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Ting KK. John Yudkin's hypothesis: sugar is a major dietary culprit in the development of cardiovascular disease. Front Nutr 2024; 11:1407108. [PMID: 39027662 PMCID: PMC11257042 DOI: 10.3389/fnut.2024.1407108] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2024] [Accepted: 06/24/2024] [Indexed: 07/20/2024] Open
Abstract
To date, the risk of developing atherosclerosis has extended beyond Western countries and now affecting individuals from various ethnic backgrounds and age groups. Traditional risk factors of atherosclerosis, such as hypercholesterolemia, has been better controlled than before due to highly effective and inexpensive therapies at lowering plasma cholesterol levels. However, the role of reducing dietary cholesterol intake, as a public healthy strategy, in preventing the occurrence of cardiovascular mortalities has been recently challenged. Indeed, despite our continuous decline of dietary cholesterol intake within the last 50 years, the incidence of cardiovascular mortalities has continued to rise, thus raising the possibility that other dietary factors, such as fructose-containing sugars, are the major culprit. In the 1970s, John Yudkin first proposed that sugar was the predominant dietary factor that underlies the majority of cardiovascular mortalities, yet his hypothesis was dismissed. However, over the last 25 years substantial scientific evidence has been accumulated to support Yudkin's hypothesis. The objectives of this review are to highlight Yudkin's significant contribution to nutritional science by reviewing his hypothesis and summarizing the recent advances in our understanding of fructose metabolism. The metabolic consequences of fructose metabolism, such as fructose-induced uricemia, insulin resistance, lipoprotein hyperproduction and chronic inflammation, and how they are linked to atherosclerosis as risk factors will be discussed. Finally, the review will explore areas that warrant future research and raise important considerations that we need to evaluate when designing future studies.
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Affiliation(s)
- Kenneth K.Y. Ting
- Department of Immunology, University of Toronto, Toronto, ON, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON, Canada
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2
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Reyes-Soffer G, Liu J, Thomas T, Matveyenko A, Seid H, Ramakrishnan R, Holleran S, Zaghloul N, Sztalryd-Woodle C, Pollin T, Ginsberg HN. TM6SF2 Determines Both the Degree of Lipidation and the Number of VLDL Particles Secreted by the Liver. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2023:2023.06.23.23291823. [PMID: 37425717 PMCID: PMC10327233 DOI: 10.1101/2023.06.23.23291823] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/11/2023]
Abstract
In 2014, exome-wide studies identified a glutamine176lysine (p.E167K) substitution in a protein of unknown function named transmembrane 6 superfamily member 2 (TM6SF2). The p.E167K variant was associated with increased hepatic fat content and reduced levels of plasma TG and LDL cholesterol. Over the next several years, additional studies defined the role of TM6SF2, which resides in the ER and the ER-Golgi interface, in the lipidation of nascent VLDL to generate mature, more TG-rich VLDL. Consistent results from cells and rodents indicated that the secretion of TG was reduced in the p.E167K variant or when hepatic TM6SF2 was deleted. However, data for secretion of APOB was inconsistent, either reduced or increased secretion was observed. A recent study of people homozygous for the variant demonstrated reduced in vivo secretion of large, TG-rich VLDL1 into plasma; both TG and APOB secretion were reduced. Here we present new results demonstrating increased secretion of VLDL APOB with no change in TG secretion in p.E167K homozygous individuals from the Lancaster Amish community compared to their wild-type siblings. Our in vivo kinetic tracer results are supported by in vitro experiments in HepG2 and McA cells with knock-down or Crispr-deletions of TM6SF2, respectively. We offer a model to potentially explain all of the prior data and our new results.
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Vatandaslar H, Garzia A, Meyer C, Godbersen S, Brandt LTL, Griesbach E, Chao JA, Tuschl T, Stoffel M. In vivo PAR-CLIP (viP-CLIP) of liver TIAL1 unveils targets regulating cholesterol synthesis and secretion. Nat Commun 2023; 14:3386. [PMID: 37296170 PMCID: PMC10256721 DOI: 10.1038/s41467-023-39135-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2022] [Accepted: 05/31/2023] [Indexed: 06/12/2023] Open
Abstract
System-wide cross-linking and immunoprecipitation (CLIP) approaches have unveiled regulatory mechanisms of RNA-binding proteins (RBPs) mainly in cultured cells due to limitations in the cross-linking efficiency of tissues. Here, we describe viP-CLIP (in vivo PAR-CLIP), a method capable of identifying RBP targets in mammalian tissues, thereby facilitating the functional analysis of RBP-regulatory networks in vivo. We applied viP-CLIP to mouse livers and identified Insig2 and ApoB as prominent TIAL1 target transcripts, indicating an important role of TIAL1 in cholesterol synthesis and secretion. The functional relevance of these targets was confirmed by showing that TIAL1 influences their translation in hepatocytes. Mutant Tial1 mice exhibit altered cholesterol synthesis, APOB secretion and plasma cholesterol levels. Our results demonstrate that viP-CLIP can identify physiologically relevant RBP targets by finding a factor implicated in the negative feedback regulation of cholesterol biosynthesis.
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Affiliation(s)
- Hasan Vatandaslar
- Institute of Molecular Health Sciences, ETH Zurich, Otto-Stern-Weg 7, 8093, Zürich, Switzerland
| | - Aitor Garzia
- Laboratory of RNA Molecular Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10021, USA
| | - Cindy Meyer
- Laboratory of RNA Molecular Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10021, USA
| | - Svenja Godbersen
- Institute of Molecular Health Sciences, ETH Zurich, Otto-Stern-Weg 7, 8093, Zürich, Switzerland
| | - Laura T L Brandt
- Institute of Molecular Health Sciences, ETH Zurich, Otto-Stern-Weg 7, 8093, Zürich, Switzerland
| | - Esther Griesbach
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, 4058, Basel, Switzerland
| | - Jeffrey A Chao
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, 4058, Basel, Switzerland
| | - Thomas Tuschl
- Laboratory of RNA Molecular Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10021, USA
| | - Markus Stoffel
- Institute of Molecular Health Sciences, ETH Zurich, Otto-Stern-Weg 7, 8093, Zürich, Switzerland.
- Medical Faculty, University of Zürich, 8091, Zürich, Switzerland.
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4
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Liu JT, Doueiry C, Jiang YL, Blaszkiewicz J, Lamprecht MP, Heslop JA, Peterson YK, Carten JD, Traktman P, Yuan Y, Khetani SR, Twal WO, Duncan SA. A human iPSC-derived hepatocyte screen identifies compounds that inhibit production of Apolipoprotein B. Commun Biol 2023; 6:452. [PMID: 37095219 PMCID: PMC10125972 DOI: 10.1038/s42003-023-04739-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Accepted: 03/21/2023] [Indexed: 04/26/2023] Open
Abstract
Familial hypercholesterolemia (FH) patients suffer from excessively high levels of Low Density Lipoprotein Cholesterol (LDL-C), which can cause severe cardiovascular disease. Statins, bile acid sequestrants, PCSK9 inhibitors, and cholesterol absorption inhibitors are all inefficient at treating FH patients with homozygous LDLR gene mutations (hoFH). Drugs approved for hoFH treatment control lipoprotein production by regulating steady-state Apolipoprotein B (apoB) levels. Unfortunately, these drugs have side effects including accumulation of liver triglycerides, hepatic steatosis, and elevated liver enzyme levels. To identify safer compounds, we used an iPSC-derived hepatocyte platform to screen a structurally representative set of 10,000 small molecules from a proprietary library of 130,000 compounds. The screen revealed molecules that could reduce the secretion of apoB from cultured hepatocytes and from humanized livers in mice. These small molecules are highly effective, do not cause abnormal lipid accumulation, and share a chemical structure that is distinct from any known cholesterol lowering drug.
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Affiliation(s)
- Jui-Tung Liu
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC, 29425, USA
| | - Caren Doueiry
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC, 29425, USA
| | - Yu-Lin Jiang
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC, 29425, USA
| | - Josef Blaszkiewicz
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC, 29425, USA
| | - Mary Paige Lamprecht
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC, 29425, USA
| | - James A Heslop
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC, 29425, USA
| | - Yuri K Peterson
- Drug Discovery and Biomedical Sciences, Medical University of South Carolina, Charleston, SC, 29425, USA
| | - Juliana Debrito Carten
- Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, 29425, USA
| | - Paula Traktman
- Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, 29425, USA
| | - Yang Yuan
- Department of Biomedical Engineering, University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Salman R Khetani
- Department of Biomedical Engineering, University of Illinois at Chicago, Chicago, IL, 60607, USA
| | | | - Stephen A Duncan
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC, 29425, USA.
- Grùthan Biosciences LLC, Hollywood, SC, 29449, USA.
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Meszaros M, Bikov A. Obstructive Sleep Apnoea and Lipid Metabolism: The Summary of Evidence and Future Perspectives in the Pathophysiology of OSA-Associated Dyslipidaemia. Biomedicines 2022; 10:2754. [PMID: 36359273 PMCID: PMC9687681 DOI: 10.3390/biomedicines10112754] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2022] [Revised: 10/27/2022] [Accepted: 10/27/2022] [Indexed: 09/29/2023] Open
Abstract
Obstructive sleep apnoea (OSA) is associated with cardiovascular and metabolic comorbidities, including hypertension, dyslipidaemia, insulin resistance and atherosclerosis. Strong evidence suggests that OSA is associated with an altered lipid profile including elevated levels of triglyceride-rich lipoproteins and decreased levels of high-density lipoprotein (HDL). Intermittent hypoxia; sleep fragmentation; and consequential surges in the sympathetic activity, enhanced oxidative stress and systemic inflammation are the postulated mechanisms leading to metabolic alterations in OSA. Although the exact mechanisms of OSA-associated dyslipidaemia have not been fully elucidated, three main points have been found to be impaired: activated lipolysis in the adipose tissue, decreased lipid clearance from the circulation and accelerated de novo lipid synthesis. This is further complicated by the oxidisation of atherogenic lipoproteins, adipose tissue dysfunction, hormonal changes, and the reduced function of HDL particles in OSA. In this comprehensive review, we summarise and critically evaluate the current evidence about the possible mechanisms involved in OSA-associated dyslipidaemia.
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Affiliation(s)
- Martina Meszaros
- Department of Pulmonology and Sleep Disorders Centre, University Hospital Zurich, 8091 Zurich, Switzerland
- Department of Pulmonology, Semmelweis University, 1083 Budapest, Hungary
| | - Andras Bikov
- North West Lung Centre, Wythenshawe Hospital, Manchester University NHS Foundation Trust, Manchester M23 9LT, UK
- Division of Infection, Immunity and Respiratory Medicine, University of Manchester, Manchester M13 9MT, UK
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Yang W, Wang S, Loor JJ, Jiang Q, Gao C, Yang M, Tian Y, Fan W, Zhao Y, Zhang B, Xu C. Role of sortilin 1 (SORT1) on lipid metabolism in bovine liver. J Dairy Sci 2022; 105:5420-5434. [DOI: 10.3168/jds.2021-21607] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2021] [Accepted: 02/27/2022] [Indexed: 11/19/2022]
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Tall AR, Thomas DG, Gonzalez-Cabodevilla AG, Goldberg IJ. Addressing dyslipidemic risk beyond LDL-cholesterol. J Clin Invest 2022; 132:148559. [PMID: 34981790 PMCID: PMC8718149 DOI: 10.1172/jci148559] [Citation(s) in RCA: 55] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Despite the success of LDL-lowering drugs in reducing cardiovascular disease (CVD), there remains a large burden of residual disease due in part to persistent dyslipidemia characterized by elevated levels of triglyceride-rich lipoproteins (TRLs) and reduced levels of HDL. This form of dyslipidemia is increasing globally as a result of the rising prevalence of obesity and metabolic syndrome. Accumulating evidence suggests that impaired hepatic clearance of cholesterol-rich TRL remnants leads to their accumulation in arteries, promoting foam cell formation and inflammation. Low levels of HDL may associate with reduced cholesterol efflux from foam cells, aggravating atherosclerosis. While fibrates and fish oils reduce TRL, they have not been uniformly successful in reducing CVD, and there is a large unmet need for new approaches to reduce remnants and CVD. Rare genetic variants that lower triglyceride levels via activation of lipolysis and associate with reduced CVD suggest new approaches to treating dyslipidemia. Apolipoprotein C3 (APOC3) and angiopoietin-like 3 (ANGPTL3) have emerged as targets for inhibition by antibody, antisense, or RNAi approaches. Inhibition of either molecule lowers TRL but respectively raises or lowers HDL levels. Large clinical trials of such agents in patients with high CVD risk and elevated levels of TRL will be required to demonstrate efficacy of these approaches.
