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Borén J, Taskinen MR, Packard CJ. Biosynthesis and Metabolism of ApoB-Containing Lipoproteins. Annu Rev Nutr 2024; 44:179-204. [PMID: 38635875 DOI: 10.1146/annurev-nutr-062222-020716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/20/2024]
Abstract
Recent advances in human genetics, together with a substantial body of epidemiological, preclinical and clinical trial evidence, strongly support a causal relationship between triglyceride-rich lipoproteins (TRLs) and atherosclerotic cardiovascular disease. Consequently, the secretion and metabolism of TRLs have a significant impact on cardiovascular health. This knowledge underscores the importance of understanding the molecular mechanisms and regulation of very-low-density lipoprotein (VLDL) and chylomicron biogenesis. Fortunately, there has been a resurgence of interest in the intracellular assembly, trafficking, degradation, and secretion of VLDL, leading to many ground-breaking molecular insights. Furthermore, the identification of molecular control mechanisms related to triglyceride metabolism has greatly advanced our understanding of the complex metabolism of TRLs. In this review, we explore recent advances in the assembly, secretion, and metabolism of TRLs. We also discuss available treatment strategies for hypertriglyceridemia.
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Affiliation(s)
- Jan Borén
- Wallenberg Laboratory, Sahlgrenska University Hospital, Gothenburg, Sweden
- Department of Molecular and Clinical Medicine, University of Gothenburg, Gothenburg, Sweden;
| | - Marja-Riitta Taskinen
- Research Programs Unit, Clinical and Molecular Metabolism, University of Helsinki, Helsinki, Finland
| | - Chris J Packard
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom
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2
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Maestri A, Garagnani P, Pedrelli M, Hagberg CE, Parini P, Ehrenborg E. Lipid droplets, autophagy, and ageing: A cell-specific tale. Ageing Res Rev 2024; 94:102194. [PMID: 38218464 DOI: 10.1016/j.arr.2024.102194] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2023] [Revised: 12/22/2023] [Accepted: 01/08/2024] [Indexed: 01/15/2024]
Abstract
Lipid droplets are the essential organelle for storing lipids in a cell. Within the variety of the human body, different cells store, utilize and release lipids in different ways, depending on their intrinsic function. However, these differences are not well characterized and, especially in the context of ageing, represent a key factor for cardiometabolic diseases. Whole body lipid homeostasis is a central interest in the field of cardiometabolic diseases. In this review we characterize lipid droplets and their utilization via autophagy and describe their diverse fate in three cells types central in cardiometabolic dysfunctions: adipocytes, hepatocytes, and macrophages.
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Affiliation(s)
- Alice Maestri
- Division of Cardiovascular Medicine, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden; Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden
| | - Paolo Garagnani
- Department of Medical and Surgical Sciences (DIMEC), University of Bologna, Bologna, Italy; IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy
| | - Matteo Pedrelli
- Cardio Metabolic Unit, Department of Laboratory Medicine, and Department of Medicine (Huddinge), Karolinska Institutet, Stockholm, Sweden; Medicine Unit of Endocrinology, Theme Inflammation and Ageing, Karolinska University Hospital, Stockholm, Sweden
| | - Carolina E Hagberg
- Division of Cardiovascular Medicine, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden; Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden
| | - Paolo Parini
- Cardio Metabolic Unit, Department of Laboratory Medicine, and Department of Medicine (Huddinge), Karolinska Institutet, Stockholm, Sweden; Medicine Unit of Endocrinology, Theme Inflammation and Ageing, Karolinska University Hospital, Stockholm, Sweden
| | - Ewa Ehrenborg
- Division of Cardiovascular Medicine, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden; Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden.
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Park SH, Kang JH, Bae YS. The role and regulation of phospholipase D in metabolic disorders. Adv Biol Regul 2024; 91:100988. [PMID: 37845091 DOI: 10.1016/j.jbior.2023.100988] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Accepted: 09/25/2023] [Indexed: 10/18/2023]
Abstract
Phospholipase D (PLD) is an enzyme that catalyzes the hydrolysis of phosphatidylcholine into phosphatidic acid and free choline. In mammals, PLD exists in two well-characterized isoforms, PLD1 and PLD2, and it plays pivotal roles as signaling mediators in various cellular functions, such as cell survival, differentiation, and migration. These isoforms are predominantly expressed in diverse cell types, including many immune cells, such as monocytes and macrophages, as well as non-immune cells, such as epithelial and endothelial cells. Several previous studies have revealed that the stimulation of these cells leads to an increase in PLD expression and its enzymatic products, potentially influencing the pathological responses in a wide spectrum of diseases. Metabolic diseases, exemplified by conditions, such as diabetes, obesity, hypertension, and atherosclerosis, pose significant global health challenges. Abnormal activation or dysfunction of PLD emerges as a potential contributing factor to the pathogenesis and progression of these metabolic disorders. Therefore, it is crucial to thoroughly investigate and understand the intricate relationship between PLD and metabolic diseases. In this review, we provide an in-depth overview of the functional roles and molecular mechanisms of PLD involved in metabolic diseases. By delving into the intricate interplay between PLD and metabolic disorders, this review aims to offer insights into the potential therapeutic interventions.
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Affiliation(s)
- Seon Hyang Park
- Department of Biological Sciences, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Ji Hyeon Kang
- Department of Biological Sciences, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Yoe-Sik Bae
- Department of Biological Sciences, Sungkyunkwan University, Suwon, 16419, Republic of Korea.
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4
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Laupsa-Borge J, Grytten E, Bohov P, Bjørndal B, Strand E, Skorve J, Nordrehaug JE, Berge RK, Rostrup E, Mellgren G, Dankel SN, Nygård OK. Sex-specific responses in glucose-insulin homeostasis and lipoprotein-lipid components after high-dose supplementation with marine n-3 PUFAs in abdominal obesity: a randomized double-blind crossover study. Front Nutr 2023; 10:1020678. [PMID: 37404855 PMCID: PMC10315503 DOI: 10.3389/fnut.2023.1020678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2022] [Accepted: 06/01/2023] [Indexed: 07/06/2023] Open
Abstract
Background Clinical studies on effects of marine-derived omega-3 (n-3) polyunsaturated fatty acids (PUFAs), mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and the plant-derived omega-6 (n-6) PUFA linoleic acid (LA) on lipoprotein-lipid components and glucose-insulin homeostasis have shown conflicting results, which may partly be explained by differential responses in females and males. However, we have lacked data on sexual dimorphism in the response of cardiometabolic risk markers following increased consumption of n-3 or n-6 PUFAs. Objective To explore sex-specific responses after n-3 (EPA + DHA) or n-6 (LA) PUFA supplementation on circulating lipoprotein subfractions, standard lipids, apolipoproteins, fatty acids in red blood cell membranes, and markers of glycemic control/insulin sensitivity among people with abdominal obesity. Methods This was a randomized double-blind crossover study with two 7-week intervention periods separated by a 9-week washout phase. Females (n = 16) were supplemented with 3 g/d of EPA + DHA (fish oil) or 15 g/d of LA (safflower oil), while males (n = 23) received a dose of 4 g/d of EPA + DHA or 20 g/d of LA. In fasting blood samples, we measured lipoprotein particle subclasses, standard lipids, apolipoproteins, fatty acid profiles, and markers of glycemic control/insulin sensitivity. Results The between-sex difference in relative change scores was significant after n-3 for total high-density lipoproteins (females/males: -11%*/-3.3%, p = 0.036; *: significant within-sex change), high-density lipoprotein particle size (+2.1%*/-0.1%, p = 0.045), and arachidonic acid (-8.3%*/-12%*, p = 0.012), and after n-6 for total (+37%*/+2.1%, p = 0.041) and small very-low-density lipoproteins (+97%*/+14%, p = 0.021), and lipoprotein (a) (-16%*/+0.1%, p = 0.028). Circulating markers of glucose-insulin homeostasis differed significantly after n-3 for glucose (females/males: -2.1%/+3.9%*, p = 0.029), insulin (-31%*/+16%, p < 0.001), insulin C-peptide (-12%*/+13%*, p = 0.001), homeostasis model assessment of insulin resistance index 2 (-12%*/+14%*, p = 0.001) and insulin sensitivity index 2 (+14%*/-12%*, p = 0.001), and quantitative insulin sensitivity check index (+4.9%*/-3.4%*, p < 0.001). Conclusion We found sex-specific responses after high-dose n-3 (but not n-6) supplementation in circulating markers of glycemic control/insulin sensitivity, which improved in females but worsened in males. This may partly be related to the sex differences we observed in several components of the lipoprotein-lipid profile following the n-3 intervention. Clinical trial registration https://clinicaltrials.gov/, identifier [NCT02647333].
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Affiliation(s)
- Johnny Laupsa-Borge
- Hormone Laboratory, Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
- Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Elise Grytten
- Hormone Laboratory, Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
- Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Pavol Bohov
- Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Bodil Bjørndal
- Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Elin Strand
- Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Jon Skorve
- Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Jan Erik Nordrehaug
- Department of Clinical Science, University of Bergen, Bergen, Norway
- Department of Heart Disease, Haukeland University Hospital, Bergen, Norway
| | - Rolf K. Berge
- Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Espen Rostrup
- Department of Heart Disease, Haukeland University Hospital, Bergen, Norway
| | - Gunnar Mellgren
- Hormone Laboratory, Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
- Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway
- Mohn Research Center for Diabetes Precision Medicine, Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Simon N. Dankel
- Hormone Laboratory, Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
- Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway
- Mohn Research Center for Diabetes Precision Medicine, Department of Clinical Science, University of Bergen, Bergen, Norway
| | - Ottar K. Nygård
- Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway
- Department of Heart Disease, Haukeland University Hospital, Bergen, Norway
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Wang H, Zhao Y, Pan Y, Yang A, Li C, Wang S, Dong Z, Li M, Wang S, Zhang Z, Zhu Y, Zhang D, Sun G. Inhibition of phospholipase D1 ameliorates hepatocyte steatosis and non-alcoholic fatty liver disease. JHEP Rep 2023; 5:100726. [PMID: 37138676 PMCID: PMC10149370 DOI: 10.1016/j.jhepr.2023.100726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/19/2022] [Revised: 02/14/2023] [Accepted: 02/27/2023] [Indexed: 05/05/2023] Open
Abstract
Background & Aims Phospholipase D1 (PLD1), a phosphatidylcholine-hydrolysing enzyme, is involved in cellular lipid metabolism. However, its involvement in hepatocyte lipid metabolism and consequently non-alcoholic fatty liver disease (NAFLD) has not been explicitly explored. Methods NAFLD was induced in hepatocyte-specific Pld1 knockout (Pld1(H)-KO) and littermate Pld1 flox/flox (Pld1-Flox) control mice feeding a high-fat diet (HFD) for 20 wk. Changes of the lipid composition in the liver were compared. Alpha mouse liver 12 (AML12) cells and mouse primary hepatocytes were incubated with oleic acid or sodium palmitate in vitro to explore the role of PLD1 in the development of hepatic steatosis. Hepatic PLD1 expression was evaluated in liver biopsy samples in patients with NAFLD. Results PLD1 expression levels were increased in the hepatocytes of patients with NAFLD and HFD-fed mice. Compared with Pld1-Flox mice, Pld1(H)-KO mice exhibited decreased plasma glucose and lipid levels as well as lipid accumulation in liver tissues after HFD feeding. Transcriptomic analysis showed that hepatocyte-specific deficiency of PLD1 decreased Cd36 expression in steatosis liver tissues, which was confirmed at the protein and gene levels. In vitro, specific inhibition of PLD1 with VU0155069 or VU0359595 decreased CD36 expression and lipid accumulation in oleic acid- or sodium palmitate-treated AML12 cells or primary hepatocytes. Inhibition of hepatocyte PLD1 significantly altered lipid composition, especially phosphatidic acid and lysophosphatidic acid levels in liver tissues with hepatic steatosis. Furthermore, phosphatidic acid, the downstream product of PLD1, increased the expression levels of CD36 in AML12 cells, which was reversed by a PPARγ antagonist. Conclusions Hepatocyte-specific Pld1 deficiency ameliorates lipid accumulation and NAFLD development by inhibiting the PPARγ/CD36 pathway. PLD1 may be a new target for the treatment of NAFLD. Impact and implications The involvement of PLD1 in hepatocyte lipid metabolism and NAFLD has not been explicitly explored. In this study, we found that the inhibition of hepatocyte PLD1 exerted potent protective effects against HFD-induced NAFLD, which were attributable to a reduction in PPARγ/CD36 pathway-mediated lipid accumulation in hepatocytes. Targeting hepatocyte PLD1 may be a new target for the treatment of NAFLD.
