Runx2 overexpression enhances osteoblastic differentiation and mineralization in adipose--derived stem cells in vitro and in vivo.

Like bone marrow stromal cells, adipose tissue-derived stem cells (ADSCs) possess multilineage potential, a capacity for self-renewal and long-term viability. To confirm whether ADSCs represent a promising source of cells for gene-enhanced bone tissue-engineering, the osteogenic potential of ADSCs under the control of certain osteoinductive genes has been evaluated. Runx2, a transcription factor at the downstream end of bone morphogenetic protein (BMP) signaling pathways, is essential for osteoblast differentiation and bone formation. In this study we used adenovirus vector to deliver Runx2 to ADSCs and then examined the enhancement of osteogenic activity. Overexpression of Runx2 inhibited adipogenesis, as demonstrated by suppression of LPL and PPARgamma expression at the mRNA level and reduced lipid droplet formation. Moreover, ADSCs transduced with Ad-Runx2 underwent rapid and marked osteoblast differentiation as determined by osteoblastic gene expression, alkaline phosphatase activity and mineral deposition. Additionally, histological examination revealed that implantation of Runx2 modified ADSCs could induce mineral deposition and bone-like tissue formation in vivo. These results confirmed, firstly, the ability of Runx2 to promote osteogenesis and cell differentiation and, secondly, the competence of ADSCs as target cells for bone tissue engineering. Our work demonstrates a potential new approach for bone repair using Runx2-modified ADSCs for bone tissue engineering.