Podcasts

Podcast – Neuroinflammation in mouse models

Hosted by Dr Megan O'Hare

Reading Time: 32 minutes

Dr Megan O’Hare is joined by three researchers based at the UK Dementia Research Institute in Cardiff – Dr Sarah Carpanini, Dr Tom Phillips and Dr Megan Torvell to discuss neuroinflammation in neurodegeneration this time using mouse models to examine underlying pathophysiology during brain development and beyond.

Join them to hear about physiological synapse loss that occurs during normal, healthy development of the brain contrasting to pathological synapse loss that occurs in disease states such as Alzheimer’s Disease.

Hear more about the role of microglia and the role of the complement cascade as well as the virtues of using mouse models in general for studying an ageing disease.

Please note, this podcast was recorded over Zoom (so apologies if the sounds quality isn’t up to our usual high standards).


Click here to read a full transcript of this podcast

Voice Over:

Welcome to the NIHR Dementia Researcher Podcast, brought to you by dementiaresearcher.nihr.ac.uk, in association with Alzheimer’s Research UK and Alzheimer’s Society, supporting early career dementia researchers across the world.

Dr Megan O’Hare:

Hello and welcome to another Dementia Researcher Podcast. I’m Megan O’Hare and today we’re going to be talking about neuroinflammation and microglia in Alzheimer’s disease, using mouse models. I am delighted to introduce our three panellists, who are all based at the UK DRI at Cardiff University. We have Dr Sarah Carpanini, a research associate who met her husband over the cooked chicken counter at a popular supermarket; Dr Tom Phillips, who initially trained as a medical doctor before being drawn to the benchside, and is now a research associate with 17 pets, I hope that’s still correct otherwise that’s a really sad story!

Dr Tom Phillips:

It’s actually more.

Dr Megan O’Hare:

Oh okay, good, more is good. And Dr Megan Torvell, a research associate but also a Dignity and Wellbeing contact, which sounds amazing, and hopefully we can find out a bit more about that and supporting ECRs later, and she also has a great name, spelt correctly.

Dr Megan O’Hare:

So hello everyone and thanks for joining us. Can we just start with just a quick… introduce yourselves, let us know who you are, so we can hear your voice? Tom, shall we start with you?

Dr Tom Phillips:

Yes, so I’m Tom. I work as a postdoc in Phil Taylor’s lab at the UK DRI, looking at presenilin-2 mutations in microglia.

Dr Megan O’Hare:

Okay, great. Next on my screen is Sarah.

Dr Sarah Carpanini:

Hi, I’m Sarah and I’m a postdoc in Paul Morgan’s group in Cardiff DRI and I work on complement at the synapse.

Dr Megan O’Hare:

Okay, and Megan.

Dr Megan Torvell:

And I’m Megan Torvell, I work with Sarah in Paul Morgan’s group and I am interested in neuroinflammation and complement in Alzheimer’s disease.

Dr Megan O’Hare:

Okay, great. So I think I’m right in saying that you all have a gene… protein of interest that is your particular focus, but more broadly, you are all studying the role of neuroinflammation in neurodegeneration. So, right back to basics, what are we talking about when we say neuroinflammation? People are probably fairly familiar with the immune system our bodies use to fight infections but how does it actually work in the brain? Maybe Megan we can come to you first as I think you’ve worked on inflammation in two different disease models, is that right?

Dr Megan Torvell:

Yeah. When we think of immunity normally, we think of immune cells fighting pathogens, whether that’s viral or bacterial invasions, but the immune system exists more broadly just to maintain what we call homeostasis, so just maintain normality. There are sensors throughout your body which exist to detect when things go awry, so that could be cancer cells dividing rapidly, or it could be a pathogen invading, or it could be a protein which is either misfolded or accumulating in the wrong place. And that’s something that happens in all sorts of neurodegenerative diseases. It’s often different proteins for different diseases.

Dr Megan Torvell:

And there are immune cells called microglia which exist in the brain, and it’s their job to detect those changes, and then respond appropriately, but unfortunately that immune response often gets out of control, and so the neuroinflammation starts to drive the disease, and that’s what all of us are focusing on is how neuroinflammation drives the disease.

Dr Megan Torvell:

During my PhD I was working on a mouse model which overexpressed a human mutant tau protein, so that was sufficient to mimic tauopathy disease, and now I’m working on a mouse model of amyloid pathology. So amyloid and tau are the proteins that accumulate in Alzheimer’s disease, and the thing that both of these models have in common is neuroinflammation.

Dr Megan Torvell:

Nowadays, I am working on a really niche part of neuroinflammation, along with Sarah, which is the complement cascade. Complement is a cascade of proteins and it looks really daunting and unfriendly to an outsider, but it can be reduced down to quite simple concepts.

Dr Megan Torvell:

There are initial proteins which are involved in recognizing invading pathogens or damage-associated signals. And then there are three outcomes from the pathway, which are: cell recruitment, that’s recruitment of immune cells to the site of damage or infections; formation of a MAC pore which is a membrane attack complex pore in the membranes of infected cells or unhealthy cell; and finally, coating cells or protein deposits with “eat me” signals, so that microbial cells can come along and eat those unhealthy cells or protein.

