Fat cell adrenergic receptors and the control of white and brown fat cell function

Adrenergic pathway activation enhances brown adipose tissue metabolism: a [¹⁸F]FDG PET/CT study in mice

OBJECTIVE

Pharmacologic approaches to study brown adipocyte activation in vivo with a potential of being translational to humans are desired. The aim of this study was to examine pre- and postsynaptic targeting of adrenergic system for enhancing brown adipose tissue (BAT) metabolism quantifiable by [(18)F]fluoro-2-deoxyglucose ([(18)F]FDG) positron emission tomography (PET)/computed tomography (CT) in mice.

METHODS

A β₃-adrenoreceptor selective agonist (CL 316243), an adenylyl cyclase enzyme activator (forskolin) and a potent blocker of presynaptic norepinephrine transporter (atomoxetine), were injected through the tail vein of Swiss Webster mice 30 minutes before intravenous (iv) administration of [(18)F]FDG. The mice were placed on the PET/CT bed for 30 min PET acquisition followed by 10 min CT acquisition for attenuation correction and anatomical delineation of PET images.

RESULTS

Activated interscapular (IBAT), cervical, periaortic and intercostal BAT were observed in 3-dimentional analysis of [(18)F]FDG PET images. CL 316243 increased the total [(18)F]FDG standard uptake value (SUV) of IBAT 5-fold greater compared to that in placebo-treated mice. It also increased the [(18)F]FDG SUV of white adipose tissue (2.4-fold), and muscle (2.7-fold), as compared to the control. There was no significant difference in heart, brain, spleen and liver uptakes between groups. Forskolin increased [(18)F]FDG SUV of IBAT 1.9-fold greater than that in placebo-treated mice. It also increased the [(18)F]FDG SUV of white adipose tissue (2.2-fold) and heart (5.4-fold) compared to control. There was no significant difference in muscle, brain, spleen, and liver uptakes between groups. Atomoxetine increased [(18)F]FDG SUV of IBAT 1.7-fold greater than that in placebo-treated mice. There were no significant differences in all other organs compared to placebo-treated mice except liver (1.6 fold increase). A positive correlation between SUV levels of IBAT and CT Hounsfield unit (HU) (R(2)=0.55, p<0.001) and between CT HU levels of IBAT and liver (R(2)=0.69, p<0.006) was observed.

CONCLUSIONS

The three pharmacologic approaches reported here enhanced BAT metabolism by targeting different sites in adrenergic system as measured by [(18)F]FDG PET/CT.

SLC27 fatty acid transport proteins

The uptake and metabolism of long chain fatty acids (LCFA) are critical to many physiological and cellular processes. Aberrant accumulation or depletion of LCFA underlie the pathology of numerous metabolic diseases. Protein-mediated transport of LCFA has been proposed as the major mode of LCFA uptake and activation. Several proteins have been identified to be involved in LCFA uptake. This review focuses on the SLC27 family of fatty acid transport proteins, also known as FATPs, with an emphasis on the gain- and loss-of-function animal models that elucidate the functions of FATPs in vivo and how these transport proteins play a role in physiological and pathological situations.

Fetal baboon sex-specific outcomes in adipocyte differentiation at 0.9 gestation in response to moderate maternal nutrient reduction

Objective

To investigate in vitro adipocyte differentiation in baboon fetuses in response to reduced maternal nutrition.

Design

Cross-sectional comparison of adipocyte differentiation in normally grown fetuses and fetuses of pregnant baboons fed 70% control global diet from 30 days of pregnancy to term.

Subjects

Control (CTR) fetuses of ad libitum fed mothers (5 females and 5 males) and fetuses of mothers fed the 70% global diet eaten by CTR (MNR, 5 females and 5 males). The expression of genes/proteins involved in adipogenesis (PPARγ, FABP4 and adiponectin) and brown adipose tissue development (UCP1, TBX15 and COXIV) were determined in in vitro differentiated stromal-vascular cultures from subcutaneous abdominal, subcutaneous femoral, and omental adipose tissue depots. Adipocyte number per area (mm²) was determined histologically to assist in evaluating adipocyte size.

Results

Maternal suboptimal nutrition suppressed growth of male but not female fetuses and led to adipocyte hypertrophy accompanied by increased markers of white and particularly brown-type adipogenesis in male but not female fetuses.

Conclusion

Adipose tissue responses to fetal nonhuman primate under nutrition are sexually dimorphic. While female fetuses adapt adequately, males enhance pathways involved in white and brown adipose tissue development but are unable to compensate for a delayed development of adipose tissue associated with intrauterine growth restriction. These differences need to be considered when assessing developmental programming of adiposity in response to sub-optimal maternal nutrition.

Contrasts between the effects of zinc-α2-glycoprotein, a putative β3/2-adrenoceptor agonist and the β3/2-adrenoceptor agonist BRL35135 in C57Bl/6 (ob/ob) mice

Previous studies by Tisdale et al. have reported that zinc-α(2)-glycoprotein (ZAG (AZGP1)) reduces body fat content and improves glucose homeostasis and the plasma lipid profile in Aston (ob/ob) mice. It has been suggested that this might be mediated via agonism of β(3)- and possibly β(2)-adrenoceptors. We compared the effects of dosing recombinant human ZAG (100 μg, i.v.) and BRL35135 (0.5 mg/kg, i.p.), which is in rodents a 20-fold selective β(3)- relative to β(2)-adrenoceptor agonist, given once daily for 10 days to male C57Bl/6 Lep(ob)/Lep(ob) mice. ZAG, but not BRL35135, reduced food intake. BRL35135, but not ZAG, increased energy expenditure acutely and after sub-chronic administration. Only BRL35135 increased plasma concentrations of glycerol and non-esterified fatty acid. Sub-chronic treatment with both ZAG and BRL35135 reduced fasting blood glucose and improved glucose tolerance, but the plasma insulin concentration 30 min after administration of glucose was lowered only by BRL35135. Both ZAG and BRL35135 reduced β(1)-adrenoceptor mRNA levels in white adipose tissue, but only BRL35135 reduced β(2)-adrenoceptor mRNA. Both ZAG and BRL35135 reduced β(1)-adrenoceptor mRNA levels in brown adipose tissue, but neither influenced β(2)-adrenoceptor mRNA, and only BRL35135 increased β(3)-adrenoceptor and uncoupling protein-1 (UCP1) mRNA levels in brown adipose tissue. Thus, ZAG and BRL35135 had similar effects on glycaemic control and shared some effects on β-adrenoceptor gene expression in adipose tissue, but ZAG did not display the thermogenic effects of the β-adrenoceptor agonist, nor did it increase β(3)-adrenoceptor or UCP1 gene expression in brown adipose tissue. ZAG does not behave as a typical β(3/2)-adrenoceptor agonist.

