Effect of Combined Action of Extracellular ATP and Elevated Calcium on Osteogenic Differentiation of Primary Cultures From Rat Calvaria

Role of estrone on the regulation of osteoblastogenesis

Although estradiol bone contribution has been deeply studied, little is known about the action of estrone. We investigated the direct action of estrone on osteoblasts growth and differentiation, with focus on the biochemical mechanism displayed by the estrogen. Murine calvarial osteoblast cultures in vitro exposed to 10 nM estrone were employed. Estrone enhanced gene expression of the osteogenic differentiation marker, Runx2 mRNA (150% above control). The hormone significantly increased cell proliferation (38% above control), nitric oxide production (108% above control), alkaline phosphatase activity (50% above control), in addition to stimulation of extracellular matrix mineralization. Using specific antagonists, we found that the mechanism of action of estrone involves estrogen receptor, nitric oxide synthase and MAPK signalling pathways participation. The hormone acts by its own and probably not via conversion to estradiol, since 17 B HSD inhibition did not affect the hormonal action. This work shows a novel action of estrone on bone cells promoting osteoblastogenesis.

Infection of Rat Osteoblasts with Junin Virus Promotes the Expression of Bone Morphogenetic Protein 6, an Osteogenic Differentiation Inducer

BACKGROUND

The arenavirus Junin virus (JUNV), causative agent of the argentine hemorrhagic fever, is able to modulate several signaling pathways involved in cell survival and multiplication.

OBJECTIVES

We aimed to characterize the infection of rat osteoblasts (OBCs) with JUNV and its consequence on the modulation of osteogenic genes expression, thus studying the ability of this virus to induce cell differentiation. In addition, we evaluated the effect of purinergic agonists on viral replication.

METHOD

Quantification of infectivity by plaque forming unit (PFU) assay, synthesis of viral proteins by western blot and immunofluorescence, and expression of osteogenic differentiation markers (ODM) by quantitative real-time polymerase chain reaction were employed.

RESULTS

Infection of OBCs with JUNV (MOI 0.01 PFU/cell) showed a peak of infectivity, reaching 1.5 × 105 PFU/mL at the second day post-infection (p.i.). A marked restriction in multiplication was detected at day 7 p.i. that did not impair the establishment of a persistent stage of infection in OBCs. Analysis of mRNAs corresponding to ODM such as alkaline phosphatase, bone sialo-protein, and bone morphogenetic proteins (BMPs) 4 and 6 revealed that only the levels of BMP-6 were significantly higher in infected cells. Treatment with the purinergic agonists ATPγS, UTP, ADP, or UDP diminished viral titer and reduced the expression of the viral nucleoprotein. Also, treatment with 10 μM ATPγS reduced the stimulation of BMP-6 expression induced by the infection.

CONCLUSIONS

These data demonstrate that JUNV is capable of infecting OBCs and point out BMP-6 as a key factor during this process.

Involvement of GSK3/β-catenin in the action of extracellular ATP on differentiation of primary cultures from rat calvaria into osteoblasts

Modulation of purinergic receptors play an important role in the regulation of osteoblasts differentiation and bone formation. In this study, we investigated the involvement of the GSK3/βcatenin signaling in the action of ATPγ-S on osteogenic differentiation of primary cell cultures from rat calvaria. Our results indicate that the cell treatment with 10 or 100 µM ATPγ-S for 96 h increase the cytoplasmic levels of β-catenin and its translocation to nucleus respect to control. A similar effect was observed after cell treatment with the GSK3 inhibitor LiCl (10 mM). Cell treatments with 4-10 mM LiCl significantly stimulated ALP activity respect to control at 4 and 7 days, suggesting that inhibition of GSK-3 mediates osteoblastic differentiation of rat calvarial cells. Effects comparison between ATP and LiCl shown that ALP activity was significantly increased by 10 µM ATPγ-S and decreased by 10 mM LiCl at 10 day of treatment, respect to control, suggesting that the effect of ATPγ-S was less potent but more persistent than of LiCl in stimulating this osteogenic marker in calvarial cells. Cell culture mineralization was significantly increased by treatment with 10 µM ATPγ-S and decreased by 10 mM LiCl, respect to control. In together, these results suggest that GSK3 inhibition is involved in ATPγ-S action on rat calvarial cell differentiation into osteoblasts at early steadies. In addition such inhibition by LiCl appear promote osteoblasts differentiation at beginning but has a deleterious effect on its function at later steadies as the extracellular matrix mineralization.

Biphasic Effect of ATP on In Vitro Mineralization of Dental Pulp Cells

Dental pulp cells release adenosine triphosphate (ATP) in response to intrapulpal pressure and the amount released depends on the magnitude of the pressure. ATP regulates the differentiation of stem cells into adipocytes and osteoblasts. However, it is unknown whether extracellular ATP influences the stemness and osteogenic differentiation of stem cells from human exfoliated deciduous teeth (SHEDs). Therefore, this study investigated the effects of extracellular ATP at a low (0.1 μM) and high (10 μM) concentration on the stemness and osteogenic differentiation of SHEDs. Cells were cultured in either growth medium or osteogenic medium with or without 0.1-10 μM ATP. In growth medium, both concentrations of ATP increased the mRNA expression of pluripotent and osteogenic markers. In contrast, in osteogenic medium, 0.1 μM ATP enhanced in vitro mineralization, whereas 10 μM ATP inhibited this process. In addition, 10 μM ATP stimulated the mRNA expression and activity of ectonucleotide pyrophosphatase/phosphodiesterase (ENPP), an enzyme that regulates the phosphate/pyrophosphate ratio. Thus, depending on the growth condition and its concentration, ATP stimulated stemness and in vitro mineralization or inhibited mineralization. In growth medium, both ATP concentrations stimulated pluripotent and osteogenic marker gene expression. However, in osteogenic medium, a biphasic effect was found on in vitro mineralization; the low concentration stimulated, whereas the high concentration inhibited, mineralization. We propose that ATP released due to mechanical stress modulates the stemness and differentiation of SHEDs. J. Cell. Biochem. 119: 488-498, 2018. © 2017 Wiley Periodicals, Inc.

The role of the progressive ankylosis protein (ANK) in adipogenic/osteogenic fate decision of precursor cells

The progressive ankylosis protein (ANK) is a transmembrane protein that transports intracellular pyrophosphate (PPi) to the extracellular milieu. In this study we show increased fatty degeneration of the bone marrow of adult ank/ank mice, which lack a functional ANK protein. In addition, isolated bone marrow stromal cells (BMSCs) isolated from ank/ank mice showed a decreased proliferation rate and osteogenic differentiation potential, and an increased adipogenic differentiation potential compared to BMSCs isolated from wild type (WT) littermates. Wnt signaling pathway PCR array analysis revealed that Wnt ligands, Wnt receptors and Wnt signaling proteins that stimulate osteoblast differentiation were expressed at markedly lower levels in ank/ank BMSCs than in WT BMSCs. Lack of ANK function also resulted in impaired bone fracture healing, as indicated by a smaller callus formed and delayed bone formation in the callus site. Whereas 5weeks after fracture, the fractured bone in WT mice was further remodeled and restored to original shape, the fractured bone in ank/ank mice was not fully restored and remodeled to original shape. In conclusion, our study provides evidence that ANK plays a critical role in the adipogenic/osteogenic fate decision of adult mesenchymal precursor cells. ANK functions in precursor cells are required for osteogenic differentiation of these cells during adult bone homeostasis and repair, whereas lack of ANK functions favors adipogenic differentiation.