The Mystery of Prions
Prions: Perfect killers and a possible key to immortality
Vasily MakagonovThroughout its history, humanity has faced a huge number of wars, epidemics, natural disasters and other cataclysms. In the XXI century, when epidemics seemed to be over, humanity had a new challenge – prions. What is it, what they threaten people with and why scientists around the world are so interested in prions – in the material M24.ru .
Do you remember how it all startedIn the twenties of the last century, doctors faced a new and hitherto unknown disease.
German neurologist Hans Gerhard Creutzfeldt observed one patient in his clinic – a 20-year-old girl. At the initial stage of the disease, she had impaired sensitivity in her arms and legs, memory disorders, nervous activity rapidly progressed, the patient increasingly fell into unconsciousness. A few months later, the girl died of respiratory and cardiac disorders. A neurologist, who in the future will become a prominent Nazi doctor and will take part in the "Euthanasia" program, documented the course of the disease.
A few months later, Dr. Alphonse Maria Jakob from Hamburg came across three similar patients. Young people suffered from disorders of nervous activity, swallowing, were practically unaware of what was happening around them and soon died. At the autopsy, Jacob saw an interesting phenomenon that doctors had not had to observe before – only the brain was affected in patients. Mass death of cells of the gray matter of the brain was recorded, and the preserved neurons were distinguished by unusual swelling. No pathological changes were recorded in any other organ. In memory of the two discoverers, the disease was named Creutzfeldt–Jakob disease.
In those early years, virology as a science was still in its infancy. Therefore, the disease was destined to remain in oblivion for a long time. The Great Depression and the Second World War contributed to this. And it was only in the fifties of the last century that scientists began to actively wonder what was happening to people who were not lucky enough to catch Creutzfeldt-Jakob disease.
At the same time, scientists are discovering two more diseases that, in their symptoms and course, are very, very similar to the terrible ailment described above – kuru and scrapy. The first disease was common among the Fore people on the island of Papua New Guinea, and the second affected sheep all over the world. But something else turned out to be important: the symptoms of the diseases were somewhat different from Creutzfeldt–Jakob disease, but the nature of the lesions was almost identical – the formation of voids in the brain tissues and the mass death of nerve cells.
It would seem that everything is clear. There is a disease, it is caused by some virus or bacterium, let's figure out who is the causative agent and eliminate the cause. But it was not there! It wasn't that simple...
ResearchesScientists managed to quickly establish why Papuans are sick.
It turned out that only those of them who participated in the ritual eating of the bodies of relatives who died from the Kuru get sick. According to local beliefs of that time, children had to taste the brain of the deceased, it was believed that this would add to their mind. It is not known whether this increased the intelligence of the children, but all the minors who participated in such meals necessarily turned out to be infected with kuru.
Especially large-scale research unfolded with agent scrapy. To begin with, its dimensions were determined, they turned out to be standard for viruses – 17-27 nanometers. After that, virologists around the world began to understand the properties of an unknown causative agent of the disease, and then surprises awaited them. It turned out that the infectious agent is completely immune to formalin, pepsin and trypsin, does not react to enzymes that destroy DNA and RNA, is resistant to boiling, ultraviolet radiation and ... penetrating radiation! Scientists have not had to deal with such viruses yet.
Moreover, the causative agent of the disease could not be seen in an electron microscope, which was very strange. At that time, scientists were already able to recognize viral particles much smaller than 17 nanometers, but the virus scrapes (scratching) so no one saw – only fragments of cell membranes were observed.
Another interesting mystery turned out to be any lack of an immune response of the body of patients. The body of people with Kuru and sheep suffering from scrapie did not react to the course of the disease in any way. In common diseases, such as flu and colds, interferon synthesis increases in the body (responsible for immunity), which leads to the rapid release of antibodies that combine with viral particles and dissolve them. Scientists tried to detect signs of at least some antibodies, but failed.
Desperate researchers began to hypothesize that the causative agent is not a virus, but a polysaccharide or protein molecule, but this version has not been confirmed. Scientists stood still until in 1982, American neurologist Stanley Prusiner announced the discovery of a new class of infectious agents – prions.
What is a prionPrior to the discovery of prions, it was believed that human and animal diseases could be caused exclusively by living organisms or at least viruses containing nucleic acid.
However, everything turned out to be not so simple. A prion is a special kind of protein that is present in any human body.
