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持有的概念，即雌性哺乳动物的生殖潜力是由出生时可获得的非生长原始卵泡的存量决定的。这些原始卵泡是当包囊中有丝分裂活性的生殖细胞停止分裂并在减数分裂中停滞时形成的，之后包囊破裂，一些卵母细胞被一些前颗粒细胞包围。这些原始卵泡中的一小部分每天离开静止池并发育成生长卵泡，最终产生可供受精的可存活雌性配子。了解这些过程的生化控制机制是重要的，因为缺陷可能导致人类的许多不孕综合征，包括卵巢早衰（POF），其中卵泡加速损失被认为是一个可能的原因。调节囊肿破裂、原始卵泡形成和原始卵泡激活过程的因素在很大程度上是未知的，但最近的进展表明激活素可能是决定卵泡池大小的关键组分。激活素是TGF 2超家族的成员，其由天然拮抗剂包括卵泡抑素（FST）调节。FST基因产生3种蛋白质异构体，它们具有不同的生化特性和生物学作用。为了确定这些作用，我们创建了小鼠模型，其中仅制备最小的FST同种型FST 288（仅FST 288）。这些小鼠生育力低下，窝仔数和频率减少。有趣的是，仅FST 288的雌性出生时具有更大的原始卵泡池，但与WT雌性相比，这些卵泡以更高的速率消耗，这表明激活素调节卵泡形成和生长起始。该提案的主要目标是确定激活素在调节卵泡形成，发育和损失中的作用。我们的中心假设是激活素增加生殖细胞增殖，减少卵母细胞形成原始卵泡时的凋亡，并增加离开静息池的原始卵泡数量。我们建议确定激活素调节目的1中卵泡形成和损失的机制。将在目标2中检查仅FST 288小鼠中额外卵泡的质量，而在目标3中，我们将检验原始卵泡丢失率增加导致仅FST 288小鼠POF的假设。这些结果将提供一个关键的基础上，激活素，激活素类似物，或FST拮抗剂的潜在应用可能被开发用于治疗POF患者。该R21的长期目标是建立内源性激活素及其通过FST的调节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和人类其他不育综合征的病理生理学相关。拟议研究的结果也将支持未来的项目，使用靶向和可调控的转基因技术来控制激活素表达的位点和时间，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的卵子数量是其生殖寿命的全部库存。当这一储备耗尽时，卵巢停止成熟新的卵子，这一过程被称为人类更年期。在某些生育障碍中，这一过程发生得比预期的要早，缩短了这些患者的生育期，使他们几乎没有治疗选择。该提案中的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期绝经的缺陷，以及这种疾病的新治疗方法。

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.