Mice expressing human but not murine β-adrenergic receptors under the control of human gene regulatory elements

beta(3)-Adrenergic receptors (ARs) are expressed predominantly in adipose tissue, and beta(3)-selective agonists are effective anti-obesity drugs in rodents. Rodent and human beta(3)-ARs differ with respect to expression in white versus brown adipocytes as well as their ability to be stimulated by beta(3)-AR-selective agonists. Humans express beta(3)-AR mRNA abundantly in brown but not white adipocytes, while rodents express beta(3)-AR mRNA abundantly in both sites. To determine the basis for this difference, we have transgenically introduced 74 kilobases (kb) of human beta(3)-AR genomic sequence into gene knockout mice lacking beta(3)-ARs. Importantly, human beta(3)-AR mRNA was expressed only in brown adipose tissue (BAT) of transgenic mice, with Little or no expression being detected in white adipose tissue (WAT), liver, stomach, small intestine, skeletal muscle, and heart. This pattern of expression differed from that observed in mice bearing a murine beta(3)-AR genomic transgene in which beta(3)-AR mRNA was expressed in both WAT and BAT, but not in other sites. Furthermore, we have transgenically introduced smaller human constructs containing -14.5 and -0.6 kb of upstream sequence into beta(3)-AR gene knockout mice. Both -14.5 and -0.6 kb constructs were expressed in BAT but not WAT. Thus, human but: not murine cis-regulatory elements direct beta(3)-AR gene expression preferentially to brown adipocytes. Identification of responsible cis-regulatory element(s) and relevant trans-acting factor(s) should provide insight into mechanisms controlling human beta(3)-AR gene expression. In addition, the beta(3)-AR agonist, CGP-12177, stimulated oxygen consumption in mice expressing human but not murine beta(3)-ARs by 91% compared with only 49% in control beta(3)-AR gene knockout mice, demonstrating that the human beta(3)-AR can functionally couple with energy expenditure. These "humanized" mice should assist us in the development of drugs that may become effective anti-obesity agents in humans.