| Summary |
Along with the two hallmark pathologies—intracellular neurofibrillary tangles (NFTs) and extracellular amyloid plaques—transcriptional studies suggest that Alzheimer's disease (AD) results from dysfunction of many cellular pathways including synaptic transmission, cytoskeletal dynamics, and apoptosis. While these studies consistently point to the same pathways involved in AD, there is no consensus on which genes in each pathway are disease-relevant, much less on whether these genes play causative roles or are downstream effects of disease progression. To address these issues, we have performed a large-scale transcriptional analysis in brain of individuals with advanced AD and non-demented controls, focusing specifically on CA1 and the relatively less affected CA3. For comparisons between regions and across disease status, we find consistency in both pathway enrichment as well as specific differentially expressed genes across several studies. Furthermore, genes that show decreased expression with AD progression also tend to show enrichment in CA3 (and vice versa), suggesting that transcription levels in a region may reflect that region's vulnerability to disease. In particular, we find several strong candidate vulnerability (ABCA1, MT1H, PDK4, RHOBTB3) and protection (FAM13A1, LINGO2, UNC13C) genes based on expression patterns. We have also applied weighted gene coexpression network analysis (WGCNA) to explore the pathophysiology of AD from a systems perspective, finding modules for major cell types, which each show distinct disease-relevant expression patterns. In particular, a microglial module shows increased expression in the brain of non-demented controls harboring early NFT pathology, suggesting that microglial activation is an early event in AD progression. |
