Distinct cultured microglia characteristics distinguish cognitive SuperAgers from their cognitively normal peers

Abstract

AbstractBackgroundSuperAgers are individuals ≥80 years with exceptional episodic memory equal to or better than individuals 20 to 30 years their junior. SuperAgers display resistance to age‐related neurofibrillary degeneration. Qualitative observations suggested that SuperAger cultured microglia display higher rates of proliferation compared to age‐matched controls. The purpose of this study was a comprehensive and quantitative investigation of potential differences between SuperAger and control microglia.MethodApproximately 6.6×103 microglia from the frontal cortex of 5 SuperAgers and 5 controls were seeded and allowed to proliferate to 80% confluence prior to passage (P). Number of cells at confluence, number of days to confluence, and highest passage reached were recorded. Gene expression profiles were investigated in P4 cultures. RNASeq libraries were prepared using the Lexogen QuantSeq 3’ RNA Library kit and assessed using the Agilent High Sensitivity DNA chip. Bioinformatic analysis was performed using the BlueBee integrated data analysis pipeline. Microglia function was assayed through uptake of fluorescently tagged oligomeric and fibrillar amyloid‐β (Aβ42) and production of reactive oxygen species (ROS) in response to the two Aβ conformations.ResultAt each passage, SuperAger cultures contained greater numbers of microglia when compared with controls (by 150% at P5, p<0.01) and reached 80% confluent faster (by 108%). On average, control microglia ceased proliferating at P9, while SuperAger microglia proliferated up to P12. RNAseq analysis identified 434 genes differentially expressed in the two groups (p<0.05). Upregulated genes in SuperAgers included genes involved in DNA repair and in membrane trafficking. SuperAgers exhibited downregulation of several transcripts involved in age‐related disease pathogenesis, including Adap2, MAP2, RBM20, CNTN3, and genes that regulate mitochondrial oxidative burst. Preliminary functional analysis revealed more efficient uptake and response to oligomeric when compared with fibrillar Aβ. SuperAger microglia displayed greater ROS production when compared with controls. No differences were observed in Aβ uptake.ConclusionThese results point to distinct characteristics of microglia that may contribute to the biological bases of the SuperAging phenotype. Upregulation of genes involved in DNA repair is likely to slow microglia senescence, allowing increased proliferation in SuperAgers. Additional studies are needed to validate and extend these findings.