine the spatial localization of several lipid classes including phosphatidylcholine (PC), phosphatidylethanolamine (PE), sphingomyelin (SM), phosphatidylinositol (PI), and phosphatidylserine (PS) along with fatty acids and their metabolites (e.g., prostaglandins) in the individual islets and surrounding tissue. Several lipids were found to be substantially enhanced in the islets indicating these lipids may be involved in insulin secretion. Remarkably different distributions were observed for several pairs of Lyso PC (LPC) and PC species differing only by one double bond, such as LPC 18:1 vs LPC 18:0, PC 32:1 vs PC 32:0, and PC 34:2 vs PC 34:1. These findings indicate that minor variations in the fatty acid chain length and saturation have a pronounced effect on the localization of PC and LPC species in pancreatic islets. Interestingly, oxidized PC species observed experimentally were found to be specifically localized to pancreatic islets. These PCs are potential biomarkers for reactive oxygen species in the islets, which could be harmful to pancreatic beta cells. The experimental approach presented in this study will provide valuable information on the heterogeneity of individual pancreatic islets, which is difficult to assess using bulk characterization techniques.
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Affiliation(s)
- Ruichuan Yin
- Department of Chemistry, Purdue University, West Lafayette, Indiana, 47907, United States
| | - Jennifer Kyle
- Pacific Northwest National Laboratory, Richland, Washington, 99352, United States
| | | | - Kent J. Bloodsworth
- Pacific Northwest National Laboratory, Richland, Washington, 99352, United States
| | - Lori Sussel
- Barbara Davis Center for Diabetes, University of Colorado, Aurora, Colorado, 80045, United States
| | - Charles Ansong
- Pacific Northwest National Laboratory, Richland, Washington, 99352, United States
| | - Julia Laskin
- Department of Chemistry, Purdue University, West Lafayette, Indiana, 47907, United States
- Pacific Northwest National Laboratory, Richland, Washington, 99352, United States
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11
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20-HETE promotes glucose-stimulated insulin secretion in an autocrine manner through FFAR1. Nat Commun 2018; 9:177. [PMID: 29330456 PMCID: PMC5766607 DOI: 10.1038/s41467-017-02539-4] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 12/07/2017] [Indexed: 01/02/2023] Open
Abstract
The long-chain fatty acid receptor FFAR1 is highly expressed in pancreatic β-cells. Synthetic FFAR1 agonists can be used as antidiabetic drugs to promote glucose-stimulated insulin secretion (GSIS). However, the physiological role of FFAR1 in β-cells remains poorly understood. Here we show that 20-HETE activates FFAR1 and promotes GSIS via FFAR1 with higher potency and efficacy than dietary fatty acids such as palmitic, linoleic, and α-linolenic acid. Murine and human β-cells produce 20-HETE, and the ω-hydroxylase-mediated formation and release of 20-HETE is strongly stimulated by glucose. Pharmacological inhibition of 20-HETE formation and blockade of FFAR1 in islets inhibits GSIS. In islets from type-2 diabetic humans and mice, glucose-stimulated 20-HETE formation and 20-HETE-dependent stimulation of GSIS are strongly reduced. We show that 20-HETE is an FFAR1 agonist, which functions as an autocrine positive feed-forward regulator of GSIS, and that a reduced glucose-induced 20-HETE formation contributes to inefficient GSIS in type-2 diabetes. FFAR1 receptor is highly expressed in beta cells and its activation has been suggested as therapy against type-2 diabetes. Here, Tunaru et al. show that 20-hydroxyeicosatetraenoic acid, produced within the islets upon glucose stimulation, acts in an autocrine manner to stimulate insulin secretion via FFAR1 activation.
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Jiao L, Gan-Schreier H, Zhu X, Wei W, Tuma-Kellner S, Liebisch G, Stremmel W, Chamulitrat W. Ageing sensitized by iPLA 2β deficiency induces liver fibrosis and intestinal atrophy involving suppression of homeostatic genes and alteration of intestinal lipids and bile acids. Biochim Biophys Acta Mol Cell Biol Lipids 2017; 1862:1520-1533. [PMID: 28888832 DOI: 10.1016/j.bbalip.2017.09.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 08/28/2017] [Accepted: 09/05/2017] [Indexed: 01/06/2023]
Abstract
Ageing is a major risk factor for various forms of liver and gastrointestinal (GI) disease and genetic background may contribute to the pathogenesis of these diseases. Group VIA phospholipase A2 or iPLA2β is a homeostatic PLA2 by playing a role in phospholipid metabolism and remodeling. Global iPLA2β-/- mice exhibit aged-dependent phenotypes with body weight loss and abnormalities in the bone and brain. We have previously reported the abnormalities in these mutant mice showing susceptibility for chemical-induced liver injury and colitis. We hypothesize that iPLA2β deficiency may sensitize with ageing for an induction of GI injury. Male wild-type and iPLA2β-/- mice at 4 and 20-22months of age were studied. Aged, but not young, iPLA2β-/-mice showed increased hepatic fibrosis and biliary ductular expansion as well as severe intestinal atrophy associated with increased apoptosis, pro-inflammation, disrupted tight junction, and reduced number of mucin-containing globlet cells. This damage was associated with decreased expression of intestinal endoplasmic stress XBP1 and its regulator HNF1α, FATP4, ACSL5, bile-acid transport genes as well as nuclear receptors LXRα and FXR. By LC/MS-MS profiling, iPLA2β deficiency in aged mice caused an increase of intestinal arachidonate-containing phospholipids concomitant with a decrease in ceramides. By the suppression of intestinal FXR/FGF-15 signaling, hepatic bile-acid synthesis gene expression was increased leading to an elevation of secondary and hydrophobic bile acids in liver, bile, and intestine. In conclusions, ageing sensitized by iPLA2β deficiency caused a decline of key intestinal homeostatic genes resulting in the development of GI disease in a gut-to-liver manner.
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Affiliation(s)
- Li Jiao
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany; Institute of Medical Biology, Chinese Academy of Medical Sciences and Peking Union Medical College, Kunming, Yunnan 650118, China
| | - Hongying Gan-Schreier
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany
| | - Xingya Zhu
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany
| | - Wang Wei
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany
| | - Sabine Tuma-Kellner
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany
| | - Gerhard Liebisch
- Institute of Clinical Chemistry and Laboratory Medicine, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany
| | - Wolfgang Stremmel
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany
| | - Walee Chamulitrat
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany.
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Deng X, Wang J, Jiao L, Utaipan T, Tuma-Kellner S, Schmitz G, Liebisch G, Stremmel W, Chamulitrat W. iPLA2β deficiency attenuates obesity and hepatic steatosis in ob/ob mice through hepatic fatty-acyl phospholipid remodeling. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1861:449-61. [PMID: 26873633 DOI: 10.1016/j.bbalip.2016.02.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Revised: 02/01/2016] [Accepted: 02/06/2016] [Indexed: 01/12/2023]
Abstract
PLA2G6 or GVIA calcium-independent PLA2 (iPLA2β) is identified as one of the NAFLD modifier genes in humans, and thought to be a target for NAFLD therapy. iPLA2β is known to play a house-keeping role in phospholipid metabolism and remodeling. However, its role in NAFLD pathogenesis has not been supported by results obtained from high-fat feeding of iPLA2β-null (PKO) mice. Unlike livers of human NAFLD and genetically obese rodents, fatty liver induced by high-fat diet is not associated with depletion of hepatic phospholipids. We therefore tested whether iPLA2β could regulate obesity and hepatic steatosis in leptin-deficient mice by cross-breeding PKO with ob/ob mice to generate ob/ob-PKO mice. Here we observed an improvement in ob/ob-PKO mice with significant reduction in serum enzymes, lipids, glucose, insulin as well as improved glucose tolerance, and reduction in islet hyperplasia. The improvement in hepatic steatosis measured by liver triglycerides, fatty acids and cholesterol esters was associated with decreased expression of PPARγ and de novo lipogenesis genes, and the reversal of β-oxidation gene expression. Notably, ob/ob livers contained depleted levels of lysophospholipids and phospholipids, and iPLA2β deficiency in ob/ob-PKO livers lowers the former, but replenished the latter particularly phosphatidylethanolamine (PE) and phosphatidylcholine (PC) that contained arachidonic (AA) and docosahexaenoic (DHA) acids. Compared with WT livers, PKO livers also contained increased PE and PC containing AA and DHA. Thus, iPLA2β deficiency protected against obesity and ob/ob fatty liver which was associated with hepatic fatty-acyl phospholipid remodeling. Our results support the deleterious role of iPLA2β in severe obesity associated NAFLD.
