Link between 5-hydroxymethycytosine levels and poly (ADP-ribosyl)ation in human MS brain

A growing body of literature suggests that MS has an epigenetic component, which may mediate the effects of common environmental risk factors such as smoking, vitamin D deficiency and Epstein–Barr virus infection. Some of the major epigenetic modifications of DNA are its methylation and hydroxymethylation, in which the addition of a methyl or an hydroxymethyl group to the C5 cytosine position, results in the formation of 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC). The non-random distribution of these DNA modifications allows the normal flux of events during cellular life, including unwanted gene silencing or cell-specific gene expression. Abnormal genomic methylation patterns have been identified in the brains of individuals suffering from several neurodegenerative disorders. Interestingly, the global DNA methylation loss observed in MS white matter has been associated to myelin destabilization. However, the origin of epigenetic deregulation in MS brain is currently an open issue, therefore requiring urgent attention. This project aims to fill this information gap by tracing the observed DNA methylation instability in MS white matter, back to the altered expression of DNA methylation/hydroxymethylation enzymes or to an abnormal epigenetic modulation, mainly carried out by poly(ADP-ribosyl)ation events. All these possibilities are prompted by the fact that changes of 5mC/5hmC levels and by abnormal expression of DNA methylation/ hydroxymethylation enzymes are well documented alterations in several other conditions, including Alzheimer's disease and cancer. The project has not yet been concluded. Here we present initial observations concerning the global levels of the DNA methylation variants and their associated enzymes. Results indicate that normal appearing white matter of MS patients shows a global 5hmC reduction, as well as a decrease of its successive oxidation products 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC). Differential 5hmC alteration in MS vs. control samples is likely associated with the observed modulation of TET2 and IDAX gene expression, which specifically act in concert to generate 5hmC, 5fC, and 5caC via 5mC iterative oxidation. Results from this study would form the basis for future investigations aimed at establishing if these changes are linked to DNA epigenetic patterns alteration in MS, thus paving the way for the clinical use of “epigenetic” drugs in the treatment of the disease.