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Determination of the half-life of lipoprotein lipase in cultured granulosa cells.

The incorporation of [3H]leucine into granulosa lipoprotein lipase was determined by an immunoadsorbent method: a sensitive, specific, and quantitative technique using antiserum to avian adipose lipoprotein lipase coupled to Sepharose 4B as the immunoadsorbent. The sole 3H-labeled protein bound to the immunoadsorbent was shown to be lipoprotein lipase by: (1) sodium dodecyl sulfate polyacrylamide gel electrophoresis, (2) gel filtration on Sephadex G-100, and (3) isoelectric focusing in 8 M urea of the dissociated protein. As measured by a specific radioimmunoassay, all but 4.5% of total enzyme protein, from 1.45 to 380 ng avian lipase, bound to 200 microliters immunoadsorbent. This immunoadsorbent has a quantitative binding capacity (96.5%) over a 200-fold range of enzyme concentration. Using this method, the half-life of lipoprotein lipase under steady-state conditions in cultured granulosa cells was found to be 11.26 h.

Animals↗

Lipoprotein lipase mediated uptake of non-degradable ether analogues of phosphatidylcholine and cholesteryl ester by cultured cells.

Lipoprotein lipase mediated transfer of cholesteryl ester and its ether analog, cholesteryl linoleyl ether, from unilamellar liposomes, prepared from a nonhydrolyzable ether analog of 1,2-diacyl-sn-glycero-3-phosphocholine (PC), 1,2-dioleyl ether-sn-glycero-3-phosphocholine (DOEPC), was studied in various cells in culture. It was found that lipoprotein lipase enhanced the uptake of cholesteryl linoleyl ether and of DOEPC. These findings provided a definitive proof that hydrolysis of liposomal PC is not needed for the lipoprotein lipase catalyzed transfer of cholesteryl linoleyl ether and cholesteryl ester to cells. The lipids transferred by lipoprotein lipase to cells were localized in three compartments, trypsin-releasable, resistant and metabolic; the latter was a chloroquine-sensitive pool as evidenced by inhibition of cholesteryl ester hydrolysis. Labeled PC and, to a lesser extent DOEPC, in the trypsin-releasable pool was able to return to the medium, while cholesteryl linoleyl ether and cholesteryl ester required cholesteryl ester transfer protein for release. The transfer of cholesteryl linoleyl ether and cholesteryl ester into a trypsin-resistant compartment did not require metabolic energy and occurred also in formaldehyde-fixed cells. Metabolic energy was needed for the translocation of cholesteryl linoleyl ether and cholesteryl ester into the lysosomal compartment, presumably by a process of endocytosis. The physiological relevance of the present findings is that as intravascular hydrolysis of triacylglycerol-rich lipoproteins is mediated by lipoprotein lipase attached to endothelial cells, the latter can provide a very extensive surface for removal and metabolism of phospholipids and cholesteryl ester by a mechanism mediated by lipoprotein lipase.

Animals↗

The functional status of lipoprotein lipase in rat liver.

1. Acetone-dried powders of liver and heart tissues from rats given a high-carbohydrate diet or a fat meal were assayed for lipoprotein lipase activity. Heart tissue showed typical lipoprotein lipase activity, whereas none was detected in liver by the usual assay procedures. 2. When mixed acetone-dried powders were prepared from heart plus liver, there was a marked suppression of the expected activity, indicating that an inhibitor was present in the liver. This inhibition was partially overcome in the presence of relatively large amounts of heparin. 3. Lipoprotein lipase was also detected in liver alone when large quantities of heparin were added to the assay system. 4. No increase in lipoprotein lipase activity in either liver or heart was detected when rats were given a fat meal. 5. It is concluded that the liver of the rat contains lipoprotein lipase that is normally present in an inactive state. The results imply that a heparinase is the agent responsible for the inactivation. 6. The significance of the non-functional status of lipoprotein lipase in the liver is discussed. The results support the view that direct hydrolysis of plasma triglycerides by the liver is not a significant physiological process.

Animals↗

Meal-induced changes in lipoprotein lipase activity in brown fat and other tissues of rats.

