Role of energy charge and AMP-activated protein kinase in adipocytes in the control of body fat stores

The effect of adenosine monophosphate-activated protein kinase on lipolysis in adipose tissue: an historical and comprehensive review

CONTEXT

Lipolysis is one of the most important pathways for energy management, its control in the adipose tissue (AT) is a potential therapeutic target for metabolic diseases. Adenosine Mono Phosphate-activated Protein Kinase (AMPK) is a key regulatory enzyme in lipids metabolism and a potential target for diabetes and obesity treatment.

OBJECTIVE

The aim of this work is to analyse the existing information on the relationship of AMPK and lipolysis in the AT.

METHODS

A thorough search of bibliography was performed in the databases Scopus and Web of Knowledge using the terms lipolysis, adipose tissue, and AMPK, the unrelated publications were excluded, and the documents were analysed.

RESULTS

Sixty-three works were found and classified in 3 categories: inhibitory effects, stimulatory effect, and diverse relationships; remarkably, the newest researches support an upregulating relationship of AMPK over lipolysis.

CONCLUSION

The most probable reality is that the relationship AMPK-lipolysis depends on the experimental conditions.

The Pancreatic β-Cell: The Perfect Redox System

Pancreatic β-cell insulin secretion, which responds to various secretagogues and hormonal regulations, is reviewed here, emphasizing the fundamental redox signaling by NADPH oxidase 4- (NOX4-) mediated H₂O₂ production for glucose-stimulated insulin secretion (GSIS). There is a logical summation that integrates both metabolic plus redox homeostasis because the ATP-sensitive K⁺ channel (K_ATP) can only be closed when both ATP and H₂O₂ are elevated. Otherwise ATP would block K_ATP, while H₂O₂ would activate any of the redox-sensitive nonspecific calcium channels (NSCCs), such as TRPM2. Notably, a 100%-closed K_ATP ensemble is insufficient to reach the -50 mV threshold plasma membrane depolarization required for the activation of voltage-dependent Ca²⁺ channels. Open synergic NSCCs or Cl^- channels have to act simultaneously to reach this threshold. The resulting intermittent cytosolic Ca²⁺-increases lead to the pulsatile exocytosis of insulin granule vesicles (IGVs). The incretin (e.g., GLP-1) amplification of GSIS stems from receptor signaling leading to activating the phosphorylation of TRPM channels and effects on other channels to intensify integral Ca²⁺-influx (fortified by endoplasmic reticulum Ca²⁺). ATP plus H₂O₂ are also required for branched-chain ketoacids (BCKAs); and partly for fatty acids (FAs) to secrete insulin, while BCKA or FA β-oxidation provide redox signaling from mitochondria, which proceeds by H₂O₂ diffusion or hypothetical SH relay via peroxiredoxin "redox kiss" to target proteins.

Impact of combined long-term fructose and prednisolone intake on glucose and lipid homeostasis in rats: benefits of intake interruption or fish oil administration

We investigated whether combined long-term fructose and prednisolone intake would be more detrimental to the glucose homeostasis than if ingested separately. We also evaluated whether fish oil administration or interruption of treatments has any positive impact. For this, male adult Wistar rats ingested fructose (20%) (F) or prednisolone (12.5 µg/mL) (P) or both (FP) through drinking water for 12 weeks. A separate group of fructose and prednisolone-treated rats received fish oil treatment (1 g/kg) in the last 6 weeks. In another group, the treatment with fructose and prednisolone was interrupted after 12 weeks, and the animals were followed for more 12 weeks. Control groups ran in parallel (C). The F group had higher plasma TG (+42%) and visceral adiposity (+63%), whereas the P group had lower insulin sensitivity (-33%) and higher insulinemia (+200%). Only the the FP group developed these alterations combined with higher circulating uric acid (+126%), hepatic triacylglycerol content (+16.2-fold), lipid peroxidation (+173%) and lower catalase activity (-32%) that were associated with lower protein kinase B content and AMP-activated protein kinase (AMPK) phosphorylation in the liver, lower AMPK phosphorylation in the adipose tissue and higher beta-cell mass. Fish oil ingestion attenuated the elevation in circulating triacylglycerol and uric acid values, while the interruption of sugar and glucocorticoid intake reverted almost all modified parameters. In conclusion, long-term intake of fructose and prednisolone by male rats are more detrimental to glucose and lipid homeostasis than if ingested separately and the benefits of treatment interruption are broader than fish oil treatment.

Tartary Buckwheat Extract Attenuated the Obesity-Induced Inflammation and Increased Muscle PGC-1a/SIRT1 Expression in High Fat Diet-Induced Obese Rats

Obesity is intimately related to a chronic inflammatory state, with augmentation of macrophage infiltration and pro-inflammatory cytokine secretion in white adipose tissue (WAT) and mitochondrial dysfunction in skeletal muscle. The specific aim of this study is to evaluate effects of tartary buckwheat extract (TB) on obesity-induced adipose tissue inflammation and muscle peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α/sirtulin 1 (SIRT1) pathway in rats fed a high-fat diet. Sprague-Dawley rats were divided into four groups and fed either a normal diet (NOR), 45% high-fat diet (HF), HF + low dose of TB (TB-L; 5 g/kg diet), or HF + high dose of TB (TB-H; 10 g/kg diet) for 13 weeks. TB significantly reduced adipose tissue mass with decreased adipogenic gene expression of PPAR-γ and aP2. Serum nitric oxide levels and adipose tissue macrophage M1 polarization gene markers, such as iNOS, CD11c, and Arg1, and pro-inflammatory gene expression, including TNF-α, IL-6, and MCP-1, were remarkably downregulated in the TB-L and TB-H groups. Moreover, TB supplementation increased gene expression of PGC-1α and SIRT1, involved in muscle biogenesis and function. These results suggested that TB might attenuate obesity-induced inflammation and mitochondrial dysfunction by modulating adipose tissue inflammation and the muscle PGC-1α/SIRT1 pathway.

Fatty Acid-Stimulated Insulin Secretion vs. Lipotoxicity

Fatty acid (FA)-stimulated insulin secretion (FASIS) is reviewed here in contrast to type 2 diabetes etiology, resulting from FA overload, oxidative stress, intermediate hyperinsulinemia, and inflammation, all converging into insulin resistance. Focusing on pancreatic islet β-cells, we compare the physiological FA roles with the pathological ones. Considering FAs not as mere amplifiers of glucose-stimulated insulin secretion (GSIS), but as parallel insulin granule exocytosis inductors, partly independent of the K_ATP channel closure, we describe the FA initiating roles in the prediabetic state that is induced by retardations in the glycerol-3-phosphate (glucose)-promoted glycerol/FA cycle and by the impaired GPR40/FFA1 (free FA1) receptor pathway, specifically in its amplification by the redox-activated mitochondrial phospholipase, iPLA2γ. Also, excessive dietary FAs stimulate intestine enterocyte incretin secretion, further elevating GSIS, even at low glucose levels, thus contributing to diabetic hyperinsulinemia. With overnutrition and obesity, the FA overload causes impaired GSIS by metabolic dysbalance, paralleled by oxidative and metabolic stress, endoplasmic reticulum stress and numerous pro-apoptotic signaling, all leading to decreased β-cell survival. Lipotoxicity is exerted by saturated FAs, whereas ω-3 polyunsaturated FAs frequently exert antilipotoxic effects. FA-facilitated inflammation upon the recruitment of excess M1 macrophages into islets (over resolving M2 type), amplified by cytokine and chemokine secretion by β-cells, leads to an inevitable failure of pancreatic β-cells.