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Affiliation(s)
- Alan R Tall
- Division of Molecular Medicine, Department of Medicine, Columbia University, New York, New York, USA
| | - David G Thomas
- Division of Molecular Medicine, Department of Medicine, Columbia University, New York, New York, USA
| | - Ainara G Gonzalez-Cabodevilla
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, New York University Grossman School of Medicine, New York, New York, USA
| | - Ira J Goldberg
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, New York University Grossman School of Medicine, New York, New York, USA
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Apolipoprotein B and Cardiovascular Disease: Biomarker and Potential Therapeutic Target. Metabolites 2021; 11:metabo11100690. [PMID: 34677405 PMCID: PMC8540246 DOI: 10.3390/metabo11100690] [Citation(s) in RCA: 98] [Impact Index Per Article: 32.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Revised: 10/04/2021] [Accepted: 10/06/2021] [Indexed: 12/19/2022] Open
Abstract
Apolipoprotein (apo) B, the critical structural protein of the atherogenic lipoproteins, has two major isoforms: apoB48 and apoB100. ApoB48 is found in chylomicrons and chylomicron remnants with one apoB48 molecule per chylomicron particle. Similarly, a single apoB100 molecule is contained per particle of very-low-density lipoprotein (VLDL), intermediate density lipoprotein, LDL and lipoprotein(a). This unique one apoB per particle ratio makes plasma apoB concentration a direct measure of the number of circulating atherogenic lipoproteins. ApoB levels indicate the atherogenic particle concentration independent of the particle cholesterol content, which is variable. While LDL, the major cholesterol-carrying serum lipoprotein, is the primary therapeutic target for management and prevention of atherosclerotic cardiovascular disease, there is strong evidence that apoB is a more accurate indicator of cardiovascular risk than either total cholesterol or LDL cholesterol. This review examines multiple aspects of apoB structure and function, with a focus on the controversy over use of apoB as a therapeutic target in clinical practice. Ongoing coronary artery disease residual risk, despite lipid-lowering treatment, has left patients and clinicians with unsatisfactory options for monitoring cardiovascular health. At the present time, the substitution of apoB for LDL-C in cardiovascular disease prevention guidelines has been deemed unjustified, but discussions continue.
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Abstract
The endothelium acts as the barrier that prevents circulating lipids such as lipoproteins and fatty acids into the arterial wall; it also regulates normal functioning in the circulatory system by balancing vasodilation and vasoconstriction, modulating the several responses and signals. Plasma lipids can interact with endothelium via different mechanisms and produce different phenotypes. Increased plasma-free fatty acids (FFAs) levels are associated with the pathogenesis of atherosclerosis and cardiovascular diseases (CVD). Because of the multi-dimensional roles of plasma FFAs in mediating endothelial dysfunction, increased FFA level is now considered an essential link in the onset of endothelial dysfunction in CVD. FFA-mediated endothelial dysfunction involves several mechanisms, including dysregulated production of nitric oxide and cytokines, metaflammation, oxidative stress, inflammation, activation of the renin-angiotensin system, and apoptosis. Therefore, modulation of FFA-mediated pathways involved in endothelial dysfunction may prevent the complications associated with CVD risk. This review presents details as to how endothelium is affected by FFAs involving several metabolic pathways.
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Gómez-Hernández A, de las Heras N, López-Pastor AR, García-Gómez G, Infante-Menéndez J, González-López P, González-Illanes T, Lahera V, Benito M, Escribano Ó. Severe Hepatic Insulin Resistance Induces Vascular Dysfunction: Improvement by Liver-Specific Insulin Receptor Isoform A Gene Therapy in a Murine Diabetic Model. Cells 2021; 10:cells10082035. [PMID: 34440804 PMCID: PMC8392327 DOI: 10.3390/cells10082035] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2021] [Revised: 07/31/2021] [Accepted: 08/06/2021] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND Cardiovascular dysfunction is linked to insulin-resistant states. In this paper, we analyzed whether the severe hepatic insulin resistance of an inducible liver-specific insulin receptor knockout (iLIRKO) might generate vascular insulin resistance and dysfunction, and whether insulin receptor (IR) isoforms gene therapy might revert it. METHODS We studied in vivo insulin signaling in aorta artery and heart from iLIRKO. Vascular reactivity and the mRNA levels of genes involved in vascular dysfunction were analyzed in thoracic aorta rings by qRT-PCR. Finally, iLIRKO mice were treated with hepatic-specific gene therapy to analyze vascular dysfunction improvement. RESULTS Our results suggest that severe hepatic insulin resistance was expanded to cardiovascular tissues. This vascular insulin resistance observed in aorta artery from iLIRKO mice correlated with a reduction in both PI3K/AKT/eNOS and p42/44 MAPK pathways, and it might be implicated in their vascular alterations characterized by endothelial dysfunction, hypercontractility and eNOS/iNOS levels' imbalance. Finally, regarding long-term hepatic expression of IR isoforms, IRA was more efficient than IRB in the improvement of vascular dysfunction observed in iLIRKO mice. CONCLUSION Severe hepatic insulin resistance is sufficient to produce cardiovascular insulin resistance and dysfunction. Long-term hepatic expression of IRA restored the vascular damage observed in iLIRKO mice.
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Affiliation(s)
- Almudena Gómez-Hernández
- Laboratory of Hepatic and Cardiovascular Diseases, Biochemistry and Molecular Biology Department, School of Pharmacy, Complutense University of Madrid, 28040 Madrid, Spain; (A.R.L.-P.); (J.I.-M.); (P.G.-L.); (T.G.-I.)
- Correspondence: (A.G.-H.); (Ó.E.)
| | - Natalia de las Heras
- Department of Physiology, School of Medicine, Complutense University of Madrid, 28040 Madrid, Spain; (N.d.l.H.); (V.L.)
| | - Andrea R. López-Pastor
- Laboratory of Hepatic and Cardiovascular Diseases, Biochemistry and Molecular Biology Department, School of Pharmacy, Complutense University of Madrid, 28040 Madrid, Spain; (A.R.L.-P.); (J.I.-M.); (P.G.-L.); (T.G.-I.)
| | - Gema García-Gómez
- Laboratory of Diabetes and Obesity, Biochemistry and Molecular Biology Department, School of Pharmacy, Complutense University of Madrid, 28040 Madrid, Spain; (G.G.-G.); (M.B.)
- Centro de Investigación Biomédica en Red (CIBER) de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), 28040 Madrid, Spain
- Mechanisms of Insulin Resistance (MOIR2), General Direction of Universities and Investigation (CCMM), 28040 Madrid, Spain
| | - Jorge Infante-Menéndez
- Laboratory of Hepatic and Cardiovascular Diseases, Biochemistry and Molecular Biology Department, School of Pharmacy, Complutense University of Madrid, 28040 Madrid, Spain; (A.R.L.-P.); (J.I.-M.); (P.G.-L.); (T.G.-I.)
| | - Paula González-López
- Laboratory of Hepatic and Cardiovascular Diseases, Biochemistry and Molecular Biology Department, School of Pharmacy, Complutense University of Madrid, 28040 Madrid, Spain; (A.R.L.-P.); (J.I.-M.); (P.G.-L.); (T.G.-I.)
| | - Tamara González-Illanes
- Laboratory of Hepatic and Cardiovascular Diseases, Biochemistry and Molecular Biology Department, School of Pharmacy, Complutense University of Madrid, 28040 Madrid, Spain; (A.R.L.-P.); (J.I.-M.); (P.G.-L.); (T.G.-I.)
| | - Vicente Lahera
- Department of Physiology, School of Medicine, Complutense University of Madrid, 28040 Madrid, Spain; (N.d.l.H.); (V.L.)
| | - Manuel Benito
- Laboratory of Diabetes and Obesity, Biochemistry and Molecular Biology Department, School of Pharmacy, Complutense University of Madrid, 28040 Madrid, Spain; (G.G.-G.); (M.B.)
- Centro de Investigación Biomédica en Red (CIBER) de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), 28040 Madrid, Spain
- Mechanisms of Insulin Resistance (MOIR2), General Direction of Universities and Investigation (CCMM), 28040 Madrid, Spain
| | - Óscar Escribano
- Laboratory of Hepatic and Cardiovascular Diseases, Biochemistry and Molecular Biology Department, School of Pharmacy, Complutense University of Madrid, 28040 Madrid, Spain; (A.R.L.-P.); (J.I.-M.); (P.G.-L.); (T.G.-I.)
- Correspondence: (A.G.-H.); (Ó.E.)
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Green CJ, Pramfalk C, Charlton CA, Gunn PJ, Cornfield T, Pavlides M, Karpe F, Hodson L. Hepatic de novo lipogenesis is suppressed and fat oxidation is increased by omega-3 fatty acids at the expense of glucose metabolism. BMJ Open Diabetes Res Care 2020; 8:8/1/e000871. [PMID: 32188593 PMCID: PMC7078804 DOI: 10.1136/bmjdrc-2019-000871] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2019] [Revised: 02/07/2020] [Accepted: 02/20/2020] [Indexed: 12/12/2022] Open
Abstract
OBJECTIVE Increased hepatic de novo lipogenesis (DNL) is suggested to be an underlying cause in the development of nonalcoholic fatty liver disease and/or insulin resistance. It is suggested that omega-3 fatty acids (FA) lower hepatic DNL. We investigated the effects of omega-3 FA supplementation on hepatic DNL and FA oxidation using a combination of human in vivo and in vitro studies. RESEARCH DESIGN AND METHODS Thirty-eight healthy men were randomized to take either an omega-3 supplement (4 g/day eicosapentaenoic acid (EPA)+docosahexaenoic acid (DHA) as ethyl esters) or placebo (4 g/day olive oil) and fasting measurements were made at baseline and 8 weeks. The metabolic effects of omega-3 FAs on intrahepatocellular triacylglycerol (IHTAG) content, hepatic DNL and FA oxidation were investigated using metabolic substrates labeled with stable-isotope tracers. In vitro studies, using a human liver cell-line was undertaken to gain insight into the intrahepatocellular effects of omega-3 FAs. RESULTS Fasting plasma TAG concentrations significantly decreased in the omega-3 group and remained unchanged in the placebo group. Eight weeks of omega-3 supplementation significantly decreased IHTAG, fasting and postprandial hepatic DNL while significantly increasing dietary FA oxidation and fasting and postprandial plasma glucose concentrations. In vitro studies supported the in vivo findings of omega-3 FAs (EPA+DHA) decreasing intracellular TAG through a shift in cellular metabolism away from FA esterification toward oxidation. CONCLUSIONS Omega-3 supplementation had a potent effect on decreasing hepatic DNL and increasing FA oxidation and plasma glucose concentrations. Attenuation of hepatic DNL may be considered advantageous; however, consideration is required as to what the potential excess of nonlipid substrates (eg, glucose) will have on intrahepatic and extrahepatic metabolic pathways. TRIAL REGISTRATION NUMBER NCT01936779.
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Affiliation(s)
| | | | | | | | | | - Michael Pavlides
- University of Oxford, Oxford, Oxfordshire, UK
- Translational Gastroenterology Unit, John Radcliffe Hospital, Oxford, UK
| | - Fredrik Karpe
- University of Oxford, Oxford, Oxfordshire, UK
- National Institute for Health Research Oxford Biomedical Research Centre, Oxford University Hospitals Foundation Trust, Oxford, UK
| | - Leanne Hodson
- University of Oxford, Oxford, Oxfordshire, UK
- National Institute for Health Research Oxford Biomedical Research Centre, Oxford University Hospitals Foundation Trust, Oxford, UK
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12
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Hansen AKG, Kortner TM, Krasnov A, Björkhem I, Penn M, Krogdahl Å. Choline supplementation prevents diet induced gut mucosa lipid accumulation in post-smolt Atlantic salmon (Salmo salar L.). BMC Vet Res 2020; 16:32. [PMID: 32005242 PMCID: PMC6995171 DOI: 10.1186/s12917-020-2252-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Accepted: 01/20/2020] [Indexed: 11/24/2022] Open
Abstract
Background Various intestinal morphological alterations have been reported in cultured fish fed diets with high contents of plant ingredients. Since 2000, salmon farmers have reported symptoms indicating an intestinal problem, which we suggest calling lipid malabsorption syndrome (LMS), characterized by pale and foamy appearance of the enterocytes of the pyloric caeca, the result of lipid accumulation. The objective of the present study was to investigate if insufficient dietary choline may be a key component in development of the LMS. Results The results showed that Atlantic salmon (Salmo salar), average weight 362 g, fed a plant based diet for 79 days developed signs of LMS. In fish fed a similar diet supplemented with 0.4% choline chloride no signs of LMS were seen. The relative weight of the pyloric caeca was 40% lower, reflecting 65% less triacylglycerol content and histologically normal gut mucosa. Choline supplementation further increased specific fish growth by 18%. The concomitant alterations in intestinal gene expression related to phosphatidylcholine synthesis (chk and pcyt1a), cholesterol transport (abcg5 and npc1l1), lipid metabolism and transport (mgat2a and fabp2) and lipoprotein formation (apoA1 and apoAIV) confirmed the importance of choline in lipid turnover in the intestine and its ability to prevent LMS. Another important observation was the apparent correlation between plin2 expression and degree of enterocyte hyper-vacuolation observed in the current study, which suggests that plin2 may serve as a marker for intestinal lipid accumulation and steatosis in fish. Future research should be conducted to strengthen the knowledge of choline’s critical role in lipid transport, phospholipid synthesis and lipoprotein secretion to improve formulations of plant based diets for larger fish and to prevent LMS. Conclusions Choline prevents excessive lipid accumulation in the proximal intestine and is essential for Atlantic salmon in seawater.
