Protein Synthesis In Adipose Tissue Research Articles

Stimulated in vivo synthesis of plasminogen activator inhibitor-1 in human adipose tissue

Plasminogen activator inhibitor type-1 (PAI-1) is one of the most important inhibitors of endogenous fibrinolysis. Adipose tissue is a suggested source of the elevated plasma levels of PAI-1 in obesity. The relation between PAI-1 and inflammation is of particular interest, but current knowledge regarding regulation of PAI-1 in adipose tissue is mainly based on animal studies or ex vivo experiments on human cultured adipocytes. So far, no study has described stimulated gene expression and protein synthesis of PAI-1 in vivo in human adipose tissue. We used open heart surgery as a model of acute systemic inflammation. Twenty-two male patients underwent blood sampling and omental and subcutaneous adipose tissue biopsies for gene expression studies before and after surgery. Expression and localisation of PAI-1 antigen was evaluated by immunohistochemistry. After surgery gene expression of PAI-1 increased 27-fold in omental adipose tissue and three-fold in subcutaneous adipose tissue, but no differences were found in tissue-type plasminogen activator (t-PA) mRNA. PAI-1 antigen was localised within endothelial cells and in the adipose tissue interstitium close to vessels. The upregulated gene expression and protein synthesis in adipose tissue was followed by increased concentrations of PAI-1 antigen in plasma. In conclusion, we present for the first time that an acute systemic inflammation in humans increased gene expression and protein synthesis of PAI-1 in adipose tissue and that this increase was most prominent in omental adipose tissue. PAI-1 synthesis in adipose tissue due to acute systemic inflammation may be a link between inflammation and impaired endogenous fibrinolysis.

Tissue-specific effects of chronic dietary leucine and norleucine supplementation on protein synthesis in rats.

Acute administration of leucine and norleucine activates the mammalian target of rapamycin (mTOR) cell-signaling pathway and increases rates of protein synthesis in a number of tissues in fasted rats. Although persistent stimulation of mTOR signaling is thought to increase protein synthetic capacity, little information is available concerning the effects of chronic administration of these agonists on protein synthesis, mTOR signal transduction, or leucine metabolism. Hence, we developed a model of chronic leucine/norleucine supplementation via drinking water and examined the effects of chronic (12 days) supplementation on protein synthesis in adipose tissue, kidney, heart, liver, and skeletal muscle from ad libitum-fed rats. The relative concentration of proteins involved in mTOR signaling and the two initial steps in leucine oxidation were also examined. Leucine or norleucine supplementation was accompanied by increased rates of protein synthesis in adipose tissue, liver, and skeletal muscle, but not in heart or kidney. Supplementation was not associated with increases in the anabolic hormones insulin or insulin-like growth factor I. Chronic supplementation did not cause apparent adaptation in either components of the mTOR cell-signaling pathway that respond to leucine (mTOR, ribosomal protein S6 kinase, and eukaryotic initiation factor 4E-binding protein-1) or the first two steps in leucine metabolism (the mitochondrial isoform of branched-chain amino acid transaminase, branched-chain keto acid dehydrogenase, and branched-chain keto acid dehydrogenase kinase), which may be involved in terminating the signal from leucine. These results suggest that provision of leucine or norleucine supplementation via the drinking water results in stimulation of postprandial protein synthesis in adipose tissue, skeletal muscle, and liver without notable adaptive changes in signaling proteins or metabolic enzymes.

Leucine is a direct-acting nutrient signal that regulates protein synthesis in adipose tissue.

In freshly isolated rat adipocytes, leucine or its analog norleucine activates the mammalian target of rapamycin (mTOR)-signaling pathway. This results in phosphorylation of the ribosomal protein S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E-binding protein-1 (4E-BP1), two proteins involved in the initiation phase of protein synthesis. The purpose of the studies reported herein was to address the question of whether or not these in vitro effects of leucine and norleucine on adipocytes could be extended to the intact animal and to other tissues. To accomplish this, food-deprived (18 h) male Sprague-Dawley rats were orally administered solutions (2.5 ml/100 g body wt) containing normal saline (0.9% NaCl), a carbohydrate mixture (26.2% D-glucose and 26.2% sucrose), leucine (5.4%), or norleucine (5.4%). The protein synthetic responses of adipose tissue were measured and compared with those of other tissues. In addition, S6K1 and 4E-BP1 phosphorylation was measured, as was the plasma concentration of insulin and tissue ATP concentrations. Leucine administration stimulated protein synthesis in adipose tissue, gastrocnemius, and kidney but not in liver and heart. Norleucine stimulated protein synthesis in all of the tissues tested but, in contrast to leucine, without affecting plasma insulin concentrations. The carbohydrate meal had no effect on protein synthesis in any tissue tested but elicited a robust increase in plasma insulin. These findings provide support for a role of leucine as a direct-acting nutrient signal for stimulation of protein synthesis in adipose tissue as well as other select tissues. In adipose tissue, the effects of the different treatment conditions on the acute regulation of protein synthesis closely correlated with changes in phosphorylation of S6K1 and 4E-BP1; however, this correlation did not exist in all tissues examined. This result implies that leucine or norleucine may acutely stimulate protein synthesis, at least in some tissues, by a mechanism that is independent of both S6K1 and 4E-BP1 phosphorylation.

