Mechanisms by which adipocytes adapt to cool environmental temperatures

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Abstract Adipocytes are distributed throughout the body in discrete depots and the intrinsic cellular and metabolic properties of different populations are shaped by the specific niches in which they reside. Whereas visceral adipocytes exist within the body’s core, other subpopulations, including subcutaneous, marrow and dermal adipocytes primarily exist in temperatures well below 37oC. Despite this, the role of environmental temperature has largely been neglected in our consideration of adipocyte molecular and functional characteristics. Hints within historical literature suggest that cooler adipose tissue temperatures are also associated with greater lipid unsaturation. We have found similar correlations in rodents and humans, with cooler distal marrow adipocytes having increased unsaturated lipid composition. Housing rats at thermoneutrality decreases formation of unsaturated lipids in triacylglycerols of marrow adipocytes within the distal tibia and caudal vertebra. Warmer temperature also decreases expression of Stearoyl CoA Desaturase I. Adaptation of cultured adipocytes to 31oC is associated with elevated oxygen consumption, altered nutrient selection, elevated anabolic and catabolic lipid metabolism, and a genetic program for cold-adaptation. We hypothesize that cold adaptation results in profound changes to gene expression and metabolism that allow adipocytes to function at temperatures well below 37oC. To test these hypotheses, we propose a series of specific aims that when successfully completed will provide fundamental insights into how cold-adapted adipocytes are functionally different from their warmer counterparts. These studies will help uncover novel mechanisms of adaptive thermogenesis and identify targets for pharmacologic interventions to increase energy expenditure and combat incidence of obesity and diabetes.