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Sun C, Holstein DJF, Garcia-Cubero N, Moulla Y, Stroh C, Dietrich A, Schön MR, Gärtner D, Lohmann T, Dressler M, Stumvoll M, Blüher M, Kovacs P, Guiu-Jurado E. The Role of Phosphatidylethanolamine N-Methyltransferase ( PEMT) and Its Waist-Hip-Ratio-Associated Locus rs4646404 in Obesity-Related Metabolic Traits and Liver Disease. Int J Mol Sci 2023; 24:16850. [PMID: 38069170 PMCID: PMC10706059 DOI: 10.3390/ijms242316850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Revised: 11/21/2023] [Accepted: 11/24/2023] [Indexed: 12/18/2023] Open
Abstract
In previous genome-wide association studies (GWAS), genetic loci associated with obesity and impaired fat distribution (FD) have been identified. In the present study, we elucidated the role of the PEMT gene, including the waist-hip-ratio-associated single nucleotide polymorphism rs4646404, and its influence on obesity-related metabolic traits. DNA from 2926 metabolically well-characterized subjects was used for genotyping. PEMT expression was analyzed in paired visceral (vis) and subcutaneous (sc) adipose tissue (AT) from a subset of 574 individuals. Additionally, PEMT expression was examined in vis, sc AT and liver tissue in a separate cohort of 64 patients with morbid obesity and liver disease. An in vitro Pemt knockdown was conducted in murine epididymal and inguinal adipocytes. Our findings highlight tissue-specific variations in PEMT mRNA expression across the three studied tissues. Specifically, vis PEMT mRNA levels correlated significantly with T2D and were implicated in the progression of non-alcoholic steatohepatitis (NASH), in contrast to liver tissue, where no significant associations were found. Moreover, sc PEMT expression showed significant correlations with several anthropometric- and metabolic-related parameters. The rs4646404 was associated with vis AT PEMT expression and also with diabetes-related traits. Our in vitro experiments supported the influence of PEMT on adipogenesis, emphasizing its role in AT biology. In summary, our data suggest that PEMT plays a role in regulating FD and has implications in metabolic diseases.
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Affiliation(s)
- Chang Sun
- Medical Department III—Endocrinology, Nephrology, Rheumatology, University of Leipzig Medical Center, 04103 Leipzig, Germany
| | - David J. F. Holstein
- Medical Department III—Endocrinology, Nephrology, Rheumatology, University of Leipzig Medical Center, 04103 Leipzig, Germany
| | - Natalia Garcia-Cubero
- Medical Department III—Endocrinology, Nephrology, Rheumatology, University of Leipzig Medical Center, 04103 Leipzig, Germany
| | - Yusef Moulla
- Clinic for Visceral, Transplantation and Thorax and Vascular Surgery, University Hospital Leipzig, 04103 Leipzig, Germany
| | - Christine Stroh
- Department of General, Abdominal and Pediatric Surgery, Municipal Hospital, 07548 Gera, Germany
| | - Arne Dietrich
- Clinic for Visceral, Transplantation and Thorax and Vascular Surgery, University Hospital Leipzig, 04103 Leipzig, Germany
| | - Michael R. Schön
- Städtisches Klinikum Karlsruhe, Clinic of Visceral Surgery, 76133 Karlsruhe, Germany
| | - Daniel Gärtner
- Städtisches Klinikum Karlsruhe, Clinic of Visceral Surgery, 76133 Karlsruhe, Germany
| | - Tobias Lohmann
- Municipal Clinic Dresden-Neustadt, 01129 Dresden, Germany
| | | | - Michael Stumvoll
- Medical Department III—Endocrinology, Nephrology, Rheumatology, University of Leipzig Medical Center, 04103 Leipzig, Germany
- Helmholtz Institute for Metabolic, Obesity and Vascular Research (HI-MAG) of the Helmholtz Zentrum München at the University of Leipzig and University Hospital Leipzig, 04103 Leipzig, Germany
| | - Matthias Blüher
- Medical Department III—Endocrinology, Nephrology, Rheumatology, University of Leipzig Medical Center, 04103 Leipzig, Germany
- Helmholtz Institute for Metabolic, Obesity and Vascular Research (HI-MAG) of the Helmholtz Zentrum München at the University of Leipzig and University Hospital Leipzig, 04103 Leipzig, Germany
| | - Peter Kovacs
- Medical Department III—Endocrinology, Nephrology, Rheumatology, University of Leipzig Medical Center, 04103 Leipzig, Germany
| | - Esther Guiu-Jurado
- Medical Department III—Endocrinology, Nephrology, Rheumatology, University of Leipzig Medical Center, 04103 Leipzig, Germany
- Deutsches Zentrum für Diabetesforschung e.V., 85764 Neuherberg, Germany
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Simon C, Asaro A, Feng S, Riezman H. An organelle-specific photoactivation and dual-isotope labeling strategy reveals phosphatidylethanolamine metabolic flux. Chem Sci 2023; 14:1687-1695. [PMID: 36819876 PMCID: PMC9930920 DOI: 10.1039/d2sc06069h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Accepted: 01/15/2023] [Indexed: 01/18/2023] Open
Abstract
Phosphatidylethanolamine metabolism plays essential roles in eukaryotic cells but has not been completely investigated due to its complexity. This is because lipid species, unlike proteins or nucleic acids, cannot be easily manipulated at the single molecule level or controlled with subcellular resolution, two of the key factors toward understanding their functions. Here, we use the organelle-targeting photoactivation method to study PE metabolism in living cells with a high spatiotemporal resolution. Containing predefined PE structures, probes which can be selectively introduced into the ER or mitochondria were designed to compare their metabolic products according to their subcellular localization. We combined photo-uncaging with dual stable isotopic labeling to track PE metabolism in living cells by mass spectrometry analysis. Our results reveal that both mitochondria- and ER-released PE participate in phospholipid remodeling, and that PE methylation can be detected only under particular conditions. Thus, our method provides a framework to study phospholipid metabolism at subcellular resolution.
