Regulation of lipoprotein lipase activity and mRNA content in rat epididymal adipose tissue in vitro by recombinant tumour necrosis factor.

Tumour necrosis factor (TNF) has previously been shown to decrease lipoprotein lipase (LPL) activity and mRNA levels in 3T3-L1 cells and in adipose tissue from rats and guinea pigs when injected in vivo, but not to alter LPL activity in human adipocytes incubated in vitro. The effect of recombinant human TNF on LPL activity and mRNA levels in rat epididymal adipose tissue incubated in vitro was examined. LPL activity and mRNA levels fell in adipose tissue taken from fed rats and incubated in Krebs-Henseleit bicarbonate medium with glucose. The addition of insulin and dexamethasone prevented these falls. TNF (400 ng/ml) produced a fall of approx. 50% in LPL activity after 2 h of incubation and of approx. 30% in LPL mRNA levels after 3 h. TNF did not decrease LPL activity in isolated adipocytes. These results demonstrate that rat adipose tissue incubated in vitro is responsive to TNF whereas isolated adipocytes are not.     

Recombinant human tumor necrosis factor does not inhibit lipoprotein lipase in primary cultures of isolated human adipocytes

Previous studies have demonstrated that cachectin/tumor necrosis factor (TNF) inhibits lipoprotein lipase (LPL) activity in cultures of 3T3-L1 cells. To determine whether TNF also inhibits LPL in human adipocytes, primary cultures of isolated human adipocytes were exposed to a spectrum of concentrations of recombinant human TNF. TNF concentrations up to 1000 pM had no effect on either LPL activity or LPL immunoreactive mass in the human adipocytes. Specific binding of 125I-labeled TNF was demonstrated in human adipocytes, and a TNF concentration of 100 pM competed for approximately 50% of the 125I-labeled TNF binding sites. In contrast, the same TNF in the same concentrations progressively inhibited LPL activity and immunoreactive mass in 3T3-L1 cells. Thus, human adipocytes respond to TNF in a different manner than 3T3-L1 cells. TNF may not cause the cachexia of cancer or chronic infection by directly inhibiting LPL in adipose tissue.     

Visceral adiposity,C-peptide levels,and low lipase activities predict HIV-dyslipidemia

Protease inhibitor-based highly active antiretroviral therapy (PI-HAART) has been implicated in dyslipidemia, peripheral insulin resistance, and abnormal adipose tissue deposition in human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome, or AIDS. In vitro evidence indicates that some PIs reduce adipocyte lipoprotein (LPL) and hepatic lipase (HL) expression and activities. We examined whether LPL and HL activities are reduced in HIV-infected patients with dyslipidemia. Fasting serum lipids, glucoregulatory hormones, and postheparin LPL and HL activities, as well as whole body and regional adiposity, were measured in 19 HIV-seronegative controls, 9 HIV+ patients naive to all anti-HIV medications, 9 HIV+ patients naive to PIs, 9 HIV+ patients with prior PI experience but not currently receiving PIs, and 47 HIV+ patients receiving PI-HAART. The PI-HAART group had low LPL and HL activities. However, multiple linear regression analysis indicated that low postheparin LPL activity contributed only partially to HIV-dyslipidemia. Central adiposity and high C-peptide levels (an indicator of high insulin secretion) were stronger predictors of HIV-dyslipidemia. Low LPL and HL activities, by themselves, were insufficient to explain HIV-dyslipidemia because the PI-naive group had low LPL and HL activities but had normal adiposity, C-peptide levels, and serum lipid and lipoprotein levels. HDL-cholesterol was lower in PI-HAART and PI-naive groups than seronegative controls and was directly associated with LPL activity. These findings suggest that HIV-dyslipidemia is mediated primarily by factors that influence triglyceride and lipoprotein synthesis (e.g., central adiposity and hyperinsulinemia) and mediated only partially by factors that influence triglyceride clearance (e.g., lipase activity).     

