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Cyr Y, Wassef H, Bissonnette S, Lamantia V, Davignon J, Faraj M. WAT apoC-I secretion: role in delayed chylomicron clearance in vivo and ex vivo in WAT in obese subjects. J Lipid Res 2016; 57:1074-85. [PMID: 27040450 DOI: 10.1194/jlr.p064170] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Indexed: 01/14/2023] Open
Abstract
Reduced white adipose tissue (WAT) LPL activity delays plasma clearance of TG-rich lipoproteins (TRLs). We reported the secretion of apoC-I, an LPL inhibitor, from WAT ex vivo in women. Therefore we hypothesized that WAT-secreted apoC-I associates with reduced WAT LPL activity and TRL clearance. WAT apoC-I secretion averaged 86.9 ± 31.4 pmol/g/4 h and 74.1 ± 36.6 pmol/g/4 h in 28 women and 11 men with BMI ≥27 kg/m(2), respectively, with no sex differences. Following the ingestion of a (13)C-triolein-labeled high-fat meal, subjects with high WAT apoC-I secretion (above median) had delayed postprandial plasma clearance of dietary TRLs, assessed from plasma (13)C-triolein-labeled TGs and apoB48. They also had reduced hydrolysis and storage of synthetic (3)H-triolein-labeled ((3)H)-TRLs in WAT ex vivo (i.e., in situ LPL activity). Adjusting for WAT in situ LPL activity eliminated group differences in chylomicron clearance; while adjusting for plasma apoC-I, (3)H-NEFA uptake by WAT, or body composition did not. apoC-I inhibited in situ LPL activity in adipocytes in both a concentration- and time-dependent manner. There was no change in postprandial WAT apoC-I secretion. WAT apoC-I secretion may inhibit WAT LPL activity and promote delayed chylomicron clearance in overweight and obese subjects. We propose that reducing WAT apoC-I secretion ameliorates postprandial TRL clearance in humans.
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Affiliation(s)
- Yannick Cyr
- Institut de Recherches Cliniques de Montréal (IRCM), Montréal, Québec, Canada Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada Montreal Diabetes Research Center (MDRC), Montréal, Québec, Canada
| | - Hanny Wassef
- Institut de Recherches Cliniques de Montréal (IRCM), Montréal, Québec, Canada Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada Montreal Diabetes Research Center (MDRC), Montréal, Québec, Canada
| | - Simon Bissonnette
- Institut de Recherches Cliniques de Montréal (IRCM), Montréal, Québec, Canada Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada Montreal Diabetes Research Center (MDRC), Montréal, Québec, Canada
| | - Valerie Lamantia
- Institut de Recherches Cliniques de Montréal (IRCM), Montréal, Québec, Canada Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada Montreal Diabetes Research Center (MDRC), Montréal, Québec, Canada
| | - Jean Davignon
- Institut de Recherches Cliniques de Montréal (IRCM), Montréal, Québec, Canada Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada Faculty of Medicine, McGill University, Montréal, Québec, Canada
| | - May Faraj
- Institut de Recherches Cliniques de Montréal (IRCM), Montréal, Québec, Canada Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada Montreal Diabetes Research Center (MDRC), Montréal, Québec, Canada
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2
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Bissonnette S, Salem H, Wassef H, Saint-Pierre N, Tardif A, Baass A, Dufour R, Faraj M. Low density lipoprotein delays clearance of triglyceride-rich lipoprotein by human subcutaneous adipose tissue. J Lipid Res 2013; 54:1466-76. [PMID: 23417739 DOI: 10.1194/jlr.p023176] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Delayed clearance of triglyceride-rich lipoprotein (TRL) by white adipose tissue (WAT) promotes hypertriglyceridemia and elevated apoB-lipoproteins, which are primarily in the form of LDL. This study examines whether LDL promotes delayed clearance of TRL by WAT. Following the ingestion of a (13)C-triolein-labeled high-fat meal, obese women with high plasma apoB (> median 0.93 g/l, N = 11, > 98% as IDL/LDL) had delayed clearance of postprandial (13)C-triglyceride and (13)C-NEFA over 6 h compared with controls. AUC6 h of plasma (13)C-triglyceride and (13)C-NEFA correlated with plasma apoB but not with LDL diameter or adipocyte area. There was no group difference in (13)C-triolein oxidation rate, which suggests lower (13)C-NEFA storage in peripheral tissue in women with high apoB. Ex vivo/in vitro plasma apoB correlated negatively with WAT (3)H-lipid following a 4 h incubation of women's WAT with synthetic (3)H-triolein-TRL. LDL-differentiated 3T3-L1 adipocytes had lower (3)H-TRL hydrolysis and (3)H-NEFA storage. Treatment of women's WAT with their own LDL decreased (3)H-TRL hydrolysis and (3)H-NEFA uptake. Finally, LDL, although not an LPL substrate, reduced LPL-mediated (3)H-TRL hydrolysis as did VLDL and HDL. Exposure to LDL decreases TRL clearance by human WAT ex vivo. This may promote production of apoB-lipoproteins and hypertriglyceridemia through a positive-feedback mechanism in vivo.
