Sugar on the Brain

We talk with Carolyn Bertozzi about her Nobel Prize-winning work in chemistry – and the impact it could have on neuroscience
Nicholas Weiler
From Our Neurons to Yours Wu Tsai Neuro Podcast

Today on the show, we bring you a conversation with Carolyn Bertozzi, the Baker Family Director of Sarafan ChEM-H and the Anne T. and Robert M. Bass Professor in the School of Humanities and Sciences. 

Bertozzi is a Nobel Laureate, a MacArthur Fellow, and an all around cool person – although it didn't come up in the conversation, she used to play in a band with Rage Against the Machine's Tom Morello.

Although Bertozzi wouldn’t call herself a neuroscientist — she’s a chemist at heart – her work is having a big impact on neuroscience. Today, she focuses on the sugar molecules that stud the outer surfaces of our cells. It turns out that these molecules are incredibly important for how cells communicate with each other. But understanding these molecules is so complex and challenging that Bertozzi had to invent a new branch of chemistry in order to study them. In this episode, we'll hear how this research is opening doors not only within neuroscience but across biology and drug development as well.

View all episodes

SUBSCRIBE on Apple Podcasts, Spotify, Amazon Music and more.

Carolyn Bertozzi
Nobel Prize-winning chemist Carolyn Bertozzi is the Baker Family Director of Sarafan ChEM-H and the Anne T. and Robert M. Bass Professor in the School of Humanities and Sciences.

Learn More

Episode credits

This episode was produced by Michael Osborne at 14th Street Studios, with sound design by Mark Bell. Social media strategy is by Julia Diaz, and additional editing by Nathan Collins. Our logo is by Aimee Garza. The show is hosted by Nicholas Weiler at Stanford's Wu Tsai Neurosciences Institute and supported in part by the Knight Initiative for Brain Resilience. 

Share the show:

If you're enjoying our show, please take a moment to give us a review on your podcast app of choice and share this episode with your friends. That's how we grow as a show and bring the stories of the frontiers of neuroscience to a wider audience. 

Get in touch:

We want to hear from YOUR neurons! Email us if you'd be willing to help out with some listener research, and we'll be in touch with some follow-up questions.

Transcript

Nicholas Weiler (00:10):

This is From Our Neurons to Yours, a podcast from the Wu Tsai Neurosciences Institute, bringing you to the frontiers of brain science.

(00:23):

Today on the show, I'm excited to bring you my conversation with Carolyn Bertozzi. She's a Nobel laureate, MacArthur genius grantee and an all around cool person. I failed to bring this up in our conversation, but she used to play with Tom Morello of Rage Against the Machine back in the day. So if the Nobel Prize doesn't impress you, she's legit.

(00:44):

Carolyn wouldn't call herself a neuroscientist. She's a chemist at heart, but her work is having a big impact on neuroscience. That work focuses on the sugar molecules that stud the surface of our cells. It turns out these molecules are incredibly important for how cells communicate with each other, but understanding these molecules is so complex and challenging that Carolyn had to invent a new branch of chemistry in order to study them.

(01:11):

So we're going to be talking about how this research is opening doors, not only within neuroscience, but across biology and drug development. We're going to get into some fun chemistry here, but we are in extremely good hands. So let's jump right into my conversation with Carolyn Bertozzi.

(01:31):

Carolyn Bertozzi, welcome to From Our Neurons to Yours. I'm so glad to have you here.

Carolyn Bertozzi  (01:32):

Thank you. Great to be here.

Nicholas Weiler (01:37):

I'm particularly excited to talk about this work because you've essentially developed a whole new branch of chemistry that's changing how we understand cell biology. And it's launched, what, a dozen now biotech companies working on therapies for a bunch of different diseases and really highlights the value and impact of basic curiosity driven science to change our understanding of ourselves, to change our ability to treat diseases. I want to get into all of that, particularly some of the implications for neuroscience since that's the focus of our show.

(02:11):

But first I'd love to start with sort of a quick primer on the big picture of your work, which is focused on an aspect of our biology that's been ignored for a long time, if that's fair to say, or had been, the fact that nearly all of our cells throughout our bodies are covered with sugars. I think that might be hard to picture for a lot of people. Are our cells candy coated like M&Ms? I wonder if you could paint us a picture of what these sugars really look like and what we think they might be doing there.

Carolyn Bertozzi  (02:45):

You bet. It's funny because when I give lectures to a non-scientific audience, I often show a slide with an M&M on the slide just to make exactly this point that cells have a sugar-coating. But then I switch to another image of the planet earth because I don't want people to think the sugars on our cells are as simple as they are on the M&M. They're much more complicated with features and patterns. So I like to think of the cell as really like the landscape of a planet where you have forests, you have open fields, you've got tall trees and short shrubs and grass. And in many ways, the complex carbohydrates form a kind of vegetation landscape on the surface of the cell and they're moving.

