3×Tg-AD小鼠大氣微粒暴露對阿茲海默症病程影響先驅研究

Abstract

過去研究顯示，PM對人體會有不良健康效應，暴露微粒與心血管、肺部疾病的發生率及死亡率相關。空氣微粒可能直接進到腦部，或經由周邊組織發炎，再藉由神經發炎、氧化壓力等對中樞神經系統(central nervous system, CNS)造成影響，PM可能影響的中樞神經系統疾病包括阿茲海默症(Alzheimer's disease,AD)及帕金森氏症(Parkinson’s disease)等神經退化疾病。阿茲海默症為漸進式神經退化性疾病，是最常見的失智症。這種疾病在神經病理學有兩種主要的病徵：由乙型類澱粉蛋白(amyloid-beta, Aβ)沉積所形成的類澱粉蛋白斑塊(amyloid plaque)，以及由過度磷酸化滔蛋白(Tau protein)聚集而成的神經纖維糾結(Neurofibrillary Tangles, NFTs)。 現今暴露大氣微粒對阿茲海默症的影響較少毒理研究，因此本研究將利用動物實驗，並著重於小鼠暴露大氣微粒對於阿茲海默症病徵及認知障礙的影響。實驗動物為阿茲海默症基因轉殖動物模式—3×Tg-AD 小鼠，為第一種能夠在阿茲海默症相關腦區同時發展出類澱粉蛋白斑塊及神經纖維纏結病徵之小鼠品系，此種小鼠形成之阿茲海默症病徵與人類相似。17周大的3×Tg-AD 隨機分為控制組(n=5)及暴露組(n=6)進行12周的全身性呼吸暴露，使用臺北空氣污染暴露系統(Taipei Air Pollution Exposure System for Health, TAPES)系統進行暴露，此系統可將外界大氣及微粒抽進暴露腔並提供非濃縮大氣微粒，暴露後進行莫氏水迷津後測，並測試腦中Aβ、磷酸化Tau蛋白及氧化、硝化壓力指標8-OHdG及8-NO2Gua。 本研究小鼠暴露期間PM2.5平均質量濃度為7.6 μg/m3。行為實驗結果顯示亞慢性暴露大氣微粒沒有造成3×Tg-AD小鼠空間學習及記憶功能受損。8-OHdG、8-NO2Gua及Aβ42於海馬迴、小腦、大腦皮質各腦區皆無顯著差異，且多低於偵測極限。組織免疫染色結果顯示Aβ1-16未偵測到訊號，磷酸化Tau蛋白則只有在暴露組其中一隻的大腦皮質偵測到訊號。肺與腦組織切片發現暴露沒有顯著發炎反應。大氣微粒影響阿茲海默症的實際機制與毒性可能需要用年紀較大的3xTg-AD 小鼠進一步探討。

Many studies have shown that particulate matter (PM) may have adverse effects on the human body. PM has been associated with mortality and morbidity of cardiopulmonary diseases. PM may affect the CNS by two pathways, through the direct or peripheral way. In the peripheral way, systemic inflammation induced by PM and transfer inflammatory response to the brain by enhanced neuroinflammation and oxidative stress. PM might contribute to neurodegeneration diseases, such as Alzheimer’s disease (AD) and Parkinson’s disease. Alzheimer’s disease is a progressive neurodegenerative disease and the most common form of dementia, which is pathologically characterized by the amyloid plaque of amyloid-beta (Aβ) , neurofibrillary tangles of hyperphosphorylated tau protein. However, few toxicology studies explored the association between PM exposure and the progress of AD. The objective of the study is to explore the ambient particulate matter induced pathological lesions and cognitive impairment of Alzheimer's disease by using 3xTg-AD mice. In the experiment, we use 3xTg-AD mice contain three mutations associated with Alzheimer's disease. This is the first transgenic model to develop both plaque and tangle pathology in AD- relevant brain regions. The pathology of Alzheimer's disease is closely mimics the distribution pattern that occurs in human AD brains. Male 3xTg-AD mice (17 weeks old) were randomly divided into control (filtered air, n=5) and exposure group (ambient PM, n=6) for about 12 weeks whole body inhalation exposure. The ambient air exposure was conducted by using Taipei Air Pollution Exposure System for Health (TAPES). The system can introduce the ambient air outside and provides non-concentrated ambient air. After exposure, Morris water maze post-test were conducted. Aβ, hyperphosphorylated tau protein and oxidative, nitrative stress marker of 8-OHdG and 8-NO2Gua were determined. The mean mass concentration for exposure ambient PM2.5 was 7.6 μg/m3 during the exposure duration. In Morris water maze test, sub-chronic exposure to ambient PM2.5 may not impair spatial learning and memory in 3xTg-AD mice. 8-OHdG, 8-NO2Gua and Aβ42 were not significantly different between the control and the exposure group in hippocampus, cerebellum and cortex. Most of the 8-OHdG, 8-NO2Gua and Aβ42 levels also below the LOD (Limit of Detection). In the immunohistochemistry stain, Aβ1-16 were not detected and one of the 3xTg-AD mice in the exposure group had more phosphorylated tau protein. We found no significant differences between the control and the exposure group in histopathology of lung and brain. Further study should be conducted to explore the mechanism and toxicity of Alzheimer's disease induced by PM in the older 3xTg-AD mice.