Bergamottin Inhibits Adipogenesis in 3T3-L1 Cells and Weight Regulation in Diet-Induced Obese Mice

Obesity is a serious and increasing health problem worldwide, and the inhibition of adipogenesis is considered to be a potential therapeutic target for it. Bergamottin (BGM), a component of grapefruit juice, has been reported to regulate lipolysis. However, the physiological role of BGM in obesity has not been evaluated so far. In the present study, we investigated the effects of BGM on obesity in 3T3-L1 cells and in mice fed a high-fat diet (HFD). BGM inhibited adipogenic differentiation of 3T3-L1 cells along with a significant decrease in the lipid content by downregulating the expression of two critical adipogenic factors, CCAAT enhancer-binding protein-alpha (C/EBP[Formula: see text]) and peroxisome proliferator activated receptor-gamma (PPAR[Formula: see text]). The expressions of target proteins such as adipocyte fatty acid-binding protein (aP2), adiponectin, and resistin were also decreased by BGM. It activated AMP-activated protein kinase (AMPK) by increasing phosphorylation of AMPK and the downstream target acetyl-CoA carboxylase (ACC), indicating that BGM exerted its antiadipogenic effect through AMPK activation. In the HFD-induced obese mouse model, BGM administration significantly reduced the weight and sizes of white adipose tissue as well as the weight gain of mice fed HFD. Moreover, UCP1 and PGC1[Formula: see text] expressions, well-known as brown adipocyte marker genes, were higher in the BGM-treated HFD mice than that in the HFD-induced obese mice. This study suggests that BGM suppress adipogenesis by AMPK activation in vitro and reduces body weight in vivo.

Dietary Restriction Ameliorates Age-Related Increase in DNA Damage, Senescence and Inflammation in Mouse Adipose Tissuey

Ageing is associated with redistribution of fat around the body and saturation of visceral adipose depots. Likewise, the presence of excess fat in obesity or during ageing places extra stress on visceral depots, resulting in chronic inflammation and increased senescence. This process can contribute to the establishment of the metabolic syndrome and accelerated ageing. Dietary restriction (DR) is known to alleviate physiological signs of inflammation, ageing and senescence in various tissues including adipose tissue.

OBJECTIVES

Our pilot study aimed to analyse senescence and inflammation parameters in mouse visceral fat tissue during ageing and by short term, late-onset dietary restriction as a nutritional intervention. Design, measurements: In this study we used visceral adipose tissue from mice between 5 and 30 months of age and analysed markers of senescence (adipocyte size, γH2A.X, p16, p21) and inflammation (e.g. IL-6, TNFα, IL-1β, macrophage infiltration) using immuno-staining, as well as qPCR for gene expression analysis. Fat tissues from 3 mice per group were analysed.

RESULTS

We found that the amount of γH2A.X foci as well as the expression of senescence and inflammation markers increased during ageing but decreased with short term DR. In contrast, the increase in amounts of single or aggregated macrophages in fat depots occurred only at higher ages. Surprisingly, we also found that adipocyte size as well as some senescence parameters decreased at very high age (30 months).

CONCLUSIONS

Our results demonstrate increased senescence and inflammation during ageing in mouse visceral fat while DR was able to ameliorate several of these parameters as well as increased adipocyte size at 17.5 months of age. This highlights the health benefits of a decreased nutritional intake over a relatively short period of time at middle age.

Fat Cell and Fatty Acid Turnover in Obesity

The ratio of free fatty acid (FFA) turnover decreases significantly with the expansion of white adipose tissue. Adipose tissue and dietary saturated fatty acid levels significantly correlate with an increase in fat cell size and number. Inhibition of adipose triglyceride lipase leads to an accumulation of triglyceride, whereas inhibition of hormone-sensitive lipase leads to the accumulation of diacylglycerol. The G0/G1 switch gene 2 increases lipid content in adipocytes and promotes adipocyte hypertrophy through the restriction of triglyceride turnover. Excess triacylglycerols (TAGs), sterols and sterol esters are surrounded by the phospholipid monolayer surface and form lipid droplets. Following the release of lipid droplets from endoplasmic reticulum, cytoplasmic lipid droplets increase their volume either by local TAG synthesis or by homotypic fusion. The number and the size of lipid droplet distribution is correlated with obesity. Obesity-associated adipocyte death exhibits feature of necrosis-like programmed cell death. NOD-like receptors family pyrin domain containing 3 (NLRP3) inflammasome-dependent caspase-1 activation in hypertrophic adipocytes induces obese adipocyte death by pyroptosis. Actually adipocyte death may be a prerequisite for the transition from hypertrophic to hyperplastic obesity. Major transcriptional factors, CCAAT/enhancer-binding proteins beta and delta, play a central role in the subsequent induction of critical regulators, peroxisome-proliferator-activated receptor gamma, CCAAT/enhancer-binding protein alpha and sterol regulatory element-binding protein 1, in the transcriptional control of adipogenesis in obesity.Collectively, in this chapter the concept of adipose tissue remodeling in response to adipocyte death or adipogenesis, and the complexity of lipid droplet interactions with the other cellular organelles are reviewed. Furthermore, in addition to lipid droplet growth, the functional link between the adipocyte-specific lipid droplet-associated protein and fatty acid turn-over is also debated.

Vitamin D Insufficiency Exacerbates Adipose Tissue Macrophage Infiltration and Decreases AMPK/SIRT1 Activity in Obese Rats

Obesity is recognized as a state of chronic low-grade systemic inflammation due to adipose tissue macrophage infiltration and production of proinflammatory adipokines. Decreased vitamin D status is associated with obesity. The specific aim of the present study is to investigate the effects of vitamin D on obesity-induced adipose tissue inflammation. Male Sprague-Dawley rats were randomized and fed a normal diet (NOR, 1000 IU vitamin D/kg diet), a 45% high-fat diet (HF, 1000 IU vitamin D/kg diet), or a 45% high-fat diet containing 25 IU vitamin D/kg diet (HF+LVD) for 12 weeks. The vitamin D-insufficient diet (HF+LVD) led to vitamin D inadequacy as determined by serum 25(OH)D level, 68.56 ± 7.97 nmol/L. The HF+LVD group exacerbated HF-increased adipocyte size, adipogenic gene expression of PPARγ, adipose tissue macrophage recruitment, and proinflammatory cytokine IL-6 and TNFα levels in epididymal white adipose tissue. In addition, vitamin D insufficiency significantly decreased mRNA levels of β-oxidation-related genes such as CPT1α, PGC1α, PPARα, VLCAD, LCAD, MCAD, and UCP1. Moreover, significant decrements of SIRT1 and AMPK activity were noted in obese rats fed with a vitamin D-insufficient diet. The observed deleterious effects of vitamin D insufficiency on adipose tissue expansion, immune cell infiltration and inflammatory status suggest vitamin D plays a beneficial role in adipocyte metabolic metabolism and obesity progression. SIRT1 and AMPK activity may play a role in the mechanism of vitamin D action.

Bardoxolone Methyl Prevents Mesenteric Fat Deposition and Inflammation in High-Fat Diet Mice

Mesenteric fat belongs to visceral fat. An increased deposition of mesenteric fat contributes to obesity associated complications such as type 2 diabetes and cardiovascular diseases. We have investigated the therapeutic effects of bardoxolone methyl (BARD) on mesenteric adipose tissue of mice fed a high-fat diet (HFD). Male C57BL/6J mice were administered oral BARD during HFD feeding (HFD/BARD), only fed a high-fat diet (HFD), or fed low-fat diet (LFD) for 21 weeks. Histology and immunohistochemistry were used to analyse mesenteric morphology and macrophages, while Western blot was used to assess the expression of inflammatory, oxidative stress, and energy expenditure proteins. Supplementation of drinking water with BARD prevented mesenteric fat deposition, as determined by a reduction in large adipocytes. BARD prevented inflammation as there were fewer inflammatory macrophages and reduced proinflammatory cytokines (interleukin-1 beta and tumour necrosis factor alpha). BARD reduced the activation of extracellular signal-regulated kinase (ERK) and Akt, suggesting an antioxidative stress effect. BARD upregulates energy expenditure proteins, judged by the increased activity of tyrosine hydroxylase (TH) and AMP-activated protein kinase (AMPK) and increased peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), and uncoupling protein 2 (UCP2) proteins. Overall, BARD induces preventive effect in HFD mice through regulation of mesenteric adipose tissue.

