Researchers probe connections of herpesviruses to Alzheimer's disease
Host Amber Smith: Upstate Medical University in Syracuse, New York, invites you to be The Informed Patient, with the podcast that features experts from Central New York's only academic medical center. I'm your host, Amber Smith.
In the ongoing search to understand why someone develops Alzheimer's, scientists have explored many potential causes, including particular genes and a history of head injuries. There's also thought to be a connection to the herpesvirus. Here to help us understand this research is Dr. Eain Murphy. He's an associate professor of microbiology and immunology at Upstate, and he's got expertise in herpesviruses.
Welcome to "The Informed Patient," Dr. Murphy.
Eain Murphy, PhD: Thank you, Amber. Good morning.
Host Amber Smith: I know there are a variety of different herpesviruses. Which one do you think might play a role in the development of Alzheimer's disease?
Eain Murphy, PhD: Actually, there's nine herpesviruses, and most people have a majority of them to begin with. EBV (Epstein-Barr virus) is an example. Chickenpox is another example. The ones that I am particularly interested in the case of Alzheimer's are herpes simplex virus 1 (HSV-1) and HHV-6 (human herpesvirus 6). Herpes simplex virus 1 causes the common cold sores you see in individuals, and HHV-6 is a virus that most kids get; it's roseola. They also call it cheek slap (or slapped cheek) syndrome, and most kids get it. You just fight it off, and it's not a big deal.
However, all herpesviruses, when you have them once, you have them for life, because they remain with the host forever, and it's spontaneous reactivations. So, on a regular basis, anybody walking around is probably harboring, I believe the current estimates are, 3.2 different herpesviruses.
Host Amber Smith: So we're not born with herpesviruses, are we?
Eain Murphy, PhD: No, we're not. We get herpesviruses in infections. The most common methodology for catching the herpesvirus is a lot of kids in day cares. Kids in day cares are great incubators for passing around viruses amongst each other.
And for the most part, if you have a healthy, competent immune system, the viruses are fairly benign. They don't cause a lot of issues. It's only after times of stress or immune suppression that the viruses come back and cause problems.
Host Amber Smith: So, you said herpes simplex 1 and 6 are the ones that you're concerned with?
Eain Murphy, PhD: Those are the ones I predominantly work on, and those are the ones that have recently been affiliated with neurological diseases, particularly Alzheimer's.
Host Amber Smith: Tell me again, how do they spread?
Eain Murphy, PhD: Herpesviruses are predominantly spread through saliva. You'll see that they're in body fluids, and so a lot of times there's other herpesviruses that are blood-borne, but for the ones that I'm particularly considering, they're neurotropic viruses, they replicate very well in neurons (nerve cells), but they're originally transmitted in saliva, and they get into cells that are called mucosal epithelial cells.
And these are cells that are basically around all of the wet parts on the inside of your body. They code our different organs. And so we have them in our mouth, and it's easy for the virus to get into those cells. It'll replicate there, a small level of replication, and then the virus will eventually find its way to neurons and replicate to high levels there and remain latent in the neurons for the rest of your life.
Host Amber Smith: You mentioned one of the herpesviruses, simplex 1, causes the cold sores.
Eain Murphy, PhD: Correct.
Host Amber Smith: Are there other symptoms? Would we know if we were infected with a herpesvirus?
Eain Murphy, PhD: Well, for the most part, there's a lot of people walking around that are asymptomatic that are carrying this virus. So it's a bigger concern for those individuals that have the virus and they don't know they have the virus. There's blood tests you can take to screen to see if you're seropositive, meaning your body's making antibodies against that virus. And that's kind of our indication that you've encountered the virus in the past, but for the most part, it isn't screened because it's not as strong a medical concern for us to be worried about.
There's other viruses, if you go in and they do a blood test to see if you're carrying antibodies against those pathogens, but for the most part, herpes simplex viruses traditionally were considered not that problematic for individuals. It's unfortunate you get a cold sore, but it wasn't really a life-or-death issue. And so it never moved up the rank to be something that was predominantly screened by blood on a regular basis.
Host Amber Smith: You said these herpesviruses, once we have them, they're with us for life.
Eain Murphy, PhD: Correct.
Host Amber Smith: They're just dormant, not necessarily doing anything?
Eain Murphy, PhD: That's correct. For the most part, these viruses remain latent. They hide in our host cells by shutting down a lot of the activities of the virus.
