Although Porphyromonas gingivalis lipopolysaccharide (P-LPS) is known to inhibit osteoblast differentiation, the exact molecular mechanisms underlying this phenomenon remain unclear. Here, we investigated the role of Notch signaling in the osteoblastic differentiation of both MC3T3E-1 cells and primary mouse bone marrow stromal cells (BMSCs). P-LPS stimulation activated the Notch1 signaling cascade and increased expression of the Notch target genes HES1 and HEY1. P-LPS can also act as an inhibitor because it is capable of suppressing Wnt/beta-catenin signaling in preosteoblasts by decreasing both glycogen synthase kinase-3beta (GSK-3beta) phosphorylation and the expression of nuclear beta-catenin. These effects were rescued, however, by inhibiting Notch1 signaling. Furthermore, P-LPS treatment inhibited osteoblast differentiation in preosteoblasts as demonstrated by reductions in alkaline phosphatase activity, osteoblast gene expression, and mineralization, all of which were rescued by suppression of Notch1 signaling. Moreover, inhibition of GSK-3beta, HES1, or HEY1 partially reversed the P-LPS-induced inhibition of osteoblast differentiation. Together, these findings suggest that P-LPS inhibits osteoblast differentiation by promoting the expression of Notch target genes and suppressing canonical Wnt/beta-catenin signaling.
(c) 2010 Wiley-Liss, Inc.