DNA methylation patterns of genes related to immune response in the different clinical forms of oral lichen planus

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Lichen planus is a chronic immunoinflammatory mucocutaneous disease,1 which can affect the skin, mucous membranes, scalp and nails.2 It affects about 0.5% to 2% of the population1 and is classified by the World Health Organization (WHO) as a potentially malignant lesion.1 Oral lichen planus (OLP) lesions may precede the disease in other locations or can occur as a single manifestation of the disease. It can manifest in six different clinical forms: reticular, plaque, papular, erosive, atrophic and bullous1 (Figure 1A). Histopathologically, OLP shows degeneration of the basal layer in addition to subepithelial T lymphocytes infiltration5 (Figure 1B).
The events involved in the aetiopathogenesis of OLP are complex, resulting from the dysregulation of the immune system caused by the interaction between genetic and environmental factors.6 Epigenetics comprises of the study of the interplay between environmental factors and the patterns of gene expression in cells.7 DNA methylation is an epigenetic mechanism that regulates gene expression through effective inhibition of genomic transcription by adding a methyl group at the 5′‐position of the cytosine ring.8
Previous studies found a hypermethylated profile of the promoter regions of the microRNA miR‐1379 and the p16 gene10 in OLP compared to in normal mucosa. In oral carcinogenesis, both miR‐137 and p16 gene are known to participate in cell cycle control.11 In another study, evaluation of the global methylation in lichenoid lesions, including OLP, showed no difference compared to the methylation levels in normal mucosa.13 Although the information regarding DNA methylation in OLP immunoinflammatory response is scarce,8 such phenomenon is being currently studied in several other inflammatory processes, including inflammatory periapical lesions,14 systemic lupus erythematosus15 and Addison's disease.16 Here, we hypothesise that the DNA methylation profile of genes related to immune response varies according to the clinical forms of OLP, harbouring different DNA methylation patterns when compared to healthy, normal oral mucosa.

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