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Osteoblast recruitment and bone formation enhanced by cell matrix-associated heparin-binding growth-associated molecule (HB-GAM).

Imai S, Kaksonen M, Raulo E, Kinnunen T, Fages C, Meng X, Lakso M, Rauvala H - J. Cell Biol. (1998)

Bottom Line: We show here that heparin-binding growth-associated molecule (HB-GAM), an extracellular matrix-associated protein that enhances migratory responses in neurons, is prominently expressed in the cell matrices that act as target substrates for bone formation.The HB-GAM transgenic mice develop a phenotype characterized by an increased bone thickness.HB-GAM may thus play an important role in bone formation, probably by mediating recruitment and attachment of osteoblasts/osteoblast precursors to the appropriate substrates for deposition of new bone.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy, Shiga University of Medical Science, Shiga-ken, 520-2192, Japan. simai@belle.shiga-med.ac.jp

ABSTRACT
Bone has an enormous capacity for growth, regeneration, and remodeling. This capacity is largely due to induction of osteoblasts that are recruited to the site of bone formation. The recruitment of osteoblasts has not been fully elucidated, though the immediate environment of the cells is likely to play a role via cell- matrix interactions. We show here that heparin-binding growth-associated molecule (HB-GAM), an extracellular matrix-associated protein that enhances migratory responses in neurons, is prominently expressed in the cell matrices that act as target substrates for bone formation. Intriguingly, N-syndecan, which acts as a receptor for HB-GAM, is expressed by osteoblasts/osteoblast precursors, whose ultrastructural phenotypes suggest active cell motility. The hypothesis that HB-GAM/N-syndecan interaction mediates osteoblast recruitment, as inferred from developmental studies, was tested using osteoblast-type cells that express N-syndecan abundantly. These cells migrate rapidly to HB-GAM in a haptotactic transfilter assay and in a migration assay where HB-GAM patterns were created on culture wells. The mechanism of migration is similar to that previously described for the HB-GAM-induced migratory response of neurons. Our hypothesis that HB-GAM/N-syndecan interaction participates in regulation of osteoblast recruitment was tested using two different in vivo models: an adjuvant-induced arthritic model and a transgenic model. In the adjuvant-induced injury model, the expression of HB-GAM and of N-syndecan is strongly upregulated in the periosteum accompanying the regenerative response of bone. In the transgenic model, the HB-GAM expression is maintained in mesenchymal tissues with the highest expression in the periosteum. The HB-GAM transgenic mice develop a phenotype characterized by an increased bone thickness. HB-GAM may thus play an important role in bone formation, probably by mediating recruitment and attachment of osteoblasts/osteoblast precursors to the appropriate substrates for deposition of new bone.

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Expression of HB-GAM and  N-syndecan in the developing rat bone  (immunodetection for the protein, a–d; in  situ hybridization for mRNA, e and f; immunoelectron microscopy for N-syndecan,  g and h; E, embryonic day). (a) Abundant  expression of HB-GAM in the cartilage  templates. (b) No expression of N-syndecan in the cartilage templates at E16 (the  same magnification as in a). (c) HB-GAM  expression persisting in the mineralized  cartilage, the structure of which is conceivable by the enlarged lacunae of the  chondrocytes (arrowheads). (d) N-syndecan  expression by the cells dispersed in the  mineralized cartilage (arrows; the same  magnification as in c). (e) Selective expression of HB-GAM mRNA by the chondrocytes in the cartilage matrix (cm). (f) Selective expression of N-syndecan mRNA by  the cells in the mineralized cartilage (mc)  and mineralized bone (the same magnification as in e; the rectangles g and h represent the regions of panels g and h). (g)  N-syndecan is localized on the surface of  the cell (arrowheads; ch-b), the phenotype  of which is distinct from a hypertrophied  chondrocyte (ch-a) (the rectangle indicates  the inset). (h) N-syndecan is expressed by  the cells in the mineralized bone (arrowheads; the rectangle indicates the inset).  The ultrastructural phenotype of the cells  suggest an active motility with well-developed cell processes. hm, humerus; rd, radius; ul, ulna; mb, mineralized bone. Bars:  (a and e) 500 μm; (c) 1,250 μm; (g) 10 μm;  (h) 8 μm.
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Figure 1: Expression of HB-GAM and N-syndecan in the developing rat bone (immunodetection for the protein, a–d; in situ hybridization for mRNA, e and f; immunoelectron microscopy for N-syndecan, g and h; E, embryonic day). (a) Abundant expression of HB-GAM in the cartilage templates. (b) No expression of N-syndecan in the cartilage templates at E16 (the same magnification as in a). (c) HB-GAM expression persisting in the mineralized cartilage, the structure of which is conceivable by the enlarged lacunae of the chondrocytes (arrowheads). (d) N-syndecan expression by the cells dispersed in the mineralized cartilage (arrows; the same magnification as in c). (e) Selective expression of HB-GAM mRNA by the chondrocytes in the cartilage matrix (cm). (f) Selective expression of N-syndecan mRNA by the cells in the mineralized cartilage (mc) and mineralized bone (the same magnification as in e; the rectangles g and h represent the regions of panels g and h). (g) N-syndecan is localized on the surface of the cell (arrowheads; ch-b), the phenotype of which is distinct from a hypertrophied chondrocyte (ch-a) (the rectangle indicates the inset). (h) N-syndecan is expressed by the cells in the mineralized bone (arrowheads; the rectangle indicates the inset). The ultrastructural phenotype of the cells suggest an active motility with well-developed cell processes. hm, humerus; rd, radius; ul, ulna; mb, mineralized bone. Bars: (a and e) 500 μm; (c) 1,250 μm; (g) 10 μm; (h) 8 μm.

