Periosteally derived osteoblast-like cells differentiate into chondrocytesin suspension culture in agarose

Pluripotent cells from the periosteal layer adjacent to cortical bone attai n an osteoblast-like phenotype in culture when reaching confluence in monol ayer. It is unknown whether such newly differentiated osteoblast-like cells preserve the chondrogenic potential characteristics for stem cells derived from the periosteum. Primary osteoprogenitor cells derived from bovine met acarpal periosteum were differentiated into alkaline phosphatase-positive o steoblast-like cells by an established monolayer culture protocol. After tr ansfer into suspension culture in agarose gels, the cells differentiated in to chondrocytes demonstrated by the production of collagen II, but not of c ollagen I, as well as alkaline phosphatase activity was abated. Contrarily, with continuation of monolayer culture, the cells maintained their osteobl ast-like phenotype and secreted large amounts of collagen I and a minor qua ntity of collagen III and V. The alkaline phosphatase activity steadily inc reased during the entire culture period of 2 weeks. Thus, our culture techn iques can serve as useful tools to study mechanisms of differentiation by m odulating the phenotypic potential of osteogenic cells. The results present ed here support the notion that the extracellular environment strongly infl uences the cell type and its metabolism. Anat Rec 259:124-130, 2000. (C) 20 00 Wiley-Liss, Inc.