Differential expression of growth factors in irradiated mouse testes

Purpose: By using as an experimental model the male mouse gonad, which cont ains both radiosensitive (germ) and radioresistant (somatic) cells, we have studied the growth factor (and/or receptor) expression of transforming gro wth factor-beta receptor (TGF beta RI), stem cell factor (SCF), c-kit, Fas- L, Fas, tumor necrosis factor receptor (TNF R55), and leukemia inhibiting f actor receptor (LIF-R) after local irradiation. Methods and Materials: Adult male mice were locally irradiated on the teste s. Induction of apoptosis in the different testicular cell types following X-ray radiation was identified by the TdT-mediated dUTP Nick End Labeling ( TUNEL) approach, Growth factor expression was evidenced by semiquantitative RT-PCR and Western blot analyses. Results: Apoptosis, identified through the TUNEI, approach, occurred in rad iosensitive testicular (premeotic) germ cells with the following kinetics: the number of apoptotic cells increased after 24 h (p < 0.001) and was maxi mal 48 h after a 2-Gy ionizing radiation (p < 0.001), Apoptotic cells were no longer observed 72 h after a 2-Gy irradiation. The number of apoptotic c ells increased with the dose of irradiation (1-4 Gy), In the seminiferous t ubules, the growth factor expression in premeiotic radiosensitive germ cell s was modulated by irradiation. Indeed Fas, c-kit, and LIF-R expression, wh ich occurs in (radiosensitive) germ cells, decreased 24 h after a 2-Gy irra diation, and the maximal decrease was observed with a 4-Gy irradiation. The decrease in Stra8 expression occurred earlier, at 4 h after a 2-Gy irradia tion. In addition, a significant (p < 0.03) decrease in Stra8 mRNA levels w as observed at the lowest dose used (0.5 Gy, 48 h), Moreover, concerning a growth factor receptor, such as TGF<beta> RI, which is expressed both in ra diosensitive and radioresistant cells, we observed a differential expressio n depending on the cell radiosensitivity after irradiation. Indeed, TGF bet a RI expression was increased after irradiation in interstitial radioresist ant testicular cells in a dose- and time-dependent manner, while it decreas ed in seminiferous radiosensitive (germ cells) testicular cells. Such a dif ferential expression between radioresistant and radiosensitive cells in TGF beta RI levels was observed in terms of both mRNA and protein. In contrast , the growth factors specifically expressed in the somatic radioresistant ( Sertoli) cells in the seminiferous tubules (SCF, Fas-L, TNF R55) were not a ffected by ionizing radiation (up to 4 Gy, 72 h), Conclusion: Growth factor expression decreased in the radiosensitive testic ular cells after irradiation. Such a decrease occurred before the detection of apoptosis using the TUNEL approach. TGF beta RI mRNA levels decreased i n the radiosensitive cells, whereas it increased in the radioresistant cell s, suggesting that TGF beta RI may represent a biomarker of the intrinsic r adiosensitivity of cells. (C) 2001 Elsevier Science Inc.