Effect of tumor necrosis factor administration in vivo on lipoprotein lipase activity in various tissues of the rat

When added to murine adipocytes in culture, tumor necrosis factor (TNF) decreases the levels of lipoprotein lipase (LPL). Semb et al (1987. J. Biol Chem. 262: 8390-8394) have shown that administration of murine TNF to rats decreases lipoprotein lipase (LPL) in the epididymal fat pad with maximal inhibition requiring several hours. We have now tested the effects of treatment of rats with TNF on LPL activity in a variety of tissues and find that few show decreases in LPL under conditions that acutely increase serum triglycerides. Ninety minutes after treatment of male rats with human TNF (25 micrograms/200 g, i.v.), serum triglycerides rose 2.2-fold but there was no decrease in LPL activity in epididymal fat. Sixteen hours after TNF treatment LPL activity had decreased by 44% in epididymal fat, consistent with the previously reported data. In contrast, in female rats, no significant decrease was seen in LPL activity in parametrial adipose tissue at either 90 min or 16 hr after TNF administration despite increases in serum triglycerides (1.8-fold and 1.5-fold, respectively). There was little change in LPL activity in most other adipose tissue sites of male or female rats at either time after TNF treatment. No effect of TNF was seen on heart or diaphragm muscle LPL at any time. TNF treatment of both male and female rats produces consistent increases in de novo hepatic lipogenesis in vivo under conditions that increase serum triglycerides. It is unlikely that the limited effects of TNF on LPL in vivo can account for the rapid and sustained increase in serum triglycerides.     

ASP enhances in situ lipoprotein lipase activity by increasing fatty acid trapping in adipocytes

Acylation-stimulating protein (ASP) increases triglyceride (TG) storage (fatty acid trapping) in adipose tissue and plays an important role in postprandial TG clearance. We examined the capacity of ASP and insulin to stimulate the activity of lipoprotein lipase (LPL) and the trapping of LPL-derived nonesterified fatty acid (NEFA) in 3T3-L1 adipocytes. Although insulin increased total LPL activity (secreted and cell-associated; P < 0.001) in 3T3-L1 adipocytes, ASP moderately stimulated secreted LPL activity (P = 0.04; 5% of total LPL activity). Neither hormone increased LPL translocation from adipocytes to endothelial cells in a coculture system. However, ASP and insulin increased the V(max) of in situ LPL activity ([(3)H]TG synthetic lipoprotein hydrolysis and [(3)H]NEFA incorporation into adipocytes) by 60% and 41%, respectively (P 相似文献   

Lipoprotein lipase mRNA in white adipose tissue but not in skeletal muscle is increased by pioglitazone through PPAR-gamma

Lipoprotein lipase (LPL), a key enzyme for triglyceride hydrolysis, is an insulin-dependent enzyme and mainly synthesized in white adipose tissue (WAT) and skeletal muscles (SM). To explore how pioglitazone, an enhancer of insulin action, affects LPL synthesis, we examined the effect of pioglitazone on LPL mRNA levels in WAT or SM of brown adipose tissue (BAT)-deficient mice, which develop insulin resistance and hypertriglyceridemia. Both LPL mRNA of WAT and SM were halved in BAT-deficient mice. Pioglitazone increased LPL mRNA in WAT by 8-fold, which was substantially associated with a 4-fold increase of peroxisome proliferator activated receptor (PPAR)-gamma mRNA (r=0.97, p<0.0001), whereas pioglitazone did not affect LPL mRNA in SM. These results suggest that pioglitazone exclusively increases LPL production in WAT via stimulation of PPAR-gamma synthesis. Since pioglitazone does not affect LPL production in SM, this would contribute to prevent the development of insulin resistance due to lipotoxicity.     

