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Thierer JH, Foresti O, Yadav PK, Wilson MH, Moll TOC, Shen MC, Busch-Nentwich EM, Morash M, Mohlke KL, Rawls JF, Malhotra V, Hussain MM, Farber SA. Pla2g12b drives expansion of triglyceride-rich lipoproteins. Nat Commun 2024; 15:2095. [PMID: 38453914 PMCID: PMC10920679 DOI: 10.1038/s41467-024-46102-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Accepted: 02/14/2024] [Indexed: 03/09/2024] Open
Abstract
Vertebrates transport hydrophobic triglycerides through the circulatory system by packaging them within amphipathic particles called Triglyceride-Rich Lipoproteins. Yet, it remains largely unknown how triglycerides are loaded onto these particles. Mutations in Phospholipase A2 group 12B (PLA2G12B) are known to disrupt lipoprotein homeostasis, but its mechanistic role in this process remains unclear. Here we report that PLA2G12B channels lipids within the lumen of the endoplasmic reticulum into nascent lipoproteins. This activity promotes efficient lipid secretion while preventing excess accumulation of intracellular lipids. We characterize the functional domains, subcellular localization, and interacting partners of PLA2G12B, demonstrating that PLA2G12B is calcium-dependent and tightly associated with the membrane of the endoplasmic reticulum. We also detect profound resistance to atherosclerosis in PLA2G12B mutant mice, suggesting an evolutionary tradeoff between triglyceride transport and cardiovascular disease risk. Here we identify PLA2G12B as a key driver of triglyceride incorporation into vertebrate lipoproteins.
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Affiliation(s)
- James H Thierer
- Department of Embryology, Carnegie Institution for Science, Baltimore, MD, 21218, USA
- Johns Hopkins University in Baltimore, Maryland Department of biology, Baltimore, MD, 21218, USA
| | - Ombretta Foresti
- Centre for Genomic Regulation (CRG), The Barcelona Institute for Science and Technology, Barcelona, 08003, ES, Spain
| | - Pradeep Kumar Yadav
- Department of Foundations of Medicine, NYU Long Island School of Medicine, Mineola, NY, 11501, USA
- Department of Botany, Faculty of Science, University of Allahabad, Prayagraj, India
| | - Meredith H Wilson
- Department of Embryology, Carnegie Institution for Science, Baltimore, MD, 21218, USA
- Johns Hopkins University in Baltimore, Maryland Department of biology, Baltimore, MD, 21218, USA
| | - Tabea O C Moll
- Department of Embryology, Carnegie Institution for Science, Baltimore, MD, 21218, USA
- Johns Hopkins University in Baltimore, Maryland Department of biology, Baltimore, MD, 21218, USA
| | - Meng-Chieh Shen
- Department of Embryology, Carnegie Institution for Science, Baltimore, MD, 21218, USA
| | | | - Margaret Morash
- Department of Molecular Genetics and Microbiology, Duke University, Durham, NC, 27708, USA
| | - Karen L Mohlke
- Department of Genetics, University of North Carolina, Chapel Hill, NC, 27599, USA
| | - John F Rawls
- Department of Molecular Genetics and Microbiology, Duke University, Durham, NC, 27708, USA
| | - Vivek Malhotra
- Centre for Genomic Regulation (CRG), The Barcelona Institute for Science and Technology, Barcelona, 08003, ES, Spain
- Universitat Pompeu Fabra, Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain
| | - M Mahmood Hussain
- Department of Foundations of Medicine, NYU Long Island School of Medicine, Mineola, NY, 11501, USA
| | - Steven A Farber
- Department of Embryology, Carnegie Institution for Science, Baltimore, MD, 21218, USA.
- Johns Hopkins University in Baltimore, Maryland Department of biology, Baltimore, MD, 21218, USA.
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Anaganti N, Chattopadhyay A, Poirier JT, Hussain MM. Generation of hepatoma cell lines deficient in microsomal triglyceride transfer protein. J Lipid Res 2022; 63:100257. [PMID: 35931202 PMCID: PMC9405095 DOI: 10.1016/j.jlr.2022.100257] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Revised: 07/03/2022] [Accepted: 07/08/2022] [Indexed: 01/05/2023] Open
Abstract
The microsomal triglyceride transfer protein (MTP) is essential for the secretion of apolipoprotein B (apoB)48- and apoB100-containing lipoproteins in the intestine and liver, respectively. Loss of function mutations in MTP cause abetalipoproteinemia. Heterologous cells are used to evaluate the function of MTP in apoB secretion to avoid background MTP activity in liver and intestine-derived cells. However, these systems are not suitable to study the role of MTP in the secretion of apoB100-containing lipoproteins, as expression of a large apoB100 peptide using plasmids is difficult. Here, we report a new cell culture model amenable for studying the role of different MTP mutations on apoB100 secretion. The endogenous MTTP gene was ablated in human hepatoma Huh-7 cells using single guide RNA and RNA-guided clustered regularly interspaced short palindromic repeats-associated sequence 9 ribonucleoprotein complexes. We successfully established three different clones that did not express any detectable MTTP mRNA or MTP protein or activity. These cells were defective in secreting apoB-containing lipoproteins and accumulated lipids. Furthermore, we show that transfection of these cells with plasmids expressing human MTTP cDNA resulted in the expression of MTP protein, restoration of triglyceride transfer activity, and secretion of apoB100. Thus, these new cells can be valuable tools for studying structure-function of MTP, roles of different missense mutations in various lipid transfer activities of MTP, and their ability to support apoB100 secretion, compensatory changes associated with loss of MTP, and in the identification of novel proteins that may require MTP for their synthesis and secretion.
