Characterization of the Regulation of DNA Methylation in Periodontal Diseases

Objectives: Gingivitis and periodontitis are infectious diseases caused by bacteria colonizing the tooth. Several factors have been suggested to contribute to disease progression, including epigenetic factors. DNA methylation (5mC) is an important epigenetic mechanism in the regulation of gene expression and has been suggested to be a key factor in inflammation. Evolving evidence suggests that TET2 protein-mediated 5mC oxidation into 5-hydroxymethylation (5hmC) contribute to dynamic changes in DNA methylation levels. The influence of DNA methylation in periodontal diseases is not fully understood. The aims of the present study are therefore to analyze the regulation of DNA methylation in periodontal diseases.
Methods: 24 subjects with generalized, severe periodontitis and 14 subjects with gingival inflammation but no attachment loss were recruited. Gingival biopsies were collected from inflamed sites and prepared for immunohistochemical analysis of 5mC, 5hmC, TET2 and DNMT1. Total RNA was extracted from paraffin-embedded biopsies and gene expression for TET2 was analyzed using qPCR. Peripheral blood samples were also collected from each subject, analyzed for global 5mC and 5hmC levels and compared to those found in gingival biopsies.
Results: In periodontitis lesions 14%±9% of the cells were positive for 5mC while 14%±7% of cells were 5hmC positive. The corresponding numbers for gingivitis lesions were 11%±4% and 12%±4%. A significant difference was found for the TET2 enzyme with 8%±6% positive cells in subjects with periodontitis while the amount of positive cells in subjects with gingivitis was 4%±2% (p=0.0492). No significant difference in TET2 gene expression was found. The global 5hmC level was higher in blood than in the inflammatory lesion, while no difference was found for 5mC.
Conclusions: The results show that TET2 is associated with periodontitis indicating that epigenetic changes in the oral mucosa may influence susceptibility for periodontitis. This difference is not due to differences in mRNA level, therefore indicating a post-transcriptional or regulatory difference in periodontitis. In addition, our data indicate a difference in methylation pattern between blood and tissue suggesting a specific pattern of DNA methylation at the site of inflammation.