Role of CCR2+ cells in the alveolar bone repair process in mice: histomorphometric and molecular characterization

The bone repair process depends of an initial and transitory inflammatory response, which involves the participation of various leukocytes subsets, as of the monocyte/macrophage lineage. The CCR2 receptor is important to macrophage recruitment during immune responses, and play an active role in the regulation of osteoclastogenesis. Thereby, the purpose of this study was to investigate the role of CCR2+ cells in the alveolar bone repair process in mice, by means of microscopic (MicroCT, histomorphometry, birefringence analysis and immunohistochemistry) and molecular (PCRArray) comparative analysis between C57BL / 6 (WT) and CCR2KO mice during periods of 0 hour, 7, 14 and 21 days post-extraction of the right upper incisor. As a result of the microscopic analysis, we noted that the absence of CCR2+ cells did not affect in the overall outcome of alveolar bone repair in CCR2KO mice, but resulted in transient and statistically significant (p<0.05) alterations of inflammatory infiltrate, blood vessels, fibroblasts, collagen fibers, osteoblasts and osteoclasts counts. Furthermore, the absence of CCR2+cells resulted in a decrease (p<0.05) of CCR5+ and F4/80+ cells in the inflammatory infiltrate along the alveolar bone repair process in CCR2KO mice, demonstrating the role of CCR2 receptor in macrophages migration (F4/80+ cells), as well as suggesting that the F4/80+ cells are double positive for CCR2 and CCR5. In this context, CCR5 receptor could be responsible for the remaining (but reduced) migration, of the F4/80 + cells in CCR2KO mice. According to molecular results, the absence of CCR2 resulted in an altered expression of different markers in CCR2KO mice, such as: growth factor TGF1, the matrix markers COL1, MMP1a, MMP2 and MMP9, the bone markers RUNX2, DMP1 RANKL, RANK and CTSK, and MSCs markers CD106, OCT-4, NANOG, CD146 and CD105, as well as immunological markers as IL-6 and TNF-, chemokine receptors CCR1, CXCR1 and CCR5, and the chemokines CCL12, CCL20, CCL25 and CXCL12. In conclusion, these results indicate that CCR2+ cells have different functions in alveolar bone repair in mice, influencing the inflammatory response and also tissue events observed throughout the process events. (AU)