Brown fat thermogenesis is increased after a single test meal. This study was conducted to determine whether lipoprotein lipase activity is higher in brown adipose and other tissues after a single large meal. Rats were trained to eat two large meals per day. Two hours after consuming a test meal, lipoprotein lipase activity was measured in interscapular brown adipose tissue, retroperitoneal and epididymal white adipose tissue, gastrocnemius and soleus skeletal muscles and heart. After a high carbohydrate test meal, lipoprotein lipase activity in white adipose tissue pads was higher (P less than 0.05) and that in brown adipose tissue was lower (P less than 0.05) than in these tissues from the meal-deprived group. Muscle lipoprotein lipase did not change significantly. A high fat test meal did not significantly alter lipoprotein lipase activity in brown adipose tissue, white adipose tissue, gastrocnemius or soleus when compared to the meal-deprived control, but heart lipoprotein lipase activity was significantly elevated. These findings indicate that after a single test meal lipoprotein lipase activity in brown adipose tissue is not higher than that from the meal-deprived group and therefore, lipoprotein lipase may not play a rate-limiting role in moving free fatty acids into this tissue in the postprandial state.

Adipose Tissue, Brown↗

Pulmonary macrophage: a major source of lipoprotein lipase in the lung.

The lipase released by heparin infusion into perfused rat lungs is shown to be identical with lipoprotein lipase on the basis of the following characteristics: 1) it required plasma for full activity; 2) it was largely inhibited by 1 M NaCl; and 3) it bound to a heparin-Sepharose gel and eluted with buffer containing 1.5 M NaCl. Macrophages prepared from rat lungs released a considerable amount of lipoprotein lipase, with characteristics similar to those of the lipoprotein lipase released from heparin-perfused rat lungs. Pulmonary surfactant-producing type II pneumocytes did not cause a significant release of lipoprotein lipase. No apparent lipoprotein lipase activities were detected in the conditioned medium of other lung cells from which macrophages had been selectively removed.

Animals↗

Triglyceride, diglyceride, monoglyceride, and cholesterol ester hydrolases in chicken adipose tissue activated by adenosine 3':5'-Monophosphate-dependent protein kinase. Chromatographic resolution and immunochemical differentiation from lipoprotein lipase.

Hormone-sensitive lipase and cholesterol ester hydrolase of chicken adipose tissue were markedly activated by adenosine 3':5'-monophosphate (cAMP)-dependent protein kinase (on the average, 235 to 275%; occasionally as much as 1000%). Diglyceride and monoglyceride hydrolases were also activated, but to a lesser extent (60 to 87%). The activation of all four hydrolases was inhibited by protein kinase inhibitor and reversed by the addition of exogenous protein kinase. Following activation by cAMP-dependent protein kinase, all four hydrolases were deactivated in a Mg2+-dependent reaction and then reactivated to or near initial levels on incubation with cAMP and Mg2+-ATP. The reversible deactivation is assumed to reflect activity of one or more protein phosphatases. The maximum activation obtainable for the four hydrolases decreased when the tissue had been previously exposed to glucagon, indicating that the glucagon-induced activation was probably similar to or identical with the activation demonstrated in cell-free preparations. The pH optima for the four hydrolase activities were similar (7.13 to 7.38). Although the absolute activities and relative degrees of kinase activation differed according to the particular emulsified substrates used, the results do not rule out the possibility that all four hydrolase activities are referable to a single hormone-sensitive hydrolase. Hormone-sensitive acyl hydrolases were separated from lipoprotein lipase by heparin-Sepharose affinity chromatography. Lipoprotein lipase was active against triolein, diolein, and monoolein, but not cholesterol oleate. Incubation of lipoprotein lipase with exogenous protein kinase, cAMP, and Mg2+ATP had no effect on any of the three hydrolase activities. Lipoprotein lipase was further purified to homogeneity and used to prepare antiserum in rabbits. The immunoglobin G fraction from these antisera completely inhibited lipoprotein lipase eluted from heparin-Sepharose columns. However, the hormone-sensitive hydrolase activities (not retained on heparin-Sepharose affinity chromatography) were not inhibited by anti-lipoprotein lipase immunoglobin G, and anti-lopoprotein lipase immunoglobin G did not affect the activation process in crude fractions. Thus, hormone-sensitive lipase and lipoprotein lipase, functionally distinct enzymes, have been physically resolved and immunochemically distinguished. Apparently lipoprotein lipase activity is not regulated, at least directly, by cAMP-dependent protein kinase.

