Role of calcium in the gating of isoproterenol-induced arylalkylamine N-acetyltransferase gene expression in the mouse pineal gland
Role of calcium in the gating of isoproterenol-induced arylalkylamine N-acetyltransferase gene expression in the mouse pineal gland
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DOI：
10.1111/j.1600-079x.2006.00341.x
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发表时间：
2006-08-01
影响因子：
10.3
通讯作者：
Fukuhara, Chiaki
中科院分区：
文献类型：
--
作者：
Chansard, Mathieu;Liang, Jian;Fukuhara, Chiaki
褪黑激素及其自主调节具有重要的生理功能。我们最近证明，β-肾上腺素能受体的刺激只增加夜间芳烷基胺N-乙酰转移酶（Aa-Nat，褪黑激素合成的限速酶）mRNA水平在体外小鼠松果体，这表明松果体时钟可能门Aa-Nat基因表达。在本研究中，我们的数据表明，cAMP类似物增加Aa-Nat在一天中的任何时间，但只有在离子霉素的存在下。使用Fura-2AM在比率钙测量，我们表明，异丙肾上腺素刺激增加细胞内游离钙水平在夜间，与以前的报告。此外，细胞内或细胞外钙耗竭抑制异丙肾上腺素诱导的钙反应以及Aa-Nat基因表达。这些结果表明，钙可能是异丙肾上腺素诱导的Aa-Nat基因表达的关键因素，这可能是在白天有限。我们还发现，基础细胞内钙水平较低，在夜间和异丙肾上腺素和氯化钾去极化的反应更强大。此外，隐花色素突变小鼠的松果体在白天和夜间基础钙或异丙肾上腺素反应之间没有显着差异。总之，这些结果表明，松果体中的基础钙水平可能是由内源性松果体时钟控制的，这可能会影响钙动力学，细胞内稳态和对外部刺激的敏感性。虽然Aa-Nat基因表达的机制已经得到了很好的研究，钙的作用，松果体时钟和Aa-Nat基因表达之间的联系被低估了在啮齿动物松果体。
Melatonin and its autonomic regulation serve important physiological functions. We recently demonstrated that stimulation of beta-adrenergic receptors only increases nighttime arylalkylamine N-acetyltransferase (Aa-Nat, the rate-limiting enzyme in melatonin synthesis) mRNA levels in mouse pineal gland in vitro, which suggests that pineal clocks may gate Aa-Nat gene expression. In the present study, our data reveal that cAMP analog increased Aa-Nat at any time of day but only in the presence of ionomycin. Using Fura-2AM in ratiometric calcium measurements, we show that isoproterenol stimulation increased intracellular free calcium levels at night, contrary to previous reports. Further, intra- or extracellular calcium depletion suppressed the isoproterenol-induced calcium responses as well as Aa-Nat gene expression. These results suggest calcium may be a critical factor in isoproterenol-induced Aa-Nat gene expression, which may be limited in the daytime. We also found that basal intracellular calcium levels were lower during the night and responses to isoproterenol and KCl depolarization were more robust. In addition, pineals of Cryptochrome mutant mice exhibited no significant difference between day and nighttime basal calcium or isoproterenol response. Together, these results suggest that basal calcium levels in the pineal may be controlled by the endogenous pineal clock, which may influence calcium dynamics, cellular homeostasis and sensitivity to external stimulation. Although the mechanism underlying Aa-Nat gene expression has been well studied, the role of calcium as a link between the pineal clock and Aa-Nat gene expression has been underestimated in rodent pineals.