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Glaucoma usually affects older people, but a form of the eye disease can strike younger patients, including children. That keeps School of Chemistry and Biochemistry Professor Raquel Lieberman hard at work studying wayward proteins that may hold the key to new treatments for the second-leading cause of blindness.
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Hello and welcome to ScienceMatters, the podcast of the Georgia Tech College of Sciences. I’m Renay San Miguel.
When it comes to the substances inside your body, nothing works harder than protein.
Your body contains millions and millions of tiny protein molecules.
They’re made of chains of amino acids, and they perform many functions. They form structure and support for cells. They transport smaller molecules throughout our bodies. As antibodies, they seek out viruses and other invaders. As hormones, they trigger processes in tissues and organs. As enzymes, they digest our food. They help our eyes see, and our brains analyze data.
Proteins do all that when everything works right. When proteins misbehave, bad things can happen. That’s when they draw the attention of Georgia Tech Professor Raquel Lieberman of the School of Chemistry and Biochemistry.
Her work on a protein associated with an inherited, early-onset form of glaucoma has yielded valuable data that is helping us learn more about this disease. Her work includes the first 3-D graphic representation of this particular protein.
The fact that this type of glaucoma can affect younger people, including children – not the usual patients for the disease -- is driving her research.
Raquel Lieberman: Our lab is interested in the category of diseases called protein-misfolding disorders. That includes diseases like Alzheimer’s and glaucoma. Proteins are the worker molecules in your body that help it accomplish all the tasks that you need to survive and there are very complicated mechanisms that make sure that only correct proteins get to do the job that they need to, and so we’re interested in what happens when your body makes the wrong protein and why it causes disease.
Renay San Miguel: That was Lieberman in 2010, when she received a Pew Scholar Award in Biomedical Science, a four-year grant to support her research into protein misfolding.
She’s won more funding grants since then, thanks to her work on glaucoma, the second leading cause of blindness, according to the World Health Organization.
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Renay San Miguel: Before we get to Lieberman’s lab work today, let’s talk more about protein folding.
When everything is right, proteins fold into 3-dimensional shapes that correspond to their specific function in your body. When they encounter a problem getting into the right shape, other proteins can help to make sure they transform properly.
But when a protein still doesn’t get to that proper three-dimensional shape, that’s when neurodegenerative diseases like Alzheimer’s, Parkinson’s, cystic fibrosis, and glaucoma can develop.
Here’s Lieberman explaining more about this process in late 2018 in her office in the Parker H. Petit Institute of Bioengineering and Bioscience.
Raquel Lieberman: Your cells are constantly making new molecules and getting rid of old ones; that’s called homeostasis. And there are genetic mutations that are encoded in your DNA that will prevent a protein from adopting its correct structure. And when that happens, there’s a whole suite of other molecules in the cell that detect that defect and triage it and say Let’s recycle this. This is not going to work. In addition, as cells in our bodies get older, the machinery to maintain homeostasis doesn’t work as well. And so even without a mutation, you can get some accumulation of proteins that are not quite folded right even though they, in principle, should be able to fold correctly. And so that causes cell stress. And that is something that affects many different kinds of diseases—age-onset diseases like Alzheimer’s, for example.
Renay San Miguel: Lieberman focused on protein misfolding during her postdoctoral studies at Harvard Medical School and Brandeis University starting in 2005. She was already deep into Alzheimer’s research when she learned about myocilin, a protein that may hold clues to glaucoma’s causes and treatment.
Raquel Lieberman: In the course of the 2 and 1/2 years that I was there, I learned a lot about protein misfolding and how proteins can aggregate, and those aggregates can be toxic to neurons and can cause Alzheimer’s disease. And I also had a side project where I was collaborating with some folks in industry, and I was kind of looking for a new project that I would begin when I started my career that was really just different from anything I had seen before, and this collaborator in industry said, “Hey, have you seen these few papers on this protein called myocilin?” He said, “I think you might have the expertise that, you know, maybe you could offer something to this project.”
So I read there were probably only 10 or so papers at the time, and I said “You know, I think I can make an impact here.” And this could be extremely interesting applying what I had learned about Alzheimer’s disease research to this new system that seemed to have a lot of potential to have parallels with this other very well-established field. So what I did is I applied for some seed grants, and actually I got them. I was able to get the project started, show that I had something interesting to share, a new perspective, and here I am sitting like 11 years later still working on the same project.
Renay San Miguel: In glaucomas, mutant myocilin proteins slowly gunk up drainage pathways between the iris and cornea, causing increased pressure on the eye. The most common kind is open-angle glaucoma, where there is space between the iris and cornea, so that clogging takes longer to develop. In closed-angle glaucomas, there isn’t as much space, which can mean faster clogging and a sudden change in eyeball pressure. In addition, misshapen proteins by themselves can damage or kill cells – that is, they are cytotoxic.
