Biased signaling pathways in cumulus-oocyte complexes

在过去的几十年里，虽然牛奶产量在增加，但奶牛群的繁殖力却在下降。利用离体培养系统是快速对抗生育力下降的一种方法。奶牛业是加拿大最重要的农业食品部门之一，2012年农场总收入为59亿美元，140万头奶牛生产了7900万升。该研究计划将研究卵母细胞体外成熟过程中减数分裂恢复的细胞内信号转导机制。卵母细胞减数分裂的恢复是卵子受精的重要环节。提高卵母细胞质量的最佳窗口出现在卵母细胞减数分裂恢复之前。卵丘细胞是已知的卵母细胞发育能力的调节剂。为了改善培养条件，如通过抑制卵母细胞减数分裂恢复来延长培养窗口期，需要更好地了解其中的信号通路，环磷酸腺苷（cAMP）是卵泡细胞对FSH（卵泡刺激素）应答的重要第二信使。环磷酸腺苷是哺乳动物卵母细胞减数分裂恢复的关键调节因子。合成和降解的产物调节细胞内cAMP浓度。除了cAMP合成之外，磷酸二酯酶（PDE）的降解是诱导细胞生理反应的强大调节剂。因此，咖啡因，一种非特异性PDE抑制剂，是我们日常生活的一部分。最引人注目的例子依赖于伟哥®，这是一种特异性PDE抑制剂，用于治疗勃起功能障碍男性近二十年。这些例子说明了PDE如何通过影响关键的哺乳动物生理事件来影响日常生活。在过去的几年里，我的实验室一直有兴趣了解PDE在不同生殖功能中的作用。尽管PDE 3A在牛卵母细胞中功能性存在，但我们最近的发现之一是PDE 8存在于牛卵母细胞和卵丘细胞中。我们的工作假设是，PDE 8降解cAMP在卵巢卵泡细胞信号传导中起生理作用，作为整合信号传导细胞反应的一部分。因此，我们将调查的作用，PDE 8在牛卵丘卵母细胞复合体在体外成熟过程中。这将通过FSH和表皮生长因子诱导体外卵母细胞减数分裂恢复以及C型利钠肽抑制进行分析。卵母细胞质量的改善将通过更好地理解在体外成熟的第一个小时期间卵母细胞减数分裂恢复之前发生的信号事件来实现。由于改善体外胚胎生产是胚胎移植公司的当务之急，该项目将揭示诊断和治疗工具开发所需的知识。这些进展对奶牛业至关重要，因为观察到奶牛群生育力下降。该计划将评估基本信号，从而在短期内提供直接有益的应用。

During the last decades while milk production is increasing, fertility of the dairy cattle herd is decreasing. The utilization of in vitro culture system is one way to rapidly counter the decline of fertility. An important need of fundamental research is crucial for dairy cow industry that is one of the most important agri-food sectors in Canada, with a total farms receipts of $5.9 billion, 79 million hectolitres produced by 1.4 million of heads in 2012. The proposed research program will study intracellular signaling mechanisms involved in oocyte meiotic resumption during in vitro maturation. Oocyte meiotic resumption is an essential event allowing the egg to be fertilized. The optimal window to improve oocyte quality occurs before oocyte meiotic resumption. Cumulus cells are the known modulators of oocyte developmental competence. The improvement of culture conditions, such as prolongation of the window by inhibiting oocyte meiotic resumption requires a better understanding of the signalling pathways involved.It is well-known that cyclic adenosine monophosphate (cAMP) is a crucial second messenger in response of follicular cells to FSH (follicle-stimulating hormone). Cyclic AMP is a key regulator of oocyte meiotic resumption in mammals. The resultant of synthesis and degradation modulates intracellular cAMP concentration. Beyond cAMP synthesis, the degradation by phosphodiesterases (PDE) is a powerful modulator inducing physiological response of the cells. It is thus that caffeine, a non-specific PDE inhibitor, is part of our daily life with a cup of coffee. The most spectacular example relies on Viagra® a specific PDE inhibitor prescribed for almost two decades in men with erectile dysfunction. These examples are illustrating how PDE may impact the daily life by affecting crucial mammalian physiological events. Over the last years my laboratory has been interested in understanding the role of PDE in different reproductive functions. Although PDE3A is functionally present in bovine oocytes, one of our recent findings is that PDE8 was present in bovine oocyte and cumulus cells. Our working hypothesis is stating that cAMP degradation by PDE8 plays a physiological role in ovarian follicular cells signaling as part of an integrative signaling cellular response. We will thus investigate the role of PDE8 in bovine cumulus-oocytes complexes during in vitro maturation. This will be analyzed in response to induction of in vitro oocyte meiotic resumption by FSH and epidermal growth factor, and in response to inhibition by C-type natriuretic peptide. The improvement of oocyte quality will be achieved through a better understanding of the signalling events occurring prior to oocyte meiotic resumption during the first hours of in vitro maturation. Because the improvement of in vitro embryo production is a matter of urgency for embryo transfer companies, this project would reveal the knowledge required to enable progress in the development of diagnostic and therapeutic tools. Such advances are of prime importance to the dairy cow industry because of the observed decreases in dairy herd fertility. This program will assess fundamental signalling and thus provide immediate beneficial applications in the short-term.