1
|
Khetarpal SA, Vitali C, Levin MG, Klarin D, Park J, Pampana A, Millar JS, Kuwano T, Sugasini D, Subbaiah PV, Billheimer JT, Natarajan P, Rader DJ. Endothelial lipase mediates efficient lipolysis of triglyceride-rich lipoproteins. PLoS Genet 2021; 17:e1009802. [PMID: 34543263 PMCID: PMC8483387 DOI: 10.1371/journal.pgen.1009802] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Revised: 09/30/2021] [Accepted: 09/02/2021] [Indexed: 11/18/2022] Open
Abstract
Triglyceride-rich lipoproteins (TRLs) are circulating reservoirs of fatty acids used as vital energy sources for peripheral tissues. Lipoprotein lipase (LPL) is a predominant enzyme mediating triglyceride (TG) lipolysis and TRL clearance to provide fatty acids to tissues in animals. Physiological and human genetic evidence support a primary role for LPL in hydrolyzing TRL TGs. We hypothesized that endothelial lipase (EL), another extracellular lipase that primarily hydrolyzes lipoprotein phospholipids may also contribute to TRL metabolism. To explore this, we studied the impact of genetic EL loss-of-function on TRL metabolism in humans and mice. Humans carrying a loss-of-function missense variant in LIPG, p.Asn396Ser (rs77960347), demonstrated elevated plasma TGs and elevated phospholipids in TRLs, among other lipoprotein classes. Mice with germline EL deficiency challenged with excess dietary TG through refeeding or a high-fat diet exhibited elevated TGs, delayed dietary TRL clearance, and impaired TRL TG lipolysis in vivo that was rescued by EL reconstitution in the liver. Lipidomic analyses of postprandial plasma from high-fat fed Lipg-/- mice demonstrated accumulation of phospholipids and TGs harboring long-chain polyunsaturated fatty acids (PUFAs), known substrates for EL lipolysis. In vitro and in vivo, EL and LPL together promoted greater TG lipolysis than either extracellular lipase alone. Our data positions EL as a key collaborator of LPL to mediate efficient lipolysis of TRLs in humans and mice.
Collapse
Affiliation(s)
- Sumeet A. Khetarpal
- Departments of Medicine and Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America,Cardiovascular Research Center, Massachusetts General Hospital, Boston, Massachusetts, United States of America
| | - Cecilia Vitali
- Departments of Medicine and Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Michael G. Levin
- Division of Cardiovascular Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America,Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America,Corporal Michael J. Crescenz VA Medical Center, Philadelphia, Pennsylvania, United States of America
| | - Derek Klarin
- Boston VA Healthcare System, Boston, Massachusetts, United States of America,Center for Genomic Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America,Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America
| | - Joseph Park
- Departments of Medicine and Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Akhil Pampana
- Cardiovascular Research Center, Massachusetts General Hospital, Boston, Massachusetts, United States of America,Center for Genomic Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America,Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America,Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America
| | - John S. Millar
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Takashi Kuwano
- Departments of Medicine and Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Dhavamani Sugasini
- Section of Endocrinology, Department of Medicine, University of Illinois at Chicago; Jesse Brown VA Medical Center, Chicago, Illinois, United States of America
| | - Papasani V. Subbaiah
- Section of Endocrinology, Department of Medicine, University of Illinois at Chicago; Jesse Brown VA Medical Center, Chicago, Illinois, United States of America
| | - Jeffrey T. Billheimer
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Pradeep Natarajan
- Cardiovascular Research Center, Massachusetts General Hospital, Boston, Massachusetts, United States of America,Center for Genomic Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America,Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America,Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Daniel J. Rader
- Departments of Medicine and Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America,* E-mail:
| |
Collapse
|
3
|
