Figure 1.

Mechanistic differentiation and function of OC under physiological conditions. OCs are the only osteolytic cells in vivo. It dissolves bone matrix in four steps. The first step is OC adhesion. The integrin and actin microfilaments expressed by OCs allows the cells to closely adhere to the bone surface and form a special cytoskeleton. The second step is OC polarisation, and the OC plasma membrane and cytoskeleton are recombined. The plasma membrane of OCs is divided into four different regions: basal region, wrinkle edge, sealing region and functional secretory region. The third step is degradation of bone matrix. H-ATPase transports H+ to the cavity, allowing the pH of the cavity microenvironment to near a pH of 4-6. This acidic environment loosens the minerals in the bone matrix, and the wrinkle edge also secretes protons and various bone resorption enzymes to degrade organic matter. The fourth step is the removal of degraded products. The degraded bone matrix products are transported from the fold edge to the functional secretory region through endocytosis, and then released extracellularly.