Amorphous Ca²⁺ polyphosphate nanoparticles regulate the ATP level in bone-like SaOS-2 cells

Area of Science:

• Biochemistry
• Cell Biology
• Biomineralization

Background:

• Polyphosphate (polyP) is a naturally occurring polyanion synthesized in osteoblasts and platelets.
• PolyP contains high-energy phosphoanhydride bonds, suggesting a role in cellular energy metabolism.
• Osteoblast-like cells (SaOS-2) were used to investigate polyP's effects on energy generation and biomineralization.

Purpose of the Study:

• To investigate the correlation between polyP's morphogenetic effect and cellular energy production.
• To determine if polyP hydrolysis contributes to ATP generation and hydroxyapatite formation in osteoblasts.

Main Methods:

• Exposure of SaOS-2 cells to amorphous polyP nanoparticles complexed with Ca(2+).
• Analysis of mitochondrial accumulation and alkaline phosphatase translocation.
• Measurement of intracellular and extracellular ATP levels following incubation with polyP and a mineralization cocktail.

Main Results:

• PolyP exposure led to increased mitochondria and alkaline phosphatase translocation to the cell surface.
• Combined treatment with polyP and mineralization cocktail caused a tenfold increase in intracellular ATP.
• An intensified release of ATP into the extracellular space was observed in treated cells.

Conclusions:

• Polyphosphate serves as a metabolic fuel source for osteoblast-like cells upon hydrolytic cleavage.
• PolyP hydrolysis contributes to ATP generation, supporting hydroxyapatite formation on osteoblast plasma membranes.
• PolyP plays a significant role in osteoblast energy metabolism and biomineralization processes.