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


METHODS
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.


RESULTS
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).


CONCLUSIONS
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.
Guo
Qi
Q
Department of Orthopedics, North China Coal Medical College, Affiliated Hospital, Tangshan Hebei 063000, PR China. guoqi168@chinaren.com
Zhang
Liu
L
D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000235:genetics / Q000378:metabolism*; D002146:Bony Callus / Q000378:metabolism; D001930:Brain Injuries / Q000150:complications / Q000378:metabolism*; D004195:Disease Models, Animal; D005264:Femoral Fractures / Q000150:complications / Q000378:metabolism*; D017102:Fracture Healing / Q000502:physiology*; D007150:Immunohistochemistry; D008297:Male; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction
C525720:Bmp2 protein, rat; D055396:Bone Morphogenetic Protein 2; D012333:RNA, Messenger