Abstract:
Background: Adenosine triphosphate (ATP) is released in response to intrapulpal pressure and its released amount depends on the magnitude of pressure. ATP is involved in the regulation of differentiation of stem cells into adipocytes and osteoblasts. However, it is unknown whether extracellular ATP influences the stemness properties and osteogenic differentiation of stem cells from human exfoliated deciduous teeth (SHEDs). Objective: To investigate the effect of extracellular ATP in a low (0.1 µM) and high (10 µM) concentration on the stemness properties and osteogenic differentiation of SHEDs. Material and methods: SHEDs were cultured in either growth medium or osteogenic medium in the presence or absence of 0.1, 1 or 10 µM ATP. The level of expression of stem cell markers, osteogenesis and mineralization modulating genes were determined by Real-time PCR. In vitro mineralization was determined by alizarin red S staining. The activity level was assessed of alkaline phosphatase (ALP) and ectonucleotide pyrophosphatase/phosphodiesterase (ENPP), a phosphate (Pi)/pyrophosphate (PPi) modulating enzyme. Results: In growth medium, both concentrations of ATP increased the mRNA expression of pluripotent and osteogenic markers. In osteogenic medium a different effect was found. Here, 0.1 µM of ATP enhanced the in vitro mineralization, whereas 10 µM of ATP inhibited this process. Under the latter conditions ATP stimulated the mRNA expression and activity of ENPP; an enzyme that regulates the Pi/PPi ratio. Conclusion: Depending on the growth condition and concentration, ATP may stimulate stemness and in vitro mineralization or inhibit the latter process. In normal medium, both concentrations of ATP stimulated gene expression of pluripotent and osteogenic markers. However, in osteogenic medium a biphasic effect was found on in vitro mineralization; a low concentration had a stimulating whereas a high concentration had an inhibiting effect. We propose that ATP released due to mechanical stress modulates stemness and differentiation of SHEDs.