So when our immune system's surveilling our cells for foreign pathogens, these viruses have adapted very, very well to remain hidden in cells and don't give any overt signs, so our immune system doesn't detect them.
It's kind of interesting, though. My laboratory works on other herpesviruses also, and the herpesvirus family predates the vertebrate/invertebrate split. So these have co-evolved with humans. In fact, one of the viruses we work on in laboratory, cytomegalovirus, you could find in mollusks, so the evolution of these herpesviruses have been hand in hand with human evolution, and as such, they've become masters at undermining a lot of our antiviral immune responses.
Host Amber Smith: All of what you just said is really scary.
Eain Murphy, PhD: Well, we harbor a lot of viruses that don't cause any problem. if you look at a predominant amount of the human genome, it's occupied by remnants of viruses we've encountered in the past, and we've passed them down genetically. And so, at any one point, if you were to surveil your skin, you'd probably be able to detect a whole bunch of different viruses.
Luckily, we have potent antiviral responses, and we have immune systems that keep those in check. And for a virus to establish a productive infection, it needs to overcome a lot of hurdles, and so we've successfully made it here this far in the evolution of life because we can fight off these viruses.
And so amongst those are herpesviruses. We get them, for the most part, they really don't cause many problems in us, but we are carriers of a lot of herpesviruses, and they remain dormant and latent in us. However, in the case of herpes simplex 1, which is what I'm predominantly working on in the case of Alzheimer's, individuals will get herpes simplex 1, and then there's sporadic reactivations of the virus, mostly during times of stress. So you'll see, like, a lot of college students when they're prepping for their exams, always get cold sores because they're under a lot of stress. It's correlated with, exposure to UV (ultraviolet) light, which is stress inducing, hormonal changes in women during their menstrual cycle -- these can all induce reactivations of the virus, and that's why we have sporadic reactivations of herpes simplex. The most overt outward signs we could see of it are lesions on the lips.
Host Amber Smith: So is it your theory that Alzheimer's is sort of a flare-up of a herpesvirus?
Eain Murphy, PhD: No. So, the way I got into this is I traditionally worked on another virus, human cytomegalovirus, but in 2018, four seminal papers came out linking herpesviruses to Alzheimer's.
The first one was a large study that was done in Taiwan in which they took 33,000 different individuals. And they were able to do a large study, prospective study, saying, what do these individuals have outwards in terms of disease? And they could correlate with anything. And what they found is there was a large incident rate of dementia in individuals who had herpesvirus infections. However, those that were undergoing antiviral therapies for herpesviruses didn't show that dementia. So it suggested that maybe the herpesviruses may be leading towards this dementia.
Another paper that came out in 2018 was mouse model systems for Alzheimer's in which they have a mouse that they transgenically, or introduce genes into the mouse, that make the mouse very prone to having Alzheimer's-like symptoms.
In that scenario, they were able to take these mice, infect them with herpesviruses, herpes simplex 1, and the mice that received the virus got dementialike symptoms a lot quicker, and Alzheimer's-like symptoms a lot quicker, to a higher degree, and many of the mice succumb to Alzheimer's-like phenotypes (observable traits). So that was indicative that maybe this might be a causative agent.
The other two papers came out, and those were in Cell Neuron, two very large journals. One showed that if you were to isolate parts of the human brain from an Alzheimer's patient, you can go ahead and notice that in the regions of the brain that had the disease versus regions of the same individual where the tissue was normal, you could find herpes simplex virus DNA, RNA and proteins, but not in the same individual in parts of the brain that were termed normal under examination.
And then another study showed that ... so, going back into the disease of Alzheimer's, you really need three conditions for Alzheimer's. One is inflammation, and we know that inflammation could be caused by viral infections. The other one is accumulation of a protein on the outside of a neuron. And that's beta-amyloid. This other paper suggests that herpesvirus infections increase the depositing of beta-amyloid outside of a neuron. So that suggests that when you infect a neuron, what we see in Alzheimer's may be an aspect of a viral infection.
That's where my work comes in. So I mentioned there's three things. The one was inflammation. The other one is accumulation of beta-amyloid on the outside of the cell. But another ingredient that you need to have a diagnosis of Alzheimer's is accumulation of a protein on the inside of the cell, and that's tau protein.
So neurons, if you could imagine it, are these cells that have these long projections that reach out to a neighboring cell, a neighboring neuron, and that's how we do our neuronal transmissions. To provide rigidity to that long arm that stretches out, the axon, we have these proteins in there called microtubules, and they're kind of like the girders in a building that provide rigidity to this long, stretching arm.
