Host – Dan Keller
Hello, and welcome to Episode Seventy-three of Multiple Sclerosis Discovery, the podcast of the MS Discovery Forum. I’m Dan Keller.
Today's interview features Donna Osterhout, a cell biologist at Upstate Medical University in Syracuse, New York, USA. Dr. Osterhout talks about a new way of looking at myelin-making cells, which move and change shape in dramatic ways. Current MS drugs take aim at preventing new immune damage. In the future, researchers hope to figure out how to repair myelin and restore function.
But first, let’s look at new content on MS Discovery Forum. Spring brings rain, flowers, and a bouquet of scientific meetings related to multiple sclerosis. See the list at msdiscovery.org under the tab “professional resources.” MSDF sent the only journalist to cover the recent meeting of the American Society of Neurochemistry in Denver, but you can count on a blitz of news from the media pack at the next meeting on the calendar – the American Academy of Neurology in April, happening this year in Vancouver, BC, Canada. The number of research papers about multiple sclerosis has doubled in the last 10 years, and many findings are first reported at meetings before publication.
Moving on, let’s sample a few of the new papers we found in our weekly PubMed search of the world’s largest medical library, the National Library of Medicine. You can link to each week’s list of curated papers at msdiscovery.org.
Related to this week’s podcast, a new paper reviews the latest research about the molecular cues that allow precursor cells to mature and go through the stages of making myelin. These cues come from axons and from other surrounding tissue. Clinical drug development efforts focus on overcoming inhibitory cues, such as with the experimental agent anti-LINGO-1, now completing phase 2 clinical trials for MS and acute optic neuritis by Biogen. The review authors suggest future drugs to repair myelin could boost permissive and promotional cues, which may go wrong in disease. The paper is published by researchers at the Virginia Commonwealth School of Medicine in the journal Experimental Neurology.
Another report updates the Cochrane systematic review on teriflunomide, a daily oral medication for relapsing remitting MS marketed under the brand name Aubagio by Sanofi Genzyme. Cochrane’s systematic reviews are ranked among the highest level of medical evidence, because of the rigorous independent analysis of multiple studies, including randomized controlled trials. The authors write that, as a single drug, the high dose of teriflunomide was as effective as interferon beta 1-a, while the low dose was less effective. They recommended longer follow-up analyses and noted that the available evidence was low-quality, as well as subject to bias, in part because all studies were sponsored by pharmaceutical companies. In general, side effects were mild to moderate and do not usually lead to treatment being stopped, but the higher dose is more prone to cause these side effects. The study is available in the Cochrane Library.
The final editor’s pick this week takes a fresh look at how medical images transform a patient’s view of her own body. The paper describes an artistic collaboration between Devan Stahl, a bioethicist at Michigan State University with multiple sclerosis, and her sister Darian Goldin Stahl, a printmaker. The resulting art – some of it life sized – superimposes Devan’s narrative and MRI images with body photos. Devan wrote in the paper that the art collaboration has made it easier to talk about her MS. The paper is published in the journal Medical Humanities. If you're in town for the big Neurology meeting, you can catch Darian’s artist talk on April 17 at 2 pm at Malaspina Printmakers in Vancouver, Canada.
And now to our interview. We caught up with Donna Osterhout in Denver, Colorado at the March meeting of the American Society for Neurochemistry. She organized a symposium that told a new story about myelin-making cells. In different labs, researchers started looking for clues in the radical shape changes that occur in the cells in their normal process of making myelin. These oligodendrocyte precursor cells sprout “arms” to reach out and touch neighboring axons. Then they push out slabs of fatty membrane and wrap them around and anchor them to the axons. In multiple sclerosis and other demyelinating diseases, the immune system attacks this myelin wrap, and the cells cannot keep up with repair. The unprotected axons may be damaged or destroyed, causing the worsening disability of MS. Learning how the cells make myelin may pave the way toward new therapeutic agents to repair demyelinated axons and restore function. Dr. Osterhout spoke with our executive editor, Carol Cruzan Morton.
Interviewer – Carol Cruzan Morton
So we are here, in Denver, at the annual meeting of the American Society for Neurochemistry, and you've put together a very interesting panel on a new way of looking at myelin. So can you sort of set the scene for us when you're talking about the myelin research that you're working on?
Interviewee – Donna Osterhout
Well, myelin is a specialized membrane that is wrapped around axons; it occurs in the last step of development. And oligodendrocyte progenitor cells are the cells that form myelin. They are going to migrate out through the developing brain and they're going to extend processes that come in contact with axons that need to be myelinated. And when they get the appropriate signals, they are going to start a process by which they synthesize and extend a large membrane, which wraps around this axon many times and compacts and forms myelin.
The way that this happens has been a mystery thus far, but recent research suggests that there has to be a lot of rearrangements of the internal cytoskeleton for this to happen. And so the symposium was organized to talk about how the cytoskeleton might be changing to allow for this membrane wrapping and myelin formation.
Can you tell me more about the cytoskeleton?
The cytoskeleton is comprised of specialized proteins within cells, and every cell has a cytoskeleton; it gives it shape, but it also allows it to migrate, differentiate, and extend processes, so cells wouldn't be able to do much without a cytoskeleton. And in the case of oligodendrocytes, there are a lot of cytoskeletal rearrangements that occur to allow for myelination.
Can you tell me more about the emerging view about how myelination may be working based on this new way of looking at it?
Initially, we know that there are early signals that trigger extensive process outgrowth from these cells. Once the axon sends a signal to the oligodendrocyte progenitor cell, they start to put out many, many processes, synthesize myelin proteins, and make this big membrane that will wrap around the axon. What winds up happening is that in the past everybody thinks that we've needed a driving force so that something pushes this forward, and it had been thought that perhaps the actin cytoskeleton was the driving force behind this.
