Hypoxia enhances the effect of lipopolysaccharide-stimulated IL-1β expression in human periodontal ligament cells

Oral infection is inflammatory disease caused by bacteria. A major component of gram negative bacteria membrane associated with inflammation is lipopolysaccharide (LPS). Currently, evidence presenting the combined effect of LPS and hypoxia to inflammatory response in human periodontal ligament cells (HPDLs) was yet lacking. Here, we studied whether the influence of oxygen on LPS-stimulated inflammatory cytokines in HPDLs. HPDLs were stimulated with LPS in normoxia and hypoxia for 24 h. The mRNA and protein expression of inflammatory cytokines were examined by polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. The intracellular mechanisms of these effects were investigated by chemical inhibitors and small interfering RNA (siRNA). The results showed that LPS-stimulated IL-1 beta, IL-6, IL-8 in HPDLs in both hypoxia and normoxia. Hypoxia condition enhanced the effect of LPS-stimulated cytokines expression. Apigenin, the hypoxia-inducible factors (HIF)-1 alpha inhibitor, totally prevented LPS-stimulated IL-1 beta expression in both normoxia and hypoxia. Similar to knockout HIF-1 alpha gene expression by siRNA did \not prevent LPS-stimulated IL-1 beta expression. These data concluded that hypoxia increased virulence of LPS-stimulated IL-1 beta production in HPDLs.