There's this protein called tau, that coats that, that provides additional structural support to those microtubules that we can establish a long axon that reaches across much larger than we see normal cells. Some of these axons are very, very long.
During Alzheimer's disease, patients have the protein tau that normally coats these long microtubule girders that provide rigidity, what they do is they get hyperphosphorylated, which is a modification of the protein. And then they accumulate and they form an aggregate inside the cell. And this does two things. It makes a cell unhealthy, and it also destabilizes the long axon supports, which we need for neuronal transmission. So what we didn't know in the case of Alzheimer's is, if herpesviruses can cause inflammation and they can cause the accumulation of beta-amyloid outside the cell, what is it doing to tau inside the cell?
And so that's where I started research projects saying, will infection of these neurons cause accumulation of tau inside the cells, the third ingredient we need for Alzheimer's? And, in fact, that is the case.
So, going into the biology of tau, there's two major alternate isoforms (similar forms) of tau. There's one with three repeats of a region. And there's another one with four repeats of a region. And in healthy individuals, we have equal molar amounts of that. So you have the same amount of 3R's, 4R. In individuals where we see that tau is accumulating inside the neuron, similar to what we see in Alzheimer's, there's a shift of that ratio, so that there's either more 3R than 4R or more 4R than 3R.
And when you have a shift in the ratios, then you have the protein start to aggregate. And that's an initiating event we see during Alzheimer's. My research was to determine whether herpesvirus infections can shift the accumulation of 3R and 4R tau. And in fact, the reason I got involved in this is, I'm, as any scientist; we find that we're standing on the shoulders of giants that went before us. And there was a lot of research that went on saying that herpesvirus infections of neuronal cells can cause alternate splicing of transcripts, and transcripts that mRNA, the blueprints making proteins, are ultimately spliced so that you can have one mRNA that encodes a protein, be adjusted in its mRNA level, and that would give rise to a different type of protein, a different isoform of the protein.
And what others have found is that herpesvirus infections can alter the splicing of transcripts, mRNA transcripts, and the result would be that you have different isoforms of proteins.
That's what occurs in tau formation. Tau is ultimately spliced so that the mRNA either includes or excludes that extra repeat region, so you have either 3R and 4R, and we know we need an equal amount of it. However, when we infect cells with herpes simplex virus, it shifts the splicing, so we get more 4R.
And so we think that this might be the last ingredient that we would need in a case where you would say herpesvirus infections may be drivers of Alzheimer's. We get the inflammation. We knew already that it causes accumulation of beta-amyloid outside the cell. And now, finally, we think we may have the link as to what's occurring inside the cell.
With this, I think it makes more sense that we should be more focused on looking at herpesviruses as being drivers of this disease than we have in the past.
Host Amber Smith: You're listening to Upstate's "The Informed Patient" podcast. I'm your host, Amber Smith, talking with associate professor Dr. Eain Murphy. He's a microbiologist at Upstate who studies the connection between herpesviruses and Alzheimer's disease.
So if someone had this herpesvirus in the past, and many of us have, is there anything we can do to guard against it doing this and setting us up for Alzheimer's?
Eain Murphy, PhD: I want to put this in proper context. I don't believe that herpesvirus infections alone may be the driver of Alzheimer's. It should be mentioned that less than 5% of Alzheimer's cases are familial linked -- only 5% are genetically linked -- 95% are of unknown etiology (cause). We don't know what the driver is for those.
Something interesting I would want to point out, too, is we do have biomarkers though, that suggest that if you have a specific gene, you're more likely to get Alzheimer's, even though it's not genetically linked. And one of those is the ApoE4 gene. If you have ApoE4 isoform of this protein, as opposed to ApoE3, which is what most people have, your incidence of getting Alzheimer's has increased eight- to tenfold.
Now what's also interesting, and it's also leading me down the pathway to think that herpesviruses are involved in the progression of Alzheimer's, is that ApoE4 has been found to increase the infectivity of cells by herpesviruses. If you take a neuronal cell and express ApoE4, it's more likely to get infected with a herpesvirus than it is if you expressed a normalized form, ApoE3.
So the biomarker we've been using for years to look to see if somebody has an increased probability of getting Alzheimer's in fact aids an infection for herpes simplex virus 1.
But going to back to your point that you raised, is there something that we should be doing, or should we be concerned if we're herpes simplex virus infected?
