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-kappa B, 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 alpha v beta 3. Osteoclast precursor migration was significantly inhibited by treatment of antibodies to integrin alpha v beta 3, resulting in the retardation of osteoclastogenesis. Taken together, these findings indicate that V-ATPase-driven acidosis modulates osteoclastogenesis.