Chromosome Y‐haplotype mediates cognitive resilience and differential expression of transposable elements in 5xFAD‐carrying AD‐BXD males

Abstract

AbstractBackgroundIn Alzheimer’s disease (AD), risk factors and clinical progression differ between sexes. Men have lower post‐diagnosis life‐expectancies 1,2, while women display worsened cognitive decline than men with similar neuropathology3‐5 or shared genetic risk6,7. Investigation of sex‐specific genetic contributions to AD has largely focused on the X‐chromosome, but emerging evidence has also linked somatic Y‐chromosomal instability to age‐linked disease outcomes, including AD8‐10. Notably, the Y‐chromosome contains few coding genes, but is enriched with transposable elements (TEs)11, enigmatic DNA sequences capable of introducing variation into the genome12. Differential expression of TEs has recently been reported in AD13‐15. We hypothesize that TEs could contribute to sex‐specific variation observed in AD onset and progression.MethodHere, we utilized bulk hippocampal RNAseq and contextual fear memory (CFM) data from a 28‐strain AD‐BXD dataset comprised of male and female 5xFAD‐carrying animals and non‐transgenic (Ntg) littermates to investigate whether expression of coding genes and/or TEs contribute to AD‐relevant sex differences and cognitive outcomes. Data were stratified by sex and Y‐chromosome haplotype (C57BL/6J‐type vs. DBA/2J‐type). TEs were quantified in RNAseq data using TETranscripts16. For each TE, we predicted genomic localization using DFAM17, and calculated sex‐specific heritability.ResultIn 5xFAD animals, C57BL/6J‐type males significantly out‐performed both DBA/2J‐type males and females on a CFM task (Fig.1). TEs identified in this dataset were differentially expressed due to both sex and Y‐chromosome haplotype in 5xFAD animals (Fig.2). Interestingly, Y‐haplotype did not affect Y‐chromosome coding gene expression. We calculated that a large portion of TEs identified in our dataset are highly heritable, with differential heritability associated with sex and 5xFAD‐transgene status (Fig.3)ConclusionWe report that the C57BL/6J Y‐chromosome confers cognitive resilience in 5xFAD males, which may undermine the utility of models maintained on a homogenous C57BL/6J background as tools for investigating age‐related cognitive decline. We speculate that differential TE expression/activity between Y‐haplotypes and between sexes may account for differential resilience, but further investigation is needed to establish this link directly. Finally, our data suggest that not only are TEs likely influencers of AD risk and disease progression, but that TE expression in disease states may be heritable, rather than stochastically induced.