Methylation Pattern of the IFN-gamma Gene in Human Dental Pulp

Introduction: DNA methylation is characterized by the addition of methyl groups in cytosines within cytosine-phosphate-guanine (CpG) islands. Unmethylated islands are related with transcriptionally active structure, whereas methylated DNA recruits methyl-binding proteins that promotes chromatin compaction. Although epigenetic events can influence the expression of cytokines, such events have not been investigated in dental pulp yet. The purpose of the present study was to evaluate the methylation status of the interferon gamma (IFN-gamma) gene in human dental pulp affected by inflammation compared with pulp tissue of impacted molar teeth and to verify the impact of methylation status in the expression pattern of the gene.

Methods: Methylation-specific polymerase chain reaction (MSP) was used to verify the DNA methylation status of the IFN-gamma gene in 16 human dental pulps affected by inflammation and in 16 pulp samples of impacted molar teeth. Histologic sections stained by hematoxylin-eosin were used for histopathological evaluation, and the expression of IFN-gamma was assessed by quantitative real-time PCR (qPCR).

Results: Although total methylation was observed in 43.75% of the samples of normal dental pulp tissues, partial methylation or unmethylation was found in 93.75% of the samples of inflamed pulp tissues. All the samples with total methylation in MSP showed no transcription of IFN-gamma. The qPCR results showed expression of IFN-gamma in 5 of 10 samples with partial methylation.

Conclusion: The present study gives the first evidence of the possible participation of epigenetic events in the development of dental pulp inflammation.