Regulation Of Follicle Development and Fertility By Activin and Follistatin

描述(由申请人提供)：目前的证据支持长期以来的观点，即雌性哺乳动物的生殖潜力取决于出生时可获得的不生长的原始卵泡的数量。这些原始卵泡是当有丝分裂活跃的生殖细胞在减数分裂过程中停止分裂和停滞时形成的，之后囊破裂，一些卵母细胞被少数颗粒前细胞包围。这些原始卵泡中的一小部分每天离开休息池，发育成不断生长的卵泡，最终产生可供受精的可存活的雌配子。了解这些过程的生化控制机制很重要，因为缺陷可能导致许多人类不孕综合征，包括卵巢早衰(POF)，卵泡加速丢失被认为是可能的原因。调控囊泡破裂、原始卵泡形成和原始卵泡激活的因素在很大程度上是未知的，但最近的研究表明激活素可能是决定卵泡池大小的关键成分。激活素是TGF2超家族的一员，受包括卵泡抑素(FST)在内的天然拮抗剂的调节。FST基因产生3种不同的蛋白质亚型，具有不同的生化特性和生物学作用。为了确定这些作用，我们创建了一个小鼠模型，其中只制作了最小的FST亚型FST288(仅FST288)。这些小鼠生育能力较差，产仔次数和产仔次数较少。有趣的是，只有FST288的雌性卵泡出生时具有更大的原始卵泡池，但与WT雌性卵泡相比，这些卵泡的耗尽速度更快，这表明激活素同时调节卵泡形成和生长启动。这项建议的主要目标是确定激活素在调节卵泡形成、发育和丢失中的作用。我们的中心假设是激活素促进生殖细胞的增殖，减少卵母细胞在形成原始卵泡时的凋亡，并增加离开休息池的原始卵泡的数量。我们建议在目标1中确定激活素调节卵泡形成和丢失的机制(S)。在目标2中，将检查仅FST288组小鼠中额外卵泡的质量，而在目标3中，我们将检验仅FST288组小鼠原始卵泡丢失率增加导致POF的假设。这些结果将为激活素、激活素类似物或FST拮抗剂在治疗POF患者中的潜在应用提供重要的基础。这个R21的长期目标是建立内源性激活素及其被FST调节的关键决定因素，作为卵泡池大小和随年龄下降的速率的关键决定因素，这可能与理解和治疗POF和其他不孕综合征的病理生理有关。拟议的研究结果还将支持未来的项目，即使用定向和可调控的转基因技术来控制激活素表达的地点和时间，这将直接测试激活素的生殖作用。 公共卫生相关性：雌性动物和人类出生时携带的卵子数量是它们生殖一生的全部卵子数量。当这种储备耗尽时，卵巢就会停止成熟新卵子，这一过程在人类被称为更年期。在一些生育障碍中，这一过程发生得比预期更早，缩短了这些患者的生育期，让他们几乎没有治疗选择。这项研究将调查激活素和卵泡抑素在调节卵子数量和成熟过程中的作用，这可能有助于确定导致早绝经期的缺陷，并为这种疾病找到新的治疗方法。

DESCRIPTION (provided by applicant): Current evidence supports the long-held concept that the reproductive potential of female mammals is determined by the stock of non-growing, primordial follicles available at birth. These primordial follicles are formed when mitotically active germ cells in cysts cease dividing and arrest in meiosis, after which the cysts break down and some oocytes become surrounded by a few pre-granulosa cells. A small portion of these primordial follicles leave the resting pool each day and develop into growing follicles that eventually produce viable female gametes ready for fertilization. Understanding the biochemical control mechanism for these processes is important as defects could lead to a number of infertility syndromes in humans including premature ovarian failure (POF) in which accelerated loss of follicles is thought to be a possible cause. The factors regulating the processes of cyst breakdown, primordial follicle formation, and activation of primordial follicles are largely unknown but recent advances suggest that activin might be a critical component determining follicle pool size. Activin is a member of the TGF2 superfamily that is regulated by natural antagonists including follistatin (FST). The FST gene produces 3 protein isoforms which have different biochemical properties and biological actions. To determine these actions we created a mouse model in which only the smallest FST isoform, FST288 is made (FST288-only). These mice are subfertile with reduced litter size and frequency. Interestingly, FST288-only females are born with a larger pool of primordial follicles, but these follicles are depleted at a greater rate compared to WT females, suggesting that activin regulates both follicle formation and growth initiation. The broad goal of this proposal is to determine the role of activin in regulating follicle formation, development, and loss. Our central hypothesis is that activin increases germ cell proliferation, reduces apoptosis of oocytes as they form primordial follicles, and increases the number of primordial follicles leaving the resting pool. We propose to determine the mechanism(s) whereby activin regulates follicle formation and loss in Aim 1. The quality of the additional follicles in FST288-only mice will be examined in Aim 2, while in Aim 3 we will test the hypothesis that increased rate of primordial follicle loss leads to POF in FST288-only mice. These results will provide a critical foundation upon which potential applications of activin, activin analogs, or FST antagonists might be developed for treating POF patients. The long term goal of this R21 is to establish endogenous activin and its regulation by FST as critical determinants of follicle pool size and rate of decline with age, which could be relevant for understanding and treating the pathophysiology of POF and other infertility syndromes in humans. Results from the proposed research would also support future projects to use targeted and regulatable transgenic technology to control the site and timing of activin expression that will directly test activin's reproductive roles. PUBLIC HEALTH RELEVANCE: The number of eggs that female animals and humans are born with is their entire stock for their reproductive lifetime. When this stock is depleted, the ovary stops maturing new eggs, a process known as menopause in humans. In some fertility disorders, this process occurs earlier than expected, shortening the reproductive period for these patients and leaving them with few treatment options. The research in this proposal will investigate the role of activin and follistatin in regulating both the number of eggs, and the process of maturation, which could help define the defects that lead to early menopause, and to new treatments for this disorder.