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Affiliation(s)
- Clémence Simon
- Department of Biochemistry, NCCR Chemical Biology, University of Geneva Geneva 1205 Switzerland
| | - Antonino Asaro
- Department of Biochemistry, NCCR Chemical Biology, University of Geneva Geneva 1205 Switzerland
| | - Suihan Feng
- Unit of Chemical Biology and Lipid Metabolism, Center for Microbes, Development and Health (CMDH), Institut Pasteur of Shanghai, Chinese Academy of SciencesShanghai200031China
| | - Howard Riezman
- Department of Biochemistry, NCCR Chemical Biology, University of Geneva Geneva 1205 Switzerland
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3
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Morita SY, Ikeda Y. Regulation of membrane phospholipid biosynthesis in mammalian cells. Biochem Pharmacol 2022; 206:115296. [DOI: 10.1016/j.bcp.2022.115296] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Revised: 10/05/2022] [Accepted: 10/05/2022] [Indexed: 11/02/2022]
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4
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Li J, Xin Y, Li J, Chen H, Li H. Phosphatidylethanolamine N-methyltransferase: from Functions to Diseases. Aging Dis 2022; 14:879-891. [PMID: 37191416 DOI: 10.14336/ad.2022.1025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Accepted: 10/25/2022] [Indexed: 11/18/2022] Open
Abstract
Locating on endoplasmic reticulum and mitochondria associated membrane, Phosphatidylethanolamine N-methyltransferase (PEMT), catalyzes phosphatidylethanolamine methylation to phosphatidylcholine. As the only endogenous pathway for choline biosynthesis in mammals, the dysregulation of PEMT can lead to imbalance of phospholipid metabolism. Dysregulation of phospholipid metabolism in the liver or heart can lead to deposition of toxic lipid species that adversely result in dysfunction of hepatocyte/cardiomyocyte. Studies have shown that PEMT-/- mice increased susceptibility of diet-induced fatty liver and steatohepatitis. However, knockout of PEMT protects against diet-induced atherosclerosis, diet-induced obesity, and insulin resistance. Thus, novel insights to the function of PEMT in various organs should be summarized. Here, we reviewed the structural and functional properties of PEMT, highlighting its role in the pathogenesis of obesity, liver diseases, cardiovascular diseases, and other conditions.
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Zacharia A, Saidemberg D, Mannully CT, Kogan NM, Shehadeh A, Sinai R, Zucker A, Bruck-Haimson R, Goldstein N, Haim Y, Dani C, Rudich A, Moussaieff A. Distinct infrastructure of lipid networks in visceral and subcutaneous adipose tissues in overweight humans. Am J Clin Nutr 2020; 112:979-990. [PMID: 32766878 PMCID: PMC7528551 DOI: 10.1093/ajcn/nqaa195] [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: 12/10/2019] [Accepted: 06/24/2020] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND Adipose tissue plays important roles in health and disease. Given the unique association of visceral adipose tissue with obesity-related metabolic diseases, the distribution of lipids between the major fat depots located in subcutaneous and visceral regions may shed new light on adipose tissue-specific roles in systemic metabolic perturbations. OBJECTIVE We sought to characterize the lipid networks and unveil differences in the metabolic infrastructure of the 2 adipose tissues that may have functional and nutritional implications. METHODS Paired visceral and subcutaneous adipose tissue samples were obtained from 17 overweight patients undergoing elective abdominal surgery. Ultra-performance LC-MS was used to measure 18,640 adipose-derived features; 520 were putatively identified. A stem cell model for adipogenesis was used to study the functional implications of the differences found. RESULTS Our analyses resulted in detailed lipid metabolic maps of the 2 major adipose tissues. They point to a higher accumulation of phosphatidylcholines, triacylglycerols, and diacylglycerols, although lower ceramide concentrations, in subcutaneous tissue. The degree of unsaturation was lower in visceral adipose tissue (VAT) phospholipids, indicating lower unsaturated fatty acid incorporation into adipose tissue. The differential abundance of phosphatidylcholines we found can be attributed at least partially to higher expression of phosphatidylethanolamine methyl transferase (PEMT). PEMT-deficient embryonic stem cells showed a dramatic decrease in adipogenesis, and the resulting adipocytes exhibited lower accumulation of lipid droplets, in line with the lower concentrations of glycerolipids in VAT. Ceramides may inhibit the expression of PEMT by increased insulin resistance, thus potentially suggesting a functional pathway that integrates ceramide, PEMT, and glycerolipid biosynthetic pathways. CONCLUSIONS Our work unveils differential infrastructure of the lipid networks in visceral and subcutaneous adipose tissues and suggests an integrative pathway, with a discriminative flux between adipose tissues.