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Affiliation(s)
- Xiuling Deng
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany; Department of Endocrinology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 430022 Wuhan, China
| | - Jiliang Wang
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Li Jiao
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Tanyarath Utaipan
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Sabine Tuma-Kellner
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Gerd Schmitz
- Institute of Clinical Chemistry and Laboratory Medicine, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany
| | - Gerhard Liebisch
- Institute of Clinical Chemistry and Laboratory Medicine, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany
| | - Wolfgang Stremmel
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Walee Chamulitrat
- Department of Internal Medicine IV, University of Heidelberg Hospital, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany.
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Inhoffen J, Tuma-Kellner S, Straub B, Stremmel W, Chamulitrat W. Deficiency of iPLA₂β Primes Immune Cells for Proinflammation: Potential Involvement in Age-Related Mesenteric Lymph Node Lymphoma. Cancers (Basel) 2015; 7:2427-42. [PMID: 26690222 PMCID: PMC4695901 DOI: 10.3390/cancers7040901] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2015] [Revised: 11/26/2015] [Accepted: 12/01/2015] [Indexed: 12/12/2022] Open
Abstract
Proinflammation can predispose the body to autoimmunity and cancer. We have reported that iPLA2β−/− mice are susceptible to autoimmune hepatitis and colitis. Here we determined whether cytokine release by immune cells could be affected by iPLA2β deficiency alone or combined with CD95/FasL-antibody treatment in vivo. We also determined whether cancer risk could be increased in aged mutant mice. Immune cells were isolated from 3-month old male WT and iPLA2β−/− mice, and some were injected with anti-CD95/FasL antibody for 6 h. Kupffer cells (KC) or splenocytes and liver lymphocytes were stimulated in vitro by lipopolysaccharide or concanavalinA, respectively. Whole-body iPLA2β deficiency caused increased apoptosis in liver, spleen, and mesenteric lymph node (MLN). KC from mutant mice showed suppressed release of TNFα and IL-6, while their splenocytes secreted increased levels of IFNγ and IL-17a. Upon CD95/FasL activation, the mutant KC in turn showed exaggerated cytokine release, this was accompanied by an increased release of IFNγ and IL-17a by liver lymphocytes. Aged iPLA2β−/− mice did not show follicular MLN lymphoma commonly seen in aged C57/BL6 mice. Thus, iPLA2β deficiency renders M1- and Th1/Th17-proinflammation potentially leading to a reduction in age-related MLN lymphoma during aging.
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Affiliation(s)
- Johannes Inhoffen
- Department of Internal Medicine IV, University Heidelberg Hospital, 69120 Heidelberg, Germany.
| | - Sabine Tuma-Kellner
- Department of Internal Medicine IV, University Heidelberg Hospital, 69120 Heidelberg, Germany.
| | - Beate Straub
- Pathology Institute of Medical Faculty Heidelberg, 69120 Heidelberg, Germany.
| | - Wolfgang Stremmel
- Department of Internal Medicine IV, University Heidelberg Hospital, 69120 Heidelberg, Germany.
| | - Walee Chamulitrat
- Department of Internal Medicine IV, University Heidelberg Hospital, 69120 Heidelberg, Germany.
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Deficiency of Group VIA Phospholipase A2 (iPLA2β) Renders Susceptibility for Chemical-Induced Colitis. Dig Dis Sci 2015; 60:3590-602. [PMID: 26182903 DOI: 10.1007/s10620-015-3807-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Accepted: 07/09/2015] [Indexed: 12/19/2022]
Abstract
BACKGROUND Inflammatory bowel disease results from a combination of dysfunction of intestinal epithelial barrier and dysregulation of mucosal immune system. iPLA2β has multiple homeostatic functions and shown to play a role in membrane remodeling, cell proliferation, monocyte chemotaxis, and apoptosis. The latter may render chronic inflammation and susceptibility for acute injury. AIMS We aim to evaluate whether an inactivation of iPLA2β would enhance the pathogenesis of experimental colitis induced by dextran sodium sulfate. METHODS iPLA2β-null male mice were administered dextran sodium sulfate in drinking water for 7 days followed by normal water for 3 days. At day 10, mice were killed, and harvested colon and ileum were subjected for evaluation by histology, immunohistochemistry, and quantitative RT-PCR. RESULTS Dextran sodium sulfate administration caused a significant increase in histological scores and cleaved caspase 3 (+) apoptosis concomitant with a decrease in colon length and crypt cell Ki67 (+) proliferation in iPLA2β-null mice in a greater extent than in control littermates. This sensitization by iPLA2β deficiency was associated with an increase in accumulation of F4/80 (+) macrophages, and expression of proinflammatory cytokines and chemokines, while the number of mucin-containing goblet cells and mucus layer thickness was decreased. Some of these abnormalities were also observed in the ileum. CONCLUSIONS An inactivation of iPLA2β exacerbated pathogenesis of experimental colitis by promoting intestinal epithelial cell apoptosis, inhibiting crypt cell regeneration, and causing damage to mucus barrier allowing an activation of innate immune response. Thus, iPLA2β may represent a susceptible gene for the development of inflammatory bowel disease.
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Rauckhorst AJ, Pfeiffer DR, Broekemeier KM. The iPLA2γ is identified as the membrane potential sensitive phospholipase in liver mitochondria. FEBS Lett 2015. [DOI: 10.1016/j.febslet.2015.07.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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17
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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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18
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Jiao L, Gan-Schreier H, Tuma-Kellner S, Stremmel W, Chamulitrat W. Sensitization to autoimmune hepatitis in group VIA calcium-independent phospholipase A2-null mice led to duodenal villous atrophy with apoptosis, goblet cell hyperplasia and leaked bile acids. Biochim Biophys Acta Mol Basis Dis 2015; 1852:1646-57. [PMID: 25957555 DOI: 10.1016/j.bbadis.2015.04.025] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 04/27/2015] [Accepted: 04/28/2015] [Indexed: 12/12/2022]
Abstract
Chronic bowel disease can co-exist with severe autoimmune hepatitis (AIH) in an absence of primary sclerosing cholangitis. Genetic background may contribute to this overlap syndrome. We previously have shown that the deficiency of iPLA2β causes an accumulation of hepatocyte apoptosis, and renders susceptibility for acute liver injury. We here tested whether AIH induction in iPLA2β-null mice could result in intestinal injury, and whether bile acid metabolism was altered. Control wild-type (WT) and female iPLA2β-null (iPLA2β(-/-)) mice were intravenously injected with 10mg/kg concanavalinA (ConA) or saline for 24h. ConA treatment of iPLA2β(-/-) mice caused massive liver injury with increased liver enzymes, fibrosis, and necrosis. While not affecting WT mice, ConA treatment of iPLA2β(-/-) mice caused severe duodenal villous atrophy concomitant with increased apoptosis, cell proliferation, globlet cell hyperplasia, and endotoxin leakage into portal vein indicating a disruption of intestinal barrier. With the greater extent than in WT mice, ConA treatment of iPLA2β(-/-) mice increased jejunal expression of innate response cytokines CD14, TNF-α, IL-6, and SOCS3 as well as chemokines CCL2 and the CCL3 receptor CCR5. iPLA2β deficiency in response to ConA-induced AIH caused a significant decrease in hepatic and biliary bile acids, and this was associated with suppression of hepatic Cyp7A1, Ntcp and ABCB11/Bsep and upregulation of intestinal FXR/FGF15 mRNA expression. The suppression of hepatic Ntcp expression together with the loss of intestinal barrier could account for the observed bile acid leakage into peripheral blood. Thus, enteropathy may result from acute AIH in a susceptible host such as iPLA2β deficiency.
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Affiliation(s)
- Li Jiao
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany; Department of Toxicology, School of Public Health, Jilin University, Changchun, China
| | - Hongying Gan-Schreier
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany
| | - Sabine Tuma-Kellner
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany
| | - Wolfgang Stremmel
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany
| | - Walee Chamulitrat
- Department of Internal Medicine IV, University of Heidelberg Hospital, Heidelberg, Germany.