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Affiliation(s)
| | - Trond M Kortner
- Department of Paraclinical Sciences, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway
| | | | - Ingemar Björkhem
- Department of Laboratory Medicine, Division for Clinical Chemistry, Karolinska University Hospital, Huddinge, Sweden
| | - Michael Penn
- Department of Paraclinical Sciences, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway.,Present Address: US Fish & Wildlife Service, Northeast Fishery Center, Lamar Fish Health Center, Lamar, PA, 16848, USA
| | - Åshild Krogdahl
- Department of Paraclinical Sciences, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway
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van Dijk PR, Abdulle AE, Bulthuis ML, Perton FG, Connelly MA, van Goor H, Dullaart RP. The Systemic Redox Status Is Maintained in Non-Smoking Type 2 Diabetic Subjects Without Cardiovascular Disease: Association with Elevated Triglycerides and Large VLDL. J Clin Med 2019; 9:jcm9010049. [PMID: 31878321 PMCID: PMC7019670 DOI: 10.3390/jcm9010049] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Revised: 12/10/2019] [Accepted: 12/22/2019] [Indexed: 12/11/2022] Open
Abstract
Decreased circulating levels of free thiols (R-SH, sulfhydryl groups) reflect enhanced oxidative stress, which plays an important role in the pathogenesis of cardiometabolic diseases. Since hyperglycemia causes oxidative stress, we questioned whether plasma free thiols are altered in patients with type 2 diabetes mellitus (T2DM) without cardiovascular disease or renal function impairment. We also determined their relationship with elevated triglycerides and very low density lipoproteins (VLDL), a central feature of diabetic dyslipidemia. Fasting plasma free thiols (colorimetric method), lipoproteins, VLDL (nuclear magnetic resonance spectrometry), free fatty acids (FFA), phospholipid transfer protein (PLTP) activity and adiponectin were measured in 79 adult non-smoking T2DM subjects (HbA1c 51 ± 8 mmol/mol, no use of insulin or lipid lowering drugs), and in 89 non-smoking subjects without T2DM. Plasma free thiols were univariately correlated with glucose (r = 0.196, p < 0.05), but were not decreased in T2DM subjects versus non-diabetic subjects (p = 0.31). Free thiols were higher in subjects with (663 ± 84 µmol/L) versus subjects without elevated triglycerides (619 ± 91 µmol/L; p = 0.002). Age- and sex-adjusted multivariable linear regression analysis demonstrated that plasma triglycerides were positively and independently associated with free thiols (β = 0.215, p = 0.004), FFA (β = 0.168, p = 0.029) and PLTP activity (β = 0.228, p = 0.002), inversely with adiponectin (β = −0.308, p < 0.001) but not with glucose (β = 0.052, p = 0.51). Notably, the positive association of free thiols with (elevated) triglycerides appeared to be particularly evident in men. Additionally, large VLDL were independently associated with free thiols (β = 0.188, p = 0.029). In conclusion, circulating free thiols are not decreased in this cohort of non-smoking and generally well-controlled T2DM subjects. Paradoxically, higher triglycerides and more large VLDL particles are likely associated with higher plasma levels of thiols, reflecting lower systemic oxidative stress.
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Affiliation(s)
- Peter R. van Dijk
- Department of Endocrinology, University Medical Center Groningen, University of Groningen, 9700 RB Groningen, The Netherlands;
- Correspondence:
| | - Amaal Eman Abdulle
- Department of Internal Medicine, division vascular medicine, University Medical Center Groningen, University of Groningen, 9700 RB Groningen, The Netherlands
| | - Marian L.C. Bulthuis
- Department of Pathology and Medical, Biology, Section Pathology, University Medical Center Groningen, University of Groningen, 9700 RB Groningen, The Netherlands (H.v.G.)
| | - Frank G. Perton
- Laboratory Center, University Medical Center Groningen, University of Groningen, 9700 RB Groningen, The Netherlands;
| | - Margery A. Connelly
- Laboratory Corporation of America® Holdings (LabCorp), Morrisville, NC 27560, USA;
| | - Harry van Goor
- Department of Pathology and Medical, Biology, Section Pathology, University Medical Center Groningen, University of Groningen, 9700 RB Groningen, The Netherlands (H.v.G.)
| | - Robin P.F. Dullaart
- Department of Endocrinology, University Medical Center Groningen, University of Groningen, 9700 RB Groningen, The Netherlands;
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14
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Koerner CM, Roberts BS, Neher SB. Endoplasmic reticulum quality control in lipoprotein metabolism. Mol Cell Endocrinol 2019; 498:110547. [PMID: 31442546 PMCID: PMC6814580 DOI: 10.1016/j.mce.2019.110547] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Revised: 08/16/2019] [Accepted: 08/17/2019] [Indexed: 12/26/2022]
Abstract
Lipids play a critical role in energy metabolism, and a suite of proteins is required to deliver lipids to tissues. Several of these proteins require an intricate endoplasmic reticulum (ER) quality control (QC) system and unique secondary chaperones for folding. Key examples include apolipoprotein B (apoB), which is the primary scaffold for many lipoproteins, dimeric lipases, which hydrolyze triglycerides from circulating lipoproteins, and the low-density lipoprotein receptor (LDLR), which clears cholesterol-rich lipoproteins from the circulation. ApoB requires specialized proteins for lipidation, dimeric lipases lipoprotein lipase (LPL) and hepatic lipase (HL) require a transmembrane maturation factor for secretion, and the LDLR requires several specialized, domain-specific chaperones. Deleterious mutations in these proteins or their chaperones may result in dyslipidemias, which are detrimental to human health. Here, we review the ER quality control systems that ensure secretion of apoB, LPL, HL, and LDLR with a focus on the specialized chaperones required by each protein.
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Affiliation(s)
- Cari M Koerner
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, USA
| | - Benjamin S Roberts
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, USA
| | - Saskia B Neher
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, USA.
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15
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Morishita H, Zhao YG, Tamura N, Nishimura T, Kanda Y, Sakamaki Y, Okazaki M, Li D, Mizushima N. A critical role of VMP1 in lipoprotein secretion. eLife 2019; 8:48834. [PMID: 31526472 PMCID: PMC6748824 DOI: 10.7554/elife.48834] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Accepted: 08/23/2019] [Indexed: 12/12/2022] Open
Abstract
Lipoproteins are lipid-protein complexes that are primarily generated and secreted from the intestine, liver, and visceral endoderm and delivered to peripheral tissues. Lipoproteins, which are assembled in the endoplasmic reticulum (ER) membrane, are released into the ER lumen for secretion, but its mechanism remains largely unknown. Here, we show that the release of lipoproteins from the ER membrane requires VMP1, an ER transmembrane protein essential for autophagy and certain types of secretion. Loss of vmp1, but not other autophagy-related genes, in zebrafish causes lipoprotein accumulation in the intestine and liver. Vmp1 deficiency in mice also leads to lipid accumulation in the visceral endoderm and intestine. In VMP1-depleted cells, neutral lipids accumulate within lipid bilayers of the ER membrane, thus affecting lipoprotein secretion. These results suggest that VMP1 is important for the release of lipoproteins from the ER membrane to the ER lumen in addition to its previously known functions.
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Affiliation(s)
- Hideaki Morishita
- Department of Biochemistry and Molecular Biology, Graduate School and Faculty of Medicine, University of Tokyo, Tokyo, Japan
| | - Yan G Zhao
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, United States
| | - Norito Tamura
- Department of Biochemistry and Molecular Biology, Graduate School and Faculty of Medicine, University of Tokyo, Tokyo, Japan
| | - Taki Nishimura
- Department of Biochemistry and Molecular Biology, Graduate School and Faculty of Medicine, University of Tokyo, Tokyo, Japan
| | - Yuki Kanda
- Department of Biochemistry and Molecular Biology, Graduate School and Faculty of Medicine, University of Tokyo, Tokyo, Japan
| | - Yuriko Sakamaki
- Microscopy Research Support Unit Research Core, Tokyo Medical and Dental University, Tokyo, Japan
| | | | - Dongfang Li
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Noboru Mizushima
- Department of Biochemistry and Molecular Biology, Graduate School and Faculty of Medicine, University of Tokyo, Tokyo, Japan
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16
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Abstract
PURPOSE OF REVIEW Sortilin, encoded SORT1 gene at chromosome 1p13.3, is a multiligand receptor that traffics protein from the Golgi to the endosomes, secretory vesicles, and the cell surface. Genome-wide association studies (GWAS) revealed an association between sortilin and reduced plasma LDL-cholesterol (LDL-C) as well as reduced coronary artery disease (CAD). This review explores the various lipid metabolism pathways that are affected by alterations in sortilin expression. RECENT FINDINGS The effects of increased hepatic sortilin on plasma LDL-C levels are mediated by increased clearance of LDL-C and decreased very LDL (VLDL) secretion because of increased autophagy-mediated lysosomal degradation of apolipoproteinB100. Sort1 knockout models have shown opposite VLDL secretion phenotypes as well as whole body lipid metabolism in response to diet challenges, leading to confusion about the true role of sortilin in the liver and other tissues. SUMMARY The regulation of VLDL secretion by hepatic sortilin is complex and remains incompletely understood. Further investigation to determine the specific conditions under which both hepatic sortilin and total body sortilin cause changes in lipid metabolism pathways is needed.
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Affiliation(s)
- Donna M Conlon
- Division of Translational Medicine and Human Genetics, Department of Medicine, University of Pennsylvania, Philadelphia, USA
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17
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Cao XF, Dai YJ, Liu MY, Yuan XY, Wang CC, Huang YY, Liu WB, Jiang GZ. High-fat diet induces aberrant hepatic lipid secretion in blunt snout bream by activating endoplasmic reticulum stress-associated IRE1/XBP1 pathway. Biochim Biophys Acta Mol Cell Biol Lipids 2018; 1864:213-223. [PMID: 30553054 DOI: 10.1016/j.bbalip.2018.12.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2018] [Revised: 11/24/2018] [Accepted: 12/11/2018] [Indexed: 12/12/2022]
Abstract
This study was conducted to understand the effect of high-fat diet challenge on lipid transport and endoplasmic reticulum stress in blunt snout bream. Ninety fish (average weight: 41.84 ± 0.07 g) were randomly fed a control diet (6% fat) or a high-fat diet (11% fat) for 9 weeks. The growth performance and feed utilization efficiency were evaluated at the end of the trial. The liver samples of both groups were harvested for molecular analysis and histological evaluation. Compared to the Control group, the high-fat diet group showed no effects on either growth performance or energy intake in blunt snout bream. However, high-fat diet resulted in a massive accumulation of lipid and pathological structural alternations, and disrupted expression of lipid transport-related genes and endoplasmic reticulum stress in the liver of the fish. In vitro, after exposure of the isolated primary hepatocytes from blunt snout bream to oleic acid, the cells showed increased intracellular TG accumulation, decreased VLDL secretion, which was attributed to altered expression levels of lipid transport-related genes through the activated IRE1/XBP1 signaling. The oleic acid-induced detrimental effects were alleviated by co-incubating the cells with an IER1 inhibitor, 4μ8c. In conclusion, high-fat diet could lead to aberrant lipid secretion by activating the ER stress-associated IRE1/XBP1 pathway. Inhibiting the activity of IRE1 represents a promising target to rescue the side-effects of high-fat diet on the liver function of blunt snout bream.
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Affiliation(s)
- Xiu-Fei Cao
- Key Laboratory of Aquatic Nutrition and Feed Science of Jiangsu Province, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, People's Republic of China
| | - Yong-Jun Dai
- Key Laboratory of Aquatic Nutrition and Feed Science of Jiangsu Province, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, People's Republic of China
| | - Ming-Yang Liu
- Key Laboratory of Aquatic Nutrition and Feed Science of Jiangsu Province, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, People's Republic of China
| | - Xiang-Yang Yuan
- Key Laboratory of Aquatic Nutrition and Feed Science of Jiangsu Province, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, People's Republic of China
| | - Cong-Cong Wang
- Key Laboratory of Aquatic Nutrition and Feed Science of Jiangsu Province, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, People's Republic of China
| | - Yang-Yang Huang
- Key Laboratory of Aquatic Nutrition and Feed Science of Jiangsu Province, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, People's Republic of China
| | - Wen-Bin Liu
- Key Laboratory of Aquatic Nutrition and Feed Science of Jiangsu Province, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, People's Republic of China
| | - Guang-Zhen Jiang
- Key Laboratory of Aquatic Nutrition and Feed Science of Jiangsu Province, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, People's Republic of China.
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18
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Thota RN, Ferguson JJA, Abbott KA, Dias CB, Garg ML. Science behind the cardio-metabolic benefits of omega-3 polyunsaturated fatty acids: biochemical effects vs. clinical outcomes. Food Funct 2018; 9:3576-3596. [PMID: 29904777 DOI: 10.1039/c8fo00348c] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Lower incidence of cardiovascular disease (CVD) in the Greenland Inuit, Northern Canada and Japan has been attributed to their consumption of seafood rich in long chain omega-3 polyunsaturated fatty acids (LCn-3PUFA). While a large majority of pre-clinical and intervention trials have demonstrated heart health benefits of LCn-3PUFA, some studies have shown no effects or even negative effects. LCn-3PUFA have been shown to favourably modulate blood lipid levels, particularly a reduction in circulating levels of triglycerides. High density lipoprotein-cholesterol (HDL-C) levels are elevated following dietary supplementation with LCn-3PUFA. Although LCn-3PUFA have been shown to increase low-density lipoprotein-cholesterol (LDL-C) levels, the increase is primarily in the large-buoyant particles that are less atherogenic than small-dense LDL particles. The anti-inflammatory effects of LCn-3PUFA have been clearly outlined with inhibition of NFkB mediated cytokine production being the main mechanism. In addition, reduction in adhesion molecules (intercellular adhesion molecule, ICAM and vascular cell adhesion molecule 1, VCAM-1) and leukotriene production have also been demonstrated following LCn-3PUFA supplementation. Anti-aggregatory effects of LCn-3PUFA have been a subject of controversy, however, recent studies showing sex-specific effects on platelet aggregation have helped resolve the effects on hyperactive platelets. Improvements in endothelium function, blood flow and blood pressure after LCn-3PUFA supplementation add to the mechanistic explanation on their cardio-protective effects. Modulation of adipose tissue secretions including pro-inflammatory mediators and adipokines by LCn-3PUFA has re-ignited interest in their cardiovascular health benefits. The aim of this narrative review is to filter out the reasons for possible disparity between cohort, mechanistic, pre-clinical and clinical studies. The focus of the article is to provide possible explanation for the observed controversies surrounding heart health benefits of LCn-3PUFA.
