Monocyte recruitment in areas of bone remodeling in the mouse tooth eruption model
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The goal of this study was to examine the recruitment of monocytes in the bony crypt surrounding the mouse molar in order to understand the role of mononuclear phagocytes in bone remodeling. Mouse molars develop in bony crypts from which they escape during eruption. Bone resorption occurs in the coronal one half of the crypt to form an eruption pathway, while bone formation occurs in the lower half. The recruitment of monocytes was quantified by immunohistochemistry using the F4/80 monoclonal antibody. Osteoclasts and pre-osteoclasts were defined as bone-associated multi- and mononuclear tartrate resistant acid phosphatase (TRAP) positive cells. Cell number was quantified using an image analysis system for animals sacrificed daily from 0 to 14 days following birth. The number of F4/80 positive monocytes in the area of bone formation generally increased with time with peaks at day 5 and 9 days. By the day 11, a decrease in monocytes was noted. In contrast, TRAP-positive mononuclear cells in this area were highest at the earliest time point and consistently decreased after day 3. Analysis was also undertaken in the area of bone resorption. An influx of F4/80 positive cells occurred in the occlusal area throughout the eruption period, with two peaks at day 5 and 9. TRAP-positive mononuclear cells were present in the same area in almost parallel changes with the F4/80 positive cells. There was a time-dependent increase in the number of osteoclasts, consistent with bone resorption in this area. To account for the recruitment of mononuclear phagocytes, expression of monocyte chemoattractant protein-1 (MCP-1) was assessed. The number of MCP-1 positive osteoblastic cells increased with time and was generally proportional to the recruitment of mononuclear phagocytes. The results suggest that the recruitment of mononuclear cells in the occlusal area is associated with osteoclast formation and bone resorption. In contrast, recruitment of mononuclear phagocytes in the apical area is associated with bone formation and a decrease in the number of osteoclasts. These results suggest that monocytes may have different functional roles in areas of bone formation compared to bone resorption. Furthemore, the expression of MCP-1 may provide a mechanistic basis to explain the recruitment of these cells.
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact firstname.lastname@example.org.Thesis (M.Sc.D.)--Boston University, Henry M. Goldman School of Dental Medicine, 1997.Includes bibliographical references: (leaves 68-87).
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