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Affiliation(s)
- Simon Bissonnette
- Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada
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3
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Shearer GC, Kaysen GA. Endothelial bound lipoprotein lipase (LpL) depletion in hypoalbuminemia results from decreased endothelial binding, not decreased secretion. Kidney Int 2006; 70:647-53. [PMID: 16807550 DOI: 10.1038/sj.ki.5000318] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Hypertriglyceridemia in nephrotic (NS) and Nagase analbuminemic rats (Analb) results from reduced triglyceride clearance. NS and Analb have reduced or absent albumin, reduced plasma oncotic pressure (pi), but Analb lack proteinuria. The heparin releasable lipoprotein lipase (LpL) pool in both models is greatly reduced, suggesting reduced LpL is related to low albumin or pi and not proteinuria. To determine the cause of endothelial LpL reduction, we studied effectors of endothelial LpL (eLpL) levels from gene expression, to delivery and endothelial binding. eLpL was measured as heparin releasable activity. eLpL and secretion rate was measured in isolated hearts perfused with heparin. mRNA levels were measured in rat hearts by kinetic RT-PCR. Finally, binding of (125)I-LpL by competition assays rat endothelial cells measured serum-induced changes in affinity. eLpL in vivo was reduced in nephrotic and Analb rats. While the eLpL pool was reduced in isolated perfused hearts, neither LpL secretion by isolated hearts nor myocardial mRNA was reduced in NS or Analb. Binding of LpL to RAEC preincubated with serum from either NS or Analb was reduced compared to control. LpL mRNA levels and release rate was not altered in hearts from NS rats, while eLpL is depleted, suggesting that reduced eLpL in NS is not the result of reduced delivery. The finding that NS serum alters LpL binding to RAEC suggests LpL depletion results from decreased binding rather than defective delivery. This in turn is a consequence of reduced serum albumin or pi but does not require proteinuria.
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Affiliation(s)
- G C Shearer
- Department of Veterans Affairs Northern California Health Care System, Mather, California 95616, USA.
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4
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Cònsol G, Moles A, Ricart-Jané D, Llobera M. An in situ perfusion protocol of rat epididymal adipose tissue useful in metabolic studies. J Lipid Res 2005; 46:1803-8. [PMID: 15863840 DOI: 10.1194/jlr.d500016-jlr200] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Experimental approaches involving the perfusion of tissues and organs offer the advantage of improved physiological relevance over the use of isolated tissues or cells while at the same time being much more controlled and tissue-specific than studies in vivo. Nevertheless, there have been few metabolic studies performed in perfused white adipose tissue, largely because of the difficulty of the surgical technique involved. Although some methods have been described, they are difficult to use as perfusion protocols and their reproducibility is poor. We have modified a rat perfusion method, based on a modification of the Ho and Meng technique, for use with epididymal white adipose tissue (eWAT), and we present it here as a protocol to be reproduced. We also offer surgical solutions for the most common variants of vessel distributions in rats. Using the protocol described here, the perfused adipose tissue is viable and metabolically active, as indicated by the maintenance of tissue ATP levels and adiponectin secretion and by endogenous lipolysis regulation. Moreover, there is a high level of lipoprotein lipase activity in the endothelium of the tissue, which is heparin-releasable. Thus, this method is a useful and reproducible tool that allows the perfusion of eWAT for use in metabolic studies.
