As requested, I AmA graduate student in a prion research lab focused on prion transmission and persistence in the environment. Ask me anything!

What is a prion?

A prion is an infectious agent that is composed primarily, if not entirely of misfolded protein. Humans and other mammals make cellular prion protein (that we call cellular prion related protein, or PrPC) whose function is thought to be for copper binding or signal transduction. When cellular prion protein misfolds (either sporadically or due to the introduction of exogenous prions), the structure changes into one very resistant to unfolding/breakdown. The misfolded prion protein is referred to as PrPTSE (or often PrPSc). PrPTSE aggregates into fibrils and amyloid plaques, and it is the accumulation of PrPTSE in the brain (and subsequent damage done to the brain tissue) that ultimately causes death.

Would I be right in saying that the particularly odd thing about Prions is that they are the only known protein to be infectious? And it was not previously thought that something even smaller and less complex than a virus could display such infectious characteristics. It's as amazing as finding a plant that can vocalize sounds.

You are correct. They have not been found to contain any genetic material, making them unlike any infectious agent ever known.

There is a scientist, Laura Manuelidis, who thinks that diseases commonly thought to be caused by prions are actually caused by an as-yet-undiscovered virus. What do you think about this?

Wired article

To be perfectly blunt, reading Laura Manuelidis' papers is like reading the diary of a girl who has been told 1200 times by her crush that he's not interested, and she still believes it will happen. Sure, she could end up proving us all wrong, but there is an ENORMOUS amount of evidence to the contrary. Now, where detractors of the prion theory (like Laura, and some others) make an argument that does make sense is within the theory of strain differences. Prion strains are defined as isolates that yield distinct disease phenotypes within a group of identical host organisms (viz. clinical symptoms, incubation times, histopathological profiles). These phenotypic differences persist upon serial transmission of disease. The PrPTSE associated with different strains can exhibit distinct biophysical properties such as migration patterns in Western blotting following PK digestion and protein secondary structure. The prevailing hypothesis is that strain properties are enciphered in the structure of PrPTSE. The difficulty of incorporating the existence and diversity of strains within the protein-only hypothesis for prions has led some to posit a role for a separate informational molecule that occurs alongside PrPTSE.

Also, is it pronounced pree-on or pry-on?

Pree-on

Ever read Patient Zero by Jonathan Maberry? The zombie plague in that one is based on using parasites to quickly infect a host with an engineered prion disease.

I have not read it, but sounds really neat (if not incredibly scientifically incorrect...) :)

Besides CJD, are there other diseases where prions are known to play a role?

Sure. Kuru was one of diseases that initally led to the discovery of prions. That was present in the Fore tribe in Papua New Guinea, and was believed to be transmitted because the tribe members ate the brains of their dead out of respect. CJD can present sporadically or as variant CJD (from eating BSE infected beef), and there is fatal familial insomnia and Gerstmann–Sträussler–Scheinker syndrome, which are both very rare genetic prion diseases that run in some families. There are also prion diseases in other mammals: scrapie in sheep and goats, chronic wasting disease (CWD) in cervids (deer, elk, moose), bovine spongiform encephalopathy (BSE) in cattle, and a couple other uncommon ones like transmissible mink encephalopathy.

i have heard that one of the major contributing factors in BSE spreading in the meat industry is the use of captive bolt pistols rupturing the cranium and somehow contaminating the meat. considering, as you stated, that kuru is spread through the eating of an infected brain, are many prion diseases spread through ingesting nervous tissue? how do they spread in sheep and deer? thanks in advance!

Prions are present in high quantities in central nervous system tissue, but are also present in the peripheral nervous system, lymphatic system, and in muscle tissue, so it is commonly spread through exposure to these things as well. In the case of CWD in cervids and scrapie in sheep and goats, prions that are present in relatively high quantities in excreta (blood, feces, saliva, etc.) are shed into the environment. There, they persist over long periods of time and can be taken up by healthy animals.

Can you explain to me why I find the idea of prions far more viscerally repulsive than bacteria or viruses?

Philosophically, because they are so foreign. Bacteria and viruses, while capable of killing us, are LIKE us. They contain DNA/RNA just as we do. Thus agents that destroy DNA and/or RNA can harm them just as they can harm us. A prion, however, is like an alien species. It goes against everything we understand about classical infectious agents. It is not alive, but can be transported, can persist outside of the host, is very hard to degrade, and can initiate diseases that are invariably fatal. That makes them way scary.

Also, why does the body give preference to replicating the misfolded protein?

