ANK1 is up-regulated in laser captured microglia in Alzheimer’s brain; the importance of addressing cellular heterogeneity

Recent epigenetic association studies have identified a new gene, ANK1, in the pathogenesis of Alzheimer’s disease (AD). Although strong associations were observed, brain homogenates were used to generate the data, introducing complications because of the range of cell types analyzed. In order to address the issue of cellular heterogeneity in homogenate samples we isolated microglial, astrocytes and neurons by laser capture microdissection from CA1 of hippocampus in the same individuals with a clinical and pathological diagnosis of AD and matched control cases. Using this unique RNAseq data set, we show that in the hippocampus, ANK1 is significantly (p.0001) up-regulated 4-fold in AD microglia, but not in neurons or astrocytes from the same individuals. These data provide evidence that microglia are the source of ANK1 differential expression previously identified in homogenate samples in AD.近期的表观遗传关联研究已在阿尔茨海默病（Alzheimer’s Disease, AD）的发病机制中鉴定出ANK1这一新基因。尽管已观测到较强的关联，但此前的相关研究均采用脑匀浆开展数据生成工作，由于分析涉及多种细胞类型，该方法引入了混杂因素。为解决脑匀浆样本中存在的细胞异质性问题，本研究通过激光捕获显微切割（Laser Capture Microdissection, LCM）技术，从经临床与病理确诊的AD患者及匹配对照个体的海马CA1区分离出小胶质细胞、星形胶质细胞与神经元。借助这套独特的RNA测序（RNA sequencing, RNAseq）数据集，本研究证实：在海马组织中，ANK1在AD患者的小胶质细胞中显著上调4倍，且具有极显著统计学差异（p<0.0001），但在同一受试者的神经元与星形胶质细胞中未出现此类表达变化。本研究数据表明，此前在AD脑匀浆样本中鉴定到的ANK1差异表达，其来源正是小胶质细胞。