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Affiliation(s)
- Huan Wang
- Immunology Research Center for Oral and Systemic Health, Beijing Friendship Hospital, Capital Medical University, Beijing, China
- Beijing Key Laboratory of Tolerance Induction and Organ Protection in Transplantation, Beijing, China
- Beijing Clinical Research Institute, Beijing, China
| | - Yushang Zhao
- Immunology Research Center for Oral and Systemic Health, Beijing Friendship Hospital, Capital Medical University, Beijing, China
- Beijing Key Laboratory of Tolerance Induction and Organ Protection in Transplantation, Beijing, China
- Beijing Clinical Research Institute, Beijing, China
- National Clinical Research Center for Digestive Diseases, Beijing, China
- Beijing Laboratory of Oral Health, Capital Medical University School of Basic Medicine, Beijing, China
| | - Yuhualei Pan
- Immunology Research Center for Oral and Systemic Health, Beijing Friendship Hospital, Capital Medical University, Beijing, China
- Beijing Key Laboratory of Tolerance Induction and Organ Protection in Transplantation, Beijing, China
- Beijing Clinical Research Institute, Beijing, China
- National Clinical Research Center for Digestive Diseases, Beijing, China
- Beijing Laboratory of Oral Health, Capital Medical University School of Basic Medicine, Beijing, China
| | - Aiting Yang
- Beijing Clinical Research Institute, Beijing, China
- National Clinical Research Center for Digestive Diseases, Beijing, China
| | - Changying Li
- Immunology Research Center for Oral and Systemic Health, Beijing Friendship Hospital, Capital Medical University, Beijing, China
- Beijing Key Laboratory of Tolerance Induction and Organ Protection in Transplantation, Beijing, China
- Beijing Clinical Research Institute, Beijing, China
- National Clinical Research Center for Digestive Diseases, Beijing, China
- Beijing Laboratory of Oral Health, Capital Medical University School of Basic Medicine, Beijing, China
| | - Song Wang
- Beijing Clinical Research Institute, Beijing, China
| | - Zhao Dong
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Mengyi Li
- General Surgery Department, Beijing Friendship Hospital, Capital Medical University, Beijing, China
| | - Songlin Wang
- Beijing Laboratory of Oral Health, Capital Medical University School of Basic Medicine, Beijing, China
| | - Zhongtao Zhang
- General Surgery Department, Beijing Friendship Hospital, Capital Medical University, Beijing, China
| | - Yanbing Zhu
- Beijing Clinical Research Institute, Beijing, China
- Corresponding author. Address: Capital Medical University Affiliated Beijing Friendship Hospital, 95 Yongan Road, Xicheng District, Beijing 100050, China. Tel.: (8610)63139309, fax: (8610)63139421.
| | - Dong Zhang
- Immunology Research Center for Oral and Systemic Health, Beijing Friendship Hospital, Capital Medical University, Beijing, China
- Beijing Key Laboratory of Tolerance Induction and Organ Protection in Transplantation, Beijing, China
- Beijing Clinical Research Institute, Beijing, China
- National Clinical Research Center for Digestive Diseases, Beijing, China
- Beijing Laboratory of Oral Health, Capital Medical University School of Basic Medicine, Beijing, China
- General Surgery Department, Beijing Friendship Hospital, Capital Medical University, Beijing, China
- Corresponding author. Address: Capital Medical University Affiliated Beijing Friendship Hospital, 95 Yongan Road, Xicheng District, Beijing 100050, China. Tel.: (8610)63139309, fax: (8610)63139421.
| | - Guangyong Sun
- Immunology Research Center for Oral and Systemic Health, Beijing Friendship Hospital, Capital Medical University, Beijing, China
- Beijing Key Laboratory of Tolerance Induction and Organ Protection in Transplantation, Beijing, China
- Beijing Clinical Research Institute, Beijing, China
- National Clinical Research Center for Digestive Diseases, Beijing, China
- Beijing Laboratory of Oral Health, Capital Medical University School of Basic Medicine, Beijing, China
- Corresponding author. Address: Capital Medical University Affiliated Beijing Friendship Hospital, 95 Yongan Road, Xicheng District, Beijing 100050, China. Tel.: (8610)63139309, fax: (8610)63139421.
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Egg Yolk Fat Deposition Is Regulated by Diacylglycerol and Ceramide Enriched by Adipocytokine Signaling Pathway in Laying Hens. Animals (Basel) 2023; 13:ani13040607. [PMID: 36830395 PMCID: PMC9951658 DOI: 10.3390/ani13040607] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 01/19/2023] [Accepted: 01/30/2023] [Indexed: 02/11/2023] Open
Abstract
The mechanism which regulates differential fat deposition in egg yolk from the indigenous breeds and commercial laying hens is still unclear. In this research, Chinese indigenous Huainan Partridge chickens and Nongda III commercial laying hens were used for egg collection and liver sampling. The weight of eggs and yolk were recorded. Yolk fatty acids were determined by gas chromatography-mass spectrometry. Lipid metabolites in the liver were detected by liquid chromatography-mass spectrometry. Yolk weight, yolk ratio and yolk fat ratio exhibited higher in the Huainan Partridge chicken than that of the Nongda III. Compared to the Nongda III, the content of total saturated fatty acid was lower, while the unsaturated fatty acid was higher in the yolk of the Huainan Partridge chicken. Metabolites of phosphatidylinositol and phosphatidylserine from glycerolphospholipids, and metabolites of diacylglycerol from glycerolipids showed higher enrichment in the Huainan Partridge chicken than that of the Nongda III, which promoted the activation of the adipocytokine signaling pathway. However, metabolites of phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine and lysophosphatidylcholine from glycerol phospholipids, and metabolites of triacylglycerol from glycerolipids showed lower enrichment in the Huainan Partridge chicken than that of the Nongda III. The high level of yolk fat deposition in the Huainan Partridge chicken is regulated by the activation of the adipocytokine signaling pathway which can promote the accumulation of diacylglycerol and ceramide in the liver.
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Auclair N, Sané AT, Delvin E, Spahis S, Levy E. Phospholipase D as a Potential Modulator of Metabolic Syndrome: Impact of Functional Foods. Antioxid Redox Signal 2021; 34:252-278. [PMID: 32586106 DOI: 10.1089/ars.2020.8081] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Significance: Cardiometabolic disorders (CMD) are composed of a plethora of metabolic dysfunctions such as dyslipidemia, nonalcoholic fatty liver disease, insulin resistance, and hypertension. The development of these disorders is highly linked to inflammation and oxidative stress (OxS), two metabolic states closely related to physiological and pathological conditions. Given the drastically rising CMD prevalence, the discovery of new therapeutic targets/novel nutritional approaches is of utmost importance. Recent Advances: The tremendous progress in methods/technologies and animal modeling has allowed the clarification of phospholipase D (PLD) critical roles in multiple cellular processes, whether directly or indirectly via phosphatidic acid, the lipid product mediating signaling functions. In view of its multiple features and implications in various diseases, PLD has emerged as a drug target. Critical Issues: Although insulin stimulates PLD activity and, in turn, PLD regulates insulin signaling, the impact of the two important PLD isoforms on the metabolic syndrome components remains vague. Therefore, after outlining PLD1/PLD2 characteristics and functions, their role in inflammation, OxS, and CMD has been analyzed and critically reported in the present exhaustive review. The influence of functional foods and nutrients in the regulation of PLD has also been examined. Future Directions: Available evidence supports the implication of PLD in CMD, but only few studies emphasize its mechanisms of action and specific regulation by nutraceutical compounds. Therefore, additional investigations are first needed to clarify the functional role of nutraceutics and, second, to elucidate whether targeting PLDs with food compounds represents an appropriate therapeutic strategy to treat CMD. Antioxid. Redox Signal. 34, 252-278.
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Affiliation(s)
- Nickolas Auclair
- Research Center, CHU Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada.,Department of Pharmacology & Physiology and Université de Montréal, Montreal, Quebec, Canada
| | - Alain T Sané
- Research Center, CHU Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada
| | - Edgard Delvin
- Research Center, CHU Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada
| | - Schohraya Spahis
- Research Center, CHU Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada.,Department of Nutrition, Université de Montréal, Montreal, Quebec, Canada
| | - Emile Levy
- Research Center, CHU Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada.,Department of Pharmacology & Physiology and Université de Montréal, Montreal, Quebec, Canada.,Department of Nutrition, Université de Montréal, Montreal, Quebec, Canada
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8
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Hepatic lipid droplet homeostasis and fatty liver disease. Semin Cell Dev Biol 2020; 108:72-81. [PMID: 32444289 DOI: 10.1016/j.semcdb.2020.04.011] [Citation(s) in RCA: 76] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 03/17/2020] [Accepted: 04/17/2020] [Indexed: 12/14/2022]
Abstract
In cells, lipids are stored in lipid droplets, dynamic organelles that adapt their size, abundance, lipid and protein composition and organelle interactions to metabolic changes. Lipid droplet accumulation in the liver is the hallmark of non-alcoholic fatty liver disease (NAFLD). Due to the prevalence of obesity, the strongest risk factor for steatosis, NAFLD and its associated complications are currently affecting more than 1 billion people worldwide. Here, we review how triglyceride and phospholipid homeostasis are regulated in hepatocytes and how imbalances between lipid storage, degradation and lipoprotein secretion lead to NAFLD. We discuss how organelle interactions are altered in NAFLD and provide insights how NAFLD progression is associated with changes in hepatocellular signaling and organ-crosstalk. Finally, we highlight unsolved questions in hepatic LD and lipoprotein biology and give an outlook on therapeutic options counteracting hepatic lipid accumulation.
