Mineralization of bone is of critical importance to its numerous functions and can be perturbed in local or systemic musculoskeletal disorders. Our understanding of skeletal development, fracture healing, and bone remodeling will be enhanced by insights into the anabolic processes of bone matrix formation and biomineralization. There is considerable interest in the identification of biological molecules which nucleate bone mineral (bioaptite). This proposal hypothesizes that newly synthesized bone sialoprotein (BSP) nucleate bioapatite when associated with membrane- delimited vesicles. This hypothesis will be tested using natural periosteum and three osteoblastic culture models. We have observed spherical (sub)micron-sized apatite-containing particles (""""""""bioapatite vesicles"""""""") in postnatal periosteum of rat tibia, as well as in primary and cell line osteoblastic cultures. They contain BSP and are strikingly similar in appearance to mineralized structures observed in osteoid (""""""""crystal ghost aggregates"""""""").
Four aims are proposed addressing the structure/function relationship of BSP and apatite in """"""""bioapatite vehicles"""""""". (1) Characterize the structure of bioapatite vehicles isolated from postnatal periosteum. (2) Spatially locate the major components of purified bioapatite vehicles in postnatal periosteum in situ. (3) Identify and structurally characterize any bioapatite vehicle counterparts from osteoblastic cultures. (4) Over-express BSP from an inducible gene construct transfected into osteoblastic cells.
Aims 1 and 2 will provide a precise compositional database to compare the structure of bioapatite vehicles to that of matrix vesicles and crystal ghost aggregates.
Aim 3 will identify relevant culture models to assess mechanisms of formation and determine essential molecular components.
Aim 4 will directly test whether over-expression of BSP enhance apatite nucleation and whether it is a critical structural component for bioapatite vehicle integrity. This proposed research will yield new insight into apatite formation by osteoblasts because it will analyze a unique nucleation structure and ascertain the function of BSP in these entities. Ultimately, e believe that characterization of these novel biomineralization structures will lead to a better understanding of the mechanisms for bine mineralization and perhaps lead to new treatments to improve mineralization disorders of bone.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR045171-02
Application #
6171830
Study Section
Orthopedics and Musculoskeletal Study Section (ORTH)
Program Officer
Sharrock, William J
Project Start
1999-08-01
Project End
2003-07-31
Budget Start
2000-08-01
Budget End
2001-07-31
Support Year
2
Fiscal Year
2000
Total Cost
$174,276
Indirect Cost
Name
Cleveland Clinic Lerner
Department
Type
DUNS #
017730458
City
Cleveland
State
OH
Country
United States
Zip Code
44195
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Midura, Ronald J; Vasanji, Amit; Su, Xiaowei et al. (2007) Calcospherulites isolated from the mineralization front of bone induce the mineralization of type I collagen. Bone 41:1005-16
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