RESUMO
To understand the biochemical response of RANKL in response to mechanical loading, MC3T3-E1 cells were biequiaxially stretched. A murine RANKL cDNA with double epitopes, pEF6 HA-RANKL-V5His, was transfected into MC3T3-E1 cells, which were then stretched. Endogenous RANKL protein expression increased in response to mechanical loading. Membrane-bound RANKL (HA-RANKL-V5His) increased in cell lysates while soluble RANKL (RANKL-V5His) decreased in the conditioned media after mechanical loading. This may have resulted from the decreased activity of TACE after mechanical loading. Increased membrane-bound RANKL may be one of the mechanisms through which osteoblasts adapt to mechanical loading by regulating osteoclastogenic activity in a region-specific manner.
Assuntos
Proteínas de Transporte/fisiologia , Glicoproteínas de Membrana/fisiologia , Osteoblastos/fisiologia , Células 3T3 , Animais , Fenômenos Biomecânicos , Proteínas de Transporte/genética , DNA Complementar/genética , Glicoproteínas de Membrana/genética , Camundongos , Condicionamento Físico Animal , Ligante RANK , Receptor Ativador de Fator Nuclear kappa-B , Suporte de CargaRESUMO
To clarify the role of calpain in the receptor activator of NF-kappaB ligand (RANKL)-supported osteoclastogenesis, RANKL-induced calpain activation was examined by using murine RAW 264.7 cells and bone marrow-derived monocyte/macrophage progenitors. We found that calpain activity increased in response to RANKL in both cell types based on alpha-spectrinolysis and that mu-calpain, rather than m-calpain, was activated during RANKL-supported osteoclastogenesis in RAW 264.7 cells. Overexpression of mu-calpain clearly augmented RANKL-supported osteoclastogenesis in RAW 264.7 cells, thereby implicating its pivotal role in this process. Cell-permeable calpain inhibitors, including calpastatin and calpeptin, were sufficient to suppress RANKL-supported osteoclastogenesis based on decreased expression of the osteoclastogenic marker, matrix metalloproteinase 9, and the generation of tartrate-resistant acid phosphatase-positive multinucleated cells in both cell types. Calpain inhibitors suppressed NF-kappaB activation via inhibition of the cleavage of inhibitor of NF-kappaB(IkappaBalpha)in RAW 264.7 cells. Taken together, our findings suggest that mu-calpain is essential to the regulation of RANKL-supported osteoclastogenesis via NF-kappaB activation.
