Expression of Activin Receptor-like Kinase 7 in Adipose Tissues

The tissue distribution of activin receptor-like kinase 7 (Alk7) expression, the signaling ability of Alk7 variants, and Alk7 expression in response to β₃-adrenergic receptor activation were examined. Expression levels of Alk7 varied greatly among tissues but were highest in white adipose tissue and brown adipose tissue. In addition to full-length Alk7 (Alk7-v1), Alk7-v3, an Alk7 variant, was expressed in adipose tissues, brain, and ovary. Nodal transmits signals via Alk7 in cooperation with its coreceptor, Cripto. Evaluation of the ability of Alk7 variants to confer Nodal signaling using luciferase-based reporter assays showed that Alk7-v3 does not transmit Nodal-Cripto-mediated signals. Expression of Alk7 was down-regulated in brown but not in white adipose tissue treated with CL316,243, a β₃-adrenergic receptor agonist. These results suggest involvement of Alk7 in modulation of metabolism in the adipose tissues in response to β₃-adrenergic receptor activation.     

Metabolic changes in adipose tissues in response to β3-adrenergic receptor activation in mice

Brown and beige adipocytes dissipate energy as heat. Thus, the activation of brown adipocytes and the emergence of beige adipocytes in white adipose tissue (WAT) are suggested to be useful for preventing and treating obesity. Although β₃-adrenergic receptor activation is known to stimulate lipolysis and activation of brown and beige adipocytes, fat depot–dependent changes in metabolite concentrations are not fully elucidated. The current study examined the effect of treatment with CL-316,243, a β₃-adrenergic receptor agonist, on the relative abundance of metabolites in interscapular brown adipose tissue (iBAT), inguinal WAT (ingWAT), and epididymal WAT (epiWAT). Intraperitoneal injection of CL-316,243 (1 mg/kg) for 3 consecutive days increased the relative abundance of several glycolysis-related metabolites in all examined fat depots. The cellular concentrations of metabolites involved in the citric acid cycle and of free amino acids were also increased in epiWAT by CL-316,243. CL-316,243 increased the expression levels of several enzymes and transporters related to glucose metabolism and amino acid catabolism in ingWAT and iBAT but not in epiWAT. CL-316,243 also induced the emergence of more beige adipocytes in ingWAT than in epiWAT. Furthermore, adipocytes surrounded by macrophages were detected in the epiWAT of mice given CL-316,243. The current study reveals the fat depot–dependent modulation of cellular metabolites in CL-316,243-treated mice, presumably resulting from differential regulation of cell metabolism in different cell populations.     

Reduced lipogenesis in cafeteria-fed rats exhibiting diet-induced thermogenesis

Fatty-acid synthesis has been measured in vivo with³H₂O in cafeteria-fed rats exhibiting diet-induced thermogenesis. Synthesis was decreased in brown adipose tissue, the liver, white adipose tissue, and the carcass of the cafeteria-fed animals compared to rats fed the normal stock diet. Whole-body synthesis was also decreased in the cafeteria-fed group. Diet-induced thermogenesis, in contrast to cold-induced non-shivering thermogenesis does not lead to increased fatty-acid synthesis and this is presumably due to the inhibitory effects on lipogenesis of the high dietary fat intake characteristic of cafeteria diets. The results also indicate that the energy cost of body fat deposition in cafeteria-fed rats is lower than in animals fed a low-fat/high-carbohydrate stock diet.     