As Lieberman continued her research, she learned just how prevalent, and insidious, glaucoma can be.
Raquel Lieberman: Glaucoma affects four percent of the population over 40, OK? So if you get glaucoma younger than 40, that’s called early onset. So for the listeners who are perhaps thinking they are nearing an old age, they are probably not. And it affects 70 million people worldwide, including one to three million children who have defects in this protein that we study. That’s a huge number of kids who are ultimately either taking drugs to control their eye pressure in the hopes that they won’t get blind before they reach old age or otherwise going blind. Glaucoma is actually a collection of eye diseases that have a particular, I don’t know, medical definition. So anyone that has gone to the eye doctor knows that the eye doctor checks for pressure and they also look at the back of your eye and that’s because they are trying to understand kind of what your baseline is so that if your pressure goes up or if something looks a little funny in the back of your eye, in your retina or the optic nerve, that maybe you’re developing symptoms of glaucoma. But there’s no like silver bullet or like a diagnostic that says for sure you have this disease.
Renay San Miguel: When the optometrist shoots a puff of air into your eye, is that the glaucoma test?
Raquel Lieberman: Yes. So that’s where they’re testing your eye pressure. And elevated pressure in your eye is like a major risk factor for developing glaucoma. And it’s a weird thing because what does pressure in the front part of your eye have anything to do with your retina degenerating, right, losing your vision in the back of your eye? Nobody really knows the answer to that question, but there is a very close connection between those two.
The protein we study, myocilin in the inherited form of open-angle glaucoma, has one of many genetic mutations, and that causes that protein to not form its correct shape and that is cytotoxic to cells that are supposed to be helping maintain your eye pressure for your entire life. So once those cells are dead, that’s it. That’s—“
Renay San Miguel: You’re not making any more?
Raquel Lieberman: You’re not making any more. And this part of the eye—it’s called trabecular meshwork—is in the front part of your eye. It’s actually kind of close to the part of the eye that hold your lens in place, and it’s allowing fluid to drain out. So you may—many listeners may not know this, but there are no blood vessels inside your eye. So how are all the parts of your eye supposed to get the nutrients that they need? Well it’s through these fluids—this aqueous humor and vitreous humor in the two parts of your eye. And so there are cells that are making the nourishing fluid and then there’s a tissue that drains it all out, and so it’s like a sieve. And if you gunk up or otherwise can’t maintain the meshwork, this trabecular meshwork that’s letting fluid out, then it’s going to, you know, build up and the inside air pressure will go up.
Renay San Miguel: It’s that mutant, misfolded myocilin that aggregates, or builds up, within the eye fluids, causing pressure to build.
Lieberman says this is why getting your eyeball pressure tested during eye exams is crucial for early detection, so special eyedrops can be prescribed.
Raquel Lieberman: So the earlier you can get diagnosed for elevated intraocular pressure, the better, because if you can control your pressure, then you can delay the onset of losing your vision in the back of your eye. But these drugs often times don’t work forever. So there are some other options. You can surgically poke a hole, so that will obviously improve the drainage, but there’s a significant number of people who go blind even with all these treatments. And of course as people are living longer, you want as many senses as possible to be working well.
Renay San Miguel: What’s going on on the molecular scale to see how you might be able to treat this, or how you might be able to alleviate symptoms?
Raquel Lieberman: The symptoms right now are controlled by basically the same drugs that control blood pressure. They work the same way and that was how some of these original drugs were discovered actually. There are a lot of people who are interested in drugs that both help control the pressure and also protect neurons. So it would protect the retina against degeneration. Our work on myocilin is really pretty focused on this heritable form of glaucoma in children, and that’s because there’s a very clear genetic connection.
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Renay San Miguel: As we’ve said, shape is everything when it comes to proteins. A misfolded protein in the wrong three-dimensional form can cause these neurodegenerative diseases such as glaucoma.
In late 2017, Lieberman’s team announced it had discovered the shape of the myocilin protein that causes the hereditary glaucoma she studies. It was a surprising shape, one that researchers rarely see exhibited by proteins.
Usually, X marks the spot. But not when Lieberman and her team were able to reproduce the mutant protein in their lab.
Raquel Lieberman: What we like to study in our lab is protein structure and function if we can, and then dysfunction, like what happens when things go wrong? And so the very first thing that we did was we made the protein in our lab—just actually the part that had most of the mutations that are associated with disease. And to our surprise, we could make it, right? It wasn’t obvious that a protein that is prone to not adopt the correct fold would be amenable to this kind of experiment in vitro, but it was. And from there we were able to introduce the mutations that are found in families throughout the world and show that there’s a pretty systematic chemical defect that is associated with the mutant forms of the protein. And then we decided to test the hypothesis that there really was a connection between Alzheimer aggregation and this protein’s aggregation, and that turned out to be true.
