Dr. Wu, thank you for being part of our OneNeuro faculty interviews. Let’s begin with a brief description of your research.
My lab is interested in the molecular and circuit mechanisms underlying sleep and circadian rhythms. I am a neurologist and a sleep medicine physician, and I’ve always been interested in sleep.
When I started my lab in 2009 here at Hopkins, it was set up as a fly sleep lab, a lab that studied the neurobiology of sleep in Drosophila. I had never worked with mice, and I had never done human research, even though I’m a physician and sleep clinician. So, what happened was we identified a novel gene from Drosophila called “Wide Awake” that acts as a clock output gene to regulate neuronal excitability ability in a time-dependent manner. And it did so in clock neurons. We discovered that this gene was conserved in mammals, including mice and humans. And, interestingly, it was enriched in the suprachiasmatic nucleus, the SCN, which is the master circadian pacemaker for mammals. Since that time, we have been studying conserved molecular and circuit principles underlying sleep and circadian rhythms mainly using fruit flies and mice.
How did you become interested in studying sleep and circadian rhythms?
Looking back on my life, when I was a child, I loved sleep and really enjoyed it! When I was interviewing for the MD/PhD program, one of the interviewers – a physician – asked, “What do you think is going to be most challenging for you in medical school and residency?” And I said, “Well, I’m not totally sure, but I really enjoy sleeping.” He laughed, and I did end up getting accepted to that program. But as far as how I got into sleep research– I fell in love with neuroscience in graduate school. I was a graduate student doing my PhD research with Dr. Hugo Bellen at Baylor College of Medicine, where I studied the molecular mechanisms of neurotransmitter release. I was a night owl, and so I’d often be in the lab until two in the morning and I would check on my flies. They all would be very quiet, sitting at the bottom of the food tray, doing nothing. I asked Hugo if flies slept, and he replied, “Well, I don’t know if they sleep or not, but they definitely have circadian rhythms.” At that time, I didn’t realize that many years later I would be studying sleep and fruit flies and, subsequently, mice and also humans.
Because I loved neuroscience, I decided to specialize in neurology and did residency training at UCLA. I was interested in a field where I thought there were major scientific questions that remained to be solved, and I felt like sleep was one of those fields. It also was a field that was very conducive to doing a lot of basic research because unlike fields like stroke, which are clinically intensive, sleep is less demanding. It’s more laid back, and that creates space to do basic research. I followed my residency with a fellowship in sleep medicine at the University of Pennsylvania and postdoctoral research with Dr. Amita Sehgal, where I began studying sleep in fruit flies.
Who are your collaborators in this research?
I think that the OneNeuro program is really great because we have such breadth and strength of neuroscience across all the campuses. In my own career, I’ve had many important and helpful collaborations within neuroscience that have shaped the direction of our research. Sometime after the discovery of the Wide-Awake gene, I approached Seth Blackshaw (Department of Neuroscience), and he was very enthusiastic to collaborate. That started a journey of us studying and working closely with Seth and also Samer Hattar, now with NIH, but at that time was still at Hopkins. Working with Samer and Seth, we started to study Wide Awake in mice, and those two were very generous with their time and sharing their resources and expertise. Over several years, my lab became completely independent in terms of studying sleep in mice as well.
In terms of human research and sleep, we work on determining connections between sleep and Alzheimer’s disease. We collaborate with several teams who are perhaps not in the OneNeuro program per se, but they could be actually. For example, my colleague Adam Spira, an epidemiologist in the School of Public Health, studies sleep, aging, and Alzheimer’s disease. I had wanted to do some human-related research because I’m a sleep clinician and was thinking to do some translational work. I met Adam, and we decided it would be great to collaborate. Over the past decade or so, we have found evidence that poor sleep is not only associated with Alzheimer’s disease pathology, but is a risk factor for it.
I think in some ways sleep is a “poster child” for OneNeuro because sleep is so multidisciplinary.
Are you working to solve an existing problem or creating new knowledge?
Sleep is a field that involves – at the clinical level – neurologists and psychiatrists, internal medical doctors and head and neck surgeons. But also at the scientific level, it involves many types of analyses and researchers, because sleep is a fundamental brain state. For example, at Hopkins, although they wouldn’t be called sleep researchers, people like Rick Huganir, Paul Worley, who study neural plasticity and Seth, who does study sleep, have all published on sleep. But the point being that, scientifically, sleep is a fundamental brain state, whose function likely is related, at least in part, to neural plasticity. And, of course, plasticity is one of the major themes in neuroscience research.
