Cooperation between BAT and WAT of rats in thermogenesis in response to cold, and the mechanism of glycogen accumulation in BAT during reacclimation

Abstract

Rats were exposed to cold and then reacclimated at neutral temperature. Changes related to fatty acid and glucose metabolism in brown and white adipose tissues (BAT and WAT) and in muscle were then examined. Of the many proteins involved in the metabolic response, two lipogenic enzymes, acetyl-coenzyme A carboxylase (ACC) and ATPcitrate lyase, were found to play a pervasive role and studied in detail. Expression of the total and phosphorylated forms of both lipogenic enzymes in response to cold increased in BAT but decreased in WAT. Importantly, in BAT, only the phosphorylation of the ACC1 isoenzyme was enhanced, whereas that of ACC2 remained unchanged. The activities of these enzymes and the in vivo rate of FFA synthesis together suggested that WAT supplies BAT with FFA and glucose by decreasing its own synthetic activity. Furthermore, cold increased the glucose uptake of BAT by stimulating the expression of components of the insulin signaling cascade, as observed by the enhanced expression and phosphorylation of Akt and GSK-3. In muscle, these changes were observed only during reacclimation, when serum insulin also increased. Such changes may be responsible for the extreme glycogen accumulation in the BAT of rats reacclimated from cold.-Jakus, P. B., A. Sandor, T. Janaky, and V. Farkas. Cooperation between BAT and WAT of rats in thermogenesis in response to cold, and the mechanism of glycogen accumulation in BAT during reacclimation. J. Lipid Res. 2008. 49: 332-339.

Intermittent Cold Exposure Enhances Fat Accumulation in Mice

“…Although cold exposure and ICE have been used in rodents and even human subjects, their effects on systemic energy metabolism and adiposity are not fully understood. For rodents, many studies reported that cold exposure enhances both fatty acid oxidation and glucose-derived lipogenesis in BAT, but its effects on WAT were controversial [14]–[16]. Furthermore, contradictory effects on body weight and WAT have been observed in both mice and rats [17]–[22].…”

Differential Effects of Cold Exposure on Gene Expression Profiles in White Versus Brown Adipose Tissue

“…Triglycerides stored in lipid droplets of brown adipocytes also seem to be used as an acute energy source of thermogenesis because sizes of lipid droplets in the brown adipocytes are known to be reduced by cold exposure of animals [12]. A possible slower response of WAT to cold exposure than that seen for BAT is also supported by the studies of Jakus et al who reported that the enzymes related to fatty acid synthesis are downregulated in the WAT of rats subjected to prolonged cold exposure for 1 week [13]. However, the expression of these enzymes in the WAT was not changed under the present experimental conditions (data not shown).…”

Effect of seasonal and experimental temperature on de novo synthesis of fatty acids in C. crangon

“…[23][24][25][26] The reason for this phenomenon is the effect of temperature on the increase of rate of de novo FAs synthesis. 27) In our manuscript, the tritium incorporation to the brown shrimp tissues in time of 1 h was examined, which gave information about the FA synthesis. The experiment had several variables: the method of tritium incorporation, the time of exposition to tritium, the experimental temperature, the influence of the season (environmental conditions) on the synthesis of FAs, and the type of analyzed tissues.…”

“…Jakus et al demonstrated that in situations when the environmental temperature is changed, there is adaptation to the prevailing conditions and the rate of lipogenesis is changing. 27) An example would be to increase the rate of lipogenesis in response to an increase of temperature ( Table 1). The maintenance of a constant membrane fluidity requires an increased amount of SFAs at elevated temperatures.…”

“…27) Another reason is the influence of a high-fat diet, which inhibits the activity of lipogenic enzymes. Lipogenic enzymes respond rapidly to the supplied lipids and after sometime work more slower.…”