DNA METHYLATION CHANGES IN THE RAT STRIATUM DUE TO L-DOPA TREATMENT IN A TIC ANIMAL MODEL

Background Tourette Syndrome (TS) is a neurodevelopmental disorder characterized by motor and vocal tics. The cause of TS remains elusive but dopamine (DA) has a central role within the cortico-striatal pathway. TS has high heritability and a complex genetic background, but environmental factors also play an important role in the development of the disorder. These factors often operate via epigenetic mechanisms (i.e. covalent chromatin modifications). Methods We used a rodent tic model to test the epigenetic alterations in the striatum. Juvenile male Wistar Kyoto rats were injected with 6-OH-dopamine in the left medial forebrain bundle resulting in degeneration of nigrostriatal dopaminergic neurons. Chronic application of L-DOPA after consolidation of the lesion leads to motor tics due to the striatal hypersensitivity to DA. We studied genome-wide DNA methylation by Reduced Representation Bisulfite Sequencing technique (RRBS) in 3 groups: animals undergoing lesion only, animals treated with L-DOPA after the lesion and animals co-treated with L-DOPA and riluzole (medication used in TS) after the lesion. Results Surprisingly, by investigating the striata we detected only a few DNA methylation changes between the lesioned and control sides of the brain in each group. However, when we compared the control or the lesioned striata of the three groups of animals we more abundant methylation differences. L-DOPA treatment brought about statistically significant DNA hypermethylation at over 1000 CpG sites and hypomethylation at around 300 sites genome-wide. Several dozens of genes were identified in the vicinity of hypermethylated sites, while considerably less were hypomethylated. Some of the relevant hits include genes coding for neurotransmitter transporters, such as SLC6A2 (Norepinephrine transporter), Cacna1h (Calcium channel alpha 1 h subunit), Tnfrsf8 (TNF receptor superfamily member 8), HAT1 (histone acetyltransferase 1), plus several microRNA genes. Discussion This project is a methylome study on a Tourette Syndrome animal model that may provide novel candidate genes and a better understanding of the molecular mechanisms behind the pathophysiology of TS.