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Host – Dan Keller
Hello, and welcome to Episode Forty-Five of Multiple Sclerosis Discovery, the podcast of the MS Discovery Forum. I’m your host, Dan Keller.
This week’s podcast features an interview with Dr. Simon Hametner, who discusses the role of iron in multiple sclerosis. But first, here are some of the new items on the MS Discovery Forum.
According to our curated list of the latest scientific articles related to MS, 59 such articles were published last week. To see the list, go to msdiscovery.org and click on Papers. We selected two of those papers as Editors’ Picks. One, published in Nature Reviews Neurology proposes a definition of aggressive multiple sclerosis as well as a treatment algorithm. The other editor’s pick, published in the journal Neurology, reports on a randomized, placebo-controlled study on patients switching from natalizumab to fingolimod, concluding that shorter washout periods may be better.
Our Drug-Development Pipeline includes continually updated information on 44 investigational agents for MS. During the past week we added 3 new trials, we updated information on 2 other trials, and we added 9 other pieces of information. The drugs with important additions and changes are daclizumab, dimethyl fumarate, fingolimod, interferon beta-1a, laquinimod, and natalizumab. To find information on all 44 compounds, visit msdiscovery.org and click first on Research Resources and then on Drug-Development Pipeline
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Now to the interview. Dr. Simon Hametner works with Hans Lassmann at the Medical University of Vienna in Austria. We spoke about iron accumulation in MS in cells of the central nervous system and what iron may be doing.
Interviewer – Dan Keller
Let's talk about iron and neurodegeneration. What specifically are you looking at?
Interviewee – Simon Hametner
We are looking at the formalin-fixed, paraffin-embedded brain tissue from multiple sclerosis patients and controls, and we're looking, for example, at iron in these tissues. We're also looking now at proteins which are engaged in the management of iron in these tissues, for example, now.
MSDF
What are you finding different in MS patients that you don't see in healthy people?
Dr. Hametner
So we see iron accumulation, for example, in microglia and macrophages in MS, which are related to MS lesions. There are, for example, some MS lesions which have macrophages around those lesions, and we don't see much of iron in macrophages and microglia in healthy control tissue. We also see iron loss in multiple sclerosis because the iron is normally stored in oligodendrocytes in the controls. And this is also the case for MS, but in MS we also see a loss of this iron in the oligodendrocytes, especially at the oligodendrocytes which are closed to MS lesions.
MSDF
Do you know the mechanism of why you're seeing these differences in iron?
Dr. Hametner
We are now performing the research to find about these mechanisms. We have some prior indications, for example, hephaestin upregulation on oligodendrocytes in the vicinity of the lesions, but these data were not so straightforward. We are now also looking for ferroportin; ferroportin is an iron exporter of glial cells, it's actually ubiquitously expressed in mammalian cells. And all the glial cells also can express ferroportin, and we found it also in the oligodendrocytes; we now undertake this research. We think that oligodendrocytes really upregulate ferroportin and hephaestin in order to export iron.
MSDF
Is the iron detrimental?
Dr. Hametner
It depends. We don't think that it is, per se, detrimental; we see loads of iron in the deep grey matter nuclei and it seems that the brain can handle that quite well. But if there is even a minor amount of iron in the extracellular space even in the ferrous form – because iron normally is stored in the ferric and the trivalent form in ferritin – but if we see even minor amounts in the ferrous form, then it might be detrimental at very low amounts actually.
MSDF
Is this a result or a marker of what's going on, or does it really contribute somehow to the disease?
Dr. Hametner
This is a very interesting question. We think that iron really colocalizes or is found and accumulated at sites where things are going on with these lesions which accumulate iron in the microglia and macrophages around them. On the other hand, you can detect it very nicely with magnetic resonance imaging today. So we think that on the one hand it does play a role in the disease pathogenesis, and on the other hand we think that we can detect really these sites of iron accumulation, for example, around MS lesions.
MSDF
Are you doing this only on fixed patient tissue, or do you have animal models of this; how are you exploring it?