Mentions: HB-GAM was intensely expressed in the matrix of the developing cartilage (Fig. 1 a), which acts as a template for endochondral bone formation (Marks and Hermey, 1996). Little if any expression of N-syndecan was detected before beginning of ossification (Fig. 1 b). HB-GAM persisted in the matrix of the mineralized cartilage (Fig. 1 c), onto which osteoblasts deposit osteoid (Marks and Hermey, 1996; Scammell and Roach, 1996). N-syndecan–expressing cells were localized in the zone of the mineralized cartilage (Fig. 1 d). The localization of the two molecules thus overlapped in the zone of the mineralized cartilage (Fig. 1 c, arrowheads, and Fig. 1 d, arrows). The overlapping expression of the two molecules was maintained while the frontier of the ossification advanced toward the ends of the cartilage template, i.e., N-syndecan–expressing cells appeared to trace the mineralized cartilage, where HB-GAM is abundantly expressed. On the other hand, N-syndecan was not expressed in the anatomical regions where formation of bone tissue had been already completed. These light microscopic localizations of N-syndecan– expressing cells suggest that N-syndecan is expressed by the osteoblast lineage cells that are migrating toward the target matrix. As for the cellular source of HB-GAM, immunolocalization of HB-GAM and in situ hybridization of its mRNA (see below) suggest that chondrocytes supplies it to the cartilage matrix.


Osteoblast recruitment and bone formation enhanced by cell matrix-associated heparin-binding growth-associated molecule (HB-GAM).

Imai S, Kaksonen M, Raulo E, Kinnunen T, Fages C, Meng X, Lakso M, Rauvala H - J. Cell Biol. (1998)

Expression of HB-GAM and  N-syndecan in the developing rat bone  (immunodetection for the protein, a–d; in  situ hybridization for mRNA, e and f; immunoelectron microscopy for N-syndecan,  g and h; E, embryonic day). (a) Abundant  expression of HB-GAM in the cartilage  templates. (b) No expression of N-syndecan in the cartilage templates at E16 (the  same magnification as in a). (c) HB-GAM  expression persisting in the mineralized  cartilage, the structure of which is conceivable by the enlarged lacunae of the  chondrocytes (arrowheads). (d) N-syndecan  expression by the cells dispersed in the  mineralized cartilage (arrows; the same  magnification as in c). (e) Selective expression of HB-GAM mRNA by the chondrocytes in the cartilage matrix (cm). (f) Selective expression of N-syndecan mRNA by  the cells in the mineralized cartilage (mc)  and mineralized bone (the same magnification as in e; the rectangles g and h represent the regions of panels g and h). (g)  N-syndecan is localized on the surface of  the cell (arrowheads; ch-b), the phenotype  of which is distinct from a hypertrophied  chondrocyte (ch-a) (the rectangle indicates  the inset). (h) N-syndecan is expressed by  the cells in the mineralized bone (arrowheads; the rectangle indicates the inset).  The ultrastructural phenotype of the cells  suggest an active motility with well-developed cell processes. hm, humerus; rd, radius; ul, ulna; mb, mineralized bone. Bars:  (a and e) 500 μm; (c) 1,250 μm; (g) 10 μm;  (h) 8 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2132954&req=5

