The application of bone morphogenetic protein 2 (BMP-2) has been extensively investigated to improve diabetes-impaired bone healing; however, the delivery of BMP-2 by gene therapy for bone regeneration has rarely been investigated in diabetic animals. In this study, we aimed to evaluate which cells induce more new bone formation in diabetic animals when cell-based BMP2 gene therapy is applied. For this purpose, we harvested bone marrow stromal cells (BMSCs) twice in the same animal before (non-diabetic BMSCs; nBMSCs) and after diabetes induction (diabetic BMSCs; dBMSCs) using modified bone marrow ablation methods. And then, cells were transduced by adenoviral vectors carrying the BMP2 gene (AdBMP2). In in vitro, AdBMP2-transfected dBMSCs (B2/dBMSCs) produced higher BMP-2 mRNA levels over 48 h, whereas AdBMP2-transfected nBMSCs (B2/nBMSCs) exhibited a transient increase in BMP-2 mRNA followed by a decrease to the baseline level within 48 h. Both B2/dBMSCs and B2/nBMSCs induced secretion of BMP-2 for 3 weeks. However, B2/dBMSC BMP-2 secretion peaked from day 3 to 10, whereas B2/nBMSC BMP-2 secretion peaked from day 1 to 7. The analysis of osteogenic activity revealed that mineralization nodule formation and the expression levels of osteogenic genes were significantly higher in B2/dBMSCs than B2/nBMSCs and were accompanied by upregulation of canonical Wnt/β-catenin and Smad signaling. AdBMP2-transfected autologous cells were implanted into critical-sized calvarial defects in diabetic animals and induced significantly more bone regeneration than non-AdBMP2-transfected cells. In addition, B2/dBMSCs led to significantly more new bone formation than B2/nBMSCs. Thus, BMP2 gene therapy using diabetic cells effectively supported diabetic bone healing and it was related to the enhanced responses to AdBMP2 of dBMSCs.
Keywords: bone marrow stromal cells; bone morphogenetic protein 2; bone regeneration; diabetes; gene therapy.