Targeting presynaptic norepinephrine transporter in brown adipose tissue: a novel imaging approach and potential treatment for diabetes and obesity

Brown adipose tissue (BAT) plays a significant role in metabolism. In this study, we report the use of atomoxetine (a clinically applicable norepinephrine reuptake inhibitor) for (18)F-FDG PET imaging of BAT and its effects on heat production and blood glucose concentration. Fasted-male Sprague-Dawley rats were administered with intravenous (18)F-FDG. The same rats were treated with atomoxetine (0.1 mg/kg, i.v.) 30 min before (18)F-FDG administration. To confirm the β-adrenergic effects, propranolol (β-adrenergic inhibitor) 5 mg/kg was given intraperitoneally 30 min prior to atomoxetine administration. The effect of atomoxetine on BAT metabolism was assessed in fasted and non-fasted rats and on BAT temperature and blood glucose in fasted rats. In (18)F-FDG PET/CT images, interscapular BAT (IBAT) and other areas of BAT were clearly visualized. When rats were fasted, atomoxetine (0.1 mg/kg) increased the (18)F-FDG uptake of IBAT by factor of 24 within 30 min. Propranolol reduced the average (18)F-FDG uptake of IBAT significantly. Autoradiography of IBAT and white adipose tissue confirmed the data obtained by PET. When rats were not fasted, atomoxetine-induced increase of (18)F-FDG uptake in IBAT was delayed and occurred in 120 min. For comparison, direct stimulation of β(3)-adrenreceptors in non-fasted rats with CL-316, 243 occurred within 30 min. Atomoxetine-induced IBAT activation was associated with higher IBAT temperature and lower blood glucose. This was mediated by inhibition of norepinephrine reuptake transporters in IBAT leading to increased norepinephrine concentration in the synapse. Increased synaptic norepinephrine activates β(3)-adrenreceptors resulting in BAT hypermetabolism that is visible and quantifiable by (18)F-FDG PET/CT.

Forskolin effect on the cryosurvival of in vitro-produced bovine embryos in the presence or absence of fetal calf serum

The objective of this study was to assess the viability and cryotolerance of zebu embryos produced in vitro with or without the addition of fetal calf serum (FCS) and forskolin (F). Embryos produced in vivo were used as a control. Presumptive zygotes were cultured in modified synthetic oviductal fluid supplemented with amino acids (SOFaa), bovine serum albumin (BSA) and with (2.5%) or without (0%) FCS. On day 6 of growth, the embryos from each group were divided into treatments with or without 10 μM F to induce embryonic lipolysis, comprising a total of four experimental groups: 2.5% FCS, 0% FCS, 2.5% + F and 0% + F. For vitrification, embryos were exposed to vitrification solution 1 (5 M EG (ethylene glycol)) for 3 min and then transferred to vitrification solution 2 (7 M EG, 0.5 M galactose solution and 18% (w/v) Ficoll 70) before being introduced to liquid nitrogen. The presence of FCS in the culture medium resulted in the production of embryos with a similar rate of damaged cells compared with in vivo-produced embryos. After vitrification, the 2.5% FCS group had a significantly higher rate of damaged cells when compared with the other groups (P < 0.05). The results of this experiment indicated that the omission of FCS and the addition of forskolin do not have deleterious effect on embryo production rates. In addition, embryos produced in the presence of FCS had greater sensitivity to cryopreservation, but this effect was reversed when forskolin was added to the medium, which improved embryo survival without affecting embryo development and quality after vitrification.

The beta-1 adrenergic antagonist, atenolol, decreases acylation stimulating protein, exercise capacity and plasma free fatty acids in men with type 2 diabetes

BACKGROUND AND AIMS

Atenolol is a beta-1 adrenergic antagonist commonly prescribed for the treatment of systemic hypertension or coronary artery disease yet its use in individuals with type 2 diabetes mellitus (T2DM) is controversial due to potentially negative side effects on insulin resistance. Non-esterified fatty acid (NEFA) metabolism is altered in T2DM especially under conditions of metabolic stress such as exercise or the postprandial state. We evaluated atenolol effects on circulating NEFA and related hormones in men with T2DM during acute cardiorespiratory exercise in both the fasting and postprandial state, including the adipokine acylation stimulating protein (ASP) which stimulates adipose tissue NEFA uptake.

METHODS AND RESULTS

Ten men with T2DM underwent four 1-h exercise sessions at 60% of their maximal oxygen uptake (VO(2max)) under the following conditions: 1) fasting (F), and 2) 2 h postprandial (PP) without medication; and 3) fasting (F-Atenolol), and 4) 2 h postprandial (PP-Atenolol) after a one-week treatment with atenolol. Results were tested for the effects of atenolol via two-way ANOVA for the F vs F-Atenolol and PP vs PP-Atenolol states separately. Atenolol treatment decreased fasting and postprandial glycerol (p < 0.0001) and NEFA (p < 0.0001), postprandial epinephrine (p = 0.048), postprandial cortisol (p = 0.02), postprandial ASP (p = 0.04) and postprandial dopamine (p < 0.004).

CONCLUSION

Atenolol alters fatty acid metabolism and associated metabolic hormones including ASP during exercise in men with T2DM and its effects are more apparent during conditions of stress such as the postprandial state, acute exercise and obesity.

Secretory patterns of catecholamines in Indo-Pacific bottlenose dolphins

Catecholamines (CAs), namely adrenaline (A), noradrenaline (NA), and dopamine (DA), are secreted by the sympathoadrenal system and participate in a diverse array of functions, e.g., heat production, cardiovascular regulation, stress response and so on. However, little is known regarding peripheral CA fluctuations in cetaceans; nevertheless aquatic animals like them have needed to modify their physiological response especially for thermoregulation in water and oxygen economy during diving. To understand CA dynamism in cetaceans, diurnal changes in serum A, NA, and DA concentrations were measured during the winter and summer solstices in four Indo-Pacific bottlenose dolphins (Tursiops aduncus). The average serum NA concentration was much higher than the average A and DA concentrations, and all concentrations were higher than those reported in other cetacean species. No distinct diurnal fluctuations were observed in CA concentrations in either solstice, suggesting inhibition of the decrease in CA concentrations during nocturnal periods by the unique sleep pattern of dolphins. All the serum CA concentrations were negatively correlated with water temperature as body temperatures were, indicating that the sympathoadrenal system might be more active during winter than in summer season, suggesting a role of CA in thermoregulation.

Catestatin (chromogranin A(352-372)) and novel effects on mobilization of fat from adipose tissue through regulation of adrenergic and leptin signaling

Chromogranin A knock-out (Chga-KO) mice display increased adiposity despite high levels of circulating catecholamines and leptin. Consistent with diet-induced obese mice, desensitization of leptin receptors caused by hyperleptinemia is believed to contribute to the obese phenotype of these KO mice. In contrast, obesity in ob/ob mice is caused by leptin deficiency. To characterize the metabolic phenotype, Chga-KO mice were treated with the CHGA-derived peptide catestatin (CST) that is deficient in these mice. CST treatment reduced fat depot size and increased lipolysis and fatty acid oxidation. In liver, CST enhanced oxidation of fatty acids as well as their assimilation into lipids, effects that are attributable to the up-regulation of genes promoting fatty acid oxidation (Cpt1α, Pparα, Acox, and Ucp2) and incorporation into lipids (Gpat and CD36). CST did not affect basal or isoproterenol-stimulated cAMP production in adipocytes but inhibited phospholipase C activation by the α-adrenergic receptor (AR) agonist phenylephrine, suggesting inhibition of α-AR signaling by CST. Indeed, CST mimicked the lipolytic effect of the α-AR blocker phentolamine on adipocytes. Moreover, CST reversed the hyperleptinemia of Chga-KO mice and improved leptin signaling as determined by phosphorylation of AMPK and Stat3. CST also improved peripheral leptin sensitivity in diet-induced obese mice. In ob/ob mice, CST enhanced leptin-induced signaling in adipose tissue. In conclusion, our results implicate CST in a novel pathway that promotes lipolysis and fatty acid oxidation by blocking α-AR signaling as well as by enhancing leptin receptor signaling.

Association of adrenergic receptor gene polymorphisms with adolescent obesity in Taiwan

BACKGROUND

Polymorphisms of β2-adrenergic receptor (ADRB2) and β3-adrenergic receptor (ADRB3) have been reported to be associated with obesity in adults and adolescents, although study results have been controversial. The aim of the present study was to investigate the association of polymorphisms of ADRB2 (Arg16Gly, Gln27Glu) and ADRB3 (Trp64Arg) with adolescent obesity in Taiwan.

