FUNCTIONAL AND STRUCTURAL INTERACTIONS BETWEEN OSTEOBLASTIC AND PREOSTEOCLASTIC CELLS IN-VITRO

Osteoblasts are involved in the bone resorption process by regulating osteoclast maturation and activity. In order to elucidate the mechanis ms underlying osteoblast/preosteoclast cell interactions, we developed an in vitro model of co-cultured human clonal cell lines of osteoclas t precursors (FLG 29.1) and osteoblastic cells (Saos-2), and evaluated the migratory, adhesive, cytochemical, morphological, and biochemical properties of the co-cultured cells. In Boyden chemotactic chambers, FLG 29.1 cells exhibited a marked migratory response toward the Saos-2 cells. Moreover, they preferentially adhered to the osteoblastic mono layer. Direct co-culture of the two cell types induced: (1) positive s taining for tartrate-resistant acid phosphatase in FLG 29.1 cells, (2) a decrease of the alkaline phosphatase activity expressed by Saos-2 c ells; (3) the appearance of typical ultrastructural features of mature osteoclasts in FLG 29.1 cells; (4) the release into the culture mediu m of granulocyte-macrophage colony stimulating factor. The addition of parathyroid hormone to the co-culture further potentiated the differe ntiation of the preosteoclasts, the cells tending td fuse into large m ultinucleated elements. These in vitro interactions between osteoblast s and osteoclast precursors offer a new model for studying the mechani sms that control osteoclastogenesis in bone tissue.