Mechanisms Leading to Adrenal Zonation

描述（由申请人提供）：人的肾上腺皮质可以分为不同的区域，这些区域在形态和生化上都有差异。肾小球带醛固酮和束状带皮质醇的产生可以追溯到参与类固醇生物合成的酶的区域特异性表达。醛固酮合成酶（CYP11B2）和112-羟化酶（CYP11B1）尤其如此。我们的初步数据表明，三种核激素受体在决定肾小球与束状肌表型中起关键作用。在此，我们验证了CYP11B2和CYP11B1的区域特异性表达是由于肾小球和束状组织之间不同的核激素受体的相反活性的总体假设。这一假设将通过四个特定目标中提出的研究进行验证：特定目标一中提出的实验将扩展申请人正在进行的项目，该项目定义了CYP11B2基因5'侧翼区域的调控元件。拟议的研究将完成对肾小球特异性表达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，NURR1刺激CYP11B2启动子活性，被血管紧张素II上调，主要在肾小球带表达。特异性目的2将确定肾小球中CYP11B2缺乏的机制。初步研究表明核受体甾体生成因子1 （SF-1; NR5A1）是CYP11B2的有效抑制因子，也是CYP11B1的有效激活因子。这些数据支持SF-1活性在肾小球向束状组织转变中的作用。特异性Aim 3将确定核激素受体翻译后修饰在肾小球细胞表型发育中的作用。初步数据表明，肾小球中有较高的sumoylation活性，SF-1的sumoylation调节其活性。特异性Aim 4将定义在束状组织中负责沉默CYP11B2表达的顺式调控元件和反式作用因子。我们已经分离出一个存在于CYP11B2而非CYP11B1基因中的100 bp插入物。初步数据支持这种插入可能包括一个沉默序列，其作用是阻断束状细胞CYP11B2的表达。意义：原发性醛固酮增多症（PA）估计发生在8%的高血压人群中。大多数PA病例是由结节性增生或醛固酮分泌腺瘤引起的。CYP11B2正常表达调控的中断似乎是该疾病过程的重要组成部分。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，并应提供对醛固酮过量疾病（包括高醛固酮增多症）的见解。公共卫生相关性：从这些研究中获得的叙述性信息将确定引起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区化的理解。此外，拟议的研究将有助于更好地确定肾上腺类固醇过量疾病的原因，包括高醛固酮增多症。

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.