Effects of X-ray irradiation and housing conditions on mitochondria in Peromyscus maniculatus

Challenging environmental conditions, such as exposure to ionizing radiation, can induce oxidative stress within mitochondria. However, organisms show variation in their capacity to cope with cellular stress. This study aimed to identify how housing conditions influence mitochondrial stress responses under exposure to radiation. We used North American deer mice (Peromyscus maniculatus), kept in standard rodent boxes or large semi-natural enclosures that allowed for natural levels of physical activity and social structures under ambient atmospheric conditions. Animals from each housing condition were exposed to 2000 mSv (2 Gy) of ionizing X-ray radiation, a dose comparable to long-term spaceflight. Animals were euthanized for analysis prior to irradiation (baseline), within four days post-irradiation, or one-month following irradiation. Relative mass of the liver was lower than the baseline for irradiated animals maintained in the semi-natural enclosures. State 4 and coupled and uncoupled state 3 respiratory capacity of liver and skeletal muscle mitochondria were lower four days after the exposure. Yet, a month after exposure these variables were comparable to baseline in muscle but remained lower in the liver. The mitochondrial volume was lower after irradiation relative to baseline and was higher in animals maintained in standard rodent boxes, in both tissues. Oxidative damage to lipids in liver was higher in animals kept in boxes, whereas in muscle it was higher in animals kept in the semi-natural enclosures, and oxidative damage to proteins did not change. These results suggest that a heterogenous environment with greater potential for activity may counter the effects of ionizing radiation, although this effect appears to be modest.