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Control of vertebrate skeletal mineralization by polyphosphates
Sidney Omelon1, John Georgiou, Zachary J Henneman
1Samuel Lunenfeld Research Institute, Mt. Sinai Hospital, Toronto, Canada.
Plos One
|June 4, 2009
Summary
Polyphosphates regulate bone mineralization by controlling calcium and phosphate levels. Their formation prevents apatite crystals in cartilage and resorbing bone, while their breakdown promotes bone formation.
Area of Science:
- Biomineralization
- Skeletal Biology
- Biochemistry
Background:
- Vertebrate skeletons are unique in their apatite composition, unlike invertebrate carbonate or silicate skeletons.
- The precise mechanisms controlling vertebrate bone and cartilage mineralization remain poorly understood.
- Previous research hypothesized a role for electron-dense granules in mineralization, but their function was unclear.
Purpose of the Study:
- To investigate the role of polyphosphates in vertebrate skeletal mineralization.
- To elucidate the mechanism by which polyphosphates influence apatite formation and control.
- To understand the relationship between polyphosphates, bone remodeling, and cartilage mineralization.
Main Methods:
- Review of bone and growth plate mineralization literature.
- Identification of polyphosphates co-located with mineralizing cartilage and resorbing bone.
- Utilizing the fluorescent reporter DAPI to identify polyphosphates in situ.
Main Results:
- Polyphosphates were found in mineralizing cartilage and resorbing bone.
- Polyphosphate formation sequesters calcium and reduces free orthophosphate, preventing apatite precipitation.
- Enzymatic degradation of polyphosphates by alkaline phosphatase releases orthophosphate, favoring apatite formation.
Conclusions:
- Polyphosphate formation and degradation provide a mechanism for enzymatic control of biological apatite saturation.
- This process allows for the accumulation of phosphate and calcium, regulating mineralization.
- This enzymatic control may have enabled the evolution of a continuously remodeled, phosphate-based vertebrate endoskeleton.
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