Think about it like this: proteins are lazy. They are all about being in a shape that is the easiest for them, that is, they will adopt a conformation that is most energetically favorable to be in. And depending on their surroundings, that conformation may have to change. There are two schools of thought in existence about how cellular prion proteins convert to misfolded prion proteins. Theory 1) is the "refolding" or template-directed assistance model, and it posits that introduction of exogenous disease-associated prion protein (PrPTSE) and its interaction with endogenous cellular prion protein (PrPC) induces PrPC to transform itself into PrPTSE. A high-energy barrier might prevent the spontaneous conversion of PrPC to PrPTSE, but at some point it becomes more favorable for the cellular prion protein to adopt a new conformation (that being the disease associated one). Theory 2) is the "seeding" or nucleation–polymerization model which proposes that PrPC and PrPTSE are constantly in a reversible thermodynamic equilibrium. So, only if several monomeric PrPTSE molecules are mounted in a highly ordered seed can more monomeric PrPTSE be recruited and eventually aggregate to form amyloid. In such a crystal-like seed, PrPTSE becomes stabilized. Fragmentation of PrPTSE aggregates increases the number of nuclei, which can recruit more PrPTSE, and so seems to result in replication of the agent.

Let me get this straight: So the first theory posits that there must be some change in environment that acts as a catalyst, while the second suggests that formation of amyloid is essentially a stochastic process where in the unlikely event that a sufficient seed forms you get positive feedback?

Do you favor one model over the other? Does amyloid form in vitro? If so, with what kinetics? It seems to me the two models imply quite different reaction kinetics.

Edit: Thinking about theory 1 more I suppose it doesnt have to be a change in the activation barrier like I was imagining, but could be extremely high concentration of protein. What sorts of 'changes in environment' do people imagine?

Sorry for the delay, I had a meeting. Your question is a great one. To answer it, let me first describe a detection method prion researchers have developed.

PMCA or protein misfolding cyclic amplifcation is a technique that is used for the detection of very small (attomole) amounts of infectious prion protein. Here's how: combine an unknown sample (that may or may not contain infectious prion protein, and if so, a very small amount, undetectable by any other biochemical method available) with non-infectious brain material. The unknown sample is the seed and the healthy brain material the substrate. The healthy brain material will be high in cellular prion protein, PrPC. The mixture then undergoes rounds of sonication and incubation (a lot like PCR for DNA). The sonication is thought to break up PrPTSE material (which likely exists in a few large aggregates) into multiple smaller seeds. Then the PrPC substrate is converted into PrPTSE by associating with the PrPTSE seeds. By the end of the treatment period (~48 hrs) you have increased the amount of PrPTSE (if there was any to start with) to an amount you can now detect more easily. This all occurs in vitro, btw.

So the theory of PMCA lends strength to theory 2 being the correct one. PrPC is in a state of conformational flux, so to speak, and through the introduction of multiple PrPTSE seeds for PrPC to associate with, it becomes favorable for PrPC to adopt the PrPTSE conformation. The fact that this occurs in vitro so quickly (24-48 hrs) seems way too fast for theory 1 to be the primary method of conversion.

If a prion is a wrongly folded protein and supplants the normal protein use in the body, how can someone be genetically resistant to it? Does their body recognize the prion and dispose of it?

The PRNP gene codes for the production of cellular prion protein. There are certain variations in the PRNP gene that can either increase the likelihood that you'll develop a sporadic form of disease, or increase your resistance to developing one of the prions diseases (the genetic susceptibility of each disease can be a little different so resistance to one doesn't necessarily mean all). I'm not entirely sure why certain mutations slow or prevent disease, but my guess is that the structure of the resulting cellular prion protein is more stable than in a person with a non-protective phenotype and thus less prone to structural modifications that can lead to disease. I know there's plenty of research out there on it, I just do more environmental work and am not as familiar with the genetic prion literature.

I just do more environmental work...

Thanks for doing this AMA. A few questions:

1. In one article I read about the current possible transmission, it mentioned that surgical instruments are typically destroyed if they are thought to be contaminated by a prion. Why wouldn't the normal sterilization techniques denature the prions and make them non-infectious?

2. What kind of prions do you work with and what have you found about their viability living outside of a host?

3. What's your dissertation on and what are your career prospects when you finish?

Thanks again.

You're welcome!

1. Prions are incredibly stable. The protein structure of PrPTSE (the disease associated prion protein) is very high in beta-sheet content. Of the two basic secondary conformations that proteins can adopt, beta sheets are more stable than helices. And beyond that, the protein adopts stable higher order structures as well (fibrils). This makes them VERY hard to unfold, so traditional decontamination methods don't often work on prions.

2. In our lab, we work with a hamster-adapted transmissible mink encephalopathy strain, as well as chronic wasting disease. Both are very stable and remain infectious outside the host (in vitro) for weeks or more. We've not directly tested longer than that, but other studies have indicated prion viability for years. We don't technically say prions are ever 'alive' because they are not living entities (no known genetic material).

