Cooperation between brown- and white adipose tissues of rats in thermogenesis in response to cold, and the mechanism of glycogen accumulation in brown adipose tissue during reacclimation

Peter B. Jakus, Attila Sandor, Tamas Janaky, and Viktoria Farkas

Bichemistry and Medical Chemistry, Univ. Pecs, Faculty of Medicine, Pecs 7624

Corresponding Author: atila.sandor{at}aok.pte.hu

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, WAT) and in muscle were then examined. Of the many proteins involved in the metabolic response, two lipogenic enzymes, acetyl-CoA carboxylase (ACC) and ATP-citrate lyase (CitLy), 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, while that of ACC2 remained unchanged. The activities of these enzymes and the in vivo rate of free fatty acid (FFA) synthesis together suggested that WAT supplies B AT 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.

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