It turned out that either under the influence of incomprehensible factors, or due to mutations in the body of some people, the normal prion protein, which is part of the cell membranes, is replaced by the "wrong" one. The second type of prion protein has a different structure, causes cell death, but the most interesting thing is that it is able to reproduce independently (without any DNA and RNA!) and change normal prions in neighboring cells to defective ones.
Naturally, the researchers were interested in the most important question – why do we need prions in the human body at all? Currently, quite a lot of prion diseases are already known. All of them are extremely rare, the most common – Creutzfeldt–Jakob disease – is observed in one in a million people. It is also known about Gerstmann–Straussler–Scheinker syndrome, fatal familial insomnia and kuru. Some researchers also include Alpers disease in children, amyotrophic leukospongiosis (described by Belarusian scientists at the end of the last century, workers of one of the farms were ill) and spongiform myositis (muscle exhaustion) in the group of human prion diseases.
All these diseases are fatal, and medicines for them have not yet been offered. But still, why does the body synthesize prions? What role does he assign to them?
Why are prions needed?In the 70s of the last century, two English researchers – Pattison and Jebet – studied the effect of a substance called cuprizon on mice.
Under normal conditions, it binds copper ions in the body. The animals were included in the mandatory diet of cuprizon in order to see what effect it would have on rodents. And they were amazed! After more than 30 days of the cuprizon diet, the previously perfectly healthy mice turned into seriously ill. Moreover, all signs of the disease fully corresponded to the symptoms of scrapie. Some of the mice participating in the experiment were opened and looked at – it turned out that absolutely the same changes occurred in the brain of animals as in prion diseases.
The question arose: what if you don't give cuprizon to mice anymore? They tried – and after a few days the rodents recovered. After 30 days, the changes in the brain tissue caused by cuprizon also disappeared.
Many years later, it was found out that prions are very, very similar to positively charged particles of divalent copper. And the changes they cause in the body are almost identical. Thus, the researchers concluded that in the normal state, prions are responsible for the turnover of metals, in particular copper. But these data are still only a hypothesis.
Another group of American researchers began to dig in a different direction. They were able to obtain data that prions help brain cells attach to each other and participate in the transmission of signals inside the cell. This means that the absence of prions or their defects do not allow brain cells to receive a signal from other cells, which leads to the development of severe disorders in the nervous and other systems of the body.
(Another hypothesis is described in the article "Healthy prions protect the membranes of nerve fibers" – VM.)
But the most interesting is the assumption that prions are involved in the mechanisms of cellular aging. It is no secret that for a long time prion diseases have been attributed to the group of senile diseases, because the changes they cause are very similar to other diseases (like Pick's disease, Alzheimer's and other neurological ailments). The presence of a prion infection, as it were, pushes the body to accelerated aging. Naturally, this raises a very important question: if a cure for such diseases is found, will it not become a kind of key to longevity or even immortality of the body? But it is impossible to give an answer to this question yet, since the functions of prions have not been studied well enough yet.
Methods of infectionIn conclusion, let's talk about ways of infection.
There are four of them. In the first and most common case, the disease appears as if from nowhere. That is, a man lived for himself, but suddenly he got sick. This way of occurrence of the disease is called sporadic and, by the way, is the most common. According to current ideas, this happens spontaneously under the influence of some factors that have not yet been established.
The second method is hereditary. Some types of diseases are familial and arise due to mutations. In turn, the genes are passed on to the offspring. There are about 40 families suffering from fatal insomnia. Every tenth person suffering from Creutzfeldt–Jakob disease suffers from a familial form of this disease.
The third method is iatrogenic. This means that infection with prions occurred due to the fault of medical workers during any surgical interventions. However, only a few such cases have been described, and all of them occurred in the 70s of the last century, when no one knew about the properties of prions yet. So, one woman got sick after she had a cornea transplant from a man suffering from Creutzfeldt–Jakob disease.
But the latter method is the most insidious and dangerous. The fact is that humans are susceptible to prions that infect cattle. And when eating the meat of sick animals, people also get sick – they develop Creutzfeldt–Jakob disease. In the nineties of the last century, a real epidemic of this suffering broke out in England.
There is no treatment yet. However, scientists have already found out that some types of prions are decomposed by lichens, others managed to describe special anti-prion antibodies (to infectious prions).
In other words, researchers are facing a very difficult task, which will not only help to find a cure for serious diseases, but also, perhaps, help to discover the secret of longevity. To do this, you need only one thing – to understand prions.
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18.06.2015