Human rheumatoid synovial fibroblasts promote osteoclastogenic activity by activating RANKL via TLR-2 and TLR-4 activation.
The interplay between the innate immune system and inflammatory bone destruction in the joints of individuals with rheumatoid arthritis (RA) remains unclear. This study was undertaken to explore the effect of toll-like receptor (TLR) signaling in fibroblast-like synoviocytes (FLS) on the expression of RANKL and induction of osteoclastogenic activity. The levels of RANKL mRNA and protein were measured using RT-PCR, real-time PCR, and immunostaining. Monocytes were cocultured with RA -FLS that had been stimulated with TLR ligands in fresh media and subsequently stained for tartrate-resistant acid phosphatase (TRAP) activity. Osteoclast molecule markers were measured using real-time PCR. Expression of TLR-2 and TLR-4 was higher in RA-FLS than in OA-FLS and normal skin fibroblasts. TLR-2 and TLR-4 ligands induced RANKL expression in RA-FLS. TLR stimulation of RA-FLS also induced the production of IL-1beta and TNF-alpha to a lesser extent; however, it had no effect on IL-17 production. Inhibition of TLR induced IL-1beta production, which partially reversed the upregulation of RANKL induced by TLR ligands. RA-FLS stimulated by TLR-2 and TLR-4 ligands and cocultured with human monocytes induced high levels of expression of TRAP, RANK, cathepsin K, calcitonin receptor, and matrix metalloproteinase-9, suggesting that RA-FLS promote osteoclast differentiation. Our results suggest that the TLR signaling pathway, through TLR-2 and TLR-4, induces RANKL expression in RA-FLS and the expression of RANKL promotes the differentiation of osteoclasts in RA synovium. Targeting specific TLRs may be a promising approach to prevent inflammatory bone destruction in the pathogenesis of RA.
Kim
Kyoung-Woon
KW
The Center for Rheumatic diseases, Kang-Nam St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, South Korea.
Cho
Mi-La
ML
Lee
Sang-Heon
SH
Oh
Hye-Joa
HJ
Kang
Chang-Min
CM
Ju
Ji Hyeon
JH
Min
So-Youn
SY
Cho
Young-Gyu
YG
Park
Sung-Hwan
SH
Kim
Ho-Youn
HY
D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000378:metabolism; D016022:Case-Control Studies; D005260:Female; D005347:Fibroblasts / Q000276:immunology*; D006801:Humans; D007113:Immunity, Innate; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000276:immunology / Q000378:metabolism; D010010:Osteoclasts / Q000276:immunology*; D053245:RANK Ligand / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
D053245:RANK Ligand; C505688:TNFSF11 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4