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Feng J, Yang J, Chang Y, Qiao L, Dang H, Luo K, Guo H, An Y, Ma C, Shao H, Tian J, Yuan Y, Xie L, Xing W, Cheng J. Caffeine-free hawk tea lowers cholesterol by reducing free cholesterol uptake and the production of very-low-density lipoprotein. Commun Biol 2019; 2:173. [PMID: 31098406 PMCID: PMC6506518 DOI: 10.1038/s42003-019-0396-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2018] [Accepted: 03/21/2019] [Indexed: 02/08/2023] Open
Abstract
Medicinal plants show important therapeutic value in chronic disease treatment. However, due to their diverse ingredients and complex biological effects, the molecular mechanisms of medicinal plants are yet to be explored. By means of several high-throughput platforms, here we show hawk tea extract (HTE) inhibits Niemann-Pick C1-like 1 (NPC1L1)-mediated free cholesterol uptake, thereby inducing the transcription of low-density lipoprotein receptor (LDLR) downstream of the sterol response element binding protein 2 (SREBP2) pathway. Meanwhile, HTE suppresses hepatocyte nuclear factor 4α (HNF4α)-mediated transcription of microsomal triglyceride transfer protein (MTP) and apolipoprotein B (APOB), thereby decreasing the production of very-low-density lipoprotein. The catechin EGCG ((-)-epigallocatechin gallate) and the flavonoids kaempferol and quercetin are identified as the bioactive components responsible for the effects on the NPC1L1-SREBP2-LDLR axis and HNF4α-MTP/APOB axis, respectively. Overall, hawk tea works as a previously unrecognized cholesterol-lowering agent in a multi-target and multi-component manner.
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Affiliation(s)
- Juan Feng
- State Key Laboratory of Membrane Biology, School of Medicine, Tsinghua University, 100084 Beijing, China
- Medical Systems Biology Research Center, School of Medicine, Tsinghua University, 100084 Beijing, China
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Jian Yang
- State Key Laboratory Breeding Base of Dao-di Herbs, National Resource Center for Chinese Materia Medica, China Academy of Chinese Medical Sciences, 100700 Beijing, China
| | - Yujun Chang
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Liansheng Qiao
- State Key Laboratory of Membrane Biology, School of Medicine, Tsinghua University, 100084 Beijing, China
- Medical Systems Biology Research Center, School of Medicine, Tsinghua University, 100084 Beijing, China
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Honglei Dang
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Kun Luo
- State Key Laboratory of Membrane Biology, School of Medicine, Tsinghua University, 100084 Beijing, China
- Medical Systems Biology Research Center, School of Medicine, Tsinghua University, 100084 Beijing, China
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Hongyan Guo
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Yannan An
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Chengmei Ma
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Hong Shao
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Jie Tian
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Yuan Yuan
- State Key Laboratory Breeding Base of Dao-di Herbs, National Resource Center for Chinese Materia Medica, China Academy of Chinese Medical Sciences, 100700 Beijing, China
| | - Lan Xie
- State Key Laboratory of Membrane Biology, School of Medicine, Tsinghua University, 100084 Beijing, China
- Medical Systems Biology Research Center, School of Medicine, Tsinghua University, 100084 Beijing, China
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Wanli Xing
- State Key Laboratory of Membrane Biology, School of Medicine, Tsinghua University, 100084 Beijing, China
- Medical Systems Biology Research Center, School of Medicine, Tsinghua University, 100084 Beijing, China
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
| | - Jing Cheng
- State Key Laboratory of Membrane Biology, School of Medicine, Tsinghua University, 100084 Beijing, China
- Medical Systems Biology Research Center, School of Medicine, Tsinghua University, 100084 Beijing, China
- National Engineering Research Center for Beijing Biochip Technology, 102206 Beijing, China
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2
