BACKGROUND Cell-to-cell propagation of α-synuclein (α-syn) aggregates is thought to contribute to the pathogenesis of Parkinson's disease (PD) and underlie the spread of α-syn neuropathology. Increased pro-inflammatory cytokine levels and activated microglia are present in PD and activated microglia can promote α-syn aggregation. However, it is unclear how microglia influence α-syn cell-to-cell transfer. METHODS We developed a clinically relevant mouse model to monitor α-syn prion-like propagation between cells; we transplanted wild-type mouse embryonic midbrain neurons into a mouse striatum overexpressing human α-syn (huα-syn) following adeno-associated viral injection into the substantia nigra. In this system, we depleted or activated microglial cells and determined the effects on the transfer of huα-syn from host nigrostriatal neurons into the implanted dopaminergic neurons, using the presence of huα-syn within the grafted cells as a readout. RESULTS First, we compared α-syn cell-to-cell transfer between host mice with a normal number of microglia to mice in which we had pharmacologically ablated 80% of the microglia from the grafted striatum. With fewer host microglia, we observed increased accumulation of huα-syn in grafted dopaminergic neurons. Second, we assessed the transfer of α-syn into grafted neurons in the context of microglia activated by one of two stimuli, lipopolysaccharide (LPS) or interleukin-4 (IL-4). LPS exposure led to a strong activation of microglial cells (as determined by microglia morphology, cytokine production and an upregulation in genes involved in the inflammatory response in the LPS-injected mice by RNA sequencing analysis). LPS-injected mice had significantly higher amounts of huα-syn in grafted neurons. In contrast, injection of IL-4 did not change the proportion of grafted dopamine neurons that contained huα-syn relative to controls. As expected, RNA sequencing analysis on striatal tissue revealed differential gene expression between LPS and IL-4-injected mice; with the genes upregulated in tissue from mice injected with LPS including several of those involved in an inflammatory response. CONCLUSIONS The absence or the hyperstimulation of microglia affected α-syn transfer in the brain. Our results suggest that under resting, non-inflammatory conditions, microglia modulate the transfer of α-syn. Pharmacological regulation of neuroinflammation could represent a future avenue for limiting the spread of PD neuropathology.

中文翻译：

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小胶质细胞影响帕金森病小鼠模型中 α-突触核蛋白的细胞间转移。


背景技术 α-突触核蛋白（α-syn）聚集体的细胞间传播被认为有助于帕金森病（PD）的发病机制，并且是 α-syn 神经病理学传播的基础。 PD 中存在促炎细胞因子水平升高和活化的小胶质细胞，活化的小胶质细胞可以促进 α-syn 聚集。然而，目前尚不清楚小胶质细胞如何影响 α-syn 细胞间转移。方法我们开发了一种临床相关的小鼠模型来监测细胞之间的α-syn朊病毒样传播；我们将腺相关病毒注射到黑质后，将野生型小鼠胚胎中脑神经元移植到过度表达人α-syn（huα-syn）的小鼠纹状体中。在该系统中，我们耗尽或激活小胶质细胞，并使用移植细胞内 huα-syn 的存在作为读数，确定对 huα-syn 从宿主黑质纹状体神经元转移到植入的多巴胺能神经元的影响。结果首先，我们比较了具有正常小胶质细胞数量的宿主小鼠与通过药物从移植纹状体中去除 80% 小胶质细胞的小鼠之间的 α-syn 细胞间转移。随着宿主小胶质细胞的减少，我们观察到移植的多巴胺能神经元中 huα-syn 的积累增加。其次，我们评估了在脂多糖（LPS）或白介素-4（IL-4）两种刺激之一激活的小胶质细胞中α-syn转移到移植神经元中的情况。 LPS 暴露导致小胶质细胞的强烈激活（通过 RNA 测序分析，通过小胶质细胞形态、细胞因子产生以及参与 LPS 注射小鼠炎症反应的基因上调来确定）。注射 LPS 的小鼠在移植神经元中的 huα-syn 含量明显更高。 相反，相对于对照组，注射IL-4并没有改变含有huα-syn的移植多巴胺神经元的比例。正如预期的那样，纹状体组织的 RNA 测序分析揭示了 LPS 和 IL-4 注射小鼠之间的基因表达差异；注射脂多糖的小鼠组织中的基因上调，其中包括一些与炎症反应有关的基因。结论 小胶质细胞的缺失或过度刺激会影响大脑中 α-syn 的转移。我们的结果表明，在静息、非炎症条件下，小胶质细胞调节 α-syn 的转移。神经炎症的药理学调节可能是限制帕金森病神经病理学传播的未来途径。