METHODS

A total of 559 adolescent volunteers with equal numbers female and male were enrolled. Participants were divided into two groups: obese (body mass index [BMI]≥ 95th percentile) and normal weight (BMI 15th-85th percentile). Genomic DNA was extracted from buccal mucosa cells and genotyped in TaqMan assays. Genotype results and clinical subject characteristics were analyzed.

RESULTS

Among the three ADRB polymorphisms, only Arg16Gly polymorphism was found to be significantly correlated with adolescent obesity, especially in girls. Girls with genotype Gly/Gly had a lower probability of obesity than those with genotypes Arg/Gly or Arg/Arg (P= 0.006; Arg/Gly: odds ratio [OR], 2.57, 95% confidence interval [95%CI]: 1.22-5.41; Arg/Arg: OR, 3.03, 95%CI: 1.50-6.12). Girls with genotype Gly/Gly had lower BMI than those with genotype Arg/Arg (P= 0.049). Obese adolescents with genotype Gly/Gly had a lower probability of hypertension than those with genotype Arg/Gly or Arg/Arg (P= 0.005).

CONCLUSIONS

Arg16Gly polymorphism of ADRB2 was significantly associated with obesity in female adolescents, and those with the Gly/Gly genotype were associated with a lower possibility of obesity and lower BMI. This polymorphism was also associated with a lower probability of hypertension in obese adolescents. The other two polymorphisms of ADRB (Gln27Glu and Trp64Arg) were not associated with adolescent obesity in Taiwan.

Adrenergic regulation of the innate immune response in common carp (Cyprinus carpio L.)

Catecholamines exert their physiological actions through α and β adrenergic receptors (ARs). As ARs are not exclusively expressed on neuroendocrine cells, but also on leukocytes, they may facilitate neuroendocrine modulation of immune responses. We sequenced the β(2a)-AR in common carp, and studied its expression profile and involvement in the regulation of teleost innate immune responses. β(2a)-AR messenger RNA was found to be constitutively expressed in brain areas, especially in the preoptic nucleus (NPO, homologous to the mammalian hypothalamus), and in immune organs. During the active phase of an in vivo inflammatory response, induced by i.p. zymosan treatment, β(2a)-AR gene expression was up-regulated in the peritoneal leukocytes. Additionally, adrenaline in vitro reduced the synthesis of oxygen radical species and nitric oxide, while it enhanced arginase activity in fish phagocytes. Furthermore, in vitro adrenaline administration inhibited expression of pro-inflammatory cytokines, chemokines and their receptors. It is therefore hypothesized that adrenaline will down-regulate phagocyte skewing toward classical/innate polarization.

Arginine 16 Glycine Polymorphism in β2-Adrenergic Receptor Gene is Associated with Obesity, Hyperlipidemia, Hyperleptinemia, and Insulin Resistance in Saudis

Background. Several studies have shown an association between codon 16 polymorphism of the β2AR gene and obesity. Methods. We studied the association between Arg16Gly polymorphism and obesity and its influence on anthropometric parameters, lipids, insulin resistance and leptin in Saudi individuals. The study group included 329 individuals (males: 109 and females: 220). Metabolic parameters, including glucose, lipids, insulin, and leptin were analyzed and anthropometric parameters including waist and hip circumference, waist/hip (W/H) ratio, and body mass index (BMI) were measured and HOMA-IR was calculated. Genotyping was conducted by DNA sequencing of 353 bp fragments, carrying the Arg16Gly polymorphic site. Results and Conclusion. Overweight and obese subjects had a significantly higher frequency of Gly16 (0.375 and 0.38, resp.) compared with normal-weight subjects (0.200). In addition, subjects carrying Gly16 allele regardless of their BMI had greater waist and hip circumference, W/H ratio, plasma lipids, leptin, glucose level, and insulin resistance as judged from the HOMA-IR, compared to those with the wild-type allele. The findings of this study show a significant association between the Arg16Gly polymorphism in β2AR gene and the development of insulin resistance, overweight, and obesity in Saudi populations with an influence on the levels of lipid and leptin.

Cold exposure down-regulates adiponutrin/PNPLA3 mRNA expression and affects its nutritional regulation in adipose tissues of lean and obese Zucker rats

Adiponutrin/PNPLA3 is a protein highly produced in adipose tissue whose expression is under tight nutritional regulation. It possesses lipogenic/lipolytic capacity and, although adiponutrin polymorphisms are related to obesity, its physiological role is not clear. To help clarify its role, we studied the effect of acute cold exposure on adiponutrin mRNA expression in different adipose tissues of lean/obese Zucker rats subjected to feeding/fasting/refeeding. The effect of cold on the expression of key lipogenic enzymes and on uncoupling protein-1 (UCP1) was evaluated in selected adipose depots. Adiponutrin mRNA levels were also determined in the adipose tissue of isoprenaline-treated rats and in cultured adipocytes treated with noradrenaline, isoprenaline and a selective β3-adrenoceptor (AR) agonist. Adiponutrin expression was strongly down-regulated by cold in the different adipose depots in lean animals, while this down-regulation was impaired in obese rats. Adiponutrin pattern of expression in response to cold correlated positively with that of the lipogenic enzymes and negatively with UCP1 expression. Acute intraperitoneal administration of isoprenaline also produced a decrease in adiponutrin expression in adipose tissue. In vitro data suggest that adiponutrin's inhibitory effect could be mediated, at least in part, by the sympathetic system via β1/β2-AR. In addition, improvement in metabolic parameters related to obesity in cold-exposed animals was related to an improvement in adiponutrin nutritional regulation. Thus, cold inhibition of adiponutrin expression in adipose tissue (which correlates with the response of lipogenic enzymes) supports a physiological role for this protein in lipogenesis. Moreover, alterations in adiponutrin expression and regulation in adipose tissue are related to obesity.

Historical perspectives in fat cell biology: the fat cell as a model for the investigation of hormonal and metabolic pathways

For many years, there was little interest in the biochemistry or physiology of adipose tissue. It is now well recognized that adipocytes play an important dynamic role in metabolic regulation. They are able to sense metabolic states via their ability to perceive a large number of nervous and hormonal signals. They are also able to produce hormones, called adipokines, that affect nutrient intake, metabolism and energy expenditure. The report by Rodbell in 1964 that intact fat cells can be obtained by collagenase digestion of adipose tissue revolutionized studies on the hormonal regulation and metabolism of the fat cell. In the context of the advent of systems biology in the field of cell biology, the present seems an appropriate time to look back at the global contribution of the fat cell to cell biology knowledge. This review focuses on the very early approaches that used the fat cell as a tool to discover and understand various cellular mechanisms. Attention essentially focuses on the early investigations revealing the major contribution of mature fat cells and also fat cells originating from adipose cell lines to the discovery of major events related to hormone action (hormone receptors and transduction pathways involved in hormonal signaling) and mechanisms involved in metabolite processing (hexose uptake and uptake, storage, and efflux of fatty acids). Dormant preadipocytes exist in the stroma-vascular fraction of the adipose tissue of rodents and humans; cell culture systems have proven to be valuable models for the study of the processes involved in the formation of new fat cells. Finally, more recent insights into adipocyte secretion, a completely new role with major metabolic impact, are also briefly summarized.

