Stimulation of osteoclastogenesis by enhanced levels of MIP-1α in BALB/c mice in vitro

Objectives We compared osteoclast (OC) formation in bone marrow–derived macrophages (BMM) from C57BL/6 (B/6) and BALB/c (B/c) mice. After stimulation of receptor activator of nuclear factor-κB ligand (RANKL), enhanced OC formation and higher level of macrophage inflammatory protein-1α (MIP-1α) were observed in the BMM from B/c mice. In this study, we determined whether MIP-1α is responsible for stimulated OC formation in the BMM. Materials and Methods OC formation was evaluated in BMM. Expression of MIP-1α during OC formation was analyzed at the mRNA and protein levels. Apoptosis of mature OCs was evaluated by observing the degradation of DNA. Activation of nuclear factor-κB (NF-κB) was measured by electrophoretic mobility shift assay. Results After stimulation by RANKL expression of MIP-1α at the mRNA and protein levels was much higher in BMM from B/c mice than in BMM from B/6 mice. Transcripts of the MIP-1α receptors, CCR1 and CCR5, were present at similar levels in unstimulated BMM of the two strains. Blockade of MIP-1α inhibited OC formation, and exogenously added MIP-1α stimulated it in RANKL-stimulated BMM. MIP-1α affected not only the early precursors but also mature OCs. It prevented apoptosis of mature OCs by activating NF-κB, and the effect of RANKL on survival was dependent on its ability to induce MIP-1α. Conclusions MIP-1α, induced by RANKL during OC differentiation, increases OC formation by acting on OC progenitor cells, and prolongs survival of mature OC via signaling through NF-κB. The enhanced OC formation in BMM from B/c mice could be due to, at least in part, to their higher levels of MIP-1α.