DNA methylation level of the neprilysin promoter in Alzheimer's disease brains

Neprilysin (NEP), a membrane-bound metalloprotease, has been shown to play an essential role in the clearance of amyloid beta (A beta) peptides. Previous studies have reported that NEP expression is downregulated in the normal aging brain as well as in the Alzheimer's disease (AD) brain, providing evidence that the downregulation of NEP expression contributes to the age-dependent deposition of A beta-containing plaques, a pathological hallmark of AD. However, the mechanisms underlying the downregulation remain unclear. In this study, we explored the relationship between DNA methylation status of CpG islands in the NEP promoter and its expression level in AD brains. We performed pyrosequencing analyses to detect the DNA methylation level in 31 postmortem AD brains and 40 normal control brains. All 30 CpG sites showed no clear difference in methylation level. To further focus on methylation changes specific to neuronal cells, we performed methylation array experiments using neuronal nuclei from postmortem brains and found no clear difference in the methylation level between AD and normal control samples. Our detailed analyses, with a substantial number of brain samples, provide the first convincing evidence that DNA methylation of the NEP promoter is not involved in AD development and progression.