Insulin regulation of lipoprotein lipase (LPL) activity and expression in gilthead sea bream (Sparus aurata)

Lipoprotein lipase (LPL) is a key enzyme in lipoprotein metabolism by virtue of its capacity to hydrolyze triglycerides circulating in the form of lipoprotein particles. Here we analyzed the fasting effects of LPL in gilthead sea bream (Sparus aurata) and also present the first study in fish of the role of insulin as a potential modulator of both LPL activity and expression. Fasting for 2 weeks provoked a clear decrease in adipose tissue LPL activity, concomitant with lower levels of plasma insulin, while no effects were observed in red muscle. To elucidate the specific role of insulin, increases of plasma insulin were experimentally induced by arginine and insulin injections. However, arginine predominantly stimulated glucagon over insulin secretion in this fish species while LPL activity did not change significantly in adipose tissue. Instead, insulin administration induced an increase in adipose tissue LPL activity 3 h after the injection, whereas LPL activity in red muscle was not affected. Changes in LPL activity were accompanied by an increase in LPL mRNA levels in the adipose tissue of insulin-injected gilthead sea bream, although changes in LPL expression were delayed in time with respect to variations in LPL activity. Finally, LPL mRNA levels in red muscle were similar between control and insulin-injected gilthead sea bream, suggesting that insulin does not play a direct role in the regulation of LPL in this tissue. The current study shows that LPL activity is regulated by nutritional condition and underscores the importance of insulin as a modulator of LPL activity and expression in the adipose tissue of gilthead sea bream.     

The effect of insulin on the synthesis of lipoprotein lipase in rat adipose tissue

A novel method is described for measuring the incorporation of radiolabelled amino acids into rat adipose tissue lipoprotein lipase (LPL) in vitro. Following the incubation of epididymal fat-bodies in the presence of [3H]leucine, the radiolabelled enzyme was isolated from extracts of the delipidated tissue, in a single step, by affinity chromatography on heparin-Sepharose, SDS-PAGE of such purified enzyme preparations revealed the presence of a single radiolabelled polypeptide of molecular weight 56 000, corresponding to LPL. In the presence of insulin, the rates of incorporation into LPL and into total tissue protein were increased respectively by 2.3 fold and 1.7 fold, compared to controls. It is concluded that part of the increase in incorporation into LPL is due to the general stimulus of protein synthesis in the tissue by insulin. Additionally insulin may either specifically increase the rate of synthesis or decrease the rate of degradation of the enzyme.     

Lipoprotein lipase deficiency is associated with elevated acylation stimulating protein plasma levels

Acylation stimulating protein (ASP, C3adesArg) is an adipose tissue derived hormone that stimulates triglyceride (TG) synthesis. ASP stimulates lipoprotein lipase (LPL) activity by relieving feedback inhibition caused by fatty acids (FA). The present study examines plasma ASP and lipids in male and female LPL-deficient subjects primarily with the P207L mutation, common in the population of Quebec, Canada. We evaluated the fasting and postprandial states of LPL heterozygotes and fasting levels in LPL homozygotes. Homozygotes displayed increased ASP (58–175% increase, P < 0.05–0.01), reduced HDL-cholesterol (64–75% decrease, P < 0.0001), and elevated levels of TG (19–38-fold, P < 0.0001) versus control (CTL) subjects. LPL heterozygotes with normal fasting TG (1.3–1.9 mmol/l) displayed increased ASP (101–137% increase, P < 0.05–0.01) and delayed TG clearance after a fatload; glucose levels remained similar to controls. Hypertriglyceridemics with no known LPL mutation also had increased ASP levels (63–192% increase, P < 0.001). High-TG LPL heterozygotes were administered a fatload before and after fibrate treatment. The treatment reduced fasting and postprandial plasma ASP, TG, and FA levels without changing insulin or glucose levels. ASP enhances adipose tissue fatty-acid trapping following a meal; however in LPL deficiency, high ASP levels are coupled with delayed lipid clearance.     