3. My thesis work is focused on finding novel methods of prion degradation, specifically ones that would be relevant to the decontamination of CWD-infected soil environments.

This makes them VERY hard to unfold, so traditional decontamination methods don't often work on prions.

for want of a better word, how exactly would you "kill" a prion?

There are ways to almost completely (if not entirely) remove prion infectivity. Some examples: exposure to high concentrations of sodium hydroxide (1-2M), autoclaving in 1M sodium hydroxide, autoclaving for longer periods of time at higher temperatures, incineration at 1000C for >5 min.

Oh wow that's really interesting! I'm only 14 but prions have always fascinated me. Anyways, do you think there is hope for a cure for prion related diseases in the near future?

I don't know. One problem is the sheer amount that is still unknown about prions. The field doesn't even 100% agree about what a prion IS, let alone all the details regarding transmission in different species. Another problem is that because prion diseases are not terribly common (like say, alzheimer's), the funding for prion research is not all that strong. With limited funding, researchers can only make limited progress in the search for a cure. But I have hope!

Is it possible that many cases of alzheimer's are misdiagnosed instances of CJD (or similar disease)? Are the symptoms different?

It's not likely. When CJD or other prion diseases are confirmed, they are done so biochemically. For example, Western blotting uses an antibody specific to certain regions of the protein's primary sequence for detection. The prion protein's primary sequence is certainly very different from the primary sequence of beta-amyloid, so it is very unlikely that the prion-specific antibody would incorrectly detect beta-amyloid.

i believe cjd is also extremely aggressive and rapid in progression, whereas alzheimer's progresses over the course of 10+ years (there are rare variants that are more aggressive). a crude (but unfortunately, mostly true) saying about cjd that neurologists sometimes make is "if the patient doesn't come back for a follow-up in six months, it was most likely cjd"

CJD is VERY slow, on the order of 10-50 years to develop.

EDIT: I should say, the disease progresses slowly, but by the time symptoms manifest, the patient is reaching clinical stage and doesn't have much time, so to an uninformed observer, it would appear as though CJD were a rapid disease.

Read it as prison and was really unsure as to why it was spelled incorrectly twice. Oh well

You do not know how many times google asks if I'm sure I didn't mean "prison" when searching for papers.

Is it a dangerous job? (In terms of getting infected)

Not for me, really. We are only a biosafety level (BSL) 2, which means none of the strains of prions that we work with are known human pathogens. If we worked with BSE, then we'd be BSL 3 and would need to take more precautions. That being said, we are cautious and I certainly wouldn't eat anything I work with.

What are the known transmission vectors for human infection (if that's the right term) for prion-related disease, and what is the certainty that we know all the ways disease can be transmitted?

To our knowledge, transmission between humans can occur when a transmissible spongiform encephalopathy (TSE; catch-all term for prion diseases)-positive human is cannibalized, or when humans consume beef from a cow with BSE. Of course we can't be certain that these are the only possible ways of disease transmission, but the incidence of transmission by any other routes are either too low to be detected or are not possible. It remains possible that another animal TSE like chronic wasting disease could result in transmission to humans, but at this point there is no evidence of that.

haven't people gotten infected from eating improperly cooked squirrel (brain)? i thought i heard of that happening, not sure if that would be cwd, scrapie, or some other form of tse.

I've never heard of humans getting a TSE from squirrel. My guess is that they got sick from bacteria from eating improperly cooked squirrel brains (yuck!)

just googled it:

"In the last four years, 11 cases of a human form of transmissible spongiform encephalopathy, called Creutzfeldt-Jakob disease, have been diagnosed in rural western Kentucky, said Dr. Erick Weisman, clinical director of the Neurobehavioral Institute in Hartford, Ky., where the patients were treated.

''All of them were squirrel-brain eaters,'' Dr. Weisman said. Of the 11 patients, at least 6 have died."

from http://www.nytimes.com/1997/08/29/us/kentucky-doctors-warn-against-a-regional-dish-squirrels-brains.html

I'll have to look for original research in a peer-reviewed journal to confirm this. Interesting.

Would you consider a prion to be, to any degree, a form of life? Is there any debate about it? I know it is debated whether a virus is ultimately alive or not as it replicates, but not on its own. So, similarly, a prion "replicates", or more like "creates other prions". Would it fulfill the definition of life?

Otherwise, would a prion be a kind of Von Neumann machine?

Based on what I have read, I personally believe the prion is not at all a form of life. It does not contain genetic material (that we know of). Prion replication should really be coined "prion protein conversion". It is "replication" in the sense that you start with 1 thing and then you have 2, and so forth, but it is not bona fide replication in the biological sense. Prions do not divide their generic material and pass it along to their offspring.

And I do not know what a Von Neumann machine is. Should I?

A machine designed to build more like itself.

