INFLUENCE OF OSTEOCLASTS AND OSTEOCLAST-LIKE CELLS ON OSTEOBLAST ALKALINE-PHOSPHATASE ACTIVITY AND COLLAGEN-SYNTHESIS

Osteoblasts have been shown to modulate osteoclast activity, but the r everse process has not been investigated. In the current study conditi oned medium (CM) was collected from osteoclasts and osteoclast-like ce lls and its effects on osteoblast alkaline phosphatase (ALPase) activi ty and collagen synthesis ([H-3]proline hydroxylation) were determined . In primary chick osteoblasts, cultured chick embryo frontal bones, a nd UMR-106-01 cells, collagen synthesis and ALPase activity, but not [ H-3]thymidine incorporation, were inhibited by CM from chick marrow-de rived giant cells, which possess some of the phenotypic characteristic s of osteoclasts. However, collagen synthesis in chick embryo fibrobla sts was not affected by giant cell CM. CM collected from cultures of c hicken osteoclasts and human osteoclastoma cells and marrow-derived gi ant cells inhibited collagen synthesis in UMR-106-01 cells, but the ef fects on ALPase activity varied with the cell type. In contrast, monon uclear cell and fibroblast CM did not alter collagen synthesis. Initia l characterization studies demonstrate that the inhibitor is a heat-la bile factor with a molecular weight greater than 3500. In summary, aut hentic osteoclasts, tumor osteoclast-like cells, and chicken and human multinucleated giant cells produce a soluble factor that alters osteo blast collagen synthesis, suggesting that osteoclasts play a role in t he modulation of osteoblast activity.