(61) The expression of H3K18ac and BRD2/3/4 in periodontitis tissues

Introduction: The goal of current periodontal therapy is to reduce the bacterial load in periodontal pockets through mechanical debridement with or without flap surgeries. However, they are not always effective, and the recurrence of hyper-inflammatory status in periodontal tissues is frequently observed. The susceptibility to periodontitis is largely determined by host response and the severity of inflammation predicts disease progression. Therefore, understanding the driving force of the uncontrolled, overly aggressive inflammation is important for future therapy. Emerging data has indicated the significant role of epigenetic control in inflammation. Acetylation of lysine residues on histones is a major epigenetic modification of chromatin. The status of histone acetylation is usually “translated” by bromodomain and extraterminal domain (BET) proteins, which include BRD2, BRD3, BRD4 and BRDT. BET proteins “read” the status of chromatin by binding to the acetylated lysine on histones (H-Ac), and therefore facilitate the recruitment and activation of transcription factors. They are required for cytokine gene expression and are regulated in inflammatory diseases. It has been shown that periodontal bacteria induce histone acetylation in oral epithelial cells and experimental periodontitis in rodents. In this study we investigated the expression of H3K18ac, an epigenetic marker that has been associated with inflammatory diseases, and its readers BRD2/3/4 in periodontitis patients. We hypothesize that the cytokine over-production in periodontitis is dictated by a specific histone acetylation pattern.

Methods: Periodontitis patients and healthy control subjects who need periodontal surgeries (pocket reduction for periodontitis or crown lengthening for healthy individuals) were enrolled into the study under IRB approval. Healthy subjects had no probing depth (PD)>3mm and no clinical attachment level (CAL)>3mm, and had less than 20% of the sites with bleeding on probing (BOP). Periodontitis patients had at least 6 teeth with PD≥6mm. Gingival tissues from diseased or healthy sites were harvested during surgeries and stored for RNA extraction or histological analysis. Immunohistochemistry (IHC) staining was used to study the expression of H3K18ac and RT-PCR was used to determine the expression of BRD genes in these tissues.

Results: So far, 19 patients in periodontitis group and 12 healthy subjects were recruited. Preliminary data showed that BRD2/3/4 are differentially expressed between the two groups. H3K18ac has more significant expression in gingival epithelium compared to connective tissues.

Conclusions: Stronger staining appears to be observed more frequently in periodontitis patients.. However, more sample sections are currently being stained for further analysis. More details will be presented in the meeting.

Lead Author’s Contributions to the Research Project: Recruiting the patients, drawing blood, performing the surgeries and obtaining the tissue and bacterial plaque samples.