Bone degrading osteoclasts (OCs) play an important role in several inflammatory skeletal disorders. They differentiate from the monocyte/macrophage lineage. In this lineage, three subsets have been identified; classical, intermediate and non-classical monocytes. The capacity of these subsets to differentiate into OCs and whether inflammatory cytokines influence this differentiation is unknown. The objective was to evaluate osteoclastogenesis of the monocyte subsets and the effect of inflammatory factor interleukin-17A (IL-17A) hereupon.
Methods: Monocytes were isolated from peripheral blood and sorted with flow cytometry based on CD14 and CD16 expression. The subsets were seeded onto plastic and bone. Differentiation was induced by osteoclastogenic medium containing 10 ng/ml M-CSF and 2 ng/ml RANKL, with or without 10 ng/ml IL-17A. After 17 days, OCs were visualised with TRACP staining and bone resorption was evaluated with Coomassie Brilliant Blue staining.
Results: All precursor subsets gave rise to OCs. IL-17A did not affect the total number of OCs in the classical subset, but a significant lower number was observed for the intermediate subset on both plastic and bone. The number of OCs derived from the non-classical subset was up-regulated on bone and an increased number of large OCs (>20 nuclei) was observed on plastic. Extensive bone resorption was only observed for the classical subset, independent of IL-17A.
Conclusion: Different subsets of human OC precursors from peripheral blood respond in distinct ways to IL-17A treatment and targeting of specific precursor subsets is a promising therapeutic approach for diseases associated with inflammatory bone loss.
Disclosure: The authors declared no competing interests. Research conducted within Euroclast, a Marie Curie FP7-People-2013-ITN: # 607446.