Department of Neurobiology, School of Basic Medical Sciences, Beijing Institute for Brain Disorders and Key Laboratory for Neurodegenerative Disorders of the Ministry of Education, Capital Medical University, Beijing 100069, China.
Department of Neurobiology, School of Basic Medical Sciences, Beijing Institute for Brain Disorders and Key Laboratory for Neurodegenerative Disorders of the Ministry of Education, Capital Medical University, Beijing 100069, China.
Mol Cell Neurosci. 2021 Jan;110:103572. doi: 10.1016/j.mcn.2020.103572. Epub 2020 Nov 25.
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对抗帕金森病（PD）中多巴胺能神经元的死亡，但目前尚无延迟或预防疾病进程的治疗方法，这表明需要早期的保护治疗。针对轴突变性，即 PD 的一个关键起始事件，需要开发新的治疗方法；然而，其潜在的分子机制尚未完全了解。在这里，我们研究了体外和体内 6-羟多巴胺（6-OHDA）诱导的轴突变性。我们发现，在原代神经元中，6-OHDA 诱导的轴突变性过程中，代谢型谷氨酸受体 5（mGluR5）的表达增加，并且其拮抗剂 2-甲基-6-（苯乙炔基）-吡啶（MPEP）和 3-（2-甲基-1,3-噻唑-4-基）乙炔基-吡啶（MTEP）阻断 mGluR5 几乎完全减弱了体外的变性过程。此外，使用钙敏荧光探针可视化 6-OHDA 处理后轴内钙水平的快速增加，并且钙螯合剂防止了 6-OHDA 在体外诱导的轴突变性过程，而 mGluR5 拮抗剂 MPEP 的应用部分减弱了轴内钙的增加。钙靶标筛选表明，在体外 6-OHDA 诱导的轴突变性过程中，钙依赖性激活钙蛋白酶和增加磷酸化细胞外信号调节激酶（p-ERK）。与这些体外发现一致，在体内动物模型中，在 PD 早期阶段，在躯体死亡之前，用 MPEP 阻断 mGluR5 可减轻 6-OHDA 注射到纹状体中引起的多巴胺能轴突变性。此外，MPEP 抑制了体内 6-OHDA 注射引起的纹状体中 mGluR5 表达水平的增加、钙蛋白酶的激活和 p-ERK 的升高。总之，这些数据确定了 mGluR5-钙依赖性级联反应导致轴突变性，并表明 mGluR5 拮抗剂可能为预防 PD 的疾病进程提供有效的治疗方法。
