What factors regulate the action of lipoprotein lipase?
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Biological Transport↗
Biomedical subjects
T Olivecrona
Publications and source records attributed to T Olivecrona.
Phospholipase activity of milk lipoprotein lipase.
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Animals↗
Effect of medium- and long-chain triglyceride infusion on lipoprotein and hepatic lipase in healthy subjects.
Plasma lipolytic activity and hydrolysis of intravenous fat were studied in six healthy subjects during infusion of a long-chain triglyceride (LCT) fat emulsion (Intralipid 20%) or of a medium-chain triglyceride (MCT)/LCT emulsion (Lipofundin MCT 20%). The fat emulsions were infused continuously at a rate of 0.17 g triglyceride kg-1 body weight (BW)h-1 for 6 h in random order at 7-day intervals. A continuous infusion of glucose (0.18 g kg-1 BW h-1) was administered for a period of 7 h and was started 1 h before the lipid infusion. Infusions of both types of fat increased plasma triglyceride (TG), free fatty acid (FFA) and lipoprotein lipase (LPL) levels and steady-state values were present during the 3rd to 5th h of infusion. MCT/LCT infusion resulted in higher plasma levels at steady-state of TG (3.63 +/- 0.45 [SEM] vs 2.73 +/- 0.45 mmol l-1; P less than 0.05), FFA (1.05 +/- 0.08 vs 0.54 +/- 0.04 mmol l-1; P less than 0.01) and LPL (4.6 +/- 0.6 vs 2.6 +/- 0.5 mU ml-1; P less than 0.05) in comparison with LCT administration. There was a positive correlation between plasma LPL activity and TG concentration (r = 0.77; P less than 0.001) when data for the two infusions were combined. Although the same amount of fat was infused on a weight basis, the molar infusion rate was 40% higher with MCT/LCT than with LCT infusion, due to differences in molecular weights (634 vs 885 Da).(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Pulse-chase study on lipoprotein lipase in perfused guinea pig heart.
Lipoprotein lipase (LPL) in guinea pig hearts was labeled by perfusion for 15 min with [35S] methionine, followed by chase perfusion with unlabeled medium for less than or equal to 90 min. Suitable conditions for pulse and chase and for immunoprecipitation of LPL were worked out. Differences in labeling between individual hearts were found to be substantial. A technique to take serial biopsies (approximately 20 mg) from the heart ventricle was therefore worked out and validated. Regional differences of LPL labeling within the ventricle were small. There was no evidence for enhanced release of LPL caused by biopsy. When heparin was present throughout the chase, labeled LPL began to appear in the medium after 30 min. Thus LPL can move rapidly from synthesis in parenchymal cells to the endothelial surface and into the medium. After 90 min chase with heparin, approximately equal amounts of LPL (approximately 32%) had been released to the medium, remained in the heart, or had been degraded, respectively. In contrast, no detectable amount of labeled LPL appeared in the medium during 90 min chase without heparin, and a heparin flush at this time brought out only approximately 9% of the pulse-labeled LPL.
Animals↗
Lipoprotein lipase in guinea-pig adrenals: activity, mRNA, immunolocalization and regulation by ACTH.
Lipase activity in homogenates of guinea-pig adrenals was studied under conditions which exclude the hormone-sensitive lipase/cholesterol ester hydrolase. Antibody inhibition and chromatography on heparin-Sepharose showed that most of the activity was due to lipoprotein lipase (LPL), and that there was only a small amount of hepatic lipase activity. Northern blot analysis of total RNA demonstrated the same three adrenal LPL mRNA species (1.8, 3.1 and 3.5 kb) as were found in adipose tissue and heart. Hence, at least part of the LPL activity in adrenals is due to enzyme synthesized within the tissue. Immunolocalization showed that LPL was associated with the endothelium of blood vessels throughout the gland. In addition, there was cytoplasmic immunoreaction, suggesting that lipase was synthesized in a subpopulation of cells in the transitional zone between the fasciculata and reticularis layer of the cortex, particularly over lipid-filled cells. There was also intense immunofluorescence over scattered cells in the adrenal medulla. Treatment with an ACTH analogue depot (20 IU, i.m.) for 11 days induced a 12-fold increase in serum cortisol and increased adrenal weight 2.2-fold. The treatment induced increases in LPL mRNA (about twofold), LPL activity and in the number of cells in the adrenal cortex which gave an immunoreaction for LPL.
