Identification Of The Key Molecules Involved In Chronic Copper Exposure-aggravated Memory Impairment In Transgenic Mice Of Alzheimer’s Disease

Objective: Alzheimer’s disease(AD) is the most common neurodegenerative disease characterized by a progressive impairment of cognitive functions including spatial learning and memory. Excess copper exposure accelerates the development of AD; however, the potential mechanisms by which copper exacerbates the symptoms of AD like memory remain unknown. In this study, we aimed at preliminarily exploring the effects of chronic copper exposure on spatial memory of AD and identifying key molecules involved in this process. Methods: In this study, we used 6 month-old triple transgenic AD(3x Tg-AD) mice as AD mice model and treated them with 250 ppm copper sulfate in drinking water for 6 months, at the same time using non-exposed 3x Tg-AD mice and wide-type(WT) mice as control. First, the Morris water maze test was employed to detect the effects of chronic copper exposure on memory of 3x Tg-AD mice. Then, we used two-dimensional fluorescence difference gel electrophoresis(2D-DIGE) coupled with mass spectrometry to study the influence of chronic copper exposure on hippocampal proteome of 3x Tg-AD mice. Finally, we used Western blot to further verify the differentially expressed protein. Results: The Morris water maze test showed that chronic copper exposure aggravated memory impairment of 3x Tg-AD mice. 2D-DIGE coupled with mass spectrometry revealed a total of 39 differentially expressed proteins in hippocampus between the wild-type(WT) mice and non-exposed 3x Tg-AD mice. A total of 37 differentially expressed proteins were revealed in hippocampus between copper exposed and non-exposed 3x Tg-AD mice. Among these differentially expressed proteins, complexin-1 and complexin-2, two memory associated proteins, were significantly decreased in hippocampus of 3x Tg-AD mice compared with the WT mice. Furthermore, the expression of these two proteins was further down-regulated in 3x Tg-AD mice when exposed to copper. The abnormal expression of complexin-1 and complexin-2 identified by proteomic analysis was verified by Western-blot analysis. Conclusion: Taken together, our data showed that chronic copper exposure accelerated memory impairment and altered the expression of proteins in hippocampus in 3x Tg-AD mice. The functional analysis on the differentially expressed protein suggested that complexin-1 and complexin-2 may be the key molecules involved in chronic copper exposure-aggravated memory impairment in AD.