Aging and β3-adrenergic stimulation alter mitochondrial lipidome of adipose tissue

Mitochondrial abundance and thermogenic capacity are two imperative components that distinguish brown, beige and white adipose tissues. Most importantly, the lipid composition is vital for maintaining the quantity, quality and function of mitochondria. Therefore, we employed quantitative lipidomics to probe the mitochondrial lipidome of adipose tissues. The mitochondrial lipidome reveals β3-adrenergic stimulation and aging drastically altered the levels of phosphatidylcholine (PC)/phosphatidylethanolamine (PE) ratio and acyl chain desaturation. Precisely, PC_36:2 and PE_38:4 levels correlate with the increased brown and beige fat activity in young mice. While aging increased lysoPC species in white adipose tissue (WAT) mitochondria, CL-316,243 administration reduced lysoPC species and increased lyso-PE_{18:1 and 18:2} content during WAT browning. Also, non-thermogenic mitochondria accumulate sphingomyelin (SM), phosphatidylserine (PS), phosphatidic acid (PA) and ether-linked PC (ePC). Similarly, enrichment of phosphatidylglycerol (PG) and cardiolipin (CL) levels are associated with thermogenic mitochondria. Also, our in vitro experiment supports that blocking the de novo sphingolipid synthesis pathway by myriocin, SPT1 inhibitor increased the thermogenic capacity and oxygen consumption rate in mature adipocytes. Overall, our study suggests mitochondria of brown, beige and white adipose tissues own a unique pattern of lipid molecular species and their levels are altered by aging and CL-316,243 administration.     

Effect of theβ-adrenoceptor agonist BRL 26830 on fatty acid synthesis and on the activities of pyruvate dehydrogenase and acetyl-CoA carboxylase in adipose tissues of the rat

BRL 26830 is a thermogenic-adrenoceptor agonist which stimulates lipolysis and fatty acid oxidationin vivo. It also stimulates insulin secretion, and hence promotes glucose utilisationin vivo. The effect of this agent on white and brown adipose tissue of the rat was investigated. BRL 26830 increased the rate of fatty acid synthesisin vivo in white adipose tissue by 135% but reduced the rate of fatty acid synthesisin vivo in brown adipose tissue by 78%. The increase was abolished in white adipose tissue of streptozotocin-diabetic rats, indicating that the effect involved a rise in circulating insulin levels. The reduction in fatty acid synthesis in brown adipose tissues was associated with a reduction in the activity of acetyl-CoA carboxylase in the tissue consistent with a direct-adrenoceptor-mediated effect. BRL 26830 also increased the proportion of pyruvate dehydrogenase in its active formin vivo in brown adipose tissue and this increase was abolished in streptozotocin-diabetic rats. These findings illustrate different sensitivities of white and brown adipose tissues to combined-adrenergic and insulin stimulation.     

The PPARγ agonist rosiglitazone promotes the induction of brite adipocytes,increasing β-adrenoceptor-mediated mitochondrial function and glucose uptake

Recruitment and activation of brite (or beige) adipocytes has been advocated as a potential avenue for manipulating whole-body energy expenditure. Despite numerous studies illustrating the differences in gene and protein markers between brown, brite and white adipocytes, there is very little information on the adrenergic regulation and function of these brite adipocytes. We have compared the functional (cyclic AMP accumulation, oxygen consumption rates, mitochondrial function, glucose uptake, extracellular acidification rates, calcium influx) profiles of mouse adipocytes cultured from three contrasting depots, namely interscapular brown adipose tissue, and inguinal or epididymal white adipose tissues, following chronic treatment with the peroxisome proliferator-activated receptor γ (PPARγ) agonist rosiglitazone. Prototypical brown adipocytes readily express β₃-adrenoceptors, and β₃-adrenoceptor stimulation increases cyclic AMP accumulation, oxygen consumption rates, mitochondrial function, glucose uptake, and extracellular acidification rates. Treatment of brown adipocytes with rosiglitazone increases uncoupling protein 1 (UCP1) levels, and increases β₃-adrenoceptor mitochondrial function but does not affect glucose uptake responses. In contrast, inguinal white adipocytes only express UCP1 and β₃-adrenoceptors following rosiglitazone treatment, which results in an increase in all β₃-adrenoceptor-mediated functions. The effect of rosiglitazone in epididymal white adipocytes, was much lower compared to inguinal white adipocytes. Rosiglitazone also increased α₁-adrenoceptor mediated increases in calcium influx and glucose uptake (but not mitochondrial function) in inguinal and epididymal white adipocytes. In conclusion, the PPARγ agonist rosiglitazone promotes the induction and function of brite adipocytes cultured from inguinal and epididymal white adipose depots.     

