Multiple Sclerosis Discovery -- Episode 32 with Dr. David Holtzman

[intro music]   Host – Dan Keller Hello, and welcome to Episode Thirty-Two 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. David Holtzman of Washington University in St. Louis about how a protein implicated in Alzheimer’s disease may also have a role in MS progression. But to begin, here's a brief summary of some of the latest developments on the MS Discovery Forum at msdiscovery.org.   We recently added a new data visualization to our growing collection. This one organizes every ongoing MS clinical trial—142 of them—into an interactive bubble chart. The size of each bubble represents the sample size of the trial, and the color indicates if the compound has been used to treat MS before. You can organize the chart 10 different ways, including by phase, compound, and sponsor. Go to the “Research Resources” section of our page and click on “data visualizations” to view it.   Yet another Phase 2 trial on autologous hematopoietic stem cell transplant was published last week. We reported on this trial’s results and how it was different from previous trials we covered. Like the last two studies we reported on, this current study yielded very encouraging results. To view all of the stem cell stories, go to the “news and future directions” section of our website and look for any story with an image of a mouse in a little white lab coat.   New research from the journal Neurology suggests that imaging measurements of the spinal cord and retina independently correlate to disability. Specifically, damage in the two structures was related to visual acuity and to the patient’s ability to discern vibration sensation. The authors suggested that clinicians may want to incorporate scans of the spinal cord and retina into their routine practice.   [transition music]   Now to the interview. Dr. David Holtzman is Chairman of the Department of Neurology at Washington University. He met with MSDF senior science journalist, Carol Cruzan Morton, at a recent Keystone meeting in Taos, New Mexico, to discuss how his work on apolipoprotein Ein Alzheimer's disease may be relevant to MS.   Interviewee – David Holtzman Most of my career has been focused on trying to understand the pathogenesis of Alzheimer's disease, as well as to develop better diagnostic and treatment methods. However, in doing that – in trying to study the science behind that disease – I've also worked a lot on how normal brain function might be related to not only Alzheimer's disease but just some of the proteins that are involved in both Alzheimer's disease and related disorders.   Interviewer – Carol Cruzan Morton We're at the Keystone meeting on neuroinflammation in Taos, New Mexico, and at the talk this morning you mentioned that there might be a connection between the ApoE and this protein involved in Alzheimer's and MS. Can you talk a little bit more about how that protein works normally in an Alzheimer's, and how you came to make that connection to multiple sclerosis?   Dr. Holtzman Sure. Apolipoprotein E first just in terms of a risk factor for Alzheimer's disease ApoE is present as a protein in all of our bodies. It's made in the brain; it's made by the liver; it's at very high levels in the bloodstream. ApoE plays a role in the bloodstream in transporting lipids around the body. It turns out, though, that if the only thing it did was to transport lipids in the blood then you would probably only need to produce it in the liver so that it was secreted into the blood. But interestingly, it's also produced in several other organs: the ovary, the testes, the brain, and a few other places. So in those other organs, it doesn't probably have exactly the same function that it does when it's made by the liver. But the form of the lipoprotein that's in the brain that ApoE is within is somewhat different than it is, for example, in the bloodstream. It's in what's called HDL or high-density lipoproteins in the brain.   MSDF That's a good thing, right?   Dr. Holtzman That's the good cholesterol. That's the good cholesterol in the blood. In the brain, it's not entirely clear what these HDL lipoprotein particles are really doing. So, for example, if ApoE is absent from the brain of a person, and there are people that have genetic mutations, they have no ApoE in their body…   MSDF Completely gone.   Dr. Holtzman Completely gone. And they have developed serious problems with cholesterol buildup in their arteries because they can't clear big lipoprotein particles from their blood, but their brain is okay, no problem. The people are born normal; brain is okay. And there are probably other proteins in the brain that may be able to takeover for its function in the brain; whereas in the blood that's not the case.   MSDF And when it goes wrong in Alzheimer's, what's happening…?   