Adrenoceptors, uncoupling proteins, and energy expenditure

In search of an ideal drug for safer treatment of obesity: The false promise of pseudoephedrine

Obesity is a major public health problem worldwide. Only relatively few treatment options are, at present, available for the management of obese patients. Furthermore, treatment of obesity is affected by the widespread misuse of drugs and food supplements. Ephedra sinica is an old medicinal herb, commonly used in the treatment of respiratory tract diseases. Ephedra species contain several alkaloids, including pseudoephedrine, notably endowed with indirect sympathomimetic pharmacodynamic properties. The anorexigenic effect of pseudoephedrine is attributable primarily to the inhibition of neurons located in the hypothalamic paraventricular nucleus (PVN), mediating satiety stimuli. Pseudoephedrine influences lipolysis and thermogenesis through interaction with β3 adrenergic receptors and reduces fat accumulation through down-regulation of transcription factors related to lipogenesis. However, its use is associated with adverse events that involve to a large extent the cardiovascular and the central nervous system. Adverse events of pseudoephedrine also affect the eye, the intestine, and the skin, and, of relevance, sudden cardiovascular death related to dietary supplements containing Ephedra alkaloids has also been reported. In light of the limited availability of clinical data on pseudoephedrine in obesity, along with its significantly unbalanced risk/benefit profile, as well as of the psychophysical susceptibility of obese patients, it appears reasonable to preclude the prescription of pseudoephedrine in obese patients of any order and degree.

Rubi Fructus (Rubus coreanus) activates the expression of thermogenic genes in vivo and in vitro

OBJECTIVE

To investigate the anti-obesity effect of Rubi Fructus (RF) extract using brown adipose tissue (BAT) and primary brown preadipocytes in vivo and in vitro.

METHODS

Male C57BL/6 J mice (n=5 per group) were fed a high-fat diet (HFD) for 10 weeks with or without RF. Brown preadipocytes from the interscapular BAT of mice (age, post-natal days 1-3) were cultured with differentiation media (DM) including isobutylmethylxanthine, dexamethasone, T3, indomethacin and insulin with or without RF.

RESULTS

In HFD-induced obese C57BL/6 J mice, long-term RF treatment significantly reduced weight gain as well as the weights of the white adipose tissue, liver and spleen. Serum levels of total cholesterol and low-density lipoprotein cholesterol were also reduced in the HFD group which received RF treatment. Furthermore, RF induced thermogenic-, adipogenic- and mitochondria-related gene expressions in BAT. In primary brown adipocytes, RF effectively stimulated the expressions of thermogenic- and mitochondria-related genes. In addition, to examine whether LIPIN1, a regulator of adipocyte differentiation, is regulated by RF, Lipin1 small interfering RNA (siRNA) and RF were pretreated in primary brown adipocytes. Pretreatment with Lipin1 siRNA and RF downregulated the DM-induced expression levels of thermogenic- and mitochondria-related genes. Moreover, RF markedly upregulated AMP-activated protein kinase. Our study shows that RF is capable of stimulating the differentiation of brown adipocytes through the modulation of thermogenic genes.

CONCLUSIONS

This study demonstrates that RF prevents the development of obesity in mice fed with a HFD and that it is also capable of stimulating the differentiation of brown adipocytes through the modulation of thermogenic genes, which suggests that RF has potential as a therapeutic application for the treatment or prevention of obesity.

Glial cell line-derived neurotrophic factor protects against high-fat diet-induced obesity

