Hippocampal DNA Methylation Profiling At The Early Stage Of Neurodegeneration In An AD Model In Mice With Presenilin-1/presenilin-2 Conditional Double Knockout

Objective: One of the most important pathological changes in the brain of Alzheimer’s disease(AD) is neuronal loss in certain specific regions such as the hippocampus and cerebral cortex. The clinical symptoms range from learning and memory deficit at the early stage, cognitive dysfunction, to dementia at the late stage. Despite that several hypotheses, such as cholinergic deficit, β-amyloid(A?)-cascade, tau pathology, free radicals damage, genetic variants, etc, have been suggested, the exact pathological mechanisms are still elusive. Recently, accumulating evidence has indicated that aberrant DNA methylation changes are implicated in the pathogenesis of AD. For example, abnormal methylation in TMEM59, SORL1, and apoe gens has been noted in AD. However, this type of studies is very difficult to be conducted at the early stage of AD in human subjects. Here, we used a validated AD model in mice, in which presenilin-1(PS1) was conditionally knocked out sine 6 months of age in neurons of the forebrain, and presenilin-2(PS2) was conventionally knocked out since the first ontogenesis, simply called dKO mice. This AD model is characterized by progressive, or age-dependent, neuronal loss, age-dependent accumulating hyperphosphorylated tau protein, neurofillament tangle-like structures, intracellular filaments, learning and memory deficits, and dementia-like phenotype at the late stage. With this AD model, we investigated genome-wide methylation profiling in the hippocampus at the early neurodegenerative stage. Methods: The wild-type(wt) mice and dKO mice were bred and reproduced respectively. The genotypes of mice were determined by PCR analysis with genomic DNA from tails of mice. The mice used in this study were all at the age of 7 months. The genomic DNA was extracted from the hippocampus of both d KO and control mice. The distribution and pattern of DNA methylation were determined with a reduced representation bisulphite sequencing(RRBS), and were analyzed with a biological software. Results: In this study, we have succeeded in breeding and reproducing dKO mice. By using Bismark(vO.7.4)software to compare with the reference genome sequence of mouse and using DAVID online site to analyze genes GO and KEGG. We identified 30 genes with abnormal methylated regions(DMR), 1338 aberrant methylated sites distributed on different chromosomes that show involvements of 873 genes. Conclusion: In this study, we obtained the global information of aberrant methylated genes of dKO mice by using RRBS, which provides an important basis for establishing genomic DNA methylation profiling map and getting aberrant methylated genes, as well as clues that may be used in the early prevention, diagnosis and treatment of Alzheimer’s disease.