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Affiliation(s)
- Anish Zacharia
- The Institute for Drug Research, Hebrew University of Jerusalem, Jerusalem, Israel
| | - Daniel Saidemberg
- The Institute for Drug Research, Hebrew University of Jerusalem, Jerusalem, Israel
| | | | - Natalya M Kogan
- The Institute for Drug Research, Hebrew University of Jerusalem, Jerusalem, Israel
| | - Alaa Shehadeh
- The Institute for Drug Research, Hebrew University of Jerusalem, Jerusalem, Israel
| | - Reut Sinai
- The Institute for Drug Research, Hebrew University of Jerusalem, Jerusalem, Israel
| | - Avigail Zucker
- The Institute for Drug Research, Hebrew University of Jerusalem, Jerusalem, Israel
| | - Reut Bruck-Haimson
- The Institute for Drug Research, Hebrew University of Jerusalem, Jerusalem, Israel
| | - Nir Goldstein
- Department of Clinical Biochemistry and Pharmacology and The National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Yulia Haim
- Department of Clinical Biochemistry and Pharmacology and The National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Christian Dani
- University Côte d'Azur, CNRS, INSERM, iBV, Faculté de Medicine, Nice, France
| | - Assaf Rudich
- Department of Clinical Biochemistry and Pharmacology and The National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva, Israel
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Pajares MA, Pérez-Sala D. Mammalian Sulfur Amino Acid Metabolism: A Nexus Between Redox Regulation, Nutrition, Epigenetics, and Detoxification. Antioxid Redox Signal 2018; 29:408-452. [PMID: 29186975 DOI: 10.1089/ars.2017.7237] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
SIGNIFICANCE Transsulfuration allows conversion of methionine into cysteine using homocysteine (Hcy) as an intermediate. This pathway produces S-adenosylmethionine (AdoMet), a key metabolite for cell function, and provides 50% of the cysteine needed for hepatic glutathione synthesis. The route requires the intake of essential nutrients (e.g., methionine and vitamins) and is regulated by their availability. Transsulfuration presents multiple interconnections with epigenetics, adenosine triphosphate (ATP), and glutathione synthesis, polyol and pentose phosphate pathways, and detoxification that rely mostly in the exchange of substrates or products. Major hepatic diseases, rare diseases, and sensorineural disorders, among others that concur with oxidative stress, present impaired transsulfuration. Recent Advances: In contrast to the classical view, a nuclear branch of the pathway, potentiated under oxidative stress, is emerging. Several transsulfuration proteins regulate gene expression, suggesting moonlighting activities. In addition, abnormalities in Hcy metabolism link nutrition and hearing loss. CRITICAL ISSUES Knowledge about the crossregulation between pathways is mostly limited to the hepatic availability/removal of substrates and inhibitors. However, advances regarding protein-protein interactions involving oncogenes, identification of several post-translational modifications (PTMs), and putative moonlighting activities expand the potential impact of transsulfuration beyond methylations and Hcy. FUTURE DIRECTIONS Increasing the knowledge on transsulfuration outside the liver, understanding the protein-protein interaction networks involving these enzymes, the functional role of their PTMs, or the mechanisms controlling their nucleocytoplasmic shuttling may provide further insights into the pathophysiological implications of this pathway, allowing design of new therapeutic interventions. Antioxid. Redox Signal. 29, 408-452.
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Affiliation(s)
- María A Pajares
- 1 Department of Chemical and Physical Biology, Centro de Investigaciones Biológicas (CSIC) , Madrid, Spain .,2 Molecular Hepatology Group, Instituto de Investigación Sanitaria La Paz (IdiPAZ) , Madrid, Spain
| | - Dolores Pérez-Sala
- 1 Department of Chemical and Physical Biology, Centro de Investigaciones Biológicas (CSIC) , Madrid, Spain
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7
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Ishii T, Miyauchi K, Nitta Y, Kaneko K, Maruyama T, Sato T. Mechanism for Decreased Gene Expression of β4-Galactosyltransferase 5 upon Differentiation of 3T3-L1 Mouse Preadipocytes to Adipocytes. Biol Pharm Bull 2018; 41:1463-1470. [PMID: 29984736 DOI: 10.1248/bpb.b18-00360] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Upon differentiation of cells, remarkable changes in the structures of glycans linked to lipids on cell surface have been observed. Lactosylceramide (Lac-Cer) serves as a common precursor for a series of glycosphingolipids with diverse structures. In the present study, we examined the underlying mechanism for the biosynthesis of Lac-Cer upon differentiation of 3T3-L1 mouse preadipocytes to adipocytes. TLC analysis showed that the amounts of Lac-Cer decrease in 3T3-L1 adipocytes compared to 3T3-L1 preadipocytes. In accordance with this change, the gene expression level of β4-galactosyltransferase (β4GalT) 5, which was identified as Lac-Cer synthase, decreased drastically upon differentiation of 3T3-L1 preadipocytes. The analysis of the transcriptional mechanism of the β4GalT5 gene demonstrated that the core promoter region is identified between nucleotides -299 and -1 relative to the translational start site. During adipocyte differentiation, the expression levels and promoter activities of the β4GalT5 gene decreased dramatically. Since the Specificity protein 1 (Sp1)-binding sites in the promoter region were critical for the promoter activity, it is suggested that Sp1 plays an important role for the expression of the β4GalT5 gene in 3T3-L1 cells. The gene and protein expression of Sp1 decreased significantly upon differentiation of 3T3-L1 preadipocytes. Taken together, the present study suggest that the expression of the β4GalT5 gene decreases through reduced expression of the Sp1 gene and protein upon differentiation of 3T3-L1 peradipocytes to adipocytes, which may lead to the decreased amounts of Lac-Cer in 3T3-L1 adipocytes.