Dr Megan Torvell:

So we think that complement becomes dysregulated and neuroinflammation becomes dysregulated in disease, and that’s what Sarah and I are trying to understand. So yeah, that’s what I’m working on at the moment.

Dr Megan O’Hare:

Okay so the complement cascade, you said there can be three pathways coming out of it: cell recruitment, a MAC pore was it?

Dr Megan Torvell:

Yeah, membrane attack complex pore.

Dr Megan O’Hare:

Okay. And coating the cell or the protein with a signal to other cells to come and destroy them because they’re-

Dr Megan Torvell:

Yes.

Dr Megan O’Hare:

What causes the complement cascade to be initiated in the first place?

Dr Megan Torvell:

That is actually what we’re trying to work on, maybe Sarah should take that question.

Dr Sarah Carpanini:

There are multiple different names. I specifically look at the synapse, so at the moment I’m trying to figure out what causes complement to bind at the synapse removal. In terms of what causes complement to be activated in the first place, there are multiple different ways that it can be activated, it’s a response to pathogens, to dead or dying cells, and basically the complement system is part of the body’s normal innate immune response. So it normally happens within the body, it has a perfectly essential role, what we’re looking at is what actually causes it to be activated within Alzheimer’s disease.

Dr Megan O’Hare:

Okay. You said it’s part of the innate immune system, just very quickly, which one’s the innate immune system? Is that the B cells and antibodies?

Dr Megan Torvell:

No it’s the other one, so innate immunity is the fast response that’s very much dependent on generic pattern recognition, so there are things that recognize like sugar molecules or the outer membranes of bacteria and that sort of thing. These are not super specific like antibodies, this is just very generic recognition.

Dr Megan O’Hare:

Okay. And the complement is obviously present in the brain, is it generated in the brain or can it cross the blood-brain barrier?

Dr Megan Torvell:

Yeah, it is generated in the brain. It’s one of those things that we’re really trying to pin down as a group, where the complement is being made. From lots of RNA-seq type experiments we know that microglia can make complement. And we know that in neurodegenerative diseases obviously we have blood-brain barrier breakdown, so infiltrating cells can come in and make complement as well, but there’s also evidence that neurons can make it. So that’s another thing we’re interested in, is what is stimulating the cells to make the complement in the first place.

Dr Megan O’Hare:

Okay-

Dr Sarah Carpanini:

It’s another program of work that we’ve got ongoing at the moment, is for all the different complement proteins, is finding what cells make them? Are they made in the brain? If they’re not, are they coming in, are they infiltrating one of our other avenues we’re looking at.

Dr Megan O’Hare:

Okay. So maybe, Sarah, we can pick up from you a bit more about the synaptic loss that you discussed, that’s your main focus.

Dr Sarah Carpanini:

Yeah, okay. So first of all, just to make sure that everyone’s aware what the synapse is. So the synapse is a microscopic gap which is actually 1000 times thinner than a normal human hair. And it separates the terminal end of one neuron from another neuron. And when neurons communicate, they release signals that must travel across this gap to the post-synapse. So it might be tempting to think of the synapse as a gap, but it’s not, it’s actually a very well-structured, with a complex infrastructure.

Dr Sarah Carpanini:

So what we know that happens is, we know that C1q and C3, which are part of the classical complement cascade, so they’re right at the top of this cascade. They tag synapses for removal. So they come along and they stick to the synapse, and they’re there. And then you’ve got the microglia, which are the immune cells in the brain that Megan and Tom work on, and they come along and they recognize these complement tags on the synapses, and they say, “actually, look, I recognize that, I’m going to come along and I’m going to eat that synapse.”

Dr Sarah Carpanini:

But what we’re not sure of is what’s causing these complement molecules to stick in the first place. Why does one synapse get eliminated and others remain intact? Is there an “eat me” signal? Or is there a “don’t eat me” signal? That’s really a very big foundation of work at the moment that loads of people around the world are trying to figure out. We know it happens, we just don’t know why.

Dr Megan O’Hare:

Okay. You said that neurons themselves can potentially make complement. Is that right? So it could be a whole internal process of that neuron making its own complement.

Dr Sarah Carpanini:

It could be but we know that C1q and C3 are mainly produced by microglia.

Dr Megan O’Hare:

So maybe, Tom, you can jump in now because we’ve heard microglia mentioned a couple of times, and you work on them, specifically. So I guess the big question is, are mouse microglia the same as human microglia?

Dr Tom Phillips:

That’s a tricky question. Yes and no. Microglia are basically just tissue-resident macrophages. So they go through the same process in the mouse, and in the human during development. So they’re derived originally from the yolk sac, and they migrate to the brain and set up there, and spread out through the brain and develop the basic system of immunity in the brain. That’s the same in the mouse and in the human.