The other thing to just consider is that sleep encompasses a substantial portion of an animal’s life. As a human, you are going to spend ~20 years of your life asleep. Yet I would say the vast majority of neuroscientists study what the brain does when awake. We know sleep is really important, but I think it’s a scientific area primed for growth and integration and for people to work together to solve really a fundamental basic science problem, which is: “Why do we sleep?” It’s the only major behavior for which the function remains unknown. We have many ideas for why we sleep and just as many hypotheses, but we still don’t know the final answer. Personally, I think the function of sleep is to provide a time for the brain to perform restorative functions it can’t do when the animal is awake. But what does that mean at the molecular, cellular, and circuit levels? This is the million-dollar question.
In our research on fruit flies, we study the molecular and circuit mechanisms of sleep. We then translate those ideas from flies to the mouse, a principle similar to what scientists like Alex Kolodkin used, which is to use the power of genetics and fruit flies to identify new things. When I say new things, I mean new molecules like Wide Awake or new circuit principles like a sleep drive circuit. Then we try to study their relevance for mammals and humans by studying them in mice, which are slower and more expensive than flies, but more related to humans.
So, in our research on mice, we subsequently showed that the functions of Wide Awake are conserved in mice and, presumably, humans. It basically serves to suppress neuronal activity at night, but in a time-dependent manner. What is interesting is that because mice are nocturnal – whereas flies are essentially diurnal, and of course humans are diurnal – the effects on behavior are a little different. In fact, the behavior is opposite. Wide Awake in a mouse reduces excitability and activity at night. It calms mice during the night when they’re normally very active. When you remove Wide Awake, mice become really hyperactive at night. In flies, we found that Wide Awake calms down neural activity at night to promote sleep. Thus, on the surface, the phenotypes are backwards because of when mice and flies sleep, but the molecular and basic function of Wide Awake is conserved in each. That’s one example of how working here at Hopkins has really changed the direction of our research.
What are a few of the most exciting and challenging projects you’re working on right now in the lab?
A very niche topic has been study of the correlation between sleep and Alzheimer’s disease. Just a few years ago, few people were working on it. What helped to spark the field was David Holtzman’s work in 2009 showing a causal relationship between poor sleep and Alzheimer’s pathology. And we were right at that beginning of the field; we received pilot funding from the Brain Science Institute, with absolutely no preliminary data, just an idea. It ended up being a very successful collaboration, which is still ongoing. We started to study sleep and Alzheimer’s in fruit flies, and we now do this in mice. We’ve also done studies in humans and in collaboration with many colleagues, such as at the Baltimore Longitudinal Study of Aging and other people like Paul Rosenberg and Barry Greenberg in Psychiatry and Neurology. For example, Adam Spira led a study where we showed that, in humans, if you have less sleep or poor sleep, you have more amyloid beta (Aβ or Abeta) in your brain. Multiple lines of research related to this have spun off into multiple grants and has led to a lot of advances.
Recently, what we’ve done is now, in addition to molecules, we’ve also looked at circuit principles for sleep that are conserved between flies and mammals. So, for example, in Drosophila in 2016, we described the first neural circuit encoding sleep drive in an animal, and recently in unpublished work, we have found a parallel circuit in mice that we think shares many of the same key features in generated persistent sleep and using neural plasticity to promote this persistence. On the surface, the circuits in flies and mice don’t look anything like each other, but the underlying principles of the circuit can be conserved. It’s been fun going back and forth between flies and mice, and our lab is doing a lot of work in mouse sleep now.
Being a sleep clinician also has given me opportunities to incorporate my clinical work into research. One example is our study of sleepwalking. It began when I met a patient in clinic who was a sleepwalker, and subsequently learned that numerous members of the family also were sleepwalkers. They were very curious as to why so many people in their family sleepwalked. They generously agreed to participate in research, and we’ve been studying them and working with them. In collaboration with other researchers here at Hopkins, like Dave Valle and Nara Sobreira in Human Genetics, we have cloned a gene from the family that we believe causes sleepwalking. We engineered the gene into mice using CRISPR, and the mice exhibit sleepwalking too!
What are a few of your goals and aspirations for your research?