Modulation of the activity of acetyl-CoA carboxylase and other lipogenic enzymes by growth hormone, insulin and dexamethasone in sheep adipose tissue and relationship to adaptations to lactation

The mechanisms whereby growth hormone and dexamethasone modulate the stimulation of fatty acid synthesis by insulin in adipose tissue from lactating and non-lactating sheep have been investigated. Maintenance of adipose tissue from wethers (castrated male sheep) in tissue culture for 24 or 48 h with insulin resulted in an increased proportion of acetyl-CoA carboxylase being present in the active state; this effect was enhanced by dexamethasone and was antagonized by growth hormone. Lactation results in a decrease in both the total acetyl-CoA carboxylase of sheep adipose tissue and the proportion of the enzyme in the active state. Maintenance of adipose tissue from lactating sheep in tissue culture for 48 h in the presence of insulin plus dexamethasone increased markedly the proportion of acetyl-CoA carboxylase in the active state and increased slightly the total activity of the enzyme. Both of these effects were prevented by actinomycin D, and the change in activation status was prevented by growth hormone. Tissue culture for 6 days showed that growth hormone could also prevent the ability of insulin plus dexamethasone to increase the total activity of the enzyme. Analogous studies showed that insulin, dexamethasone and growth hormone modulated the activities of other lipogenic enzymes, but the effects were proportionately smaller than for acetyl-CoA carboxylase. Insulin also increased total protein synthesis in adipose tissue, but this was not antagonized by growth hormone. The results suggest that the fall in fatty acid synthesis in sheep adipose tissue during lactation is due to a decrease in both the total acetyl-CoA carboxylase activity and the proportion of the enzyme in the active state; these changes are probably induced by known changes in the serum concentrations of insulin and growth hormone. Lactation appears to result in the loss of a protein that is required for activation of acetyl-CoA carboxylase by insulin; production of this component appears to be prevented by growth hormone.

The Role of Calcium in Insulin Action - V. Importance of Cyclic Guanosine 3':5' Monophosphate and Calcium Ions in Insulin Stimulation of Lipoprotein Lipase Activity and Protein Synthesis in Adipose Tissue

The Role of Calcium in Insulin Action - V. Importance of Cyclic Guanosine 3':5' Monophosphate and Calcium Ions in Insulin Stimulation of Lipoprotein Lipase Activity and Protein Synthesis in Adipose Tissue

The effect of dietary lipids on lipolysis in rat adipose tissue.

1. Rats were fed for 8 weeks on one of five diets differing in the amount of fatty acids 18:1, 18:2 and 18:3. Lipolysis, in vitro, of epididymal fat from fed and fasted rats was measured both basally and in the presence of noradrenaline with and without prostaglandin E1. 2. Lipolysis was markedly influenced by the type of dietary fat. In particular, lipolysis in adipose tissue from rats given diets rich in the fatty acid 18:3 was higher than in the rats given diets containing 18:2. 3. Results showing the effects of fasting on adipose tissue lipolysis are also presented. 4. The results are discussed in relation to the known effects of unsaturated fats on hyperplasia and protein synthesis in adipose tissue and on the possible role of prostaglandins.

Dissociation of lipolysis and protein anabolism by acth, bovine growth hormone, and thyroid stimulating hormone in adipose tissue with dibutyryl cyclic AMP and theophylline

1. 1. To determine whether cyclic AMP mediates the effect of ACTH, bovine growth hormone and thyroid stimulating hormone (TSH) on protein synthesis in adipose tissue in a manner similar to its role in mediating the lipolytic effect of these hormones, glycerol release and amino acid incorporation into protein were determined in the presence of dibutyryl cyclic AMP and theophylline. 2. 2. ACTH, bovine growth hormone and TSH promoted [ 14C]histidine incorporation into protein of epididymal fat pads while they stimulated glycerol release therefrom. 3. 3. Dibutyryl cyclic AMP at 10 mM or at 1 mM plus added theophylline (2.5 mM) inhibited [ 14C]histidine uptake and incorporation into protein while enhancing glycerol release. 4. 4. The protein anabolic effects of ACTH, bovine growth hormone and TSH were abolished by theophylline. 5. 5. Low concentrations of dibutyryl cyclic AMP (0.1 mM) inhibited glycerol production in contrast to concentrations of 1 mM and above which had a stimulatory effect. Butyrate at 2 mM inhibited basal lipolysis.

