Expressions of mRNA and encoded proteins of mitochondrial uncoupling protein genes (UCP1, UCP2, and UCP3) in epicardial and mediastinal adipose tissue and associations with coronary artery disease

Objective

To evaluate the expression of UCP1, UCP2, and UCP3 mRNA and encoded proteins in epicardial and mediastinal adipose tissues in patients with coronary artery disease (CAD).

Subjects and methods

We studied 60 patients with CAD and 106 patients undergoing valve replacement surgery (controls). Expression levels of UCP1, UCP2, and UCP3 mRNA and encoded proteins were measured by quantitative real-time PCR and Western blot analysis, respectively.

Results

: We found increased UCP1, UCP2, and UCP3 mRNA levels in the epicardial adipose tissue in the CAD versus the control group, and higher UCP1 and UCP3 mRNA expression in the epicardial compared with the mediastinal tissue in the CAD group. There was also increased expression of UCP1 protein in the epicardial tissue and UCP2 protein in the mediastinum tissue in patients with CAD. Finally, UCP1 expression was associated with levels of fasting plasma glucose, and UCP3 expression was associated with levels of high-density lipoprotein cholesterol and low-density cholesterol in the epicardial tissue.

Conclusion

Our study supports the hypothesis that higher mRNA expression by UCP genes in the epicardial adipose tissue could be a protective mechanism against the production of reactive oxygen species and may guard the myocardium against damage. Thus, UCP levels are essential to maintain the adaptive phase of cardiac injury in the presence of metabolic disorders.

On the potential role of globins in brown adipose tissue: a novel conceptual model and studies in myoglobin knockout mice

Myoglobin (Mb) regulates O₂ bioavailability in muscle and heart as the partial pressure of O₂ (Po₂) drops with increased tissue workload. Globin proteins also modulate cellular NO pools, "scavenging" NO at higher Po₂ and converting NO₂^- to NO as Po₂ falls. Myoglobin binding of fatty acids may also signal a role in fat metabolism. Interestingly, Mb is expressed in brown adipose tissue (BAT), but its function is unknown. Herein, we present a new conceptual model that proposes links between BAT thermogenic activation, concurrently reduced Po₂, and NO pools regulated by deoxy/oxy-globin toggling and xanthine oxidoreductase (XOR). We describe the effect of Mb knockout (Mb^-/-) on BAT phenotype [lipid droplets, mitochondrial markers uncoupling protein 1 (UCP1) and cytochrome C oxidase 4 (Cox4), transcriptomics] in male and female mice fed a high-fat diet (HFD, 45% of energy, ∼13 wk), and examine Mb expression during brown adipocyte differentiation. Interscapular BAT weights did not differ by genotype, but there was a higher prevalence of mid-large sized droplets in Mb^-/-. COX4 protein expression was significantly reduced in Mb^-/- BAT, and a suite of metabolic/NO/stress/hypoxia transcripts were lower. All of these Mb^-/--associated differences were most apparent in females. The new conceptual model, and results derived from Mb^-/- mice, suggest a role for Mb in BAT metabolic regulation, in part through sexually dimorphic systems and NO signaling. This possibility requires further validation in light of significant mouse-to-mouse variability of BAT Mb mRNA and protein abundances in wild-type mice and lower expression relative to muscle and heart.NEW & NOTEWORTHY Myoglobin confers the distinct red color to muscle and heart, serving as an oxygen-binding protein in oxidative fibers. Less attention has been paid to brown fat, a thermogenic tissue that also expresses myoglobin. In a mouse knockout model lacking myoglobin, brown fat had larger fat droplets and lower markers of mitochondrial oxidative metabolism, especially in females. Gene expression patterns suggest a role for myoglobin as an oxygen/nitric oxide-sensor that regulates cellular metabolic and signaling pathways.

Ellagic Acid Affects Metabolic and Transcriptomic Profiles and Attenuates Features of Metabolic Syndrome in Adult Male Rats

Ellagic acid, a natural substance found in various fruits and nuts, was previously shown to exhibit beneficial effects towards metabolic syndrome. In this study, using a genetic rat model of metabolic syndrome, we aimed to further specify metabolic and transcriptomic responses to ellagic acid treatment. Adult male rats of the SHR-Zbtb16^Lx/k.o. strain were fed a high-fat diet accompanied by daily intragastric gavage of ellagic acid (50 mg/kg body weight; high-fat diet–ellagic acid (HFD-EA) rats) or vehicle only (high-fat diet–control (HFD-CTL) rats). Morphometric and metabolic parameters, along with transcriptomic profile of liver and brown and epididymal adipose tissues, were assessed. HFD-EA rats showed higher relative weight of brown adipose tissue (BAT) and decreased weight of epididymal adipose tissue, although no change in total body weight was observed. Glucose area under the curve, serum insulin, and cholesterol levels, as well as the level of oxidative stress, were significantly lower in HFD-EA rats. The most differentially expressed transcripts reflecting the shift induced by ellagic acid were detected in BAT, showing downregulation of BAT activation markers Dio2 and Nr4a1 and upregulation of insulin-sensitizing gene Pla2g2a. Ellagic acid may provide a useful nutritional supplement to ameliorate features of metabolic syndrome, possibly by suppressing oxidative stress and its effects on brown adipose tissue.

Beige Adipose Tissue Identification and Marker Specificity-Overview

Adipose tissue (AT) is classified based on its location, physiological and functional characteristics. Although there is a clear demarcation of anatomical and molecular features specific to white (WAT) and brown adipose tissue (BAT), the factors that uniquely differentiate beige AT (BeAT) remain to be fully elaborated. The ubiquitous presence of different types of AT and the inability to differentiate brown and beige adipocytes because of similar appearance present a challenge when classifying them one way or another. Here we will provide an overview of the latest advances in BeAT, BAT, and WAT identification based on transcript markers described in the literature. The review paper will highlight some of the difficulties these markers pose and will offer new perspectives on possible transcript-specific identification of BeAT. We hope that this will advance the understanding of the biology of different ATs. In addition, concrete strategies to distinguish different types of AT may be relevant to track the efficacy and mechanisms around interventions aimed to improve metabolic health and thwart excessive weight gain.

Comprehensive proteomics and functional annotation of mouse brown adipose tissue

Knowledge about the mouse brown adipose tissue (BAT) proteome can provide a deeper understanding of the function of mammalian BAT. Herein, a comprehensive analysis of interscapular BAT from C57BL/6J female mice was conducted by 2DLC and high-resolution mass spectrometry to construct a comprehensive proteome dataset of mouse BAT proteins. A total of 4949 nonredundant proteins were identified, and 4495 were quantified using the iBAQ method. According to the iBAQ values, the BAT proteome was divided into high-, middle- and low-abundance proteins. The functions of the high-abundance proteins were mainly related to glucose and fatty acid oxidation to produce heat for thermoregulation, while the functions of the middle- and low-abundance proteins were mainly related to protein synthesis and apoptosis, respectively. Additionally, 497 proteins were predicted to have signal peptides using SignalP4 software, and 75 were confirmed in previous studies. This study, for the first time, comprehensively profiled and functionally annotated the BAT proteome. This study will be helpful for future studies focused on biomarker identification and BAT molecular mechanisms.

Near-Infrared Time-Resolved Spectroscopy for Assessing Brown Adipose Tissue Density in Humans: A Review

Brown adipose tissue (BAT) mediates adaptive thermogenesis upon food intake and cold exposure, thus potentially contributing to the prevention of lifestyle-related diseases. ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) with computed tomography (CT) (¹⁸FDG-PET/CT) is a standard method for assessing BAT activity and volume in humans. ¹⁸FDG-PET/CT has several limitations, including high device cost and ionizing radiation and acute cold exposure necessary to maximally stimulate BAT activity. In contrast, near-infrared spectroscopy (NIRS) has been used for measuring changes in O₂-dependent light absorption in the tissue in a non-invasive manner, without using radiation. Among NIRS, time-resolved NIRS (NIR_TRS) can quantify the concentrations of oxygenated and deoxygenated hemoglobin ([oxy-Hb] and [deoxy-Hb], respectively) by emitting ultrashort (100 ps) light pulses and counts photons, which are scattered and absorbed in the tissue. The basis for assessing BAT density (BAT-d) using NIR_TRS is that the vascular density in the supraclavicular region, as estimated using Hb concentration, is higher in BAT than in white adipose tissue. In contrast, relatively low-cost continuous wavelength NIRS (NIR_CWS) is employed for measuring relative changes in oxygenation in tissues. In this review, we provide evidence for the validity of NIR_TRS and NIR_CWS in estimating human BAT characteristics. The indicators (Ind_NIRS) examined were [oxy-Hb]_sup, [deoxy-Hb]_sup, total hemoglobin [total-Hb]_sup, Hb O₂ saturation (StO_2sup), and reduced scattering coefficient ( μs sup' ) in the supraclavicular region, as determined by NIR_TRS, and relative changes in corresponding parameters, as determined by NIR_CWS. The evidence comprises the relationships between the Ind_NIRS investigated and those determined by ¹⁸FDG-PET/CT; the correlation between the Ind_NIRS and cold-induced thermogenesis; the relationship of the Ind_NIRS to parameters measured by ¹⁸FDG-PET/CT, which responded to seasonal temperature fluctuations; the relationship of the Ind_NIRS and plasma lipid metabolites; the analogy of the Ind_NIRS to chronological and anthropometric data; and changes in the Ind_NIRS following thermogenic food supplementation. The [total-Hb]_sup and [oxy-Hb]_sup determined by NIR_TRS, but not parameters determined by NIR_CWS, exhibited significant correlations with cold-induced thermogenesis parameters and plasma androgens in men in winter or analogies to ¹⁸FDG-PET. We conclude that NIR_TRS can provide useful information for assessing BAT-d in a simple, rapid, non-invasive way, although further validation study is still needed.

