Clark J A, Flick R B, Pai L-Y, Szalayova I, Key S, Conley R K, Deutch A Y, Hutson P H, Mezey E
Stroke and Neurodegeneration, Merck Research Laboratories, West Point, PA 19486, USA.
Mol Psychiatry. 2008 May;13(5):498-506. doi: 10.1038/sj.mp.4002041. Epub 2007 Jul 10.
Considerable attention has focused on regulation of central tryptophan hydroxylase (TPH) activity and protein expression. At the time of these earlier studies, it was thought that there was a single central TPH isoform. However, with the recent identification of TPH2, it becomes important to distinguish between regulatory effects on the protein expression and activity of the two isoforms. We have generated a TPH2-specific polyclonal antiserum (TPH2-6361) to study regulation of TPH2 at the protein level and to examine the distribution of TPH2 expression in rodent and human brain. TPH2 immunoreactivity (IR) was detected throughout the raphe nuclei, in lateral hypothalamic nuclei and in the pineal body of rodent and human brain. In addition, a prominent TPH2-IR fiber network was found in the human median eminence. We recently reported that glucocorticoid treatment of C57/Bl6 mice for 4 days markedly decreased TPH2 messenger RNA levels in the raphe nuclei, whereas TPH1 mRNA was unaffected. The glucocorticoid-elicited inhibition of TPH2 gene expression was blocked by co-administration of the glucocorticoid receptor antagonist mifepristone (RU-486). Using TPH2-6361, we have extended these findings to show a dose-dependent decrease in raphe TPH2 protein levels in response to 4 days of treatment with dexamethasone; this effect was blocked by co-administration of mifepristone. Moreover, the glucocorticoid-elicited inhibition of TPH2 was functionally significant: serotonin synthesis was significantly reduced in the frontal cortex of glucocorticoid-treated mice, an effect that was blocked by mifepristone co-administration. This study provides further evidence for the glucocorticoid regulation of serotonin biosynthesis via inhibition of TPH2 expression, and suggest that elevated glucocorticoid levels may be relevant to the etiology of psychiatric diseases, such as depression, where hypothalamic-pituitary-adrenal axis dysregulation has been documented.
相当多的注意力集中在中枢色氨酸羟化酶（TPH）活性和蛋白质表达的调节上。在这些早期研究时，人们认为存在单一的中枢TPH同工型。然而，随着最近TPH2的鉴定，区分对这两种同工型的蛋白质表达和活性的调节作用变得很重要。我们制备了一种TPH2特异性多克隆抗血清（TPH2 - 6361），以在蛋白质水平研究TPH2的调节，并检查TPH2在啮齿动物和人类大脑中的表达分布。在啮齿动物和人类大脑的中缝核、下丘脑外侧核和松果体中均检测到TPH2免疫反应性（IR）。此外，在人类正中隆起中发现了一个显著的TPH2 - IR纤维网络。我们最近报道，用糖皮质激素处理C57/Bl6小鼠4天可显著降低中缝核中TPH2信使RNA水平，而TPH1 mRNA不受影响。糖皮质激素引起的TPH2基因表达抑制可通过同时给予糖皮质激素受体拮抗剂米非司酮（RU - 486）来阻断。使用TPH2 - 6361，我们扩展了这些发现，表明地塞米松处理4天会导致中缝TPH2蛋白质水平呈剂量依赖性下降；米非司酮同时给药可阻断此效应。此外，糖皮质激素引起的TPH2抑制在功能上具有重要意义：糖皮质激素处理的小鼠额叶皮质中5-羟色胺合成显著减少，米非司酮同时给药可阻断此效应。本研究为糖皮质激素通过抑制TPH2表达调节5-羟色胺生物合成提供了进一步证据，并表明糖皮质激素水平升高可能与精神疾病如抑郁症的病因有关，在抑郁症中已记录到下丘脑-垂体-肾上腺轴失调。
