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Zhou J, Lu Y, Lin Y, Li C, Liu J, Jiang Z, Chen K. Overexpression of hepatic pescadillo 1 in obesity induces lipid dysregulation by inhibiting autophagy. Transl Res 2023:S1931-5244(23)00021-X. [PMID: 36775058 DOI: 10.1016/j.trsl.2023.02.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Revised: 02/01/2023] [Accepted: 02/03/2023] [Indexed: 02/12/2023]
Abstract
Previous studies indicated that increased hepatic pescadillo 1 (PES1) in type II diabetic mice was associated with lipid dysregulation. However, the role of PES1 in obesity-associated lipid dysregulation is still unknown. This study investigates the effects and underlying mechanism. Livers from obese and healthy humans and mice were collected, and C57BL/6J mice were either fed on standard diet or high fat diet (HFD). McArdle 7777 rat hepatoma cells were treated with phosphate-buffered saline and oleic acid (OA)+ palmitic acid (PA), respectively. In vitro Pes1 knockdown or overexpression and in vivo Pes1 knockdown or liver-specific ablation or supplementation of Pes1 were used to explore the modulating role of PES1. We found that obesity in humans enhanced hepatic PES1 protein, accompanied by increased plasma TG. These data are consistent with those from OA+PA-treated cells and from HFD- or Pes1 overexpression-treated C57BL/6J mice. In vitro and in vivo Pes1 knockdown in cultured cells and in ob/ob mice promoted the expression of autophagy markers (TFEB, Beclin1 and LC3B-Ⅱ) while decreasing p62 and TG, contrary to Pes1 overexpression in cells and in normal mice. Moreover, liver-specific knockout of Pes1 protected the mice fed on HFD from increased TG levels, facilitating the TFEB, Beclin1 and LC3B-Ⅱ and curbing p62. Mechanistically, OA+PA increased C/EBPβ binding to the Pes1 promoter, leading to the elevation of PES1, and subsequently enhancing PES1-facilitated ubiquitination of TFEB. Our findings reveal that overexpression of hepatic PES1 in obesity may induce TG dysregulation by inhibiting autophagy.
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Affiliation(s)
- Jielin Zhou
- Department of Nutrition and Food Hygiene, School of Public Health, Anhui Medical University, Hefei, Anhui 230032, P.R. China; Department of Oncology, Anhui Provincial Cancer Hospital, The First Affiliated Hospital of the University of Science and Technology of China, Hefei, Anhui 230031, P.R. China
| | - Yao Lu
- Department of Anesthesiology, the First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230022, P.R. China
| | - Yan Lin
- Department of Health Inspection and Quarantine, School of Public Health, Anhui Medical University, Hefei, Anhui 230032, P.R. China
| | - Chengcheng Li
- Department of Nutrition and Food Hygiene, School of Public Health, Anhui Medical University, Hefei, Anhui 230032, P.R. China
| | - Juan Liu
- Department of Health Inspection and Quarantine, School of Public Health, Anhui Medical University, Hefei, Anhui 230032, P.R. China
| | - Zhengxuan Jiang
- Department of Ophthalmology, the Second Affiliated Hospital, Anhui Medical University, Hefei, Anhui 230032, P.R. China.
| | - Keyang Chen
- Department of Nutrition and Food Hygiene, School of Public Health, Anhui Medical University, Hefei, Anhui 230032, P.R. China; Department of Health Inspection and Quarantine, School of Public Health, Anhui Medical University, Hefei, Anhui 230032, P.R. China.
