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Abstract
Lipoprotein lipase (LPL) is a rate-limiting enzyme for hydrolysing circulating triglycerides (TG) into free fatty acids that are taken up by peripheral tissues. Postprandial LPL activity rises in white adipose tissue (WAT), but declines in the heart and skeletal muscle, thereby directing circulating TG to WAT for storage; the reverse is true during fasting. However, the mechanism for the tissue-specific regulation of LPL activity during the fed–fast cycle has been elusive. Recent identification of lipasin/angiopoietin-like 8 (Angptl8), a feeding-induced hepatokine, together with Angptl3 and Angptl4, provides intriguing, yet puzzling, insights, because all the three Angptl members are LPL inhibitors, and the deficiency (overexpression) of any one causes hypotriglyceridaemia (hypertriglyceridaemia). Then, why does nature need all of the three? Our recent data that Angptl8 negatively regulates LPL activity specifically in cardiac and skeletal muscles suggest an Angptl3-4-8 model: feeding induces Angptl8, activating the Angptl8–Angptl3 pathway, which inhibits LPL in cardiac and skeletal muscles, thereby making circulating TG available for uptake by WAT, in which LPL activity is elevated owing to diminished Angptl4; the reverse is true during fasting, which suppresses Angptl8 but induces Angptl4, thereby directing TG to muscles. The model suggests a general framework for how TG trafficking is regulated.
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Affiliation(s)
- Ren Zhang
- Center for Molecular Medicine and Genetics, School of Medicine, Wayne State University, 540 East Canfield Street, Detroit, MI 48201, USA
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Evans RD, Hauton D. The role of triacylglycerol in cardiac energy provision. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1861:1481-91. [DOI: 10.1016/j.bbalip.2016.03.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 03/08/2016] [Accepted: 03/09/2016] [Indexed: 02/07/2023]
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Fu Z, Abou-Samra AB, Zhang R. A lipasin/Angptl8 monoclonal antibody lowers mouse serum triglycerides involving increased postprandial activity of the cardiac lipoprotein lipase. Sci Rep 2015; 5:18502. [PMID: 26687026 PMCID: PMC4685196 DOI: 10.1038/srep18502] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Accepted: 11/19/2015] [Indexed: 12/23/2022] Open
Abstract
Lipasin/Angptl8 is a feeding-induced hepatokine that regulates triglyceride (TAG) metabolism; its therapeutical potential, mechanism of action, and relation to the lipoprotein lipase (LPL), however, remain elusive. We generated five monoclonal lipasin antibodies, among which one lowered the serum TAG level when injected into mice, and the epitope was determined to be EIQVEE. Lipasin-deficient mice exhibited elevated postprandial activity of LPL in the heart and skeletal muscle, but not in white adipose tissue (WAT), suggesting that lipasin suppresses the activity of LPL specifically in cardiac and skeletal muscles. Consistently, mice injected with the effective antibody or with lipasin deficiency had increased postprandial cardiac LPL activity and lower TAG levels only in the fed state. These results suggest that lipasin acts, at least in part, in an endocrine manner. We propose the following model: feeding induces lipasin, activating the lipasin-Angptl3 pathway, which inhibits LPL in cardiac and skeletal muscles to direct circulating TAG to WAT for storage; conversely, fasting induces Angptl4, which inhibits LPL in WAT to direct circulating TAG to cardiac and skeletal muscles for oxidation. This model suggests a general mechanism by which TAG trafficking is coordinated by lipasin, Angptl3 and Angptl4 at different nutritional statuses.
