Transcription factor DEC1 is required for maximal experimentally induced periodontal inflammation

Abstract

Background and objectives: Disruption of transcriptional regulation is a confounding factor associated with a wide range of human inflammatory diseases. To investigate mechanistic links between transcription factor DEC1 and pathways underlying inflammation, wild-type and DEC1 knockout (KO) C57BL/6 mice were treated with Porphyromonas gingivalis (or carboxymethyl cellulose as a control) to induce periodontal inflammation. It provoked an inflammatory response within the oral environment, which showed robust variation in alveolar bone resorption and expression of inflammatory cytokines.

Material and methods: Male DEC1KO mice and their wild-type littermates were used for the experimental periodontitis model. Measurement of alveolar bone resorption, micro-computed tomography, isolation of gingival mononuclear cells (GMCs), flow cytometry and immunohistochemical analysis were used in this study. Human gingival fibroblast cells (HGF-1) were used for DEC1 over-expression and short interference RNA (siRNA) studies and quantitative real-time polymerase chain reaction and western blot analysis were performed.

Results: Micro-computed tomography analysis demonstrated that P. gingivalis caused a decrease in bone area of wild-type mice compared with DEC1KO mice. Expression of inflammatory and immune markers in GMCs was significantly decreased in DEC1KO mice after treatment with P. gingivalis. Conversely, interleukin (IL)-4 and IL-10 mRNAs were significantly increased in GMCs isolated from DEC1KO mice. The results show that treatment of DEC1KO mice with P. gingivalis decreased the numbers of CD11b⁺ F4/80⁺ and CD4⁺ RANKL⁺ T cells. Moreover, expression of CD4, F4/80, RANKL and cathepsin K in inflammatory cell infiltrates was significantly reduced in DEC1KO mice treated with P. gingivalis compared with controls. Furthermore, over-expression of DEC1 in HGF-1 cells increased the expression of IL-1β and tumor necrosis factor-α mRNAs and their expression levels reached a maximum in response to treatment with lipopolysaccharide. Inhibition of DEC1 by short interference RNA interference suppressed the P. gingivalis-derived lipopolysaccharide-induced expression of IL-1β, tumor necrosis factor-α and toll-like receptor4.

Conclusion: These results suggest that transcription factor DEC1 can modulate P. gingivalis-induced periodontitis in the oral mucosa.

Keywords: P. gingivalis; DEC1; immunoregulation; periodontal inflammation; transcription factor.