2Alzheimer's disease (AD) has been categorized by the Centers for Disease Control and 3 Prevention (CDC) as the 6 th leading cause of death in the United States. AD is a significant 4 health-care burden because of its increased occurrence (specifically in the elderly population) 5 and the lack of effective treatments and preventive methods. With an increase in life expectancy, 6 the CDC expects AD cases to rise to 15 million by 2060. Aging has been previously associated 7 with susceptibility to AD, and there are ongoing efforts to effectively differentiate between normal 8 and AD age-related brain degeneration and memory loss. AD targets neuronal function and can 9 cause neuronal loss due to the buildup of amyloid-beta plaques and intracellular neurofibrillary 10 tangles.
11Our study aims to identify temporal changes within gene expression profiles of healthy controls 12 and AD subjects. We conducted a meta-analysis using publicly available microarray expression 13 data from AD and healthy cohorts. For our meta-analysis, we selected datasets that reported 14 donor age and gender, and used Affymetrix and Illumina microarray platforms (8 datasets, 2,088 15 samples). Raw microarray expression data were re-analyzed, and normalized across arrays. We 16 then performed an analysis of variance, using a linear model that incorporated age, tissue type, 17 sex, and disease state as effects, as well as study to account for batch effects, and including 18 binary interaction between factors. Our results identified 3,735 statistically significant (Bonferroni 19 adjusted p<0.05) gene expression differences between AD and healthy controls, which we 20 filtered for biological effect (10% two-tailed quantiles of mean differences between groups) to 21 obtain 352 genes. Interesting pathways identified as enriched comprised of neurodegenerative 22 diseases pathways (including AD), and also mitochondrial translation and dysfunction, synaptic 23 vesicle cycle and GABAergic synapse, and gene ontology terms enrichment in neuronal system, 24 transmission across chemical synapses and mitochondrial translation. 25 Overall our approach allowed us to effectively combine multiple available microarray datasets 26 and identify gene expression differences between AD and healthy individuals including full age 27 and tissue type considerations. Our findings provide potential gene and pathway associations 28 that can be targeted to improve AD diagnostics and potentially treatment or prevention. (US). 29