Doctoral Dissertation Improvement: Conceptualizing the Adaptive Significance of Brown Adipose Tissue in Cold Climates

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Arctic regions present extreme environmental stresses, such as severe cold and low biodiversity; yet, human populations have managed to survive in these territories for thousands of years. As human populations migrated into high-latitude regions, they underwent an adaptive shift that included cultural, behavioral and biological dimensions. Contemporary circumpolar populations appear to adapt to cold temperatures physiologically by generating high metabolic rates; however, the mechanisms that control this biological adaptation are poorly understood. Brown adipose tissue (BAT), a special type of fat that is highly metabolically active, has been recognized for decades as the primary source of heat production among infants. However, it was previously assumed that as humans develop, BAT levels decrease to trace amounts. Within recent years, BAT has been discovered to be present and active among many adults. Furthermore, due its ability to convert stored fats and sugars into heat, the presence of BAT may have protective effects against obesity. It is not known why some adults have BAT while others do not, and whether BAT activity is adaptive against cold temperatures. This project will examine variation in BAT activity among indigenous and non-indigenous populations living in cold climates to enhance our understanding of biological adaptations to cold; early-life factors that may shape adult metabolism; and population variation in metabolic disease risk. In addition, the project will support training of a female graduate student in the STEM sciences, foster research collaborations, and provide a new, portable method for quantifying fat metabolic activity. An elevated resting metabolic rate (RMR) and efficient non-shivering thermogenesis (NST) are central biological adaptations to cold climates, but the mechanisms that dictate these metabolic adaptations are poorly understood. Researchers have recently discovered that brown adipose tissue (BAT), a form of fat that is highly thermogenic, is present among adults. This study investigates multiple levels of adaptation to cold stress by testing hypotheses regarding variation in adult BAT heat production. The proposed one-year study will compare groups living in Siberia that have been exposed to cold stress over various time depths. BAT activity will be quantified using infrared thermal imaging of the neck and shoulders. RMR will be measured using indirect calorimetry. Participants will wear temperature loggers for 72 hours to quantify average daily cold exposure. Anthropometric measurements will be taken using standardized techniques. Finally, a modified survey will be used to collect data on lifestyle, socioeconomic status and early-life cold exposure.