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Affiliation(s)
- Gemma Cònsol
- Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, E-08071 Barcelona, Spain
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5
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Ballart X, Siches M, Peinado-Onsurbe J, López-Tejero D, Llobera M, Ramírez I, Robert MQ. Isoproterenol increases active lipoprotein lipase in adipocyte medium and in rat plasma. Biochimie 2004; 85:971-82. [PMID: 14644552 DOI: 10.1016/j.biochi.2003.09.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
White adipose tissue (WAT) lipoprotein lipase (LPL) activity channels diet fat towards storage in adipocytes. Adrenaline (ADR) is accepted to reduce WAT or adipocyte LPL activity (LPLa), but available data are not clear-cut regarding long exposure to ADR in vitro or in vivo. We studied the effects of long exposures to ADR or beta-adrenergic agonist on LPL: in isolated rat adipocytes (3 h) and in rats (>1 day). Isoproterenol (ISO) (1 microM) did not alter LPLmRNA nor LPLa in adipocytes, but increased LPLa in medium more than twofold (3.58 +/- 0.35 vs. 1.32 +/- 0.35 mU/10(6) adipocytes, P < 0.001). Effect was time (not present at 1 h, clear at 2 h) and concentration dependent (high sensitivity from 10 to 100 nM, max at 1 microM). Adenylate cyclase activator or cyclic AMP (cAMP) analogue produced a similar increase. Thus in adipocytes ISO produced an increase in LPLa release and/or a decrease in extracellular LPLa degradation. ADR or ISO treated rats had a two to fourfold decrease in WAT LPLa vs. unchanged LPLmRNA. This decrease was 10-fold in WAT heparin-releasable LPLa (5.7 +/- 0.6 vs. 57.3 +/- 10.2 mU/g, P < 0.001), which represents peri/extracellular LPLa. Plasma LPLa was increased 11-fold by ADR (3.30 +/- 0.58 vs. 0.32 +/- 0.08 mU/ml, P < 0.001) whereas only threefold by ISO (P > 0.01). We suggest that in vivo ADR increased release of active LPL to plasma from endothelial cells of LPL-rich tissue(s)-WAT was probably one of these tissues releasing LPL since it lost 90% of its peri/extracellular LPLa-and/or decreased degradation of plasma active LPL. Since liver LPLa was not increased, plasma active LPL might be kept away from hepatic degradation by binding to stabilising entities in plasma (fatty acids (FA), lipoproteins or soluble heparan sulphates (HS)). In conclusion, we believe this is the first report stating that: (a) ISO increases LPLa in isolated adipocyte medium, and (b) ADR administration to rats decreases WAT extracellular active LPL and increases preheparin plasma active LPL.
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Affiliation(s)
- Xavier Ballart
- Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain
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6
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Ng DS, Xie C, Maguire GF, Zhu X, Ugwu F, Lam E, Connelly PW. Hypertriglyceridemia in Lecithin-cholesterol Acyltransferase-deficient Mice Is Associated with Hepatic Overproduction of Triglycerides, Increased Lipogenesis, and Improved Glucose Tolerance. J Biol Chem 2004; 279:7636-42. [PMID: 14668345 DOI: 10.1074/jbc.m309439200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lecithin-cholesterol acyltransferase deficiency is frequently associated with hypertriglyceridemia (HTG) in animal models and humans. We investigated the mechanism of HTG in the ldlr-/- x lcat-/- (double knockout (dko)) mice using the ldlr-/- x lcat+/+ (knock-out (ko)) littermates as control. Mean fasting triglyceride (TG) levels in the dko mice were elevated 1.75-fold compared with their controls (p < 0.002). Both the very low density lipoprotein and the low density lipoprotein/intermediate density lipoprotein fractions separated by fast protein liquid chromatography were TG-enriched in the dko mice. In vitro lipolysis assay revealed that the dko mouse very low density lipoprotein (d < 1.019 g/ml) fraction separated by ultracentrifugation was a more efficient substrate for lipolysis by exogenous bovine lipoprotein lipase. Post-heparin lipoprotein lipase activity was reduced by 61% in the dko mice. Hepatic TG production rate, determined after intravenous Triton WR1339 injection, was increased 8-fold in the dko mice. Hepatic mRNA levels of sterol regulatory element binding protein-1 (srebp-1) and its target genes acetyl-CoA carboxylase-1 (acc-1), fatty acid synthase (fas), and stearoyl-CoA desaturase-1 (scd-1) were significantly elevated in the dko mice compared with the ko control. The hepatic mRNA levels of LXRalpha (lxralpha) and its target genes including angiopoietin-like protein 3 (angptl-3) in the dko mice were unchanged. Fasting glucose and insulin levels were reduced by 31 and 42%, respectively in the dko mice, in conjunction with a 49% reduction in hepatic pepck-1 mRNA (p = 0.014). Both the HTG and the improved fasting glucose phenotype seen in the dko mice are at least in part attributable to an up-regulation of the hepatic srebp-1c gene.