Analysis of fatty acids in mouse tissue via in situ transmethylation with biochar

Lipid derivatization technology-mediated fatty acid profiling studies have been suggested to dissect the contents of lipids in white fat and brown fat tissue. The focus of this study is to profile fatty acid lipidomics in brown adipose tissue and white adipose tissue of mice by derivatizing their lipids into fatty acid methyl esters via in situ transmethylation using a rice husk-derived biochar as porous media. The in situ transmethylation using biochar is advantageous in biological analysis because there was no loss of samples inevitably occurring in the loss of lipid in solvent extraction and purification steps.

Active individuals have high mitochondrial content and oxidative markers in their abdominal subcutaneous adipose tissue

OBJECTIVE

Exercise training (training) effects on white adipose tissue (WAT) thermogenic and oxidative capacities in humans are inconclusive. This study aimed to investigate whether an active lifestyle is characterized by thermogenic and/or oxidative transcriptional markers in human WAT.

METHODS

In vivo maximal muscle ATP synthetic rates (ATPmax) were measured by ³¹ P-MRS, body composition by DXA, and peak oxygen uptake (VO₂ peak) by cycle ergometry in active (n = 7) and sedentary (SED) individuals before and after 3 weeks of training (n = 9, SED only). mRNA expressions of brown adipose and β-oxidation markers, as well as mitochondrial DNA content (mtDNA), were measured by qRT-PCR and qPCR, respectively, in WAT.

RESULTS

ATPmax and VO₂ peak were higher in active versus SED individuals. Following training in SED individuals, ATPmax and VO₂ peak increased. Proliferator-activated receptor gamma coactivator-1α and carnitine palmitoyltransferase-1β gene expressions and mtDNA content were significantly higher in WAT of active versus SED individuals before training. mRNA contents of brown and beige-specific markers were not different between cohorts. Training effectively increased ATPmax and VO₂ peak but had no effect on mtDNA content or expressions of genes that regulate thermogenic and oxidative capacities in WAT.

CONCLUSIONS

Results indicate that an active lifestyle is characterized by elevated mitochondrial content and oxidative, not thermogenic, markers of WAT.

Construction of Nanodroplet/Adiposome and Artificial Lipid Droplets

The lipid droplet (LD) is a cellular organelle that consists of a neutral lipid core with a monolayer-phospholipid membrane and associated proteins. Recent LD studies demonstrate its importance in metabolic diseases and biofuel development. However, the mechanisms governing its formation and dynamics remain elusive. Therefore, we developed an in vitro system to facilitate the elucidation of these mechanisms. We generated sphere-shaped structures with a neutral lipid core and a monolayer-phospholipid membrane by mechanically mixing neutral lipids and phospholipids followed by a two-step purification. We named the nanodroplet "adiposome". We then recruited LD structure-like/resident proteins to the adiposome, including the bacterial MLDS, Caenorhabditis elegans MDT-28/PLIN-1, or mammalian perilipin-2. In addition, adipose triglyceride lipase (ATGL) and apolipoprotein A1 (apo A-I) were recruited to adiposome. We termed the functional protein-coated adiposomes, Artificial Lipid Droplets (ALDs). With this experimental system, different proteins can be recruited to build ALDs for some biological goals and potential usage in drug delivery.

Brown adipose tissue triglyceride content is associated with decreased insulin sensitivity, independently of age and obesity

The aim of the present study was to determine whether single-voxel proton magnetic resonance spectroscopy ((1)H-MRS) can non-invasively assess triglyceride content in both supraclavicular fat depots and subcutaneous white adipose tissue (WAT) to determine whether these measurements correlate to metabolic variables. A total of 25 healthy volunteers were studied using (18)F-fluorodeoxyglucose positron emission tomography (PET) and (15)O-H2O PET perfusion during cold exposure, and (1)H-MRS at ambient temperature. Image-guided biopsies were collected from nine volunteers. The supraclavicular triglyceride content determined by (1)H-MRS varied between 60 and 91% [mean ± standard deviation (s.d.) 77 ± 10%]. It correlated positively with body mass index, waist circumference, subcutaneous and visceral fat masses and 8-year diabetes risk based on the Framingham risk score and inversely with HDL cholesterol and insulin sensitivity (M-value; euglycaemic-hyperinsulinaemic clamp). Subcutaneous WAT had a significantly higher triglyceride content, 76-95% (mean ± s.d. 87 ± 5%; p = 0.0002). In conclusion, the triglyceride content in supraclavicular fat deposits measured by (1)H-MRS may be an independent marker of whole-body insulin sensitivity, independent of brown adipose tissue metabolic activation.

Human brown adipose tissue assessed by simple, noninvasive near-infrared time-resolved spectroscopy

OBJECTIVE

Human brown adipose tissue (BAT) activity has been typically evaluated by (18) F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) combined with computed tomography (CT). However, FDG-PET/CT has serious limitations (e.g., radiation and cold exposure). This study evaluated BAT density using near-infrared time-resolved spectroscopy (NIRTRS ), a simple and noninvasive method of measuring the indices of tissue hemoglobin concentration [total-Hb] and mitochondrial density (µs ').

METHODS

The NIRTRS parameters at 760, 800, and 830 nm in the supraclavicular region potentially containing BAT were evaluated. First, the NIRTRS parameters were compared at 27 °C and during a 2-h cold exposure (19 °C) in 18 men. Then, NIRTRS parameters at 27 °C were compared with mean standardized uptake values (SUVmean ) assessed by FDG-PET/CT after the 2-h cold exposure (19 °C) in 29 men.

RESULTS

There was no significant difference between the NIRTRS parameters at 27 °C and 19°C. The [total-Hb] and µs ' were significantly correlated to SUVmean (r = 0.73 and r = 0.64, respectively). A receiver operating characteristic analysis revealed that the sensitivity (75.0-82.4%), specificity (91.7-100%), and accuracy (82.8-86.2%) of the NIRTRS parameters were all good to determine the NIRTRS reliability.

CONCLUSIONS

Our novel NIRTRS method is noninvasive and simple and can reliably assess human BAT density in the supraclavicular region.

Adipose fatty acid oxidation is required for thermogenesis and potentiates oxidative stress-induced inflammation

To understand the contribution of adipose tissue fatty acid oxidation to whole-body metabolism, we generated mice with an adipose-specific knockout of carnitine palmitoyltransferase 2 (CPT2(A-/-)), an obligate step in mitochondrial long-chain fatty acid oxidation. CPT2(A-/-) mice became hypothermic after an acute cold challenge, and CPT2(A-/-) brown adipose tissue (BAT) failed to upregulate thermogenic genes in response to agonist-induced stimulation. The adipose-specific loss of CPT2 resulted in diet-dependent changes in adiposity but did not result in changes in body weight on low- or high-fat diets. Additionally, CPT2(A-/-) mice had suppressed high-fat diet-induced oxidative stress and inflammation in visceral white adipose tissue (WAT); however, high-fat diet-induced glucose intolerance was not improved. These data show that fatty acid oxidation is required for cold-induced thermogenesis in BAT and high-fat diet-induced oxidative stress and inflammation in WAT.