The role of the sympathetic nervous system in the regulation of leptin synthesis in C57BL/6 mice

The objectives of this study were to determine whether leptin synthesis is regulated by the sympathetic nervous system and if so whether beta-adrenergic receptors mediate this effect. We show that sympathetic blockade by reserpine increases leptin mRNA levels in brown but not white adipose tissue, while acute cold-exposure decreases leptin expression 10-fold in brown adipose tissue and 2-fold in white adipose tissue. The cold-induced reduction in leptin mRNA can be prevented by a combination of propranolol and SR 59230A but not by either antagonist alone, indicating that beta3-adrenergic receptors and classical beta1/beta2-adrenergic receptors both mediate responses to sympathetic stimulation. Circulating leptin levels reflect synthesis in white adipose tissue but not in brown adipose tissue.     

UCP1 Induction during Recruitment of Brown Adipocytes in White Adipose Tissue Is Dependent on Cyclooxygenase Activity

Background

The uncoupling protein 1 (UCP1) is a hallmark of brown adipocytes and pivotal for cold- and diet-induced thermogenesis.

Methodology/Principal Findings

Here we report that cyclooxygenase (COX) activity and prostaglandin E₂ (PGE₂) are crucially involved in induction of UCP1 expression in inguinal white adipocytes, but not in classic interscapular brown adipocytes. Cold-induced expression of UCP1 in inguinal white adipocytes was repressed in COX2 knockout (KO) mice and by administration of the COX inhibitor indomethacin in wild-type mice. Indomethacin repressed β-adrenergic induction of UCP1 expression in primary inguinal adipocytes. The use of PGE₂ receptor antagonists implicated EP₄ as a main PGE₂ receptor, and injection of the stable PGE₂ analog (EP_3/4 agonist) 16,16 dm PGE₂ induced UCP1 expression in inguinal white adipose tissue. Inhibition of COX activity attenuated diet-induced UCP1 expression and increased energy efficiency and adipose tissue mass in obesity-resistant mice kept at thermoneutrality.

Conclusions/Significance

Our findings provide evidence that induction of UCP1 expression in white adipose tissue, but not in classic interscapular brown adipose tissue is dependent on cyclooxygenase activity. Our results indicate that cyclooxygenase-dependent induction of UCP1 expression in white adipose tissues is important for diet-induced thermogenesis providing support for a surprising role of COX activity in the control of energy balance and obesity development.     

Thermogenic and metabolic consequences of thyroid hormone treatment in brown and white adipose tissue

Male rats were treated with triiodothyronine in the drinking water for 12 days. In vitro rates of isoprenaline stimulated lipolysis were significantly greater in brown but not white adipose tissue. Rates of [¹⁴C]glucose incorporation into triacylglycerols were significantly reduced in BAT (brown adipose tissue) and WAT (white adipose tissue) under basal and isoprenaline stimulated conditions, in a second experiment, hyperthyroid animals showed impaired weight gain, despite increased food intake during t9 days' treatment. Energy expenditure on days 5 and 12, and BAT core temperature differences (TBAT - T_CORE) on day 19, were significantly greater than in control animals. Epididymal white fat pad weight was reduced and interscapular brown fat pad weight increased by triiodothyronine treatment.     

