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.
Calcif Tissue Int. 2010 Nov;87(5):461-8. doi: 10.1007/s00223-010-9407-7. Epub 2010 Aug 20.
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.
在高骨负荷区域，机械敏感的成骨细胞通过产生信号分子来抑制破骨细胞的骨吸收。一种可能的候选物是基质细胞外磷蛋白（MEPE），因为酸性丝氨酸和天冬氨酸富含 MEPE 相关基序肽上调了核因子κB 受体激活剂配体（RANKL）的基因表达，而 RANKL 是破骨细胞生成的负调节剂。当存在相对较多的 MEPE 而不是 PHEX（具有跨染色体内肽酶同源性的磷酸盐调节基因）时，这些肽从 MEPE 中被切割出来。我们研究了成骨细胞的机械负荷是否通过 MEPE 的参与影响成骨细胞刺激的破骨细胞生成。通过 1 小时的脉动液流（PFF；0.7±0.3 Pa，5 Hz）对 MLO-Y4 成骨细胞进行机械加载或保持在静态对照条件下。向一些静态培养物中添加重组 MEPE（0.05、0.5 或 5 μg/ml）。将小鼠骨髓细胞播种在成骨细胞上以确定破骨细胞生成。在 PFF 后测定成骨细胞中 MEPE、PHEX、核因子κB 受体激活剂配体（RANKL）和 OPG 的基因表达。在静态对照条件下，成骨细胞支持破骨细胞形成。PFF 和重组 MEPE 均抑制成骨细胞刺激的破骨细胞生成。PFF 将 MEPE 的基因表达上调了 2.5 倍，但不上调 PHEX 的表达。PFF 在 1 小时 PFF 处理时降低了 RANKL/OPG 比值。我们的数据表明，机械负荷通过成骨细胞诱导基因表达发生变化，这可能有助于在骨的机械负荷后抑制破骨细胞生成。由于机械负荷上调了 MEPE 的基因表达，但不上调 PHEX 的表达，可能导致 OPG 基因表达上调，我们推测 MEPE 是一种参与成骨细胞抑制破骨细胞生成的可溶性因子。