Miglitol protects against age-dependent weight gain in mice: A potential role of increased UCP1 content in brown adipose tissue

Miglitol is an absorbable alpha-glucosidase inhibitor that is used to control post-prandial hyperglycemia. We previously found that miglitol stimulates brown adipose tissue and prevents diet-induced obesity in mice that are fed a high-fat, high-carbohydrate diet. In this study, we examined whether miglitol can also protect against aging-dependent weight gain in mice that are fed a normal chow diet. Male C57Bl/6J mice were fed normal chow with or without miglitol (800 ppm) for 12 weeks, starting at 12 weeks of age. Food intake and body weight were monitored. After 12 weeks, adiposity, energy expenditure, and locomotor activities were measured. After sacrifice, weight of the epididymal white adipose tissue and adipocyte size were measured. Finally, Ucp1 gene expression and UCP1 protein abundance in brown adipose tissue were quantified by RT-PCR and Western analyses, respectively. Miglitol prevented age-related weight gain without affecting growth of the animals. Miglitol-treated mice showed reduced adiposity and increased oxygen consumption compared to controls, accompanied by higher UCP1 protein abundance in brown adipose tissue. Food intake and locomotor activities were not affected. These results suggest that miglitol can protect against age-dependent weight gain. Elucidating the molecular targets of miglitol in brown adipose tissue and optimizing drug delivery and efficacy may provide new strategies to combat obesity.

Treatment of rats with a self-selected hyperlipidic diet, increases the lipid content of the main adipose tissue sites in a proportion similar to that of the lipids in the rest of organs and tissues

Adipose tissue (AT) is distributed as large differentiated masses, and smaller depots covering vessels, and organs, as well as interspersed within them. The differences between types and size of cells makes AT one of the most disperse and complex organs. Lipid storage is partly shared by other tissues such as muscle and liver. We intended to obtain an approximate estimation of the size of lipid reserves stored outside the main fat depots. Both male and female rats were made overweight by 4-weeks feeding of a cafeteria diet. Total lipid content was analyzed in brain, liver, gastrocnemius muscle, four white AT sites: subcutaneous, perigonadal, retroperitoneal and mesenteric, two brown AT sites (interscapular and perirenal) and in a pool of the rest of organs and tissues (after discarding gut contents). Organ lipid content was estimated and tabulated for each individual rat. Food intake was measured daily. There was a surprisingly high proportion of lipid not accounted for by the main macroscopic AT sites, even when brain, liver and BAT main sites were discounted. Muscle contained about 8% of body lipids, liver 1–1.4%, four white AT sites lipid 28–63% of body lipid, and the rest of the body (including muscle) 38–44%. There was a good correlation between AT lipid and body lipid, but lipid in “other organs” was highly correlated too with body lipid. Brain lipid was not. Irrespective of dietary intake, accumulation of body fat was uniform both for the main lipid storage and handling organs: large masses of AT (but also liver, muscle), as well as in the ”rest” of tissues. These storage sites, in specialized (adipose) or not-specialized (liver, muscle) tissues reacted in parallel against a hyperlipidic diet challenge. We postulate that body lipid stores are handled and regulated coordinately, with a more centralized and overall mechanisms than usually assumed.

Normal Distribution of Body Weight Gain in Male Sprague-Dawley Rats Fed a High-Energy Diet

OBJECTIVE

To investigate the effect of a high-energy (HE) diet on caloric intake, body weight, and related parameters in outbred male Sprague-Dawley (SD) rats.

RESEARCH METHODS AND PROCEDURES

Twenty-eight SD rats were fed either chow (C) for 19 weeks or HE diet for 14 weeks and then C for 5 weeks. Blood hormones and metabolites were assayed, and expression of uncoupling protein-1 and hypothalamic energy-balance-related genes were determined by Northern blotting and in situ hybridization, respectively.

RESULTS

HE rats gained body weight more rapidly than C animals with a range of weight gains, but there was no evidence that weight gain was bimodally distributed. Caloric intake was transiently elevated after introduction of the HE diet. Transfer of HE rats back to C resulted in a drop in caloric intake, but a stable body weight. In terminal analysis, two of four dissected adipose tissue depots were heavier in rats that had previously been fed HE diet. Blood leptin, insulin, glucose, and nonesterified fatty acids were not different between the groups. Uncoupling protein-1 mRNA was elevated in interscapular brown adipose tissue from HE rats. There was a trend for agouti-related peptide mRNA in the hypothalamic arcuate nucleus to be higher in HE rats.

DISCUSSION

Contrary to other studies of the SD rat on HE diet, body weight and other measured parameters were normally distributed. There was no segregation into two distinct populations on the basis of susceptibility to diet-induced obesity. This characteristic may be dependent on the breeding colony from which animals were sourced.

Inhibition of soluble epoxide hydrolase reduces food intake and increases metabolic rate in obese mice

BACKGROUND AND AIMS

This study evaluated the responses to soluble epoxide hydrolase (s-EH) inhibition, an essential enzyme in the metabolism of arachidonic acid, on food intake, body weight and metabolic parameters in mice fed a high fat-high fructose diet (HFD) for 10 weeks.

METHODS AND RESULTS

After 5 weeks of HFD, mice were divided into two groups: 1) s-EH inhibitor (AR9281, 200mg/kg/day by gavage twice daily), and 2) vehicle (0.3ml per gavage). Food intake, body weight, oxygen consumption (VO(2)), carbon dioxide production (VCO(2)), respiratory quotient (RQ), and motor activity were measured weekly for more 5 weeks. HFD increased body weight (37±1 vs. 26±1g), and plasma of glucose (316±8 vs. 188±27mg/dl), insulin (62.1±8.1 vs. 15.5±5.0μU/ml), and leptin levels (39.4±3.6 vs. 7.5±0.1ng/ml) while reducing VO(2), VCO(2) and motor activity. s-EH inhibition for 5 weeks decreased caloric intake by ~32% and increased VO(2) by ~17% (42.8±1.4 vs. 50.2±1.5ml/kg/min) leading to significant weight loss. Inhibition of s-EHi also caused significant reductions in plasma leptin levels and visceral fat content. Uncoupling protein 1 (UCP1) content in brown adipose tissue was also elevated by ~50% during s-EH inhibition compared to vehicle treatment.

CONCLUSION

These results suggest that s-EH inhibition with AR9281 promotes weight loss by reducing appetite and increasing metabolic rate, and that increased UCP1 content may contribute to the increase in energy expenditure.

A black soybean seed coat extract prevents obesity and glucose intolerance by up-regulating uncoupling proteins and down-regulating inflammatory cytokines in high-fat diet-fed mice

Black soybean seed coat extract (BE) is a polyphenol-rich food material consisting of 9.2% cyanidin 3-glucoside, 6.2% catechins, 39.8% procyanidins, and others. This study demonstrated that BE ameliorated obesity and glucose intolerance by up-regulating uncoupling proteins (UCPs) and down-regulating inflammatory cytokines in C57BL/6 mice fed a control or high-fat diet containing BE for 14 weeks. BE suppressed fat accumulation in mesenteric adipose tissue, reduced the plasma glucose level, and enhanced insulin sensitivity in the high-fat diet-fed mice. The gene and protein expression levels of UCP-1 in brown adipose tissue and UCP-2 in white adipose tissue were up-regulated by BE. Moreover, the gene expression levels of major inflammatory cytokines, tumor necrosis factor-α and monocyte chemoattractant protein-1 were remarkably decreased by BE in white adipose tissue. BE is a beneficial food material for the prevention of obesity and diabetes by enhancing energy expenditure and suppressing inflammation.

Adrenocorticotrophic hormone retarded metabolism of low‐density lipoprotein in rats

In humans, treatment with adrenocorticotrophic hormone (ACTH) has well-documented plasma cholesterol lowering and low-density lipoprotein (LDL) lowering effects. Moreover, it has recently been demonstrated that ACTH directly inhibits apolipoprotein B expression and secretion in the HepG2 cell line. The aim of the present study was to demonstrate the effects of ACTH on lipid metabolism in the rat, and particularly on LDL metabolism. Rats were treated with porcine ACTH for 3 days and plasma lipid parameters were determined. Surprisingly, the total cholesterol level and LDL-cholesterol level were increased in plasma after ACTH administration, displaying an opposite effect of ACTH in humans. Furthermore, clearance and distribution of radiolabeled human LDL in different tissues were investigated in the rat after ACTH treatment. The clearance of radiolabeled LDL was slightly decreased after ACTH treatment suggesting that ACTH can inhibit LDL catabolism in the rat. Unlike previous observations performed in human hepatic cell cultures, there was no change in apoB expression in rat liver, or in apoE and apoM expression, after treatment with ACTH. This study clearly demonstrates that ACTH has species specificity differences in humans and in the rat.

Detection of prion infectivity in fat tissues of scrapie-infected mice

Distribution of prion infectivity in organs and tissues is important in understanding prion disease pathogenesis and designing strategies to prevent prion infection in animals and humans. Transmission of prion disease from cattle to humans resulted in banning human consumption of ruminant nervous system and certain other tissues. In the present study, we surveyed tissue distribution of prion infectivity in mice with prion disease. We show for the first time detection of infectivity in white and brown fat. Since high amounts of ruminant fat are consumed by humans and also incorporated into animal feed, fat-containing tissues may pose a previously unappreciated hazard for spread of prion infection.