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Yan J, Hu C, Jiang F, Zhang R, Wang J, Tang S, Peng D, Chen M, Bao Y, Jia W. Genetic variants of PLA2G6 are associated with Type 2 diabetes mellitus and triglyceride levels in a Chinese population. Diabet Med 2015; 32:280-6. [PMID: 25207958 DOI: 10.1111/dme.12587] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 07/15/2014] [Accepted: 09/01/2014] [Indexed: 01/24/2023]
Abstract
AIM To test the association of PLA2G6 variants with Type 2 diabetes and clinical characteristics in large Chinese population-based samples. METHODS A total of 6822 people were recruited. In the first stage, 15 single nucleotide polymorphisms within the PLA2G6 region were selected and genotyped in 3700 Chinese Han people. In the second stage, the single nucleotide polymorphisms that showed a significant association were genotyped in an additional 3122 samples for replication. Genotype-phenotype association studies and meta-analyses were performed after combining data from the two stages. RESULTS In the first stage, we detected rs132984 and rs2284060 as significantly associated with Type 2 diabetes with odds ratios of 1.247 (95% CI 1.074-1.449, P = 0.004, empirical P = 0.047) and 1.173 (95% CI 1.059-1.299, P = 0.002, empirical P = 0.029), respectively. In the second stage, a similar effect of rs132984 on Type 2 diabetes was observed (odds ratio 1.280, 95% CI 1.094-1.497, P = 0.002). The meta-analysis showed a significant effect of the two single nucleotide polymorphisms on Type 2 diabetes (odds ratio 1.254, 95% CI 1.104-1.451, P = 4.85 × 10⁻⁵ for rs132984; odds ratio 1.120, 95% CI 1.046-1.195, P = 0.003 for rs2284060). Moreover, genotype-phenotype association analysis showed that rs132984 was associated with triglyceride levels (P = 0.022, empirical P = 0.044) and area under the curve for glucose (P = 0.015, empirical P = 0.030). CONCLUSIONS Our data imply that common single nucleotide polymorphisms within the PLA2G6 region are associated with Type 2 diabetes and triglyceride levels in the Chinese population.
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Affiliation(s)
- J Yan
- Department of Endocrinology and Metabolism, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Key Clinical Centre for Metabolic Diseases, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China
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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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Mouse Models of Neuroaxonal Dystrophy Caused by PLA2G6 Gene Mutations. Mov Disord 2015. [DOI: 10.1016/b978-0-12-405195-9.00061-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Zhang L, Zhong S, Li Y, Ji G, Sundaram M, Yao Z. Global Inactivation of the Pla2g6 Gene in Mice Does Not Cause Dyslipidemia under Chow or High-fat Diet Conditions. J Cancer Prev 2014; 18:235-48. [PMID: 25337551 PMCID: PMC4189460 DOI: 10.15430/jcp.2013.18.3.235] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Revised: 09/10/2013] [Accepted: 09/10/2013] [Indexed: 01/30/2023] Open
Abstract
Background: Genome-wide association studies suggest that plasma triacylglyceride (TAG) in humans was associated with variation in the PLA2G6 locus, a gene that encodes calcium-independent phospholipase A2 (iPLA2β). The objective of the present study is to understand the impact of genetic inactivation of iPLA2β on hepatic TAG metabolism in C57BL/6 mice. Methods: Male iPLA2β+/− mice were backcrossed with female iPLA2β−/− mice for up to 10 generations prior to experiments. Lipid and lipoprotein metabolism from plasma, hepatocytes, thigh subcutaneous adipose and thigh skeletal muscle tissues of the mice were determined under various experimental conditions. Results: The iPLA2β−/− mice, either male or female as compared with iPLA2β+/+ littermates, showed no change in fasted or postprandial plasma TAG or total cholesterol at young (12–15 weeks) or old (40–44 weeks) ages under chow diet or high-fat diet (HFD) conditions. However, fractionation of plasma lipoproteins showed that under HFD conditions, there was a significant increase (by 40%) in apoB-100 association with VLDL1 fractions in iPLA2β−/− mice as compared with iPLA2β+/+ littermates. There was no significant difference in triglyceride or cholesterol contents in the liver, muscle, or adipose tissue between iPLA2β−/− and iPLA2β+/+ littermates. Metabolic labeling experiments with cultured primary hepatocytes isolated from iPLA2β−/− mice also showed 2-fold increase in the secretion of [35S]methionine-labeled apoB-100 in VLDL1 fractions as compared with that from iPLA2β+/+ hepatocytes. Likewise, secretion of [3H]palmitate-labeled TAG from the iPLA2β−/− hepatocytes was increased by 2-fold. Conclusions: Although iPLA2β may play a role in TAG-rich VLDL1 production from cultured hepatocytes, there is no evidence that inactivation of iPLA2β would lead to dyslipidemia in mice in vivo.
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Affiliation(s)
- Li Zhang
- Institute of Digestive Disease, Longhua Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, China
| | - Shumei Zhong
- Department of Biochemistry, Microbiology and Immunology, Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, Canada
| | - Ying Li
- College of Life Science, Chongqing Normal University, Chongqing, China
| | - Guang Ji
- Institute of Digestive Disease, Longhua Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, China
| | - Meenakshi Sundaram
- Department of Biochemistry, Microbiology and Immunology, Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, Canada
| | - Zemin Yao
- Department of Biochemistry, Microbiology and Immunology, Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, Canada
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Shridas P, Zahoor L, Forrest KJ, Layne JD, Webb NR. Group X secretory phospholipase A2 regulates insulin secretion through a cyclooxygenase-2-dependent mechanism. J Biol Chem 2014; 289:27410-7. [PMID: 25122761 DOI: 10.1074/jbc.m114.591735] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Group X secretory phospholipase A2 (GX sPLA2) potently hydrolyzes membrane phospholipids to release arachidonic acid (AA). While AA is an activator of glucose-stimulated insulin secretion (GSIS), its metabolite prostaglandin E2 (PGE2) is a known inhibitor. In this study, we determined that GX sPLA2 is expressed in insulin-producing cells of mouse pancreatic islets and investigated its role in beta cell function. GSIS was measured in vivo in wild-type (WT) and GX sPLA2-deficient (GX KO) mice and ex vivo using pancreatic islets isolated from WT and GX KO mice. GSIS was also assessed in vitro using mouse MIN6 pancreatic beta cells with or without GX sPLA2 overexpression or exogenous addition. GSIS was significantly higher in islets isolated from GX KO mice compared with islets from WT mice. Conversely, GSIS was lower in MIN6 cells overexpressing GX sPLA2 (MIN6-GX) compared with control (MIN6-C) cells. PGE2 production was significantly higher in MIN6-GX cells compared with MIN6-C cells and this was associated with significantly reduced cellular cAMP. The effect of GX sPLA2 on GSIS was abolished when cells were treated with NS398 (a COX-2 inhibitor) or L-798,106 (a PGE2-EP3 receptor antagonist). Consistent with enhanced beta cell function, GX KO mice showed significantly increased plasma insulin levels following glucose challenge and were protected from age-related reductions in GSIS and glucose tolerance compared with WT mice. We conclude that GX sPLA2 plays a previously unrecognized role in negatively regulating pancreatic insulin secretion by augmenting COX-2-dependent PGE2 production.
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Affiliation(s)
- Preetha Shridas
- From Saha Cardiovascular Research Center and Departments of Internal Medicine and
| | - Lubna Zahoor
- From Saha Cardiovascular Research Center and Departments of Internal Medicine and
| | - Kathy J Forrest
- From Saha Cardiovascular Research Center and Departments of Internal Medicine and
| | - Joseph D Layne
- From Saha Cardiovascular Research Center and Pharmacology and Nutritional Sciences, Division of Nutritional Sciences, University of Kentucky Medical Center, Lexington Kentucky 40536
| | - Nancy R Webb
- From Saha Cardiovascular Research Center and Pharmacology and Nutritional Sciences, Division of Nutritional Sciences, University of Kentucky Medical Center, Lexington Kentucky 40536
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24
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Stremmel W, Staffer S, Wannhoff A, Pathil A, Chamulitrat W. Plasma membrane phospholipase A2 controls hepatocellular fatty acid uptake and is responsive to pharmacological modulation: implications for nonalcoholic steatohepatitis. FASEB J 2014; 28:3159-70. [PMID: 24719358 DOI: 10.1096/fj.14-249763] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Excess hepatic fat accumulation leads to nonalcoholic steatohepatitis (NASH), a serious threat to health for which no effective treatment is available. However, the mechanism responsible for fatty acid uptake by hepatocytes remains unclear. Using the human hepatocyte-derived tumor cell line HepG2, we found that fatty acid influx is mediated by a heterotetrameric plasma membrane protein complex consisting of plasma membrane fatty acid-binding protein, caveolin-1, CD36, and calcium-independent membrane phospholipase A2 (iPLA2β). Blocking iPLA2β with the bile acid-phospholipid conjugate ursodeoxycholate-lysophosphatidylethanolamide (UDCA-LPE) caused the dissociation of the complex, thereby inhibiting fatty acid influx (IC50 47 μM), and suppressed the synthesis of all subunits through a reduction in lysophosphatidylcholine from 8.0 to 3.5 μmol/mg of protein and corresponding depletion of phosphorylated c-Jun N-terminal kinase. These findings were substantiated by an observed 56.5% decrease in fatty acid influx in isolated hepatocytes derived from iPLA2β-knockout mice. Moreover, steatosis and inflammation were abrogated by UDCA-LPE treatment in a cellular model of NASH. Thus, iPLA2β acts as an upstream checkpoint for mechanisms that regulate fatty acid uptake, and its inhibition by UDCA-LPE qualifies this nontoxic compound as a therapeutic candidate for the treatment of NASH.-Stremmel, W., Staffer, S., Wannhoff, A., Pathil, A., Chamulitrat, W. Plasma membrane phospholipase A2 controls hepatocellular fatty acid uptake and is responsive to pharmacological modulation: implications for nonalcoholic steatohepatitis.
