[Bone and Stem Cells. The mechanism of osteogenic differentiation from mesenchymal stem cell]

Osteoblasts and osteocytes originate from pluripotent mesenchymal stem cells. Mesenchymal stem cells commit to osteogenic lineage and differentiate into mature osteoblasts and osteocytes through osteoprogenitor cells and preosteoblasts in response to multiple stimuli. The osteoblast commitment, differentiation, and functions are governed by several transcription factors. Among these transcription factors, runt-related transcription factor 2 (Runx2) is a crucial factor in osteoblast differentiation and controls bone formation. Differentiation toward these osteogenic lineage is controlled by a multitude of cytokines including WNTs, bone morphogenetic protein (BMP) , transforming growth factor-β (TGF-β) , hedgehog, parathyroid hormone (PTH) /parathyroid hormone related protein (PTHrP) , insulin-like growth factor-1 (IGF-1) , fibroblast growth factor (FGF) , and Notch. Although regulation of Runx2 activity is a point of convergence of many of the signal transduction routes, there is also a high degree of cross-talk between these pathways. Thus, the combined action of the signal transduction pathways induced by some cytokines determines the commitment and differentiation of mesenchymal stem cells toward the osteogenic lineage.