Left: Image of Dr. Daniel Yoo
Right: Image of a subretinal fibrotic lesion
Can you please tell me a bit about yourself and what inspired you to enter research.
My name is Daniel Yoo. I was originally born in Seoul, South Korea, and then I moved to Canada at the age of 14. I spent my time doing my PhD in neuroscience at Carleton University in Ottawa, and then I decided to move to Vancouver to pursue my postdoc training.
I was never actually good at science as a kid. During high school, I was just okay at chemistry, biology and physics. However, I decided to start studying biochemistry for my undergraduate studies, mainly because I wanted to become a dentist, and dentistry programs require you to take undergraduate biology, chemistry and biochemistry courses. And then after a couple of years into the undergraduate biochemistry program at Carleton University, I realized it's super hard, but I decided to persevere and then see if I can actually get the degree. I ended up doing pretty well, even though it took six years to complete my undergraduate education (with a high distinction). Towards the end of my undergraduate studies, I ended up taking a 4th year biochemistry course called “Biochemistry of Disease” where I learned about Alzheimer’s and Parkinson's disease for the first time. I was amazed that tiny proteins can wreak havoc in the brain and disable our ability to remember and control movements. Through this course, I became really interested in learning about the biochemistry of neurodegenerative diseases and figuring out how to promote neural repair in the central nervous system (i.e. the brain, spinal cord and, most importantly, retina).
So I ended up doing my master's in neuroscience with Dr. Patrice Smith, who is one of the pioneers in optic nerve regeneration research. She used retinal ganglion cells in the retina to study how axons can regenerate after injury. She did some genetic manipulations to figure out the mechanisms of how neurons in the central nervous system can regenerate their axons. I initially wanted to do Parkinson’s disease research with Dr. Smith, but her work was largely focused on the eye (more specifically the retina and optic nerve). So I actually kind of got into eye research by accident, as I assumed she would be still pursuing Parkinson’s research after studying the disease for her PhD. But after hearing about the retina research from her, I thought it was pretty interesting, so I decided to pursue retina research.
Going back to my initial interest in becoming a dentist, I couldn’t get into Canadian dental schools but got into a couple of American dental schools. But the tuition was too expensive ($400,000 USD for four years). So I decided to just continue with my neuroscience research. I did my PhD in neuroscience with the same supervisor. Then COVID happened, which delayed my progress, but I managed to graduate within four years.
Towards the end of my PhD, I wanted to start studying a specific eye disease. The model I used to study the retina is called optic nerve crush, where you crush the optic nerve with microforceps. And that leads to specific death of retinal ganglion cells in the retina. And then, using that model, you can do genetic manipulations or pharmacological treatments to see what can regenerate axons of these retinal ganglion cells. There are so many different eye diseases, but age-related macular degeneration (AMD) seemed pretty interesting to me at that time. The retinal degeneration in AMD is actually caused by tissue growth processes, namely abnormal blood vessel growth (termed choroidal neovascularization) and scar tissue formation (termed subretinal fibrosis). Having studied both neurodegeneration and neural repair, I thought I was in a unique position to study this unique retinal neurodegenerative disease involving both neurodegeneration and tissue growth processes.
Can you please share about what age-related macular degeneration (AMD) is?
Age-related macular degeneration is a retinal neurodegenerative disease in the elderly population, and it causes the degeneration of the part of the eye known as macula, which is responsible for your central vision and has the highest visual acuity. There are two different forms of AMD. The most common form is called dry AMD, and it doesn't necessarily cause blindness. This is good since dry AMD is the most common form of AMD. It's not as threatening as the less common form of AMD, which is known as wet AMD. Wet AMD involves a very rapid abnormal growth which is called choroidal neovascularization (CNV), and although less common, it accounts for 90% of AMD-associated vision loss. Thankfully, we do have a treatment option for CNV, which is called anti-VEGF therapy; it basically suppresses the activity of a growth factor that promotes blood vessel growth (i.e. VEGF). But the problem is that it only works on roughly 30% of people with wet AMD. And even if it works initially, people seem to start developing drug resistance over time. So researchers are now actively trying to seek out more effective therapeutic targets that can address these problems.
And is it ineffective in some populations because of the fibrosis component of wet AMD?
We actually do not know why anti-VEGF therapy is ineffective in some people. Researchers are still trying to figure it out. But the fibrosis component of wet AMD seems to happen regardless of anti-VEGF therapy in more than half of patients with wet AMD. Right now, we don't really know how fibrosis happens in wet AMD. And because we don't know how it happens, we don’t have any treatment options for subretinal fibrosis.
What is fibrosis? How does it manifest?