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Affiliation(s)
- Rohith N Thota
- Nutraceuticals Research Program, School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, NSW, Australia.
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19
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Benes LB, Bassi NS, Kalot MA, Davidson MH. Evolution of Omega-3 Fatty Acid Therapy and Current and Future Role in the Management of Dyslipidemia. Cardiol Clin 2018; 36:277-285. [DOI: 10.1016/j.ccl.2017.12.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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20
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Doonan LM, Fisher EA, Brodsky JL. Can modulators of apolipoproteinB biogenesis serve as an alternate target for cholesterol-lowering drugs? Biochim Biophys Acta Mol Cell Biol Lipids 2018; 1863:762-771. [PMID: 29627384 DOI: 10.1016/j.bbalip.2018.03.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2017] [Revised: 03/07/2018] [Accepted: 03/27/2018] [Indexed: 12/23/2022]
Abstract
Understanding the molecular defects underlying cardiovascular disease is necessary for the development of therapeutics. The most common method to lower circulating lipids, which reduces the incidence of cardiovascular disease, is statins, but other drugs are now entering the clinic, some of which have been approved. Nevertheless, patients cannot tolerate some of these therapeutics, the drugs are costly, and/or the treatments are approved for only rare forms of disease. Efforts to find alternative treatments have focused on other factors, such as apolipoproteinB (apoB), which transports cholesterol in the blood stream. The levels of apoB are regulated by endoplasmic reticulum (ER) associated degradation as well as by a post ER degradation pathway in model systems, and we suggest that these events provide novel therapeutic targets. We discuss first how cardiovascular disease arises and how cholesterol is regulated, and then summarize the mechanisms of action of existing treatments for cardiovascular disease. We then review the apoB biosynthetic pathway, focusing on steps that might be amenable to therapeutic interventions.
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Affiliation(s)
- Lynley M Doonan
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, United States
| | - Edward A Fisher
- Departments of Medicine (Cardiology) and Cell Biology and the Marc and Ruti Bell Program in Vascular Biology, New York University School of Medicine, New York, NY 10016, United States
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, United States.
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21
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Amengual J, Guo L, Strong A, Madrigal-Matute J, Wang H, Kaushik S, Brodsky JL, Rader DJ, Cuervo AM, Fisher EA. Autophagy Is Required for Sortilin-Mediated Degradation of Apolipoprotein B100. Circ Res 2018; 122:568-582. [PMID: 29301854 DOI: 10.1161/circresaha.117.311240] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Revised: 12/28/2017] [Accepted: 12/29/2017] [Indexed: 12/30/2022]
Abstract
RATIONALE Genome-wide association studies identified single-nucleotide polymorphisms near the SORT1 locus strongly associated with decreased plasma LDL-C (low-density lipoprotein cholesterol) levels and protection from atherosclerotic cardiovascular disease and myocardial infarction. The minor allele of the causal SORT1 single-nucleotide polymorphism locus creates a putative C/EBPα (CCAAT/enhancer-binding protein α)-binding site in the SORT1 promoter, thereby increasing in homozygotes sortilin expression by 12-fold in liver, which is rich in this transcription factor. Our previous studies in mice have showed reductions in plasma LDL-C and its principal protein component, apoB (apolipoprotein B) with increased SORT1 expression, and in vitro studies suggested that sortilin promoted the presecretory lysosomal degradation of apoB associated with the LDL precursor, VLDL (very-low-density lipoprotein). OBJECTIVE To determine directly that SORT1 overexpression results in apoB degradation and to identify the mechanisms by which this reduces apoB and VLDL secretion by the liver, thereby contributing to understanding the clinical phenotype of lower LDL-C levels. METHODS AND RESULTS Pulse-chase studies directly established that SORT1 overexpression results in apoB degradation. As noted above, previous work implicated a role for lysosomes in this degradation. Through in vitro and in vivo studies, we now demonstrate that the sortilin-mediated route of apoB to lysosomes is unconventional and intersects with autophagy. Increased expression of sortilin diverts more apoB away from secretion, with both proteins trafficking to the endosomal compartment in vesicles that fuse with autophagosomes to form amphisomes. The amphisomes then merge with lysosomes. Furthermore, we show that sortilin itself is a regulator of autophagy and that its activity is scaled to the level of apoB synthesis. CONCLUSIONS These results strongly suggest that an unconventional lysosomal targeting process dependent on autophagy degrades apoB that was diverted from the secretory pathway by sortilin and provides a mechanism contributing to the reduced LDL-C found in individuals with SORT1 overexpression.
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Affiliation(s)
- Jaume Amengual
- From the Division of Cardiology (J.A., L.G., H.W., E.A.F.), Department of Medicine (J.A., L.G., H.W., E.A.F.), and Marc and Ruti Bell Program in Vascular Biology (J.A., E.A.F., L.G, H.W.), NYU School of Medicine; Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia (A.S., D.J.R.); Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, New York (J.M.-M., S.K., A.M.C.); and Department of Biological Sciences, University of Pittsburgh, PA (J.L.B.)
| | - Liang Guo
- From the Division of Cardiology (J.A., L.G., H.W., E.A.F.), Department of Medicine (J.A., L.G., H.W., E.A.F.), and Marc and Ruti Bell Program in Vascular Biology (J.A., E.A.F., L.G, H.W.), NYU School of Medicine; Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia (A.S., D.J.R.); Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, New York (J.M.-M., S.K., A.M.C.); and Department of Biological Sciences, University of Pittsburgh, PA (J.L.B.)
| | - Alanna Strong
- From the Division of Cardiology (J.A., L.G., H.W., E.A.F.), Department of Medicine (J.A., L.G., H.W., E.A.F.), and Marc and Ruti Bell Program in Vascular Biology (J.A., E.A.F., L.G, H.W.), NYU School of Medicine; Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia (A.S., D.J.R.); Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, New York (J.M.-M., S.K., A.M.C.); and Department of Biological Sciences, University of Pittsburgh, PA (J.L.B.)
| | - Julio Madrigal-Matute
- From the Division of Cardiology (J.A., L.G., H.W., E.A.F.), Department of Medicine (J.A., L.G., H.W., E.A.F.), and Marc and Ruti Bell Program in Vascular Biology (J.A., E.A.F., L.G, H.W.), NYU School of Medicine; Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia (A.S., D.J.R.); Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, New York (J.M.-M., S.K., A.M.C.); and Department of Biological Sciences, University of Pittsburgh, PA (J.L.B.)
| | - Haizhen Wang
- From the Division of Cardiology (J.A., L.G., H.W., E.A.F.), Department of Medicine (J.A., L.G., H.W., E.A.F.), and Marc and Ruti Bell Program in Vascular Biology (J.A., E.A.F., L.G, H.W.), NYU School of Medicine; Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia (A.S., D.J.R.); Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, New York (J.M.-M., S.K., A.M.C.); and Department of Biological Sciences, University of Pittsburgh, PA (J.L.B.)
| | - Susmita Kaushik
- From the Division of Cardiology (J.A., L.G., H.W., E.A.F.), Department of Medicine (J.A., L.G., H.W., E.A.F.), and Marc and Ruti Bell Program in Vascular Biology (J.A., E.A.F., L.G, H.W.), NYU School of Medicine; Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia (A.S., D.J.R.); Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, New York (J.M.-M., S.K., A.M.C.); and Department of Biological Sciences, University of Pittsburgh, PA (J.L.B.)
| | - Jeffrey L Brodsky
- From the Division of Cardiology (J.A., L.G., H.W., E.A.F.), Department of Medicine (J.A., L.G., H.W., E.A.F.), and Marc and Ruti Bell Program in Vascular Biology (J.A., E.A.F., L.G, H.W.), NYU School of Medicine; Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia (A.S., D.J.R.); Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, New York (J.M.-M., S.K., A.M.C.); and Department of Biological Sciences, University of Pittsburgh, PA (J.L.B.)
| | - Daniel J Rader
- From the Division of Cardiology (J.A., L.G., H.W., E.A.F.), Department of Medicine (J.A., L.G., H.W., E.A.F.), and Marc and Ruti Bell Program in Vascular Biology (J.A., E.A.F., L.G, H.W.), NYU School of Medicine; Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia (A.S., D.J.R.); Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, New York (J.M.-M., S.K., A.M.C.); and Department of Biological Sciences, University of Pittsburgh, PA (J.L.B.)
| | - Ana Maria Cuervo
- From the Division of Cardiology (J.A., L.G., H.W., E.A.F.), Department of Medicine (J.A., L.G., H.W., E.A.F.), and Marc and Ruti Bell Program in Vascular Biology (J.A., E.A.F., L.G, H.W.), NYU School of Medicine; Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia (A.S., D.J.R.); Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, New York (J.M.-M., S.K., A.M.C.); and Department of Biological Sciences, University of Pittsburgh, PA (J.L.B.)
| | - Edward A Fisher
- From the Division of Cardiology (J.A., L.G., H.W., E.A.F.), Department of Medicine (J.A., L.G., H.W., E.A.F.), and Marc and Ruti Bell Program in Vascular Biology (J.A., E.A.F., L.G, H.W.), NYU School of Medicine; Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia (A.S., D.J.R.); Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, New York (J.M.-M., S.K., A.M.C.); and Department of Biological Sciences, University of Pittsburgh, PA (J.L.B.).
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22
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Luukkonen PK, Zhou Y, Nidhina Haridas PA, Dwivedi OP, Hyötyläinen T, Ali A, Juuti A, Leivonen M, Tukiainen T, Ahonen L, Scott E, Palmer JM, Arola J, Orho-Melander M, Vikman P, Anstee QM, Olkkonen VM, Orešič M, Groop L, Yki-Järvinen H. Impaired hepatic lipid synthesis from polyunsaturated fatty acids in TM6SF2 E167K variant carriers with NAFLD. J Hepatol 2017; 67:128-136. [PMID: 28235613 DOI: 10.1016/j.jhep.2017.02.014] [Citation(s) in RCA: 79] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Revised: 02/07/2017] [Accepted: 02/10/2017] [Indexed: 02/07/2023]
Abstract
BACKGROUND Carriers of the transmembrane 6 superfamily member 2 E167K gene variant (TM6SF2EK/KK) have decreased expression of the TM6SF2 gene and increased risk of NAFLD and NASH. Unlike common 'obese/metabolic' NAFLD, these subjects lack hypertriglyceridemia and have lower risk of cardiovascular disease. In animals, phosphatidylcholine (PC) deficiency results in a similar phenotype. PCs surround the core of VLDL consisting of triglycerides (TGs) and cholesteryl-esters (CEs). We determined the effect of the TM6SF2 E167K on these lipids in the human liver and serum and on hepatic gene expression and studied the effect of TM6SF2 knockdown on hepatocyte handling of these lipids. METHODS Liver biopsies were taken from subjects characterized with respect to the TM6SF2 genotype, serum and liver lipidome, gene expression and histology. In vitro, after TM6SF2 knockdown in HuH-7 cells, we compared incorporation of different fatty acids into TGs, CEs, and PCs. RESULTS The TM6SF2EK/KK and TM6SF2EE groups had similar age, gender, BMI and HOMA-IR. Liver TGs and CEs were higher and liver PCs lower in the TM6SF2EK/KK than the TM6SF2EE group (p<0.05). Polyunsaturated fatty acids (PUFA) were deficient in liver and serum TGs and liver PCs but hepatic free fatty acids were relatively enriched in PUFA (p<0.05). Incorporation of PUFA into TGs and PCs in TM6SF2 knockdown hepatocytes was decreased (p<0.05). Hepatic expression of TM6SF2 was decreased in variant carriers, and was co-expressed with genes regulated by PUFAs. CONCLUSIONS Hepatic lipid synthesis from PUFAs is impaired and could contribute to deficiency in PCs and increased intrahepatic TG in TM6SF2 E167K variant carriers.
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Affiliation(s)
- Panu K Luukkonen
- Department of Medicine, University of Helsinki and Helsinki University Hospital, Helsinki, Finland; Minerva Foundation Institute for Medical Research, Helsinki, Finland.
| | - You Zhou
- Minerva Foundation Institute for Medical Research, Helsinki, Finland; Systems Immunity University Research Institute and Division of Infection and Immunity, School of Medicine, Cardiff University, Cardiff, United Kingdom
| | | | - Om P Dwivedi
- Institute for Molecular Medicine Finland, Helsinki, Finland
| | | | - Ashfaq Ali
- Steno Diabetes Center, Gentofte, Denmark
| | - Anne Juuti
- Department of Surgery, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
| | - Marja Leivonen
- Department of Surgery, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
| | - Taru Tukiainen
- Institute for Molecular Medicine Finland, Helsinki, Finland
| | | | - Emma Scott
- Institute of Cellular Medicine, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Jeremy M Palmer
- Institute of Cellular Medicine, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Johanna Arola
- Department of Pathology, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
| | | | | | - Quentin M Anstee
- Institute of Cellular Medicine, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Vesa M Olkkonen
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Matej Orešič
- Turku Centre for Biotechnology, University of Turku and Åbo Akademi University, Turku, Finland
| | - Leif Groop
- Institute for Molecular Medicine Finland, Helsinki, Finland; Lund University, Malmö, Sweden
| | - Hannele Yki-Järvinen
- Department of Medicine, University of Helsinki and Helsinki University Hospital, Helsinki, Finland; Minerva Foundation Institute for Medical Research, Helsinki, Finland
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23
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Zamani M, Taher J, Adeli K. Complex role of autophagy in regulation of hepatic lipid and lipoprotein metabolism. J Biomed Res 2017; 31:377-385. [PMID: 27346467 PMCID: PMC5706430 DOI: 10.7555/jbr.30.20150137] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Discovering new therapeutic interventions to treat lipid and lipoprotein disorders is of great interest and the discovery of autophagy as a regulator of lipid metabolism has opened up new avenues for targeting modulators of this pathway. Autophagy is a degradative process that targets cellular components to the lysosome and recent studies have indicated a role for autophagy in regulating hepatic lipid metabolism (known as lipophagy) as well as lipoprotein assembly. Autophagy directly targets apolipoprotein B-100 (apoB100), the structural protein component of very low-density lipoproteins (VLDLs), and further targets lipid droplets (LDs), the cellular storage for neutral lipids. Autophagy thus plays a complex and dual role in VLDL particle assembly by regulating apoB100 degradation as well as aiding the maturation of VLDL particles by hydrolyzing lipid from LDs. The purpose of this article is to review our current understanding of molecular and cellular mechanisms mediating authophagic control of hepatic lipid biogenesis and VLDL production as well as dysregulation in insulin resistance and dyslipidemia.
