[Effect of brain injury on expression of bone morphogenetic protein 2 in fracture healing process]

To investigate the changes in the expression level of bone morphogenetic protein 2 (BMP-2) in the bone callus of rats with femoral fracture and brain injury to explore the effect of the brain injury on the fracture healing and to explore the related mechanism.

Thirty-two 12-week-old SD rats weighing 368 +/- 25 g were randomly divided into 4 groups of 8 rats in each. The rats in Group A had a femoral fracture and a brain injury for 1 week; the rats in Group B had a femoral fracture but without brain injury for 1 week; the rats in Group C had a fracture and a brain injury for 2 weeks; and the rats in Group D had a fracture but without brain injury for 2 weeks. Thus, Groups A and C were used as the femoral fracture and brain injury models, and Groups B and D as the pure femoral fracture models for the controlled study. After the X-ray films were taken, the bone callus was obtained 1 week and 2 weeks after operation, respectively. Then, the bone callus growth and its histology were examined with the HE staining, the expression and changes in the level of BMP-2 were examined with the immunohistochemical staining, and the level of BMP-2 mRNA was measured with the RT-PCR.

The X-ray films showed that less bone callus formation was found in Group A, and the fracture line in Group B was clearer than that in Group A. There was a greater amount of callus in Group C, and the fracture line was blurred. Only a little bone callus formation was found in Group D. The HE staining indicated that more fibroblasts and early-stage chondrocytes were found in Group A; some fibroblasts in the fracture interspace and fewer early-stage chondrocytes in Group B; some newly-formed trabecular bone at the end of the fracture in Group C; but no trabecular bone formation in Group D. The immunohistochemical staining indicated that the positive expression of BMP-2 was strong in the cytoplasms of the fibroblasts, the mesenchymal cells, the vascular endothelial cells, the early-stage chondrocytes, and the osteoblasts. The number of the positive cells was greater in Group A than in Group B, with a higher color intensity. The number of the positive cells was greater in Group C than in Group D, with a higher color intensity. The percentages of the cells positive for BMP-2 in the callus were greater in Groups A and C (0.762% +/- 0.052%, 0.756% +/- 0.079%) than in Groups B and D (0.702% +/- 0.052%, 0.672% +/- 0.044%) at the same time point, with a statistically significant difference (P < 0.05). The RT-PCR analysis showed that the expression of BMP-2 mRNA in the callus in Groups A-D was decreased in sequence. There was a significantly higher level of the expression in Groups A and C (1.07 +/- 0.13, 0.78 +/- 0.11) than in Groups B and D (0.91 +/- 0.12, 0.61 +/- 0.08) at the same time point (P < 0.05).

The brain injury can promote the fracture healing process, which is probably related to an increase in the expression level of BMP-2 after the brain injury.