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McDermott MI, Wang Y, Wakelam MJO, Bankaitis VA. Mammalian phospholipase D: Function, and therapeutics. Prog Lipid Res 2019; 78:101018. [PMID: 31830503 DOI: 10.1016/j.plipres.2019.101018] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Revised: 10/08/2019] [Accepted: 10/14/2019] [Indexed: 01/23/2023]
Abstract
Despite being discovered over 60 years ago, the precise role of phospholipase D (PLD) is still being elucidated. PLD enzymes catalyze the hydrolysis of the phosphodiester bond of glycerophospholipids producing phosphatidic acid and the free headgroup. PLD family members are found in organisms ranging from viruses, and bacteria to plants, and mammals. They display a range of substrate specificities, are regulated by a diverse range of molecules, and have been implicated in a broad range of cellular processes including receptor signaling, cytoskeletal regulation and membrane trafficking. Recent technological advances including: the development of PLD knockout mice, isoform-specific antibodies, and specific inhibitors are finally permitting a thorough analysis of the in vivo role of mammalian PLDs. These studies are facilitating increased recognition of PLD's role in disease states including cancers and Alzheimer's disease, offering potential as a target for therapeutic intervention.
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Affiliation(s)
- M I McDermott
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, TX 77843-1114, United States of America.
| | - Y Wang
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, TX 77843-1114, United States of America; Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128, United States of America
| | - M J O Wakelam
- Babraham Institute, Babraham Research Campus, Cambridge CB22 3AT, United Kingdom
| | - V A Bankaitis
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, TX 77843-1114, United States of America; Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128, United States of America; Department of Chemistry, Texas A&M University, College Station, Texas 77840, United States of America
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10
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Kumar M, Ojha S, Rai P, Joshi A, Kamat SS, Mallik R. Insulin activates intracellular transport of lipid droplets to release triglycerides from the liver. J Cell Biol 2019; 218:3697-3713. [PMID: 31604801 PMCID: PMC6829650 DOI: 10.1083/jcb.201903102] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2019] [Revised: 06/18/2019] [Accepted: 07/26/2019] [Indexed: 01/13/2023] Open
Abstract
Kumar et al. describe a detailed pathway for channeling fat from the liver into blood across fed/fasted cycles. Insulin, phosphatidic acid, and kinesin collaborate in hepatocytes to deliver lipid droplets to the smooth ER, where they are catabolized to supply fat for lipoprotein production and secretion. Triglyceride-rich lipid droplets (LDs) are catabolized with high efficiency in hepatocytes to supply fatty acids for producing lipoprotein particles. Fasting causes a massive influx of adipose-derived fatty acids into the liver. The liver in the fasted state is therefore bloated with LDs but, remarkably, still continues to secrete triglycerides at a constant rate. Here we show that insulin signaling elevates phosphatidic acid (PA) dramatically on LDs in the fed state. PA then signals to recruit kinesin-1 motors, which transport LDs to the peripherally located smooth ER inside hepatocytes, where LDs are catabolized to produce lipoproteins. This pathway is down-regulated homeostatically when fasting causes insulin levels to drop, thus preventing dangerous elevation of triglycerides in the blood. Further, we show that a specific peptide against kinesin-1 blocks triglyceride secretion without any apparent deleterious effects on cells. Our work therefore reveals fundamental mechanisms that maintain lipid homeostasis across metabolic states and leverages this knowledge to propose a molecular target against hyperlipidemia.
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Affiliation(s)
- Mukesh Kumar
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Srikant Ojha
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Priyanka Rai
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Alaumy Joshi
- Department of Biology, Indian Institute of Science Education and Research, Pune, India
| | - Siddhesh S Kamat
- Department of Biology, Indian Institute of Science Education and Research, Pune, India
| | - Roop Mallik
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
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11
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Su Y, Foppen E, Mansur Machado FS, Fliers E, Kalsbeek A. The role of the daily feeding rhythm in the regulation of the day/night rhythm in triglyceride secretion in rats. Chronobiol Int 2018; 35:885-895. [PMID: 29446660 DOI: 10.1080/07420528.2018.1438456] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Plasma triglyceride (TG) levels show a clear daily rhythm, however, thus far it is still unknown whether this rhythm results from a daily rhythm in TG production, TG uptake or both. Previous studies have shown that feeding activity affects plasma TG concentrations, but it is not clear how the daily rhythm in feeding activity affects plasma TG concentrations. In the present study, we measured plasma TG concentrations and TG secretion rates in rats at 6 Zeitgeber times to investigate whether plasma TG concentrations and TG secretion show a daily rhythm. We found that plasma TG concentrations and TG secretion show a significant day/night rhythm. Next, we removed the daily rhythm in feeding behavior by introducing a 6-meals-a-day (6M) feeding schedule to investigate whether the daily rhythm in feeding behavior is necessary to maintain the daily rhythm in TG secretion. We found that the day/night rhythm in TG secretion was abolished under 6M feeding conditions. Hepatic apolipoprotein B (ApoB) and microsomal TG transfer protein (Mttp), which are both involved in TG secretion, also lost their daily rhythmicity under 6M feeding conditions. Together, these results indicate that: (1) the daily rhythm in TG secretion contributes to the formation of a day/night rhythm in plasma TG levels and (2) a daily feeding rhythm is essential for maintaining the daily rhythm in TG secretion.
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Affiliation(s)
- Yan Su
- a Hypothalamic Integration Mechanisms , Netherlands Institute for Neuroscience , Amsterdam , The Netherlands
| | - Ewout Foppen
- b Department of Endocrinology and Metabolism , Academic Medical Center (AMC), University of Amsterdam , Amsterdam , The Netherlands
| | | | - Eric Fliers
- b Department of Endocrinology and Metabolism , Academic Medical Center (AMC), University of Amsterdam , Amsterdam , The Netherlands
| | - Andries Kalsbeek
- a Hypothalamic Integration Mechanisms , Netherlands Institute for Neuroscience , Amsterdam , The Netherlands.,b Department of Endocrinology and Metabolism , Academic Medical Center (AMC), University of Amsterdam , Amsterdam , The Netherlands
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12
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Abstract
The liver secretes lipids in a controlled manner despite vast changes in its internal lipid content. This buffering function of the liver is essential for lipid/energy homeostasis, but its molecular and cellular mechanism is unknown. We show that motor protein kinesin transports lipid droplets (LDs) to the endoplasmic reticulum (ER) in liver cells, engineering ER−droplet contacts and supplying lipids to the ER for secretion as lipoprotein. However, when fasting induces massive lipid accumulation in liver, kinesin is removed from LDs, inhibiting lipid supply to the ER and homeostatically tempering lipid secretion from liver in a fasted state. Interestingly, reducing kinesin also blocks propagation of hepatitis-C virus inside liver cells, possibly because viral proteins cannot transfer from the ER to LDs. Despite massive fluctuations in its internal triglyceride content, the liver secretes triglyceride under tight homeostatic control. This buffering function is most visible after fasting, when liver triglyceride increases manyfold but circulating serum triglyceride barely fluctuates. How the liver controls triglyceride secretion is unknown, but is fundamentally important for lipid and energy homeostasis in animals. Here we find an unexpected cellular and molecular mechanism behind such control. We show that kinesin motors are recruited to triglyceride-rich lipid droplets (LDs) in the liver by the GTPase ARF1, which is a key activator of lipolysis. This recruitment is activated by an insulin-dependent pathway and therefore responds to fed/fasted states of the animal. In fed state, ARF1 and kinesin appear on LDs, consequently transporting LDs to the periphery of hepatocytes where the smooth endoplasmic reticulum (sER) is present. Because the lipases that catabolize LDs in hepatocytes reside on the sER, LDs can now be catabolized efficiently to provide triglyceride for lipoprotein assembly and secretion from the sER. Upon fasting, insulin is lowered to remove ARF1 and kinesin from LDs, thus down-regulating LD transport and sER–LD contacts. This tempers triglyceride availabiity for very low density lipoprotein assembly and allows homeostatic control of serum triglyceride in a fasted state. We further show that kinesin knockdown inhibits hepatitis-C virus replication in hepatocytes, likely because translated viral proteins are unable to transfer from the ER to LDs.
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13
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Nelson RK, Ya-Ping J, Gadbery J, Abedeen D, Sampson N, Lin RZ, Frohman MA. Phospholipase D2 loss results in increased blood pressure via inhibition of the endothelial nitric oxide synthase pathway. Sci Rep 2017; 7:9112. [PMID: 28831159 PMCID: PMC5567230 DOI: 10.1038/s41598-017-09852-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Accepted: 07/14/2017] [Indexed: 11/10/2022] Open
Abstract
The Phospholipase D (PLD) superfamily is linked to neurological disease, cancer, and fertility, and a recent report correlated a potential loss-of-function PLD2 polymorphism with hypotension. Surprisingly, PLD2 -/- mice exhibit elevated blood pressure accompanied by associated changes in cardiac performance and molecular markers, but do not have findings consistent with the metabolic syndrome. Instead, expression of endothelial nitric oxide synthase (eNOS), which generates the potent vasodilator nitric oxide (NO), is decreased. An eNOS inhibitor phenocopied PLD2 loss and had no further effect on PLD2 -/- mice, confirming the functional relationship. Using a human endothelial cell line, PLD2 loss of function was shown to lower intracellular free cholesterol, causing upregulation of HMG Co-A reductase, the rate-limiting enzyme in cholesterol synthesis. HMG Co-A reductase negatively regulates eNOS, and the PLD2-deficiency phenotype of decreased eNOS expression and activity could be rescued by cholesterol supplementation and HMG Co-A reductase inhibition. Together, these findings identify a novel pathway through which the lipid signaling enzyme PLD2 regulates blood pressure, creating implications for on-going therapeutic development of PLD small molecule inhibitors. Finally, we show that the human PLD2 polymorphism does not trigger eNOS loss, but rather creates another effect, suggesting altered functioning for the allele.
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Affiliation(s)
- Rochelle K Nelson
- The Graduate Program in Physiology & Biophysics, Stony Brook University, New York, USA
| | - Jiang Ya-Ping
- Department of Physiology & Biophysics, Stony Brook University, New York, USA
| | - John Gadbery
- Biochemistry and Structural Biology, Stony Brook University, New York, USA
| | - Danya Abedeen
- The Undergraduate Program in Biochemistry, Stony Brook University, New York, USA
| | - Nicole Sampson
- Biochemistry and Structural Biology, Stony Brook University, New York, USA
- Department of Chemistry, Stony Brook University, New York, USA
| | - Richard Z Lin
- Department of Physiology & Biophysics, Stony Brook University, New York, USA
- Medical Service, Northport Veterans Affairs Medical Center, Northport, NY, USA
| | - Michael A Frohman
- Department of Pharmacological Sciences, Stony Brook University, New York, USA.