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Affiliation(s)
- Zhiyao Fu
- Center for Molecular Medicine and Genetics, School of Medicine, Wayne State University, 540 East Canfield Street, Detroit, MI 48201, USA
| | - Abdul B Abou-Samra
- Division of Endocrinology, School of Medicine, Wayne State University, Detroit, MI 48201, USA.,Department of Medicine, Hamad Medical Corporation, Doha, Qatar
| | - Ren Zhang
- Center for Molecular Medicine and Genetics, School of Medicine, Wayne State University, 540 East Canfield Street, Detroit, MI 48201, USA.,Division of Endocrinology, School of Medicine, Wayne State University, Detroit, MI 48201, USA
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Savonen R, Hiden M, Hultin M, Zechner R, Levak-Frank S, Olivecrona G, Olivecrona T. The tissue distribution of lipoprotein lipase determines where chylomicrons bind. J Lipid Res 2015; 56:588-598. [PMID: 25589507 DOI: 10.1194/jlr.m056028] [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] [Indexed: 12/23/2022] Open
Abstract
To determine the role of LPL for binding of lipoproteins to the vascular endothelium, and for the distribution of lipids from lipoproteins, four lines of induced mutant mice were used. Rat chylomicrons labeled in vivo with [(14)C]oleic acid (primarily in TGs, providing a tracer for lipolysis) and [(3)H]retinol (primarily in ester form, providing a tracer for the core lipids) were injected. TG label was cleared more rapidly than core label. There were no differences between the mouse lines in the rate at which core label was cleared. Two minutes after injection, about 5% of the core label, and hence chylomicron particles, were in the heart of WT mice. In mice that expressed LPL only in skeletal muscle, and had much reduced levels of LPL in the heart, binding of chylomicrons was reduced to 1%, whereas in mice that expressed LPL only in the heart, the binding was increased to over 10%. The same patterns of distribution were evident at 20 min when most of the label had been cleared. Thus, the amount of LPL expressed in muscle and heart governed both the binding of chylomicron particles and the assimilation of chylomicron lipids in the tissue.
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Affiliation(s)
- Roger Savonen
- Department of Medical Biosciences, Physiological Chemistry, Umeå University, Umeå, Sweden
| | - Michaela Hiden
- Institut für Medizinische Biochemie, Abteilung für Molekülarbiologie, Karl Franzens Universität, Graz, Austria
| | - Magnus Hultin
- Department of Medical Biosciences, Physiological Chemistry, Umeå University, Umeå, Sweden
| | - Rudolf Zechner
- Institut für Medizinische Biochemie, Abteilung für Molekülarbiologie, Karl Franzens Universität, Graz, Austria
| | - Sanja Levak-Frank
- Department of Medical Biosciences, Physiological Chemistry, Umeå University, Umeå, Sweden
| | - Gunilla Olivecrona
- Department of Medical Biosciences, Physiological Chemistry, Umeå University, Umeå, Sweden
| | - Thomas Olivecrona
- Department of Medical Biosciences, Physiological Chemistry, Umeå University, Umeå, Sweden.
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Kersten S. Physiological regulation of lipoprotein lipase. Biochim Biophys Acta Mol Cell Biol Lipids 2014; 1841:919-33. [PMID: 24721265 DOI: 10.1016/j.bbalip.2014.03.013] [Citation(s) in RCA: 341] [Impact Index Per Article: 34.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 03/27/2014] [Accepted: 03/30/2014] [Indexed: 01/01/2023]
Abstract
The enzyme lipoprotein lipase (LPL), originally identified as the clearing factor lipase, hydrolyzes triglycerides present in the triglyceride-rich lipoproteins VLDL and chylomicrons. LPL is primarily expressed in tissues that oxidize or store fatty acids in large quantities such as the heart, skeletal muscle, brown adipose tissue and white adipose tissue. Upon production by the underlying parenchymal cells, LPL is transported and attached to the capillary endothelium by the protein GPIHBP1. Because LPL is rate limiting for plasma triglyceride clearance and tissue uptake of fatty acids, the activity of LPL is carefully controlled to adjust fatty acid uptake to the requirements of the underlying tissue via multiple mechanisms at the transcriptional and post-translational level. Although various stimuli influence LPL gene transcription, it is now evident that most of the physiological variation in LPL activity, such as during fasting and exercise, appears to be driven via post-translational mechanisms by extracellular proteins. These proteins can be divided into two main groups: the liver-derived apolipoproteins APOC1, APOC2, APOC3, APOA5, and APOE, and the angiopoietin-like proteins ANGPTL3, ANGPTL4 and ANGPTL8, which have a broader expression profile. This review will summarize the available literature on the regulation of LPL activity in various tissues, with an emphasis on the response to diverse physiological stimuli.