Adenosine Triphosphate↗

Isolation of an active-site peptide of lipoprotein lipase from bovine milk and determination of its amino acid sequence.

Lipoprotein lipase from bovine milk reacted stoichiometrically with diisopropylphosphorofluoridate (DFP), an inactivator of serine esterases, resulting in the loss of enzymatic activity against triacylglycerols. The reaction obeyed first-order kinetics with a rate constant of 0.69 h-1. In order to isolate the peptide containing the diisopropylphosphoryl moiety (DIP), partially purified lipoprotein lipase was covalently labeled with [3H]DFP, and the labeled protein was reduced, carboxymethylated, and further purified to about 90% homogeneity. Cyanogen bromide cleavage followed by gel filtration yielded a radioactive peptide of 6-8 kDa. This peptide was succinylated and then digested with Staphylococcus aureus V8 proteinase. From this digest, a peptide containing 0.95 mol of [3H] DIP/mol of peptide was isolated by gel-permeation chromatography followed by reverse-phase high performance liquid chromatography. Automated Edman degradation provided the following sequence: Ala-Ile-Gly-Ile-His-Trp-Gly-Gly- (DIP)Ser-Pro-Asn-Gln-Lys-Asn-Gly-Ala-Val-Phe-Ile-Asn-(Ser, Leu)-Glu. Analysis of the sequence for secondary structure suggests that the reactive serine of lipoprotein lipase is in a beta-turn, a structure similar to those of the active sites of most other serine proteinases. Lipoprotein lipase appears to share this secondary structure with other serine hydrolases despite significant differences in the primary structure of this domain.

Amino Acid Sequence↗

A study of lipoprotein lipase gene intron 8 polymorphisms in Chinese Han race essential hypertension patients.

OBJECTIVE: To investigate the association of lipoprotein lipase gene intron 8 polymorphisms and Essential Hypertension in Han race Chinese. METHODS AND RESULTS: 116 patients with Essential Hypertension were enrolled and another 116 normal people were served as controls. All cases were examined for the genotypes of intron 8 in lipoprotein lipase gene by the methods of polymerase chain reaction restriction fragment length polymorphism, and the serum lipoprotein levels were also observed. Results showed that body mass index blood pressure and the serum triglyceride level were obviously increased in the Essential Hypertension group. The genotype and allele frequency of intron 8 in lipoprotein lipase in the Essential Hypertension group showed obvious differences compared with the control group. Serum triglyceride levels were higher in the patients with H+H+ genotype than in those in non H+H+ genotype of intron 8 in lipoprotein lipase by HindIII digestion. The systolic blood pressure showed a decreasing tendency among the H+H+ genotype, the H+H- genotype and the H-H- genotype individuals. CONCLUSION: The results suggest that lipoprotein lipase may be an important genetic factor associated with the Chinese Han race Essential Hypertension patients. The polymorphisms of intron 8 in lipoprotein lipase influence the blood-lipid metabolism, induce blood vessel rebuilding and play an important role in the invasion and development of Essential Hypertension.

Asian People↗

Lipoprotein lipase secretion by human monocytes and rabbit alveolar macrophages in culture.

Human peripheral blood monocytes and rabbit alveolar macrophages secreted lipoprotein lipase during culture. Within hours after plating, lipoprotein lipase had accumulated in the culture medium of monocytes, and the rate of accumulation increased with time in culture. The initial rate of secretion of lipoprotein lipase by alveolar macrophages was higher than in monocytes but decreased after 8--10 hr to values similar to those expressed by monocytes cultured for the same length of time. The enzyme was characterized as lipoprotein lipase (triacylglycero-protein acylhydrolase, EC 3.1.1.34) on the basis of pH optimum (7.8--8.2 for monocytes, 8.1 for alveolar macrophages), dependence on apolipoprotein C-II for activity, inhibition by 0.3--0.5 M sodium chloride and protamine sulfate, and retention of a heparin-Sepharose gel. The expression of lipoprotein lipase secretion by human monocytes may have important implications with respect to the development of foam cells in the arterial wall during atherogenesis.

