18 September 2015

The liver ages faster than the brain

Department of Science "Newspapers.Ru" figured out why this is happening, and talks about how the discovery of researchers can help in the fight against aging.

Scientists have known for a long time that the real reflection of the physical state of the human body is not the year of birth indicated in the passport, but the biological age. So, more recently, researchers have found out that people age at very different rates: for example, the biological age of a 38-year-old person can vary from 28 years to 61 years. This means that some people's bodies age by three years in 12 months, while others age by only a year in 16.5 months. Answering the question of why this happens, the authors of the study stated that the primary role in the formation of such differences is played not by internal factors (genetics is only 20% responsible for the rate of aging), but by external factors, such as the quality of nutrition and living conditions, the intensity of sports, regular medical examinations.

However, the authors of the article published on the evening of September 17 in the journal Cell Systems, argue: the aging of the body depends more on the processes that occur over time with each specific type of cells in our body (Ori et al., Integrated Transcriptome and Proteome Analyzes Reveal Organ-Specific Proteome Determination in Old Rats, in the public domain). A research team led by Martin Beck from the European Molecular Biology Laboratory found out that different organs age at different rates, and this happens because of the different rate of aging of individual cells. 

Drawing from the press release of the Salk Institute for Biological Studies: Not all organs age alike – VM.

The scientists analyzed the condition of liver and brain cells of laboratory mice aged six months (equivalent to 18 "human" years) and 24 months. Unlike previous researchers, the authors focused not on studying gene expression (that is, understanding which genes "turn on" and "turn off" with age), but on what types of proteins the cells of these organs produce. The researchers were able to detect 468 differences in the state of proteins in old and young rodents, a significant part of which arose in the process of protein synthesis. In addition, it was found that during the aging process of the body 130 proteins change their location in the cell, in a different way they carry out the process of phosphorylation (changing the protein after its creation) and splicing ("cutting out" certain nucleotide sequences from RNA molecules and their subsequent connection, which is preserved in the "mature" molecule). 

Most of all, scientists were struck by the fact that age-related changes in proteins turned out to be very specific: the vast majority of them were characteristic of only one organ. The authors of the article explain this by the fact that cells of different organs have different properties: for example, liver cells are updated quite often during the life of the body, therefore they are not resistant to age-related changes. At the same time, most of the neurons of the brain "live" in it from the birth of the organism to its death, which means that they must have an "innate" ability to resist time. It turns out that the liver ages much faster than the brain.

In addition, liver and brain cells perform completely different functions: if the main task of the former is the implementation of metabolism, then the latter are responsible for the neuroplasticity of the brain (its ability to change and restore lost connections after damage or as a response to external influences). 

"Our work proves that the aging mechanisms of different organs differ from each other and that they are controlled by the processes of protein production and renewal. We think that the situation is the same with other bodies. Now we are faced with another question: can one organ influence the aging rate of another?"– comments one of the authors of the article Martin Getzer. 

Correspondent of "Gazeta.Ru" talked with the head of the research group Martin Beck and found out what role the conclusions made by scientists can play in the development of methods to combat aging. 

– Martin, is it possible to say – if, of course, to simplify the results you have obtained – that our internal organs have different biological ages? 

– That's not quite true. They have the same age – it just affects each organ differently. The liver has a high ability to self–renew – this means that its cells divide and renew throughout life - and the brain does not know how to do this. We compared the molecules (RNA and proteins) contained in both organs of old and young animals. We found differences that mean that the liver (which, in principle, is constantly being updated) suffers much more from age-related changes. In addition, these changes differ from each other: for example, in the brain, molecules that are responsible for communication between cells are more affected, and in the liver there are no such molecules at all. In the liver, the molecules of enzymes that provide metabolism suffer. They are present in many tissues, but they do not degrade so much in the brain.

– Is this mechanism the result of the evolutionary development of tissues? Can you explain why aging occurs so unevenly? 

– To the question of whether this is a product of evolution, one can unequivocally answer "yes", because the lower eukaryotes (living organisms whose cells contain nuclei. - "Newspaper.Ru") have no fabrics at all. Although we know that even yeast cells age, there are organisms that can be called "potentially immortal". 

Specific aging of organs is a consequence of the development of specialized cells and tissues that contain specialized molecules and perform special tasks.

– Will the results of your work help in understanding how the body as a whole ages? Is it possible to say that a person dies when the amount of damage accumulated by different organs reaches a certain value? 

– Yes, of course, to understand how the system is aging, you need to understand how its parts do it. Some scientists also hope that this will help develop new – more "direct" – methods of treating certain age-related diseases. As for the second question… It would be better to ask a doctor. But I would say no. Death can occur due to a sharp deterioration in the condition of just one vital organ. 

– Is it possible in the future to somehow influence the rate of aging of various organs and thereby prolong a person's life? 

– Well, we can say that this is already happening: you can eat healthy food, not drink, not smoke, thereby "helping" the liver and lungs. Although, of course, in order to create special medicines, it will take a long time to study the aging processes of different organs.

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