Bone Abstracts

Osteoclasts are multinucleated bone-resorbing cells and can be cultured from different monocytic precursors. It is unknown whether osteoclasts derived from different precursors are phenotypically different. One of the aspects not known is the life span of the different osteoclasts and the effect of IL-1β hereupon. Here, we studied this using time-lapse microscopy. Bone marrow cells were isolated from 6-week-old male mice. Early blasts (CD31^hiLy-6C^-), myeloid blasts (CD31⁺Ly-6C⁺) and monocytes (CD31⁻Ly-6C^hi) were sorted using flow cytometry. Cells were cultured in the presence of M-CSF and RANKL, with or without 10 ng/ml IL-1β on plastic and visualized by time-lapse microscopy. The stimulatory effect on multinucleation by IL-1β, as shown previously by others, was confirmed. We found that large osteoclasts (>10 nuclei) generated from the three subsets in the presence of IL-1β differed remarkably in their life span. The myeloid blast-derived large osteoclasts were found earliest, after 75 h; these cells survived for only 30 h. The monocyte-derived large osteoclasts were found 20 h later, after 95 h. These cells, however, survived the longest, being 50 h. The early blast-derived-large osteoclasts were in between, appeared after 85 h with life span of 40 h. Next we analyzed the life span of individual osteoclasts and found that osteoclasts that became large (>10 nuclei) had a significantly shorter life span than osteoclasts that remained small (<10 nuclei), being 13±7 h for large osteoclasts and 51±16 h for the smaller ones. The large osteoclasts generated by monocytes in the presence of IL-1β had a significantly longer life span (22±8 hours/osteoclast) than the osteoclasts generated by early blasts (12±4 hours/osteoclast) and myeloid blasts (12±3 hours/osteoclast). In conclusion, considerable differences occur between the life span of osteoclasts derived from different bone marrow precursors. We propose that depending on the inflammatory situation, osteoclasts with various life span can be generated.