Lipolytic function of adipocyte/endothelial cocultures

The rising incidence of adipose-related disorders such as obesity has prompted increased interest in the in vitro development of functional human soft tissues to study the disease and treatment options. Further, soft tissues maintained in vitro with a capacity to resemble in vivo tissues in structure and metabolic function would help gain insight into mechanisms involved in adipose tissue development. In the current study, the metabolic potential of adipose/endothelial cocultures on three-dimensional silk fibroin scaffolds was studied. Endothelial contributions to adipose lipogenesis and lipolysis were the focus of the study. Triglyceride accumulation, adipogenic gene transcript expression, and basal lipolysis measurements demonstrated the ability of this coculture system to retain metabolic levels obtained in adipocyte monocultures. Additionally, basal lipolysis was stimulated in mono- and coculture systems to a similar extent at 1.6- and 1.9-fold over controls, respectively. The ability to maintain adipose functions in these cocultures represents a step forward in the development of a tissue-engineered adipose tissue system exhibiting both endothelial lumens and metabolic functions.

Lifestyle and socioeconomic-status modify the effects of ADRB2 and NOS3 on adiposity in European-American and African-American adolescents

The aim of the study is to investigate the influence of and interaction between lifestyle behaviors (diet and physical activity (PA)) and single-nucleotide polymorphisms (SNPs) in obesity-candidate genes (ADRB2, APOB and NOS3) on general and central adiposity. Six-hundred-and-twenty-one European-American (EA) and African-American (AA) youths aged 13-19 years were classified by ethnicity (49% AA), gender (45% male), and socioeconomic status (SES). PA and dietary intake with up to seven 24-h recalls were reported for all subjects. Percent body fat (%BF) was measured by dual-energy X-ray absorptiometry, visceral adipose tissue (VAT), and subcutaneous abdominal adipose tissue (SAAT) by magnetic resonance imaging. Reported energy intake (EI) and vigorous PA (VPA) were negative predictors of %BF and SAAT. Carriers of the NOS3 Asp298 allele had higher %BF only in the presence of an adverse environment (low SES). Compared to the most common NOS3 haplotype, homozygotes for haplotype A-non4r-Asp had 6.1% higher %BF. Significant interactions were revealed between the ADRB2 Arg16Gly SNP and VPA on VAT, SAAT and waist circumference (WC) such that Gly16 homozygotes may benefit less from increased VPA to reduce their weight. Genetic susceptibility to increased general and central adiposity is dependent on several factors, such as SES and vigorous exercise. Improved understanding of the joint effect of genes and lifestyle on adiposity will offer new insights into obesity and may provide new avenues for personalized prevention and treatment.

The β3-adrenergic agonist (BRL35135A) acutely increases oxygen consumption and plasma intermediate metabolites in sheep

There is evidence that an atypical adrenoreceptor subtype is involved in mediating some of the physiological effects of catecholamines, particularly in some adipose tissue sites. Therefore, three experiments were conducted to determine the metabolic and energetic responses to oral administration of the purported β3-agonist BRL35135A in ruminant lambs. The post-prandial increase in O2 consumption (0.109 versus 0.139 L/min) and CO2 production (0.102 versus 0.127 L/min) at 30 min after feeding was greater (P < 0.05) in the lambs receiving 5 mg of the BRL35135A. Treatment × time interactions over the period between –50 and 220 min indicate significant increases in plasma non-esterified fatty acids (P < 0.001), glucose (P < 0.001) and lactate (P = 0.024) in lambs consuming a single oral dose of 5 mg BRL35135A. In a subsequent experiment there were similar interactions over the period between –120 and 1440 min for non-esterified fatty acids (P < 0.001), glucose (P < 0.001) and lactate (P < 0.001) in lambs consuming a lower oral dose of 1 mg BRL35135A. The effects of BRL35135A on plasma non-esterified fatty acids (P = 0.95), glucose (P = 0.84) and lactate (P = 0.68) were not modified by the β1- and β2-adrenergic antagonist alprenolol suggesting that the effects were mediated via β3-adrenergic receptor subtypes. In conclusion, these experiments indicate that BRL35135A is acutely active in sheep when given with feed, as indicated by increases in respiratory gas exchange and plasma metabolite concentrations.

Fat as a fuel: emerging understanding of the adipose tissue-skeletal muscle axis

The early pioneers in the field of metabolism during exercise such as Lindhard and Krogh understood the importance of fat as a fuel for muscle contraction. But they could not have understood the details of the pathways involved, as neither the metabolic role of adipose tissue nor the transport role of non-esterified fatty acids (NEFA) in the plasma was clearly understood at the time. We now recognize that the onset of muscular contraction coincides with an increase in the delivery of NEFA from adipose tissue, probably coordinated by the sympatho-adrenal system. During light exercise, adipose tissue-derived NEFA make up the majority of the oxidative fuel used by muscle. As exercise is prolonged, the importance of NEFA increases. The onset of exercise is marked by an increased proportion of NEFAs entering beta-oxidation rather than re-esterification and recycling. At moderate intensities of exercise, other sources of fat, potentially plasma- and intramyocellular-triacylglycerol, supplement the supply of plasma NEFA. The delivery of NEFA is augmented by increased adipose tissue blood flow and by other stimuli such as atrial natriuretic peptide. Only during high-intensity exercise is there a failure of adipose tissue to deliver sufficient fatty acids for muscle (which is coupled with an inability of muscle to use them, even when fatty acids are supplied artificially). This limitation of adipose tissue NEFA delivery may reflect some feedback inhibition of lipolysis, perhaps via lactate, or possibly alpha-adrenergic inhibition of lipolysis at very high catecholamine concentrations.

Substrate utilization during exercise and recovery at moderate altitude

Recent studies have shown that exercise training at moderate altitude or in moderate hypoxia improved glycemic parameters. From these data, it has been supposed that endurance exercise in moderate hypoxia affects substrate utilization and that exposure to moderate hypoxia in combination with exercise may be utilized as part of metabolic or diabetes prevention program. However, the influence of exercise at moderate hypoxia on circulating metabolites and hormones in terms of substrate utilization is unclear. The purpose of this study was to elucidate the influence of exercise in moderate hypoxia on substrate utilization. We determined cardiorespiratory, metabolic, and hormonal parameters during exercise and postexercise recovery at a simulated moderate altitude of 2000 m, and then we compared these variables with values obtained at sea level. Seven men participated in this study; subjects reported to the laboratory on 4 occasions. Two maximal exercise tests were performed to estimate peak oxygen uptake at the simulated 2000-m altitude and sea level on different days. Afterward, submaximal exercise tests were carried out at a simulated altitude of 2000 m or sea level, separated by 1 week. Subjects performed submaximal exercise at the same relative exercise intensity (50% peak oxygen uptake) at a simulated altitude of 2000 m and at sea level for 30 minutes. The tests were performed in random order, and subjects were blinded to the respective altitudes. Venous blood samples and expired gases were obtained before, during exercise (15 and 30 minutes), and during postexercise recovery periods (15, 30, 45, and 60 minutes). The respiratory exchange ratio during exercise and recovery at moderate altitude was greater than at sea level. The epinephrine and norepinephrine concentrations during exercise and recovery were higher (P < .05) at moderate altitude than at sea level. Free fatty acids and glycerol concentrations during recovery were lower (P < .05) at moderate altitude than at sea level. These results suggest that carbohydrate utilization is increased during exercise and postexercise recovery period in moderate hypoxia as compared with normoxia. It is also suggested that moderate hypoxia influences the changes in circulating metabolites and hormones in terms of substrate metabolism during exercise and the recovery.

