UCP1 and obesity due to melanocortin 4 receptor deficiency: Elevated TNF-α mRNA expression has been shown in ob/ob, tub/tub, and KKA mice, and Zucker fa/fa rats [13] as well as transgenic model of obesity/insulin resistance created by ablation of brown adipose tissue (BAT) via a bacterial toxin gene driven by the UCP promoter [4], [14].