Prion diseases, also known as transmissible spongiform encephalopathies, are infectious progressive fatal neurodegenerative diseases which affect humans as well as wild and domestic animals. Distribution of prion infectivity in organs and tissues is important in understanding prion disease pathogenesis and designing strategies to prevent prion infection in animals and humans. We show for the first time the presence of prion infectivity in white fat and brown fat tissues of mice with prion disease. Our results suggest that fat tissues of domestic or wild animals infected with prions may pose an unappreciated hazard for spread of infection to humans or domestic animals. The presence of prion infectivity in fat suggests that additional consideration may be required to eliminate from the food chain any fat from ruminants suspected of exposure to or infection with prions. Thus, this finding has implications for public health, food safety, and prion disease prevention strategies.

Comparative expression analysis of the renin-angiotensin system components between white and brown perivascular adipose tissue

Recent studies have demonstrated that the rat adipose tissue expresses some of the components necessary for the production of angiotensin II (Ang II) and the receptors mediating its actions. The aim of this work is to characterize the expression of the renin-angiotensin system (RAS) components in perivascular adipose tissue and to assess differences in the expression pattern depending on the vascular bed and type of adipose tissue. We analyzed Ang I and Ang II levels as well as mRNA levels of RAS components by a quantitative RT-PCR method in periaortic (PAT) and mesenteric adipose tissue (MAT) of 3-month-old male Wistar-Kyoto rats. PAT was identified as brown adipose tissue expressing uncoupling protein-1 (UCP-1). It had smaller adipocytes than those from MAT, which was identified as white adipose tissue. All RAS components, except renin, were detected in both PAT and MAT. Levels of expression of angiotensinogen, Ang-converting enzyme (ACE), and ACE2 were similar between PAT and MAT. Renin receptor expression was five times higher, whereas expression of chymase, AT(1a), and AT(2) receptors were significantly lower in PAT compared with MAT respectively. In addition, three isoforms of the AT(1a) receptor were found in perivascular adipose tissue. The AT(1b) receptor was found at very a low expression level. Ang II levels were higher in MAT with no differences between tissues in Ang I. The results show that the RAS is differentially expressed in white and brown perivascular adipose tissues implicating a different role for the system depending on the vascular bed and the type of adipose tissue.

Expression of deoxynucleoside kinases and 5'-nucleotidases in mouse tissues: implications for mitochondrial toxicity

Anti-HIV nucleoside therapy can result in mitochondrial toxicity affecting muscles, peripheral nerves, pancreas and adipose tissue. The cytosolic deoxycytidine kinase (dCK; EC 2.7.1.74) and thymidine kinase (TK1; EC 2.7.1.21), the mitochondrial thymidine kinase (TK2) and deoxyguanosine kinase (dGK; EC 2.7.1.113) as well as 5'-deoxynucleotidases (5'-dNT; EC 3.1.3.5) are enzymes that control rate-limiting steps in formation of intracellular and intra-mitochondrial nucleotides. The mRNA levels and activities of these enzymes were determined in mouse tissues, using real-time PCR and selective enzyme assays. The expression of mRNA for all these enzymes and the mitochondrial deoxynucleotide carrier was detected in all tissues with a 5-10-fold variation. TK1 activities were only clearly detected in spleen and testis, while TK2, dGK and dCK activities were found in all tissues. dGK activities were higher than any other dNK in all tissues, except spleen and testis. In skeletal muscle dGK activity was 5-fold lower, TK2 and dCK levels were 10-fold lower as compared with other tissues. The variation in 5'-dNT activities was about eight-fold with the highest levels in brain and lowest in brown fat. Thus, the salvage of deoxynucleosides in muscles is 5-10-fold lower as compared to other non-proliferating tissues and 100-fold lower compared to spleen. These results may help to explain tissue specific toxicity observed with nucleoside analogs used in HIV treatment as well as symptoms in inherited mitochondrial TK2 deficiencies.

Adrenomedullin and its receptor components in adipose tissues: Differences between white and brown fats and the effects of adrenergic stimulation

Male Sprague-Dawley rats were subcutaneously injected with 2.5mg/kg phenylephrine or 2.5mg/kg isoproterenol or both (2.5mg/kg for each drug) for 4 days, twice a day. Samples of scapular brown adipose tissue (BAT) and epididymal white adipose tissue (WAT) were collected for the measurement of adrenomedullin (AM) levels and the gene expression of preproAM, calcitonin receptor like receptor (CRLR) and its activity modifying proteins (RAMPs) by radioimmunoassay and RT-PCR. These values were compared with those in the rats that received 0.9% saline. The gene expression of AM and AM receptor components in BAT are much less than that in epididymal WAT. In BAT there were an increase in AM peptide level after a combined treatment of alpha(1) and beta adrenoceptor agonists and increases in preproAM mRNA levels for rats treated with alpha(1) and beta receptor agonists alone or in combination. Both CRLR and RAMP2 mRNA levels of alphabeta group were increased significantly. In WAT, AM peptide level, RAMP1 and RAMP2 mRNA expression levels were augmented in the alpha group while CRLR mRNA level was enhanced in the beta group. The levels of AM, its receptor and RAMPs are much less in BAT than in WAT but adrenergic stimulation has a greater effect on the AM and its receptor components in BAT than those in WAT. AM stimulates lipolysis and increases the level of uncoupling protein-1 (UCP-1) in BAT. It may therefore enhance thermogenesis by increasing the availability of free fatty acids substrate as well as the UCP-1 level on the mitochondrial membrane.

AQP7 is localized in capillaries of adipose tissue, cardiac and striated muscle: implications in glycerol metabolism

Aquaporin (AQP7) is expressed in proximal tubules and is involved in glycerol uptake. The cellular expression and physiological function in other organs remain largely undefined. AQP7 knockout (KO) mice were generated and used for immunohistochemical analyses to define the organ and cellular expression of AQP7. AQP7 labeling was found in kidney proximal tubule, heart, skeletal muscle, testis, epididymis, as well as in white and brown adipose tissue (WAT and BAT) of wild-type mice. Importantly, immunoreactivity was completely absent from these tissues in AQP7 KO mice. At the cellular level, the capillary endothelium WAT and BAT displayed prominent staining, whereas AQP7 labeling in adipocyte membranes was undetectable. Double-labeling confocal microscopy revealed coexpression of AQP7 with capillary AQP1 but not with adipocyte GLUT4. Moreover, immunoelectron microscopy and RT-PCR of isolated microvessels confirmed the vascular AQP7 expression. Distinct immunolabeling of the capillary endothelium was also observed in both skeletal and heart muscle with no apparent staining of skeletal or cardiac myocytes. As previously reported, specific immunolabeling was confined to brush border in segment 3 renal proximal tubules and to spermatids and spermatozoa in male reproductive tract. The expression of AQP7 was induced up to 2.2-fold in WAT of mice with streptozotocin-induced diabetes mellitus (S-DM) compared with controls and fasting for 72 h (but not 24 h) induced significant increase in AQP7 expression. In conclusion, AQP7 is expressed in capillary endothelia of adipose tissue (and cardiac and striated muscle) and is upregulated in WAT in response to S-DM supporting its role in glycerol metabolism.

Ectopic brown adipose tissue in muscle provides a mechanism for differences in risk of metabolic syndrome in mice

C57BL/6 (B6) mice subjected to a high-fat diet develop metabolic syndrome with obesity, hyperglycemia, and insulin resistance, whereas 129S6/SvEvTac (129) mice are relatively protected from this disorder because of differences in higher basal energy expenditure in 129 mice, leading to lower weight gain. At a molecular level, this difference correlates with a marked higher expression of uncoupling protein 1 (UCP1) and a higher degree of uncoupling in vitro in mitochondria isolated from muscle of 129 versus B6 mice. Detailed histological examination, however, reveals that this UCP1 is in mitochondria of brown adipocytes interspersed between muscle bundles. Indeed, the number of UCP1-positive brown fat cells in intermuscular fat in 129 mice is >700-fold higher than in B6 mice. These brown fat cells are subject to further up-regulation of UCP1 after stimulation with a beta3-adrenergic receptor agonist. Thus, ectopic deposits of brown adipose tissue in intermuscular depots with regulatable expression of UCP1 provide a genetically based mechanism of protection from weight gain and metabolic syndrome between strains of mice.