Dr Tom Phillips:

But, obviously the mouse and human split off evolutionarily, however many million years ago. And immunity itself is a site of high-degree change evolutionary-wise. And they’ve got lots of different immunity challenges, lots of different things encountered by the mouse not encountered by the human. So there are some quite key differences in [receptauxentation 00:11:24] for example. Interferon gamma, [torlite-4 00:11:27], are all different in the human compared to the mouse. And some drugs, that we put in mice, completely wipe out… A disease drug you can put into mice that wipe out microglia in the mouse, but in the human seems harmless.

Dr Tom Phillips:

So there are differences, but, it is important that the key things about the microglia are really maintained throughout. So they are cross-comparable, as long as you’re very careful about what you’re looking at.

Dr Megan O’Hare:

This is sort of a Megan and Tom question. You said you worked on a model during your PhD that was using tau in mouse, and was that human tau in mouse?

Dr Megan Torvell:

Yeah, so that model was overexpressing human tau, so it was quite an artificial model.

Dr Megan O’Hare:

But the mouse microglia, they still responded in the same way did they? So this is back to Tom maybe.

Dr Megan Torvell:

Yeah.

Dr Tom Phillips:

So the-

Dr Megan Torvell:

Go for it.

Dr Tom Phillips:

Usually these models, the microglia respond almost exactly the same way as they will in the humans, but there are nuance differences which you have to be careful with. But the basic structure and the basic response systems are the same.

Dr Megan Torvell:

Yeah, so if you’re overexpressing a human protein-

Dr Tom Phillips:

When you’re looking at a mouse brain model overexpressing tau, or amyloid, or anything like that, really, you’ve got an artificial system anyway. The mouse brain doesn’t experience dementia the same way the human brain does. It doesn’t even really experience aging you get in the human brain because mice just don’t live along enough and they just don’t have the complexity to get that sort of level of dementia and aging.

Dr Tom Phillips:

So anything you do there is slightly artificial. But, the main processes, the main systems are maintained. So you can cross-compare between the two, as long as you are careful, you don’t extrapolate too far.

Dr Megan O’Hare:

Yeah. Maybe you want to talk a little bit about what your specific project is with microglia.

Dr Tom Phillips:

We’re looking… a few years back now, a GWAS study came out, which picked out some changes in mutated genes, which can be either protective, or increase the likelihood that you’re going to get Alzheimer’s disease. And so one of them that came up was the presenilin-2 mutation. This mutation… a slight change in one of the amino acids in presenilin-2, which is bound in the brain in microglia, and only in microglia in the brain, for the most part. And if you have this particular mutation, you’re slightly less likely to develop late-onset Alzheimer’s than someone without this mutation. So what we have been trying to do is work out what this mutation does to the protein, what changes that causes, and how we can replicate it.

Dr Tom Phillips:

Now this was found in the humans, but presenilin-2 is in mice, and we were able to induce the same mutation in the mouse that we find in humans, and so we can study that effect in that system. And the idea from then, because presenilin-2 is an enzyme, it’s classically druggable. So we’ll be able to work on activators and inhibitors, and develop drugs with various drug companies, to look at treatments, to see if we can get people with the standard wild type form of presenilin-2, give them the same protection these people with the mutation has, and maybe extend it.

Dr Megan O’Hare:

Okay, great. And how’s that going?

Dr Tom Phillips:

It’s going. No, we’re only so far in, but we’ve discovered… a paper just on the pre-print service now, about presenilin-2, there’s a lot of people working on this, so it’s a bit competitive at the moment, but we’ve found that it’s a hyperactive function, so it’s more activated in this mutation than it is in the wild type. There’s a lot of other caveats on that, and downstream effects, but it does give us a way that we can easily manipulate this system… I say easily… We can manipulate this system, and hopefully lead to more clinical work years down the line.

Dr Megan O’Hare:

Mm-hmm (affirmative). That was interesting actually, you said about, because it’s an enzyme, that opens maybe more or easier, I don’t know-

Dr Tom Phillips:

Well it’s classically druggable, so it’s vulnerable to activators and inhibitors, which we can slip in. One interesting thing, is because these microglia, are basically as I say tissue macrophages, there’s been a lot of work done on macrophages and in presenilin-2, which in macrophages in other parts of the body, rather than in the microglia in the brain, where there are mutations and this that cause various diseases like [blab 00:16:03], where if this particular protein isn’t functioning properly, you get a particularly immune syndrome.

Dr Tom Phillips:

So there’s lots of work done that’s outside the brain, but because classical neuroscientists, like myself, haven’t really thought about immunity, for more… It’s really just come into the system in the last 10 years, that people have been starting to think about neuroinflammation, and the immunity side of the brain for that we were all saying, it’s immune protective, it’s all about neurons, maybe we’ll talk about astrocytes sometimes, but microglia weren’t really thought about. The fact that we called them “the little blue cell” is probably indication of how much we thought about them.

Dr Tom Phillips:

So there’s a lot of open work here to be looked at, and we can pull a lot from people who haven’t worked in neuroscience before, for example, Phil Taylor, my boss, and Paul, Megan and Sarah’s boss, aren’t actually neuroscientists, they come from an immunity background. So we’re pulling all these different things in there to have a look at systems that haven’t really been studied in the brain before.

