Table_2_Chronic Microglial Activation in the GFAP-IL6 Mouse Contributes to Age-Dependent Cerebellar Volume Loss and Impairment in Motor Function.DOCX

Chronic microglial activation is a prominent feature of many chronic neurodegenerative diseases, including Parkinson’s and Alzheimer’s disease. To investigate the effects of chronic microglial activation on cerebellar structure and motor function throughout the lifespan, the transgenic GFAP-IL6 mouse model was used. The aim of the study was to examine inflammatory markers and neuronal degeneration while simultaneously characterizing the motor performance of GFAP-IL6 mice at 3, 6, 14, and 24 months of age in comparison to WT (C57BL/6) mice. In respect to markers of neuroinflammation in the cerebellum, increased numbers of Iba1+ microglia were observed as early as at 3 months of age. In addition, TNF-α levels proved to be significantly higher in the GFAP-IL6 compared to WT mice at all time points. A difference in cerebellar volume between the GFAP-IL6 and WT mice was observed later in life, starting at 6 months and increasing to a loss of about 50% in aged (24 months old) GFAP-IL6 mice. Synaptic deficits were also assessed by using pre- (synaptophysin) and post-synaptic (PSD95) markers. While synaptophysin levels remained unchanged, PSD95 levels decreased in the aging GFAP-IL6 mice compared to their WT littermates from 14 months onward. To assess the effect of microglia activation and neurodegeneration on behavior, a variety of motor function tests, semi-quantitative cerebellar ataxia score, accelerod, beam walking, and open field tests were performed. An age-dependent difference between the genotypes was observed in many of the motor function tests. For example, reduced performance on the accelerod and higher ataxia scores were observed at 6 months of age, followed by the beam walking test showing differences at 14 months of age. In summary, this study constitutes a comprehensive, age-dependent examination of inflammatory, synaptic and neurodegenerative changes in the brains of GFAP-IL6 mice leading to a deterioration in motor performance. The results also indicate that early chronic microglia activation in the GFAP-IL6 mouse leads to observable cerebellar volume loss and motor deficits later in life.

慢性小胶质细胞活化（chronic microglial activation）是众多慢性神经退行性疾病的显著特征，涵盖帕金森病与阿尔茨海默病。为探究慢性小胶质细胞活化在整个生命周期中对小脑结构与运动功能的影响，本研究采用了转基因GFAP-IL6小鼠模型。本研究旨在检测炎症标志物与神经元变性情况，同时对比分析3、6、14及24月龄GFAP-IL6小鼠与野生型（WT，C57BL/6）小鼠的运动表现。针对小脑神经炎症标志物，研究人员早在3月龄时便观察到Iba1阳性小胶质细胞数量增多。此外，在所有时间节点中，GFAP-IL6小鼠的肿瘤坏死因子-α（TNF-α）水平均显著高于野生型小鼠。GFAP-IL6小鼠与野生型小鼠的小脑体积差异在生命周期后期显现：自6月龄起出现差异，至24月龄的老年GFAP-IL6小鼠时，小脑体积已减少约50%。本研究同时采用突触前标志物（synaptophysin，突触素）与突触后标志物（PSD95）评估突触功能缺损。与同窝野生型小鼠相比，14月龄及以上的老年GFAP-IL6小鼠中，突触素水平未发生明显变化，但PSD95水平出现下降。为探究小胶质细胞活化与神经变性对行为学的影响，本研究开展了多项运动功能测试，包括半定量小脑共济失调评分、转棒实验（accelerod）、平衡木行走实验与旷场实验。多项运动功能测试均观察到不同基因型小鼠的运动表现存在年龄依赖性差异。例如，6月龄时即可观察到GFAP-IL6小鼠在转棒实验中表现下滑、共济失调评分升高，而平衡木行走实验的组间差异则在14月龄时显现。综上，本研究对GFAP-IL6小鼠脑部的炎症、突触及神经变性变化进行了全面的年龄依赖性分析，这些变化最终导致其运动功能衰退。研究结果同时表明，GFAP-IL6小鼠早期出现的慢性小胶质细胞活化，会在生命周期后期引发可观测的小脑体积丢失与运动功能缺损。