Mechanisms Leading to Adrenal Zonation

描述(申请人提供)：人的肾上腺皮质可以被分成不同的区域，这些区域在形态和生化上都有差异。球状带中的醛固酮和束状带中的皮质醇的产生可以追溯到参与类固醇生物合成的酶的区带特异性表达。尤其是醛固酮合成酶(CYP11B2)和112-羟基酶(CYP11B1)。我们的初步数据表明，三种核激素受体在决定肾小球和束状核的表型中起着关键作用。在这里，我们测试了整个假设，即CYP11B2和CYP11B1的区带特异性表达是由于肾小球和束状核之间不同的核激素受体的相反活动造成的。这一假设将通过在四个特定目标中提出的研究来验证：在特定目标一中提出的实验将扩展申请人正在进行的定义了CYP11B2基因5‘侧翼区调控元件的项目。拟议的研究将完成对导致肾小球特异性表达CYP11B2的反式作用因子的定义。重点将放在核受体NURR1(NR4A2)的作用上，它刺激CYP11B2启动子的活性，由血管紧张素II上调，主要在肾小球带表达。具体目标二将确定在肾小球中看到的缺乏CYP11B2的机制。初步研究表明，核受体类固醇生成因子1(SF-1；NR5A1)是细胞色素P11B2的有效抑制因子，同时也是细胞色素P11B1的激活因子。这些数据支持SF-1活性在肾小球向束状结构转变过程中的作用。具体目标3将确定核激素受体翻译后修饰在肾小球细胞表型发展中的作用。初步数据表明，肾小球具有升高的总甲基化活性，而SF-1的总甲基化调节其活性。具体目标4将确定负责沉默束状结构中CYP11B2表达的顺式调控元件和反式作用因子。我们已经分离到一个100bp的插入片段，该片段存在于CYP11B2基因中，但不存在于CYP11B1基因中。初步数据支持这样一种可能性，即该插入片段包括一段沉默序列，该序列可阻断CYP11B2的束状细胞表达。意义：据估计，原发性醛固酮增多症(PA)发生在8%的高血压人群中。大多数PA病例是由结节状增生或产生醛固酮腺瘤引起的。细胞色素P11B2表达的正常调节中断似乎是这一疾病过程的重要部分。这项拟议的研究将提供对正常肾上腺中调节CYP11B2表达的分子机制的详细了解，并将为包括醛固酮增多症在内的醛固酮过剩疾病提供洞察力。公共卫生相关性：从这些研究中获得的叙述性信息将确定导致CYP11B2和CYP11B1区域特异性表达的分子机制，从而促进我们对肾上腺分区的理解。此外，拟议的研究将有助于更好地确定肾上腺类固醇激素过多的疾病的原因，包括醛固酮增多症。

DESCRIPTION (provided by applicant): The human adrenal cortex can be divided into distinct zones that have both morphologic and biochemical differences. The production of aldosterone in the zona glomerulosa and cortisol in the zona fasciculate can be traced to the zone-specific expression of the enzymes involved in steroid biosynthesis. This is particularly true for aldosterone synthase (CYP11B2) and 112-hydroxylase (CYP11B1). Our preliminary data suggest that three nuclear hormone receptors play pivotal roles in determining a glomerulosa versus fasciculata phenotype. Herein, we test the overall hypothesis that zone-specific expression of CYP11B2 and CYP11B1 results from the opposing activities of nuclear hormone receptors that differ between the glomerulosa and fasciculata. This hypothesis will be tested by the studies proposed in four Specific Aims: The experiments proposed in Specific Aim One will extend the applicant's ongoing project that has defined the regulatory elements in the 5'-flanking region of CYP11B2 gene. The proposed studies will complete the definition of the trans-acting factors responsible for glomerulosa specific expression of CYP11B2. Focus will be placed on the role of nuclear receptor, NURR1 (NR4A2), which stimulates CYP11B2 promoter activity, is up-regulated by angiotensin II and is expressed primarily in the zona glomerulosa. Specific Aim Two will determine the mechanisms responsible for the lack of CYP11B2 seen in the glomerulosa. Preliminary studies indicate that the nuclear receptor, steroidogenic factor 1 (SF-1; NR5A1) is a potent repressor of CYP11B2 but potent activator of CYP11B1. These data support a role for SF-1 activity in the transition of glomerulosa to fasciculata. Specific Aim 3 will determine the role of nuclear hormone receptor post-translational modification in the development of a glomerulosa cell phenotype. Preliminary data indicate that the glomerulosa has elevated sumoylation activities and sumoylation of SF-1 regulates its activity. Specific Aim 4 will define the cis-regulatory elements and trans-acting factors responsible for silencing CYP11B2 expression in the fasciculata. We have isolated a 100 bp insert that is present in the CYP11B2 but not CYP11B1 gene. Preliminary data support the possibility that this insert includes a silencer sequence that acts to block fasciculata cell expression of CYP11B2. SIGNIFICANCE: Primary aldosteronsism (PA) is estimated to occur in 8 % of the hypertensive population. Most PA cases are caused by nodular hyperplasia or aldosterone-producing adenoma. A disruption in the normal regulation of CYP11B2 expression appears to be an important part of this disease process. The proposed studies will provide a detailed understanding of the molecular mechanisms regulating CYP11B2 expression within the normal adrenal and should provide insight into diseases of aldosterone excess including hyperaldosteronism. PUBLIC HEALTH RELEVANCE: Narrative Information obtained from these studies will determine the molecular mechanisms causing zone- specific expression of CYP11B2 and CYP11B1 thereby advancing our understanding of adrenal zonation. In addition, the proposed studies will help to better define the causes of diseases of adrenal steroid excess including hyperaldosteronism.