EXPRESSION OF VACUOLAR H+-ATPASE IN MOUSE OSTEOCLASTS DURING INVITRO DIFFERENTIATION

Osteoclasts express high levels of a vacuolar H+-adenosinetriphosphatase (H+-ATPase) on the ruffled membrane which they employ to dissolve bone mineral by acidifying their site of attachment on bone. The factors that control amplification of H+-ATPase during osteoclast differentiation are poorly understood. We examined the expression of vacuolar H+-ATPase in a cell culture system in which mouse spleen cells can be induced to differentiate into osteoclasts by coculture with a mouse bone marrow stromal cell line. We found that the coculture system produced active osteoclasts, identified as multinucleated cells with staining for tartrate-resistant acid phosphatase activity that formed genuine resorption pits in bone. These cells developed high levels of H+-ATPase expression in culture, and omission of dexamethasone or 1-alpha,25-dihydroxyvitamin D3 from the coculture system each partially suppressed the expression of H+-ATPase. The results demonstrate that the spleen and PA6 cell coculture system may be useful for investigating the factors that control the induction of H+-ATPase amplification that occurs during osteoclast differentiation.