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Affiliation(s)
- Takayuki Ishii
- Laboratory of Glycobiology, Department of Bioengineering, Nagaoka University of Technology
| | - Kana Miyauchi
- Laboratory of Glycobiology, Department of Bioengineering, Nagaoka University of Technology
| | - Yoshiharu Nitta
- Laboratory of Glycobiology, Department of Bioengineering, Nagaoka University of Technology
| | - Kazuhiro Kaneko
- Laboratory of Glycobiology, Department of Bioengineering, Nagaoka University of Technology
| | - Takuro Maruyama
- Laboratory of Glycobiology, Department of Bioengineering, Nagaoka University of Technology
| | - Takeshi Sato
- Laboratory of Glycobiology, Department of Bioengineering, Nagaoka University of Technology
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8
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van der Veen JN, Kennelly JP, Wan S, Vance JE, Vance DE, Jacobs RL. The critical role of phosphatidylcholine and phosphatidylethanolamine metabolism in health and disease. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:1558-1572. [PMID: 28411170 DOI: 10.1016/j.bbamem.2017.04.006] [Citation(s) in RCA: 893] [Impact Index Per Article: 127.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 03/27/2017] [Accepted: 04/09/2017] [Indexed: 12/11/2022]
Abstract
Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are the most abundant phospholipids in all mammalian cell membranes. In the 1950s, Eugene Kennedy and co-workers performed groundbreaking research that established the general outline of many of the pathways of phospholipid biosynthesis. In recent years, the importance of phospholipid metabolism in regulating lipid, lipoprotein and whole-body energy metabolism has been demonstrated in numerous dietary studies and knockout animal models. The purpose of this review is to highlight the unappreciated impact of phospholipid metabolism on health and disease. Abnormally high, and abnormally low, cellular PC/PE molar ratios in various tissues can influence energy metabolism and have been linked to disease progression. For example, inhibition of hepatic PC synthesis impairs very low density lipoprotein secretion and changes in hepatic phospholipid composition have been linked to fatty liver disease and impaired liver regeneration after surgery. The relative abundance of PC and PE regulates the size and dynamics of lipid droplets. In mitochondria, changes in the PC/PE molar ratio affect energy production. We highlight data showing that changes in the PC and/or PE content of various tissues are implicated in metabolic disorders such as atherosclerosis, insulin resistance and obesity. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.
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Affiliation(s)
- Jelske N van der Veen
- Group on the Molecular and Cell Biology of Lipids, Canada; Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2S2, Canada
| | - John P Kennelly
- Group on the Molecular and Cell Biology of Lipids, Canada; Department of Agricultural, Food and Nutritional Science, 4-002 Li Ka Shing Centre for Heath Research Innovations, University of Alberta, Edmonton, AB T6G 2E1, Canada
| | - Sereana Wan
- Group on the Molecular and Cell Biology of Lipids, Canada; Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2S2, Canada
| | - Jean E Vance
- Group on the Molecular and Cell Biology of Lipids, Canada; Department of Medicine, University of Alberta, Edmonton, AB T6G 2S2, Canada
| | - Dennis E Vance
- Group on the Molecular and Cell Biology of Lipids, Canada; Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2S2, Canada
| | - René L Jacobs
- Group on the Molecular and Cell Biology of Lipids, Canada; Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2S2, Canada; Department of Agricultural, Food and Nutritional Science, 4-002 Li Ka Shing Centre for Heath Research Innovations, University of Alberta, Edmonton, AB T6G 2E1, Canada.
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9
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Jacobs RL, Jiang H, Kennelly JP, Orlicky DJ, Allen RH, Stabler SP, Maclean KN. Cystathionine beta-synthase deficiency alters hepatic phospholipid and choline metabolism: Post-translational repression of phosphatidylethanolamine N-methyltransferase is a consequence rather than a cause of liver injury in homocystinuria. Mol Genet Metab 2017; 120:325-336. [PMID: 28291718 DOI: 10.1016/j.ymgme.2017.02.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Accepted: 02/28/2017] [Indexed: 12/27/2022]
Abstract
Classical homocystinuria (HCU) due to inactivating mutation of cystathionine β-synthase (CBS) is a poorly understood life-threatening inborn error of sulfur metabolism. A previously described cbs-/- mouse model exhibits a semi-lethal phenotype due to neonatal liver failure. The transgenic HO mouse model of HCU exhibits only mild liver injury and recapitulates multiple aspects of the disease as it occurs in humans. Disruption of the methionine cycle in HCU has the potential to impact multiple aspect of phospholipid (PL) metabolism by disruption of both the Kennedy pathway and phosphatidylethanolamine N-methyltransferase (PEMT) mediated synthesis of phosphatidylcholine (PC). Comparative metabolomic analysis of HO mouse liver revealed decreased levels of choline, and choline phosphate indicating disruption of the Kennedy pathway. Alterations in the relative levels of multiple species of PL included significant increases in PL degradation products consistent with enhanced membrane PL turnover. A significant decrease in PC containing 20:4n6 which primarily formed by the methylation of phosphatidylethanolamine to PC was consistent with decreased flux through PEMT. Hepatic expression of PEMT in both the cbs-/- and HO models is post-translationally repressed with decreased levels of PEMT protein and activity that inversely-correlates with the scale of liver injury. Failure to induce further repression of PEMT in HO mice by increased homocysteine, methionine and S-adenosylhomocysteine or depletion of glutathione combined with examination of multiple homocysteine-independent models of liver injury indicated that repression of PEMT in HCU is a consequence rather than a cause of liver injury. Collectively, our data show significant alteration of a broad range of hepatic PL and choline metabolism in HCU with the potential to contribute to multiple aspects of pathogenesis in this disease.
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Affiliation(s)
- René L Jacobs
- Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta T6G2E1, Canada; Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G2E1, Canada
| | - Hua Jiang
- Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - John P Kennelly
- Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta T6G2E1, Canada; Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G2E1, Canada
| | - David J Orlicky
- Department of Pathology, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Robert H Allen
- Department of Medicine, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Sally P Stabler
- Department of Medicine, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Kenneth N Maclean
- Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045, USA.
