Cold acclimation enhances UCP1 content, lipolysis, and triacylglycerol resynthesis, but not mitochondrial uncoupling and fat oxidation, in rat white adipocytes

Abstract

The objective of this study was to investigate whether cold-induced browning of the subcutaneous (Sc) inguinal (Ing) white adipose tissue (WAT) increases the capacity of this tissue to oxidize fatty acids through uncoupling protein 1 (UCP1)-mediated thermogenesis. To accomplish that, rats were acclimated to cold (4°C for 7 days). Subsequently, interscapular and aortic brown adipose tissues (iBAT and aBAT, respectively), epididymal (Epid), and Sc Ing WAT were used for adipocyte isolation. In BAT adipocytes, cold acclimation increased UCP1 content and palmitate oxidation either in the absence or presence of oligomycin, whereas in Sc Ing adipocytes glucose and palmitate oxidation were not affected, although multilocular adipocytes were formed and UCP1 content increased upon cold acclimation in the WAT. Furthermore, isoproterenol-stimulated cold Sc Ing adipocytes exhibited significantly lower rates of palmitate oxidation than control cells when exposed to oligomycin. These findings provide evidence that, despite increasing UCP1 levels, cold acclimation essentially reduced mitochondrial uncoupling-mediated fat oxidation in Sc Ing adipocytes. Conversely, glycerol kinase and phosphoenolpyruvate carboxykinase levels, isoproterenol-induced lipolysis, as well as glycerol and palmitate incorporation into lipids significantly increased in these cells. Therefore, instead of UCP1-mediated mitochondrial uncoupling, cold acclimation increased the capacity of Sc Ing adipocytes to export fatty acids and enhanced key components of the triacylglycerol resynthesis pathway in the Sc Ing WAT.