Effects of ¹³⁷Cs γ-rays on proliferation, differentiation and mineralization of osteoblastic cells in vitro

Objective: To evaluate the effect of gamma irradiation on the proliferation, differentiation, and mineralization of murine osteoblastic cells, and to investigate the related molecular mechanism. Methods: Osteoblastic cells were irradiated by different doses (0, 0.5, 1.0, 2.0, 5.0 Gy) of ¹³⁷Cs γ-rays. Cell morphology was observed with a microscopy,cell viability was analyzed by MTT assay, and ALP activity was analyzed by the methods of enzyme histochemistry and PNPP. Meanwhile,gene expressions of ALP, osteocalcin (OC), collagen Ⅰ, osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) were measured by semi-quantified RT-PCR. Results: Cell viability decreased with the radiation doses over 1.0 Gy (t=6.197-18.677, P<0.05). After radiation with a dose over 2.0 Gy, the cell number and the junctions of cell protrusions decreased, the cells had low refractivity and the activity and mineralization ability of ALP were also inhibited (t=2.790-2l.374, P<0.05). In addition, the expressions of ALP and OC mRNA were down-regulated significantly (t=3.563-16.508, P<0.05) when the radiation dose was higher than 0.5 Gy, and the expressions of OPG, OPG/RANKL mRNA were down-regulated (t=12.942, 4.954, P<0.05) at 5 Gy. But the expressions of collagen Ⅰ and RANKL mRNA were not affected by irradiation. Conclusions: The osteoblastic cells were significantly influenced by γ-irradiation,including morphological changes, inhibition of cell proliferation, differentiation and mineralization ability. Meanwhile, mRNA expressions of ALP and OC were down regulated. OPG/RANKL may be a main pathway of osteoblastic cell damage under high dose radiation. (authors)