%0 Journal Article
%T Infection of RANKL-Primed RAW-D Macrophages with Porphyromonas gingivalis Promotes Osteoclastogenesis in a TNF-¦Á-Independent Manner
%A Akiko Kukita
%A Yuka Ichigi
%A Ippei Takigawa
%A Toshiyuki Watanabe
%A Toshio Kukita
%A Hiroshi Miyamoto
%J PLOS ONE
%D 2012
%I Public Library of Science (PLoS)
%R 10.1371/journal.pone.0038500
%X Infection of macrophages with bacteria induces the production of pro-inflammatory cytokines including TNF-¦Á. TNF-¦Á directly stimulates osteoclast differentiation from bone marrow macrophages in vitro as well as indirectly via osteoblasts. Recently, it was reported that bacterial components such as LPS inhibited RANKL-induced osteoclastogenesis in early stages, but promoted osteoclast differentiation in late stages. However, the contribution to osteoclast differentiation of TNF-¦Á produced by infected macrophages remains unclear. We show here that Porphyromonas gingivalis, one of the major pathogens in periodontitis, directly promotes osteoclastogenesis from RANKL-primed RAW-D (subclone of RAW264) mouse macrophages, and we show that TNF-¦Á is not involved in the stimulatory effect on osteoclastogenesis. P. gingivalis infection of RANKL-primed RAW-D macrophages markedly stimulated osteoclastogenesis in a RANKL-independent manner. In the presence of the TLR4 inhibitor, polymyxin B, infection of RANKL-primed RAW-D cells with P. gingivalis also induced osteoclastogenesis, indicating that TLR4 is not involved. Infection of RAW-D cells with P. gingivalis stimulated the production of TNF-¦Á, whereas the production of TNF-¦Á by similarly infected RANKL-primed RAW-D cells was markedly down-regulated. In addition, infection of RANKL-primed macrophages with P. gingivalis induced osteoclastogenesis in the presence of neutralizing antibody against TNF-¦Á. Inhibitors of NFATc1 and p38MAPK, but not of NF-¦ÊB signaling, significantly suppressed P. gingivalis-induced osteoclastogenesis from RANKL-primed macrophages. Moreover, re-treatment of RANKL-primed macrophages with RANKL stimulated osteoclastogenesis in the presence or absence of P. gingivalis infection, whereas re-treatment of RANKL-primed macrophages with TNF-¦Á did not enhance osteoclastogenesis in the presence of live P. gingivalis. Thus, P. gingivalis infection of RANKL-primed macrophages promoted osteoclastogenesis in a TNF-¦Á independent manner, and RANKL but not TNF-¦Á was effective in inducing osteoclastogenesis from RANKL-primed RAW-D cells in the presence of P. gingivalis.
%U http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0038500