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Affiliation(s)
- Mostafa Zamani
- Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.,Department of Biochemistry, University of Toronto, ON M5G 0A4, Canada
| | - Jennifer Taher
- Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.,Department of Laboratory Medicine and Pathobiology, University of Toronto, ON M5G 0A4, Canada
| | - Khosrow Adeli
- Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.,Department of Laboratory Medicine and Pathobiology, University of Toronto, ON M5G 0A4, Canada.,Department of Biochemistry, University of Toronto, ON M5G 0A4, Canada
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24
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Reyes-Soffer G, Moon B, Hernandez-Ono A, Dionizovik-Dimanovski M, Dionizovick-Dimanovski M, Jimenez J, Obunike J, Thomas T, Ngai C, Fontanez N, Donovan DS, Karmally W, Holleran S, Ramakrishnan R, Mittleman RS, Ginsberg HN. Complex effects of inhibiting hepatic apolipoprotein B100 synthesis in humans. Sci Transl Med 2016; 8:323ra12. [PMID: 26819195 DOI: 10.1126/scitranslmed.aad2195] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Mipomersen is a 20mer antisense oligonucleotide (ASO) that inhibits apolipoprotein B (apoB) synthesis; its low-density lipoprotein (LDL)-lowering effects should therefore result from reduced secretion of very-low-density lipoprotein (VLDL). We enrolled 17 healthy volunteers who received placebo injections weekly for 3 weeks followed by mipomersen weekly for 7 to 9 weeks. Stable isotopes were used after each treatment to determine fractional catabolic rates and production rates of apoB in VLDL, IDL (intermediate-density lipoprotein), and LDL, and of triglycerides in VLDL. Mipomersen significantly reduced apoB in VLDL, IDL, and LDL, which was associated with increases in fractional catabolic rates of VLDL and LDL apoB and reductions in production rates of IDL and LDL apoB. Unexpectedly, the production rates of VLDL apoB and VLDL triglycerides were unaffected. Small interfering RNA-mediated knockdown of apoB expression in human liver cells demonstrated preservation of apoB secretion across a range of apoB synthesis. Titrated ASO knockdown of apoB mRNA in chow-fed mice preserved both apoB and triglyceride secretion. In contrast, titrated ASO knockdown of apoB mRNA in high-fat-fed mice resulted in stepwise reductions in both apoB and triglyceride secretion. Mipomersen lowered all apoB lipoproteins without reducing the production rate of either VLDL apoB or triglyceride. Our human data are consistent with long-standing models of posttranscriptional and posttranslational regulation of apoB secretion and are supported by in vitro and in vivo experiments. Targeting apoB synthesis may lower levels of apoB lipoproteins without necessarily reducing VLDL secretion, thereby lowering the risk of steatosis associated with this therapeutic strategy.
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Affiliation(s)
- Gissette Reyes-Soffer
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA.
| | - Byoung Moon
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | - Antonio Hernandez-Ono
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | | | | | - Jhonsua Jimenez
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | - Joseph Obunike
- Biological Sciences Department, New York City College of Technology, 300 Jay Street, Brooklyn, NY 11201, USA
| | - Tiffany Thomas
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | - Colleen Ngai
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | - Nelson Fontanez
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | - Daniel S Donovan
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | - Wahida Karmally
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | - Stephen Holleran
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | - Rajasekhar Ramakrishnan
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | | | - Henry N Ginsberg
- Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA.
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25
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Mobin MB, Gerstberger S, Teupser D, Campana B, Charisse K, Heim MH, Manoharan M, Tuschl T, Stoffel M. The RNA-binding protein vigilin regulates VLDL secretion through modulation of Apob mRNA translation. Nat Commun 2016; 7:12848. [PMID: 27665711 PMCID: PMC5052685 DOI: 10.1038/ncomms12848] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 08/01/2016] [Indexed: 01/07/2023] Open
Abstract
The liver is essential for the synthesis of plasma proteins and integration of lipid metabolism. While the role of transcriptional networks in these processes is increasingly understood, less is known about post-transcriptional control of gene expression by RNA-binding proteins (RBPs). Here, we show that the RBP vigilin is upregulated in livers of obese mice and in patients with fatty liver disease. By using in vivo, biochemical and genomic approaches, we demonstrate that vigilin controls very-low-density lipoprotein (VLDL) secretion through the modulation of apolipoproteinB/Apob mRNA translation. Crosslinking studies reveal that vigilin binds to CU-rich regions in the mRNA coding sequence of Apob and other proatherogenic secreted proteins, including apolipoproteinC-III/Apoc3 and fibronectin/Fn1. Consequently, hepatic vigilin knockdown decreases VLDL/low-density lipoprotein (LDL) levels and formation of atherosclerotic plaques in Ldlr−/− mice. These studies uncover a role for vigilin as a key regulator of hepatic Apob translation and demonstrate the therapeutic potential of inhibiting vigilin for cardiovascular diseases. RNA-binding proteins (RBP) are an emerging group of post-translational regulators. Here the authors show that the RBP vigilin regulates translation of mRNA encoding for proatherogenic proteins—apoB, apoC-III and fibronectin—representing a potential therapeutic target in cardiovascular diseases.
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Affiliation(s)
- Mehrpouya B Mobin
- Institute of Molecular Health Sciences, ETH Zurich, Otto-Stern Weg 7, 8093 Zurich, Switzerland
| | - Stefanie Gerstberger
- Howard Hughes Medical Institute, The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA
| | - Daniel Teupser
- Institute of Laboratory Medicine, Ludwig-Maximilians-University Munich, Marchioninistr. 15, 81377 Munich, Germany
| | - Benedetta Campana
- Department of Biomedicine and Clinic for Gastroenterology and Hepatology, University Hospital Basel, Hebelstrasse 20, 4031 Basel, Switzerland
| | - Klaus Charisse
- Alnylam Pharmaceuticals, 300 Third Street, Cambridge, Massachusetts 02142, USA
| | - Markus H Heim
- Department of Biomedicine and Clinic for Gastroenterology and Hepatology, University Hospital Basel, Hebelstrasse 20, 4031 Basel, Switzerland
| | - Muthiah Manoharan
- Alnylam Pharmaceuticals, 300 Third Street, Cambridge, Massachusetts 02142, USA
| | - Thomas Tuschl
- Howard Hughes Medical Institute, The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA
| | - Markus Stoffel
- Institute of Molecular Health Sciences, ETH Zurich, Otto-Stern Weg 7, 8093 Zurich, Switzerland
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26
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Ma S, Li T, Guo K, Li X, An S, Hou S, Chen R, Yang B, Liu S, Fu J. Effective treatment with combination of peripheral 5-hydroxytryptamine synthetic inhibitor and 5-hydroxytryptamine 2 receptor antagonist on glucocorticoid-induced whole-body insulin resistance with hyperglycemia. J Diabetes Investig 2016; 7:833-844. [PMID: 27177506 PMCID: PMC5089945 DOI: 10.1111/jdi.12526] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Revised: 02/24/2016] [Accepted: 03/16/2016] [Indexed: 12/12/2022] Open
Abstract
AIMS/INTRODUCTION Our previous study found that dexamethasone-induced insulin resistance (IR) was involved in 5-hydroxytryptamine (5-HT) synthesis and 5-hydroxytryptamine 2 receptor (5-HT2 R) in the periphery. The present study examined the effects of inhibitions of both peripheral 5-HT synthesis and 5-HT2 R on dexamethasone-induced IR. MATERIALS AND METHODS Male rats were exposed to dexamethasone for 10 days, then treated with or without a 5-HT2 R antagonist, sarpogrelate, a 5-HT synthetic inhibitor, carbidopa, alone or in combination for 20 days. RESULTS Dexamethasone-induced whole-body IR, with glucose intolerance, decreased insulin sensitivity, hyperglycemia, hyperinsulinemia and dyslipidemia, could be effectively abolished by sarpogrelate or/and carbidopa, whereas IR-related actions of dexamethasone in tissues were accompanied by increased 5-HT synthesis in the liver and visceral adipose, and upregulated 5-HT2 R (5-HT2A R and 5-HT2B R) expression in these two tissues as well as in skeletal muscle. Sarpogrelate or/and carbidopa treatment significantly abolished dexamethasone-caused tissue-specific IR. In the liver, increased gluconeogenesis, triglycerides and very low-density lipoprotein syntheses with steatosis, and downregulated expression of plasmalemmal glucose transporter-2 were markedly reversed. In the visceral adipose and skeletal muscle, downregulated expression of plasmalemmal glucose transporter-4 was significantly reversed, and increased lipolysis was also reversed in the visceral adipose. Dexamethasone-induced activations of hepatic mammalian target of rapamycin serine2448 , and S6K threonine389/412 phosphorylation were also abolished markedly by sarpogrelate or/and carbidopa. Co-treatment with sarpogrelate and carbidopa showed a synergistic effect on suppressing dexamethasone actions. CONCLUSION Inhibitions of both peripheral 5-HT synthesis and 5-HT2 R are expected to be a dependable target for treatment of steroid-induced diabetes.
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Affiliation(s)
- Shaoxin Ma
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Tao Li
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Keke Guo
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Xin Li
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Shanshan An
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Shanshan Hou
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Ru Chen
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Bo Yang
- Undergraduates of China Pharmaceutical University, Nanjing, China
| | - Siyu Liu
- Undergraduates of China Pharmaceutical University, Nanjing, China
| | - Jihua Fu
- Department of Physiology, China Pharmaceutical University, Nanjing, China.
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27
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Li X, Guo K, Li T, Ma S, An S, Wang S, Di J, He S, Fu J. 5-HT 2 receptor mediates high-fat diet-induced hepatic steatosis and very low density lipoprotein overproduction in rats. Obes Res Clin Pract 2016; 12:16-28. [PMID: 27133527 DOI: 10.1016/j.orcp.2016.03.015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Revised: 03/27/2016] [Accepted: 03/31/2016] [Indexed: 11/27/2022]
Abstract
BACKGROUND 5-HT has been shown to mediate abnormality of hepatic lipid metabolism through activation of mammalian target of rapamycin (mTOR). However, it is unclear whether 5-HT is directly involved in high-fat diet (HFD)-induced hepatic steatosis. MATERIALS AND METHODS Male rats were allocated into seven groups with control, either HFD feeding, 5-HT treatment, or HFD feeding and 5-HT treatment with or without sarpogrelate treatment, all of which were executed for 4 weeks. HepG2 cells were exposed to 5-HT or palmitic acid (PA) with or without rapamycin or Sar treatment. RESULTS Rats fed with HFD or exposed to 5-HT led to abnormalities with activated hepatic mTOR-S6K pathway, overproduction of hepatic triglycerides and VLDL with steatosis, and hyperlipidemia, which were exacerbated by a combination of HFD and 5-HT. Sarpogrelate significantly inhibited above abnormalities induced by HFD and 5-HT, alone or in a combination. Additionally, HFD caused up-regulation of 5-HT2 receptors (5-HT2R), including 5-HT2AR and 5-HT2BR, and 5-HT synthesis in the liver, without obvious influence on other 5-HT receptors gene expression. In HepG2 cells, both PA and 5-HT induced overproduction of triglycerides and VLDL with lipid droplets, and PA up-regulated 5-HT2AR and 5-HT2BR expression and 5-HT synthesis as well. Rapamycin fully abolished PA or 5-HT-induced mTOR activation, which was more effective than sarpogrelate. However, the inhibitory effects of rapamycin on PA or 5-HT-induced overproduction of triglycerides and VLDL were less than sarpogrelate. CONCLUSIONS Up-regulation of hepatic 5-HT2R and 5-HT synthesis by HFD is crucial for HFD-induced overproduction of hepatic triglycerides and VLDL with hyperlipidemia.
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Affiliation(s)
- Xin Li
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Keke Guo
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Tao Li
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Shaoxin Ma
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Shanshan An
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Shanshan Wang
- Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Jiao Di
- Undergraduates of China Pharmaceutical University, Nanjing, China
| | - Siyu He
- Undergraduates of China Pharmaceutical University, Nanjing, China
| | - Jihua Fu
- Department of Physiology, China Pharmaceutical University, Nanjing, China.