One goal, and this is a big ask, is to try to shed light on the function of sleep. That’s our number one goal and a very broad one. Another broad goal is to try to understand the relationship between sleep and neurological diseases like Alzheimer’s and how improving sleep could prevent or slow neurodegeneration.
We have several more specific goals. We’re trying to deep phenotype sleep in flies. Flies are incredibly powerful from a molecular and genetic standpoint, but the phenotyping of sleep is cruder than in mice and humans. For example, in mice and humans, we can do electroencephalography, which precisely identifies sleep. So deeply phenotyping sleep in flies, looking at the neurophysiological signals underlying sleep, is one of our short-term, more narrow goals.
Also In the short term, we’re interested in using our findings in the sleepwalking work to understand how the brain can operate in half-awake and half-asleep states. Most people think of sleep and wakefulness as distinct states– I’m either awake, or I’m asleep. Yet clinically, there are many examples of when the brain is actually partly awake and partly asleep. One simple example is if you’re in a boring lecture and you feel half asleep, your brain literally is half asleep. When we do a high-density EEG on someone’s brain in that situation, we can see that parts of the brain are awake, and parts are asleep. For conditions such as sleepwalking, the question is how does a human, while they are essentially asleep, walk around and engage in complex behaviors? I think using the results of our genetic and molecular studies will lead, potentially, to new understandings of how these kinds of questions can be addressed at the circuit level.
Considering our Hopkins students, what do you recommend that they do or what could help them along their path to perhaps working in your lab someday and being successful in the lab?
Number one – we’re interested in people who are curious, who are very interested in big problems. As I mentioned, some of the questions that we’re asking about the function of sleep and other, similar topics are big problems. The other thing is a little bit of independence. What do I mean by that? Some students are naturally a little more independent, while others seek a little more guidance at a very close level. The reason I say that is because we are not a huge lab, but we cover a lot of topics and do research in flies, mice, and humans. Students who do well in our lab have some degree of independence, where they’re not afraid of asking people inside and outside of the lab for advice. Our style of science in the lab is to have each trainee lead their own project, but then also for those trainees to be intertwined and collaborate with others.
What do you enjoy doing in your spare time?
In my life, a long-running theme has been music. I played a lot of piano and violin when I was young. Then in college, my musical interests evolved, and I became a DJ, which I did through college and medical school. I was a dance music or club DJ. It was a lot of fun and something that I did for many years. Now my interests revolve around what my children do. So, besides science, most of my time is spent with my kids. What we’re doing a lot lately is softball and baseball. It’s fun, with lots of cheering, and because of that, I’ve learned a great deal about the softball/baseball swing, and the little details that go into having a smooth, efficient swing, etc. It’s been fun, but I’ve been buying too many softball and baseball bats!
Recent Publications from Mark Wu’s Lab:
Brown, M.P., Verma, S., Palmer, I., Zuniga, A.G., Mehta, A., Rosensweig, C., Keles, M.F., and Wu, M.N. (2024). A subclass of evening cells promotes the switch from arousal to sleep at dusk. Curr Biol 34, 2186-2199.
Han, E., Lee, S.-S., Park, K.H., Blum, I.D., Liu, Q., Mehta, A., Palmer, I., Issa, H., Han, A., Brown, M.P., Sanchez-Franco, V.M., Velasco, M., Tabuchi, M., and Wu, M.N. (2024). Tob Regulates the Timing of Sleep Onset at Night in Drosophila. J. Neurosci 44, doi.org/10.1523.
Liu, Q., Bell, B.J., Kim, D.-W., Lee, S.-S., Keles, M.F., Liu, Q., Blum, I.D., Wang, A.A., Blank, E.J., Xiong, J., Bedont, J.L., Chang, A.J., Issa, H., Cohen, J.Y., Blackshaw, S., and Wu, M.N. (2023). A Clock-Dependent Brake for Rhythmic Arousal in the Dorsomedial Hypothalamus. Nat Commun 14, 6381.
Above Image: Mark Wu’s Lab Matt’s Thesis Defense, Summer 2023 – The lab celebrattes Matt becoming Dr. Brown! / Wu Lab
Above Image: Picnic Spring 2023 – Korean BBQ and sand volleyball at the park to celebrate Emily, Isabelle, and Shubhi graduating and welcoming Anu and Zhengyu to the Lab! / Wu Lab
