PSEN1ΔE9, APPswe, and APOE4 Confer Disparate Phenotypes in Human iPSC-Derived Microglia

Abstract

SummaryHere we elucidate the effect of Alzheimer disease (AD)-predisposing genetic backgrounds, APOE4, PSEN1ΔE9, and APPswe, on functionality of human microglia-like cells (iMGLs). We present a physiologically relevant high-yield protocol for producing iMGLs from induced pluripotent stem cells. Differentiation is directed with small molecules through primitive erythromyeloid progenitors to re-create microglial ontogeny from yolk sac. The iMGLs express microglial signature genes and respond to ADP with intracellular Ca2+ release distinguishing them from macrophages. Using 16 iPSC lines from healthy donors, AD patients and isogenic controls, we reveal that the APOE4 genotype has a profound impact on several aspects of microglial functionality, whereas PSEN1ΔE9 and APPswe mutations trigger minor alterations. The APOE4 genotype impairs phagocytosis, migration, and metabolic activity of iMGLs but exacerbates their cytokine secretion. This indicates that APOE4 iMGLs are fundamentally unable to mount normal microglial functionality in AD.

Tackling challenges in care of Alzheimer's disease and other dementias amid the COVID‐19 pandemic, now and in the future

“…In the brain, ApoE4 is known to exacerbate microgliamediated neuroinflammation and subsequent neurodegeneration. 18,19 Peripherally, ApoE4 has also been shown to increase macrophage production of cytokine (eg, interleukin 6, tumor necrosis factor, compared to E2 or E3) in response to proinflammatory stimuli. 20 As cytokine storm is thought to account for COVID-19 disease manifestations, ApoE genotype may thereby augment disease severity by impacting host immune response.…”

WITHDRAWN: Apolipoprotein E4 expressed by microglia impairs microglial functions and enhances neurotoxicity

“…In Tarja Malm [94], Li-Huei Tsai [95] and Julia TCW (preprint, bioRxiv, doi: https://doi.org/10.1101/713362)'s studies using human iPSC-derived microglia models, they observed a dysfunctional or impaired phenotype of APOE4 iPSC-derived microglia when compared with that of APOE3, indicating that APOE4 might contribute to AD risk via dysregulating microglia. However, the opposite conclusion has been reported in another study performed with an murine microglial cell line [96].…”

Emerging Developments in Human Induced Pluripotent Stem Cell-Derived Microglia: Implications for Modelling Psychiatric Disorders With a Neurodevelopmental Origin

“…Third, the protocol should be reproducible and reliable, within and between laboratories. On this point, there has been a limited effort to compare MGLs generated in any given protocol, to those generated by another, for example at the level of transcriptional profiling by RNA sequencing (115). A systematic comparison of such data across all protocols however, to the best of our knowledge, has yet to be performed.…”

“…So far however, this only considers simple 2D monocultures of MGLs. This does offer the advantage of studying microglia phenotypes without interference from other cell types, as exemplified by recent work in the context of neurodegenerative diseases (63,115). It may equally be argued however, that important phenotypic information is also lost due to the absence of interactions with other cell types including neurons and astrocytes, which is also required for evaluation of synaptic pruning (116).…”

“…Another key characteristic of an "ideal" hiPSC-microglia model is that it should be genetically modifiable. Advances in genome editing have rendered it potentially straightforward to assay genotype differences due to single gene mutations of disease relevant genes, with appropriate isogenic control lines as reported recently for Alzheimer's disease (AD) relevant genetic variants using MGL monocultures (63,115). This has, to the best of our knowledge yet to be extended to neuron-microglia co-culture models.…”