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28
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Dijk W, Beigneux AP, Larsson M, Bensadoun A, Young SG, Kersten S. Angiopoietin-like 4 promotes intracellular degradation of lipoprotein lipase in adipocytes. J Lipid Res 2016; 57:1670-83. [PMID: 27034464 DOI: 10.1194/jlr.m067363] [Citation(s) in RCA: 77] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Indexed: 01/17/2023] Open
Abstract
LPL hydrolyzes triglycerides in triglyceride-rich lipoproteins along the capillaries of heart, skeletal muscle, and adipose tissue. The activity of LPL is repressed by angiopoietin-like 4 (ANGPTL4) but the underlying mechanisms have not been fully elucidated. Our objective was to study the cellular location and mechanism for LPL inhibition by ANGPTL4. We performed studies in transfected cells, ex vivo studies, and in vivo studies with Angptl4(-/-) mice. Cotransfection of CHO pgsA-745 cells with ANGPTL4 and LPL reduced intracellular LPL protein levels, suggesting that ANGPTL4 promotes LPL degradation. This conclusion was supported by studies of primary adipocytes and adipose tissue explants from wild-type and Angptl4(-/-) mice. Absence of ANGPTL4 resulted in accumulation of the mature-glycosylated form of LPL and increased secretion of LPL. Blocking endoplasmic reticulum (ER)-Golgi transport abolished differences in LPL abundance between wild-type and Angptl4(-/-) adipocytes, suggesting that ANGPTL4 acts upon LPL after LPL processing in the ER. Finally, physiological changes in adipose tissue ANGPTL4 expression during fasting and cold resulted in inverse changes in the amount of mature-glycosylated LPL in wild-type mice, but not Angptl4(-/-) mice. We conclude that ANGPTL4 promotes loss of intracellular LPL by stimulating LPL degradation after LPL processing in the ER.
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Affiliation(s)
- Wieneke Dijk
- Nutrition, Metabolism, and Genomics Group, Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands
| | - Anne P Beigneux
- Departments of Medicine David Geffen School of Medicine, University of California, Los Angeles, CA
| | - Mikael Larsson
- Departments of Medicine David Geffen School of Medicine, University of California, Los Angeles, CA
| | - André Bensadoun
- Division of Nutritional Sciences, Cornell University, Ithaca, NY
| | - Stephen G Young
- Departments of Medicine David Geffen School of Medicine, University of California, Los Angeles, CA Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, CA
| | - Sander Kersten
- Nutrition, Metabolism, and Genomics Group, Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands Division of Nutritional Sciences, Cornell University, Ithaca, NY
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29
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Imbalanced insulin action in chronic over nutrition: Clinical harm, molecular mechanisms, and a way forward. Atherosclerosis 2016; 247:225-82. [PMID: 26967715 DOI: 10.1016/j.atherosclerosis.2016.02.004] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Revised: 12/31/2015] [Accepted: 02/02/2016] [Indexed: 02/08/2023]
Abstract
The growing worldwide prevalence of overnutrition and underexertion threatens the gains that we have made against atherosclerotic cardiovascular disease and other maladies. Chronic overnutrition causes the atherometabolic syndrome, which is a cluster of seemingly unrelated health problems characterized by increased abdominal girth and body-mass index, high fasting and postprandial concentrations of cholesterol- and triglyceride-rich apoB-lipoproteins (C-TRLs), low plasma HDL levels, impaired regulation of plasma glucose concentrations, hypertension, and a significant risk of developing overt type 2 diabetes mellitus (T2DM). In addition, individuals with this syndrome exhibit fatty liver, hypercoagulability, sympathetic overactivity, a gradually rising set-point for body adiposity, a substantially increased risk of atherosclerotic cardiovascular morbidity and mortality, and--crucially--hyperinsulinemia. Many lines of evidence indicate that each component of the atherometabolic syndrome arises, or is worsened by, pathway-selective insulin resistance and responsiveness (SEIRR). Individuals with SEIRR require compensatory hyperinsulinemia to control plasma glucose levels. The result is overdrive of those pathways that remain insulin-responsive, particularly ERK activation and hepatic de-novo lipogenesis (DNL), while carbohydrate regulation deteriorates. The effects are easily summarized: if hyperinsulinemia does something bad in a tissue or organ, that effect remains responsive in the atherometabolic syndrome and T2DM; and if hyperinsulinemia might do something good, that effect becomes resistant. It is a deadly imbalance in insulin action. From the standpoint of human health, it is the worst possible combination of effects. In this review, we discuss the origins of the atherometabolic syndrome in our historically unprecedented environment that only recently has become full of poorly satiating calories and incessant enticements to sit. Data are examined that indicate the magnitude of daily caloric imbalance that causes obesity. We also cover key aspects of healthy, balanced insulin action in liver, endothelium, brain, and elsewhere. Recent insights into the molecular basis and pathophysiologic harm from SEIRR in these organs are discussed. Importantly, a newly discovered oxide transport chain functions as the master regulator of the balance amongst different limbs of the insulin signaling cascade. This oxide transport chain--abbreviated 'NSAPP' after its five major proteins--fails to function properly during chronic overnutrition, resulting in this harmful pattern of SEIRR. We also review the origins of widespread, chronic overnutrition. Despite its apparent complexity, one factor stands out. A sophisticated junk food industry, aided by subsidies from willing governments, has devoted years of careful effort to promote overeating through the creation of a new class of food and drink that is low- or no-cost to the consumer, convenient, savory, calorically dense, yet weakly satiating. It is past time for the rest of us to overcome these foes of good health and solve this man-made epidemic.
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30
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Fisher EA. Regression of Atherosclerosis: The Journey From the Liver to the Plaque and Back. Arterioscler Thromb Vasc Biol 2016; 36:226-35. [PMID: 26681754 PMCID: PMC4732981 DOI: 10.1161/atvbaha.115.301926] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2015] [Accepted: 11/18/2015] [Indexed: 11/16/2022]
Abstract
Cardinal events in atherogenesis are the retention of apolipoprotein B-containing lipoproteins in the arterial wall and the reaction of macrophages to these particles. My laboratory has been interested in both the cell biological events producing apolipoprotein B-containing lipoproteins, as well as in the reversal of the damage they cause in the plaques formed in the arterial wall. In the 2013 George Lyman Duff Memorial Lecture, as summarized in this review, I covered 3 areas of my past, present, and future interests, namely, the regulation of hepatic very low density lipoprotein production by the degradation of apolipoprotein B100, the dynamic changes in macrophages in the regression of atherosclerosis, and the application of nanoparticles to both image and treat atherosclerotic plaques.
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Affiliation(s)
- Edward A Fisher
- From the Department of Medicine (Cardiology), the Marc and Ruti Bell Program in Vascular Biology and the Center for the Prevention of Cardiovascular Disease, New York University School of Medicine.
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31
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Hur SK, Park SH, Oh GT. The Role of Autophagy in the Pathogenesis of Atherosclerosis. J Lipid Atheroscler 2016. [DOI: 10.12997/jla.2016.5.1.1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Affiliation(s)
- Shin Kyoung Hur
- Department of Life Sciences, Ewha Womans University, Seoul, Korea
| | - Seung Hee Park
- Department of Life Sciences, Ewha Womans University, Seoul, Korea
| | - Goo Taeg Oh
- Department of Life Sciences, Ewha Womans University, Seoul, Korea
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32
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Fu J, Ma S, Li X, An S, Li T, Guo K, Lin M, Qu W, Wang S, Dong X, Han X, Fu T, Huang X, Wang T, He S. Long-term Stress with Hyperglucocorticoidemia-induced Hepatic Steatosis with VLDL Overproduction Is Dependent on both 5-HT2 Receptor and 5-HT Synthesis in Liver. Int J Biol Sci 2016; 12:219-34. [PMID: 26884719 PMCID: PMC4737678 DOI: 10.7150/ijbs.13062] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2015] [Accepted: 10/23/2015] [Indexed: 01/09/2023] Open
Abstract
Hepatic triglycerides production and adipose lipolysis are pivotal for long-term stress (LTS) or hyperglucocorticoidemia-induced insulin resistance. 5-hydroxytryptamine (5-HT) has been demonstrated to induce hepatic lipid metabolic abnormality by activating mammalian target of rapamycin (mTOR). In present study, we explored whether 5-HT is involved in LTS effects in liver using restraint stress-exposed rats and cultured primary rat hepatocytes and HepG2 cells. LTS with hyperglucocorticoidemia induced hepatic 5-HT synthetic increase with tryptophan hydroxylase 1 (Tph1) up-regulation, and 5-HT2 receptor (5-HT2R, including 5-HT2A, 2B receptor) up-regulation in liver and visceral adipose, as well as hepatic mTOR activation with triglycerides and VLDL overproduction with steatosis, and visceral adipose lipolytic increase with high blood free fatty acids (FFAs) level. 5-HT exposure exhibited LTS-like effects in both tissues, and both LTS and 5-HT effects could be abolished significantly by blocking 5-HT2R. In HepG2 cells dexamethasone or palmitate-induced mTOR activation with triglycerides and VLDL overproduction were accompanied by up-regulations of 5-HT synthesis and 5-HT2R, which were significantly abolished by gene silencing Tph1 or 5-HT2R and were almost fully abolished by co-silencing of both, especially on VLDL overproduction. Chemical inhibition of Tph1 or/and 5-HT2R in both hepatocytes exhibited similar abolishment with genetic inhibition on dexamethason-induced effects. 5-HT-stimulated effects in both hepatocytes were fully abolished by blocking 5-HT2R, while 5-HT itself also up-regulated 5-HT2R. In conclusion, up-regulated hepatic 5-HT synthesis and 5-HT2R induced by both glucocorticoid and FFAs are crucial for LTS-induced hepatic steatosis with VLDL overproduction, while 5-HT by acting on 5-HT2R mediates mTOR activation in liver.
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Affiliation(s)
- Jihua Fu
- 1. Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Shaoxin Ma
- 1. Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Xin Li
- 1. Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Shanshan An
- 1. Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Tao Li
- 1. Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Keke Guo
- 1. Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Min Lin
- 1. Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Wei Qu
- 1. Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Shanshan Wang
- 1. Postgraduates of China Pharmaceutical University, Nanjing, China
| | - Xinyue Dong
- 2. Undergraduates of China Pharmaceutical University, Nanjing, China
| | - Xiaoyu Han
- 2. Undergraduates of China Pharmaceutical University, Nanjing, China
| | - Ting Fu
- 2. Undergraduates of China Pharmaceutical University, Nanjing, China
| | - Xinping Huang
- 2. Undergraduates of China Pharmaceutical University, Nanjing, China
| | - Tianying Wang
- 2. Undergraduates of China Pharmaceutical University, Nanjing, China
| | - Siyu He
- 2. Undergraduates of China Pharmaceutical University, Nanjing, China
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Li JY, Zhang DD, Jiang GZ, Li XF, Zhang CN, Zhou M, Liu WB, Xu WN. Cloning and characterization of microsomal triglyceride transfer protein gene and its potential connection with peroxisome proliferator-activated receptor (PPAR) in blunt snout bream (Megalobrama amblycephala). Comp Biochem Physiol B Biochem Mol Biol 2015. [PMID: 26210738 DOI: 10.1016/j.cbpb.2015.07.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Microsomal triglyceride transfer protein (MTTP), a major intracellular protein capable of transferring neutral lipids, plays a pivotal role in the assembly and secretion of apolipoprotein B-containing lipoproteins. In this study, MTTP cDNA was firstly cloned from the liver of blunt snout bream (Megalobrama amblycephala), the full-length cDNA covered 3457-bp with an open reading frame of 2661-bp, which encodes 886 amino acids, including a putative signal peptide of 24 amino acids long. After the feeding trial, a graded tissue-specific expression pattern of MTTP was observed and high expression abundance in the liver and intestine indicated its major function in lipid transport in this fish species. In addition, expression of genes encoding MTTP as well as peroxisome proliferator-activated receptor (PPAR), which are transcription factors and serve as key regulators in lipid homoeostasis, was all affected by dietary lipid and choline supplementations. Elevated dietary lipid levels significantly increased the liver, intestinal and muscle MTTP mRNA abundance. Additionally, the down-regulation of MTTP expression in the liver and muscle was observed when fish were fed with inadequate choline supplementation in high-fat diet, yet up-regulated as supplementing extra choline in diet. Expressions of PPARα and PPARβ in the liver and muscle showed similar trend of MTTP expression. The results suggested the potential connection of MTTP and PPAR in response to different dietary nutritional factors. Furthermore, extra choline supplementations could promote lipid transfer and enhance fatty acid oxidation, which indicated a molecular mechanism of choline on diminishing fat accumulation in blunt snout bream.
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Affiliation(s)
- Jun-Yi Li
- Laboratory of Aquatic Nutrition and Ecology, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, China
| | - Ding-Dong Zhang
- Laboratory of Aquatic Nutrition and Ecology, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, China
| | - Guang-Zhen Jiang
- Laboratory of Aquatic Nutrition and Ecology, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, China
| | - Xiang-Fei Li
- Laboratory of Aquatic Nutrition and Ecology, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, China
| | - Chun-Nuan Zhang
- Laboratory of Aquatic Nutrition and Ecology, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, China
| | - Man Zhou
- Laboratory of Aquatic Nutrition and Ecology, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, China
| | - Wen-Bin Liu
- Laboratory of Aquatic Nutrition and Ecology, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, China.
| | - Wei-Na Xu
- Laboratory of Aquatic Nutrition and Ecology, College of Animal Science and Technology, Nanjing Agricultural University, No. 1 Weigang Road, Nanjing 210095, China.
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Abstract
Cardiovascular disease is a major cause of morbidity and mortality in patients with type 2 diabetes mellitus, with a two- to fourfold increase in cardiovascular disease risk compared with non-diabetic individuals. Abnormalities in lipid metabolism that are observed in the context of type 2 diabetes are among the major factors contributing to an increased cardiovascular risk. Diabetic dyslipidaemia includes not only quantitative lipoprotein abnormalities, but also qualitative and kinetic abnormalities that, together, result in a shift towards a more atherogenic lipid profile. The primary quantitative lipoprotein abnormalities are increased triacylglycerol (triglyceride) levels and decreased HDL-cholesterol levels. Qualitative lipoprotein abnormalities include an increase in large, very low-density lipoprotein subfraction 1 (VLDL1) and small, dense LDLs, as well as increased triacylglycerol content of LDL and HDL, glycation of apolipoproteins and increased susceptibility of LDL to oxidation. The main kinetic abnormalities are increased VLDL1 production, decreased VLDL catabolism and increased HDL catabolism. In addition, even though LDL-cholesterol levels are typically normal in patients with type 2 diabetes, LDL particles show reduced turnover, which is potentially atherogenic. Although the pathophysiology of diabetic dyslipidaemia is not fully understood, the insulin resistance and relative insulin deficiency observed in patients with type 2 diabetes are likely to contribute to these lipid changes, as insulin plays an important role in regulating lipid metabolism. In addition, some adipocytokines, such as adiponectin or retinol-binding protein 4, may also contribute to the development of dyslipidaemia in patients with type 2 diabetes.