β₁-Adrenergic receptors increase UCP1 in human MADS brown adipocytes and rescue cold-acclimated β₃-adrenergic receptor-knockout mice via nonshivering thermogenesis

With the finding that brown adipose tissue is present and negatively correlated to obesity in adult man, finding the mechanism(s) of how to activate brown adipose tissue in humans could be important in combating obesity, type 2 diabetes, and their complications. In mice, the main regulator of nonshivering thermogenesis in brown adipose tissue is norepinephrine acting predominantly via β(3)-adrenergic receptors. However, vast majorities of β(3)-adrenergic agonists have so far not been able to stimulate human β(3)-adrenergic receptors or brown adipose tissue activity, and it was postulated that human brown adipose tissue could be regulated instead by β(1)-adrenergic receptors. Therefore, we have investigated the signaling pathways, specifically pathways to nonshivering thermogenesis, in mice lacking β(3)-adrenergic receptors. Wild-type and β(3)-knockout mice were either exposed to acute cold (up to 12 h) or acclimated for 7 wk to cold, and parameters related to metabolism and brown adipose tissue function were investigated. β(3)-knockout mice were able to survive both acute and prolonged cold exposure due to activation of β(1)-adrenergic receptors. Thus, in the absence of β(3)-adrenergic receptors, β(1)-adrenergic receptors are effectively able to signal via cAMP to elicit cAMP-mediated responses and to recruit and activate brown adipose tissue. In addition, we found that in human multipotent adipose-derived stem cells differentiated into functional brown adipocytes, activation of either β(1)-adrenergic receptors or β(3)-adrenergic receptors was able to increase UCP1 mRNA and protein levels. Thus, in humans, β(1)-adrenergic receptors could play an important role in regulating nonshivering thermogenesis.     

β3-Adrenergic activation of adenylyl cyclase in mouse white adipocytes: modulation by GTP and effect of obesity

Lipolysis and adenylyl cyclase (AC) activation in response to β-adrenergic agents are abnormally low in white epididymal adipose tissue (WAT) of the ob/ob mouse. The abundance of G-proteins (G_sα and G_iα) linked to AC is also abnormally low. By contrast, β-adrenergic receptor (β-AR) levels were previously found to be normal in WAT and elevated in liver. The relative importance of various forms of the β-AR in mouse WAT was reassessed in view of the discovery of the β₃-AR. The results show that (1) the β₃-AR is mainly responsible for AC activation in lean-mouse WAT; (2) the β₃-AR is only partly responsible for AC activation in obese mouse WAT; and (3) GTP modulates β₃—-but not β₁—-or β₂-AR activation of AC in a biphasic manner. Therefore, the β₃-AR appears responsible for the well-known bimodal effect of GTP on β-adrenergic receptor-mediated AC activity in WAT.     

Cell proliferation and apoptosis inhibition: essential processes for recruitment of the full thermogenic capacity of brown adipose tissue

In mice living under normal animal house conditions, the brown adipocytes in classical brown adipose tissue depots are already essentially fully differentiated: UCP1 mRNA and UCP1 protein levels are practically saturated. This means that any further recruitment – in response to cold exposure or any other browning agent - does not result in significant augmentation of these parameters. This may easily be construed to indicate that classical brown adipose tissue cannot be further recruited. However, this is far from the case: the capacity for further recruitment instead lies in the ability of the tissue to increase the number of brown-fat cells, a remarkable and highly controlled physiological recruitment process. We have compiled here the available data concerning the unique ability of norepinephrine to increase cell proliferation and inhibit apoptosis in brown adipocytes. Adrenergically stimulated cell proliferation is fully mediated via β₁-adrenoceptors and occurs through activation of stem cells in the tissue; intracellular mediation of the signal involves cAMP and protein kinase A activation, but activation of Erk1/2 is not part of the pathway. Apoptosis inhibition in brown adipocytes is induced by both β- and α₁-adrenergic receptors and here the intracellular pathway includes Erk1/2 activation. This unique ability of norepinephrine to increase cell number in an apparently mitogenically dormant tissue provides possibilities to augment the metabolic capacity of brown adipose tissue, also for therapeutic purposes.     

