OP0241 IL9 MODULATION OF OSTEOCLASTS DIFFERENTIATION AND IMPACTS ON BONE METABOLISM
Authors: M. Saad, S. Rauber, G. Schett, A. Ramming
Journal: Annals of the Rheumatic Diseases (2020)

Background: Osteoclasts are multinucleated cells originating from the monocytes/macrophage lineage and require receptor activator of NF-κB ligand (RANK-L) and macrophage-colony-stimulating factor (M-CSF) for their development. They play a major role in bone remodeling by degrading the calcified bone matrix. They are considered as one of the culprits in bone destruction in many inflammatory diseases e.g. rheumatoid arthritis and osteoporosis. In previous work by our group, it was observed that IL-9 mediated the resolution of inflammation in rheumatoid arthritis and hence protected against bone degradation in animal models. Despite this protection was particularly associated to the resolution of inflammation, our data also supported the hypothesis of a direct signalling of IL-9 to osteoclasts. Objectives: The aim of this study was to investigate the modulating effect of IL-9 on osteoclasts and on the bone metabolism. Methods: Osteoclasts differentiation was studied in the mouse models of antigen induced arthritis (AIA) and KBxN serum induced arthritis (SIA) in the presence and absence of IL-9 by histomorphometric analysis and microcomputed tomography scans (µCT). Osteoclasts were generated from bone marrow derived monocytes of BALB/c mice with M-CSF, RANKL and IL-9, which were added in varying concentrations to induce osteoclast differentiation. Tartrate-resistant acid phosphatase (TRAP) staining was performed to follow the differentiation steps from monocytes into multinucleated osteoclasts and to determine the effects of IL-9 on osteoclastogenesis. Additionally, we performed RNA-seq and seahorse analysis to detect IL-9 dependent, differentially expressed genes and metabolites. Intracellular signaling as induced by IL9R activation was followed by western blot analysis. Results: IL-9 KO mice showed higher numbers of osteoclasts as compared to wild-type mice in the mouse models of AIA and SIA. Microcomputed tomography showed pronounced loss of the trabecular network and bone volume as signs of inflammation-induced osteopenia in Il9−/− mice. We found that osteoclasts express high levels of IL-9R. Next, monocytes were differentiated into osteoclasts in the presence of different concentrations of recombinant IL-9. Cells cultured in the presence of IL-9 showed significantly impaired differentiation into osteoclasts. We observed phosphorylation of STAT3 and STAT5 in cultured osteoclasts in dependency of IL-9. Furthermore, the presence of IL-9 during osteoclast differentiation impacted the gene expression levels of characteristic osteoclast related genes such as NFATc1, Cathepsin K and TRAP. Furthermore, IL-9 showed a major impact on mitochondrial respiration rate and glycolysis as assessed by Seahorse assays. Conclusion: IL-9 exerted direct effects on osteoclast differentiation and modulated the expression of several genes that are related to osteoclast differentiation and function. Disclosure of Interests: mina saad: None declared, Simon Rauber: None declared, Georg Schett Speakers bureau: AbbVie, BMS, Celgene, Janssen, Eli Lilly, Novartis, Roche and UCB, Andreas Ramming Grant/research support from: Pfizer, Novartis, Consultant of: Boehringer Ingelheim, Novartis, Gilead, Pfizer, Speakers bureau: Boehringer Ingelheim, Roche, Janssen