(03:42):

And I'm here in the Bay Area, so from time to time I'll go down to Monterey where there's a very famous aquarium. And in that aquarium, there's a kelp forest where you stand there looking in this giant tank with the kelp sort of swaying back and forth in the waves of the water. And I like to think of the cell surface carbohydrates as being like that. They're these long chains protruding from the surface of the cell, swaying as fluid flows by our cells in our bodies. And they're very structurally complex and also a very rich code of information about the biological state of the cell. So different cell types have different kinds of forests on their cell surface. And that turns out to be important in the way that cells interact with other cells and the way that they form organs and tissues and pretty much all human biology at some level involves these sugars.

Nicholas Weiler (04:51):

When I was taking biology classes and things, we learned about the cell surface proteins, things like there are ion channels, there are various mechanisms sitting in the lipid membrane of the cell. You're painting a picture, and I love this picture of the cell as the surface of a planet with different ecosystems and forests and things. What does that add to our picture of the biology of the cell to have a sense of that there are these long chains of carbohydrates? What do we think they might be doing that's different from some of the proteins that we've been able to study for a long time?

Carolyn Bertozzi  (05:31):

Well, first of all, I should say that it's probably helpful to think about the sugars holistically along with those other molecules like the ion channels and the lipids. For example, all of those ion channels are decorated with polysaccharides. They're glycosylated, they're glycoproteins, and the sugars attached to the ion channels regulate their functions. So they affect their folding, they affect the way that subunits come together to form a multi-subunit complex. In the case of ion channels, they very explicitly can control basically the electric potential across the ion channel because some of these sugars are highly negatively charged, so they'll actually influence the rate of flow of cations through the channel. And many of the lipids in your membranes are glycolipids, so they have sugars attached to them as well.

(06:27):

So the sugars and the proteins and the lipids, they're all part of this molecular landscape. They're all part of this collection. And in many cases, you can't really discuss the function of one without the other. So a description of an ion channel is incomplete without also including its glycosylation pattern. And likewise, the description of what the glycans are doing would be incomplete without understanding what the underlying scaffolds are. And the kinds of biological processes that glycans participate in, there's a lot of overlap with proteins, right? They're involved in interactions with receptors. They can be ligands for receptors. They can have structural roles. They can have biochemical interactions of their own. It's kind of all of the above.

Nicholas Weiler (07:16):

Okay, so we shouldn't think of them at all in isolation. We should think of them together and think about how they're complimenting and working together in this broader ecosystem of what's going on on the cell surface. But for many decades, biologists did kind of ignore them, did look at the proteins and try to look at the lipids. Why is that? Why had these sugars been so hard to study? And maybe you can give us a sort of a primer on how you tackled that with the new chemistry you developed.

Carolyn Bertozzi  (07:48):

Yes. It's funny, if you look back through the history of molecular biology, there was a time in the 1960s and 70s where carbohydrates had just as much attention, I would say, as other types of biopolymers. And people worked on them and tried to understand their biosynthetic origins, their structures, their roles in cell biology.

(08:15):

But what happened was the molecular biology revolution as it's often described, so this is the advent of recombinant DNA technology, which allowed people for the first time to be able to clone a gene, express a protein heterogously, for example, take a human gene, put it in E. Coli, use the E. Coli as a factory to make the protein and then study the protein. This was so powerful and so enabling and people really gravitated to the areas of biology that could be accelerated immediately using these recombinant DNA technologies. And the glycans were not directly addressable with that technology because they're not part of the so-called central dogma. So there's not like-

Nicholas Weiler (09:02):

There isn't a gene to transcript to protein, right?

Carolyn Bertozzi  (09:05):

Exactly.

Nicholas Weiler (09:06):

That was what that was all based on.

Carolyn Bertozzi  (09:07):

Exactly. Proteins are primary gene products. So you clone a gene, you put it in an organism, it will make the protein. Glycans are not primary gene products. They are the product of hundreds of genes working together, genes that encode all the different enzymes that are required to build the glycans. And so they weren't manipulatable using those molecular biology techniques. And as a consequence, what happens in science is when there's a really powerful new tool, people want to use it and science starts to move faster by virtue of having those tools. And so people gravitate to the areas of science that are moving fast. By contrast, areas of science that remain technically difficult, laborious, can't move at quick a pace because the technologies aren't available, those areas sometimes get left behind. And that's what happened with glycoscience.

(10:06):

So from the '60s and '70s where there was quite a significant bunch of people working in carbohydrates, fast-forward to the '80s and '90s and people just shifted away and towards other areas of biology, but not working on an area doesn't make it unimportant. And I think people who are thoughtful biologists recognize that obviously these molecules are very important. They're structurally complex, they're cell type specific, they change in the context of disease. I mean, all the signs were there that-

Nicholas Weiler (10:43):

Our blood types are based on these molecules, right?

Carolyn Bertozzi  (10:45):

That's correct. Yes. If your blood type A, B and O-

Nicholas Weiler (10:49):

A, B, O, right.

Carolyn Bertozzi  (10:50):

Exactly. And that was discovered in the 1950s and '60s at a time when people were putting a lot of thought into what cell surface sugars were doing. So during the kind of, I would say the heady decades of the biotechnology industry and recombinant DNA technology, glycoscience kind of fell out of favor amongst biologists. But interestingly, in parallel, it became interesting to chemists because chemists of the 1980s had developed some powerful tools to chemically synthesize large, complicated, natural products. And this was a really hot area in organic synthesis was to pick the biggest, most difficult, complicated molecule you could find and then figure out how to make it from scratch. And that was like the Mount Everest type of science of the day was the bigger, the more complicated, the more kudos you get for having been able to make it from scratch.

