The Roslin Institute and Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Easter Bush, Midlothian EH25 9RG, UK.
Bone. 2012 Sep;51(3):418-30. doi: 10.1016/j.bone.2012.06.022. Epub 2012 Jul 7.
Matrix extracellular phosphoglycoprotein (MEPE) belongs to the SIBLING protein family which play key roles in biomineralization. Although the growth plates of MEPE-overexpressing mice display severe morphological disruption, the expression and function of MEPE in growth plate matrix mineralization remains largely undefined. Here we show MEPE and its cleavage product, the acidic serine aspartate-rich MEPE-associated motif (ASARM) peptide, to be localised to the hypertrophic zone of the growth plate. We also demonstrate that the phosphorylated (p)ASARM peptide inhibits ATDC5 chondrocyte matrix mineralization. Stable MEPE-overexpressing ATDC5 cells also had significantly reduced matrix mineralization in comparison to the control cells. Interestingly, we show that the addition of the non-phosphorylated (np)ASARM peptide promoted mineralization in the ATDC5 cells. The peptides and the overexpression of MEPE did not affect the differentiation of the ATDC5 cells. For a more physiologically relevant model, we utilized the metatarsal organ culture model. We show the pASARM peptide to inhibit mineralization at two stages of development, as shown by histological and μCT analysis. Like in the ATDC5 cells, the peptides did not affect the differentiation of the metatarsals indicating that the effects seen on mineralization are direct, as is additionally confirmed by no change in alkaline phosphatase activity or mRNA expression. In the metatarsal organ cultures, the pASARM peptide also reduced endothelial cell markers and vascular endothelial growth factor mRNA expression. Taken together these results show MEPE to be an important regulator of growth plate chondrocyte matrix mineralization through its cleavage to an ASARM peptide.
基质细胞外磷蛋白（MEPE）属于 SIBLING 蛋白家族，在生物矿化中发挥关键作用。尽管 MEPE 过表达小鼠的生长板显示出严重的形态破坏，但 MEPE 在生长板基质矿化中的表达和功能在很大程度上仍未得到定义。在这里，我们发现 MEPE 及其裂解产物、酸性丝氨酸天冬氨酸富含 MEPE 相关基序（ASARM）肽，定位于生长板的肥大区。我们还证明磷酸化（p）ASARM 肽抑制 ATDC5 软骨细胞基质矿化。与对照细胞相比，稳定过表达 MEPE 的 ATDC5 细胞的基质矿化也显著减少。有趣的是，我们发现添加非磷酸化（np）ASARM 肽可促进 ATDC5 细胞的矿化。这些肽和 MEPE 的过表达不影响 ATDC5 细胞的分化。为了建立更具生理相关性的模型，我们利用跖骨器官培养模型。我们通过组织学和 μCT 分析表明，pASARM 肽在两个发育阶段抑制矿化。与 ATDC5 细胞一样，这些肽不影响跖骨的分化，这表明对矿化的影响是直接的，这也被碱性磷酸酶活性或 mRNA 表达没有变化进一步证实。在跖骨器官培养物中，pASARM 肽还降低了内皮细胞标志物和血管内皮生长因子 mRNA 的表达。总之，这些结果表明，MEPE 通过其裂解为 ASARM 肽成为生长板软骨细胞基质矿化的重要调节剂。