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Affiliation(s)
- Wolfgang Stremmel
- Department of Gastroenterology, University Hospital Heidelberg, Heidelberg, Germany
| | - Simone Staffer
- Department of Gastroenterology, University Hospital Heidelberg, Heidelberg, Germany
| | - Andreas Wannhoff
- Department of Gastroenterology, University Hospital Heidelberg, Heidelberg, Germany
| | - Anita Pathil
- Department of Gastroenterology, University Hospital Heidelberg, Heidelberg, Germany
| | - Walee Chamulitrat
- Department of Gastroenterology, University Hospital Heidelberg, Heidelberg, Germany
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25
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Song H, Wohltmann M, Tan M, Ladenson JH, Turk J. Group VIA phospholipase A2 mitigates palmitate-induced β-cell mitochondrial injury and apoptosis. J Biol Chem 2014; 289:14194-210. [PMID: 24648512 DOI: 10.1074/jbc.m114.561910] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Palmitate (C16:0) induces apoptosis of insulin-secreting β-cells by processes that involve generation of reactive oxygen species, and chronically elevated blood long chain free fatty acid levels are thought to contribute to β-cell lipotoxicity and the development of diabetes mellitus. Group VIA phospholipase A2 (iPLA2β) affects β-cell sensitivity to apoptosis, and here we examined iPLA2β effects on events that occur in β-cells incubated with C16:0. Such events in INS-1 insulinoma cells were found to include activation of caspase-3, expression of stress response genes (C/EBP homologous protein and activating transcription factor 4), accumulation of ceramide, loss of mitochondrial membrane potential, and apoptosis. All of these responses were blunted in INS-1 cells that overexpress iPLA2β, which has been proposed to facilitate repair of oxidized mitochondrial phospholipids, e.g. cardiolipin (CL), by excising oxidized polyunsaturated fatty acid residues, e.g. linoleate (C18:2), to yield lysophospholipids, e.g. monolysocardiolipin (MLCL), that can be reacylated to regenerate the native phospholipid structures. Here the MLCL content of mouse pancreatic islets was found to rise with increasing iPLA2β expression, and recombinant iPLA2β hydrolyzed CL to MLCL and released oxygenated C18:2 residues from oxidized CL in preference to native C18:2. C16:0 induced accumulation of oxidized CL species and of the oxidized phospholipid (C18:0/hydroxyeicosatetraenoic acid)-glycerophosphoethanolamine, and these effects were blunted in INS-1 cells that overexpress iPLA2β, consistent with iPLA2β-mediated removal of oxidized phospholipids. C16:0 also induced iPLA2β association with INS-1 cell mitochondria, consistent with a role in mitochondrial repair. These findings indicate that iPLA2β confers significant protection of β-cells against C16:0-induced injury.
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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
| | - Jack H Ladenson
- 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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26
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Rauckhorst AJ, Broekemeier KM, Pfeiffer DR. Regulation of the Ca(2+)-independent phospholipase A2 in liver mitochondria by changes in the energetic state. J Lipid Res 2014; 55:826-36. [PMID: 24586040 DOI: 10.1194/jlr.m043307] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The effect of electron transport chain redox status on activity of the mitochondrial Ca(2+)-independent phospholipase A2 (iPLA2) has been examined. When oxidizing NAD-linked substrates, the enzyme is not active unless deenergization occurs. Uncoupler, rotenone, antimycin A, and cyanide are equally effective at upregulating the enzyme, while oligomycin is ineffective. Thenoyltrifluoroacetone causes deenergization and activates the enzyme, but only if succinate is the respiratory substrate. These findings show that the mitochondrial iPLA2 responds to the energetic state overall, rather than to the redox status of individual electron transport chain complexes. With NAD-linked substrates, and using rotenone to deenergize, iPLA2 activation can be reversed by adding succinate to reestablish a membrane potential. For this purpose, ascorbate plus N,N,N'N'-tetramethyl-phenylenediamine can be used instead of succinate and is equally effective. With succinate as substrate, the membrane potential can be reduced in a graded and stable fashion by adding increasing concentrations of malonate, which is a competitive inhibitor of succinate utilization. A partial and stable activation of the iPLA2 accompanies partial deenergization. These findings suggest that in addition to the several functions that have been proposed, the mitochondrial iPLA2 may help to coordinate local capillary blood flow with changing energy demands.
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Affiliation(s)
- Adam J Rauckhorst
- Departments of Molecular and Cellular Biochemistry Ohio State University, Columbus, OH 43210
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27
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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: 26] [Impact Index Per Article: 2.4] [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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28
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Klett EL, Chen S, Edin ML, Li LO, Ilkayeva O, Zeldin DC, Newgard CB, Coleman RA. Diminished acyl-CoA synthetase isoform 4 activity in INS 832/13 cells reduces cellular epoxyeicosatrienoic acid levels and results in impaired glucose-stimulated insulin secretion. J Biol Chem 2013; 288:21618-29. [PMID: 23766516 DOI: 10.1074/jbc.m113.481077] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucose-stimulated insulin secretion (GSIS) in pancreatic beta-cells is potentiated by fatty acids (FA). The initial step in the metabolism of intracellular FA is the conversion to acyl-CoA by long chain acyl-CoA synthetases (Acsls). Because the predominantly expressed Acsl isoforms in INS 832/13 cells are Acsl4 and -5, we characterized the role of these Acsls in beta-cell function by using siRNA to knock down Acsl4 or Acsl5. Compared with control cells, an 80% suppression of Acsl4 decreased GSIS and FA-potentiated GSIS by 32 and 54%, respectively. Knockdown of Acsl5 did not alter GSIS. Acsl4 knockdown did not alter FA oxidation or long chain acyl-CoA levels. With Acsl4 knockdown, incubation with 17 mm glucose increased media epoxyeicosatrienoic acids (EETs) and reduced cell membrane levels of EETs. Further, exogenous EETs reduced GSIS in INS 832/13 cells, and in Acsl4 knockdown cells, an EET receptor antagonist partially rescued GSIS. These results strongly suggest that Acsl4 activates EETs to form EET-CoAs that are incorporated into glycerophospholipids, thereby sequestering EETs. Exposing INS 832/13 cells to arachidonate or linoleate reduced Acsl4 mRNA and protein expression and reduced GSIS. These data indicate that Acsl4 modulates GSIS by regulating the levels of unesterified EETs and that arachidonate controls the expression of its activator Acsl4.
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Affiliation(s)
- Eric L Klett
- Department of Medicine, Division of Endocrinology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7172, USA.
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29
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Saab-Aoudé S, Bron AM, Creuzot-Garcher CP, Bretillon L, Acar N. A mouse model of in vivo chemical inhibition of retinal calcium-independent phospholipase A2 (iPLA2). Biochimie 2013; 95:903-11. [DOI: 10.1016/j.biochi.2012.12.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2012] [Accepted: 12/11/2012] [Indexed: 10/27/2022]
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30
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Lei X, Zhang S, Bohrer A, Barbour SE, Ramanadham S. Role of calcium-independent phospholipase A(2)β in human pancreatic islet β-cell apoptosis. Am J Physiol Endocrinol Metab 2012; 303:E1386-95. [PMID: 23074238 PMCID: PMC3774083 DOI: 10.1152/ajpendo.00234.2012] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [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
Death of β-cells due to apoptosis is an important contributor to β-cell dysfunction in both type 1 and type 2 diabetes mellitus. Previously, we described participation of the Group VIA Ca(2+)-independent phospholipase A(2) (iPLA(2)β) in apoptosis of insulinoma cells due to ER stress. To examine whether islet β-cells are similarly susceptible to ER stress and undergo iPLA(2)β-mediated apoptosis, we assessed the ER stress response in human pancreatic islets. Here, we report that the iPLA(2)β protein is expressed predominantly in the β-cells of human islets and that thapsigargin-induced ER stress promotes β-cell apoptosis, as reflected by increases in activated caspase-3 in the β-cells. Furthermore, we demonstrate that ER stress is associated with increases in islet iPLA(2)β message, protein, and activity, iPLA(2)β-dependent induction of neutral sphingomyelinase and ceramide accumulation, and subsequent loss of mitochondrial membrane potential. We also observe that basal activated caspase-3 increases with age, raising the possibility that β-cells in older human subjects have a greater susceptibility to undergo apoptotic cell death. These findings reveal for the first time expression of iPLA(2)β protein in human islet β-cells and that induction of iPLA(2)β during ER stress contributes to human islet β-cell apoptosis. We hypothesize that modulation of iPLA(2)β activity might reduce β-cell apoptosis and this would be beneficial in delaying or preventing β-cell dysfunction associated with diabetes.
