Identification of APOE phenotypes in microglia and neurons derived from isogenic hips cells: A study of the IMI ADAPTED consortium

Abstract

AbstractBackgroundOne of the most prominent genetic risk factors for Alzheimer’s Disease (AD) is the Apolipoprotein E (APOE) ε4 allele. Unlike the “neutral” ε3 variant, or the protective ε2variant, the ε4 variant is strongly associated with late‐onset AD, albeit by mechanisms that are not well‐understood.MethodsTo shed light on the biology of APOE in the development of AD, as part of the IMI (Innovative Medicines Initiative) consortium “ADAPTED”, we acquired two human induced pluripotent stem cell (hiPSC) lines, that were isogenically modified to carry the alleles ε2/ε2, ε3/ε3, ε3/ε4, ε4/ε4, as well as a knockout line. Neurons and the phagocytic cells of the CNS, the microglia were differentiated from all ten lines and subjected to thorough phenotyping, including RNA‐seq and proteomics analysis.ResultsCortical neurons do not secrete apoE under normal conditions and treatment of these cells with microglia‐enriched factors and apoE increased their overall Abeta secretion, without significant differences between the various genotypes. Microglia, on the other hand, secrete large amounts of apoE in varying quantities depending on the APOE genotype. Additionally, microglia carrying the ε4/ε4 genotype have a significantly reduced phagocytic capacity compared to their ε3/ε3 counterparts. These observations were supported by whole transcriptome sequencing, which revealed major differences in inflammatory and phagocytic activity‐related gene expression between the different APOE genotypes.ConclusionsThis unique set of ten isogenic hiPSC lines enabled us to assess the cellular phenotypes in functional human neuronal cells. Microglia omics show changes in an array of AD‐relevant pathways, and being the main producers of apoE, these changes need to be understood in depth. Follow‐up experiments will validate candidate genes that might help design new therapies for APOE ε4 AD patients. Disclosure: This project has received funding from the Innovative Medicines Initiative 2 Joint Undertaking under grant agreement No 115975. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme and EFPIA. This study was sponsored by AbbVie Deutschland GmbH & Co. KG. AbbVie contributed to the study design, research, and interpretation of data, writing, reviewing, and approving the abstract. Some authors are currently employed by AbbVie and may own AbbVie stock.