Sex Differences in Brown Adipose Tissue Thermogenic Features During Caloric Restriction

Caloric restriction (CR) studies have shown that females rats conserve energy more efficiently, showing a higher resistance to weight loss and higher protection of vital organs mass than male rats. Gender-dependent inactivation of thermogenesis in brown adipose tissue (BAT) has been proposed as one of these possible energy conserving mechanisms. To study the changes underlying this inactivation in rats, a three month study with 40% CR was undertaken to unravel the effects on BAT recruitment. Under ad libitum conditions female rats had greater BAT recruitment and greater oxygen consumption than their male counterparts. Total and mitochondrial protein, as well as triglyceride and DNA content were more reduced in restricted female rats than in restricted males. Similarly, the levels of key BAT functional proteins (UCP1, LPL, HSL, TFAM) were more reduced in restricted females, whereas no changes were found in mitochondrial DNA levels (mtDNA) and OXPHOS activities in males and females. Furthermore, alpha (2A)/beta (3) adrenergic receptor ratio remained constant in male rats whereas in female rats CR increased 60%. In conclusion, our results suggest that female rats, whose BAT thermogenic activity is higher in ad libitum conditions, is depressed during CR. This inactivation involves the mitochondrial differentiation process and lipolytic system and could be due, at least in part, to the unfavourable adrenergic receptor balance for thermogenic activation.

Adrenergic receptor density in brown adipose tissue of active and hibernating hamsters and ground squirrels

The ligand-binding characteristics (B(max) and K(D)) of alpha(1)- and beta(1)/beta(2)-adrenoceptors were investigated in membranes prepared from brown adipose tissue (BAT) of warm-acclimated, cold-acclimated, hibernating and arousing ground squirrels (Spermophillus undulatus) and hamsters (Mesocricetus auratus) by specific binding of [(3)H]prazosin and [(3)H]CGP-12177, respectively. The physiological state did not change the affinity for the adrenoceptors in the BAT of ground squirrels and hamsters. There was a significant decrease in alpha(1)-receptor density in arousing ground squirrels and a significant decrease in beta(1)/beta(2) density in hibernating ground squirrels. The level of alpha(1)-receptors was in all conditions higher than that of beta(1)/beta(2) receptors. The results indicate a possible change in balance of adrenoceptor density in the processes of cold acclimation, hibernation and arousal. The balance between the various adrenoceptor subtypes may be important for the final effect of catecholamines in BAT in different physiological states.

Regulation of UCP1 and UCP3 in arctic ground squirrels and relation with mitochondrial proton leak

Uncoupling protein (UCP) 1 (UCP1) catalyzes a proton leak in brown adipose tissue (BAT) mitochondria that results in nonshivering thermogenesis (NST), but the extent to which UCP homologs mediate NST in other tissues is controversial. To clarify the role of UCP3 in mediating NST in a hibernating species, we measured Ucp3 expression in skeletal muscle of arctic ground squirrels in one of three activity states (not hibernating, not hibernating and fasted for 48 h, or hibernating) and housed at 5°C or −10°C. We then compared Ucp3 mRNA levels in skeletal muscle with Ucp1 mRNA and UCP1 protein levels in BAT in the same animals. Ucp1 mRNA and UCP1 protein levels were increased on cold exposure and decreased with fasting, with the highest UCP1 levels in thermogenic hibernators. In contrast, Ucp3 mRNA levels were not affected by temperature but were increased 10-fold during fasting and >3-fold during hibernation. UCP3 protein levels were increased nearly fivefold in skeletal muscle mitochondria isolated from fasted squirrels compared with nonhibernators, but proton leak kinetics in the presence of BSA were unchanged. Proton leak in BAT mitochondria also did not differ between fed and fasted animals but did show classical inhibition by the purine nucleotide GDP. Levels of nonesterified fatty acids were highest during hibernation, and tissue temperatures during hibernation were related to Ucp1, but not Ucp3, expression. Taken together, these results do not support a role for UCP3 as a physiologically relevant mediator of NST in muscle.

Seasonal regulations of energetics, serum concentrations of leptin, and uncoupling protein 1 content of brown adipose tissue in root voles (Microtus oeconomus) from the Qinghai-Tibetan plateau

Survival of small mammals in winter requires proper adjustments in physiology, behavior and morphology. The present study was designed to examine the changes in serum leptin concentration and the molecular basis of thermogenesis in seasonally acclimatized root voles (Microtus oeconomus) from the Qinghai-Tibetan plateau. In January root voles had lower body mass and body fat mass coupled with higher nonshivering thermogenesis (NST) capacity. Consistently, cytochrome c oxidase activity and mitochondrial uncoupling protein-1 (UCP1) protein contents in brown adipose tissues were higher in January as compared to that in July. Circulating level of serum leptin was significantly lower in winter and higher in July. Correlation analysis showed that serum leptin levels were positively related with body mass and body fat mass while negatively correlated with UCP1 protein contents. Together, these data provided further evidence for our previous findings that root voles from the Qinghai-Tibetan plateau mainly depend on higher NST coupled with lower body mass to enhance winter survival. Further, fat deposition was significantly mobilized in cold winter and leptin was potentially involved in the regulation of body mass and thermogenesis in root voles. Serum leptin might act as a starvation signal in winter and satiety signal in summer.

The hydrolipidic ratio in age-related maturation of adipose tissues

The hydrolipidic ratio (HLR) expresses the amount of water and fat in a tissue. HLR can be studied non-invasively in the living organism and can be mapped in different areas of the body with high spatial and temporal resolution. In the present work we have evaluated the HLR in different adipose tissue depots in young or adult rats using tissue arrays of fat fragments by 1H-spectroscopy. In young animals, the highest percentage of water (33%) was found in the interscapular brown adipose tissue (iBAT). Mesenteric fat (mWAT) also appeared highly hydrated (24%). The deposits composed of epididymal, retroperitoneal and pelvic white adipose tissue (eWAT, rWAT and pWAT, respectively) contained an amount of water ranging from 14% to 17%. In adult animals, a reduction of the water content was found in all the depots. In e/r/pWAT, the age-related maturation was characterized by large changes in adipocyte diameter accompanied by a small change in HLR. In the iBAT, the maturation was accompanied by small change in adipocyte diameter and a greater diminution of HLR. mWAT showed an intermediate pattern between e/r/pWAT and iBAT. In all the studied depots, an age-related increase in leptin expression was found. This increase was relatively low in iBAT (40%) and high in the e/r/pWAT (204-273%). The work expand the knowledge about the physiological significance of the HLR by 1H-spectroscopy.

Assessment of a high-throughput screening methodology for the measurement of purified UCP1 uncoupling activity

Three mitochondrial uncoupling proteins (UCP1, 2, 3) have been described. The proton transport activity of UCP1 triggers mitochondrial uncoupling and thermogenesis but the roles of UCP2 and UCP3 remain debated. Accordingly, compounds able to finely control the proton permeability of the mitochondrial inner membrane where and when needed may have enormous practical consequences. Using purified hamster brown adipose tissue UCP1 reconstituted in liposomes, we describe herein a robust assay allowing the measurement of this artificial membrane conductance to protons in a format compatible with high-throughput screening. The assay was initially developed with a known chemical protonophore in an aproteic system. Then, using the proteolipid reconstituted UCP1 preparation, we assessed the assay with known modulators of UCP1, particularly retinoic acid and guanosine 5'-triphosphate. The system was developed for a 96-well plate format. We then exemplified its use by generating primary data on a set of compounds screened in this system. These primary data will open new routes for the search of candidate compounds that will help biochemical studies on UCPs.

Differential effects of leptin administration on the abundance of UCP2 and glucocorticoid action during neonatal development

In the neonate, adipose tissue and the lung both undergo a rapid transition after birth, which results in dramatic changes in uncoupling protein abundance and glucocorticoid action. Leptin potentially mediates some of these adaptations and is known to promote the loss of uncoupling protein (UCP)1, but its effects on other mitochondrial proteins or glucocorticoid action are not known. We therefore determined the effects of acute and chronic administration of ovine recombinant leptin on brown adipose tissue (BAT) and/or lung in neonatal sheep. For the acute study, eight pairs of 1-day-old lambs received, sequentially, 10, 100, and 100 mug of leptin or vehicle before tissue sampling 4 h from the start of the study, whereas in the chronic study, nine pairs of 1-day-old lambs received 100 mug of leptin or vehicle daily for 6 days before tissue sampling on day 7. Acute leptin decreased the abundance of UCP2, glucocorticoid receptor, and 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 1 mRNA and increased 11beta-HSD type 2 mRNA abundance in BAT, a pattern that was reversed with chronic leptin administration, which also diminished lung UCP2 protein abundance. In BAT, UCP2 mRNA abundance was positively correlated to plasma leptin and nonesterified fatty acids and negatively correlated to mean colonic temperature in the leptin group at 7 days. In conclusion, leptin administration to the neonatal lambs causes differential effects on UCP2 abundance in BAT and lung. These effects may be important in the development of these tissues, thereby optimizing lung function and fat growth.

