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Liu Y, Conlon DM, Bi X, Slovik KJ, Shi J, Edelstein HI, Millar JS, Javaheri A, Cuchel M, Pashos EE, Iqbal J, Hussain MM, Hegele RA, Yang W, Duncan SA, Rader DJ, Morrisey EE. Lack of MTTP Activity in Pluripotent Stem Cell-Derived Hepatocytes and Cardiomyocytes Abolishes apoB Secretion and Increases Cell Stress. Cell Rep 2018; 19:1456-1466. [PMID: 28514664 DOI: 10.1016/j.celrep.2017.04.064] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Revised: 02/22/2017] [Accepted: 04/21/2017] [Indexed: 01/26/2023] Open
Abstract
Abetalipoproteinemia (ABL) is an inherited disorder of lipoprotein metabolism resulting from mutations in microsomal triglyceride transfer protein (MTTP). In addition to expression in the liver and intestine, MTTP is expressed in cardiomyocytes, and cardiomyopathy has been reported in several ABL cases. Using induced pluripotent stem cells (iPSCs) generated from an ABL patient homozygous for a missense mutation (MTTPR46G), we show that human hepatocytes and cardiomyocytes exhibit defects associated with ABL disease, including loss of apolipoprotein B (apoB) secretion and intracellular accumulation of lipids. MTTPR46G iPSC-derived cardiomyocytes failed to secrete apoB, accumulated intracellular lipids, and displayed increased cell death, suggesting intrinsic defects in lipid metabolism due to loss of MTTP function. Importantly, these phenotypes were reversed after the correction of the MTTPR46G mutation by CRISPR/Cas9 gene editing. Together, these data reveal clear cellular defects in iPSC-derived hepatocytes and cardiomyocytes lacking MTTP activity, including a cardiomyocyte-specific regulated stress response to elevated lipids.
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Affiliation(s)
- Ying Liu
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Institute for Regenerative Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Donna M Conlon
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Xin Bi
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Katherine J Slovik
- Institute for Regenerative Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Jianting Shi
- Institute for Regenerative Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Hailey I Edelstein
- Institute for Regenerative Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - John S Millar
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Ali Javaheri
- Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Marina Cuchel
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Institute for Translational Medicine and Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Evanthia E Pashos
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Jahangir Iqbal
- Department of Cell Biology and Pediatrics, State University of New York Downstate Medicine Center, Brooklyn, NY 11203, USA
| | - M Mahmood Hussain
- Department of Cell Biology and Pediatrics, State University of New York Downstate Medicine Center, Brooklyn, NY 11203, USA
| | - Robert A Hegele
- Department of Medicine and Robarts Research Institute, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, N6A 5C1, Canada
| | - Wenli Yang
- Institute for Regenerative Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Stephen A Duncan
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC 29425, USA
| | - Daniel J Rader
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | - Edward E Morrisey
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Institute for Regenerative Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
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Ha JS, Theriault A, Bhagavan NV, Ha CE. Fatty acids bound to human serum albumin and its structural variants modulate apolipoprotein B secretion in HepG2 cells. Biochim Biophys Acta Mol Cell Biol Lipids 2006; 1761:717-24. [PMID: 16843720 DOI: 10.1016/j.bbalip.2006.05.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2005] [Revised: 05/04/2006] [Accepted: 05/31/2006] [Indexed: 11/26/2022]
Abstract
Epidemiologic studies have shown an inverse relationship between human serum albumin (HSA) levels and coronary heart disease (CHD). However, no mechanisms have been identified to explain this relationship. We hypothesized that this relationship is due to differences in binding affinity of fatty acids to HSA and subsequent atherogenic lipoprotein synthesis and secretion from hepatocytes. To test our hypothesis we undertook the current study. Using HepG2 cells, we demonstrated that oleic acid (OA) bound to HSA in a molar ratio of 4:1 and after incubation for 24 h stimulated apolipoprotein B (apoB) secretion. We also tested whether mutant forms of HSA could alter the binding affinity for fatty acids and change the availability of substrate for lipoprotein secretion. Based on the results obtained in this study using 11 HSA mutant proteins complexed with OA, we were able to classify into three major mutant groups based on their effects on apoB secretion. One group in particular (R410Q/Y411W, R410A/Y411A, and W214L/Y411W) showed a significantly diminished effect on apoB secretion when compared to the wild type HSA/OA complex. Furthermore, the amount of free OA internalized in HepG2 cells in the presence of HSA mutant proteins was in good agreement with the effects seen on apoB secretion by the various HSA mutants. This suggests that some mutant forms of HSA might potentially bind fatty acids with a much higher binding affinity and thus deprive fatty acids available for lipoprotein assembly in hepatocytes. In conclusion, our data illustrate that certain HSA polymorphic forms may be protective against the development of CHD and warrants further investigation.
