POS0361 DNA METHYLATION SIGNATURES CHARACTERIZE PSORIASIS AND PSORIATIC ARTHRITIS IN MONOZYGOTIC TWINS DISCORDANT FOR THE DISEASE
Background:Psoriatic disease is a chronic inflammatory disorder spanning from skin disease (psoriasis) to psoriatic arthritis (PsA). The genetic background is insufficient to explain disease onset as illustrated by not very informative Genome Wide Association Studies and monozygotic (MZ) twin studies recently performed. It is strongly assumed that epigenetics may contribute to disease susceptibility modulating gene expression. DNA methylation has been found involved in several autoimmune inflammatory rheumatic diseases. Here we have analysed the DNA methylation profile of a selected cohort of MZ twins discordant for psoriasis/PsA.Objectives:To identify the methylome associated with psoriasis and PsA in the peripheral blood of MZ twins discordant for these conditions.Methods:Peripheral blood from 7 couples of MZ twins discordant for psoriatic disease was collected and DNA extracted for a genome-wide evaluation of the DNA methylation profile, with the Infinium MethylationEPIC BeadChip. Minfi and the packages of the Bioconductor were used to analyse the data obtained. Quality control and exclusion criteria were applied to the raw data having a final number of 762.451 probes, which accounts for 88% of the total.Results:The approach first identified 2564 differentially methylated positions (DMPs; *p<0.005) with 19 genes potentially affected (with at least two DMPs within 1 kb of distance), including SMAD3 and SMARCA4/BRG1 involved in the Interferon and TGFβ pathways. Gene Ontology (GO) analysis of DMP-associated genes showed a significative enrichment (*p<0.005) in transcription factor binding, transcription corepressor and transcription coactivator activity, SMAD binding and histone -lysine-N-methyltransferase activity. To further validate the results, 5’-methylcytosine immunoprecipitation (MedIP) followed by Real Time PCR was performed to assess the methylation level of SMAD3 and SMARCA4/BRG1 promoters in the same cohort of MZ twins. We found significantly DNA methylation enrichment in SMARCA4/BRG1 promoter in psoriatic disease twins (p<0.05). SMAD3 and SMARCA4/BRG1 mRNA expression was also assessed to evaluate any inverse correlation with promoter methylation level, on the MZ cohort used for the EPIC array (n=4) and on a cohort of PsA/Ps patients (n=8) and appropriate healthy controls (n=3). Reduced mRNA expression (p<0.05) was demonstrated for SMARCA4/BRG1 (n=4). Conversely, no changes were found for SMAD3.Conclusion:We report the first DNA methylation approach in MZ twins discordant for psoriatic disease. We believe that the observed changes in SMAD3 and SMARCA/BRG1 genes may suggest an epigenetic imbalance of chromatin remodelling factors involved in inflammation pathways with a potential role in PsA/psoriasis immunopathogenesis.Disclosure of Interests:None declared