Active Amyloid-β Vaccination Results in Epigenetic Changes in the Hippocampus of an Alzheimer's Disease-Like Mouse Model.

Background: While evidence accumulates for a role of epigenetic modifications in the pathophysiological cascade of Alzheimer's disease (AD), amyloid-beta (A beta)-targeted active immunotherapy approaches are under investigation to prevent or slow the progression of AD. The impact of A beta active vaccines on epigenetic markers has not been studied thus far. Objective: The current study aims to establish the relationship between active immunotherapy with a MER5101-based vaccine (consisting of A beta 1-15 copies conjugated with a 7 aa spacer to the diphtheria toxoid carrier protein, formulated in a Th2-biased adjuvant) and epigenetic DNA modifications in the hippocampus of APPswe/PS1dE9 mice. Methods: As we previously reported, immunotherapy started when the mice were 10 months of age and behavioral testing occurred at 14 months of age, after which the mice were sacrificed for further analysis of their brains. In this add-on study, global levels of DNA methylation and hydroxymethylation, and DNA methyltransferase 3A (DNMT3A) were determined using quantitative immunohistochemistry, and compared to our previously analyzed immunization-induced changes in AD-related neuropathology and cognition. Results: Active immunization did not affect global DNA methylation levels but instead, resulted in decreased DNA hydroxymethylation and DNMT3A levels. Independent of immunization, inverse correlations with behavioral performance were observed for levels of DNA methylation and hydroxymethylation, as well as DNMT3A, while A beta pathology and synaptic markers did not correlate with DNA methylation levels but did positively correlate with DNA hydroxymethylation and levels of DNMT3A. Conclusion: Our results indicate that active A beta vaccination has significant effects on the epigenome in the hippocampus of APPswe/PS1dE9 mice, and suggest that DNA methylation and hydroxymethylation may be involved in cognitive functioning.