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Affiliation(s)
- Narasimha Anaganti
- Department of Foundations of Medicine, NYU Long Island School of Medicine, Mineola, NY, USA
| | - Atrayee Chattopadhyay
- Department of Foundations of Medicine, NYU Long Island School of Medicine, Mineola, NY, USA
| | - John T Poirier
- Perlmutter Cancer Center, New York University Langone Health, New York, NY, USA
| | - M Mahmood Hussain
- Department of Foundations of Medicine, NYU Long Island School of Medicine, Mineola, NY, USA; VA New York Harbor Healthcare System, Brooklyn, NY, USA.
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3
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Anaganti N, Rajan S, Hussain MM. An improved assay to measure the phospholipid transfer activity of microsomal triglyceride transport protein. J Lipid Res 2021; 62:100136. [PMID: 34673018 PMCID: PMC8569553 DOI: 10.1016/j.jlr.2021.100136] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Revised: 09/27/2021] [Accepted: 10/07/2021] [Indexed: 12/02/2022] Open
Abstract
Microsomal triglyceride transfer protein (MTP) is essential for the assembly and secretion of apolipoprotein B-containing lipoproteins. MTP transfers diverse lipids such as triacylglycerol (TAG) and phospholipids (PLs) between vesicles in vitro. Previously, we described methods to measure these transfer activities using N-7-nitro-2-1,3-benzoxadiazol-4-yl (NBD)-labeled lipids. The NBD-TAG transfer assay is sensitive and can measure MTP activity in cell and tissue homogenates. In contrast, the NBD-PL transfer assay shows high background and is less sensitive; therefore, purified MTP is required to measure its PL transfer activity. Here, we optimized the assay to measure also the PL transfer activity of MTP in cell and tissue homogenates. We found that donor vesicles containing dioleoylphosphoethanolamine and palmitoyloleoylphosphoethanolamine result in a low background signal and are suitable to assay the PL transfer activity of MTP. This assay was capable of measuring protein-dependent and substrate-dependent saturation kinetics. Furthermore, the MTP inhibitor lomitapide blocked this transfer activity. One drawback of the PL transfer assay is that it is less sensitive at physiological temperature than at room temperature, and it requires longer incubation times than the TAG transfer assay. Nevertheless, this significantly improved sensitive assay is simple and easy to perform, involves few steps, can be conducted at room temperature, and is suitable for high-throughput screening to identify inhibitors. This assay can be adapted to measure other PL transfer proteins and to address biological and physiological importance of these activities.
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Affiliation(s)
- Narasimha Anaganti
- Department of Foundations of Medicine, New York University Long Island School of Medicine, Mineola, NY 11501, USA
| | - Sujith Rajan
- Department of Foundations of Medicine, New York University Long Island School of Medicine, Mineola, NY 11501, USA
| | - M Mahmood Hussain
- Department of Foundations of Medicine, New York University Long Island School of Medicine, Mineola, NY 11501, USA; VA New York Harbor Healthcare System, Brooklyn, NY 11209, USA.
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Rajan S, de Guzman HC, Palaia T, Goldberg IJ, Hussain MM. A simple, rapid, and sensitive fluorescence-based method to assess triacylglycerol hydrolase activity. J Lipid Res 2021; 62:100115. [PMID: 34508728 PMCID: PMC8488599 DOI: 10.1016/j.jlr.2021.100115] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Revised: 08/26/2021] [Accepted: 08/30/2021] [Indexed: 01/22/2023] Open
Abstract
Lipases constitute an important class of water-soluble enzymes that catalyze the hydrolysis of hydrophobic triacylglycerol (TAG). Their enzymatic activity is typically measured using multistep procedures involving isolation and quantification of the hydrolyzed products. We report here a new fluorescence method to measure lipase activity in real time that does not require the separation of substrates from products. We developed this method using adipose triglyceride lipase (ATGL) and lipoprotein lipase (LpL) as model lipases. We first incubated a source of ATGL or LpL with substrate vesicles containing nitrobenzoxadiazole (NBD)-labeled TAG, then measured increases in NBD fluorescence, and calculated enzyme activities. Incorporation of NBD-TAG into phosphatidylcholine (PC) vesicles resulted in some hydrolysis; however, incorporation of phosphatidylinositol into these NBD-TAG/PC vesicles and increasing the ratio of NBD-TAG to PC greatly enhanced substrate hydrolysis. This assay was also useful in measuring the activity of pancreatic lipase and hormone-sensitive lipase. Next, we tested several small-molecule lipase inhibitors and found that orlistat inhibits all lipases, indicating that it is a pan-lipase inhibitor. In short, we describe a simple, rapid, fluorescence-based triacylglycerol hydrolysis assay to assess four major TAG hydrolases: intracellular ATGL and hormone-sensitive lipase, LpL localized at the extracellular endothelium, and pancreatic lipase present in the intestinal lumen. The major advantages of this method are its speed, simplicity, and elimination of product isolation. This assay is potentially applicable to a wide range of lipases, is amenable to high-throughput screening to discover novel modulators of triacylglycerol hydrolases, and can be used for diagnostic purposes.
