Department of Molecular and Integrative Physiology, University of Michigan Medical School, 7301 MSRB III, 1150 W. Medical Center Dr., Ann Arbor, MI, 48109-0644, USA.
Department of Internal Medicine, Division of Cardiovascular Medicine, University of Michigan Medical School, Ann Arbor, MI, USA.
J Neuroinflammation. 2023 Mar 2;20(1):56. doi: 10.1186/s12974-023-02748-3.
Noradrenergic neurons in the locus coeruleus (LC) are the primary source of norepinephrine (NE) in the brain and degeneration of these neurons is reported in the early stages of Parkinson's disease (PD), even prior to dopaminergic neuron degeneration in the substantia nigra (SN), which is a hallmark of PD pathology. NE depletion is generally associated with increased PD pathology in neurotoxin-based PD models. The effect of NE depletion in other models of PD-like α-synuclein-based models is largely unexplored. In PD models and in human patients, β-adrenergic receptors' (AR) signaling is associated with a reduction of neuroinflammation and PD pathology. However, the effect of NE depletion in the brain and the extent of NE and β-ARs signaling involvement in neuroinflammation, and dopaminergic neuron survival is poorly understood.
Two mouse models of PD, a 6OHDA neurotoxin-based model and a human α-synuclein (hα-SYN) virus-based model of PD, were used. DSP-4 was used to deplete NE levels in the brain and its effect was confirmed by HPLC with electrochemical detection. A pharmacological approach was used to mechanistically understand the impact of DSP-4 in the hα-SYN model of PD using a norepinephrine transporter (NET) and a β-AR blocker. Epifluorescence and confocal imaging were used to study changes in microglia activation and T-cell infiltration after β1-AR and β2-AR agonist treatment in the hα-SYN virus-based model of PD.
Consistent with previous studies, we found that DSP-4 pretreatment increased dopaminergic neuron loss after 6OHDA injection. In contrast, DSP-4 pretreatment protected dopaminergic neurons after hα-SYN overexpression. DSP-4-mediated protection of dopaminergic neurons after hα-SYN overexpression was dependent on β-AR signaling since using a β-AR blocker prevented DSP-4-mediated dopaminergic neuron protection in this model of PD. Finally, we found that the β-2AR agonist, clenbuterol, reduced microglia activation, T-cell infiltration, and dopaminergic neuron degeneration, whereas xamoterol a β-1AR agonist showed increased neuroinflammation, blood brain barrier permeability (BBB), and dopaminergic neuron degeneration in the context of hα-SYN-mediated neurotoxicity.
Our data demonstrate that the effects of DSP-4 on dopaminergic neuron degeneration are model specific, and suggest that in the context of α-SYN-driven neuropathology, β2-AR specific agonists may have therapeutic benefit in PD.
蓝斑核（LC）中的去甲肾上腺素能神经元是大脑中去甲肾上腺素（NE）的主要来源，据报道，这些神经元在帕金森病（PD）的早期阶段就会退化，甚至在黑质（SN）中的多巴胺能神经元退化之前，这是 PD 病理学的一个标志。在基于神经毒素的 PD 模型中，NE 耗竭通常与 PD 病理学的增加有关。在其他类似 PD 的α-突触核蛋白模型中，NE 耗竭的影响在很大程度上尚未得到探索。在 PD 模型和人类患者中，β-肾上腺素能受体（AR）信号与神经炎症和 PD 病理学的减少有关。然而，大脑中 NE 耗竭的影响以及 NE 和β-AR 信号在神经炎症和多巴胺能神经元存活中的参与程度尚不清楚。
使用了两种 PD 小鼠模型，一种是 6OHDA 神经毒素模型，另一种是人类α-突触核蛋白（hα-SYN）病毒 PD 模型。DSP-4 用于耗竭大脑中的 NE 水平，并通过高效液相色谱法（HPLC）与电化学检测进行了确认。使用药理学方法，使用去甲肾上腺素转运体（NET）和β-AR 阻滞剂来研究 DSP-4 在 hα-SYN 病毒 PD 模型中的影响。在 hα-SYN 病毒 PD 模型中，使用β1-AR 和β2-AR 激动剂治疗后，通过荧光和共聚焦成像研究小胶质细胞激活和 T 细胞浸润的变化。
与先前的研究一致，我们发现 DSP-4 预处理会增加 6OHDA 注射后的多巴胺能神经元丢失。相比之下，DSP-4 预处理可保护 hα-SYN 过表达后的多巴胺能神经元。hα-SYN 过表达后，DSP-4 介导的多巴胺能神经元保护依赖于β-AR 信号，因为使用β-AR 阻滞剂可防止该 PD 模型中 DSP-4 介导的多巴胺能神经元保护。最后，我们发现β2-AR 激动剂克仑特罗可减少小胶质细胞激活、T 细胞浸润和多巴胺能神经元变性，而β1-AR 激动剂二甲麦角新碱则可增加 hα-SYN 介导的神经毒性中的神经炎症、血脑屏障通透性（BBB）和多巴胺能神经元变性。
我们的数据表明，DSP-4 对多巴胺能神经元变性的影响是模型特异性的，并表明在α-SYN 驱动的神经病理学中，β2-AR 特异性激动剂可能对 PD 具有治疗益处。