Dr. Holtzman So that's a different issue. So in Alzheimer's disease, there's no lack of ApoE. In humans, there's three different flavors of ApoE: ApoE2, ApoE3, or ApoE4. And there's a very, very subtle difference between the ApoE2, 3, and 4; just really, really small difference. So brain function in people that are of different ApoE types is normal when they're born and when they grow up and as adults. But for some reason – which we'll talk about in a moment – when people have the ApoE4 form of ApoE, it causes a higher risk for Alzheimer's disease probably because it's promoting the buildup of one of the proteins that's really important in causing Alzheimer's disease earlier. So this amyloid protein that builds up in Alzheimer's is strongly influenced by the form of ApoE that you produce. So if you make the E4 form, it's probably because amyloid doesn't get cleared away as well; it builds up earlier. And if you have the ApoE2 form, which is protective against Alzheimer's disease, it pushes out the development of amyloid deposition until very old ages, if ever. That may be something that's related to Alzheimer's disease that's distinct from what it might do in other diseases of the brain like MS, for example.   MSDF How did you make that connection to MS?   Dr. Holtzman Right. So over the years, there's been a number of scientists and physicians around the world who have studied the many possible functions of ApoE in the body. And for gosh it's been about 30 years or so, there's been reports that one of the things that ApoE does is to influence inflammatory cells: T cells, macrophages, etc.   MSDF All over the body or in the brain and spine?   Dr. Holtzman Yeah, in different locations actually. It's never been completely clear exactly what ApoE is doing to the immune system. A lot of studies individually show effects, but it's not entirely clear what it's doing. And so, I got interested in this personally a few years ago there was a prominent paper published suggesting that one of the things that ApoE does to the immune system outside the brain is to help present antigens to the immune system if they contain lipids. And so, that caught my attention because, one, ApoE carries lipids. And just naively I thought well if it helps present lipid antigens in multiple sclerosis the antigens that are being attacked generally are the lipid related antigens.   MSDF The myelin.   Dr. Holtzman The myelin, right, exactly. So I thought well that seems, you know, maybe there's something to this that one could study in relation to MS because of that.   MSDF And then how did you go about asking those question? Where did you start?   Dr. Holtzman Basically, I thought alright, well a lot of people who work on MS if they use animal studies use the model EAE. So we thought well some of my colleagues at Washington University have been using the EAE model for years – like many people have – and so we thought well the obvious experiment to try first is just compare animals that express ApoE in their body versus those that don't. And simply ask the question is there anything different about EAE in an animal that lacks ApoE or not? And so, first, we started working with Anne Cross and then later with Greg Wu together who are experts in using animal models of MS. And ultimately published findings showing – and a few other groups have worked on this, as well – showing that there appears to be decreased clinical severity of EAE in a slightly later onset of disease in animals that lack ApoE.   MSDF And what does that tell you…there might be a role or…?   Dr. Holtzman Obviously many other studies would need to be done to know if it has a role in human MS. But once we found that, particularly Greg's lab began to ask the question well if that's true what's the mechanism? If there is a mechanism that we could hone in on, is that something that seems logical based on what we actually know about ApoE already? And so, the things that kind of came out of our first series of studies was that – unlike what I initially had thought from this earlier paper – it doesn't appear that ApoE is modifying antigen presentation of cells or the ability of T cells to react against the brain. But something once T cells do get in the brain to attack myelin and other components, there's something about that ApoE is acting on at that point. It could be that it's involved in allowing the myelin to repair, or alternatively it could be that when T cells get into the brain and interact with other cells in the brain – like other immune cells like microglial cells or dendritic cells – that that interaction is altered by ApoE within the brain. That might make sense given that ApoE is highly expressed by macrophages outside the brain, and inside the brain it's highly expressed by what are called activated microglial cells. So kind of the macrophages of the brain. So that's where we kind of are now, and I think there's a lot more studies that could be done to really understand both that interaction as well as whether human ApoE causes the same effect that we saw in animals as mouse ApoE. Because they're not exactly the same; they're similar but not the same.   MSDF Is there other evidence connecting ApoE or its various forms with MS?   