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各个阶段都起着关键作用，包括青春期发育、月经周期、妊娠、产后和更年期。生育能力取决于这一轴的精确荷尔蒙调节。最关键的两种荷尔蒙，黄体生成素(LH)和卵泡刺激素(FSH)，只在垂体前叶的促性腺细胞中产生。黄体生成素和卵泡刺激素调节性腺生殖的关键方面，包括类固醇发生、配子发生和排卵。促性腺激素是常见的α亚基和独特的β亚基的异源二聚体，具有生物学特异性，是成熟激素合成的限制性成分。它们主要是在下丘脑分泌促性腺激素释放激素(GnRH)的情况下合成的。在此之前，我们建立了调节促性腺激素基因表达的基本机制，并确定了GnRH信号通路。我们确定促性腺激素释放激素通过诱导cfos和cjun即刻早期基因的表达来增加促性腺激素β亚单位的表达，这两个基因异源二聚化形成ap1转录因子。促性腺激素β的表达增加会导致血液中促性腺激素水平的升高，因为大多数促性腺激素是结构性分泌的。利用已有的模型和迄今发展起来的理解，我们提出了三个新的目标，以弥合我们在体外和体内促性腺激素表达调控方面的差距，促性腺激素表达的功能障碍会导致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了，但对于我们理解生育的调节至关重要。基于初步数据，我们首先关注抑制促性腺激素水平和维持正常生殖功能的关键因素，因为高水平的促性腺激素也会导致病理生理学。我们发现了AP1超家族的另一个成员--Jun二聚化蛋白2，它调控着卵泡刺激素β亚单位的表达。第一个目标是研究JDP2在体内的作用，特别是在垂体促性腺激素中的作用。这一目的将分析JDP2的作用机制，作为一种新的转录抑制因子，取代CFO成为cJun结合伙伴，从而对基因表达产生负面影响。第二个目的是分析组蛋白修饰酶组蛋白脱乙酰酶3(HDAC3)在生殖功能中的作用，因为组蛋白脱乙酰酶3被JDP2招募。第三个目标将确定与其表达相关的卵泡刺激素β基因的染色质重塑和组蛋白乙酰化。这一目标集中在由转录抑制物和激活子招募辅助调节因子和组蛋白修饰酶所调控的表观遗传变化。阐明有关促性腺激素基因表达的基本生理学问题将有助于我们理解促性腺激素合成和分泌失调的分子基础，如闭经、多囊卵巢综合征和卵巢早衰，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.