Background Osteoclast-derived exosomes play an important role in cell-to-cell communication during bone remodeling. However, it remains to be further studied whether the exosomes from precursor and mature osteoclast have distinct effects on osteoblast differentiation.
Objective To investigate the effects of exosomes derived from precursor osteoclasts (pOC) and mature osteoclasts (mOC) on osteoblast differentiation.
Methods Bone marrow macrophages (BMMs) were stimulated with receptor activator of nuclear factor κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) to induce osteoclast differentiation. Exosomes secreted by pOC and mOC were extracted and characterized. The obtained exosomes were then separately used to intervene with primary mouse calvaria osteoblasts and induce osteogenic differentiation. The uptake of exosomes was observed using fluorescence labeling. The effects of the two types of exosomes on osteoblast differentiation were identified by alizarin red (ARS) staining, alkaline phosphatase (ALP) staining and RT-qPCR.
Results mOCs exhibited a more typical multinuclear fusion structure compared to pOCs. The particle size of both types of exosomes was concentrated at 100 nm, with a cup-shaped circular morphology and expression of exosome-specific proteins. Both types of exosomes could be taken up by osteoblasts. Staining results of osteoblasts showed that the number of calcium nodules stained with ARS and the intensity of ALP staining increased significantly in the mOC-exosome intervention group compared to the pOC-exosome intervention group. The expression of bone formation genes in the mOC-exosome intervention group was significantly higher than that in the pOC-exosome group and control group.
Conclusion Mature osteoclast-derived exosomes may have a stronger ability to promote osteoblast differentiation compared to precursor osteoclast-derived exosomes.
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