FABP3 and brown adipocyte-characteristic mitochondrial fatty acid oxidation enzymes are induced in beige cells in a different pathway from UCP1

Cold exposure and β₃-adrenergic receptor agonist (CL316,243) treatment induce the production of beige cells, which express brown adipocytes(BA)-specific UCP1 protein, in white adipose tissue (WAT). It remains unclear whether the beige cells, which have different gene expression patterns from BA, express BA-characteristic fatty acid oxidation (FAO) proteins. Here we found that 5 day cold exposure and CL316,243 treatment of WAT, but not CL316,243 treatment of primary adipocytes of C57BL/6J mice, increased mRNA levels of BA-characteristic FAO proteins. These results suggest that BA-characteristic FAO proteins are induced in beige cells in a different pathway from UCP1.     

Long photophase is not a sufficient stimulus to reduce thermogenic capacity in winter-acclimatized short-tailed field voles (Microtus agrestis) during long-term cold acclimation

The thermogenic capacity of brown adipose tissue in winter- and summer-acclimatized short-tailed field voles (Microtus agrestis) was investigated by examining changes in mass of brown adipose tissue, the ratio of white adipose tissue to brown adipose tissue, the concentration of the uncoupling protein (thermogenin) in whole depots (μg) and in mitochondrial mass (μg·mg^-1) and the activity of cytochrome c oxidase in the depots (mmol·min^-1). The concentration of thermogenin in winter-acclimatized voles (n=8), per brown adipose tissue depot and per mitochondrial mass, was significantly higher than in summer-acclimatized voles (n=6). There was no significant difference in the level of cytochrome c oxidase activity between these two groups. Four groups of winter-acclimatized voles (n=6 in each group) were exposed to 5°C for 10, 20, 50 and 100 days in a 14L:10D photoperiod. Body mass, brown adipose tissue mass, white adipose tissue mass and basal metabolic rate were significantly positively related to the length of time cold exposed up to 100 days. There was a significant inverse relationship between the ratio of white to brown adipose tissue mass and the duration of cold exposure. There was no significant relationship between thermogenin concentration, either per depot or in mitochondrial mass of brown adipose tissue, with the length of time cold exposed. The level of cytochrome c oxidase activity increased significantly from control levels to a maximum after 10 days in the cold but decreased from 10 days onwards. In winter-acclimatized M. agrestis, a 14L:10D photoperiod is not a sufficient stimulus to reduce thermogenic capacity during cold acclimation. Indeed, some changes in the indirect parameters reflecting thermogenesis, notably the increase in basal metabolic rate and the decrease in the ratio of white to brown adipose tissue mass, indicated that despite the long photophase the thermogenic capacity was slightly further enhanced during the cold acclimation.     

ADD1/SREBP1c activates the PGC1-α promoter in brown adipocytes

Cold adaptation elicits a paradoxical simultaneous induction of fatty acid synthesis and β-oxidation in brown adipose tissue. We show here that cold exposure coordinately induced liver X receptor α (LXRα), adipocyte determination and differentiation-dependent factor 1 (ADD1)/sterol regulatory element-binding protein-1c (SREBP1c) and peroxisome proliferator-activated receptor γ coactivator-1α (PGC1α) in brown and inguinal white adipose tissues, but not in epididymal white adipose tissue. Using in vitro models of white and brown adipocytes we demonstrate that β-adrenergic stimulation induced expression of LXRα, ADD1/SREBP1c and PGC1α in cells with a brown-like adipose phenotype. We demonstrate that ADD1/SREBP1c is a powerful inducer of PGC1α expression via a conserved E box in the proximal promoter and that β-adrenergic stimulation led to recruitment of ADD1/SREBP1c to this E box. The ability of ADD1/SREBP1c to activate the PGC1α promoter exhibited a striking cell type dependency, suggesting that additional cell type-restricted factors contribute to ADD1/SREBP1c-mediated activation. In conclusion, our data demonstrate a novel role of ADD1/SREBP1c as a regulator of PGC1α expression in brown adipose tissue.     

