4-(5-benzo(1-3)dioxol-5-yl-4-pyridin-2-yl-1h-imidazol-2-yl)benzamide and Periodontitis

Periodontitis is the most prevalent infectious disease caused by periodontopathic bacteria and is also a chronic inflammatory disease. Gingival crevicular fluid (GCF) is an inflammatory exudate that seeps into the gingival crevices or periodontal pockets around teeth with inflamed gingiva, and contains various materials including leukocytes and cytokines. Since gingival epithelial cells, which form a barrier against bacterial challenges, are affected by GCF, cytokines or other materials contained within GCF are engaged in the maintenance and disruption of the epithelial barrier. Accordingly, its compositional pattern has been employed as a reliable objective index of local inflammation. Transforming growth factor β1 (TGF-β1) levels in GCF were previously shown to be markedly higher in patients with periodontitis than in healthy subject. However, it currently remains unclear how TGF-β1 affects gingival epithelial cell growth or apoptosis; therefore, elucidating the mechanism responsible may lead to a deeper understanding of pathogenic periodontitis. In the present study, the human gingival epithelial cell line, OBA9 cells were stimulated with recombinant TGF-β1. Apoptosis-related protein levels were determined by Western blotting. Caspase-3/7 activity was measured with a Caspase-Glo assay kit. Surviving and apoptotic cells were detected using an MTS assay and TUNEL staining, respectively. TGF-βRI siRNA and smad2 siRNA were transfected into cells using the lipofectamine RNAiMAX reagent. TGF-β1 elevated caspase-3 activity and the number of TUNEL-positive apoptotic cells in OBA9 cells. Furthermore, while the levels of the pro-apoptotic proteins Bax, Bak, Bim, and Bad were increased in OBA9 cells stimulated with TGF-β1, the TGF-β1 treatment also decreased the levels of anti-apoptotic proteins such as Bcl-2 and Bcl-xL in a time-dependent manner. Additionally, TGF-β1 up-regulated the protein levels of cleaved caspase-9. These results indicated that TGF-β1-induced apoptosis was involved in a mitochondria-related intrinsic pathway. TGF-β1 phosphorylated smad2 in OBA9 cells and this phosphorylation was clearly reduced by SB431542 (a TGF-β type I receptor inhibitor). Consistent with this result, SB431542 or smad2 siRNA-induced reductions in smad2 protein expression levels attenuated TGF-β1-induced apoptosis. On the other hand, the ligation of TGF-β1 on its receptor also stimulated the phosphorylation of Erk and Akt, which are smad2-independent pathways. However, the

Topics: Acetylcysteine; Apoptosis; Benzamides; Caspase 3; Caspase 7; Cell Line; Cell Line, Tumor; Cell Proliferation; Cell Survival; Dioxoles; Epithelial Cells; Extracellular Signal-Regulated MAP Kinases; Gingiva; Humans; Inflammation; MAP Kinase Signaling System; Periodontitis; Phosphorylation; Proto-Oncogene Proteins c-akt; RNA, Small Interfering; Signal Transduction; Smad2 Protein; Transforming Growth Factor beta; Transforming Growth Factor beta1

Apoptosis is thought to contribute to the progression of periodontitis. It has been suggested that the apoptosis of epithelial cells may contribute to the loss of epithelial barrier function. Smad2, a downstream signaling molecule of TGF-β receptors (TGF-βRs), is critically involved in apoptosis in several cell types. However, the relationship between smad2 and bacteria-induced apoptosis has not yet been elucidated. It is possible that the regulation of apoptosis induced by periodontopathic bacteria may lead to novel preventive therapies for periodontitis. Therefore, in the present study, we investigated the involvement of smad2 phosphorylation in apoptosis of human gingival epithelial cells induced by Aggregatibacter actinomycetemcomitans (Aa). Aa apparently induced the phosphorylation of smad2 in primary human gingival epithelial cells (HGECs) or the human gingival epithelial cell line, OBA9 cells. In addition, Aa induced phosphorylation of the serine residue of the TGF-β type I receptor (TGF-βRI) in OBA9 cells. SB431542 (a TGF-βRI inhibitor) and siRNA transfection for TGF-βRI, which reduced both TGF-βRI mRNA and protein levels, markedly attenuated the Aa-induced phosphorylation of smad2. Furthermore, the disruption of TGF-βRI signaling cascade by SB431542 and siRNA transfection for TGF-βRI abrogated the activation of cleaved caspase-3 expression and repressed apoptosis in OBA9 cells treated with Aa. Thus, Aa induced apoptosis in gingival epithelial cells by activating the TGF-βRI-smad2-caspase-3 signaling pathway. The results of the present study may suggest that the periodontopathic bacteria, Aa, activates the TGF-βR/smad2 signaling pathway in human gingival epithelial cells and induces apoptosis in epithelial cells, which may lead to new therapeutic strategies that modulate the initiation of periodontitis.

Topics: Aggregatibacter actinomycetemcomitans; Apoptosis; Benzamides; Caspase 3; Caspase Inhibitors; Cell Line; Cells, Cultured; Dioxoles; Epithelial Attachment; Epithelial Cells; Gene Silencing; Humans; Periodontitis; Phosphorylation; Protein Serine-Threonine Kinases; Receptor, Transforming Growth Factor-beta Type I; Receptors, Transforming Growth Factor beta; RNA, Small Interfering; Serine; Signal Transduction; Smad2 Protein; Transfection