Inflammation and intracellular metabolism: new targets in OA

Articular cartilage degeneration is hallmark of osteoarthritis (OA). Low-grade chronic inflammation in the joint can promote OA progression. Emerging evidence indicates that bioenergy sensors couple metabolism with inflammation to switch physiological and clinical phenotypes. Changes in cellular bioenergy metabolism can reprogram inflammatory responses, and inflammation can disturb cellular energy balance and increase cell stress. AMP-activated protein kinase (AMPK) and sirtuin 1 (SIRT1) are two critical bioenergy sensors that regulate energy balance at both cellular and whole-body levels. Dysregulation of AMPK and SIRT1 has been implicated in diverse human diseases and aging. This review reveals recent findings on the role of AMPK and SIRT1 in joint tissue homeostasis and OA, with a focus on how AMPK and SIRT1 in articular chondrocytes modulate intracellular energy metabolism during stress responses (e.g., inflammatory responses) and how these changes dictate specific effector functions, and discusses translational significance of AMPK and SIRT1 as new therapeutic targets for OA.

Rutin Increases Muscle Mitochondrial Biogenesis with AMPK Activation in High-Fat Diet-Induced Obese Rats

Decreased mitochondrial number and dysfunction in skeletal muscle are associated with obesity and the progression of obesity-associated metabolic disorders. The specific aim of the current study was to investigate the effects of rutin on mitochondrial biogenesis in skeletal muscle of high-fat diet-induced obese rats. Supplementation with rutin reduced body weight and adipose tissue mass, despite equivalent energy intake (p < 0.05). Rutin significantly increased mitochondrial size and mitochondrial DNA (mtDNA) content as well as gene expression related to mitochondrial biogenesis, such as peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), nuclear respiratory factor-1 (NRF-1), transcription factor A (Tfam), and nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, sirtulin1 (SIRT1) in skeletal muscle (p < 0.05). Moreover, rutin consumption increased muscle adenosine monophosphate-activated protein kinase (AMPK) activity by 40% (p < 0.05). Taken together, these results suggested at least partial involvement of muscle mitochondria and AMPK activation in the rutin-mediated beneficial effect on obesity.

Effect of high hydrostatic pressure extract of fresh ginseng on adipogenesis in 3T3-L1 adipocytes

BACKGROUND

Red ginseng is produced by steaming and drying fresh ginseng. Through this processing, chemical compounds are modified, and then biological activities are changed. In the food-processing industry, high hydrostatic pressure (HHP) has become an alternative to heat processing to make maximum use of bioactive compounds in food materials. This study comparatively investigated the anti-adipogenic effects of water extract of red ginseng (WRG) and high hydrostatic pressure extract of fresh ginseng (HPG) in 3T3-L1 adipocytes.

RESULTS

Both WRG and HPG inhibited the accumulation of intracellular lipids and triglycerides, and the activity of glycerol-3-phosphate dehydrogenase (GPDH), a key enzyme in triglyceride biosynthesis. Intracellular lipid content and GPDH activity were significantly lower in the HPG group compared to the WRG group. In addition, mRNA expression of adipogenic genes, including CEBP-α, SREBP-1c and aP2, were lower in HPG-treated cells compared to WRG-treated cells. HPG significantly increased the activity of AMPK, and WRG did not.

CONCLUSION

Results suggested that HPG may have superior beneficial effects on the inhibition of adipogenesis compared with WRG. The anti-adipogenic effects of HPG were partially associated with the inhibition of GPDH activity, suppression of adipogenic gene expression and activation of AMPK in 3T3-L1 adipocytes.

Development of radiometric assays for quantification of enzyme activities of the key enzymes of thyroid hormones metabolism

We newly elaborated and adapted several radiometric enzyme assays for the determination of activities of the key enzymes engaged in the biosynthesis (thyroid peroxidase, TPO) and metabolic transformations (conjugating enzymes and iodothyronine deiodinases, IDs) of thyroid hormones (THs) in the thyroid gland and in peripheral tissues, especially in white adipose tissue (WAT). We also elaborated novel, reliable radiometric methods for extremely sensitive determination of enzyme activities of IDs of types 1, 2 and 3 in microsomal fractions of different rat and human tissues, as well as in homogenates of cultured mammalian cells. The use of optimized TLC separation of radioactive products from the unconsumed substrates and film-less autoradiography of radiochromatograms, taking advantage of storage phosphor screens, enabled us to determine IDs enzyme activities as low as 10(-18) katals. In studies of the interaction of fluoxetine (Fluox) with the metabolism of THs, we applied adapted radiometric enzyme assays for iodothyronine sulfotransferases (ST) and uridine 5'-diphospho-glucuronyltransferase (UDP-GT). Fluox is the most frequently used representative of a new group of non-tricyclic antidepressant drugs--selective serotonin re-uptake inhibitors. We used the elaborated assays for quantification the effects of Fluox and for the assessment of the degree of potential induction of rat liver ST and/or UDP-GT enzyme activities by Fluox alone or in combination with T(3). Furthermore, we studied possible changes in IDs activities in murine adipose tissue under the conditions that promoted either tissue hypertrophy (obesogenic treatment) or involution (caloric restriction), and in response to leptin, using our newly developed radiometric enzyme assays for IDs. Our results suggest that deiodinase D1 has a functional role in WAT, with D1 possibly being involved in the control of adipose tissue metabolism and/or accumulation of the tissue. Significant positive correlation between specific enzyme activity of D1 in WAT and plasma leptin levels was found. The newly developed and adapted radiometric enzyme assays proved to be very useful tools for studies of factors modulating THs metabolism, not only in model animals but also in clinical studies of human obesity.

Longitudinal profiling of the tissue-specific expression of genes related with insulin sensitivity in dairy cows during lactation focusing on different fat depots

In dairy cows the milk associated energy output in early lactation exceeds the input via voluntary feed intake. To spare glucose for mammary lactose synthesis, peripheral insulin sensitivity (IS) is reduced and fat mobilization is stimulated. For these processes a link between IS and the endocrine functions of adipose tissue (AT) is likely; we thus aimed to characterise the mRNA expression from bovine AT derived proteins and receptors that are related to IS according to the literature in metabolically active tissues plus systemic IS throughout lactation. Conjugated linoleic acids (CLA) reduce milk fat thus decreasing the milk drain of energy and potentially dampening lipolysis, but may also affect IS. Subcutaneous (s.c.) AT and liver from pluriparous cows receiving either control fat or CLA supplement (100 g/day from 1 to 182 days in milk each) were biopsied covering week -3 to 36 relative to parturition. In an additional trial with primiparous cows treated analogously and slaughtered on days in milk 1, 42 or 105, samples from liver, udder, skeletal muscle and 3 visceral and 3 s.c. AT were obtained and assayed for mRNA abundance of adiponectin, its receptors, leptin, leptin receptor, PPARγ, PPARγ2, IL-6, and TNF-α. In pluriparous animals, the mRNA abundance of most of the target genes decreased after parturition in s.c. AT but increased in liver. In primiparous cows, AT depot specific differences were mostly related to retroperitoneal AT; adiponectin receptor 1 and TNF-α were affected predominantly. CLA effects in primiparous cows were largely limited to decreased PPARγ2 mRNA abundance in udder tissue. In pluriparous cows, insulin secretion was increased by CLA resulting in decreased systemic IS but without consistent changes in tissue target mRNA abundance. The temporal gene expression profiles from the adipokines and related receptors support their coactive function in adapting to the needs of lactation.