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Sparks JD, Magra AL, Chamberlain JM, O'Dell C, Sparks CE. Insulin dependent apolipoprotein B degradation and phosphatidylinositide 3-kinase activation with microsomal translocation are restored in McArdle RH7777 cells following serum deprivation. Biochem Biophys Res Commun 2015; 469:326-31. [PMID: 26616056 DOI: 10.1016/j.bbrc.2015.11.068] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Accepted: 11/16/2015] [Indexed: 11/18/2022]
Abstract
Previous studies in rat hepatocytes demonstrated that insulin-dependent apolipoprotein (apo) B degradation (IDAD) is lost when cells are maintained for 3 d under enriched culture conditions. Loss of IDAD correlates with increased expression of protein tyrosine phosphatase 1B (PTP1B) known to be associated with resistance to insulin signaling in the liver. McArdle RH7777 hepatoma (McA) cells cultured in serum containing medium are resistant to IDAD; demonstrate a 30% increase in apo B secretion, and express increased levels of PTP1B protein and mRNA. In addition, insulin-stimulated Class I phosphatidylinositide 3-kinase (PI3K) activity of anti-pY immunoprecipitates is severely blunted. IDAD resistance in McA cells correlates with diminished translocation of insulin-stimulated pY-IRS1 to intracellular membranes. Incubation of McA cells with RK682, a protein tyrosine phosphatase inhibitor, is sufficient to restore IDAD in resistant McA cells. Overall, results further support the importance of Class I PI3K activity in IDAD, and suggest that loss of this activity is sufficient to cause resistance. Although other factors are involved in downstream events including sortilin binding to apo B, autophagy, and lysosomal degradation, loss of signal generation and reduced localization of Class I PI3K to intracellular membranes plays a significant role in IDAD resistance.
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Affiliation(s)
- Janet D Sparks
- Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine and Dentistry, Box 626, 601 Elmwood Avenue, Rochester, NY 14642, USA.
| | - Amy L Magra
- Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine and Dentistry, Box 626, 601 Elmwood Avenue, Rochester, NY 14642, USA
| | - Jeffrey M Chamberlain
- Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine and Dentistry, Box 626, 601 Elmwood Avenue, Rochester, NY 14642, USA
| | - Colleen O'Dell
- Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine and Dentistry, Box 626, 601 Elmwood Avenue, Rochester, NY 14642, USA
| | - Charles E Sparks
- Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine and Dentistry, Box 626, 601 Elmwood Avenue, Rochester, NY 14642, USA
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Chamberlain JM, O'Dell C, Sparks CE, Sparks JD. Insulin suppression of apolipoprotein B in McArdle RH7777 cells involves increased sortilin 1 interaction and lysosomal targeting. Biochem Biophys Res Commun 2012; 430:66-71. [PMID: 23159624 DOI: 10.1016/j.bbrc.2012.11.022] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2012] [Accepted: 11/06/2012] [Indexed: 12/16/2022]
Abstract
Insulin suppresses secretion of very low density lipoprotein (VLDL) apolipoprotein (apo) B in primary rodent hepatocytes (RH) by favoring the degradation of B100, the larger form of apo B, through post-endoplasmic reticulum proteolysis. Sortilin 1 (sort1), a multi-ligand sorting receptor, has been proposed as a mediator of lysosomal B100 degradation by directing B100 in pre-VLDL to lysosomes rather than allowing maturation to VLDL and secretion. The purpose of our studies was to investigate the role of sort1 in insulin-dependent degradation of apo B. Using liver derived McArdle RH7777 (McA) cells, we demonstrate that insulin suppresses VLDL B100 secretion via a phosphatidylinositide 3-kinase (PI3K) dependent process that is inhibitable by wortmannin in a fashion similar to RH. Using McA cells and in situ cross-linking, we demonstrate that insulin acutely (30min) stimulates the interaction of B100 with sort1. The insulin-induced interaction of sort1-B100 is markedly enhanced when lysosomal degradation is inhibited by Bafilomycin A1 (BafA1), an inhibitor of lysosomal acidification. As BafA1 also prevents insulin suppressive effects on apo B secretion, our results suggest that sort1-B100 interaction stimulated by insulin transiently accumulates with BafA1 and favors B100 secretion by default.