Then yes, it sounds exactly like that!

Have you ever made a cow angry enough to make it mad?

I've only made them angry when I've gone to collect manure and gotten too close. But I've never driven one to insanity (I hope).

Was this for work or your own personal collection?

I collect manure for composting - part of my attempts at environmentally relevant prion degradation.

I wondered this my entire undergraduate career, are there any examples of DNA mutations causing proteins to misfold and behave like prions?

I'm unfamiliar with this occurrence in other proteins, but that's exactly what happens in the case of genetic/spontaneous human prion diseases. I don't know if beta-amyloid or the amyloid precursor protein are thought to be produced because of mutations in the gene encoding for APP.

If a human contracts a prion disease through cannibalism, how does the prion survive the stomach and make its way to the brain?

That's the million dollar question! You figure that out, and you'll have a paper in Nature.

That being said, I'll tell you what is known/theorized. Some fraction of prions consumed orally must be able to survive the low pH of the stomach and travel to the small intestine with the other food being digested, and there are perhaps picked up by microfold cells in the Peyer's patches in the small intestine. Microfold cells are constantly sampling the gut contents to build immunity. The microfold cells then deliver their contents to follicular dendritic cells (which are immune system cells). The FDC's carry their contents/passengers/however you want to think about it (prions) to germinal centers where they display their contents on their surface in order to educate B-cells (for immunity). While here, the prion-loaded FDCs are in proximity of the peripheral nervous system, and once there, they can get to the central nervous system and ultimately, the brain. A lot of this is still unclear though.

That being said, I'll tell you what is known/theorized. Some fraction of prions consumed orally must be able to survive the low pH of the stomach and travel to the small intestine with the other food being digested, and there are perhaps picked up by microfold cells in the Peyer's patches in the small intestine. Microfold cells are constantly sampling the gut contents to build immunity. The microfold cells then deliver their contents to follicular dendritic cells (which are immune system cells). The FDC's carry their contents/passengers/however you want to think about it (prions) to germinal centers where they display their contents on their surface in order to educate B-cells (for immunity). While here, the prion-loaded FDCs are in proximity of the peripheral nervous system, and once there, they can get to the central nervous system and ultimately, the brain. A lot of this is still unclear though.

Do you actively search for ways prion's could be used in a productive way? I have looked into a few global studies of red meat consumption in general that could be related to cancer, most Americans eat about 20% to 15% over what is actually needed for dietary protein intake. With that being said, what do you believe your research should be used for? If Prion producing cows are detected, how are they detected and later dealt with? I think people in general need to rethink their diets, so is the recent exposure to Creutzfeldt-Jakob disease a reason of concern to the american public that could cause a reconsideration of their animal protein intake? EDIT: I like meat :) but i think some enjoy it to the point of glutony

We don't look at prions for productive use. I'll leave that research for someone to do once we understand how to effectively slow/prevent disease spread and/or find a cure for prion disease. By learning how prions interact with the soil environment, how they transmit disease and how to break them down, then perhaps we can help mitigate the further spread of disease and prevent animal/human deaths. Testing is conducted periodically to look (biochemically) for the presence of the disease-associated prion protein in cattle. Cows that are suspected of having BSE are often killed and disposed of properly to prevent spread of other cattle and humans. Variant CJD is fairly rare. I wouldn't go so far as to say people should be very concerned about eating beef for that reason, when there are other more important reasons to perhaps choose not to (energy efficiency, etc.).

So if a fox/wolf/vulture/crow ate a deer carcass that had succumb to CWD, will those animals "catch" it? How does it spread in cases of wild animals like deer that just eat plants?

I'd have to go and look at the exact details on transmission in a laboratory setting of CWD to fox/wolves/vultures/crows, as I'm not sure what the likelihood of those species succumbing to a prion disease follwing ingestion of CWD-infected deer meet would be (but my guess is low, if not zero). However, it is possible that some species could serve as vectors. For example, perhaps a species that scavenges dead deer could transport prions to other locations and infect naive animals.

As to your second question, CWD and scrapie can be transmitted directly (animal to animal) as well as indirectly, through the soil environment. Infected animals shed prions in excreta (blood, feces, saliva, etc) and prions bind tightly to whole soils and soil minerals. Prions are also very persistent, and can remain infectious in the environment for long periods of time. Then naive animals that ingest infected soil (either accidentally while feeding or on purpose to supplement a mineral need) can get sick.

What makes prions so goddamn stable?

The disease-associated prion protein has amino acids that are arranged in a sheet-like pattern (versus a helix). The beta-sheet conformation lends stability to proteins due the increased level of hydrogen bonding that can occur between sheets. So the protein is in a very stable secondary structure, and also has one disulfate bond (cys-cys) that further increases stability. Combine that with the fact that the protein tends to stack into trimers and those trimers aggregate into tightly bound fibrils, you are left with an incredibly stable protein. It takes a great deal of energy to unfold the protein in such a state.