Animals↗

Possible role of lipoprotein lipase in the regulation of endogenous triacylglycerols in the rat heart.

1. Adrenaline has a biphasic effect on intracellular lipoprotein lipase activity and on endogenous triacylglycerol content in heparin-perfused heart. 2. A high concentration of adrenaline (1 microM in the perfusion buffer) activated endogenous lipoprotein lipase activity and, at the same time, decreased intracellular triacylglycerol stores. 3. In contrast, a low concentration (0.005 microM-adrenaline) inhibited intracellular lipoprotein lipase activity. Under these conditions, cardiac triacylglycerol content was elevated above control values. 4. Perfusing the heart with high and low concentrations of 3-isobutyl-1-methylxanthine elicited a biphasic effect on endogenous lipoprotein lipase activity and triacylglycerol content similar to that seen with adrenaline treatment. 5. The effect of adrenaline on intracellular lipoprotein lipase activity appears to be mediated by cyclic AMP through protein kinase. 6. A possible role for intracellular lipoprotein lipase in the regulation of endogenous triacylglycerol in rat heart is proposed.

1-Methyl-3-isobutylxanthine↗

Hypertriglyceridemia and its relation to tissue lipoprotein lipase activity in endotoxemic, Escherichia coli bacteremic, and polymicrobial septic rats.

Hypertriglyceridemia, commonly observed in septic patients, may result from a decreased ability of tissues to remove plasma triacylglycerol due to depressed lipoprotein lipase activity. While endotoxin administration results in substantial decreases in muscle lipoprotein lipase activity, enzyme activity is increased in animals subjected to other forms of stress and trauma. The present study was initiated to compare changes in plasma triacylglycerol concentrations and tissue lipoprotein lipase activities in rats challenged with endotoxin or live Escherichia coli (iv or ip) or rats subjected to polymicrobial peritoneal sepsis. Sixteen hours post-treatment plasma triacylglycerol levels were increased 200 to 300% in endotoxin- and E. coli-treated rats but did not differ from control animals subjected to peritoneal sepsis. At the same time, endotoxin administration resulted in significant decreases in heart (71-80%), soleus muscle (52-74%), and adipose tissue (21-32%) lipoprotein lipase activity regardless of the route injected. Intravenous E. coli also lead to a decrease in the three tissues examined while ip administration of E. coli reduced muscle and adipose tissue but not heart lipoprotein lipase activity. In contrast to endotoxemic and E. coli bacteremic rats, polymicrobial peritonitis resulted in significant increases in heart (46-89%) and skeletal muscle (18-39%) lipoprotein lipase activity. Thus, hypertriglyceridemia is not necessarily a consequence of sepsis but occurred in endotoxemic and bacteremic states when muscle and adipose tissue lipoprotein lipase activities were reduced. These findings support the postulate that sepsis-induced hypertriglyceridemia is likely to be associated with a decreased ability of lipoprotein lipase-containing tissues to clear circulating triacylglycerol.

Animals↗

Kinetics of acylglycerol hydrolysis by human milk lipoprotein lipase.

The incubation of human plasma very-low-density lipoprotein with human milk lipoprotein lipase results in an almost complete hydrolysis of triacylglycerols. The degradation of these substrates can be described by a consecutive reaction as follows: (Formula: see text), where k1, k2 and k3 are the apparent first-order rate constants of degradation. Using least-squares non-linear curve fitting, k1 and k2 are determined to be directly proportional to enzyme concentration. k1/k2 ratio of 1:12 is similar for both VLDL and trioleoylglycerol substrates of lipoprotein lipase. However, when trioleoylglycerol and rac-1,2-dioleoylglycerol are used as substrates, a direct measurement indicates a k1/k2 ratio of 1:1.5. This result suggests that the intermediary diacylglycerol produced by the lipoprotein reaction is incompletely re-equilibrated with the bulk of the substrate in the assay mixture. The k3 value is not proportional to lipoprotein lipase concentration, and in the enzyme concentration range studied, the value decreases when the enzyme concentration increases.

Female↗

Isolation and characterization of lipoprotein lipase activators from bovine blood serum.

