Limits...
Control of vertebrate skeletal mineralization by polyphosphates.

Omelon S, Georgiou J, Henneman ZJ, Wise LM, Sukhu B, Hunt T, Wynnyckyj C, Holmyard D, Bielecki R, Grynpas MD - PLoS ONE (2009)

Bottom Line: Sequestering calcium into amorphous calcium polyphosphate complexes can reduce the concentration of free calcium.The resulting reduction of both free PO(4)(3-) and free calcium lowers the relative apatite saturation, preventing formation of apatite crystals.When mineralization is required, tissue non-specific alkaline phosphatase, an enzyme associated with skeletal and cartilage mineralization, cleaves orthophosphates from polyphosphates.

View Article: PubMed Central - PubMed

Affiliation: Samuel Lunenfeld Research Institute, Mt. Sinai Hospital, Toronto, Canada.

ABSTRACT

Background: Skeletons are formed in a wide variety of shapes, sizes, and compositions of organic and mineral components. Many invertebrate skeletons are constructed from carbonate or silicate minerals, whereas vertebrate skeletons are instead composed of a calcium phosphate mineral known as apatite. No one yet knows why the dynamic vertebrate skeleton, which is continually rebuilt, repaired, and resorbed during growth and normal remodeling, is composed of apatite. Nor is the control of bone and calcifying cartilage mineralization well understood, though it is thought to be associated with phosphate-cleaving proteins. Researchers have assumed that skeletal mineralization is also associated with non-crystalline, calcium- and phosphate-containing electron-dense granules that have been detected in vertebrate skeletal tissue prepared under non-aqueous conditions. Again, however, the role of these granules remains poorly understood. Here, we review bone and growth plate mineralization before showing that polymers of phosphate ions (polyphosphates: (PO(3)(-))(n)) are co-located with mineralizing cartilage and resorbing bone. We propose that the electron-dense granules contain polyphosphates, and explain how these polyphosphates may play an important role in apatite biomineralization.

Principal findings/methodology: The enzymatic formation (condensation) and destruction (hydrolytic degradation) of polyphosphates offers a simple mechanism for enzymatic control of phosphate accumulation and the relative saturation of apatite. Under circumstances in which apatite mineral formation is undesirable, such as within cartilage tissue or during bone resorption, the production of polyphosphates reduces the free orthophosphate (PO(4)(3-)) concentration while permitting the accumulation of a high total PO(4)(3-) concentration. Sequestering calcium into amorphous calcium polyphosphate complexes can reduce the concentration of free calcium. The resulting reduction of both free PO(4)(3-) and free calcium lowers the relative apatite saturation, preventing formation of apatite crystals. Identified in situ within resorbing bone and mineralizing cartilage by the fluorescent reporter DAPI (4',6-diamidino-2-phenylindole), polyphosphate formation prevents apatite crystal precipitation while accumulating high local concentrations of total calcium and phosphate. When mineralization is required, tissue non-specific alkaline phosphatase, an enzyme associated with skeletal and cartilage mineralization, cleaves orthophosphates from polyphosphates. The hydrolytic degradation of polyphosphates in the calcium-polyphosphate complex increases orthophosphate and calcium concentrations and thereby favors apatite mineral formation. The correlation of alkaline phosphatase with this process may be explained by the destruction of polyphosphates in calcifying cartilage and areas of bone formation.

Conclusions/significance: We hypothesize that polyphosphate formation and hydrolytic degradation constitute a simple mechanism for phosphate accumulation and enzymatic control of biological apatite saturation. This enzymatic control of calcified tissue mineralization may have permitted the development of a phosphate-based, mineralized endoskeleton that can be continually remodeled.

Show MeSH

Related in: MedlinePlus

Transient staining of vertebral growth plates with toluidine blue.Growth plate sections (EDTA-decalcified, 3-month-old murine vertebral body) (A) 1 minute and (B) 10 minutes after toluidine blue staining. Note reduced staining of hypertrophic zone matrix after 10 minutes.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2683572&req=5

pone-0005634-g004: Transient staining of vertebral growth plates with toluidine blue.Growth plate sections (EDTA-decalcified, 3-month-old murine vertebral body) (A) 1 minute and (B) 10 minutes after toluidine blue staining. Note reduced staining of hypertrophic zone matrix after 10 minutes.

Mentions: For this study, we repeated the transient staining of fresh epiphyseal cartilage reported by Hirschman [51]. Figure 4A shows the toluidine blue stain one minute after staining, while Figure 4B shows fading of the stain in the hypertrophic zone matrix of the same section 10 minutes after staining. The resting zone stain also transformed from purple to blue. The growth plate regions that were transiently stained with toluidine blue are similar to the regions that fluoresced with the DAPI-polyP signature (∼520–580 nm emission maximum, Figure 3).


