TARGETED DISRUPTION OF THE BETA(3)-ADRENERGIC RECEPTOR GENE

beta(3)-Adrenergic receptors (beta(3)-ARs) are expressed predominantly in white and brown adipose tissue, and beta(3)-selective agonists are potential anti-obesity drugs. However, the role of beta(3)-ARs in nor mal physiology is unknown. To address this issue, homologous recombina tion was used to generate mice that lack beta(3)-ARs. This was accompl ished by direct injection of a DNA-targeting construct into mouse zygo tes. Twenty-three transgenic mice were generated, of which two had tar geted disruption of the beta(3)-AR gene. Mice that were homozygous for the disrupted allele had undetectable levels of intact beta(3)-AR mRN A, as assessed by RNase protection assay and Northern blotting, and la cked functional beta(3)-ARs, as demonstrated by complete loss of beta( 3)-agonist (CL 316,243)-induced stimulation of adenylate cyclase activ ity and lipolysis. beta(3)-AR-deficient mice had modestly increased fa t stores (females more than males), indicating that beta(3)-ARs play a role in regulating energy balance. Importantly, beta(1) but not beta( 2)-AR mRNA levels up-regulated in white and brown adipose tissue of be ta(3)-AR-deficient mice (brown more than white), strongly implying tha t beta(3)-ARs mediate physiologically relevant signaling under normal conditions and that ''cross-talk'' exists between beta(3)-ARs and beta (1)-AR gene expression. Finally, acute treatment of normal mice with C L 316,243 increased serum levels of free fatty acids (FFAs) (3.2-fold) and insulin (140-fold), increased energy expenditure (2-fold), and re duced food intake (by 45%). These effects were completely absent in be ta(3)-AR-deficient mice, proving that the actions of CL are mediated e xclusively by beta(3)-ARs. beta(3)-AR-deficient mice should be useful as a means to a better understanding of the physiology and pharmacolog y of beta(3)-ARs.