Dr Megan O’Hare:

Mm-hmm (affirmative). Was there a pivotal point? Was there a big study that showed that microglia were important somehow, or suddenly picked up that complements overactivated? Maybe we could come back to you Megan, to talk a bit more about complement and your actual project, and maybe what’s changed in the field for people to-

Dr Megan Torvell:

Yeah, so I don’t think there’s been a really pivotal point where the field has suddenly woken up to inflammation, I think people have been quietly working on it for decades. But the recent genetics studies have really suggested actually this could be causative. So I think before, neuroinflammation was seen as, maybe a consequence of the disease, maybe it’s just something’s gone wrong with the neurons and the immune cells start responding later on. But now the genetic studies are suggesting, maybe actually these inflammatory differences, they could be driving the disease. And there are studies that’ve started to show, actually these inflammatory changes start earlier and earlier than we’ve realized.

Dr Megan O’Hare:

And that’s because you’ve found mutations in certain genes that are part of inflammation pathways.

Dr Megan Torvell:

Yeah. They’ve done these massive genome-wide association studies, where they basically look at variations across enormous populations, and they show that these small variants add up, but you can increase your genetic risk, this is Sarah’s area of expertise more than mine really, but they took about polygenic risk scores, and basically by having lots of mutations with relatively low risk, then you can increase your overall risk of Alzheimer’s disease

Dr Megan O’Hare:

[crosstalk 00:18:55] nodding.

Dr Megan Torvell:

Yeah, lots of nodding going on. They basically looked at all the pathways that these variations are in, and they’ve found that a lot of them are immune cells, predominantly microglia.

Dr Megan O’Hare:

Sorry, just to jump in. Although what Tom was talking about was a protective mutation [crosstalk 00:19:19] inflammation pathway gene or protein.

Dr Megan Torvell:

Yeah. So that would be that the protective variant is just that it’s causing less damage than the detrimental variant if that makes sense. Someone reword that for me, my brain’s not doing that.

Dr Megan O’Hare:

Sarah?

Dr Tom Phillips:

I mean-

Dr Sarah Carpanini:

There’s some complement genes that have also come up in these GWAS studies, and we know that if you’ve got variations in those genes you are increasing your risk of Alzheimer’s disease. And that could be because these are regulators, so they’ve got an inhibitory role.

Dr Tom Phillips:

In presenilin-2, the mutation itself is the protective. So if you have this mutation, you are protected.

Dr Megan O’Hare:

Yeah, so that wouldn’t-

Dr Megan Torvell:

I think that depends on what the function of the protein is, whether you’re making the protein do its job better or worse. That’s what we’re trying to say.

Dr Megan O’Hare:

That then wouldn’t add to your risk score?

Dr Tom Phillips:

[crosstalk 00:20:13] No it would reduce it.

Dr Megan O’Hare:

Yeah, it would reduce it.

Dr Megan O’Hare:

Okay, so actually Megan, let’s come back to you again, because one of the questions I’ve got is about your work, and how is it clinically relevant? But you haven’t told us that much about your work, so maybe combine the two, a bit more about your work and how is it clinically relevant?

Dr Megan Torvell:

With Sarah, I’m interested in trying to work out at what point complement becomes dysregulated. So we have this triple knock-in Alzheimer’s model. Hang on, triple knock-in amyloid model of Alzheimer’s disease. And we’ve back-crossed it onto various complement-deficient mouse models. And we’re basically interested in trying to teethe apart the pathway to work out at which point complement becomes dysregulated in the disease, and how that’s contributing to Alzheimer’s disease. We also have some complement therapeutic drugs in the lab, and we’re trying to use those to see whether we can impact on the trajectory of the decline in various measures of disease pathology.

Dr Megan O’Hare:

And they use the drugs that you feed to the mice.

Dr Megan Torvell:

Yes, so these are antibodies that are made in-house, and they basically target complement proteins and block the pathway.

Dr Megan O’Hare:

What stage of the mouse’s life do you use them, because this comes up a lot about, you have some very effective drugs but you have to use them 20 years before…

Dr Megan Torvell:

Yeah, there is a project going on in the group at the moment, where they’re looking at treating with an anti-complement drug early and late in the disease and seeing how that affects the outcome.

Dr Megan O’Hare:

Because what we’ve talked about is that now neuroinflammation, and specifically with you guys, the complement cascade, is not a late-stage phenomenon. It’s potentially the cause, so it would be early on in the disease pathway, so you’d want to get in early.

Dr Megan Torvell:

I wouldn’t go so far as to say it’s the cause, because there’s probably some other trigger, but I would say it’s probably driving the disease, and possibly from quite early on, so if we can target that earlier on, then that would be awesome. The problem with that obviously is that when somebody presents to the clinic with symptoms, they’re possibly quite late on in the disease, so what we would really love to be able to do is try and identify some biomarkers, or some way of identifying people who might be at risk of getting dementia, and people in whom anti-complement treatment might be beneficial.

