AB0110 Anti-Rankl Treatment Inhibits Erosive Joint Destruction But Has No Effect on Bone Formation in the DTH Arthritis Model

BackgroundThe delayed-type hypersensitivity arthritis (DTHA) model combines collagen type II antibody (anti-CII) treatment with local DTH induction in the footpad [1] which induces a strong arthritis accompanied by bone destruction and excessive peri-articular bone formation.ObjectivesHere we analyzed the impact of osteoclasts on inflammation, joint damage and bone formation in the DTHA model.MethodsC57BL/6 mice were immunized with methylated BSA (mBSA) in CFA, given 1000 μg anti-CII four days later [1] and challenged seven days after immunization with 200 μg mBSA in PBS in one hind foot pad and with 20 μl PBS only in the other foot pad (control). Osteoclast activity was determined in vivo by fluorescence imaging using the Cat K 680 FAST probe. Receptor-activator of nuclear factor kappa B (RANKL), TRAP and Cathespin K (CatK) mRNA expression was analyzed in arthritic paw tissue by mRNA deep sequencing. TRAP5b, CTX-I and CTX-II serum levels were determined by ELISA. In situ expression of tartrate-resistant acid phosphatase (TRAP), collagen 10 (COL10) and osteocalcin was detected by immunohistochemical staining. Inflammation, erosive joint damage and peri-articular bone formation were semi-quantitatively scored.ResultsIn vivo imaging of osteoclast activity showed increased CatK activity on days 3 and 8 after arthritis induction in the arthritic paw. RANKL mRNA expression peaked on d3 while TRAP and CatK mRNA expression peaked on d8. Erosive joint damage was driven from the subchrondal bone marrow side. Here, TRAP-positive osteoclasts were located at the borders of a granulation tissue which eroded the subchondral bone plate. Peri-articular bone formation involved COL10 expressing hypertrophic chondrocytes as well as osteocalcin–expressing osteoblasts. Treatment with anti-RANKL antibody did not affect footpad swelling (p>0.05) but reduced the serum levels of TRAP5b (p