Obesity is a growing epidemic with limited effective treatments. The neurotrophic factor glial cell line-derived neurotrophic factor (GDNF) was recently shown to enhance β-cell mass and improve glucose control in rodents. Its role in obesity is, however, not well characterized. In this study, we investigated the ability of GDNF to protect against high-fat diet (HFD)-induced obesity. GDNF transgenic (Tg) mice that overexpress GDNF under the control of the glial fibrillary acidic protein promoter and wild-type (WT) littermates were maintained on a HFD or regular rodent diet for 11 wk, and weight gain, energy expenditure, and insulin sensitivity were monitored. Differentiated mouse brown adipocytes and 3T3-L1 white adipocytes were used to study the effects of GDNF in vitro. Tg mice resisted the HFD-induced weight gain, insulin resistance, dyslipidemia, hyperleptinemia, and hepatic steatosis seen in WT mice despite similar food intake and activity levels. They exhibited significantly (P<0.001) higher energy expenditure than WT mice and increased expression in skeletal muscle and brown adipose tissue of peroxisome proliferator activated receptor-α and β1- and β3-adrenergic receptor genes, which are associated with increased lipolysis and enhanced lipid β-oxidation. In vitro, GDNF enhanced β-adrenergic-mediated cAMP release in brown adipocytes and suppressed lipid accumulation in differentiated 3T3L-1 cells through a p38MAPK signaling pathway. Our studies demonstrate a novel role for GDNF in the regulation of high-fat diet-induced obesity through increased energy expenditure. They show that GDNF and its receptor agonists may be potential targets for the treatment or prevention of obesity.

ROS and Sympathetically Mediated Mitochondria Activation in Brown Adipose Tissue Contribute to Methamphetamine-Induced Hyperthermia

Methamphetamine (Meth) abuse has been shown to induce alterations in mitochondrial function in the brain as well as to induce hyperthermia, which contributes to neurotoxicity and Meth-associated mortality. Brown adipose tissue (BAT), a thermogenic site known to be important in neonates, has recently regained importance since being identified in significant amounts and in correlation with metabolic balance in human adults. Given the high mitochondrial content of BAT and its role in thermogenesis, we aimed to investigate whether BAT plays any role in the development of Meth-induced hyperthermia. By ablating or denervating BAT, we identified a partial contribution of this organ to Meth-induced hyperthermia. BAT ablation decreased temperature by 0.5°C and reduced the length of hyperthermia by 1 h, compared to sham-operated controls. BAT denervation also affected the development of hyperthermia in correlation with decreased the expression of electron transport chain molecules, and increase on PCG1a levels, but without affecting Meth-induced uncoupling protein 1 upregulation. Furthermore, in isolated BAT cells in culture, Meth, but not Norepinephrine, induced H2O2 upregulation. In addition, we found that in vivo Reactive Oxygen Species (ROS) play a role in Meth hyperthermia. Thus, sympathetically mediated mitochondrial activation in the BAT and Meth-induced ROS are key components to the development of hyperthermia in Meth abuse.

Association of the UCP-1 single nucleotide polymorphism A-3826G with the dampness-phlegm pattern among Korean stroke patients

Background

Patients with stroke have various syndromes and symptoms. Through pattern identification (PI), traditional Korean medicine (TKM) classifies the several syndromes and symptoms of stroke patients into five categories: Fire-heat (FH), Dampness-phlegm (DP), Yin-deficiency (YD), Qi-deficiency (QD) and Blood-stasis (BS). DP has been associated with obesity and hyperlipidemia. Uncoupling protein-1 (UCP-1), which plays a major role in thermogenesis and energy expenditure can increase the risk of obesity and can be related metabolic disorders. In this study, we elucidated the association of three polymorphisms located in the UCP-1 promoter and coding region with DP among Korean stroke patients.

Methods

1,593 patients with cerebral infarction (583/DP, 1,010/non-DP) and 587 normal subjects were enrolled. The genotypes A-3826G, G-1766A and Ala64Thr (G+1068A) for each subject were determined by polymerase chain reaction with TaqMan probes and five percent of subjects were re-genotyped by sequencing method to confirm the accuracy of genotyping. The results were analyzed using a multiple logistic regression model to evaluate the genetic associations: the UCP-1polymorphisms of normal versus those of DP subjects and those of normal versus those of non-DP subjects.

Results

A significantly higher percentage of subjects in the DP group possessed the A-3826G G allele than the A allele (OR=1.508, p=0.006). Furthermore, the number of subjects with the GG type of A-1766G was significantly lower in the non-DP group than the normal group in the recessive model (OR=0.606, p=0.042). In addition, an analysis of the relationship among 2 SNPs of UCP-1 and lipid serum concentration showed that the serum level of HDL cholesterol was significantly higher in subjects with the A-3826G G allele in the normal group (p=0.032). Serum triglyceride and HDL cholesterol were also associated with the A-1766G variant in the recessive model (p=0.002, p=0.046).

