El Hadri K, Fève B, Pairault J
Institut National de la Santé et de la Recherche Médicale U 282, Hôpital Henri Mondor, Créteil, France.
Eur J Pharmacol. 1996 Feb 15;297(1-2):107-19. doi: 10.1016/0014-2999(95)00723-7.
Beta 1- and beta 3-adrenoceptor mRNA and protein expression, and contribution of each subtype to the catecholamine-sensitive adenylyl cyclase system were studied during the adipose conversion of the murine 3T3-F442A cell line. Northern and reverse transcriptase-polymerase chain reaction analyses indicated that emergence of beta 3-adrenoceptor transcripts was concomittant with that of the gene encoding adipsin, a very late marker of adipose differentiation. Conversely, the induction of the beta 1-adrenoceptor mRNA occurred early after cell commitment towards adipose conversion. Changes in beta-subtype gene expression were accompanied by parallel modifications in receptor expression and function. 125I-cyanopindolol saturation and competition binding experiments showed a 3-fold increase in beta 1-adrenoceptor density in day 3 post-confluent cells. The beta 3-subtype population became detectable later and represented approximately 95% of total beta-adrenoceptors in day 8 and day 12 post-confluent cells. Adenylyl cyclase activity in response to the beta 3-adrenoceptor-selective agonists CGP12177 (4-(3-t-butylamino-2-hydroxypropoxy)-benzimidazol-2-one), ICI201651 ([(R)-4-(2 hydroxy-3-phenoxypropylamino-ethoxy)-N-(2- methoxyethyl)phenoxy-acetamide]) and cyanopindolol was virtually absent in young adipocytes, but dramatically increased in mature cells. The respective contributions of the beta 1- and the beta 3-subtypes to the production of cAMP were resolved by an Eadie-Hofstee computer analysis of isoproterenol and norepinephrine concentration-response curve of adenylyl cyclase activity. Agonist response curves in the presence of beta 1- and beta 2-adrenoceptor antagonist indicated that the beta 1-subtype accounted for the totality of beta-adrenoceptor-mediated adenylyl cyclase activation in young adipocytes. In mature adipose cells approximately 90% of this response was due to an activation of the beta 3-adrenoceptor. In addition, approximately 84% of the maximal norepinephrine-stimulated lipolysis was mediated by the beta 3-adrenoceptor in fully differentiated adipocytes. The differentiation-dependent expression of beta-subtypes in adipocytes is a biphasic process involving an initial and moderate induction of beta 1-adrenoceptors followed by the emergence of a prominent beta 3-adrenoceptor population. Compared analysis of both receptor occupancy and cAMP production shows that the beta 3-subtype is more efficiently coupled to the adenylyl cyclase system than the beta 1-adrenoceptor. Thus in mature adipose cells this receptor subtype represents the core of cAMP-dependent regulation of the lipolytic, antilipogenic and thermogenic effects of catecholamines.
在小鼠3T3-F442A细胞系的脂肪转化过程中，研究了β1-和β3-肾上腺素能受体的mRNA和蛋白质表达，以及每种亚型对儿茶酚胺敏感的腺苷酸环化酶系统的作用。Northern印迹分析和逆转录-聚合酶链反应分析表明，β3-肾上腺素能受体转录本的出现与编码脂肪分化晚期标志物——脂肪酶的基因同步。相反，β1-肾上腺素能受体mRNA的诱导在细胞开始脂肪转化后早期就发生了。β亚型基因表达的变化伴随着受体表达和功能的平行改变。125I-氰吲哚洛尔饱和及竞争结合实验表明，汇合后第3天的细胞中β1-肾上腺素能受体密度增加了3倍。β3-亚型群体在之后才被检测到，在汇合后第8天和第12天的细胞中占总β-肾上腺素能受体的约95%。对β3-肾上腺素能受体选择性激动剂CGP12177（4-(3-叔丁基氨基-2-羟基丙氧基)-苯并咪唑-2-酮）、ICI201651（[(R)-4-(2-羟基-3-苯氧基丙基氨基)-乙氧基]-N-(2-甲氧基乙基)苯氧基-乙酰胺）和氰吲哚洛尔的腺苷酸环化酶活性在年轻脂肪细胞中几乎不存在，但在成熟细胞中显著增加。通过对异丙肾上腺素和去甲肾上腺素刺激腺苷酸环化酶活性的浓度-反应曲线进行伊迪-霍夫斯泰计算机分析，确定了β1-和β3-亚型对cAMP产生的各自贡献。在存在β1-和β2-肾上腺素能受体拮抗剂的情况下，激动剂反应曲线表明，β1-亚型在年轻脂肪细胞中占β-肾上腺素能受体介导的腺苷酸环化酶激活的全部。在成熟脂肪细胞中，这种反应的约90%是由于β3-肾上腺素能受体的激活。此外，在完全分化的脂肪细胞中，最大去甲肾上腺素刺激的脂解作用的约84%是由β3-肾上腺素能受体介导的。脂肪细胞中β亚型的分化依赖性表达是一个双相过程，包括β1-肾上腺素能受体的初始适度诱导，随后是显著的β3-肾上腺素能受体群体的出现。对受体占有率和cAMP产生的比较分析表明，β3-亚型比β1-肾上腺素能受体更有效地与腺苷酸环化酶系统偶联。因此，在成熟脂肪细胞中，这种受体亚型代表了儿茶酚胺脂解、抗脂生成和产热作用的cAMP依赖性调节的核心。