The Distinctive Role of Positron Emission Tomography/Computed Tomography in Breast Carcinoma with Brown Adipose Tissue 2-Fluoro-2-Deoxy-D-Glucose Uptake

The diagnostic power of an integrated positron emission tomography/computed tomography (PET/CT) system for whole-body 2-fluoro-2-deoxy-d-glucose (FDG) imaging is clearly demonstrated in this case report. The precise anatomic localization of FDG uptake with CT in a PET/CT scan of a patient with known breast carcinoma helped identify a contralateral breast tumor with axillary lymph node metastasis despite the presence of extensive physiologic brown fat FDG uptake. Accordingly, the patient received appropriate surgical management and pathologic confirmation of the disease.

Noradrenaline represses PPAR (peroxisome-proliferator-activated receptor) gamma2 gene expression in brown adipocytes: intracellular signalling and effects on PPARgamma2 and PPARgamma1 protein levels

PPAR (peroxisome-proliferator-activated receptor) gamma is expressed in brown and white adipose tissues and is involved in the control of differentiation and proliferation. Noradrenaline stimulates brown pre-adipocyte proliferation and brown adipocyte differentiation. The aim of the present study was thus to investigate the influence of noradrenaline on PPARgamma gene expression in brown adipocytes. In primary cultures of brown adipocytes, PPARgamma2 mRNA levels were 20-fold higher than PPARgamma1 mRNA levels. PPARgamma expression occurred during both the proliferation and the differentiation phases, with the highest mRNA levels being found at the time of transition between the phases. PPARgamma2 mRNA levels were downregulated by noradrenaline treatment (EC50, 0.1 microM) in both proliferative and differentiating cells, with a lagtime of 1 h and lasting up to 4 h, after which expression gradually recovered. The down-regulation was beta-adrenoceptor-induced and intracellularly mediated via cAMP and protein kinase A; the signalling pathway did not involve phosphoinositide 3-kinase, Src, p38 mitogen-activated protein kinase or extracellular-signal-regulated kinases 1 and 2. Treatment of the cells with the protein synthesis inhibitor cycloheximide not only abolished the noradrenaline-induced down-regulation of PPARgamma2 mRNA, but also in itself induced PPARgamma2 hyperexpression. The down-regulation was probably the result of suppression of transcription. The down-regulation of PPARgamma2 mRNA resulted in similar down-regulation of PPARgamma2 and phosphoPPARgamma2 protein levels. Remarkably, the level of PPARgamma1 protein was similar to that of PPARgamma2 (despite almost no PPARgamma1 mRNA), and the down-regulation by noradrenaline demonstrated similar kinetics to that of PPARgamma2; thus PPARgamma1 was apparently translated from the PPARgamma2 template. It is suggested that beta-adrenergic stimulation via cAMP and protein kinase A represses PPARgamma gene expression, leading to reduction of PPARgamma2 mRNA levels, which is then reflected in down-regulated levels of PPARgamma2, phosphoPPARgamma2 and PPARgamma1.

Quantitative rt-PCR analysis of uncoupling protein isoforms in mouse brain cortex: methodological optimization and comparison of expression with brown adipose tissue and skeletal muscle

Uncoupling proteins (UCPs) present in the inner mitochondrial membrane are involved in uncoupling respiration from ATP synthesis. Five UCP isoforms have been identified but information about their presence and level of expression in the central nervous system remains incomplete. To determine the nature and proportion of UCP isoform mRNAs present in brain cortex, we developed and optimized a specific quantitative reverse-transcription polymerase chain reaction procedure. Optimal range of RNA concentrations to be used in the reverse-transcriptase reaction was determined. Primer design and concentration were optimized for each target gene while polymerase chain reaction efficiency was assessed for a range of reverse-transcriptase dilutions. Genomic contribution to the quantitative signal was evaluated for each isoform and minimized. Three reference genes were tested for normalization, and beta-actin was found to be the most stable among tissues. Results indicate that brain cortex contains significant amounts of all UCP mRNAs, with UCP5 and UCP4 being the most abundant, as opposed to brown adipose tissue and skeletal muscle, which predominantly express UCP1 and UCP3, respectively. These data provide a first quantitative assessment of UCP mRNA expression in mouse brain, showing the presence of all five isoforms with distinct proportions, thus suggesting specific roles in the central nervous system.

Inhibition of uncoupling protein expression during lactation: role of leptin

Uncoupling proteins (UCPs) are mitochondrial proteins that play a role in regulation of energy expenditure by uncoupling respiration from ATP synthesis. Lactation is a physiological condition characterized by negative energy balance due to the loss of energy sources to the production of milk. The objective of the current study was to investigate whether UCP mRNA and protein expressions were altered during lactation compared with those after 48 h of fasting. Lactation significantly reduced serum leptin levels, and removal of pups for 48 h increased serum leptin to higher levels than those observed in control rats. Compared with control rats, mRNA expression of UCP1 and UCP3 in brown adipose tissue (BAT) was dramatically reduced during lactation and fasting. The reduction in mRNAs was reflected by a lowered UCP1 protein level, and to some extent, UCP3 protein. Treatment of lactating rats with exogenous leptin (3 mg/kg) or removal of pups for 48 h completely reversed the down-regulation of UCP1 and UCP3 mRNA expression in BAT, and pup removal led to a recovery of protein expression. In contrast to BAT, UCP3 expression in skeletal muscle was increased in fasted rats and decreased during lactation. Similar changes were observed in serum free fatty acid levels. These changes are consistent with the idea that the utilization of free fatty acids as a fuel source is spared during lactation. As in BAT, leptin treatment and removal of pups were able to restore changes in mRNA expression of UCP3 in skeletal muscle during lactation. The present results suggest that the inhibition of leptin secretion during lactation is involved in the down-regulation of UCP expression in BAT and skeletal muscle, which, in turn, is responsible for the decrease in metabolic fuel oxidation and thermogenesis.

Green tea reduces body fat accretion caused by high-fat diet in rats through β-adrenoceptor activation of thermogenesis in brown adipose tissue

The aim of the present study was to investigate body fat-suppressive effects of green tea in rats fed on a high-fat diet and to determine whether the effect is associated with beta-adrenoceptor activation of thermogenesis in brown adipose tissue. Feeding a high-fat diet containing water extract of green tea at the concentration of 20g/kg diet prevented the increase in body fat gain caused by high-fat diet without affecting energy intake. Energy expenditure was increased by green tea extract which was associated with an increase in protein content of interscapular brown adipose tissue. The simultaneous administration of the beta-adrenoceptor antagonist propranolol(500 mg/kg diet) inhibited the body fat-suppressive effect of green tea extract. Propranolol also prevented the increase in protein content of interscapular brown adipose tissue caused by green tea extract. Digestibility was slightly reduced by green tea extract and this effect was not affected by propranolol. Therefore it appeared that green tea exerts potent body fat-suppressive effects in rats fed on a high-fat diet and the effect was resulted in part from reduction in digestibility and to much greater extent from increase in brown adipose tissue thermogenesis through beta-adrenoceptor activation.

Corticotropin-releasing hormone-mediated pathway of leptin to regulate feeding, adiposity, and uncoupling protein expression in mice

To examine the functional role of CRH in the regulation of energy homeostasis by leptin, we measured the effects of the CRH antagonist, alpha-helical CRH 8-41 (alphaCRH) on a number of factors affected by leptin activity. These included food intake, body weight, hypothalamic c-fos-like immunoreactivity (c-FLI), weight and histological characterization of white adipose tissue, and mRNA expressions of uncoupling protein (UCP) in brown adipose tissue (BAT) in C57Bl/6 mice. Central infusion of leptin into the lateral cerebroventricle (icv) caused significant induction of c-FLI in the paraventricular nucleus (PVN), ventromedial hypothalamic nucleus (VMH), dorsomedial hypothalamic nucleus, and arcuate nucleus. In all these nuclei, the effect of leptin on expression of cFLI in the PVN and VMH was decreased by treatment with alphaCRH. Administration of leptin markedly decreased cumulative food intake and body weight with this effect being attenuated by pretreatment with alphaCRH. In peripheral tissue, leptin up-regulated BAT UCP1 mRNA expression and reduced fat depositions in this tissue. Those changes in BAT were also decreased by treatment with alphaCRH. As a consequence of the effects on food intake or energy expenditure, treatment with alphaCRH attenuated the leptin-induced reduction of body adiposity, fat cell size, triglyceride contents, and ob mRNA expression in white adipose tissue. Taken together, these results indicate that CRH neurons in the PVN and VMH may be an important mediator for leptin that contribute to regulation of feeding, adiposity, and UCP expression.

