Low-Dose Radiation Exposure with ⁵⁶MnO₂ Powder Changes Gene Expressions in the Testes and the Prostate in Rats

To investigate the biological effects of internal exposure of radioactive ⁵⁶MnO₂ powder, the major radioisotope dust in the soil after atomic bomb explosions, on male reproductive function, the gene expression of the testes and the prostate was examined. Ten-week-old male Wistar rats were exposed to three doses of radioactive ⁵⁶MnO₂ powder (41-100 mGy in whole body doses), stable MnO₂ powder, or external ⁶⁰Co γ-rays (2 Gy). Animals were necropsied on Days 3 and 61 postexposure. The mRNA expressions of testicular marker protein genes and prostatic secretory protein genes were quantified by Q-RT-PCR. On Day 3 postexposure, the testicular gene expressions of steroidogenesis-related enzymes, Cyp17a1 and Hsd3b1, decreased in ⁵⁶MnO₂-exposed groups. Germ cell-specific Spag4 and Zpbp mRNA levels were also reduced. On postexposure Day 61, the Cyp11a1 gene expression became significantly reduced in the testes in the group exposed to the highest dose of ⁵⁶MnO₂, while another steroidogenesis-related StAR gene mRNA level reduced in the ⁶⁰Co γ-rays group. There were no differences in Spag4 and Zpbp mRNA levels among groups on Day 61. No histopathological changes were observed in the testes in any group following exposure. Expression in the prostatic protein genes, including CRP1, KS3, and PSP94, significantly decreased in ⁵⁶MnO₂-exposed groups as well as in the ⁶⁰Co γ-rays group on Day 61 postexposure. These data suggest that the internal exposure to ⁵⁶MnO₂ powder, at doses of less than 100 mGy, affected the gene expressions in the testis and the prostate, while 2 Gy of external γ-irradiation was less effective.