Living longer doesn't mean living better
A study conducted by scientists at the University of Massachusetts Medical School, working under the guidance of Professor Heidi A. Tissenbaum, showed that long-lived genetically modified nematodes Caenorhabditis elegans spend most of their lives in poor health and in old age demonstrate less activity and resistance to adverse environmental factors compared to ordinary individuals. Based on these data, the authors concluded that genes that increase life expectancy cannot significantly increase the so-called healthy life expectancy, which indicates the need to assess the health status of model organisms when studying the mechanisms of their aging.
Advances in genetics and technology have allowed researchers to identify several groups of genes that control the longevity of C.elegans – roundworms, which are one of the most popular animal models among geneticists. Further studies have shown that these genes have analogues in the human genome. When carrying out such work, scientists adhered to the assumption that an increase in life expectancy would automatically prolong the period during which the body maintains a good state of health. However, for a number of reasons, when conducting such studies, a thorough analysis of the health status of model organisms is usually carried out only at a relatively young age, while the health status of aging individuals is undeservedly neglected.
The authors decided to test the validity of the assumption that prolongation of life is equivalent to long-term preservation of good health. To do this, they developed a system of simple parameters that allows assessing the condition of nematodes as they age.
For their experiments, the researchers used four mutant lines of roundworms (daf-2, eat-2, ife-2 and clk-1) that live longer than ordinary nematodes. The results obtained by studying the mobility of these organisms on a solid surface and in a liquid medium, as well as their resistance to high temperature and oxidative stress, were compared with the results obtained in similar experiments with ordinary C.elegans.
The comparison showed that the physical condition of all nematodes, without exception, worsened with aging. However, the physical extinction of individuals of different lines and estimated parameters occurred at different rates. In general, it turned out that, compared with wild-type individuals, the physical activity of long-lived mutant nematodes was reduced by more than 50% during a more significant (percentage) part of their life. The worms of these lines paid for the increased life expectancy with a weakened painful condition.
The graphs below from additional materials to the PNAS article show the life expectancy of wild-type nematodes and mutant long-lived lines, as well as periods of health and senile infirmity (in days and as a percentage of the maximum life expectancy) according to the four indicators studied.
The authors note that researchers studying aging should take into account that genes that affect life expectancy do not necessarily have to do with the duration of a healthy life. Apparently, there is a separate complex of genes that has not been studied to date, allowing some people to keep fit until a very old age. Therefore, when studying the issues of aging, life expectancy should not be the only parameter to be evaluated. As a separate no less important parameter should be the state of health.
Article by Ankita Bansal et al. Uncoupling lifespan and healthspan in Caenorhabditis eleganslongevity mutants is published in the journal Proceedings of the National Academy of Sciences.
Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on EurekAlert!: Living longer, not healthier.
21.01.2015