Adrenal Glands↗
Lipoprotein lipase in lungs, spleen, and liver: synthesis and distribution.
Lipoprotein lipase (LPL, E C 3.1.1.34) is the enzyme responsible for hydrolysis of triacylglycerols in plasma lipoproteins, making the fatty acids available for use by subjacent tissues. LPL is functional at the surface of endothelial cells, but it is not clear which cells synthesize the enzyme and what its distribution within tissues and vessels is. In previous studies we reported that in the major LPL-producing tissues (muscles, adipose tissue, and mammary gland) the enzyme is made by the major cell types. In the present work we have studied in adult guinea pigs some tissues that present LPL activity but in lower amounts (lung, spleen, and liver). On cryosections of these tissues we have searched for specific cell expression of the LPL gene (by in situ hybridization using a RNA probe) and for the corresponding protein distribution (by immunocytochemistry). Based on morphological criteria we can suggest that, contrary to the main LPL-producing tissues, in these tissues the enzyme is made by scattered cells, such as macrophages in the lung and spleen and Kupffer cells in the liver; endothelial cells present but do not synthesize the enzyme, indicating that the endothelial LPL originates in other cells. In the liver strong immunoreaction was detected in the sinusoid in contrast to the low level of mRNA expression, suggesting that liver takes up circulating LPL from blood.
Animals↗
Medium-chain versus long-chain triacylglycerol emulsion hydrolysis by lipoprotein lipase and hepatic lipase: implications for the mechanisms of lipase action.
To explore how enzyme affinities and enzyme activities regulate hydrolysis of water-insoluble substrates, we compared hydrolysis of phospholipid-stabilized emulsions of medium-chain (MCT) versus long-chain triacylglycerols (LCT). Because substrate solubility at the emulsion surface might modulate rates of hydrolysis, the ability of egg yolk phosphatidylcholine to solubilize MCT was examined by NMR spectroscopy. Chemical shift measurements showed that 11 mol % of [13C]carbonyl enriched trioctanoin was incorporated into phospholipid vesicles as a surface component. Similar methods with [13C]triolein showed a maximum solubility in phospholipid bilayers of 3 mol % (Hamilton & Small, 1981). Line widths of trioctanoin surface peaks were half that of LCT, and relaxation times, T1, were also shorter for trioctanoin, showing greater mobility for MCT in phospholipid. In assessing the effects of these differences in solubility on lipolysis, we found that both purified bovine milk lipoprotein lipase and human hepatic lipase hydrolyzed MCT at rates at least 2-fold higher than for LCT. With increasing concentrations of MCT, saturation was not reached, indicating low affinities of lipase for MCT emulsions, but with LCT emulsion incubated with lipoprotein lipase, saturation was reached at relatively low concentration, demonstrating higher affinity of lipase for LCT emulsions. Differences in affinity were also demonstrated in mixed incubations where increasing amounts of LCT emulsion resulted in decreased hydrolysis of MCT emulsions. Increasing MCT emulsion amounts had little or no effect on LCT emulsion hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Localization of lipoprotein lipase to discrete areas of the guinea pig brain.
Lipoprotein lipase is a key enzyme in lipoprotein metabolism present primarily in extrahepatic tissues with high turnover of fatty acids. Using immunocytochemistry we have explored where lipoprotein lipase is localized in guinea pig brain. The enzyme was found to be associated with neuronal cells and vascular endothelial surfaces. The distribution was strikingly uneven with intense reaction in some areas, and virtually no reaction in adjacent areas. The highest reactivity was in neocortex, in hippocampus, in Purkinje cells of the cerebellum and in some motor nuclei of the brainstem. The results suggest marked differences between individual brain areas in utilization of plasma lipoproteins.
