The Role of Fas in Radiation Induced Apoptosis in vivo

Kim, Sung Hee; Seong, Jinsil; Seong, Je Kyung

Abstract

PURPOSE: It has been recognized that interaction of the Fas : Fas ligand plays an important role in radiation-induced apoptosis. The purpose of this study was to investigate the role of Fas mutation in radiation-induced apoptosis in vivo.
MATERIALS AND METHODS
Mice with mutations in Fas, MRL/Mpj-Fas(lpr), and its normal control, MRL/Mpj, were used in this study. Eight-week old male mice were given whole body radiation. After irradiation, the mice were killed and their spleens were collected at different time intervals. Tissue samples were stained with hematoxylin-eosin and the numbers of apoptotic cells were scored. Regulating molecules of apoptosis including p53, Bcl-2, Bax, Bcl-XL, and Bcl-XS were also analyzed by Western blotting.
RESULTS
At 25 Gy irradiation, the level of apoptosis reached the peak value at 8 hr after radiation and recovered to the normal value at 24 hr after radiation in MRL/Mpj mice. In contrast, the peak apoptosis level appeared at 4 hr after radiation in MRL/Mpj-Fas(lpr) mice. At 8 hr after radiation, the levels of apoptosis in MRL/Mpj mice and MRL/Mpj-Fas(lpr) mice were 52.3+/-7.8% and 8.0+/-8.6%, respectively (p<0.05). The expression of apoptosis regulating molecules, p53, Bcl-XL and Bcl-XS, increased in MRL/Mpj mice in response to radiation; p53 with a peak level of 3-fold at 8 h, Bcl-XL with a peak level of 3.3-fold at 12 h, and Bcl-XS with a peak level of 3-fold at 12 h after 25 Gy radiation. Bcl-2 and Bax did not show significant change in MRL/Mpj mice. However in MRL/Mpj-Fas(lpr) mice, the expression levels of p53, Bcl-2, Bax, Bcl-XL and Bcl-XS showed no significant change.
CONCLUSION
The level of radiation-induced apoptosis was lower in Fas mutated mice, lpr, than in control mice. This seemed to be related to the lack of radiation-induced p53 activation in the lpr mice. This result suggests that Fas plays an important role in radiation-induced apoptosis in vivo.