Characteristics of diet-induced brown adipose tissue growth and thermogenesis in rats

The characteristics of regional brown (BAT) and white adipose tissue (WAT) growth and of thermogenesis following experimental overfeeding were studied in groups of male Sprague-Dawley rats fed lab chow or cafeteria diets for 8 weeks postweaning. Regional BAT and WAT growth was determined by dissection and weighing, and thermogenesis was characterized by measurements of resting and norepinephrine (NE)-stimulated oxygen consumption, of serum thyroid hormone concentrations, and of 24-hour urinary NE excretion levels. Cafeteria feeding resulted in a 113% increase in total BAT, with the most prominent increases in the interscapular, thoracic, and perirenal regions. Retroperitoneal, epididymal, and omental WAT were significantly greater in cafeteria than in chow-fed rats. Resting oxygen consumption of cafeteria-fed rads increased by 10% and NE excretion by 64% compared to chow-fed controls, while serum T₃ concentrations were nearly doubled in the cafeteria-fed rats. The thermogenic response to NE injection in cafeteria-fed rats was 102% of their resting levels, compared to a 51% increase in the chow-fed controls. The results indicate that increased BAT growth occurs in all primary BAT depots following cafeteria-feeding in rats, and that the greater BAT mass is qualitatively proportional to their greater capacity for non-shivering thermogenesis. Also, the increased NE excretion and greater serum T₃ concentration are consistent with increased sympathetic and thyroidal activity and may in part explain the thermogenic response to diet in the rat.     

Perilipin overexpression in white adipose tissue induces a brown fat-like phenotype

Background

Perilipin A (PeriA) exclusively locates on adipocyte lipid droplets and is essential for lipid storage and lipolysis. Previously, we reported that adipocyte specific overexpression of PeriA caused resistance to diet-induced obesity and resulted in improved insulin sensitivity. In order to better understand the biological basis for this observed phenotype, we performed additional studies in this transgenic mouse model.

Methodology and Principal Findings

When compared to control animals, whole body energy expenditure was increased in the transgenic mice. Subsequently, we performed DNA microarray analysis and real-time PCR on white adipose tissue. Consistent with the metabolic chamber data, we observed increased expression of genes associated with fatty acid β-oxidation and heat production, and a decrease in the genes associated with lipid synthesis. Gene expression of Pgc1a, a regulator of fatty acid oxidation and Ucp1, a brown adipocyte specific protein, was increased in the white adipose tissue of the transgenic mice. This observation was subsequently verified by both Western blotting and histological examination. Expression of RIP140, a regulator of white adipocyte differentiation, and the lipid droplet protein FSP27 was decreased in the transgenic mice. Importantly, FSP27 has been shown to control gene expression of these crucial metabolic regulators. Overexpression of PeriA in 3T3-L1 adipocytes also reduced FSP27 expression and diminished lipid droplet size.

Conclusions

These findings demonstrate that overexpression of PeriA in white adipocytes reduces lipid droplet size by decreasing FSP27 expression and thereby inducing a brown adipose tissue-like phenotype. Our data suggest that modulation of lipid droplet proteins in white adipocytes is a potential therapeutic strategy for the treatment of obesity and its related disorders.     

Reduced noradrenaline turnover in brown adipose tissue of lactating rats

Brown adipose tissue properties as well as noradrenaline turnover in the tissue were determined in 15-day lactating rats and virgin controls. Brown adipose tissue thermogenic activity was reduced in lactating rats as shown by a decrease in weight, cytochrome oxidase activity and mitochondrial GDP-binding. The noradrenaline turnover rate was lower in brown adipose tissue from lactating rats. It is suggested that diminished sympathetic activity in brown adipose tissue may be a major cause of the reduced tissue thermogenic activity during lactation.     

