THE STRO-1(-MARROW CONTAINS THE OSTEOGENIC PRECURSORS() FRACTION OF ADULT HUMAN BONE)

The monoclonal antibody STRO-1 identifies clonogenic bone marrow strom al cell progenitors (fibroblast colony-forming units [CFU-F]) in adult human bone marrow. These STRO-1(+) CFU-F have previously been shown t o give rise to cells with the phenotype of fibroblasts, adipocytes, an d smooth muscle cells. In this study, the osteogenic potential of CFU- F derived from the STRO-1(+) fraction of adult human bone marrow was d etermined. CFU-F were isolated from normal bone marrow aspirates by fl uorescence activated cell sorting, based on their expression of the ST RO-1 antigen. Osteogenic differentiation was assessed by the induction of alkaline phosphatase expression, by the formation of a mineralized matrix (hydroxyapatite), and by the production of the bone-specific p rotein osteocalcin. STRO-1(+) cells were cultured in the presence of d examethasone (DEX; 10(-8) mol/L), ascorbic acid 2-phosphate (ASC-2P; 1 00 mu mol/L), and inorganic phosphate (PO4i; 2.9 mmol/L), After 2 week s of culture, greater than 90% of the cells in each CFU-F colony stain ed positive for alkaline phosphatase using a monoclonal antibody speci fic for bone and liver alkaline phosphatase. Alkaline phosphatase acti vity was confirmed by histochemistry. A mineralized matrix developed i n the CFU-F cultures, after 4 weeks of culture in the presence of DEX, ASC-2P, and PO4i. Mineralization was confirmed by both light and elec tron microscopy. The mineral was identified as hydroxyapatite by elect ron dispersive x-ray microanalysis and by x-ray diffraction analysis, In replicate cultures, osteocalcin release was shown after exposure of the cells to 1,25-dihydroxyvitamin D-3 (10(-7) mol/L) both by radioim munoassay and Northern blot analysis. This work provides direct eviden ce that adult human bone marrow-derived CFU-F are capable of different iating into functional osteoblasts and that osteoprogenitors are prese nt in the STRO-1(+) population. (C) 1994 by The American Society of He matology.