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Matrix GLA protein is a developmental regulator of chondrocyte mineralization and, when constitutively expressed, blocks endochondral and intramembranous ossification in the limb.

Yagami K, Suh JY, Enomoto-Iwamoto M, Koyama E, Abrams WR, Shapiro IM, Pacifici M, Iwamoto M - J. Cell Biol. (1999)

Bottom Line: Warfarin effects on mineralization were highly selective, were accompanied by no appreciable changes in MGP expression, alkaline phosphatase activity, or cell number, and were counteracted by vitamin K cotreatment.Virally driven MGP overexpression in cultured chondrocytes greatly decreased mineralization.The results show that MGP is a powerful but developmentally regulated inhibitor of cartilage mineralization, controls mineral quantity but not type, and appears to have a previously unsuspected role in regulating chondrocyte maturation and ossification processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Oral Surgery, Showa University, Dental School, Ohta-Ku, Tokyo 145, Japan.

ABSTRACT
Matrix GLA protein (MGP), a gamma-carboxyglutamic acid (GLA)-rich, vitamin K-dependent and apatite-binding protein, is a regulator of hypertrophic cartilage mineralization during development. However, MGP is produced by both hypertrophic and immature chondrocytes, suggesting that MGP's role in mineralization is cell stage-dependent, and that MGP may have other roles in immature cells. It is also unclear whether MGP regulates the quantity of mineral or mineral nature and quality as well. To address these issues, we determined the effects of manipulations of MGP synthesis and expression in (a) immature and hypertrophic chondrocyte cultures and (b) the chick limb bud in vivo. The two chondrocyte cultures displayed comparable levels of MGP gene expression. Yet, treatment with warfarin, a gamma-carboxylase inhibitor and vitamin K antagonist, triggered mineralization in hypertrophic but not immature cultures. Warfarin effects on mineralization were highly selective, were accompanied by no appreciable changes in MGP expression, alkaline phosphatase activity, or cell number, and were counteracted by vitamin K cotreatment. Scanning electron microscopy, x-ray microanalysis, and Fourier-transform infrared spectroscopy revealed that mineral forming in control and warfarin-treated hypertrophic cell cultures was similar and represented stoichiometric apatite. Virally driven MGP overexpression in cultured chondrocytes greatly decreased mineralization. Surprisingly, MGP overexpression in the developing limb not only inhibited cartilage mineralization, but also delayed chondrocyte maturation and blocked endochondral ossification and formation of a diaphyseal intramembranous bone collar. The results show that MGP is a powerful but developmentally regulated inhibitor of cartilage mineralization, controls mineral quantity but not type, and appears to have a previously unsuspected role in regulating chondrocyte maturation and ossification processes.

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Histograms showing levels of APase activity and DNA content in hypertrophic chondrocyte cultures. Confluent cultures grown in medium A (A and C) and medium B (B and D) were left untreated (solid bars) or were treated with 10 μM warfarin (open bars) for 4 d in the absence or presence of indicated doses of vitamin K. After treatment, aliquots of the cell layer were used for determination of APase activity and DNA content.
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Figure 4: Histograms showing levels of APase activity and DNA content in hypertrophic chondrocyte cultures. Confluent cultures grown in medium A (A and C) and medium B (B and D) were left untreated (solid bars) or were treated with 10 μM warfarin (open bars) for 4 d in the absence or presence of indicated doses of vitamin K. After treatment, aliquots of the cell layer were used for determination of APase activity and DNA content.

Mentions: Since APase is an enzyme whose activity is closely associated with the mineralization process, we determined the activity of the phosphatase in control and warfarin-treated hypertrophic cultures. We found no change in APase activity per cell as a result of warfarin and vitamin K treatments or cotreatments in either medium A or medium B (Fig. 4A and Fig. B). This analysis also showed that warfarin treatment had no effect on cell number (Fig. 4C and Fig. D). Thus, MGP function in mineralization as revealed by warfarin interference depends on the stage of chondrocyte maturation, does not appear to be related to MGP expression levels, and does not involve changes in APase activity.


