Ultrastructural alteration of osteoclasts treated with brefeldin A and wortmannin

Osteoclasts secrete protons and lysosomal enzymes through ruffled borders, resulting in demineralization and degradation of bone matrix. Golgi apparatus is thought to play a key role in this process. In order to elucidate the specific functions of Golgi apparatus in osteoclasts, we observed the ultrastructural and cytochemical changes resulting from the administration of brefeldin A (BFA), an inhibitor of Golgi structures, and wortmannin (WT), an inhibitor of phosphatidylinositol 3-kinase (PIS-kinase). When treated with BFA, osteoclasts showed a dissociated Golgi apparatus, while the peanut agglutinin (PMA)-positive ruffled borders were poorly developed or disappeared. Moreover, the acid phosphatase (ACPase) activity was somewhat reduced. WT-treated osteoclasts, on the other hand, exhibited no ultrastructural alteration of the Golgi apparatus, but were marked by the disappearance of PNA-positive ruffled borders, and a consequent increase in the number of ACPase-positive vesicles and vacuoles in the cytoplasm. These results indicate that the Golgi apparatus of osteoclasts not only plays an important role in the formation of lysosomal enzymes but also the supply of ruffled border membranes. Furthermore, PI 3-kinase appears to be involved in the transport of lysosomal enzymes and the maintenance of ruffled borders.