OBJECTIVE

To investigate the effects of silencing P75 neurotrophin receptor (P75NTR) and nerve growth factor (NGF) overexpression on the proliferative activity and ectopic osteogenesis ability of bone marrow mesenchymal stem cells (BMSCs) combined with demineralized bone matrix for heterotopic osteogenesis.

METHODS

BMSCs of Sprague Dawley (SD) rats were cultured and passaged by adherent isolation method. The third generation BMSCs were transfected with lentivirus mediated P75NTR gene silencing (group B), NGF overexpression gene (group C), P75NTR silencing and NGF overexpression double genes (group D), respectively, and untransfected cells as control (group A). After 7 days of transfection, the expression of fluorescent protein of the target gene was observed by fluorescence microscope; cell counting kit 8 method was used to detect the cells activity for 8 days after transfection; the expressions of P75NTR and NGF proteins in each group were detected by Western blot. The adhesion of BMSCs to demineralized bone matrix (DBM) was observed by inverted phase contrast microscope and scanning electron microscope after transfection of p75NTR silencing and NGF overexpression double genes. After transfection, BMSCs and DBM were co-cultured to prepare 4 groups of tissue engineered bone, which were respectively placed in the dorsal subcutaneous tissue of 8-week-old SD rats to construct subcutaneous ectopic osteogenesis model ( =6). HE staining was performed at 4 and 8 weeks after operation. ALP staining was used to observe the formation of calcium nodules at 8 weeks after operation. The expressions of Runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), and osteocalcin (OCN) were detected by real-time fluorescent quantitative PCR.

RESULTS

At 7 days after transfection, there was no fluorescence expression in group A, red fluorescence expression was seen in group B, green fluorescence expression in group C, and red-green compound fluorescence expression in group D. The fluorescence expression rate of target gene was about 70%. Western blot detection showed that the relative expression of P75NTR protein in groups A and C was significantly higher than that in groups B and D, and the relative expression of NGF protein in groups C and D was significantly higher than that in groups A and B ( <0.05). With the passage of time, the cell proliferation activity increased in all groups, especially in group D, which was significantly higher than that in group A at 3-8 days ( <0.05). The results of inverted phase contrast microscope and scanning electron microscope showed that BMSCs could adhere well to DBM. In the subcutaneous ectopic osteogenesis experiment, HE staining showed that at 4 and 8 weeks after operation, the more bone tissue was formed in group D than in the other 3 groups. ALP staining showed that group D had the highest ALP activity and better osteogenic expression. Compared with group A, the relative expressions of Runx2, ALP, and OCN mRNAs in group D were significantly higher than those in group A ( <0.05).

CONCLUSION

Silencing P75NTR and NGF overexpression double genes co-transfected BMSCs with DBM to construct tissue engineered bone has good ectopic osteogenic ability. By increasing NGF level and closing P75NTR apoptosis channel, it can not only improve cell activity, but also promote bone tissue regeneration.