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Manchekar M, Kapil R, Sun Z, Segrest JP, Dashti N. Relationship between Amphipathic β Structures in the β 1 Domain of Apolipoprotein B and the Properties of the Secreted Lipoprotein Particles in McA-RH7777 Cells. Biochemistry 2017; 56:4084-4094. [PMID: 28702990 DOI: 10.1021/acs.biochem.6b01174] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Our previous studies demonstrated that the first 1000 amino acid residues (the βα1 domain) of human apolipoprotein (apo) B-100, termed apoB:1000, are required for the initiation of lipoprotein assembly and the formation of a monodisperse stable phospholipid (PL)-rich particle. The objectives of this study were (a) to assess the effects on the properties of apoB truncates undergoing sequential inclusion of the amphipathic β strands in the 700 N-terminal residues of the β1 domain of apoB-100 and (b) to identify the subdomain in the β1 domain that is required for the formation of a microsomal triglyceride transfer protein (MTP)-dependent triacylglycerol (TAG)-rich apoB-containing particle. Characterization of particles secreted by stable transformants of McA-RH7777 cells demonstrated the following. (1) The presence of amphipathic β strands in the 200 N-terminal residues of the β1 domain resulted in the secretion of apoB truncates (apoB:1050 to apoB:1200) as both lipidated and lipid-poor particles. (2) Inclusion of residues 300-700 of the β1 domain led to the secretion of apoB:1300, apoB:1400, apoB:1500, and apoB:1700 predominantly as lipidated particles. (3) Particles containing residues 1050-1500 were all rich in PL. (4) There was a marked increase in the lipid loading capacity and TAG content of apoB:1700-containing particles. (5) Only the level of secretion of apoB:1700 was markedly diminished by MTP inhibitor BMS-197636. These results suggest that apoB:1700 marks the threshold for the formation of a TAG-rich particle and support the concept that MTP participates in apoB assembly and secretion at the stage where particles undergo a transition from PL-rich to TAG-rich.
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Affiliation(s)
| | | | | | - Jere P Segrest
- Division of Cardiovascular Medicine, Department of Medicine, Vanderbilt University Medical Center , Nashville, Tennessee 37232, United States
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Role of Tribbles Pseudokinase 1 (TRIB1) in human hepatocyte metabolism. Biochim Biophys Acta Mol Basis Dis 2015; 1862:223-32. [PMID: 26657055 DOI: 10.1016/j.bbadis.2015.12.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Revised: 11/18/2015] [Accepted: 12/01/2015] [Indexed: 01/23/2023]
Abstract
Genome-wide association studies for plasma triglycerides and hepatic steatosis identified a risk locus on chromosome 8q24 close to the TRIB1 gene, encoding Tribbles Pseudokinase 1 (TRIB1). In previous studies conducted in murine models, hepatic over-expression of Trib1 was shown to increase fatty acid oxidation and decrease triglyceride synthesis whereas Trib1 knockdown mice exhibited hypertriglyceridemia. Here we have examined the impact of TRIB1 suppression in human and mouse hepatocytes. Examination of a panel of lipid regulator transcripts revealed species-specific effects, prompting us to focus on human models for the remainder of the study. Acute knockdown of TRIB1 in human primary hepatocytes resulted in decreased expression of MTTP and APOB, required for very low density lipoprotein (VLDL) assembly although particle secretion was not significantly affected. A parallel analysis performed in HepG2 revealed reduced MTTP, but not APOB, protein as a result of TRIB1 suppression. Global gene expression changes of human primary hepatocytes upon TRIB1 suppression were analyzed by clustering algorithms and found to be consistent with dysregulation of several pathways fundamental to liver function, including altered CEBPA and B transcript levels and impaired glucose handling. Indeed, TRIB1 expression in HepG2 cells was found to be inversely proportional to glucose concentration. Lastly TRIB1 downregulation in primary hepatocytes was associated with suppression of the HNF4A axis. In HepG2 cells, TRIB1 suppression resulted in reduced HNF4A protein levels while HNF4A suppression increased TRIB1 expression. Taken together these studies reveal an important role for TRIB1 in human hepatocyte biology.
