Ito M, Grujic D, Abel E D, Vidal-Puig A, Susulic V S, Lawitts J, Harper M E, Himms-Hagen J, Strosberg A D, Lowell B B
Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
Diabetes. 1998 Sep;47(9):1464-71. doi: 10.2337/diabetes.47.9.1464.
Beta-adrenergic receptors (ARs) are expressed predominantly in adipose tissue, and beta3-selective agonists are effective anti-obesity drugs in rodents. Rodent and human beta3-ARs differ with respect to expression in white versus brown adipocytes as well as their ability to be stimulated by beta3-AR-selective agonists. Humans express beta3-AR mRNA abundantly in brown but not white adipocytes, while rodents express beta3-AR mRNA abundantly in both sites. To determine the basis for this difference, we have transgenically introduced 74 kilobases (kb) of human beta3-AR genomic sequence into gene knockout mice lacking beta3-ARs. Importantly, human beta3-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 beta3-AR genomic transgene in which beta3-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 beta3-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 beta3-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 beta3-AR gene expression. In addition, the beta3-AR agonist, CGP-12177, stimulated oxygen consumption in mice expressing human but not murine beta3-ARs by 91% compared with only 49% in control beta3-AR gene knockout mice, demonstrating that the human beta3-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.
β-肾上腺素能受体（ARs）主要在脂肪组织中表达，β3 选择性激动剂是啮齿动物有效的抗肥胖药物。啮齿动物和人类的β3-ARs在白色脂肪细胞与棕色脂肪细胞中的表达以及它们被β3-AR 选择性激动剂刺激的能力方面存在差异。人类在棕色脂肪细胞中大量表达β3-AR mRNA，而在白色脂肪细胞中不表达，而啮齿动物在这两个部位都大量表达β3-AR mRNA。为了确定这种差异的基础，我们将 74 千碱基（kb）的人类β3-AR 基因组序列转基因导入缺乏β3-ARs 的基因敲除小鼠中。重要的是，人类β3-AR mRNA 仅在转基因小鼠的棕色脂肪组织（BAT）中表达，在白色脂肪组织（WAT）、肝脏、胃、小肠、骨骼肌和心脏中几乎未检测到表达。这种表达模式与携带小鼠β3-AR 基因组转基因的小鼠不同，在后者中β3-AR mRNA 在 WAT 和 BAT 中均有表达，但在其他部位无表达。此外，我们将包含-14.5 和-0.6 kb 上游序列的较小人类构建体转基因导入β3-AR 基因敲除小鼠中。-14.5 和-0.6 kb 的构建体均在 BAT 中表达，但不在 WAT 中表达。因此，人类而非小鼠的顺式调控元件将β3-AR 基因表达优先导向棕色脂肪细胞。鉴定负责的顺式调控元件和相关的反式作用因子应能深入了解控制人类β3-AR 基因表达的机制。此外，β3-AR 激动剂 CGP-12177 使表达人类而非小鼠β3-ARs 的小鼠的耗氧量增加了 91%，而对照β3-AR 基因敲除小鼠仅增加了 49%，这表明人类β3-AR 可以在功能上与能量消耗偶联。这些“人源化”小鼠应有助于我们开发可能成为人类有效抗肥胖药物的药物。