Role of beta-adrenergic receptors in the hyperphagic and hypermetabolic responses to dietary methionine restriction

Dietary methionine restriction (MR) limits fat deposition and decreases plasma leptin, while increasing food consumption, total energy expenditure (EE), plasma adiponectin, and expression of uncoupling protein 1 (UCP1) in brown and white adipose tissue (BAT and WAT). beta-adrenergic receptors (beta-AR) serve as conduits for sympathetic input to adipose tissue, but their role in mediating the effects of MR on energy homeostasis is unclear. Energy intake, weight, and adiposity were modestly higher in beta(3)-AR(-/-) mice on the Control diet compared with wild-type (WT) mice, but the hyperphagic response to the MR diet and the reduction in fat deposition did not differ between the genotypes. The absence of beta(3)-ARs also did not diminish the ability of MR to increase total EE and plasma adiponectin or decrease leptin mRNA, but it did block the MR-dependent increase in UCP1 mRNA in BAT but not WAT. In a further study, propranolol was used to antagonize remaining beta-adrenergic input (beta(1)- and beta(2)-ARs) in beta(3)-AR(-/-) mice, and this treatment blocked >50% of the MR-induced increase in total EE and UCP1 induction in both BAT and WAT. We conclude that signaling through beta-adrenergic receptors is a component of the mechanism used by dietary MR to increase EE, and that beta(1)- and beta(2)-ARs are able to substitute for beta(3)-ARs in mediating the effect of dietary MR on EE. These findings are consistent with the involvement of both UCP1-dependent and -independent mechanisms in the physiological responses affecting energy balance that are produced by dietary MR.

Programming of rat adrenal medulla by neonatal hyperleptinemia: adrenal morphology, catecholamine secretion, and leptin signaling pathway

Leptin serum concentration in early life is an important factor for adequate future development of the offspring. Previously, we demonstrated that hyperleptinemia on lactation programmed for hyperleptinemia, central leptin resistance with lower expression of the long form of leptin receptor at hypothalamus, and higher medullary catecholamine levels with cardiovascular consequences at adulthood. The central objective of this study was to determine the direct effect of leptin on adrenal medullary function of adult rats that were leptin treated during lactation. Adrenal morphology was also accessed. Recombinant murine leptin was injected in the pups during the first 10 days of life (group L, leptin-programmed) or at adulthood during 6 days (group LC). The controls of both experiments received saline (groups C and CC). Both treatments resulted in hyperleptinemia at 150 days old (+78% and 2-fold increase, respectively; P < 0.05). Programmed animals showed hypertrophy of adrenal and higher adrenal catecholamine content at 150 days old (3-fold increase, P < 0.05), and no changes were observed in the LC group. However, LC rats had lower adrenal content of tyrosine hydroxylase (-17%, P < 0.05). Leptin-programmed rats had a lower response to leptin in vitro stimulation (-22%, P < 0.05) and lower expression of key proteins of the leptin signaling pathway, leptin receptor and janus tyrosine kinase 2 in the medullas (-61% and -29%, respectively, P < 0.05). However, they presented higher expression of phosphorylated signal transducer and activator of transcription 3 (+2-fold, P < 0.05). Leptin treatment at adulthood did not affect these parameters. The higher catecholamine synthesis and secretion in the leptin-programmed rats observed in our previous study does not seem to be a consequence of the direct effect of leptin on the medullas. We suggest that the hyperleptinemia of the programmed animals increases adrenal medullary function through sympathetic nervous system activation. In conclusion, high leptin levels on lactation program the activity of the sympathoadrenal system at adulthood that may contribute to the development of adult chronic diseases such as hypertension.

Fatty acid flux in adipocytes: the in's and out's of fat cell lipid trafficking

The trafficking of fatty acids into and out of adipocytes is regulated by a complex series of proteins and enzymes and is under control by a variety of hormonal and metabolic factors. The biochemical basis of fatty acid influx, despite its widespread appreciation, remains enigmatic with regard to the biophysical and biochemical properties that facilitate long-chain fatty acid uptake. Fatty acid efflux is initiated by hormonally controlled lipolysis of the droplet stores and produces fatty acids that must transit from their site of production to the plasma membrane and subsequently out of the cells. This review will focus on the "in's and out's" of fatty acid trafficking and summarize the current concepts in the field.

Sensory and sympathetic nervous system control of white adipose tissue lipolysis

Circulating factors are typically invoked to explain bidirectional communication between the CNS and white adipose tissue (WAT). Thus, initiation of lipolysis has been relegated primarily to adrenal medullary secreted catecholamines and the inhibition of lipolysis primarily to pancreatic insulin, whereas signals of body fat levels to the brain have been ascribed to adipokines such as leptin. By contrast, evidence is given for bidirectional communication between brain and WAT occurring via the sympathetic nervous system (SNS) and sensory innervation of this tissue. Using retrograde transneuronal viral tract tracers, the SNS outflow from brain to WAT has been defined. Functionally, sympathetic denervation of WAT blocks lipolysis to a variety of lipolytic stimuli. Using anterograde transneuronal viral tract tracers, the sensory input from WAT to brain has been defined. Functionally, these WAT sensory nerves respond electrophysiologically to increases in WAT SNS drive suggesting a possible neural negative feedback loop to regulate lipolysis.

Comparative effects of oleoyl-estrone and a specific beta3-adrenergic agonist (CL316, 243) on the expression of genes involved in energy metabolism of rat white adipose tissue

Background

The combination of oleoyl-estrone (OE) and a selective β₃-adrenergic agonist (B3A; CL316,243) treatment in rats results in a profound and rapid wasting of body reserves (lipid).

Methods

In the present study we investigated the effect of OE (oral gavage) and/or B3A (subcutaneous constant infusion) administration for 10 days to overweight male rats, compared with controls, on three distinct white adipose tissue (WAT) sites: subcutaneous inguinal, retroperitoneal and epididymal. Tissue weight, DNA (and, from these values cellularity), cAMP content and the expression of several key energy handling metabolism and control genes were analyzed and computed in relation to the whole site mass.

Results

Both OE and B3A significantly decreased WAT mass, with no loss of DNA (cell numbers). OE decreased and B3A increased cAMP. Gene expression patterns were markedly different for OE and B3A. OE tended to decrease expression of most genes studied, with no changes (versus controls) of lipolytic but decrease of lipogenic enzyme genes. The effects of B3A were widely different, with a generalized increase in the expression of most genes, including the adrenergic receptors, and, especially the uncoupling protein UCP1.

Discussion

OE and B3A, elicit widely different responses in WAT gene expression, end producing similar effects, such as shrinking of WAT, loss of fat, maintenance of cell numbers. OE acted essentially on the balance of lipolysis-lipogenesis and the blocking of the uptake of substrates; its decrease of synthesis favouring lipolysis. B3A induced a shotgun increase in the expression of most regulatory systems in the adipocyte, an effect that in the end favoured again the loss of lipid; this barely selective increase probably produces inefficiency, which coupled with the increase in UCP1 expression may help WAT to waste energy through thermogenesis.

Conclusions

There were considerable differences in the responses of the three WAT sites. OE in general lowered gene expression and stealthily induced a substrate imbalance. B3A increasing the expression of most genes enhanced energy waste through inefficiency rather than through specific pathway activation. There was not a synergistic effect between OE and B3A in WAT, but their combined action increased WAT energy waste.