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Manchekar M, Liu Y, Sun Z, Richardson PE, Dashti N. Phospholipid transfer protein plays a major role in the initiation of apolipoprotein B-containing lipoprotein assembly in mouse primary hepatocytes. J Biol Chem 2015; 290:8196-205. [PMID: 25638820 DOI: 10.1074/jbc.m114.602748] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
In this study, we tested the hypothesis that phospholipid transfer protein (PLTP) is a plausible mediator of phospholipid (PL) transfer to the N-terminal 1000 residues of apoB (apoB:1000) leading to the initiation of apoB-containing lipoprotein assembly. To this end, primary hepatocytes from wild type (WT) and PLTP knock-out (KO) mice were transduced with adenovirus-apoB:1000 with or without co-transduction with adenovirus-PLTP, and the assembly and secretion of apoB:1000-containing lipoproteins were assessed. PLTP deficiency resulted in a 65 and 72% reduction in the protein and lipid content, respectively, of secreted apoB:1000-containing lipoproteins. Particles secreted by WT hepatocytes contained 69% PL, 9% diacylglycerol (DAG), and 23% triacylglycerol (TAG) with a stoichiometry of 46 PL, 6 DAG, and 15 TAG molecules per apoB:1000. PLTP absence drastically altered the lipid composition of apoB:1000 lipoproteins; these particles contained 46% PL, 13% DAG, and 41% TAG with a stoichiometry of 27 PL, 10 DAG, and 23 TAG molecules per apoB:1000. Reintroduction of Pltp gene into PLTP-KO hepatocytes stimulated the lipidation and secretion of apoB:1000-containing lipoproteins by ∼3-fold; the lipid composition and stoichiometry of these particles were identical to those secreted by WT hepatocytes. In contrast to the WT, apoB:1000 in PLTP-KO hepatocytes was susceptible to intracellular degradation predominantly in the post-endoplasmic reticulum, presecretory compartment. Reintroduction of Pltp gene into PLTP-KO hepatocytes restored the stability of apoB:1000. These results provide compelling evidence that in hepatocytes initial recruitment of PL by apoB:1000 leading to the formation of the PL-rich apoB-containing initiation complex is mediated to a large extent by PLTP.
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Affiliation(s)
- Medha Manchekar
- From the Department of Medicine, Division of Gerontology, Geriatrics, and Palliative Care, Basic Sciences Section, University of Alabama, Birmingham, Alabama 35294 and
| | - Yanwen Liu
- From the Department of Medicine, Division of Gerontology, Geriatrics, and Palliative Care, Basic Sciences Section, University of Alabama, Birmingham, Alabama 35294 and
| | - Zhihuan Sun
- From the Department of Medicine, Division of Gerontology, Geriatrics, and Palliative Care, Basic Sciences Section, University of Alabama, Birmingham, Alabama 35294 and
| | - Paul E Richardson
- the Department of Chemistry and Physics, Coastal Carolina University, Conway, South Carolina 29528
| | - Nassrin Dashti
- From the Department of Medicine, Division of Gerontology, Geriatrics, and Palliative Care, Basic Sciences Section, University of Alabama, Birmingham, Alabama 35294 and
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Fisher E, Lake E, McLeod RS. Apolipoprotein B100 quality control and the regulation of hepatic very low density lipoprotein secretion. J Biomed Res 2014; 28:178-93. [PMID: 25013401 PMCID: PMC4085555 DOI: 10.7555/jbr.28.20140019] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 02/15/2014] [Indexed: 12/19/2022] Open
Abstract
Apolipoprotein B (apoB) is the main protein component of very low density lipoprotein (VLDL) and is necessary for the assembly and secretion of these triglyceride (TG)-rich particles. Following release from the liver, VLDL is converted to low density lipoprotein (LDL) in the plasma and increased production of VLDL can therefore play a detrimental role in cardiovascular disease. Increasing evidence has helped to establish VLDL assembly as a target for the treatment of dyslipidemias. Multiple factors are involved in the folding of the apoB protein and the formation of a secretion-competent VLDL particle. Failed VLDL assembly can initiate quality control mechanisms in the hepatocyte that target apoB for degradation. ApoB is a substrate for endoplasmic reticulum associated degradation (ERAD) by the ubiquitin proteasome system and for autophagy. Efficient targeting and disposal of apoB is a regulated process that modulates VLDL secretion and partitioning of TG. Emerging evidence suggests that significant overlap exists between these degradative pathways. For example, the insulin-mediated targeting of apoB to autophagy and postprandial activation of the unfolded protein response (UPR) may employ the same cellular machinery and regulatory cues. Changes in the quality control mechanisms for apoB impact hepatic physiology and pathology states, including insulin resistance and fatty liver. Insulin signaling, lipid metabolism and the hepatic UPR may impact VLDL production, particularly during the postprandial state. In this review we summarize our current understanding of VLDL assembly, apoB degradation, quality control mechanisms and the role of these processes in liver physiology and in pathologic states.
