Gender-related differences in morphology and thermogenic capacity of brown adipose tissue mitochondrial subpopulations

To investigate the possible existence of a gender dimorphism in the morphology and functionality of brown adipose tissue (BAT) mitochondrial subpopulations, we obtained three mitochondrial fractions - heavy, medium and light - by differential centrifugation. Electron microscopic analysis was carried out and mitochondrial protein content, cytochrome c oxidase and ATP synthase activities, mitochondrial DNA content and UCP1 protein levels were measured in each mitochondrial fraction. Female rats showed a greater mitochondrial size than males, with a different distribution pattern of the subpopulations. These differences were accompanied by higher oxidative and thermogenic capacities and a higher protein content in female rat BAT. This tissue also showed a greater tendency to respiratory chain uncoupling, as well as a close coordination between the oxidative, phosphorylative and thermogenic processes. These differences were found in the heavy subpopulation but not in the light one. Our results demonstrate that female rat BAT shows a highly differentiated mitochondrial pool, with the heavy mitochondrial subpopulation as the main responsible for the greater thermogenic activity of this tissue. In addition, it seems that there is a differential regulation of the mitochondrial growth cycle between genders in BAT, which leads to enhanced thermogenic capacity in female rat mitochondria.     

Cold-induced changes in brown adipose tissue thermogenic capacity of immunocompetent and immunodeficient hairless mice

Mild cold acclimation (22°C, 3 weeks) of hairless mice was shown to increase 5-fold the brown adipose tissue uncoupling protein content in immunodeficient BALB/c nu/nu mice, but by only 2.3-fold in immunocompetent BFU mice. The difference in activation of brown adipose tissue thermogenic capacity was due to a 2-fold increase in the content of brown adipose tissue in nu/nu mice only, which was paralleled by an increase in brown adipose tissue protein but not DNA content. Likewise, only in nu/nu mice the cold acclimation increased the reaction of natural killer cells in blood and peritoneal exudate with a shift from spleen to lymph nodes and increased the phagocytic index. The results indicate that the immune system may influence the defence against cold at the level of brown adipose tissue thermogenesis.Abbreviations AU arbitrary unit(s) - bw body weight - HEMA 2-hydromethyl-metacrylate copolymer - BAT brown adipose tissue - UCP uncoupling protein - ATPase mitochondrial F_oF₁-ATPsynthase - IL-1 interleukin 1 - TNF tumour necrosis factor - NK cells natural killer cells - T _a ambient temperature     

Increased GDP binding and thermogenic activity in brown adipose tissue mitochondria during arousal of the hibernating garden dormouse (Eliomys quercinus L.).

1. The thermogenic activity of brown adipose tissue in hibernating garden dormice during hypothermic torpor and at different states of arousal were studied. High levels of GDP binding were observed on isolated brown fat mitochondria, indicating that the thermogenic proton conductance pathway is very active in brown fat during arousal. 2. In order to investigate this phenomenon, the uncoupling protein was assessed by immunological assay and the mRNA for UCP was analysed. 3. Animals during arousal exhibited neither increase in UCPmRNA nor an increase in UCP. 4. Our results suggest that during the rewarming of garden dormice there is an acute unmasking of GDP binding sites on the protein.     

Increased contribution of brown adipose tissue to nonshivering thermogenesis in the Djungarian hamster during cold-adaptation