Matrix GLA protein is a developmental regulator of chondrocyte mineralization and, when constitutively expressed, blocks endochondral and intramembranous ossification in the limb.

Yagami K, Suh JY, Enomoto-Iwamoto M, Koyama E, Abrams WR, Shapiro IM, Pacifici M, Iwamoto M - J. Cell Biol. (1999)

Histograms showing levels of APase activity and DNA content in hypertrophic chondrocyte cultures. Confluent cultures grown in medium A (A and C) and medium B (B and D) were left untreated (solid bars) or were treated with 10 μM warfarin (open bars) for 4 d in the absence or presence of indicated doses of vitamin K. After treatment, aliquots of the cell layer were used for determination of APase activity and DNA content.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2169349&req=5

Figure 4: Histograms showing levels of APase activity and DNA content in hypertrophic chondrocyte cultures. Confluent cultures grown in medium A (A and C) and medium B (B and D) were left untreated (solid bars) or were treated with 10 μM warfarin (open bars) for 4 d in the absence or presence of indicated doses of vitamin K. After treatment, aliquots of the cell layer were used for determination of APase activity and DNA content.
Mentions: Since APase is an enzyme whose activity is closely associated with the mineralization process, we determined the activity of the phosphatase in control and warfarin-treated hypertrophic cultures. We found no change in APase activity per cell as a result of warfarin and vitamin K treatments or cotreatments in either medium A or medium B (Fig. 4A and Fig. B). This analysis also showed that warfarin treatment had no effect on cell number (Fig. 4C and Fig. D). Thus, MGP function in mineralization as revealed by warfarin interference depends on the stage of chondrocyte maturation, does not appear to be related to MGP expression levels, and does not involve changes in APase activity.

Bottom Line: Warfarin effects on mineralization were highly selective, were accompanied by no appreciable changes in MGP expression, alkaline phosphatase activity, or cell number, and were counteracted by vitamin K cotreatment.Virally driven MGP overexpression in cultured chondrocytes greatly decreased mineralization.The results show that MGP is a powerful but developmentally regulated inhibitor of cartilage mineralization, controls mineral quantity but not type, and appears to have a previously unsuspected role in regulating chondrocyte maturation and ossification processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Oral Surgery, Showa University, Dental School, Ohta-Ku, Tokyo 145, Japan.

ABSTRACT
Matrix GLA protein (MGP), a gamma-carboxyglutamic acid (GLA)-rich, vitamin K-dependent and apatite-binding protein, is a regulator of hypertrophic cartilage mineralization during development. However, MGP is produced by both hypertrophic and immature chondrocytes, suggesting that MGP's role in mineralization is cell stage-dependent, and that MGP may have other roles in immature cells. It is also unclear whether MGP regulates the quantity of mineral or mineral nature and quality as well. To address these issues, we determined the effects of manipulations of MGP synthesis and expression in (a) immature and hypertrophic chondrocyte cultures and (b) the chick limb bud in vivo. The two chondrocyte cultures displayed comparable levels of MGP gene expression. Yet, treatment with warfarin, a gamma-carboxylase inhibitor and vitamin K antagonist, triggered mineralization in hypertrophic but not immature cultures. Warfarin effects on mineralization were highly selective, were accompanied by no appreciable changes in MGP expression, alkaline phosphatase activity, or cell number, and were counteracted by vitamin K cotreatment. Scanning electron microscopy, x-ray microanalysis, and Fourier-transform infrared spectroscopy revealed that mineral forming in control and warfarin-treated hypertrophic cell cultures was similar and represented stoichiometric apatite. Virally driven MGP overexpression in cultured chondrocytes greatly decreased mineralization. Surprisingly, MGP overexpression in the developing limb not only inhibited cartilage mineralization, but also delayed chondrocyte maturation and blocked endochondral ossification and formation of a diaphyseal intramembranous bone collar. The results show that MGP is a powerful but developmentally regulated inhibitor of cartilage mineralization, controls mineral quantity but not type, and appears to have a previously unsuspected role in regulating chondrocyte maturation and ossification processes.

Show MeSH
Related in: MedlinePlus