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Affiliation(s)
- Eric Fisher
- Biochemistry & Molecular Biology, Faculty of Medicine, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Elizabeth Lake
- Biochemistry & Molecular Biology, Faculty of Medicine, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Roger S McLeod
- Biochemistry & Molecular Biology, Faculty of Medicine, Dalhousie University, Halifax, NS B3H 4R2, Canada
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Hu YW, Zhang P, Yang JY, Huang JL, Ma X, Li SF, Zhao JY, Hu YR, Wang YC, Gao JJ, Sha YH, Zheng L, Wang Q. Nur77 decreases atherosclerosis progression in apoE(-/-) mice fed a high-fat/high-cholesterol diet. PLoS One 2014; 9:e87313. [PMID: 24498071 PMCID: PMC3909091 DOI: 10.1371/journal.pone.0087313] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Accepted: 12/20/2013] [Indexed: 12/04/2022] Open
Abstract
Rationale It is clear that lipid disorder and inflammation are associated with cardiovascular diseases and underlying atherosclerosis. Nur77 has been shown to be involved in inflammatory response and lipid metabolism. Objective Here, we explored the role of Nur77 in atherosclerotic plaque progression in apoE−/− mice fed a high-fat/high cholesterol diet. Methods and Results The Nur77 gene, a nuclear hormone receptor, was highly induced by treatment with Cytosporone B (Csn-B, specific Nur77 agonist), recombinant plasmid over-expressing Nur77 (pcDNA-Nur77), while inhibited by treatment with siRNAs against Nur77 (si-Nur77) in THP-1 macrophage-derived foam cells, HepG2 cells and Caco-2 cells, respectively. In addition, the expression of Nur77 was highly induced by Nur77 agonist Csn-B, lentivirus encoding Nur77 (LV-Nur77), while silenced by lentivirus encoding siRNA against Nur77 (si-Nur77) in apoE−/− mice fed a high-fat/high cholesterol diet, respectively. We found that increased expression of Nur77 reduced macrophage-derived foam cells formation and hepatic lipid deposition, downregulated gene levels of inflammatory molecules, adhesion molecules and intestinal lipid absorption, and decreases atherosclerotic plaque formation. Conclusion These observations provide direct evidence that Nur77 is an important nuclear hormone receptor in regulation of atherosclerotic plaque formation and thus represents a promising target for the treatment of atherosclerosis.
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MESH Headings
- Animals
- Apolipoproteins E/genetics
- Apolipoproteins E/metabolism
- Atherosclerosis/etiology
- Atherosclerosis/genetics
- Atherosclerosis/metabolism
- Blotting, Western
- Caco-2 Cells
- Cell Line, Tumor
- Cholesterol, Dietary/adverse effects
- Diet, High-Fat/adverse effects
- Disease Progression
- Foam Cells/drug effects
- Foam Cells/metabolism
- Gene Expression/drug effects
- Hep G2 Cells
- Humans
- Inflammation/genetics
- Inflammation/metabolism
- Lipid Metabolism/drug effects
- Liver/drug effects
- Liver/metabolism
- Liver/pathology
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Nuclear Receptor Subfamily 4, Group A, Member 1/agonists
- Nuclear Receptor Subfamily 4, Group A, Member 1/genetics
- Nuclear Receptor Subfamily 4, Group A, Member 1/metabolism
- Phenylacetates/pharmacology
- Plaque, Atherosclerotic/etiology
- Plaque, Atherosclerotic/genetics
- Plaque, Atherosclerotic/metabolism
- RNA Interference
- Reverse Transcriptase Polymerase Chain Reaction
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Affiliation(s)
- Yan-Wei Hu
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Peng Zhang
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Jun-Yao Yang
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Jin-Lan Huang
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Xin Ma
- Department of Anesthesiology, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Shu-Fen Li
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Jia-Yi Zhao
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Ya-Rong Hu
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Yan-Chao Wang
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Ji-Juan Gao
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Yan-Hua Sha
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Lei Zheng
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
- * E-mail: (QW); (LZ)
| | - Qian Wang
- Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, China
- * E-mail: (QW); (LZ)