Dr. Holtzman There are human studies that have been done trying to ask the very simple questions of is the ApoE4, which is a risk factor for Alzheimer's, is that over represented in MS? Or is the ApoE2 form, which is under represented in Alzheimer's, is that protective against MS? And the studies on this some have suggested effects, some haven't. There's no clear answer. But I think if ApoE is involved in MS, it would be less likely to be involved in whether you get MS but more likely involved in the progression of the disease. And I know in the MS field one of the big areas now – now that there's so many studies and as well as treatments that have emerged that are quite effective at suppressing the initial phases of MS, the immune response phases – a lot the work is going into understanding this prolonged progressive phase of MS. And that's where ApoE could be important in sort of the repair and recovery of neurons and axons, for example. Because the fact it transports lipids between cells, maybe it has something to do with recovery of the brain after injury. And that's been speculated on for some time, although not as much work on that has been done in MS.   MSDF Has it been speculated on in MS or MS and Alzheimer's both or…?   Dr. Holtzman No, it's been speculated on after a variety of different brain injuries that it plays a role in redistributing lipids in the brain after injury, and that might be promoting recovery. So one possibility that still hasn't really been tested that I'm aware of in models of MS or in human MS is to whether that really happens for ApoE in the human brain or animal models.   MSDF Can that be tested now?   Dr. Holtzman Absolutely, absolutely. Those are some of the studies that I think are really critical as the next step.   MSDF Is it conceivable that the body of knowledge for Alzheimer's research on ApoE might yield a treatment for progressive MS?   Dr. Holtzman It's possible. I mean a lot of the understanding of what ApoE might be doing in the brain has really expanded because people have been studying Alzheimer's disease and its relationship with ApoE. So I can't imagine it wouldn't help with that because we've learned a lot so far.   MSDF Are there other treatments in the pipeline for Alzheimer's related to ApoE?   Dr. Holtzman There are. There's not too many things yet that have reached human trials, but there are groups trying to alter the level of ApoE in the brain or to alter its receptors in the brain as potential treatments for affecting Alzheimer's disease. So yeah, I mean those are the kind of things, as they advance, depending on what's found in regard to the relationship between ApoE and MS could be tried in MS. I don't see why not.   MSDF That's interesting. What else should I be asking?   Dr. Holtzman I think what scientifically what I think is really important to still sort out in this area is that when the innate immune cells of the brain – the microglial cells or even macrophages when they get into the brain – they produce tremendous levels of ApoE when that happens. And I think understanding what that protein is really doing in that setting could provide insight into future treatments. So that's what I think is really fascinating to try to understand.   MSDF Well if it happens in Alzheimer's, as well, it happens before the blood-brain barrier breaks down and then after it, it sounds like.   Dr. Holtzman Well, in MS, it's probably occurring after there's cell entry into the brain. But the upregulation of ApoE by these innate immune cells is much higher in MS than it is in Alzheimer's disease.   MSDF Oh, is that right?   Dr. Holtzman Yeah, yeah.   MSDF That's interesting. That's even more interesting.   Dr. Holtzman Yeah, I know. That's why it's really, really fascinating. I think one of the figures from the paper that we published last year from Greg's lab showed that the level of ApoE increasing in microglial cells versus similar cells that are present in the spleen of an animal is like 25 times higher in the setting of an EAE model than normal. So it's really, really high. Is it really doing anything, or is it just a byproduct? I suspect it probably is doing something. So that's what I think would be really interesting to figure out.   MSDF Thanks. Well I appreciate your taking time out at the Keystone meeting to talk with MS Discovery Forum.   Dr. Holtzman Yeah, it's great. Well good luck. MS is such a…the treatments that have been evolving are so exciting compared to Alzheimer's disease where we don't yet have good treatments. So I think there will be soon, but I think it's a great opportunity to even advance for ...   MSDF Is there a chance that the reverse could be true? That treatments existing for MS would be helpful in Alzheimer's?   Dr. Holtzman That's a good question. I don't know if any of the frequently used ones where you're preventing cell entry into the brain necessarily would be useful for Alzheimer's. But like one of the new drugs, Tecfidera, this oral medication does do some interesting things to cells in the brain that might be useful in a disease like Alzheimer's. So maybe there will be some things that we can translate.   MSDF I appreciate it. Thank you so much.   Dr. Holtzman Thank you.   [transition music]   Thank you for listening to Episode Thirty-Two 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 [email protected].   [outro music]