Summary The effect of cold-adaptation was investigated on the brown adipose tissue of Djungarian hamsters. Animals maintained at 23°C and 16 hours light per day (controls) were exposed to 5°C. The wet weight of the total brown fat is reduced by some 40% within 4 days of coldexposure, as a result of extensive triacylglycerol depletion of the tissue with no reduction in DNA; the tissue mass remains constant unde persistent cold influence. The total amount of tissue mitochondria is doubled by 24 h and increases by a factor of 3 under persistent cold-stimulus, the specific respiratory capacity of the organelles remaining unchanged. The amount of 32 kDa regulatory protein per mg mitochondrial protein quantified from high-affinity GDP-binding, is increased by a factor of 2.7 after 21 days of cold-adaptation; a 9-fold increment is found of the total mitochondrial GDB-binding capacity.Comparison of nonshivering thermogenesis and the maximal thermogenic capacity of brown fat, estimated from the maximal respiration of the isolated mitochondria and the total amount of mitochondria in the tissue, suggests that brown fat may contribute about 20% to the whole-body nonshivering thermogenesis in warm-adapted controls and 45% in cold-adapted hamsters. The estimated increase in thermogenic capacity of the tissue in response to 21 days of cold-adaptation corresponds to the increase in nonshivering thermogenesis, suggesting a central thermoregulatory role of brown fat during cold-adaptation.Abbreviation FCCP carbonylcyanide-p-trifluoromethoxyphenylhydrazone     

Effects of resveratrol and its derivative pterostilbene on brown adipose tissue thermogenic activation and on white adipose tissue browning process

Journal of Physiology and Biochemistry - The main function of brown adipose tissue (BAT) is thermogenesis, a process mediated by uncoupling protein 1 (UCP1), which is located in the inner...     

Perilipin regulates the thermogenic actions of norepinephrine in brown adipose tissue

In response to cold, norepinephrine (NE)-induced triacylglycerol hydrolysis (lipolysis) in adipocytes of brown adipose tissue (BAT) provides fatty acid substrates to mitochondria for heat generation (adaptive thermogenesis). NE-induced lipolysis is mediated by protein kinase A (PKA)-dependent phosphorylation of perilipin, a lipid droplet-associated protein that is the major regulator of lipolysis. We investigated the role of perilipin PKA phosphorylation in BAT NE-stimulated thermogenesis using a novel mouse model in which a mutant form of perilipin, lacking all six PKA phosphorylation sites, is expressed in adipocytes of perilipin knockout (Peri KO) mice. Here, we show that despite a normal mitochondrial respiratory capacity, NE-induced lipolysis is abrogated in the interscapular brown adipose tissue (IBAT) of these mice. This lipolytic constraint is accompanied by a dramatic blunting ( approximately 70%) of the in vivo thermal response to NE. Thus, in the presence of perilipin, PKA-mediated perilipin phosphorylation is essential for NE-dependent lipolysis and full adaptive thermogenesis in BAT. In IBAT of Peri KO mice, increased basal lipolysis attributable to the absence of perilipin is sufficient to support a rapid NE-stimulated temperature increase ( approximately 3.0 degrees C) comparable to that in wild-type mice. This observation suggests that one or more NE-dependent mechanism downstream of perilipin phosphorylation is required to initiate and/or sustain the IBAT thermal response.     

Decreasing temperature shifts hippocampal function from memory formation to modulation of hibernation bout duration in Syrian hamsters

Previous studies in hibernating species have characterized two forms of neural plasticity in the hippocampus, long-term potentiation (LTP) and its reversal, depotentiation, but not de novo long-term depression (LTD), which is also associated with memory formation. Studies have also shown that histamine injected into the hippocampus prolonged hibernation bout duration. However, spillover into the ventricles may have affected brain stem regions, not the hippocampus. Here, we tested the hypothesis that decreased brain temperature shifts the major function of the hippocampus in the Syrian hamster (Mesocricetus auratus) from one of memory formation (via LTP, depotentiation, and de novo LTD) to increasing hibernation bout duration. We found reduced evoked responses in hippocampal CA1 pyramidal neurons following low-frequency stimulation in young (<30 days old) and adult (>60 days old) hamsters, indicating that de novo LTD was generated in hippocampal slices from both pups and adults at temperatures >20°C. However, at temperatures below 20°C, synchronization of neural assemblies (a requirement for LTD generation) was markedly degraded, implying that de novo LTD cannot be generated in hibernating hamsters. Nonetheless, even at temperatures below 16°C, pyramidal neurons could still generate action potentials that may traverse a neural pathway, suppressing the ascending arousal system (ARS). In addition, histamine increased the excitability of these pyramidal cells. Taken together, these findings are consistent with the hypothesis that hippocampal circuits remain operational at low brain temperatures in Syrian hamsters and suppress the ARS to prolong bout duration, even though memory formation is muted at these low temperatures.     