Dr Megan Torvell:

But there are already anti-complement drugs being used in the clinic to treat neuromyelitis optica, which we just know as NMO, and that’s basically an inflammatory demyelinating disease that affects the nerves that innovate the eye. And there’s a drug called eculizumab, which targets C5, which is part of the complement cascade, and so that’s used as a drug in clinic. So we’re hoping that we might be able to work out how complement is dysregulated in Alzheimer’s disease, and then work out which parts of the pathway need to be targeted, and then work out how to do that. So that’s the end goal.

Dr Megan O’Hare:

This a quite a simple question but how many complement proteins are there? You mentioned C5- [crosstalk 00:24:03]

Dr Megan Torvell:

Not a simple question!

Dr Megan O’Hare:

[crosstalk 00:24:07]

Dr Megan Torvell:

Not a simple question!

Dr Megan Torvell:

They say there’s like, over 40 proteins. The pathway itself isn’t too terrible, in that in theory it only goes up to C9, with a couple of caveats to that sentence, there’s C1q, C1r, C1s. There’s loads of enzymatic steps throughout the pathway where they get broken down into subunits or parts that then go on and do different things, but the bit where it gets confusing is that there are actually lots of proteins that have multiple functions and regulators.

Dr Megan Torvell:

So for instance, clusterin is a protein which has a bajillion functions throughout the body, and is known as a risk factor for Alzheimer’s disease, and there’s a huge field of research on clusterin, which I’m not super familiar with, but it is also a complement regulator. That’s where the line gets a bit blurred.

Dr Megan O’Hare:

20 years ago? Yeah, that’s about right, 20 years ago I did a project in a heart transplant lab, and we were using complement as the biomarker, so we were taking biopsies from people’s heart transplants, and looking for complement protein as the biomarker for eventual humoral rejection. Could you use complement as your biomarker? I guess it depends how early on in the process you think that it’s being over-

Dr Sarah Carpanini:

There have been quite a few studies for people looking at complement biomarkers, and they’ve got age-matched controls, patients who have mild cognitive impairment, and people that go on to develop Alzheimer’s disease, and trying to see, can you identify biomarkers that were [di virgo 00:25:46] in the progression from control to emphysema, cognitive impairment, or involved in the progression from mild cognitive impairment to Alzheimer’s disease. And there’ve been a few studies that’ve come out from our lab as well, before we started, when I think factor H has come out of one, and there have been a few others.

Dr Megan O’Hare:

Oh okay. So, promising work?

Dr Sarah Carpanini:

Yeah, promising. It’s ways that you can look at it as well, because you want to be able to not only look for biomarkers, but look for biomarkers as well in readily available substance, so you want to look at the main blood. So you can easily get people coming into clinic and you can get blood from them and then you can look for biomarkers there.

Dr Sarah Carpanini:

If you’ve got to look for a biomarker say in CSF, that’s an invasive procedure for someone who’s already ill, you don’t want to be doing that. So it’s a really difficult study and there are people looking for biomarkers everywhere, I’m not sure we’ve got any projects on the go any more in the lab, looking for biomarkers, but I think if we find something interesting, we do have access to samples that we can say, “Well actually, do you see this as an early time point, could this be used as a biomarker?”

Dr Megan O’Hare:

And complement itself is in place, isn’t it? The complement proteins are, say, on the synapse, or on a protein, they’re not freely circulating in the blood, handily for biomarker studies.

Dr Megan Torvell:

Some of them are-

Dr Sarah Carpanini:

Some of them are.

Dr Megan Torvell:

Some of them bind to the cell membranes and they’re deposited all over. But a lot of them are in fluid phase, and a lot of the time, when the membrane-bound fragments… So, for example, C3 is a protein which forms a covalent bond to a target membrane. It’s only the C3b fragment that forms that covalent bond, and the C3a fragment is released in circulation.

Dr Megan Torvell:

And that is in cell recruitment, chemotactic factor, but then, C3b then goes on to form convertases, and is then degraded into iC3b and then C3c and then C3dg, and it goes all the way through the alphabet, it’s ridiculous. But by looking at the ratios of the different breakdown fragments, then you can get an indication of where the complement has been activated.

Dr Megan O’Hare:

Okay. That sounds cool.

Dr Megan Torvell:

Yeah. Well, cool in theory, except that it’s actually very difficult to raise antibodies against that, so there are projects in other groups where they’re trying to do mass spec stuff, to try and identify different fragments.

Dr Megan O’Hare:

Yeah, I was using antibody to C3d and C4d I think, in heart tissue. But obviously, biopsying a heart is easier than biopsying someone’s brain.

Dr Megan O’Hare:

Sarah, I’ve got a question for you here that says, “How can studying development aid our understanding of Alzheimer’s?” Would you like to pick up that quickly?

Dr Sarah Carpanini:

Yeah, so I’m going to answer this based on the synapse, because that’s my area of expertise, so-

Dr Megan O’Hare:

Also the synapse is great, I don’t think we talked about the synapse enough.

Dr Sarah Carpanini:

I like it. So as the brain develops, it produces more connections than it’s ever going to need. So these connections, these synapses, need to be eliminated to increase the efficiency of your brain, and this process is called synaptic pruning. There’s an analogy… You can think of this as a rose bush. So when you prune a rose bush, you cut off the weaker, dying branches, so that the bigger ones, the stronger ones will flourish. And that’s really what happens in the brain.