Bovine serum lipoproteins were fractionated into high density and low and very low density lipoproteins by precipitation with sodium phosphotungstate and magnesium chloride. From each lipoprotein fraction seven apo C peptides were isolated by gel filtration and ion exchange chromatography. The two lipoprotein fractions probably contain identical apo C peptides but in different proportions. Two of the apo C peptides activated lipoprotein lipase from milk in vitro. Their specific activities were about 2000 times as high as that of the original serum. The apo C fraction from low-very low density lipoproteins had a specific activity three times that from high density lipoproteins. Also, the activator peptides from low and very low density lipoproteins gave one band on alkaline urea gel electrophoresis whereas corresponding peptides from high density lipoproteins were slightly heterogeneous. The low and very low density lipoproteins, therefore, seem to be the fraction of choice for isolation of activators for lipoprotein lipase.

Amino Acids↗

Lipoprotein lipase and acid lipase activity in rabbit brain microvessels.

A preparation of cerebral microvessels was used to demonstrate the presence of lipoprotein lipase and acid lipase activity in the microvasculature of rabbit brain. Microvessels, consisting predominantly of capillaries, small arterioles, and venules, were islated from rabbit brain. Homogenates were assayed for lipolytic activity using a glycerol-stabilized trioleoylglycerol-phospholipid emulsion as substrate. Lipoprotein lipase activity was characterized with this substrate by previously established criteria including an alkaline pH optimum, increased activity in the presence of heparin and heat-inactivated plasma, and reduced activity in the presence of NaCl and protamine sulfate. A different substrate, containing trioleoylglycerol incorporated into phospholipid vesicles, was used to reveal acid lipase activity that was not affected by heparin, plasma, NaCl, or protamine sulfate. Lipoprotein lipase did not show activity with the vesicle preparation as substrate. Intact microvessels, when incubated in the presence of heparin, release lipoprotein lipase into the incubation solution. In contrast, release of acid lipase activity from intact microvessels was not dependent on heparin. The data show the presence of both lipoprotein lipase and acid lipase in brain microvessels and suggest that lipoproteins are metabolized within the cerebral vasculature.

Animals↗

The C-terminus of lipoprotein lipase is essential for biological function but contains no domain for glycosylphosphatidylinositol anchoring.

In this study we present evidence that the C-terminus of lipoprotein lipase contains no glycosylphosphatidylinositol addition signal and is therefore not a glycosylphosphatidylinositol-anchored protein. Furthermore, we present additional evidence that the C-terminus of lipoprotein lipase is essential for biological function. Flow cytometric analysis and enzyme-activity monitoring experiments revealed no pool of lipoprotein lipase releasable by phosphatidylinositol-specific phospholipase present on the membrane of COS cells transfected with the human lipoprotein lipase gene while, in contrast, a heparin-releasable pool could be demonstrated. [14C]Ethanolamine, a constituent of the glycosylphosphatidylinositol anchor, was not incorporated into lipoprotein lipase during metabolic labeling. C-terminal deletion mutants were constructed and expressed in COS cells to investigate the presence of glycosylphosphatidylinositol addition signal on the C-terminus of human lipoprotein lipase (LPL). The specific activities of the mutants M442 [des-(Leu443-Gly448)-LPL] and M437 [des-(Cys438-Gly448)-LPL] were 78% and 59%, respectively, less than the wild type, while the M432 mutant [des-(Ala433-Gly449)-LPL] was catalytically inactive. Determination of the stability of the mutants revealed a decreased stability of the M437, compared with wild-type, whereas M442 showed the same stability. Flow cytometric analysis showed sustained membrane expression for all mutants including the inactive M432 mutant. These results suggest that the C-terminus of lipoprotein lipase is essential for maintaining intact catalytic activity but is not involved in any posttranslational proteolytic processing, including cleavage of a glycosylphosphatidylinositol addition signal. We therefore conclude that membrane-binding of the lipase is not mediated by such anchoring.

Amino Acid Sequence↗

Severe hypertriglyceridemia, reduced high density lipoprotein, and neonatal death in lipoprotein lipase knockout mice. Mild hypertriglyceridemia with impaired very low density lipoprotein clearance in heterozygotes.