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MESH Headings
- Acetyl-CoA Carboxylase/genetics
- Animals
- Blood Glucose/analysis
- CCAAT-Enhancer-Binding Proteins/genetics
- Cholesterol/blood
- DNA-Binding Proteins/genetics
- Fasting
- Fatty Acid Synthases/genetics
- Fatty Acids, Nonesterified/metabolism
- Hypertriglyceridemia/enzymology
- Insulin/blood
- Lecithin Cholesterol Acyltransferase Deficiency/blood
- Lipids/blood
- Lipoproteins, HDL/blood
- Lipoproteins, LDL/blood
- Lipoproteins, VLDL/blood
- Lipoproteins, VLDL/metabolism
- Liver/chemistry
- Liver/metabolism
- Liver X Receptors
- Mice
- Mice, Knockout
- Orphan Nuclear Receptors
- Phosphatidylcholine-Sterol O-Acyltransferase/genetics
- Phosphatidylcholine-Sterol O-Acyltransferase/physiology
- RNA, Messenger/analysis
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, LDL/deficiency
- Receptors, LDL/genetics
- Reverse Transcriptase Polymerase Chain Reaction
- Sterol Regulatory Element Binding Protein 1
- Transcription Factors
- Triglycerides/blood
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Affiliation(s)
- Dominic S Ng
- Department of Medicine, St. Michael's Hospital, Toronto, Ontario M5B 1A6, Canada.
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7
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Faraj M, Sniderman AD, Cianflone K. ASP enhances in situ lipoprotein lipase activity by increasing fatty acid trapping in adipocytes. J Lipid Res 2004; 45:657-66. [PMID: 14703506 DOI: 10.1194/jlr.m300299-jlr200] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Acylation-stimulating protein (ASP) increases triglyceride (TG) storage (fatty acid trapping) in adipose tissue and plays an important role in postprandial TG clearance. We examined the capacity of ASP and insulin to stimulate the activity of lipoprotein lipase (LPL) and the trapping of LPL-derived nonesterified fatty acid (NEFA) in 3T3-L1 adipocytes. Although insulin increased total LPL activity (secreted and cell-associated; P < 0.001) in 3T3-L1 adipocytes, ASP moderately stimulated secreted LPL activity (P = 0.04; 5% of total LPL activity). Neither hormone increased LPL translocation from adipocytes to endothelial cells in a coculture system. However, ASP and insulin increased the V(max) of in situ LPL activity ([(3)H]TG synthetic lipoprotein hydrolysis and [(3)H]NEFA incorporation into adipocytes) by 60% and 41%, respectively (P </= 0.01) without affecting K(m). Tetrahydrolipstatin (LPL inhibitor) diminished baseline, ASP-, and insulin-stimulated in situ LPL activity, resulting in [(3)H]TG accumulation (P < 0.0001). Unbound oleate inhibited in situ LPL activity (P < 0.0001) but did not eliminate the ASP stimulatory effect. Therefore, 1) the clearance of TG-rich lipoproteins is enhanced by ASP through increasing TG storage and relieving NEFA inhibition of LPL; and 2) the effectiveness of adipose tissue trapping of LPL-derived NEFAs determines overall LPL activity, which in turn determines the efficiency of postprandial TG clearance.