Animals↗
Postprandial lipemia, fenofibrate and coronary artery disease.
This report describes the response of patients with severe coronary artery disease to a dynamic fat load test and monitors the change induced by fenofibrate therapy. The presence of disease was associated with prolonged and exaggerated hypertriglyceridemia following the meal and with lower basal HDL cholesterol and HDL subfraction masses. A further indicator of risk was the persistence of increased amounts of retinyl palmitate in the plasma of severely affected individuals 24 h after its ingestion with the meal. These observations are consistent with the proposal that the clearance of chylomicrons and their remnants is impaired in coronary atherosclerosis. Fenofibrate reduced alimentary lipemia following the fat load in both normo- and hypercholesterolemic subjects. This was associated with a 10% rise in plasma HDL cholesterol levels. The improvement in chylomicron catabolism probably derived from a 37% increase (P less than 0.001) in lipoprotein lipase activity induced by fenofibrate. Hepatic lipase on the other had was only slightly affected by treatment.
Adult↗
Fatty acid control of lipoprotein lipase: a link between energy metabolism and lipid transport.
Lipoprotein lipase (LPL) catalyzes the flux-generating step in transport of fatty acids from lipoprotein triacylglycerols into tissues for use in metabolic reactions. In vitro studies have shown that fatty acids can bind to the enzyme and impede its other interactions. In this study we have searched for evidence of fatty acid control of LPL in vivo by rapid infusion of a triacylglycerol emulsion to healthy volunteers. During infusion the activity of LPL but not of hepatic lipase increased in plasma, but to different degrees in different individuals. The time course for the increase in LPL activity differed from that for triacylglycerols but followed the plasma levels of free fatty acids. This was true during infusions and when the emulsion was given as a bolus injection. In particular there were several instances when plasma triacylglycerol levels were very high but free fatty acids and LPL activity remained low. Model studies with bovine LPL showed that fatty acids displace the enzyme from heparin-agarose. We suggest that in situations when fatty acids are generated more rapidly by LPL than they are used by the local tissue, they cause dissociation of the enzyme from its binding to endothelial heparin sulfate and are themselves released into circulation.
Adult↗
In vitro remodelling of plasma lipoproteins in whole plasma by lipoprotein lipase in primary and secondary hypertriglyceridaemia.
In patients with familial lipoprotein lipase deficiency (FLPL-d) and glycogen storage disease type I (GSD-I), hypertriglyceridaemia (1445 +/- 247 and 1082 +/- 312 mg dl-1, n = 5 per group) was associated primarily with reduced extrahepatic lipoprotein lipase (LPL) activity (0.33 +/- 0.33 and 1.69 +/- 0.38 mumol FFA ml-1 h-1) when compared with controls (4.83 +/- 0.90). Hypercholesterolaemia was characterized by elevated LDL cholesterol (191 +/- 30 and 344 +/- 34 vs. 115 +/- 5 mg dl-1 in controls P less than 0.01) and low HDL cholesterol (12 +/- 2 and 22 +/- 2 vs. 56 +/- 3 in controls, P less than 0.001). In order to ascertain the role of LPL in the interconversion and remodelling of lipoproteins in these disorders, we analysed lipid and lipoprotein profiles before and following in vitro incubation of patient plasma with purified milk LPL (EC 3.1.1.34) for 6 h at 37 degrees C. The efficiency of exogenous LPL in vitro was demonstrated by the extent of hydrolysis of chylomicrons and of VLDL-TG in both groups. Concomitant with the disappearance of TG-rich lipoprotein particles, a consistent per cent increment of IDL (99.2 +/- 30.8 and 43.9 +/- 70.5), LDL (152.8 +/- 36.2 and 137.0 +/- 36.1) and of HDL2 (144.8 +/- 29.4 and 99.8 +/- 18.7) was observed in both groups of patients. The enhancement of the latter fractions contrasted with the decline of HDL3 mass concentration (25.4 +/- 7.7 and 51.4 +/- 5.8%), suggesting that a major shift of HDL3----HDL2 occurs following in vitro lipolysis by LDL. Simultaneous compositional and morphological changes of individual lipoprotein particles were noted, confirming