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van der Veen JN, Lingrell S, Gao X, Quiroga AD, Takawale A, Armstrong EA, Yager JY, Kassiri Z, Lehner R, Vance DE, Jacobs RL. Pioglitazone attenuates hepatic inflammation and fibrosis in phosphatidylethanolamine N-methyltransferase-deficient mice. Am J Physiol Gastrointest Liver Physiol 2016; 310:G526-38. [PMID: 26797396 DOI: 10.1152/ajpgi.00243.2015] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Accepted: 12/21/2015] [Indexed: 01/31/2023]
Abstract
Phosphatidylethanolamine N-methyltransferase (PEMT) is an important enzyme in hepatic phosphatidylcholine (PC) biosynthesis. Pemt(-/-) mice are protected against high-fat diet (HFD)-induced obesity and insulin resistance; however, these mice develop nonalcoholic fatty liver disease (NAFLD). We hypothesized that peroxisomal proliferator-activated receptor-γ (PPARγ) activation by pioglitazone might stimulate adipocyte proliferation, thereby directing lipids from the liver toward white adipose tissue. Pioglitazone might also act directly on PPARγ in the liver to improve NAFLD. Pemt(+/+) and Pemt(-/-) mice were fed a HFD with or without pioglitazone (20 mg·kg(-1)·day(-1)) for 10 wk. Pemt(-/-) mice were protected from HFD-induced obesity but developed NAFLD. Treatment with pioglitazone caused an increase in body weight gain in Pemt(-/-) mice that was mainly due to increased adiposity. Moreover, pioglitazone improved NAFLD in Pemt(-/-) mice, as indicated by a 35% reduction in liver weight and a 57% decrease in plasma alanine transaminase levels. Livers from HFD-fed Pemt(-/-) mice were steatotic, inflamed, and fibrotic. Hepatic steatosis was still evident in pioglitazone-treated Pemt(-/-) mice; however, treatment with pioglitazone reduced hepatic fibrosis, as evidenced by reduced Sirius red staining and lowered mRNA levels of collagen type Iα1 (Col1a1), tissue inhibitor of metalloproteinases 1 (Timp1), α-smooth muscle actin (Acta2), and transforming growth factor-β (Tgf-β). Similarly, oxidative stress and inflammation were reduced in livers from Pemt(-/-) mice upon treatment with pioglitazone. Together, these data show that activation of PPARγ in HFD-fed Pemt(-/-) mice improved liver function, while these mice were still protected against diet-induced obesity and insulin resistance.
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Affiliation(s)
- Jelske N van der Veen
- Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada; Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Susanne Lingrell
- Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada; Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Xia Gao
- Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada; Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Ariel D Quiroga
- Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada; Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - Abhijit Takawale
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada; and
| | - Edward A Armstrong
- Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - Jerome Y Yager
- Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - Zamaneh Kassiri
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada; and
| | - Richard Lehner
- Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada; Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - Dennis E Vance
- Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada; Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - René L Jacobs
- Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada; Department of Agricultural, Food, and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada
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11
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Lack of phosphatidylethanolamine N -methyltransferase in mice does not promote fatty acid oxidation in skeletal muscle. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1861:119-129. [DOI: 10.1016/j.bbalip.2015.11.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Revised: 10/08/2015] [Accepted: 11/16/2015] [Indexed: 01/01/2023]
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12
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Gao X, van der Veen JN, Hermansson M, Ordoñez M, Gomez-Muñoz A, Vance DE, Jacobs RL. Decreased lipogenesis in white adipose tissue contributes to the resistance to high fat diet-induced obesity in phosphatidylethanolamine N-methyltransferase-deficient mice. Biochim Biophys Acta Mol Cell Biol Lipids 2015; 1851:152-62. [DOI: 10.1016/j.bbalip.2014.11.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Revised: 10/21/2014] [Accepted: 11/10/2014] [Indexed: 10/24/2022]
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13
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Fang Q, Yang W, Li H, Hu W, Chen L, Jiang S, Dong K, Song Q, Wang C, Chen S, Liu F, Jia W. Negative regulation of DsbA-L gene expression by the transcription factor Sp1. Diabetes 2014; 63:4165-71. [PMID: 25024375 PMCID: PMC4237990 DOI: 10.2337/db14-0182] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Disulfide-bond A oxidoreductase-like protein (DsbA-L) possesses beneficial effects such as promoting adiponectin multimerization and stability, increasing insulin sensitivity, and enhancing energy metabolism. The expression level of DsbA-L is negatively correlated with obesity in mice and humans, but the underlying mechanisms remain unknown. To address this question, we generated reporter gene constructs containing the promoter sequence of the mouse DsbA-L gene. Deletion analysis showed that the proximal promoter of mouse DsbA-L is located between -186 and -34 bp relative to the transcription start site. In silico analysis identified a putative Sp1 transcription factor binding site in the first intron of the DsbA-L gene. Electrophoretic mobility shift assay and chromatin immunoprecipitation analysis indicated that Sp1 bound to this intron region in vitro and in intact cells. Overexpression of Sp1 or suppressing Sp1 expression by siRNA reduced or increased DsbA-L promoter activity, respectively. The binding activity of Sp1 was gradually decreased during 3T3-L1 cell differentiation and was significantly increased in adipose tissues of obese mice. Our results identify Sp1 as an inhibitor of DsbA-L gene transcription, and the Sp1-mediated inhibition of DsbA-L gene expression may provide a mechanism underlying obesity-induced adiponectin downregulation and insulin resistance.
