Increase in membrane cholesterol of neurons in culture recapitulates Alzheimer’s disease early phenotypes.

Levels of membrane-associated cholesterol were shown to be increased in the brain of individuals with sporadic Alzheimer’s disease (AD) and correlated with the severity of the disease. We previously found that heavy membrane cholesterol burden promotes amyloid precursor protein (APP) endocytosis and processing, leading to increased amyloid-¿¿¿A¿) secretion. We hypothesized that such an increase of cholesterol could trigger sporadic AD. We thus acutely loaded the plasma membrane of neurons in culture with cholesterol to reach the 30 % increase observed in AD brains. We showed by multiplex electro-chemiluminescence immuno-assay that transient membrane cholesterol loading produced a significant increase of A¿42 secretion. We also found that early endosomes were enlarged and more prone to aggregation using confocal and electron microscopy and that APP vesicular transport in neuronal processes was slowed down using fluorescence live-imaging. In addition, treatment of neurons with cholesterol induced changes in gene expression profile that are reminiscent of early AD. This model of membrane cholesterol increase in cultured neurons reproduces most of early AD changes and could thus be relevant for deciphering early mechanisms and design new targets for sporadic AD.研究表明，散发性阿尔茨海默病（sporadic Alzheimer’s disease, AD）患者大脑中的膜结合胆固醇（membrane-associated cholesterol）水平升高，且与疾病严重程度相关。本团队前期发现，过量膜胆固醇负荷可促进淀粉样前体蛋白（amyloid precursor protein, APP）的内吞与加工过程，进而提升淀粉样β肽（amyloid-β, Aβ）的分泌水平。本研究推测胆固醇水平升高可能诱发散发性AD，因此通过体外培养神经元的质膜急性胆固醇负载处理，使胆固醇水平达到AD大脑中观测到的30%升高幅度。经多重电化学发光免疫分析法（multiplex electro-chemiluminescence immuno-assay）检测证实，瞬时膜胆固醇负载可显著增加Aβ42的分泌量。借助共聚焦显微镜与电子显微镜（confocal and electron microscopy）观察发现，早期内体出现膨大且更易发生聚集；通过活细胞荧光成像（fluorescence live-imaging）验证，神经元突起内的APP囊泡运输速率显著减慢。此外，胆固醇处理神经元可诱导出与早期AD相似的基因表达谱（gene expression profile）改变。该体外培养神经元的膜胆固醇升高模型可复现早期AD的多数病理特征，因此可用于解析散发性AD的早期发病机制，并为开发新型治疗靶点提供研究基础。