Caloric restriction leads to regional specialisation of adipocyte function in the rat. (1/1971)

The study analysed the responses of three metabolic parameters in five distinct adipose tissue depots to caloric restriction (4 weeks) in the rat. The aims were to evaluate whether specific adipose tissue depots were recruited for triacylglycerol (TAG) storage and/or mobilisation, and to determine to what extent specific adipose tissue depots exhibited preferences for the source of fatty acid (FA) for TAG storage. Caloric restriction led to a general enhancement of the response of lipoprotein lipase (LPL), FA synthesis and glucose utilisation to a meal. Effects were particularly marked in the parametrial, perirenal and interscapular depots compared with mesenteric and subcutaneous depots. There was no evidence that individual depots selectively expressed a preference for the pathways concerned with the generation of FA for storage (the exogenous (LPL) and the endogenous (synthesis) pathway). However, the temporal sequence of activation of these pathways differed in a manner consistent with a switch from preponderant use of FA produced via de novo synthesis during the very early phase of feeding towards later use of FA derived from circulating TAG. The overall excursions in insulin levels observed in the calorie-restricted rats were comparable to those found in free-feeding rats, but the magnitude and the rapidity of the individual metabolic responses of the adipocyte were augmented. The data are consistent with a general enhancement of insulin sensitivity and responsiveness in adipose tissue of calorie-restricted rats, together with adaptive regional specialisation of adipocyte function. These adaptations would be predicted to facilitate the immediate conservation of dietary nutrients by promoting their storage as the FA or glycerol moieties of adipose tissue TAG and thereby to ensure the regulated release of FA and glycerol from adipose tissue in accordance with the requirement for glucose conservation and/or production.  (+info)

Binding of beta-VLDL to heparan sulfate proteoglycans requires lipoprotein lipase, whereas ApoE only modulates binding affinity. (2/1971)

The binding of beta-VLDL to heparan sulfate proteoglycans (HSPG) has been reported to be stimulated by both apoE and lipoprotein lipase (LPL). In the present study we investigated the effect of the isoform and the amount of apoE per particle, as well as the role of LPL on the binding of beta-VLDL to HSPG. Therefore, we isolated beta-VLDL from transgenic mice, expressing either APOE*2(Arg158-->Cys) or APOE*3-Leiden (E2-VLDL and E3Leiden-VLDL, respectively), as well as from apoE-deficient mice containing no apoE at all (Enull-VLDL). In the absence of LPL, the binding affinity and maximal binding capacity of all beta-VLDL samples for HSPG-coated microtiter plates was very low. Addition of LPL to this cell-free system resulted in a 12- to 55-fold increase in the binding affinity and a 7- to 15-fold increase in the maximal binding capacity (Bmax). In the presence of LPL, the association constant (Ka) tended to increase in the order Enull-VLDL+info)

Induced mutant mouse lines that express lipoprotein lipase in cardiac muscle, but not in skeletal muscle and adipose tissue, have normal plasma triglyceride and high-density lipoprotein-cholesterol levels. (3/1971)

The tissue-specific expression of lipoprotein lipase (LPL) in adipose tissue (AT), skeletal muscle (SM), and cardiac muscle (CM) is rate-limiting for the uptake of triglyceride (TG)-derived free fatty acids and decisive in the regulation of energy balance and lipoprotein metabolism. To investigate the tissue-specific metabolic effects of LPL, three independent transgenic mouse lines were established that expressed a human LPL (hLPL) minigene predominantly in CM. Through cross-breeding with heterozygous LPL knockout mice, animals were generated that produced hLPL mRNA and enzyme activity in CM but lacked the enzyme in SM and AT because of the absence of the endogenous mouse LPL gene (L0-hLPL). LPL activity in CM and postheparin plasma of L0-hLPL mice was reduced by 34% and 60%, respectively, compared with control mice. This reduced LPL expression was sufficient to rescue LPL knockout mice from neonatal death. L0-hLPL animals developed normally with regard to body weight and body-mass composition. Plasma TG levels in L0-hLPL animals were increased up to 10-fold during the suckling period but normalized after weaning and decreased in adult animals. L0-hLPL mice had normal plasma high-density lipoprotein (HDL)-cholesterol levels, indicating that LPL expression in CM alone was sufficient to allow for normal HDL production. The absence of LPL in SM and AT did not cause detectable morphological or histopathological changes in these tissues. However, the lipid composition in AT and SM exhibited a marked decrease in polyunsaturated fatty acids. From this genetic model of LPL deficiency in SM and AT, it can be concluded that CM-specific LPL expression is a major determinant in the regulation of plasma TG and HDL-cholesterol levels.  (+info)

Response of adipose tissue lipoprotein lipase to the cephalic phase of insulin secretion. (4/1971)

