Down‐regulation of epidermal growth factor receptor‐dependent signaling by Porphyromonas gingivalis lipopolysaccharide in life‐expanded human gingival fibroblasts

Abstract

Human gingival fibroblasts exhibit proliferative responses following epidermal growth factor exposure, which are thought to enhance periodontal regeneration in the absence of bacterial products such as lipopolysacharide. However, lipopolysaccharide challenge activates human gingival fibroblasts to release several inflammatory mediators that contribute to the immune response associated with periodontitis and attenuate wound repair. We tested the hypothesis that Porphyromonas gingivalis lipopolysaccharide-activated signaling pathways down-regulate epidermal growth factor receptor-dependent events. To study lipopolysaccharide/epidermal growth factor interactions in human gingival fibroblasts, we introduced the catalytic subunit of human telomerase into human gingival fibroblasts, thereby generating a more long-lived cellular model. These cells were characterized and evaluated for lipopolysaccharide/epidermal growth factor responsiveness and regulation of epidermal growth factor-dependent pathways. Comparison of human telomerase-transduced gingival fibroblasts with human gingival fibroblasts revealed that both cell lines exhibit a spindle-like morphology and express similar levels of epidermal growth factor receptor, CD14 and Toll-like receptors 2 and 4. Importantly, human telomerase-transduced gingival fibroblasts proliferation rates are increased 5-9 fold over human gingival fibroblasts and exhibit a longer life span in culture. In addition, human telomerase-transduced gingival fibroblasts and human gingival fibroblasts exhibit comparable profiles of mitogen-activated protein kinase kinase (extracellular signal-regulated kinase 1/2) activation upon epidermal growth factor or P. gingivalis lipopolysaccharide administration. Interestingly, treatment with P. gingivalis lipopolysaccharide leads to a down-regulation of epidermal growth factor-dependent extracellular signal-regulated kinase 1/2, p38 and cyclic-AMP response element binding protein phosphorylation in both cell types. These studies demonstrate that human telomerase-transduced gingival fibroblasts exhibit an extended life span and recapitulate human gingival fibroblasts biology. Moreover, this system has allowed for the first demonstration of lipopolysaccharide down-regulation of epidermal growth factor activated pathways in human gingival fibroblasts and should facilitate the analysis of signaling events relevant to the pathogenesis and treatment of periodontitis.