Problems of Radiation Medicine and Radiobiology

B. I. Gerashchenko¹, K. Salmina², J. Krigerts², J. Erenpreisa², A. M. Babsky³

¹R.E. Kavetsky Institute of Experimental Pathology, Oncology and Radiobiology, National Academy of Sciences of Ukraine, 45 Vasylkivska St., Kyiv, 03022, Ukraine
²Latvian Biomedical Research and Study Centre, 1 Ratsupites St., Riga, LV-1067, Latvia
³Ivan Franko National University of Lviv, Faculty of Biology, 4 Mykhaila Hrushevskoho St., Lviv, 79005, Ukraine

INDUCED POLYPLOIDY AND SORTING OF DAMAGED DNA BY MICRONUCLEATION IN RADIORESISTANT RAT LIVER EPITHELIAL STEM/LIKE CELLS EXPOSED TO X-RAYS

Objective. Rat liver stem-like epithelial cells (WB-F344) that under certain conditions may differentiate into hepatocyte and biliary lineages were subjected to acute X-irradiation with the aim to examine cell cycle peculiarities during the course of survival.
Materials and methods. Suspensions of WB-F344 cells that grew as a monolayer and reached sub-confluence were irradiated with 1, 5, and 10 Gy of X-rays (2 Gy/min). As an intact control, sham-irradiated cells were used. After irradiation, cells were plated into 25-cm² tissue culture flasks to culture them for over several days without reaching contact inhibition. On days 1, 2, 3, and 5 post-irradiation, cells were harvested and examined for nuclear morphology and DNA ploidy by stoichiometric toluidine blue reaction and image cytometry. On days 7 and 9 post-irradiation, only heavily irradiated (10 Gy) cells were examined. Also, 10 Gy-irradiated cells were chosen for immunofluorescence staining to monitor persistence of DNA lesions (γ-H2AX), cell proliferation (Ki-67), and self-renewal factors characteristic for stem cells (OCT4 and NANOG).
Results. Radioresistance of WB-F344 cells was evidenced by the findings that they do not undergo rapid and massive cell death that in fact was weakly manifested as apoptotic even in heavily irradiated cells. Instead, there was cell cycle progression delay accompanied by polyploidization (via Ki-67-positive mitotic slippage or via impaired cytokinesis) and micronucleation in a dose-dependent manner, although micronucleation to some extent went ahead of polyploidization. Polyploid cells amenable for recovering from DNA damage can mitotically depolyploidize. Many micronuclei contained γ-H2AX clusters, suggesting isolation of severely damaged DNA fragments. Both factors, OCT4 and NANOG, were expressed in the intact control, but became enhanced after irradiation.
Conclusions. Although the fact of micronucleation is indicative of genotoxic effect, WB-F344 cells can probably escape cell death via sorting of damaged DNA by micronuclei. Induction of polyploidy in these cells can be adaptive to promote cell survival and tissue regeneration with possible involvement of self-renewal mechanism.
Key words: WB-F344 cells, X-irradiation, cell survival, polyploidization, micronucleation, self-renewal.

Problems of Radiation Medicine and Radiobiology.
2019;24:220-234. doi: 10.33145/2304-8336-2019-24-220-234

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