Nicotinamide, a glucose-6-phosphate dehydrogenase non-competitive mixed inhibitor, modifies redox balance and lipid accumulation in 3T3-L1 cells

AIMS

Excessive energy uptake of dietary carbohydrates results in their storage as fat and requires glucose-6-phosphate dehydrogenase (G6PD)-mediated NADPH production. We sought to assess whether the nicotinamide-induced reduction of G6PD activity might modulate redox balance and lipid accumulation in 3T3-L1 cells.

MAIN METHODS

3T3-L1 preadipocytes (days 4 and 6 of differentiation) and adipocytes were cultured in the presence of 5 or 25 mM glucose. The cells cultured in 25 mM glucose were supplemented with nicotinamide (5-15 mM). Next, we evaluated the following parameters: cell viability, apoptosis, lipid accumulation, lipolysis, reducing power, reactive oxygen species (ROS), NAD(P)H and NAD(P)(+), isocitrate dehydrogenase (IDP), malic enzyme and G6PD, as well as the protein and mRNA levels of G6PD. We also analysed the kinetics of the nicotinamide-induced inhibition of G6PD.

KEY FINDINGS

G6PD mRNA levels increased at day 4 of adipocyte differentiation, whereas G6PD activity progressively increased at days 4 and 6 of differentiation and was reduced in adipocytes. Concomitantly, ROS, reducing power and lipid accumulation increased gradually as the preadipocytes matured into adipocytes. High glucose increased the activity of G6PD, which coincided with an increase in ROS, reducing power and lipid accumulation. All of these changes are prevented by nicotinamide, with the exception of lipid accumulation in adipocytes. Nicotinamide increased IDP activity without affecting NADPH levels. Lastly, nicotinamide inhibited G6PD in a non-competitive mixed way.

SIGNIFICANCE

Nicotinamide modulates G6PD via a non-competitive mixed inhibition and decreases high glucose-dependent oxidative stress and lipid accumulation. Nicotinamide maintains NADPH levels by increasing the activity of IDP.

Anti-obesity efficacy of nanoemulsion oleoresin capsicum in obese rats fed a high-fat diet

PURPOSE

This study determined the effects of oleoresin capsicum (OC) and nanoemulsion OC (NOC) on obesity in obese rats fed a high-fat diet.

METHODS

THE RATS WERE RANDOMLY SEPARATED INTO THREE GROUPS: a high-fat (HF) diet group, HF + OC diet group, and HF + NOC diet group. All groups were fed the diet and water ad libitum for 14 weeks.

RESULTS

NOC reduced the body weight and adipose tissue mass, whereas OC did not. OC and NOC reduced mRNA levels of adipogenic genes, including peroxisome proliferator-activated receptor (PPAR)-γ, sterol regulatory element-binding protein-1c, and fatty acid-binding protein in white adipose tissue. The mRNA levels of genes related to β-oxidation or thermogenesis including PPAR-α, palmitoyltransferase-1α, and uncoupling protein-2 were increased by the OC and NOC relative to the HF group. Both OC and NOC clearly stimulated AMP-activated protein kinase (AMPK) activity. In particular, PPAR-α, palmitoyltransferase-1α, uncoupling protein-2 expression, and AMPK activity were significantly increased in the NOC group compared to in the OC group. NOC decreased glycerol-3-phosphate dehydrogenase activity whereas OC did not.

CONCLUSION

From these results, NOC could be suggested as a potential anti-obesity agent in obese rats fed a HF diet. The effects of the NOC on obesity were associated with changes of multiple gene expression, activation of AMPK, and inhibition of glycerol-3-phosphate dehydrogenase in white adipose tissue.

Lipolysis in early lactation is associated with an increase in phosphorylation of adenosine monophosphate-activated protein kinase (AMPK)α1 in adipose tissue of dairy cows

Adenosine monophosphate-activated protein kinase (AMPK)α1 is activated in the context of triacylglycerol hydrolysis in adipose tissue in monogastric animals. This study describes AMPKα1 protein expression and the occurrence of its phosphorylated form (pAMPKα1) in different adipose tissue depots as influenced by time and postpartum diet in dairy cows. Biopsy samples were obtained from subcutaneous (SCAT) and retroperitoneal (RPAT) adipose tissues of 20 Holstein cows 21 d prepartum (ap) and 1 and 21 d postpartum (pp). After d 1 pp, cows were randomly assigned to 2 groups (n=10) and fed different amounts of concentrate until the third biopsy sampling at 21 d pp. Protein expression of AMPK and the extent of its phosphorylation in adipose tissue were measured by semiquantitative Western blotting. Results were not influenced by postpartum feeding. Therefore, both groups were pooled and data analyzed together. Expression of AMPKα1 in SCAT showed a decrease over time, resulting in lower expression at 1d pp compared with 21 d ap. Expression in RPAT was maintained over time. Phosphorylation increased in SCAT, showing a greater extent of phosphorylation at d 21 pp compared with 21 d ap. In RPAT, this could be seen as a trend. The proportion of pAMPKα1 to AMPKα1 significantly increased over time in both tissues. In the first adipose tissue sampling (21 d ap), AMPKα1 protein expression and extent of phosphorylation were significantly higher in RPAT than in SCAT. Lipolysis in early lactation of dairy cows was associated with an increase in phosphorylation of AMPKα1 and ratio of pAMPKα1 to AMPKα1 in bovine adipose tissues. This indicates that AMPKα1 may be involved in the regulation of energy metabolism of bovine adipose tissues.

AMP-activated protein kinase: an emerging drug target to regulate imbalances in lipid and carbohydrate metabolism to treat cardio-metabolic diseases

The adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor of energy metabolism at the cellular as well as whole-body level. It is activated by low energy status that triggers a switch from ATP-consuming anabolic pathways to ATP-producing catabolic pathways. AMPK is involved in a wide range of biological activities that normalizes lipid, glucose, and energy imbalances. These pathways are dysregulated in patients with metabolic syndrome (MetS), which represents a clustering of major cardiovascular risk factors including diabetes, lipid abnormalities, and energy imbalances. Clearly, there is an unmet medical need to find a molecule to treat alarming number of patients with MetS. AMPK, with multifaceted activities in various tissues, has emerged as an attractive drug target to manage lipid and glucose abnormalities and maintain energy homeostasis. A number of AMPK activators have been tested in preclinical models, but many of them have yet to reach to the clinic. This review focuses on the structure-function and role of AMPK in lipid, carbohydrate, and energy metabolism. The mode of action of AMPK activators, mechanism of anti-inflammatory activities, and preclinical and clinical findings as well as future prospects of AMPK as a drug target in treating cardio-metabolic disease are discussed.

Methyl cinnamate inhibits adipocyte differentiation via activation of the CaMKK2-AMPK pathway in 3T3-L1 preadipocytes

Methyl cinnamate, an active component of Zanthoxylum armatum , is a widely used natural flavor compound with antimicrobial and tyrosinase inhibitor activities. However, the underlying bioactivity and molecular mechanisms of methyl cinnamate on adipocyte function and metabolism remain unclear. The aim of this study was to investigate the inhibitory effect of methyl cinnamate on adipogenesis in 3T3-L1 preadipocytes. Methyl cinnamate markedly suppressed triglyceride accumulation associated with down-regulation of adipogenic transcription factor expression, including sterol regulatory element binding protein-1 (SREBP-1), peroxisome proliferator-activated receptor γ (PPARγ), and CCAAT/enhancer-binding protein α (C/EBPα). Additionally, methyl cinnamate-inhibited PPARγ activity and adipocyte differentiation were partially reversed by the PPARγ agonist troglitazone. Furthermore, methyl cinnamate stimulated Ca(2+)/calmodulin-dependent protein kinase kinase 2 (CaMKK2) and phospho-AMP-activated protein kinase (AMPK) expression during adipogenesis. This study first revealed methyl cinnamate has antiadipogenic activity through mechanisms mediated, in part, by the CaMKK2-AMPK signaling pathway in 3T3-L1 cells.

