Department of Anatomy, Integrative Research Support Center, The Catholic University of Korea, Seoul, Korea.
J Neurotrauma. 2012 May 1;29(7):1530-8. doi: 10.1089/neu.2011.2078. Epub 2012 Jan 13.
Osteopontin (OPN), an adhesive glycoprotein, has recently been proposed to act as an opsonin that facilitates phagocytosis of neuronal debris by macrophages in the ischemic brain. The present study was designed to elucidate the process whereby OPN binds to neuronal cell debris in a rat model of ischemic stroke. Significant co-localization of the OPN protein and calcium deposits in the ischemic core were observed by combining alizarin red staining and OPN immunohistochemistry. In addition, electron microscopy (EM) using the osmium/potassium dichromate method revealed that electron-dense precipitates, typical of calcium deposits, were localized mainly along the periphery of putative degenerating neurites. This topical pattern of calcium precipitates resembled the distribution of OPN as detected by immunogold-silver EM. Combining immunogold-silver EM and electron probe microanalysis further demonstrated that the OPN protein was localized at the periphery of cell debris or degenerating neurites, corresponding with locally higher concentrations of calcium and phosphorus, and that the relative magnitude of OPN accumulation was comparable to that of calcium and phosphorus. These data suggest that calcium precipitation provides a matrix for the binding of the OPN protein within the debris or degenerating neurites induced by ischemic injury. Therefore, OPN binding to calcium deposits may be involved in phagocytosis of such debris, and may participate in the regulation of ectopic calcification in the ischemic brain.
骨桥蛋白（OPN）是一种黏附糖蛋白，最近有人提出它作为调理素，促进巨噬细胞吞噬缺血性脑内的神经元碎片。本研究旨在阐明在缺血性中风大鼠模型中 OPN 与神经元细胞碎片结合的过程。通过茜素红染色和 OPN 免疫组化相结合，观察到 OPN 蛋白与缺血核心中的钙沉积有明显的共定位。此外，采用锇/重铬酸钾法的电子显微镜（EM）显示，电子致密沉淀物，典型的钙沉积，主要定位于推测退化的神经突的周围。这种钙沉淀的局部模式类似于免疫金银 EM 检测到的 OPN 分布。免疫金银 EM 与电子探针微量分析相结合进一步表明，OPN 蛋白定位于细胞碎片或退化神经突的周围，与局部更高浓度的钙和磷相对应，并且 OPN 积累的相对程度与钙和磷相当。这些数据表明，钙沉淀为缺血损伤诱导的细胞碎片或退化神经突内 OPN 蛋白的结合提供了基质。因此，OPN 与钙沉积的结合可能参与了对这种碎片的吞噬作用，并可能参与了缺血性脑内异位钙化的调节。