Nicholas Weiler (11:49):

We're going to climb this mountain of making a really complex carbohydrate molecule.

Carolyn Bertozzi  (11:52):

Yeah. Right. And so chemists started looking at these complex carbohydrates and thinking, "Well, that's pretty complicated. I wonder if we could make that from scratch." And it became sort of an interesting challenge in some of the very top organic chemistry labs in the world.

(12:07):

So in a way, the center of gravity of glycoscience kind of shifted from the world of biology over to the world of chemistry in the 1980s and '90s. And those were the decades where I went to college and then graduate school and then did my postdoc. And I was a chemistry PhD student looking for interesting problems in synthesis, interesting molecules to make. So that's how I was first introduced to the world of glycoscience was the challenge of the chemical synthesis. And that was my focus in my PhD work.

(12:44):

But all the while I was reading the papers from the biology labs around the interesting biological roles that glycans played. And I had in my head an idea that maybe I should go do a postdoctoral position in a biology lab, at one of the small number at this point that actually focused on cell surface carbohydrates and their biological functions. And by the way, the 1980s was also the decade in which x-ray crystallography using synchrotron radiation sources became available to structural biologists.

Nicholas Weiler (13:19):

You could actually see the shape of some of these molecules.

Carolyn Bertozzi  (13:22):

You could see the shapes of proteins initially. So focus was on proteins, but what was interesting is there was a lot of interest in structure guided drug development. People thought back then that if you could solve a structure of a protein with atomic resolution and you could see each bond in each atom, then you could just develop drugs just like that. And it turned out to be, of course, much more complicated.

Nicholas Weiler (13:48):

Design the key to go in the lock, right?

Carolyn Bertozzi  (13:48):

Yes. Yes.

Nicholas Weiler (13:50):

It turns out that it doesn't work quite as simply as that. Yeah.

Carolyn Bertozzi  (13:52):

Yeah. At the time, people thought all drugs would now be easy to make because of the availability of these structures. That turned out, of course, not to be true, but there were a few instances where it really was true. And one of those was in the development of the first generation of drugs for the flu. And it turns out the flu is a virus that binds a sugar on the surface of host cells to kick off the infection. And this first wave of flu drugs were sugar analogs that were interacting with this sugar binding receptor on the flu. So that was kind of a big story actually at the time. And it kind of pointed towards the fact that if you knew more about sugar biology and sugar chemistry, you might be able to make a lot of interesting drugs. So that kind of also sort of sucked me in to the glycobiology part of it.

Nicholas Weiler (14:45):

So tell us about, I mean, one of the challenges, if I understand correctly, was it's just hard to see what these sugars were doing. Where are they going? What are different kinds of these chains of carbohydrates? Yeah. And so it seems like the challenge was how do we just get a handle on these things and actually manipulate them without upsetting their actual function in the cell? Was that sort of at the heart of what you were trying to do?

Carolyn Bertozzi  (15:14):

That's part of it. Yeah. I mean, what my experience was during my postdoctoral years, so this would have been like 1993, 4, 5, around that time, I had jumped ship out of a chemistry lab and into a biology lab, and that lab was studying the roles of cell surface sugars in the immune system. So it was an immunology lab essentially. And when I entered that lab, the biology was new to me. So I didn't have any experience as a cell biologist. So I was kind of learning from scratch these new techniques.

(15:48):

And that's when I really saw the frustrations of glycobiology because in the '90s, if you were studying proteins, you had really great automated, commoditized tools at your disposal, both to sequence the proteins and to image them in living systems. And those are two really important tools, like being able to just understand what proteins are there, just sequencing the proteins from cells that, we call that today proteomics. Being able to sequence a protein and know what proteins are there and how they change from this cell to that cell, that's an important thing to be able to do to study proteins.

(16:29):

And then the other is to actually be able to visualize those proteins in a living cell or in a living animal and see how it moves around in its native habitat. And so the tool that people use for that is the green fluorescent protein fusion. We have these genetically encoded fluorescent proteins that we can fuse at the DNA level to our protein of interest and we express our protein as a GFP fusion and then we can see where it goes. And by the way, that green fluorescent protein technology was recognized with a Nobel Prize in the 1990s, that's how impactful that was.

(17:06):

And those two capabilities, just sequencing the molecules so that you know what structures are there and being able to see where they are, those two things were not available for glycoscience.

(17:19):

So when I started my own lab as a new professor at Berkeley at the time, this is like 1996, the goal of my lab initially was to try and develop the tools for those two problems. How do you figure out what are the structures that are there? How do you sequence them? And then how do you see them in their native habitat and watch them, follow them around? Those were the two things that we kind of focused on.

Nicholas Weiler (17:46):

And it seems like the immediate applications for that, you said that this was sort of developed with your experience in an immunology lab, but maybe we've been talking about these sugars as sort of a cellular identity as one of the things, one of the ways you can think about them. They're a way that the immune system can recognize different kinds of cells and whether this is a self cell versus another cell and what type of cell it is, and I'm sure there's more to it than that. But it seems like a lot of those early applications, once you had these techniques to see these, is that you could then start basically adding this to this growing field of immunotherapies where you could support the immune system in doing things like attacking cancer cells and the like. Is that a fair description of sort of how this went from now we can see these to what can we do with this understanding?