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Affiliation(s)
- Qichen Fang
- Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai, China
| | - Wenjing Yang
- Department of Medicine, Medical School of Soochow University, Suzhou, China
| | - Huating Li
- Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai, China
| | - Wenxiu Hu
- Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai, China
| | - Lihui Chen
- Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, Second Xiangya Hospital, Central South University, Changsha, China
| | - Shan Jiang
- Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai, China
| | - Kun Dong
- Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai, China
| | - Qianqian Song
- Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai, China
| | - Chen Wang
- Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai, China
| | - Shuo Chen
- Department of Developmental Dentistry, University of Texas Health Science Center at San Antonio, San Antonio, TX
| | - Feng Liu
- Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, Second Xiangya Hospital, Central South University, Changsha, China Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, TX
| | - Weiping Jia
- Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai, China
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14
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Vance DE. Phospholipid methylation in mammals: from biochemistry to physiological function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:1477-87. [PMID: 24184426 DOI: 10.1016/j.bbamem.2013.10.018] [Citation(s) in RCA: 116] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 10/18/2013] [Accepted: 10/19/2013] [Indexed: 11/29/2022]
Abstract
Phosphatidylcholine is made in the liver via the CDP-choline pathway and via the conversion of phosphatidylethanolamine to phosphatidylcholine by 3 transmethylation reactions from AdoMet catalyzed by phosphatidylethanolamine N-methyltransferase (PEMT). PEMT is a 22.3kDa integral transmembrane protein of the endoplasmic reticulum and mitochondria-associated membranes. The only tissue with quantitatively significant PEMT activity is liver; however, low levels of PEMT in adipocytes have been implicated in lipid droplet formation. PEMT activity is regulated by the concentration of substrates (phosphatidylethanolamine and AdoMet) as well as the ratio of AdoMet to AdoHcy. Transcription of PEMT is enhanced by estrogen whereas the transcription factor Sp1 is a negative regulator of PEMT transcription. Studies with mice that lack PEMT have provided novel insights into the function of this enzyme. PEMT activity is required to maintain hepatic membrane integrity and for the formation of choline when dietary choline supply is limited. PEMT is required for normal secretion of very low-density lipoproteins. The lack of PEMT protects against diet-induced atherosclerosis in two mouse models. Most unexpectedly, mice that lack PEMT are protected from diet-induced obesity and insulin resistance. Moreover, mice lacking PEMT have increased susceptibility to diet-induced fatty liver and steatohepatitis. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.
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Affiliation(s)
- Dennis E Vance
- Group on the Molecular and Cell Biology of Lipids, Department of Biochemistry, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada; Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada.
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15
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Lagace TA, Ridgway ND. The role of phospholipids in the biological activity and structure of the endoplasmic reticulum. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:2499-510. [PMID: 23711956 DOI: 10.1016/j.bbamcr.2013.05.018] [Citation(s) in RCA: 153] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Revised: 05/09/2013] [Accepted: 05/15/2013] [Indexed: 01/22/2023]
Abstract
The endoplasmic reticulum (ER) is an interconnected network of tubular and planar membranes that supports the synthesis and export of proteins, carbohydrates and lipids. Phospholipids, in particular phosphatidylcholine (PC), are synthesized in the ER where they have essential functions including provision of membranes required for protein synthesis and export, cholesterol homeostasis, and triacylglycerol storage and secretion. Coordination of these biological processes is essential, as highlighted by findings that link phospholipid metabolism in the ER with perturbations in lipid storage/secretion and stress responses, ultimately contributing to obesity/diabetes, atherosclerosis and neurological disorders. Phospholipid synthesis is not uniformly distributed in the ER but is localized at membrane interfaces or contact zones with other organelles, and in dynamic, proliferating ER membranes. The topology of phospholipid synthesis is an important consideration when establishing the etiology of diseases that arise from ER dysfunction. This review will highlight our current understanding of the contribution of phospholipid synthesis to proper ER function, and how alterations contribute to aberrant stress responses and disease. This article is part of a Special Issue entitled: Functional and structural diversity of endoplasmic reticulum.
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Affiliation(s)
- Thomas A Lagace
- University of Ottawa Heart Institute, Ottawa, Ontario, Canada.
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16
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Xiong J, Che X, Li X, Yu H, Gong Z, Li W. Cloning and characterization of the human USP22 gene promoter. PLoS One 2012; 7:e52716. [PMID: 23300749 PMCID: PMC3530469 DOI: 10.1371/journal.pone.0052716] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2012] [Accepted: 11/20/2012] [Indexed: 12/23/2022] Open
Abstract
Ubiquitin-specific processing enzyme 22 (USP22) plays a direct role in regulating cell cycle, and its overexpression has been reported to be involved in tumor progression. However, little is known about the regulation of USP22 transcription. In this study, we cloned and characterized the human USP22 promoter. Using 5' RACE (rapid amplification of cDNA ends) analysis, the transcriptional initiation site was identified. Promoter deletion analysis showed that the sequence between -210 and -7 contains the basal promoter for USP22 in human fibroblast and tumor cells. Surprisingly, mutations in a putative Sp1 binding site immediately upstream of the USP22 transcriptional start site (-13 to -7) resulted in a significant induction of promoter activity. Further study revealed that Sp1 binds to this site in human normal fibroblast cells, and treatment with the Sp1 inhibitor mithramycin A led to a marked increase in USP22 transcript levels. Forced expression of exogenous Sp1 repressed the USP22 promoter activity in HeLa cells. In contrast, knockdown of Sp1 enhanced USP22 promoter activity and mRNA levels. These data suggest that Sp1 is a crucial regulator of USP22 transcription.
