Cryonics: Another reason why the cannon won't fire
Changing the activity of genes prevented cryonics
Experiments made it possible to exclude the possible impact of cryoprotectors and associate the effect with freezing; the discovery raises the question of how effective defrosting of cells, tissues and the body as a whole stored at low temperature is possible. Details of the discovery are given in an article by scientists for the journal PLoS One (Marta F. Riesco, Vanesa Robles, Cryopreservation Causes Genetic and Epigenetic Changes in Zebrafish Genital Ridges).
The researchers compared the activity of genes in cells before and after freezing. They managed to find out that the activity determined by the level of expression (that is, by the number of synthesized RNA and protein molecules) varied both in the direction of decrease and increase: different genes reacted to freezing differently. Many proteins began to be synthesized in a smaller volume, but the so-called heat shock proteins, on the contrary, were produced more actively by thawed cells.
Scientists note this result as not so paradoxical, since heat shock proteins begin to be synthesized not only in response to overheating, but also in response to a number of other adverse effects. Much more important, the researchers found that they were able to detect not only changes in the level of expression, but also DNA damage: the level of damage does not lead to massive cell death, but it is quite large compared to the background. Scientists have checked different genes for damage and found out that not the whole genome is equally vulnerable: there are areas in it that are more likely to suffer when frozen.
To exclude the influence of some other factor, the researchers conducted experiments without cooling, but with placing cells in a medium with the addition of those reagents that are used as cryoprotectors during freezing. These experiments showed small DNA damage and changes in gene expression, but only a small part of the detected differences can be attributed to this. The repetition of experiments with samples of human sperm rather than fish embryos (freezing of sperm is widely used in medicine: for example, to preserve genetic material before chemotherapy, in order to preserve the possibility of conceiving a healthy child) suggested that along with DNA damage and inactivation of some genes due to DNA methylation, freezing can cause changes in RNA molecules.
The researchers suggest that in thawed cells, the molecules of informational (transferring genetic information from DNA to protein synthesis sites) RNA change, which can also affect gene expression. However, how exactly these changes occur, how the contributions of DNA damage and RNA modification correlate in the observed changes and what needs to be done to minimize them — all this scientists have yet to find out.
The work of scientists can be important both for doctors working with frozen sperm and human embryos at an early stage of development (several dozen cells), and for specialists trying to develop a way to freeze mammals with subsequent revival. This technology, which has not yet existed, called cryonics, is considered as one of the hypothetical ways to radically prolong life: enthusiasts are already trying to freeze the human body in order to try to resuscitate it in the future using the achievements of medical and biological science. Most experts are skeptical about the prospects of cryonics because of a number of processes occurring in a multicellular organism after freezing, and the new study adds another one to all potential problems: changes in gene activity.
Portal "Eternal youth" http://vechnayamolodost.ru24.06.2013