Osteogenesic differentiation of medenchymal stem cells is regulated by Osteocyte and Osteoblast cells in a simplified bone niche.

Mesenchymal stem cells (MSCs) within their nativeenvironment of the stem cell niche in bone receivebiochemical stimuli from surrounding cells. These stimulilikely infl uence how MSCs differentiate to become boneprecursors. The ability of MSCs to undergo osteogenicdifferentiation is well established in vitro; however, therole of the natural cues from bones regulatory cells,osteocytes and osteoblasts in regulating the osteogenicdifferentiation of MSCs in vivo are unclear. In this studywe delineate the role of biochemical signalling fromosteocytes and osteoblasts, using conditioned media andco-culture experiments, to understand how they directosteogenic differentiation of MSCs. Furthermore, thesynergistic relationship between osteocytes and osteoblastsis examined by transwell co-culturing of MSCs with bothsimultaneously. Osteogenic differentiation of MSCs wasquantified by monitoring alkaline phosphatase (ALP)activity, calcium deposition and cell number. IntracellularALP was found to peak earlier and there was greater calciumdeposition when MSCs were co-cultured with osteocytesrather than osteoblasts, suggesting that osteocytes are moreinfl uential than osteoblasts in stimulating osteogenesisin MSCs. Osteoblasts initially stimulated an increasein the number of MSCs, but ultimately regulated MSCdifferentiation down the same pathway. Our novel coculturesystem confi rmed a synergistic relationship betweenosteocytes and osteoblasts in producing biochemical signalsto stimulate the osteogenic differentiation of MSCs. Thisstudy provides important insights into the mechanismsat work within the native stem cell niche to stimulateosteogenic differentiation and outlines a possible role forthe use of co-culture or conditioned media methodologiesfor tissue engineering applications.