Al Kawas S, Amizuka N, Bergeron J J, Warshawsky H
Department of Anatomy and Cell Biology, Faculty of Medicine, McGill University, Montreal, Quebec, Canada, H3A 2B2.
Calcif Tissue Int. 1996 Sep;59(3):192-9. doi: 10.1007/s002239900108.
In order to examine our hypothesis that maturation ameloblasts could degrade the enamel matrix in a manner analogous to bone resorption mediated by osteoclasts, we have assessed the distribution of lysosomal enzymes in the enamel organ by immunolocalizing the cation-in-independent mannose 6-phosphate receptor (MPR) and the lysosomal enzyme cathepsin B at all stages of amelogenesis. Secretory ameloblasts showed strong immunoreactivity for MPR in the supranuclear Golgi region and in the cytoplasm between the Golgi region and the distal junctional complexes. However, cathepsin B immunoreactivity was mainly seen in the distal portion of Tomes' process, which was unreactive for MPR immunogenicity. In maturation ameloblasts, the MPR was observed on the ruffled border of the ruffle-ended ameloblast (RA) but not on the distal cell membrane of the smooth-ended ameloblast (SA), although both cell types demonstrated strong immunoreactivity for MPR in the Golgi region. Immunoreactive cathepsin B was seen at the distal ends of both RA and SA. It is postulated that the nascent lysosomal enzymes bind to the mannose 6-phosphate receptors which target them not only to intracellular lysosomes, but also to the ruffled border of maturation ameloblasts where these enzymes are secreted into the enamel. Since MPR and lysosomal enzymes were also detected on the ruffled border of osteoclasts (Ocl) adjacent to alveolar bone, our immunocytochemical approach provides strong evidence for a similarity between the maturation process in enamel, as mediated by the ruffle-ended maturation ameloblasts, and bone resorption mediated by osteoclasts. This study has established that a common mechanism, based on MPR-targeted lysosomal secretion and matrix degradation, is basic to the maturation process involved in calcified tissues as different as bone and enamel.
为了验证我们的假设，即成熟的成釉细胞能够以类似于破骨细胞介导的骨吸收方式降解釉质基质，我们通过免疫定位不依赖阳离子的甘露糖6 - 磷酸受体（MPR）和溶酶体酶组织蛋白酶B，评估了成釉器在釉质形成各阶段的溶酶体酶分布。分泌期成釉细胞在核上高尔基体区域以及高尔基体区域与远端连接复合体之间的细胞质中显示出强烈的MPR免疫反应性。然而，组织蛋白酶B免疫反应性主要见于托姆斯突的远端部分，该部分对MPR免疫原性无反应。在成熟的成釉细胞中，在褶缘末端成釉细胞（RA）的褶缘边界观察到MPR，但在平滑末端成釉细胞（SA）的远端细胞膜上未观察到，尽管两种细胞类型在高尔基体区域均显示出强烈的MPR免疫反应性。在RA和SA的远端均可见免疫反应性组织蛋白酶B。据推测，新生的溶酶体酶与甘露糖6 - 磷酸受体结合，这些受体不仅将它们靶向细胞内的溶酶体，还靶向成熟成釉细胞的褶缘边界，在那里这些酶被分泌到釉质中。由于在邻近牙槽骨的破骨细胞（Ocl）的褶缘边界也检测到MPR和溶酶体酶，我们的免疫细胞化学方法为褶缘末端成熟成釉细胞介导的釉质成熟过程与破骨细胞介导的骨吸收之间的相似性提供了有力证据。本研究证实，基于MPR靶向的溶酶体分泌和基质降解的共同机制是骨和釉质等不同钙化组织成熟过程的基础。
