兒茶素預防醋酸鉛引起果蠅長期記憶損傷的機轉

Mechanism that epigallocatechin gallate prevents the long-term memory impairment by lead acetate in Drosophila

盧德蔚(Te-Wei Lu)

指導教授 ： 楊嘉鈴

國立清華大學/生命科學院/生物科技研究所/碩士(2020年)

摘要

鉛是普遍存在環境的毒性物質且會干擾神經系統，但是它影響記憶形成及機制仍然不清楚。先前我們利用嗅覺搭配電擊厭惡聯想的行為學實驗，發現果蠅終生暴露於醋酸鉛會顯著造成長期記憶的損害，但不會影響抗昏迷記憶和學習能力；協同餵食抗氧化劑包括穀胱甘肽、白藜蘆醇或蝦青素可以挽救鉛所引起的長期記憶損害。本論文首先利用嗅覺厭惡聯想之十次間隔訓練一天後的行為學實驗，證實抗氧化劑表沒食子兒茶素沒食子酸酯（EGCG）協同處理亦可消弭鉛終生暴露之果蠅長期記憶的損害，然而單獨餵食高劑量的EGCG也可降低長期記憶。電感耦合電漿體質譜分析發現終生暴露果蠅的大腦中有明顯的鉛積累，但不影響組織內錳與銅含量；EGCG協同處理不會改變腦鉛積累量，但可能會增加錳含量。我們進而研究鉛對成年果蠅是否也會損害長期記憶。結果顯示，羽化後2天內的果蠅經由10-100 μM 醋酸鉛餵食三天會顯著損害長期記憶形成，並隨著劑量增高而加強損害程度。以30 μM EGCG協同餵食成蟲可恢復鉛造成的長期記憶損害，而在添加蛋白合成抑制劑cycloheximide之下則無效。利用光轉換螢光蛋白KAEDE之新蛋白合成報導系統，我們發現鉛暴露的成蟲DAL神經元喪失長期記憶形成所需之經由CaMKII啟動子誘導的新蛋白合成，而EGCG協同處理可挽救之。總言，本論文研究結果推測鉛累積於果蠅腦，並藉由誘引氧化自由基生成而抑制長期記憶形成所需要的新蛋白質合成。本研究也暗示維持大腦之氧化還原穩定狀態對長期記憶形成極為重要。

關鍵字

兒茶素 ； 醋酸鉛 ； 果蠅 ； 長期記憶

並列摘要

Lead is a ubiquitous environmental toxicant that can disturb nerve system, however, memory formation interference and the underlying mechanism by this metal remain unclear. By using an olfactory-electric aversive associative behavior assay, we have previously found that Drosophila whole lifetime exposure to lead acetate (Pb(II)) resulted in long-term memory (LTM) impairment without affecting anesthesia-resistance memory and learning ability, while co-treatment with antioxidants including glutathione, resveratrol, or astaxanthin could rescue the Pb(II)-elicited LTM impairment.1 By using the olfactory-electric aversive associative 10X spaced training, this thesis started to prove that antioxidant epigallocatechin gallate (EGCG) co-treatment could also dispel the LTM impairment caused by lifetime Pb(II) exposure, yet, high doses of EGCG alone may decrease LTM formation. Inductively coupled plasma-mass spectrometry analysis indicated that lifetime Pb(II) exposure could increase Pb accumulation in the brain without affecting Mn and Cu levels. EGCG co-treatment did not alter brain Pb accumulation, but may increase Mn amounts. We further studied whether adult exposure to Pb(II) also impairs LTM. Exposure flies within 2 days post-eclosion to 10-100 μM Pb(II) for 3 days markedly impaired one-day memory following spaced training in a dose-dependent manner. EGCG (30 μM) co-treatment of the adults rescued the Pb(II)-elicited memory impairment, which was invalid in the presence of protein synthesis inhibitor cycloheximide. By using a photoconvertible fluorescent KAEDE de novo protein synthesis reporter system2, we found that Pb(II) exposure blocked the CaMKII promoter-directed new protein synthesis in DAL neurons, whereas EGCG co-treatment rescued it. In summary, results obtained from this thesis suggest that Pb accumulation in fly brains induces ROS generation to inhibit new protein synthesis required for LTM formation. This study also implies maintaining the brain redox homeostasis is extremely important for the control of LTM formation.

並列關鍵字

Epigallocatechin gallate ； Lead acetate ； Long-term memory ； Drosophila

參考文獻

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