Effect of alpha2A-adrenoceptor C-1291G genotype and maltreatment on hyperactivity and inattention in adolescents

The C-1291G polymorphism (rs1800544) in the promoter region of the alpha(2A)-adrenoceptor gene (ADRA2A) has been associated with attention deficit and hyperactivity in clinical samples. We have examined the effect of ADRA2A C-1291G on inattentive, hyperactive and aggressive behaviour in a population representative cohort of healthy schoolchildren, and possible interaction of genotype with family relations. Ratings on aggressiveness, motor restlessness and concentration difficulties were obtained from the class teachers by using the Hyperactivity Scale of af Klinteberg, and the teacher-report version of SNAP-IV. The relations in the family were reported by children. Symptom scores, self-reports and genotype data of 429 15-years old children (196 boys, 233 girls) were available for analysis. There was a significant interaction effect of maltreatment and the ADRA2A genotype on behavioural functioning in 15years old boys. Boys with CC genotype and higher score of maltreatment demonstrated more overactive behaviour and concentration difficulties than boys with CC genotype and low maltreatment score. They also had more inattentive symptoms measured by SNAP-IV. Among boys with low maltreatment score, subjects with CC genotype demonstrated less overactivity than G allele carriers. In girls, the G allele carriers did not differ from the CC genotype, but in maltreated girls with GG genotype aggression and inattention symptoms were reduced, and the score of aggressive behaviour was also lower compared to maltreated girls with CC genotype. Our data suggest that family environmental factors may act together with the alpha(2A)-adrenoceptor genotype to increase the expression of hyperactive and inattentive symptoms in adolescents.

Fat storage and the biology of energy expenditure

Excessive adiposity results from an imbalance in energy homeostasis, whereby the consequences of excessive food intake are not balanced by increased energy expenditure. The increasing prevalence of excessive adiposity now involves more than 1 billion individuals worldwide. Of these, one half is obese and susceptible to comorbidities such as insulin resistance, type 2 diabetes, hyperlipidemia, and hypertension, which accelerate atherosclerosis. Lifestyle changes that have resulted largely in decreased physical activity now require a greater understanding of energy use that may allow better strategies for obesity control, because traditional methods of decreasing food intake and/or increasing exercise have not been successful without considerable behavioral counseling. This review focuses on the cell biology of white and brown fat tissue as well as on the central obesity that explains the comorbidities of the metabolic syndrome. Recent advances regarding the roles of central and autonomic nervous system regulation involved in fat remodeling are discussed, including the hypothalamic regulation of food intake and intestinal modulation, which affects satiety and peripheral energy expenditure. Finally, the new knowledge of cellular transcription factor regulation of energy expenditure is explained, whereby genes regulate mitochondriogenesis within adipocytes, liver, and muscle for both coupled and uncoupled oxidative phosphorylation-induced energy and heat expenditure, respectively. Newly discovered agonists of these transcription factors may now be realized that enhance energy expenditure. Strategies that combine such pharmacotherapies with lifestyle changes including enhanced physical activity and proper dietary intake may then provide the deterrents to excessive adiposity and its comorbidities, which now threaten human longevity.

Acute cold exposure-induced down-regulation of CIDEA, cell death-inducing DNA fragmentation factor-alpha-like effector A, in rat interscapular brown adipose tissue by sympathetically activated beta3-adrenoreceptors

The thermogenic activity of brown adipose tissue (BAT) largely depends on the mitochondrial uncoupling protein 1 (UCP1), which is up-regulated by environmental alterations such as cold. Recently, CIDEA (cell death-inducing DNA fragmentation factor-alpha-like effector A) has also been shown to be expressed at high levels in the mitochondria of BAT. Here we examined the effect of cold on the mRNA and protein levels of CIDEA in interscapular BAT of conscious rats with regard to the sympathetic nervous system. Cold exposure (4 degrees C for 3h) elevated the plasma norepinephrine level and increased norepinephrine turnover in BAT. Cold exposure resulted in down-regulation of the mRNA and protein levels of CIDEA in BAT, accompanied by up-regulation of mRNA and protein levels of UCP1. The cold exposure-induced changes of CIDEA and UCP1 were attenuated by intraperitoneal pretreatment with propranolol (a non-selective beta-adrenoreceptor antagonist) (2mg/animal) or SR59230A (a selective beta(3)-adrenoreceptor antagonist) (2mg/animal), respectively. These results suggest that acute cold exposure resulted in down-regulation of CIDEA in interscapular BAT by sympathetically activated beta(3)-adrenoreceptor-mediated mechanisms in rats.

Lipolysis and lipid mobilization in human adipose tissue

Triacylglycerol (TAG) stored in adipose tissue (AT) can be rapidly mobilized by the hydrolytic action of the three main lipases of the adipocyte. The non-esterified fatty acids (NEFA) released are used by other tissues during times of energy deprivation. Until recently hormone-sensitive lipase (HSL) was considered to be the key rate-limiting enzyme responsible for regulating TAG mobilization. A novel lipase named adipose triglyceride lipase/desnutrin (ATGL) has been identified as playing an important role in the control of fat cell lipolysis. Additionally perilipin and other proteins of the surface of the lipid droplets protecting or exposing the TAG core of the droplets to lipases are also potent regulators of lipolysis. Considerable progress has been made in understanding the mechanisms of activation of the various lipases. Lipolysis is under tight hormonal regulation. The best understood hormonal effects on AT lipolysis concern the opposing regulation by insulin and catecholamines. Heart-derived natriuretic peptides (i.e., stored in granules in the atrial and ventricle cardiomyocytes and exerting stimulating effects on diuresis and natriuresis) and numerous autocrine/paracrine factors originating from adipocytes and other cells of the stroma-vascular fraction may also participate in the regulation of lipolysis. Endocrine and autocrine/paracrine factors cooperate and lead to a fine regulation of lipolysis in adipocytes. Age, anatomical site, sex, genotype and species differences all play a part in the regulation of lipolysis. The manipulation of lipolysis has therapeutic potential in the metabolic disorders frequently associated with obesity and probably in several inborn errors of metabolism.

Adrenaline but not noradrenaline is a determinant of exercise-induced lipid mobilization in human subcutaneous adipose tissue

The relative contribution of noradrenaline (norepinephrine) and adrenaline (epinephrine) in the control of lipid mobilization in subcutaneous adipose tissue (SCAT) during exercise was evaluated in men treated with a somatostatin analogue, octreotide. Eight lean and eight obese young men matched for age and physical fitness performed 60 min exercise bouts at 50% of their maximal oxygen consumption on two occasions: (1) during i.v. infusion of octreotide, and (2) during placebo infusion. Lipolysis and local blood flow changes in SCAT were evaluated using in situ microdialysis. Infusion of octreotide suppressed plasma insulin and growth hormone levels at rest and during exercise. It blocked the exercise-induced increase in plasma adrenaline while that of noradrenaline was unchanged. Plasma natriuretic peptides (NPs) level was higher at rest and during exercise under octreotide infusion in lean men. Under placebo, no difference was found in the exercise-induced increase in glycerol between the probe perfused with Ringer solution alone and that with phentolamine (an alpha-adrenergic receptor antagonist) in lean subjects while a greater increase in glycerol was observed in the obese subjects. Under placebo, propranolol infusion in the probe containing phentolamine reduced by about 45% exercise-induced glycerol release; this effect was fully suppressed under octreotide infusion while noradrenaline was still elevated and exercise-induced lipid mobilization maintained in both lean and obese individuals. In conclusion, blockade of beta-adrenergic receptors during exercise performed during infusion of octreotide (blocking the exercise-induced rise in adrenaline but not that of noradrenaline) does not alter the exercise-induced lipolysis. This suggests that adrenaline is the main adrenergic agent contributing to exercise-induced lipolysis in SCAT. Moreover, it is the combined action of insulin suppression and NPs release which explains the lipolytic response which remains under octreotide after full local blockade of fat cell adrenergic receptors. For the moment, it is unknown if results apply specifically to SCAT and exercise only or if conclusions could be extended to all forms of lipolysis in humans.