Carolyn Bertozzi  (18:43):

Yeah, I think that describes sort of like the first 20 years of my academic career.

Nicholas Weiler (18:49):

I hate to describe 20 years of important and difficult science in like two sentences.

Carolyn Bertozzi  (18:54):

Well, but I would say it took about 10 years for us to develop a technology for the imaging part, for being able to see those sugars. And in fact, that was the motivation behind this type of chemistry that we developed called bioorthogonal chemistry, which now is kind of used across all of life sciences as an enabling tool for various applications. But its origin story was it was a tool that we developed to be able to visualize sugars on cells in cell culture and in animal models. And it took 10 years to kind of optimize that and get that all worked out. But once we had the ability to see the sugars and we could see how they were changing in different cell types, that's when we became interested in their role in cancer immune modulation. And that was another story that we started working in that area in Berkeley, continued that into my current lab at Stanford. And I would say that was kind of like the next decade of my research was focused on that, yeah. And we did make a discovery, a fundamental discovery about cancer and immunology.

Nicholas Weiler (20:39):

I hate to fast-forward so much through these seminal discoveries, many of which led directly to your Nobel Prize a couple of years ago, but I do want to get to some of the implications for neuroscience. And maybe there are some connections here between what you were discovering about the role of these cell surface sugars in cancer and what you and your team have been discovering in the brain. So do you mind if we jump into what is going on in glyconeurobiology these days?

Carolyn Bertozzi  (21:13):

Absolutely. And it absolutely all does flow actually because the investment that we made in those first 15 years in developing tools to image the sugars and look at different classes of sugars, and we developed tools for different types that we could use to image them.

(21:34):

And using those tools, once you have those tools, you could look at the sugars in any context. You can look at them on cancers, you can look at them on immune cells, and it turns out you can look at them on the blood vessels that innervate the brain. And so what happened was about six, seven years ago, a graduate student at Stanford who was in the chemistry department, she was a first year student and in her first years they do rotations, lab rotations. So she rotated in my lab and she developed some reagents to image sugars and the application at the time was around cancer.

(22:12):

But then in her next rotation, she went to a neuroscience lab and that was the lab of Tony Wyss-Coray, who's a Stanford professor here. And he is kind of a leading figure in studies of aging in the brain and in how the blood-brain barrier changes as we age. And he had a project going in his lab where his students were looking for molecular changes in the brain endothelium, so these are the cells that line the blood vessels that are all innervating the brain. And they are the cells that constitute the blood brain barrier. So these-

Nicholas Weiler (22:55):

And this is basically this, just to make sure that all of our listeners are following along, this is basically the idea that the brain is supposed to be, and the nervous system are supposed to be sort of a specialized compartment. We don't want immune cells getting in there too easily. We don't want toxins and things from the blood able to access the brain. So there's this idea that there's a barrier that carefully controls the kinds of things that can get into the central nervous system that's sort of like big picture there.

Carolyn Bertozzi  (23:21):

That's exactly right. And the brain is full of blood vessels. In fact, someone told me that if you take all the blood vessels and put them in a big line, it's 400 miles of vasculature. So you could drive from Palo Alto to San Diego on the blood vasculature in your brain. It's a lot.

Nicholas Weiler (23:39):

Amazing.

Carolyn Bertozzi  (23:40):

Because your brain needs a continuous supply of energy and oxygen and everything, right? You know how it is, if you don't breathe for a couple minutes, your brain, you pass out, your brain shuts down.

Nicholas Weiler (23:52):

Your brain shuts down. Yeah.

Carolyn Bertozzi  (23:55):

And that oxygen has to get in there and your brain needs glucose. If you have low blood sugar, you can't think straight.

(24:04):

So the blood brain barrier keeps the bad stuff out because it's such an important organ to protect, but it also has to carefully regulate who comes in. And a lot of things have to get in there. So it's not just a barrier, like a physical barrier. It's a highly regulated barrier with transporters that bring in the good stuff and pumps that pump out the bad stuff.

(24:26):

And it was known that as we age, our blood brain barrier becomes more leaky. And there are some theories that stuff leaking into our brain can lead to inflammation in the brain and inflammation contributes to neurodegenerative diseases like Alzheimer's disease and Parkinson's disease and ALS and so on.

(24:47):

So Tony studies these things. And at the time that our student, Sophia, is her name, she was rotating in Tony's lab and he had a project where they were looking at changes in the transcriptome, so the RNAs in the brain endothelium during aging, and they were also looking at changes in the proteins, so the proteome in those brain endothelial cells during aging. And they were looking for things that change, like what happens when we get older and could some of those molecular changes explain those broader physiological changes? Right, that was-

Nicholas Weiler (25:25):

Back to the central dogma, what genes are being turned on and off, what proteins are being made, how does that affect the function of these cells?