And my point would be, I don't know if herpes simplex virus infection alone is sufficient for promoting the whole disease. I would strongly lay the claim that I think it's definitely involved, but there could easily also be environmental factors or genetic factors we haven't identified yet.
So the sheer fact that you're herpes simplex virus positive, you have the virus, it doesn't dictate that you're going to get Alzheimer's. So I don't want to cause a panic on that. In fact, many people have herpes simplex virus infections and progressed a hundred years, and they don't have any symptoms of Alzheimer's. So, not to start a huge panic.
But I do think that because these viruses sporadically reactivate on a regular basis, we talked about that before, with stress and different conditions, that continued insult of the virus replicating in neurons may be something that just pushes a cell to an environment where Alzheimer's disease and Alzheimer's progression may be favored, as opposed to somebody who was not harboring the virus, if that makes sense.
Host Amber Smith: Do scientists generally agree with you? Do they think that herpesvirus plays a role in Alzheimer's?
Eain Murphy, PhD: Well, this is a brand-new field, and the funny thing is, you'll probably get (more) scientists using each other's dirty laundry than they would grasping onto each other's ideas if they differ with their own. But in all fairness, I think we're going to find the case that herpesvirus infections are going to be underlying a lot of diseases. And a specific example is, just recently, Epstein-Barr virus, which is mononucleosis, and people joke around EBV stands for "everybody's virus." I mean, the seropositivity, meaning the individuals encountered, are massive, over 90%. They just found a link between that and multiple sclerosis. That was just a strong study that came out just about a year ago.
And so I think that it's not surprising. I think if you make a strong enough claim and provide enough evidence, I think you would convince people that this is easily a plausible cause of what might be driving somebody to be prone to getting Alzheimer's disease.
Host Amber Smith: At this point, do we have theories about what triggers it from going from probable or maybe to having Alzheimer's?
Eain Murphy, PhD: No. This is a problem with Alzheimer's, and I think anybody who's going to be looking at an Alzheimer's situation, is the disease is very, very slow, and it's a progressive disease, and it takes over a decade before we start seeing outward symptoms of it. So making those links are problematic.
And the other thing that we do then to get around that is we use model systems. And so right now, a lot of people use murine model systems, mouse models, in which they can replicate the phenotypes of Alzheimer's and see if you can manipulate that situation. The problem is, mice aren't humans, right? They're very much different. And so it's very hard to model on that.
So what I've done is, I've set up a collaboration with a very, very good group that's run by my friend who's at Albany in the Neural Stem Cell Institute. What they do is, they develop these organoids, and these organoids, what they can do is, they can take a skin cell from an adult, de-differentiate them to make them look like a stem cell, and then they can re-differentiate them down specific pathways.
So you could take a stem cell, make it into a neuron. They do this for making livers and all these other things. My friend, david Butler, who's at the Neural Stem Cell Institute right up here at Albany, very close to us, has a team there that are making these small organoids, which are like little mini brains.
They're smaller than a pea, and if you dissect them, you could see that these organoids have all of the differentiated cells you would find in a small brain. And so what we're doing now is we're using this as a model system. It's human tissue, and we're now infecting these and finding in these tissues, we're seeing that our hypothesis is correct, that there's alternate splicing of tau, this protein that accumulates inside a cell. And we could see aggregation of the protein based on its modification states afterwards, phosphorylation.
The other thing that's really interesting now is because this group is so good at it, they're able to take skin cells from people who have the ApoE4 isoform, and people who have the ApoE3 isoform make them stem cells.
And then you can go in and use a technology called CRISPR technology, and they could switch in one person's cell, stem cell, the ApoE4 isoform to the ApoE3 isoform and then make organoids of both. So now, genetically, these organoids are identical except for one gene, and now this will allow us to dissect the impact of ApoE4 expression on herpesviruses, promoting a pro-Alzheimer's disease state.
David Butler's been instrumental in this work, and he works in a group with another skilled scientist, Sally Temple, and the two of them have developed this model system that we're able to use here. And it's the case that I'll run over to Albany, or he'll drive the two hours this way, and we swap cells and viruses and do our experiments on both ends. So it's been a great, beneficial situation for both of us.
Host Amber Smith: You're focused on herpesviruses, but are there other viruses that you're looking at as playing a role in Alzheimer's development, as well?
