Heavy ion radiation-induced DNA damage mediates apoptosis via the Rpl27a-Rpl5-MDM2-p53/E2F1 signaling pathway in mouse spermatogonia

Abstract

The risk of exposure to ionizing radiation (IR) environments has increased with the development of nuclear technology. IR exposure induces excessive apoptosis of the spermatogonia, which leads to male infertility. Spermatogonia apoptosis may be involved in ribosomal stress triggered by DNA damage following exposure to IR because ribosomal proteins (RPs) directly interact with mouse double minute 2 homolog (MDM2) to induce apoptosis. This study aimed to use comparative proteomics and transcriptomics approach to screen the differential RPs and ribosomal mRNAs in mouse testes following high linear energy transfer (LET) carbon ion radiation (CIR). The expression of ribosomal large subunit protein 27a (Rpl27a) decreased at both protein and mRNA levels in the spermatogonia in vivo. After 6 h of CIR, the immunofluorescence signal of 8-oxo-dG and phosphorylated ataxia-telangiectasia-mutated protein (ATM)/histone H2Ax increased, but that of Rpl27a decreased in the spermatogonia of p53 wild-type and knockout mouse testes. Moreover, the nucleolin was scattered throughout the nucleoplasm after CIR. These results suggested that CIR-induced DNA damage might trigger ribosomal stress, and the reduction in the expression of Rpl27a was associated with DNA damage in the spermatogonia. Similarly, in vitro, the immunofluorescence signal of 8-oxo-dG increased in the GC-1 cells after CIR. Moreover, the expression of Rpl27a was regulated by DNA damage because the co-transfection of ATM and Rpl27a or inhibition of ATM-treated CIR could restore the expression of Rpl27a. Furthermore, the reduction in the expression of Rpl27a led to weakened binding of E2F transcription factor 1 (E2F1) and p53 to MDM2, causing p53 activation and E2F1 degradation in p53 wild-type and knockdown GC-1 cells. This study proposed that heavy ion radiation-induced DNA damage mediated spermatogonia apoptosis via the Rpl27a-Rpl5-MDM2-p53/E2F1 signaling pathway. The results provided the underlying molecular mechanisms of spermatogonia apoptosis following exposure to high LET radiation.

Keywords: Apoptosis; Ionizing radiation; MDM2–p53 loop; Reproductive toxicology; Ribosomal stress.