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Affiliation(s)
- Jeffrey M Chamberlain
- Department of Pathology & Laboratory Medicine, University of Rochester School of Medicine & Dentistry, Box 626, 601 Elmwood Avenue, Rochester, NY 14642, USA
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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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Liu Y, Manchekar M, Sun Z, Richardson PE, Dashti N. Apolipoprotein B-containing lipoprotein assembly in microsomal triglyceride transfer protein-deficient McA-RH7777 cells. J Lipid Res 2010; 51:2253-64. [PMID: 20181985 DOI: 10.1194/jlr.m005371] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Microsomal triglyceride transfer protein (MTP) is required for the assembly and secretion of apolipoprotein (apo) B-containing lipoproteins. Previously, we demonstrated that the N-terminal 1,000 residues of apoB (apoB:1000) are necessary for the initiation of apoB-containing lipoprotein assembly in rat hepatoma McA-RH7777 cells and that these particles are phospholipid (PL) rich. To determine if the PL transfer activity of MTP is sufficient for the assembly and secretion of primordial apoB:1000-containing lipoproteins, we employed microRNA-based short hairpin RNAs (miR-shRNAs) to silence Mttp gene expression in parental and apoB:1000-expressing McA-RH7777 cells. This approach led to 98% reduction in MTP protein levels in both cell types. Metabolic labeling studies demonstrated a drastic 90-95% decrease in the secretion of rat endogenous apoB100-containing lipoproteins in MTP-deficient McA-RH7777 cells compared with cells transfected with negative control miR-shRNA. A similar reduction was observed in the secretion of rat endogenous apoB48 under the experimental conditions employed. In contrast, MTP absence had no significant effect on the synthesis, lipidation, and secretion of human apoB:1000-containing particles. These results provide strong evidence in support of the concept that in McA-RH7777 cells, acquisition of PL by apoB:1000 and initiation of apoB-containing lipoprotein assembly, a process distinct from the conventional first-step assembly of HDL-sized apoB-containing particles, do not require MTP. This study indicates that, in hepatocytes, a factor(s) other than MTP mediates the formation of the PL-rich primordial apoB:1000-containing initiation complex.
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Affiliation(s)
- Yanwen Liu
- Department of Medicine, Basic Sciences Section, Atherosclerosis Research Unit, University of Alabama at Birmingham Medical Center, Birmingham, AL 35294, USA
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6
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Abstract
PURPOSE OF REVIEW: This review summarizes recent research implicating Forkhead box (Fox)O1, a key transcription factor in glucose metabolism, in the regulation of hepatic lipid metabolism. Insulin dysregulation leading to hypertriglyceridemia is associated with increased hepatic VLDL secretion. FoxO1 is integrated in action with other regulatory factors in VLDL metabolism. The role of FoxO1 is defined in context of recent controversies. RECENT FINDINGS: FoxO1 regulates transcription of microsomal triglyceride transfer protein and apolipoprotein (apo)CIII involved in hepatic assembly and postsecretory catabolism of VLDL. Insulin activation of Akt leads to the phosphorylation of FoxO1 with nuclear exclusion and loss of transcriptional activity. Reduced insulin action increases FoxO1 activity and induces microsomal triglyceride transfer protein favoring VLDL assembly and induces apoCIII reducing peripheral triglyceride catabolism. This new mechanistic link between insulin resistance and VLDL overproduction and hypertriglyceridemia compounds effects of other known VLDL regulatory factors. SUMMARY: This review highlights recent advances in research of insulin regulation of hepatic VLDL metabolism. Formation of VLDL requires lipid, apoB structural protein, and microsomal triglyceride transfer protein. FoxO1 is a major factor in hepatic microsomal triglyceride ransfer protein regulation. A unifying hypothesis is presented linking regulation of the three necessary hepatic components for VLDL assembly with insulin action and insulin resistance.