Modulation of lipoprotein lipase (LPL) allows a tissue-specific partitioning of triglyceride-derived fatty acids, and insulin is a major modulator of its activity. The present studies were aimed to assess in rats the contribution of insulin to the response of adipose tissue and muscle LPL to food intake. Epididymal and retroperitoneal adipose LPL rose 65% above fasting values as early as 1 h after the onset of a 30-min high-carbohydrate meal, with a second activity peak 1 h later that was maintained for an additional 2 h. Soleus muscle LPL was decreased by 25% between 0.5 and 4 h after meal intake. The essential contribution of insulin to the LPL response to food intake was determined by preventing the full insulin response to meal intake by administration of diazoxide (150 mg/kg body wt, in the meal). The usual postprandial changes in adipose and muscle LPL did not occur in the absence of an increase in insulinemia. However, the early (60 min) increase in adipose tissue LPL was not prevented by the drug, likely because of the maintenance of the early centrally mediated phase of insulin secretion. In a subsequent study, rats chronically implanted with a gastric cannula were used to demonstrate that the postprandial rise in adipose LPL is independent of nutrient absorption and can be elicited by the cephalic (preabsorptive) phase of insulin secretion. Obese Zucker rats were used because of their strong cephalic insulin response. After an 8-h fast, rats were fed a liquid diet ad libitum (orally, cannula closed), sham fed (orally, cannula opened), or fed directly into the stomach via the cannula during 4 h. Insulinemia increased 10-fold over fasting levels in ad libitum- and intragastric-fed rats and threefold in sham-fed rats. Changes in adipose tissue LPL were proportional to the elevation in plasma insulin levels, demonstrating that the cephalic-mediated rise in insulinemia, in the absence of nutrient absorption, stimulates adipose LPL. These results demonstrate the central role of insulin in the postprandial response of tissue LPL, and they show that cephalically mediated insulin secretion is able to stimulate adipose LPL.  (+info)

Sortilin/neurotensin receptor-3 binds and mediates degradation of lipoprotein lipase. (5/1971)

Lipoprotein lipase and the receptor-associated protein (RAP) bind to overlapping sites on the low density lipoprotein receptor-related protein/alpha2-macroglobulin receptor (LRP). We have investigated if lipoprotein lipase interacts with the RAP binding but structurally distinct receptor sortilin/neurotensin receptor-3. We show, by chemical cross-linking and surface plasmon resonance analysis, that soluble sortilin binds lipoprotein lipase with an affinity similar to that of LRP. The binding was inhibited by heparin and RAP and by the newly discovered sortilin ligand neurotensin. In 35S-labeled 3T3-L1 adipocytes treated with the cross-linker dithiobis(succinimidyl propionate), lipoprotein lipase-containing complexes were isolated by anti-sortilin antibodies. To elucidate function in cells, sortilin-negative Chinese hamster ovary cells were transfected with full-length sortilin and shown to express about 8% of the receptors on the cell surface. These cells degraded 125I-labeled lipoprotein lipase much faster than the wild-type cells. The degradation was inhibited by unlabeled lipoprotein lipase, indicating a saturable pathway, and by RAP and heparin. Moreover, inhibition by the weak base chloroquine suggested that degradation occurs in an acidic vesicle compartment. The results demonstrate that sortilin is a multifunctional receptor that binds lipoprotein lipase and, when expressed on the cell surface, mediates its endocytosis and degradation.  (+info)

Role of protein kinase C in the translational regulation of lipoprotein lipase in adipocytes. (6/1971)

The hypertriglyceridemia of diabetes is accompanied by decreased lipoprotein lipase (LPL) activity in adipocytes. Although the mechanism for decreased LPL is not known, elevated glucose is known to increase diacylglycerol, which activates protein kinase C (PKC). To determine whether PKC is involved in the regulation of LPL, we studied the effect of 12-O-tetradecanoyl phorbol 13-acetate (TPA) on adipocytes. LPL activity was inhibited when TPA was added to cultures of 3T3-F442A and rat primary adipocytes. The inhibitory effect of TPA on LPL activity was observed after 6 h of treatment, and was observed at a concentration of 6 nM. 100 nM TPA yielded maximal (80%) inhibition of LPL. No stimulation of LPL occurred after short term addition of TPA to cultures. To determine whether TPA treatment of adipocytes decreased LPL synthesis, cells were labeled with [35S]methionine and LPL protein was immunoprecipitated. LPL synthetic rate decreased after 6 h of TPA treatment. Western blot analysis of cell lysates indicated a decrease in LPL mass after TPA treatment. Despite this decrease in LPL synthesis, there was no change in LPL mRNA in the TPA-treated cells. Long term treatment of cells with TPA is known to down-regulate PKC. To assess the involvement of the different PKC isoforms, Western blotting was performed. TPA treatment of 3T3-F442A adipocytes decreased PKC alpha, beta, delta, and epsilon isoforms, whereas PKC lambda, theta, zeta, micro, iota, and gamma remained unchanged or decreased minimally. To directly assess the effect of PKC inhibition, PKC inhibitors (calphostin C and staurosporine) were added to cultures. The PKC inhibitors inhibited LPL activity rapidly (within 60 min). Thus, activation of PKC did not increase LPL, but inhibition of PKC resulted in decreased LPL synthesis by inhibition of translation, indicating a constitutive role of PKC in LPL gene expression.  (+info)