Conclusions

These results suggest that that the A-3826G and A-1766G UCP-1 polymorphisms, which are related to obesity, might be candidate genetic markers for the DP pattern in the TKM diagnosis system.

Myostatin inhibits brown adipocyte differentiation via regulation of Smad3-mediated β-catenin stabilization

Brown adipocytes play an important role in regulating energy balance, and there is a good correlation between obesity and the amount of brown adipose tissue. Although the molecular mechanism of white adipocyte differentiation has been well characterized, brown adipogenesis has not been studied extensively. Moreover, extracellular factors that regulate brown adipogenic differentiation are not fully understood. Here, we assessed the mechanism of the regulatory action of myostatin in brown adipogenic differentiation using primary brown preadipocytes. Our results clearly showed that differentiation of brown adipocytes was significantly inhibited by myostatin treatment. In addition, myostatin-induced suppression of brown adipogenesis was observed during the early phase of differentiation. Myostatin induced the phosphorylation of Smad3, which led to increased β-catenin stabilization. These effects were blocked by treatment with a Smad3 inhibitor. Expression of brown adipocyte-related genes, such as PPAR-γ, UCP-1, PGC-1α, and PRDM16, were dramatically down-regulated by treatment with myostatin, and further down-regulated by co-treatment with a β-catenin activator. Taken together, the present study demonstrated that myostatin is a potent negative regulator of brown adipogenic differentiation by modulation of Smad3-induced β-catenin stabilization. Our findings suggest that myostatin could be used as an extracellular factor in the control of brown adipocyte differentiation.

Regulation of the hypothalamic thyrotropin releasing hormone (TRH) neuron by neuronal and peripheral inputs

The hypothalamic-pituitary-thyroid (HPT) axis plays a critical role in mediating changes in metabolism and thermogenesis. Thus, the central regulation of the thyroid axis by Thyrotropin Releasing Hormone (TRH) neurons in the paraventricular nucleus of the hypothalamus (PVN) is of key importance for the normal function of the axis under different physiological conditions including cold stress and changes in nutritional status. Before the TRH peptide becomes biologically active, a series of tightly regulated processes occur including the proper folding of the prohormone for targeting to the secretory pathway, its post-translational processing, and targeting of the processed peptides to the secretory granules near the plasma membrane of the cell ready for secretion. Multiple inputs coming from the periphery or from neurons present in different areas of the brain including the hypothalamus are responsible for the activation or inhibition of the TRH neuron and in turn affect the output of TRH and the set point of the axis.

Divergent physical activity and novel alternative responses to high fat feeding in polygenic fat and lean mice

We determined whether altered physical activity levels might underlie the contrasting adiposity of a divergently selected polygenic murine model of metabolic syndrome (Fat; F) and leanness (Lean; L) mice. We measured physical activity with a long term running wheel experiment and performed an additional high fat diet intervention. Further, we measured posture allocation by visual monitoring within the home cage as a non-exercise correlate of 'normal' physical activity. Whilst initially similar, running wheel activity of the F line declined with age, while the activity of the L line increased. Food intake was higher in the L line and increased with wheel exposure. Vertical rearing measured by video quantification in the home cage, without the stimulus of a running wheel was also significantly higher in the L line. The two lines developed novel alternate strategies to defend their body weight when exposed to high fat diets with a running wheel. F mice increased their running wheel activity, and despite unaltered food intake, still gained weight. L mice reduced their food intake and maintained activity levels without a significant change in body weight. Phenotypic selection for divergence in body fat content has co-segregated with a genetic predisposition for divergent physical activity levels and different strategies for coping with exposure to high fat diets that will facilitate the discovery of the genes underlying these important obesity related traits.

