14.10.2019: Many mammals survive the cold winter months by lowering body temperature and metabolic rate during hibernation. The lower their body temperature, the more energy hibernators can save. However, winter dormancy also comes at a cost. Low body temperatures increase the rate at which the protective endcaps of the chromosomes shorten, which can lead to cell death and requires an enormous energy expenditure to correct. These are the findings of a research team from Vetmeduni Vienna in a recently published study.

During hibernation at low body temperatures, mammals can reduce their energy expenditure by more than 90%. This is of great benefit when food is scarce. However, hibernating at drastically low body temperatures can also have disadvantages, such as the shortening of the protective ends of the chromosomes known as telomeres. In an experiment with edible dormice (Glis glis) and garden dormice (Eliomys quercinus), researchers from Vetmeduni Vienna discovered that animals that hibernate at warmer temperatures show less telomere attrition but also spend more energy. Julia Nowack, who is one of the leading authors of the study and is now working at Liverpool John Moores University in the UK, says: “There appears to be a trade-off between maintaining intact telomeres, which constitutes an investment in cell survival, and maximizing energy savings through hibernation at low body temperatures.”

A trade-off between energy savings and telomere attrition

The research team found marked temperature effects on the shortening of the telomeres in the two species studied – edible dormice and garden dormice – hibernating in the laboratory at either 3°C or 14°C. The animals that hibernated at 14°C spent more energy than the animals that hibernated at 3°C. Conversely, however, the individual´s telomeres shortened less at 14°C. This new insight supports the widely accepted assumption that hibernation comes at a cost. “In summary, our study suggests that deep hibernation comes with costs on a cellular level, i.e. increased telomere attrition, which requires a lot of energy to repair,” says Julia Nowack.

Hibernation – a successful evolutionary strategy with certain disadvantages

Hibernation is a state of prolonged inactivity associated with a reduced metabolic rate and lower body temperature. It is considered to be the most efficient energy-saving strategy in mammals and birds. Despite its many benefits, it is increasingly clear that hibernation also comes with certain disadvantages, such as reduced immune function, slowed reactions and increased oxidative stress. Frequent arousals from hibernation lead to a rapid depletion of energy reserves and the upregulation of the metabolic rate is associated with the production of reactive oxygen species that causes a faster rate of telomere shortening via DNA breaks.

Telomeres – important, stress-sensitive ends of the chromosomes

Telomeres are non-coding, repetitive sequences of DNA at the end of chromosomes, which, together with telomere-associated proteins, prevent the degradation of the coding DNA during replication. Telomere length is often used as a marker of somatic aging. Telomeres shorten after each somatic cell division, i.e. mitosis, but telomere attrition can be accelerated by oxidative stress. If telomere length is not restored, the cell eventually dies. During hibernation, mitosis is arrested at low temperatures and, therefore, telomere degradation is paused.

Also important in humans

Telomeres are also of great significance in human medicine. Studies have shown that chronic stress in humans accelerates telomere shortening. Conversely, changes in lifestyle can slow telomere attrition and thereby positively affect the aging process of the cells and of the whole organism.

The article “Always a price to pay: hibernation at low temperatures comes with a trade-off between energy savings and telomere damage” by Julia Nowack, Iris Tarmann, Franz Hölzl, Steve Smith, Sylvain Giroud and Thomas Ruf was published in Biology Letters.