Kobayashi K, Ota A, Togari A, Morita S, Mizuguchi T, Sawada H, Yamada K, Nagatsu I, Matsumoto S, Fujita K
Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Japan.
J Neurochem. 1995 Aug;65(2):492-501. doi: 10.1046/j.1471-4159.1995.65020492.x.
Agonist-induced regulation of adrenergic receptors (ARs) has an important role in controlling physiological functions in response to changes in catecholamine stimulation. We previously generated transgenic mice expressing phenylethanolamine N-methyltransferase (PNMT) under the control of a human dopamine beta-hydroxylase gene promoter to switch catecholamine specificity from the norepinephrine phenotype to the epinephrine phenotype. In the present study, we first examined changes in catecholamine metabolism in peripheral tissues innervated by sympathetic neurons of the transgenic mice. In the transgenic target tissues, a high-level expression of PNMT led to a dramatic increase in the epinephrine levels, whereas the norepinephrine levels were decreased to 48.6-87.9% of the nontransgenic control levels. Analysis of plasma catecholamines in adrenalectomized mice showed large amounts of epinephrine derived from sympathetic neurons in the transgenic mice. Subsequently, we performed radioligand binding assays with (-)-[125I]iodocyanopindolol to determine changes in binding sites of beta-AR subtypes. In transgenic mice, the number of beta 2-AR binding sites was 56.4-74.9% of their nontransgenic values in the lung, spleen, submaxillary gland, and kidney, whereas the beta 1-AR binding sites were regulated in a different fashion among these tissues. Moreover, northern blot analysis of total RNA from the lung tissues showed that down-regulation of beta 2 binding sites was accompanied by a significant decrease in steady-state levels of the receptor mRNA. These results strongly suggest that alteration of catecholamine specificity in the transgenic sympathetic neurons leads to regulated expression of the beta-AR subtypes in their target tissues.
激动剂诱导的肾上腺素能受体（ARs）调节在响应儿茶酚胺刺激变化时控制生理功能方面具有重要作用。我们之前构建了在人多巴胺β-羟化酶基因启动子控制下表达苯乙醇胺N-甲基转移酶（PNMT）的转基因小鼠，以将儿茶酚胺特异性从去甲肾上腺素表型转变为肾上腺素表型。在本研究中，我们首先检查了转基因小鼠交感神经元支配的外周组织中儿茶酚胺代谢的变化。在转基因靶组织中，PNMT的高水平表达导致肾上腺素水平显著升高，而去甲肾上腺素水平降至非转基因对照水平的48.6 - 87.9%。对肾上腺切除小鼠血浆儿茶酚胺的分析表明，转基因小鼠中来自交感神经元的肾上腺素大量存在。随后，我们用（-）-[125I]碘氰吲哚洛尔进行放射性配体结合测定，以确定β-AR亚型结合位点的变化。在转基因小鼠中，肺、脾、颌下腺和肾中β2-AR结合位点的数量为非转基因值的56.4 - 74.9%，而β1-AR结合位点在这些组织中的调节方式不同。此外，对肺组织总RNA的Northern印迹分析表明，β2结合位点的下调伴随着受体mRNA稳态水平的显著降低。这些结果强烈表明，转基因交感神经元中儿茶酚胺特异性的改变导致其靶组织中β-AR亚型的表达受到调节。
