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Fas is involved in the p53-dependent apoptotic response to ionizing radiation in mouse testis
Michelle Embree-Ku1, Deborah Venturini, Kim Boekelheide
1Department of Pathology and Laboratory Medicine, Brown University, 171 Meeting Street, Providence, Rhode Island 02912, USA.
Abstract:
Apoptosis induced in male germ cells following ionizing radiation is dependent on functional p53 (Trp53) being present. We sought to determine whether Fas (Tnfrsf6/CD95/APO-1), an apoptotic factor, is involved in this p53-dependent germ cell death. In p53 knock-out mice exposed to 5 Gy of x-radiation, germ cells were protected from cell death, as assessed by counting apoptotic seminiferous tubules 12 h following radiation. Similarly, spermatid head counts in p53 knock-out mice remained near normal 29 days after exposure to 0.5 Gy of radiation, whereas wild-type animals had a more than twofold reduction in spermatid head counts. Fas mRNA expression remained at pretreatment levels in p53 knock-out mice; however, Fas increased in a time-dependent manner in wild-type mice following exposure to 5 Gy of radiation, indicating that radiation-induced Fas expression is p53-dependent. The functional significance of Fas involvement was demonstrated when lpr(cg) mice, having a nonfunctional Fas receptor, were exposed to 5 Gy of radiation; the number of apoptotic seminiferous tubules 12 h following radiation was significantly reduced compared to that of wild-type mice. Additionally, lpr(cg) mice exposed to 0.5 Gy of radiation had increased spermatid head counts 29 days following radiation compared to wild-type mice. Interestingly, gld mice with a non-functional Fas ligand (Tnfsf6/FasL/CD95L) were as sensitive to radiation as wild-type animals, and levels of FasL mRNA were not affected by radiation treatment. These results indicate that apoptosis and up-regulation of Fas following radiation are both p53-dependent events. Although Fas is necessary, in part, for radiation-induced p53-dependent apoptosis, FasL is not.
Insights
Ionizing radiation induces male germ cell apoptosis via p53 (Trp53) and Fas. Fas is essential for this p53-dependent cell death, but Fas ligand (FasL) is not involved in radiation-induced apoptosis.
Area of Science:
- Cell Biology
- Radiation Biology
- Molecular Biology
Background:
- Apoptosis in male germ cells after ionizing radiation exposure is dependent on functional p53 (Trp53).
- The role of Fas (Tnfrsf6/CD95/APO-1), a key apoptotic factor, in this process remains unclear.
Purpose of the Study:
- To investigate the involvement of Fas in p53-dependent germ cell apoptosis induced by ionizing radiation.
- To elucidate the specific roles of Fas and Fas ligand (FasL) in radiation-induced male germ cell death.
Main Methods:
- Utilized p53 knock-out mice and wild-type mice exposed to varying doses of x-radiation (5 Gy and 0.5 Gy).
- Assessed germ cell apoptosis by counting apoptotic seminiferous tubules and spermatid head counts.
- Quantified Fas and FasL mRNA expression levels post-radiation.
- Examined radiation sensitivity in lpr(cg) mice (nonfunctional Fas receptor) and gld mice (nonfunctional Fas ligand).
Main Results:
- p53 knock-out mice showed protection from radiation-induced germ cell death and maintained normal spermatid counts.
- Fas mRNA expression increased in wild-type mice post-radiation but remained unchanged in p53 knock-out mice, indicating p53-dependent Fas regulation.
- Mice with a nonfunctional Fas receptor (lpr(cg)) exhibited reduced apoptosis and higher spermatid counts after radiation compared to wild-type.
- Mice with a nonfunctional Fas ligand (gld) showed similar radiation sensitivity to wild-type mice, with no change in FasL mRNA levels.
Conclusions:
- Both radiation-induced apoptosis and Fas up-regulation in male germ cells are p53-dependent events.
- Fas is a necessary component for radiation-induced p53-dependent germ cell apoptosis.
- Fas ligand (FasL) does not play a significant role in this radiation-induced apoptotic pathway.