Low density lipoprotein (LDL) receptor-related protein 6 (LRP6) regulates body fat and glucose homeostasis by modulating nutrient sensing pathways and mitochondrial energy expenditure

Body fat, insulin resistance, and type 2 diabetes are often linked together, but the molecular mechanisms that unify their association are poorly understood. Wnt signaling regulates adipogenesis, and its altered activity has been implicated in the pathogenesis of type 2 diabetes and metabolic syndrome. LRP6(+/-) mice on a high fat diet were protected against diet-induced obesity and hepatic and adipose tissue insulin resistance compared with their wild-type (WT) littermates. Brown adipose tissue insulin sensitivity and reduced adiposity of LRP6(+/-) mice were accounted for by diminished Wnt-dependent mTORC1 activity and enhanced expression of brown adipose tissue PGC1-α and UCP1. LRP6(+/-) mice also exhibited reduced endogenous hepatic glucose output, which was due to diminished FoxO1-dependent expression of the key gluconeogenic enzyme glucose-6-phosphatase (G6pase). In addition, in vivo and in vitro studies showed that loss of LRP6 allele is associated with increased leptin receptor expression, which is a likely cause of hepatic insulin sensitivity in LRP6(+/-) mice. Our study identifies LRP6 as a nutrient-sensitive regulator of body weight and glucose metabolism and as a potential target for pharmacological interventions in obesity and diabetes.

Augmenting energy expenditure by mitochondrial uncoupling: a role of AMP-activated protein kinase

Strategies to prevent and treat obesity aim to decrease energy intake and/or increase energy expenditure. Regarding the increase of energy expenditure, two key intracellular targets may be considered (1) mitochondrial oxidative phosphorylation, the major site of ATP production, and (2) AMP-activated protein kinase (AMPK), the master regulator of cellular energy homeostasis. Experiments performed mainly in transgenic mice revealed a possibility to ameliorate obesity and associated disorders by mitochondrial uncoupling in metabolically relevant tissues, especially in white adipose tissue (WAT), skeletal muscle (SM), and liver. Thus, ectopic expression of brown fat-specific mitochondrial uncoupling protein 1 (UCP1) elicited major metabolic effects both at the cellular/tissue level and at the whole-body level. In addition to expected increases in energy expenditure, surprisingly complex phenotypic effects were detected. The consequences of mitochondrial uncoupling in WAT and SM are not identical, showing robust and stable obesity resistance accompanied by improvement of lipid metabolism in the case of ectopic UCP1 in WAT, while preservation of insulin sensitivity in the context of high-fat feeding represents the major outcome of muscle UCP1 expression. These complex responses could be largely explained by tissue-specific activation of AMPK, triggered by a depression of cellular energy charge. Experimental data support the idea that (1) while being always activated in response to mitochondrial uncoupling and compromised intracellular energy status in general, AMPK could augment energy expenditure and mediate local as well as whole-body effects; and (2) activation of AMPK alone does not lead to induction of energy expenditure and weight reduction.

A new era for brown adipose tissue: New insights into brown adipocyte function and differentiation

Until quite recently, brown adipose tissue was considered of metabolic significance only in small mammals and human newborns, since it was thought to disappear rapidly after birth in humans. However, nowadays this tissue is known to play a role in the regulation of energy balance not only in rodents, but also in humans. In this review we highlight new features regarding brown adipose tissue origin and function and revise old paradigms about brown adipocyte differentiation.

The cannabinoid receptor agonist THC attenuates weight loss in a rodent model of activity-based anorexia

Anorexia nervosa (AN) is characterized by anhedonia whereby patients experience little pleasure or reward in many aspects of their lives. Reward pathways and the endocannabionid system have been implicated in the mediation of food intake. The potential to exploit these systems to reverse weight loss is investigated in a rodent model of activity-based anorexia (ABA). The effect of subchronic (6 days) Δ(9)-tetrahydrocannabinol (THC) treatment (0.1, 0.5, or 2.0 mg/kg/day) was assessed on chow and high-fat diet (HFD) intake, body weight, running wheel activity (RWA) as well as thermogenesis in brown adipose tissue (BAT) and lipid metabolism in white adipose tissue (WAT). Limited time availability of food and continuous access to running wheels led to anorexia and significantly reduced body weight. THC treatment (0.5 and 2.0 mg/kg/day) transiently stimulated chow intake with a moderate effect on RWA. THC (2.0 mg/kg/day) significantly reduced body weight loss and shifted markers of thermogenesis in BAT and lipid metabolism in WAT in directions consistent with reduced energy expenditure and lipolysis. THC (2.0 mg/kg/day) combined with HFD, produced a transient increase in food intake, reduction in RWA, attenuation of body weight loss, and changes in markers of thermogensis in BAT and lipolysis in the WAT. These changes were significantly greater than those seen in vehicle (HFD), vehicle (chow), and THC (chow)-treated animals. These data show for the first time the effectiveness of the endocannabinoid system in attenuating the weight loss associated with the development of ABA via a mechanism involving reduced energy expenditure.

Proadipogenic effects of lactoferrin in human subcutaneous and visceral preadipocytes

Lactoferrin has been associated with insulin sensitivity in vivo and in vitro studies. We aimed to test the effects of lactoferrin on human subcutaneous and visceral preadipocytes. Human subcutaneous and visceral preadipocytes were cultured with increasing lactoferrin (hLf, 0.1, 1, 10 μM) under differentiation conditions. The effects of lactoferrin on adipogenesis were studied through the expression of different adipogenic and inflammatory markers, AMPK activation and Retinoblastoma 1 (RB1) activity. The response to insulin was evaluated through (Ser473)AKT phosphorylation. In both subcutaneous and visceral preadipocytes, lactoferrin (1 and 10 μM) increased adipogenic gene expressions and protein levels (fatty acid synthase, PPARγ, FABP4, ADIPOQ, ACC and STAMP2) and decreased inflammatory markers (IL8, IL6 and MCP1) dose-dependently in parallel to increased insulin-induced (Ser473)AKT phosphorylation. In addition to these adipogenic effects, lactoferrin decreased significantly AMPK activity (reducing (pThr172)AMPK and (pSer79)ACC) and RB1 activity (increasing the (pser807/811)RB1/RB1 ratio). In conclusion, these results suggest that lactoferrin promotes adipogenesis in human adipocytes by enhancing insulin signaling and inhibiting RB1 and AMPK activities.

Central infusion of leptin does not increase AMPK signaling in skeletal muscle of sheep

In sheep, central leptin infusion reduces food intake and increases energy expenditure in adipose tissue and skeletal muscle. The mechanisms for these peripheral effects of central leptin in sheep are not known but, on the basis of rodent studies, may involve AMPK. In mice, central leptin acutely increases both skeletal muscle AMPK activation and glucose uptake. Thus, to investigate whether these effects exist in higher-order mammals, ovariectomized Corriedale ewes (n = 4 per group) received a continuous lateral ventricular infusion (60 μl/h) of either leptin (50 μg/h) or artificial cerebrospinal fluid (aCSF; CON) for 8 days. Tritiated glucose (3-(3)H-glucose) was infused intravenously for calculation of whole body glucose turnover during both acute (6 h) and chronic (7-8 days) leptin/aCSF infusion. Muscle biopsies were also obtained. Leptin infusion reduced (P < 0.05) food intake and body weight, and it also increased plasma epinephrine concentration at 6 h and 7 days, suggesting increased sympathetic nerve activity. Despite this, and in contrast to rodent studies, central leptin infusion did not increase skeletal muscle AMPKα Thr(172) phosphorylation or ACCβ Ser(221) phosphorylation. Surprisingly, the glucose rate of appearance (glucose Ra) and rate of disappearance (glucose Rd) were reduced by both acute and chronic leptin infusion. Direct infusion of the AMPK activator 5-aminoimidazole-4-carboxyamide-ribonucleoside (AICAR) into the femoral artery increased skeletal muscle AMPK phosphorylation. In conclusion, although central leptin infusion in sheep caused the predicted reduction in food intake and increases plasma epinephrine concentration, it had no effect on AMPK activation in skeletal muscle and actually reduced glucose disposal. This suggests that there are species differences in the peripheral responses to central leptin infusion.

