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

雌性动物和人类的生育能力需要从配对的卵巢中正确定时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，卵泡也产生一些关键的激素，没有这些激素就不可能繁殖。这项研究将研究这些激素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时间产生。雄激素由被称为卵泡膜细胞（TC）的细胞产生，而雌激素由被称为颗粒细胞（GC）的细胞产生。GC只有在邻近TC提供雄激素的情况下才能合成雌激素。GC自身不能合成雄激素，雄激素是雌激素合成的必需前体。卵泡从微观结构生长成大型多层，充满液体的结构，直径约2厘米（人类和牛）。来自垂体的促黄体激素（LH）脉冲刺激TC产生雄激素，而垂体促卵泡激素（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，等待来自垂体的激素触发（称为LH峰），使它们排卵并释放卵子进行可能的受精。反过来，这种LH激增取决于生长卵泡分泌的雌激素量的增加。在动物中，这种雌激素的增加也会引发重要的行为变化（“热”），没有这种变化，交配就不会发生。雌激素在准备生殖道怀孕中也起着关键作用，雄激素和雌激素都会影响许多其他组织和器官。因此，卵泡发育障碍导致TC产生雄激素或GC产生雌激素的失衡不仅会导致不孕，而且会影响许多其他生理方面。例如，女性不孕/生育力低下的一个非常常见的原因称为多囊卵巢疾病综合征（PCOS）与卵巢雄激素过多有关;这种情况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，仍然知之甚少。最近人们认识到，卵巢本身产生了许多信号分子，使不同的细胞类型能够相互交流。这种“局部”细胞间的通讯必须与来自垂体的信号（LH，FSH）协同工作，以协调卵泡生长和类固醇产生。在这个项目中，我们将调查的行动和相互作用的两个不同的“本地”信号系统调节LH诱导雄激素的生产TC -的INSL 3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可以关闭卵泡膜细胞产生雄激素和INSL 3;（2）一种称为BMP 3的GC产物可以反过来关闭BMP信号传导并提高雄激素的产生。在该项目中，我们将绘制INSL 3（及其受体）和各种BMP系统组件（配体，受体，结合蛋白）在不同生长阶段的卵泡中的分布。我们还将对TC（从屠宰场的牛卵巢中分离）进行详细的体外研究，以确定添加（或去除）INSL 3，BMP或BMP-bin系统的不同组分是否会影响雄激素的产生。通过这种方式，我们将识别这些不同系统之间的功能相互作用。最后，我们将发现INSL 3的血液水平在奶牛的发情周期中是否会发生变化，如果是这样，这些变化是否与卵泡生长模式以及垂体（LH，FSH）和卵巢（类固醇）激素分泌水平有关。总的来说，这些研究将大大促进对卵巢生理学的理解，并为不孕症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.