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Host – Dan Keller
Hello, and welcome to Episode Seventeen 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. Hans Lassmann about the usefulness of animal models for studying multiple sclerosis. But to begin, here’s a brief summary of the developments at the MS Discovery Forum at msdiscovery.org.
In the progressive stage of multiple sclerosis, some astrocytes appear to upregulate genes that intensify inflammation and neurodegeneration. Researchers think that genetic changes cause astrocytes to release a fatty molecule that beckons inflammatory monocytes from the blood into the brain. A drug, miglustat, currently used in the treatment of Gaucher’s disease, may be a good candidate to repurpose as a drug to inhibit astrocytes from initiating this destructive process.
The so-called “long life” protein, Klotho, may hold the keys to remyelination. Named after the Greek goddess responsible for “spinning the thread of life,” an abundance of Klotho leads to longer lifespans in mice. The protein has also been associated with numerous age-related conditions such as Alzheimer’s disease. Recent research noted that reduced Klotho was associated with myelin degeneration in normal, aging Rhesus monkeys. A small molecule, currently known as ‘Compound A’ can promote Klotho in the CNS of mice, enhancing remyelination in the cuprizone mouse model.
We recently released a new data visualization comparing various characteristics – such as age, gender, and EDSS scores – across 74 clinical trials. You can look at each characteristic in every trial, or compare the means of all the trials. To view, go to the “research resources” tab at msdiscovery.org and click on “data visualizations.” Then click on “RRMS and CIS – Baseline Characteristics.”
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Now to the interview. Dr. Hans Lassmann studies the pathogenesis of inflammatory diseases at the Center for Brain Research at the Medical University of Vienna in Austria. He met with MSDF at the MS Boston meeting in September to discuss demyelinating disorders.
Interviewer – Dan Keller
In terms of what we can learn from other demyelinating diseases, ones caused by infectious agents, how can this shed light on the processes and possible treatment of MS?
Interviewee – Hans Lassmann
That depends, obviously, on the models which we are looking. I think there is a major difference between multiple sclerosis and these other experimental models, because the experimental models which really induce large areas of demyelination always are associated with infection of oligodendrocytes. But in multiple sclerosis, there is actually no indication that oligodendrocytes are infected. Now this has consequences that also the demyelination is different in these experimental models because it follows the death of single infected oligodendrocytes. That means that lesions have, more or less, some sort of moth-eaten edges where single oligodendrocytes are falling apart with small pieces of demyelination in between intact myelin, whereas in multiple sclerosis the demyelination is a sharply demarcated lesion which does not follow the oligodendrocyte territories. What we, however, can learn from the models is the question how the brain handles an infectious process in the white matter with respect to inflammation and the amplification mechanisms of tissue injury in the demyelinating process.
MSDF
So are they similar enough that we can discern something useful from it, even though the patterns do seem to differ in some ways?
Dr. Lassmann
Yes, we can. For instance, there is a major difference between the autoimmune models which we have and the virus models. The autoimmune models are predominantly mediated, or driven, by an MHC class 2 CD4-positive T cell response, whereas the virus models are predominantly driven by a CD8 T cell response. Interestingly, in multiple sclerosis, also the CD8 T cell response dominates. So we can actually learn a lot from these models on the mechanisms of CD8-mediated inflammation in the brain, and also on what are the consequences of a CD8-mediated inflammation in the brain with respect to tissue injury.
MSDF
What about some of the diseases that are closely associated with MS but are distinct from it, like neuromyelitis optica and, I guess, concentric sclerosis and others, how do they shed light on things, if they do?
Dr. Lassmann
I think they shed a lot of lights on that. Let’s take first neuromyelitis optica. Here we are in a very favored situation because we know it is an autoimmune disease and we know the specific target antigen, and the specific target antigen is a water channel in astrocytes. So from that we have actually learned how antibodies against these astrocytes actually induce the tissue injury, in that case, by first destroying the astrocytes themselves, and then secondarily leading to oligodendrocyte destruction and demyelination, and also some axonal loss. So that actually is a perfect model for a scenario where T cells and pathogenic antibodies play a role in disease mechanisms, and that is apparently also the case in a subset of multiple sclerosis patients, but only in a subset.
MSDF
How does the glia enter into this, both as a target and maybe as a mediator or effector?
Dr. Lassmann
Now, obviously, the prime target in multiple sclerosis is the oligodendrocyte and the myelin sheath, but there is obviously also pathology in other glial cells. There is an astrocytic pathology, and there is also a microglia activation and pathology in these cases. Now, the astrocytic pathology itself may also contribute to the lesion propagation because when astrocytes are also destroyed in the lesion, or primarily destroyed in the lesion, it will also secondarily lead to the oligodendrocyte loss and demyelination. This is a classical example of neuromyelitis optica.
MSDF
Is that through mechanisms of macrophage activation, or debris, or mediator release, or toxic release?
Dr. Lassmann
No. From the astrocyte pathology, it’s so that the astrocytes and the oligodendrocytes are connected with gap junctions, and the astrocytes play a major role in supporting the energy demand of oligodendrocytes. So if you kill out the astrocytes, the oligodendrocytes starve to death.
MSDF
Now that you bring up energy, can we learn anything from mitochondrial diseases and their consequences?
