Tetrahydrobiopterin Biosynthesis by Dopamine Neurons

描述(由申请人提供)：GTP环水解酶I(GCH1)催化四氢生物蝶呤合成的第一步，也是限速步骤，四氢生物蝶呤是酪氨酸羟化酶的重要辅助因子，并在黑质纹状体DA(NSDA)神经元中产生多巴胺(DA)。对GCH1近端启动子中基础转录和cAMP依赖转录所需的顺式作用元件的完整分析即将完成，目标1的目标是识别GC-box的同源结合蛋白，并确定它们在基础转录和cAMP依赖GCH1转录中的作用。这些c/selements招募的反式作用因子也很重要，目标2的目标是在C/EBPbeta和NF-Y的磷酸化与cAMP依赖的GCH1转录之间建立联系。人们对NSDA神经元如何调控GCH1基因表达知之甚少。目标3的目的是了解NSDA神经元中cAMP依赖的GCH1转录过程中蛋白质-启动子DNA相互作用的时间变化，并验证GCH1转录与躯体树突状细胞D2自身受体张力负耦合的假设。GCH1杂合突变可导致DOPA反应性肌张力障碍(DRD)，这是一种常染色体显性遗传性疾病，具有部分外显性，选择性地减少NSDA神经元中DA的合成，在童年时表现为肌张力障碍，成年时表现为帕金森病(PD)。一半的DRD患者的GCH1开放阅读框没有突变，推测GCH1基因调控区有突变。因此，我们已经描述的保守的基因组顺式元件可能是与GCH1缺乏症相关的突变的位置。DRD患者的未受影响的一级亲属帕金森综合症的发病率也是正常对照组的23倍，这表明DRD、GCH1和PD之间存在联系。假设GCH1的背景遗传变异可能促进家族性帕金森病和特发性帕金森病的易感性，我们在目标4中建议对家族性帕金森病GCH1近端启动子和编码区的突变进行测序和功能特征分析。由于关联图谱可能是识别遗传变异性的一种更有效的策略，目标4中的其他研究将评估帕金森病患者和对照组中GCH1基因的遗传变异性。目标5的目的是确定人类GCH1基因的遗传变异是否影响GCH1转录或GCH1酶活性。我们期望这种多学科的方法将产生关于GCH1在NSDA神经元功能中的作用的重要的新信息，并将导致对DRD以及家族性和特发性PD的新的理解。

DESCRIPTION (provided by applicant): GTP cyclohydrolase I (GCH1) catalyzes the first and rate-limiting step in the synthesis of tetrahydrobiopterin, the essential cofactor for tyrosine hydroxylase and the production of dopamine (DA) within nigrostriatal DA (NSDA) neurons. A complete analysis of the cis-acting elements in the GCH1 proximal promoter necessary for basal and cAMP-dependent transcription is near and the goal of Aim 1 is to identify cognate binding proteins for the GC-box and determine their role in basal and cAMP-dependent GCH1 transcription. The trans-acting factors recruited by these c/selements are also important and the goal of Aim 2 is to forge a link between phosphorylation of C/EBPbeta and NF-Y and cAMP-dependent GCH1 transcription. Little is known about how NSDA neurons regulate GCH1 gene expression. The goal of Aim 3 is to understand the temporal changes in protein-promoter DNA interactions that take place during cAMP-dependent GCH1 transcription in NSDA neurons and to test the hypothesis that GCH1 transcription is negatively coupled to somatodendritic D2 autoreceptor tone. Heterozygous mutations in GCH1 can cause DOPA-responsive dystonia (DRD), an autosomal dominant disorder with partial penetrance that selectively decreases DA synthesis within NSDA neurons and presents in childhood as a dystonia and in adulthood as Parkinson's disease (PD). Half of DRD patients have no mutation in the GCH1 open reading frame and presumably have mutations in GCH1 gene regulatory regions. The conserved genomic cis-elements we have already described are therefore likely sites for mutations associated with GCH1 deficiency. Unaffected first-degree relatives of DRD patients are also known to have a 23-fold higher incidence of parkinsonism than do normal controls, suggesting a link between DRD, GCH1 and PD. With the hypothesis that background genetic variability in GCH1 may promote susceptibility to familial parkinsonism and idiopathic PD, we propose in Aim 4 to sequence and functionally characterize mutations in GCH1 proximal promoter and coding regions in familial parkinsonism. Because association mapping is potentially a more powerful strategy for identifying genetic variability additional studies in Aim 4 will assess genetic variability within the GCH1 gene in PD cases versus controls. The goal of Aim 5 is to determine whether genetic variability in the human GCH1 gene influences GCH1 transcription or GCH1 enzyme activity. We expect that this multidisciplinary approach will yield important new information on the role of GCH1 in NSDA neuron function and will lead to a new understanding of DRD and familial and idiopathic PD.