HUMAN ALZHEIMER´S ASTROCYTES BEARING THE APOE4/4 GENOTYPE DEVELOP A SENESCENT AND PRO-INFLAMMATORY PHENOTYPE

Alzheimer´s disease (AD) is dominated by a complex cellular pathology which involves most brain cell types with glial cells increasingly recognized as playing fundamental roles in neurodegeneration. Astrocytes, which perform essential functions in preserving brain homeostasis, present a reactive phenotype in the AD brains with still unknown consequences.
In this study, we generated and characterized human induced pluripotent stem cell (hiPSC)-derived astrocytes from AD patients harboring the APOE4/4 genotype, the greatest genetic risk factor for late-onset AD. Disease astrocytes showed a reactive phenotype. In addition, they showed altered mitochondrial network including perinuclear clustering of mitochondria, enhanced mitochondrial fusion and higher production of reactive oxygen species which, unexpectedly, were coincident with increased oxidative phosphorylation and glycolysis. As these mitochondrial features are related to the acquisition of cell senescence, we evaluated this at the transcriptome level and found that these AD-derived astrocytes significantly upregulated gene signatures of cellular senescence and displayed a senescence-associated secretory phenotype. To verify this finding, we observed senescence-related DNA damage response in a significant proportion of cells in the cerebral cortex of AD patients, with most of these cells being astrocytes. Finally, we confirmed that this astrocytic senescent and proinflammatory phenotype is associated with a reduced neuronal support, evidencing that APOE4/4 AD astrocytes present intrinsic features that may compromise brain homeostasis and promote neurodegeneration.
Addressing the causes and consequences of this astrocytic dysfunctionality should help to elucidate novel therapeutic targets able to modify the neurodegeneration present in AD.