A single Citrobacter rodentium infection in Pink1 knockout and wild type mice leads to regional blood-brain-barrier perturbation and limited microglial activation without dopamine neuron axon terminal loss

A growing body of research suggests a link between immune system activation and the development of Parkinson’s disease (PD). Previous work showed that repeated gastrointestinal infection with Citrobacter rodentium can induce PD-like motor dysfunction in Pink1 knockout (KO) mice, along with immune cell infiltration into the brain. To better understand mechanisms underlying immune-mediated brain attack in this model, we tested whether mild infections are sufficient to increase blood-brain barrier (BBB) permeability and trigger brain inflammation. Pink1 wild-type (WT) and KO mice were infected with C. rodentium, and gadolinium-enhanced magnetic resonance imaging (MRI) was performed at days 13 and 26 post-infection to assess BBB integrity. Quantitative MRI analysis revealed increased BBB permeability at day 26 in both WT and KO mice, particularly in the striatum, dentate gyrus, somatosensory cortex, and thalamus. Notably, this permeability was not associated with changes in tight junction protein expression or dopamine system markers in the striatum at either time point. However, persistent microglial activation was observed at day 26 post-infection, along with elevated levels of inflammatory mediators such as eotaxin, IFNγ, CXCL9, IL-17, and MIP-2 in the striatum. Additionally, serum levels of IL-17 and CXCL1 were increased in infected Pink1 KO mice. Flow cytometry revealed neutrophil infiltration in the brain at day 26 post-infection. Finally, a bulk RNA-seq transcriptome analysis revealed that gene sets related to synaptic function were particularly influenced by the infection and that inflammation-related genes were upregulated by the infection in the Pink1 KO mice. These findings support the hypothesis that even mild gastrointestinal infections can increase BBB permeability, disrupt brain homeostasis, and promote chronic neuroinflammation. In genetically susceptible individuals, such as those with Pink1 deficiency, this may represent a first hit that contributes to subsequent induction of PD pathology with aging.越来越多的研究表明，免疫系统激活与帕金森病（Parkinson’s disease, PD）的发生发展存在关联。既往研究显示，反复感染鼠柠檬酸杆菌（Citrobacter rodentium）可在Pink1敲除（Pink1 knockout, KO）小鼠中诱导出类帕金森病样运动功能障碍，并伴随免疫细胞向脑组织浸润。为了更好地阐明该模型中免疫介导性脑损伤的潜在机制，我们探究了轻度感染是否足以提升血脑屏障（blood-brain barrier, BBB）通透性并诱发脑部炎症。我们对Pink1野生型（Pink1 wild-type, WT）小鼠与KO小鼠均感染鼠柠檬酸杆菌，并于感染后第13天和第26天进行钆增强磁共振成像（gadolinium-enhanced magnetic resonance imaging, MRI），以评估血脑屏障完整性。定量磁共振成像分析显示，感染后第26天，WT与KO小鼠的血脑屏障通透性均有所升高，尤其在纹状体（striatum）、齿状回（dentate gyrus）、躯体感觉皮层（somatosensory cortex）以及丘脑（thalamus）中更为显著。值得注意的是，在两个时间点的纹状体中，该通透性变化均与紧密连接蛋白表达或多巴胺系统标志物的改变无关联。然而，在感染后第26天，我们观察到小胶质细胞持续激活，同时纹状体中嗜酸性粒细胞趋化因子（eotaxin）、干扰素γ（Interferon γ, IFNγ）、CXC趋化因子配体9（CXCL9）、白细胞介素17（Interleukin 17, IL-17）以及巨噬细胞炎性蛋白2（Macrophage Inflammatory Protein 2, MIP-2）等炎性介质水平升高。此外，感染后的Pink1 KO小鼠血清中IL-17与CXC趋化因子配体1（CXCL1）的水平均有所升高。流式细胞术检测结果显示，感染后第26天小鼠脑组织中出现中性粒细胞浸润。最后，批量RNA测序（bulk RNA-seq）转录组分析显示，与突触功能相关的基因集受感染的影响尤为显著，且Pink1 KO小鼠体内的炎症相关基因在感染后被上调。上述研究结果支持这一假说：即便是轻度胃肠道感染，也可提升血脑屏障通透性、破坏脑组织稳态，并促进慢性神经炎症的发生。对于存在遗传易感性的个体（例如携带Pink1缺陷的人群），这一过程可能作为首次打击，随着年龄增长进而诱发帕金森病的病理改变。