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14
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Rojas JM, Bruinstroop E, Printz RL, Alijagic-Boers A, Foppen E, Turney MK, George L, Beck-Sickinger AG, Kalsbeek A, Niswender KD. Central nervous system neuropeptide Y regulates mediators of hepatic phospholipid remodeling and very low-density lipoprotein triglyceride secretion via sympathetic innervation. Mol Metab 2015; 4:210-21. [PMID: 25737956 PMCID: PMC4338317 DOI: 10.1016/j.molmet.2015.01.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2014] [Revised: 12/29/2014] [Accepted: 01/09/2015] [Indexed: 12/26/2022] Open
Abstract
OBJECTIVE Elevated very low-density lipoprotein (VLDL)-triglyceride (TG) secretion from the liver contributes to an atherogenic dyslipidemia that is associated with obesity, diabetes and the metabolic syndrome. Numerous models of obesity and diabetes are characterized by increased central nervous system (CNS) neuropeptide Y (NPY); in fact, a single intracerebroventricular (icv) administration of NPY in lean fasted rats elevates hepatic VLDL-TG secretion and does so, in large part, via signaling through the CNS NPY Y1 receptor. Thus, our overarching hypothesis is that elevated CNS NPY action contributes to dyslipidemia by activating central circuits that modulate liver lipid metabolism. METHODS Chow-fed Zucker fatty (ZF) rats were pair-fed by matching their caloric intake to that of lean controls and effects on body weight, plasma TG, and liver content of TG and phospholipid (PL) were compared to ad-libitum (ad-lib) fed ZF rats. Additionally, lean 4-h fasted rats with intact or disrupted hepatic sympathetic innervation were treated with icv NPY or NPY Y1 receptor agonist to identify novel hepatic mechanisms by which NPY promotes VLDL particle maturation and secretion. RESULTS Manipulation of plasma TG levels in obese ZF rats, through pair-feeding had no effect on liver TG content; however, hepatic PL content was substantially reduced and was tightly correlated with plasma TG levels. Treatment with icv NPY or a selective NPY Y1 receptor agonist in lean fasted rats robustly activated key hepatic regulatory proteins, stearoyl-CoA desaturase-1 (SCD-1), ADP-ribosylation factor-1 (ARF-1), and lipin-1, known to be involved in remodeling liver PL into TG for VLDL maturation and secretion. Lastly, we show that the effects of CNS NPY on key liporegulatory proteins are attenuated by hepatic sympathetic denervation. CONCLUSIONS These data support a model in which CNS NPY modulates mediators of hepatic PL remodeling and VLDL maturation to stimulate VLDL-TG secretion that is dependent on the Y1 receptor and sympathetic signaling to the liver.
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Key Words
- AGPAT, 1-acyl-glycerol-3-phosphate acyltransferase
- ARF-1, ADP-ribosylation factor-1
- ApoB, apolipoprotein B
- CNS, central nervous system
- Cyto, cytoplasmic
- DAG, diacylglycerol
- DGAT, diacylglycerol acyltransferase
- ER, endoplasmic reticulum
- FFA(s), free fatty acid(s)
- GAPDH, glyceraldehyde 3-phosphate dehydrogenase
- HDAC-1, histone deacetylase-1
- Lipin-1
- NE, norepinephrine
- NPY Y1 receptor
- NPY, neuropeptide Y
- Nuc, nuclear
- PA, phosphatidic acid
- PAP-1, phosphatidic acid phosphatase-1
- PF, pair-fed
- PL, phospholipid
- PLD, phospholipase D
- POMC, proopiomelanocortin
- Phospholipid
- RPL13A, ribosomal protein L13a
- RT-PCR, real-time PCR
- SCD-1, stearoyl-CoA desaturase-1
- SNS, sympathetic nervous system
- Sham, sham-denervation
- Sx, sympathetic denervation
- Sympathetic denervation
- TG, triglyceride
- Triglyceride
- VLDL
- VLDL, very low-density lipoprotein
- Veh, vehicle
- ZF, Zucker fatty
- ad-lib, ad-libitum
- icv, intracerebroventricular
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Affiliation(s)
- Jennifer M. Rojas
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, United States
| | - Eveline Bruinstroop
- Department of Endocrinology and Metabolism, Laboratory of Endocrinology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Richard L. Printz
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, United States
| | - Aldijana Alijagic-Boers
- Department of Hypothalamic Integration Mechanisms, Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Science, Amsterdam, The Netherlands
| | - Ewout Foppen
- Department of Endocrinology and Metabolism, Laboratory of Endocrinology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Maxine K. Turney
- Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN, United States
| | - Leena George
- Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN, United States
| | - Annette G. Beck-Sickinger
- Institute of Biochemistry, Faculty of Bioscience, Pharmacy and Psychology, Leipzig University, Leipzig, Germany
| | - Andries Kalsbeek
- Department of Endocrinology and Metabolism, Laboratory of Endocrinology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
- Department of Hypothalamic Integration Mechanisms, Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Science, Amsterdam, The Netherlands
| | - Kevin D. Niswender
- Department of Veterans Affairs, Tennessee Valley Healthcare System, Nashville, TN, United States
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, United States
- Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN, United States
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15
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Abstract
Lipid homeostasis is maintained through the coordination of lipid metabolism in various tissues, including adipose tissue and the liver. The disruption of lipid homeostasis often results in the development of metabolic disorders such as obesity, diabetes mellitus, liver steatosis, and cardiovascular diseases. Cell death-inducing DNA fragmentation factor 45-like effector family proteins, including Cidea, Cideb, and Fsp27 (Cidec), are emerging as important regulators of various lipid metabolic pathways and play pivotal roles in the development of metabolic disorders. This review summarizes the latest cell death-inducing DNA fragmentation factor 45-like effector protein discoveries related to the control of lipid metabolism, with emphasis on the role of these proteins in lipid droplet growth in adipocytes and in the regulation of very low-density lipoprotein lipidation and maturation in hepatocytes.
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Affiliation(s)
- Li Xu
- Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, China
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16
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Bruinstroop E, Pei L, Ackermans MT, Foppen E, Borgers AJ, Kwakkel J, Alkemade A, Fliers E, Kalsbeek A. Hypothalamic neuropeptide Y (NPY) controls hepatic VLDL-triglyceride secretion in rats via the sympathetic nervous system. Diabetes 2012; 61:1043-50. [PMID: 22461566 PMCID: PMC3331766 DOI: 10.2337/db11-1142] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Excessive secretion of triglyceride-rich very low-density lipoproteins (VLDL-TG) contributes to diabetic dyslipidemia. Earlier studies have indicated a possible role for the hypothalamus and autonomic nervous system in the regulation of VLDL-TG. In the current study, we investigated whether the autonomic nervous system and hypothalamic neuropeptide Y (NPY) release during fasting regulates hepatic VLDL-TG secretion. We report that, in fasted rats, an intact hypothalamic arcuate nucleus and hepatic sympathetic innervation are necessary to maintain VLDL-TG secretion. Furthermore, the hepatic sympathetic innervation is necessary to mediate the stimulatory effect of intracerebroventricular administration of NPY on VLDL-TG secretion. Since the intracerebroventricular administration of NPY increases VLDL-TG secretion by the liver without affecting lipolysis, its effect on lipid metabolism appears to be selective to the liver. Together, our findings indicate that the increased release of NPY during fasting stimulates the sympathetic nervous system to maintain VLDL-TG secretion at a postprandial level.
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Affiliation(s)
- Eveline Bruinstroop
- Department of Endocrinology and Metabolism, Academic Medical Center (AMC), University of Amsterdam, Amsterdam, the Netherlands.
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17
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Role for ADP ribosylation factor 1 in the regulation of hepatitis C virus replication. J Virol 2010; 85:946-56. [PMID: 21068255 DOI: 10.1128/jvi.00753-10] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
We hypothesized that ADP-ribosylation factor 1 (Arf1) plays an important role in the biogenesis and maintenance of infectious hepatitis C virus (HCV). Huh7.5 cells, in which HCV replicates and produces infectious viral particles, were exposed to brefeldin A or golgicide A, pharmacological inhibitors of Arf1 activation. Treatment with these agents caused a reduction in viral RNA levels, the accumulation of infectious particles within the cells, and a reduction in the levels of these particles in the extracellular medium. Fluorescence analyses showed that the viral nonstructural (NS) proteins NS5A and NS3, but not the viral structural protein core, shifted their localization from speckle-like structures in untreated cells to the rims of lipid droplets (LDs) in treated cells. Using pulldown assays, we showed that ectopic overexpression of NS5A in Huh7 cells reduces the levels of GTP-Arf1. Downregulation of Arf1 expression by small interfering RNA (siRNA) decreased both the levels of HCV RNA and the production of infectious viral particles and altered the localization of NS5A to the peripheries of LDs. Together, our data provide novel insights into the role of Arf1 in the regulation of viral RNA replication and the production of infectious HCV.
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18
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Abnormal hepatic apolipoprotein B metabolism in type 2 diabetes. Atherosclerosis 2010; 211:353-60. [DOI: 10.1016/j.atherosclerosis.2010.01.028] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Revised: 01/20/2010] [Accepted: 01/21/2010] [Indexed: 11/24/2022]
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19
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Uronen RL, Lundmark P, Orho-Melander M, Jauhiainen M, Larsson K, Siegbahn A, Wallentin L, Zethelius B, Melander O, Syvänen AC, Ikonen E. Niemann-Pick C1 modulates hepatic triglyceride metabolism and its genetic variation contributes to serum triglyceride levels. Arterioscler Thromb Vasc Biol 2010; 30:1614-20. [PMID: 20489167 DOI: 10.1161/atvbaha.110.207191] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE To study how Niemann-Pick disease type C1 (NPC1) influences hepatic triacylglycerol (TG) metabolism and to determine whether this is reflected in circulating lipid levels. METHODS AND RESULTS In Npc1(-/-) mice, the hepatic cholesterol content is increased but the TG content is decreased. We investigated lipid metabolism in Npc1(-/-) mouse hepatocytes and the association of NPC1 single-nucleotide polymorphisms with circulating TGs in humans. TGs were reduced in Npc1(-/-) mouse serum and hepatocytes. In Npc1(-/-) hepatocytes, the incorporation of [3H]oleic acid and [3H]acetate into TG was decreased, but shunting of oleic acid- or acetate-derived [3H]carbons into cholesterol was increased. Inhibition of cholesterol synthesis normalized TG synthesis, content, and secretion in Npc1(-/-) hepatocytes, suggesting increased hepatic cholesterol neogenesis as a cause for the reduced TG content and secretion. We found a significant association between serum TG levels and 5 common NPC1 single-nucleotide polymorphisms in a cohort of 1053 men, with the lowest P=8.7 x 10(-4) for the single-nucleotide polymorphism rs1429934. The association between the rs1429934 A allele and higher TG levels was replicated in 2 additional cohorts, which included 8041 individuals. CONCLUSIONS This study provides evidence of the following: (1) in mice, loss of NPC1 function reduces hepatocyte TG content and secretion by increasing the metabolic flux of carbons into cholesterol synthesis; and (2) common variation in NPC1 contributes to serum TG levels in humans.
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20
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Sundaram M, Yao Z. Recent progress in understanding protein and lipid factors affecting hepatic VLDL assembly and secretion. Nutr Metab (Lond) 2010; 7:35. [PMID: 20423497 PMCID: PMC2873297 DOI: 10.1186/1743-7075-7-35] [Citation(s) in RCA: 118] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Accepted: 04/27/2010] [Indexed: 02/06/2023] Open
Abstract
Excess lipid induced metabolic disorders are one of the major existing challenges for the society. Among many different causes of lipid disorders, overproduction and compromised catabolism of triacylglycerol-rich very low density lipoproteins (VLDL) have become increasingly prevalent leading to hyperlipidemia worldwide. This review provides the latest understanding in different aspects of VLDL assembly process, including structure-function relationships within apoB, mutations in APOB causing hypobetalipoproteinemia, significance of modulating microsomal triglyceride-transfer protein activity in VLDL assembly, alterations of VLDL assembly by different fatty acid species, and hepatic proteins involved in vesicular trafficking, and cytosolic lipid droplet metabolism that contribute to VLDL assembly. The role of lipoprotein receptors and exchangeable apolipoproteins that promote or diminish VLDL assembly and secretion is discussed. New understanding on dysregulated insulin signaling as a consequence of excessive triacylglycerol-rich VLDL in the plasma is also presented. It is hoped that a comprehensive view of protein and lipid factors that contribute to molecular and cellular events associated with VLDL assembly and secretion will assist in the identification of pharmaceutical targets to reduce disease complications related to hyperlipidemia.