Dr. Lassmann
Yes, here we can learn a lot because the mitochondrial injury and damage is in the center of neurodegeneration and demyelination in multiple sclerosis. In that case, in the disease the mitochondrial injury is apparently driven and induced by oxidative injury, but that it leads in a secondary consequence also to mitochondrial gene deletion, so to deletions of mitochondrially-encoded genes. And here the mitochondrially-encoded gene deletions are also present in many mitochondrial diseases, and for that, obviously, mitochondrial diseases are perfect models to study these aspects of multiple sclerosis pathogenesis. A key issue, for instance, is the mechanisms of mitochondrial quality control. Normally, it’s so that the damaged mitochondrion is just removed from the cell in autophagosomes. But this needs very specific mechanisms of recognition. If this quality control is actually missing or disturbed, then these damaged mitochondria can expand, can clonally expand, and then you get an upward cells having more and more and more damaged mitochondria. And that’s, for instance, also a mechanism which is very prominent in mitochondrial diseases.
MSDF
Is that a failure of phagosomes? Is there a defect at that level?
Dr. Lassmann
No, I think it’s rather a defect in the mitochondrial proteins, because the mitochondrial proteins are expressed on the surface indicating the phagocytic system, whether they are intact or damaged. And when this process is more or less disturbed, then the phagosomes don’t recognize the damaged mitochondria anymore.
MSDF
What are you doing now? What sort of paths are you pursuing in terms of these things that we’ve been discussing?
Dr. Lassmann
We have in principles three major projects. The first is that we try to define more precisely what is the nature of the inflammatory response in multiple sclerosis and in to what extent this is different from what is seen in the respective experimental autoimmune models. Now, the second project deals with mechanisms of demyelination, and here the key question is there is soluble demyelinating factor in multiple sclerosis, but it’s not very clear what exactly the soluble factor is; it could be demyelinating antibodies, and that can be modeled in experimental models, like autoimmune encephalitis. But many data suggests that there must be other factors which are not immunoglobulin and not antibodies which are responsible for this demyelination. And then the third project deals with the progressive stage of multiple sclerosis, and here it’s the central pathogenic pathways, oxidative injury and mitochondrial injury. And our projects now go in the direction of what is the course of this massive oxidative damage in multiple sclerosis, how does that relate to mitochondrial injury, and what is the consequences then on the tissue with respect to energy deficiency and other things.
MSDF
In progressive disease, do you see a shift towards more mitochondrial damage and oxidative damage or stress?
Dr. Lassmann
We have oxidative damage already in the early stages of MS, but in the early stages of MS the oxidative injury seems to be mainly driven by the inflammatory component; that means by inflammation, activation of microglia and then the production of reactive oxygen-producing enzymes. In the progressive stage of MS, we get additional amplification factors for oxidative injury, and they are related to brain aging and related to accumulation of lesion burden. So what we get, on the one hand, an age-related increase of iron in the human brain, and iron can massively potentiate oxidative injury by a reaction which is the so-called Fenton reaction. The second thing is that you have accumulated tissue injury in multiple sclerosis with retrograde and anterograde degeneration, and that leads to progressive microglia activation, which then can actually be transformed more easily in cytotoxic microglia cells by additional proinflammatory stimuli. And the third mechanism is that the mitochondrial injury increases, and in particular the mitochondrial gene deletion and the clonal expansion of defective mitochondria expand in the progressive stage with disease duration. And mitochondria, when they are damaged, they can liberate electrons, and the electrons can actually, again, react with oxygen, producing a reactive oxygen species. And so this is a more or less self-amplifying process which then leads to enhancement of neurodegeneration and demyelination.
MSDF
Is there a role for glutathione here?
Dr. Lassmann
Yes. Glutathione is one of the key molecules for the oxidative injury, and obviously this is one of the players, but it’s only one.
MSDF
It’s a player in the injury or in limiting injury?
Dr. Lassmann
That is not entirely clear yet.
MSDF
What have we missed or you think is important to discuss or add?
Dr. Lassmann
There is certainly in the multiple sclerosis therapy also the tests to increase remyelination and possible regeneration in the lesions, including stem cell therapies or increasing remyelination by soluble factors by cytokines and growth factors. This is all very interesting, but the key point is that as long as the disease process is active, newly-formed myelin is destroyed relatively quickly.
MSDF
It seems that there’s almost an analogy to osteoporosis where it’s a balance between formation and destruction. Is there ongoing remyelination or turnover in the healthy brain?
Dr. Lassmann
Yes, there is a myelin turnover in the healthy brain, but there is also a profound attempt for remyelination in multiple sclerosis lesions. And what you see even in the early stages in very active MS lesions, you always find signs of ongoing remyelination. But, interestingly, in these early stages, really established remyelination is generally missing, and we have performed a study on that issue showing that if you have disease activity, the remyelinated areas are actually more prone to show new demyelination compared to the normal old myelin which is in there. So that suggests that this remyelination is present and all attempts are present, but this process is relatively instable as long as the disease process is active.
MSDF
Is there a thought of being able to inhibit that further, or accelerate a destructive process in these remyelinated areas?
Dr. Lassmann
I think this is not really specific for the remyelinated areas. If we are a [?], for instance, that disease process or the progression of the tissue damage can be stopped, for instance, with measurements making some sort of mitochondrial protection, or with certain antioxidative therapeutic strategies, then it will certainly be beneficial both for the old lesions and the newly formed lesions and the remyelinated lesions. But that’s more or less something which has to be solved before we can think of really effective remyelinating strategy.
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Thank you for listening to Episode Seventeen 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.
We’re interested in your opinions. Please join the discussion on one of our online forums or send comments, criticisms, and suggestions to editor@msdiscovery.org.
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