Potentiation of endothelin-1-induced prostaglandin E2 formation by Ni(2+) and Sr(2+) in murine osteoblastic MC3T3-E1 cells

Phospholipase D1 activity is crucial for cytosolic phospholipase A2 -dependent prostaglandin E2 formation in murine osteoblastic MC3T3-E1 cells

In bone, prostaglandin E2 (PGE2) is highly osteogenic and formed by osteoblasts, a key modulatory event in the regulation of bone cell activity. MC3T3-E1 cells are widely used as an in vitro model of osteoblast function. It is still not clear which pathways contribute to the release of AA in these cells. In this study we have focussed on the contribution of phospholipase D (PLD) enzymes to osteoblastic PGE2 formation after stimulation with endothelin-1 (ET-1). Using specific inhibitors of PLD1 and PLD2 we could show that PGE2 formation was strictly dependent on PLD1 but not PLD2 activity and cytosolic phospholipase A2 (cPLA2) was activated by triggering through PLD1. We have identified diacyl glycerol (DAG) as a possible effector molecule which may serve as a triggering signal for PKC activation and subsequent cPLA2 phosphorylation.

[Effect of FTY720-P on the differentiation and maturation of MC3T3-E1 cells]

Objective

To investigate the effect of FTY720-P on the differentiation and maturation of MC3T3-E1 cells.

Methods

The MC3T3-E1 cells were divided into the experimental group and the control group. In the experimental group, the cells were induced by the medium containing 400 ng/mL FTY720-P (chloroform as solubilizer) in vitro. In the control group, the cells were cultured with the medium only containing chloroform. The cell morphology of 2 groups were observed by inverted phase contrast microscope; the expression of osteoblast related protein (collagen type Ⅰ and collagen type Ⅲ) was detected by immunofluorescence staining; the alkaline phosphatase (ALP) staining and alizarin red staining were used to observe the formation of osteoblasts and the formation of mineralized nodules in 2 groups; and the TUNEL fluorescence assay was used to detect the cell apoptosis.

Results

After 48 hours of culture, the cells of 2 groups had grown into slender fusiform at the bottom of the bottle, and there was no significant difference in cell morphology between 2 groups. Immunofluorescence staining showed that the expression of collagen type Ⅰ was positive in the experimental group and weakly positive in the control group; the integrated absorbance ( IA) value of the experimental group was 187 600±7 944, which was significantly higher than that of the control group (14 230±1 070) ( t=43.680, P=0.001). The expression of collagen type Ⅲ was weakly positive in the experimental group and the control group, and there was no significant difference in IA value between 2 groups ( t=1.976, P=0.119). ALP staining and alizarin red staining were positive in the experimental group and negative in the control group. TUNEL staining was positive in the experimental group and negative in the control group; the rate of TUNEL staining positive cells in the experimental group was 35.82%±2.99%, which was significantly higher than that in the control group (2.28%±0.51%) ( t=23.420, P=0.002).

Conclusion

FTY720-P can promote the osteogenic differentiation of MC3T3-E1 cells with speeding up maturation and mineralization of extracellular matrix and affect the apoptosis of the cells.

Ionomycin induces prostaglandin E2 formation in murine osteoblastic MC3T3-E1 cells via mechanisms independent of its ionophoric nature

Ionomycin and A23187 are divalent cation ionophores with a marked preference for calcium. Studies using these ionophores have almost exclusively interpreted their results in the light of calcium elevation. It was the aim of this study to investigate the effects of ionomycin in osteoblatic MC3T3-E1 cells that are not attributable to its ionophoric properties. Thus, we have found that in contrast to A23187, ionomycin shows similar effects on prostaglandin E2 formation as bradykinin and endothelin-1, being potentiated by extracellular nickel and inhibited by cholera toxin and pertussis toxin. Our data strongly suggest that inomycin, at least in part, exerts its effects via specific binding to a G-protein coupled receptor, thereby evoking downstream cellular events like arachidonate release with subsequent prostaglandin formation.