APOE 4/4 promotes dysfunctional and inflammatory phenotypes concomitant with impaired maturation of hiPSC-derived astrocytes
TL;DR
The results indicate that APOE 4/4 alters astrocyte morphological and molecular maturation while promoting inflammation, disturbing glutamate and Aβ handling under basal conditions and suggests that APOE ε4/ε4 genotype disrupts astrocyte development and key processes of cellular homeostasis early in Alzheimer’s disease etiopathology.
Abstract
Alzheimer’s disease (AD) is the leading cause of dementia in the aging population, with the ε4 allele of apolipoprotein E (APOE) being the strongest genetic risk factor. Although astrocytes are a major source of APOE, how APOE alleles affect astrocyte maturation and function remains unclear. We generated human induced pluripotent stem cell (hiPSC)-derived astrocytes from AD patients carrying ε3/ε3 and ε4/ε4 alleles and from healthy controls (HC). We also used isogenic gene-edited hiPSC lines homozygous for each APOE allele and an APOE knock-out line to identify allele-specific phenotypes and distinguish gain- from loss-of-function mechanisms. APOE 4/4 astrocyte cultures showed significant reductions in GFAP- and S100β-positive cell percentages compared to APOE 2/2 and APOE 3/3, with no changes in GLT-1- and AQP4-positive cells. Astrocytes of all genotypes responded to IL-1β + TNFα by increasing proinflammatory cytokine expression and release, and to both IL-1β + TNFα and Aβ1-42 by changing morphology, with APOE 4/4 astrocytes showing increased IL6 mRNA and morphological branching upon IL-1β + TNFα stimulation. Notably, under basal conditions, APOE 4/4 astrocytes showed significant reductions in glutamate uptake capacity and cell size alongside increased IL-6 release and CXCL3 mRNA expression. In Aβ1-42 uptake experiments, the proportion of Aβ+astrocytes was higher in APOE 4/4 than in APOE KO cultures. Most phenotypes were absent in APOE KO astrocytes, suggesting that the effects of APOE 4/4 were predominantly mediated through gain-of-function mechanisms. Our results indicate that APOE 4/4 alters astrocyte morphological and molecular maturation while promoting inflammation, disturbing glutamate and Aβ handling under basal conditions. It suggests that APOE ε4/ε4 genotype disrupts astrocyte development and key processes of cellular homeostasis early in Alzheimer’s disease etiopathology.