the dynamic movement and exchange of neutral lipids and proteins. Specificity of LPL results was demonstrated by experiments in which incubation of the whole plasma at 37 degrees C without exogenous lipolytic enzyme did not cause any substantial changes. The present study, therefore, demonstrates a correction of the major lipoprotein abnormalities associated with FLPL-d and GSD-I by exogenous LPL. No substantial difference was noted between primary (FLPL-d) and secondary (GSD-I) hyperlipidaemias. These studies allow us to conclude that a simple in vitro system, utilizing an exogenous source of LPL and plasma from patients, may serve as a suitable model for the study of the metabolic relationships of lipoproteins. However, in view of the fact that the extent of lipolysis achieved in vitro did not differ between FLPL-d and GSD-I, it may not be able to separate primary from secondary hyperlipaemias.
Adolescent↗
Lipoprotein lipase: cellular origin and functional distribution.
Lipoprotein lipase (LPL, E.C. 3.3.1.34) is the enzyme responsible for hydrolysis of triacylglycerols in plasma lipoproteins, making the fatty acids available for use by subjacent tissues. LPL is functional at the surface of endothelial cells, but it is not clear which cells synthesize the enzyme and what its distribution is within tissues and vessels. We have searched for specific cell expression of the LPL gene by in situ hybridization using a RNA probe and for the corresponding protein distribution by immunocytochemistry on cryosections of some LPL-producing tissues of guinea pigs. In white and brown adipose tissues, heart and skeletal muscle, and lactating mammary gland, there was positive hybridization for LPL mRNA over all members of the major cell types, indicating that mature and immature adipocytes, muscle cells, and mammary epithelial cells are main sources of LPL. In large vessels, LPL expression was detected in some smooth muscle cells in the media layer. There was no positive hybridization for LPL mRNA over endothelial cells in any of the tissues studied, but there was immunoreaction for LPL protein at endothelial surfaces of all blood vessels. In the kidney, there was strong immunofluorescence at the vascular endothelium, particularly in the glomeruli, but little or no LPL mRNA was detected in the surrounding cells. These observations suggest that in some tissues LPL is synthesized by parenchymal cells and spreads along the vascular mesh. Transfer to the vascular endothelium is, however, not the only route taken by LPL. In the mammary gland most of the enzyme protein appeared to be secreted, partly in association with milk fat droplets.(ABSTRACT TRUNCATED AT 250 WORDS)
Adipose Tissue↗
Hyperlipoproteinemia type I in a patient with active lipoprotein lipase in adipose tissue and indications of defective transport of the enzyme.
This paper presents a case of typical hyperlipoproteinemia type I in a young woman. Her serum triglycerides varied between 2 and 90 mmol/l and she had substantial amounts of apolipoprotein B-48 in fasting plasma. She had no detectable lipoprotein lipase (LPL) activity in post-heparin plasma (less than 0.2 percent of normal). Southern blot analysis suggested no major defect in her LPL gene and Northern blot analysis of adipose tissue RNA showed normal-sized LPL-mRNA. A 2-h [35S]methionine incorporation experiment with adipose tissue pieces in vitro showed that she produced normal-sized LPL and had LPL catalytic activity in the tissue. The amounts were, however, only 5-10% of control. No detectable LPL radioactivity or catalytic activity was released from patient tissue even in the presence of heparin in the incubations. Immunofluorescent staining of adipose tissue biopsies from the patient showed LPL immunoreactivity only in adipocytes and little or none within the capillaries. Treatment of immunoprecipitated labeled LPL with endoglycosidase H showed that the oligosaccharide chains on her enzyme were of the high-mannose type and not processed as in controls. Taken together the data suggest that the patient synthesizes a relatively normal LPL protein which is core-glycosylated and folded into active enzyme as in normal subjects, but is not effectively transported via the Golgi to the cell surface.
