Abstract
The Apolipoprotein-E4 allele (APOE) is the strongest genetic risk factor for sporadic Alzheimer’s disease but its role in disease pathogenesis is incompletely understood. The APOE gene encodes Apolipoprotein E (ApoE). Astrocytes are the main source of ApoE in the central nervous system (CNS) and are essential for homeostasis in health and disease. In response to CNS insult, a coordinated multicellular inflammatory response is triggered causing reactive astrogliosis with changes in astrocytic gene expression, cellular structure and function.
Human embryonic stem-cells with the ‘neutral’ APOE33 genotype were edited using CRISPR Cas-9 gene-editing to create isogenic APOE lines with an APOE44 genotype. Quiescent astrocytes were differentiated then stimulated with TNF-α, IL1α and C1q inducing an astrogliotic A1 phenotype. Several potentially pathological APOE44-related phenotypes were identified in both quiescent cells and reactive A1 astrocytes including significantly decreased phagocytosis, impaired glutamate and a defective immunomodulatory response.
In quiescent APOE44 astrocytes there was significantly decreased secretion of IL6, IL8 and several oxylipins. In A1 astrocytes there was a pro-inflammatory phenotype in APOE44 astrocytes with increases in GRO, ENA78, IL6 and IL8, a decrease in IL10 as well as significant differences in oxylipin expression. As TNF-α induced signaling in astrocytes is driven by Nuclear factor kappa B (NF-κB) proteins of this pathway were measured. Significantly higher levels of the p50, p65 and IκBα sub-units were found in both quiescent and A1 APOE44 astrocytes. This suggests that perturbation of NF-κB signaling may contribute to the damaging APOE44 cell phenotypes observed providing a new direction for targeted disease therapeutics.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Competing Interest Statement: None.
Data availability statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.
The addition of Branduff McAllister as an author. Data availability statement included. Figure 1A revised. Figure 3B revised. Figure 4C revised.