Correlation of neuropeptides substance P and neuropeptide Y and their receptors with fracture healing in rats

Abstract

Bone fracture healing is a complex process involving a cascade of cellular and molecular events that are orchestrated by a variety of factors, including neuropeptides and their receptors. However, the roles of neuropeptides and their receptors in the fracture healing process are controversial. We monitored the expression and distribution of the neuropeptides, substance P (SP) and neuropeptide Y (NPY) and their receptors, neurokinin 1 receptor (NK1) and neuropeptide Y1 receptor (NPY1R), in rats undergoing fracture healing. Total RNA was extracted using Fe3O4 and was retrieved into DNA using the MagBeads Total RNA Extraction Kit. The expression levels of SP, NK1, and NPY at each time point in the healing bone tissue were found to be higher than the levels in normal bone tissue. Their location and expression levels correlated with the healing process. In the callus formation stage, the expression levels of SP, NK1, and NPY were found to be increased in the matrix of the cartilage, in chondrocytes, and in the subperiosteal region. At the bone remodeling stage, they were located in the periosteum, new bone tissue, and perivascular regions, and their expression levels gradually reduced. Therefore, we conclude that SP was involved in callus formation and bone resorption at different physiological concentrations. At some concentrations, SP positively regulated new bone formation via NK1. At other concentrations, the SP-NK1 interaction promoted bone resorption. Very low expression levels of NPY1R were observed at the early healing stage, but they increased at the middle stage and then decreased at the late stage. This indicated that NPY was involved in bone formation through NPY1R-unrelated mechanisms. NPY1R was more involved at the later stage of bone remodeling, according to its expression levels. NPY1R contributed to callus formation and remodeling.