Effects of pterostilbene in brown adipose tissue from obese rats

In recent years, much attention has been paid by the scientific community to phenolic compounds as active biomolecules naturally present in foods. Pterostilbene is a resveratrol dimethylether derivative which shows higher bioavailability. The aim of the present study was to analyze the effect of pterostilbene on brown adipose tissue thermogenic markers in a model of genetic obesity, which shows reduced thermogenesis. The experiment was conducted with 30 Zucker (fa/fa) rats that were distributed in three experimental groups: control and two groups orally administered with pterostilbene at 15 and 30 mg/kg body weight/day for 6 weeks. Gene expression of uncoupling protein 1 (Ucp1), peroxisome proliferator-activated receptor γ co-activator 1 α (Pgc-1α), carnitine palmitoyl transferase 1b (Cpt1b), peroxisome proliferator-activated receptor α (Pparα), nuclear respiratory factor 1 (Nfr1), and cyclooxygenase-2 (Cox-2); protein expression of PPARα, PGC-1α, p38 mitogen-activated protein kinase (p38 MAPK), UCP1 and glucose transporter (GLUT4); and enzyme activity of CPT 1b and citrate synthase (CS) were assessed in interscapular brown adipose tissue. With the exception of Pgc-1α expression, all these parameters were significantly increased by pterostilbene administration. These results show for the first time that pterostilbene increases thermogenic and oxidative capacity of brown adipose tissue in obese rats. Whether these effects effectively contribute to the antiobesity properties of these compound needs further research.     

Melatonin induces hypertrophy of brown adipose tissue in Spermophilus tridecemlineatus

Nonshivering thermogenesis (NST) plays an important role in hibernators during cold exposure and arousal periods. Brown adipose tissue (BAT), an important site of NST, displays seasonal changes in S. tridecemlineatus while cold exposure and short photoperiods stimulate hypertrophy of BAT.The pineal gland and melatonin have been implicated in thermoregulation but relatively little is known about the pineal's role in hibernation. In this investigation chronic melatonin administration via both silicone rubber implants containing 3 mg of melatonin and daily intraperitoneal injections of saline containing 50 μg of melatonin induced hypertrophy of BAT in young-of-the-year S. tridecemlineatus. Chronic melatonin administration appears to mimic the effects of cold exposure and/or short photoperiods on the hypertrophy of BAT.     

Insulin modifies the properties of glucose transporters in rat brown adipose tissue.

The influence of cyclic AMP on cartilage degradation was investigated by using phosphodiesterase inhibitors [theophylline and 3-isobutyl-1-methylxanthine (IBMX)], forskolin (which activates the catalytic subunit of adenylate cyclase) and cyclic AMP analogues (dibutyryl and 8-bromo). Breakdown was assessed by quantification of proteoglycans released into the media of 8-day bovine nasal-septum cartilage cultures. Theophylline (1-20 mM), IBMX (0.01-2 mM) and dibutyryl cyclic AMP (0.1-2 mM) had little or no influence on the rate of proteoglycan release from unstimulated (no-endotoxin) cartilages. A small but detectable increase in breakdown was observed with 8-bromo cyclic AMP (0.5-2 mM) and forskolin (50-75 micrograms/ml). To examine potential inhibitory influences of these agents, the cyclic AMP modulators were added to cultures simultaneously treated with Salmonella typhosa endotoxin (12-25 micrograms/ml), a potent stimulator of cartilage degradation. The 3-4-fold stimulation of breakdown by endotoxin was strikingly inhibited by all three classes of cyclic AMP regulators. Optimal inhibition was found at 10-20 mM-theophylline, 1-2 mM-IBMX, 50-75 micrograms of forskolin/ml, 2 mM-dibutyryl cyclic AMP and 2 mM-8-bromo cyclic AMP. Inhibition was shown to be reversible, indicating that cartilages were viable after treatment. Sepharose CL-2B chromatography of proteoglycan products released from treated cartilages showed that the endotoxin-stimulated shift to lower average Mr was significantly prevented by cyclic AMP analogues and phosphodiesterase inhibitors. Together, these results show that agents which increase cyclic AMP inhibit both quantitative and qualitative aspects of endotoxin-mediated cartilage degradation.     

A protein kinase inhibitor in brown adipose tissue of developing rats

A heat-stable protein was extracted from brown adipose tissue of infant rats that inhibited both purified bovine heart protein kinase and a crude preparation of protein kinase from brown fat. It did not act as an adenosine triphosphatase nor did it exert its effect by proteolytic action. Inhibition of protein kinase was affected in both the presence and the absence of cyclic AMP. Most of the inhibitory activity was present in the 100000g supernatant fraction of tissue homogenates. Inhibitory activity was highest perinatally and it declined 10 days after birth. It is suggested that the protein kinase inhibitor may play a role in regulating cyclic AMP actions.     

