Tumor necrosis factor receptor-associated factor 6 (TRAF6) inhibition modulates bone loss and matrix metalloproteinase expression levels in collagen-induced rheumatoid arthritis rat.

Background: Rheumatoid arthritis (RA) is a main characterized by persistent synovitis, systemic inflammation, and autoantibodies. Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an E3 ubiquitin ligase and is a crucial cytoplasm signal adaptor that can regulate critical biological processes. This research aims to explore the function of TRAF6 on bone loss and matrix metalloproteinase (MMP) expression in collagen-induced RA rats.

Methods: The RA model in rats (Sprague Dawley rat, 5-6 weeks old, weight 246.88±8.31 g) was set up via using collagen-induced RA. The shRNA-TRAF6 knockdown efficiency was tested using real-time reverse transcription-polymerase chain reaction (qRT-PCR) and western blot, respectively. The rats were divided into four groups: the control group, RA group, RA + shRNA-NC group, and RA + TRAF6-shRNA group. The tartrate-resistant acidic phosphatase (TRAP), hematoxylin and eosin (H&E), and Saffron O staining were employed to test the bone injury. The mRNA and protein expressive of Osteoclast-associated receptor (OSCAR), TRAP, Osterix (Osx), Collagen type I alpha 1 (COL1A1), Distal-less homeobox2 (Dlx2), tissue inhibitor of metalloproteinase (TIMP), matrix metalloproteinase-1(MMP-1), Cyclooxygenase 2 (COX2) and qRT-PCR performed MMP-13 and western blot, respectively.

Results: The mRNA and protein expression levels of TRAF6 were down-regulated in the RA + TRAF6- shRNA group. After the levels of TRAF6 were inhibited, the levels of bone volume/total volume (BV/TV), trabecular bone thickness (Tb.Th), and trabecular bone number (Tb.N) were increased, while the levels of trabecular bone space (Tb.Sp), Osteocalcin and ALP were deceased. The mRNA and protein expression levels of OSCAR, TRAP, MMP-1, COX2, and MMP-13 were reduced obviously in the RA + TRAF6- shRNA group compared with the RA + shRNA-NC group, while the levels of TIMP-1, OSX, CoL1A1, and DLx2 were enhanced obviously.

Conclusions: Inhibition of TRAF6 reduces bone loss and MMP expression levels in collagen-induced RA rat, and supplies an alternative treatment method in RA.