Local injection of angiopoietin 2 promotes angiogenesis in tissue engineered bone and repair of bone defect with autophagy induction in vivo

Abstract

To investigate the mechanism of early vascularization of the tissue engineered bone in the treatment of rabbit radial bone defect by local injection of angiopoietin 2 (Ang-2). A single 1.5 cm long radius defect model (left and right sides randomised) was constructed from 48 New Zealand white rabbits. After implantation of hydroxyapatite/collagen scaffolds in bone defects, the rabbits were randomly divided into 2 groups: control group (group A) and Ang-2 group (group B) were injected with 1 mL normal saline and 1 mL saline-soluble 400 ng/mL Ang-2 daily at the bone defect within 2 weeks after operation, respectively. Western blot was used to detect the expressions of autophagy related protein [microtubule associated protein 1 light chain 3 (LC3), Beclin-1], angiogenesis related protein [vascular endothelial growth factor (VEGF)], and autophagy degradable substrate protein (SQSTMl/p62) in callus. X-ray films examination and Lane-Sandhu X-ray scoring were performed to evaluate the bone defect repair at 4, 8, and 12 weeks after operation. The rabbits were sacrificed at 12 weeks after operation for gross observation, and the angiogenesis of bone defect was observed by HE staining. Western blot assay showed that the relative expression of LC3-II/LC3-I, Beclin-1, and VEGF in group B was significantly higher than that in group A, and the relative expression of SQSTMl/p62 was significantly lower than that in group A ( P<0.05). Radiographic and gross observation of specimens showed that only a small number of callus were formed in group A, the bone defect was not repaired; more callus were formed and complete repair of bone defect was observed in group B. The Lane-Sandhu scores in group B were significantly higher than those in group A at 4, 8, and 12 weeks after operation ( P<0.05). HE staining showed that the Harvard tubes in group B were well arranged and the number of new vessels was significantly higher than that in group A ( t=-11.879, P=0.000). Local injection of appropriate concentration of Ang-2 may promote early vascularization and bone defect repair of rabbit tissue engineered bone by enhancing autophagy.