Lipoprotein lipase (LPL)-deficient mice have been created by gene targeting in embryonic stem cells. At birth, homozygous knockout pups have threefold higher triglycerides and sevenfold higher VLDL cholesterol levels than controls. When permitted to suckle, LPL-deficient mice become pale, then cyanotic, and finally die at approximately 18 h of age. Before death, triglyceride levels are severely elevated (15,087 +/- 3,805 vs 188 +/- 71 mg/dl in controls). Capillaries in tissues of homozygous knockout mice are engorged with chylomicrons. This is especially significant in the lung where marginated chylomicrons prevent red cell contact with the endothelium, a phenomenon which is presumably the cause of cyanosis and death in these mice. Homozygous knockout mice also have diminished adipose tissue stores as well as decreased intracellular fat droplets. By crossbreeding with transgenic mice expressing human LPL driven by a muscle-specific promoter, mouse lines were generated that express LPL exclusively in muscle but not in any other tissue. This tissue-specific LPL expression rescued the LPL knockout mice and normalized their lipoprotein pattern. This supports the contention that hypertriglyceridemia caused the death of these mice and that LPL expression in a single tissue was sufficient for rescue. Heterozygous LPL knockout mice survive to adulthood and have mild hypertriglyceridemia, with 1.5-2-fold elevated triglyceride levels compared with controls in both the fed and fasted states on chow, Western-type, or 10% sucrose diets. In vivo turnover studies revealed that heterozygous knockout mice had impaired VLDL clearance (fractional catabolic rate) but no increase in transport rate. In summary, total LPL deficiency in the mouse prevents triglyceride removal from plasma, causing death in the neonatal period, and expression of LPL in a single tissue alleviates this problem. Furthermore, half-normal levels of LPL cause a decrease in VLDL fractional catabolic rate and mild hypertriglyceridemia, implying that partial LPL deficiency has physiological consequences.

Adipose Tissue↗

Lipoprotein lipase mRNA expression in brown adipose tissue: translational and/or posttranslational events are involved in the modulation of enzyme activity.

Lipoprotein lipase mRNA abundance in rat brown adipose tissue increases during the first 24 h of cold exposure. Lipoprotein lipase mRNA levels do not change in brown fat throughout pregnancy and lactation, whereas enzyme activity is significantly lowered. After 5 h of acute cold or noradrenaline administration there is a 2-fold increase in lipoprotein lipase mRNA abundance, whereas lipoprotein lipase activity is stimulated to more than 6-fold the basal values. It is concluded that translational and/or posttranslational mechanisms are involved in the noradrenergic modulation of lipoprotein lipase activity in brown fat.

Acclimatization↗

No linkage of the lipoprotein lipase locus to hypertension in Caucasians.

OBJECTIVE: A previous study has shown significant linkage of five markers near the lipoprotein lipase locus to systolic blood pressure, but not to diastolic blood pressure, in nondiabetic members of 48 Taiwanese families selected for noninsulin-dependent diabetes. However, lipoprotein lipase markers did not appear strongly linked to systolic blood pressure in a study of Mexican-Americans using a variety of selection schemes. The objective of the current study was to test whether markers near the lipoprotein lipase gene were linked to hypertension in Caucasians. DESIGN: To test for linkage of genetic markers in or near the lipoprotein lipase gene to hypertension in Caucasians, two sets of Caucasian hypertensive sibships were genotyped. The samples included 261 sibships (431 effective sibpairs) from four field centers of the National Heart, Lung and Blood Institute Family Heart Study and 211 sibships (282 effective sibpairs) from the Health Family Tree database in Utah. RESULTS: Two highly polymorphic markers in or near the lipoprotein lipase gene showed no evidence of excess allele sharing in either set of hypertensive sibships. Combining the two datasets resulted in 653 and 713 effective sibpairs for the two markers, sharing 0.495 +/- 0.30 and 0.486 +/- 0.28 alleles identical by descent compared to an expected sharing of 0.50. Multipoint analysis of the two loci also did not show linkage (P = 0.95). CONCLUSIONS: We conclude that the lipoprotein lipase locus and nearby regions do not appear to be linked to hypertension in Caucasians.

Alleles↗