The three objectives of this investigation are to understand the role of MGP in preventing calcification of growth plate cartilage, to establish the role of MGP as a calcification inhibitor in mediating the action of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on bone, and to determine the molecular mechanism by which MGP inhibits calcification. These studies are based solidly on the evidence that MGP is the in vivo inhibitor of cartilage calcification, evidence which has come from studies of the MGP gene knock-out mouse, and the warfarin-treated rat. The applicants' first Aim is to study the role of MGP in growth plate cartilage calcification in the rat. They will determine the first sites of warfarin-induced abnormal calcification in the growth plate of the proximal tibia in order to establish the points at which MGP normally acts to prevent cartilage calcification. They will also identify the mechanisms by which the activity of MGP is reduced in areas of normal growth plate mineralization; these studies include measuring the level of MGP expression in chondrocytes in normal areas of calcification, and investigating the post-translational modifications of MGP which are used to inactivate the protein at normal calcification sites.
Their second Aim i s to determine the role of MGP as a mediator of the action of 1,25(OH)2D3 on bone. They have recently found that 1,25(OH)2D3 causes a 35% decrease in the uptake of 45[Ca] into the epiphysis and metaphysis of the proximal tibia and that warfarin treatment completely blocks this decrease. They will further examine this effect in order to establish the role of MGP as a calcification inhibitor in this action of vitamin D on bone. They will also test the ability of MGP infusion to reduce the rate of mineralization in the proximal tibia. Finally, they will establish the role of MGP as a mediator of the action of 1,25(OH)2D3 on bone dietary calcium deficiency.
Their third Aim i s to carry out in vitro studies on the mechanism by which MGP inhibits calcification. They will use the recently discovered soluble form of MGP to investigate calcium and phosphate binding to the protein, to study the structure of the protein, and to investigate its interactions with apatite isolated from bone. They will also investigate the mechanism by which MGP inhibits calcification in vitro. The investigators will further study the demonstrated ability of MGP to inhibit calcification in supersaturated solutions, and will investigate the ability of MGP to inhibit matrix vesicle -initiated calcification.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR025921-18
Application #
6171444
Study Section
Orthopedics and Musculoskeletal Study Section (ORTH)
Program Officer
Sharrock, William J
Project Start
1979-07-01
Project End
2002-06-30
Budget Start
2000-07-01
Budget End
2001-06-30
Support Year
18
Fiscal Year
2000
Total Cost
$231,681
Indirect Cost
Name
University of California San Diego
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
077758407
City
La Jolla
State
CA
Country
United States
Zip Code
92093
Toroian, Damon; Lim, Joo Eun; Price, Paul A (2007) The size exclusion characteristics of type I collagen: implications for the role of noncollagenous bone constituents in mineralization. J Biol Chem 282:22437-47
Simes, D C; Williamson, M K; Schaff, B J et al. (2004) Characterization of osteocalcin (BGP) and matrix Gla protein (MGP) fish specific antibodies: validation for immunodetection studies in lower vertebrates. Calcif Tissue Int 74:170-80
Hamlin, N J; Price, P A (2004) Mineralization of decalcified bone occurs under cell culture conditions and requires bovine serum but not cells. Calcif Tissue Int 75:231-42
Price, Paul A; Lim, Joo Eun (2003) The inhibition of calcium phosphate precipitation by fetuin is accompanied by the formation of a fetuin-mineral complex. J Biol Chem 278:22144-52
Price, Paul A; Nguyen, Thao Minh Thi; Williamson, Matthew K (2003) Biochemical characterization of the serum fetuin-mineral complex. J Biol Chem 278:22153-60
Simes, D C; Williamson, M K; Ortiz-Delgado, J B et al. (2003) Purification of matrix Gla protein from a marine teleost fish, Argyrosomus regius: calcified cartilage and not bone as the primary site of MGP accumulation in fish. J Bone Miner Res 18:244-59
Price, Paul A; Caputo, Jeffrey M; Williamson, Matthew K (2002) Bone origin of the serum complex of calcium, phosphate, fetuin, and matrix Gla protein: biochemical evidence for the cancellous bone-remodeling compartment. J Bone Miner Res 17:1171-9
Price, Paul A; Thomas, Gethin R; Pardini, Aaron W et al. (2002) Discovery of a high molecular weight complex of calcium, phosphate, fetuin, and matrix gamma-carboxyglutamic acid protein in the serum of etidronate-treated rats. J Biol Chem 277:3926-34
Cancela, M L; Ohresser, M C; Reia, J P et al. (2001) Matrix Gla protein in Xenopus laevis: molecular cloning, tissue distribution, and evolutionary considerations. J Bone Miner Res 16:1611-21
Kirfel, J; Kelter, M; Cancela, L M et al. (1997) Identification of a novel negative retinoic acid responsive element in the promoter of the human matrix Gla protein gene. Proc Natl Acad Sci U S A 94:2227-32

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