Transcription factor DEC1 is required for maximal experimentally induced periodontal inflammation

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.

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.

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.

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