Role of thecal inhibin alpha subunit in the regulation of INSL3-dependent androgen production in the ovary

雌性动物和人类的生育需要从卵巢中适时释放一个或多个健康的卵子（卵母细胞）。卵子在一种叫做卵泡的结构中发育，卵泡也会合成重要的激素，没有这些激素，生殖就会失败。这项研究将调查这些激素的产生是如何被调节的。特别是，两种相关的激素，雄激素和雌激素，必须由专门的卵泡细胞在女性月经周期的适当时间产生。雄激素由卵泡细胞（TC）产生，而雌激素由颗粒细胞（GC）产生。GC只有在邻近的TC提供雄激素时才能合成雌激素。卵泡从微小的结构生长成大的多层结构，直径约2cm（人类和奶牛）。垂体促黄体生成素（LH）脉冲刺激TC产生雄激素，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伸出，等待垂体（LH激增）的激素触发，使它们排卵并释放卵子，以进行可能的受精。这种黄体生成素的激增，反过来又依赖于生长中的卵泡分泌越来越多的雌激素。对动物来说，这种雌激素的上升还会引发重要的行为变化（“热度”），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身体周围的许多其他组织和器官。因此，卵泡发育紊乱导致TC分泌雄激素或GC分泌雌激素失衡，不仅会导致不育，还会影响生理的许多其他方面。例如，女性不孕症/生育能力低下的一个非常常见的原因是多囊卵巢疾病综合征（PCOS），它与卵巢雄激素分泌过多有关；这种情况导致月经周期紊乱，面部和身体毛发过度生长。卵泡发育是一个复杂的过程，至今仍知之甚少。现在很清楚，卵巢内部产生了许多信号分子，使不同类型的细胞能够相互交流。这种“局部”细胞间的交流与来自垂体（LH， FSH）的激素信号协同工作，以协调卵泡生长和类固醇的产生。在这个项目中，我们将扩展我们之前bbsrc资助的研究结果，重点关注两个不同的“局部”信号系统在调节卵巢雄激素产生中的作用和相互作用- INSL3系统和BMP系统。特别是，我们将研究另一种称为抑制素α亚基的分子的功能作用，我们最近发现TC产生了惊人的大量抑制素α亚基。虽然该分子在TC中的作用目前尚不清楚，但我们预测其“局部”功能是“保护”TC免受来自卵泡中邻近GC的抑制素的刺激。这可能是一个非常重要的作用，因为我们之前已经表明抑制素可以拮抗bmp对TC雄激素产生的抑制作用。反过来，bmp抑制TC中INSL3的表达，而INSL3似乎是TC雄激素产生的关键要求。我们预测上述信号之间的相对“平衡”在卵泡发育过程中会发生变化，我们将通过实验来检验这一点。此外，我们将研究奶牛TC、卵泡液和外周血样本中抑制素α亚基水平的关系。通过分析先前研究中收集的奶牛血液样本，我们还将验证我们的预测，即在免疫抑制素α亚基的奶牛中，循环INSL3和雄激素水平升高。总的来说，这些研究将显著促进对卵巢生理学的理解，并为不孕不育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 ovaries. Eggs develop within structures called ovarian follicles that also synthesise important hormones, without which reproduction would fail. 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) whilst oestrogen is produced by granulosa cells (GC). GC can only synthesize oestrogen when supplied with androgen by neighbouring TC. Follicles grow from microscopic structures into large multi-layered structures ~ 2cm across (in human & cow). Pulses of luteinizing hormone (LH) from the pituitary stimulate TC to produce androgen while follicle-stimulating hormone (FSH) stimulates GC to proliferate and convert androgen into oestrogen. Mature follicles protrude from the ovary surface awaiting a hormonal trigger from the pituitary (LH surge) that causes them to ovulate and release the egg(s) 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 around the body. 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 an intricate process that is still poorly understood. It is now clear 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 works in concert with hormonal signals from the pituitary (LH, FSH) to coordinate follicle growth and steroid production. In this project we will extend the findings of our previous BBSRC-funded grant that focused on the actions and interactions of two different 'local' signaling systems in regulating ovarian androgen production - the INSL3 system and the BMP system. In particular, we will investigate the functional role of another molecule called inhibin alpha subunit that we recently found to be produced in surprisingly large amounts by TC. While the role of this molecule in TC is currently unknown, we predict that its 'local' function is to 'protect' TC from stimulation by inhibin from neighbouring GC in the follicle. This is potentially a very important role since we have previously shown that inhibin can antagonise the suppressive action of BMPs on TC androgen production. BMPs, in turn, suppress TC expression of INSL3 that seems to be a critical requirement for TC androgen production. We predict that the relative 'balance' between the above signals varies during the course of follicle development and we will examine this experimentally. In addition, we will investigate the relationship between inhibin alpha subunit levels in TC, follicular fluid and peripheral blood samples from cows. By analysing cow blood samples collected for a previous study we will also test our prediction that circulating INSL3 and androgen levels are raised in cows immunized against inhibin alpha subunit. Collectively, these studies will significantly advance understanding of ovarian physiology and provide insights into a major cause of infertility.