How long can prion diseases lay dormant, or not manifest symptoms, after infection?

It depends on the length of life of the species and the aggressiveness of the strain, but for human vCJD, for example, I've heard everything from 10-50 years.

How worried are you that you'll start presenting symptoms of neurodegeneration sometime in the next 5-20 years?

Probably not as worried as I should be...

how do you stain your slides? IHC? if so, which antibodies do you use?

my lab uses F99 antibody, but we have used in the past for special cases - F89, 8G8, 6H4, P4, and a couple others I can't think off the top of my head.

We mostly do Western blotting, and we use the 3F4 antibody for our hamster agent, and Bar224/8G8 mix or 6H4 for CWD agent.

My father passed away from CJD in '06. Neurologists at U-Mass told me "unlikely" that it could have been passed on to me. As I understand it's not genetic, I'm still irrationally fearful that I could have passed it along to my children. As it is I am NOT allowed to donate blood, understandably. I could handle dying from it myself but the thought of it being passed to them is unbearable. No idea where he contracted it from or how he could have been exposed. Never been out of the country, not a hunter etc.. Anyway, should I be concerned? I wish I had a better, more thought out question to ask but that's it.

Did the doctors have any information about your father's genetics? Here's what I would recommend: https://www.23andme.com/. This is a private company that runs a host of genetic tests on the sample you send them, including which variant in the PRNP gene allele you have that can indicate an increased susceptibility to prion disease. It's only like $100 and might give you some peace of mind.

Hey thanks for the reply! No. All they seemed to be interested in were spinal taps. They kept us in the dark right up into the last few weeks and I haven't much info. Would something like this come up in a DNA test? I was under the impression that is isn't genetic?

Classical CJD can definitely be genetic, and if his was, it is possible you carry the same mutation in your PRNP gene that he may have. However, if he acquired variant CJD from eating BSE+ beef, you will not develop vCJD (presuming you didn't consume his brain).

I live in the Northeast and I have an irrational but still severe fear of contracting a prion disease after watching an episode of a television show where some dude had Creutzfeldt-Jakob disease. What can I do to successfully avoid such a similar fate?

I'd honestly be more concerned if I lived in Colorado/Wyoming or southern Wisconsin. These two regions have a very high incidence of CWD in deer and elk. Now, while there is no evidence to date of CWD transmission to humans, it always remains a possibility. Another possibility is that CWD may someday transmit to cattle, and then as we already know, to humans. That being said, human TSEs are very rare, and some people have a genetic mutation in the PRNP gene that can increase their resistance to developing a prion disease should they be exposed. I wouldn't lose any sleep over it.

Prions really, really scare me. Is my fear overblown or are they are horrifying as my freshmen bio teacher made them sound?

They are scary, but they are scary because we don't fully understand them and anything we don't understand can come across as very frightening. Prion diseases in humans are quite rare, and as long as you are cautious with meat-eating and blood transfusions, chances are that you'll be okay.

Are there any regular cleaning procedures that are effective with prions? The hospital in referenced in the title is local to me and I've been following it closely; all reports seem to indicate they did their due diligence with the rented neuro equipment but that makes me wonder if there's anything at all one can to do sterilize equipment to prevent CJD contamination.

Yes, soaking equipment in 2M NaOH or 20,000 ppm chlorine bleach, autoclaving after or with exposure to 1M sodium hydroxide or 10,000 ppm chlorine bleach, or use of a proprietary phenolic disinfectant called Environ LpH are all methods known to significantly reduce prion infectivity. The trouble is that these treatments are very hard on the medical equipment itself.

China banned the import of US beef in 2003 saying that they were concerned about transmissible spongiform encephalopathy from US beef.

The Beef industry has protested that this ban is still in place. They complain " China uses non-science based standards to keep out U.S. beef." Link to testimony

What are they talking about? What are the "science based standards" that would allow China to accept US Beef?

Also, is it correct that you can't destroy prions with cooking or sterilization?

I believe there is a controversy about testing standards. I recall Japan wanted 100 percent testing and "The American Meat Institute, the meatpacking industry's trade association, opposes 100 percent testing, calling it an unnecessary expense not warranted by science." (link)

If China (!) won't allow imports of our beef, why should we allow it?

I can't speak to China's beef standards as I'm unfamiliar with them, but you're correct about Japan. I'll share some statistics that I posted elsewhere.