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Affiliation(s)
- Xiaoyong Lei
- Dept. of Cell, Developmental, and Integrative Biology, Univ. of Alabama at Birmingham, Birmingham, AL 35294, USA
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31
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Tanaka K, Siddiqi NJ, Alhomida AS, Farooqui AA, Ong WY. Differential regulation of cPLA2 and iPLA2 expression in the brain. ACTA ACUST UNITED AC 2012. [DOI: 10.1007/s11515-012-9247-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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32
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Glynn P. Neuronal phospholipid deacylation is essential for axonal and synaptic integrity. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1831:633-41. [PMID: 22903185 DOI: 10.1016/j.bbalip.2012.07.023] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Revised: 07/20/2012] [Accepted: 07/31/2012] [Indexed: 12/24/2022]
Abstract
Recessively-inherited deficiency in the catalytic activity of calcium-independent phospholipase A2-beta (iPLA2β) and neuropathy target esterase (NTE) causes infantile neuroaxonal dystrophy and hereditary spastic paraplegia, respectively. Thus, these two related phospholipases have non-redundant functions that are essential for structural integrity of synapses and axons. Both enzymes are expressed in essentially all neurons and also have independent roles in glia. iPLA2β liberates sn-2 fatty acid and lysophospholipids from diacyl-phospholipids. Ca(2+)-calmodulin tonically-inhibits iPLA2β, but this can be alleviated by oleoyl-CoA. Together with fatty acyl-CoA-mediated conversion of lysophospholipid to diacyl-phospholipid this may regulate sn-2 fatty acyl composition of phospholipids. In the nervous system, iPLA2β is especially important for the turnover of polyunsaturated fatty acid-associated phospholipid at synapses. More information is required on the interplay between iPLA2β and iPLA2-gamma in deacylation of neuronal mitochondrial phospholipids. NTE reduces levels of phosphatidylcholine (PtdCho) by degrading it to glycerophosphocholine and two free fatty acids. The substrate for NTE may be nascent PtdCho complexed with a phospholipid-binding protein. Protein kinase A-mediated phosphorylation enhances PtdCho synthesis and may allow PtdCho accumulation by coordinate inhibition of NTE activity. NTE operates primarily at the endoplasmic reticulum in neuronal soma but is also present in axons. NTE-mediated PtdCho homeostasis facilitates membrane trafficking and this appears most critical for the integrity of axon terminals in the spinal cord and hippocampus. For maintenance of peripheral nerve axons, iPLA2β activity may be able to compensate for NTE-deficiency but not vice-versa. Whether agonists acting at neuronal receptors modulate the activity of either enzyme remains to be determined. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.
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Affiliation(s)
- Paul Glynn
- Department of Cell Physiology & Pharmacology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK.
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33
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Maintenance of synaptic stability requires calcium-independent phospholipase A₂ activity. Neural Plast 2012; 2012:569149. [PMID: 22685677 PMCID: PMC3364014 DOI: 10.1155/2012/569149] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2011] [Revised: 02/03/2012] [Accepted: 02/07/2012] [Indexed: 12/31/2022] Open
Abstract
Phospholipases A₂ (PLA₂s) represent one of the largest groups of lipid-modifying enzymes. Over the years, significant advances have been made in understanding their potential physiological and pathological functions. Depending on their calcium requirement for activation, PLA₂s are classified into calcium dependent and independent. This paper mainly focuses on brain calcium-independent PLA₂ (iPLA₂) and on the mechanisms by which they influence neuronal function and regulate synaptic plasticity. Particular attention will be given to the iPLA₂γ isoform and its role in the regulation of synaptic glutamate receptors. In particular, the paper discusses the possibility that brain iPLA₂γ deficiencies could destabilise normal synaptic operation and might contribute to the aetiology of some brain disorders. In this line, the paper presents new data indicating that iPLA₂γ deficiencies accentuate AMPA receptor destabilization and tau phosphorylation, which suggests that this iPLA₂ isoform should be considered as a potential target for the treatment of Tau-related disorders.
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34
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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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35
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Ma ZA. The role of peroxidation of mitochondrial membrane phospholipids in pancreatic β -cell failure. Curr Diabetes Rev 2012; 8:69-75. [PMID: 22414059 PMCID: PMC4884441 DOI: 10.2174/157339912798829232] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Revised: 08/15/2011] [Accepted: 09/13/2011] [Indexed: 12/28/2022]
Abstract
Type 2 diabetes (T2D) is characterized by peripheral insulin resistance and pancreatic islet β-cell failure. Accumulating evidence indicates that mitochondrial dysfunction is a central contributor to β-cell failure in the pathogenesis of T2D. This review focuses on mechanisms whereby reactive oxygen species (ROS) produced by β-cell in response to metabolic stress affect mitochondrial structure and function and lead to β-cell failure. Specifically, ROS oxidize mitochondrial membrane phospholipids such as cardiolipin, which impairs membrane integrity and leads to cytochrome c release and apoptosis. In addition, ROS activate UCP2 via peroxidation of the mitochondrial membrane phospholipids, which results in proton leak leading to reduced ATP synthesis and content in β-cells - critical parameters in the regulation of glucose-stimulated insulin secretion. Group VIA Phospholipase A2 (iPLA2β) appears to be a component of a mechanism for repairing mitochondrial phospholipids that contain oxidized fatty acid substituents, and genetic or acquired iPLA2β-deficiency increases β-cell mitochondrial susceptibility to injury from ROS and predisposes to development of T2D. Interventions that attenuate the adverse effects of ROS on β-cell mitochondrial phospholipids may prevent or retard the development of T2D.
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Affiliation(s)
- Zhongmin A Ma
- Division of Experimental Diabetes and Aging, Department of Geriatrics and Palliative Medicine, Mount Sinai School of Medicine, New York, NY 10029, USA.
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36
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Guo Y, Xu M, Deng B, Frontera JR, Kover KL, Aires D, Ding H, Carlson SE, Turk J, Wang W, Zhu H. Beta-Cell Injury in Ncb5or-null Mice is Exacerbated by Consumption of a High-Fat Diet. EUR J LIPID SCI TECH 2011; 114:233-243. [PMID: 22582025 DOI: 10.1002/ejlt.201100309] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
NADH-cytochrome b5 oxidoreductase (Ncb5or) in endoplasmic reticulum (ER) is involved in fatty acid metabolism, and Ncb5or(-/-) mice fed standard chow (SC) are insulin-sensitive but weigh less than wild type (WT) littermates. Ncb5or(-/-) mice develop hyperglycemia at about age 7 weeks due to β-cell dysfunction and loss associated with saturated fatty acid accumulation and manifestations of ER and oxidative stress. Here we report that when Ncb5or(-/-) mice born to heterozygous mothers fed a high fat (HF) diet continue to ingest HF, they weigh as much as SC-fed WT at age 5 weeks. By age 7 weeks, diabetes mellitus develops in all HF-fed vs. 68% of SC-fed Ncb5or(-/-) mice. Islet β-cell content in age 5-week Ncb5or(-/-) mice fed HF for 7 days is lower (53%) than for those fed SC (63%), and both are lower than for WT (75%, SC, vs. 69%, HF). Islet transcript levels for markers of mitochondrial biogenesis (PGC-1α) and ER stress (ATF6α) are higher in Ncb5or(-/-) than WT mice but not significantly affected by diet. Consuming a HF diet exacerbates Ncb5or(-/-) β-cell accumulation of intracellular saturated fatty acids and increases the frequency of ER distention from 11% (SC) to 47% (HF), thus accelerates β-cell injury in Ncb5or(-/-) mice.
