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Osteoclast fusion is based on heterogeneity between fusion partners.

Hobolt-Pedersen AS, Delaissé JM, Søe K - Calcif. Tissue Int. (2014)

Bottom Line: These stainings revealed heterogeneous localization patterns of all three factors within a given culture of osteoclasts.CD47 was found to be localized primarily in small osteoclasts and preosteoclasts, which were also positive for DC-STAMP but negative for cathepsin K expression.Considering the in vivo environment in which osteoclasts develop and fuse, our findings seem very applicable and provide novel, important insight into key issues in bone and fusion research.

View Article: PubMed Central - PubMed

Affiliation: Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark, Kabbeltoft 25, 7100, Vejle, Denmark.

ABSTRACT
Bone-resorbing osteoclasts are formed through fusion of mononucleated precursors. Their choice of partners during the fusion process remains unclear. We hypothesized that osteoclasts are selective in their choice of fusion partner and that this selectivity is based on heterogeneity among the cells with respect to their maturation stage and their expression and cellular organization of fusion factors. Support for this hypothesis was found from immunofluorescence staining of the osteoclast fusion factors CD47, dendritic cell-specific transmembrane protein (DC-STAMP), and syncytin-1. These stainings revealed heterogeneous localization patterns of all three factors within a given culture of osteoclasts. CD47 was found to be localized primarily in small osteoclasts and preosteoclasts, which were also positive for DC-STAMP but negative for cathepsin K expression. A role of CD47 in the early osteoclast fusion steps was also suggested from experiments with a CD47 blocking antibody, which resulted in an inhibition of the fusion of small osteoclasts. Conversely, blocking of connexin 43 affected the fusion of larger osteoclasts with four or more nuclei. The suggestion that different fusion factors function at different stages of osteoclast fusion supports the idea of heterogeneity in the osteoclast population; our results suggest that osteoclast fusion is indeed based on heterogeneity. Considering the in vivo environment in which osteoclasts develop and fuse, our findings seem very applicable and provide novel, important insight into key issues in bone and fusion research.

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Related in: MedlinePlus

Visualization by confocal microscopy of CD47 in fusing (pre)OCs. Staining of CD47 (red) and F-actin (green) in (pre)OCs (1 × 105 per well) differentiated for 5 days with RANKL. Nuclei were visualized with DAPI (blue). Z stacks along the x- and y-axes are presented at bottom and on right side of images. a CD47 is localized to the part of the cell membrane where a preOC is tightly interacting with a binucleated OC. b Two preOCs in close proximity. Both show strong CD47 signals at the part of their membrane facing the other cell
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Fig4: Visualization by confocal microscopy of CD47 in fusing (pre)OCs. Staining of CD47 (red) and F-actin (green) in (pre)OCs (1 × 105 per well) differentiated for 5 days with RANKL. Nuclei were visualized with DAPI (blue). Z stacks along the x- and y-axes are presented at bottom and on right side of images. a CD47 is localized to the part of the cell membrane where a preOC is tightly interacting with a binucleated OC. b Two preOCs in close proximity. Both show strong CD47 signals at the part of their membrane facing the other cell

Mentions: The use of confocal microscopy revealed in detail the localization of CD47 in fusing (pre)OCs. Figure 4 shows (pre)OCs interacting in close proximity, which strongly indicates forthcoming fusion. In the examples shown in Fig. 4a, b, CD47 was clearly concentrated at the part of the preOC membrane facing the fusion partner in Fig. 4a in the smaller of the two partners and in Fig. 4b in both partners. From the cross-sectional representation in Fig. 4a, a clear front of CD47 is revealed at the part of the preOC cell membrane that is in contact with the fusion partner.Fig. 4


Osteoclast fusion is based on heterogeneity between fusion partners.

Hobolt-Pedersen AS, Delaissé JM, Søe K - Calcif. Tissue Int. (2014)

Visualization by confocal microscopy of CD47 in fusing (pre)OCs. Staining of CD47 (red) and F-actin (green) in (pre)OCs (1 × 105 per well) differentiated for 5 days with RANKL. Nuclei were visualized with DAPI (blue). Z stacks along the x- and y-axes are presented at bottom and on right side of images. a CD47 is localized to the part of the cell membrane where a preOC is tightly interacting with a binucleated OC. b Two preOCs in close proximity. Both show strong CD47 signals at the part of their membrane facing the other cell
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4048669&req=5

Fig4: Visualization by confocal microscopy of CD47 in fusing (pre)OCs. Staining of CD47 (red) and F-actin (green) in (pre)OCs (1 × 105 per well) differentiated for 5 days with RANKL. Nuclei were visualized with DAPI (blue). Z stacks along the x- and y-axes are presented at bottom and on right side of images. a CD47 is localized to the part of the cell membrane where a preOC is tightly interacting with a binucleated OC. b Two preOCs in close proximity. Both show strong CD47 signals at the part of their membrane facing the other cell
Mentions: The use of confocal microscopy revealed in detail the localization of CD47 in fusing (pre)OCs. Figure 4 shows (pre)OCs interacting in close proximity, which strongly indicates forthcoming fusion. In the examples shown in Fig. 4a, b, CD47 was clearly concentrated at the part of the preOC membrane facing the fusion partner in Fig. 4a in the smaller of the two partners and in Fig. 4b in both partners. From the cross-sectional representation in Fig. 4a, a clear front of CD47 is revealed at the part of the preOC cell membrane that is in contact with the fusion partner.Fig. 4

Bottom Line: These stainings revealed heterogeneous localization patterns of all three factors within a given culture of osteoclasts.CD47 was found to be localized primarily in small osteoclasts and preosteoclasts, which were also positive for DC-STAMP but negative for cathepsin K expression.Considering the in vivo environment in which osteoclasts develop and fuse, our findings seem very applicable and provide novel, important insight into key issues in bone and fusion research.

View Article: PubMed Central - PubMed

Affiliation: Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark, Kabbeltoft 25, 7100, Vejle, Denmark.

ABSTRACT
Bone-resorbing osteoclasts are formed through fusion of mononucleated precursors. Their choice of partners during the fusion process remains unclear. We hypothesized that osteoclasts are selective in their choice of fusion partner and that this selectivity is based on heterogeneity among the cells with respect to their maturation stage and their expression and cellular organization of fusion factors. Support for this hypothesis was found from immunofluorescence staining of the osteoclast fusion factors CD47, dendritic cell-specific transmembrane protein (DC-STAMP), and syncytin-1. These stainings revealed heterogeneous localization patterns of all three factors within a given culture of osteoclasts. CD47 was found to be localized primarily in small osteoclasts and preosteoclasts, which were also positive for DC-STAMP but negative for cathepsin K expression. A role of CD47 in the early osteoclast fusion steps was also suggested from experiments with a CD47 blocking antibody, which resulted in an inhibition of the fusion of small osteoclasts. Conversely, blocking of connexin 43 affected the fusion of larger osteoclasts with four or more nuclei. The suggestion that different fusion factors function at different stages of osteoclast fusion supports the idea of heterogeneity in the osteoclast population; our results suggest that osteoclast fusion is indeed based on heterogeneity. Considering the in vivo environment in which osteoclasts develop and fuse, our findings seem very applicable and provide novel, important insight into key issues in bone and fusion research.

Show MeSH
Related in: MedlinePlus