Carolyn Bertozzi  (25:32):

Right. And looking at differential transcriptomics and differential proteomics, that's now kind of standard practice in biology. Lots of labs ask those kinds of questions in their various organ of interest. But in typical fashion, nobody had thought to ask about the glycans or the complex carbohydrates that are on these cells. We would call that now the glycome. So that's the modern descriptor of the total collection of these cell surface glycans, that's the glycome, glycomics.

Nicholas Weiler (26:08):

Right. So there was this open question, what is changing about those glycans as we age?

Carolyn Bertozzi  (26:14):

Right. No one had asked that question. And nobody in Tony's lab would've asked that question if the student who had rotated in my lab hadn't also shown up in his lab because she had just come out of the glyco lab. So she said, "How about I go back to Carolyn's lab, get all those reagents out of the freezer that her lab uses to image and visualize these different kinds of sugars and use them to test the blood vessels in the old mouse and in the young mouse and see if there are any differences," just as a rotation project. And what she saw was absolutely stunning and shocking, huge differences and much more dramatic than any of the phenotypes that Tony's lab had observed in the transcriptome or in the proteome.

Nicholas Weiler (27:06):

So when you change these sugars, you see a bigger effect on the blood-brain barrier than when you're messing with some of the proteins?

Carolyn Bertozzi  (27:15):

Well, at the time, all we saw initially was that there are big changes. We didn't know-

Nicholas Weiler (27:21):

Oh, that the [inaudible 00:27:21].

Carolyn Bertozzi  (27:21):

Yeah. You don't know cause and effect and you just see big changes with aging.

(27:26):

So then that kind of launched her thesis project and she spent the next six years kind of diving into that. And one big change she found is in the glycosylation of abundant cell surface proteins called mucins, which is M-U-C-I-N, mucin. Mucins, I won't go into the gory details, but they have a pretty amazing structure. And the best analogy I can use is on the planet earth of your cell surface, the mucins are the giant redwood trees. They're tall and stiff and straight and majestic and they protrude up above everything else and they overshadow a lot of other stuff.

Nicholas Weiler (28:07):

Interesting.

Carolyn Bertozzi  (28:08):

And what we've discovered using our reagents is that the brain endothelial cells have a very thick giant redwood forest compared to other endothelial cells in other organs.

Nicholas Weiler (28:21):

And these are the cells that are making up that blood-brain barrier.

Carolyn Bertozzi  (28:24):

They are the blood-brain barrier, yes. They are the blood-brain barrier. And they have a totally different landscape than the blood vessels that innervate the heart or the kidney or a muscle. They were quite distinctive. And again, nobody would've known this because nobody would've looked. And this is how it works in biology, right? When a flashlight is on, that's where you look, but you don't see all the dark spaces. You need to have a different flashlight.

(28:51):

And so the reagents that we had for visualizing sugars, that was like a whole new flashlight that you could shine on the blood-brain barrier. And we saw this big change in these mucins. So then the next question Sophia asked is, what do they contribute to the blood-brain barrier and do the changes that we observe relate to this leakiness that happens when people get older? And it turns out, at least in the mouse model that we used to study this, the answer was yes. So what Sophia did is she figured out what are all the genes that were contributing to the mucin biosynthesis? And there's many because these are big molecules with big sugars and lots of enzymes are needed.

(29:31):

And what she found is that some of those enzymes seem to have had reduced abundance in older mice versus younger mice, and that was the root cause of the change in these mucins with aging. And then she made a gene therapy vector to put those enzymes that had been diminished in the older mouse, and that gene therapy vector she used to infect the old mouse to sort of boost the levels of the enzymes back up again. That restored the mucins at the blood-brain barrier and it made those brains less leaky. So that was kind of the killer experiment that showed that the change in the mucins actually resulted in increased leakiness and that you could reverse it.

Nicholas Weiler (30:13):

So just to sum up, to make sure I'm following. So the mucins, they're actually a combination of protein and carbohydrates and sugars, right? So there's a mesh or a big protein that's covered in sugars that what you saw with age was that those proteins were losing their sugars. They were losing some of the sugars on the proteins, if that's the right way to describe it?

Carolyn Bertozzi  (30:42):

That's right.

Nicholas Weiler (30:42):

And that Sophia's work suggested this is because the cells are losing some of these enzymes that are putting those sugars there. And if you restore those enzymes, you restore the sugars and you restore the health of the blood-brain barrier. I'm simplifying, but that's sort of the big picture.

Carolyn Bertozzi  (30:59):

Yeah. And for the listeners who live in a place with seasons, which I do not,-

Nicholas Weiler (31:03):

Unlike us here in California.

Carolyn Bertozzi  (31:06):

... you'll recognize that the older endothelial cells have the forest of the wintertime. All the leaves are gone, the trees are bare, you can see through them, you have good visibility into the forest. But in the younger mouse, spring has returned and the leaves have fleshed out. And now there's a lot of foliage and it's thick and you can't see through the forest anymore. And so that seems to be kind of what's happening to these mucins. And when we draw cartoons of these mucins, we draw them like a bottle brush. They have a rigid rod in the backbone and all these bristles sticking out all across it. And the bristles had crumbled in the older mouse, but you could restore them with this gene therapy vector. And not only did the leaves come back, but the cognitive performance of these mice improved, so like humans-

Nicholas Weiler (31:58):

So there's less inflammation?

