Induced Torpor: An Experimental Model to Investigate the Effects of Chronic Low-Dose Radiation Exposure on Zebrafish Liver

We hypothesised that induction of a torpor-like state would confer a radioprotective effect given the evidence that hibernation extends survival times in irradiated squirrels compared to active controls. To test this hypothesis, a torpor-like state was induced in zebrafish using melatonin treatment and cold temperatures, and radiation exposure was administered twice over the course of 10 days. The protective effects of induced-torpor were assessed via RNA sequencing of mRNA extracted from the liver. A systems-level analysis was performed on the transcriptomic data to characterise the cellular phenotypes in radiation (28.5-rad), temperature+melatonin (18.5-mel), temperature+radiation (18.5-rad), and temperature+melatonin+radiation (18.5-mel-rad) groups compared with a control group (28.5-Ctrl). The results revealed that the torpor group experiences a reduction in metabolic genes, and increased pro-survival, antiapoptotic and DNA repair genes. The radiation group had changes to lipid metabolism and absorptions, a wound healing response and an immune response. While the induced torpor group showed a response to stress including changes to metabolism and perturbation of the circadian rhythm, it also maintained the pro-survival, anti-apoptotic and DNA repair genes seen in the torpor group suggesting a conferred radio-protective effect. Overall design: Transcriptomic analysis of zebrafish liver assessing the protective effects of induced torpor on the harmful effects of low dose radiation