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Prion diseases are a group of rare, terminal neurodegenerative disorders that cause brain damage and dementia. They are caused by a misfolded protein that induces misfolding in normal proteins, leading to cellular death and brain damage. These diseases are progressive and invariably fatal, with no known cure or effective treatment. They can affect both humans and animals and are spread to humans through infected meat products. Prion proteins have been detected in skeletal muscle, and some muscles are intrinsically capable of accumulating substantial titers of prions, which is a major concern as it may lead to significant dietary exposure through the consumption of meat.
| Characteristics | Values |
|---|---|
| Prion diseases | Transmissible spongiform encephalopathies (TSEs) |
| Type of protein | Abnormal, misfolded protein that induces misfolding in normal variants of the same protein |
| Occurrence | Found in skeletal muscle of wild-type mice inoculated with the Me7 or Rocky Mountain Laboratory strain of murine prions |
| Prion protein | PrPC – the cellular prion protein |
| Infectious form | PrPSc – the "scrapie" prion |
| Prion diseases in humans | Creutzfeldt-Jakob disease (CJD), sporadic CJD, familial CJD, variant CJD, and variably protease-sensitive prionopathy (VPSPr) |
| Prion diseases in animals | Scrapie in sheep, chronic wasting disease (CWD) in deer, bovine spongiform encephalopathy (BSE) in cattle (mad cow disease) |
| Symptoms | Memory loss, issues with thinking and judgment, hypokinetic movement disorders, myoclonus, personality changes, psychological issues like anxiety and depression, visual hallucinations |
| Diagnosis | Real-time quaking-induced conversion assay (RT-QuIC), genetic tests, brain biopsy or other tests |
| Treatment | No cure or treatment, palliative care to manage symptoms with medication |
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What You'll Learn
Prions in skeletal muscle
Prion diseases are a group of conditions that affect both humans and animals. They are caused by a type of protein that triggers normal proteins in the brain to fold abnormally, leading to brain damage. This abnormal buildup of protein in the brain can cause memory problems, personality changes, and movement issues. Prion diseases are rare, with about 300 cases reported each year in the US, and they are always fatal.
Prions have been found to be present in skeletal muscle cells and the epithelial layer in the tongue following the spread of the prion agent from nerve terminals and/or axons that innervate the tongue. In particular, the presence of the prion agent in skeletal muscle is thought to be due to the infection of nerve fibers located within the muscle. The prion agent has been found to accumulate within skeletal muscle cells, in addition to axons, in the tongue of hamsters following intracerebral inoculation of the HY strain of the transmissible mink encephalopathy agent.
Prion infectivity or accumulation of the abnormal form of the prion protein, PrPSc, in skeletal muscle has been described in experimental prion infection of rodents and in sporadic Creutzfeldt-Jakob disease (CJD) in humans. Mouse skeletal muscle can propagate prions and accumulate substantial titers of these pathogens. High prion titers and the disease-causing isoform of the prion protein (PrPSc) have been found in the skeletal muscle of wild-type mice inoculated with either the Me7 or Rocky Mountain Laboratory strain of murine prions. Particular muscles accumulated distinct levels of PrPSc, with the highest levels observed in muscle from the hind limb.
The detection of prions in skeletal muscle has important implications for human health, as significant dietary exposure to prions can occur through the consumption of meat. While neural and lymphatic tissues are known to contain high titers of prions and have been excluded from foods destined for human consumption, meat that is largely free of these tissues may still contain prions. Therefore, a comprehensive effort to map the distribution of prions in the muscle of infected livestock is needed to prevent human exposure to prion diseases.
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Prion diseases
The most common prion disease in humans is Creutzfeldt-Jakob disease (CJD), which can be inherited or occur sporadically. Other forms of human prion diseases include variant CJD, fatal familial insomnia, Gerstmann-Straussler-Scheinker syndrome, and Kuru. In livestock and wildlife, prion diseases such as scrapie in sheep, chronic wasting disease in deer, elk, and moose, and mad cow disease in cattle can spread by casual contact or contamination of feeds or the environment.
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Prion protein (PrP)
PrP plays a fundamental role in the nervous system and throughout the human body. It has been implicated in the biology of glioblastoma, breast cancer, prostate cancer, and gastric cancer. Over-expression of PrP is correlated with the acquisition of a phenotype for resistance to cell death induced by TNF-alpha, TRAIL, or antitumor drugs. PrP may also promote tumorigenesis, proliferation, and G1/S transition in gastric cancer cells.
PrP is necessary to bind and draw beclin 1 into lipid rafts, where it can associate with PIK3C3 to initiate autophagy and promote neuronal survival. It has been proposed to function in signaling pathways and cell signaling, and it may play a role in the transport of ionic copper into cells. PrP has also been shown to interact with ion channels and metabotropic glutamate receptors, suggesting a role in modulating synaptic mechanisms and neuronal excitability at a molecular level.
