title: Smad2 is involved in Aggregatibacter actinomycetemcomitans-induced apoptosis.
abstract: 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.
authors.affiliation: Department of Periodontal Medicine, Division of Applied Life Sciences, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Yoshimoto
authors.affiliation: Department of Periodontal Medicine, Division of Applied Life Sciences, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan tfuji@hiroshima-u.ac.jp.
authors.forename: T
authors.initials: T
authors.lastname: Fujita
authors.affiliation: Department of Periodontal Medicine, Division of Applied Life Sciences, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ouhara
authors.affiliation: Department of Periodontal Medicine, Division of Applied Life Sciences, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kajiya
authors.affiliation: Department of Periodontal Medicine, Division of Applied Life Sciences, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Imai
authors.affiliation: Department of Periodontal Medicine, Division of Applied Life Sciences, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Shiba
authors.affiliation: Department of Periodontal Medicine, Division of Applied Life Sciences, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kurihara
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000502:physiology*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001549:Benzamides / Q000494:pharmacology; D053148:Caspase 3 / Q000187:drug effects; D061945:Caspase Inhibitors / Q000494:pharmacology; D002460:Cell Line; D002478:Cells, Cultured; D004149:Dioxoles / Q000494:pharmacology; D004846:Epithelial Attachment / Q000382:microbiology* / Q000473:pathology; D004847:Epithelial Cells / Q000382:microbiology / Q000502:physiology; D020868:Gene Silencing; D006801:Humans; D010518:Periodontitis / Q000382:microbiology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051899:Smad2 Protein / Q000502:physiology*; D014162:Transfection
chemical_list: C459179:4-(5-benzo(1,3)dioxol-5-yl-4-pyridin-2-yl-1H-imidazol-2-yl)benzamide; D001549:Benzamides; D061945:Caspase Inhibitors; D004149:Dioxoles; D034741:RNA, Small Interfering; D018125:Receptors, Transforming Growth Factor beta; C497782:SMAD2 protein, human; D051899:Smad2 Protein; D012694:Serine; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; C505407:CASP3 protein, human; D053148:Caspase 3
keywords: TGF-β type I receptor; cleaved caspase-3; epithelial cells; gingival epithelium; periodontitis; periodontopathic bacteria