van den Boogert MAW, Rader DJ, Holleboom AG. New insights into the role of glycosylation in lipoprotein metabolism. Curr Opin Lipidol 2017; 28:502-506. [PMID: 28922188 DOI: 10.1097/mol.0000000000000461] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE OF REVIEW Human genetics has provided new insights into the role of protein glycosylation in regulating lipoprotein metabolism. Here we review these new developments and discuss the biological insights they provide. RECENT FINDINGS Case descriptions of patients with congenital defects in N-glycosylation (CDG-I) frequently describe a distinct hypocholesterolemia in these rare multisystem clinical syndromes. Two novel CDGs with disturbed Golgi homeostasis and trafficking defects result in mixed glycosylation disorders, hepatic steatosis and hypercholesterolemia. In addition, the presence of particular N-glycans is essential for physiological membrane expression of scavenger receptor B1 and for adequate lipolytic activity of endothelial lipase. GalNAc-T2, a specific O-glycosyl transferase, was found to be a direct modulator of HDL metabolism across mammals, validating its relationship with HDL-c found in genome-wide association studies. Furthermore, genetic variation in ASGR1, the major subunit of the asialoglycoprotein receptor (ASGPR), was found to be associated with a reduction in LDL-c and risk of coronary artery disease. SUMMARY Protein glycosylation plays an important regulatory role in lipoprotein metabolism. Greater insight into how protein glycosylation regulates lipoprotein metabolism could provide novel approaches for the treatment of dyslipidemia.
Collapse
Affiliation(s)
- Marjolein A W van den Boogert
- aDepartment of Vascular Medicine, Academic Medical Center, Amsterdam, The Netherlands bDepartments of Genetics and Medicine, Institute for Translational Medicine and Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, USA
| | | | | |
Collapse
|
4
|
Yu JE, Han SY, Wolfson B, Zhou Q. The role of endothelial lipase in lipid metabolism, inflammation, and cancer. Histol Histopathol 2017; 33:1-10. [PMID: 28540715 DOI: 10.14670/hh-11-905] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Endothelial lipase (LIPG) plays a critical role in lipoprotein metabolism, cytokine expression, and the lipid composition of cells. Thus far, the extensive investigations of LIPG have focused on its mechanisms and involvement in metabolic syndromes such as atherosclerosis. However, recent developments have found that LIPG plays a role in cancer. This review summarizes the field of LIPG study. We focus on the role of LIPG in lipid metabolism and the inflammatory response, and highlight the recent insights in its involvement in tumor progression. Finally, we discuss potential therapeutic strategies for targeting LIPG in cancer, and the therapeutic potential of LIPG as a drug target.
Collapse
Affiliation(s)
- Justine E Yu
- Department of Biochemistry and Molecular Biology, Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, USA
| | - Shu-Yan Han
- Department of Biochemistry and Molecular Biology, Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, USA.,Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Department of Integration of Chinese and Western Medicine, Peking University Cancer Hospital and Institute, Beijing, People's Republic of China
| | - Benjamin Wolfson
- Department of Biochemistry and Molecular Biology, Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, USA
| | - Qun Zhou
- Department of Biochemistry and Molecular Biology, Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, USA.
| |
Collapse
|
6
|
Sun L, Ishida T, Miyashita K, Kinoshita N, Mori K, Yasuda T, Toh R, Nakajima K, Imamura S, Hirata KI. Plasma activity of endothelial lipase impacts high-density lipoprotein metabolism and coronary risk factors in humans. J Atheroscler Thromb 2013; 21:313-21. [PMID: 24369272 DOI: 10.5551/jat.20131] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
AIM Endothelial lipase (EL) is a determinant of plasma levels of high-density lipoprotein cholesterol (HDL-C). However, little is known about the impact of EL activity on plasma lipid profile. We aimed to establish a new method to evaluate EL-specific phospholipase activity in humans. METHODS Plasma samples were obtained from 115 patients with coronary artery disease (CAD) and 154 patients without CAD. Plasma EL protein was immunoprecipitated using an anti-EL monoclonal antibody after plasma non-specific immunoglobulins were removed by incubation with ProteinA. The phospholipase activity of the immunoprecipitated samples was measured using a fluorogenic phospholipase substrate, Bis-BODIPY FL C11-PC. RESULTS The EL-specific phospholipase assay revealed that plasma EL activity was inversely correlated with HDL-C levels (R = -0.3088, p<0.0001). In addition, the EL activity was associated with cigarette smoking. Furthermore, EL activity in CAD patients was significantly higher than that in nonCAD patients. Concomitantly, the HDL-C level in CAD patients were significantly lower than that in non-CAD patients. CONCLUSION We have established a method for human plasma EL-specific phospholipase activity by combination of EL immunoprecipitation and a fluorogenic phospholipid substrate. Plasma EL activity was associated with not only plasma HDL-C levels but also the risks for CAD.
