TH GENE REGULATION IN HEALTHY AND LESIONED MIDBRAIN

随着黑质纹状体神经元的退化，无论是在帕金森氏病期间还是在暴露于神经毒素之后，存活的纹状体神经末梢的代偿机制被激活，以增加多巴胺的生物合成和释放。相比之下，催化多巴胺生物合成限速步骤的酪氨酸羟化酶(TH)的基因表达在中脑细胞体中并没有明显诱导。缺乏TH基因的代偿性诱导是令人惊讶的，因为人们预计强大的自我平衡机制可以上调TH基因的表达，从而进一步增强备用黑质纹状体神经元中多巴胺的生物合成。关于黑质纹状体神经元中调节TH基因表达的受体和细胞内信号机制的信息很少。如果没有这些信息，就不可能理解代偿诱导的缺乏，也很难设计新的疗法来上调帕金森病早期或暴露于神经毒素后存活的黑质纹状体神经元的TH。这项建议中的研究旨在填补我们知识上的这一空白。该提案中测试的假设是，兴奋多巴胺能中脑神经元的激动剂会刺激健康动物中脑中TH基因的转录速率。然而，在黑质纹状体通路受损的动物的存活神经元中，这种反应可能被抑制。将检验这一假说的几个方面，具体目的如下：(1)测试M受体激动剂和/或其他刺激激动剂是否能激活健康大鼠中脑细胞体中TH基因的转录速率并使其磷酸化或诱导相关转录因子；(2)测试候选转录因子是否对于TH基因对M胆碱的反应至关重要；以及(3)测试在黑质纹状体通路部分受损后，TH基因是否对M胆碱(或其他刺激激动剂)有反应，以及是否可在这些存活的神经元中以药物的方式诱导TH基因的表达。这些研究将阐明调节中脑TH基因的分子机制，并可能为帕金森病的治疗带来新的治疗策略。

As nigrostriatal neurons degenerate, either during Parkinson's disease or after exposure to neurotoxins, compensatory mechanisms are activated in the surviving striatal nerve terminals to increase dopamine biosynthesis and release. In contrast, gene expression of tyrosine hydroxylase (TH), the enzyme that catalyzes the rate-limiting step in dopamine biosynthesis, is not apparently induced in midbrain cell bodies. This lack of compensatory induction of TH mRNA is surprising, since one would expect robust homeostatic mechanisms to up-regulate TH gene expression and consequently further enhance dopamine biosynthesis in spared nigrostriatal neurons. There is very little information concerning the receptors and intracellular signaling mechanisms that regulate TH gene expression in nigrostriatal neurons. Without this information, it is impossible to understand this lack of compensatory induction and it is difficult to design new therapies to up-regulate TH in surviving nigrostriatal neurons during Early Parkinson's disease or after exposed to neurotoxins. The studies in this proposal are aimed at filling in this gap in our knowledge. The hypotheses being tested in the proposal is that agonists which excite dopaminergic midbrain neurons lead to stimulation of TH gene transcription rate in the midbrain of healthy animals. However, this response may be inhibited in the surviving neurons of animals with lesions of the nigrostriatal pathway. Several aspects of this hypothesis will be tested under the following specific aims: (1) To test whether muscarinic and/or other stimulatory agonists activate whether muscarinic and/or other stimulatory agonists activate TH gene transcription rate and phosphorylate or induce pertinent transcription factors in midbrain cell bodies of healthy rats; (2) To test whether candidate transcription factors are essential for the response of the TH gene to muscarine; and (3) To test whether the TH gene responds to muscarinic (or other stimulatory agonists) in surviving midbrain cell bodies after partial lesions of the nigrostriatal pathway and whether TH gene expression can be induced pharmacologically in these surviving neurons. These studies will shed light on the molecular mechanisms regulating the TH gene in the midbrain and may lead to new therapeutic strategies for the treatment of Parkinson's disease.