Dr Sarah Carpanini:

We know that synaptic pruning is a normal event during development. But we also know that synaptic loss is a very early event in Alzheimer’s disease. And we know from mouse models that both during development, and in mouse models of Alzheimer’s disease, complement proteins are tagging synapses for removal by microglia. But what we don’t know is if the triggers are the same. If the trigger that causes synaptic pruning in development, is the same trigger that’s reactivated within Alzheimer’s disease, at the moment we just don’t know that. We’d like to know that, but we just don’t.

Dr Sarah Carpanini:

The other aspect we can use mouse models, is they enable us to look at synapses at very early time points in development. We can also look at early time points in disease.

Dr Sarah Carpanini:

Now, if you think, if you can compare animal models to humans. We have a cohort of mice, that we know, we can 100% guarantee that these mice are going to develop Alzheimer’s. We can look at early time points, so we can look at the equivalent of decades before in the mouse, and say, “What is a very early event?” We can’t do that in humans. Even if you could get brains from the Brain Bank, we don’t know if those people are definitively… Would they have got Alzheimer’s disease if they lived another 20, 30 years? We just don’t know that.

Dr Megan O’Hare:

Question, quickly, more about the human point. You said about synaptic pruning happens, it’s a regular event during development. Does that mean it’s happening just in the embryo stage? Foetus stage? While we’re growing up? Is it an adult event as well? It sounds very much like it’s a very early baby stage.

Dr Sarah Carpanini:

Yeah. So you’re thinking after birth. So if you’re thinking when the baby’s born, and then it’s producing all these excess neural circuits. And then you get to about toddlerhood, and if you think of a toddler, and you think of a child that’s… can’t cope-

Dr Megan O’Hare:

Blood might appear at any moment if you say “can’t cope” too loudly!

Dr Sarah Carpanini:

Can’t cope with their emotions, is all over the place, and everything is so confusing, it’s because they’ve got all this haywire in their brain, they’ve got all these excess connections. So by the time you’re about 10 years old, you’ve actually got half the number of synapses in your brain than you had when you were two year-old. So it’s really in that young childhood, and it does make sense when you think of it, and you think of a child’s behaviour, and you think of the first two years of your life, think of how much you have to learn. You need-

Dr Megan O’Hare:

Lots.

Dr Sarah Carpanini:

You need to strengthen. You need to strengthen those synapses that you are using all the time. But those that are underused, those that are weak and not required, they are the ones that are getting pruned, but we just don’t know what the triggers are to initiate this at this moment.

Dr Megan O’Hare:

Throughout development, you don’t have the same amount, or the same genes aren’t used at exactly the same levels throughout development, so it could be a completely different process, it could be that this gene is switched on that controls synaptic pruning during early development and then just isn’t switched on again and it’s a completely different system, is that right? Or alternatively it could be exactly the same system?

Dr Sarah Carpanini:

Yeah, it could be. As I said, we just don’t know at the moment. But we can use mouse models to look at development and we can try and understand what’s going on there. That’s not to say that’s exactly what’s happening in Alzheimer’s disease, but this is a fantastic model that we can have, and if we can understand it here, and is that going to aid our understanding, it would give us a starting point in Alzheimer’s disease to focus on this. And really, that’s what we need.

Dr Megan O’Hare:

Mm-hmm (affirmative). And to then overlay this human situation we’ve just talked about into mice, Tom obviously pointed out that mice just don’t live as long as humans, not even cutting it close. So, it’s all sped up is it? They do all their development within the first few weeks-

Dr Sarah Carpanini:

Yes.

Dr Megan O’Hare:

The equivalent that we do as a toddler? Okay.

Dr Sarah Carpanini:

Yeah, so we look at synaptic pruning, and we say that synaptic pruning has finished by the age of about P28, so that’s 28 days postnatal. So you’re looking within the first month of life, of a mouse, that these pruning processes are taking place.

Dr Megan O’Hare:

What’s happening to your mice right now? Now we’re all at home.

Dr Megan Torvell:

That’s me that’s in charge of maintaining things at the moment. We are trying to maintain the colonies on minimum tick over, so that we’ve just got enough breeding pairs that we can keep them going. We are quite fortunate in that we were not in the middle of any big, cohort experiments. So we’ve not had to lose anything. I know that quite a few groups have been really affected by that, by having to cull mice from experiments, which is really horrible. So, it will take us a while once this is over to ramp up again, but in the meantime, we’re just keeping them on minimum tick over. I’m classed, somehow, as a key worker, so I can hop in every so often to get tissue for time points. So I just identify the really essential mice that we need to collect tissue from. So I’m going in like once a month.

Dr Tom Phillips:

[inaudible 00:34:53]

Dr Megan O’Hare:

I guess it’s kind of [inaudible 00:34:54] Sarah’s point about, by P28, these mice have finished that development stage [crosstalk 00:34:59]

Dr Megan Torvell:

Yeah. But then the plus side of looking at the early stages though is that it doesn’t take that long to age the mice to that stage.

