The Role of Na⁺/Ca²⁺ Exchanger in Osteoclast Differentiation

Abstract

Na⁺/Ca²⁺+ exchanger (NCX) catalyzes the electrogenic exchange of 3 Na⁺ for 1 Ca²⁺+ across the plasma membrane in many mammalian cells. We have previously reported that the Na⁺/Ca²⁺+ exchange activity had an important role for CSF-1-induced osteoclast differentiation. In the present study, we sought the effect of KB-R7943, a new NCX inhibitor, to confirm the role of NCX1, an isoform of NCX that imports Ca²⁺+ into the cells from extracellular in the reverse mode in osteoclast formation and activation.
Bone marrow cells were obtained from the tibiae and femur of 5-to 8-week-old male ddY mice. We used Sephadex G-10 column (G10) to remove macrophages and stroma cells. Nonadherent G10-passed cells were cultured in α-MEM containing the final concentration of 15% FBS, 100 ng/ml RANKL, 20 ng/ml CSF-1. KB-R7943 inhibited the osteoclast differentiation and bone resorption in vivo dose-dependently. Furthermore, NCX1 antisense oligo deoxy nucleotide (ODN) reduced the number of tartrate-resistant acid phosphatase-positive multinucleated cells and decreased the amount of NCX1 in protein level. Eight-week-old female ddY mice received sham operations or ovariectomy (OVX) and were fed a laboratory chow for 4 weeks following the operation. Animals were given subcutaneously 337.5 mg/kg KB-R7943 or DMSO every other day for 4 weeks. After 4 weeks of treatment with KB-R7943, the BMD in the femur of OVX group was significantly decreased compared with the sham group. However, the BMD in the KB-R7943-treated OVX group was quantitatively similar to the sham group. These results suggest that bone resorption was also blocked by treatment with KB-R7943 in vivo.
In conclusion, the activation of NCX1 plays an important role for osteoclast differentiation and activation.