Association of lipoprotein lipase gene polymorphisms with coronary artery disease. (7/1971)

OBJECTIVES: The purpose of this study was to test whether the HindIII (+) and PvuII (-) or (+) restriction enzyme-defined alleles are associated with angiographic coronary artery disease (CAD). BACKGROUND: Lipoprotein lipase (LPL) plays a central role in lipid metabolism, hydrolyzing triglyceride in chylomicrons and very low density lipoproteins. Polymorphic variants of the LPL gene are common and might affect risk of CAD. METHODS: Blood was drawn from 725 patients undergoing coronary angiography. Leukocyte deoxyribonucleic acid segments containing the genomic sites were amplified by the polymerase chain reaction and digested, and polymorphisms were identified after electrophoresis in 1.5% agarose gel. RESULTS: In no-CAD control subjects (n = 168), HindIII (-) and (+) allelic frequencies were 28.6% and 71.4%, and (-) and (+) alleles were carried by 44.0% and 86.9% of subjects, respectively. Control PvuII (-) and (+) allelic frequencies were 41.7% and 58.3%, and (-) and (+) alleles were carried by 64.3% and 81.0%, respectively. In CAD patients (>60% stenosis; n = 483), HindIII (+) allelic carriage was increased (93.8% of patients, odds ratio [OR] = 2.28, confidence interval [CI] 1.27 to 4.00). Also, PvuII (-) allelic carriage tended to be more frequent in CAD patients (OR = 1.33, CI 0.92 to 1.93). Adjusted for six CAD risk factors and the other polymorphism, HindIII (+) carriage was associated with an OR = 2.86, CI 1.50 to 5.42, p = 0.0014, and PvulI (-) carriage, OR = 1.42, CI 0.95 to 2.12, p = 0.09. The two polymorphisms were in strong linkage disequilibrium, and a haplotype association was suggested. CONCLUSIONS: The common LPL polymorphic allele, HindIII (+), is moderately associated with CAD, and the PvuII (-) allele is modestly associated (trend). Genetic variants of LPL deserve further evaluation as risk factors for CAD.  (+info)

Lipoprotein lipase activity is decreased in a large cohort of patients with coronary artery disease and is associated with changes in lipids and lipoproteins. (8/1971)

Lipoprotein lipase (LPL) is crucial in the hydrolysis of triglycerides (TG) in TG-rich lipoproteins in the formation of HDL particles. As both these lipoproteins play an important role in the pathogenesis of atherosclerotic vascular disease, we sought to assess the relationship between post-heparin LPL (PH-LPL) activity and lipids and lipoproteins in a large, well-defined cohort of Dutch males with coronary artery disease (CAD). These subjects were drawn from the REGRESS study, totaled 730 in number and were evaluated against 75 healthy, normolipidemic male controls. Fasting mean PH-LPL activity in the CAD subjects was 108 46 mU/ml, compared to 138 44 mU/ml in controls (P < 0.0001). When these patients were divided into activity quartiles, those in the lowest versus the highest quartile had higher levels of TG (P < 0.001), VLDLc and VLDL-TG (P = 0.001). Conversely, levels of TC, LDL, and HDLc were lower in these patients (P = 0.001, P = 0.02, and P = 0.001, respectively). Also, in this cohort PH-LPL relationships with lipids and lipoproteins were not altered by apoE genotypes. The frequency of common mutations in the LPL gene associated with partial LPL deficiency (N291S and D9N carriers) in the lowest quartile for LPL activity was more than double the frequency in the highest quartile (12.0% vs. 5.0%; P = 0.006). By contrast, the frequency of the S447X LPL variant rose from 11.5% in the lowest to 18.3% (P = 0.006) in the highest quartile. This study, in a large cohort of CAD patients, has shown that PH-LPL activity is decreased (22%; P = 0.001) when compared to controls; that the D9N and N291S, and S447X LPL variants are genetic determinants, respectively, in CAD patients of low and high LPL PH-LPL activities; and that PH-LPL activity is strongly associated with changes in lipids and lipoproteins.  (+info)