Dr Megan O’Hare:

Maths, again.

Dr Megan Torvell:

Yeah. Maths. Getting good at it. It’s when you’re looking at the two year-old mice, if you’ve got partway through aging mice for time point tissue and you’ve lost mice at this stage, that can be… I mean, if you’re looking at the average postdoc, it’s two to three years. If you’ve lost mice that you’ve been aging for a very long time, then this is a very devastating situation, but then… COVID, there’s no good time to have a pandemic, and there are much worse problems associated with the whole situation, so…

Dr Megan O’Hare:

Yeah. This is where I feel I should bring up about flies. I think I mention this fairly regularly, I used to work on Drosophila, and their lifespan is like 40 days guys, it’s great.

Dr Megan Torvell:

Mm-hmm (affirmative). We’ve got some people in work who work on flies.

Dr Megan O’Hare:

Yes! Maybe I can interview them too.

Dr Megan Torvell:

Yeah! I’m sure they’d be very keen.

Dr Tom Phillips:

[inaudible 00:36:06]

Dr Megan Torvell:

They often turn up in my staining jars full of alcohol.

Dr Megan O’Hare:

Yeah, they’re really attracted to that, they love it, but it kills them. I guess, like humans.

Dr Megan Torvell:

Yeah! Just like them.

Dr Megan O’Hare:

Okay. So is there anything else you’d like to add? Tom, you haven’t said anything for a while. Do you want to tell us something more about microglia, or what’s happening to your mice?

Dr Tom Phillips:

Well, we’ve suffered quite badly for our mice. We had quite a lot going on, and lots of aging studies that were set up. So we did have to cull back quite a few lines at the beginning of this. Because we didn’t know, obviously, how the staff at the facilities would be affected, and what would have to be shut down and how bad this was going to get, so we had to take precautions.

Dr Tom Phillips:

A few things we have kept going, we had some behaviour work, some people in the lab were doing, that was just too far gone to risk losing, so that is kept going. But similarly to-

Dr Megan O’Hare:

Sorry, is that in relation to Alzheimer’s disease, and microglia?

Dr Tom Phillips:

Yeah.

Dr Megan O’Hare:

So, what sort of things, I know it’s not your research but just out of interest, what kind of behavioural studies do you use?

Dr Tom Phillips:

This particular one that is looking at a different genetic variant, which is a risk factor, a bit more simply. We’re just looking at, how if you knockout this protein, how does that change the mouse’s behaviour later in life? Especially if you cross it into one of the Alzheimer’s models we talked about. So, the APP model. So I think the person doing it is doing basic light maze tests, nothing too invasive, sucrose tests, to see how they respond to increased sucrose, to look at their depression levels, things like that.

Dr Megan O’Hare:

So you said you’ve made a complete knockout of this gene, or maybe not you personally, someone else. And then you’re crossing it into another mouse with another genetic background. So you’re, sort of, gene on gene on gene, a bit like how you were talking about how people can have added up risk factors by having various mutations.

Dr Tom Phillips:

One of the best thing about the mice of course, is that we have all of these multiple strains, and people have been studying the mice for 100 years, so we understand it really well. So we have in our lab, I don’t know how many strains, a couple of thousand different strains, of different type of mice with different risk genes, so the presenilin-2 one, ABI3, various other ones, and then we have the models of disease as well, like the triple knocking APP mouse, which has three different mutations that leads to increased amyloid inside the brain. Then we can easily cross these back and forth because we understand their genetic lines, and some of where they’ve been, we’ve geotagged them, so it’s easy for us to cross these, and make multiple knockouts.

Dr Tom Phillips:

We’ve got some mice with the APP, one of the risk genes, and a gene that makes microglia have GFP in, so you can identify them easily with a [inaudible 00:39:04] green fluorescence.

Dr Megan O’Hare:

Everyone loves a fluorescent mouse, just saying.

Dr Tom Phillips:

These mice are a bit crazy. When we first crossed them, the entire mouse was fluorescent, it was weird. So we had to do that down a bit, so just the brain was fluorescent. So it had these weird fluorescent ears, it was very strange. But-

Dr Megan O’Hare:

Megan you had your hand up like we’re-

Dr Megan Torvell:

Yeah.

Dr Megan O’Hare:

Cool.

Dr Megan Torvell:

Yeah, so I just wanted to add to that. A lot of the time, when you’ve got gene mutations in immune-related genes, you might not expect to see any overt phenotype, and it’s not until you cross it onto something like an amyloid model, where there’s a trigger, that then you see… well, normally the amyloid does X to the microbial cell, but when you’ve got rid of such and such of regulator, and then you give it amyloid, then you see this really exaggerated immune response. And so that’s why a lot of the time, we cross immune gene variations or mutations onto Alzheimer’s disease models.

Dr Megan O’Hare:

And that’s exaggerated to be more like the human disease, or exaggerated so you can do more functional assays, behavioural assays, drill down a bit more into the function of the protein.

Dr Megan Torvell:

Yeah. It depends on what your gene of interest is, but it allows you to probe what the gene is doing in that context.

