Mechanisms Leading to Adrenal Zonation

描述(申请人提供)：背景：人的肾上腺皮质作为一个复合内分泌腺，既分泌矿质皮质激素又分泌糖皮质激素。这些类固醇来自肾上腺皮质的不同区域，这些区域在形态和生化上都有差异。皮质区干细胞的来源和导致区域特异性类固醇产生的机制都没有明确的定义。肾上腺皮质的功能分区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)、11β-羟基酶(CYP11B1)和17α-羟基酶(CYP17)。 目的：在特定目标一中提出的实验将扩展申请者正在进行的合作项目，该项目定义了(CYP11B2)和11β-羟基酶(CYP11B1)基因5‘侧翼区的调控元件。这些研究将完成对肾小球特异性表达和束状抑制细胞色素P11B2的调控因素的定义。重点将放在核受体NURR1(NR4A2)的作用上，它刺激CYP11B2启动子的活性，该活性由血管紧张素II上调，主要在肾小球带表达。 具体目标二将确定肾小球中出现的CYP17缺失的机制。初步研究表明，这是多种机制共同作用的结果，包括血管紧张素II增加AP-1转录因子和WNT信号转导。WNT下游负责抑制细胞色素P17的因子和AP-1抑制细胞色素P17转录的机制将被定义。 具体目标三将把我们正在进行的肾上腺细胞培养研究扩展到体内情况，使用细菌人工染色体(BAC)转基因来靶向带有NURR1抑制剂的球状带。小鼠肾上腺和人类肾上腺一样，将CYP11B2的表达限制在肾小球带，使其成为定义调节醛固酮产生的因素的极佳模型。我们还将使用这一策略来培育一只肾小球-Cre小鼠，这将成为进一步研究可能调节肾小球功能的基因的重要工具。 意义：醛固酮增多症是由于结节状增生和产生醛固酮的腺瘤中的带状结构的破坏，特别是细胞色素P11B2的异常表达所致。这项拟议的研究将提供对肾上腺内调节CYP11B2表达的分子机制的详细了解，并应提供对与异常表达相关的疾病的洞察。

DESCRIPTION (provided by applicant): BACKGROUND: The human adrenal cortex acts as a compound endocrine gland that secretes both mineralocorticoids and glucocorticoids. These steroids arise from distinct zones of the adrenal cortex that have both morphologic and biochemical differences. Neither the origin of the stem cells of the cortical zones nor the mechanisms leading to the zone-specific production of steroids is clearly defined. The functional zonation of the adrenal cortex can be traced to the zone-specific expression of the enzymes involved in steroid biosynthesis. This is particularly true for aldosterone synthase (CYP11B2), 11 beta-hydroxylase (CYP11B1) and 17alpha-hydroxylase (CYP17). AIMS: The experiments proposed in Specific Aim One will extend the applicants ongoing collaborative project that has defined the regulatory elements in the 5'-flanking region of the (CYP11B2) and 11beta-hydroxylase (CYP11B1) genes. These studies will complete the definition of the transacting factors responsible for glomerulosa-specific expression and fasciculata repression of CYP11B2. Focus will be placed on the role of the nuclear receptor, NURR1 (NR4A2), which stimulates CYP11B2 promoter activity, which 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 CYP17 seen in the glomerulosa. Preliminary studies indicate that this results from multiple mechanisms including angiotensin II increased AP-1 transcription factors and WNT signaling. The WNT downstream factors responsible for CYP17 repression and the mechanisms of AP-1 repression of CYP17 transcription will be defined. Specific Aim Three will extend our ongoing adrenal cell culture studies to the in vivo situation using bacterial artificial chromosome (BAC) transgenesis to target the zona glomerulosa with an inhibitor of NURR1. The murine adrenal, like the human adrenal, limits expression of CYP11B2 to the zona glomerulosa making it an excellent model to define the factors regulating aldosterone production. We will also use this strategy to produce a glomerulosa-CRE mouse that will be an important tool for further study of genes that may regulate glomerulosa function. SIGNIFICANCE: Hyperaldosteronism results from the disruption of zonation, and particularly aberrant CYP11B2 expression, in nodular hyperplasia and aldosterone-producing adenomas. The proposed studies will provide a detailed understanding of the molecular mechanisms regulating CYP11B2 expression within the adrenal and should provide insight into the diseases associated with aberrant expression.