Control of vertebrate skeletal mineralization by polyphosphates.

Omelon S, Georgiou J, Henneman ZJ, Wise LM, Sukhu B, Hunt T, Wynnyckyj C, Holmyard D, Bielecki R, Grynpas MD - PLoS ONE (2009)

Transient staining of vertebral growth plates with toluidine blue.Growth plate sections (EDTA-decalcified, 3-month-old murine vertebral body) (A) 1 minute and (B) 10 minutes after toluidine blue staining. Note reduced staining of hypertrophic zone matrix after 10 minutes.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2683572&req=5

pone-0005634-g004: Transient staining of vertebral growth plates with toluidine blue.Growth plate sections (EDTA-decalcified, 3-month-old murine vertebral body) (A) 1 minute and (B) 10 minutes after toluidine blue staining. Note reduced staining of hypertrophic zone matrix after 10 minutes.
Mentions: For this study, we repeated the transient staining of fresh epiphyseal cartilage reported by Hirschman [51]. Figure 4A shows the toluidine blue stain one minute after staining, while Figure 4B shows fading of the stain in the hypertrophic zone matrix of the same section 10 minutes after staining. The resting zone stain also transformed from purple to blue. The growth plate regions that were transiently stained with toluidine blue are similar to the regions that fluoresced with the DAPI-polyP signature (∼520–580 nm emission maximum, Figure 3).

Bottom Line: Sequestering calcium into amorphous calcium polyphosphate complexes can reduce the concentration of free calcium.The resulting reduction of both free PO(4)(3-) and free calcium lowers the relative apatite saturation, preventing formation of apatite crystals.When mineralization is required, tissue non-specific alkaline phosphatase, an enzyme associated with skeletal and cartilage mineralization, cleaves orthophosphates from polyphosphates.

View Article: PubMed Central - PubMed

Affiliation: Samuel Lunenfeld Research Institute, Mt. Sinai Hospital, Toronto, Canada.

ABSTRACT

Background: Skeletons are formed in a wide variety of shapes, sizes, and compositions of organic and mineral components. Many invertebrate skeletons are constructed from carbonate or silicate minerals, whereas vertebrate skeletons are instead composed of a calcium phosphate mineral known as apatite. No one yet knows why the dynamic vertebrate skeleton, which is continually rebuilt, repaired, and resorbed during growth and normal remodeling, is composed of apatite. Nor is the control of bone and calcifying cartilage mineralization well understood, though it is thought to be associated with phosphate-cleaving proteins. Researchers have assumed that skeletal mineralization is also associated with non-crystalline, calcium- and phosphate-containing electron-dense granules that have been detected in vertebrate skeletal tissue prepared under non-aqueous conditions. Again, however, the role of these granules remains poorly understood. Here, we review bone and growth plate mineralization before showing that polymers of phosphate ions (polyphosphates: (PO(3)(-))(n)) are co-located with mineralizing cartilage and resorbing bone. We propose that the electron-dense granules contain polyphosphates, and explain how these polyphosphates may play an important role in apatite biomineralization.

Principal findings/methodology: The enzymatic formation (condensation) and destruction (hydrolytic degradation) of polyphosphates offers a simple mechanism for enzymatic control of phosphate accumulation and the relative saturation of apatite. Under circumstances in which apatite mineral formation is undesirable, such as within cartilage tissue or during bone resorption, the production of polyphosphates reduces the free orthophosphate (PO(4)(3-)) concentration while permitting the accumulation of a high total PO(4)(3-) concentration. Sequestering calcium into amorphous calcium polyphosphate complexes can reduce the concentration of free calcium. The resulting reduction of both free PO(4)(3-) and free calcium lowers the relative apatite saturation, preventing formation of apatite crystals. Identified in situ within resorbing bone and mineralizing cartilage by the fluorescent reporter DAPI (4',6-diamidino-2-phenylindole), polyphosphate formation prevents apatite crystal precipitation while accumulating high local concentrations of total calcium and phosphate. When mineralization is required, tissue non-specific alkaline phosphatase, an enzyme associated with skeletal and cartilage mineralization, cleaves orthophosphates from polyphosphates. The hydrolytic degradation of polyphosphates in the calcium-polyphosphate complex increases orthophosphate and calcium concentrations and thereby favors apatite mineral formation. The correlation of alkaline phosphatase with this process may be explained by the destruction of polyphosphates in calcifying cartilage and areas of bone formation.

Conclusions/significance: We hypothesize that polyphosphate formation and hydrolytic degradation constitute a simple mechanism for phosphate accumulation and enzymatic control of biological apatite saturation. This enzymatic control of calcified tissue mineralization may have permitted the development of a phosphate-based, mineralized endoskeleton that can be continually remodeled.

Show MeSH
Related in: MedlinePlus