The Role of AP1 Family Members in Hormone Gene Expression

下丘脑-垂体-性腺（HPG）轴在哺乳动物生命的每个阶段都起着关键作用，包括青春期发育、月经周期、妊娠、产后和绝经。生育能力取决于对这一轴的精确激素调节。两种最关键的激素，促黄体激素（LH）和促卵泡激素（FSH），专门在垂体前叶的促性腺细胞中产生。LH和FSH调节性腺生殖的关键方面，包括类固醇生成、配子生成和排卵。促性腺激素是一个共同的α亚基和一个独特的β亚基的异二聚体，它提供了生物学特异性，是成熟激素合成的限制性组分。它们主要是对来自下丘脑的促性腺激素释放激素（GnRH）作出反应而合成的。在此之前，我们建立了基本的机制，并确定了调节促性腺激素基因表达的GnRH信号通路。我们确定GnRH通过诱导cFos和cJun立即早期基因增加FSHβ亚基表达，这些基因异源二聚体化形成AP 1转录因子。FSHβ表达增加导致循环中FSH水平升高，因为大部分FSH是组成性分泌的。利用良好的特征模型和迄今为止开发的理解，我们提出了三个新的目标，以弥补我们的理解的差距，促性腺激素的表达在体外和体内的调节，功能障碍的结果在不适当的激素水平和病理。这项建议侧重于基因表达和染色质修饰的表观遗传机制，这些机制在以前的研究中被忽视，但对我们理解生育调控至关重要。基于初步的数据，我们首先集中在阻遏关键约束促性腺激素水平和维持正常的生殖功能，因为高水平的促性腺激素也会导致病理生理。我们鉴定了AP 1超家族的另一个成员Jun二聚化蛋白2（JDP 2），其调节FSHβ亚基的表达。第一个目的是解决JDP 2在体内的作用，特别是在垂体促性腺激素。这个目标将分析JDP 2的作用机制，作为一种新的转录抑制因子，取代cFos作为cJun结合伴侣，从而对基因表达产生负面影响。第二个目标将分析组蛋白修饰酶，组蛋白脱乙酰基酶3（HDAC 3）在生殖功能中的作用，因为HDAC 3被JDP 2招募。第三个目标是确定与FSHβ基因表达相关的染色质重塑和组蛋白乙酰化。这一目标的重点是表观遗传的变化所规定的招聘辅调节和组蛋白修饰酶的阻遏物和转录激活剂。阐明有关促性腺激素基因表达的基本生理问题将有助于我们理解促性腺激素合成和分泌失调的疾病（如闭经、多囊卵巢综合征和卵巢早衰）的分子基础，并为设计新的治疗方法提供背景。

The hypothalamic-pituitary-gonadal (HPG) axis plays a pivotal role in every phase of mammalian life, including pubertal development, the menstrual cycle, pregnancy, postpartum, and menopause. Fertility depends on precise hormonal regulation of this axis. Two of the most critical hormones, luteinizing hormone (LH) and follicle- stimulating hormone (FSH), are produced exclusively in the gonadotrope cells of the anterior pituitary. LH and FSH regulate crucial aspects of reproduction in the gonads, including steroidogenesis, gametogenesis, and ovulation. Gonadotropin hormones are heterodimers of a common α subunit and a unique β subunit, which provides biological specificity and is a limiting component of the mature hormone synthesis. They are synthesized primarily in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus. Previously, we established fundamental mechanisms and identified GnRH signaling pathways that regulate gonadotropin gene expression. We determined that GnRH increases FSHβ subunit expression via induction of cFos and cJun immediate early genes, which heterodimerize to form AP1 transcription factor. Increased FSHβ expression results in higher FSH levels in the circulation since the majority of FSH is constitutively secreted. Taking advantage of well-characterized models and the understanding developed thus far, we propose three novel aims to bridge a gap in our understanding of the regulation of gonadotropin expression in vitro and in vivo, dysfunction of which results in inappropriate hormone levels and pathology. This proposal focuses on epigenetic mechanisms of gene expression and chromatin modifications that have been overlooked in previous investigations, but are critical for our understanding of regulation of fertility. Based on preliminary data, we first focus on repressors critical to constrain gonadotropin hormone levels and maintain normal reproductive function, since high levels of gonadotropins also lead to pathophysiology. We identified an additional member of AP1 superfamily, Jun Dimerization Protein 2 (JDP2), which regulates the expression of the FSHβ subunit. The first aim addresses the role of JDP2 in vivo, particularly in the pituitary gonadotrope. This aim will analyze JDP2 mechanism of action, as a novel transcriptional repressor that displaces cFos as a cJun binding partner, thereby negatively impacting gene expression. The second aim will analyze the role of histone modification enzyme, histone deacetylase 3 (HDAC3) in reproductive function since HDAC3 is recruited by JDP2. The third aim will determine chromatin remodeling and histone acetylation of the FSHβ gene that correlate with its expression. This aim focuses on epigenetic changes regulated by recruitment of coregulators and histone modifying enzymes by repressors and activators of transcription. Elucidating fundamental physiological questions regarding gene expression in the gonadotrope will contribute to our understanding of the molecular basis of disorders with dysregulated gonadotropin synthesis and secretion, such as amenorrhea, polycystic ovary syndrome and premature ovarian failure, and provide a context for the design of novel therapeutic approaches.