ABSTRACT
Periodontitis is induced by periodontal dysbiosis characterized by the predominance of anaerobic species. TLRs constitute the classical pathway for cell activation by infection. Interestingly, the Toll/IL-1 receptor homology domain adapters initiate signaling events, leading to the activation of the expression of the genes involved in the host immune response. The aim of this study was to evaluate the effects of Porphyromonas gingivalis on the expression and protein-protein interactions among five TIR adapters (MAL, MyD88, TRIF, TRAM and SARM) in gingival epithelial cells and endothelial cells. It was observed that P. gingivalis is able to modulate the signaling cascades activated through its recognition by TLR4/2 in gingival epithelial cells and endothelial cells. Indeed, MAL-MyD88 protein-protein interactions associated with TLR4 was the main pathway activated by P. gingivalis infection. When transient siRNA inhibition was performed, cell viability, inflammation, and cell death induced by infection decreased and such deleterious effects were almost absent when MAL or TRAM were targeted. This study emphasizes the role of such TIR adapter proteins in P. gingivalis elicited inflammation and the precise evaluation of TIR adapter protein interactions may pave the way for future therapeutics in both periodontitis and systemic disease with a P. gingivalis involvement, such as atherothrombosis.
Subject(s)
Bacteroidaceae Infections/metabolism , Bacteroidaceae Infections/microbiology , Gingivitis/metabolism , Gingivitis/microbiology , Porphyromonas gingivalis , Receptors, Interleukin-1/genetics , Toll-Like Receptors/genetics , Adolescent , Adult , Aged , Cell Survival , Dysbiosis , Female , Gene Expression Regulation , Humans , Male , Middle Aged , RNA, Small Interfering/pharmacology , Receptors, Interleukin-1/metabolism , Signal Transduction/drug effects , Toll-Like Receptor 2/genetics , Toll-Like Receptor 4/genetics , Toll-Like Receptors/metabolism , Young AdultABSTRACT
Porphyromonas gingivalis is able to invade and modulate host-immune response to promote its survival. This bacterium modulates the cell cycle and programed cell death, contributing to periodontal lesion worsening. Several molecular pathways have been identified as key triggers of apoptosis, including apoptosome apoptotic peptidase activating factor 1 (APAF-1). Apaf-1 and X-linked inhibitor of apoptosis protein (Xiap) mRNA were differentially expressed between gingival samples harvested from human healthy and chronic periodontitis tissues (Apaf-1, 19.2-fold; caspase-9, 14.5-fold; caspase-3, 6.8-fold; Xiap: 2.5-fold in chronic periodontitis) (P < 0.05), highlighting their potential role in periodontitis. An increased proteic expression of APAF-1 was also observed in a murine experimental periodontitis model induced by P. gingivalis-soaked ligatures. In vitro, it was observed that P. gingivalis targets APAF-1, XIAP, caspase-3, and caspase-9, to inhibit epithelial cell death at both mRNA and protein levels. Opposite effect was observed in fibroblasts in which P. gingivalis increased cell death and apoptosis. To assess if the observed effects were associated to APAF-1, epithelial cells and fibroblasts were transfected with siRNA targeting Apaf-1. Herein, we confirmed that APAF-1 is targeted by P. gingivalis in both cell types. This study identified APAF-1 apoptosome and XIAP as intracellular targets of P. gingivalis, contributing to the deterioration of periodontal lesion through an increased persistence of the bacteria within tissues and the subversion of host-immune response.