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Affiliation(s)
- Sujith Rajan
- Department of Foundations of Medicine, NYU Long Island School of Medicine, and Diabetes and Obesity Research Center, NYU Langone Hospitals - Long Island, Mineola, NY, USA
| | - Hazel C de Guzman
- Department of Foundations of Medicine, NYU Long Island School of Medicine, and Diabetes and Obesity Research Center, NYU Langone Hospitals - Long Island, Mineola, NY, USA; Department of Environmental Medicine, NYU Grossman School of Medicine, New York, NY, USA
| | - Thomas Palaia
- Department of Foundations of Medicine, NYU Long Island School of Medicine, and Diabetes and Obesity Research Center, NYU Langone Hospitals - Long Island, Mineola, NY, USA
| | - Ira J Goldberg
- Division of Endocrinology, Department of Medicine, NYU Grossman School of Medicine, New York, NY, USA
| | - M Mahmood Hussain
- Department of Foundations of Medicine, NYU Long Island School of Medicine, and Diabetes and Obesity Research Center, NYU Langone Hospitals - Long Island, Mineola, NY, USA; VA New York Harbor Healthcare System, Brooklyn, NY, USA.
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Twair A, Kassem I, Murad H, Abbady AQ. Secretion of Recombinant Human Annexin V in Fusion with the Super Folder GFP for Labelling Phosphatidylserine-Exposing Membranes. J Membr Biol 2021; 254:175-187. [PMID: 33604692 DOI: 10.1007/s00232-021-00169-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2020] [Accepted: 01/05/2021] [Indexed: 11/26/2022]
Abstract
Annexin V (ANXV), mostly characterized by its ability to interact with biological membranes in a calcium-dependent manner. ANXV interacts mainly with phosphatidylserine (PS), for that fluorescent ANXV widely produced and used as a sensitive and specific probe to mark apoptotic cells or any PS-containing bilayers membranes. Many reports described the prokaryotic expression of recombinant human ANXV. To overcome some of E. coli expression limitations, we aimed in this work to investigate unconventional alternative expression system in mammalian cells for producing secreted human ANXV in fusion with the super folder green fluorescent protein (sfGFP). HEK239T cells were transfected using polyethylenimine (PEI) and pcDNA-sfGFP-ANXV plasmid. Forty-eight hours post transfection, direct fluorescence measurement, immunoblotting and ELISA confirmed the presence of secreted sfGFP-ANXV in cells supernatant. The yield of secreted 6 × His-tagged sfGFP-ANXV after affinity purification was estimated to be around 2 µg per 1 ml of cells supernatant. The secretion system was proper to produce a fully functional sfGFP-ANXV fusion protein in quantities enough to recognize and bind PS-containing surfaces or liposomes. Besides, biological assays such as flow cytometry and fluorescent microscopy confirmed the capacity of the secreted sfGFP-ANXV to detect PS exposure on apoptotic cells. Taken together, we present mammalian expression as a quick, affordable and endotoxin-free system to produce sfGFP-ANXV fusion protein. The secreted sfGFP-ANXV in eukaryotic system is a promising biotechnological tool, it opens up new horizons for additional applications in the detection of PS bearing surfaces and apoptosis in vitro and in vivo assays.
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Affiliation(s)
- Aya Twair
- Division of Molecular Biomedicine, Department of Molecular Biology and Biotechnology, Atomic Energy Commission of Syria (AECS), P. O. Box 6091, Damascus, Syria
- Department of Animal Biology, Faculty of Sciences, Damascus University, Damascus, Syria
| | - Issam Kassem
- Department of Animal Biology, Faculty of Sciences, Damascus University, Damascus, Syria
- National Commission for Biotechnology (NCBT), Damascus, Syria
| | - Hossam Murad
- Division of Human Genetics, Department of Molecular Biology and Biotechnology, Atomic Energy Commission of Syria (AECS), P. O. Box 6091, Damascus, Syria
| | - Abdul Qader Abbady
- Division of Molecular Biomedicine, Department of Molecular Biology and Biotechnology, Atomic Energy Commission of Syria (AECS), P. O. Box 6091, Damascus, Syria.
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