Increased α1 receptor density in brown adipose tissue of cafeteria-fed rats

A possible general corollary between ₁-receptor density in brown adipose tissue and the degree of activation of the tissue was investigated. For this purpose, the effect of cafeteria feeding on ₁-adrenergic receptors in brown adipose tissue of seven-week-old female rats was studied by the use of the ₁-antagonist (³H)prazosin. In cafeteria-fed rats, the K_D of the ₁-receptor for (³H)prazosin was unchanged (about 0.35 nM), but the receptor density was doubled (up to 40 fmol per mg of membrane protein). This was also observed when the results were expressed per unit of a plasma-membrane marker (5-nucleotidase). It was concluded that an increased ₁-receptor density is seen not only in cold-acclimated rats, but also in other conditions where brown fat is activated, and a possible general physiological significance of ₁-adrenergic pathways in brown adipose tissue is discussed.     

Comparison of the Lipolytic Effects of Norepinephrine and BRL 37344 in Rat Brown and White Adipocytes

The lipolytic effects of norepinephrine (a non-selective β-agonist) and BRL 37344 (a selective β₃-agonist) were compared in isolated rat brown and white adipocytes. Norepinephrine and BRL 37344 maximally stimulated lipolysis in brown and white adipocytes, approximately 10 times above basal values. However, adipocyte sensitivity for BRL 37344 was greater than that for norepinephrine, particularly in brown adipocytes [the EC₅₀ values (nM) for BRL 37344 and norepinephrine were 5 ± 1 and 103 ± 31 in brown adipocytes (P <0.01) versus 56 ± 9 and 124 ± 17 in white adipocytes (P <0.05), respectively]. On the other hand, the lipolytic effects of norepinephrine were totally blocked by 20–40 times superior concentrations of propranolol or bupranolol in brown as well as in white adipocytes. In contrast, the lipolytic effects of BRL 37344 were fully inhibited by concentrations of propranolol or bupranolol that were 200–1000 superior to the β₃ agonist concentration. The results demonstrate that: (1) the (β₃-agonist BRL 37344 is as effective as norepinephrine for maximally stimulating lipolysis in rat brown and white adipocytes, (2) both adipocyte types are more sensitive to the lipolytic effects of BRL 37344 than to those of norepinephrine, (3) although bupranolol is a better antagonist than propranolol on BRL 37344-stimulated lipolysis, it cannot be considered as a specific β₃-antagonist, (4) brown adipocytes are 10 times more sensitive than white adipocytes to the lipolytic effects of BRL 37344, suggesting an important role of β₃-receptors in brown adipose tissue.     

Sex differences in sympathetic innervation and browning of white adipose tissue of mice

Background

The higher prevalence of obesity-related metabolic disease in males suggests that female sex hormones provide protective mechanisms against the pathogenesis of metabolic syndrome. Because browning of white adipose tissue (WAT) is protective against obesity-related metabolic disease, we examined sex differences in β3-adrenergic remodeling of WAT in mice.

Methods

Effects of the β3-adrenergic receptor agonist CL316,243 (CL) on browning of white adipose tissue were investigated in male and female C57BL mice. The role of ovarian hormones in female-specific browning was studied in control female C57BL mice and mice with ovarian failure induced by 4-vinylcyclohexene diepoxide treatment for 15 days.

Results

We found that treatment with CL-induced upregulation of brown adipocyte markers and mitochondrial respiratory chain proteins in gonadal WAT (gWAT) of female mice, but was without effect in males. In contrast, CL treatment was equally effective in males and females in inducing brown adipocyte phenotypes in inguinal WAT. The tissue- and sex-specific differences in brown adipocyte recruitment were correlated with differences in sympathetic innervation, as determined by tyrosine hydroxylase immunostaining and western blotting. Levels of the neurotrophins NGF and BDNF were significantly higher in gWAT of female mice. CL treatment significantly increased NGF levels in gWAT of female mice but did not affect BDNF expression. In contrast, estradiol treatment doubled BDNF expression in female adipocytes differentiated in vitro. Ovarian failure induced by 4-vinylcyclohexene diepoxide treatment dramatically reduced BDNF and TH expression in gWAT, eliminated induction of UCP1 by CL, and reduced tissue metabolic rate.