Nonshivering thermogenesis capacity associated to mitochondrial DNA haplotypes and gender in the greater white-toothed shrew, Crocidura russula

A selection gradient was recently suggested as one possible cause for a clinal distribution of mitochondrial DNA (mtDNA) haplotypes along an altitudinal transect in the greater white-toothed shrew, Crocidura russula (Ehinger et al. 2002). One mtDNA haplotype (H1) rare in lowland, became widespread when approaching the altitudinal margin of the distribution. As H1 differs from the main lowland haplotype by several nonsynonymous mutations (including on ATP6), and as mitochondria play a crucial role in metabolism and thermogenesis, distribution patterns might stem from differences in the thermogenic capacity of different mtDNA haplotypes. In order to test this hypothesis, we measured the nonshivering thermogenesis (NST) associated with different mtDNA haplotypes. Sixty-two shrews, half of which had the H1 haplotype, were acclimated in November at semioutdoor conditions and measured for NST throughout winter. Our results showed the crucial role of NST for winter survival in C. russula. The individuals that survived winter displayed a higher significant increase in NST during acclimation, associated with a significant gain in body mass, presumably from brown fat accumulation. The NST capacity (ratio of NST to basal metabolic rate) was exceptionally high for such a small species. NST was significantly affected by a gender x haplotype interaction after winter-acclimation: females bearing the H1 haplotype displayed a better thermogenesis at the onset of the breeding season, while the reverse was true for males. Altogether, our results suggest a sexually antagonistic cyto-nuclear selection on thermogenesis.

Evolution of mitochondrial uncoupling proteins: novel invertebrate UCP homologues suggest early evolutionary divergence of the UCP family

Current hypothesis about the evolution of uncoupling proteins (UCPs) proposed by suggests that UCP4 is the earliest form of UCP ancestral to all other UCP orthologues. However, this hypothesis is difficult to reconcile with a narrow tissue distribution of UCP4 (which is a brain-specific isoform), suggesting highly specialized rather than anfcestral function for this protein. We searched for UCP2, UCP3, and UCP5 homologues in invertebrate genomes using amplification with degenerate primers designed against UCP2-specific conserved sequences and/or BLASTP search with stringent ad hoc criteria to distinguish between homologues and orthologues of different UCPs. Our study identified invertebrate UCP homologues similar to UCP2 and 3 (which we termed UCP6) and an invertebrate homologue of UCP5. Phylogenetic analysis indicates that there are at least three clades of UCPs in invertebrates, which are closely related to vertebrate UCP1-3, UCP4, and UCP5, respectively, and shows early evolutionary divergence of UCPs, which pre-dates the divergence of protostomes and deuterostomes. It also suggests that the newly identified UCP6 proteins from invertebrates are ancestral to the vertebrate UCP1, UCP2, and UCP3, and that divergence of these three vertebrate orthologues occurred late in evolution of the vertebrates. This study refutes the hypothesis of Hanak and Jezek (2001) that UCP4 is an ancestral form for all UCPs, and shows early evolutionary diversification of this protein family, which corresponds to their proposed functional diversity in regulation of proton leak, antioxidant defense and apoptosis.

Lessons learned from gene expression profile studies of aging and caloric restriction

To examine molecular events associated with aging and its retardation by caloric restriction (CR), we have employed high-density oligonucleotide microarrays to define transcriptional patterns in mouse tissues, including skeletal muscle, brain, heart, and adipose. Aging results in a differential gene expression pattern specific to each tissue, and most alterations can be completely or partially prevented by CR. Transcriptional patterns of tissues from calorie-restricted animals suggest that CR retards the aging process by reducing endogenous damage and by inducing metabolic shifts associated with specific transcriptional profiles. These studies demonstrate that DNA microarrays can be used in aging research to generate panels of hundreds of transcriptional biomarkers, providing a new tool to measure biological age on a tissue-specific basis and to evaluate interventions designed to mimic the effects of CR.

Hetero-oligomerization between β2- and β3-Adrenergic Receptors Generates a β-Adrenergic Signaling Unit with Distinct Functional Properties

