P031/O12 Sialic acids negatively affect the bone resorptive capacity of osteoclasts

Career situation of first and presenting author Student for a master or a PhD. Introduction In rheumatoid arthritis the imbalance between osteoblasts and osteoclasts leads to an increased bone resorption, resulting in extensive bone destruction. Osteoclasts are multinucleated cells formed after fusion of macrophages. Macrophages are known to acquire an anti-inflammatory phenotype upon engagement of the carbohydrate sialic acid1, however whether triggering by sialic acids affects osteoclastogenesis is unknown. Therefore, we investigated the effect of sialic acids on osteoclastogenesis and their expression of the sialic acid binding receptors, called Siglecs. Methods Human monocytes were plated on either plastic, glass or bone slices and stimulated with M-CSF and RANK-L to generate osteoclasts. We designed a novel sorting methodology to separate the osteoclasts and the residual macrophages in our osteoclast-derived cultures. Purified osteoclasts were reanalyzed by microscopy and assessed for gene expression of osteoclast-specific genes by RT-PCR. Flow cytometry was used to obtain a full expression profile of the different siglec receptors in the osteoclasts, macrophages and monocytes precursor cells. Stimulation of pre-osteoclasts with sialic acids was done at day 7 and 10 of the culture. Supernatants were assessed for IL-6 and IL-10 production. Results Our novel osteoclast purification method resulted in pure osteoclasts expressing the classical genetic osteoclast markers such as cathepsin K and TRAP, while being negative for CD14. During the transition to osteoclasts, expression of siglec-1, −5/14 and −7 was lost, while siglec-6, –9 and −15 expression was maintained or gained. Osteoclasts are known for their effectively bone resorption, however after adding sialic acids to the pre-osteoclasts, both osteoclast formation and bone resorption were reduced, while an increase of IL-6 and IL-10 cytokines was observed. Conclusions Pre-osteoclasts stimulated with sialic acids display reduced osteoclast formation and bone resorption. Based on the siglec profiling we hypothesize that sialic acids engage siglec-9 on osteoclasts. Macrophages stimulated via siglec-9 produce IL-10 cytokine,1 similarly as we observed in our stimulation experiments. Currently, we are addressing the role of siglec-9 in osteoclastogenesis. Reference Ando M, et al. Siglec-9 enhances IL-10 production in macrophages via tyrosine-based motifs. Biochem Biophys Res Commun 2008;369(3):878–83. Disclosure of Interest None declared.