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Affiliation(s)
- May Faraj
- Mike Rosenbloom Laboratory for Cardiovascular Research, McGill University Health Center, Montréal, Canada
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8
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Conde-Knape K. Heparan sulfate proteoglycans in experimental models of diabetes: a role for perlecan in diabetes complications. Diabetes Metab Res Rev 2001; 17:412-21. [PMID: 11757076 DOI: 10.1002/dmrr.236] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Proteoglycans are ubiquitous extracellular proteins that serve a variety of functions throughout the organism. Unlike other glycoproteins, proteoglycans are classified based on the structure of the glycosaminoglycan carbohydrate chains, not the core proteins. Perlecan, a member of the heparan sulfate proteoglycan (HSPG) family, has been implicated in many complications of diabetes. Decreased levels of perlecan have been observed in the kidney and in other organs, both in patients with diabetes and in animal models. Perlecan has an important role in the maintenance of the glomerular filtration barrier. Decreased perlecan in the glomerular basement membrane has a central role in the development of diabetic albuminuria. The involvement of this proteoglycan in diabetic complications and the possible mechanisms underlying such a role have been addressed using a variety of models. Due to the importance of nephropathy among diabetic patients most of the studies conducted so far relate to diabetes effects on perlecan in different types of kidney cells. The various diabetic models used have provided information on some of the mechanisms underlying perlecan's role in diabetes as well as on possible factors affecting its regulation. However, many other aspects of perlecan metabolism still await full elucidation. The present review provides a description of the models that have been used to study HSPG and in particular perlecan metabolism in diabetes and some of the factors that have been found to be important in the regulation of perlecan.
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Affiliation(s)
- K Conde-Knape
- Department of Medicine, Division of Preventive Medicine, Columbia University, 630 W 168th St, New York, NY 10032, USA.
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9
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Kaysen GA, de Sain-van der Velden MG. New insights into lipid metabolism in the nephrotic syndrome. KIDNEY INTERNATIONAL. SUPPLEMENT 1999; 71:S18-21. [PMID: 10412729 DOI: 10.1046/j.1523-1755.1999.07105.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Hyperlipidemia in the nephrotic syndrome results from increased synthesis and decreased catabolism of lipoproteins. The contribution of each to establishing blood lipid levels is unknown. Increased triglyceride rich lipoprotein concentration, very low density lipoprotein (VLDL) and intermediate density lipoprotein (IDL) primarily results from decreased clearance. This defect is due in part to reduced lipoprotein lipase (LPL) on the vascular endothelium resulting either from decreased synthesis or inadequate binding of this enzyme to endothelial surfaces. In contrast, both low density lipoprotein (LDL) and lipoprotein(a) [Lp(a)] concentrations are increased. Unlike the case of albumin or transferrin, or apoA-I in the rat, LDL apoB 100 synthesis is not related to that of albumin, suggesting a different mechanism of regulation or a response to a stimulus that is not the same as that augmenting the synthesis of nonlipoproteins. Evidence is presented for synthesis of LDL through a mechanism that bypasses the normal delipidation pathway that requires a VLDL precursor for LDL formation. HDL concentration is normal but maturation is impaired leading to a shift from the larger HDL2 to the smaller HDL3, a variant that is less effective as a transporter of the LPL cofactor apolipoprotein C II.
