Release date: 2016-04-14 Amyloid fibrils are formed from abnormally folded proteins associated with Alzheimer's disease. Image source: Science Source/SPL John Collinge has been studying neurology for 25 years and he has seen thousands of human brains. But in January 2015, what he saw under the microscope was different from the past. He and other pathologists in the team examined the brains of four corpses, all of whom had been injected with cadaveric growth hormone. Autopsy results showed that some preparations were infected with a misfolded protein, a prion protein (or infectious protein), which caused a rare and fatal disease (CJD), resulting in 4 people. He died at the age of forty or fifty. However, for Collinge, the abnormalities of these brains are not the damage caused by prion diseases, but the scars caused by another way. “It’s clear that there is something unexpected about it,†he said. Significant white patches in the brain of Alzheimer's patients are present in the brain. In other words, they saw that young patients were infected with a geriatric disease. For Collinge, this raises a worrying conclusion: the disease may have metastasized with prions during the injection of growth hormone, which is about Alzheimer's disease being able to move from one person to another. The first evidence in a person's body. If this is true, it will have a profound impact: the “seed†of Alzheimer's β-amyloid may be transferred from one patient to another in blood transfusions, organ transplants, and other common medical procedures. The patient's body. Collinge believes that he has a responsibility to quickly let the public know about the news, and he has done the same. He published his research in Nature in September 2015 and quickly occupied the headlines of the world. But Collinge is very cautious about his own words. "Our research does not mean that Alzheimer's disease does contagious," he stressed. "But it raises the question that some medical processes may irreversibly transfer the seeds of beta-amyloid." Since then, relevant research and discussion in the scientific community has followed. So, is the seed of β-amyloid really transferred? If so, are they harmless or can cause disease? Will other disease seeds with misfolded proteins be transferred in the same way? Over the past decade, “rogue protein†– a collective term for amyloids associated with neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's disease – may have similar transferability to prions. The evidence for the characteristics is increasing. Collinge's evidence also reinforces this view. Dangerous folding Few decades ago, few people believed that proteins without genetic material or any other self-replicating characteristics could cause infectious diseases. But this view changed in 1982, when Stanley Prusiner (now working at the University of California, San Francisco) found evidence of a pathogenic prion. Prusiner showed that prion protein (PRP) exists in a normal cell form and exists in a misfolded form of infection. This misfolding causes the normal protein to fold as well, creating a tandem mechanism that destroys and kills healthy cells. It can cause the animal's brain to become a spongy chaotic body, such as letting the sheep suffer from scrapie, or causing bovine spongiform encephalopathy ("mad cow disease"), and also causing prion diseases such as CJD. Prusiner and others studied how prions spread. They say that injecting prion-infused brain extract into the brains of healthy animals will bury the seeds of the disease. Prions are very aggressive, and at some point, if you eat the brain of an infected animal, it is enough to cause illness. For example, many of the mutated CJD (vCJD) patients in the UK are now believed to have been caused by the consumption of mad cow disease beef in the 1990s. Since then, scientists have gradually identified a variety of proteins associated with neurodegenerative diseases, such as beta-amyloid associated with Alzheimer's disease, taurine, and alpha-synuclein associated with Parkinson's disease. Proteins, etc., are all proteins that cause fatal misfolding. Structural biologists collectively refer to such misfolded proteins as amyloid. Ten years ago, this question inspired the neuroscientist Mathias Jucker of the University of Tübingen in Germany to experiment with the injection of beta-amyloid containing misfolded mice into the brain to see if they would plant abnormal diseases in their brains. seed. He did find this, and it would be the same after injecting amyloid into the muscle. "We feel that there is no reason not to believe that if amyloid seeds enter the human brain, they will not cause amyloid lesions in the same way," Jucker said. This time, CJD brain research provides an insight into the spread of the protein. Between 1958 and 1985, about 30,000 people worldwide injected growth hormone from the pituitary gland of the body to treat growth problems. Some of these preparations are infected with prions that can cause CJD. Like all prions, CJD has a long incubation period, and once the virus begins to develop, it quickly spreads throughout the brain, destroying all tissues in its pathways, especially leading to the death of people in their late 40s and older. According to 2012 data, 6,226 people worldwide have died of CJD due to the injection of prion-infected growth hormone. "seed" doubt