Department of Reproductive Medicine, University of California, San Diego, La Jolla, California 92093, USA.
Biol Reprod. 2013 Jun 13;88(6):146. doi: 10.1095/biolreprod.113.108555. Print 2013 Jun.
Kisspeptin stimulates gonadotropin-releasing hormone (GnRH) neurons via the kisspeptin receptor, Kiss1r. In rodents, estrogen-responsive kisspeptin neurons in the rostral hypothalamus have been postulated to mediate estrogen-induced positive feedback induction of the preovulatory luteinizing hormone (LH) surge. However, conflicting evidence exists regarding the ability of mice lacking Kiss1r to display LH surges in response to exogenous hormones. Whether the discrepancy reflects different mouse strains used and/or utilization of different surge-induction paradigms is unknown. Here, we tested multiple hormonal paradigms in one Kiss1r knockout (KO) model to see which paradigms, if any, could generate circadian-timed LH surges. Kiss1r KO and wild-type (WT) females were ovariectomized, given sex steroids in various modes, and assessed several days later for LH levels in the morning or evening (when surges occur). Serum LH levels were very low in all morning animals, regardless of genotype or hormonal paradigm. In each paradigm, virtually all WT females displayed clear LH surges in the evening, whereas none of the KO females demonstrated LH surges. The lack of LH surges in KO mice reflects a lack of GnRH secretion rather than diminished pituitary responsiveness from a lifetime lack of GnRH exposure because KO mice responded to GnRH priming with robust LH secretion. Moreover, high cfos-GnRH coexpression was detected in WT females in the evening, whereas low cfos-GnRH coexpression was present in KO females at all time points. Our findings conclusively demonstrate that WT females consistently display LH surges under multiple hormonal paradigms, whereas Kiss1r KO mice do not, indicating that kisspeptin-Kiss1r signaling is mandatory for GnRH/LH surge induction.
Kisspeptin 通过 kisspeptin 受体 Kiss1r 刺激促性腺激素释放激素 (GnRH) 神经元。在啮齿动物中,推测头端下丘脑中雌激素反应性 kisspeptin 神经元介导促性腺激素释放激素 (GnRH) 诱导的促黄体生成素 (LH) 峰的雌激素诱导的正反馈。然而,关于缺乏 Kiss1r 的小鼠是否能够对外源性激素显示 LH 峰存在相互矛盾的证据。这种差异是否反映了使用的不同小鼠品系和/或使用不同的诱导峰范式尚不清楚。在这里,我们在一个 Kiss1r 敲除 (KO) 模型中测试了多种激素范式,以了解哪些范式(如果有的话)可以产生节律性 LH 峰。Kiss1r KO 和野生型 (WT) 雌性小鼠被卵巢切除术,以各种方式给予性激素,并在数天后评估清晨或傍晚 (发生峰时) 的 LH 水平。无论基因型或激素范式如何,所有清晨动物的血清 LH 水平都非常低。在每种范式中,几乎所有 WT 雌性动物在傍晚都表现出明显的 LH 峰,而 KO 雌性动物都没有表现出 LH 峰。KO 小鼠中 LH 峰的缺失反映了 GnRH 分泌的缺乏,而不是由于终生缺乏 GnRH 暴露导致的垂体反应性降低,因为 KO 小鼠对 GnRH 启动有强烈的 LH 分泌反应。此外,在傍晚检测到 WT 雌性中 cfos-GnRH 的共表达很高,而 KO 雌性在所有时间点都存在低 cfos-GnRH 共表达。我们的研究结果明确表明,WT 雌性在多种激素范式下始终显示 LH 峰,而 Kiss1r KO 小鼠则不显示,这表明 kisspeptin-Kiss1r 信号传导对于 GnRH/LH 峰诱导是必需的。