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Affiliation(s)
- Meenakshi Sundaram
- Department of Biochemistry, Microbiology and Immunology, Ottawa Institute of Systems Biology, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada
| | - Zemin Yao
- Department of Biochemistry, Microbiology and Immunology, Ottawa Institute of Systems Biology, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada
- Department of Pathology and Laboratory Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada
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21
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Sundaram M, Zhong S, Bou Khalil M, Zhou H, Jiang ZG, Zhao Y, Iqbal J, Hussain MM, Figeys D, Wang Y, Yao Z. Functional analysis of the missense APOC3 mutation Ala23Thr associated with human hypotriglyceridemia. J Lipid Res 2010; 51:1524-34. [PMID: 20097930 DOI: 10.1194/jlr.m005108] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have shown that expression of apolipoprotein (apo) C-III promotes VLDL secretion from transfected McA-RH7777 cells under lipid-rich conditions. To determine structural elements within apoC-III that confer to this function, we contrasted wild-type apoC-III with a mutant Ala23Thr originally identified in hypotriglyceridemia subjects. Although synthesis of [(3)H]glycerol-labeled TAG was comparable between cells expressing wild-type apoC-III (C3wt cells) or Ala23Thr mutant (C3AT cells), secretion of [(3)H]TAG from C3AT cells was markedly decreased. The lowered [(3)H]TAG secretion was associated with an inability of C3AT cells to assemble VLDL(1). Moreover, [(3)H]TAG within the microsomal lumen in C3AT cells was 60% higher than that in C3wt cells, yet the activity of microsomal triglyceride-transfer protein in C3AT cells was not elevated. The accumulated [(3)H]TAG in C3AT microsomal lumen was mainly associated with lumenal IDL/LDL-like lipoproteins. Phenotypically, this [(3)H]TAG fractionation profiling resembled what was observed in cells treated with brefeldin A, which at low dose specifically blocked the second-step VLDL(1) maturation. Furthermore, lumenal [(35)S]Ala23Thr protein accumulated in IDL/LDL fractions and was absent in VLDL fractions in C3AT cells. These results suggest that the presence of Ala23Thr protein in lumenal IDL/LDL particles might prevent effective fusion between lipid droplets and VLDL precursors. Thus, the current study reveals an important structural element residing within the N-terminal region of apoC-III that governs the second step VLDL(1) maturation.
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Affiliation(s)
- Meenakshi Sundaram
- Department of Biochemistry, Ottawa Institute of Systems Biology, University of Ottawa, Canada
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22
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Biogenesis of cytoplasmic lipid droplets: from the lipid ester globule in the membrane to the visible structure. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1791:399-407. [PMID: 18996222 DOI: 10.1016/j.bbalip.2008.10.002] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2008] [Revised: 08/09/2008] [Accepted: 10/06/2008] [Indexed: 01/22/2023]
Abstract
The cytoplasmic lipid droplet (CLD) and very low-density lipoprotein are generated from the lipid ester synthesized in the endoplasmic reticulum. The lipid ester deposited between the two membrane leaflets is supposed to bulge toward the cytoplasm to make a nascent CLD, but its size must be below the resolution limit of conventional techniques and the detectable CLD should only form after acquisition of additional lipid esters. The CLD is different from vesicular organelles in that the internal content is highly hydrophobic and the shape is invariably spherical. Due to its unique characteristics, quantitative discordance between the surface and the volume may occur in the growth and/or involution processes of the CLD. The possibility that these processes may give rise to the structural and functional diversities of the CLD is discussed.
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23
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Brodsky JL, Fisher EA. The many intersecting pathways underlying apolipoprotein B secretion and degradation. Trends Endocrinol Metab 2008; 19:254-9. [PMID: 18691900 PMCID: PMC3216472 DOI: 10.1016/j.tem.2008.07.002] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/25/2008] [Revised: 07/07/2008] [Accepted: 07/07/2008] [Indexed: 02/06/2023]
Abstract
Because the levels of secreted apolipoprotein B (apoB) directly correlate with circulating serum cholesterol levels, there is a pressing need to define how the biosynthesis of this protein is regulated. Most commonly, the concentration of a secreted, circulating protein corresponds to transcriptionally and/or translationally regulated events. By contrast, circulating apoB levels are controlled by degradative pathways in the cell that select the protein for disposal. This article summarizes recent findings on two apoB disposal pathways, endoplasmic reticulum (ER)-associated degradation and autophagy, and describes a role for post-ER degradation in the increased circulating lipid levels in insulin-resistant diabetics.
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Affiliation(s)
- Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA.
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24
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Olofsson SO, Boström P, Andersson L, Rutberg M, Perman J, Borén J. Lipid droplets as dynamic organelles connecting storage and efflux of lipids. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1791:448-58. [PMID: 18775796 DOI: 10.1016/j.bbalip.2008.08.001] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2008] [Revised: 06/24/2008] [Accepted: 08/05/2008] [Indexed: 02/06/2023]
Abstract
Neutral lipids are stored in the cytosol in so-called lipid droplets. These are dynamic organelles with neutral lipids as the core surrounded by a monolayer of amphipathic lipids (phospholipids and cholesterol) and specific proteins (PAT proteins and proteins involved in the turnover of lipids and in the formation and trafficking of the droplets). Lipid droplets are formed at microsomal membranes as primordial droplets with a diameter of 0.1-0.4 microm and increase in size by fusion. In this article, we review the assembly and fusion of lipid droplets, and the processes involved in the secretion of triglycerides. Triglycerides are secreted from cells by two principally different processes. In the mammary gland, lipid droplets interact with specific regions of the plasma membrane and bud off with an envelope consisting of the membrane, to form milk globules. In the liver and intestine, very low-density lipoproteins (VLDL) and chylomicrons are secreted by using the secretory pathway of the cell. Finally, we briefly review the importance of lipid droplets in the development of insulin resistance and atherosclerosis.
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Affiliation(s)
- Sven-Olof Olofsson
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden.
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25
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Stafford JM, Yu F, Printz R, Hasty AH, Swift LL, Niswender KD. Central nervous system neuropeptide Y signaling modulates VLDL triglyceride secretion. Diabetes 2008; 57:1482-90. [PMID: 18332095 PMCID: PMC3968924 DOI: 10.2337/db07-1702] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
OBJECTIVE Elevated triglyceride (TG) is the major plasma lipid abnormality in obese and diabetic patients and contributes to cardiovascular morbidity in these disorders. We sought to identify novel mechanisms leading to hypertriglyceridemia. Resistance to negative feedback signals from adipose tissue in key central nervous system (CNS) energy homeostatic circuits contributes to the development of obesity. Because triglycerides both represent the largest energy depot in the body and are elevated in both the plasma and adipose in obesity and diabetes, we hypothesized that the same neural circuits that regulate energy balance also regulate the secretion of TGs into plasma. RESEARCH DESIGN AND METHODS In normal fasting rats, the TG secretion rate was estimated by serial blood sampling after intravascular tyloxapol pretreatment. Neuropeptide Y (NPY) signaling in the CNS was modulated by intracerebroventricular injection of NPY, receptor antagonist, and receptor agonist. RESULTS A single intracerebroventricular injection of NPY increased TG secretion by 2.5-fold in the absence of food intake, and this was determined to be VLDL by fast performance liquid chromatography (FPLC). This effect was recapitulated by activating NPY signaling in downstream neurons with an NPY-Y5 receptor agonist. An NPY-Y1 receptor antagonist decreased the elevated TGs in the form of VLDL secretion rate by 50% compared with vehicle. Increased TG secretion was due to increased secretion of VLDL particles, rather than secretion of larger particles, because apolipoprotein B100 was elevated in FPLC fractions corresponding to VLDL. CONCLUSIONS We find that a key neuropeptide system involved in energy homeostasis in the CNS exerts control over VLDL-TG secretion into the bloodstream.
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Affiliation(s)
- John M Stafford
- Division of Diabetes, Endocrinology, and Metabolism, Department of Internal Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
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26
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Abstract
Cholesterol is an essential structural component in the cell membranes of most vertebrates. The biophysical properties of cholesterol and the enzymology of cholesterol metabolism provide the basis for how cells handle cholesterol and exchange it with one another. A tightly controlled--but only partially characterized--network of cellular signalling and lipid transfer systems orchestrates the functional compartmentalization of this lipid within and between organellar membranes. This largely dictates the exchange of cholesterol between tissues at the whole body level. Increased understanding of these processes and their integration at the organ systems level provides fundamental insights into the physiology of cholesterol trafficking.
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Affiliation(s)
- Elina Ikonen
- Institute of Biomedicine/Anatomy, University of Helsinki, Haartmaninkatu 8, University of Helsinki, Helsinki FI-00014, Finland.
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27
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Gusarova V, Seo J, Sullivan ML, Watkins SC, Brodsky JL, Fisher EA. Golgi-associated maturation of very low density lipoproteins involves conformational changes in apolipoprotein B, but is not dependent on apolipoprotein E. J Biol Chem 2007; 282:19453-62. [PMID: 17500069 DOI: 10.1074/jbc.m700475200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The major protein component in secreted very low density lipoproteins (VLDL) is apoB, and it is established that these particles can reach sizes approaching 100 nm. We previously employed a cell-free system to investigate the nature of the vesicles in which this large cargo exits the endoplasmic reticulum (ER) (Gusarova, V., Brodsky, J. L., and Fisher, E. A. (2003) J. Biol. Chem. 278, 48051-48058). We found that apoB-containing lipoproteins exit the ER as dense lipid-protein complexes regardless of the final sizes of the particles and that further expansion occurs via post-ER lipidation. Here, we focused on maturation in the Golgi apparatus. In three separate approaches, we found that VLDL maturation (as assessed by changes in buoyant density) was associated with conformational changes in apoB. In addition, as the size of VLDL expanded, apoE concentrated in a subclass of Golgi microsomes or Golgi-derived vesicles that co-migrated with apoB-containing microsomes or vesicles, respectively. A relationship between apoB and apoE was further confirmed in co-localization studies by immunoelectron microscopy. These combined results are consistent with previous suggestions that apoE is required for VLDL maturation. To our surprise, however, we observed robust secretion of mature VLDL when apoE synthesis was inhibited in either rat hepatoma cells or apoE(-/-) mouse primary hepatocytes. We conclude that VLDL maturation in the Golgi involves apoB conformational changes and that the expansion of the lipoprotein does not require apoE; rather, the increase in VLDL surface area favors apoE binding.