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Affiliation(s)
- Janet D. Sparks
- Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine & Dentistry, Rochester, New York
| | - Henry H. Dong
- Rangos Research Center, Children's Hospital of Pittsburgh, Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
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7
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Anderson N, Borlak J. Molecular Mechanisms and Therapeutic Targets in Steatosis and Steatohepatitis. Pharmacol Rev 2008; 60:311-57. [DOI: 10.1124/pr.108.00001] [Citation(s) in RCA: 291] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
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Duez H, Pavlic M, Lewis GF. Mechanism of intestinal lipoprotein overproduction in insulin resistant humans. ATHEROSCLEROSIS SUPP 2008; 9:33-8. [DOI: 10.1016/j.atherosclerosissup.2008.05.013] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2008] [Revised: 02/25/2008] [Accepted: 05/13/2008] [Indexed: 10/21/2022]
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Duez H, Lamarche B, Valéro R, Pavlic M, Proctor S, Xiao C, Szeto L, Patterson BW, Lewis GF. Both intestinal and hepatic lipoprotein production are stimulated by an acute elevation of plasma free fatty acids in humans. Circulation 2008. [PMID: 18443237 DOI: 10.1161/circulationaha.107] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
BACKGROUND Hepatic lipoprotein production has been shown previously to be regulated by free fatty acid (FFA) flux to the liver, whereas intestinal lipoprotein production is stimulated mainly by ingested fat absorbed from the intestinal lumen. Emerging evidence indicates that intestinal lipoprotein production is increased in insulin resistance and type 2 diabetes mellitus, conditions that are associated with increased levels of circulating FFAs. Here we investigated whether short-term elevation of plasma FFAs stimulates intestinal apolipoprotein (apo) B-48- and hepatic apoB-100-containing triglyceride-rich lipoprotein (TRL) production in humans in the fed state. METHODS AND RESULTS TRL apoB-48 and apoB-100 metabolism were examined in 12 healthy men during a constant fed state. The studies were as follows, respectively: (1) Intralipid/heparin was infused intravenously immediately before and during the kinetics study to induce an approximately 3-fold difference in plasma FFA compared with the saline study; (2) saline was infused intravenously as a control. ApoB-48- and apoB-100-containing TRL production and clearance were determined with a 12-hour primed constant infusion of [D3]L-leucine and multicompartmental kinetic modeling. TRL apoB-48 production rate was 69% higher in the Intralipid/heparin study than in the saline control (5.95+/-1.13 versus 3.53+/-0.58 mg/kg per day; P=0.027), and there was no significant difference in TRL apoB-48 clearance. TRL apoB-100 concentrations were also increased (P<0.001) and TRL apoB-100 production rate was 35% higher in the Intralipid/heparin study compared with saline (28+/-4 versus 21+/-3 mg/kg per day; P=0.020). CONCLUSIONS This is the first study to demonstrate that intestinal TRL apoB-48 production is increased after short-term elevation of plasma FFAs in humans in the fed state, similar to the well-described stimulation of hepatic TRL apoB100-containing particles by FFAs.
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Affiliation(s)
- Hélène Duez
- Department of Medicine, Division of Endocrinology and Metabolism, University of Toronto, Toronto, Canada
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10
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Duez H, Lamarche B, Valéro R, Pavlic M, Proctor S, Xiao C, Szeto L, Patterson BW, Lewis GF. Both intestinal and hepatic lipoprotein production are stimulated by an acute elevation of plasma free fatty acids in humans. Circulation 2008; 117:2369-76. [PMID: 18443237 DOI: 10.1161/circulationaha.107.739888] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
BACKGROUND Hepatic lipoprotein production has been shown previously to be regulated by free fatty acid (FFA) flux to the liver, whereas intestinal lipoprotein production is stimulated mainly by ingested fat absorbed from the intestinal lumen. Emerging evidence indicates that intestinal lipoprotein production is increased in insulin resistance and type 2 diabetes mellitus, conditions that are associated with increased levels of circulating FFAs. Here we investigated whether short-term elevation of plasma FFAs stimulates intestinal apolipoprotein (apo) B-48- and hepatic apoB-100-containing triglyceride-rich lipoprotein (TRL) production in humans in the fed state. METHODS AND RESULTS TRL apoB-48 and apoB-100 metabolism were examined in 12 healthy men during a constant fed state. The studies were as follows, respectively: (1) Intralipid/heparin was infused intravenously immediately before and during the kinetics study to induce an approximately 3-fold difference in plasma FFA compared with the saline study; (2) saline was infused intravenously as a control. ApoB-48- and apoB-100-containing TRL production and clearance were determined with a 12-hour primed constant infusion of [D3]L-leucine and multicompartmental kinetic modeling. TRL apoB-48 production rate was 69% higher in the Intralipid/heparin study than in the saline control (5.95+/-1.13 versus 3.53+/-0.58 mg/kg per day; P=0.027), and there was no significant difference in TRL apoB-48 clearance. TRL apoB-100 concentrations were also increased (P<0.001) and TRL apoB-100 production rate was 35% higher in the Intralipid/heparin study compared with saline (28+/-4 versus 21+/-3 mg/kg per day; P=0.020). CONCLUSIONS This is the first study to demonstrate that intestinal TRL apoB-48 production is increased after short-term elevation of plasma FFAs in humans in the fed state, similar to the well-described stimulation of hepatic TRL apoB100-containing particles by FFAs.