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7
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Eresheim C, Plieschnig J, Ivessa NE, Schneider WJ, Hermann M. Expression of microsomal triglyceride transfer protein in lipoprotein-synthesizing tissues of the developing chicken embryo. Biochimie 2014; 101:67-74. [PMID: 24394625 PMCID: PMC4008936 DOI: 10.1016/j.biochi.2013.12.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Accepted: 12/21/2013] [Indexed: 12/01/2022]
Abstract
In contrast to mammals, in the chicken major sites of lipoprotein synthesis and secretion are not only the liver and intestine, but also the kidney and the embryonic yolk sac. Two key components in the assembly of triglyceride-rich lipoproteins are the microsomal triglyceride transfer protein (MTP) and apolipoprotein B (apoB). We have analyzed the expression of MTP in the embryonic liver, small intestine, and kidney, and have studied the expression of MTP in, and the secretion of apoB from, the developing yolk sac (YS). Transcript and protein levels of MTP increase during embryogenesis in YS, liver, kidney, and small intestine, and decrease in YS, embryonic liver, and kidney after hatching. In small intestine, the MTP mRNA level rises sharply during the last trimester of embryo development (after day 15), while MTP protein is detectable only after hatching (day 21). In the YS of 15- and 20-day old embryos, apoB secretion was detected by pulse-chase metabolic radiolabeling experiments and subsequent immunoprecipitation. Taken together, our data reveal the importance of coordinated production of MTP and apoB in chicken tissues capable of secreting triglyceride-rich lipoproteins even before hatching. MTP is expressed in liver, small intestine, and kidney of chicken embryos. MTP is expressed in the chicken yolk sac. ApoB is secreted from the chicken yolk sac. Embryonic tissues contribute to the lipoprotein pool of the developing chick.
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Affiliation(s)
- Christine Eresheim
- Max F. Perutz Laboratories, Department of Medical Biochemistry, Medical University of Vienna, Dr. Bohr-Gasse 9/2, 1030 Vienna, Austria
| | - Julia Plieschnig
- Max F. Perutz Laboratories, Department of Medical Biochemistry, Medical University of Vienna, Dr. Bohr-Gasse 9/2, 1030 Vienna, Austria
| | - N Erwin Ivessa
- Max F. Perutz Laboratories, Department of Medical Biochemistry, Medical University of Vienna, Dr. Bohr-Gasse 9/2, 1030 Vienna, Austria
| | - Wolfgang J Schneider
- Max F. Perutz Laboratories, Department of Medical Biochemistry, Medical University of Vienna, Dr. Bohr-Gasse 9/2, 1030 Vienna, Austria
| | - Marcela Hermann
- Max F. Perutz Laboratories, Department of Medical Biochemistry, Medical University of Vienna, Dr. Bohr-Gasse 9/2, 1030 Vienna, Austria.
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Sparks JD, Sparks CE, Adeli K. Selective hepatic insulin resistance, VLDL overproduction, and hypertriglyceridemia. Arterioscler Thromb Vasc Biol 2012; 32:2104-12. [PMID: 22796579 DOI: 10.1161/atvbaha.111.241463] [Citation(s) in RCA: 150] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Insulin plays a central role in regulating energy metabolism, including hepatic transport of very low-density lipoprotein (VLDL)-associated triglyceride. Hepatic hypersecretion of VLDL and consequent hypertriglyceridemia leads to lower circulating high-density lipoprotein levels and generation of small dense low-density lipoproteins characteristic of the dyslipidemia commonly observed in metabolic syndrome and type 2 diabetes mellitus. Physiological fluctuations of insulin modulate VLDL secretion, and insulin inhibition of VLDL secretion upon feeding may be the first pathway to become resistant in obesity that leads to VLDL hypersecretion. This review summarizes the role of insulin-related signaling pathways that determine hepatic VLDL production. Disruption in signaling pathways that reduce generation of the second messenger phosphatidylinositide (3,4,5) triphosphate downstream of activated phosphatidylinositide 3-kinase underlies the development of VLDL hypersecretion. As insulin resistance progresses, a number of pathways are altered that further augment VLDL hypersecretion, including hepatic inflammatory pathways. Insulin plays a complex role in regulating glucose metabolism, and it is not surprising that the role of insulin in VLDL and lipid metabolism will prove equally complex.
