Bone formation by transplanted human osteoblasts cultured within collagen sponge with dexamethasone in vitro

To apply osteoblasts to bone reconstruction, we proved that transplanted os teoblasts possessed the differentiated osteoblastic function and formed bon elike tissue in vivo after transplantation. First, we confirmed that dexame thasone (Dex) promoted the expression of osteoblastic phenotype in human os teoblast culture using reverse-transcription-polymerase chain reaction (RT- PCR), These osteoblasts were cultured for 10 days within collagen sponge, w hich consists of denatured type I collagen, in the presence or absence of 1 0(-7) M Dex, The osteoblasts along with collagen sponge were transplanted i nto the trapezius muscles of 8-week-old severe combined immunodeficiency (S CID) mice, and the transplants were harvested at 2, 4, 6, and 8 weeks, At 2 weeks, Des-treated osteoblasts formed bonelike tissue, the quantity of whi ch increased in a time-dependent manner to 8 weeks. This bonelike tissue wa s composed of mineralized collagen matrix newly synthesized by the transpla nted osteoblasts, This mineralized matrix was separated from the osteoblast s by nonmineralized matrixlike osteoid, Furthermore, many osteocytic cells were observed in this mineralized matrix. A high expression of alkaline pho sphatase (ALPase) and osteocalcin was detected in the transplanted cells su rrounding the bonelike tissue. In situ hybridization for human-specific alu sequence indicated that newly formed bone was of donor origin. The transpl ants of nontreated cells failed to form bonelike tissue. The transplants of collagen sponge alone formed no bonelike tissue. These studies indicate th at Dex-treated human osteoblasts possess the differentiated osteoblastic fu nction and are able to form bone tissue in vivo. These new findings are of use in facilitating the application of osteoblasts to bone reconstruction.