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Affiliation(s)
- Viktoria Gusarova
- Department of Medicine, Leon Charney Division of Cardiology, New York University School of Medicine, New York, New York 10016, USA
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28
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Bykov I, Jauhiainen M, Olkkonen VM, Saarikoski ST, Ehnholm C, Junnikkala S, Väkevä A, Lindros KO, Meri S. Hepatic gene expression and lipid parameters in complement C3(-/-) mice that do not develop ethanol-induced steatosis. J Hepatol 2007; 46:907-14. [PMID: 17321001 DOI: 10.1016/j.jhep.2006.11.020] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/29/2006] [Revised: 10/24/2006] [Accepted: 11/24/2006] [Indexed: 01/07/2023]
Abstract
BACKGROUND/AIMS Fatty infiltration initiates alcohol-induced liver changes and complement component C3 affects lipid metabolism. We recently observed that ethanol-induced steatosis seen in normal (C3(+/+)) mice was absent in livers of C3-deficient (C3(-/-)) mice. To understand the underlying molecular mechanisms we analyzed lipid parameters and liver gene expression profiles in these mice. METHODS A Western-type high-fat diet with ethanol or carbohydrates (control) was fed for 6 weeks to C3(+/+) and C3(-/-) mice. Serum and liver lipid parameters were analyzed and liver mRNA expression patterns studied by micro-array analysis and RT-PCR. RESULTS In both genotypes ethanol markedly reduced serum cholesterol, apolipoprotein A-I, phospholipid transfer protein activity and hepatic mRNA levels of fatty acid-binding proteins and fatty acid beta-oxidation enzymes. In contrast, exclusively in C3(-/-) mice, ethanol treatment increased serum and liver adiponectin levels but down-regulated transcripts of lipogenic enzymes, adiponectin receptor 2 and adipose differentiation-related protein and up-regulated phospholipase D1. CONCLUSIONS We propose that these ethanol-induced alterations observed exclusively in C3(-/-) mice contribute to protection against fatty infiltration and subsequent inflammatory processes in the liver of these mice. The results suggest important cross-talk between complement factor C3 and lipid regulators in ethanol-induced steatosis.
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Affiliation(s)
- Igor Bykov
- National Public Health Institute, Departments of Mental Health and Alcohol Research, Finland
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29
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Tsai J, Qiu W, Kohen-Avramoglu R, Adeli K. MEK-ERK inhibition corrects the defect in VLDL assembly in HepG2 cells: potential role of ERK in VLDL-ApoB100 particle assembly. Arterioscler Thromb Vasc Biol 2006; 27:211-8. [PMID: 17038630 DOI: 10.1161/01.atv.0000249861.80471.96] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
OBJECTIVE Hepatic VLDL assembly is defective in HepG2 cells, resulting in the secretion of immature triglyceride-poor LDL-sized apoB particles. We investigated the mechanisms underlying defective VLDL assembly in HepG2 and have obtained evidence implicating the MEK-ERK pathway. METHODS AND RESULTS HepG2 cells exhibited considerably higher levels of the ERK1/2 mass and activity compared with primary hepatocytes. Inhibition of ERK1/2 using the MEK1/MEK2 inhibitor, U0126 (but not the inactive analogue) led to a significant increase in apoB secretion. In the presence of oleic acid, ERK1/2 inhibition caused a major shift in the lipoprotein distribution with a majority of particles secreted as VLDL, an effect independent of insulin. In contrast, overexpression of constitutively active MEK1 decreased apoB and large VLDL secretion. MEK1/2 inhibition significantly increased both cellular and microsomal TG mass, and mRNA levels for DGAT-1 and DGAT-2. In contrast to ERK, modulation of the PI3-K pathway or inhibition of the p38 MAP kinase, had no effect on lipoprotein density profile. Modulation of the MEK-ERK pathway in primary hamster hepatocytes led to changes in apoB secretion and altered the density profile of apoB-containing lipoproteins. CONCLUSIONS Inhibition of the overactive ras-MEK-ERK pathway in HepG2 cells can correct the defect in VLDL assembly leading to the secretion of large, VLDL-sized particles, similar to primary hepatocytes, implicating the MEK-ERK cascade in VLDL assembly in the HepG2 model. Modulation of this pathway in primary hepatocytes also regulates apoB secretion and appears to alter the formation of VLDL-1 sized particles.
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Affiliation(s)
- Julie Tsai
- Division of Clinical Biochemistry, Hospital for Sick Children, University of Toronto, Ontario, Canada M5G 1X8
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30
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Abstract
PURPOSE OF REVIEW Diabetic dyslipidaemia is a cluster of plasma lipid and lipoprotein abnormalities that are metabolically interrelated. The increase of large type 1 very low density lipoprotein particles in type 2 diabetes initiates a sequence of events that generates atherogenic remnants, small dense low-density lipoprotein and small dense high-density lipoprotein particles. Thus, it is of great importance to elucidate the mechanisms behind the overproduction of large very low density lipoprotein particles in diabetic dyslipidaemia. This review discusses the pathophysiology of very low density lipoprotein metabolism in type 2 diabetes and recent concepts of lipid management of diabetic dyslipidaemia. RECENT FINDINGS Results indicate that triglyceride and apolipoprotein B production in types 1 and 2 very low density lipoprotein are significantly correlated, suggesting a coupling of the two processes governing the metabolism of these lipoprotein subpopulations. Insulin resistance, hyperglycaemia, and liver fat were associated with excess hepatic production of type 1 but not type 2 very low density lipoprotein particles. These data provide support for the independent regulation of types 1 and 2 very low density lipoprotein apolipoprotein B production. SUMMARY Recent data suggest that the assembly of very low density lipoprotein is fundamentally altered in type 2 diabetes, explaining the overproduction of large type 1 very low density lipoprotein as well as the inability of insulin to suppress production of type 1 very low density lipoprotein in type 2 diabetes. Future discoveries hopefully will delineate the regulatory steps to allow more targeted treatment of diabetic dyslipidaemia.
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Affiliation(s)
- Martin Adiels
- Sahlgrenska Center for Metabolism and Cardiovascular Research, Wallenberg Laboratory for Cardiovascular Research and the Department of Metabolism and Cardiovascular Research, The Sahlgrenska Academy at Göteborg University, Göteborg, Sweden
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31
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Olofsson SO, Borèn J. Apolipoprotein B: a clinically important apolipoprotein which assembles atherogenic lipoproteins and promotes the development of atherosclerosis. J Intern Med 2005; 258:395-410. [PMID: 16238675 DOI: 10.1111/j.1365-2796.2005.01556.x] [Citation(s) in RCA: 204] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Apolipoprotein (apo) B exists in two forms apoB100 and apoB48. ApoB100 is present on very low-density lipoproteins (VLDL), intermediate density lipoproteins (IDL) and LDL. ApoB100 assembles VLDL particles in the liver. This process starts by the formation of a pre-VLDL, which is retained in the cell unless converted to the triglyceride-poor VLDL2. VLDL2 is secreted or converted to VLDL1 by a bulk lipidation in the Golgi apparatus. ApoB100 has a central role in the development of atherosclerosis. Two proteoglycan-binding sequences in apoB100 have been identified, which are important for retaining the lipoprotein in the intima of the artery. Retention is essential for the development of the atherosclerotic lesion.
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Affiliation(s)
- S-O Olofsson
- Wallenberg Laboratory for Cardiovascular Research, Göteborg University, Sahlgrenska University Hospital, Göteborg, Sweden.
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32
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Lay D, L Grosshans B, Heid H, Gorgas K, Just WW. Binding and functions of ADP-ribosylation factor on mammalian and yeast peroxisomes. J Biol Chem 2005; 280:34489-99. [PMID: 16100119 DOI: 10.1074/jbc.m503497200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have analyzed in vitro the binding characteristics of members of the ADP-ribosylation factor (ARF) family of proteins to a highly purified rat liver peroxisome preparation void of Golgi membranes and studied in vivo a role these proteins play in the proliferation of yeast peroxisomes. Although both ARF1 and ARF6 were found on peroxisomes, coatomer recruitment only depended on ARF1-GTP. Recruitment of ARF1 and coatomer to peroxisomes was significantly affected both by pretreating the animals with peroxisome proliferators and by ATP and a cytosolic fraction designated the intermediate pool fraction depleted of ARF and coatomer. In the presence of ATP, the concentrations of ARF1 and coatomer on peroxisomes were reduced, whereas intermediate pool fraction led to a concentration-dependent decrease in ARF and increase in coatomer. Brefeldin A, a fungal toxin that is known to reduce ARF1 binding to Golgi membranes, did not affect ARF1 binding to peroxisomes. In Saccharomyces cerevisiae, both ScARF1 and ScARF3, the yeast orthologs of mammalian ARF1 and ARF6, were implicated in the control of peroxisome proliferation. ScARF1 regulated this process in a positive manner, and ScARF3 regulated it in a negative manner.
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Affiliation(s)
- Dorothee Lay
- Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, D-69120 Heidelberg, Germany
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33
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Peretti N, Marcil V, Drouin E, Levy E. Mechanisms of lipid malabsorption in Cystic Fibrosis: the impact of essential fatty acids deficiency. Nutr Metab (Lond) 2005; 2:11. [PMID: 15869703 PMCID: PMC1134666 DOI: 10.1186/1743-7075-2-11] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2005] [Accepted: 05/03/2005] [Indexed: 12/26/2022] Open
Abstract
Transport mechanisms, whereby alimentary lipids are digested and packaged into small emulsion particles that enter intestinal cells to be translocated to the plasma in the form of chylomicrons, are impaired in cystic fibrosis. The purpose of this paper is to focus on defects that are related to intraluminal and intracellular events in this life-limiting genetic disorder. Specific evidence is presented to highlight the relationship between fat malabsorption and essential fatty acid deficiency commonly found in patients with cystic fibrosis that are often related to the genotype. Given the interdependency of pulmonary disease, pancreatic insufficiency and nutritional status, greater attention should be paid to the optimal correction of fat malabsorption and essential fatty acid deficiency in order to improve the quality of life and extend the life span of patients with cystic fibrosis.
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Affiliation(s)
- N Peretti
- Department of Nutrition, CHU-Sainte-Justine, Université de Montréal, Montréal, Québec, Canada
| | - V Marcil
- Department of Nutrition, CHU-Sainte-Justine, Université de Montréal, Montréal, Québec, Canada
| | - E Drouin
- Department of Pediatrics, CHU-Sainte-Justine, Université de Montréal, Montréal, Québec, Canada
| | - E Levy
- Department of Nutrition, CHU-Sainte-Justine, Université de Montréal, Montréal, Québec, Canada
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34
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Asp L, Magnusson B, Rutberg M, Li L, Borén J, Olofsson SO. Role of ADP Ribosylation Factor 1 in the Assembly and Secretion of ApoB-100–Containing Lipoproteins. Arterioscler Thromb Vasc Biol 2005; 25:566-70. [PMID: 15618550 DOI: 10.1161/01.atv.0000154135.21689.47] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE We investigated the role of ADP ribosylation factor 1 (ARF1) in the assembly of very-low-density lipoproteins (VLDLs). METHODS AND RESULTS The dominant-negative ARF1 mutant, T31N, decreased the assembly of apoB-100 VLDL 1 (Svedberg floatation units [Sf] 60 to 400) by 80%. The decrease coincided with loss of coatamer I (COPI) from the Golgi apparatus and inhibition of anterograde transport, as demonstrated by time-lapse studies of the vesicular stomatitis virus G protein. The VLDL 1 assembly was also completely inhibited at 15 degrees C. Thus, the antegrade transport is essential for the assembly of VLDL 1. Intracellular localization of N-acetylgalactosaminyl transferase 2 indicated that the Golgi apparatus was at least partly intact when the VLDL assembly was inhibited. Transient transfection with phospholipase D 1 increased the assembly of VLDL 1 and VLDL 2 (Sf 20 to 60). Overexpression of ARF1 in stably transfected McA-RH7777 cells increased the secretion of VLDL 2 but not of VLDL 1, which was dependent on the availability of oleic acid. Secretion of VLDL 1 increased with increasing amounts of oleic acid, and VLDL 2 secretion decreased simultaneously. CONCLUSIONS Overexpression of ARF1 increased the assembly of VLDL 2 but not of VLDL 1, whose production was dependent on both anterograde transport and the availability of fatty acids.