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Affiliation(s)
- Sander Kersten
- Nutrition, Metabolism and Genomics Group, Division of Human Nutrition, Wageningen University, Bomenweg 2, 6703HD Wageningen, The Netherlands
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Dijk W, Kersten S. Regulation of lipoprotein lipase by Angptl4. Trends Endocrinol Metab 2014; 25:146-55. [PMID: 24397894 DOI: 10.1016/j.tem.2013.12.005] [Citation(s) in RCA: 139] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Revised: 11/30/2013] [Accepted: 12/02/2013] [Indexed: 02/07/2023]
Abstract
Triglyceride (TG)-rich chylomicrons and very low density lipoproteins (VLDL) distribute fatty acids (FA) to various tissues by interacting with the enzyme lipoprotein lipase (LPL). The protein angiopoietin-like 4 (Angptl4) is under sensitive transcriptional control by FA and the FA-activated peroxisome proliferator activated receptors (PPARs), and its tissue expression largely overlaps with that of LPL. Growing evidence indicates that Angptl4 mediates the physiological fluctuations in LPL activity, including the decrease in adipose tissue LPL activity during fasting. This review focuses on the major ambiguities concerning the mechanism of LPL inhibition by Angptl4, as well as on the physiological role of Angptl4 in lipid metabolism, highlighting its function in a variety of tissues, and uses this information to make suggestions for further research.
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Affiliation(s)
- Wieneke Dijk
- Nutrition, Metabolism, and Genomics group, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands
| | - Sander Kersten
- Nutrition, Metabolism, and Genomics group, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands.
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Hultin M, Savonen R, Chevreuil O, Olivecrona T. Chylomicron metabolism in rats: kinetic modeling indicates that the particles remain at endothelial sites for minutes. J Lipid Res 2013; 54:2595-605. [PMID: 23922383 DOI: 10.1194/jlr.m032979] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Chylomicrons labeled in vivo with (14)C-oleic acid (primarily in triglycerides, providing a tracer for lipolysis) and (3)H-retinol (primarily in ester form, providing a tracer for the core lipids) were injected into rats. Radioactivity in tissues was followed at a series of times up to 40 min and the data were analyzed by compartmental modeling. For heart-like tissues it was necessary to allow the chylomicrons to enter into a compartment where lipolysis is rapid and then transfer to a second compartment where lipolysis is slower. The particles remained in these compartments for minutes and when they returned to blood they had reduced affinity for binding in the tissue. In contrast, the data for liver could readily be fitted with a single compartment for native and lipolyzed chylomicrons in blood, and there was no need for a pathway back to blood. A composite model was built from the individual tissue models. This whole-body model could simultaneously fit all data for both fed and fasted rats and allowed estimation of fluxes and residence times in the four compartments; native and lipolyzed chylomicrons ("remnants") in blood, and particles in the tissue compartments where lipolysis is rapid and slow, respectively.