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Affiliation(s)
- Bruno Vergès
- Service Endocrinologie, Diabétologie et Maladies Métaboliques, Hôpital du Bocage, 2 bd Maréchal de Lattre de Tassigny, 21000, Dijon, France,
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Kawakami Y, Yamanaka-Okumura H, Naniwa-Kuroki Y, Sakuma M, Taketani Y, Takeda E. Flaxseed oil intake reduces serum small dense low-density lipoprotein concentrations in Japanese men: a randomized, double blind, crossover study. Nutr J 2015; 14:39. [PMID: 25896182 PMCID: PMC4409715 DOI: 10.1186/s12937-015-0023-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Accepted: 04/01/2015] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND The effects of alpha-linolenic acid (ALA) on cardiovascular risk factors considerably vary between published reports. Therefore, we investigated the effects of 12-week supplementation with flaxseed oil (FO), which is a rich source of ALA, on cardiovascular risk factors such as serum small dense low-density lipoprotein (sd-LDL) concentrations. METHODS In a randomized, double blind, crossover study, 15 subjects ingested 10 g of FO or corn oil (CO), containing 5.49 g and 0.09 g of ALA, respectively, once daily with dinner. Blood samples were collected at 0, 4 and 12 weeks, and were used for analysis of serum lipid, lipid-related proteins, serum fatty acids and serum sd-LDL cholesterol. Differences during the test period were identified using a repeated-measures analysis of variance (ANOVA) for within-group effects. Group differences were identified using paired t-test at each blood sampling time point. RESULTS ALA and eicosapentaenoic acid concentrations were significantly higher in the FO period at 4 and 12 weeks than in the CO period. No significant differences in docosahexaenoic acid concentrations were observed between two periods, and cholesteryl ester transfer protein and apolipoprotein B concentrations were significantly lower in the FO period than in the CO period at 12 weeks. FO supplementation was associated with a significant decrease in sd-LDL concentrations at 4 and 12 weeks, and CO supplementation had no effect. Moreover, sd-LDL concentrations were significantly lower in the FO period than in the CO period at 4 weeks. Among subjects with triglyceride (TG) concentrations of >100 mg/dl, FO supplementation markedly reduced sd-LDL concentrations at 4 and 12 weeks compared with baseline. Sd-LDL concentrations significantly differed between the periods at both 4 and 12 weeks. CONCLUSION This study indicates that the FO, which is a rich source of ALA, leads to lower sd-LDL cholesterol concentrations.
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Affiliation(s)
- Yuka Kawakami
- Department of Clinical Nutrition and Food Management, Institute of Health Biosciences, University of Tokushima Graduate School, 3-18-15 Kuramoto, Tokushima, 770-8503, Japan.
| | - Hisami Yamanaka-Okumura
- Department of Clinical Nutrition and Food Management, Institute of Health Biosciences, University of Tokushima Graduate School, 3-18-15 Kuramoto, Tokushima, 770-8503, Japan.
| | - Yuko Naniwa-Kuroki
- Department of Clinical Nutrition and Food Management, Institute of Health Biosciences, University of Tokushima Graduate School, 3-18-15 Kuramoto, Tokushima, 770-8503, Japan.
| | - Masae Sakuma
- Department of Clinical Nutrition and Food Management, Institute of Health Biosciences, University of Tokushima Graduate School, 3-18-15 Kuramoto, Tokushima, 770-8503, Japan.
| | - Yutaka Taketani
- Department of Clinical Nutrition and Food Management, Institute of Health Biosciences, University of Tokushima Graduate School, 3-18-15 Kuramoto, Tokushima, 770-8503, Japan.
| | - Eiji Takeda
- Department of Clinical Nutrition and Food Management, Institute of Health Biosciences, University of Tokushima Graduate School, 3-18-15 Kuramoto, Tokushima, 770-8503, Japan.
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Giammanco A, Cefalù AB, Noto D, Averna MR. The pathophysiology of intestinal lipoprotein production. Front Physiol 2015; 6:61. [PMID: 25852563 PMCID: PMC4367171 DOI: 10.3389/fphys.2015.00061] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Accepted: 02/14/2015] [Indexed: 12/12/2022] Open
Abstract
Intestinal lipoprotein production is a multistep process, essential for the absorption of dietary fats and fat-soluble vitamins. Chylomicron assembly begins in the endoplasmic reticulum with the formation of primordial, phospholipids-rich particles that are then transported to the Golgi for secretion. Several classes of transporters play a role in the selective uptake and/or export of lipids through the villus enterocytes. Once secreted in the lymph stream, triglyceride-rich lipoproteins (TRLs) are metabolized by Lipoprotein lipase (LPL), which catalyzes the hydrolysis of triacylglycerols of very low density lipoproteins (VLDLs) and chylomicrons, thereby delivering free fatty acids to various tissues. Genetic mutations in the genes codifying for these proteins are responsible of different inherited disorders affecting chylomicron metabolism. This review focuses on the molecular pathways that modulate the uptake and the transport of lipoproteins of intestinal origin and it will highlight recent findings on TRLs assembly.
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Affiliation(s)
| | | | | | - Maurizio R. Averna
- Dipartimento Biomedico di Medicina Interna e Specialistica, Università degli Studi di PalermoPalermo, Italy
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Han Y, Lin M, Wang X, Guo K, Wang S, Sun M, Wang J, Han X, Fu T, Hu Y, Fu J. Basis of aggravated hepatic lipid metabolism by chronic stress in high-fat diet-fed rat. Endocrine 2015; 48:483-92. [PMID: 24895043 DOI: 10.1007/s12020-014-0307-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Accepted: 05/16/2014] [Indexed: 01/22/2023]
Abstract
Our previous study has demonstrated that long-term stress, known as chronic stress (CS), can aggravate nonalcoholic fatty liver disease in high-fat diet (HFD)-fed rat. In this study, we tried to figure out which lipid metabolic pathways were impacted by CS in the HFD-fed rat. Male Sprague-Dawley rats (6 weeks of age, n = 8 per group) were fed with either standard diet or HFD with or without CS exposure for 8 weeks. Hepatic lipidosis, biochemical, hormonal, and lipid profile markers in serum and liver, and enzymes involved in de novo lipogenesis (DNL) of fatty acids (FAs) and cholesterol, β-oxidation, FAs uptake, triglycerides synthesis, and very low-density lipoprotein (VLDL) assembly in the liver were detected. CS exposure reduced hepatic lipidosis but further elevated hepatic VLDL content with aggravated dyslipidemia in the HFD-fed rats. There was a synergism between CS and HFD on VLDL production and dyslipidemia. PCR and western blot assays showed that CS exposure significantly promoted hepatic VLDL assembly in rats, especially in the HFD-fed rats, while it had little impact on DNL, β-oxidation, FAs uptake, and triglycerides synthesis in the HFD-fed rats. This phenomenon was in accordance with elevated serum glucocorticoid level. The critical influence of CS exposure on hepatic lipid metabolism in the HFD-fed rats is VLDL assembly which might be regulated by glucocorticoid.
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Affiliation(s)
- Ying Han
- Department of Physiology, China Pharmaceutical University, 639 Long Mian Road, Nanjing, 211198, Jiangsu Province, China
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Wilson GJ, Lennox BA, She P, Mirek ET, Al Baghdadi RJT, Fusakio ME, Dixon JL, Henderson GC, Wek RC, Anthony TG. GCN2 is required to increase fibroblast growth factor 21 and maintain hepatic triglyceride homeostasis during asparaginase treatment. Am J Physiol Endocrinol Metab 2015; 308:E283-93. [PMID: 25491724 PMCID: PMC4329494 DOI: 10.1152/ajpendo.00361.2014] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The antileukemic agent asparaginase triggers the amino acid response (AAR) in the liver by activating the eukaryotic initiation factor 2 (eIF2) kinase general control nonderepressible 2 (GCN2). To explore the mechanism by which AAR induction is necessary to mitigate hepatic lipid accumulation and prevent liver dysfunction during continued asparaginase treatment, wild-type and Gcn2 null mice were injected once daily with asparaginase or phosphate buffered saline for up to 14 days. Asparaginase induced mRNA expression of multiple AAR genes and greatly increased circulating concentrations of the metabolic hormone fibroblast growth factor 21 (FGF21) independent of food intake. Loss of Gcn2 precluded mRNA expression and circulating levels of FGF21 and blocked mRNA expression of multiple genes regulating lipid synthesis and metabolism including Fas, Ppara, Pparg, Acadm, and Scd1 in both liver and white adipose tissue. Furthermore, rates of triglyceride export and protein expression of apolipoproteinB-100 were significantly reduced in the livers of Gcn2 null mice treated with asparaginase, providing a mechanistic basis for the increase in hepatic lipid content. Loss of AAR-regulated antioxidant defenses in Gcn2 null livers was signified by reduced Gpx1 gene expression alongside increased lipid peroxidation. Substantial reductions in antithrombin III hepatic expression and activity in the blood of asparaginase-treated Gcn2 null mice indicated liver dysfunction. These results suggest that the ability of the liver to adapt to prolonged asparaginase treatment is influenced by GCN2-directed regulation of FGF21 and oxidative defenses, which, when lost, corresponds with maladaptive effects on lipid metabolism and hemostasis.
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Affiliation(s)
- Gabriel J Wilson
- Department of Nutritional Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey
| | - Brittany A Lennox
- Department of Nutritional Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey
| | - Pengxiang She
- Department of Nutritional Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey
| | - Emily T Mirek
- Department of Nutritional Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey
| | - Rana J T Al Baghdadi
- Endocrinology and Animal Biosciences Graduate Program, Rutgers, The State University of New Jersey, New Brunswick, New Jersey
| | - Michael E Fusakio
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Joseph L Dixon
- Department of Nutritional Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey; New Jersey Institute for Food, Nutrition and Health, Rutgers, The State University of New Jersey, New Brunswick, New Jersey
| | - Gregory C Henderson
- Department of Exercise Science and Sport Studies, Rutgers, The State University of New Jersey, New Brunswick, New Jersey; and
| | - Ronald C Wek
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Tracy G Anthony
- Department of Nutritional Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey; New Jersey Institute for Food, Nutrition and Health, Rutgers, The State University of New Jersey, New Brunswick, New Jersey; Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, New Jersey; Endocrinology and Animal Biosciences Graduate Program, Rutgers, The State University of New Jersey, New Brunswick, New Jersey;
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New insights into the pathophysiology of dyslipidemia in type 2 diabetes. Atherosclerosis 2015; 239:483-95. [PMID: 25706066 DOI: 10.1016/j.atherosclerosis.2015.01.039] [Citation(s) in RCA: 266] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Revised: 01/28/2015] [Accepted: 01/30/2015] [Indexed: 02/06/2023]
Abstract
Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality for patients with type 2 diabetes, despite recent significant advances in management strategies to lessen CVD risk factors. A major cause is the atherogenic dyslipidemia, which consists of elevated plasma concentrations of both fasting and postprandial triglyceride-rich lipoproteins (TRLs), small dense low-density lipoprotein (LDL) and low high-density lipoprotein (HDL) cholesterol. The different components of diabetic dyslipidemia are not isolated abnormalities but closely linked to each other metabolically. The underlying disturbances are hepatic overproduction and delayed clearance of TRLs. Recent results have unequivocally shown that triglyceride-rich lipoproteins and their remnants are atherogenic. To develop novel strategies for the prevention and treatment of dyslipidaemia, it is essential to understand the pathophysiology of dyslipoproteinaemia in humans. Here, we review recent advances in our understanding of the pathophysiology of diabetic dyslipidemia.
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Stieb S, Roth Z, Dal Magro C, Fischer S, Butz E, Sagi A, Khalaila I, Lieb B, Schenk S, Hoeger U. One precursor, three apolipoproteins: The relationship between two crustacean lipoproteins, the large discoidal lipoprotein and the high density lipoprotein/β-glucan binding protein. Biochim Biophys Acta Mol Cell Biol Lipids 2014; 1841:1700-8. [DOI: 10.1016/j.bbalip.2014.09.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Revised: 09/19/2014] [Accepted: 09/24/2014] [Indexed: 12/28/2022]
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Lord CC, Brown JM. Distinct roles for alpha-beta hydrolase domain 5 (ABHD5/CGI-58) and adipose triglyceride lipase (ATGL/PNPLA2) in lipid metabolism and signaling. Adipocyte 2014; 1:123-131. [PMID: 23145367 PMCID: PMC3492958 DOI: 10.4161/adip.20035] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Catabolism of stored triacylglycerol (TAG) from cytoplasmic lipid droplets is critical for providing energy substrates, membrane building blocks and signaling lipids in most cells of the body. However, the lipolytic machinery dictating TAG hydrolysis varies greatly among different cell types. Within the adipocyte, TAG hydrolysis is dynamically regulated by hormones to ensure appropriate metabolic adaptation to nutritional and physiologic cues. In other cell types such as hepatocytes, myocytes and macrophages, mobilization of stored TAG is regulated quite differently. Within the last decade, mutations in two key genes involved in TAG hydrolysis, α-β hydrolase domain 5 (ABHD5/CGI-58) and adipose triglyceride lipase (ATGL/PNPLA2), were found to cause two distinct neutral lipid storage diseases (NLSD) in humans. These genetic links, along with supporting evidence in mouse models, have prompted a number of studies surrounding the biochemical function(s) of these proteins. Although both CGI-58 and ATGL have been clearly implicated in TAG hydrolysis in multiple tissues and have even been shown to physically interact with each other, recent evidence suggests that they may also have distinct roles. The purpose of this review is to summarize the most recent insights into how CGI-58 and ATGL regulate lipid metabolism and signaling.
