The Roles of TNFR1 in Lipopolysaccharide-Induced Bone Loss: Dual Effects of TNFR1 on Bone Metabolism via Osteoclastogenesis and Osteoblast Survival

LPS (lipopolysaccharide), a major constituent of Gram-negative bacteria, regulates proliferation and differentiation of osteoclasts directly or indirectly. This study sought to investigate the functions of the RANK/RANKL pathway in LPS-induced bone loss in vivo. Wild-type mice or TNFR1-/- mice were injected LPS with or without osteoprotegerin (OPG) and analyzed histologically. Bone volume was reduced by LPS injection in all groups, and OPG administration prevented the LPS-induced bone loss regardless of genotypes. LPS-induced enhancement of osteoclastogenesis in wild-type mice was blocked by OPG administration. LPS or OPG did not affect osteoclastogenesis in TNFR1-/- mice. Interestingly, osteoblast surface was remarkably reduced in LPS-treated TNFR1-/- mice as a result of enhanced osteoblast apoptosis. TRAIL, induced by TNF-alpha. in BMC, triggered apoptosis of primary osteoblast only when TNFR1 signal was ablated in vitro. In conclusion, RANK signaling plays a prominent role in osteoclastogenesis downstream of LPS. Furthermore, TNFR1 regulates bone metabolism through not only the regulation of osteoclast differentiation but also osteoblast survival. (C) 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:657-663, 2010