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Affiliation(s)
- Magnus Hultin
- Departments of Surgical and Perioperative Sciences, Anaesthesiology and Intensive Care, Umeå University, S-901 87 Umeå, Sweden
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Kroupa O, Vorrsjö E, Stienstra R, Mattijssen F, Nilsson SK, Sukonina V, Kersten S, Olivecrona G, Olivecrona T. Linking nutritional regulation of Angptl4, Gpihbp1, and Lmf1 to lipoprotein lipase activity in rodent adipose tissue. BMC PHYSIOLOGY 2012; 12:13. [PMID: 23176178 PMCID: PMC3562520 DOI: 10.1186/1472-6793-12-13] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/04/2012] [Accepted: 11/09/2012] [Indexed: 12/17/2022]
Abstract
Background Lipoprotein lipase (LPL) hydrolyzes triglycerides in lipoproteins and makes fatty acids available for tissue metabolism. The activity of the enzyme is modulated in a tissue specific manner by interaction with other proteins. We have studied how feeding/fasting and some related perturbations affect the expression, in rat adipose tissue, of three such proteins, LMF1, an ER protein necessary for folding of LPL into its active dimeric form, the endogenous LPL inhibitor ANGPTL4, and GPIHBP1, that transfers LPL across the endothelium. Results The system underwent moderate circadian oscillations, for LPL in phase with food intake, for ANGPTL4 and GPIHBP1 in the opposite direction. Studies with cycloheximide showed that whereas LPL protein turns over rapidly, ANGPTL4 protein turns over more slowly. Studies with the transcription blocker Actinomycin D showed that transcripts for ANGPTL4 and GPIHBP1, but not LMF1 or LPL, turn over rapidly. When food was withdrawn the expression of ANGPTL4 and GPIHBP1 increased rapidly, and LPL activity decreased. On re-feeding and after injection of insulin the expression of ANGPTL4 and GPIHBP1 decreased rapidly, and LPL activity increased. In ANGPTL4−/− mice adipose tissue LPL activity did not show these responses. In old, obese rats that showed signs of insulin resistance, the responses of ANGPTL4 and GPIHBP1 mRNA and of LPL activity were severely blunted (at 26 weeks of age) or almost abolished (at 52 weeks of age). Conclusions This study demonstrates directly that ANGPTL4 is necessary for rapid modulation of LPL activity in adipose tissue. ANGPTL4 message levels responded very rapidly to changes in the nutritional state. LPL activity always changed in the opposite direction. This did not happen in Angptl4−/− mice. GPIHBP1 message levels also changed rapidly and in the same direction as ANGPTL4, i.e. increased on fasting when LPL activity decreased. This was unexpected because GPIHBP1 is known to stabilize LPL. The plasticity of the LPL system is severely blunted or completely lost in insulin resistant rats.
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Affiliation(s)
- Olessia Kroupa
- Department of Medical Biosciences/Physiological Chemistry, Umeå University, Umeå SE-90187, Sweden
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Zhou H, Hou SZ, Luo P, Zeng B, Wang JR, Wong YF, Jiang ZH, Liu L. Ginseng protects rodent hearts from acute myocardial ischemia-reperfusion injury through GR/ER-activated RISK pathway in an endothelial NOS-dependent mechanism. JOURNAL OF ETHNOPHARMACOLOGY 2011; 135:287-298. [PMID: 21396997 DOI: 10.1016/j.jep.2011.03.015] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2010] [Revised: 02/26/2011] [Accepted: 03/03/2011] [Indexed: 05/30/2023]
Abstract
ETHNOPHARMACOLOGICAL RELEVANCE Ginseng (Panax ginseng C.A. Meyer) is widely used in Asian communities for treating cardiovascular diseases. However, the mechanism by which it protects the myocardium in ischemia-reperfusion (I/R) injury remains unclear. In this study, we aim to investigate whether a standardized ginseng extract (RSE) protects rodent hearts against I/R injury and if glucocorticoid and/or estrogen receptor-mediated activation of Akt and Erk1/2 (the reperfusion injury salvage kinase pathway, RISK) and subsequent nitric oxide (NO) synthesis signaling are involved in this effect. MATERIALS AND METHODS Rats or gene-deleted mice were subjected to 30 min ischemia by occluding the left anterior descending coronary artery and 90 min reperfusion. Infarct size, serum level of creatine kinase (CK), lactate dehydrogenase (LDH), and NO, expression and phosphorylation of glucocorticoid receptor (GR), estrogen receptor (ER), phosphatidylinositol-3 kinase (PI3K), Akt, NO synthase (NOS), extracellular signal-regulated kinase (Erk) 1/2, p38, and c-Jun NH2 terminal kinases (JNK) were examined in rat or mice treated with or without RSE in the absence or presence of pharmacological inhibitors. RESULTS RSE significantly reduced infarct size in a dose-dependent manner and reduced the incidence of arrhythmia, increased serum NO production, reduced serum activities of creatine kinase and lactate dehydrogenase. The infarct size reduction effect of RSE was abolished by RU468 (an inhibitor of GR), tamoxifen (an inhibitor of ER), LY294002 (an inhibitor of PI3K), Akt inhibitor IV (an inhibitor of Akt protein kinase), U0126 (an inhibitor of Erk1/2) and NG-nitro-l-arginine methyl ester hydrochloride (an inhibitor of NOS), but not actinomycin D (an inhibitor of transcription process). RSE also significantly increased the activation of GR/ER, PI3K-Akt-eNOS cascades and Erk1/2 signaling in rat heart. However, RSE did not markedly reduce infarct size in endothelium NOS(-/-) mice. This differs from its effect in inducible NOS(-/-) and wild type mice, suggesting that endothelium NOS is required for the beneficial effect of RSE on the heart. CONCLUSION Our findings showed for the first time that RSE protects hearts subjected to acute I/R injury and the infarct size reduction effect of RSE is associated with GR and/or ER-mediated Akt and Erk1/2 activation in an endothelium NOS-dependent manner.