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10
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Pillarisetti S, Paka L, Sasaki A, Vanni-Reyes T, Yin B, Parthasarathy N, Wagner WD, Goldberg IJ. Endothelial cell heparanase modulation of lipoprotein lipase activity. Evidence that heparan sulfate oligosaccharide is an extracellular chaperone. J Biol Chem 1997; 272:15753-9. [PMID: 9188470 DOI: 10.1074/jbc.272.25.15753] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
A unique feature of lipoprotein lipase (LpL), the rate-limiting enzyme in the hydrolysis of circulating triglycerides, is its movement from its cell of synthesis, adipocyte or myocyte, to its site of action, the luminal endothelial surface. This involves processes that allow LpL to be released from the adipocyte cell surface and transferred against the flow of interstitial fluid to the luminal surface of endothelial cells. LpL, an unstable enzyme, must retain its activity during this process. Whether a chaperone-like molecule is involved in LpL stabilization and transport is unclear. In the present study, we tested the hypothesis that endothelial cells secrete factors that release LpL and promote its transfer to the luminal endothelial surface. Incubation of adipocytes with endothelial cell conditioned medium (ECCM) led to release of about 2-fold more LpL activity than control medium. Medium from endothelial cells exposed to lysophosphatidylcholine (lyso-ECCM), a product of LpL lipolysis of lipoproteins, released approximately 3-fold more LpL than ECCM. Concomitant with the release of LpL, adipocyte cell surface heparan sulfate (HS) proteoglycans were degraded suggesting that lyso-ECCM contained a heparanase-like activity. More heparanase was found in media from the basolateral than the apical side of lysolecithin-stimulated polarized endothelial cells. In coculture experiments, lipolysis and lysolecithin stimulation of endothelial cells increased LpL release from adipocytes. LpL released by lyso-ECCM remained stable and did not lose enzymatic activity at 37 degrees C for 1 h. LpL activity was also stabilized by heparanase-digested fragments of HS (HS oligosaccharide) and by purified LpL binding decasaccharide. Moreover, LpL.HS oligosaccharide complexes crossed endothelial cell monolayers and bound to the apical side of the cells. Thus, an endothelial heparanase may play a critical role in releasing subendothelial HS bound proteins, and specific HS oligosaccharides produced by this enzyme may serve as extracellular chaperones.
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Affiliation(s)
- S Pillarisetti
- Division of Preventive Medicine, Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
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11
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Abstract
Triacylglycerols make up 98% of the lipid content of milk, ranging in different species from 0 to 50% of the total milk volume. The fatty aid composition of the triacylglycerols depends on the species, the dietary fatty acid composition, and the carbohydrate-to-lipid ratio of the diet. The rate of lipid synthesis in the lactating mammary gland depends on the stage of mammary development and is decreased by fasting and starvation in ruminants and rodents but not in species that fast during lactation, such as seals and hibernating bears. Regulatory agents include insulin, prolactin, and non-esterified fatty acids. Dietary trans fatty acids may depress milk lipid synthesis under certain conditions. Evidence is presented that fatty acids may play a major regulatory role in acute changes in de novo mammary fatty acid synthesis, acting primarily on the activity of acetyl coenzyme A carboxylase.
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Affiliation(s)
- M C Neville
- Department of Physiology, University of Colorado Health Science Center, Denver 80262, USA.
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12
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Obunike JC, Sivaram P, Paka L, Low MG, Goldberg IJ. Lipoprotein lipase degradation by adipocytes: receptor-associated protein (RAP)-sensitive and proteoglycan-mediated pathways. J Lipid Res 1996. [DOI: 10.1016/s0022-2275(20)37492-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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13
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Parthasarathy N, Goldberg IJ, Sivaram P, Wagner WD. Isolation of heparin-derived oligosaccharides containing 2-O-sulfated hexuronic acids, by lipoprotein lipase affinity chromatography. JOURNAL OF BIOCHEMICAL AND BIOPHYSICAL METHODS 1996; 32:27-32. [PMID: 8773545 DOI: 10.1016/0165-022x(95)00045-s] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Oligosaccharides (hexa to dodeca) terminating with [3H]2,5-anhydromannitol (AManR) were isolated from heparin by partial cleavage with nitrous acid at low pH (pH 1.5) followed by gel filtration and reduction with [3H]NaBH4. They were subsequently chromatographed on a lipoprotein lipase (LpL)-Sepharose column. High- and low-affinity oligosaccharides for LpL were isolated and characterized. Disaccharide analysis revealed the presence of (IdceA(2-SO4)-->AManR6-SO4) and (IdceA(2-SO4)-->AManR) as the major disaccharide products after low pH nitrous acid treatment. The oligosaccharides are, therefore, enriched in IdceA(2-SO4)-(GlcNSO4 +/- 6-SO4) sequences. Furthermore, they are found to be composed of 2-O-sulfated hexuronic acid-containing sequences, structural features, characteristic of heparin and heparan sulfate oligosaccharides with potential antiproliferative activities. These oligosaccharides may have the potential as lipase-releasing agents from endothelial and adipocyte surfaces.