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Affiliation(s)
- Hélène Duez
- Department of Medicine, Division of Endocrinology and Metabolism, University of Toronto, Toronto, Canada
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11
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Ota T, Gayet C, Ginsberg HN. Inhibition of apolipoprotein B100 secretion by lipid-induced hepatic endoplasmic reticulum stress in rodents. J Clin Invest 2008; 118:316-32. [PMID: 18060040 PMCID: PMC2104481 DOI: 10.1172/jci32752] [Citation(s) in RCA: 288] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2007] [Accepted: 10/03/2007] [Indexed: 12/30/2022] Open
Abstract
ER stress can cause hepatic insulin resistance and steatosis. Increased VLDL secretion could protect the liver from ER stress-induced steatosis, but the effect of lipid-induced ER stress on the secretion of VLDL is unknown. To determine the effect of lipids on hepatic ER stress and VLDL secretion, we treated McA-RH7777 liver cells with free fatty acids. Prolonged exposure increased cell triglycerides, induced steatosis, and increased ER stress. Effects on apoB100 secretion, which is required for VLDL assembly, were parabolic, with moderate free fatty acid exposure increasing apoB100 secretion, while greater lipid loading inhibited apoB100 secretion. This decreased secretion at higher lipid levels was due to increased protein degradation through both proteasomal and nonproteasomal pathways and was dependent on the induction of ER stress. These findings were supported in vivo, where intravenous infusion of oleic acid (OA) in mice increased ER stress in a duration-dependent manner. apoB secretion was again parabolic, stimulated by moderate, but not prolonged, OA infusion. Inhibition of ER stress was able to restore OA-stimulated apoB secretion after prolonged OA infusion. These results suggest that excessive ER stress in response to increased hepatic lipids may decrease the ability of the liver to secrete triglycerides by limiting apoB secretion, potentially worsening steatosis.
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Affiliation(s)
- Tsuguhito Ota
- Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA
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12
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Avramoglu RK, Basciano H, Adeli K. Lipid and lipoprotein dysregulation in insulin resistant states. Clin Chim Acta 2006; 368:1-19. [PMID: 16480697 DOI: 10.1016/j.cca.2005.12.026] [Citation(s) in RCA: 188] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2005] [Revised: 12/15/2005] [Accepted: 12/20/2005] [Indexed: 12/30/2022]
Abstract
Insulin resistant states are commonly associated with an atherogenic dyslipidemia that contributes to significantly higher risk of atherosclerosis and cardiovascular disease. Indeed, disorders of carbohydrate and lipid metabolism co-exist in the majority of subjects with the "metabolic syndrome" and form the basis for the definition and diagnosis of this complex syndrome. The most fundamental defect in these patients is resistance to cellular actions of insulin, particularly resistance to insulin-stimulated glucose uptake. Insulin insensitivity appears to cause hyperinsulinemia, enhanced hepatic gluconeogenesis and glucose output, reduced suppression of lipolysis in adipose tissue leading to a high free fatty acid flux, and increased hepatic very low density lipoprotein (VLDL) secretion causing hypertriglyceridemia and reduced plasma levels of high density lipoprotein (HDL) cholesterol. Although the link between insulin resistance and dysregulation of lipoprotein metabolism is well established, a significant gap of knowledge exists regarding the underlying cellular and molecular mechanisms. Emerging evidence suggests that insulin resistance and its associated metabolic dyslipidemia result from perturbations in key molecules of the insulin signaling pathway, including overexpression of key phosphatases, downregulation and/or activation of key protein kinase cascades, leading to a state of mixed hepatic insulin resistance and sensitivity. These signaling changes in turn cause an increased expression of sterol regulatory element binding protein (SREBP) 1c, induction of de novo lipogensis and higher activity of microsomal triglyceride transfer protein (MTP), which together with high exogenous free fatty acid (FFA) flux collectively stimulate the hepatic production of apolipoprotein B (apoB)-containing VLDL particles. VLDL overproduction underlies the high triglyceride/low HDL-cholesterol lipid profile commonly observed in insulin resistant subjects.
