DNA Methylation Profiles In The Hippocampus Of An Alzheimer's Disease Mouse Model At Late Stage Of Neurodegeneration

Objective: As one of the most common types of dementia,Alzheimer's disease(AD)is characterized by a progressive decline in learning and memory,visuospatial and attentional impairment,cognitive and executive dysfunction,and neuropsychiatric problems at the late stage.In correspondently,the pathological changes,especially synapse loss and neuronal degeneration occur at the first in the hippocampus.Moreover,senile plaques(SP)and neurofibrillary tangles(NFTs)are also typical pathological features.SP are mainly composed of ?-amyloid(A?),while NFTs are aggregates of hyperphosphorylated microtubule-associated tau protein.Although several hypotheses,such as cholinergic damage hypothesis,A? hypothesis,microtubule-related protein hypothesis,free radical damage hypothesis,inflammatory hypothesis,etc,have been suggested,the pathogenesis of AD is still far from clear.Recently,mounting evidence suggests that many abnormal methylated genes are related to the pathogenesis of AD.For example,aberrant methylation in presenilin-1(PS1),amyloid precursor protein(APP)and beta-site APP cleving enzyme 1(BACE1)genes have been found in early-onset Alzheimer's disease(EOAD),as well as transmembrane protein 59(TMEM59),brain-derived neurotrophic factor(BDNF)and sortilin-related receptor 1(SORL1)in late-onset Alzheimer's disease(LOAD).To date,few studies have been undertaken on a genome-wide scale to distinguish latent genes/sites involved in the disease.Here,we report DNA methylation profiles in the hippocampus of PS1/PS2 conditional double knockout(dKO)mice that show AD-like neurodegeneration since 7 months in age(early stage)together with impairment in learning and memory,progress into significant neuronal loss at the middle stage(12 months old),and massive neuronal loss and dementia-like phenotype at the late stage(18 months old).Methods: The wild-type mice and dKO mice were bred and reproduced,respectively.Genotyping of dKO mice was determined by polymerase chain reaction(PCR)analyses of tail genomic DNA.Here,we employed reduced representation bisulfite sequencing(RRBS),together with analytical tools including FastQC(v0.11.4)and Bismark(v0.7.11)softwares,to compare the difference in DNA methylation profiles in the hippocampus between dKO mice and their wild-type littermates at the late stage neurodegeneration(18 months old),and analyse the biological annotation terms and pathways of the aberrant methylated genes with Gene ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)enrichment.Results: The analysis revealed 1387 differentially methylated regions(DMRs)existed in dKO mice,representing 602 unique genes as potentially associated with AD and these methylated DNA fragments distributed in different chromosomes.And we identified 110 aberrant methylated genes with DMRs.Conclusions: There was a significant difference in DNA methylation sites between dKO mice and corresponding wild-type mice.Our results provide the first line of evidence showing that specific pattern of abnormal DNA methylation in the hippocampus is associated with the AD-like neurodegeneration at the late stage disease,and furthering our understanding on how aberrant DNA methylation is involved in AD pathology.