Collapse
Affiliation(s)
- Li Sun
- Division of Cardiovascular Medicine, Kobe University Graduate School of Medicine
| | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Hydrolysis products generated by lipoprotein lipase and endothelial lipase differentially impact THP-1 macrophage cell signalling pathways. Lipids 2013; 48:769-778. [PMID: 23794138 DOI: 10.1007/s11745-013-3810-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Accepted: 06/06/2013] [Indexed: 12/11/2022]
Abstract
Macrophages express lipoprotein lipase (LPL) and endothelial lipase (EL) within atherosclerotic plaques; however, little is known about how lipoprotein hydrolysis products generated by these lipases might affect macrophage cell signalling pathways. We hypothesized that hydrolysis products affect macrophage cell signalling pathways associated with atherosclerosis. To test our hypothesis, we incubated differentiated THP-1 macrophages with products from total lipoprotein hydrolysis by recombinant LPL or EL. Using antibody arrays, we found that the phosphorylation of six receptor tyrosine kinases and three signalling nodes--most associated with atherosclerotic processes--was increased by LPL derived hydrolysis products. EL derived hydrolysis products only increased the phosphorylation of tropomyosin-related kinase A, which is also implicated in playing a role in atherosclerosis. Using electrospray ionization-mass spectrometry, we identified the species of triacylglycerols and phosphatidylcholines that were hydrolyzed by LPL and EL, and we identified the fatty acids liberated by gas chromatography-mass spectrometry. To determine if the total liberated fatty acids influenced signalling pathways, we incubated differentiated THP-1 macrophages with a mixture of the fatty acids that matched the concentrations of liberated fatty acids from total lipoproteins by LPL, and we subjected cell lysates to antibody array analyses. The analyses showed that only the phosphorylation of Akt was significantly increased in response to fatty acid treatment. Overall, our study shows that macrophages display potentially pro-atherogenic signalling responses following acute treatments with LPL and EL lipoprotein hydrolysis products.
Collapse
|
10
|
Griffon N, Jin W, Petty TJ, Millar J, Badellino KO, Saven JG, Marchadier DH, Kempner ES, Billheimer J, Glick JM, Rader DJ. Identification of the active form of endothelial lipase, a homodimer in a head-to-tail conformation. J Biol Chem 2009; 284:23322-30. [PMID: 19567873 DOI: 10.1074/jbc.m109.037002] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Endothelial lipase (EL) is a member of a subfamily of lipases that act on triglycerides and phospholipids in plasma lipoproteins, which also includes lipoprotein lipase and hepatic lipase. EL has a tropism for high density lipoprotein, and its level of phospholipase activity is similar to its level of triglyceride lipase activity. Inhibition or loss-of-function of EL in mice results in an increase in high density lipoprotein cholesterol, making it a potential therapeutic target. Although hepatic lipase and lipoprotein lipase have been shown to function as homodimers, the active form of EL is not known. In these studies, the size and conformation of the active form of EL were determined. Immunoprecipitation experiments suggested oligomerization. Ultracentrifugation experiments showed that the active form of EL had a molecular weight higher than the molecular weight of a simple monomer but less than a dimer. A construct encoding a covalent head-to-tail homodimer of EL (EL-EL) was expressed and had similar lipolytic activity to EL. The functional molecular weights determined by radiation inactivation were similar for EL and the covalent homodimer EL-EL. We previously showed that EL could be cleaved by proprotein convertases, such as PC5, resulting in loss of activity. In cells overexpressing PC5, the covalent homodimeric EL-EL appeared to be more stable, with reduced cleavage and conserved lipolytic activity. A comparative model obtained using other lipase structures suggests a structure for the head-to-tail EL homodimer that is consistent with the experimental findings. These data confirm the hypothesis that EL is active as a homodimer in head-to-tail conformation.