And that can explain a lot of things like cytotoxicity, right? Why is it that the cell can’t handle this mutant protein? It helps us understand better, kind of at a molecular level, what might be going on or at least give us some inspiration for other kinds of experiments from these other fields to adopt to this system. And so then, from there we kind of branched out. And this protein is kind of big, and so we kind of went from the part that has the strongest association to glaucoma to then looking at the whole thing, and that’s where we discovered that it has a very weird shape. It has kind of a Y-shape, and we don’t know of any other Y-shaped proteins made from a single gene. Antibodies are actually Y-shaped, but those are made from different genes. Like they’re different independent pieces of polypeptide that come together. This is all from the same thing.
For 20 years we have known that this protein causes glaucoma, and for 20 years nobody has been able to figure out what this protein is doing when it’s not causing trouble. And if it were easy, somebody would have figured it out. But the Y-shape gives us a clue because it’s almost like it’s a spacer. The Y-shape is like a spacer, so you have to have you know paired on either side, maybe they’re reaching in some way like if you think of your body as being the stem and then your arms are the dimer. Maybe you’re reaching for two different parts? And we know from other similar families of proteins that they are probably holding on to different parts of things that they can reach. And so we’re just trying to figure out now what it’s reaching for. But that’s a big—that’s a big mountain to climb.
Renay San Miguel: But it’s a good clue?
Raquel Lieberman: It is a good clue. I think it’s a good clue. There’s a lot of precedent for trying to understand the inherited form of the disease first and then branching out, kind of what we’re doing here where we have studied the mutated form—OK, now we have the structure, this Y-shaped structure, that’s leading us in these other directions that could help more broadly.”
Renay San Miguel: Lieberman uses x-ray crystallography to form accurate 3-D models of her mutant myocilin proteins. Her team also relies on nuclear magnetic resonance imaging to look at the tiny fibrils that sprout from mutant proteins, making them clog up the eye’s drainage systems.
Renay San Miguel: The ultimate goal is to find some chemical, some kind of way, to fix the protein that is dysfunctional in the eye? I mean, is that possible? Is that doable? Is this something we can get to eventually?
Raquel Lieberman: We think we’ve made a lot of progress in that direction. One thing we haven’t really talked about is that we know a little bit more about—in the cell, when mutant myocilin is aggregating, who’s trying to help myocilin and failing to do so? And it turns out that if you can block this key interaction with the molecular chaperone, part of this cellular homeostasis network, you can degrade the mutant myocilin. And it’s actually better to not have myocilin around at all than to have the mutant form aggregating. This is still -- there aren’t that many examples, but there are a few examples of people who don’t have this protein at all and they don’t have glaucoma. And so the idea is that you don’t really need myocilin at all to kind of live a happy life and so maybe if you could just get rid of this protein, that would be good enough.
The other way would be to clear the aggregates. So you can imagine having some sort of reagent like an antibody that would capture the aggregates and help them get digested or broken down a different way. That’s a little bit pie in the sky. The chemistry of the molecular chaperones inhibiting, that’s already been shown to work in mice. So we’re pretty excited about that route.
Renay San Miguel: What are you going to focus on in 2019? In terms of glaucoma and these proteins, where will you be focusing your studies?
Raquel Lieberman: The trabecular meshwork, the little sieve that helps the aqueous humor fluid drain, that’s a key disease tissue in all types of glaucoma. And so we think that, in addition to this myocilin-associated glaucoma route with the inhibitors and the chemistry and the amyloid and everything, we have a lot to offer in understanding the physiology of the trabecular meshwork by understanding what myocilin is doing there when it’s not causing trouble, when it’s properly folded and holding on to whatever it’s trying to hold on to—what are those things and what happens over time? And then developing the reagents that hopefully people will be able to use to better understand the system, this trabecular meshwork in general. And then maybe that will open up some new avenues for glaucoma that’s caused by any number of other factors besides just this particular protein. We’re working really hard on that right now.
This disease effects a lot of people, and one to three million children worldwide is a large population. And I always believe that children are our future and we want them to be as healthy as possible.
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Renay San Miguel: In addition to her research, Lieberman is also in the middle of a three-year term as an academic editor of the Public Library of Science, or PLoS Biology publication, a highly-regarded journal that spotlights innovation in biological sciences.
My thanks to Raquel Lieberman, professor in the School of Chemistry and Biochemistry, and a member of Georgia Tech’s Parker H. Petit Institute for Bioengineering and Bioscience. Her research at Georgia Tech has been funded by the National Institutes of Health, the National Science Foundation, and the Department of Energy’s Office of Science.
Siyan Zhou, a former research associate with the School of Psychology, composed our theme music.
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You’ve been listening to ScienceMatters, the podcast of the Georgia Tech College of Sciences. I’m Renay San Miguel. Thanks for listening.
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