title: Targeted disruption of the beta 3-adrenergic receptor gene.
abstract: 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 normal physiology is unknown. To address this issue, homologous recombination was used to generate mice that lack beta 3-ARs. This was accomplished by direct injection of a DNA-targeting construct into mouse zygotes. Twenty-three transgenic mice were generated, of which two had targeted disruption of the beta 3-AR gene. Mice that were homozygous for the disrupted allele had undetectable levels of intact beta 3-AR mRNA, as assessed by RNase protection assay and Northern blotting, and lacked functional beta 3-ARs, as demonstrated by complete loss of beta 3-agonist (CL 316,243)-induced stimulation of adenylate cyclase activity and lipolysis. beta 3-AR-deficient mice had modestly increased fat 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 beta 3-AR-deficient mice (brown more than white), strongly implying that 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 CL 316,243 increased serum levels of free fatty acids (FFAs) (3.2-fold) and insulin (140-fold), increased energy expenditure (2-fold), and reduced food intake (by 45%). These effects were completely absent in beta 3-AR-deficient mice, proving that the actions of CL are mediated exclusively by beta 3-ARs. beta 3-AR-deficient mice should be useful as a means to a better understanding of the physiology and pharmacology of beta 3-ARs.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000273:Adipose Tissue / Q000737:chemistry; D000818:Animals; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D018390:Gene Targeting; D008066:Lipolysis; D008297:Male; D051379:Mice; D010641:Phenotype; D012333:RNA, Messenger / Q000032:analysis; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000235:genetics*; D018342:Receptors, Adrenergic, beta-1 / Q000235:genetics; D018343:Receptors, Adrenergic, beta-2 / Q000235:genetics; D022702:Receptors, Adrenergic, beta-3
chemical_list: D005230:Fatty Acids, Nonesterified; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D022702:Receptors, Adrenergic, beta-3; D000262:Adenylyl Cyclases