Temperature Effects on DNA Damage during Hibernation.

AbstractDuring multiday torpor, deep-hibernating mammals maintain a hypometabolic state where heart rate and ventilation are reduced to 2%-4% of euthermic rates. It is hypothesized that this ischemia-like condition may cause DNA damage through reactive oxygen species production. The reason for intermittent rewarming (arousal) during hibernation might be to repair the accumulated DNA damage. Because increasing ambient temperatures (T_a's) shortens torpor bout duration, we hypothesize that hibernating at higher T_a's will result in a faster accumulation of genomic DNA damage. To test this, we kept 39 male and female garden dormice at a T_a of either 5°C or 10°C and obtained tissue at 1, 4, and 8 d in torpor to assess DNA damage and recruitment of DNA repair markers in splenocytes. DNA damage in splenocytes measured by comet assay was significantly higher in almost all torpor groups than in summer euthermic groups. Damage accumulates in the first days of torpor at $T_a=5^{°}\text{C}$ (between days 1 and 4) but not at $T_a={10}^{°}\text{C}$. At the higher T_a, DNA damage is high at 24 h in torpor, indicating either a faster buildup of DNA damage at higher T_a's or an incomplete repair during arousals in dormice. At 5°C, recruitment of the DNA repair protein 53BP1 paralleled the increase in DNA damage over time during torpor. In contrast, after 1 d in torpor at 10°C, DNA damage levels were high, but 53BP1 was not recruited to the nuclear DNA yet. The data suggest a potential mismatch in the DNA damage/repair dynamics during torpor at higher T_a's.