Characteristic change and loss of in vivo osteogenic abilities of human bone marrow stromal cells during passage.

Although human bone marrow stromal cells (BMSCs) have the ability to form bone when transplanted, the responsible factors for in vivo osteogenic abilities are poorly understood. Here we report conditions that are required for human BMSCs to demonstrate their in vivo osteogenic abilities. BMSCs were obtained from healthy donors and their in vivo osteogenic abilities were analyzed. Transplantation analyses revealed that the passage number and length of osteogenic induction significantly affected ectopic bone formation. Although 2-week induction increased the percentage of success in bone formation compared with the 1-week induction, BMSCs completely lost their in vivo osteogenic ability after passage 4 regardless of the length of osteogenic induction. Despite their in vivo osteogenic ability, no significant difference was observed in alkaline phosphatase activity or gene expression of osteogenic markers between BMSCs at passages 1 and 3. Differences were only observed in in vitro mineralizing abilities. Application of basic fibroblast growth factor helped to maintain the BMSCs in vivo osteogenic ability; basic fibroblast growth factor altered cell growth and expression of HLA-DR. The results strongly suggest that there are several required conditions for human BMSCs to demonstrate their bone-forming capabilities, which should be further investigated and considered when designing a protocol for clinical bone tissue engineering.