Compensatory Regulation of Dopamine after Ablation of the Tyrosine Hydroxylase Gene in the Nigrostriatal Projection*
Compensatory Regulation of Dopamine after Ablation of the Tyrosine Hydroxylase Gene in the Nigrostriatal Projection*
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DOI：
10.1074/jbc.m111.284729
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发表时间：
2011-10
期刊：
影响因子：
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通讯作者：
H. Tokuoka;S. Muramatsu;C. Sumi-Ichinose;Hiroaki Sakane;M. Kojima;Yoshinori Aso;T. Nomura;D. Met
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文献类型：
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作者：
H. Tokuoka;S. Muramatsu;C. Sumi-Ichinose;Hiroaki Sakane;M. Kojima;Yoshinori Aso;T. Nomura;D. Met
背景：多巴胺合成所必需的酪氨酸羟化酶（TH）基因在成人黑质纹状体投射中部分缺失。结果：轴突终末的TH下降比索马慢，多巴胺的维持比TH好。结论：纹状体多巴胺受轴突TH水平及相应TH水平的左旋多巴合成活性的补偿性调节。意义：这种调节可能与帕金森病和其他多巴胺相关精神疾病的发病机制有关。酪氨酸羟化酶（TH; EC 1.14.16.2）是多巴胺合成中的限速酶，并且对于控制自主运动和奖励依赖性行为的中枢多巴胺能系统是重要的。为了进一步探讨成年小鼠脑内TH对多巴胺水平的调节机制，我们采用基因工程方法，利用Cre-loxP系统对黑质纹状体投射区的Th基因进行了克隆。将表达Cre重组酶的腺相关病毒（AAV-Cre）立体定位注射到多巴胺能细胞体所在的黑质（substantia nigra pars rectata，SNc）中，特异性地灭活Th基因。在AAV-Cre注射后2周，SNc中TH表达细胞的数量减少至小于40%，而纹状体TH蛋白水平在注射后2、4和8周分别减少至75%、50%和39%。因此，出乎意料的是，TH蛋白的减少在纹状体，其中SNc多巴胺能轴突密集地支配，是慢于在SNc。此外，尽管TH是多巴胺合成的基本要求，但纹状体多巴胺含量仅适度降低，甚至在AAV-Cre注射后8周降至70%。同时，l-二羟基苯丙氨酸，多巴胺前体，每TH蛋白水平的体内合成活性增强，表明在完整的黑质纹状体轴突的多巴胺合成活性的上调。总的来说，我们的条件性Th基因靶向方法证明了两种调节机制TH在轴突末梢多巴胺体内稳态：局部调节TH蛋白量独立的索马和跨轴突调节表观l-二羟基苯丙氨酸合成活性每TH蛋白。
Background: The tyrosine hydroxylase (TH) gene, essential for dopamine synthesis, is partially ablated in adult nigrostriatal projection. Results: TH reduction in axon terminals is slower than in soma, and dopamine is better maintained than TH. Conclusion: Striatal dopamine is compensatorily regulated by axonal TH level and l-DOPA synthesis activity per TH level. Significance: This regulation has potential relevance to pathogenesis of Parkinson disease and other dopamine-related psychiatric disorders. The tyrosine hydroxylase (TH; EC 1.14.16.2) is a rate-limiting enzyme in the dopamine synthesis and important for the central dopaminergic system, which controls voluntary movements and reward-dependent behaviors. Here, to further explore the regulatory mechanism of dopamine levels by TH in adult mouse brains, we employed a genetic method to inactivate the Th gene in the nigrostriatal projection using the Cre-loxP system. Stereotaxic injection of adeno-associated virus expressing Cre recombinase (AAV-Cre) into the substantia nigra pars compacta (SNc), where dopaminergic cell bodies locate, specifically inactivated the Th gene. Whereas the number of TH-expressing cells decreased to less than 40% in the SNc 2 weeks after the AAV-Cre injection, the striatal TH protein level decreased to 75%, 50%, and 39% at 2, 4, and 8 weeks, respectively, after the injection. Thus, unexpectedly, the reduction of TH protein in the striatum, where SNc dopaminergic axons innervate densely, was slower than in the SNc. Moreover, despite the essential requirement of TH for dopamine synthesis, the striatal dopamine contents were only moderately decreased, to 70% even 8 weeks after AAV-Cre injection. Concurrently, in vivo synthesis activity of l-dihydroxyphenylalanine, the dopamine precursor, per TH protein level was augmented, suggesting up-regulation of dopamine synthesis activity in the intact nigrostriatal axons. Collectively, our conditional Th gene targeting method demonstrates two regulatory mechanisms of TH in axon terminals for dopamine homeostasis in vivo: local regulation of TH protein amount independent of soma and trans-axonal regulation of apparent l-dihydroxyphenylalanine synthesis activity per TH protein.