The newer research indicates that initially you have to have signals that trigger the process outgrowth, but this is followed by an actual disassembly of the actin cytoskeleton. So it's somewhat opposite of what we had thought previously.
Can you tell me more about the steps that are involved in the process of myelinating that you and your colleagues have been discovering?
Well, the initial step is the activation of a cellular kinase called Fyn tyrosine kinase; this is the earliest step in the differentiation of these progenitor cells. Fyn will be activated by any number of signals from the axon including, for example, glutamate that's released. And once Fyn is active, it initiates a rearrangement of cytoskeletal proteins called microtubules in order to facilitate process outgrowth so we can extend processes to form this membrane.
In later stages, then we have Fyn helping to trigger the synthesis of myelin proteins, and then you start to get other proteins active that will disassemble the actin cytoskeleton. There is even some evidence that perhaps myelin basic protein can do this. So Fyn signaling will turn on early and promote the synthesis of myelin basic protein, and then myelin basic protein will proceed down these processes and help to disassemble the actin cytoskeleton so the membrane can wrap around the axon.
Can you describe what the cells look like when they're going through this process?
Well, this is really interesting to study, especially in vitro. You can set up myelinating cultures of oligodendrocyte progenitor cells. They're very simple cells, they're like bipolar, two to three processes, and that's the earliest progenitor that we might look at. But once you trigger differentiation, they start to put out processes in a somewhat predictable manner. They will first extend five processes, and then these five processes start branching And they produce these intricate branches. At some point these mature cells will actually look like a lace doily; they are spectacular with the cell body in the center and all these highly branched processes surrounding it. And then you see a transformation of these processes into this huge membrane sheet, and in the absence of an axon it's just going to cover the tissue culture dish; it's amazing how large this can get. But if you had an axon in the culture, this membrane sheet would just form myelin. They would form a myelin segment wrapping around the axon.
That’s so interesting. And then can you say, adding to that picture, the steps that are happening in those process that you and your colleagues have been discovering?
So when you have the initial process outgrowth, you have Fyn tyrosine kinase active, and that facilitates the initiation and that extensive process outgrowth. But the transition between the process outgrowth and the formation of membrane sheets is going to be the disassembly of the actin cytoskeleton.
And that's the big news is that the actin cytoskeleton is breaking down instead of pushing the myelin forward as it's making its multiple wraps around?
Yes, this seems to be the way that this is happening mechanistically. The formation of that myelin membrane requires the actin disassembly, and two of the speakers that we had in our symposium gave evidence to this, using several different experimental systems. And then ultimately when you're going to anchor this myelin sheath, and you can get some specializations in the axonal membrane, and this is what one of the speakers talked about, anchoring the perinodal loops, kind of the ends of the myelin segment. And so we have a process by which we have extensive process outgrowth triggered by Fyn. Then once you get the process outgrowth, you have actin disassembly and you form these membrane sheets, and then they would wrap around the axon, forming myelin, and then you would stabilize it with special proteins in the axon that stabilize the ends at the perinodal loops.
So what does this have to do with diseases like multiple sclerosis?
That's a very good question. If we understand what goes on in development, then we might be able to predict how we could facilitate this process in a demyelinating disease like multiple sclerosis. We do have oligodendrocyte progenitor cells in our brain and spinal cord. They persist as a population throughout adulthood. And any time you have a lesion or a trauma to the brain, and especially if you get demyelination, then you'll have these cells migrate to the area of demyelination. And if we can encourage them to remyelinate, they would undergo the same steps.
We have shown evidence that the inflammation and other conditions in a demyelinating disease upregulates chondroitin sulfate proteoglycans, and these can actually inhibit the process outgrowth and remyelination by oligodendrocytes, because they ultimately inhibit the activation of Fyn kinase.
So if you're considering a disease process, you want to stimulate these steps. And you want to look for agents that might trigger and make sure that these steps proceed, or neutralize things that would be present in the lesion that would inhibit this.
One interesting aspect of your work, and perhaps of science more generally, is that some of these discoveries with relevance to multiple sclerosis come from your work on spinal cord injury. Can you talk about how that works in science?
Well, spinal cord injury is another type of lesion, it's a specialized lesion; you have damage to axons as well as demyelination due to trauma. But in diseases in general in the brain and the spinal cord, whenever you have an injury process or inflammation or some kind of destruction of tissue, you get an inflammation and immune influx, and you will get a process called reactive gliosis. And this is common to many diseases that you see in the brain. For example, you can see it easily in spinal cord injury, it's been well documented. You can see these proteoglycans' reactive gliosis in multiple sclerosis, you can see it in Alzheimer's disease, Parkinson's disease, and other conditions, because they all have a common element that you've got some kind of inflammation occurring and tissue destruction occurring at a specific place.
Getting back to multiple sclerosis and the work on how cells myelinate axons, what are the next big questions that you and your colleagues are asking?
Well, there still are a lot of questions about exactly how this myelination process is accomplished even during development; we don't fully understand all of the triggers that would activate this process. And, likewise, we don't always understand things that might inhibit this process. So we need to more fully characterize what's going on in development so that we can take a look at it in the remyelinating situations, either in spinal cord injury, or multiple sclerosis, or any other demyelinating condition.
Well, that's really interesting. Well, thank you for taking the time to explain the research.
And thank you for your interest; it's been my pleasure.
Thank you for listening to Episode Seventy-three 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 Carol Cruzan Morton. Msdiscovery.org is part of the nonprofit 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.