Ascorbic acid induces alkaline phosphatase, type X collagen, and calcium deposition in cultured chick chondrocytes.
During the process of endochondral bone formation, proliferating chondrocytes give rise to hypertrophic chondrocytes, which then deposit a mineralized matrix to form calcified cartilage. Chondrocyte hypertrophy and matrix mineralization are associated with expression of type X collagen and the induction of high levels of the bone/liver/kidney isozyme of alkaline phosphatase. To determine what role vitamin C plays in these processes, chondrocytes derived from the cephalic portion of 14-day chick embryo sternae were grown in the absence or presence of exogenous ascorbic acid. Control untreated cells displayed low levels of type X collagen and alkaline phosphatase activity throughout the culture period. However, cells grown in the presence of ascorbic acid produced increasing levels of alkaline phosphatase activity and type X collagen mRNA and protein. Both alkaline phosphatase activity and type X collagen mRNA levels began to increase within 24 h of ascorbate treatment; by 9 days, the levels of both alkaline phosphatase activity and type X collagen mRNA were 15-20-fold higher than in non-ascorbate-treated cells. Ascorbate treatment also increased calcium deposition in the cell layer and decreased the levels of types II and IX collagen mRNAs; these effects lagged significantly behind the elevation of alkaline phosphatase and type X collagen. Addition of beta-glycerophosphate to the medium increased calcium deposition in the presence of ascorbate but had no effect on levels of collagen mRNAs or alkaline phosphatase. The results suggest that vitamin C may play an important role in endochondral bone formation by modulating gene expression in hypertrophic chondrocytes.
Leboy
P S
PS
Department of Biochemistry School of Dental Medicine, University of Pennsylvania, Philadelphia 19104-6003.
Vaias
L
L
Uschmann
B
B
Golub
E
E
Adams
S L
SL
Pacifici
M
M
D000469:Alkaline Phosphatase / Q000096:biosynthesis*; D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002356:Cartilage / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D002642:Chick Embryo; D003094:Collagen / Q000096:biosynthesis* / Q000235:genetics; D004790:Enzyme Induction / Q000187:drug effects; D005994:Glycerophosphates / Q000494:pharmacology; D007700:Kinetics; D012333:RNA, Messenger / Q000096:biosynthesis
D005994:Glycerophosphates; D012333:RNA, Messenger; D003094:Collagen; D000469:Alkaline Phosphatase; D001205:Ascorbic Acid; D002118:Calcium; C031463:beta-glycerophosphoric acid