Dr Tom Phillips:

And it also gives us the controls, we have these two lines that we understand very well, and have been crossed with each other, so you then have all these other genetic factors coming in, and we can directly control them, compare them to each other. And they can grow at the same age, we can have the same controls, same rooms and everything. It will allow us very easy, “This is the effect because of this,” rather than any other outside effects.

Dr Megan Torvell:

So an example of that is, we’ve got a mouse model which is lacking a complement regulator called Crry, I call them “curry mice,” and not having that receptor isn’t a problem in a normal, otherwise healthy mouse. But in an Alzheimer’s diseased mouse, they have an accumulation of C3, which is one of the core complement molecules. And so not having that regulator then, means that there’s a stimulus [reinclination 00:41:43] and then you don’t have the regulation and so it just gets out of control.

Dr Tom Phillips:

The other thing of course, we can take out particular stimulus, so we have the APP model, Megan you worked on the tau model before, yeah?

Dr Megan Torvell:

Yeah.

Dr Tom Phillips:

So we can see how exactly this particular stimulus is affecting them compared to this one, rather than having a whole of the thing mixed together as you have in the humans answers.

Dr Megan O’Hare:

Mm-hmm (affirmative). It just allows you to ask quite specific questions?

Dr Megan Torvell:

Mm-hmm (affirmative).

Dr Tom Phillips:

Yeah.

Dr Megan O’Hare:

Okay, great. I think we’re coming to the end now, so is there… Oh, very quickly Megan, because I’ve said at the beginning we might get onto the-

Dr Megan Torvell:

Oh, yeah.

Dr Megan O’Hare:

What’s your role of Dignity and Wellbeing contact?

Dr Megan Torvell:

We all know that science can be quite tricky sometimes? Not just science, lots of jobs, the high-pressure jobs. Basically as a Dignity and Wellbeing contact, I’ve been on some training courses which have helped me in learning what the procedures are at the university, and the point of the role is primarily a support role, so I’m just around to listen to people, if they’re having a hard time. But the training courses mean that I am vaguely, hopefully aware of where the procedures that are in place, so if someone’s having some work problems or home problems or they need some mental health support then I’m able to point them in the right direction to get the help that they need.

Dr Megan Torvell:

And then there’s also loads of really great schemes in the university that people aren’t necessarily aware of, so it’s drawing attention to things like, “Oh, you guys should all be getting out and doing some exercise and there’s this great walking group,” or that sort of thing. And also kind of standing up for people’s wellbeing a lot of the time, you have PAs who are a little bit over-excited about getting the work done and maybe not super understanding, and it’s about saying, “Okay, but let’s consider these people and their wellbeing,” and that sort of thing-

Dr Megan O’Hare:

And don’t talk about how when you worked in America you worked 16 hours a day and you picked [crosstalk 00:43:56]

Dr Megan Torvell:

Yeah, not healthy!

Dr Megan O’Hare:

-for not doing that.

Dr Megan Torvell:

So Cardiff’s very good at trying to encourage a really good working environment and looking after people’s mental health, and I think Dignity and Wellbeing contacts are kind of common across universities? I’m not sure how common, but they have them in Edinburgh University when I was there as well.

Dr Megan O’Hare:

Also at UK DRI place. Just com-

Dr Megan Torvell:

Yes, but completely unrelated, because it’s not a DRI thing. But yeah, so we’re basically just there to promote health and wellbeing in work.

Dr Megan O’Hare:

Great. I think that is a very lovely end to today’s podcast. So I’d like to say thank you very much to everyone. Thank you.

Dr Megan Torvell:

Thank you!

Dr Sarah Carpanini:

Thank you.

Dr Tom Phillips:

[inaudible 00:44:46]

Dr Megan O’Hare:

And we will have profiles of all today’s panellists on the website, including details of their Twitter accounts, if they have them. This is the point where at least half of the people go “Oh I don’t have one.”

Dr Megan O’Hare:

If you have any questions, please join our WhatsApp group, chat to people about it. And finally, please remember to like, subscribe, and leave a review of this podcast through our website, iTunes, Spotify, Stitcher, Podbean and SoundCloud, and all the other places you find our podcast. And remember to visit our website for other information to support your work. Thank you!

Voice Over:

Brought to you by dementiaresearcher.nihr.ac.uk, in association with Alzheimer’s Research UK and Alzheimer’s Society, supporting early career dementia researchers across the world.

END


Like what you hear? Please review, like, and share our podcast – and don’t forget to subscribe to ensure you never miss an episode.

If you would like to share your own experiences or discuss your research in a blog or on a podcast, drop us a line to adam.smith@nihr.ac.uk or find us on twitter @dem_researcher

You can find our podcast on iTunes, SoundCloud and Spotify (and most podcast apps).

This podcast is brought to you in association with Alzheimer’s Research UK and Alzheimer’s Society, who we thank for their ongoing support.

Leave a comment

Your email address will not be published. Required fields are marked *

Get all the support you need sent straight to your inbox. Research news, oppertunities, blogs, podcasts, jobs, events, funding calls and much more – every friday!

No Thanks

Translate »