Synergistic effects of the dual release of stromal cell-derived factor-1 and bone morphogenetic protein-2 from hydrogels on bone regeneration

The objective of this study is to evaluate the activity of gelatin hydrogels incorporating combined stromal cell-derived factor-1 (SDF-1) and bone morphogenetic protein-2 (BMP-2) on the in vivo bone regeneration at an ulna critical-sized defect and subcutaneous site of rats, and compared with that of those incorporating either SDF-1 or BMP-2. The similar release profile of SDF-1 and BMP-2 from the hydrogels was observed with or without the combination of BMP-2 and SDF-1, respectively. An enhanced bone regeneration by the hydrogels incorporating combined SDF-1 and BMP-2 was observed. In addition, the implantation of hydrogels incorporating combined SDF-1 and BMP-2 enhanced the expression level of CXC chemokine cell-surface receptor-4 (Cxcr4), Runt-related factor-2 (Runx2), and Osteocalcin genes. The experiments with green fluorescent protein (GFP)-positive Chimeric mice revealed that the recruitment of bone marrow-derived cells was promoted and a vascular-like structure together with strong accumulation of CD31- and CD34-positive cells was observed at the site of hydrogels incorporating combined SDF-1 and BMP-2 implanted. In addition, a large fraction of CD29- and CD44-positive non-hematopoietic cells was detected. It is concluded that the combined release of SDF-1 and BMP-2 enhanced the recruitment of osteogenic cells and angiogenesis, resulting in the synergistic effect on bone regeneration.