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Affiliation(s)
- Jianjun Xiong
- College of Basic Medical Science, Jiujiang University, Jiujiang, China
- Key Laboratory of Jiangxi for the Systems Bio-medicine, Jiujiang, China
| | - Xiangxin Che
- College of Basic Medical Science, Jiujiang University, Jiujiang, China
- Key Laboratory of Jiangxi for the Systems Bio-medicine, Jiujiang, China
| | - Xueqin Li
- College of Basic Medical Science, Jiujiang University, Jiujiang, China
| | - Huan Yu
- College of Basic Medical Science, Jiujiang University, Jiujiang, China
| | - Zhen Gong
- College of Basic Medical Science, Jiujiang University, Jiujiang, China
| | - Weidong Li
- Key Laboratory of Jiangxi for the Systems Bio-medicine, Jiujiang, China
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17
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Vance DE. Physiological roles of phosphatidylethanolamine N-methyltransferase. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1831:626-32. [PMID: 22877991 DOI: 10.1016/j.bbalip.2012.07.017] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Revised: 07/20/2012] [Accepted: 07/23/2012] [Indexed: 01/12/2023]
Abstract
Phosphatidylethanolamine N-methyltransferase (PEMT) catalyzes the methylation of phosphatidylethanolamine to phosphatidylcholine (PC). This 22.3 kDa protein is localized to the endoplasmic reticulum and mitochondria associated membranes of liver. The supply of the substrates AdoMet and phosphatidylethanolamine, and the product AdoHcy, can regulate the activity of PEMT. Estrogen has been identified as a positive activator, and Sp1 as a negative regulator, of transcription of the PEMT gene. Targeted inactivation of the PEMT gene produced mice that had a mild phenotype when fed a chow diet. However, when Pemt(-/-) mice were fed a choline-deficient diet steatohepatitis and liver failure developed after 3 days. The steatohepatitis was due to a decreased ratio of PC to phosphatidylethanolamine that caused leakage from the plasma membrane of hepatocytes. Pemt(-/-) mice exhibited attenuated secretion of very low-density lipoproteins and homocysteine. Pemt(-/-) mice bred with mice that lacked the low-density lipoprotein receptor, or apolipoprotein E were protected from high fat/high cholesterol-induced atherosclerosis. Surprisingly, Pemt(-/-) mice were protected from high fat diet-induced obesity and insulin resistance compared to wildtype mice. If the diet were supplemented with additional choline, the protection against obesity/insulin resistance in Pemt(-/-) mice was eliminated. Humans with a Val-to-Met substitution in PEMT at residue 175 may have increased susceptibility to nonalcoholic liver disease. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.
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Affiliation(s)
- Dennis E Vance
- Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada.
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18
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Morita SY, Ikeda N, Horikami M, Soda K, Ishihara K, Teraoka R, Terada T, Kitagawa S. Effects of phosphatidylethanolamine N-methyltransferase on phospholipid composition, microvillus formation and bile salt resistance in LLC-PK1 cells. FEBS J 2011; 278:4768-81. [PMID: 21958070 DOI: 10.1111/j.1742-4658.2011.08377.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Bile salts are potent detergents and can disrupt cellular membranes, which causes cholestasis and hepatocellular injury. However, the mechanism for the resistance of the canalicular membrane against bile salts is not clear. Phosphatidylethanolamine (PE) is converted to phosphatidylcholine (PC) in the liver by phosphatidylethanolamine N-methyltransferase (PEMT). In this study, to investigate the effect of PEMT expression on the resistance to bile salts, we established an LLC-PK1 cell line stably expressing PEMT. By using enzymatic assays, we showed that the expression of PEMT increased the cellular PC content, lowered the PE content, but had no effect on the sphingomyelin content. Consequently, PEMT expression led to reductions in PE/PC and sphingomyelin/PC ratios. Mass spectrometry demonstrated that PEMT expression increased the levels of PC species containing longer acyl chains and almost all ether-linked PC species. PEMT expression enhanced the resistance to duramycin and lysenin, suggesting decreased ratios of PE and sphingomyelin in the apical membrane, respectively. In addition, SEM revealed that PEMT expression increased the diameter of microvilli. The expression of PEMT resulted in reduced resistance to unconjugated bile salts, but surprisingly in increased resistance to conjugated bile salts, which might be attributable to modifications of the phospholipid composition and/or structure in the apical membrane. Because most bile salts exist as conjugated forms in the bile canaliculi, PEMT may be important in the protection of hepatocytes from bile salts and in cholestatic liver injury.
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Affiliation(s)
- Shin-ya Morita
- Department of Pharmacy, Shiga University of Medical Science Hospital, Otsu City, Shiga, Japan.
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19
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Homocysteine as a risk factor for atherosclerosis: is its conversion to s-adenosyl-L-homocysteine the key to deregulated lipid metabolism? J Lipids 2011; 2011:702853. [PMID: 21837278 PMCID: PMC3151505 DOI: 10.1155/2011/702853] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Accepted: 06/04/2011] [Indexed: 11/17/2022] Open
Abstract
Homocysteine (Hcy) has been recognized for the past five decades as a risk factor for atherosclerosis. However, the role of Hcy in the pathological changes associated with atherosclerosis as well as the pathological mechanisms triggered by Hcy accumulation is
poorly understood. Due to the reversal of the physiological direction of the reaction catalyzed by S-adenosyl-L-homocysteine
hydrolase Hcy accumulation leads to the synthesis of S-adenosyl-L-homocysteine (AdoHcy). AdoHcy is a strong product
inhibitor of S-adenosyl-L-methionine (AdoMet)-dependent methyltransferases, and to date more than 50 AdoMet-dependent
methyltransferases that methylate a broad spectrum of cellular compounds including nucleic acids, proteins and lipids have been
identified. Phospholipid methylation is the major consumer of AdoMet, both in mammals and in yeast. AdoHcy accumulation induced
either by Hcy supplementation or due to S-adenosyl-L-homocysteine hydrolase deficiency results in inhibition of phospholipid
methylation in yeast. Moreover, yeast cells accumulating AdoHcy also massively accumulate triacylglycerols (TAG). Similarly, Hcy
supplementation was shown to lead to increased TAG and sterol synthesis as well as to the induction of the unfolded protein
response (UPR) in mammalian cells. In this review a model of deregulation of lipid metabolism in response to accumulation of
AdoHcy in Hcy-associated pathology is proposed.
