Inhibitory roles ofApolipoprotein EChristchurch astrocytes in curbing tau propagation using human pluripotent stem cell-derived models

Genetic variants in the apolipoprotein E ( APOE ) gene affect the onset and progression of Alzheimer's disease (AD). The APOE Christchurch ( APOE Ch) variant has been identified as the most prominent candidate for preventing the onset and progression of AD. In this study, we generated isogenic APOE3 Ch/ 3 Ch human-induced pluripotent stem cells (iPSCs) from APOE3 / 3 healthy control female iPSCs and induced them into astrocytes. RNA expression analysis revealed the inherent resilience of APOE3 Ch/ 3 Ch astrocytes to induce a reactive state in response to inflammatory cytokines. Moreover, cytokine treatment changed astrocytic morphology with more complexity in APOE3 / 3 astrocytes, but not in APOE3 Ch/ 3 Ch astrocytes, indicating resilience of the rare variant to a reactive state. Interestingly, we observed robust morphological alterations containing more intricate processes when cocultured with iPSC-derived cortical neurons, in which APOE3 Ch/ 3 Ch astrocytes reduced complexity compared with APOE3 / 3 astrocytes. To assess the impacts of tau propagation effects, we next developed a sophisticated and sensitive assay utilizing cortical neurons derived from human iPSCs, previously generated from donors of both sexes. We showed that APOE3 Ch/ 3 Ch astrocytes effectively mitigated tau propagation within iPSC-derived neurons. This study provides important experimental evidence of the characteristic functions exhibited by APOE3Ch/3Ch astrocytes, thereby offering valuable insights for the advancement of novel clinical interventions in AD research.