Reduced brown adipose tissue thermogenesis of obese rats after ovariectomy

Brown adipose tissue (BAT) thermogenesis was assessed by measuring mitochondrial guanosine diphosphate (GDP) binding, cytochrome oxidase activity and oxygen consumption in ovariectomized (OVX) and sham-operated rats. The food intake and body weight of OVX rats increased more than those of controls and OVX rats became obese. Mitochondrial GDP binding, as an indicator of thermogenic activity, cytochrome oxidase activity, as a marker of mitochondrial abundance, and mitochondrial respiration of BAT in OVX rats were significantly reduced compared with those in controls. And, also, even when OVX rats were restricted in food intake (pair-gained) to produce comparable changes in body weight with sham-controls, or matched in food intake (pair-fed) with sham-controls, these parameters in both pair-gained and pair-fed OVX groups were decreased markedly compared to those in sham-controls. As expected, body weight in pair-fed OVX rats increased significantly more than that in sham-controls. In response to cold exposure, these parameters of OVX rats increased as much as those of controls did. These results suggest that reduced brown adipose tissue thermogenesis might be one of the important factors that are responsible for the development of obesity after OVX.     

Sympathetic activation of glucose utilization in brown adipose tissue in rats.

The effects of norepinephrine (NE) infusion and surgical denervation or electrical stimulation of the sympathetic nerves on 2-deoxyglucose (2-DG) uptake in interscapular brown adipose tissue (BAT) were investigated in vivo in rats to obtain direct evidence for sympathetic control of glucose utilization in this tissue. 2-DG uptake was rather low in fasted rats, but after refeeding it increased in the BAT as well as the heart, skeletal muscle, and white adipose tissue, in parallel with an increase in plasma insulin level. Cold exposure also enhanced 2-DG uptake in the BAT without the increase in plasma insulin level, while it had no appreciable effect on 2-DG uptake in other tissues. Sympathetic denervation greatly attenuated the stimulatory effect of cold exposure on 2-DG uptake in BAT, but it did not affect the increased 2-DG uptake after refeeding. Electrical stimulation of the sympathetic nerves entering BAT or NE infusion produced a marked increase in 2-DG uptake in BAT without noticeable effects in other tissues. beta-Adrenergic blockade, but not alpha-blockade, abolished the increased 2-DG uptake in BAT. It was concluded that glucose utilization in BAT is activated directly, independently of the action of insulin, by sympathetic nerves via the beta-adrenergic pathway.     

Cold exposure or chronic noradrenaline treatment induces an increase in the calmodulin-like immunoreactivity of brown adipose tissue of rats

Cell proliferation is often associated with an increase in calmodulin, the ubiquitous intracellular calcium receptor of non-muscle cells. A long lasting increase in the proliferative activity of brown adipose tissue is induced by cold exposure in the rat. The present work showed that this phenomenon is also associated with a rapid and long lasting increase in the calmodulin content of this tissue. It was equally shown that this increase can be reproduced by noradrenaline admini-stration.     

Effects of thyroxine and 3,5,3'-triiodothyronine in brown adipose tissue of rats

Rats of both sexes were either cold acclimated (6 +/- 1 degree C) or treated with thyroxine (T4) or 3,5,3'-triiodothyronine (T3) (500 micrograms/kg body wt daily s.c. for 3 weeks). Wet weight, total proteins, lipids and nucleic acids in the interscapular brown adipose tissue (IBAT) were measured. Values obtained with T4 treatment were similar to those obtained with T3 treatment. T3 is the main thyroidal hormone in the rat and it is formed from T4 deiodination in liver and kidney. As T4-treated rats have not received T3 directly and its IBAT has a similar composition to that of T3-treated rats, it is concluded that peripheral T4 deiodination is governed by the plasma T4 levels. Total proteins and DNA content were similar in cold-acclimated and T3- or T4-treated rats, which is interpreted as thyroidal hormones having an action at these levels.