EXPRESSION OF OSTEOBLASTIC MARKERS IN CULTURED HUMAN BONE AND FRACTURE CALLUS CELLS

We compared the expression of osteoblastic markers in cultured human c ells isolated from fracture calluses of various histological states of development with that in cells from adult and fetal bone. Adult osteo blasts and all callus cells produced almost exclusively type I collage n, whereas fetal osteoblasts produced also considerable amounts of typ e III collagen in vitro. 1,25-Dihydroxyvitamin D-3 induced the synthes is of osteocalcin in all bone and callus cells but to varying extents. Fetal bone cells and early-stage callus cells synthesized less than 1 0% the amount of osteocalcin produced by adult bone cells. Late-stage callus cells produced intermediate levels of osteocalcin. Fetal bone c ells and early-stage callus cells responded to parathyroid hormone wit h a less pronounced increase in intracellular cAMP than did adult bone cells. Late-stage callus cells showed the best response to parathyroi d hormone. The activity of alkaline phosphatase was highest in fetal b one cells. These observations show that cells isolated from fetal bone and from fracture callus tissues express a pattern of markers clearly relating them to the osteoblastic lineage, On the basis of the differ ent patterns of osteoblastic markers ex pressed in vitro we conclude t hat functionally distinct subtypes of osteoblasts do exist in differen t mineralized tissues and at different developmental stages.