Antidyskinetic effects of MEK inhibitor are associated with multiple neurochemical alterations in the striatum of hemiparkinsonian rats

L-DOPA-induced dyskinesia (LID) represents one of the major problems of the long-term therapy of patients with Parkinson's disease (PD). Although the pathophysiologic mechanisms underlying LID are not completely understood, activation of the extracellular signal regulated kinase (ERK) is recognized to play a key role. ERK is phosphorylated by mitogen-activated protein kinase kinase (MEK), and thus MEK inhibitor can prevent ERK activation. Here the effect of the MEK inhibitor PD98059 on LID and the associated molecular changes were examined. Rats with unilateral 6-OHDA lesions of the nigrostriatal pathway received daily L-DOPA treatment for three weeks, and abnormal involuntary movements (AIMs) were assessed every other day. PD98059 was injected in the lateral ventricle daily for 12 days starting from day 10 of L-DOPA treatment. Striatal molecular markers of LID were analyzed together with gene regulation using microarray. The administration of PD98059 significantly reduced AIMs. In addition, ERK activation and other associated molecular changes including ¿FosB were reversed in rats treated with the MEK inhibitor. PD98059 induced significant up-regulation of 418 transcripts and down-regulation of 378 transcripts in the striatum. Tyrosine hydroxylase (Th) and aryl hydrocarbon receptor nuclear translocator (Arnt) genes were down-regulated in lesioned animals and up-regulated in L-DOPA-treated animals. Analysis of protein levels showed that PD98059 reduced the striatal TH. These results support the association of p-ERK1/2, ¿FosB, p-H3 to the regulation of TH and ARNT in the mechanisms of LID, and pinpoint other gene regulatory changes, thus providing clues for identifying new targets for LID therapy.左旋多巴诱发的异动症（L-DOPA-induced dyskinesia, LID）是帕金森病（Parkinson's disease, PD）患者长期治疗过程中面临的主要难题之一。尽管LID的病理生理机制尚未完全阐明，但目前公认细胞外信号调节激酶（extracellular signal regulated kinase, ERK）的激活在其中发挥关键作用。ERK可由丝裂原活化蛋白激酶激酶（mitogen-activated protein kinase kinase, MEK）磷酸化，因此MEK抑制剂能够阻断ERK的激活。 本研究探讨了MEK抑制剂PD98059对LID及相关分子变化的影响。实验中，单侧黑质纹状体通路6-羟基多巴胺（6-OHDA）损伤的大鼠每日接受左旋多巴治疗，持续三周，每隔一天对异常不自主运动（abnormal involuntary movements, AIMs）进行评估。自左旋多巴治疗第10天起，每日向大鼠侧脑室内注射PD98059，连续给药12天。本研究通过基因芯片（microarray）同步分析了纹状体中LID相关分子标志物与基因表达调控情况。 结果显示，PD98059给药可显著降低大鼠的异常不自主运动评分。此外，MEK抑制剂处理可逆转大鼠体内ERK激活及包括ΔFosB在内的其他相关分子变化。PD98059可诱导纹状体中418个转录本显著上调、378个转录本显著下调。酪氨酸羟化酶（tyrosine hydroxylase, TH）与芳香烃受体核转位蛋白（aryl hydrocarbon receptor nuclear translocator, ARNT）基因在损伤组大鼠中表达下调，而在左旋多巴处理组大鼠中表达上调。蛋白水平检测结果显示，PD98059可降低纹状体中TH的表达水平。 本研究结果证实，p-ERK1/2、ΔFosB及p-H3与LID发病机制中TH与ARNT的调控过程密切相关，同时明确了其他基因表达调控变化，为筛选LID治疗的全新靶点提供了重要线索。