Abstract

Aim: Epigenetic regulation of the key inflammatory genes plays a crucial role in controlling monocyte/macrophage-mediated local and systemic responses to bacterial challenges. However, it has not been addressed in apical periodontitis (AP). We aimed to explore the methylation pattern of the TNF-alpha gene promoter and its association with the inflammatory phenotype of peripheral blood monocytes from individuals with AP and controls. Methods: A cross-sectional study was conducted, including otherwise healthy individuals with AP (n = 25) and controls (n = 29). Monocytes were isolated from the volunteer's blood samples using a Ficoll gradient followed by negative immunoselection. RNA and DNA were extracted. The DNA methylation profiles of the TNF-alpha gene promoter region were analyzed using bisulfite sequencing PCR. The mRNA expression levels of DNA methyltransferases 3a (DNMT3a) and Ten Eleven Translocation enzymes 1(TET1) were assessed by qPCR. A fraction of primary monocytes was also cultured for 24 h, and the supernatant was collected to measure cytokine levels through a Luminex assay. Generalized structural equation models (GSEM) evaluated the association between AP, DNA methylation, and TNF-alpha protein expression controlled for potential covariates. Models included the effect of the methylation of TNF-alpha gene promoter as a mediator of the association between AP and TNF-alpha protein expression levels. Results: Monocytes from AP individuals exhibited a heightened secretion of TNF-alpha and IL-1 beta and hypomethylation of the TNF gene promoter (p < .05). AP diagnosis was associated with the TNF-alpha gene promoters hypomethylated profile and enhanced pro-inflammatory cytokine levels, while lower methylation of the gene promoter region and -163 CpG single site mediated TNF-alpha overexpression (p < .05). Conclusions: DNA hypomethylation at the TNF-alpha gene mediates a proinflammatory phenotype in monocytes from AP patients, supporting a role in the systemic response.