The US has roughly 90 million head of cattle. (We slaughter about 34 million a year on average). Of the 34 million slaughtered, approximately 40,000 are tested for BSE. That's 0.1% tested and the US has had 4 confirmed BSE cases since testing began. Japan, on the other hand, has about 1.2 million head of cattle (and I presume about that many are slaughtered each year). They test every single animal, 100%. They have had 36 positive BSE cases.This concerns me a little, because it suggests that we are likely missing positive cases by testing such a small fraction of our cattle population. I wouldn't say most of our meat is at risk of being TSE+ but I would imagine the numbers are a little higher than 4 out of 34 million (times all the years we've been testing for).

What type of safety precautions do you have to take in the lab? Are you in any danger of infecting yourself with lab samples?

We wear gloves, safety glasses, and lab coats. We also take care to dispose of all of our waste carefully. We are also especially careful when using needles. However, we don't work with strains that are known human pathogens, so I'm less afraid than if we worked with BSE or CJD material.

I recall watching something on The History Channel (wait for it) a few months ago about zombies, and it mentioned something about a prion-based disease being a possible source for a zombie outbreak or zombie-like characteristics in humans. It even mentioned the Kuru outbreak as how this is theoretically possible. So, what I'm asking is this:

1. Is a prion actually capable of causing this, or is this just crap History Channel made up in their quest for ratings?
2. If there is no known prion capable of causing this, could one be engineered to zombify humans in any way, shape or form?
3. If such a zombifying prion was unleashed on the general human population, could it work fast enough to cause a large-scale zombie apocalypse? Or would the prion infection be incapable of overpowering quarantines?

1. It's total crap. Prion diseases in humans take DECADES to manifest. That would make for the slowest, most boring zombie outbreak EVER.

2. I don't see how you could engineer one to "zombify" people. Even in animal experiments where transgenic mice were modified to contain more copies of the PRNP gene than normal (and thus produce more PrPC), they experienced a moderate shortening of incubation period, but it was still a slow disease progression.

3. I've clearly not watched enough zombie films. You're hurting my brain. (pun intended)

Also relevant

How would one go about getting into this field or research?

Stay in school! Go to graduate school and look for work with a professor who is doing prion research.

Has anyone yet figured out what, exactly, properly folded PrP does? I had to do a couple of papers/presentations on prions way back in school, and all that was known at the time was that its multiple histidines lent it an affinity for nickel and copper, and that knockout mice without the gene demonstrated no noticeable deficiencies.

Also, people were always arguing with me about the pronunciation of prion. I called it “pree-on”, as an early reference I came across spelt it out. Lots of others though (including professors) insisted it’s “pry-on”, and to this day I still here some scientists call it that. So which is it, exactly?

PrPC is a surface-bound neuronal protein that is found ubiquitously throughout mammalian tissues. There are papers that suggest PrPC may play a role in copper binding, modulation of metal uptake (iron, for example), and/or signal transduction.

Stanley Prusiner (who won the noble prize for the discovery of prions) says pree-on, so most in the field say it "pree-on" as well. Brits tend to say "pry-on".

So if someone contracts prions from cannibalism, the person they ate must have been a cannibal too? (Sorry if this is dumb)

Not necessarily. That person could have contracted vCJD from eating BSE-contaminated beef.

I've been toying with the idea of using prions as a therapy (e.g. bad example since they're always changing, but to an HIV surface receptor). How feasible would that be?

I guess I'm not sure what you mean exactly. Do you mind expanding a little?

[deleted]

Well I'm glad they're very dead and not just sorta dead. Prions can be transmitted via aerosol, but the rate of transmission in animal studies in fairly low. You might want to consider wearing a mask if it don't already, but I wouldn't worry too much.

I think you're thinking of chronic traumatic encephalopathy, which primarily occurs in football players and boxers who have sustained chronic head impact injuries. And I guess I'm a believer. I wouldn't be surprised at all if traumatic impact to the brain induced protein misfolding. Whether or not those proteins are prion proteins, specifically, I don't know.

It's my understanding that there's some relationship between prion diseases and neural degenerative diseases like Alzheimer's and Huntington's. Can you expound on that a little?

Sure. Alzheimer's and Huntington's are both being re-classified as "prion-like" diseases. That means that in experimental studies, researchers are able to take brain material from an Alzheimer's infected mouse (for example), inject it into a healthy mouse, and the healthy mouse will (or at least sometimes will) get Alzheimer's. This doesn't mean you can catch Alzheimer's from your grandmother, but it does suggest that beta-amyloid and Tau which are the proteins that compose plaques found in the brain in Alzheimer's and Huntington's, respectively, are able to induce the conversion of normal protein in the brain to beta-amyloid or tau, much like the disease-associated prion protein converts normal cellular prion protein to its misfolded form.

a minor correction (you probably won't read it, but i want the record to be correct): tau is not found in huntington's. tau and a-beta are both found in alzheimer's, tau as intracellular tangles (that are eventually thought to propagate synaptically) and a-beta as extracellular plaques. huntingtin is the protein that is mis-aggregated in huntington's disease.