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Affiliation(s)
- Lennart Asp
- Department of Medical Biochemistry, Wallenberg Laboratory for Cardiovascular Research, Göteborg University, Göteborg, Sweden
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35
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Jirholt P, Adiels M, Borén J. How Does Mutant Proprotein Convertase Neural Apoptosis-Regulated Convertase 1 Induce Autosomal Dominant Hypercholesterolemia? Arterioscler Thromb Vasc Biol 2004; 24:1334-6. [PMID: 15297286 DOI: 10.1161/01.atv.0000133682.97348.ff] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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36
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Zhang YL, Hernandez-Ono A, Ko C, Yasunaga K, Huang LS, Ginsberg HN. Regulation of Hepatic Apolipoprotein B-lipoprotein Assembly and Secretion by the Availability of Fatty Acids. J Biol Chem 2004; 279:19362-74. [PMID: 14970200 DOI: 10.1074/jbc.m400220200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The in vivo effects of increased delivery of fatty acids (FA) to the liver are poorly defined. Therefore, we compared the effects of infusing either 6 mM oleic acid (OA) bound to albumin, 0.5-20% Intralipid, or saline for 3 or 6 h into male C57BL/6J mice. Infusions were followed by studies of triglyceride (TG) and apoB secretion. Although plasma FA levels increased similarly after either 20% Intralipid or 6 mM OA, TG secretion increased only after infusion of 4-20% Intralipid; TG secretion was unchanged by 6 mM OA. By contrast, 6-h infusions of either 6 mM OA or 4-20% Intralipid increased apoB secretion. 6 mM OA and 20% Intralipid each increased secretion of apoB from primary hepatocytes ex vivo. Importantly, 0.5-2% Intralipid, which delivered more FA to the liver than 6 mM OA, did not stimulate apoB secretion. Hepatic apoB mRNA levels were unaffected by either 6 mM OA or 20% Intralipid, but microsomal triglyceride transfer protein mRNA was significantly lower after 6-h infusions with 6 mM OA versus either saline or 20% Intralipid. Lower microsomal triglyceride transfer protein mRNA levels were associated with reduced hepatic TG mass after 6-h infusions of 6 mM OA. We conclude that 1) increased FA delivery to the liver in vivo increases secretion of apoB-lipoproteins via post-transcriptional mechanisms, 2) OA-induced apoB-lipoprotein secretion occurred at least in part via mechanisms other than by providing substrate for TG synthesis, and 3) the route of delivery of FA is important for its effects on apoB secretion.
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Affiliation(s)
- Yuan-Li Zhang
- Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA
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37
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Mensenkamp AR, Van Luyn MJA, Havinga R, Teusink B, Waterman IJ, Mann CJ, Elzinga BM, Verkade HJ, Zammit VA, Havekes LM, Shoulders CC, Kuipers F. The transport of triglycerides through the secretory pathway of hepatocytes is impaired in apolipoprotein E deficient mice. J Hepatol 2004; 40:599-606. [PMID: 15030975 DOI: 10.1016/j.jhep.2003.12.011] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/30/2003] [Revised: 10/23/2003] [Accepted: 12/08/2003] [Indexed: 12/04/2022]
Abstract
BACKGROUND/AIMS Apolipoprotein E (apoE)-deficient mice develop hepatic steatosis and secrete reduced levels of VLDL-TG. METHODS AND RESULTS We examined the effects of apoE-deficiency on intracellular lipid homeostasis and secretion of triglycerides (TG). We show that intracellular TG turnover and activities of diacylglycerol acyltransferase (DGAT) and microsomal triglyceride transfer protein (MTP) are similar in Apoe(-/-) and wild type mice. In addition, apoB synthesis was not decreased in Apoe(-/-) cells. Thus, the accumulation of lipid in these cells is not attributable to perturbed TG turnover, apoB synthesis, and the activities of DGAT and MTP. Inhibition of MTP had a more profound impact on the secretion of VLDL-TG from wild type hepatocytes than Apoe(-/-) hepatocytes, indicating that MTP was more limiting for the production of VLDL-TG from wild type cells. In marked contrast to the MTP-deficient model of fatty liver, electron microscopy of lipid-stained liver sections of Apoe(-/-) mice revealed an accumulation of lipid in numerous small, putative ER-derived vesicles and in the cytosol. No abnormalities were observed in the Golgi of Apoe(-/-) mice. CONCLUSIONS These results suggest that the removal of lipids from the early or intermediary compartments of the secretory pathway of hepatocytes is impaired in Apoe(-/-) mice.
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Affiliation(s)
- Arjen R Mensenkamp
- Department of Cell Biology, Faculty of Medical Sciences, University Hospital Groningen, 9713 GZ Groningen, The Netherlands.
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38
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Gusarova V, Brodsky JL, Fisher EA. Apolipoprotein B100 exit from the endoplasmic reticulum (ER) is COPII-dependent, and its lipidation to very low density lipoprotein occurs post-ER. J Biol Chem 2003; 278:48051-8. [PMID: 12960170 DOI: 10.1074/jbc.m306898200] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hepatic apolipoprotein B100 (apoB100) associates with lipids to form dense lipoprotein particles in the endoplasmic reticulum (ER) and is further lipidated to very low density lipoproteins (VLDL). Because the VLDL diameter can exceed 200 nm, classical ER-derived vesicles may be unable to accommodate VLDLs. Using hepatic membranes and cytosol to reconstitute ER budding, apoB100-containing vesicles sedimented distinct from those harboring more typical cargo but contained Sec23. Moreover, ER exit of apoB was inhibited by dominant-negative Sar1. Budding required Sar1 regardless of whether oleic acid (OA) was added to stimulate apoB lipidation; therefore, either large apoB100-lipoproteins reside in secretory vesicles, or full lipidation occurs post-ER. Using membranes from cells incubated in the presence or absence of OA, we determined that apoB100-lipoproteins in ER vesicles had not become lipidated to VLDLs. VLDL particles resided in the Golgi, but not the ER, after fractionation of OA-treated cells. We conclude that apoB100-lipoproteins exit the ER in COPII vesicles, but under conditions favorable for VLDL formation final lipid loading occurs post-ER.
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Affiliation(s)
- Viktoria Gusarova
- Department of Medicine and The Cardiovascular Institute, Mount Sinai School of Medicine, New York, New York 10029, USA
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39
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Yamaguchi J, Gamble MV, Conlon D, Liang JS, Ginsberg HN. The conversion of apoB100 low density lipoprotein/high density lipoprotein particles to apoB100 very low density lipoproteins in response to oleic acid occurs in the endoplasmic reticulum and not in the Golgi in McA RH7777 cells. J Biol Chem 2003; 278:42643-51. [PMID: 12917397 DOI: 10.1074/jbc.m306920200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The site where bulk lipid is added to apoB100 low density lipoproteins (LDL)/high density lipoproteins (HDL) particles to form triglyceride-enriched very low density lipoproteins (VLDL) has not been identified definitively. We employed several strategies to address this question. First, McA RH7777 cells were pulse-labeled for 20 min with [35S]methionine/cysteine and chased for 1 h (Chase I) to allow study of newly synthesized apoB100 LDL/HDL remaining in the endoplasmic reticulum (ER). After Chase I, cells were incubated for another hour (C2) with/without brefeldin A (BFA) and nocodazole (Noc) (to block ER to Golgi trafficking) and with/without oleic acid (OA). OA treatment alone during C2 increased VLDL secretion. This was prevented by the addition of BFA/Noc in C2. When C2 media were replaced by control media for another 1-h chase (C3), VLDL formed during OA treatment in C2 were secreted into C3 medium. Thus, OA-induced conversion of apoB100 LDL/HDL to VLDL during C2 occurred in the ER. Next, newly synthesized apoB100 lipoproteins were trapped in the Golgi by treatment with Noc and monensin during Chase I (C1), and C2 was carried out in the presence of BFA/Noc with/without OA and without monensin. Under these conditions, OA treatment during C2 did not stimulate VLDL secretion. The same pulse/chase protocols were followed by iodixanol subcellular fractionation, extraction of lipoproteins from ER and Golgi, and sucrose gradient separation of extracted lipoproteins. Cells treated with BFA/Noc and OA in C2 had VLDL in the ER. In the absence of OA, only LDL/HDL were present in the ER. The density of Golgi lipoproteins in these cells was not affected by OA. Similar results were obtained when ER were immuno-isolated with anti-calnexin antibodies. In conclusion, apoB100 bulk lipidation, resulting in conversion of LDL/HDL to VLDL, can occur in the ER, but not in the Golgi, in McA RH7777 cells.
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Affiliation(s)
- Junji Yamaguchi
- Department of Medicine, Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
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40
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Marchesan D, Rutberg M, Andersson L, Asp L, Larsson T, Borén J, Johansson BR, Olofsson SO. A phospholipase D-dependent process forms lipid droplets containing caveolin, adipocyte differentiation-related protein, and vimentin in a cell-free system. J Biol Chem 2003; 278:27293-300. [PMID: 12730229 DOI: 10.1074/jbc.m301430200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
We developed a microsome-based, cell-free system that assembles newly formed triglyceride (TG) into spherical lipid droplets. These droplets were recovered in the d </= 1.055 g/ml fraction by gradient ultracentrifugation and were similar in size and appearance to those isolated from rat adipocytes and 3T3-L1 cells. Caveolin 1 and 2, vimentin, adipocyte differentiation-related protein, and the 78-kDa glucose regulatory protein were identified on the droplets from the cell-free system. The caveolin was soluble in 1% Triton X-100, as was the caveolin on lipid droplets from 3T3-L1 cells. The lipid droplets from the cell-free system, like those from 3T3-L1 cells, contained TG, diacylglycerol, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine. The assembly of these TG-containing structures was dependent on the rate of TG biosynthesis and required an activator present in the 160,000 x g supernatant from homogenized rat adipocytes. The activator induced phospholipase D (PLD) activity, and its effect on the release of the TG-containing structures from the microsomes was inhibited by 1-butanol (but not 2-butanol) or 2,3-diphosphoglycerate. The activator could be replaced by a constitutively active PLD or phosphatidic acid. These results indicate that PLD and the formation of phosphatidic acid are important in the assembly of the TG-containing structures.
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Affiliation(s)
- Denis Marchesan
- Department of Medical Biochemistry and the Wallenberg Laboratory for Cardiovascular Research, Göteborg University, SE-413 45 Göteborg, Sweden
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41
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Dohke Y, Fujita-Yoshigaki J, Sugiya H, Furuyama S, Hara-Yokoyama M. Involvement of phospholipase D in the cAMP-regulated exocytosis of rat parotid acinar cells. Biochem Biophys Res Commun 2002; 299:663-8. [PMID: 12459191 DOI: 10.1016/s0006-291x(02)02713-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The activation of beta-adrenergic receptors in rat parotid acinar cells causes intracellular cAMP elevation and appreciably stimulates the exocytotic release of amylase into saliva. The activation of Ca(2+)-mobilizing receptors also induces some exocytosis. We investigated the role of phospholipase D (PLD) in regulated exocytosis in rat parotid acinar cells. A transphosphatidylation assay detected GTPgammaS (a nonhydrolyzable analogue of GTP)-dependent PLD activity in lysates of rat parotid acinar cells, suggesting that PLD is activated by small molecular mass GTP-binding proteins. The PLD inhibitor, neomycin, suppressed cAMP-dependent exocytosis in saponin-permeabilized cells. Signaling downstream of PLD was disrupted by 1-butanol due to conversion of the PLD reaction product (phosphatidic acid) to phosphatidylbutanol. The stimulation of exocytosis by isoproterenol as well as by a Ca(2+)-mobilizing agonist (methacholine) was inhibited by 1-butanol. These results suggest that PLD is important for regulated exocytosis in rat parotid acinar cells.