Fibrosis is a part of the wound healing process. So let's say you cut your skin by accident, you will bleed first, and then eventually the bleeding stops. And then different types of immune cells get recruited towards the wound, and they start releasing all these different chemicals towards the wound. These chemicals eventually promote new blood vessels to grow so that more oxygen and nutrients can be delivered to the wound. So that's the first few steps towards wound healing, and then eventually that blood vessel growth turns into scar tissue, which is known as fibrosis. And fibrosis is basically a process that tries to close up the wound. There are a lot of different processes involved in fibrosis, but there are these cells called myofibroblasts, and they are the ones that basically patch up the wound. And then eventually your skin regenerates itself. A similar process happens in the eye, but somehow the fibrotic process in the eye just gets worse over time. In the skin, these myofibroblasts eventually die off once they close up the wound. But they survive and persist in the eye, making the scar tissue get bigger and bigger and eventually resulting in death of these light-sensitive neurons in the retina (i.e. photoreceptors) and thus irreversible blindness in wet AMD.
Do we know why it continues to persist?
We have no idea!
Could you please share how the symptoms of wet AMD manifest?
In terms of symptoms, the first thing people notice is that their central vision gets very blurry, and they have a harder time seeing what is directly in front of them. So once they start developing wet AMD, they have to rely on their peripheral vision to navigate their environment. For instance, if I have wet AMD and try to take a look at your laptop, then I'll have to actually move my head and view it using my peripheral vision.
And so with dry AMD, there's less of a visual impact?
Yeah, so it doesn't necessarily always cause blindness, but you might start seeing blurry spots in your central vision. Worst case scenario, dry AMD can eventually progress into wet AMD. So it could lead to irreversible blindness once it transforms into wet AMD.
And I can imagine that would be very debilitating. What are the social factors in AMD, for both patients and their families?
It can be very depressing, and AMD patients do have a higher risk of developing mental disorders like depression and anxiety. It can be harder for patients with wet AMD to socialize with other people, so they may be less inclined to talk with others. It can be hard on their family members because, through blindness, the person's behaviour will change drastically. Usually the family members are the first ones to notice. And it can be depressing for them too. Accessibility to care is another thing I should mention. If the patients live far away from the hospital, then they have to commute to get the anti-VEGF injections regularly (usually once a month). And with central vision problems, they can’t drive safely. And it is also harder for them to get on and off the bus.
What age does AMD typically occur at?
Typically, over the age of 50 or 60. That's why it's called age-related macular degeneration, because age seems to be the single best risk factor.
Is AMD related to other neurodegenerative diseases?
So drusen is protein deposits that start appearing at the back of the eye during the early stages of AMD. Drusen actually contains a protein called amyloid beta, which is also found in abundance in Alzheimer's patients’ brain and retina, so there is some connection there. They actually might share similar neurodegenerative mechanisms.
How is AMD diagnosed?
Early AMD is usually diagnosed by looking at yellow protein deposits or drusen, which can occur in both dry and wet AMD. Drusen is the earliest pathological indication that you are starting to develop AMD. And as I mentioned before, dry AMD can actually transition into wet AMD as well. Once you have wet AMD, you will have bleeding inside your eye, especially around your macula. This bleeding is caused by these newly formed vessels in the macula, and it could be treated by anti-VEGF therapy.
How do they detect these changes?
They use in vivo retinal imaging technique or fundus imaging. So your optometrist or ophthalmologist will use a fancy machine to take a look at the back of your eye. And they will see these yellow spots around the area of the retina known as macula - which is where abnormal blood vessel growth, fibrosis and retinal degeneration take place.
And so you’ve been researching the role of granzyme B in AMD. Can you please share a bit about your research?
Granzyme B is an enzyme that's released by a certain group of immune cells, and it's mostly known to kill off bacteria and viruses in our body. Emerging evidence is now showing that granzyme B is also known to cleave all these different types of proteins on healthy cells (kind of like a scissor), and that can either kill off these healthy cells or change the cellular environment in such a way that cells start proliferating when they shouldn’t. This proliferation can lead to abnormal blood vessel growth and also scar tissue formation. Our studies show that pharmacological or genetic deletion of granzyme B can suppress abnormal blood vessel growth in eye tissue cultures or in mice. My recent study also indicates that genetic deletion of granzyme B can attenuate scar tissue formation in mice. So we think that, based on our studies, pharmacological inhibition of granzyme B might be a viable/more effective option for treating wet AMD.
So the current treatments for AMD are not effective in addressing this?
Anti-VEGF specifically targets that VEGF growth factor, so it doesn't actually target any other proteins, including granzyme B. Granzyme B actually causes more release of VEGF, so that's how it's tied to CNV. Since anti-VEGF can’t prevent granzyme B from releasing more VEGF, this might be the reason why it doesn’t work all the time and stops working over time.
Many of the studies exploring AMD utilize animal models. Could you please share a bit about the importance of using animal models in research?
Yeah, sure. Animal models are very useful because they are biologically very similar to us. In AMD research, mice are the most commonly used animals, and thanks to them, we ended up discovering anti-VEGF therapy. And you might be wondering how we induce wet AMD in mice, right? So we basically shoot the laser at the back of the eye to initially cause abnormal blood vessel growth. And then if we want to study scar tissue formation, we shoot the laser again on the same spot, and that turns that blood vessel growth into scar tissue formation. It’s officially known as two-stage laser-induced mouse model of subretinal fibrosis, and that's the animal model I've been using to study the role granzyme B in subretinal fibrosis.
