Using Genome Editing to Switch APOE4 to APOE3

Posted October 25, 2018

Discussion of CRISPR-Cas9 genome editing has been making the rounds of 60 Minutes, Radiolab, and the pages of the New York Times. Dr. Li-Huei Tsai, member of the Cure Alzheimer’s Fund Research Leadership Group whose work on the subject has been published in Neuron, has used this powerful technique in order to provide new insights into the single greatest risk factor for sporadic Alzheimer’s disease, the APOE4 variant. Dr. Tsai and her colleagues have used CRISPR to convert APOE4 to the normal APOE3, alleviating Alzheimer’s-related phenotypes in neurons, glia, and organoids.

Link to the Paper on Neuron website:
https://www.cell.com/neuron/fulltext/S0896-6273(18)30380-5
APOE4 causes widespread molecular and cellular alterations associated with Alzheimer’s disease phenotypes in Human iPSC-derived brain cell types

The APOE4 variant affected the transcriptional profile of induced neurons and glia

Isogenic APOE4 neurons exhibited early neuronal differentiation

Isogenic APOE4 glial cells were impaired in their ability to clear extracellular Aβ

APOE4 organoids displayed increased Aβ aggregates and hyperphosphorylation of tau

Summary

The apolipoprotein E4 ( APOE4) variant is the single greatest genetic risk factor for sporadic Alzheimer’s disease (sAD). However, the cell-type-specific functions of APOE4 in relation to AD pathology remain understudied. Here, we utilize CRISPR/Cas9 and induced pluripotent Stem cells (iPSCs) to examine APOE4 effects on human brain cell types. Transcriptional profiling identified hundreds of differentially expressed genes in each cell type, with the most affected involving synaptic function (neurons), lipid metabolism (astrocytes), and immune response (microglia-like cells). APOE4neurons exhibited increased synapse number and elevated Aβ 42 secretion relative to isogenic APOE3 cells while APOE4astrocytes displayed impaired Aβ uptake and cholesterol accumulation. Notably, APOE4 microglia-like cells exhibited altered morphologies, which correlated with reduced Aβ phagocytosis. Consistently, converting APOE4 to APOE3 in brain cell types from sAD iPSCs was sufficient to attenuate multiple AD-related pathologies. Our study establishes a reference for human cell-type-specific changes associated with the APOE4 variant.