The ability of the closely related beta(2)- and beta(3)-adrenergic receptors (AR) to form hetero-oligomers was assessed by bioluminescence resonance energy transfer. Quantitative bioluminescence resonance energy transfer titration curves revealed that the beta(2)AR has identical propensity to hetero-oligomerize with the beta(3)AR than to form homo-oligomers. To determine the influence of heterooligomerization, a HEK293 cell line stably expressing an excess of beta(3)AR over beta(2)AR was generated so that all beta(2)AR are engaged in hetero-oligomerization with beta(3)AR, providing a tool to study the effect of hetero-oligomerization on beta(2)AR function in the absence of any beta(2)AR homooligomer. The hetero-oligomerization had no effect on the ligand binding properties of various beta(2)AR ligands and did not affect the potency of isoproterenol to stimulate adenylyl cyclase. Despite the unaltered ligand binding properties of the beta(2/3)AR hetero-oligomer, the stable association of the beta(2)AR with the beta(3)AR completely blocked agonist-stimulated internalization of the beta(2)AR. Given that the beta(3)AR is resistant to agonist-promoted endocytosis, the results indicate that the beta(3)AR acted as a dominant negative of the beta(2)AR endocytosis process. Consistent with this notion, the beta(2/3)AR hetero-oligomer displayed a lower propensity to recruit beta-arrestin-2 than the beta(2)AR. The hetero-oligomerization also led to a change in G protein coupling selectivity. Indeed, in contrast to beta(2)AR and beta(3)AR, which regulate adenylyl cyclase and extracellular signal-regulated kinase activity through a coupling to G(s) and G(i/o), no G(i/o) coupling was observed for the beta(2/3)AR hetero-oligomer. Together, these results demonstrate that hetero-oligomerization between beta(2)AR and beta(3)AR forms a beta-adrenergic signaling unit that possesses unique functional properties.

Differential roles of insulin receptor substrates in brown adipocyte differentiation

Insulin promotes adipocyte differentiation via a complex signaling network involving multiple insulin receptor substrates (IRSs). In cultured brown preadipocytes, expression of IRS-1 and IRS-2 mRNAs and proteins was at relatively high levels before and after differentiation into mature fat cells, while IRS-3 transcript was not detectable in preadipocytes but increased during the course of differentiation, and IRS-4 mRNA was barely detected in both states. To determine more precisely the roles of various IRS proteins in adipogenesis, we established and characterized brown preadipocyte cell lines from wild-type and IRS knockout (KO) animals. While wild-type, IRS-2 KO, and IRS-4 KO cells fully differentiated into mature adipocytes, IRS-3 KO cells showed a moderate defect in differentiation and IRS-1 KO cells exhibited a severe defect in the process. Cells lacking both IRS-1 and IRS-3 completely failed to differentiate. Expression of the adipogenic markers peroxisome proliferator-activated receptor gamma (PPARgamma), CCAAT/enhancer-binding protein alpha, fatty acid synthase, glucose transporter 4, and the transcription factor signal transducer and activator of transcription 5, as well as the brown-fat-specific markers PPARgamma coactivator 1 alpha and uncoupling protein 1, mirrored the differentiation pattern. Reconstitution of the IRS-1 KO cells with IRS-1 and IRS-4, but not IRS-2 or IRS-3, compensated for the lack of differentiation in IRS-1 KO cells. A chimeric molecule containing the N terminus of IRS-1 and the C terminus of IRS-2, but not one with the N terminus of IRS-2 and the C terminus of IRS-1, also rescued differentiation. Expression of Wnt 10a, a molecule known to inhibit adipogenesis, was dramatically increased in the IRS-1 KO cells, and this could be reduced by overexpression of IRS-1 or IRS-4, which was correlated with restoration of differentiation. These data indicate that both IRS-1 and -3 play important roles in the differentiation of brown adipocytes and that the N terminus of IRS-1 is more important for this function of the molecule. Although IRS-4 is not essential for the process, overexpression of IRS-4 can compensate for the deficiency in differentiation in IRS-1 KO cells.

The Trp64Arg polymorphism of the beta3-adrenergic receptor is not increased in women with preeclampsia

OBJECTIVE

Insulin resistance is greater and obesity is more common in women with preeclampsia. The Trp64Arg polymorphism in the beta(3)-adrenergic receptor is associated with these metabolic changes. This study investigated whether the Trp64Arg polymorphism is more common in women with preeclampsia.

STUDY DESIGN

beta(3)-Adrenergic receptor genotypes were determined in 177 women with a history of preeclampsia and in 179 normal pregnancies. We also compared prepregnancy body mass index (BMI), length of gestation, baby weight percentile, and glucose values during an oral tolerance test in women with and without the polymorphism.

RESULTS

The genotypes and allele frequency did not differ significantly between women with preeclamptic and normal pregnancies (P=.17). Women with and without the polymorphism had similar prepregnancy BMI, glucose at 1-hour screening, gestational age at delivery, and adjusted baby weight.