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Affiliation(s)
- Ying Guo
- Department of Endocrinology, The Second Affiliated Hospital of Sun Yat-sen University, Guangzhou, China 510275
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37
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Mitochondrial dysfunction and β-cell failure in type 2 diabetes mellitus. EXPERIMENTAL DIABETES RESEARCH 2011; 2012:703538. [PMID: 22110477 PMCID: PMC3216264 DOI: 10.1155/2012/703538] [Citation(s) in RCA: 146] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Accepted: 09/03/2011] [Indexed: 01/09/2023]
Abstract
Type 2 diabetes mellitus (T2DM) is the most common human endocrine disease and is characterized by peripheral insulin resistance and pancreatic islet β-cell failure. Accumulating evidence indicates that mitochondrial dysfunction is a central contributor to β-cell failure in the evolution of T2DM. As reviewed elsewhere, reactive oxygen species (ROS) produced by β-cell mitochondria as a result of metabolic stress activate several stress-response pathways. This paper focuses on mechanisms whereby ROS affect mitochondrial structure and function and lead to β-cell failure. ROS activate UCP2, which results in proton leak across the mitochondrial inner membrane, and this leads to reduced β-cell ATP synthesis and content, which is a critical parameter in regulating glucose-stimulated insulin secretion. In addition, ROS oxidize polyunsaturated fatty acids in mitochondrial cardiolipin and other phospholipids, and this impairs membrane integrity and leads to cytochrome c release into cytosol and apoptosis. Group VIA phospholipase A2 (iPLA2β) appears to be a component of a mechanism for repairing mitochondrial phospholipids that contain oxidized fatty acid substituents, and genetic or acquired iPLA2β-deficiency increases β-cell mitochondrial susceptibility to injury from ROS and predisposes to developing T2DM. Interventions that attenuate ROS effects on β-cell mitochondrial phospholipids might prevent or retard development of T2DM.
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Zhao Z, Wang J, Zhao C, Bi W, Yue Z, Ma ZA. Genetic ablation of PLA2G6 in mice leads to cerebellar atrophy characterized by Purkinje cell loss and glial cell activation. PLoS One 2011; 6:e26991. [PMID: 22046428 PMCID: PMC3203935 DOI: 10.1371/journal.pone.0026991] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2011] [Accepted: 10/07/2011] [Indexed: 12/15/2022] Open
Abstract
Infantile neuroaxonal dystrophy (INAD) is a progressive, autosomal recessive neurodegenerative disease characterized by axonal dystrophy, abnormal iron deposition and cerebellar atrophy. This disease was recently mapped to PLA2G6, which encodes group VI Ca(2+)-independent phospholipase A(2) (iPLA(2) or iPLA(2)β). Here we show that genetic ablation of PLA2G6 in mice (iPLA(2)β(-/-)) leads to the development of cerebellar atrophy by the age of 13 months. Atrophied cerebella exhibited significant loss of Purkinje cells, as well as reactive astrogliosis, the activation of microglial cells, and the pronounced up-regulation of the pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). Moreover, glial cell activation and the elevation in TNF-α and IL-1β expression occurred before apparent cerebellar atrophy. Our findings indicate that the absence of PLA2G6 causes neuroinflammation and Purkinje cell loss and ultimately leads to cerebellar atrophy. Our study suggests that iPLA(2)β(-/-) mice are a valuable model for cerebellar atrophy in INAD and that early anti-inflammatory therapy may help slow the progression of cerebellar atrophy in this deadly neurodegenerative disease.
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Affiliation(s)
- Zhengshan Zhao
- Division of Experimental Diabetes and Aging, Department of Geriatrics and Palliative Medicine, Mount Sinai School of Medicine, New York, New York, United States of America
| | - Jing Wang
- Department of Neurology, Mount Sinai School of Medicine, New York, New York, United States of America
| | - Chunying Zhao
- Division of Experimental Diabetes and Aging, Department of Geriatrics and Palliative Medicine, Mount Sinai School of Medicine, New York, New York, United States of America
| | - Weina Bi
- Division of Experimental Diabetes and Aging, Department of Geriatrics and Palliative Medicine, Mount Sinai School of Medicine, New York, New York, United States of America
| | - Zhenyu Yue
- Department of Neurology, Mount Sinai School of Medicine, New York, New York, United States of America
| | - Zhongmin Alex Ma
- Division of Experimental Diabetes and Aging, Department of Geriatrics and Palliative Medicine, Mount Sinai School of Medicine, New York, New York, United States of America
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Dennis EA, Cao J, Hsu YH, Magrioti V, Kokotos G. Phospholipase A2 enzymes: physical structure, biological function, disease implication, chemical inhibition, and therapeutic intervention. Chem Rev 2011; 111:6130-85. [PMID: 21910409 PMCID: PMC3196595 DOI: 10.1021/cr200085w] [Citation(s) in RCA: 804] [Impact Index Per Article: 61.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Edward A. Dennis
- Department of Chemistry and Biochemistry and Pharmacology, School of Medicine, University of California, San Diego, La Jolla, California 92093-0601
| | - Jian Cao
- Department of Chemistry and Biochemistry and Pharmacology, School of Medicine, University of California, San Diego, La Jolla, California 92093-0601
| | - Yuan-Hao Hsu
- Department of Chemistry and Biochemistry and Pharmacology, School of Medicine, University of California, San Diego, La Jolla, California 92093-0601
| | - Victoria Magrioti
- Laboratory of Organic Chemistry, Department of Chemistry, University of Athens, Panepistimiopolis, Athens 15771, Greece
| | - George Kokotos
- Laboratory of Organic Chemistry, Department of Chemistry, University of Athens, Panepistimiopolis, Athens 15771, Greece
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Ueno N, Taketomi Y, Yamamoto K, Hirabayashi T, Kamei D, Kita Y, Shimizu T, Shinzawa K, Tsujimoto Y, Ikeda K, Taguchi R, Murakami M. Analysis of two major intracellular phospholipases A(2) (PLA(2)) in mast cells reveals crucial contribution of cytosolic PLA(2)α, not Ca(2+)-independent PLA(2)β, to lipid mobilization in proximal mast cells and distal fibroblasts. J Biol Chem 2011; 286:37249-63. [PMID: 21880721 DOI: 10.1074/jbc.m111.290312] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mast cells release a variety of mediators, including arachidonic acid (AA) metabolites, to regulate allergy, inflammation, and host defense, and their differentiation and maturation within extravascular microenvironments depend on the stromal cytokine stem cell factor. Mouse mast cells express two major intracellular phospholipases A(2) (PLA(2)s), namely group IVA cytosolic PLA(2) (cPLA(2)α) and group VIA Ca(2+)-independent PLA(2) (iPLA(2)β), and the role of cPLA(2)α in eicosanoid synthesis by mast cells has been well documented. Lipidomic analyses of mouse bone marrow-derived mast cells (BMMCs) lacking cPLA(2)α (Pla2g4a(-/-)) or iPLA(2)β (Pla2g6(-/-)) revealed that phospholipids with AA were selectively hydrolyzed by cPLA(2)α, not by iPLA(2)β, during FcεRI-mediated activation and even during fibroblast-dependent maturation. Neither FcεRI-dependent effector functions nor maturation-driven phospholipid remodeling was impaired in Pla2g6(-/-) BMMCs. Although BMMCs did not produce prostaglandin E(2) (PGE(2)), the AA released by cPLA(2)α from BMMCs during maturation was converted to PGE(2) by microsomal PGE synthase-1 (mPGES-1) in cocultured fibroblasts, and accordingly, Pla2g4a(-/-) BMMCs promoted microenvironmental PGE(2) synthesis less efficiently than wild-type BMMCs both in vitro and in vivo. Mice deficient in mPGES-1 (Ptges(-/-)) had an augmented local anaphylactic response. These results suggest that cPLA(2)α in mast cells is functionally coupled, through the AA transfer mechanism, with stromal mPGES-1 to provide anti-anaphylactic PGE(2). Although iPLA(2)β is partially responsible for PGE(2) production by macrophages and dendritic cells, it is dispensable for mast cell maturation and function.
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Affiliation(s)
- Noriko Ueno
- Lipid Metabolism Project, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo 256-8506, Japan
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Hermansson M, Hokynar K, Somerharju P. Mechanisms of glycerophospholipid homeostasis in mammalian cells. Prog Lipid Res 2011; 50:240-57. [DOI: 10.1016/j.plipres.2011.02.004] [Citation(s) in RCA: 129] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2011] [Revised: 02/21/2011] [Accepted: 02/25/2011] [Indexed: 01/09/2023]
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Han MS, Lim YM, Quan W, Kim JR, Chung KW, Kang M, Kim S, Park SY, Han JS, Park SY, Cheon HG, Dal Rhee S, Park TS, Lee MS. Lysophosphatidylcholine as an effector of fatty acid-induced insulin resistance. J Lipid Res 2011; 52:1234-1246. [PMID: 21447485 DOI: 10.1194/jlr.m014787] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The mechanism of FFA-induced insulin resistance is not fully understood. We have searched for effector molecules(s) in FFA-induced insulin resistance. Palmitic acid (PA) but not oleic acid (OA) induced insulin resistance in L6 myotubes through C-Jun N-terminal kinase (JNK) and insulin receptor substrate 1 (IRS-1) Ser307 phosphorylation. Inhibitors of ceramide synthesis did not block insulin resistance by PA. However, inhibition of the conversion of PA to lysophosphatidylcholine (LPC) by calcium-independent phospholipase A₂ (iPLA₂) inhibitors, such as bromoenol lactone (BEL) or palmitoyl trifluoromethyl ketone (PACOCF₃), prevented insulin resistance by PA. iPLA₂ inhibitors or iPLA₂ small interfering RNA (siRNA) attenuated JNK or IRS-1 Ser307 phosphorylation by PA. PA treatment increased LPC content, which was reversed by iPLA₂ inhibitors or iPLA₂ siRNA. The intracellular DAG level was increased by iPLA₂ inhibitors, despite ameliorated insulin resistance. Pertussis toxin (PTX), which inhibits LPC action through the G-protein coupled receptor (GPCR)/Gα(i), reversed insulin resistance by PA. BEL administration ameliorated insulin resistance and diabetes in db/db mice. JNK and IRS-1Ser307 phosphorylation in the liver and muscle of db/db mice was attenuated by BEL. LPC content was increased in the liver and muscle of db/db mice, which was suppressed by BEL. These findings implicate LPC as an important lipid intermediate that links saturated fatty acids to insulin resistance.
