Homocysteine modulates 5‐lipoxygenase expression level via DNA methylation

Summary Elevated levels of homocysteinemia (Hcy), a risk factor for late‐onset Alzheimer's disease ( AD ), have been associated with changes in cell methylation. Alzheimer's disease is characterized by an upregulation of the 5‐lipoxygenase (5 LO ), whose promoter is regulated by methylation. However, whether Hcy activates 5 LO enzymatic pathway by influencing the methylation status of its promoter remains unknown. Brains from mice with high Hcy were assessed for the 5 LO pathway and neuronal cells exposed to Hcy implemented to study the mechanism(s) regulating 5 LO expression levels and the effect on amyloid β formation. Diet‐ and genetically induced high Hcy resulted in 5 LO protein and mRNA upregulation, which was associated with a significant increase of the S ‐adenosylhomocysteine (SAH)/ S ‐adenosylmethionine ratio, and reduced DNA methyltrasferases and hypomethylation of 5‐lipoxygenase DNA . In vitro studies confirmed these results and demonstrated that the mechanism involved in the Hcy‐dependent 5 LO activation and amyloid β formation is DNA hypomethylation secondary to the elevated levels of SAH. Taken together these findings represent the first demonstration that Hcy directly influences 5 LO expression levels and establish a previously unknown cross talk between these two pathways, which is highly relevant for AD pathogenesis. The discovery of such a novel link not only provides new mechanistic insights in the neurobiology of Hcy, but most importantly new therapeutic opportunities for the individuals bearing this risk factor for the disease.