Circadian Regulation of Gonadotropin-Releasing Hormone

描述（由申请人提供）：尽管人们早就知道正常的哺乳动物繁殖依赖于下丘脑的促性腺激素释放激素（GnRH）的脉动分泌，但尚不清楚这种异常定时脉冲释放的核心是什么细胞和分子机制。此外，虽然先前的研究表明24小时生物钟控制生殖激素分泌，但仍不清楚生物钟如何调节GnRH同步分泌释放的幅度或频率来调节生殖。本实验室的初步工作表明，不仅所有的分子钟成分都在分泌gnrh的GT1-7细胞系中表达，而且这些转录物在这些培养细胞中以昼夜节律周期振荡。引人注目的是，通过短暂转染显性阴性时钟，干扰周围GT1-7细胞中的时钟，破坏正常的分泌脉冲模式，表明grrh神经元内的细胞内生物钟可以调节分泌。为了进一步研究这一点，以下建议将1)使用体外和体内模型来确定GnRH特异性分子钟对正常生殖状态所需释放模式的必要性，2)检查潜在的细胞内机制，包括转录调节和细胞兴奋性的特性，潜在的GnRH昼夜节律时钟调节，以及3)探索视交叉上核（SCN）的作用，大脑的主时钟。影响GnRH分泌，以及细胞特异性分子振荡器参与这种调节。这一提议的结果有可能回答许多关于GnRH“脉冲发生器”性质的基本问题，以及分泌模式如何通过细胞间的交流而改变，从而产生排卵前的激增。此外，这些研究可以提供更广泛的内分泌神经分泌机制，并通过展示转录振荡如何控制多细胞和组织水平的同步事件，从而调节从细胞代谢到胞吐，甚至协调一系列复杂的行为，从而推进昼夜节律生物学领域。潜在的应用可能为治疗一系列由下丘脑生殖神经分泌功能障碍引起的生理疾病带来新的方向，包括多囊卵巢综合征和原发性特发性性腺功能减退。

DESCRIPTION (provided by applicant): Whereas it has long been known that normal mammalian reproduction depends upon the pulsatile secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus, it is yet unclear what cellular and molecular mechanisms lie at the heart of this exceptionally timed pulse release. Additionally, while previous studies have implicated the 24-hour biological clock in the control of reproductive hormone secretion, it remains unknown how the circadian clock might modulate the amplitude or frequency of synchronous GnRH secretory release to regulate reproduction. Preliminary work in this laboratory demonstrates that not only are all molecular clock components expressed in the GnRH-secreting GT1-7 cell line, but that transcripts oscillate in these cultured cells with a circadian period. Strikingly, perturbation of the clock in perifused GT1-7 cells, via transient transfection of a dominant-negative Clock, disrupts normal secretory pulse patterns, showing that an intracellular circadian clock within GriRH neurons can modulate secretion. To investigate this further, the following proposal will 1) use in vitro and in vivo models to determine the necessity of a GnRH-specific molecular clock on patterns of release required for proper reproductive status, 2) examine potential intracellular mechanisms, including transcriptional regulation and properties of cell excitability, underlying circadian clock modulation of GnRH, and 3) explore the role of the suprachiasmatic nucleus (SCN), the brain's master clock, in influencing GnRH secretion, and the involvement of cell-specific molecular oscillators in this regulation. Results from this proposal have the potential to answer many fundamental questions regarding the nature of the GnRH "pulse generator", and how patterns of secretion may be altered by cell-cell communication to produce preovulatory surges. Additionally, these studies could provide insight into broader mechanisms of endocrine neurosecretion, and advance the field of circadian biology by demonstrating how transcriptional oscillations can control synchronous events at the multi-cellular and tissue level, in order to regulate numerous biological processes, from cellular metabolism to exocytosis, and even to orchestrate complex series of behaviors. Potential applications could lead to new directions in treating a range of physiological disorders that result from malfunction of hypothalamic reproductive neurosecretion, including polycystic ovarian syndrome and primary ideopathic hypogonadism.