Dr. Hametner
We have this fixed material on the MS, and I think it's really important to also characterize the human material in very detail to perform all the necessary analysis to characterize what's going on in the human tissue. But, of course, as you mentioned animal models, it's very important to look at the EAE models. And collaboration partners have done that from McGill University in Montreal, Juan Zarruk and Sam David, and we are collaborating with them. And actually now they have been looking at some iron transporters and we are looking at exactly the same iron transporters now in the MS tissue. And they have found it in the same cell types, these iron transporters, in the EAE model being upregulated in the course of EAE as we see now in the MS tissues actually. So we really look for confirmation also from animal models from our collaboration partners.
MSDF
And does this work with various kinds of animal models, or is it restricted to the EAE?
Dr. Hametner
This survey has now been performed on the EAE, so it is a mock EAE actually and that they have performed a relapsing-remitting mock EAE in the chronic EAE model, and they have characterized those proteins, but they also do spinal cord injury models and they have performed a very interesting experiment on iron-loading in macrophages in the course of spinal cord injury where the iron gets into the macrophages possibly from a hemoglobin source from erythrocytes in the traumatic lesional tissue. And we think that regardless of the source of iron, it has these detrimental effects in the macrophages and triggers them to have a pre-inflammatory – or so to speak, M1 state – and are detrimental to the surrounding tissue.
MSDF
This is macrophages or also microglia?
Dr. Hametner
So in the spinal cord injury model, it was mainly macrophages. In the acute phases of the EAE at the peak of the disease, it was also mainly macrophages, but later they also found iron in the animal model within microglia, as we do also in MS. We have these early lesions where there are a bunch of macrophages in these classical active lesions, and these are mainly macrophages, and if they are iron-loaded, it is in the macrophages. But for the later lesions for these chronic active lesions which have this iron ring around the lesion, we find it also within macrophages but also microglia.
MSDF
So does this change the oxidative environment inside the macrophage?
Dr. Hametner
That's a good question. We think that it does change something with the macrophages because they seem to die. So we have these dying macrophages in the EAE model, as they have observed it, but in the MS we saw this dystrophic microglia at the lesion edge. So these are microglia which are highly iron-loaded probably for some time, and they have these nice processes. And if these processes get those beads and the process fragmentation and these process budding and blips in the processes, we call them senescent or that dystrophic microglia. And we have indications that this is really related to the iron load of this microglia. And then they get diminished towards the inactive centers of the lesion. So we think that at the edge of chronic active or slowly expanding MS lesions, these get iron-loaded in microglia and they don't handle it quite well, and then they die and get diminished towards the inactive centers.
MSDF
So when they die, do they release this and is it affecting other cells?
Dr. Hametner
We believe so. We think more or less that it is necessarily released into the extracellular space if an iron-loaded cells just dies by necrosis, or apoptosis, or something in between. So it is just released into the extracellular space. It has to be taken up by other cells; for example, other microglia, or other macrophages, or even astrocytes; it seems that it is really liberated. But, of course, it is hard to say whether iron within a specific microglia has been acquired by some other microglia which has died, or by some oligodendrocyte which has died, or even another source. But the fact is although we are sure that they have really accumulated lots of iron, and given actually the concentration of iron in these microglia and the surrounding tissue, we do think that there must be other sources than only oligodendrocytes by which iron gets into these microglia.
MSDF
Where do you go from here? What do you see the steps in the research?
Dr. Hametner
I think it is necessary to characterize these rings around lesions which have these iron-loaded microglia and macrophages, to characterize at which disease phases these rings occur, and, of course, this is very interesting because you can use it in vivo. Because one of the things we are really sure is that we can image iron within microglia at the lesion edge of those lesions very nicely at 7 Tesla of magnetic resonance imaging; we are very sure that this is iron then within microglia and macrophages. And if we can relate pathologically the disease mechanisms or the degenerative actions going on in these lesions to the presence of iron, we then can also relate our in vivo findings from MRI with the things which are going on there, like neural degeneration and demyelination, for example.
MSDF
Do you find that the iron-sensitive MRI imaging correlates with duration of the disease or stage or clinical condition?