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Affiliation(s)
- Ji-Sook Ha
- Department of Anatomy, Biochemistry, and Physiology, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, HI 96822, USA
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Gusarova V, Caplan AJ, Brodsky JL, Fisher EA. Apoprotein B degradation is promoted by the molecular chaperones hsp90 and hsp70. J Biol Chem 2001; 276:24891-900. [PMID: 11333259 DOI: 10.1074/jbc.m100633200] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Apoprotein B (apoB) is the major protein of liver-derived atherogenic lipoproteins. The net production of apoB can be regulated by presecretory degradation mediated by the ubiquitin-proteasome pathway and cytosolic hsp70. To further explore the mechanisms of apoB degradation, we have established a cell-free system in which degradation can be faithfully recapitulated. Human apoB48 synthesized in vitro was translocated into microsomes, glycosylated, and ubiquitinylated. Subsequent incubation with rat hepatic cytosol led to proteasome-mediated degradation. To explore whether hsp90 is required for apoB degradation, geldanamycin (GA) was added during the degradation assay. GA increased the recovery of microsomal apoB48 approximately 3-fold and disrupted the interaction between hsp90 and apoB48. Confirming the hsp90 effect in the cell-free system, we also found that transfection of hsp90 cDNA into rat hepatoma cells enhanced apoB48 degradation. Finally, apoB48 degradation was reconstituted in vitro using cytosol prepared from wild type yeast. Notably, degradation was attenuated when apoB48-containing microsomes were incubated with cytosol supplemented with GA or with cytosol prepared from yeast strains with mutations in the homologues of mammalian hsp70 and hsp90. Overall, our data suggest that hsp90 facilitates the interaction between endoplasmic reticulum-associated apoB and components of the proteasomal pathway, perhaps in cooperation with hsp70.
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Affiliation(s)
- V Gusarova
- Department of Medicine, Cardiovascular Institute, Mount Sinai School of Medicine, 1 Gustave Levy Place, New York, NY 10029, USA
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Burch WL, Herscovitz H. Disulfide bonds are required for folding and secretion of apolipoprotein B regardless of its lipidation state. J Biol Chem 2000; 275:16267-74. [PMID: 10747912 DOI: 10.1074/jbc.m000446200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apolipoprotein (apo) B-100, an essential protein for the assembly and secretion of very low density lipoproteins depends on lipid binding (lipidation) for its secretion. Seven of its 8 disulfides are clustered within the N-terminal 21%. The role of these disulfides in the secretion of lipidated or unlipidated truncated forms of apoB was studied in C127 cells expressing apoB-17, apoB-29, or apoB-41. These cells do not express microsomal triglyceride transfer protein yet secrete apoB-41 on triacylglycerol-rich lipoproteins while apoB-29 and apoB-17 are secreted with little or no lipid, respectively. Dithiothreitol utilized in pulse-chase studies prevented the cotranslational formation of disulfides and when added posttranslationally reduced native disulfides. As a result, the secretion of reduced apoB forms was blocked and they were retained in the cells. Reduced apoB polypeptides were rescued following removal of dithiothreitol, as they underwent post-translational disulfide bonding, attained their mature form, and were subsequently secreted. Together the data suggest that in C127 cells the formation of native disulfides is critical for the folding and secretion of apoB independent of its length, its requirement for lipidation or microsomal triglyceride transfer protein expression. Therefore, these cells provide an appropriate model to study the folding of apoB in great detail.
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Affiliation(s)
- W L Burch
- Department of Biophysics, Center for Advanced Biomedical Research, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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Sakata N, Stoops JD, Dixon JL. Cytosolic components are required for proteasomal degradation of newly synthesized apolipoprotein B in permeabilized HepG2 cells. J Biol Chem 1999; 274:17068-74. [PMID: 10358059 DOI: 10.1074/jbc.274.24.17068] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recent studies have proposed that post-translational degradation of apolipoprotein B100 (apoB) involves the cytosolic ubiquitin-proteasome pathway. In this study, immunocytochemistry indicated that endoplasmic reticulum (ER)-associated proteasome molecules were concentrated in perinuclear regions of digitonin-permeabilized HepG2 cells. Signals produced by antibodies that recognize both alpha- and beta-subunits of the proteasome co-localized in the ER with specific domains of apoB. The mechanism of apoB degradation in the ER by the ubiquitin-proteasome pathway was studied using pulse-chase labeling and digitonin-permeabilized cells. ApoB in permeabilized cells incubated at 37 degrees C in buffer alone was relatively stable. When permeabilized cells were incubated with both exogenous ATP and rabbit reticulocyte lysate (RRL) as a source of ubiquitin-proteasome factors, >50% of [3H]apoB was degraded in 30 min. The degradation of apoB in the intact ER of permeabilized cells was much more rapid than that of extracted [3H]apoB incubated with RRL and ATP in vitro. The degradation of apoB was reduced by clasto-lactacystin beta-lactone, a potent proteasome inhibitor, and by ubiquitin K48R mutant protein, an inhibitor of polyubiquitination. ApoB in HepG2 cells was ubiquitinated, and polyubiquitination of apoB was stimulated by incubation of permeabilized cells with RRL. These results suggest that newly synthesized apoB in the ER is accessible to the cytoplasmic ubiquitin-proteasome pathway and that factors in RRL stimulate polyubiquitination of apoB, leading to rapid degradation of apoB in permeabilized cells.
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Affiliation(s)
- N Sakata
- Department of Food Science and Human Nutrition, University of Missouri, Columbia, Missouri 65211, USA
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