Beta-arrestin inhibits CAMKKbeta-dependent AMPK activation downstream of protease-activated-receptor-2

Background

Proteinase-activated-receptor-2 (PAR₂) is a seven transmembrane receptor that can activate two separate signaling arms: one through Gαq and Ca²⁺ mobilization, and a second through recruitment of β-arrestin scaffolds. In some cases downstream targets of the Gαq/Ca²⁺ signaling arm are directly inhibited by β-arrestins, while in other cases the two pathways are synergistic; thus β-arrestins act as molecular switches capable of modifying the signal generated by the receptor.

Results

Here we demonstrate that PAR₂ can activate adenosine monophosphate-activated protein kinase (AMPK), a key regulator of cellular energy balance, through Ca²⁺-dependent Kinase Kinase β (CAMKKβ), while inhibiting AMPK through interaction with β-arrestins. The ultimate outcome of PAR₂ activation depended on the cell type studied; in cultured fibroblasts with low endogenous β-arrestins, PAR₂ activated AMPK; however, in primary fat and liver, PAR₂ only activated AMPK in β-arrestin-2^-/- mice. β-arrestin-2 could be co-immunoprecipitated with AMPK and CAMKKβ under baseline conditions from both cultured fibroblasts and primary fat, and its association with both proteins was increased by PAR₂ activation. Addition of recombinant β-arrestin-2 to in vitro kinase assays directly inhibited phosphorylation of AMPK by CAMKKβ on Thr172.

Conclusions

Studies have shown that decreased AMPK activity is associated with obesity and Type II Diabetes, while AMPK activity is increased with metabolically favorable conditions and cholesterol lowering drugs. These results suggest a role for β-arrestin in the inhibition of AMPK signaling, raising the possibility that β-arrestin-dependent PAR₂ signaling may act as a molecular switch turning a positive signal to AMPK into an inhibitory one.

The role of mitochondria in the pathogenesis of type 2 diabetes

The pathophysiology of type 2 diabetes mellitus (DM) is varied and complex. However, the association of DM with obesity and inactivity indicates an important, and potentially pathogenic, link between fuel and energy homeostasis and the emergence of metabolic disease. Given the central role for mitochondria in fuel utilization and energy production, disordered mitochondrial function at the cellular level can impact whole-body metabolic homeostasis. Thus, the hypothesis that defective or insufficient mitochondrial function might play a potentially pathogenic role in mediating risk of type 2 DM has emerged in recent years. Here, we summarize current literature on risk factors for diabetes pathogenesis, on the specific role(s) of mitochondria in tissues involved in its pathophysiology, and on evidence pointing to alterations in mitochondrial function in these tissues that could contribute to the development of DM. We also review literature on metabolic phenotypes of existing animal models of impaired mitochondrial function. We conclude that, whereas the association between impaired mitochondrial function and DM is strong, a causal pathogenic relationship remains uncertain. However, we hypothesize that genetically determined and/or inactivity-mediated alterations in mitochondrial oxidative activity may directly impact adaptive responses to overnutrition, causing an imbalance between oxidative activity and nutrient load. This imbalance may lead in turn to chronic accumulation of lipid oxidative metabolites that can mediate insulin resistance and secretory dysfunction. More refined experimental strategies that accurately mimic potential reductions in mitochondrial functional capacity in humans at risk for diabetes will be required to determine the potential pathogenic role in human insulin resistance and type 2 DM.

Differences in AMPK expression between subcutaneous and visceral adipose tissue in morbid obesity

Adenine monophosphate (AMP) activated protein kinase (AMPK) is an important regulator of obesity. The objective of the present work was to study and compare AMPK protein expression in visceral vs. subcutaneous adipose tissue of morbid obese subjects and to correlate it with adipose tissue characteristics. We selected a total population of 17 extreme obese (BMI>or=40 kg/m2) aged 42.8+/-10.2 years were included in this study. We measured anthropometric and body composition parameters. Adiponectin expression by qRT-PCR, isoproterenol-stimulated lipolytic rates, and AMPK alpha subunits expression by Western blot in adipose tissue explants were determined. Finally plasma concentrations of glucose, triacylglycerols, total cholesterol, HDL-c, LDL-c and insulin were also measured. Our results showed that AMPK alpha expression was higher in subcutaneous than in visceral tissue. A positive correlation between AMPK expression and adiponectin expression in human subcutaneous adipose tissue was observed. Furthermore, a positive correlation between AMPK expression and isoproterenol evoked upregulation of lipolysis rate was also observed. In conclusion, AMPK alpha expression differed according to adipose tissue location. The positive correlation between subcutaneous adipose tissue AMPK and adiponectin or the evoked lipolysis rate could indicate a protective role of AMPK in this tissue, counteracting insulin resistance in morbid obese patients.

Aging-related gene expression in hippocampus proper compared with dentate gyrus is selectively associated with metabolic syndrome variables in rhesus monkeys

Age-dependent metabolic syndrome (MetS) is a well established risk factor for cardiovascular disease, but it also confers major risk for impaired cognition in normal aging or Alzheimer's disease (AD). However, little is known about the specific pathways mediating MetS-brain interactions. Here, we performed the first studies quantitatively linking MetS variables to aging changes in brain genome-wide expression and mitochondrial function. In six young adult and six aging female rhesus monkeys, we analyzed gene expression in two major hippocampal subdivisions critical for memory/cognitive function [hippocampus proper, or cornu ammonis (CA), and dentate gyrus (DG)]. Genes that changed with aging [aging-related genes (ARGs)] were identified in each region. Serum variables reflecting insulin resistance and dyslipidemia were used to construct a quantitative MetS index (MSI). This MSI increased with age and correlated negatively with hippocampal mitochondrial function (state III oxidation). More than 2000 ARGs were identified in CA and/or DG, in approximately equal numbers, but substantially more ARGs in CA than in DG were correlated selectively with the MSI. Pathways represented by MSI-correlated ARGs were determined from the Gene Ontology Database and literature. In particular, upregulated CA ARGs representing glucocorticoid receptor (GR), chromatin assembly/histone acetyltransferase, and inflammatory/immune pathways were closely associated with the MSI. These results suggest a novel model in which MetS is associated with upregulation of hippocampal GR-dependent transcription and epigenetic coactivators, contributing to decreased mitochondrial function and brain energetic dysregulation. In turn, these MSI-associated neuroenergetic changes may promote inflammation, neuronal vulnerability, and risk of cognitive impairment/AD.

Multiple molecular targets underlie the antidiabetic effect of Nigella sativa seed extract in skeletal muscle, adipocyte and liver cells

AIM

Nigella sativa (N. sativa) is a plant widely used in traditional medicine of North African countries. During the last decade, several studies have shown that extracts from the seeds of N. sativa have antidiabetic effects.

METHODS

Our group has recently demonstrated that N. sativa seed ethanol extract (NSE) induces an important insulin-like stimulation of glucose uptake in C2C12 skeletal muscle cells and 3T3-L1 adipocytes following an 18 h treatment. The purpose of the present study was to elucidate the pathways mediating this insulin-like effect and the mechanisms through which these pathways are activated.

RESULTS

Results from western immunoblot experiments indicate that in C2C12 cells as well as in H4IIE hepatocytes, but not in 3T3-L1 cells, NSE increases activity of Akt, a key mediator of the effects of insulin, and activity of AMP-activated protein kinase (AMPK), a master metabolic regulating enzyme. To test whether the activation of AMPK resulted from a disruption of mitochondrial function, the effects of NSE on oxygen consumption were assessed in isolated liver mitochondria. NSE was found to exhibit potent uncoupling activity.

