Metabolic basis of thermogenesis in cold exposed humans

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The increase in heat production is achieved voluntarily through exercise or involuntarily by the activation of non-shivering thermogenesis (NST) and shivering thermogenesis (ST). When exercise is not possible, activation of NST and ST is essential for maintaining core temperature. Research in newborn humans has shown that NST is associated with the activation of large superficial and deep brown adipose tissue (BAT) depots. While it is clear that NST is an essential means of thermogenesis in cold-exposed infants, the exact contribution of this pathway in adults remains controversial. However, recent evidence has clearly shown that adult humans still retain significant amounts of BAT. Both quantity and metabolic activity of BAT are highly variable among individuals. In view of the very recent demonstration of the presence of BAT metabolic activity in humans, this phenomenon has attracted the attention of fundamental and health researchers alike and needs to be revisited. Therefore, the purpose of this proposal is to measure the effects of cold-exposure and cold-acclimation on thermogenesis and tissues-specific metabolism in adult humans. To achieve this goal, three short-term objectives must be carried out: we will 1) determine whole-body and tissue-specific glucose and fatty acid uptake, 2) quantify the effect of BAT activation on ST responses and, 3) determine the effects of cold-acclimation changes in BAT activation, energy metabolism and ST activity. Studies will be based on an experimental paradigm developed as part of our previous work which has been primarily directed to the quantification of thermal, metabolic and electrophysiological. Whole-body metabolic responses will be determined by whole-body indirect calorimetry and isotopic methodologies whereas tissue-specific metabolism will be measured using PET/CT. The proposed studies will provide building blocks for developing strategies through dietary and/or physical interventions to improve chances of survival in the cold. This is particularly relevant for many athletic activities as well as industrial and military applications. The proposed investigations are but the necessary first step of a broader research program on BAT metabolism.