Dr. Hametner
Yes, we think so from our pathological material. So we think that in the progressive stage of MS, there are these lesions which are the slowly-expanding lesions, and they have these chronic activity, chronic demyelinating activity at the lesion edge. And we think it's a typical feature of progressive MS. It remains to be determined whether this also holds true in vivo. If you make an MRI, an iron-sensitive MRI, and you look for iron rings around MS lesions, for example, by susceptibility-weighted imaging or by quantitative susceptibility mapping or even Ultrastar imaging, if you look at these iron rings around lesions, it remains to be determined at which disease phase is, because in the pathological material we have more of the chronic cases and we have very few relapsing-remitting. So we cannot say what's really going on in the relapsing-remitting disease because we don't have this material pathologically.
MSDF
Right, you would have to find people in various stages who probably died from something else; they're not going to be advanced MS patients at that point. Is there some relationship of your findings to the idea of oxidative stress?
Dr. Hametner
Yes, we have these overactivity for malondialdehyde or E06, which is this antibody against oxidized phospholipids, and we have found actually by working performed partly in this lab that there is a higher activity for oxidative stress of various glial cells in the lesions. But as for the microglial degeneration, we did not see so many microglia being positive for these markers. So the microglia, they seem to die, but we only have these morphological features of dystrophic or senescent microglia actually from the pathological side. On adjacent side, if you stain for iron and you stain for oxidized phospholipids, you see partly that there is a 1:1 colocalization. But we don’t see these always actually.
I think what's really clear is that there is lots of oxidative stress in MS lesions, but even in early MS lesions which on iron stainings don't have so much iron, because on these early lesions we actually see predominant iron loss. If you have a very highly active MS lesion in the early stages, you see iron loss, and you will see also oxidative damage there. So there is also other factors leading to oxidative stress, like NADPH oxidase, for example, the p22phox, the functional subunit of NADPH oxidase, which we have shown in this lab that it is upregulated on macrophages and microglia, but also in the absence of iron.
MSDF
What tips the balance between loss and iron accumulation?
Dr. Hametner
That's an interesting question, actually a complicated one. You're right, we see on the one hand iron loss, and we see iron accumulation. So in the early stages, we see iron loss around MS lesions, in the MS lesions, because oligodendrocytes try to get rid of their intracellular iron possibly to prevent the iron efflux or iron liberation, which is uncontrolled if there is demyelination and oligodendrocyte degeneration actually. So we think that inflammation in the early phases of the disease leads to this efflux, which we think also involves not only oligodendrocytes, but also astrocytes. So we now think actually that oligodendrocytes probably efflux the iron towards astrocytes, and those astrocytes then might efflux it towards the periphery even. So I think inflammation is an obvious candidate to trigger this upregulation of iron efflux mechanisms.
I think what drives the iron accumulation within the microglia at the lesion edges is a different story. We think that these are two unrelated processes. On the one hand you have these iron loss mechanisms, the iron efflux mechanisms from the oligos leading to iron loss in early MS lesions, and this seems to be a protective phenomenon; this is, so to speak, a protective reaction of the glial cells against oxidative stress. But in later lesions, in chronic active lesions with this iron accumulation within microglia and macrophages, and we don't think that they are really correlated. So we think these are two distinct processes going on in MS, probably even in two distinct phases of the disease.
MSDF
Is there anything interesting to add?
Dr. Hametner
I think the really crucial question is now to find out about the source of iron for microglia and macrophages, and even to find out about the source of iron for the oligodendrocytes. We are not so sure whether this is really transferrin-bound iron entering the brain and being loaded in oligodendrocytes, as you find it in control tissue, control brains. And we don't think that this is only this iron from the oligodendrocytes which is then loaded into the microglia and macrophages; we think there are additional sources possibly from the vasculature.
MSDF
Very good, thank you.
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Thank you for listening to Episode Forty-five of Multiple Sclerosis Discovery. This podcast was produced by the MS Discovery Forum, MSDF, the premier source of independent news and information on MS research. MSDF’s executive editor is Robert Finn. Msdiscovery.org is part of the non-profit Accelerated Cure Project for Multiple Sclerosis. Robert McBurney is our President and CEO, and Hollie Schmidt is vice president of scientific operations.
Msdiscovery.org aims to focus attention on what is known and not yet known about the causes of MS and related conditions, their pathological mechanisms, and potential ways to intervene. By communicating this information in a way that builds bridges among different disciplines, we hope to open new routes toward significant clinical advances.
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