Track: Discovery and Basic Research - Biology - Cellular and Molecular Pathways
Category: Poster Abstract
The BHMT-betaine Methylation Pathway Plays a Role in Oligodendrocyte Maturation under Oxidative Stress
Purpose: Multiple Sclerosis (MS) is a demyelinating disease of the central nervous system wherein oligodendrocytes are killed off and myelin production is halted, with progenitor cells (OPCs) unable to differentiate. Prior studies have implicated aberrant DNA and histone methylation in MS disease pathogenesis. We have previously reported methionine metabolism dysregulation in MS; the methyl donor betaine is depleted and is linked to changes in histone H3 trimethylation (H3K4me3) in neurons. However, activation of the betaine homocysteine methyltransferase (BHMT)–betaine pathway contributes to epigenetic changes on histone H3 and alleviates neurological deficits in the cuprizone and EAE models of MS. The role of the BHMT-betaine pathway in oligodendrocytes is not known. The purpose of this study was to investigate the role of BHMT and the BHMT-betaine methylation pathway in oligodendrocytes. Methods: To determine BHMT localization in oligodendrocytes, immunofluorescence was performed on primary rat oligodendrocytes, human MO3.13 oligodendrocytes, and postmortem human MS brain tissue with antibodies to BHMT and oligodendrocyte lineage markers. To identify the effects of betaine administration on gene expression, qRT-PCR analyses were performed with RNA isolated from MO3.13 oligodendrocytes treated with 400 µM sodium nitroprusside (SNP) and/or 1 mM betaine. Histone and DNA methyltransferase activity assays were done with MO3.13 oligodendrocyte nuclear lysates treated with BHMT-targeting siRNA and/or 1 mM betaine. Results: The BHMT enzyme is present in the nucleus of primary rat oligodendrocytes, human MO3.13 oligodendrocyte cells, and oligodendrocytes in postmortem MS brain. BHMT expression is increased under conditions of SNP-induced oxidative stress, and betaine increases oligodendrocyte differentiation factors under these conditions of stress. Activity assays indicate histone and DNA methylation are increased significantly following betaine administration, and these effects were shown to be dependent upon BHMT expression following siRNA knockdown. Conclusion: The presence of BHMT in the nucleus of oligodendrocytes indicates a potential for modulation of gene expression as seen in neurons. QRT-PCR analyses suggest that the BHMT-betaine pathway is activated under conditions of oxidative stress and influences oligodendrocyte-specific gene expression. In addition, the BHMT-betaine pathway is responsible for modulating total DNMT activity and HMT activity on H3K4, and betaine administration increases these activities in MO3.13 oligodendrocytes. This is the first report of BHMT expression in oligodendrocytes and suggests that betaine acts through BHMT to modulate histone and DNA methyltransferase activity on chromatin. These data suggest that methyl donor availability can impact epigenetic changes and maturation in oligodendrocytes.