Insights Into the Role of DNA Methylation and Gene Expression in Graves Orbitopathy.

Context: A role of DNA methylation in Graves orbitopathy (GO) has been proposed.

Objective: This work aimed to investigate DNA methylation and gene expression in orbital fibroblasts from control and GO patients, under basal conditions or following challenge with an anti- thyrotropin (TSH) receptor antibody (M22) or cytokines involved in GO; to investigate the relationship between DNA methylation and cell function (proliferation); and to perform a methylome analysis.

Methods: Orbital fibroblasts from 6 GO and 6 control patients from a referral center underwent methylome analysis of the whole genome.

Results: Global DNA methylation increased significantly both in control and GO fibroblasts on incubation with M22. Expression of 2 selected genes (CYP19A1 and AIFM2) was variably affected by M22 and interleukin-6. M22 increased cell proliferation in control and GO fibroblasts, which correlated with global DNA methylation. Methylome analysis revealed 19 869 DNA regions differently methylated in GO fibroblasts, encompassing 3957 genes and involving CpG islands, shores, and shelves. A total of 119 gene families and subfamilies, 89 protein groups, 402 biological processes, and 7 pathways were involved. Three genes found to be differentially expressed were concordantly hypermethylated or hypomethylated. Among the differently methylated genes, insulin-like growth factor-1 receptor and several fibroblast growth factors and receptors were included.

Conclusion: We propose that, when exposed to an autoimmune environment, orbital fibroblasts undergo hypermethylation or hypomethylation of certain genes, involving CpG promoters, which results in differential gene expression, which may be responsible for functional alterations, in particular higher proliferation, and ultimately for the GO phenotype in vivo.