Brown adipose tissue (BAT) thermogenesis affects energy expenditure, as well as glucose and lipid clearance. Thus, making BAT an attractive target in obesity/type-2 diabetes. Adiponectin (Apn) regulates whole-body metabolism and lowered Apn levels are associated with obesity and increased type-2 diabetes risk. Apn has been suggested to be required for maintaining normal body temperature in cold environment, but the role of Apn in BAT functionality is not clear. Here, we have studied BAT in adiponectin overexpressing (Apn-Tg) mice. During unchallenged chow-diet conditions, BAT of Apn-Tg mice was enlarged, fibrotic and more whitish. This phenotype was, as judged by tracer experiments, associated with lower lipid and glucose uptake, decreased de novo lipogenesis and decreased fatty acid oxidation in BAT. High-fat diet (HFD)-induced obesity increased these differences between genotypes. The BAT mRNA expression of thermogenesis markers such as UCP-1 and DIO-2 were down-regulated in BAT of obese, but not lean, Apn-Tg mice. Moreover, Seahorse-based analysis revealed reduced mitochondrial function in Apn-Tg BAT in ex vivo-differentiated brown adipocytes. To test whether increased Apn levels affect cold-induced BAT activation, we exposed Apn-tg and littermate control mice to cold temperature (6°C) for four weeks. Under this setting, the BAT lipid and glucose uptake, and body temperature were similar between genotypes. Accordingly, UCP-1 and DIO-2 mRNA levels were not different between Apn-Tg and WT mice, and highly induced by chronic cold exposure. Nevertheless, Seahorse data from isolated BAT mitochondria from cold-exposed animals still indicate mitochondrial dysfunction in Apn-Tg mice. Thus, our data suggest that increased adiponectin levels are associated with metabolic dysfunction in BAT. We propose that the increased BAT expansion in Apn-Tg mice occurs at the expense of the mitochondrial function.
B. Chanclon: None. M. Bauza-Thorbrugge: None. A. Benrick: None. I. Wernstedt-Asterholm: None.