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Affiliation(s)
- Yoko Dohke
- Department of Physiology, Nihon University School of Dentistry at Matsudo, 2-870-1 Sakae-cho Nishi, Matsudo, Chiba 271-8587, Japan
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42
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Noga AA, Zhao Y, Vance DE. An unexpected requirement for phosphatidylethanolamine N-methyltransferase in the secretion of very low density lipoproteins. J Biol Chem 2002; 277:42358-65. [PMID: 12193594 DOI: 10.1074/jbc.m204542200] [Citation(s) in RCA: 178] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Phosphatidylethanolamine N-methyltransferase (PEMT) catalyzes the conversion of phosphatidylethanolamine to phosphatidylcholine (PC). We investigated whether there was diminished secretion of lipoproteins from hepatocytes derived from mice that lacked PEMT (Pemt(-/-)) compared with Pemt(+/+) mice. Hepatocytes were incubated with 0.75 mm oleate, the media were harvested, and triacylglycerol (TG), PC, apolipoprotein (apo) B100, and apoB48 were isolated and quantified. Compared with hepatocytes from Pemt(+/+) mice, hepatocytes from Pemt(-/-) mice secreted 50% less TG, whereas secretion of PC was unaffected. Fractionation of the secreted lipoproteins on density gradients demonstrated that the decrease in TG was in the very low density lipoprotein (VLDL)/low density lipoprotein fractions. The secretion of apoB100 was decreased by approximately 70% in VLDLs/low density lipoproteins, whereas there was no significant decrease in apoB48 secretion in any fraction. Transfection of McArdle hepatoma cells (that lack PEMT) with PEMT cDNA enhanced secretion of TG in the VLDLs. Because the levels of PC in the hepatocytes and hepatoma cells were unaffected by the lack of PEMT expression, there appears to be an unexpected requirement for PEMT in the secretion of apoB100-containing VLDLs.
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Affiliation(s)
- Anna A Noga
- Department of Biochemistry and the Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Canada
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43
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Abstract
Phospholipase D1 and D2 (PLD1, PLD2) both have PX and PH domains in their N-terminal regions with these inositol lipid binding domains playing key roles in regulating PLD activity and localisation. The activity of PLD1 is also regulated by protein kinase C and members of the Rho and Arf families of GTPases. Each of these proteins binds to unique sites; however, there appears to be little in vitro discrimination between individual family members. In agonist-stimulated cells, however, there is specificity, with, for example in RBL-2H3 cells, antigen stimulating the activation of PLD1 by association with Arf6, Rac1 and protein kinase Calpha. PLD2 appears to be less directly regulated by GTPases and rather is primarily controlled through interaction with phosphatidylinositol 4-phosphate 5-kinase that generates the activating phosphatidylinositol 4,5-bisphosphate.
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Affiliation(s)
- Dale J Powner
- CR UK Institute for Cancer Studies, Birmingham University, B15 2TT, Birmingham, UK
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Valyi-Nagy K, Harris C, Swift LL. The assembly of hepatic very low density lipoproteins: evidence of a role for the Golgi apparatus. Lipids 2002; 37:879-84. [PMID: 12458623 DOI: 10.1007/s11745-002-0974-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Previous studies from our laboratory have suggested that the assembly of lipoproteins by the liver is not completed in the rough endoplasmic reticulum but continues while the particles are en route to or within the Golgi apparatus. To investigate further the role of the Golgi apparatus in lipoprotein assembly, mice were injected with [3H]glycerol and killed 7.5 to 45 min after injection. Microsomes and Golgi apparatus-rich fractions were isolated from the livers and separated into membrane and content fractions. TG within microsomal and Golgi membranes were labeled, rapidly reaching peak specific activity within 7.5 min of isotope injection. The specific activity of TG in microsomal membranes decreased to approximately 40% of peak values by 45 min, whereas the specific activity of TG in the Golgi membranes decreased to approximately 30% of peak values by 45 min. To determine whether the turnover of the Golgi membrane TG pool was dependent on microsomal TG transfer protein (MTP), mice were gavaged with an MTP inhibitor, and the labeling experiments were repeated. Inhibition of MTP attenuated the turnover of newly synthesized Golgi membrane TG by approximately 50% and the turnover of microsomal membrane TG by approximately 40%. Based on the rapid turnover of the Golgi membrane TG pool and the attenuation of the turnover of this pool by MTP inhibitor, we propose that lipid is transferred from the Golgi membrane to luminal lipoproteins in an MTP-dependent manner. The results support our hypothesis that assembly of VLDL continues within the Golgi apparatus.
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Affiliation(s)
- Klara Valyi-Nagy
- Department of Pathology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2561, USA
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Rashid KA, Hevi S, Chen Y, Le Cahérec F, Chuck SL. A proteomic approach identifies proteins in hepatocytes that bind nascent apolipoprotein B. J Biol Chem 2002; 277:22010-7. [PMID: 11934886 DOI: 10.1074/jbc.m112448200] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The biogenesis of apolipoprotein B is quite complex in view of its huge size, hydrophobicity, obligate association with lipids such as cholesterol and triglycerides prior to secretion, and intracellular degradation of a substantial proportion of newly synthesized molecules. Multiple proteins likely serve roles as molecular chaperones to assist in folding, assembly with lipids, and regulation of the secretion of apolipoprotein B. In these studies, we developed a strategy to isolate proteins associated with apolipoprotein B in rat livers. The purification consisted of two stages: first, microsomes were prepared from rat liver and treated with chemical cross-linkers, and second, the solubilized proteins were co-immunoprecipitated with antibody against apolipoprotein B. We found that several proteins were cross-linked to apolipoprotein B. The proteins were digested with trypsin, and the released peptides were sequenced by tandem mass spectrometry. The sequences precisely matched 377 peptides in 99 unique proteins. We show that at least two of the identified proteins, ferritin heavy and light chains, can directly bind apolipoprotein B. These and possibly other proteins identified by this proteomic approach are novel candidates for proteins that affect apolipoprotein B during its biogenesis.
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Affiliation(s)
- K Aftab Rashid
- Molecular Medicine Unit, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA
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46
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Hannuksela ML, Liisanantti MK, Savolainen MJ. Effect of alcohol on lipids and lipoproteins in relation to atherosclerosis. Crit Rev Clin Lab Sci 2002; 39:225-83. [PMID: 12120782 DOI: 10.1080/10408360290795529] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Several studies indicate that light-to-moderate alcohol consumption is associated with a low prevalence of coronary heart disease. An increase in high-density lipoprotein (HDL) cholesterol is associated with alcohol intake and appears to account for approximately half of alcohol's cardioprotective effect. In addition to changes in the concentration and composition of lipoproteins, alcohol consumption may alter the activities of plasma proteins and enzymes involved in lipoprotein metabolism: cholesteryl ester transfer protein, phospholipid transfer protein, lecithin:cholesterol acyltransferase, lipoprotein lipase, hepatic lipase, paraoxonase-1 and phospholipases. Alcohol intake also results in modifications of lipoprotein particles: low sialic acid content in apolipoprotein components of lipoprotein particles (e.g., HDL apo E and apo J) and acetaldehyde modification of apolipoproteins. In addition, "abnormal" lipids, phosphatidylethanol, and fatty acid ethyl esters formed in the presence of ethanol are associated with lipoproteins in plasma. The effects of lipoproteins on the vascular wall cells (endothelial cells, smooth muscle cells, and monocyte/macrophages) may be modulated by ethanol and the alterations further enhanced by modified lipids. The present review discusses the effects of alcohol on lipoproteins in cholesterol transport, as well as the novel effects of lipoproteins on vascular wall cells.
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Affiliation(s)
- Minna L Hannuksela
- Department of Internal Medicine, Biocenter Oulu, University of Oulu, Finland
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Fisher EA, Ginsberg HN. Complexity in the secretory pathway: the assembly and secretion of apolipoprotein B-containing lipoproteins. J Biol Chem 2002; 277:17377-80. [PMID: 12006608 DOI: 10.1074/jbc.r100068200] [Citation(s) in RCA: 343] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Affiliation(s)
- Edward A Fisher
- Cardiovascular Institute and Departments of Medicine and Biochemistry, Mount Sinai School of Medicine, New York, New York 10029, USA.
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48
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Hui TY, Olivier LM, Kang S, Davis RA. Microsomal triglyceride transfer protein is essential for hepatic secretion of apoB-100 and apoB-48 but not triglyceride. J Lipid Res 2002. [DOI: 10.1016/s0022-2275(20)30121-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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49
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Pan M, Liang Js JS, Fisher EA, Ginsberg HN. The late addition of core lipids to nascent apolipoprotein B100, resulting in the assembly and secretion of triglyceride-rich lipoproteins, is independent of both microsomal triglyceride transfer protein activity and new triglyceride synthesis. J Biol Chem 2002; 277:4413-21. [PMID: 11704664 DOI: 10.1074/jbc.m107460200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although microsomal triglyceride transfer protein (MTP) and newly synthesized triglyceride (TG) are critical for co-translational targeting of apolipoprotein B (apoB100) to lipoprotein assembly in hepatoma cell lines, their roles in the later stages of lipoprotein assembly remain unclear. Using N-acetyl-Leu-Leu-norleucinal to prevent proteasomal degradation, HepG2 cells were radiolabeled and chased for 0-90 min (chase I). The medium was changed and cells chased for another 150 min (chase II) in the absence (control) or presence of Pfizer MTP inhibitor CP-10447 (CP). As chase I was extended, inhibition of apoB100 secretion by CP during chase II decreased from 75.9% to only 15% of control (no CP during chase II). Additional studies were conducted in which chase I was either 0 or 90 min, and chase II was in the presence of [(3)H]glycerol and either BSA (control), CP (inhibits both MTP activity and TG synthesis),BMS-1976360-1) (BMS) (inhibits only MTP activity), or triacsin C (TC) (inhibits only TG synthesis). When chase I was 0 min, CP, BMS, and TC reduced apoB100 secretion during chase II by 75.3, 73.9, and 53.9%. However, when chase I was 90 min, those agents reduced apoB100 secretion during chase II by only 16.0, 19.2, and 13.9%. Of note, all three inhibited secretion of newly synthesized TG during chase II by 80, 80, and 40%, whether chase I was 0 or 90 min. In both HepG2 cells and McA-RH7777 cells, if chase I was at least 60 min, inhibition of TG synthesis and/or MTP activity did not affect the density of secreted apoB100-lipoproteins under basal conditions. Oleic acid increased secretion of TG-enriched apoB100-lipoproteins similarly in the absence or presence of either of CP, BMS, or TC. We conclude that neither MTP nor newly synthesized TG is necessary for the later stages of apoB100-lipoprotein assembly and secretion in either HepG2 or McA-RH7777 cells.
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Affiliation(s)
- Meihui Pan
- Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA
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50
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Hebbachi AM, Gibbons GF. Microsomal membrane-associated apoB is the direct precursor of secreted VLDL in primary cultures of rat hepatocytes. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)32215-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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