Regulation of fat metabolism during resistance exercise in sedentary lean and obese men

The effect of acute resistance exercise (RE) on whole body energy expenditure (EE) and α2-adrenergic receptor (α2-AR) regulation of lipolysis in subcutaneous abdominal adipose tissue (SCAAT) was determined in sedentary lean (LN) and obese (OB) men. Lipolysis was monitored using microdialysis in 10 LN [body mass index (BMI) 20.9 ± 0.6] and 10 OB (BMI 36.2 ± 2.7) men before, during, and for 24 h after RE. EE was measured before and immediately after RE for 40 min. Changes in interstitial glycerol were measured in SCAAT with three microdialysis probes perfused with a control solution, phentolamine (α2-AR antagonist), or propranolol (β-AR antagonist). EE and fat oxidation (FOX) were significantly ( P < 0.001) elevated immediately post-RE compared with pre-RE in LN and OB subjects, with no differences between groups. RE-induced increases in SCAAT glycerol concentrations from rest to peak exercise were greater in LN than in OB men in the control (LN 142.1 ± 30.8 vs. OB 65.4 ± 14.2%, P = 0.03) and phentolamine probes (LN 187.2 ± 29.6 vs. OB 66.7 ± 11.0%, P = 0.002). Perfusion of propranolol had no effect on interstitial glycerol concentrations over the time course of the experiment in either group. Plasma insulin concentrations were significantly lower ( P = 0.002) and plasma growth hormone (GH) was significantly higher ( P = 0.03) in LN compared with OB men. The mechanism behind RE contributing to improved body composition may in part be due to enhanced SCAAT lipolysis and improved EE and FOX in response to RE in LN and OB men. The blunted SCAAT lipolytic response to RE in OB compared with LN men is unrelated to RE-induced catecholamine activation of the antilipolytic α2-ARs and may be due to depressed GH in OB subjects.

Cold exposure increases adiponectin levels in men

Sympathetic nerve activation is recognized at the adipose tissue level during cold exposure. Adiponectin is a key protein produced by adipose tissue, but its acute modulation remains unknown in humans exposed to cold. The aim of this study were (1) to examine the acute effects of cold exposure on circulating adiponectin and (2) to determine whether the changes are modulated by (a) an acute glucose ingestion as well as (b) a short-term modulation in carbohydrate (CHO) availability. Using a random crossover design, 6 healthy men were exposed to cold for 120 minutes with ingestion of beverages containing low (Control, 0.04 g/min) or high (High, 0.8 g/min) amounts of glucose during the course of the experiment (study 1). In study 2, 6 healthy men were exposed twice to cold for 120 minutes after equicaloric low-CHO diet and exercise and high-CHO diet without exercise. Plasma adiponectin concentrations were quantified before and during cold exposure. In study 1, adiponectin levels did not change during High, whereas a 20% rise was observed during Control (condition x time interaction, P = .06). In study 2, adiponectin levels increased by approximately 70% during cold exposure after both low- and high-CHO diets (effect of time, P < .05). A 120-minute period of cold exposure is accompanied by a significant increase in adiponectin levels in young healthy men. The rise in adiponectin levels observed during shivering is inhibited with glucose ingestion but not after diets varying in CHO content.

Cigarette smoking induces overexpression of a fat-depleting gene AZGP1 in the human

BACKGROUND

Smokers weigh less and have less body fat than nonsmokers. Increased body fat and weight gain are observed following smoking cessation. To assess a possible molecular mechanism underlying the inverse association between smoking and body weight, we hypothesized that smoking may induce the expression of a fat-depleting gene in the airway epithelium, the cell population that takes the brunt of the stress of cigarette smoke.

METHODS

To assess whether smoking up-regulates expression in the airway epithelium of genes associated with weight loss, microarray analysis was used to evaluate genes associated with fat depletion in large airway epithelial samples obtained by fiberoptic bronchoscopy from healthy smokers and healthy nonsmokers. As a candidate gene we further evaluated the expression of alpha(2)-zinc-glycoprotein 1 (AZGP1), a soluble protein that stimulates lipolysis, induces a reduction in body fat in mice, is associated with the cachexia related to cancer, and is known to be expressed in secretory cells of lung epithelium. AZGP1 protein expression was assessed by Western analysis and localization in the large airway epithelium by immunohistochemistry.

RESULTS

Both microarray and TaqMan analysis demonstrated that AZGP1 messenger RNA levels were higher in the large airway epithelium of healthy smokers compared to healthy nonsmokers (p < 0.05, all comparisons). Western analysis of airway biopsy specimens from smokers compared with those from nonsmokers demonstrated up-regulation of AZGP1 at the protein level, and immunohistochemical analysis demonstrated up-regulation of AZGP1 in secretory as well as neuroendocrine cells of smokers.

CONCLUSIONS

In the context that AZGP1 is involved in lipolysis and fat loss, its overexpression in the airway epithelium of chronic smokers may represent one mechanism for the weight difference in smokers vs nonsmokers.

Adipose triglyceride lipase and the lipolytic catabolism of cellular fat stores

Fatty acids (FAs) are essential components of all lipid classes and pivotal substrates for energy production in all vertebrates. Additionally, they act directly or indirectly as signaling molecules and, when bonded to amino acid side chains of peptides, anchor proteins in biological membranes. In vertebrates, FAs are predominantly stored in the form of triacylglycerol (TG) within lipid droplets of white adipose tissue. Lipid droplet-associated TGs are also found in most nonadipose tissues, including liver, cardiac muscle, and skeletal muscle. The mobilization of FAs from all fat depots depends on the activity of TG hydrolases. Currently, three enzymes are known to hydrolyze TG, the well-studied hormone-sensitive lipase (HSL) and monoglyceride lipase (MGL), discovered more than 40 years ago, as well as the relatively recently identified adipose triglyceride lipase (ATGL). The phenotype of HSL- and ATGL-deficient mice, as well as the disease pattern of patients with defective ATGL activity (due to mutation in ATGL or in the enzyme's activator, CGI-58), suggest that the consecutive action of ATGL, HSL, and MGL is responsible for the complete hydrolysis of a TG molecule. The complex regulation of these enzymes by numerous, partially uncharacterized effectors creates the "lipolysome," a complex metabolic network that contributes to the control of lipid and energy homeostasis. This review focuses on the structure, function, and regulation of lipolytic enzymes with a special emphasis on ATGL.

Exercise-induced lipid mobilization in subcutaneous adipose tissue is mainly related to natriuretic peptides in overweight men

Involvement of sympathetic nervous system and natriuretic peptides in the control of exercise-induced lipid mobilization was compared in overweight and lean men. Lipid mobilization was determined using local microdialysis during exercise. Subjects performed 35-min exercise bouts at 60% of their maximal oxygen consumption under placebo or after oral tertatolol [a beta-adrenergic receptor (AR) antagonist]. Under placebo, exercise increased dialysate glycerol concentration (DGC) in both groups. Phentolamine (alpha-AR antagonist) potentiated exercise-induced lipolysis in overweight but not in lean subjects; the alpha(2)-antilipolytic effect was only functional in overweight men. After tertatolol administration, the DGC increased similarly during exercise no matter which was used probe in both groups. Compared with the control probe under placebo, lipolysis was reduced in lean but not in overweight men treated with the beta-AR blocker. Tertatolol reduced plasma nonesterified fatty acids and insulin concentration in both groups at rest. Under placebo or tertatolol, the exercise-induced changes in plasma nonesterified fatty acids, glycerol, and insulin concentrations were similar in both groups. Exercise promoted a higher increase in catecholamine and ANP plasma levels after tertatolol administration. In conclusion, the major finding of our study is that in overweight men, in addition to an increased alpha(2)-antilipolytic effect, the lipid mobilization in subcutaneous adipose tissue that persists during exercise under beta-blockade is not dependent on catecholamine action. On the basis of correlation findings, it seems to be related to a concomitant exercise-induced rise in plasma ANP when exercise is performed under tertatolol intake and a decrease in plasma insulin.

