Tetrahydrobiopterin Biosynthesis by Dopamine Neurons

描述（由申请人提供）：GTP环水解酶I （GCH1）催化合成四氢生物蝶呤的第一步和限速步骤，四氢生物蝶呤是酪氨酸羟化酶和黑纹状体DA （NSDA）神经元内多巴胺（DA）产生的必需辅因子。对GCH1近端启动子中基础和camp依赖转录所必需的顺式作用元件的完整分析即将完成，Aim 1的目标是鉴定GC-box的同源结合蛋白，并确定它们在基础和camp依赖的GCH1转录中的作用。这些c/元件募集的反式作用因子也很重要，Aim 2的目标是在c/ EBPbeta和NF-Y的磷酸化和camp依赖性GCH1转录之间建立联系。NSDA神经元如何调节GCH1基因表达尚不清楚。Aim 3的目的是了解在NSDA神经元中camp依赖性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转录与体树突D2自身受体张力负偶联的假设。GCH1的杂合突变可引起多巴反应性肌张力障碍（DRD），这是一种常染色体显性疾病，具有部分外显性，选择性地减少NSDA神经元内的DA合成，在儿童期表现为肌张力障碍，在成年期表现为帕金森病（PD）。一半的DRD患者在GCH1开放阅读框中没有突变，可能在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缺乏症相关的突变位点。DRD患者未受影响的一级亲属的帕金森病发病率也比正常对照高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Aim 4中提出对家族性帕金森病中GCH1近端启动子和编码区的突变进行测序和功能表征。由于关联作图可能是识别遗传变异性的一种更强大的策略，Aim 4中的其他研究将评估PD病例与对照组GCH1基因内的遗传变异性。Aim 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新信息，并将导致对DRD和家族性和特发性PD的新认识。

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.