A CLU/APOJ GWAS AD risk variant suppresses the astrocytic response to plaques and reduces axonal and neuritic damage in 5xFAD mice

Abstract

AbstractBackgroundGenome‐Wide Association Studies (GWAS) implicate clusterin (CLU, also known as apolipoprotein J) as a risk factor for late‐onset Alzheimer’s disease (LOAD), with elevated expression of CLU being associated with increased risk of LOAD. The region surrounding the SNP risk allele rs2279590 is poorly conserved within the mouse genome. Consequently, to model the effect of the rs2279590 risk allele on development of AD‐related pathology in mice we developed mice with a partially humanized allele of Clu.MethodCRISPR was used to substitute a 2kb region of human CLU (intron 7 to exon 9) containing the enhancer region and the rs2279590 SNP variant for the orthologous region of Clu within the C57BL/6J mouse genome. Clu‐rs2279590_h2kb mice were crossed with 5xFAD mice and aged to 4 and 12. Coronal brain sections were immunolabeled to visualize dense‐core plaques (ThioS), microglia (IBA1), astrocytes (S100β and GFAP), axonal (NfL) and neuritic (LAMP1) damage, confocal images of subiculum and cortical regions were taken and analyzed using Imaris software. In addition, brain Aβ and plasma NfL levels were quantified using meso scale discovery technology.Result5xFAD;Clu‐rs2279590_h2kb showed significantly reduced microglial density compared to 5xFAD mice in both brain areas at 4 months. By 12 months of age, microglial density was comparable between genotypes in cortex while in subiculum, elevated IBA1 cell density was observed in 5xFAD;Clu‐rs2279590_h2kb mice. Clu‐rs2279590_h2kb variant in 5xFAD background increased the density of S100β astrocytes in subiculum at 4 months and decreased the total S100β volume at 12 months. Reduced GFAP (reactive astrocytes) levels were found in cortex but not subiculum at 12 months. Despite comparable plaque load and insoluble Aβ42 levels, neuritic and axonal damage was decreased in the brain of 5xFAD;Clu‐rs2279590_h2kb compared to 5xFAD mice at 12 months. Plasma NfL was also significantly decreased.ConclusionDespite the minimal impact on Aβ plaque deposition, humanization of 2kb of Clu allele and introduction of rs2279590 risk SNP suppresses astrocytic response to plaques and is protective against axonal and neuritic damage which is mirrored by the reduced levels of plasma NfL.