Soluble oligomers of amyloid ? cause oxidative stress and alter redox/methylation-linked gene transcription by disrupting EAAT3-mediated cysteine uptake

Abstract

Depletion of GSH, oxidative stress and hyperhomocysteinemia have been linked to AlzheimerÍs disease. Recent work has shown that soluble oligomers of amyloid ?, the pathological protein of AlzheimerÍs disease, disrupts glutamate uptake via EAAT3. EAAT3 is the transporter responsible for neuronal cysteine uptake. Cysteine is the rate-limiting precursor of the antioxidant glutathione (GSH) which establishes the redox potential of a cell. Changes in redox state modify the activity of redox-sensitive enzymes such as methionine synthase, the enzyme that methylates homocysteine to methionine. Since methionine is subsequently adenosylated to S-adenosylmethionine (SAM), the major methyl donor of biological reactions including DNA methylation, methionine synthase links redox status to epigenetic regulation of gene expression. We examined the influence of soluble A? oligomers on [35S]-labeled cysteine uptake, intracellular thiol and thioester metabolism, global DNA methylation and transcription of a panel of select redox and methylation-linked genes in SH-SY5Y cells, a human neuroblastoma cell line. Soluble A? oligomers significantly decreased cysteine uptake, caused oxidative stress, and decreased the ratio of SAM to SAH which was accompanied by a decrease in global DNA methylation. Finally, soluble A? oligomers were shown to change the transcription of a number of redox and methylation-linked genes.