The lipogenic enzymes DGAT1, FAS, and LPL in adipose tissue: effects of obesity, insulin resistance, and TZD treatment

Acyl-coenzyme A:diacylglycerol transferase (DGAT), fatty acid synthetase (FAS), and LPL are three enzymes important in adipose tissue triglyceride accumulation. To study the relationship of DGAT1, FAS, and LPL with insulin, we examined adipose mRNA expression of these genes in subjects with a wide range of insulin sensitivity (SI). DGAT1 and FAS (but not LPL) expression were strongly correlated with SI. In addition, the expression of DGAT1 and FAS (but not LPL) were higher in normal glucose-tolerant subjects compared with subjects with impaired glucose tolerance (IGT) (P < 0.005). To study the effects of insulin sensitizers, subjects with IGT were treated with pioglitazone or metformin for 10 weeks, and lipogenic enzymes were measured in adipose tissue. After pioglitazone treatment, DGAT1 expression was increased by 33 +/- 10% (P < 0.05) and FAS expression increased by 63 +/- 8% (P < 0.05); however, LPL expression was not altered. DGAT1, FAS, and LPL mRNA expression were not significantly changed after metformin treatment. The treatment of mice with rosiglitazone also resulted in an increase in adipose expression of DGAT1 by 2- to 3-fold, as did the treatment of 3T3 F442A adipocytes in vitro with thiazolidinediones. These data support a more global concept suggesting that adipose lipid storage functions to prevent peripheral lipotoxicity.     

Lipoprotein lipase gene variation is associated with adipose tissue lipoprotein lipase activity, and lipoprotein lipid and glucose concentrations in overweight postmenopausal women

Adipose tissue lipoprotein lipase (LPL) activity is under strong genetic control in both mice and humans. This study determines whether common DNA variation in the LPL gene (PvuII and HindIII polymorphisms) is associated with adipose tissue LPL activity and metabolic risk factors in a homogeneous population of 75 overweight postmenopausal women (body mass index >25 kg/m2; age: 51-69 years old). The allele frequencies for the presence of the cut-sites for LPL HindIII and PvuII were 0.71 and 0.49, respectively. There were no associations between the HindIII polymorphism and any of the measured variables. Age, body mass index, percent body fat, waist-hip ratio, visceral and subcutaneous fat area, and gluteal (GLT) and abdominal (ABD) adipocyte size did not differ by LPL PvuII genotype. However, adipose tissue LPL activity at both GLT and ABD sites was higher in women without the LPL PvuII cut-site (-/-) compared with women who were heterozygous (+/-) or homozygous (+/+) for the cut-site (P<0.05). Total and LDL cholesterol were lower in women without the LPL PvuII cut-site (-/-) compared with women who were heterozygous or homozygous for the cut-site (P<0.05), whereas triglyceride and HDL levels were similar between LPL PvuII genotypes. Fasting glucose, but not insulin, was lower in women without the LPL PvuII cut-site (-/-). These data suggest that the LPL PvuII polymorphism is a possible marker for a functional mutation that is found in the LPL gene and that alters LPL activity in older overweight women.     

Lipoprotein lipase in human milk: compartmentalization and effect of fasting, insulin, and glucose

The object of this study was to investigate the effect of maternal metabolic state on the activity of lipoprotein lipase (LPL) in human milk. Although the total LPL activity in milk was not significantly affected by up to three cycles of freezing and thawing, the amount of LPL associated with the cream fraction of the milk increased from an average of less than 10% to about 70% after this treatment. The enzyme was relatively stable when the milk was stored on ice, losing activity at a rate of about 1% per hour. At 37 degrees C degradation was more rapid, about 7% per hour. When LPL activity was measured in samples taken at hourly intervals by breast pump, using oxytocin to achieve a complete letdown at each pumping, activity was found to double from the first to the third pumping. Thereafter the activity was stable under fasting conditions. Hyperglycemic and euglycemic, hyperinsulinemic glucose clamp protocols were used to evaluate the effects of glucose and insulin. Both high plasma glucose and high plasma insulin in the presence of normal glucose significantly increased LPL activity within 4 hours. We conclude that, like adipose, tissue LPL, mammary LPL is regulated by plasma insulin.     

