NPY and CGRP Inhibitor Influence on ERK Pathway and Macrophage Aggregation during Fracture Healing

Aim: The aims of this study are to investigate the effects of neurotransmitters NPY and CGRP on ERK signaling in fracture healing, and to identify the correlation between macrophage aggregation and fracture healing.

Methods: Male Sprague-Dawley rats were used to build a fracture model. The neurotransmitter receptor inhibitors were injected intraperitoneally into the rats. Immunofluorescence staining and ELISA were employed to determine the expression of NPY and CGRP in fracture area and the peripheral blood, respectively. Micro-CT together with histological staining were utilized to assess the fracture healing conditions. Relative protein expression was determined using western blot. Immunofluorescence staining was used to detect the aggregation of macrophages in the injury area.

Results: During fracture healing, the serum NPY and CGRP significantly increased. The levels of NPY and CGRP reached a peak in the 8th week and reduced significantly thereafter. NPY and CGRP inhibitors could inhibit fracture healing and down-regulate the phosphorylated ERK. Macrophages (NPY+ and CGRP+) aggregated in the injury area.

Conclusion: NPY and CGRP participated in fracture healing, in which they were also shown to influence phosphorylated ERK expression. In addition, macrophages are involved in the fracture healing process.