Selective detection of UCP 3 expression in skeletal muscle: effect of thyroid status and temperature acclimation

A novel peptide antibody to UCP 3 is characterized which is sensitive and discriminatory for UCP 3 over UCP 2, UCP 1 and other mitochondrial transporters. The peptide antibody detects UCP 3 expression in E. coli, COS cells and yeast expression systems. The peptide antibody detects a single approximately 33 kDa protein band in mitochondria from isolated rat skeletal muscle, mouse and rat brown adipose tissue, and in whole muscle groups (soleus and extensor digitorum longus) from mice. No 33 kDa band is detectable in isolated mitochondria from liver, heart, brain, kidney and lungs of rats, or gastrocnemius mitochondria from UCP 3 knock-out mice. From our data, we conclude that the peptide antibody is detecting UCP 3 in skeletal muscle, skeletal muscle mitochondria and brown adipose tissue mitochondria. It is also noteworthy that the peptide antibody can detect human, mouse and rat forms of UCP 3. Using the UCP 3 peptide antibody, we confirm and quantify the increased (2.8-fold) UCP 3 expression observed in skeletal muscle mitochondria isolated from 48-h-starved rats. We show that UCP 3 expression is increased (1.6-fold) in skeletal muscle of rats acclimated over 8 weeks to 8 degrees C and that UCP 3 expression is decreased (1.4-fold) in rats acclimated to 30 degrees C. Furthermore, UCP 3 expression is increased (2.3-fold) in skeletal muscle from hyperthyroid rats compared to euthyroid controls. In addition, we show that UCP 3 expression is only coincident with the mitochondrial fraction of skeletal muscle homogenates and not peroxisomal, nuclear or cytosolic and microsomal fractions.

Neuronal histamine regulates food intake, adiposity, and uncoupling protein expression in agouti yellow (A(y)/a) obese mice

Hypothalamic neuronal histamine and its H(1) receptor (H(1)-R) form a part of the leptin-signaling pathway in the brain and have been shown to regulate body weight and adiposity in diabetic (db/db) and diet-induced obese mice by affecting food intake and uncoupling protein mRNA expression. The proopiomelanocortin (POMC) melanocortin-4 receptor (MC-4R) is also important for leptin signaling. The present study had two aims: first, to clarify the antiobesity action of neuronal histamine in agouti yellow (A(y)/a) obese mice, a model of obesity in which POMC/MC-4R signaling is disrupted by blockade of MC-4R and second, to investigate the functional relationship between neuronal histamine and POMC/MC-4R signaling. Central administration of histamine into the lateral cerebroventricle decreased cumulative food intake and body weight in A(y)/a obese mice. Histamine treatment also decreased mRNA expression of ob gene in epididymal white adipose tissue and up-regulated uncoupling protein 1 mRNA expression in brown adipose tissue. These effects were attenuated in A(y)/a obese mice with histamine H(1)-receptor (H(1)-R) knockout. Histamine treatment induced c-Fos-like immunoreactivity in both paraventricular and arcuate nucleus. There was no significant difference in histamine-induced c-Fos-like immunoreactivity in the hypothalamus between A(y)/a obese mice and lean littermates, indicating histamine signaling was not disrupted at the hypothalamic level in A(y)/a obese mice. These results suggest that neuronal histamine have an antiobese action, even in A(y)/a obese mice despite a deficiency in POMC/MC-4R signaling. In addition, it appears that the histamine H(1)-R signaling pathway may be independent or downstream of the POMC/MC-4R signaling.

Identification and characterization of the imidazoline I2b-binding sites in the hamster brown adipose tissue as a study model for imidazoline receptors

The imidazoline-type compound, MPV-1743, has been found to activate nonshivering thermogenesis (NST) in brown adipose tissue (BAT) of the genetically obese Zucker rats. The regulation of NST in BAT is linked to the catecholamine metabolism, and the imidazoline I2-binding sites have been found on the monoamine oxidase, a catecholamine metabolising enzyme. In this study, the I2-binding sites of hamster BAT have been characterised using a receptor binding assay with 3H-idazoxan as a radioligand, and the interaction of MPV-1743 with these I2-binding sites has been studied using the enantiomers of MPV 1743, that is, MPV 2088 and MPV 2089. Cirazoline was used to determine the specific binding of 3H-idazoxan to the imidazoline I2-binding sites. Rauwolscine was added in the 3H-idazoxan binding assay in order to inhibit any binding to potential alpha2-adrenergic sites. In the presence of rauwolscine mask 3H-Idazoxan labelled a population of non-adrenergic binding sites expressing the properties of the imidazoline I2b-receptor subtype similar to that found in the rat liver (cirazoline >> guanabenz = amiloride >> clonidine). The binding of 3H-idazoxan to the I2b-binding sites could be displaced by the imidazole compounds with the following affinities: detomidine (KiHigh 9.2 nM; KiLow 3200 nM), MPV-2088 (KiHigh 19 nM; IKiLow 760 nM) and MPV-2089 (KiHigh 190 nM; KiLow 1300 nM), atipamezole (3500 nM) and dexmedetomidine (Ki 8400 nM). These results have shown that the hamster BAT contains the imidazoline I2b-binding sites with heterogeneous binding properties for some test compounds. In addition, the enantiomers of MPV 1743, that is, MPV 2088 and MPV 2089, had high affinity to these BAT imidazoline I2b-binding sites. Therefore, it is suggested that the regulation of NST in the hamster BAT may be an attractive model to study the role of imidazoline I2b-binding sites.

Thyroxine and tri-iodothyronine differently affect uncoupling protein-1 content and antioxidant enzyme activities in rat interscapular brown adipose tissue

The activity of the antioxidant enzymes copper-zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD) and catalase (CAT), as well as mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH) activity, uncoupling protein-1 (UCP1) content, catecholamine degrading enzyme monoamine oxidase (MAO) activity and malonyl dialdehyde (MDA) concentration were studied in rat interscapular brown adipose tIssue (IBAT). Rats were treated with either thyroxine (T4) or tri-iodothyronine (T3) for five days and then exposed to cold (4 degrees C, 24 h) or housed at room temperature (22 degrees C). Under basal conditions, T3 treatment significantly increased UCP1 content and MnSOD activity whereas CuZnSOD, CAT and MAO activities were significantly decreased. Thyroxine treatment significantly decreased IBAT CAT activity while MDA levels markedly increased. Cold exposure induced a significant augmentation of UCP1 content and MnSOD and mGPDH activities only in animals that were rendered hyperthyroid by T4 treatment. In T3-treated animals acutely exposed to cold stress, MDA concentration, an indicator of lipid peroxidation, was significantly higher compared with that of T3-treated animals housed at room temperature. However, in T4-treated animals, MDA concentrations were markedly lower. These results show that T4 and T3 differently affect IBAT parameters studied not only under basal but also under cold-stimulated conditions.

Adaptive changes in adipocyte gene expression differ in AKR/J and SWR/J mice during diet-induced obesity

Obesity-prone (AKR/J) and obesity-resistant (SWR/J) mice were weaned onto low (LF) or high fat (HF) diets to identify adaptive changes in adipocyte gene expression that are associated with differences between the strains in fat deposition. Food consumption was monitored at weekly intervals and all mice were evaluated after consuming their respective diets for 4 wk for analysis of mRNA levels of selected metabolic genes. Despite similar food consumption, body weight and fat deposition were significantly greater in AKR/J than in SWR/J mice, and this difference was greatly accentuated by the HF diet. The HF diet produced distinct differences between strains in gene expression patterns among fat depots. In AKR/J mice, UCP1 mRNA was decreased 10-fold in interscapular brown adipose tissue (BAT) and four- to fivefold in retroperitoneal and inguinal white adipose tissue (WAT). The HF diet also decreased PGC-1 and beta(3)-adrenergic receptor mRNA by two- and ninefold in BAT from AKR/J mice. In contrast, the HF diet either increased uncoupling protein (UCP)1 in BAT or had no effect on expression of these genes in adipose tissues from SWR/J mice. UCP2 mRNA was fourfold higher in WAT from AKR/J compared with SWR/J mice and increased by an additional twofold in WAT from AKR/J mice fed the HF diet. UCP2 was unaffected by diet in SWR/J mice. These studies show that the diet-induced obesity of AKR/J mice is characterized by increased metabolic efficiency and is associated with changes in adipocyte gene expression that limit the adaptive thermogenic response to increased energy density.