CONCLUSION

Finally, to provide an explanation for the effects of NSE in adipocytes, PPARgamma stimulating activity was tested using a reporter gene assay. Results indicate that NSE behaves as an agonist of PPARgamma. The data supports the ethnobotanical use of N. sativa seed oil as a treatment for diabetes, and suggests potential uses of this product, or compounds derived thereof, against obesity and the metabolic syndrome.

Transcription factor AP-2beta inhibits expression and secretion of leptin, an insulin-sensitizing hormone, in 3T3-L1 adipocytes

BACKGROUND

We have previously reported an association between the activator protein-2beta (AP-2beta) transcription factor gene and type 2 diabetes. This gene is preferentially expressed in adipose tissue, and subjects with a disease-susceptible allele of AP-2beta showed stronger AP-2beta expression in adipose tissue than those without the susceptible allele. Furthermore, overexpression of AP-2beta led to lipid accumulation and induced insulin resistance in 3T3-L1 adipocytes.

RESULT

We found that overexpression of AP-2beta in 3T3-L1 adipocytes decreased the promoter activity of leptin, and subsequently decreased both messenger RNA (mRNA) and protein expression and secretion. Furthermore, knockdown of endogenous AP-2beta by RNA-interference increased mRNA and protein expression of leptin. Electrophoretic mobility shift and chromatin immunoprecipitation assays revealed specific binding of AP-2beta to leptin promoter regions in vitro and in vivo. In addition, site-directed mutagenesis of the AP-2-binding site located between position +34 and +42 relative to the transcription start site abolished the inhibitory effect of AP-2beta. Our results clearly showed that AP-2beta directly inhibited insulin-sensitizing hormone leptin expression by binding to its promoter.

CONCLUSION

AP-2beta modulated the expression of leptin through direct interaction with its promoter region.

Adenylate kinase and AMP signaling networks: metabolic monitoring, signal communication and body energy sensing

Adenylate kinase and downstream AMP signaling is an integrated metabolic monitoring system which reads the cellular energy state in order to tune and report signals to metabolic sensors. A network of adenylate kinase isoforms (AK1-AK7) are distributed throughout intracellular compartments, interstitial space and body fluids to regulate energetic and metabolic signaling circuits, securing efficient cell energy economy, signal communication and stress response. The dynamics of adenylate kinase-catalyzed phosphotransfer regulates multiple intracellular and extracellular energy-dependent and nucleotide signaling processes, including excitation-contraction coupling, hormone secretion, cell and ciliary motility, nuclear transport, energetics of cell cycle, DNA synthesis and repair, and developmental programming. Metabolomic analyses indicate that cellular, interstitial and blood AMP levels are potential metabolic signals associated with vital functions including body energy sensing, sleep, hibernation and food intake. Either low or excess AMP signaling has been linked to human disease such as diabetes, obesity and hypertrophic cardiomyopathy. Recent studies indicate that derangements in adenylate kinase-mediated energetic signaling due to mutations in AK1, AK2 or AK7 isoforms are associated with hemolytic anemia, reticular dysgenesis and ciliary dyskinesia. Moreover, hormonal, food and antidiabetic drug actions are frequently coupled to alterations of cellular AMP levels and associated signaling. Thus, by monitoring energy state and generating and distributing AMP metabolic signals adenylate kinase represents a unique hub within the cellular homeostatic network.

Cellular and molecular effects of n-3 polyunsaturated fatty acids on adipose tissue biology and metabolism

Adipose tissue and its secreted products, adipokines, have a major role in the development of obesity-associated metabolic derangements including Type 2 diabetes. Conversely, obesity and its metabolic sequelae may be counteracted by modulating metabolism and secretory functions of adipose tissue. LC-PUFAs (long-chain polyunsaturated fatty acids) of the n-3 series, namely DHA (docosahexaenoic acid; C(22:6n-3)) and EPA (eicosapentaenoic acid; C(20:5n-3)), exert numerous beneficial effects, such as improvements in lipid metabolism and prevention of obesity and diabetes, which partially result from the metabolic action of n-3 LC-PUFAs in adipose tissue. Recent studies highlight the importance of mitochondria in adipose tissue for the maintenance of systemic insulin sensitivity. For instance, both n-3 LC-PUFAs and the antidiabetic drugs TZDs (thiazolidinediones) induce mitochondrial biogenesis and beta-oxidation. The activation of this 'metabolic switch' in adipocytes leads to a decrease in adiposity. Both n-3 LC-PUFAs and TZDs ameliorate a low-grade inflammation of adipose tissue associated with obesity and induce changes in the pattern of secreted adipokines, resulting in improved systemic insulin sensitivity. In contrast with TZDs, which act as agonists of PPARgamma (peroxisome-proliferator-activated receptor-gamma) and promote differentiation of adipocytes and adipose tissue growth, n-3 LC-PUFAs affect fat cells by different mechanisms, including the transcription factors PPARalpha and PPARdelta. Some of the effects of n-3 LC-PUFAs on adipose tissue depend on their active metabolites, especially eicosanoids. Thus treatments affecting adipose tissue by multiple mechanisms, such as combining n-3 LC-PUFAs with either caloric restriction or antidiabetic/anti-obesity drugs, should be explored.

Mild mitochondrial uncoupling induces 3T3-L1 adipocyte de-differentiation by a PPARgamma-independent mechanism, whereas TNFalpha-induced de-differentiation is PPARgamma dependent

Impairment of mitochondrial activity affects lipid-metabolizing tissues and mild mitochondrial uncoupling has been proposed as a possible strategy to fight obesity and associated diseases. In this report, we characterized the 3T3-L1-adipocyte ;de-differentiation' induced by carbonyl cyanide (p-trifluoromethoxy)-phenylhydrazone (FCCP), a mitochondrial uncoupler. We found a decrease in triglyceride (TG) content in adipocytes incubated with this molecule. We next analyzed the expression of genes encoding adipogenic markers and effectors and compared the differentially expressed genes in adipocytes treated with FCCP or TNFalpha (a cytokine known to induce adipocyte de-differentiation). Furthermore, a significant decrease in the transcriptional activity of PPARgamma and C/EBPalpha transcription factors was found in adipocytes with impaired mitochondrial activity. However, although these modifications were also found in TNFalpha-treated adipocytes, rosiglitazone and 9-cis retinoic acid (PPARgamma and RXR ligands) were unable to prevent triglyceride loss in FCCP-treated cells. Metabolic assays also revealed that TG reduction could be mediated by a downregulation of lipid synthesis rather than an upregulation of fatty acid oxidation. Finally, lipolysis stimulated by the uncoupler also seems to contribute to the TG reduction, a process associated with perilipin A downregulation. These results highlight some new mechanisms that might potentially be involved in adipocyte de-differentiation initiated by a mitochondrial uncoupling.

Fate of fat: the role of adipose triglyceride lipase in lipolysis

Lipolysis, the coordinated catabolism of triacylglycerol (TG) stored in cellular lipid droplets, provides fatty acids, di-, and monoglycerides. These products are important energy substrates, precursors for other lipids, or lipid signaling molecules. Following their discovery by Hollenberg, C.H., Raben, M.S., and Astwood, E.B.(1961) and Vaughan, M., Berger, J.E., and Steinberg, D. (1964), hormone-sensitive lipase (HSL) and monoacylglycerol lipase stayed in the focus of research for three decades. Within the last decade, however, it became evident that the lipolytic pathway is incompletely understood. Studies on the regulation of lipolysis and the characterization of HSL-deficient mice indicated that additional previously unrecognized factors that contribute to fat catabolism must exist. This led to the discovery of the perilipin, adipophilin, Tip47 (PAT) family of lipid droplet binding proteins and the identification of a novel TG hydrolase named adipose triglyceride lipase (ATGL). This review focuses on the importance of ATGL as TG lipase within the "lipolytic machinery" and the current knowledge of molecular mechanisms that regulate ATGL activity.

