Oxygen is toxic in the cold in C. elegans

Abstract

Introduction: Temperature and oxygen are two factors that profoundly affect survival limits of animals; too much or too little of either is lethal. However, humans and other animals can exhibit exceptional survival when oxygen and temperature are simultaneously low. This research investigates the role of oxygen in the cold shock death of Caenorhabditis elegans.

Methods: The survival of C. elegans populations in combinations of oxygen concentrations and was assayed. Additionally, the effect of cold acclimatization, mutations in the cold acclimatization pathway, compounds, and antioxidant proteins on survival in low temperatures and high oxygen were investigated.

Results: We demonstrate that C. elegans have increased survival in 2°C when deprived of oxygen, and an increase to just 0.25 kPa of oxygen decreased survival. Additionally, we show that oxygen toxicity produced by a 35-fold increase above atmospheric oxygen levels was fatal for nematodes in 8 h at room temperature and 2 h at 2°C. We found that cold acclimatization and mutations in the cold acclimatization pathway improve survival in room temperature oxygen toxicity. Furthermore, we found that the compounds glucose, manganese (II), and ascorbate improve both cold shock and high oxygen survival, while the antioxidant proteins catalase and peroxiredoxin are essential to wild type survival in these conditions.

Discussion: Our results suggest that oxygen toxicity contributes to the death of C. elegans during cold shock. The changes in survival induced by cold acclimatization and mutations in the cold acclimatization pathway suggest that oxygen toxicity in the cold exerts evolutionary pressure, leading to the development of protections against it. Additionally, the resistance provided by diverse compounds and antioxidant proteins in both low temperature and high oxygen suggests these conditions have similar chemical environments. We discuss evidence that similar phenomena may function in humans.

Keywords: C. elegans; ROS; cold acclimatization; cold shock; oxidative stress; oxygen; survival; temperature.

FIGURE 1

Effect of Oxygen Concentration on C. elegans Cold Shock Survival. (A) Survival after 48 h 23°C nitrogen, 2°C room air, and 2°C nitrogen. The probability of no interaction between nitrogen and 2°C is less than 0.05. See ST1 and ST2. (B) Survival after a 24-h 2°C cold shock in nitrogen containing low oxygen concentrations. See ST3.

FIGURE 2

Hyperbaric oxygen (HBO) is toxic. Survival of C. elegans in pure oxygen at high pressure. Duration of high oxygen exposure in hours is 2 , 4 , 8 . *P < 0.05 when comparing to 377 kPa. See ST4.

FIGURE 3

Effect of 2-hour exposure to combined cold shock and HBO. Survival of C. elegans after a 2-hour exposure to 23°C HBO, 2°C HBO, or 2°C room air. The probability of no interaction between HBO and 2°C is less than 0.05. See ST5 and ST6.

FIGURE 4

Cold acclimatization provides resistance to hyperbaric oxygen. Survival of animals grown from L1 stage at 23°C or 12°C and subsequently exposed to HBO as adults. Duration of HBO exposure in hours is 2 , 4 , 8 , 12 . *P < 0.05 when comparing to animals grown at 23°C. See ST7.

FIGURE 5

Genetic background affects survival in hyperbaric oxygen. Survival of mutant strains in HBO. Duration of HBO exposure in hours is 2 , 4 , 8 . *P < 0.05 when comparing to wild type (N2). See ST8.

FIGURE 6

Glucose, MnCl₂, and ascorbate increase both cold shock and hyperbaric oxygen resistance. Nematodes were grown on plates containing 3 mM MnCl₂, 300 mM Glucose, or 100 mM Ascorbate. (A) Survival in 2°C cold shock, duration in hours 2 , 6 , 12 . See ST9. (B) Survival in HBO, duration in hours 2 , 4 , 8 . *P < 0.05 when comparing to control (untreated) animals. See ST10.

FIGURE 7

Antioxidant proteins are required for wild type survival during cold shock and HBO exposure. Survival of peroxiredoxin (prdx) and catalase (ctl) knockout strains relative to wild type. (A) Survival in 2°C cold shock, duration in hours 2 , 6 , 12 . See ST11. (B) Survival in HBO, duration in hours 2 , 4 , 8 . *P < 0.05 when comparing to control (untreated) animals. See ST12.