cloud As soon as Collinge saw the brain sample, he knew that he might be involved in the storm of controversy. In order to alert people to potential public health risks without causing panic, he was very cautious at the press conference and set up a hotline for patients who had received growth hormone therapy in the past. As a result, the study did not cause panic, only one or two overly tense headlines reported that most news reports were moderate. And only about 10 people called the hotline. However, for scientists, this paper has become a dangerous signal. “After the publication of the article, we realized the health risks behind it and began collecting brain slices and paraffin-embedded specimens from patients,†said Jiri Safar, National Center for Plague Pathology, Case Western Reserve University, Ohio. However, these case studies have also shown that beta-amyloid seeds have metastasized during treatment. However, they do not completely rule out the treatment itself or the patient's initial medical condition, leading to the possibility of amyloidosis. And there is another problem: no one knows exactly what the size and shape of amyloid seeds are. Jucker is looking for abnormal points in human brain tissue samples that are not related to CJD. A team in Bonn, Germany, collected frozen samples from the brains of more than 700 patients with epilepsy. "This is the latest source of human brain tissue samples available for the next year." Jucker said he plans to study the samples carefully under a microscope to look for any tiny bumps or seeds like beta-amyloid. If the hypothesis that amyloid transfer is confirmed, its meaning will be extremely profound. Amyloids attach to metal surgical equipment like glue, and conventional sterilization does not remove them, so amyloid seeds may metastasize during surgery. But these seeds may lurk in the body for years or even decades before they cause disease, and may cause other lesions that cause Alzheimer's disease. If amyloid is present in the cerebral blood vessels, other risks may arise because they increase the risk of vascular wall rupture and mild stroke. But if regular medical procedures do increase the risk of neurodegenerative diseases, has this problem been discovered so far? This is not the case, said Roy Anderson, an epidemiologist at Imperial College London. "So far, appropriate epidemiological studies have not been conducted," he said, and this requires a large, carefully planned database of Alzheimer's patients, including symptoms of disease progression and autopsy data. Examine the strain Similar features of prions and other amyloid proteins are currently opening pathways for other studies. Prions can exist as unique strains (proteins that share the same amino acid sequence but are folded in different ways and have different biological behaviors), just like a strain with a different pathogenic virus, which may be highly aggressive. It may also be less aggressive. The vCJD that broke out in the 1990s can be traced back to beef infected with mad cow disease because the prion strain is the same in both bodies. In the past few years, animal studies have shown that different strains exist between β-amyloid and α-synuclein. A 2013 landmark paper reported that beta-amyloid strains have different three-dimensional structures and are associated with different disease processes in two Alzheimer's patients. Now, Robert Tycko, a structural biologist at the National Center for Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland, is working on more brain samples through patients. Understanding the pathogenic patterns of these amyloid seeds helps to design small molecules that bind to them, stopping their destruction, says Ronald Melki, a biophysicist at the Institute of Neurology at the University of Sacramento in Paris, France. He is studying alpha-synuclein strains. Despite this, in the face of numerous uncertainties, some researchers and public health agencies have taken a sit-and-see attitude. “We are still at the beginning of this story.†Some experts said, “If you want to say something now, you can only say that we need to do more work to understand whether this is the relevant communication mechanism.†US Centers for Disease Control and Prevention The European Centers for Disease Control and Prevention have stated that they are being wary of this issue. For Collinge's paper, the turmoil caused earlier can be attributed to the semantic level. Some scientists don't like to associate the term "prion" with amyloid folding errors in common neurodegenerative diseases, or "like prions" to describe the characteristics of those lesions because the term implies infectious and fatal. The meaning of the disease. Others, however, believe that doing so helps to see prions and other amyloids as part of a single problem with protein folding errors and abnormalities. Although the two sides are not sure what will happen in the future, they are all cautious about ringing the alarm too early. Jucker said half-jokingly that he could imagine that in the future people would go to the hospital every ten years or so to use antibodies to remove amyloid seeds from the brain. "Then you can continue to live healthy for ten years," Jucker said. Source: Chinese Journal of Science Electric Hydraulic Operating Table
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