Enhanced RNA and protein synthesis in adipose tissue of rats adapted to periodic hyperphagia.

RNA synthesis measured by the incorporation of orotic acid-6-14C into RNA was investigated in isolated adipose tissue of control rats and of rats adapted to periodic hyperphagia, evoked by meal-feeding (a single 2-h meal per day). Both groups were fasted for 22 h and subsequently fed a measured test meal for another 2 h. It was revealed that 2 and 4 h after feeding there was no significant change in comparison with values during fasting, whereas in tissue of meal-fed rats the specific activity of RNA gradually increased by 22% and 41% respectively. The difference between controls and meal-fed rats was even much more marked if the specific activity of RNA in fat cells, isolated after incubation of the tissue, was measured. A significantly greater response of meal-fed rats was found when protein synthesis and lipogenesis in adipose tissue were assessed under the same experimental conditions. The possibility is discussed that the enhanced RNA and protein synthesis in adipose tissue of meal-fed rats is associated with de novo synthesis of enzymes involved in adaptive hyperlipogenesis.

The effects of starvation and refeeding on hexosemonophosphate shunt enzyme activity and DNA, RNA, and nitrogen content of rat adipose tissue

The activities of the enzymes glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconic dehydrogenase (6PGD), and the RNA, DNA, and nitrogen content of rat adipose tissue have been estimated during periods of starvation and refeeding. The activities of the enzymes fall on starvation and rise on refeeding, and the RNA content of the fat shows a similar pattern. There is no change in DNA content and adipose tissue nitrogen rises on starvation, remaining high after refeeding has been commenced following a 9-day fast. These data are interpreted as being consistent with the idea that the changes in enzyme activity observed are directly related to changes in protein synthesis in adipose tissue, and reflect atrophy and resynthesis of enzymes during the period studied.

SPECIFICITY OF INSULIN OR OXYTOCIN STIMULATION OF PROTEIN SYNTHESIS IN ADIPOSE TISSUE.

Insulin stimulates glucose uptake, fat synthesis, and incorporation of amino acids into protein of rat adipose tissue. Other agents having insulinlike effects on glucose metabolism have now been tested for their ability to promote protein synthesis in this in vitro system. Rat epididymal fat pads were incubated in Krebs bicarbonate medium containing glucose or pyruvate, acetate-1-C14 as precursor for lipids, or (in separate experiments) histidine-2(ring)-C14 as precursor for protein. Glucose uptake was measured by the glucose oxidase method, and radioactivity of lipid and protein fractions was estimated. Synthetic oxytocin (Sandoz), 0.1–10 U/ml, stimulated glucose uptake, acetate incorporation into lipid, and histidine-C14 incorporation into protein when glucose was present; unlike insulin, oxytocin did not enhance protein synthesis when pyruvate replaced glucose in the medium. RNA (1 mg/ml), nicotinic acid (0.001 m), and protamine sulfate (1 mg/ml) each stimulated glucose uptake and acetate incorporation into lipid, but did not enhance histidine-C14 incorporation into protein. It is concluded that in adipose tissue insulin has a specific effect on protein synthesis which cannot be mimicked by other agents which stimulate glucose uptake or lipid synthesis.

STIMULATION OF PEPTIDE SYNTHESIS IN ADIPOSE TISSUE BY INSULIN WITHOUT GLUCOSE.

The ability of insulin to stimulate incorporation of histidine-2(ring)-C14 into rat epididymal adipose tissue protein in absence of added glucose was investigated. Insulin alone was without effect, but a significant insulin stimulation was obtained when 10, 20, or 40 mm sodium pyruvate was added to the Krebs-bicarbonate incubation medium. This stimulation was not dependent on traces of glucose, since the pyruvate contained no detectable glucose; moreover, the concentration of glucose required to support the insulin stimulation was found to be not markedly different from that for pyruvate. The conclusion is that the effect of insulin on protein synthesis in adipose tissue is not dependent on any effect it may have on glucose entry.