Vacuolar-type H+-ATPase-mediated acidosis promotes in vitro osteoclastogenesis via modulation of cell migration

Localized acidification of the osteoclast-bone interface is driven by a vacuolar-type H+-ATPase (V-ATPase) in the plasma membrane in a process thought to be associated with bone resorption. The present study investigated the mechanism underlying the roles of V-ATPase-induced acidosis in osteoclastogenesis. Active proton pumping due to increased V-ATPase activity during RANKL-induced osteoclastogenesis induced intracellular and extracellular acidification of osteoclast precursors. Subsequent analysis revealed blockage of extracellular acidification and induction of intracellular acidification by bafilomycin A1, a specific inhibitor of V-ATPase, indicating that extracellular acidification is mostly induced by V-ATPase-mediated proton pumping into extracellular space. Low-pH media controlled by HEPES-buffered conditions to mimic metabolic acidosis led to synergistic activation of RANKL-stimulated signals, including mitogen-activated protein kinases and transcription factor NF-κB, resulting in enhanced osteoclastogenesis. Low-pH media also upregulated the expression of osteopontin secreted into extracellular space, which is required for cell migration by binding to cell surface integrin αvβ3. Osteoclast precursor migration was significantly inhibited by treatment of antibodies to integrin αvβ3, resulting in the retardation of osteoclastogenesis. Taken together, these findings indicate that V-ATPase-driven acidosis modulates osteoclastogenesis.