Conclusions

Collectively, these data demonstrate that female mice are more responsive than males to the recruitment of brown adipocytes in gonadal WAT and this difference corresponds to greater levels of estrogen-dependent sympathetic innervation.

     

Growth Hormone Treatment of Hypophysectomized Rats Increases Catecholamine-induced Lipolysis and the Number of β-Adrenergic Receptors in Adipocytes: No Differences in the Effects of Growth Hormone on Different Fat Depots

Growth hormone (GH) has a lipolytic effect in adipose tissue but this effect may differ in adipose tissue from various fat depots. This latter possibility was investigated in the present study, in which the effects of GH in vivo on catecholamine-induced lipolysis and the number of β-adrenergic receptors in isolated adipocytes from different fat depots of hypophysectomized rats were investigated. Female and male Sprague-Dawley rats were hypophysectomized or sham-operated at 45 days of age. One week after the operation, hormonal replacement therapy with L-thyroxine and hydrocortisone acetate was given. In addition, groups of rats were treated with GH (1.33 mg/kg per day, given as two daily subcutaneous injections). After 1 week of hormonal treatment, adipocytes were isolated from the parametrial, epididymal and inguinal fat pads, and glycerol release after catecholamine-stimulation and ¹²⁵I-cyanopindolol binding were measured. Hypophysectomy resulted in a marked decrease in the lipolytic response to catecholamines. GH treatment significantly increased catecholamine-induced lipolysis with similar effects in adipocytes from parametrial or epididymal and inguinal fat depots in both female and male rats. There were no differences between norepinephrine compared with isoproterenol-induced responses. ¹²⁵I-cyanopindolol binding was reduced after hypophysectomy and normalized by GH treatment, without differences between parametrial and inguinal adipose tissue regions. We conclude that the lipolytic effects of GH in the rat may partly be mediated by a stimulatory effect on β-adrenergic receptors in adipocytes. In addition, GH exerted similar effect on catecholamine-induced lipolysis and β-adrenergic receptors in adipocytes from parametrial, epididymal and inguinal fat depots.     

Reversine promotes browning of white adipocytes by suppressing miR-133a

Brown adipocytes are characterized by a high number of uncoupling protein 1 (UCP1)-positive mitochondrial content and increased thermogenic capacity. As UCP1-enriched cells can consume lipids by generating heat, browning of white adipocytes is now highlighted as a promising approach for the prevention of obesity and obesity-associated metabolic diseases. Upon cold exposure or β-adrenergic stimuli, downregulation of microRNA-133 (miR-133) elevates the expression levels of PR domain containing 16 (Prdm16), which has been shown to be a brown adipose determination factor, in brown adipose tissue and subcutaneous white adipose tissues (WAT). Here, we show that treatment of reversine to white adipocytes induces browning via suppression of miR-133a. Reversine treatment promoted the expression of brown adipocyte marker genes, such as Prdm16 and UCP1, increasing the mitochondrial content, while decreasing the levels of miR-133a and white adipocyte marker genes. Ectopic expression of miR-133a mimic reversed the browning effects of the reversine treatment. Moreover, intraperitoneal administration of reversine in mice upregulated thermogenesis and resulted in resistance to high-fat diet-mediated weight gain as well as browning of subcutaneous and epididymal WAT. Taken together, we found a novel way to promote browning of white adipocytes through downregulation of miR-133a followed by activation of Prdm16, with a synthetic chemical, reversine.