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) reduces lipoprotein lipase activity in the adipose tissue of the guinea pig

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) administered to young male guinea pigs at a dose of 1 microgram/kg (single intraperitoneal injection) caused a large reduction in adipose tissue lipoprotein lipase (LPL) activity. This effect occurred rapidly; a 70% decrease was noticed after 24 hour and 80% of LPL activity was lost by 48 hours when the serum triglyceride levels increased to 175% of control levels. LPL is known to play an important role in controlling the amount of free fatty acids supplied to adipose tissues. Administration of a large dose of glucose to fasted guinea pigs, which have shown a similar weight loss, but less LPL loss than TCDD-treated animals, had the effect of elevating their adipose LPL levels back to a near normal level, whereas the same treatment caused no significant increase in the LPL levels of TCDD-treated animals. Evidence indicates that the TCDD-caused decline in LPL activity is irreversible. As a consequence, the affected guinea pigs are incapable of responding to changes in nutritional status.     

Brown adipose tissue activity controls triglyceride clearance

Brown adipose tissue (BAT) burns fatty acids for heat production to defend the body against cold and has recently been shown to be present in humans. Triglyceride-rich lipoproteins (TRLs) transport lipids in the bloodstream, where the fatty acid moieties are liberated by the action of lipoprotein lipase (LPL). Peripheral organs such as muscle and adipose tissue take up the fatty acids, whereas the remaining cholesterol-rich remnant particles are cleared by the liver. Elevated plasma triglyceride concentrations and prolonged circulation of cholesterol-rich remnants, especially in diabetic dyslipidemia, are risk factors for cardiovascular disease. However, the precise biological role of BAT for TRL clearance remains unclear. Here we show that increased BAT activity induced by short-term cold exposure controls TRL metabolism in mice. Cold exposure drastically accelerated plasma clearance of triglycerides as a result of increased uptake into BAT, a process crucially dependent on local LPL activity and transmembrane receptor CD36. In pathophysiological settings, cold exposure corrected hyperlipidemia and improved deleterious effects of insulin resistance. In conclusion, BAT activity controls vascular lipoprotein homeostasis by inducing a metabolic program that boosts TRL turnover and channels lipids into BAT. Activation of BAT might be a therapeutic approach to reduce elevated triglyceride concentrations and combat obesity in humans.     

The acute phase response stimulates the expression of angiopoietin like protein 4

The acute phase response is characterized by elevations in serum triglyceride levels due to both an increase in hepatic VLDL production and a delay in the clearance of triglyceride rich lipoproteins secondary to a decrease in lipoprotein lipase (LPL) activity. Recently there has been a marked increase in our understanding of factors that regulate LPL activity. GPIHBP1 facilitates the interaction of LPL and lipoproteins thereby allowing lipolysis to occur. Angiopoietin like proteins (ANGPTL) 3 and 4 inhibit LPL activity. In the present study, treatment of mice with LPS, an activator of TLR4 and a model of Gram-negative infections, did not alter the expression of GPIHBP1 in heart or adipose tissue. However, LPS decreased the expression of ANGPTL3 in liver and increased the expression of ANGPTL4 in heart, muscle, and adipose tissue. Serum ANGPTL4 protein levels were markedly increased at 8 and 16 h following LPS treatment. Administration of zymosan, an activator of TLR2 and a model of fungal infections, also increased serum ANGPTL4 protein and mRNA levels in liver, heart, muscle, and adipose tissue. Finally, treatment of 3T3-L1 adipocytes with LPS or cytokines (TNF alpha, IL-1 beta, and interferon gamma) stimulated ANGPTL4 expression. These studies demonstrate that ANGPTL4 is a positive acute phase protein and the increase in ANGPTL4 could contribute to the hypertriglyceridemia that characteristically occurs during the acute phase response by inhibiting LPL activity.     

Sub-chronic administration of stable GIP analog in mice decreases serum LPL activity and body weight