Collapse
Affiliation(s)
- Nathalie Griffon
- Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
11
|
Skropeta D. The effect of individual N-glycans on enzyme activity. Bioorg Med Chem 2009; 17:2645-53. [PMID: 19285412 DOI: 10.1016/j.bmc.2009.02.037] [Citation(s) in RCA: 138] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2008] [Revised: 02/11/2009] [Accepted: 02/13/2009] [Indexed: 01/08/2023]
Abstract
In a series of investigations, N-glycosylation has proven to be a key determinant of enzyme secretion, activity, binding affinity and substrate specificity, enabling a protein to fine-tune its activity. In the majority of cases elimination of all putative N-glycosylation sites of an enzyme results in significantly reduced protein secretion levels, while removal of individual N-glycosylation sites often leads to the expression of active enzymes showing markedly reduced catalytic activity, with the decreased activity often commensurate with the number of glycosylation sites available, and the fully deglycosylated enzymes showing only minimal activity relative to their glycosylated counterparts. On the other hand, several cases have also recently emerged where deglycosylation of an enzyme results in significantly increased catalytic activity, binding affinity and altered substrate specificity, highlighting the very unique and diverse roles that individual N-glycans play in regulating enzyme function.
Collapse
Affiliation(s)
- Danielle Skropeta
- School of Chemistry, University of Wollongong, Wollongong, NSW 2522, Australia.
| |
Collapse
|
13
|
Skropeta D, Settasatian C, McMahon MR, Shearston K, Caiazza D, McGrath KC, Jin W, Rader DJ, Barter PJ, Rye KA. N-Glycosylation regulates endothelial lipase-mediated phospholipid hydrolysis in apoE- and apoA-I-containing high density lipoproteins. J Lipid Res 2007; 48:2047-57. [PMID: 17545692 DOI: 10.1194/jlr.m700248-jlr200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Endothelial lipase (EL) is a member of the triglyceride lipase gene family with high phospholipase and low triacylglycerol lipase activities and a distinct preference for hydrolyzing phospholipids in HDL. EL has five potential N-glycosylation sites, four of which are glycosylated. The aim of this study was to determine how glycosylation affects the phospholipase activity of EL in physiologically relevant substrates. Site-directed mutants of EL were generated by replacing asparagine (N) 62, 118, 375, and 473 with alanine (A). These glycan-deficient mutants were used to investigate the kinetics of phospholipid hydrolysis in fully characterized preparations of spherical reconstituted high density lipoprotein (rHDL) containing apolipoprotein E2 (apoE2) [(E2)rHDL], apoE3 [(E3)rHDL], apoE4 [(E4)rHDL], or apoA-I [(A-I)rHDL] as the sole apolipoprotein. Wild-type EL hydrolyzed the phospholipids in (A-I)rHDL, (E2)rHDL, (E3)rHDL, and (E4)rHDL to similar extents. The phospholipase activities of EL N118A, EL N375A, and EL N473A were significantly diminished relative to that of wild-type EL, with the greatest reduction being apparent for (E3)rHDL. The phospholipase activity of EL N62A was increased up to 6-fold relative to that of wild-type EL, with the greatest enhancement of activity being observed for (E2)rHDL. These data show that individual N-linked glycans have unique and important effects on the phospholipase activity and substrate specificity of EL.
Collapse
Affiliation(s)
- Danielle Skropeta
- Lipid Research Group, Heart Research Institute, Camperdown, New South Wales 2050, Australia
| | | | | | | | | | | | | | | | | | | |
Collapse
|