RXR controlled regulatory networks identified in mouse brain counteract deleterious effects of Aβ oligomers.

Bexarotene, a selective agonist for Retinoid X receptors (RXR) improves cognitive deficits and amyloid-β (Aβ) clearance in mice. Here we examine if the effect of bexarotene on RXR cistrome and transcriptomes depend on APOE isoform and Aβ deposition. We found bexarotene increased RXR binding to promoter regions in cortex of APOE3 mice. Rho family GTPases and Wnt signaling pathway were highly enriched in ChIP-seq and RNA-seq datasets and members of those pathways - Lrp1, Lrp5, Sfrp5 and Sema3f were validated. The effect of APOE isoform was compared in APOE3 and APOE4 mice and we found significant overlapping in affected pathways. ChIP-seq using mouse embryonic stem cells and enrichment levels of histone marks H3K4me3 and H3K27me3 revealed that, bexarotene induced epigenetic changes, consistent with increased neuronal differentiation and in correlation with changes in transcription. Comparison of transcriptome in APOE3 and APP/APOE3 mice revealed that amyloid deposition significantly affects the response to bexarotene. In primary neurons, bexarotene ameliorated the damaged dendrite complexity and loss of neurites caused by Aβ42. Finally, we show that the disruption of actin cytoskeleton induced by Aβ42 in vitro was inhibited by bexarotene treatment. Our results suggest a mechanism to establish RXR therapeutic targets with significance in neurodegeneration.