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Affiliation(s)
- Janet D Sparks
- University of Rochester Medical Center, Department of Pathology and Laboratory Medicine, Rochester, NY, USA
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9
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Abstract
PURPOSE OF REVIEW A strong positive correlation between plasma apolipoprotein (apo) C-III and triglyceride concentrations has been invariably observed in human and animal studies. The hypertriglyceridemic effect of apo C-III has been conventionally explained by its extracellular roles in inhibiting lipolysis catalysed by lipoprotein lipase and attenuating triglyceride-rich lipoprotein clearance through receptor-dependent and/or independent mechanisms. However, recent experimental evidence suggests that apo C-III may also play an intracellular role in promoting hepatic triglyceride-rich lipoprotein production. RECENT FINDINGS Kinetic studies with humans and genetically modified mice have shown that apo C-III is linked with increased production of triglyceride-rich lipoproteins, such as very-low-density lipoprotein 1 (VLDL1). Mutational studies on human apo C-III variants (originally identified in humans with hypotriglyceridemia or hyperalphalipoproteinemia) provide the structure-function analysis of human apo C-III, demonstrating that loss-of-function mutations within human apo C-III impair the assembly and secretion of triglyceride-rich VLDL1 under lipid-rich conditions. SUMMARY The current review summarizes recent experimental evidence for an intrahepatic role of human apo C-III in promoting mobilization and utilization of triglyceride during VLDL1 assembly/secretion. Understanding mechanisms by which hepatic apo C-III expression is regulated under insulin resistance and diabetic conditions will lead to better and more rational strategies for the prevention and treatment of diabetic hypertriglyceridemia that is closely related to premature atherosclerosis.
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Affiliation(s)
- Zemin Yao
- Department of Biochemistry, Microbiology and Immunology, Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, Ontario, Canada
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10
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De Smet E, Mensink RP, Plat J. Effects of plant sterols and stanols on intestinal cholesterol metabolism: suggested mechanisms from past to present. Mol Nutr Food Res 2012; 56:1058-72. [PMID: 22623436 DOI: 10.1002/mnfr.201100722] [Citation(s) in RCA: 178] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Revised: 02/27/2012] [Accepted: 04/03/2012] [Indexed: 11/07/2022]
Abstract
Plant sterols and stanols are natural food ingredients found in plants. It was already shown in 1950 that they lower serum low-density lipoprotein cholesterol (LDL-C) concentrations. Meta-analysis has reported that a daily intake of 2.5 g plant sterols/stanols reduced serum LDL-C concentrations up to 10%. Despite many studies, the underlying mechanism remains to be elucidated. Therefore, the proposed mechanisms that have been presented over the past decades will be described and discussed in the context of the current knowledge. In the early days, it was suggested that plant sterols/stanols compete with intestinal cholesterol for incorporation into mixed micelles as well as into chylomicrons. Next, the focus shifted toward cellular processes. In particular, a role for sterol transporters localized in the membranes of enterocytes was suggested. All these processes ultimately lowered intestinal cholesterol absorption. More recently, the existence of a direct secretion of cholesterol from the circulation into the intestinal lumen was described. First results in animal studies suggested that plant sterols/stanols activate this pathway, which also explains the increased fecal neutral sterol content and as such could explain the cholesterol-lowering activity of plant sterols/stanols.
