Abstract:

To investigate the effect of ionizing radiation on the expressions of receptor activator for NF-κB(RANK) mRNA and protein in  differentiation process of osteoclasts and to discuss the molecular mechanism of bone injury induced by ionizing radiation.Methods The osteoblasts were differentiated from RAW264.7 cells after treated by 50 μg•L-1 receptor activatorfor NF-κB ligand(RANKL).The RAW264.7 cells were divided into   control group (normal RAW264.7 cells without treatment),RANKL treatment  group(RAW264.7 cells treated with   50 μg•L-1  RANKL), radiation treatment group (RAW264.7 cells exposed to 2 Gy γ-rays) and  radiation combined with RANKL treatment group(RAW264.7 cells treated with both 2 Gy  γ-rays and 50 μg•L-1  RANKL).Tartrate resistant acid phosphatase(TRAP) staining method was used to assess the osteoclast differentiation status;the expression levels of RANK mRNA and protein of  ostoclasts were detected by  PCR method and Western blotting method,respectivly.Results After treated with RANKL for 7 d,the RAW264.7 cells showed TRAP positive result,which indicated the formation of osteoclasts.Compared with control group,the expression levels of  RANK mRNA and protein  of  osteoclast precursors in RANKL treatment group and radiation treatment group  were increased (P<0.05).Compared with RANKL treatment group,the expression levels of RANK mRNA  and protein in radiation  combined  with RANKL  treatment group were decreased(P<0.05). Conclusion Ionizing radiation  may promote the proliferation and mature,and increase the activity of osteoclast precursors,but it  can inhibit the proliferation,mature,and activity of osteoclasts.

Key words: ionizing radiation, RAW264.7, osteoclasts, radiotherapy