Biglycan modulates osteoblast differentiation and matrix mineralization.
MC3T3-E1 cell-derived clones expressing higher (S) or lower (AS) levels of biglycan were generated and characterized. The processes of cell differentiation and matrix mineralization were accelerated in S but delayed in AS, indicating that BGN modulates osteoblastic cell differentiation.


BACKGROUND
Biglycan (BGN), a member of the small leucine-rich proteoglycan family, is one of the major proteoglycans found in bone and has been implicated in bone formation. In this study, the effects of over- or underexpression of BGN on osteoblastic cell phenotypes and matrix mineralization were studied.


METHODS
MC3T3-E1 cells were transfected with vectors containing the BGN cDNA in a sense or antisense orientation to generate clones expressing higher (S clones) or lower (AS clones) levels of BGN. MC3T3-E1 cells and those transfected with an empty vector (EV) were used as controls. The levels of BGN synthesized by these clones were evaluated by Western blot analysis. Cell growth was analyzed by cell counting and cell differentiation by the gene expression patterns of several osteoblastic markers using quantitative real-time PCR. The abilities of these clones to form mineralized matrices were evaluated by in vitro and in vivo mineralization assays. Furthermore, the clones were treated with BMP-4 and their responsiveness was assessed.


RESULTS
The cell growth in these clones was unaffected; however, osteoblast differentiation was significantly accelerated in S clones and suppressed in AS clones. The in vitro matrix mineralization in S clones was significantly enhanced but severely impaired in AS clones. When transplanted into immunodeficient mice, S clone transplants exhibited larger areas of lamellar bonelike matrices, whereas only minute amounts of woven bone-type structure was found in AS transplants. The response to BMP-4 was higher in S clones but poorer in AS clones compared with that of controls.


CONCLUSIONS
BGN modulates osteoblast differentiation, possibly by regulating BMP signaling, and consequently matrix mineralization.
Parisuthiman
Duenpim
D
Dental Research Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
Mochida
Yoshiyuki
Y
Duarte
Wagner R
WR
Yamauchi
Mitsuo
M
D000818:Animals; D019898:Autocrine Communication / Q000187:drug effects / Q000235:genetics; D058578:Biglycan; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology; D002113:Calcification, Physiologic / Q000187:drug effects / Q000235:genetics; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D005109:Extracellular Matrix / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D005822:Genetic Vectors; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism*; D011509:Proteoglycans / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics
C546885:Bgn protein, mouse; D058578:Biglycan; C525810:Bmp4 protein, mouse; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D016326:Extracellular Matrix Proteins; D011509:Proteoglycans