Osteoclast differentiation by human osteoblastic cell line SaOS-2 primed with bacterial lipid A

We examined the responses of human osteoblastic cell line SaOS-2 to bacterial lipid A, a bioactive center of lipopolysaccharide, during osteoclast differentiation of human peripheral blood mononuclear cells (PBMC). SaOS-2 cells expressed mRNA for Toll-like receptor (TLR) 4, MD-2, CD14, and myeloid differentiation factor 88, whereas they failed to express mRNA for TLR2. Escherichia coli-type synthetic lipid A (compound 506) induced cytokine mRNA expression and nuclear factor (NF)-kappaB activation in SaOS-2 cells. Compound 506 also increased the expression of receptor activator of NF-kappaB ligand. Further, cells primed with compound 506 augmented the differentiation of PBMC into osteoclastic cells, and the effect was inhibited by anti-TLR4 monoclonal antibody. These findings suggest that the TLR signaling cascade in osteoblastic cells is involved in regulating the function of osteoclastogenesis.