When pigs fly, UCP1 makes heat.

Brown and beige adipose tissue may represent important therapeutic targets for the treatment of diabetes and obesity as these organs dissipate nutrient energy as heat through the thermogenic uncoupling protein 1 (UCP1). While mice are commonly used to mimic the potential effects of brown/beige adipose tissue that may act in human metabolism, new animal models are edging into the market for translational medicine. Pigs reflect human metabolism better than mice in multiple parameters such as obesity-induced hyperglycemia, cholesterol profiles and energy metabolism. Recently, it was reported that energy expenditure and body temperature in pigs is induced by the hormone leptin, and that leptin's action is mediated by UCP1 in adipose tissue. Given the tremendous importance of identifying molecular mechanisms for targeting therapeutics, we critically examine the evidence supporting the presence of UCP1 in pigs and conclude that methodological shortcomings prevent an unequivocal claim for the presence of UCP1 in pigs. Despite this, we believe that leptin's effects on energy expenditure in pigs are potentially more transformative to human medicine in the absence of UCP1, as adult and obese humans possess only minor amounts of UCP1. In general, we propose that the biology of new animal models requires attention to comparative studies with humans given the increasing amount of genomic information for various animal species.