P4-191: PS1 promoter is regulated by methylation

Abstract

Although there are a crescent number of studies on the significance of high homocysteine levels in Alzheimer, the existence of a causal correlation is still far to be ascertained. Years ago we postulated a molecular mechanism responsible for amyloid accumulation in AD, involving changes in methylation of specific genes. We evidenced that a nutritional model of homocysteine cycle alteration could lead to increase amyloid production both in SK-N-BE neuroblastoma cells and in TgCRND8 mice (carrying a double mutated APP). Amyloid increase was due to PS1 and BACE over-expression and the consequent increase in secretase activity. Our hypothesis is that nutritional factors causing vitamin B and folate deficiency and homocysteine cycle alterations could induce a decrease in sequence-specific DNA methylation and the “aberrant” activation of genes involved in amyloid processing. The aim of the present study is to verify the hypothesised hypomethylation of PS1 promoter in SK-N-BE neuroblastoma cells and in TgCRND8 mice, in conditions of vitamin B (folate, B12 and B6) deficiency. Supplementation with S-adenosylmethionine as methyl donor represents the tentative to reverse this effect. DNA is extracted both from SK-N-BE neuroblastoma cells cultured either in control or vitamin B deficient, with or without S-adenosylmethionine 100 μM and from brains collected from TgCRND8 or wt 129SV mice grown either with control or vitamin B deficient diet, with or without oral supplementation of S-adenosylmethionine 400 μg/day. Methylation status of PS1 promoter is evaluated through bisulphite modification and genomic sequencing. Deficiency of folate, vitamin B12 and vitamin B6 induces the hypomethylation of specific CpG moieties in the 5'-flanking region of PS1 promoter with no changes in overall DNA methylation. S-adenosylmethionine is able to prevent the observed sequence-specific hypomethylation without increase in overall DNA methylation. PS1 promoter methylation status appears to be correlated with the level of gene expression. This finding allows to directly correlating the vitamin B-dependent alteration of homocysteine cycle with DNA methylation and clearly evidences that PS1 promoter is regulated by methylation status of specific CpG moieties.