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Butkinaree C, Guo L, Ramkhelawon B, Wanschel A, Brodsky JL, Moore KJ, Fisher EA. A regulator of secretory vesicle size, Kelch-like protein 12, facilitates the secretion of apolipoprotein B100 and very-low-density lipoproteins--brief report. Arterioscler Thromb Vasc Biol 2013; 34:251-4. [PMID: 24334870 DOI: 10.1161/atvbaha.113.302728] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
OBJECTIVE One of the major risk factors for atherosclerosis is the plasma level of low-density lipoprotein (LDL), which is a product of very-low-density lipoprotein (VLDL). Hepatic apolipoprotein B100 (apoB100) is the essential component that provides structural stability to VLDL particles. Newly translated apoB100 is partially lipidated in the endoplasmic reticulum (ER), forming nascent apoB100-VLDL particles. These particles are further modified to form fully mature VLDLs in the Golgi apparatus. Therefore, the transport of nascent VLDL from the ER to the Golgi represents a critical step during VLDL maturation and secretion and in regulating serum LDL cholesterol levels. Our previous studies showed that apoB100 exits the ER in coat complex II vesicles (COPII), but the cohort of related factors that control trafficking is poorly defined. APPROACH AND RESULTS Expression levels of Kelch-like protein 12 (KLHL12), an adaptor protein known to assist COPII-dependent transport of procollagen, were manipulated by using a KLHL12-specific small interfering RNA and a KLHL12 expression plasmid in the rat hepatoma cell line, McArdle RH7777. KLHL12 knockdown decreased the secreted and intracellular pools of apoB100, an effect that was attenuated in the presence of an autophagy inhibitor. KLHL12 knockdown also significantly reduced secretion of the most lipidated apoB100-VLDL species and led to the accumulation of apoB100 in the ER. Consistent with these data, KLHL12 overexpression increased apoB100 recovery and apoB100-VLDL secretion. Images obtained from confocal microscopy revealed colocalization of apoB100 and KLHL12, further supporting a direct link between KLHL12 function and VLDL trafficking from the ER. CONCLUSIONS KLHL12 plays a critical role in facilitating the ER exit and secretion of apoB100-VLDL particles, suggesting that KLHL12 modulation would influence plasma lipid levels.
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Affiliation(s)
- Chutikarn Butkinaree
- From the Department of Medicine, Leon H. Charney Division of Cardiology, Department of Cell Biology, and the Marc and Ruti Bell Vascular Biology and Disease Program, New York University School of Medicine (C.B., L.G., B.R., A.W., K.J.M., E.A.F.); and Department of Biological Sciences, University of Pittsburgh, PA (J.L.B.). C.B. is currently affiliated with Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, Montreal, Quebec, Canada
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Abstract
The liver plays a unique, central role in regulating lipid metabolism. In addition to influencing hepatic function and disease, changes in specific pathways of fatty acid (FA) metabolism have wide-ranging effects on the metabolism of other nutrients, extra-hepatic physiology, and the development of metabolic diseases. The high prevalence of nonalcoholic fatty liver disease (NAFLD) has led to increased efforts to characterize the underlying biology of hepatic energy metabolism and FA trafficking that leads to disease development. Recent advances have uncovered novel roles of metabolic pathways and specific enzymes in generating lipids important for cellular processes such as signal transduction and transcriptional activation. These studies have also advanced our understanding of key branch points involving FA partitioning between metabolic pathways and have identified new roles for lipid droplets in these events. This review covers recent advances in our understanding of FA trafficking and its regulation. An emphasis will be placed on branch points in these pathways and how alterations in FA trafficking contribute to NAFLD and related comorbidities.
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Maitin V, Andreo U, Guo L, Fisher EA. Docosahexaenoic acid impairs the maturation of very low density lipoproteins in rat hepatic cells. J Lipid Res 2013; 55:75-84. [PMID: 24136824 DOI: 10.1194/jlr.m043026] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
One mechanism of the lipid-lowering effects of the fish oil n-3 fatty acids [e.g., docosahexaenoic acid (DHA)] in cell and animal models is induced hepatic apolipoprotein B100 (apoB) presecretory degradation. This degradation occurs post-endoplasmic reticulum, but whether DHA induces it before or after intracellular VLDL formation remains unanswered. We found in McA-RH7777 rat hepatic cells that DHA and oleic acid (OA) treatments allowed formation of pre-VLDL particles and their transport to the Golgi, but, in contrast to OA, with DHA pre-VLDL particles failed to quantitatively assemble into fully lipidated (mature) VLDL. This failure required lipid peroxidation and was accompanied by the formation of apoB aggregates (known to be degraded by autophagy). Preventing the exit of proteins from the Golgi blocked the aggregation of apoB but did not restore VLDL maturation, indicating that failure to fully lipidate apoB preceded its aggregation. ApoB autophagic degradation did not appear to require an intermediate step of cytosolic aggresome formation. Taken with other examples in the literature, the results of this study suggest that pre-VLDL particles that are competent to escape endoplasmic reticulum quality control mechanisms but fail to mature in the Golgi remain subject to quality control surveillance late in the secretory pathway.
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Affiliation(s)
- Vatsala Maitin
- Departments of Medicine (Leon H. Charney Division of Cardiology) and Cell Biology and the Marc and Ruti Bell Vascular Biology and Disease Program, New York University School of Medicine, New York, NY 10016; and
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Ohsaki Y, Cheng J, Yamairi K, Pan X, Hussain MM, Fujimoto T. Inhibition of ADP-ribosylation suppresses aberrant accumulation of lipidated apolipoprotein B in the endoplasmic reticulum. FEBS Lett 2013; 587:3696-702. [PMID: 24100140 DOI: 10.1016/j.febslet.2013.09.036] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Revised: 09/17/2013] [Accepted: 09/17/2013] [Indexed: 11/19/2022]
Abstract
ApoB-crescent, an endoplasmic reticulum (ER)-lipid droplet amalgamation structure, is a useful marker to indicate aberrant lipidated apolipoprotein B accumulation in the hepatocyte ER. Blockade of the ER-to-Golgi transport by either vesicle transport inhibitors or dominant-negative Arf1 caused a significant increase in ApoB-crescents. However, a low concentration of Brefeldin A induced the same result without affecting protein secretion, suggesting ADP-ribosylation as an additional mechanism. ADP-ribosylation inhibitors not only suppressed the increase of ApoB-crescents, but also rapidly dissolved existing ApoB-crescents. These results implicate the involvement of ADP-ribosylation in the ApoB-crescent formation and maintenance process at the ER.
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Affiliation(s)
- Yuki Ohsaki
- Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan
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Borén J, Taskinen MR, Olofsson SO, Levin M. Ectopic lipid storage and insulin resistance: a harmful relationship. J Intern Med 2013; 274:25-40. [PMID: 23551521 DOI: 10.1111/joim.12071] [Citation(s) in RCA: 157] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Obesity increases the risk of metabolic diseases, including insulin resistance and type 2 diabetes, as well as cardiovascular disease. In addition to lipid accumulation in adipose tissue, obesity is associated with increased lipid storage in ectopic tissues, such as skeletal muscle and liver. Furthermore, lipid accumulation in the heart may result in cardiac dysfunction and heart failure. It has recently been demonstrated that intracellular lipid accumulation in ectopic tissues leads to pathological responses and impaired insulin signalling. Here, we will review the current understanding of how lipid storage and lipid droplet physiology affect the risk of developing metabolic diseases.
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Affiliation(s)
- J Borén
- Department of Molecular and Clinical Medicine, University of Gothenburg, Gothenburg, Sweden.
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Hashimoto Y, Yamada K, Tsushima H, Miyazawa D, Mori M, Nishio K, Ohkubo T, Hibino H, Ohara N, Okuyama H. Three dissimilar high fat diets differentially regulate lipid and glucose metabolism in obesity-resistant Slc:Wistar/ST rats. Lipids 2013; 48:803-15. [PMID: 23807365 DOI: 10.1007/s11745-013-3805-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2012] [Accepted: 05/15/2013] [Indexed: 12/25/2022]
Abstract
Epidemiologic and ecologic studies suggest that dietary fat plays an important role in the development of obesity. Certain Wistar rat strains do not become obese when fed high-fat diets unlike others. In a preliminary study, we confirmed that Slc:Wistar/ST rats did not become obese when fed high-fat diets. The mechanisms governing the response of hepatic lipid-metabolizing enzymes to large quantities of dietary lipids consumed by obesity-resistant animals are unknown. The aim of the present study is to examine how obesity-resistant animals metabolize various types of high-fat diets and why they do not become obese. For this purpose, male Slc:Wistar/ST rats were fed a control low-fat diet (LS) or a high-fat diet containing fish oil (HF), soybean oil (HS), or lard (HL) for 4 weeks. We observed their phenotypes and determined lipid profiles in plasma and liver as well as mRNA expression levels in liver of genes related to lipid and glucose metabolism using DNA microarray and quantitative reverse transcriptase polymerase chain analyses. The body weights of all dietary groups were similar due to isocaloric intakes, whereas the weight of white adipose tissues in the LS group was significantly lower. The HF diet lowered plasma lipid levels by accelerated lipolysis in the peroxisomes and suppressed levels of very-low-density lipoprotein (VLDL) secretion. The HS diet promoted hepatic lipid accumulation by suppressed lipolysis in the peroxisomes and normal levels of VLDL secretion. The lipid profiles of rats fed the LS or HL diet were similar. The HL diet accelerated lipid and glucose metabolism.
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Affiliation(s)
- Yoko Hashimoto
- Department of Biochemistry, School of Dentistry, Aichi-Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya 464-8650, Japan.
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Insulin-stimulated degradation of apolipoprotein B100: roles of class II phosphatidylinositol-3-kinase and autophagy. PLoS One 2013; 8:e57590. [PMID: 23516411 PMCID: PMC3596368 DOI: 10.1371/journal.pone.0057590] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Accepted: 01/27/2013] [Indexed: 11/24/2022] Open
Abstract
Both in humans and animal models, an acute increase in plasma insulin levels, typically following meals, leads to transient depression of hepatic secretion of very low density lipoproteins (VLDL). One contributing mechanism for the decrease in VLDL secretion is enhanced degradation of apolipoprotein B100 (apoB100), which is required for VLDL formation. Unlike the degradation of nascent apoB100, which occurs in the endoplasmic reticulum (ER), insulin-stimulated apoB100 degradation occurs post-ER and is inhibited by pan-phosphatidylinositol (PI)3-kinase inhibitors. It is unclear, however, which of the three classes of PI3-kinases is required for insulin-stimulated apoB100 degradation, as well as the proteolytic machinery underlying this response. Class III PI3-kinase is not activated by insulin, but the other two classes are. By using a class I-specific inhibitor and siRNA to the major class II isoform in liver, we now show that it is class II PI3-kinase that is required for insulin-stimulated apoB100 degradation in primary mouse hepatocytes. Because the insulin-stimulated process resembles other examples of apoB100 post-ER proteolysis mediated by autophagy, we hypothesized that the effects of insulin in autophagy-deficient mouse primary hepatocytes would be attenuated. Indeed, apoB100 degradation in response to insulin was significantly impaired in two types of autophagy-deficient hepatocytes. Together, our data demonstrate that insulin-stimulated apoB100 degradation in the liver requires both class II PI3-kinase activity and autophagy.
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Christian P, Sacco J, Adeli K. Autophagy: Emerging roles in lipid homeostasis and metabolic control. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1831:819-24. [PMID: 23274236 DOI: 10.1016/j.bbalip.2012.12.009] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Revised: 12/13/2012] [Accepted: 12/18/2012] [Indexed: 02/06/2023]
Abstract
Current evidence implicates autophagy in the regulation of lipid stores within the two main organs involved in maintaining lipid homeostasis, the liver and adipose tissue. Critical to this role in hepatocytes is the breakdown of cytoplasmic lipid droplets, a process referred to as lipophagy. Conversely, autophagy is required for adipocyte differentiation and the concurrent accumulation of lipid droplets. Autophagy also affects lipid metabolism through contributions to lipoprotein assembly. A number of reports have now implicated autophagy in the degradation of apolipoprotein B, the main structural protein of very-low-density-lipoprotein. Aberrant autophagy may also be involved in conditions of deregulated lipid homeostasis in metabolic disorders such as the metabolic syndrome. First, insulin signalling and autophagy activity appear to diverge in a mechanism of reciprocal regulation, suggesting a role for autophagy in insulin resistance. Secondly, upregulation of autophagy may lead to conversion of white adipose tissue into brown adipose tissue, thus regulating energy expenditure and obesity. Thirdly, upregulation of autophagy in hepatocytes could increase breakdown of lipid stores controlling triglyceride homeostasis and fatty liver. Taken together, autophagy appears to play a very complex role in lipid homeostasis, affecting lipid stores differently depending on the tissue, as well as contributing to pathways of lipoprotein metabolism.
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Affiliation(s)
- Patricia Christian
- Molecular Structure and Function, Research Institute, The Hospital for Sick Children, University of Toronto, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8
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