title: Hypoxia-inducible factor-1α inhibits interleukin-6 and -8 production in gingival epithelial cells during hypoxia.
abstract: OBJECTIVE
  Hypoxia has been widely studied in inflammatory diseases as it can modulate the inflammatory response, mainly via the hypoxia-inducible factor (HIF). However, little is known about the effects of hypoxia and the role of HIF in the inflammatory responses to periodontitis. In this study, we focused on the gingival epithelium that is exposed to relatively low levels of oxygen. We investigated whether hypoxic conditions have an impact on inflammatory responses in human gingival epithelial cells (HGECs).
  
  
  METHODS
  Pimonidazole HCl, which accumulates in hypoxic cells, was administered intraperitoneally to C57BL/6 mice with or without Porphyromonas gingivalis infection. Immunohistochemistry was then performed to detect the hypoxic cells in periodontal tissue. Immortalized HGECs were cultured under hypoxic conditions with or without interleukin (IL)-1β, and the expression levels of IL-6 and IL-8 were measured by real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. HIF-1α expression was detected by western blotting. The DNA-binding activity of HIF-1α was determined by a DNA-binding enzyme-linked immunosorbent assay. The involvement of HIF-1α in the hypoxic response was examined by transfection with HIF-1α siRNA.
  
  
  RESULTS
  Immunohistochemistry revealed pimonidazole HCl accumulation in the gingival epithelium of both normal and P. gingivalis-infected mice, with a slightly stronger signal in the P. gingivalis-infected mice than in the normal mice. The IL-1β-induced IL-6 and IL-8 production by HGECs was suppressed under hypoxic conditions. HIF-1α accumulated during hypoxia, and this accumulation was further enhanced by IL-1β treatment. The hypoxia-dependent suppression of IL-6 and IL-8 expression was reversed by treating the cells with HIF-1α siRNA.
  
  
  CONCLUSIONS
  Our results suggest that the gingival epithelium is exposed to low oxygen tension in periodontal tissue and that this hypoxic condition modulates the local inflammatory response of gingival epithelial cells in an HIF-1α-dependent manner.
authors.affiliation: Department of Periodontology, Osaka University Graduate School of Dentistry, Osaka, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Takedachi
authors.affiliation: Department of Periodontology, Osaka University Graduate School of Dentistry, Osaka, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Iyama
authors.affiliation: Department of Periodontology, Osaka University Graduate School of Dentistry, Osaka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Sawada
authors.affiliation: Department of Periodontology, Osaka University Graduate School of Dentistry, Osaka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Mori
authors.affiliation: Department of Periodontology, Osaka University Graduate School of Dentistry, Osaka, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Yamamoto
authors.affiliation: Department of Periodontology, Osaka University Graduate School of Dentistry, Osaka, Japan.
authors.forename: C
authors.initials: C
authors.lastname: Morimoto
authors.affiliation: Department of Periodontology, Osaka University Graduate School of Dentistry, Osaka, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Yanagita
authors.affiliation: Department of Periodontology, Osaka University Graduate School of Dentistry, Osaka, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Murakami
mesh_terms: D000818:Animals; D015153:Blotting, Western; D004797:Enzyme-Linked Immunosorbent Assay; D004848:Epithelium / Q000378:metabolism*; D005881:Gingiva / Q000378:metabolism*; D000860:Hypoxia / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D015850:Interleukin-6 / Q000378:metabolism*; D016209:Interleukin-8 / Q000378:metabolism*; D008297:Male; D008810:Mice, Inbred C57BL; D060888:Real-Time Polymerase Chain Reaction
chemical_list: C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D015850:Interleukin-6; D016209:Interleukin-8
keywords: gingival epithelial cell; hypoxia; hypoxia-inducible factor-1α; inflammatory response