Osteoblastic regulation of osteoclast survival: effects of calcitriol.

Throughout life, bone is remodelled in a dynamic process which results in a balance between bone formation by osteoblasts and bone resorption by osteo clasts. It is now clearly established that osteoblasts/stromal cells are cr ucial for differentiation of osteoclasts, through a mechanism involving cel l-to-cell contact. However, the possible involvement of osteoblasts and str omal cells in the survival of osteoclasts has not yet been clearly demonstr ated. In this study, we assessed the influence of cellular microenvironment , especially osteoblasts, on the osteoclast survival. Our results have show n significant differences in osteoclastic survival between unfractionated b one cells and pure osteoclasts. Furthermore, we have shown that addition of 1.25(OH)(2)D-3 to unfractionated bone cells resulted in a dose-dependant i ncrease in osteoclast survival. Finally, we have shown that a conditioned m edium obtained from rat osteoblastic cells cultured with calcitriol was abl e to increase significantly survival of pure osteoclasts. Taken together, t hese results strongly suggest that osteoblastic cells present in the bone m icroenvironment might play a role in the osteoclastic survival by producing soluble factor which modulate osteoclast apoptosis. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.