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-kappaB, 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 alphavbeta3. Osteoclast precursor migration was significantly inhibited by treatment of
antibodies to
integrin alphavbeta3, resulting in the retardation of osteoclastogenesis. Taken together, these findings indicate that V-
ATPase-driven
acidosis modulates osteoclastogenesis.