The synergistic effect of peptidoglycan and lipopolysaccaride on osteoclast formation

The purpose of this study was to investigate the mechanisms leading to periapical tissue destruction by the Gram-positive bacterial cell component, peptidoglycan (PGN) and Gram-negative bacterial cell component lipopolysaccaride (LPS).

Osteoclast precursor RAW 264.7 cells were cultured with 50 ng/ml receptor activator of NF-kappaB ligand (RANKL) for 72 hours. RANKL was then removed and the cells were treated with various concentrations of PGN in the presence or absence of various concentration of LPS for an additional 48 hours. RT-PCR analysis was performed to examine the presence of receptors on osteoclasts known to be involved in mediating cellular activation in response to PGN (TLR2) and LPS (TLR 4).

PGN dose dependently and reproducibly stimulated TRAP-positive multinucleated osteoclast-like (OCL) cell formation. PGN and LPS had synergistic effects on the induction of OCL cell formation. Both unstimulated and RANKL-stimulated RAW 264.7 cells expressed TLR2 and TLR4 mRNA.

The results underscore the importance of considering both Gram-positive and Gram-negative bacteria when interpreting findings associated with primary and secondary periapical lesions.