You are correct, thank you!!

Is there any history of weaponization? Can they be inhaled or transmitted by breath? Can they be synthesized?

No history of weaponization, since the goal of a biological weapon would be to harm a large number of people quickly. Prion diseases are fairly rare, not always transmissible, and progress in humans over decades. That would make them a pretty shitty weapon. There is evidence of prions being transmitted via aerosol, but the transmission rate (at least in rodent models) is very low. Do you mean synthesized chemically from scratch (not possible) or synthesized in vitro from PrPC? Bacteria can be engineered to produce recombinant PrP, but it is not quite the same as traditional PrPTSE.

How likely is someone to develop disease if they had been exposed to tainted beef in the UK during the late 80s-early 90s "mad cow" crisis?

It is possible, but I don't know statistically. Depending on what amino acid substitution occurs at a specific allele in the PRNP gene, some people are more genetically prone to acquiring prion disease, whereas others are more resistant, so you could in theory have eaten BSE+ beef, but not ever succumb to vCJD.

1. If my local farmer Brown sells me meat infected with prions and I eat it, am I necessarily screwed in about a few decades?

2. Are there any other prions that infects something other than brain tissue?

3. If I think of any other questions, may I ask more?

1. You are not necessarily screwed. Some people are genetically resistant to getting certain prion diseases (in this case, vCJD).

2. Prions will be at highest concentration in the central nervous system tissue (brain, spinal cord) but also in the peripheral nervous system, lymphatic tissues, muscle, and even in blood and saliva.

3. Sure.

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I would say take precaution with safety, and BE PATIENT. Prions are very tricky to work with and experiments very often do not go as you had planned because prions are such weirdos. I swear sometimes, it's like voodoo. But be consistent, don't be afraid of them, and learn as much as you can!

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I forgot! On it right now!

Obligatory: proof?

Curiosity: which lab / university do you work in / at?

I provided proof to the mods. I work at an R1 university in the US.

What causes the initial missfolding of a protein to become a prion? is it always inherited through contact with already existing prions, or can a healthy animal spontaneously have a prion disease develop in them without any previous contact?

I answered this in two separate questions above and have copied my answers below. Prion diseases in humans can develop sporadically (although that just usually means you were genetically susceptible), genetically transmitted through families, or from the consumption of BSE+ beef.

A prion is an infectious agent that is composed primarily, if not entirely of misfolded protein. Humans and other mammals make cellular prion protein (that we call cellular prion related protein, or PrPC) whose function is thought to be for copper binding or signal transduction. When cellular prion protein misfolds (either sporadically or due to the introduction of exogenous prions), the structure changes into one very resistant to unfolding/breakdown. The misfolded prion protein is referred to as PrPTSE (or often PrPSc). PrPTSE aggregates into fibrils and amyloid plaques, and it is the accumulation of PrPTSE in the brain (and subsequent damage done to the brain tissue) that ultimately causes death.

Think about it like this: proteins are lazy. They are all about being in a shape that is the easiest for them, that is, they will adopt a conformation that is most energetically favorable to be in. And depending on their surroundings, that conformation may have to change. There are two schools of thought in existence about how cellular prion proteins convert to misfolded prion proteins. Theory 1) is the "refolding" or template-directed assistance model, and it posits that introduction of exogenous disease-associated prion protein (PrPTSE) and its interaction with endogenous cellular prion protein (PrPC) induces PrPC to transform itself into PrPTSE. A high-energy barrier might prevent the spontaneous conversion of PrPC to PrPTSE, but at some point it becomes more favorable for the cellular prion protein to adopt a new conformation (that being the disease associated one). Theory 2) is the "seeding" or nucleation–polymerization model which proposes that PrPC and PrPTSE are constantly in a reversible thermodynamic equilibrium. So, only if several monomeric PrPTSE molecules are mounted in a highly ordered seed can more monomeric PrPTSE be recruited and eventually aggregate to form amyloid. In such a crystal-like seed, PrPTSE becomes stabilized. Fragmentation of PrPTSE aggregates increases the number of nuclei, which can recruit more PrPTSE, and so seems to result in replication of the agent.

I've learned about prion diseases from a medical standpoint, but I'm still unclear on how the PrP^SC protein catalyzes the conversion of normal PrP into PrP^SC. It's all been pretty vague, and we've been told to just accept it. How does it work?

I've replied to a question like this earlier.

