Although there are numerous strategies to counteract the death of dopaminergic neurons in Parkinson's disease (PD), there are currently no treatments that delay or prevent the disease course, indicating that early protective treatments are needed. Targeting axonal degeneration, a key initiating event in PD, is required to develop novel therapies; however, its underlying molecular mechanisms are not fully understood. Here, we studied axonal degeneration induced by 6-hydroxydopamine (6-OHDA) in vitro and in vivo. We found that metabotropic glutamate receptor 5 (mGluR5) expression increased during 6-OHDA-induced axonal degeneration in primary neurons and that blockade of mGluR5 by its antagonists 2-methyl-6-(phenylethynyl)-pyridine (MPEP) and 3-[(2-methyl-1, 3-thiazol-4-yl) ethynyl]-pyridine (MTEP) almost completely attenuated the degenerative process in vitro. Furthermore, a rapid increase in intra-axonal calcium levels following 6-OHDA treatment was visualized using a calcium-sensitive fluorescence probe and a calcium chelator prevented the axonal degenerative process induced by 6-OHDA in vitro, whereas application of the mGluR5 antagonist MPEP partially attenuated the increase in intra-axonal calcium. The screening of calcium targets revealed that calpain activation and an increase in phosphorylated extracellular signal-regulated kinase (p-ERK) were calcium dependent during 6-OHDA-induced axonal degeneration in vitro. Consistent with these in vitro findings, blockade of mGluR5 with MPEP attenuated the degeneration of dopaminergic axons induced by 6-OHDA injection into the striatum prior to soma death in the early stage of PD in an in vivo animal model. In addition, MPEP inhibited the increase in mGluR5 expression levels, calpain activation and the elevation of p-ERK in the striatum triggered by 6-OHDA injection in vivo. Taken together, these data identify an mGluR5-calcium-dependent cascade that causes axonal degeneration, and suggest that mGluR5 antagonists could provide effective therapy to prevent the disease process of PD.

尽管有许多策略可以抵消帕金森病 (PD) 中多巴胺能神经元的死亡，但目前还没有延迟或预防病程的治疗方法，这表明需要早期保护性治疗。开发新疗法需要靶向轴突变性，这是 PD 的一个关键起始事件；然而，其潜在的分子机制尚未完全了解。在这里，我们在体外和体内研究了 6-羟基多巴胺 (6-OHDA) 诱导的轴突变性. 我们发现代谢型谷氨酸受体 5 (mGluR5) 表达在 6-OHDA 诱导的原代神经元轴突变性期间增加，并且 mGluR5 通过其拮抗剂 2-甲基-6-(苯乙炔基)-吡啶 (MPEP) 和 3-[( 2-methyl-1, 3-thiazol-4-yl) ethynyl]-pyridine (MTEP)在体外几乎完全减弱了退化过程。此外，使用钙敏感荧光探针观察 6-OHDA 治疗后轴突内钙水平的快速增加，钙螯合剂在体外防止了 6-OHDA 诱导的轴突退化过程，而 mGluR5 拮抗剂 MPEP 的应用部分减弱了轴突内钙的增加。钙靶点的筛选表明，在体外6-OHDA 诱导的轴突变性过程中，钙蛋白酶激活和磷酸化细胞外信号调节激酶 (p-ERK) 的增加是钙依赖性的。与这些体外发现一致，在体内动物模型中，在PD 的早期阶段，在体细胞死亡之前，用 MPEP 阻断 mGluR5 减弱了由 6-OHDA 注射到纹状体中诱导的多巴胺能轴突的退化。此外，MPEP抑制了体内注射6-OHDA引发的纹状体中mGluR5表达水平的增加、钙蛋白酶激活和p-ERK的升高. 综上所述，这些数据确定了导致轴突变性的 mGluR5-钙依赖性级联反应，并表明 mGluR5 拮抗剂可以提供有效的治疗方法来预防 PD 的疾病进程。