RhoV mediates apoptosis of RAW264.7 macrophages caused by osteoclast differentiation

Abstract

Macrophages, a type of immune cell, are the precursors of osteoclasts, and have important roles in bone remodeling and the immune system. In the present study, the RAW264.7 cell line was used as a macrophage model in order to study the macrophage changes during osteoclastogenesis. Receptor activator of nuclear factor κB ligand (RANKL) and macrophage colonystimulating factor (MCSF) induce the formation of osteoclasts from several precursor cells. Observation of RAW264.7 macrophage osteoclastogenesis under the induction of RANKL and MCSF revealed that except the few RAW264.7 macrophages that were differentiated into osteoclasts, almost all undifferentiated RAW264.7 macrophages underwent apoptosis. BRL3A cells have no differentiation ability, and RANKL and MCSF treatments did not induce BRL3A cell apoptosis. When osteoprotegerin (OPG) was used to completely inhibit the differentiation of RAW264.7 macrophages to osteoclasts, apoptosis did not occur amongst the RAW264.7 macrophages despite the action of RANKL and MCSF. Rac1, RhoA and RhoV are apoptosisassociated genes in the Rho guanosine triphosphate (GTP)ase family. Their expression levels were detected using quantitative polymerase chain reaction (qPCR). During the process of osteoclast differentiation, the mRNA expression of RhoV was significantly upregulated, while apoptosis occurred in a large proportion of macrophages. However, when macrophage apoptosis was inhibited by OPG, RhoV expression was significantly downregulated. Conversely, Rac1 and RhoA expression did not vary in correspondence with the apoptotic rate of the RAW264.7 macrophages. In conclusion, differentiation of RAW264.7 macrophages into osteoclasts resulted in their apoptosis. OPG inhibited RAW264.7 macrophage differentiation into osteoclasts, and thereby inhibited the apoptosis of RAW264.7 macrophages. RhoV mediated the apoptosis of RAW264.7 macrophages during osteoclast differentiation.