Localization of E11/gp38, Osteocyte-Marker, in Odontoblasts and Mineralizing Odontoblast Cell-lines

Objectives: Odontoblasts share morphological features with osteoblasts, such as a cuboidal body, and with osteocytes, such as dendritic processes. Osteocytes begin to express E11/gp38 upon embedding in bone. E11 is a 40kD transmembrane protein that is essential for dendrite elongation in osteocyte-like cells in response to shear stress. E11 expression is regulated by mechanical strain as shown by both in vitro and in vivo experiments. As E11 is also found in cementocytes, cementoblasts and in presecretory stage ameloblasts, suggesting a role in tooth formation, the present studies were performed to determine the expression and function in odontoblasts. Methods: Mandibles from 4, 12 and 15 day old wild type mice and 6 day old DMP1-GFP mouse were immunostained with E11 antibody. Mineralization assays and western blots were performed using three odontoblasts cells lines, derived from first molars of E18 transgenic mice with recombinant plasmid adeno-SV40. Mineralization was assayed using von Kossa and alizarin red staining at 0, 3, 6, 9 and 12 days. Results: E11 was localized in the odontoblast cell layer and in osteocytes of decalcified alveolar bone at 4, 12, and 15 days. Odontoblast staining intensity decreased with age in the molars but was maintained in the incisors. In the non-decalcified DMP1-GFP mouse mandible, E11 was also localized in the ameloblast layer but with much lower intensity compared to odontoblasts. E11 was expressed continuously in the odontoblast cell lines, 4IIG8 which did not mineralize and 17IA4 which mineralized in disperse nodules. However, E11 was not expressed in the 17IIA11 cells until homogeneous mineralization occurred in a honeycomb pattern. Conclusion: E11 is expressed in odontoblasts in the forming tooth and expression coincides with mineralization. Future studies are required to determine if E11 is responsible for odontoblast dendrite formation and its role in mechanosensation and dentin formation. DEO7294