Glycogen synthase kinase-3 beta inhibitor suppresses Porphyromonas gingivalis lipopolysaccharide-induced CD40 expression by inhibiting nuclear factor-kappa B activation in mouse osteoblasts

Bone-forming osteoblasts have been recently reported capable of expressing the critical co-stimulatory molecule CD40 upon exposure to bacterial infection, which supports the unappreciated role of osteoblasts in modulating bone inflammation. Recent studies highlight the anti-inflammatory potential of glycogen synthase kinase-3 beta (GSK-3 beta) inhibitors; however, their effect on osteoblasts remains largely unclear. In the present study, we showed that treatment with SB216763, a highly specific GSK-3 beta inhibitor, resulted in a dose-dependent decrease in the mRNA and protein expression of CD40, as well as production of pro-inflammatory cytokines IL-6, TNF-alpha and IL-1 beta, in the Porphyromonas gingivalis-lipopolysaccharide (LPS)-stimulated murine osteoblastic-like MC3T3-E1 cells. Furthermore, inhibition of GSK-3 beta remarkably represses the LPS-induced activation of the nuclear factor kappa B (NF-kappa B) signaling pathway by suppressing I kappa B alpha phosphorylation, NF-kappa Bp65 nuclear translocation, and NF-kappa Bp65 DNA binding activity. Closer investigation by immunoprecipitation assay revealed that beta-catenin can physically interact with NF-kappa Bp65. The negative regulation effect of GSK-3 beta inhibitor on CD40 expression is mediated through beta-catenin, for siRNA of beta-catenin attenuated the GSK-3 beta inhibitor-induced repression of NF-kappa B activation and, consequently, the expression of CD40 and production of pro-inflammatory cytokines in LPS-stimulated MC3T3-E1 cells. Thus our results elucidate the molecular mechanisms whereby GSK-3 beta inhibitor prevents the LPS-induced CD40 expression on osteoblasts and provide supportive evidence of the potential role of GSK-3 beta inhibitors in suppressing the immune function of osteoblasts in inflammatory bone diseases. (C) 2012 Elsevier Ltd. All rights reserved.