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Understanding the molecular and biochemical basis of radiation-induced oxidative stress tolerance across extremo-tolerant eukaryotes

par Lentze, Capucine
Président du jury Roisin, Yves
Promoteur Van Doninck, Karine
Publication Non publié, 2023-06-28

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Résumé :

Due to extreme or unstable environmental conditions, certain organisms have developed uniquesurvival strategies. The bacteria Deinococcus radiodurans is known for its unique adaptationsto desiccation and ionizing-radiation (IR), and it is assumed that its tolerance to IR is anincidental consequence of its desiccation resistance. Some eukaryotes, such as the bdelloidrotifer Adineta vaga, is also known for its desiccation and radiation resistance. One of the mainconsequences of exposure to exogenic stresses is oxidative stress which causes a higherproduction of reactive oxygen species (ROS). Essentially, ROS create cellular damagesincluding DNA and proteins oxidation. To protect themselves from ROS and deal withoxidative damage, living organisms acquire specific mechanisms to eliminate these toxicproducts, particularly using antioxidants. The role of antioxidants is primarily to scavenge ROSthereby limiting damages in cells. Some organisms have evolved manganese-based (Mn)antioxidants, such as the Mn-superoxide dismutase, and it has been shown that high Mn/Feratios are indispensable for radiation resistance in IR-tolerant prokaryotic species.To explore if high Mn/Fe ratio also plays a role in increased radiation resistance in eukaryotes,we tested the ability to survive IR in Acanthamoeba castellanii, a unicellular amoeba highlyIR-resistant. We optimized a medium (DGM) where Mn starvation could be achieved. Oursurvival assays using a hemocytometer show that A. castellanii irradiated with Mn reached aLD10 around 7000 Gy whereas A. castellanii irradiated without Mn reached a LD10 around5000 Gy two days after radiation exposure. Our results of ICP-MS confirm a higher ratio ofMn/Fe in A. castellanii in DGM+Mn (0,14) whereas in DGM-Mn, the Mn/Fe ratio in A. castellaniiwas lower (0,04). Furthermore, protein carbonylation assay showed a protein oxidation increasein Mn-starved conditions, although this was not observed for all the doses tested, suggestingthat Mn might contribute to radiation-resistance of A. castellanii. Finally, the superoxidescavenging complexes assay confirmed the presence of superoxide scavenging complexes innon-irradiated and irradiated A. castellanii followed by Mn starvation. Further analyses, suchas proteomic analyses or Mn inhibition assays, might confirm if the superoxide scavengingcomplexes are linked to Mn in A. castellanii’s antioxidant system.