Carolyn Bertozzi  (32:00):

Yeah, we don't know exactly why to be honest, but the observation here is that when you restore a youthful blood-brain barrier, mice have a better memory. They can find their way out of a maze quicker and things like that. There's a big distance between a molecular change and a behavior and understanding everything in between is kind of the ongoing challenge, but that was a revelation for me. And I had never really given much thought to neuroscience, honestly. Most of the biology that we focused on had to do with cancer and the immune system. So the brain is something I've been very intimidated of my entire life. It's so complicated, then glycoscience is so complicated and the idea of putting two big complicated things together is kind of intimidating. But Tony, my close collaborator, he's a brain scientist and he made this possible.

(32:55):

So that was how I entered the world of neuroscience, from the tiptoeing into the shallow end of the pool. But then it got even more interesting because in the course of her work, what Sophia discovered, and this was total serendipity, one of the reagents that we used that binds to mucins, and we use it as a staining reagent so that we can see with a fluorescent tag on it, she had injected this reagent into mice to allow it to accumulate in the blood vessels and then typically she would then surgically open up the mouse and look and see where all the mucins were. And what she noticed is that if she waited a couple hours after injecting this reagent into the mice, first it would bind to the vasculature, you would see it on the blood vessels, but it would then cross into the brain, into the parenchyma of the brain, the innards of the brain.

Nicholas Weiler (33:50):

Which theoretically it's not supposed to be able to do.

Carolyn Bertozzi  (33:53):

It's not supposed to do that. Yeah. This is a reagent that is a protein and the textbooks would tell you that proteins on their own don't just cross the blood-brain barrier. In fact, this is the biggest problem in the biotech industry for companies that want to make biologic drugs to treat the brain, their drugs can't get into the brain, so that's a real frustration for the business. And here we had this reagent that for reasons that we didn't understand, it just had crossed the blood-brain barrier all by itself and gone into the brain. And to make a long story short, we realized that this reagent could actually be used as a shuttle to shuttle cargo across the blood-brain barrier for therapeutic purposes.

Nicholas Weiler (34:37):

We have these drugs that we can't get into the brain, you could use this as almost a ferry to bring it in.

Carolyn Bertozzi  (34:43):

That's the idea. Yeah, and by the way, the development of brain shuttles for biologic drugs is a really hot area right now in the biotech startup world. There's a couple of companies that are really doubling down on developing these shuttles, and here we just stumbled into one. And so Sophia, the student, this was her final project before she graduated. Now she's got her own lab at Harvard and she and I and Tony and another student from my lab who's still finishing his PhD have decided to spin out a company to take this brain shuttle into therapeutic applications, so that's right now happening.

Nicholas Weiler (35:26):

That's so exciting. As you said, I've been reading about these various attempts to shuttle across the blood-brain barrier for a while now, and this seems like a really promising approach to that. Again, it takes us back a little bit to the lock and key, but how do you get permission to cross over the blood-brain barrier? Maybe we need to understand, I don't know, the sugary password to get through. I was going to ask you about what are some of the things that we'd like to be able to get across the blood-brain barrier?

Carolyn Bertozzi  (35:56):

Yeah. Well, the drugs that people would like to get into the brain more efficiently are protein therapeutics like monoclonal antibodies, enzymes for enzyme replacement therapies, specifically for rare diseases, genetic diseases, oligonucleotide therapeutics like siRNA and antisense oligonucleotides, mRNA lipid nanoparticle complexes, gene therapy vectors, both viral and non-viral. I mean, there's lots of things [inaudible 00:36:29].

Nicholas Weiler (36:28):

So all kinds of these frontier therapies, all this fancy biotechnology, which just hasn't been able to have a foothold in neuroscience unless you want to start injecting stuff into the brain, which we normally try to avoid.

Carolyn Bertozzi  (36:43):

Yeah. And in fact, we did some data analysis on drugs for different indications, and here's some numbers. So right now there are more than 150 biologic drugs approved to treat immune diseases, like autoimmune diseases. There's a similar number approved to treat cancer. There's only 15 biologic drugs that have been approved for central nervous system disorders, and most of them are administered by intrathecal injection. So that's lumbar puncture, which is horrible and invasive and takes all day in a clinic and doesn't scale very well. It's very limiting. So if we can even just take some of those drugs that have to right now go into the spinal cord and make them administrable through just an IV, a regular old garden variety IV, that would be really transformational for the patient.

Nicholas Weiler (37:44):

I'm so excited to see where that company goes, because as you say, that unlocks the potential of so many things. We talked with John Long recently, who's one of the fellows in the Sarafan ChEM-H Institute that you lead about peptides and a similar kind of opening up with GLP-1s where once we realize we can use drugs of that class that people will take injections and that this is a possibility, suddenly there are all these possibilities. Suddenly there are all these things that were just technically difficult to administer before. Now, if we have a pathway, if we have a way to do it, that opens up a lot of possibilities for further drug development.