Adipose Tissue↗
Two different mechanisms are involved in nutritional regulation of lipoprotein lipase in guinea-pig adipose tissue.
Lipoprotein lipase activity in adipose tissue responds rapidly to changes in the physiological state. To study what mechanisms are involved in the regulation, guinea pigs were fasted and the decrease in adipose-tissue lipoprotein lipase activity was compared with the decreases in mRNA and lipase synthesis. The mRNA pattern (three species) did not change. There was a close parallelism between the abundance of lipase mRNA and relative lipase synthesis (immunoprecipitable 35S-labelled lipoprotein lipase as fraction of total [35S]protein after pulse-labelling with [35S]methionine). Total protein synthesis decreased on fasting, compounding the decrease in relative lipase synthesis. Lipoprotein lipase mRNA changed similarly in fat-pads and in isolated adipocytes, whereas lipase activity changed more in the pads, indicating disproportionally large changes in extracellularly located lipase. In old guinea pigs the decreases in lipoprotein lipase activity and lipase synthesis were comparable, but in young animals the change in lipase activity was substantially larger than the change in lipase synthesis. Refeeding of fasted young guinea pigs with glucose resulted in a rapid increase in lipoprotein lipase activity, but there was only a small change in lipase mRNA. Old animals responded slowly to refeeding. The results indicate that in older animals the major mechanism for regulation of adipose lipoprotein lipase activity is a relatively slow change in lipase mRNA, whereas in younger animals an additional, more rapid, regulation is exerted on the transport and turnover of the enzyme.
Adipose Tissue↗
The relation between glycosylation and activity of guinea pig lipoprotein lipase.
Previous studies have indicated that the processing of oligosaccharide chains is necessary for lipoprotein lipase to become catalytically active and may be involved in the regulation of lipase release. Guinea pig adipocytes and perfused guinea pig hearts were labeled with [35S]methionine, and lipoprotein lipase was immunoprecipitated. Digestion with endo-beta-N-acetylglucosaminidase H (Endo H) showed that the mature enzyme contains one high mannose and two complex oligosaccharide chains. Limited proteolysis indicated where in the molecule the chains are attached. Pulse-chase experiments showed that some lipase molecules were rapidly processed and appeared in the medium within 40 min. Other lipase molecules remained fully Endo H-sensitive for more than 2 h, and this form of the lipase did not appear in the medium. Both forms co-eluted with the sole lipoprotein lipase activity peak from heparin-Sepharose; this indicates that both were dimeric. Separation of the two forms was achieved by lectin chromatography and demonstrated that both were catalytically active. Cells treated with methyl-deoxynojirimycin or with deoxymannojirimycin produced and released active lipoprotein lipase which was fully Endo H-sensitive. These studies demonstrate that the trimming and processing of the oligosaccharide chains is not necessary for lipoprotein lipase to become catalytically active and be secreted, and they suggest that a comparatively large fraction of the lipase molecules is retained in the endoplasmic reticulum. Whether they ever reach the processing apparatus in the Golgi or are degraded is not clear.
1-Deoxynojirimycin↗
Structural features of lipoprotein lipase. Lipase family relationships, binding interactions, non-equivalence of lipase cofactors, vitellogenin similarities and functional subdivision of lipoprotein lipase.