Eain Murphy, PhD: I recently wrote a grant, which was funded by the NIH (National Institutes of Health) to pursue this research, and we originally wanted to look at both HHV-6 and the other virus I mentioned and herpes simplex 1, but the scope of that grant got very large, and we decided for our first pass, we're going to look at predominantly the herpes simplex virus, and so we're doing that first, but we hope to expand this also to HHV-6A, the other virus I talked about as being a possible causative agent.
The reason we focused on herpes simplex 1 is that there was a lot more resources and reagents available to us to start that research sooner. HHV-6A is an understudied virus, and there's not a lot of resources for us to do the work. And so we wanted to prioritize our efforts on the one virus that the resources were there for.
Host Amber Smith: As you learn more about what these viruses do and how they work, are you thinking at all of a way to stop them in their tracks?
Eain Murphy, PhD: Well, that study I originally mentioned, in 2018, they did a prospective study on these more than 33,000 individuals in Taiwan. And they found that individuals that had herpesvirus infections and were taking antiviral medications had reduced levels of dementia. And so it could very well be that we have had drugs that are sitting around for the last 30 years -- acyclovir, valganciclovir -- things we use to block herpesvirus infections may slow the progressive state of Alzheimer's.
I would like to say that. I don't have the evidence to say it yet, but part of the problem with making an Alzheimer's drug pharmaceutically would be that, and this may be a bit political, but patents last 20 years. And so if a company's going to go and make a drug, and it takes them 15 years to get through a clinical trial, they only have a five-year patent window on the drug.
So it might not be financially viable for a company to make a drug along the scenario to block Alzheimer's. However, we may already have, on the shelf, drugs that may slow the progressive state of Alzheimer's, if it comes to pass that I'm correct that herpes simplex virus infections are involved in the progression of Alzheimer's.
The other solution people have mentioned, the solution to that problem, would be for things that are slow, progressive diseases, we extend the patent window to 35 years or 40 years for that one type of family of drugs. I don't want to get into that or not, but right now it's problematic. And a lot of companies don't want to invest in slow progressive disease therapeutics because the window for determining whether there's efficacy is really, really long, and it chews up the patent window.
Host Amber Smith: So, potentially, if someone is diagnosed with Alzheimer's and they are found through a blood test to have herpes simplex 1, are clinicians using herpes medications or could they at this point, and would it have any effect?
Eain Murphy, PhD: They're not, at this point. This is still new research. We're just making these links. And so it has to go through a lot of validation, and they'll have to go through clinical trials and all that. So I don't see any clinicians at this point providing antiviral drugs as a therapeutic remedy for Alzheimer's progression. We're hoping to get to that point. And so we need to publish our work and get it more generally accepted after peer review.
But at this point, where we're at right now is, still doing the bench science (laboratory research). So my laboratory is a bench science and we'd love to do the bench side to bedside, but that involves a lot larger study than we have the resources and capacity to do just in my laboratory.
Host Amber Smith: So we're a long ways off from knowing this for sure, but could you envision that these herpesviruses are more meaningful than we're treating them now, and do we need to come up with some vaccines or something to protect people from being infected with a herpesvirus to begin with?
Eain Murphy, PhD: That's a great point. An example would be Epstein-Barr virus, and it's linked now to MS (multiple sclerosis).
And so I think that there is now going to be a reprioritization of generation of vaccines that are targeting. So they've made a lot of vaccines against herpes simplex virus in the past, both simplex 1 and simplex 2, with limited results. But now, I think, with new vaccine methodologies on the horizon here with mRNA vaccines and things like that, we may be at a point now that we can expand our ability to make, quickly, effective vaccines. And now that herpes simplex viruses where I said before they're uncomfortable, but they're fairly benign, and it wasn't really a priority. If they find that it is linked to something as a progressive disease, like Alzheimer's, then maybe it'll move up the food chain on which ones get a vaccine priority versus others.
Host Amber Smith: Well, Dr. Murphy, you've got some fascinating research underway, and I really appreciate you making time to tell us about it.
Eain Murphy, PhD: Oh, thank you very much. I hope to come back and tell you more of our exciting results soon.
Host Amber Smith: My guest has been Dr. Eain Murphy, an associate professor of microbiology and immunology at Upstate. "The Informed Patient" is a podcast covering health, science and medicine, brought to you by Upstate Medical University in Syracuse, New York, and produced by Jim Howe.
Find our archive of previous episodes at upstate.edu/informed. This is your host, Amber Smith, thanking you for listening.