Ovarian androgen synthesis: unravelling the roles of INSL3 and BMP signalling

雌性动物和人类的生育需要正确的时间从配对的卵巢释放一个或多个健康的卵子(卵母细胞)。卵子在称为卵泡的结构中发育，卵泡也会产生许多关键荷尔蒙，如果没有这些荷尔蒙，繁殖是不可能的。这项研究将调查这些荷尔蒙的产生是如何调节的。特别是，两种相关的激素，称为雄激素和雌激素，必须由专门的卵泡细胞在女性周期的正确数量和正确的时间产生。雄激素是由称为卵泡膜细胞(TC)的细胞产生的，而雌激素是由称为颗粒细胞(GC)的细胞产生的。只有当邻近的TC提供雄激素时，GC才能合成雌激素。GC本身不能合成雄激素，雄激素是雌激素合成的重要前体。卵泡从微观结构发育成直径约2厘米的多层充满液体的大结构(在人和牛中)。促黄体生成素(LH)刺激TC产生雄激素，而促卵泡激素(FSH)刺激GC增殖并将雄激素转化为雌激素。成熟的卵泡从卵巢表面突出，等待脑下垂体的激素触发(称为促黄体生成素激增)，使它们排卵并释放卵子，以便可能的受精。黄体生成素的激增，反过来又依赖于生长中的卵泡分泌越来越多的雌激素。在动物身上，雌激素的增加也会引发重要的行为变化(“热”)，如果没有这种变化，交配就不会发生。雌激素在为怀孕准备生殖道方面也起着关键作用，雄激素和雌激素都会影响许多其他组织和器官。因此，卵泡发育紊乱导致TC产生雄激素或GC产生雌激素的不平衡，不仅会导致不孕，还会影响到生理的许多其他方面。例如，妇女不孕不育/不育的一种非常常见的原因称为多囊卵巢综合征(PCOS)，与卵巢雄激素分泌过多有关；这种情况会导致月经周期紊乱以及面部和身体毛发过度生长。卵泡发育是一个非常复杂的过程，目前仍知之甚少。最近人们已经认识到，卵巢本身产生了许多信号分子，使不同类型的细胞能够相互通信。这种“局部”的细胞-细胞通讯必须与来自脑下垂体(黄体生成素、卵泡刺激素)的信号协同工作，以协调卵泡的生长和类固醇的产生。在这个项目中，我们将研究两个不同的“局部”信号系统在TC调节黄体生成素诱导的雄激素产生中的作用和相互作用--INSL3系统和BMP系统。我们决定专注于这两个系统是基于我们最近的发现：(1)BMP可以关闭膜细胞产生雄激素和INSL3(2)一种名为抑制素的GC产品可以反过来关闭BMP信号并增加雄激素的产生。在该项目中，我们将绘制不同生长阶段卵泡中INSL3(及其受体)和各种BMP系统组件(配体、受体、结合蛋白)的分布。我们还将对TC(从屠宰场分离的奶牛卵巢)进行详细的体外研究，以了解添加(或移除)INSL3、BMP或抑制素系统的不同成分是否会影响雄激素的产生。通过这种方式，我们将确定这些不同系统之间的功能交互。最后，我们将找出在奶牛发情周期中，血液中INSL3水平是否会发生变化，如果是，这些变化是否与卵泡生长模式以及脑垂体(黄体生成素、卵泡刺激素)和卵巢(类固醇、抑制素)激素分泌水平有关。总而言之，这些研究将极大地促进对卵巢生理学的理解，并为不孕的主要原因提供见解。

Fertility of female animals and humans requires the correctly-timed release of one or more healthy eggs (oocytes) from the paired ovaries. Eggs develop within structures called ovarian follicles which also produce a number of key hormones, without which reproduction is simply not possible. This research will investigate how the production of these hormones is regulated. In particular, two related hormones called androgen and oestrogen must be produced by specialized follicle cells in the right amounts - and at the right time - of the female cycle. Androgen is produced by cells called theca cells (TC) while oestrogen is produced by cells called granulosa cells (GC). GC can only synthesize oestrogen when they are supplied with androgen by neighboring TC. GC cannot synthesize androgen themselves and androgen is the essential precursor for oestrogen synthesis. Follicles grow from microscopic structures into large multi-layered, fluid filled structures ~ 2cm across (in human & cow). Pulses of luteinizing hormone (LH) from the pituitary stimulate TC to produce androgen while pituitary follicle-stimulating hormone (FSH) stimulates GC to proliferate and convert androgen into oestrogen. Mature follicles protrude from the ovary surface awaiting a hormone trigger from the pituitary (called the LH surge) that causes them to ovulate and release the egg for possible fertilization. This LH surge, in turn, depends on the secretion of increasing amounts of oestrogen by the growing follicle. In animals, this oestrogen rise also triggers vital behavioural changes ('heat') without which mating would not occur. Oestrogen also plays a key role in preparing the reproductive tract for pregnancy and both androgen and oestrogen affect many other tissues and organs. Thus, disordered follicle development leading to an imbalance in production of androgen by TC or of oestrogen by GC can not only cause infertility, but can affect many other aspects of physiology. For instance, a very common cause of infertility/subfertility in women called polycystic ovarian disease syndrome (PCOS) is associated with excess ovarian androgen production; this condition leads to disturbed menstrual cycles and excess growth of facial and body hair. Follicle development is a very complex process that is still poorly understood. It has been recognised recently that numerous signaling molecules are produced within the ovary itself that enable different cell-types to communicate with each other. This 'local' cell-cell communication must work in concert with signals from the pituitary (LH, FSH) to coordinate follicle growth and steroid production. In this project we will investigate the actions and interactions of two different 'local' signaling systems in regulating LH-induced androgen production by TC - the INSL3 system and the BMP system. Our decision to focus on these two systems is based on our recent discovery that (1) BMP can switch off production of both androgen and INSL3 by theca cells (2) a GC product called inhibin can, in turn, switch off BMP signaling and raise androgen production. In the project we will map the distribution of INSL3 (and its receptor) and various BMP system components (ligands, receptors, binding proteins) in follicles at different growth stages. We will also carry out detailed in vitro studies on TC (isolated from cow ovaries from the abattoir) to find out whether adding (or removing) different components of the INSL3, BMP or inhibin systems affects androgen production. In this way we will identify functional interactions between these different systems. Finally, we will find out if blood levels of INSL3 vary during the cow's oestrous cycle and if so, whether these changes are linked to patterns of follicle growth and levels of pituitary (LH, FSH) and ovarian (steroids, inhibin) hormone secretion. Collectively, these studies will significantly advance understanding of ovarian physiology and provide insights into a major cause of infertility.