(38:35):

I want to ask you about one more area of neuroscience that your lab has been getting into, I think also with Tony's lab. I'd love for you to just say a few words about, there's sort of a... A lot of your work has, as we've said, has focused on the connection between glycobiology and immunology. How do you influence the immune system in cancer and so on to recognize cancer cells and fight them and that kind of thing. But you've seen some similar things with the immune cells of the nervous system in the brain, the microglia of the nervous system. There appears to be a glycobiology connection there that could help us understand, again, neurodegenerative disorders, why all of these protein junk and lipids and things start to build up as we age. Can you give us a quick capsule summary of what you're learning about glycans in those microglia?

Carolyn Bertozzi  (39:29):

Sure. Again, this is one of those situations where it's really great to be like the glycoscientist at a university surrounded by-

Nicholas Weiler (39:40):

Everyone wants to collaborate.

Carolyn Bertozzi  (39:41):

Yeah. Well, so inevitably, if someone is studying deeply a biological system, they're going to stumble into glycoscience. It's inevitable because they're there and they're important and they're doing things.

Nicholas Weiler (39:54):

Right, and it's still catching up with all of our other knowledge and tools.

Carolyn Bertozzi  (39:57):

Yeah. But I'm here, everybody knows it. And so now what happens at Stanford at least is if somebody runs into some unanticipated glycoscience, they get on the phone and they call me and they say, "Hey, before we quit, can we talk to you about this and tell us if you think there's a path forward?" And that's where the magic happens.

(40:16):

And so that's what happened with this microglia project with Tony. So his lab was interested in basically how microglia change in neurodegenerative disease and also in aging. There's always overlap between these two situations. It was known that microglia, they're like the macrophages of the brain and macrophages are famous for eating stuff and they clean out the junk. They're like garbage destructors. In the brain, the microglia, one of their functions is to eat up garbage and especially protein aggregates. And that's important because if protein aggregates accumulate, that can be neurotoxic and that's kind of the root cause of Alzheimer's disease. Right?

Nicholas Weiler (41:03):

We get these amyloid plaques and tau tangles and all these things.

Carolyn Bertozzi  (41:06):

Right. And so there was evidence that microglia in the aged brain and in the Alzheimer's brain have become kind of dysfunctional. They're not eating as much as they should or one would think. And so Tony's lab was looking at what are the differences in the expression of genes in these old microglia versus the young microglia? They found a big change in the expression of a receptor that binds to glycans. It's a receptor called CD22. It has another name called Siglec-2, which is Sialic acid-binding immunoglobulin-like lectins-2.

(41:53):

Anyways, point is that my lab had been studying that family of receptors because of their role in cancer immune suppression. Tony found one of them is upregulated in the microglia of the brain. We already knew from our work in cancer that when these receptors are upregulated, that can lead to basically suppression and inactivation of the immune cell and that is how cancers are able to shut down the immune system so that they can thrive unimpeded.

Nicholas Weiler (42:22):

Right, they're like flicking on the brakes on those immune cells that are supposed to be clearing them out.

Carolyn Bertozzi  (42:27):

That's right, right. CD22 is a break type of receptor. It's inhibitory when it gets engaged with its ligands. When Tony found the upregulation of that receptor in these old microglia, of course he reached out to me, said, "Hey, what do you think of this?" I said, "Wow, that's quite parallel to what we see in the setting of cancer." We started working on that together and turns out that if you block CD22, which you can do with an antibody, then the microglia are more active and the older mouse does better. It has a cleaner brain. And so that sort of suggested a therapeutic approach towards treating older people or people with neurodegenerative disease, which is to treat them with a blocking antibody against CD22. But you have to get that antibody into the brain.

(43:20):

So when we first made this discovery, we didn't have brain shuttles back then. This was many years ago now. We had to administer that antibody through an intracranial injection in the mouse to prove this was the case, and that's fine for the mouse. Well, it's not fine, but it's at least legal and ethical to do it to the mouse, but you really can't make a human therapeutic where you have to drill a hole in your head every month to administer it. So we didn't really pursue the therapeutic idea at the time, but now that we have some brain shuttle technologies, it would be fun to go back and revisit that CD22 antibody. We should look at that.

Nicholas Weiler (44:03):

Well, as we were saying, once you have a tool, once you have a way of... Just like once you have a tool for studying these glycans, you start learning all this stuff about their biology. Once you have a tool for getting stuff in the brain, it makes a lot of things possible. And it paints this picture of... I mean, immunotherapies have been incredibly successful in cancer, and if I understand correctly, most of those have focused on proteins and the ability to look at these glycans expands the range of that tremendously in cancer, but also having these shuttles to get into the brain, okay, maybe we have an immunotherapy for neurodegeneration in the future.

Carolyn Bertozzi  (44:38):

Yeah, or I think even a lower hanging piece of fruit is how about an immunotherapy for brain metastases? Because cancers often get into the brain, but our drugs don't. So once a patient has a tumor that's metastasized to the brain, there's not much you can do. And these immunotherapies that might work in other organs, they just don't work in the brain. Maybe we could change that.

Nicholas Weiler (45:04):

Well, Carolyn, we only have a few minutes left, and so I'm going to throw you a big picture reflection to end on. It's so inspiring, as I said, the way that just this curiosity about how this stuff works leads to new science, new technologies that change the field. For you, it led to a Nobel Prize recognizing how much this has changed the field, and I think a dozen companies that are really taking this to the next level.

