Removal of Osteoclast Bone Resorption Products by Transcytosis

TLDR

Osteoclasts are multinucleated bone‑resorbing cells that, during the resorption cycle, reorganize their polarity to expose four distinct membrane domains. They endocytose bone degradation products from the ruffled border and transcytose them in vesicles to a central basal membrane domain where the products are released extracellularly. This transcytosis mechanism allows osteoclasts to simultaneously remove large amounts of matrix degradation products and penetrate bone.

Abstract

Osteoclasts are multinucleated cells responsible for bone resorption. During the resorption cycle, osteoclasts undergo dramatic changes in their polarity, and resorbing cells reveal four functionally and structurally different membrane domains. Bone degradation products, both organic and inorganic, were endocytosed from the ruffled border membrane. They were then found to be transported in vesicles through the cell to the plasma membrane domain, located in the middle of the basal membrane, where they were liberated into the extracellular space. These results explain how resorbing osteoclasts can simultaneously remove large amounts of matrix degradation products and penetrate into bone.