Biorhythmology of mortality

Russian scientists have discovered periods
increased risk to life

Natalia Reznik, Informnauka

They say life is striped. Recently, this folk wisdom has received experimental justification. Investigating the life expectancy of mice, a leading researcher at the Laboratory of Protein Biosynthesis Regulation at the A.N. Bach Institute of Biochemistry of the Russian Academy of Sciences, Doctor of Biological Sciences Alexander Malygin, found that there are periods when the probability of death of mice increases dramatically. These periods of time alternate with periods of increased resilience. Whether this pattern is true for humans remains to be seen. According to the researchers, the proof of this hypothesis in relation to humans would allow people to extend their life to a species maximum – about 105 years.

"This work began with the fact that we accidentally found a male with growth retardation in a laboratory mouse population," he says in an interview with a correspondent STRF.ru Alexander Malygin. – We have established that such a delay is caused by an inherited mutation and leads to partial death of mice at a certain age. This served as the basis for continuing systematic studies of the patterns of their natural mortality."

If mutant males are crossed with normal females, the offspring are mixed. Some of the animals develop normally, while others at the age of 15-30 days, when ordinary mice gain weight strenuously, lag behind in growth, but then within 2 months they catch up with their peers and are outwardly indistinguishable from them. However, adult mutant females, despite their similarity to normal mice, are either infertile or bear offspring that die within the first day after birth. Therefore, in order to maintain the mutation, stunted males are crossed with normally developing females.

Female (1) with 40-day-old offspring: normally developing individuals (2, 3) and stunted mutants (4, 5)

Not all mutants could survive the critical period of stunting, some of them died at the age of 25 to 35 days. The researchers did not stop monitoring the lifespan of mice. The experiment lasted 3 years and 9 months, during which time scientists traced the fate of 118 animals. Alexander Malygin found two more periods with increased mortality in mutant mice: 270-400 days and 520-670 days, and periods separating them with minimal mortality. In independent groups of mice, the results were reproduced, and this convinced the researchers that the variations in mortality were not random. They are characteristic of both males and females.

After the third peak of mortality, the probability of death fell, and the last mouse died at the age of 3 years 2 months. The maximum lifespan of mutant mice does not differ from the maximum duration of normal mice. This means that the developmental lag experienced by mutants at the beginning of life does not significantly affect the duration of subsequent life.

And what about normal mice? Their mortality increases smoothly with age, and has no jumps noticeable in mutant animals. But when the mice were separated by sex, it turned out that normal males can also be distinguished by three periods of increased mortality, and they fall at the same ages as the mutants. Normal females also have these periods, but they are very poorly expressed. Alexander Malygin explains the difference between mutant and normal females by the fact that mutant females are not able to bear offspring and this is similar to males. And normal females have a whole complex of physiological functions that allow them to give birth and nurse cubs. Probably, some of these functions directly or indirectly affect the resilience and risk of death.

Since, like puberty, fetal gestation and other physiological processes, variations in life expectancy depend on age, it can be assumed that they are programmed. The only difference is that it is not death itself that is programmed, but changes in the sensitivity of the body to the destructive effects of the external environment. If it increases during certain periods of life, then the risk of dying increases. But the body can avoid death if it is in favorable conditions during this period.

If such "jumps in mortality" are natural, then why have they not been noticed before? Because life expectancy is traditionally described using a smooth function based on averaged data. In the present experiment, the researchers did not average the results and therefore were able to detect the existence of periods with an increased risk of death. Mutant mice have only attracted attention to this phenomenon.

Naturally, everyone is concerned about the question of whether there are jumps in human mortality. It's possible. The researchers note that the period of rapid growth of mice (15-30 days) corresponds to the time of weight gain in humans, which falls at the age of 12-19 years. At the end of this period, both mice and humans have a peak in mortality. Who knows, perhaps, the frequent death from heart attacks of men aged about 60 years is explained precisely by the fact that they reach another critical period that they are unable to overcome. "It goes without saying that with the availability of appropriate funds, we could expand the initiated research more widely and deeper, including cellular and molecular levels, and even extend them to humans up to practical application," says Alexander Malygin. But there are no such funds, but it's a pity. According to the researchers, proving the validity of this hypothesis in relation to humans would allow people to extend their lives to a species maximum of about 105 years. People would know at what periods they need to beware of infections and adverse environmental conditions, eat right, in general, to protect their health.

The work was carried out with the support of the RFBR.

Source of information: A.G. Malygin, Stepwise change in the lifespan of mice in ontogenesis. Ontogenesis, 2013, volume 44, No. 1.

Portal "Eternal youth" http://vechnayamolodost.ru01.03.2013