Characterization of the development of ectopic chondroid/bone matrix and chondrogenic/osteogenic cells during osteoinduction by rhBMP-2: a histochemical and ultrastructural study.
OBJECTIVE
To investigate the characteristics of ectopic chondroid/bone matrix and chondrogenic/osteogenic cells induced by recombinant human bone morphogenetic protein-2 (rhBMP-2).


METHODS
rhBMP-2 (5 microg) combined with atelocollagen was implanted into calf muscles of rats and removed on days 7, 10, 14, 21, or 28. Tissue sections were examined using: (i) hematoxylin/Alcian blue/Sirius red stain, (ii) enzyme histochemistry for alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase activity, (iii) immunohistochemistry for types I, II, and X collagen, and (iv) electron microscopy.


RESULTS
On day 7, numerous fibroblast-like cells with ALP activity were present on the pellet rim. On day 10, chondroid matrix (CM) had formed, contained both type I collagen and proteoglycans, and often continued into the BMP pellet. On day 14, bone-like matrix formed around hypertrophic chondrocytes simultaneously with endochondral ossification. Coexpression of types I and II collagen within chondrocytes and osteocytes was observed throughout the time course of the experiment.


CONCLUSIONS
These results suggest that fibroblast-like cells invading the pellet differentiate into chondrocytes and form CM under the scaffold of the carrier component. It appears that some chondrocytes change their phenotype to produce the bone-like matrix and remain within the endochondral bone. This process enables rapid osteogenesis to occur.
Nakagawa
T
T
Department of Oral and Maxillofacial Surgery, Faculty of Medicine, Mie University, Tsu, Mie, Japan. toshi@clin.medic.mie-u.ac.jp
Sugiyama
T
T
Shimizu
K
K
Murata
T
T
Narita
M
M
Nakamura
S
S
Tagawa
T
T
D000135:Acid Phosphatase / Q000032:analysis; D000469:Alkaline Phosphatase / Q000032:analysis; D000818:Animals; D015415:Biomarkers / Q000032:analysis; D001857:Bone Matrix / Q000187:drug effects / Q000648:ultrastructure*; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology*; D002356:Cartilage / Q000187:drug effects / Q000648:ultrastructure; D019902:Chondrocytes / Q000187:drug effects / Q000648:ultrastructure*; D020219:Chondrogenesis / Q000187:drug effects*; D024042:Collagen Type I / Q000032:analysis; D024043:Collagen Type II / Q000032:analysis; D024121:Collagen Type X / Q000032:analysis; D005347:Fibroblasts / Q000187:drug effects / Q000648:ultrastructure; D006801:Humans; D007527:Isoenzymes / Q000032:analysis; D008297:Male; D018482:Muscle, Skeletal / Q000601:surgery; D009999:Ossification, Heterotopic / Q000473:pathology*; D010011:Osteocytes / Q000187:drug effects / Q000648:ultrastructure*; D010012:Osteogenesis / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins; D000071681:Tartrate-Resistant Acid Phosphatase; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
C525718:BMP2 protein, human; D015415:Biomarkers; C525720:Bmp2 protein, rat; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D024042:Collagen Type I; D024043:Collagen Type II; D024121:Collagen Type X; D007527:Isoenzymes; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2; D000469:Alkaline Phosphatase; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase