A bit of sluggishness can be a good thing, at least when it comes to slowing down ageing. Scientists at the University of Veterinary Medicine, Vienna have found a relationship between torpor frequency and telomere length in a study of Djungarian hamsters. Their results are published in the current issue of the Royal Society journal Biology Letters.
Named after the region in northwest China from where it originates, the Djungarian hamster (Phodopus sungorus) is well adapted to the extremely seasonal climatic conditions of its steppe habitat. One of the ways it deals with the cold in winter is by spontaneous daily torpor, a short-term state of decreased metabolic rate and lowered body temperature that enables the animals to save resources. Christopher Turbill and colleagues at the Research Institute of Wildlife Ecology (FIWI) at the University of Veterinary Medicine, Vienna have now shown that such bouts of torpor in hamsters also seem to be associated with increases in the length of the hamsters’ telomeres.
Telomeres are repeated pieces of DNA that shield the ends of chromosomes against wear and tear. Previous research, including some performed in humans, has linked their maintenance to longevity. As animals age, their telomeres tend to become shorter, a process that is exacerbated by oxidative stress, but can be attenuated and even reversed by repair mechanisms. Shortened telomeres have been shown to increase the risk of reproductive failure and to compromise future survival.
Experts had suspected that the use of natural hypothermia (either through hibernation or daily torpor bouts) might slow down ageing. The FIWI researchers came up with the novel idea of testing this hypothesis by measuring changes in telomere length. The scientists triggered the hamsters´ seasonal response mechanism by subjecting them to shortened daylight hours (to simulate winter) and either a warm or a cold temperature for a period of 180 days. They used micro-transponders, like those routinely injected under the skin for identification, to measure subcutaneous body temperature. These measurements provided an index of either shallow or deep torpor. At the beginning and at the end of the experiment the scientists took a DNA sample from every hamster and analyzed how the telomere length changed over this period.
At the start of the experiment, hamsters in both groups had telomeres of about the same length but at the end of the study period almost all of the hamsters kept in the cold showed an increase in the length of their telomeres. These hamsters were also found to use deep torpor most frequently. Statistical analysis revealed that the most influential factors determining telomere length were not food intake itself – an index of energy metabolism, which was actually higher in the cold group – but rather body mass and the frequency and depth of torpor. The correlation between torpor use and telomere length supported the authors’ hypothesis that torpor appears to be a physiological state linked with slower rates of ageing. Possible explanations are that cell turnover is slowed by torpor use and/or that torpor increases cellular stress resistance.
Lead author Christopher Turbill explains, "It seems that daily torpor not only serves to save energy during winter but also could act to slow the physiological processes that cause biological ageing. That way, these small rodents can wait over the long winter season, remaining in a relatively youthful state until the next breeding opportunity in the following spring. This is significant for such short-lived animals. The effect could also be an important reason for the evolution of natural hypothermic states such as daily torpor and hibernation."
The paper “Daily torpor is associated with telomere length change over winter in Djungarian hamsters” by Christopher Turbill, Steve Smith, Caroline Deimel and Thomas Ruf is published in the Royal Society journal “Biology Letters”.