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Inhibition of osteoclastogenesis by mechanically loaded osteocytes: involvement of MEPE.

Kulkarni RN, Bakker AD, Everts V, Klein-Nulend J - Calcif. Tissue Int. (2010)

Bottom Line: One possible candidate is matrix extracellular phosphoglycoprotein (MEPE) because acidic serine- and aspartate-rich MEPE-associated motif peptides upregulate osteoprotegerin (OPG) gene expression, a negative regulator of osteoclastogenesis.PFF decreased the RANKL/OPG ratio at 1-h PFF treatment.Because mechanical loading upregulated gene expression of MEPE but not PHEX, possibly resulting in the upregulation of OPG gene expression, we speculate that MEPE is a soluble factor involved in the inhibition of osteoclastogenesis by osteocytes.

View Article: PubMed Central - PubMed

Affiliation: Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam, University of Amsterdam and VU University Amsterdam, Research Institute MOVE, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands.

ABSTRACT
In regions of high bone loading, the mechanoresponsive osteocytes inhibit osteoclastic bone resorption by producing signaling molecules. One possible candidate is matrix extracellular phosphoglycoprotein (MEPE) because acidic serine- and aspartate-rich MEPE-associated motif peptides upregulate osteoprotegerin (OPG) gene expression, a negative regulator of osteoclastogenesis. These peptides are cleaved from MEPE when relatively more MEPE than PHEX (phosphate-regulating gene with homology to endopeptidases on the X chromosome) is present. We investigated whether mechanical loading of osteocytes affects osteocyte-stimulated osteoclastogenesis by involvement of MEPE. MLO-Y4 osteocytes were mechanically loaded by 1-h pulsating fluid flow (PFF; 0.7 ± 0.3 Pa, 5 Hz) or kept under static control conditions. Recombinant MEPE (0.05, 0.5, or 5 μg/ml) was added to some static cultures. Mouse bone marrow cells were seeded on top of the osteocytes to determine osteoclastogenesis. Gene expression of MEPE, PHEX, receptor activator of nuclear factor kappa-B ligand (RANKL), and OPG by osteocytes was determined after PFF. Osteocytes supported osteoclast formation under static control conditions. Both PFF and recombinant MEPE inhibited osteocyte-stimulated osteoclastogenesis. PFF upregulated MEPE gene expression by 2.5-fold, but not PHEX expression. PFF decreased the RANKL/OPG ratio at 1-h PFF treatment. Our data suggest that mechanical loading induces changes in gene expression by osteocytes, which likely contributes to the inhibition of osteoclastogenesis after mechanical loading of bone. Because mechanical loading upregulated gene expression of MEPE but not PHEX, possibly resulting in the upregulation of OPG gene expression, we speculate that MEPE is a soluble factor involved in the inhibition of osteoclastogenesis by osteocytes.

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Effect of recombinant human MEPE on osteocyte-stimulated osteoclastogenesis. Recombinant MEPE at 5 μg/mL dowregulated the number of a TRACP-positive multinucleated cells, and b TRACP-positive mononuclear cells after 7 days of co-culture of MLO-Y4 osteocytes and mouse bone marrow cells. Values are means ± SEM from 3 separate experiments. * Significant effect of PFF, P < 0.05
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Fig4: Effect of recombinant human MEPE on osteocyte-stimulated osteoclastogenesis. Recombinant MEPE at 5 μg/mL dowregulated the number of a TRACP-positive multinucleated cells, and b TRACP-positive mononuclear cells after 7 days of co-culture of MLO-Y4 osteocytes and mouse bone marrow cells. Values are means ± SEM from 3 separate experiments. * Significant effect of PFF, P < 0.05

Mentions: Mechanical loading of osteocytes with 1-h PFF significantly increased MEPE gene expression. We also studied whether recombinant human MEPE could modulate osteocyte-stimulated osteoclastogenesis. We found that MEPE at 5 μg/ml inhibited the number of TRACP-positive multinucleated cells (Fig. 4a) and TRACP-positive mononuclear cells (Fig. 4b).Fig. 4


Inhibition of osteoclastogenesis by mechanically loaded osteocytes: involvement of MEPE.