Lipolysis in brown adipose tissue of cold- and heat-acclimated hamsters

Rates of release of free fatty acids (FFA) and glycerol to the incubation medium by brown adipose tissue (BAT) slices isolated from heat-acclimated (H), cold-acclimated (C), and control (N) hamsters in the absence or presence of epinephrine (E) were studied. Rates of FFA and glycerol release by tissue slices isolated from H and N animals were similar. In tissue slices isolated from C animals rate of release of FFA and glycerol was three times as high. Addition of E to the incubation medium (200 microgram/ml) had no effect on the rate of FFA and glycerol release of slices from C animals, but tripled the rates of slices from N, resulting in similar values for the two groups. In slices from H animals the rate of release was lower than in the other two groups, increasing only 1.5-fold. Pretreatment of N animals with triiodothyronine (T3; 0.8 microgram/100 g daily for 7 days) doubled the rates of FFA and glycerol release. Addition of E to the medium affected both pretreated and nontreated slices similarly. Two possible mechanisms by which temperature acclimation controls the lipolytic rate of BAT are suggested by 1) the concentration of specific enzymes and 2) cellular metabolites and hormones which activate existing systems. It seems that both operate in temperature-acclimated hamsters.     

Effects of high fat diets on hibernation and adipose tissue in Turkish hamsters

Summary The effects of dietary fat saturation and fat content on hibernation and several properties of white and brown adipose tissue (WAT and BAT, respectively) were investigated in Turkish hamsters (Mesocricetus brandti). Male hamsters were housed in a long photoperiod (LD 16:8) at 23°C and fed one of three diets: (1) chow (6.5% fat per weight), (2) chow+13.5% vegetable oil (OIL, 20% fat per weight [largely unsaturated fat]) and (3) chow+13.5% vegetable shortening [SHORTENING, 20% fat per weight (largely saturated fat)]. Five weeks later body weights had stabilized and the animals were transferred to a short photoperiod (LD 8:16) at 3°C. At the peak of the hibernation season (17 weeks) the animals were sacrificed within 24 h of arousal. Chow-fed hamsters had the greatest percentage of animals hibernating and days found torpid compared with the two fat-fed groups, with no differences found between the latter two groups for these measures. There were no differences between hibernating (HIB) and nonhibernating (NON-HIB) hamsters across or within the diet groups for any of the BAT measures [uncoupling protein content, mitochondrial mass, lipoprotein lipase (LPL) activity, and in vivo lipogenesis], nor were there significant effects of the diet on these measures. CHOW-and OIL-fed HIB hamsters showed decreases in body weight. All HIB groups had decreases in each carcass component, several fat pad weights, testes weight, and food intake. No consistent differences in WAT LPL activity or in vivo lipogenesis were found between HIB and NON-HIB hamsters. Feeding saturated high fat diets inhibits hibernation in some species; however, in the present experiment, feeding of both saturated and unsaturated fat-laden diets inhibited hibernation to a similar degree.Abbreviations BAT brown adipose tissue - COA cytochrome-c oxidase - DS dorsal subcutaneus - DSWAT dorsal subcutaneous white adipose tissue - E epididymal - EWAT epididymal white adipose tissue - FFDM fat-free dry mass - HIB hibernating - I interscapular - IBAT intercapsular brown adipose tissue - IS inguinal subeutaneus - ISWAT inguinal subcutaneous white adipose tissue - LPL lipoprotein lipase - NON-HIB non-hibernating - R retroperitoneal - RWAT retroperitoneal white adipose tissue - SDS sodium dodecyl sul - UCP uncoupling protein - WAT white adipose tissue     

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.