SPECIFIC INHIBITORS OF VACUOLAR H-ATPASE TRIGGER APOPTOTIC CELL-DEATHOF OSTEOCLASTS()

Osteoclasts are multinucleated bone-resorbing cells that play a critic al role in bone remodeling, Specific inhibitors of vacuolar H+-ATPase (V-ATPase), concanamycin A and bafilomycin A1, abolish bone resorption by osteoclasts. In this study, we examined whether these V-ATPase inh ibitors trigger apoptotic cell death in osteoclasts, using murine oste oclast-like multinucleated cells (OCLs) formed in vitro. Acridine oran ge staining revealed that the treatment of OCLs with concanamycin A re sulted in chromatin condensation and alterations in nuclear morphology within a few hours, The TdT-mediated dUTP-nick-end labeling (TUNEL) r eaction confirmed the apoptotic features of OCLs treated with concanam ycin A. The accelerated apoptotic cell death induced by concanamycin A occurred in OCLs treated with interleukin-1 alpha or macrophage colon y-stimulating factor as well, which are known to elongate the survival time of osteoclasts, In contrast, these inhibitors did not induce cel l death of osteoblastic cells isolated from mouse calvaria, These resu lts suggest that functional impairment of V-ATPase triggers apoptotic cell death in osteoclasts.