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Affiliation(s)
- Rita Kohen Avramoglu
- Clinical Biochemistry Division, Department of Paediatric Laboratory Medicine, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada M5G 1X8
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13
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Zhang YL, Hernandez-Ono A, Ko C, Yasunaga K, Huang LS, Ginsberg HN. Regulation of Hepatic Apolipoprotein B-lipoprotein Assembly and Secretion by the Availability of Fatty Acids. J Biol Chem 2004; 279:19362-74. [PMID: 14970200 DOI: 10.1074/jbc.m400220200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The in vivo effects of increased delivery of fatty acids (FA) to the liver are poorly defined. Therefore, we compared the effects of infusing either 6 mM oleic acid (OA) bound to albumin, 0.5-20% Intralipid, or saline for 3 or 6 h into male C57BL/6J mice. Infusions were followed by studies of triglyceride (TG) and apoB secretion. Although plasma FA levels increased similarly after either 20% Intralipid or 6 mM OA, TG secretion increased only after infusion of 4-20% Intralipid; TG secretion was unchanged by 6 mM OA. By contrast, 6-h infusions of either 6 mM OA or 4-20% Intralipid increased apoB secretion. 6 mM OA and 20% Intralipid each increased secretion of apoB from primary hepatocytes ex vivo. Importantly, 0.5-2% Intralipid, which delivered more FA to the liver than 6 mM OA, did not stimulate apoB secretion. Hepatic apoB mRNA levels were unaffected by either 6 mM OA or 20% Intralipid, but microsomal triglyceride transfer protein mRNA was significantly lower after 6-h infusions with 6 mM OA versus either saline or 20% Intralipid. Lower microsomal triglyceride transfer protein mRNA levels were associated with reduced hepatic TG mass after 6-h infusions of 6 mM OA. We conclude that 1) increased FA delivery to the liver in vivo increases secretion of apoB-lipoproteins via post-transcriptional mechanisms, 2) OA-induced apoB-lipoprotein secretion occurred at least in part via mechanisms other than by providing substrate for TG synthesis, and 3) the route of delivery of FA is important for its effects on apoB secretion.
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Affiliation(s)
- Yuan-Li Zhang
- Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA
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Kummrow E, Hussain MM, Pan M, Marsh JB, Fisher EA. Myristic acid increases dense lipoprotein secretion by inhibiting apoB degradation and triglyceride recruitment. J Lipid Res 2002; 43:2155-63. [PMID: 12454278 DOI: 10.1194/jlr.m200249-jlr200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Fatty acids of varying lengths and saturation differentially affect plasma apolipoprotein B-100 (apoB-100) levels. To identify mechanisms at the level of production, rat hepatoma cells, McA-RH7777, were incubated with [(35)S]methionine and either fatty acid-BSA complexes or BSA alone. There were increases in labeled apoB-100 secretion with saturated fatty acids palmitic and myristic (MA) (153 +/- 20% and 165 +/- 11%, respectively, relative to BSA). Incubation with polyunsaturated docosahexaenoic acid (DHA) decreased secretion to 26 +/- 2.0%, while monounsaturated oleic acid (OA) did not change it. In pulse-chase studies, MA treatment resulted in reduced apoB-100 degradation, in agreement with its promotion of secretion. In triglyceride (TG) studies, synthesis was stimulated equally by OA, MA, and DHA, but TG secretion was relatively decreased with MA and DHA. With OA, the majority of newly secreted apoB100-lipoproteins was d < or = 1.006, but with MA, they were much denser (1.063 < d). Furthermore, the relative recruitment of newly synthesized TG to lipoproteins was impaired with MA. We conclude that mechanisms for effects of specific dietary fatty acids on plasma lipoprotein levels may include changes in hepatic production. In turn, hepatic production may be regulated by specific fatty acids at the steps of apoB-100 degradation and the recruitment of nascent TG to lipoprotein particles.
