ABSTRACT
BACKGROUND: Repair of tendon interface is a difficulty in orthopedics and sports medicine, and the formation of new bone is conducive to its healing. Calcitonin gene-related peptide (CGRP) plays a critical role in tissue homeostasis and repair, but its effect on the bone-tendon interface repair is unknown. OBJECTIVE: To investigate the effect of CGRP on the expression of osteocalcin and to evaluate the effect of CGRP on the early healing of rotator cuff injury in a mouse model. METHODS: A mouse model of supraspinatus insertion-humerus injury was created. All model mice were then randomized into two groups, and given the injection of 5 nmol/kg CGRP (experimental group) or same volume of normal saline (control group) through the glenohumeral joint immediately after operation, thrice weekly, for 2 weeks. The mice were sacrificed at postoperative 4 and 6 weeks to remove the rotator cuff samples for hematoxylin-eosin staining and biomechanical test. The mRNA and protein expression levels of osteocalcin were surveyed by qRT-PCR, immunohistochemistry, and western blot assay. RESULTS AND CONCLUSION: At postoperative 4 and 6 weeks, the mRNA and protein expression of osteocalcin in the experimental group were significantly higher than those in the control group (P < 0.05). Compared with the control group, there were more fibrocartilages in the experimental group at 4 weeks postoperatively, and more new bone formation in the experimental group at 6 weeks postoperatively. At 4 weeks postoperatively, failure load in the experimental group increased slightly, but it was not significantly different from that in the control group (P > 0.05); at 6 weeks postoperatively, failure load in the experimental group was significantly higher than that in the control group (P<0.05). To conclude, local injection of CGRP can up-regulate the expression of osteocalcin and the formation of new bone at the injury site, which can enhance early healing the injured rotator cuff.