The normal form of the prion protein is called PrPC, the cellular prion protein. During the pathogenesis of a prion disease, this protein misfolds into an insoluble form, PrPSc, that aggregates into large assemblies, including amyloid fibrils and plaques. This misfolded protein accumulates during the disease in the brain, leading to death. PrPSc is a conformational isoform of PrPC with a different secondary and tertiary structure. It tends to accumulate in compact, protease-resistant aggregates within neural tissue and causes brain damage.
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Prion disease diagnosis and treatment
Prion diseases are a group of rare, terminal neurodegenerative diseases that cause brain damage. They can affect both humans and animals. The abnormal prion proteins clump together or bind with normal prion proteins to make more prions. Over time, the abnormal prions damage or destroy nerve cells in the brain, leading to a loss of brain function. The most common form of prion disease that affects humans is Creutzfeldt-Jakob disease (CJD).
Diagnosis
Prion diseases can be challenging to diagnose, and they should be considered in individuals with rapidly progressing dementia. Currently, the only way to confirm a prion disease is by taking a brain tissue sample during a biopsy or after death. However, due to the risks associated with brain biopsies, doctors often rely on other tests to aid in diagnosis or rule out similar conditions. These tests include blood tests, lumbar puncture, and brain MRI scans. Additionally, muscle biopsies have been suggested as a potential diagnostic tool, as prions can accumulate in skeletal muscle.
Treatment
Currently, there is no cure or treatment available for prion diseases. The focus of management is on palliative care and medication to alleviate symptoms and improve the patient's comfort. Antiseizure medications, muscle relaxants, and opioids may be prescribed to manage specific symptoms. Research is ongoing to develop treatments, with promising approaches including the RT-QuIC test for early diagnosis and the suppression of prion protein levels in brain cells using techniques like CHARM and CRISPRoff.
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Prion disease transmission
Prion diseases are a family of illnesses that can affect both people and animals. They are rare but always fatal, leading to death within months or years of the onset of symptoms. Prion diseases occur when a benign protein (PrPC) in the body misfolds and forms assemblies of abnormal proteins (PrPSc) that cause brain damage and other symptoms. The misfolding of the prion protein is central to the process of prion propagation.
Prion diseases can be transmitted to humans through infected meat products, organ transplants, or exposure to contaminated equipment during surgery. The most common form of prion disease in humans is Creutzfeldt-Jakob disease (CJD), which can also be inherited or occur sporadically without any known risk factors. Variant CJD (vCJD) is an infectious type of CJD related to ""mad cow disease"" that can be caused by eating diseased meat. Other prion diseases in humans include variably protease-sensitive prionopathy (VPSPr), sporadic or familial fatal insomnia (FI), and kuru. Kuru is caused by the consumption of human brain tissue contaminated with infectious prions and is now rare due to increased awareness.
In animals, prion diseases include scrapie in sheep and goats, bovine spongiform encephalopathy (BSE) in cattle, and chronic wasting disease (CWD) in deer, elk, moose, and reindeer. BSE was first identified in the mid-1980s and led to a major outbreak in the United Kingdom in the 1990s, affecting millions of cows. CWD has been found in North America, Europe, and Asia, and while there are no known cases in humans, it is believed to pose a theoretical risk, especially to those consuming meat from infected animals.
Prion diseases are difficult to diagnose, and confirmation typically requires a brain biopsy or examination of brain tissue after death. However, due to the risks associated with brain biopsies, alternative tests are often performed to aid in diagnosis or rule out other diseases. There is currently no cure or vaccine for prion diseases, but certain medications may help slow their progression. Proper cleaning and sterilization of medical equipment are crucial to prevent the spread of prion diseases.
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Frequently asked questions
Prions are misfolded proteins that induce misfolding in other normal proteins, leading to cellular death. They are responsible for prion diseases, known as transmissible spongiform encephalopathy (TSEs), which are fatal and transmissible neurodegenerative diseases affecting both humans and animals.
Yes, prions have been found in skeletal muscle. Mouse studies have shown that skeletal muscle can propagate prions and accumulate substantial titers of these pathogens.
The discovery of prions in skeletal muscle suggests that dietary exposure to prions can occur through the consumption of meat, even if it is largely free of neural and lymphatic tissue. This highlights the need for a comprehensive effort to map the distribution of prions in the muscle of infected livestock to prevent the spread of prion diseases.
Some common prion diseases include Creutzfeldt-Jakob disease (CJD), bovine spongiform encephalopathy (BSE), chronic wasting disease (CWD), and scrapie. The most common form of prion disease in humans is sporadic CJD, which develops suddenly without any known risk factors.
Prion diseases are typically diagnosed through a brain biopsy or by evaluating other tissues, such as muscle, which may be more accessible for biopsy. However, there is currently no known treatment for prion diseases, and they are always fatal.
