Odontoblasts Express E11/gp38 and Respond to FFSS with Increased-Dendrite Elongation

Objectives: Odontoblasts share morphologic features with osteocytes including dendritic processes and markers such as DMP1 and E11/gp38. The dendrites of osteocytes form networks essential to cell viability and cell communication. They may also be important for mechanosensation and signal transduction. Expression of E11/gp38 is essential for dendrite elongation in osteocyte-like cells in response to fluid flow shear stress (FFSS) as shown both in-vitro and in-vivo. E11/gp38 is also highly expressed in odontoblasts suggesting a role in mechanosensation and in tertiary dentin formation. The present study was performed to determine if E11/gp38 plays a role in dendrite elongation in odontoblasts in response to FFSS. Methods: A previously characterized odontoblast-like cell line, 17IIA11, derived from the first molars of E18 transgenic mice expressing SV40 was used in this study. Cells were cultured in media containing beta-glycerophosphate and ascorbic acid to induce mineralization. Expression of E11/gp38 was assessed using Western blot. The 17IIA11 cells were exposed to 8 dynes/cm2 FFSS for 2hrs, fixed and stained with crystal violet 24hrs later. siRNA was used to inhibit E11/gp38 expression in these cultures. Results: The 17IIA11 cells mineralize forming honey-combed structures, similar to lamellar bone. E11/gp38 is expressed throughout the mineralization time course of 0, 3, 6, 9 and 12 days and peaks at day 6 coinciding with the onset of mineralization. 17IIA11 cells respond to FFSS with a 1-fold increase in dendrite lengthening at 24hrs post-FFSS. Conclusion: 17IIA11 cells respond similarly to osteocyte-like cells following FFSS, both showing an elongation of dendrites. These cells also differentiate and mineralize in culture over a 2 week period. These data suggest that odontoblast dendrites in-vivo may require E11/gp38 in order to respond to dentinal fluid movement and initiate signaling for pulpal pluripotent cell differentiation and tertiary dentin formation.