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Affiliation(s)
- Els De Smet
- Department of Human Biology, School for Nutrition, Toxicology and Metabolism, Maastricht University, Maastricht, The Netherlands
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11
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Hussain MM, Rava P, Walsh M, Rana M, Iqbal J. Multiple functions of microsomal triglyceride transfer protein. Nutr Metab (Lond) 2012; 9:14. [PMID: 22353470 PMCID: PMC3337244 DOI: 10.1186/1743-7075-9-14] [Citation(s) in RCA: 175] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2011] [Accepted: 02/21/2012] [Indexed: 02/08/2023] Open
Abstract
Microsomal triglyceride transfer protein (MTP) was first identified as a major cellular protein capable of transferring neutral lipids between membrane vesicles. Its role as an essential chaperone for the biosynthesis of apolipoprotein B (apoB)-containing triglyceride-rich lipoproteins was established after the realization that abetalipoproteinemia patients carry mutations in the MTTP gene resulting in the loss of its lipid transfer activity. Now it is known that it also plays a role in the biosynthesis of CD1, glycolipid presenting molecules, as well as in the regulation of cholesterol ester biosynthesis. In this review, we will provide a historical perspective about the identification, purification and characterization of MTP, describe methods used to measure its lipid transfer activity, and discuss tissue expression and function. Finally, we will review the role MTP plays in the assembly of apoB-lipoprotein, the regulation of cholesterol ester synthesis, biosynthesis of CD1 proteins and propagation of hepatitis C virus. We will also provide a brief overview about the clinical potentials of MTP inhibition.
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Affiliation(s)
- M Mahmood Hussain
- Department of Cell Biology and Pediatrics, SUNY Downstate Medical Center, Brooklyn, NY 11203, USA
| | - Paul Rava
- Department of Cell Biology and Pediatrics, SUNY Downstate Medical Center, Brooklyn, NY 11203, USA
| | - Meghan Walsh
- Department of Cell Biology and Pediatrics, SUNY Downstate Medical Center, Brooklyn, NY 11203, USA
| | - Muhammad Rana
- Department of Cell Biology and Pediatrics, SUNY Downstate Medical Center, Brooklyn, NY 11203, USA
| | - Jahangir Iqbal
- Department of Cell Biology and Pediatrics, SUNY Downstate Medical Center, Brooklyn, NY 11203, USA
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12
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Fu S, Deng Q, Yang W, Ding H, Wang X, Li P, Li X, Wang Z, Li X, Liu G. Increase of Fatty Acid Oxidation and VLDL Assembly and Secretion Overexpression of PTEN in Cultured Hepatocytes of Newborn Calf. Cell Physiol Biochem 2012; 30:1005-13. [DOI: 10.1159/000341477] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/05/2012] [Indexed: 11/19/2022] Open
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13
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Soriguer F, García-Serrano S, Garrido-Sánchez L, Gutierrez-Repiso C, Rojo-Martínez G, Garcia-Escobar E, García-Arnés J, Gallego-Perales JL, Delgado V, García-Fuentes E. Jejunal wall triglyceride concentration of morbidly obese persons is lower in those with type 2 diabetes mellitus. J Lipid Res 2010; 51:3516-23. [PMID: 20855567 DOI: 10.1194/jlr.m007815] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The overproduction of intestinal lipoproteins may contribute to the dyslipidemia found in diabetes. We studied the influence of diabetes on the fasting jejunal lipid content and its association with plasma lipids and the expression of genes involved in the synthesis and secretion of these lipoproteins. The study was undertaken in 27 morbidly obese persons, 12 of whom had type 2 diabetes mellitus (T2DM). The morbidly obese persons with diabetes had higher levels of chylomicron (CM) triglycerides (P < 0.001) and apolipoprotein (apo)B48 (P = 0.012). The jejunum samples obtained from the subjects with diabetes had a lower jejunal triglyceride content (P = 0.012) and angiopoietin-like protein 4 (ANGPTL4) mRNA expression (P = 0.043). However, the apoA-IV mRNA expression was significantly greater (P = 0.036). The jejunal triglyceride content correlated negatively with apoA-IV mRNA expression (r = -0.587, P = 0.027). The variables that explained the jejunal triglyceride content in a multiple linear regression model were the insulin resistance state and the apoA-IV mRNA expression. Our results show that the morbidly obese subjects with diabetes had lower jejunal lipid content and that this correlated negatively with apoA-IV mRNA expression. These findings show that the jejunum appears to play an active role in lipid homeostasis in the fasting state.
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Affiliation(s)
- F Soriguer
- Servicios de Endocrinología y Nutrición y Cirugía General, Málaga, Spain
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