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標題: | 慢性暴露大氣懸浮微粒對阿茲海默症三基因轉殖小鼠腦白質病理學之影響 Effects of chronic exposure to ambient particles on white matter pathology in 3xTg-AD mice |
作者: | Wan-Ru Zheng 鄭琬儒 |
指導教授: | 鄭尊仁(Tsun-Jen Cheng) |
關鍵字: | 大氣細懸浮微粒,阿茲海默症,白質病理變化,脫髓鞘,核磁共振成像,擴散張量成像, PM2.5,Alzheimer's disease,White matter changes,Demyelination,Magnetic resonance imaging,Diffusion tensor imaging, |
出版年 : | 2020 |
學位: | 碩士 |
摘要: | 過去許多研究指出空氣中懸浮微粒(particulate matter,PM)會對呼吸系統、心血管系統產生危害,近年更是發現可能對中樞神經系統(central nervous system,CNS)產生不良影響,進而引起神經退化性疾病,其中阿茲海默症(Alzheimer’s disease,AD)因高盛行率備受各界關注。近年利用神經影像學對大腦白質(white matter,WM)纖維微結構變化的研究顯示,AD患者普遍存在廣泛的WM損傷,其可能透過如髓鞘變性、寡突細胞損傷或是神經軸突損失等因素,加重AD的風險及疾病進程。 人類流行病學研究發現居住高汙染地區的民眾,顯示白質高張訊號(white matter hyperintensities)、白質體積減小等變化,動物研究也顯示,暴露微粒會減少髓鞘數量或改變髓鞘型態。但是迄今為止,調查PM2.5與WM變化之間關聯的研究有限,現有研究證據大多來自觀察居住高濃度空氣污染地區民眾的研究,其PM2.5濃度高於WHO所建議標準,或使用濃縮暴露系統進行動物實驗,故本研究的目的是想探討長期暴露於非濃縮的環境PM2.5,是否會加速AD動物模式的WM病理。 本研究選用6個月大雌性阿茲海默症三基因轉殖小鼠(3xTg-AD mice),該品系可發展出與人類相似之阿茲海默症病徵,並使用台北空氣汙染暴露系統(TAPES)模擬真實人類暴露之大氣環境,將小鼠放置其中進行5個月(2018年11月26日開始) 全身連續性呼吸暴露。犧牲後先進行小鼠全腦核磁共振成像(magnetic resonance imaging,MRI)了解其腦部體積變化,及擴散張量成像(diffusion tensor imaging,DTI) 量化WM微結構的變化。之後取腦組織包含皮質(又稱灰質)、髓質(又稱白質),以西方墨點法(western blot)測定阿茲海默症病徵Aβ42、P-tau、髓鞘鹼性蛋白(myelin basic protein,MBP)以及微膠細胞活化指標CD11b之蛋白表現量。於組織病理染色分析,使用Luxol fast blue stain以定量髓鞘之密度、Nissl stain以進行神經元細胞計數。 研究期間暴露總微粒PM2.5濃度為13.85 μg/m3,MRI影像結果顯示暴露組的全腦體積顯著小於對照組(462.15 ± 5.69 mm3;490.24 ± 13.93 mm3,p<0.05),但胼胝體(corpus callosum,CC)體積兩組間並無顯著差異。DTI結果顯示暴露組的胼胝體、前連合體(anterior commissure)、穹窿(fimbria)、視神經束(optic tract,OpT)及嗅神經束(olfactory tract)的擴散不等向性(fractional anisotropy)降低,CC的軸向擴散率(axial diffusivity)降低,OpT的徑向擴散率(radial diffusivity)和平均擴散率(mean diffusivity)增加(所有p<0.05)。另外,我們發現暴露組相較控制組WM組織中的MBP表現量顯著降低(1.28 ± 0.33;2.2 ± 0.59,p<0.05),但在皮質並未發現MBP表現量有明顯變化,Aβ42、P-tau及CD11b在兩個腦區皆無顯著差異。由染色的結果顯示,暴露組CC中髓鞘密度顯著降低(0.48 ± 0.09;1.00 ± 0.45,p<0.05),暴露組的皮質神經元數量相較對照組顯著減少(487.00 ± 30.26;560.60 ± 37.62,p <0.05)。 就我們所知,本研究是第一篇使用AD動物模型有系統地、完整地探討暴露PM2.5與WM變化的研究。我們的結果表明,長期暴露於環境水平的PM2.5會加速AD小鼠中樞神經系統WM病理學的惡化,之後可能會影響神經元減少,導致較差的認知能力,並可能在未來進一步發展為AD。由於在我們研究暴露的過程中有老鼠死亡的情形,這可能使我們的結果低估,未來期望能使用轉殖更多AD基因的小鼠,以提前相關病徵出現的時間,來更加釐清PM對中樞神經的影響,並且探討暴露微粒造成白質變化的可能機制。 Accumulating evidence have shown that PM2.5 may cause central nervous system (CNS) diseases, including Alzheimer’s disease (AD). White matter (WM) is observed in the early stage of AD and seen as an early marker of AD. To date, there are still few studies investigating associations between PM2.5 and WM change. The purpose of my study is to determine whether long-term exposure to non-concentrated ambient PM2.5 accelerates the WM pathology in AD animal model. In this study, we assessed the change of WM following chronic PM2.5 exposure in 6-month-old female triple-transgenic AD (3xTg-AD) mice using the Taipei Air Pollution Exposure System (TAPES). The treated mice were whole-bodily and continuously exposed to real world and non-concentrated PM2.5 for 5 months, while the control mice inhaled filtered air. The magnetic resonance imaging (MRI) was used to observe the brain structures. The diffusion tensor imaging (DTI) method was used to quantify changes in WM microstructure. We used the western blot to determine the level of the myelin basic protein (MBP), and the Luxol fast blue stain was used to assess the myelin or myelinated axons. The number of neuronal cells was scored on the histological preparation with Nissl staining. The average PM2.5 concentration in our study was 13.85 μg/m3. The exposure group has smaller total cerebral brain volumes than the control group by MRI (p < 0.05). The DTI demonstrated a decreased fractional anisotropy in corpus callosum (CC), anterior commissure, fimbria, optic tract (OpT), and olfactory tract; a decreased axial diffusivity in the CC; an increased radial diffusivity and mean diffusivity in the OpT in the exposure group (all p < 0.05). We found both MBP level in WM tissue and the density of stained myelin in CC were decreased (p<0.05) in the exposure group. Neuron number in cortex was decreased (p<0.05) in the exposure group compared to the control group. To the best of our knowledge, this is the first study to use AD animal models to systematically and comprehensively describe changes in WM. Our results indicate that chronic exposure to environmental level PM2.5 may accelerate the deterioration of WM pathology in the CNS of AD mice. It may subsequently affect neuron, which may lead to poor cognitive ability and may develop into AD in the future. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/59994 |
DOI: | 10.6342/NTU202003264 |
全文授權: | 有償授權 |
顯示於系所單位: | 環境與職業健康科學研究所 |
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