NUTRITIONAL REGULATION OF CYSTEINE DIOXYGENASE

半胱氨酸双加氧酶（CDO, EC 1.13.11.20）活性异常或缺乏，据称在患有多种疾病的个体中都可以看到，包括非神经和神经疾病。低CDO活性可能会导致问题，要么是因为半胱氨酸分解代谢的产物硫酸盐（或牛磺酸）供应不足，而半胱氨酸分解代谢的产物需要用于各种目的，包括II期偶联反应，要么是因为半胱氨酸或有毒代谢产物的积累。我们已经确定CDO是参与调节半胱氨酸分解代谢的主要肝酶。这种调节反应是强有力的，在喂食低蛋白质饲料的动物肝脏中几乎检测不到CDO活性，而在喂食含有高水平蛋白质或含硫氨基酸的饲料的大鼠肝脏中，CDO活性增加了170倍。长期目标是进一步阐明参与CDO调控的分子机制，并了解CDO的遗传或其他损伤在类风湿关节炎等疾病病因学中的可能贡献。拟开展的研究包括：(1)两种CDO亚型的表征；(2)研究半胱氨酸在非肝组织（脑、肾和肺）中对CDO的表达和调控，作为了解半胱氨酸代谢与某些与衰老相关的神经和非神经疾病发生进展关系的一步；(3)评估CDO水平增加的机制——在半胱氨酸存在下增加mRNA翻译率或增加CDO蛋白的稳定性，并且，如果合适，检查可能形成的替代处理的CDO mRNA转录物；(4)评估完整大鼠组织半胱氨酸浓度与CDO水平的关系。实验将包括大鼠的饮食处理和评估饮食对CDO在各组织中表达的影响，研究CDO丰度调节的分子机制，以及从这些大鼠或原代培养的肝细胞中分离的CDO蛋白和CDO mRNA的特性。

Abnormal or deficient cysteine dioxygenase (CDO, EC 1.13.11.20) activity has been claimed to be seen in individuals with a variety of diseases, both non-neurological and neurological. Low CDO activity may result in problems, either because of insufficient supply of sulfate (or taurine) as products of cysteine catabolism that are needed for a variety of purposes including phase II conjugation reactions or because of accumulation of cysteine or toxic metabolites. We have identified CDO as the major hepatic enzyme involved in regulation of cysteine catabolism. The regulatory response is robust, with CDO activity being barely detectable in liver of animals fed low protein diets and increasing up to 170-fold in rats fed diets containing high levels of protein or sulfur amino acids. The long-term objective is to further elucidate the molecular mechanisms involved in the regulation of CDO and to understand the possible contribution of genetic or other impairments in CDO in the etiology of diseases such as rheumatoid arthritis. Proposed studies include (1) the characterization of the two CDO isoforms; (2) studies of CDO expression and regulation by cysteine in nonhepatic tissues (brain, kidney, and lung) as a step in understanding the relation of cysteine metabolism to the development and progression of certain neurological and nonneurological diseases associated with aging; (3) assessment of the mechanism by which CDO levels are increased -- an increased rate of mRNA translation or an increased stability of CDO protein in the presence of cysteine, and, if appropriate, examination of the possible formation of an alternatively processed mRNA transcript for CDO; and (4) assessment of the relationship of tissue cysteine concentration to CDO levels in intact rats. Experiments will involve dietary treatments of rats and assessment of the effects of diet on CDO expression in various tissues, studies of the molecular mechanisms involved in regulation of CDO abundance, and characterization of CDO protein and CDO mRNA isolated from these rats or from hepatocytes in primary culture.