BIOPTERIN & CATECHOLAMINES IN AGING & NEURO-DEGENERATION

四氢生物蝶呤(BH4)是酪氨酸羟化酶的辅因子 酪氨酸羟基酶和色氨酸羟基酶，它们是 儿茶酚胺和5-羟色胺合成中的限速酶。BH4是一种 BH4给药以来儿茶酚胺合成的重要调节因子 增加大脑多巴胺合成，而抑制BH4合成 导致儿茶酚胺缺乏症。在BH4生物合成中，GTP环水解酶 是起始酶，而sepiapterin还原酶催化最后的 反应。在啮齿动物中，GTP环水解酶可能是主要的速率控制酶 BH4合成中的酶；在人类中，其他酶，如sepiapterin 通过进一步的研究，还原酶可能有助于调节BH4的产生 是必需的。在大鼠肾上腺髓质中，儿茶酚胺耗竭升高 酪氨酸羟基酶和GTP环水解酶活性与BH4 水平，这表明这些酶的“协调调节”可能发生。 协调调节是指酪氨酸的协调反应 羟基酶、GTP环水解酶和海燕草素还原酶基因的表达 当BH4和儿茶酚胺代谢改变时。肾上腺升高症 由儿茶酚胺耗竭引起的BH4被认为是维持 当催化活性较低时，体内酪氨酸羟基化增加 酪氨酸羟基酶分子是在早期合成的。在大脑中， 初步数据显示，红藻氨酸损害了非多巴胺细胞 纹状体中纹状体酪氨酸羟基酶和CTP环水解酶升高 活动。在患有非典型苯丙酮尿症(PKU)的新生儿中，遗传 几种BH4生物合成酶中任何一种的缺陷都会导致BH4 肝脑两虚。这导致生物胺缺乏。 在大脑和神经损伤方面。由于许多其他系统需要 这些患者的生物胺合成功能正常，不典型PKU 可能是由BH4代谢的组织特异性调控突变引起的。 BH4生物合成突变可能解释BH4和儿茶酚胺的改变 在正常衰老、阿尔茨海默氏症和帕金森氏症中观察到的缺陷， 和家族性肌张力障碍。对BH4生物合成的进一步了解将是 通过研究酪氨酸羟化酶GTP的协调调节而获得 环水解酶和海风蝶呤还原酶基因在动物模型中的表达 衰老和神经变性，以及随后的药物治疗影响 肾上腺髓质肿瘤细胞系中BH4和儿茶酚胺的合成， 嗜铬细胞瘤(PC12)细胞。作为动物的替代品，PC12细胞可以 接触到更多影响肾上腺BH4和BH4的药物 控制良好的组织培养条件下的儿茶酚胺代谢。 因此，BH4和儿茶酚胺基因在水平上的协调调节 将研究在大鼠肾上腺髓质、PC12细胞中的表达，并为 第一次在大脑中。这些酶的表达将由 测量组织mRNAs(Northern杂交或核糖核酸酶保护分析)， 酶的量(Western Blotts)、酶活性和最终产物 生物合成(BH4和儿茶酚胺) 这些酶的抑制剂；2)BH4和儿茶酚胺的激活剂 3)和纹状体中的红藻氨酸。海藻酸也将被 用来检测衰老对存活的黑质纹状体基因表达的影响 神经毒性损伤后的多巴胺神经元。这些结果将提供 检测人类BH4和儿茶酚胺相关基因的研究方向 表达，并存在与以下相关的神经精神疾病 BH4生物合成的调控突变。人体研究可以是 一旦人类BH4相关基因探针被克隆，这是 在私家侦探的实验室里进行。

Tetrahydrobiopterin (BH4) is the cofactor for tyrosine hydroxylase and tyrosine hydroxylase and tryptophan hydroxylase, which are the initial and rate-limiting enzymes in catecholamine and serotonin synthesis. BH4 is an important regulator of catecholamine synthesis, since BH4 administration increases brain dopamine synthesis, whereas inhibition of BH4 synthesis leads to catecholamine deficits. In BH4 biosynthesis, GTP cyclohydrolase is the initial enzyme, whereas sepiapterin reductase catalyzes the final reaction. In rodent, GTP cyclohydrolase may be the main rate-controlling enzyme in BH4 synthesis; in humans, other enzymes such as sepiapterin reductase may contribute to regulating BH4 production, though further study is required. In rat adrenal medulla, catecholamine depletion elevates tyrosine hydroxylase and GTP cyclohydrolase activities and raises BH4 levels, indicating that "coordinate regulation" of these enzymes may occur. Coordinate regulation refers to a coordinated response in tyrosine hydroxylase, GTP cyclohydrolase, and sepiapterin reductase gene expression when BH4 and catecholamine metabolism is altered. The elevation of adrenal BH4 due to catecholamine depletion is thought o be crucial for maintaining increased tyrosine hydroxylation in vivo when less catalytically-active tyrosine hydroxylase molecules are synthesized at early stages. In brain, preliminary data indicates that kainic acid lesions of non-dopamine cells in striatum elevates striatal tyrosine hydroxylase and CTP cyclohydrolase activities. In newborns with atypical phenylketonuria (PKU), genetic defects in any one of the several BH4 biosynthetic enzymes lead to BH4 deficiency in liver and brain. This results in a biogenic amine deficiency in brain and neurological impairment. Since many other systems requiring biogenic amine synthesis function normally in these patients, atypical PKU may be caused by tissue-specific regulatory mutations of BH4 metabolism. Mutations of BH4 biosynthesis may explain altered BH4 and catecholamine deficits observed in normal aging, Alzheimer's and Parkinson's diseases, and familial dystonia. Further understanding of BH4 biosynthesis will be obtained by studying coordinate regulation of tyrosine hydroxylase, GTP cyclohydrolase, and sepiapterin reductase gene expression in animal models of aging and neuro-degeneration, and following drug treatments influencing BH4 and catecholamine synthesis in the adrenal medulla tumor cell line, pheochromocytoma (PC12) cells. As a substitute for animals, PC12 cells can be exposed to a wider variety of drugs affecting adrenal BH4 and catecholamine metabolism under well-controlled tissue culture conditions. Thus, coordinate regulation at the level of BH4 and catecholamine gene expression will be studied in rat adrenal medulla, PC12 cells, and for the first time in brain. Expression of these enzymes will be monitored by measuring tissue MRNAS (Northern blots or ribonuclease protection assays), amounts of enzymes (Western blots), enzyme activities, and end-products of biosynthesis (BH4 and catecholamines) following treatments with: 1) inhibitors of each of these enzymes; 2)activators of BH4 and catecholamine synthesis, and 3) and kainic acid in striatum. Kainic acid will also be used to examine aging effects on gene expression in surviving nigrostriatal dopamine neurons following neurotoxic damage. These results will provide direction for studies examining human BH4 and catecholamine-related gene expression, and the existence of neuropsychiatric diseases related to regulatory mutations of BH4 biosynthesis. Human studies can be accomplished once the human BH4-related gene probes are cloned, which is ongoing in the PI's laboratory.