A structural homology between lipoprotein lipase, pancreatic lipase and hepatic lipase is known and indicates that all three lipases are members of a common protein family. Lipoprotein lipase and pancreatic lipase utilize small protein co-factors, apolipoprotein C-II and co-lipase, respectively, but comparisons reveal no homology between the co-factor molecules. Hence, they do not show the same relationship as their target enzymes. Neither do screenings detect any extensive similarities between lipoprotein lipase, serine hydrolases, or apolipoproteins. Scannings against data bank proteins show that a 105-residue segment of lipoprotein lipases exhibits a 35-40% residue identity with a sub-region of Drosophila vitellogenins. One fifth of the conserved amino acid residues (8 of 40) are glycine, a pattern which is typical of distantly related forms of protein families. This supports a true relationship between large segments of Drosophila vitellogenins and lipases. Physiological and functional aspects of the vitellogenin/lipoprotein lipase similarities are given. The region concerned is entirely within the N-terminal domain of lipoprotein lipase and constitutes the segment where the similarity to hepatic and pancreatic lipases is most pronounced. Within this lipase region a 10-residue putative lipid-binding site exists for which further similarities have been found to the otherwise not closely related lingual/gastric lipases, prokaryotic lipases and lecithin-cholesterol acyltransferase. Another segment in lipoprotein lipase, where the heparin-binding site has been mapped, exhibits a correlation between strength of heparin binding and extent of basic residues among members of the lipase family. It further exhibits weak similarities with the 'Zn-finger' DNA-binding segment of steroid hormone receptors and may indicate convergence in a binding interaction. Thus, a functional subdivision of lipoprotein lipase into different segments can be distinguished.
Amino Acid Sequence↗
Lipoprotein lipase in myocytes and capillary endothelium of heart: immunocytochemical study.
Lipoprotein lipase was immunolocalized by electron microscopy in hearts of young mice; 78% of lipoprotein lipase was in myocytes, 3-6% in extracellular space, and 18% in capillary endothelium. Lipoprotein lipase in myocytes was located primarily in sarcoplasmic reticulum, Golgi sacs, and transport vesicles and also in secretory vesicles at the cell periphery. Lipoprotein lipase in extracellular space was present near the orifice of secretory vesicles of myocytes and in narrow zones spanning the space between myocytes and capillary endothelium. The lowest concentration of lipase associated with endothelial cells was at the basal plasma membrane, whereas the highest concentration was at the surface of luminal projections. Lipoprotein lipase was associated with chylomicrons at the capillary surface but not with chylomicron remnants. Fasting mice for 48 h increased, in heart, lipoprotein lipase activity by 120% and immunolocalized lipase by 270%. The greatest increase (5-fold) occurred at the surface of intraluminal endothelial projections. The findings indicate that lipoprotein lipase in heart is synthesized by myocytes, transferred across extracellular space along cell surfaces and across endothelial cells via vesicles or intracellular channels, and concentrated at the surface of luminal projections of endothelium where the enzyme hydrolyzes triacylglycerol of chylomicrons and very low-density lipoproteins.
Animals↗
Changes of testicular cholesteryl ester hydrolase activity in experimentally cryptorchid rats.
A simple and reliable method was developed to determine the neutral cholesteryl ester hydrolase (CEH) activity in rat testes, using cholesteryl-[1-14C]-oleate as substrate. The activity was due to a soluble enzyme present in the cytoplasm of predominantly Sertoli cells, which could be shown after depleting the testes of Leydig cells with ethane dimethyl sulphonate. This treatment also revealed that the loss of CEH activity in abdominal testes of experimentally cryptorchid rats takes place in the Sertoli cells. In prepubertal rats made unilaterally cryptorchid at birth, the CEH activity was significantly higher in the abdominal than in the scrotal testes at 16 days of age. This is earlier than any previously described biochemical change and coincides with, or may even precede, the earliest morphological changes which are accumulation of lipid droplets in the Sertoli cells. The testicular CEH activity then decreased to 30 days of age in the abdominal testes, whereas the activity increased in the contralateral, scrotal testes. When adult rats were made unilaterally cryptorchid for 24 h, the CEH activity decreased rapidly in the abdominal testes. These results suggest that a derangement in cholesteryl ester metabolism is an early event in the pathogenesis of testicular degeneration in cryptorchidism.
Animals↗