Site-specific in vivo calcification and osteogenesis stimulated by bone sialoprotein.
Bone sialoprotein (BSP) is one of the major non-collagenous glycosylated phosphoproteins of the extracellular matrix in bone. In vitro studies suggest that BSP may play important roles in the initiation and/or growth of calcium-phosphate crystals. To investigate the potential role of BSP in more complex in vivo environments, we implanted purified bovine BSP with type-I collagen as a carrier into surgically created rat calvarial defects and thoracic subcutaneous pouches. The responses to the implants were assessed by histochemistry, immunohistochemistry, in situ hybridization, quantitative real-time PCR, and biochemical analyses. BSP-collagen, but not collagen alone, elicited mineral deposition in the matrix of proliferating cells near the dura at days 4-5 followed by osteoblast differentiation and synthesis of new bone in the mid-portion of the calvarial defects. In contrast, implantation of BSP-collagen into subcutaneous pouches did not induce calcification or osteogenesis over the same experimental period. We explored the underlying mechanisms for the site-specific responses to BSP-collagen implants and found that higher levels of calcium content and alkaline phosphatase activity at the cranial site at days 2-5 were associated with the BSP-mediated calcification. We also found that BSP stimulated osteoblast differentiation through up-regulation of cbfa1 and osterix, key transcription factors of osteoblast differentiation, which occurred in the calvarial defects but not in the subcutaneous tissue. These results demonstrate that BSP stimulates calcification and osteogenesis in a site-specific manner, and that local environment and the specificities of responding cells may play critical roles in the function of BSP in vivo.
Wang
Jinxi
J
Laboratory for the Study of Skeletal Disorders and Rehabilitation, Department of Orthopedic Surgery, Harvard Medical School, Children's Hospital, Boston, MA 02115, USA. jwang@kumc.edu
Zhou
Hai-Yan
HY
Salih
Erdjan
E
Xu
Lan
L
Wunderlich
Livius
L
Gu
Xuesong
X
Hofstaetter
Jochen G
JG
Torres
Marie
M
Glimcher
Melvin J
MJ
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002113:Calcification, Physiologic; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D002454:Cell Differentiation / Q000502:physiology; D003094:Collagen / Q000378:metabolism; D050659:Core Binding Factor Alpha 1 Subunit / Q000378:metabolism; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008297:Male; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects; D010012:Osteogenesis / Q000502:physiology*; D053495:Osteopontin; D010758:Phosphorus / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012795:Sialoglycoproteins / Q000378:metabolism*; D012886:Skull / Q000293:injuries / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism
D050659:Core Binding Factor Alpha 1 Subunit; D012795:Sialoglycoproteins; C495181:Sp7 protein, rat; C506897:Spp1 protein, rat; D014157:Transcription Factors; D053495:Osteopontin; D010758:Phosphorus; D003094:Collagen; D000469:Alkaline Phosphatase; D002118:Calcium