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Affiliation(s)
- Hua Zhou
- Centre for Cancer and Inflammation Research, School of Chinese Medicine, Hong Kong Baptist University, 7 Baptist University Road, Kowloon, Hong Kong.
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Abstract
Lipoprotein lipase (LPL) is a multifunctional enzyme produced by many tissues, including adipose tissue, cardiac and skeletal muscle, islets, and macrophages. LPL is the rate-limiting enzyme for the hydrolysis of the triglyceride (TG) core of circulating TG-rich lipoproteins, chylomicrons, and very low-density lipoproteins (VLDL). LPL-catalyzed reaction products, fatty acids, and monoacylglycerol are in part taken up by the tissues locally and processed differentially; e.g., they are stored as neutral lipids in adipose tissue, oxidized, or stored in skeletal and cardiac muscle or as cholesteryl ester and TG in macrophages. LPL is regulated at transcriptional, posttranscriptional, and posttranslational levels in a tissue-specific manner. Nutrient states and hormonal levels all have divergent effects on the regulation of LPL, and a variety of proteins that interact with LPL to regulate its tissue-specific activity have also been identified. To examine this divergent regulation further, transgenic and knockout murine models of tissue-specific LPL expression have been developed. Mice with overexpression of LPL in skeletal muscle accumulate TG in muscle, develop insulin resistance, are protected from excessive weight gain, and increase their metabolic rate in the cold. Mice with LPL deletion in skeletal muscle have reduced TG accumulation and increased insulin action on glucose transport in muscle. Ultimately, this leads to increased lipid partitioning to other tissues, insulin resistance, and obesity. Mice with LPL deletion in the heart develop hypertriglyceridemia and cardiac dysfunction. The fact that the heart depends increasingly on glucose implies that free fatty acids are not a sufficient fuel for optimal cardiac function. Overall, LPL is a fascinating enzyme that contributes in a pronounced way to normal lipoprotein metabolism, tissue-specific substrate delivery and utilization, and the many aspects of obesity and other metabolic disorders that relate to energy balance, insulin action, and body weight regulation.
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Affiliation(s)
- Hong Wang
- Division of Endocrinology, Metabolism and Diabetes, University of Colorado Denver Anschutz Medical Campus, Aurora, Colorado 80045, USA
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Trost Z, Sok M, Marc J, Cerne D. Increased lipoprotein lipase activity in non-small cell lung cancer tissue predicts shorter patient survival. Arch Med Res 2009; 40:364-8. [PMID: 19766899 DOI: 10.1016/j.arcmed.2009.05.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2008] [Accepted: 04/27/2009] [Indexed: 11/15/2022]
Abstract
BACKGROUND AND AIMS Cumulative evidence suggests the involvement of lipoprotein lipase (LPL) in tumor progression. We tested the hypothesis that increased LPL activity in resectable non-small cell lung cancer (NSCLC) tissue and the increased LPL gene expression in the surrounding non-cancer lung tissue found in our previous study are predictors of patient survival. METHODS Forty two consecutive patients with resected NSCLC were enrolled in the study. Paired samples of lung cancer tissue and adjacent non-cancer lung tissue were collected from resected specimens for baseline LPL activity and gene expression estimation. During a 4-year follow-up, 21 patients died due to tumor progression. One patient died due to a non-cancer reason and was not included in Cox regression analysis. RESULTS High LPL activity in cancer tissue (relative to the adjacent non-cancer lung tissue) predicted shorter survival, independently of standard prognostic factors (p=0.003). High gene expression in the non-cancer lung tissue surrounding the tumor had no predictive value. CONCLUSIONS Our study further underlines the involvement of cancer tissue LPL activity in tumor progression.
