Pseudomonas aeruginosa lipopolysaccharide induces osteoclastogenesis through a toll-like receptor 4 mediated pathway in vitro and in vivo.
OBJECTIVE
Bacterial infections near bone result in localized inflammatory osteolysis, a significant complication of chronic ear infections. While many bacterial products may be involved, lipopolysaccharide (LPS) has been implicated as a major mediator of inflammation and osteolysis. However, the mechanisms by which LPS promotes bone resorption have not been clearly established. There is no consensus on whether LPS acts directly or indirectly on osteoclast precursors (bone marrow monocytes [BMM]) to induce bone resorption. In light of the role of Pseudomonas aeruginosa, in chronic ear infections, we investigated the effects of P. aeruginosa LPS on osteoclastogenesis in vivo and in vitro.


METHODS
Wild-type C57BL/6J and toll-like receptor 4 knock-out (TLR4-/-) mice received subcutaneous calvarial injections of 250 mug of P. aeruginosa LPS or phosphate buffered saline (PBS) only (n = 5 per group). Osteoclastic bone resorption was assessed histologically. The effect of P. aeruginosa LPS on bone resorption was assessed in vitro using combinations of BMMs and osteoblasts with and without functional toll-like receptor 4 (TLR4).


RESULTS
In vivo, P. aeruginosa LPS induced robust osteolysis, and this effect was completely abrogated in mice lacking expression of TLR4. In vitro, P. aeruginosa LPS failed to induce development of osteoclasts directly in BMMs. However, P. aeruginosa LPS did stimulate osteoclastogenesis in BMM-osteoblast cocultures.


CONCLUSIONS
P. aeruginosa LPS acts indirectly through osteoblasts to induce bone resorption. Optimal osteoclastogenesis in vitro required functional TLR4 expression in both BMMs and osteoblasts.
Zhuang
Lei
L
Department of Otolaryngology, Washington University School of Medicine, Saint Louis, MO 63110, USA.
Jung
Jae Y
JY
Wang
Eric W
EW
Houlihan
Patrick
P
Ramos
Lisette
L
Pashia
Mary
M
Chole
Richard A
RA
D000704:Analysis of Variance; D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects* / Q000378:metabolism; D001862:Bone Resorption; D002478:Cells, Cultured; D066298:In Vitro Techniques; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism; D010010:Osteoclasts / Q000187:drug effects* / Q000378:metabolism; D010641:Phenotype; D011550:Pseudomonas aeruginosa; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
D008070:Lipopolysaccharides; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4