Figure 1: Expression of HB-GAM and N-syndecan in the developing rat bone (immunodetection for the protein, a–d; in situ hybridization for mRNA, e and f; immunoelectron microscopy for N-syndecan, g and h; E, embryonic day). (a) Abundant expression of HB-GAM in the cartilage templates. (b) No expression of N-syndecan in the cartilage templates at E16 (the same magnification as in a). (c) HB-GAM expression persisting in the mineralized cartilage, the structure of which is conceivable by the enlarged lacunae of the chondrocytes (arrowheads). (d) N-syndecan expression by the cells dispersed in the mineralized cartilage (arrows; the same magnification as in c). (e) Selective expression of HB-GAM mRNA by the chondrocytes in the cartilage matrix (cm). (f) Selective expression of N-syndecan mRNA by the cells in the mineralized cartilage (mc) and mineralized bone (the same magnification as in e; the rectangles g and h represent the regions of panels g and h). (g) N-syndecan is localized on the surface of the cell (arrowheads; ch-b), the phenotype of which is distinct from a hypertrophied chondrocyte (ch-a) (the rectangle indicates the inset). (h) N-syndecan is expressed by the cells in the mineralized bone (arrowheads; the rectangle indicates the inset). The ultrastructural phenotype of the cells suggest an active motility with well-developed cell processes. hm, humerus; rd, radius; ul, ulna; mb, mineralized bone. Bars: (a and e) 500 μm; (c) 1,250 μm; (g) 10 μm; (h) 8 μm.
Mentions: HB-GAM was intensely expressed in the matrix of the developing cartilage (Fig. 1 a), which acts as a template for endochondral bone formation (Marks and Hermey, 1996). Little if any expression of N-syndecan was detected before beginning of ossification (Fig. 1 b). HB-GAM persisted in the matrix of the mineralized cartilage (Fig. 1 c), onto which osteoblasts deposit osteoid (Marks and Hermey, 1996; Scammell and Roach, 1996). N-syndecan–expressing cells were localized in the zone of the mineralized cartilage (Fig. 1 d). The localization of the two molecules thus overlapped in the zone of the mineralized cartilage (Fig. 1 c, arrowheads, and Fig. 1 d, arrows). The overlapping expression of the two molecules was maintained while the frontier of the ossification advanced toward the ends of the cartilage template, i.e., N-syndecan–expressing cells appeared to trace the mineralized cartilage, where HB-GAM is abundantly expressed. On the other hand, N-syndecan was not expressed in the anatomical regions where formation of bone tissue had been already completed. These light microscopic localizations of N-syndecan– expressing cells suggest that N-syndecan is expressed by the osteoblast lineage cells that are migrating toward the target matrix. As for the cellular source of HB-GAM, immunolocalization of HB-GAM and in situ hybridization of its mRNA (see below) suggest that chondrocytes supplies it to the cartilage matrix.

Bottom Line: We show here that heparin-binding growth-associated molecule (HB-GAM), an extracellular matrix-associated protein that enhances migratory responses in neurons, is prominently expressed in the cell matrices that act as target substrates for bone formation.The HB-GAM transgenic mice develop a phenotype characterized by an increased bone thickness.HB-GAM may thus play an important role in bone formation, probably by mediating recruitment and attachment of osteoblasts/osteoblast precursors to the appropriate substrates for deposition of new bone.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy, Shiga University of Medical Science, Shiga-ken, 520-2192, Japan. simai@belle.shiga-med.ac.jp

ABSTRACT
Bone has an enormous capacity for growth, regeneration, and remodeling. This capacity is largely due to induction of osteoblasts that are recruited to the site of bone formation. The recruitment of osteoblasts has not been fully elucidated, though the immediate environment of the cells is likely to play a role via cell- matrix interactions. We show here that heparin-binding growth-associated molecule (HB-GAM), an extracellular matrix-associated protein that enhances migratory responses in neurons, is prominently expressed in the cell matrices that act as target substrates for bone formation. Intriguingly, N-syndecan, which acts as a receptor for HB-GAM, is expressed by osteoblasts/osteoblast precursors, whose ultrastructural phenotypes suggest active cell motility. The hypothesis that HB-GAM/N-syndecan interaction mediates osteoblast recruitment, as inferred from developmental studies, was tested using osteoblast-type cells that express N-syndecan abundantly. These cells migrate rapidly to HB-GAM in a haptotactic transfilter assay and in a migration assay where HB-GAM patterns were created on culture wells. The mechanism of migration is similar to that previously described for the HB-GAM-induced migratory response of neurons. Our hypothesis that HB-GAM/N-syndecan interaction participates in regulation of osteoblast recruitment was tested using two different in vivo models: an adjuvant-induced arthritic model and a transgenic model. In the adjuvant-induced injury model, the expression of HB-GAM and of N-syndecan is strongly upregulated in the periosteum accompanying the regenerative response of bone. In the transgenic model, the HB-GAM expression is maintained in mesenchymal tissues with the highest expression in the periosteum. The HB-GAM transgenic mice develop a phenotype characterized by an increased bone thickness. HB-GAM may thus play an important role in bone formation, probably by mediating recruitment and attachment of osteoblasts/osteoblast precursors to the appropriate substrates for deposition of new bone.

Show MeSH
Related in: MedlinePlus