Kulkarni RN, Bakker AD, Everts V, Klein-Nulend J - Calcif. Tissue Int. (2010)

Effect of recombinant human MEPE on osteocyte-stimulated osteoclastogenesis. Recombinant MEPE at 5 μg/mL dowregulated the number of a TRACP-positive multinucleated cells, and b TRACP-positive mononuclear cells after 7 days of co-culture of MLO-Y4 osteocytes and mouse bone marrow cells. Values are means ± SEM from 3 separate experiments. * Significant effect of PFF, P < 0.05
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2964475&req=5

Fig4: Effect of recombinant human MEPE on osteocyte-stimulated osteoclastogenesis. Recombinant MEPE at 5 μg/mL dowregulated the number of a TRACP-positive multinucleated cells, and b TRACP-positive mononuclear cells after 7 days of co-culture of MLO-Y4 osteocytes and mouse bone marrow cells. Values are means ± SEM from 3 separate experiments. * Significant effect of PFF, P < 0.05
Mentions: Mechanical loading of osteocytes with 1-h PFF significantly increased MEPE gene expression. We also studied whether recombinant human MEPE could modulate osteocyte-stimulated osteoclastogenesis. We found that MEPE at 5 μg/ml inhibited the number of TRACP-positive multinucleated cells (Fig. 4a) and TRACP-positive mononuclear cells (Fig. 4b).Fig. 4

Bottom Line: One possible candidate is matrix extracellular phosphoglycoprotein (MEPE) because acidic serine- and aspartate-rich MEPE-associated motif peptides upregulate osteoprotegerin (OPG) gene expression, a negative regulator of osteoclastogenesis.PFF decreased the RANKL/OPG ratio at 1-h PFF treatment.Because mechanical loading upregulated gene expression of MEPE but not PHEX, possibly resulting in the upregulation of OPG gene expression, we speculate that MEPE is a soluble factor involved in the inhibition of osteoclastogenesis by osteocytes.

View Article: PubMed Central - PubMed

Affiliation: Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam, University of Amsterdam and VU University Amsterdam, Research Institute MOVE, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands.

ABSTRACT
In regions of high bone loading, the mechanoresponsive osteocytes inhibit osteoclastic bone resorption by producing signaling molecules. One possible candidate is matrix extracellular phosphoglycoprotein (MEPE) because acidic serine- and aspartate-rich MEPE-associated motif peptides upregulate osteoprotegerin (OPG) gene expression, a negative regulator of osteoclastogenesis. These peptides are cleaved from MEPE when relatively more MEPE than PHEX (phosphate-regulating gene with homology to endopeptidases on the X chromosome) is present. We investigated whether mechanical loading of osteocytes affects osteocyte-stimulated osteoclastogenesis by involvement of MEPE. MLO-Y4 osteocytes were mechanically loaded by 1-h pulsating fluid flow (PFF; 0.7 ± 0.3 Pa, 5 Hz) or kept under static control conditions. Recombinant MEPE (0.05, 0.5, or 5 μg/ml) was added to some static cultures. Mouse bone marrow cells were seeded on top of the osteocytes to determine osteoclastogenesis. Gene expression of MEPE, PHEX, receptor activator of nuclear factor kappa-B ligand (RANKL), and OPG by osteocytes was determined after PFF. Osteocytes supported osteoclast formation under static control conditions. Both PFF and recombinant MEPE inhibited osteocyte-stimulated osteoclastogenesis. PFF upregulated MEPE gene expression by 2.5-fold, but not PHEX expression. PFF decreased the RANKL/OPG ratio at 1-h PFF treatment. Our data suggest that mechanical loading induces changes in gene expression by osteocytes, which likely contributes to the inhibition of osteoclastogenesis after mechanical loading of bone. Because mechanical loading upregulated gene expression of MEPE but not PHEX, possibly resulting in the upregulation of OPG gene expression, we speculate that MEPE is a soluble factor involved in the inhibition of osteoclastogenesis by osteocytes.

Show MeSH