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Affiliation(s)
- Myoung Sook Han
- Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea
| | - Yu-Mi Lim
- Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea
| | - Wenying Quan
- Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea
| | - Jung Ran Kim
- Lee Gil Ya Cancer and Diabetes Institute, Gachon University of Medicine and Science, Inchon 406-840, Korea
| | - Kun Wook Chung
- Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea
| | - Mira Kang
- Center for Health Promotion, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea
| | - Sunshin Kim
- Carcinogenesis Branch, Korean National Cancer Center, Goyang 410-769, Korea
| | - Sun Young Park
- Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea
| | - Joong-Soo Han
- Institute of Biomedical Science, College of Medicine, Hanyang University, Seoul 133-791, Korea; Department of Biochemistry and Molecular Biology, College of Medicine, Hanyang University, Seoul 133-791, Korea
| | - Shin-Young Park
- Institute of Biomedical Science, College of Medicine, Hanyang University, Seoul 133-791, Korea; Department of Biochemistry and Molecular Biology, College of Medicine, Hanyang University, Seoul 133-791, Korea
| | - Hyae Gyeong Cheon
- Lee Gil Ya Cancer and Diabetes Institute, Gachon University of Medicine and Science, Inchon 406-840, Korea
| | - Sang Dal Rhee
- Bio-Organic Science Division, Korea Research Institute of Chemical Technology, Daejon 305-343, Korea
| | - Tae-Sik Park
- Lee Gil Ya Cancer and Diabetes Institute, Gachon University of Medicine and Science, Inchon 406-840, Korea.
| | - Myung-Shik Lee
- Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea.
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Li H, Zhang H, Wei G, Cai Q, Yan L, Xu Y. Tumor cell group via phospholipase A₂ is involved in prostate cancer development. Prostate 2011; 71:373-84. [PMID: 20812222 DOI: 10.1002/pros.21251] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/20/2010] [Accepted: 07/22/2010] [Indexed: 11/11/2022]
Abstract
BACKGROUND Prostate cancer (PCa) is one of the most common malignancies among men in the United States. Further understanding of the molecular mechanisms underlying PCa tumorigenic development is critical for advancing treatment strategies for PCa. The role of Group VIA phospholipase A₂β (iPLA₂β) in cancers has recently emerged. However, the biological functions of iPLA₂β in PCa development have been minimally investigated and only in vitro studies have been reported. METHODS We tested the role of iPLA₂β in host cells using an iPLA₂β deficient mouse model and the role of iPLA₂β in tumor cells by comparing the proliferation, migration, and invasion in vitro and tumorigenesis in vivo. CONCLUSIONS iPLA₂β deficiency did not affect tumor development in C57BL/6 mice injected with syngeneic PCa cell line TRAMP-C1P3 in any of three models (subcutaneous, orthotopic, or intratibia injection) tested, suggesting that host cell iPLA₂β is not required for PCa tumorigenesis and metastasis. In contrast, when iPLA₂β was down-regulated in TRAMP-C1P3 cells, cell proliferation was reduced in vitro and tumor growth was suppressed in vivo compared to control cells. In particular, iPLA₂β was required for lysophosphatidic acid (LPA)-induced migration and invasion in TRAMP-C1P3 cells. We compared human and mouse PCa cells and showed that they shared high similarities in LPA-stimulated effects and signaling pathways. LPA stimulated cell migration and/or invasion via a PI3K-dependent pathway. Together, our results suggest that the tumor cell iPLA₂β-LPA axis may represent a novel target for PCa.
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Affiliation(s)
- Hui Li
- Department of Obstetrics and Gynecology, Indiana University, Indianapolis, Indiana 46202, USA
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McHowat J, Gullickson G, Hoover RG, Sharma J, Turk J, Kornbluth J. Platelet-activating factor and metastasis: calcium-independent phospholipase A2β deficiency protects against breast cancer metastasis to the lung. Am J Physiol Cell Physiol 2011; 300:C825-32. [PMID: 21228317 DOI: 10.1152/ajpcell.00502.2010] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We determined the contribution of calcium-independent phospholipase A(2)β (iPLA(2)β) to lung metastasis development following breast cancer injection into wild-type (WT) and iPLA(2)β-knockout (iPLA(2)β-KO) mice. WT and iPLA(2)β-KO mice were injected in the mammary pad with 200,000 E0771 breast cancer cells. There was no difference in primary tumor size between WT and iPLA(2)β-KO mice at 27 days postinjection. However, we observed an 11-fold greater number of breast cancer cells in the lungs of WT mice compared with iPLA(2)β-KO animals (P < 0.05). Isolated WT lung endothelial cells demonstrated a significant increase in platelet-activating factor (PAF) production when stimulated with thrombin [1 IU/ml, 10 min, 4,330 ± 555 vs. 15,227 ± 1,043 disintegrations per minute (dpm), P < 0.01] or TNF-α (10 ng/ml, 2 h, 16,532 ± 538 dpm, P < 0.01). Adherence of E0771 cells to WT endothelial cells was increased by thrombin (4.8 ± 0.3% vs. 70.9 ± 6.3, P < 0.01) or TNF-α (60.5 ± 4.3, P < 0.01). These responses were blocked by pretreatment with the iPLA(2)β-selective inhibitor (S)-bromoenol lactone and absent in lung endothelial cells from iPLA(2)β-KO mice. These data indicate that endothelial cell iPLA(2)β is responsible for PAF production and adherence of E0771 cells and may play a role in cancer cell migration to distal locations.
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Affiliation(s)
- Jane McHowat
- Department of Pathology, Saint Louis University School of Medicine, Missouri 63104, USA.
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Murakami M, Taketomi Y, Miki Y, Sato H, Hirabayashi T, Yamamoto K. Recent progress in phospholipase A₂ research: from cells to animals to humans. Prog Lipid Res 2010; 50:152-92. [PMID: 21185866 DOI: 10.1016/j.plipres.2010.12.001] [Citation(s) in RCA: 368] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Mammalian genomes encode genes for more than 30 phospholipase A₂s (PLA₂s) or related enzymes, which are subdivided into several classes including low-molecular-weight secreted PLA₂s (sPLA₂s), Ca²+-dependent cytosolic PLA₂s (cPLA₂s), Ca²+-independent PLA₂s (iPLA₂s), platelet-activating factor acetylhydrolases (PAF-AHs), lysosomal PLA₂s, and a recently identified adipose-specific PLA. Of these, the intracellular cPLA₂ and iPLA₂ families and the extracellular sPLA₂ family are recognized as the "big three". From a general viewpoint, cPLA₂α (the prototypic cPLA₂ plays a major role in the initiation of arachidonic acid metabolism, the iPLA₂ family contributes to membrane homeostasis and energy metabolism, and the sPLA₂ family affects various biological events by modulating the extracellular phospholipid milieus. The cPLA₂ family evolved along with eicosanoid receptors when vertebrates first appeared, whereas the diverse branching of the iPLA₂ and sPLA₂ families during earlier eukaryote development suggests that they play fundamental roles in life-related processes. During the past decade, data concerning the unexplored roles of various PLA₂ enzymes in pathophysiology have emerged on the basis of studies using knockout and transgenic mice, the use of specific inhibitors, and information obtained from analysis of human diseases caused by mutations in PLA₂ genes. This review focuses on current understanding of the emerging biological functions of PLA₂s and related enzymes.
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Affiliation(s)
- Makoto Murakami
- Lipid Metabolism Project, The Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo 156-8506, Japan.