(45:35):

If you could give us just a couple minutes reflection on what does it take for curiosity to change the world, and what do you see as... Maybe the more pointed end of that is, what do you see as the opportunities for the next five to 10 years? What are the ways in which you hope science will continue to give us these tools and abilities by following our curiosity?

Carolyn Bertozzi  (46:06):

Well, I would hope that we will continue as a nation to invest in early discovery oriented basic science. I think that's really important because that's the seed from which everything else grows. And lately, there's been a shift more towards valuing translation and application oriented science where you have a clear end goal and you, "All right, what do I have to develop? What technologies, what science do I have to do to get to that end goal?" And that's important too, because we have to solve problems. There are urgent problems, they need solutions. But you don't have to look very hard to realize that the solutions coming online for the problems of today have their origins in some very untargeted basic science from decades, maybe even centuries earlier. And ll of this is a giant foundation, brick by brick, that's been built that we benefit from today without even really thinking about it.

(47:13):

Just as a case in point, bioorthogonal chemistry is now... We first developed those chemistries quarter of a century ago, it was the early 2000s, and now they're used all the time. They're just baked into the fabric of the toolkit that chemists and biologists use. People have made drugs that are approved and sold commercially with the chemistry baked into the drug. So you might say, "Oh, well, today's drugs that use bioorthogonal chemistry, oh, that's based on the basic science from 25 years ago." But that's not even true because the basic science that we did 25 years ago to make these reaction leveraged chemistries from a hundred years earlier than that.

(48:01):

When I gave my Nobel lecture on the history of bioorthogonal chemistry, I went back to some of the reactions that we used to develop these chemistries in the first place. One of them was published in 1915, another was published in 1919, one was published in 1950 from Germany. These were old journal articles in German that we had to get translated and stuff. And at the time, those chemists were describing these reactions. There is no way they could have anticipated that a hundred years later somebody might make a cancer drug. The reason that they developed these chemistries and published them is because they were cool and interesting and unexpected at the time, and it was just describing how molecules behave. Very, very fundamental basic research.

(48:56):

Had it not been for that work, we would not have created bioorthogonal chemistry because it was all based on that. Had we not developed these chemistries with our particular application in glycoscience at the time, but other people said, "Hey, we could use that chemistry for this other thing." And so all these other applications, and so that's just the way science works. You met with John Long. He's following the playbook that led to the development of Ozempic and the GLP-1 receptor agonist drugs, the obesity drugs. And it's a famous story because Ozempic is based on a discovery from the weird metabolism of a desert lizard called the Gila monster. And this is a lizard that eats one meal every two months, and then in between these meals, somehow it maintains a very steady blood glucose level.

(49:54):

Humans is very different, and it turns out it's because of a hormone, and that hormone is GLP-1. It's the Gila monster version of GLP-1, but it has a lot longer half-life in the blood of the Gila monster than human GLP-1 has in the blood of the human. The very first GLP-1 drug was the Gila monster GLP-1 put into the human, and Ozempic is kind of like a third generation from that Gila Monster hormone. So that's a great example where somebody was like, "How is it that this lizard only has to eat once every two months? Let's study that."

Nicholas Weiler (49:55):

Right, it doesn't-

Carolyn Bertozzi  (50:27):

At the time, nobody was like, "Oh, and someday we'll have a billion dollar obesity drug." Nobody thought that, right? You couldn't have. You could not have foreseen that. That's just reality. Most scientists right now will not know the true impact of their work in their own lifetime. That's reality, right? And you have to acknowledge that and you have to invest in that science without knowing what its impact will be and on what timeline. You just have to make the investment. Otherwise, the whole pipeline will eventually dry up.

Nicholas Weiler (50:58):

It goes back to the old saying about knowledge being power, but it's true in science as well. The more we know, the more we can do. The more we can do, the more we can find out and it feeds on itself. Well, Carolyn, I want to let you go. I know you have other places you need to be, but thank you so much for coming on From Our Neurons to Yours. This has been fantastic.

Carolyn Bertozzi  (51:15):

Thank you for the conversation. I appreciate it.

Nicholas Weiler (51:18):

Thanks again so much to our guest, Carolyn Bertozzi. She's the Baker Family Director of Sarafan ChEM-H and the Anne and Robert M. Bass professor in the Stanford School of Humanities and Sciences. To read more about her work, check out the links in the show notes.

(51:34):

If you enjoyed the episode, please be sure to subscribe for more conversations from the frontiers of brain science and send us an email. If you have thoughts about the show or questions about the brain you'd like to hear us discuss in a future episode, we'd love to hear from you. We're at neuronspodcast@stanford.edu. You can also leave us a comment on your favorite podcast platform. While you're at it, please give us a rating and share the show with your friends. It may seem like a small thing, but it's tremendously valuable for us to be able to bring more listeners to the frontiers of neuroscience.

(52:05):

From Our Neurons to Yours is produced by Michael Osborne at 14th Street Studios with sound design by Mark Bell. Our social media strategy is by Julia Diaz. Additional editing by Nathan Collins. Our logo was designed by Amy Garza. I'm Nicholas Weiler. Until next time.

Related News

More News