What ethical factors you need to consider when conducting research involving animals?
Researchers and the animal ethics committees care really deeply about animals and their overall well-being. We make sure that they're eating well and regularly check their cages to see if they have enough food and water. And we also make sure that we change the bedding every once in a while. Mice are known as social animals, so they actually have to be caged together, not by themselves. Although, the problem with caging them together is that potentially they (especially males) can get into fights. But it's better to keep them together, because if they're by themselves, they actually tend to stress a lot, and then, as you learned in your neuroscience program, stress can lead to too much release of stress hormones, and these hormones can damage all your essential organs, including your brain.
Handling animals can often induce stress. What protocols do you take when handling the mice to minimize the amount of stress experienced?
Sometimes I talk to them, like “okay, buddy, let's go.” And just let them know that I am there. I try to be very nice and gentle with them. I don't try to scare them when I handle them. I make sure that they are aware of what I am about to do (e.g. measuring their weight, giving them injections or eye drops, etc.). We also provide nesting materials and hiding places for them so that they feel at home in their cages.
What are some future areas of research that you and your team are interested in?
We have recently established that granzyme B is involved in both abnormal blood vessel growth and scar tissue formation in wet AMD. My first author paper on the role of granzyme B in subretinal fibrosis is currently under review for publication, and once it’s accepted by the journal, hopefully soon, it'll be available for the public. Up till now, we have been using the genetic model to study the role of granzyme B in wet AMD. Now that we know that granzyme B actually plays a crucial role in wet AMD, the next step would be to inject a granzyme B specific inhibitor into the eye and see if this could suppress the development of wet AMD in mice.
What does a typical day of work look like for you?
I usually wake up at around like 5 or 6 AM. And then I go to the gym because it's important for maintaining my physical and mental health. Then I usually come into the lab at around 10 am. If I have long experiments to do, I come to the lab as early as 6 AM. Sometimes I'll be here running western blots or doing immunohistochemistry. Sometimes I'll be at the Jack Bell Research Centre, which is where we house all our animals and do our laser experiments to study wet AMD. Sometimes, I'll be just working on my research grant applications or working on lectures for my courses I teach at UBC.
What do you love most about your work?
My work allows me to be creative. That's the main reason I like it. As a kid, I wasn't really creative or into being creative, but by getting into science research, I realized how fun it is to be creative. What's cool about science research is that you get to come up with the craziest idea, and you get to actually test it. So that's what I like the most about my job. And then I get to work with a variety of people from different walks of life, and I get to teach/mentor a lot of students aspiring to be scientists or health professionals.
What's the most surprising thing you have learned from your research? Either from working in the field or directly related to your lab experiences.
Oftentimes people describe scientists as these crazy people who work alone at a small lab bench, but that's not really the case. You can't do science in silos. You have to work with others. It's actually really hard to do research by yourself, because you need to get research grants to do your own research, and they are really hard to come by. But if you collaborate with others, they can partially cover your research costs. And by interacting with other people from different disciplines, you can also come up with more creative research ideas and use different lab techniques to test them. I am currently being supervised by Dr. Joanne Matsubara (AMD expert) and Dr. David Granville (Granzyme B expert). Without their expertise and research funding, I would not have been able to design and execute my postdoctoral project on the role of granzyme B in wet AMD. I also have been collaborating with Dr. Myeong Jin Ju (in vivo retina imaging expert) and his biomedical engineering team, and they helped me image abnormal blood vessels and scar tissues in mouse eyes.
What are you most excited about as you look towards the future?
I'm excited to see that vision scientists are really expanding the knowledge of AMD in general. I'm actually quite optimistic about finding the cure for AMD. Research is progressing very quickly, and vision scientists are publishing a lot of interesting studies deciphering pathophysiology of AMD and identifying novel therapeutic targets for AMD. So I think we are going to eventually cure AMD.
And you may be personally interested in knowing how all this can relate back to the brain. Based on our research, granzyme B has a clear role in AMD, but other studies have shown that granzyme B is also involved in TBI, stroke, and other neurodegenerative diseases, like multiple sclerosis. So whatever I end up finding in my AMD research, I can directly apply it to studying other brain conditions. Eyes are basically windows to the brain, and nowadays people are trying to use the retina as a tool to early diagnose these neurodegenerative diseases. My postdoc colleague, Dr. Printha Wijesinghe, in Dr. Matsubara’s lab is studying whether tears can be used to early diagnose Alzheimer’s disease.
If you give one piece of advice to people interested in science or research, what would it be?
If they're generally interested in science, I would say, keep their options open. Don't just narrow down to like, biology, chemistry, or physics. Take different science courses and then see which one sticks with you and continue pursuing that. This is one thing I would like to emphasize, you really need to keep your options open. The thing is, you know, you never know what happens in your life. Your interests can change throughout life, so it's good to keep your options open. I initially wanted to be a dentist, but then eventually, after doing years of research, I realized that neuroscience is what I want to pursue.