GIP receptor knockout mice were shown to be protected from the development of obesity on a high fat diet, suggesting a role of GIP in the development of obesity. In our study we aimed to test the hypothesis if excess of GIP could accelerate development of obesity and to identify GIP gene targets in adipose tissue. Therefore, mice were kept on a chow or a high fat diet and during the last 2 weeks D-Ala²-GIP or PBS injections were performed. Afterwards, serum LPL activity and several biochemical parameters (TG, FFA, cholesterol, glucose, insulin, resistin, IL-6, IL-1β, TNFα, GIP) were measured. Fat tissue was isolated and QPCR was performed for a set of genes involved in energy metabolism and inflammation. A DNA-microarray was used to identify GIP gene targets in adipose tissue of the chow diet group. We found that the D-Ala²-GIP injections caused a significant decrease in both body weight and LPL activity compared to controls. Serum biochemical parameters were not affected by D-Ala²-GIP, with an exception for resistin and insulin. The set of inflammatory genes were significantly decreased in adipose tissue in the D-Ala²-GIP injected animals on a chow diet. A DNA-microarray revealed that APO-genes and CYP-genes were affected by D-Ala²-GIP treatment in adipose tissue. These results suggest that the body weight-reducing effect of D-Ala²-GIP may be explained by lower LPL activity and insulin serum level. Moreover, the identified GIP candidate gene targets in adipose tissue link GIP action to lipid metabolism exerted by APO and CYP genes.     

Regulation of lipoprotein lipase synthesis by recombinant tumor necrosis factor--the primary regulatory role of the hormone in 3T3-L1 adipocytes

Tumor necrosis factor (TNF), a protein homologous to cachectin, has been implicated in mediating cachexia. This effect at least in part has been suggested to occur through the influence of the hormone on adipose tissue metabolism. Using fully differentiated 3T3-L1 adipocytes as a model system, we have been investigating the effects of recombinant TNF (rTNF) on key features of adipocyte metabolism. Exposure of fully differentiated 3T3-L1 adipocytes to recombinant tumor necrosis factor resulted in a dose and time-dependent suppression of the activity of lipoprotein lipase. The loss in activity results from an effect on the synthesis of the enzyme, as determined by a decreased incorporation of [35S]methionine into immunoprecipitable lipoprotein lipase. No effect of rTNF on the half-life of the enzyme was observed. General protein synthesis, as judged by [35S]methionine incorporation into acid-insoluble protein, was minimally affected by exposure of the cells to rTNF; this was further confirmed by sodium dodecyl sulfate-polyacrylamide gel analysis of total cellular protein. As opposed to our previously reported results with crude preparations of TNF, no effect on either the ability of the adipocytes to synthesize and store or mobilize triacylglycerol was observed. Our results are consistent with the hypothesis that other hormones present in crude preparations of TNF acting either alone or synergistically with TNF play a major role in the further metabolic derangements associated with adipose tissue during cachexia.     

PPARγ2 Pro12Ala polymorphism is associated with improved lipoprotein lipase functioning in adipose tissue of insulin resistant obese women

Lipoprotein lipase (LPL) plays a pivotal role in lipid metabolism, contributes to metabolic disorders related to insulin action and body weight regulation, and is influenced by inflammation. The Pro12Ala polymorphism of the peroxisome proliferator-activated receptor (PPAR)γ2 gene seems to influence LPL functioning, but its role in obesity and insulin resistance status, which usually coexist in the clinical setting, has not been explored. Our aim was to analyze the association of obesity and insulin resistance with adipose LPL activity and expression, and the influence of the PPARγ2 Pro12Ala polymorphism. A cross-sectional study was conducted in 58 reproductive-age women who underwent elective abdominal surgery. Free-fatty acids, glucose, insulin, and selected adipokines were measured in fasting blood samples. DNA was isolated and the polymorphism genotyped. Biopsies of abdominal subcutaneous adipose tissue obtained during surgery were used to determine enzymatic LPL activity and expression; and expression of selected cytokines. Overweight/obese women presented lower LPL activity (P = 0.022) and higher circulating TNF-α (P = 0.020) than controls. Insulin resistant women also showed borderline lower LPL activity than non-resistant (P = 0.052), but adiposity and inflammatory molecules were comparable. Nevertheless, LPL activity was higher in Pro12Ala carriers than in non-carriers after adjusting for obesity, insulin resistance and inflammation. Likewise, adipose LPL expression was increased in carriers while expression of cytokines was decreased. Our data suggest that insulin resistance is associated with low adipose LPL activity independently of obesity, but the PPARγ2 Pro12Ala polymorphism seems to protect the LPL functioning of obese insulin resistant women, likely through regulating inflammation in adipose tissue.