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Affiliation(s)
- N Parthasarathy
- Department of Comparative Medicine, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27157-1040, USA
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14
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Müller G, Wetekam EM, Jung C, Bandlow W. Membrane association of lipoprotein lipase and a cAMP-binding ectoprotein in rat adipocytes. Biochemistry 1994; 33:12149-59. [PMID: 7918436 DOI: 10.1021/bi00206a018] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
cAMP-binding ectoprotein (Gce1) and lipoprotein lipase (LPL) are anchored to plasma membranes of rat adipocytes by glycosylphosphatidylinositol (GPI) moieties as demonstrated by cleavage by bacterial phosphatidylinositol-specific phospholipase C (PI-PLC), reactivity with anti-crossreacting determinant antibodies (anti-CRD), and metabolic labeling with radiolabeled palmitic acid and myo-inositol. Quantitative release from the membrane of LPL and Gce1 requires both lipolytic removal of their GPI anchors and the presence of either 2 M NaCl or 1 mM inositol 1,2-cyclic monophosphate or inositol 1-monophosphate. PI-PLC-cleaved and released LPL or Gce1 reassociates with isolated plasma membranes of rat adipocytes and, less efficiently, with membranes of 3T3 fibroblasts. The specificity of the reassociation is demonstrated (i) by its inhibition after pretreatment of the membranes with trypsin, (ii) by its competition with inositol 1,2-cyclic monophosphate and inositol 1-monophosphate in a concentration-dependent manner, and (iii) by the limited number of binding sites. Enzymic or chemical removal as well as masking with anti-CRD antibodies of the terminal inositol (cyclic) monophosphate moiety of hydrophilic Gce1 and LPL significantly impairs the reassociation. These data suggest that in rat adipocytes GPI-proteins are not readily released from the cell surface upon lipolytic cleavage, but remain associated through a receptor which specifically recognizes the terminal inositol (cyclic) monophosphate epitope of the (G)PI-PLC-cleaved GPI moiety. This interaction may have implications for the regulated membrane release of GPI-proteins and for their possible internalization.
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Affiliation(s)
- G Müller
- Hoechst Aktiengesellschaft Frankfurt am Main, SBU Metabolic Diseases H 825, Germany
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Sasaki A, Sivaram P, Goldberg IJ. Lipoprotein lipase binding to adipocytes: evidence for the presence of a heparin-sensitive binding protein. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 265:E880-8. [PMID: 8279543 DOI: 10.1152/ajpendo.1993.265.6.e880] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Lipoprotein lipase (LPL) is synthesized by adipocytes, associated with the cell surface, and released from the cells when they are treated with heparin. Release of LPL from the adipocyte is required for LPL to migrate to its physiological site of action on the luminal surface of capillary endothelial cells. To better understand this process, we studied the interaction of LPL with adipocyte cell membrane proteins. With the use of a ligand blot method, LPL specifically bound to a heparin-releasable, 116-kDa protein on mouse-derived brown fat adipose cell (BFC-1 beta) and rat adipocyte membranes. A 116-kDa cell surface protein was metabolically labeled with [35S]methionine and bound to LPL-Sepharose. This suggested that the LPL-binding protein was synthesized by the cells. When BFC-1 beta were treated with heparin to eliminate heparin-sensitive cell surface binding sites, LPL binding to the cells decreased and release of newly synthesized LPL activity increased. 125I-labeled LPL binding to control cells was reduced (> 70%) by a 50-fold excess of unlabeled LPL. The residual LPL binding to heparin-treated cells was, however, not decreased by the addition of unlabeled LPL. These data imply that specific adipocyte surface LPL binding involves heparin-sensitive sites. We hypothesize that the heparin-releasable, 116-kDa LPL-binding protein mediates specific LPL binding to adipocytes and that LPL activity within adipose tissue is regulated, in part, by the interaction of LPL with this binding protein.
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Affiliation(s)
- A Sasaki
- Department of Medicine and Specialized Center of Research in Arteriosclerosis, Columbia University College of Physicians and Surgeons, New York, New York 10032
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Stins MF, Sivaram P, Sasaki A, Goldberg IJ. Specificity of lipoprotein lipase binding to endothelial cells. J Lipid Res 1993. [DOI: 10.1016/s0022-2275(20)35103-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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