Weight loss and brown adipose tissue reduction in rat model of sleep apnea

Background -

Obesity is related to obstructive sleep apnea-hypopnea syndrome (OSAHS), but its roles in OSAHS as cause or consequence are not fully clarified. Isocapnic intermittent hypoxia (IIH) is a model of OSAHS. We verified the effect of IIH on body weight and brown adipose tissue (BAT) of Wistar rats.

Methods

Nine-month-old male breeders Wistar rats of two groups were studied: 8 rats submitted to IIH and 5 control rats submitted to sham IIH. The rats were weighed at the baseline and at the end of three weeks, after being placed in the IIH apparatus seven days per week, eight hours a day, in the lights on period, simulating an apnea index of 30/hour. After experimental period, the animals were weighed and measured as well as the BAT, abdominal, perirenal, and epididymal fat, the heart, and the gastrocnemius muscle.

Results

Body weight of the hypoxia group decreased 17 ± 7 grams, significantly different from the variation observed in the control group (p = 0,001). The BAT was 15% lighter in the hypoxia group and reached marginally the alpha error probability (p = 0.054).

Conclusion

Our preliminary results justify a larger study for a longer time in order to confirm the effect of isocapnic intermittent hypoxia on body weight and BAT.

Role of beta-adrenoceptor signaling in skeletal muscle: implications for muscle wasting and disease

The importance of beta-adrenergic signaling in the heart has been well documented, but it is only more recently that we have begun to understand the importance of this signaling pathway in skeletal muscle. There is considerable evidence regarding the stimulation of the beta-adrenergic system with beta-adrenoceptor agonists (beta-agonists). Although traditionally used for treating bronchospasm, it became apparent that some beta-agonists could increase skeletal muscle mass and decrease body fat. These so-called "repartitioning effects" proved desirable for the livestock industry trying to improve feed efficiency and meat quality. Studying beta-agonist effects on skeletal muscle has identified potential therapeutic applications for muscle wasting conditions such as sarcopenia, cancer cachexia, denervation, and neuromuscular diseases, aiming to attenuate (or potentially reverse) the muscle wasting and associated muscle weakness, and to enhance muscle growth and repair after injury. Some undesirable cardiovascular side effects of beta-agonists have so far limited their therapeutic potential. This review describes the physiological significance of beta-adrenergic signaling in skeletal muscle and examines the effects of beta-agonists on skeletal muscle structure and function. In addition, we examine the proposed beneficial effects of beta-agonist administration on skeletal muscle along with some of the less desirable cardiovascular effects. Understanding beta-adrenergic signaling in skeletal muscle is important for identifying new therapeutic targets and identifying novel approaches to attenuate the muscle wasting concomitant with many diseases.

Associations between an alpha 2A adrenergic receptor gene polymorphism and adolescent personality

The aim of this study was to investigate the impact of the C-1291G polymorphism in the promoter region of the alpha 2A adrenoreceptor gene (ADRA2A) to the personality traits. In the present study, data of the younger cohort of the Estonian Children Personality Behaviour and Health Study was used (N = 419). Personality traits were assessed by 240-item (Estonian Personality Item Pool NEO (EPIP-NEO)). Restriction enzyme MspI was used after PCR amplification to genotype the subjects according to C-1291G polymorphism of the ADRA2A. There were no significant differences on the level of the Big Five personality domains between genotypes; however, there were three significant differences on the level of different subscales. The subjects with GG genotype had significantly higher scores on Depression and significantly lower scores on Morality and Orderliness compared to subjects with CC and CG genotypes. There was a significant interaction between sex and ADRA2A polymorphism regarding E1, Friendliness; E2, Gregariousness; and E6, Cheerfulness. With CC and CG genotypes girls had higher scores on extraversion scales than boys, but with GG genotype boys score higher than girls with GG genotype. It is concluded that the gene polymorphism in the ADRA2A has an influence on personality traits in adolescents.

Association of the beta3-adrenergic receptor Trp64Arg polymorphism with common metabolic traits: studies of 7605 middle-aged white people

AIM/HYPOTHESIS

The functional variant Trp64Arg in the beta(3)-adrenergic receptor has previously been examined for association with obesity and insulin resistance with ambiguous results. For further evaluation the present study examined the impact of the Trp64Arg variant on the pathogenesis of type 2 diabetes and obesity in a relatively large, homogenous study population.

METHODS

The Trp64Arg polymorphism was genotyped in 7605 Danish subjects using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Association was examined in case-control studies of obesity (1529 cases and 6049 controls) and type 2 diabetes (1373 cases and 4742 controls) and quantitative trait analyses among 5822 individuals. Furthermore, the association of Trp64Arg with type 2 diabetes was examined in a meta-analysis.

RESULTS

The Trp64Arg polymorphism was not associated with obesity. However, the Arg-allele was associated with a slightly increased risk of type 2 diabetes (OR1.15 (CI: 1.01-1.31); p=0.04), increased insulin resistance estimated by homeostasis model assessment (p=0.01), higher fasting serum insulin levels (p=0.01), and higher levels of plasma glucose 2-h after glucose ingestion (p=0.02). After sex stratification these associations were only present among women. Furthermore, the Arg-allele was borderline associated with type 2 diabetes in a meta-analysis of the present and 26 previous studies (p=0.06, OR1.27 (CI: 0.99-1.63)) (n=18891).

CONCLUSION/INTERPRETATION

Trp64Arg does not confer an increased risk of obesity among Danes. Yet, in the present study of 7605 Danes the variant is associated with type 2 diabetes and quantitative traits related to type 2 diabetes.

Role of uncoupling protein 1 in the anti-obesity effect of beta3-adrenergic agonist in the dog

We have reported that chronic treatment with beta3-adrenoceptor agonists reduces body fat content and induces the expression of mitochondrial thermogenic uncoupling protein 1 (UCP1) in adipose tissue in the dog. To evaluate the role of UCP1 in the anti-obesity effect of the agonists, we isolated adipocytes from subcutaneous fat pad of beagles before and after a 2-week treatment with AJ-9677, a specific beta3-adrenoceptor agonist, and examined their thermogenic activity in vitro. Histological and protein analysis revealed that adipose tissues before the treatment were composed of unilocular cells filled with a single large droplet, while the tissues after the treatment contained many smaller and some multilocular adipocytes expressing UCP1 and abundant mitochondrial proteins. Before the treatment, oxygen consumption rate was very low and did not change even when the cells were stimulated by AJ-9677. Two-week AJ-9677 treatment increased basal oxygen consumption rate by 7-fold, and produced a clear responsiveness to AJ-9677 stimulation. Thus, chronic treatment with AJ-9677 induced UCP1 in adipocytes, where oxygen consumption increased in response to AJ-9677 stimulation. It was suggested that UCP1-dependent energy expenditure in adipose tissue contributes to the anti-obesity effect of beta3-adrenoceptor agonist in dogs.

Choosing an adipose tissue depot for sampling: factors in selection and depot specificity

The importance and the role of adipose tissues are now largely expanded not only because the very high occurrence of obesity but also because the emerging view that adipose tissue could be a reservoir of therapeutic cells. A critical examination of the adipose tissue features according to their location shows that sampling is not as easy as previously thought and needs special attention to heterogeneity and differences. We discussed here these different points and give precise protocols to sample the different adipose tissues and manipulate them.