Think about it like this: proteins are lazy. They are all about being in a shape that is the easiest for them, that is, they will adopt a conformation that is most energetically favorable to be in. And depending on their surroundings, that conformation may have to change. There are two schools of thought in existence about how cellular prion proteins convert to misfolded prion proteins. Theory 1) is the "refolding" or template-directed assistance model, and it posits that introduction of exogenous disease-associated prion protein (PrPTSE) and its interaction with endogenous cellular prion protein (PrPC) induces PrPC to transform itself into PrPTSE. A high-energy barrier might prevent the spontaneous conversion of PrPC to PrPTSE, but at some point it becomes more favorable for the cellular prion protein to adopt a new conformation (that being the disease associated one). Theory 2) is the "seeding" or nucleation–polymerization model which proposes that PrPC and PrPTSE are constantly in a reversible thermodynamic equilibrium. So, only if several monomeric PrPTSE molecules are mounted in a highly ordered seed can more monomeric PrPTSE be recruited and eventually aggregate to form amyloid. In such a crystal-like seed, PrPTSE becomes stabilized. Fragmentation of PrPTSE aggregates increases the number of nuclei, which can recruit more PrPTSE, and so seems to result in replication of the agent.

Do you learn much about yeast prions? From what I recall, heat-shock proteins can re-fold amyloid fibrils. Are there any similar proteins in mammals?

In my non-scientific opinion, yeast prions are hella lame. They aren't infectious, they are just wannabes. That said, I don't know a huge amount about them, but just from a quick glace at the literature, it looks like Hsp104, a heat-shock enzyme from yeast can actually break up amyloid. I'm not sure if/what heat shock proteins that humans make.

Do prions hail from Madagascar?

Are you thinking of Papua New Guinea?

My grandmother died of Kroutsfeld Jakobs (Mad Cow) disease, One of 300 deaths that year. In the book, Deadly Feast, The author suggests that America has the potential to reach an epidemic like level of infections because of the way we processes meat in the country. I figured that this is the worst case scenario, and that the author was writing a sort of panic mongering. In your field, what is the general assumption about the danger twords humans? Is it really true that we risk pandemic levels? IS most of our meat actually infected?

To some degree, it was likely fear mongering, but it is a scientist's way to never rule out any possibility that doesn't have significant evidence to be ruled out. It is of course, a possibility that vCJD could reach endemic levels in humans, but it is very unlikely. BSE in cattle is fairly rare, and with practices like the feeding of meat and bone meal to cattle (cannibalism, in essence) banned is most places, BSE rates are relatively stable. Prion diseases are also very slow in progression, especially in humans. However, here are some statistics that are a little alarming:

The US has roughly 90 million head of cattle. (We slaughter about 34 million a year on average). Of the 34 million slaughtered, approximately 40,000 are tested for BSE. That's 0.1% tested and the US has had 4 confirmed BSE cases since testing began.

Japan, on the other hand, has about 1.2 million head of cattle (and I presume about that many are slaughtered each year). They test every single animal, 100%. They have had 36 positive BSE cases.

This concerns me a little, because it suggests that we are likely missing positive cases by testing such a small fraction of our cattle population. I wouldn't say most of our meat is at risk of being TSE+ but I would imagine the numbers are a little higher than 4 out of 34 million (times all the years we've been testing for).

Yeah, my grandmother was in Europe during the Mad Cow panic in the 1980s, and we assume thats when she got it. What blows my mind is how long it can remain dormant before showing signs. For example if she got it in the 80s, she didnt die from it till 2006. Thats mind blowing to me. Furthermore its scares me taht I could in theory have it, and wouldnt know till much later.

You wouldn't get vCJD from your grandmother if she got it from eating BSE+ beef. You'd only be at risk of developing classical CJD if she developed classical CJD as well as a result of a genetic mutation in the PRNP gene that was passed along to you.

How does an ingested prion make its way from the lumen of the GI tract to the brain/rest of the body?

I'll tell you what I wrote to someone above. It's not completely understood yet.

That being said, I'll tell you what is known/theorized. Some fraction of prions consumed orally must be able to survive the low pH of the stomach and travel to the small intestine with the other food being digested, and there are perhaps picked up by microfold cells in the Peyer's patches in the small intestine. Microfold cells are constantly sampling the gut contents to build immunity. The microfold cells then deliver their contents to follicular dendritic cells (which are immune system cells). The FDC's carry their contents/passengers/however you want to think about it (prions) to germinal centers where they display their contents on their surface in order to educate B-cells (for immunity). While here, the prion-loaded FDCs are in proximity of the peripheral nervous system, and once there, they can get to the central nervous system and ultimately, the brain. A lot of this is still unclear though.

Two questions: How long have prions been around/when did they evolve? Does the immune system do anything to fight the spread of prions?

That's a good question. I would presume as long as mammals have been making cellular prion protein. The oldest known TSE is scrapie in sheep and goats and has been documented for the last 250 years or so (though it wasn't known to be a TSE until more recently). The immune system is involved to a small degree, but only at fairly baseline levels. No specific, full-scale immune response is triggered when the body encounters prions.