Evidence for the existence of distinct central appetite, energy expenditure, and ghrelin stimulation pathways as revealed by hypothalamic site-specific leptin gene therapy

To identify the specific hypothalamic sites in which leptin acts to decrease energy intake and/or increase energy expenditure, recombinant adeno-associated virus vector-encoding leptin was microinjected bilaterally into one of four hypothalamic sites in female rats. Leptin transgene expression in the ventromedial nucleus and paraventricular nucleus induced comparable decreases in daily food intake (FI; 18-20%) and body weight (BW; 26-29%), accompanied by drastic reductions in serum leptin (81-97%), insulin (92-93%), free fatty acids (35-36%), and normoglycemia. Leptin transgene expression in the arcuate nucleus (ARC) decreased BW gain (21%) and FI (11%) to a lesser range, but the metabolic hormones were suppressed to the same extent. Leptin transgene expression in the medial preoptic area (MPOA) decreased BW and metabolic hormones without decreasing FI. Finally, leptin transgene expression in all four sites augmented serum ghrelin and thermogenic energy expenditure, as shown by uncoupling protein-1 mRNA expression in brown adipose tissue. Proopiomelanocortin gene expression in the ARC was up-regulated by leptin expression in all four sites, but neuropeptide Y gene expression in the ARC was suppressed by leptin transgene expression in the ARC but not in the MPOA. Thus, whereas leptin expression in the paraventricular nucleus, ventromedial nucleus, or ARC suppresses adiposity and insulin by decreasing energy intake and increasing energy expenditure, in the MPOA it suppresses these variables by increasing energy expenditure alone.

The effect of maternal prolactin infusion during pregnancy on fetal adipose tissue development

The present study determines whether maternal administration of prolactin (PRL) to dams promotes the abundance of the brown adipose tissue-specific uncoupling protein-1 (UCP1) in fetal and neonatal rat pups. Recombinant PRL (24 micro g/kg per day), or an equivalent volume of saline, were infused into dams (n=19 per group) throughout pregnancy from 12 h after mating. Interscapular brown adipose tissue was sampled either from fetuses at 19.5 days of gestation (term=21.5 days) or from neonatal rat pups at approximately 18 h after birth. The abundance of UCP1 was determined by immunoblotting on adipose tissue samples from individual pups and pooled from groups of pups. This analysis was complemented by immunocytochemistry on representative adipose tissue samples. Maternal PRL infusion resulted in a greater abundance of UCP1 in fetal rats at 19.5 days of gestation (control: 97.2+/-8.4% reference; PRL: 525.6+/-74.4% reference; P<0.001) and in neonates 18 h after birth. In contrast, the abundance of the outer mitochondrial membrane protein voltage-dependent anion channel was unaffected by PRL. Neonatal adipose tissue sampled from pups born to PRL-infused dams possessed fewer lipid droplets, but more UCP1, as determined by immunocytochemistry. Fetal, but not maternal, plasma leptin concentrations were also increased by maternal PRL administration. In conclusion, as rats are altricial, and the potential thermogenic activity of brown adipose tissue develops over the first few days of postnatal life, these changes prior to, and at the time of, birth implicate PRL in fetal and neonatal adipose tissue maturation.

Differential expression of mitochondria-encoded genes in a hibernating mammal

A cDNA library constructed from kidney of the thirteen-lined squirrel, Spermophilus tridecemlineatus, was differentially screened for genes that were upregulated during hibernation. A clone encoding cytochrome c oxidase subunit 1 was found and confirmed to have been upregulated by northern blotting. Differential expression of Cox1 mRNA occurred in multiple organs during hibernation; in hibernating animals transcript levels were twofold higher in kidney and fourfold higher in heart and brown adipose tissue than in euthermic animals, but were unchanged in skeletal muscle. Transcript levels of mitochondrial-encoded ATP synthase 6/8 were similarly upregulated in these tissues whereas transcript levels of the nuclear encoded subunits Cox4 and ATP synthase α did not change during hibernation. Immunoblot analysis revealed a 2.4-fold increase in Cox 1 protein and a slight decrease in Cox 4 protein in kidney of hibernating squirrels, compared with euthermic controls. Hibernating mammals may increase the expression of the mitochondrial genome in general, and Cox1specifically, to prevent or minimize the damage to the electron transport chain caused by the cold and ischemia experienced during a hibernation bout.

Effects of energy expenditure and Ucp1 on photoperiod-induced weight gain in collard lemmings

OBJECTIVE

To determine the role of total energy expenditure (TEE) and its components in the ability of collared lemmings to increase weight in response to a decrease in photoperiod.

RESEARCH METHODS AND PROCEDURES

Energy expenditure was measured by 24-hour indirect calorimetry concurrent with food-intake studies. TEE and resting and nonresting energy expenditure (REE and NREE, respectively) were adjusted for body weight by analysis of covariance (ANCOVA). Uncoupling protein 1 (Ucp1) mRNA levels from interscapular brown adipose tissue were determined by Northern blot.

RESULTS

TEE and REE of lemmings exposed to a short photoperiod for 10 days were significantly lower than that of lemmings exposed to a long photoperiod (p < 0.05), whereas NREE was not significantly different (p = 0.44). Ucp1 mRNA levels in interscapular brown adipose tissue were 50% lower in short- vs. long-photoperiod lemmings (p < 0.01). Ucp1 mRNA levels were positively related to REE (r2 = 0.79, p < 0.01). After adjustment of REE for differences in Ucp1 mRNA levels, there was no longer a significant difference attributable to photoperiod treatment (p = 0.54).

DISCUSSION

The results of this study indicate that the increase in body mass that occurs when collared lemmings are exposed to a short photoperiod may be primarily fueled by a decrease in REE and is correlated with a decrease in Ucp1 mRNA levels.

Central leptin gene therapy blocks high-fat diet-induced weight gain, hyperleptinemia, and hyperinsulinemia: increase in serum ghrelin levels

Recombinant adeno-associated virus (rAAV), encoding either rat leptin (rAAV-lep) or green fluorescent protein (rAAV-GFP, control), was injected intracerebroventricularly in rats consuming a high-fat diet (HFD; 45 kcal%). Caloric consumption and body weight were monitored weekly until the rats were killed at 9 weeks. Untreated control rats consuming regular rat diet (RCD; 11 kcal%) were monitored in parallel. Body weight gain was accelerated in rAAV-GFP + HFD control rats relative to those consuming RCD, despite equivalent kcal consumption. At 9 weeks, serum leptin, free fatty acids, triglycerides, and insulin were elevated in HFD control rats. In contrast, rAAV-lep treatment reduced intake and blocked the HFD-induced increase in weight, adiposity, and metabolic variables. Blood glucose was slightly reduced but within the normal range, and serum ghrelin levels were significantly elevated in rAAV-lep + HFD rats. Uncoupling protein-1 (UCP1) mRNA in brown adipose tissue (BAT), an index of energy expenditure through nonshivering thermogenesis, was decreased in rats consuming HFD. Treatment with rAAV-lep significantly augmented BAT UCP1 mRNA expression, indicating increased thermogenic energy expenditure. These findings demonstrate that central leptin gene therapy efficiently prevents weight gain, increased adiposity, and hyperinsulinemia in rats consuming an HFD by decreasing energy intake and increasing thermogenic energy expenditure.

Phytanic acid, but not pristanic acid, mediates the positive effects of phytol derivatives on brown adipocyte differentiation

The phytol derivatives phytanic acid and pristanic acid may activate nuclear hormone receptors and influence gene expression and cell differentiation. Phytanic acid induces brown adipocyte differentiation. It was determined that brown fat and brown adipocytes are sites of high gene expression of phytanoyl-CoA hydroxylase, the enzyme required for initiation of peroxisomal alpha-oxidation of phytanic acid. However, the effects of phytanic acid were not mediated by its alpha-oxidation product pristanic acid, which did not promote brown adipocyte differentiation or stimulate transcription of the uncoupling protein-1 gene. Moreover, acute cold exposure of mice caused a dramatic mobilization of the phytanic acid stores in brown adipose tissue thus suggesting that a high local exposure to phytanic acid in brown fat may contribute to signalling adaptive changes in the tissue in response to thermogenic activation.

Evidence for a functional nitric oxide synthase system in brown adipocyte nucleus

The intracellular localization and activity of the nitric oxide synthase (NOS) isoforms were investigated in rat brown adipocytes. Immunohistochemistry showed cytoplasmic and nuclear staining for the endothelial NOS (eNOS) and inducible NOS (iNOS) isoforms; accordingly, anti-L-citrulline antibody, a marker of NOS activity, immunostained both the cytoplasm and the nucleus. The presence of metabolically active NOS in the nucleus was further confirmed by immunoblotting analyses of subcellular fractions of homogenates from cultured brown adipocytes and by measurements of NOS activity in the cytosol and nucleus. Sympathetic stimulation in vivo (i.e. cold exposure or beta(3)-adrenergic agonist treatment) and in vitro (i.e. noradrenaline treatment of cultured cells) significantly increased both cytosolic and nuclear eNOS and iNOS expression and activities. By contrast, the number of iNOS-positive, but not eNOS-positive, nuclei was significantly lower in the functionally impaired brown fat of genetically obese Zucker fa/fa rats. These data suggest the existence of a noradrenaline-modulated functional NOS system in the nucleus of brown adipocytes.