Genes and networks expressed in perioperative omental adipose tissue are correlated with weight loss from Roux-en-Y gastric bypass

CONTEXT

Gastric bypass surgery is the most commonly performed bariatric surgical procedure in the United States. Variable weight loss following this relatively standardized intervention has been reported. To date, a method for reliable profiling of patients who will successfully sustain weight loss for the long term has not been established. In addition, the mechanisms of action in accomplishing major weight loss as well as the explanation for the variable weight loss have not been established.

OBJECTIVE

To examine whether gene expression in perioperative omental adipose is associated with gastric bypass-induced weight loss.

DESIGN

Cross-sectional study of gene expression in perisurgical omental adipose tissues taken/available at the time of operation and total excess weight loss (EWL).

SUBJECTS

Fifteen overweight individuals who underwent Roux-en-Y gastric bypass (RYGB) surgery at the University of California Davis Medical Center (BMI: 40.6-72.8 kg/m(2)).

MEASUREMENTS

Body weight before and following weight stabilization 18-42 months after surgery. Perioperative omental adipose RNA isolated from 15 subjects was hybridized to Affymetrix HG-U133A chips for 22,283 transcript expression measurements.

RESULTS

Downstream analysis identified a set of genes whose expression was significantly correlated with RYGB-induced weight loss. The significant individual genes include acyl-coenzyme A oxidase 1 (ACOX1), phosphodiesterase 3A cGMP-inhibited (PDE3A) and protein kinase, AMP-activated, beta 1 non-catalytic subunit (PRKAB1). Specifically, ACOX1 plays a role in fatty acid metabolism. PDE3A is involved in purine metabolism and hormone-stimulated lipolysis. PRKAB1 is involved in adipocytokine signaling pathway. Gene network analysis revealed that pathways for glycerolipid metabolism, breast cancer and apoptosis were significantly correlated with long-term weight loss.

CONCLUSION

This study demonstrates that RNA expression profiles from perioperative adipose tissue are associated with weight loss outcome following RYGB surgery. Our data suggest that EWL could be predicted from preoperative samples, which would allow for informed decisions about whether or not to proceed to surgery.

Maternal diabetes adversely affects AMP-activated protein kinase activity and cellular metabolism in murine oocytes

Maternal diabetes is associated with an increased risk of miscarriages and congenital anomalies. Preovulatory oocytes in murine models also experience maturational delay and greater granulosa cell apoptosis. The objective of this study was to examine whether maternal diabetes influences preovulatory oocyte metabolism and impacts meiotic maturation. Streptozotocin-induced diabetic B6SJLF1 mice were superovulated, and oocytes were collected at 0, 2, and 6 h after human chorionic gonadotropin (hCG) injection. Individual oocyte concentrations of ATP, 5'-AMP, glycogen, and fructose-1,6-phosphate (FBP) and enzyme activities of glucose-6-phosphate dehydrogenase (G6PDH), adenylate kinase, hydroxyacyl-CoA dehydrogenase (Hadh2), and glutamic pyruvate transaminase (Gpt2) were measured. Protein levels of phosphorylated AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) were also measured. ATP levels were significantly lower in oocytes from diabetic mice, and the percent change in the AMP-to-ATP ratio was significantly higher in these oocytes. In contrast, activities of Hadh2 and Gpt2, two enzymes activated by AMPK, were significantly less in these oocytes. Additionally, glycogen and FBP levels, both endogenous inhibitors of AMPK, were elevated. Phosphorylated ACC, a downstream target of AMPK, and phosphorylated AMPK were both decreased in diabetic oocytes, thus confirming decreased AMPK activity. Finally, addition of the activator AICAR to the in vitro maturation assay restored AMPK activity and corrected the maturation defect experienced by the oocytes from diabetic mice. In conclusion, maternal diabetes adversely alters cellular metabolism leading to abnormal AMPK activity in murine oocytes. Increasing AMPK activity in these oocytes during the preovulatory phase reverses the metabolic changes and corrects delays in meiotic maturation.

Short-term oleoyl-estrone treatment affects capacity to manage lipids in rat adipose tissue

BACKGROUND

Short-term OE (oleoyl-estrone) treatment causes significant decreases in rat weight mainly due to adipose tissue loss. The aim of this work was to determine if OE treatment affects the expression of genes that regulate lipid metabolism in white adipose tissue.

RESULTS

Gene expression in adipose tissue from female treated rats (48 hours) was analysed by hybridization to cDNA arrays and levels of specific mRNAs were determined by real-time PCR. Treatment with OE decreased the expression of 232 genes and up-regulated 75 other genes in mesenteric white adipose tissue. The use of real-time PCR validate that, in mesenteric white adipose tissue, mRNA levels for Lipoprotein Lipase (LPL) were decreased by 52%, those of Fatty Acid Synthase (FAS) by 95%, those of Hormone Sensible Lipase (HSL) by 32%, those of Acetyl CoA Carboxylase (ACC) by 92%, those of Carnitine Palmitoyltransferase 1b (CPT1b) by 45%, and those of Fatty Acid Transport Protein 1 (FATP1) and Adipocyte Fatty Acid Binding Protein (FABP4) by 52% and 49%, respectively. Conversely, Tumour Necrosis Factor (TNFalpha) values showed overexpression (198%).

CONCLUSION

Short-term treatment with OE affects adipose tissue capacity to extract fatty acids from lipoproteins and to deal with fatty acid transport and metabolism.

Lipodystrophy in HIV 1-infected patients: lessons for obesity research

Lipodystrophy is a common alteration in HIV 1-infected patients under anti-retroviral treatment. This syndrome is usually associated with peripheral lipoatrophy, central adiposity and, in some cases, lipomatosis, as well as systemic insulin resistance and hyperlipidemia. Research on the ethiopathogenesis of the disease revealed novel aspects of adipose tissue biology highly relevant to obesity research: the pivotal role of mitochondria in white adipose tissue function, the role that interference with master transcription factors of adipogenesis may have in human adipose tissue, the capacity of human white adipose tissue to acquire brown fat-like features, as well as the importance of apoptosis and the potential impact of viral infections in adipose tissue. The dramatic difference between subcutaneous adipose depots, prone to lipoatrophy, and the visceral adipose depots, prone to enlargement, has been further evidenced in the study of the lipodystrophy syndrome. The recognition of a local pro-inflammatory environment in lipoatrophic adipose tissue from affected patients, including macrophage infiltration and enhanced expression of chemokines and cytokines, points to events paradoxically similar to those in the hypertrophied adipose tissue in obesity. However, this also potentially provides an explanation for the existence of systemic alterations common to lipodystrophy and obese patients and reminiscent of the metabolic syndrome.

Triacylglycerol metabolism in adipose tissue

Triacylglycerol (TAG) in adipose tissue serves as the major energy storage form in higher eukaryotes. Obesity, resulting from excess white adipose tissue, has increased dramatically in recent years resulting in a serious public health problem. Understanding of adipocyte-specific TAG synthesis and hydrolysis is critical to the development of strategies to treat and prevent obesity and its closely associated diseases, for example, Type 2 diabetes, hypertension and atherosclerosis. In this review, we present an overview of the major enzymes in TAG synthesis and lipolysis, including the recent discovery of a novel adipocyte TAG hydrolase.

Adipose targets for obesity drug development

The prevalence of obesity is increasing rapidly in most parts of the world and effective therapeutic drugs are urgently needed. The discovery of leptin in 1994 initiated a new understanding of adipose tissue function, and adipose tissue is now known to not only store and release fatty acids, but also to produce a wealth of factors that have an impact on the regulation of body weight and blood glucose homeostasis. Also, adipocytes express proteins that engage signalling pathways playing important roles in fuel substrate and energy metabolism. These proteins constitute a diverse array of adipose target candidates for the development of drugs to treat obesity. Some of these potential targets have been validated and are now in drug development stages, providing hope that the current obesity epidemic can be addressed by effective drug treatments in the near future.