Multilayer OMICS characterization of APOE‐modulated isogenic hiPSCs elucidates cell‐type–specific mechanisms modified by APOE: A study of the IMI ADAPTED Consortium

Abstract

AbstractBackgroundAlzheimer’s Disease (AD) is the most common cause of dementia in the elderly and affects over 35 million people worldwide, imposing increasing social and economic burden as the population ages. While it is widely known that the most prominent genetic risk factor for AD is the presence of the Apolipoprotein E (APOE) ε4 allele, the effects of APOE in the development of AD is still poorly understood. As part of the IMI ADAPTED consortium, we aim to clarify the role of APOE as a risk factor in the development of AD. Here we present an in‐depth analysis of the effect of the APOE genotype on the transcriptome of brain cells derived from human‐induced pluripotent stem cells (hiPSCs).MethodIsogenic hiPSC lines were modified to carry different APOE genotypes: ε3/ε3, ε4/ε4, ε3/ε4, ε2/ε2, as well as an APOE knock‐out (KO) cell line. Lines carrying each of these genotypes were differentiated into distinct cell types. Differential gene expression (DGE) and protein expression (DPE) was calculated, followed by gene set enrichment. Clustering approaches were used to identify shared and differing gene signatures across genotypes. We further applied upstream regulator and network analysis on the individual cell‐type results and integrated these results across cell types. The results were compared with DGE and DEP results from an APOE mouse model. Finally, the identified genes and mechanisms were combined with the results of data from postmortem human brain samples of AD cases and controls.ResultsThe observed transcriptional changes confirmed phenotypic observations made for the hiPSCs and refined the insight of genes identified human brain OMICS data. Several genes and pathways were identified, which showed consistent gene expression on transcriptome and proteome level. Further, shared patterns of expressions of genes across genotypes and potential mechanisms involved in this were detected.ConclusionsIn depth transcriptomics and proteomics analysis of APOE modified hiPSCs enabled to study cell type specific effects and contributed with this to the understanding of mechanisms affected by different APOE genotypes.