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Affiliation(s)
- Emma Kummrow
- Department of Biochemistry, Medical College of Pennsylvania-Hahnemann School of Medicine, Philadelphia, PA 19129, USA
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15
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Lewis GF, Carpentier A, Adeli K, Giacca A. Disordered fat storage and mobilization in the pathogenesis of insulin resistance and type 2 diabetes. Endocr Rev 2002; 23:201-29. [PMID: 11943743 DOI: 10.1210/edrv.23.2.0461] [Citation(s) in RCA: 744] [Impact Index Per Article: 33.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The primary genetic, environmental, and metabolic factors responsible for causing insulin resistance and pancreatic beta-cell failure and the precise sequence of events leading to the development of type 2 diabetes are not yet fully understood. Abnormalities of triglyceride storage and lipolysis in insulin-sensitive tissues are an early manifestation of conditions characterized by insulin resistance and are detectable before the development of postprandial or fasting hyperglycemia. Increased free fatty acid (FFA) flux from adipose tissue to nonadipose tissue, resulting from abnormalities of fat metabolism, participates in and amplifies many of the fundamental metabolic derangements that are characteristic of the insulin resistance syndrome and type 2 diabetes. It is also likely to play an important role in the progression from normal glucose tolerance to fasting hyperglycemia and conversion to frank type 2 diabetes in insulin resistant individuals. Adverse metabolic consequences of increased FFA flux, to be discussed in this review, are extremely wide ranging and include, but are not limited to: 1) dyslipidemia and hepatic steatosis, 2) impaired glucose metabolism and insulin sensitivity in muscle and liver, 3) diminished insulin clearance, aggravating peripheral tissue hyperinsulinemia, and 4) impaired pancreatic beta-cell function. The precise biochemical mechanisms whereby fatty acids and cytosolic triglycerides exert their effects remain poorly understood. Recent studies, however, suggest that the sequence of events may be the following: in states of positive net energy balance, triglyceride accumulation in "fat-buffering" adipose tissue is limited by the development of adipose tissue insulin resistance. This results in diversion of energy substrates to nonadipose tissue, which in turn leads to a complex array of metabolic abnormalities characteristic of insulin-resistant states and type 2 diabetes. Recent evidence suggests that some of the biochemical mechanisms whereby glucose and fat exert adverse effects in insulin-sensitive and insulin-producing tissues are shared, thus implicating a diabetogenic role for energy excess as a whole. Although there is now evidence that weight loss through reduction of caloric intake and increase in physical activity can prevent the development of diabetes, it remains an open question as to whether specific modulation of fat metabolism will result in improvement in some or all of the above metabolic derangements or will prevent progression from insulin resistance syndrome to type 2 diabetes.
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Affiliation(s)
- Gary F Lewis
- Department of Medicine, Division of Endocrinology, University of Toronto, Canada M5G 2C4.
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Adeli K, Taghibiglou C, Van Iderstine SC, Lewis GF. Mechanisms of hepatic very low-density lipoprotein overproduction in insulin resistance. Trends Cardiovasc Med 2001; 11:170-6. [PMID: 11597827 DOI: 10.1016/s1050-1738(01)00084-6] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
An important complication of insulin-resistant states, such as obesity and type 2 diabetes, is an atherogenic dyslipidemia profile characterized by hypertriglyceridemia, low plasma high-density lipoproteins (HDL) cholesterol and a small, dense low-density lipoprotein (LDL) particle profile. The physiological basis of this metabolic dyslipidemia appears to be hepatic overproduction of apoB-containing very low-density lipoprotein (VLDL) particles. This has focused attention on the mechanisms that regulate VLDL secretion in insulin-resistant states. Recent studies in animal models of insulin resistance, particularly the fructose-fed hamster, have enhanced our understanding of these mechanisms, and certain key factors have recently been identified that play important roles in hepatic insulin resistance and dysregulation of the VLDL secretory process. This review focuses on these recent developments as well as on the hypothesis that an interaction between enhanced flux of free fatty acids from peripheral tissues to liver, chronic up-regulation of de novo lipogenesis by hyperinsulinemia and attenuated insulin signaling in the liver may be critical to the VLDL overproduction state observed in insulin resistance. It should be noted that the focus of this review is on molecular mechanisms of the hypertriglyceridemic state associated with insulin resistance and not that observed in association with insulin deficiency (e.g., in streptozotocin-treated animals), which appears to have a different etiology and is related to a catabolic defect rather than secretory overproduction of triglyceride-rich lipoproteins.
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Affiliation(s)
- K Adeli
- Division of Clinical Biochemistry, Department of Laboratory Medicine & Pathobiology, Hospital for Sick Children, University of Toeonto, Toronto, Ontario, Canada.
