The Effect of αCGRP on Macrophages Polarization in Osseointegration

Objectives: M1/M2 polarization of macrophages has been reported to play important roles in regulating the bone formation and osseointegration. Several studies have shown that calcitonin gene-related peptide-alpha (αCGRP) may influence the macrophages polarization in inflammatory responses. Additionally, our previous studies proposed that αCGRP overexpression at peri-implant sites resulted in greater gains in osseointegration. Therefore, the purpose of this study was to elucidate the influence of αCGRP on macrophages polarization in osseointegration.
Methods: In vitro tests, bone marrow derived macrophages (BMDMs) from C57BL/6 or αCGRP^-/- mice were obtained and then treated with LPS for M1-like activation, IL-4 for M2-like activation. Flow cytometry was used to identify the M1/M2 polarization. Real-time PCR were performed to evaluate inflammatory functions. To further investigate the role of αCGRP in vivo, mice were divided into wild-type group, αCGRP^-/- group, or αCGRP^-/- with αCGRP lentivirus transfection group. The inflammation and bone formation around implants in murine maxillae were observed and analyzed.
Results: In vitro, flow cytometry results demonstrated that αCGRP deficiency promoted the M1 polarization and inhibits the M2 polarization in BMDMs, which were consistent with pro-inflammation and anti-inflammatory cytokines expression levels in real-time PCR. In vivo, compared to αCGRP^-/- group, knock-out group received αCGRP gene transfection displayed better osseointegration and lower inflammation levels.
Conclusions: Our results demonstrate that αCGRP may play roles in macrophages polarization. αCGRP deficiency might influence the osseointegration, and αCGRP recovery with lentivirus transfection might improve osseointegration and reduce inflammation infiltration in a continuous and effective manner.