Parkinson's disease (PD) is a neurodegenerative disorder for which environmental factors influence disease risk and may act via an epigenetic mechanism. The microtubule-associated protein tau (MAPT) is a susceptibility gene for idiopathic PD. Methylation levels were determined by pyrosequencing of bisulfite-treated DNA in a leukocyte cohort (358 PD patients and 1084 controls) and in two brain cohorts (Brain1, comprising 69 cerebellum controls; and Brain2, comprising 3 brain regions from 28 PD patients and 12 controls). In vitro assays involved the transfection of methylated promoter-luciferase constructs or treatment with an exogenous micronutrient. In normal leukocytes, the MAPT H1/H2 diplotype and sex were predictors of MAPT methylation. Haplotype-specific pyrosequencing confirmed that the H1 haplotype had higher methylation than the H2 haplotype in normal leukocytes and brain tissues. MAPT methylation was negatively associated with MAPT expression in the Brain1 cohort and in transfected cells. Methylation levels differed between three normal brain regions (Brain2 cohort, putamen < cerebellum < anterior cingulate cortex). In PD samples, age at onset was positively associated with MAPT methylation in leukocytes. Moreover, there was hypermethylation in the cerebellum and hypomethylation in the putamen of PD patients compared with controls (Brain2 cohort). Finally, leukocyte methylation status was positively associated with blood vitamin E levels, and the effect was more significant in H2 haplotype carriers; this result was confirmed in cells that were exposed to 100 μM vitamin E. The significant effects of sex, diplotype, and brain region suggest that hypermethylation of the MAPT gene is neuroprotective by reducing MAPT expression. The effect of vitamin E on MAPT represents a possible gene-environment interaction.
Keywords: DNA methylation; Parkinson's disease; microtubule-associated protein tau; vitamin E.
© 2013 International Parkinson and Movement Disorder Society.