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Li Z, Kako Y, Pang L, Freeman MW, Glick JM, Wang X, Goldberg IJ. Effects of overexpression of the amino-terminal fragment of apolipoprotein B on apolipoprotein B and lipoprotein production. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)32352-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Collins HL, Sparks CE, Sparks JD. B48 is preferentially translated over B100 in cells with increased endogenous apo B mRNA. Biochem Biophys Res Commun 2000; 273:1156-60. [PMID: 10891388 DOI: 10.1006/bbrc.2000.3074] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We recently demonstrated that expression of BHMT in McArdle RH-7777 (McA-BHMT) cells increases apo B mRNA abundance, leading to parallel increases in apo B secretion. The ratio of unedited to edited apo B mRNA was unchanged by BHMT expression. Based on the observation that secretion of B48 is increased relative to B100 in McA-BHMT cells, current studies now include comparison of B48 and B100 synthesis and intracellular degradation. Minor differences in co- and posttranslational degradation were unable to account for relative increase in B48 secretion, and the disappearance kinetics of B48 were similar in McA-BHMT and control cells. Consistent with the increase in endogenous apo B mRNA in McA-BHMT cells, B48 synthesis is increased significantly. In contrast, synthesis of B100 was not significantly increased. We conclude that B48 is preferentially translated compared to B100 when endogenous apo B mRNA is increased.
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Affiliation(s)
- H L Collins
- Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA
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Intracellular mechanisms regulating apoB-containing lipoprotein assembly and secretion in primary hamster hepatocytes. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)32397-x] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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20
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Abstract
Synthesis and secretion of chylomicrons by the intestine is essential to transport dietary fats in the circulation and to deliver these fats to the appropriate peripheral tissues. The assembly of chylomicrons within the enterocyte and the subsequent secretion of these lipoprotein particles into the lymph is a complex, multi-step process that includes absorption of lipids by the enterocytes, cellular lipid (re)synthesis and translocation of cellular lipid pools, synthesis and post-translational modification of various apolipoproteins and, finally, the assembly of lipid and lipoprotein components into a chylomicron. The key process in chylomicron synthesis is the intracellular association of apolipoprotein (apo)B48, the structural protein of chylomicrons, with lipids.
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Affiliation(s)
- M M van Greevenbroek
- Laboratory for Molecular Metabolism and Endocrinology, Maastricht University, The Netherlands
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Zhou Z, Luchoomun J, Bakillah A, Hussain MM. Lysophosphatidylcholine increases apolipoprotein B secretion by enhancing lipid synthesis and decreasing its intracellular degradation in HepG2 cells. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1391:13-24. [PMID: 9518534 DOI: 10.1016/s0005-2760(97)00200-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Free fatty acids and lysophosphatidylcholine (lysoPC) are the major lipids bound to human plasma albumin. The effects of fatty acids on the hepatic production of Apolipoprotein B (apo B) have been studied but those of lysoPC have not. In HepG2 cells, lysoPC increased apo B secretion in different experiments by 50-120%, but did not affect the flotation properties of secreted lipoproteins. LysoPC affected neither the cellular protein levels nor apo A-I secretion suggesting that its effect was specific to apo B. Apo B secretion was maximum after incubating cells for 6 h with 0.2 mM lysoPC as equimolar fatty acid free bovine serum albumin (BSA) complexes. LysoPC was metabolized by cells and its fatty acids were used for the synthesis of phosphatidylcholine and triglycerides (TG). Experiments were performed to understand the mechanism of lysoPC action. LysoPC increased the incorporation of 3H-glycerol into newly synthesized cellular (3-fold) and secreted (4-fold) triglycerides, and increased the synthesis (40%) and secretion (4-fold) of phospholipids. LysoPC did not affect apo B synthesis, but inhibited the intracellular degradation of apo B and increased its secretion. Triacsin C (5 microM), an inhibitor of long chain acyl-CoA synthase, completely inhibited the induction of lipid synthesis and abolished the effect of lysoPC on apo B secretion. These studies indicated that lysoPC increased apo B secretion by inducing lipid synthesis; newly synthesized lipids probably protected apo B from intracellular degradation and enhanced secretion. These studies are consistent with the hypothesis that physiologic concentrations of lysoPC can be an important modulator for hepatic apo B secretion.
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Affiliation(s)
- Z Zhou
- Department of Pathology, The Allegheny University of the Health Sciences, MCP Hahnemann School of Medicine, 2900 Queen Lane, Philadelphia, PA 19129, USA
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