CONCLUSION

The Trp64Arg polymorphism of the beta(3)-receptor does not predispose to preeclampsia, and it is it not associated with obesity and carbohydrate intolerance in a population of young pregnant women.

Adipose tissue energy metabolism: altered gene expression profile of mice subjected to long-term caloric restriction

We investigated the influences of short-term and lifespan-prolonging long-term caloric restriction (LCR) on gene expression in white adipose tissue (WAT). Over 11,000 genes were examined using high-density oligonucleotide microarrays in four groups of 10- to 11-month-old male C57Bl6 mice that were either fasted for 18 h before death (F), subjected to short-term caloric restriction for 23 days (SCR), or LCR for 9 months and compared with nonfasted control (CO) mice. Only a few transcripts of F and SCR were differentially expressed compared with CO mice. In contrast, 345 transcripts of 6,266 genes found to be expressed in WAT were altered significantly by LCR. The expression of several genes encoding proteins involved in energy metabolism was increased by LCR. Further, many of the shifts in gene expression after LCR are known to occur during adipocyte differentiation. Selected LCR-associated alterations of gene expression were supported by quantitative reverse transcriptase-polymerase chain reaction, histology, and histochemical examinations. Our data provide new insights on the metabolic state associated with aging retardation by LCR.

Intrinsic and extrinsic uncoupling of oxidative phosphorylation

This article reviews parameters of extrinsic uncoupling of oxidative phosphorylation (OxPhos) in mitochondria, based on induction of a proton leak across the inner membrane. The effects of classical uncouplers, fatty acids, uncoupling proteins (UCP1-UCP5) and thyroid hormones on the efficiency of OxPhos are described. Furthermore, the present knowledge on intrinsic uncoupling of cytochrome c oxidase (decrease of H(+)/e(-) stoichiometry=slip) is reviewed. Among the three proton pumps of the respiratory chain of mitochondria and bacteria, only cytochrome c oxidase is known to exhibit a slip of proton pumping. Intrinsic uncoupling was shown after chemical modification, by site-directed mutagenesis of the bacterial enzyme, at high membrane potential DeltaPsi, and in a tissue-specific manner to increase thermogenesis in heart and skeletal muscle by high ATP/ADP ratios, and in non-skeletal muscle tissues by palmitate. In addition, two mechanisms of respiratory control are described. The first occurs through the membrane potential DeltaPsi and maintains high DeltaPsi values (150-200 mV). The second occurs only in mitochondria, is suggested to keep DeltaPsi at low levels (100-150 mV) through the potential dependence of the ATP synthase and the allosteric ATP inhibition of cytochrome c oxidase at high ATP/ADP ratios, and is reversibly switched on by cAMP-dependent phosphorylation. Finally, the regulation of DeltaPsi and the production of reactive oxygen species (ROS) in mitochondria at high DeltaPsi values (150-200 mV) are discussed.

Military infrared technology advances diabetes research

All living organisms produce heat as a by-product of metabolism. For centuries, clinicians and scientists have been interested in measuring heat output (thermogenesis) as an indicator of metabolic state. This paper briefly reviews current methods for metabolic measurements and describes recent results in diabetes research with a novel infrared thermal imaging technology, Thermal Signature Analysis (TSA). TSA measures unique thermal signatures in cells and animals that are indicative of disease, genetic variations, or drug function.

Beta(1)/beta(2)/beta(3)-adrenoceptor knockout mice are obese and cold-sensitive but have normal lipolytic responses to fasting

Catecholamines are viewed as major stimulants of diet- and cold-induced thermogenesis and of fasting-induced lipolysis, through the beta-adrenoceptors (beta(1)/beta(2)/beta(3)). To test this hypothesis, we generated beta(1)/beta(2)/beta(3)-adrenoceptor triple knockout (TKO) mice and compared them to wild type animals. TKO mice exhibited normophagic obesity and cold-intolerance. Their brown fat had impaired morphology and lacked responses to cold of uncoupling protein-1 expression. In contrast, TKO mice had higher circulating levels of free fatty acids and glycerol at basal and fasted states, suggesting enhanced lipolysis. Hence, beta-adrenergic signalling is essential for the resistance to obesity and cold, but not for the lipolytic response to fasting.