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Affiliation(s)
- Zoran Trost
- Faculty of Pharmacy, University of Ljubljana, Ljubljana, Slovenia
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Goldberg IJ, Eckel RH, Abumrad NA. Regulation of fatty acid uptake into tissues: lipoprotein lipase- and CD36-mediated pathways. J Lipid Res 2008; 50 Suppl:S86-90. [PMID: 19033209 DOI: 10.1194/jlr.r800085-jlr200] [Citation(s) in RCA: 279] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Cells obtain FAs either from LPL-catalyzed hydrolysis of lipoprotein triglyceride or from unesterified FFAs associated with albumin. LPL also influences uptake of esterified lipids such as cholesteryl and retinyl esters that are not hydrolyzed in the plasma. This process might not involve LPL enzymatic activity. LPL is regulated by feeding/fasting, insulin, and exercise. Although a number of molecules may affect cellular uptake of FFAs, the best characterized is CD36. Genetic deletion of this multiligand receptor reduces FFA uptake into skeletal muscle, heart, and adipose tissue, and impairs intestinal chylomicron production and clearance of lipoproteins from the blood. CD36 is regulated by some of the same factors that regulate LPL, including insulin, muscle contraction, and fasting, in part, via ubiquitination. LPL and CD36 actions in various tissues coordinate biodistribution of fat-derived calories.
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Affiliation(s)
- Ira J Goldberg
- Division of Preventive Medicine and Nutrition, Department of Medicine, Columbia University, New York, NY, USA.
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Cheng Y, Hauton D. Cold acclimation induces physiological cardiac hypertrophy and increases assimilation of triacylglycerol metabolism through lipoprotein lipase. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1781:618-26. [PMID: 18722549 PMCID: PMC2568868 DOI: 10.1016/j.bbalip.2008.07.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Revised: 07/15/2008] [Accepted: 07/15/2008] [Indexed: 12/24/2022]
Abstract
The contribution of triacylglycerol to energy provision in the hypertrophied heart, mediated through lipoprotein lipase (LPL) is largely unknown and the contribution of very-low-density lipoprotein (VLDL) receptor to control of LPL presentation at the endothelium is unclear. For isolated perfused rat hearts, cold acclimation (CA) induced volume-overload hypertrophy, with decreased developed pressure (P < 0.01), increased end-diastolic volume of the left ventricle (P < 0.001) and a loss of contractile reserve in response to dobutamine challenge (P < 0.01). Oleate utilisation by perfused hearts was unchanged by CA, however uptake of intralipid emulsion increased 3-fold (P < 0.01). CA increased the proportion of lipid deposited in tissue lipids from 10% in euthermic controls to 40% (P < 0.01) although the overall contribution of individual lipid classes was unaffected. Cold acclimation significantly increased heparin-releasable LPL (P < 0.05) and tissue residual LPL (P < 0.01). Western blot analysis indicated preserved expression of proteins coding for SERCA2, muscle-CPT1 and VLDL-receptor following CA, while AMPKα2 and phospho-AMPKα2 were unaffected. These observations indicate that for physiological hypertrophy AMPK phosphorylation does not mediate the enhanced translocation of LPL to cardiac endothelium.
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Affiliation(s)
- Y Cheng
- Department of Physiology, Division of Medical Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
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