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20
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Hörl G, Wagner A, Cole LK, Malli R, Reicher H, Kotzbeck P, Köfeler H, Höfler G, Frank S, Bogner-Strauss JG, Sattler W, Vance DE, Steyrer E. Sequential synthesis and methylation of phosphatidylethanolamine promote lipid droplet biosynthesis and stability in tissue culture and in vivo. J Biol Chem 2011; 286:17338-50. [PMID: 21454708 DOI: 10.1074/jbc.m111.234534] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Triacylglycerols are stored in eukaryotic cells within lipid droplets (LD). The LD core is enwrapped by a phospholipid monolayer with phosphatidylcholine (PC), the major phospholipid, and phosphatidylethanolamine (PE), a minor component. We demonstrate that the onset of LD formation is characterized by a change in cellular PC, PE, and phosphatidylserine (PS). With induction of differentiation of 3T3-L1 fibroblasts into adipocytes, the cellular PC/PE ratio decreased concomitant with LD formation, with the most pronounced decline between confluency and day 5. The mRNA for PS synthase-1 (forms PS from PC) and PS decarboxylase (forms PE from PS) increased after day 5. Activity and protein of PE N-methyltransferase (PEMT), which produces PC by methylation of PE, are absent in 3T3-L1 fibroblasts but were induced at day 5. High fat challenge induced PEMT expression in mouse adipose tissue. PE, produced via PS decarboxylase, was the preferred substrate for methylation to PC. A PEMT-GFP fusion protein decorated the periphery of LD. PEMT knockdown in 3T3-L1 adipocytes correlated with increased basal triacylglycerol hydrolysis. Pemt(-/-) mice developed desensitization against adenosine-mediated inhibition of basal hydrolysis in adipose tissue, and adipocyte hypotrophy was observed in Pemt(-/-) animals on a high fat diet. Knock-out of PEMT in adipose tissue down-regulated PS synthase-1 mRNA, suggesting coordination between PE supply and converting pathways during LD biosynthesis. We conclude that two consecutive processes not previously related to LD biogenesis, (i) PE production via PS and (ii) PE conversion via PEMT, are implicated in LD formation and stability.
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Affiliation(s)
- Gerd Hörl
- Department of Molecular Biology and Biochemistry, Center for Molecular Medicine, Medical University of Graz, A-8010 Graz, Austria
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21
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Tasseva G, Cole L, Vance JE. N-Myc and SP regulate phosphatidylserine synthase-1 expression in brain and glial cells. J Biol Chem 2010; 286:1061-73. [PMID: 21068393 DOI: 10.1074/jbc.m110.158709] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Phosphatidylserine (PS) is an essential constituent of biological membranes and plays critical roles in apoptosis and cell signaling. Because no information was available on transcriptional mechanisms that regulate PS biosynthesis in mammalian cells, we investigated the regulation of expression of the mouse PS synthase-1 (Pss1) gene. The Pss1 core promoter was characterized in vitro and in vivo through gel shift and chromatin immunoprecipitation assays. Transcription factor-binding sites, such as a GC-box cluster that binds Sp1/Sp3/Sp4 and N-Myc, and a degenerate E-box motif that interacts with Tal1 and E47, were identified. Pss1 transactivation was higher in brain of neonatal mice than in other tissues, consistent with brain being a major site of expression of Pss1 mRNA and PSS1 activity. Enzymatic assays revealed that PSS1 activity is enriched in primary cortical astrocytes compared with primary cortical neurons. Site-directed mutagenesis of binding sites within the Pss1 promoter demonstrated that Sp and N-Myc synergistically activate Pss1 expression in astrocytes. Chromatin immunoprecipitation indicated that Sp1, Sp3, and Sp4 interact with a common DNA binding site on the promoter. Reduction in levels of Sp1, Sp3, or N-Myc proteins by RNA interference decreased promoter activity. In addition, disruption of Sp/DNA binding with mithramycin significantly reduced Pss1 expression and PSS1 enzymatic activity, underscoring the essential contribution of Sp factors in regulating PSS1 activity. These studies provide the first analysis of mechanisms that regulate expression of a mammalian Pss gene in brain.
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Affiliation(s)
- Guergana Tasseva
- Department of Medicine, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
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Cole LK, Jacobs RL, Vance DE. Tamoxifen induces triacylglycerol accumulation in the mouse liver by activation of fatty acid synthesis. Hepatology 2010; 52:1258-65. [PMID: 20658461 DOI: 10.1002/hep.23813] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
UNLABELLED Tamoxifen is an anti-estrogen drug widely used for the treatment of hormone-sensitive breast cancer. Approximately 43% of breast cancer patients treated with tamoxifen develop hepatic steatosis. The mechanism or mechanisms by which tamoxifen may induce lipid accumulation in the liver are unclear. Mice were injected with tamoxifen or vehicle (sesame oil containing 1% benzyl alcohol) for 5 consecutive days. In comparison with the vehicle, tamoxifen increased hepatic triacylglycerol levels by 72%. The levels of plasma triacylglycerol were similar between the tamoxifen-treated and control groups. We found increased radiolabeling of triacylglycerol and phospholipids from [(3)H]acetate (∼50%) but not [(14)C]oleate in hepatocytes from tamoxifen-treated mice versus control mice. Fatty acid uptake, triacylglycerol secretion, and fatty acid oxidation remained unchanged in isolated hepatocytes after tamoxifen treatment. The apparent increase in fatty acid synthesis was explained by a marked decrease in the phosphorylation of acetyl coenzyme A carboxylase, which resulted in its activation. CONCLUSION Our data suggest that increased de novo fatty acid synthesis is the primary event leading to tamoxifen-induced steatosis in the mouse liver. Inhibition of fatty acid synthesis might, therefore, ameliorate steatosis/steatohepatitis in breast cancer patients treated with tamoxifen.
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Affiliation(s)
- Laura K Cole
- Group on Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada
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