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Fèvre C, Bellenger S, Pierre AS, Minville M, Bellenger J, Gresti J, Rialland M, Narce M, Tessier C. The metabolic cascade leading to eicosanoid precursors--desaturases, elongases, and phospholipases A2--is altered in Zucker fatty rats. Biochim Biophys Acta Mol Cell Biol Lipids 2010; 1811:409-17. [PMID: 21172452 DOI: 10.1016/j.bbalip.2010.12.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Revised: 11/18/2010] [Accepted: 12/10/2010] [Indexed: 11/15/2022]
Abstract
Metabolic syndrome characterized by insulin resistance and obesity is accompanied by severe lipid metabolism perturbations and chronic low-grade inflammation. However, many unresolved questions remained regarding the regulation that underlie dyslipidemia, particularly the regulation of the metabolic cascade (synthesis and release) leading to eicosanoid precursors release. This study was undertaken to investigate the regulation of desaturases/elongases and phospholipases A(2) during the establishment of metabolic syndrome. Our results showed that delta-6 desaturase as well as elongase-6 expressions were upregulated in 3-month-old Zucker fatty rats as compared to lean littermates, independently of SREBP-1c activation. We also demonstrated for the first time an increase of liver group VII phospholipase A(2) gene expression in the obese animals together with a strong specific inhibition of type IVA and VIA phospholipases A(2). These results suggest that the regulation of unsaturated fatty acids biosynthesis and signalling cascade could contribute to the development of liver lipid dysregulation related to metabolic syndrome and may be considered as new potential targets in such pathological conditions.
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Affiliation(s)
- Cécile Fèvre
- INSERM UMR 866/Université de Bourgogne, Lipides Nutrition Cancer, Faculté des Sciences Gabriel, 6 Bd Gabriel, 21000 Dijon, France
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Li H, Zhao Z, Wei G, Yan L, Wang D, Zhang H, Sandusky GE, Turk J, Xu Y. Group VIA phospholipase A2 in both host and tumor cells is involved in ovarian cancer development. FASEB J 2010; 24:4103-16. [PMID: 20530749 PMCID: PMC2996900 DOI: 10.1096/fj.10-161356] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2010] [Accepted: 05/20/2010] [Indexed: 11/11/2022]
Abstract
Host-tumor cell interactions are recognized to be critical in tumor development. We have shown that group VIA phospholipase A(2) [calcium-independent phospholipase A(2)β (iPLA(2)β)] is important in regulating extracellular lysophosphatidic acid (LPA) levels around human epithelial ovarian cancer (EOC) cells. To explore the role of iPLA(2)β in host-tumor cell interactions, we have used immunocompetent iPLA(2)β knockout (iPLA(2)β(-/-)) mice and the mouse EOC cell line ID8. Tumorigenesis and ascites formation were reduced in iPLA(2)β(-/-) mice compared with wild-type (WT) mice by more >50% and were reduced further when ID8 cell iPLA(2)β levels were lowered (by>95%) with shRNA. LPA and lysophosphatidylcholine (LPC) levels in the tumor microenvironment were reduced to ∼80% of WT levels in iPLA(2)β(-/-) mice. LPA, but not LPC, stimulated ID8 cell migration and invasion with cells in which iPLA(2)β expression had been down-regulated in vitro. LPA, but not LPC, also enhanced in vivo ascites formation (by ∼5-fold) and tumorigenesis in iPLA(2)β(-/-) mice. This is the first demonstration of a role for host cell iPLA(2)β in cancer, and these findings suggest that iPLA(2)β is a potential target for developing novel antineoplastic therapeutic strategies.
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Affiliation(s)
- Hui Li
- Department of Obstetrics and Gynecology and
| | | | - Gang Wei
- Department of Obstetrics and Gynecology and
| | - Libo Yan
- Department of Obstetrics and Gynecology and
| | | | - Hong Zhang
- Department of Obstetrics and Gynecology and
- Department of Pathology and Laboratory Medicine, Indiana University, Indianapolis, Indiana, USA
- Department of General Surgery, Second Hospital of Jilin University, Changchun, Jilin, China; and
| | - George Earl Sandusky
- Department of Pathology and Laboratory Medicine, Indiana University, Indianapolis, Indiana, USA
- Department of General Surgery, Second Hospital of Jilin University, Changchun, Jilin, China; and
| | - John Turk
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Yan Xu
- Department of Obstetrics and Gynecology and
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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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Sharma J, Turk J, McHowat J. Endothelial cell prostaglandin I(2) and platelet-activating factor production are markedly attenuated in the calcium-independent phospholipase A(2)beta knockout mouse. Biochemistry 2010; 49:5473-81. [PMID: 20521843 DOI: 10.1021/bi100752u] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Damage and activation of lung endothelium can lead to interstitial edema, infiltration of inflammatory cells into the interstitium and airways, and production of inflammatory metabolites, all of which propagate airway inflammation in a variety of diseases. We have previously determined that stimulation of human microvascular endothelial cells from lung (HMVEC-L) results in activation of a calcium-independent phospholipase A(2) (iPLA(2)), and this leads to arachidonic acid release and production of prostaglandin I(2) (PGI(2)) and platelet-activating factor (PAF). We stimulated lung endothelial cells isolated from iPLA(2)beta-knockout (KO) and wild type (WT) mice with thrombin and tryptase to determine the role of iPLA(2)beta in endothelial cell membrane phospholipid hydrolysis. Thrombin or tryptase stimulation of WT lung endothelial cells resulted in increased arachidonic acid release and production of PGI(2) and PAF. Arachidonic acid release and PGI(2) production by stimulated iPLA(2)beta-KO endothelial cells were significantly reduced compared to WT. Measured PLA(2) activity and PGI(2) production by iPLA(2)beta-KO cells were suppressed by pretreatment with (R)-bromoenol lactone (R-BEL), which is a selective inhibitor of iPLA2gamma. In contrast to the increase in PAF production induced by stimulation of WT endothelial cells, none was observed for KO cells, and this suggests that endothelial PAF production is entirely dependent on iPLA(2)beta activity. Because inflammatory cell recruitment involves the interaction of endothelial cell PAF with PAF receptors on circulating cells, these data suggest that iPLA(2)beta may be a suitable therapeutic target for the treatment of inflammatory lung diseases.
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Affiliation(s)
- Janhavi Sharma
- Department of Pathology, Saint Louis University School of Medicine, St. Louis, Missouri 63104, USA
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50
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Zhao Z, Zhang X, Zhao C, Choi J, Shi J, Song K, Turk J, Ma ZA. Protection of pancreatic beta-cells by group VIA phospholipase A(2)-mediated repair of mitochondrial membrane peroxidation. Endocrinology 2010; 151:3038-48. [PMID: 20463052 PMCID: PMC2903934 DOI: 10.1210/en.2010-0016] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Mitochondrial production of reactive oxygen species and oxidation of cardiolipin are key events in initiating apoptosis. We reported that group VIA Ca(2+)-independent phospholipase A(2) (iPLA(2)beta) localizes in and protects beta-cell mitochondria from oxidative damage during staurosporine-induced apoptosis. Here, we used iPLA(2)beta-null (iPLA(2)beta(-/-)) mice to investigate the role of iPLA(2)beta in the repair of mitochondrial membranes. We show that islets isolated from iPLA(2)beta(-/-) mice are more sensitive to staurosporine-induced apoptosis than those from wild-type littermates and that 2 wk of daily ip administration of staurosporine to iPLA(2)beta(-/-) mice impairs both the animals' glucose tolerance and glucose-stimulated insulin secretion by their pancreatic islets. Moreover, the iPLA(2)beta inhibitor bromoenol lactone caused mitochondrial membrane peroxidation and cytochrome c release, and these effects were reversed by N-acetyl cysteine. The mitochondrial antioxidant N-t-butyl hydroxylamine blocked staurosporine-induced cytochrome c release and caspase-3 activation in iPLA(2)beta(-/-) islets. Furthermore, the collapse of mitochondrial membrane potential in INS-1 insulinoma cells caused by high glucose and fatty acid levels was attenuated by overexpressing iPLA(2)beta. Interestingly, iPLA(2)beta was expressed only at low levels in islet beta-cells from obesity- and diabetes-prone db/db mice. These findings support the hypothesis that iPLA(2)beta is important in repairing oxidized mitochondrial membrane components (e.g. cardiolipin) and that this prevents cytochrome c release in response to stimuli that otherwise induce apoptosis. The low iPLA(2)beta expression level in db/db mouse beta-cells may render them vulnerable to injury by reactive oxygen species.
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Affiliation(s)
- Zhengshan Zhao
- Division of Experimental Diabetes and Aging, Department of Geriatrics and Adult Development, One Gustave L. Levy Place, Mount Sinai School of Medicine, New York, NY 10029, USA
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