CALCITONIN PROMOTES OSTEOCLAST SURVIVAL IN-VITRO

Inactivation of resorbing osteoclasts by calcitonin is associated with typical morphological changes and alteration of the specific organiza tion of osteoclast cytoskeleton. Here we show that calcitonin also pro motes the survival of rat osteoclasts in vitro, cultured either on gla ss or bone, by delaying the onset of apoptosis. Parathyroid hormone ha d no effect on osteoclasts cultured on glass but it slightly increased apoptosis index of osteoclasts cultured on bone. Calcitonin was also able to rescue osteoclasts in calvarial explant cultures. The survival effect of calcitonin was mimicked by dibutyryl cAMP and could not be blocked by various metabolic inhibitors known to affect the apoptotic pathway. However, clodronate-induced apoptosis of osteoclasts could no t be reversed by calcitonin and neither could calcitonin rescue osteoc lasts already committed to apoptosis. It did not alter the distributio n of Bcl-2 in osteoclasts. Our results show that at least in vitro cal citonin protects osteoclasts from apoptosis and suggest that it regula tes the onset of apoptosis.