Cell Scientist to Watch – Maria Ioannou

Maria Ioannou. Photo credit: Brian Marriott.

Starting at the beginning, how did you first become interested in science?

I generally did quite well at school, and although my grades were highest in mathematics, I thought that biology was a lot more interesting and so I decided to do an undergraduate degree in a life sciences program. I took a course called ‘molecular biology of the nucleus’, and I can remember the moment I learned about GFP. I thought it was so cool how researchers could attach it to proteins and watch them move, because up until that point, everything that I learned in undergrad was based on experiments that are quite static. Then, about a year later, I started working in the lab of Margaret Fahnestock for my undergraduate thesis. We studied neurotrophins and nerve growth factor (NGF), and I really enjoyed the experiments. So, I thought, ‘I'm just going to stick with this until it stops being fun’… and here I still am!

You completed your PhD at McGill University, Canada. What did your research focus on here?

Prior to my PhD, I studied NGF–receptor binding and downstream signalling for my Master's thesis. But I was particularly fascinated with the fact that this ligand–receptor complex would get endocytosed and trafficked along the neurons. So for my PhD, I went to work with Peter McPherson to learn more about endocytic trafficking. My project was on the Rab GTPase, Rab13, and we looked at how it regulates recycling endosomes. We identified its activator, a guanine nucleotide exchange factor (GEF) called DENND2B, and we figured out how it mediates trafficking of Rab13 to the leading edge of cells, which facilitates cancer cell migration, invasion and metastasis. So, even though I was in a neuroscience program, the project meandered to epithelial cancer biology, and Peter was very supportive of just going where the data takes you, which I really appreciated and learned a lot from.

It was during my PhD that I also really started to get into microscopy. I took a course called ‘analytical and quantitative light microscopy’ at the Marine Biological Laboratory, Woods Hole, USA, and I think this is when I really started to see myself as a microscopist, or at least the desire to establish myself as one. I wanted to apply everything I had learned in that course to my research in Peter's lab, so I started live imaging Rab13 vesicles, and that's how we learned about their localized trafficking at the leading edge of the cell. We also collaborated with Louis Hodgson from the Albert Einstein College of Medicine, New York, USA. His lab creates FRET-based GTP biosensors, and so we collaborated with his lab to generate one for Rab13. The biosensor takes advantage of the small GTPase's specificity for effector proteins when active. When Rab13 is active, it binds to the effector binding domain and brings two fluorescent proteins in close enough proximity for energy to transfer and alter the fluorescence emitted. The result is that inactive Rab13 will fluoresce blue and active Rab13 will fluoresce yellow. Using this sensor, we were able to show where Rab13 is being activated in real-time, which was just fascinating. I've been hooked on microscopy ever since.

You then moved to the Janelia Research Campus for a postdoc co-supervised by Drs Zhe (James) Liu and Jennifer Lippincott-Schwartz. Why did you decide to move here and what was it like to work between two groups?

I originally moved to Janelia for the microscopy; both James and Jennifer are incredible cell biologists and experts in quantitative light microscopy. Jennifer focuses on organelle trafficking, similar to what I had focused on in my PhD, whereas James is interested in transcription factors and imaging single-molecule dynamics. I thought that their skill bases would complement each other, and so I convinced them to co-supervise me. Having the joint expertise of two brilliant scientists who had different biological interests and were at different career stages allowed me to have input on my project from different angles, and this was really helpful. Just like Peter did in my PhD, both of them gave me the space I needed to take my project in the direction the data dictated. I originally started working on an extracellular vesicle (EV) project to study their transport from neurons to glia; I set up co-culture assays to follow EV transport, but had difficulties visualizing the vesicles. So, I subbed in fluorescent lipids, and that worked a lot better and actually revealed that lipids were being transported between these cells, not just EVs. The data on the lipid experiments were so robust that it just became my main postdoc project. I'm really grateful they allowed me to shift my focus, as this is what I ended up building my lab on! I really believe that if you just follow the science, you don't necessarily need to know where you're going. Having mentors that allowed me to explore the science freely was really helpful to my career.

You then started your lab in 2019 at the University of Alberta, Canada, where your research focuses on lipid homeostasis in the brain. How did you find the transition from postdoc to group leader?

I really enjoyed the process of becoming a PI, and one thing that went a long way with this is that the people in my department are exceptional and supportive; I got a lot of help from the senior faculty in the department, who helped me go through some of the ins and outs of starting a lab that you don't really know about beforehand. There is a mountain of administrative work that you're not really prepared for, and so I think just having people that were willing to go out of their way to help me navigate the part of the job that I'd never been trained in before, made my transition a lot smoother.

With that said, I do have to make sure that I'm careful and that I rein myself in sometimes; I often have more ideas than I have hands or time to commit to. I think it's important to be balanced on what's actually feasible. You have to understand that projects move slowly at the beginning, even with the most exceptional trainees, and so some advice I was given early on is to do as many experiments alongside your students as you can. Even now, I try to make sure I carve out time to be in the lab and do experiments, particularly when it comes to imaging; I love being on the microscope, as I get to see the science happening while also getting hands on with training my students. It's a win–win.

What are the main questions your lab is trying to answer?

The overarching theme of my lab is to understand how lipids are regulated in the brain in both healthy and disease contexts. Specifically, we focus on how neurons release lipids. In my postdoc project, we found that neurons release lipids in response to different types of oxidative stress. Now, we are trying to hone in on the mechanisms that neurons use to expel lipids. We think that there are a lot of different mechanisms at play, so we want to know what they are, when they are used and whether they are implicated in different diseases. Also, how do they contribute to different types of cell death? For instance, ferroptosis is a type of cell death caused by accumulation of iron and consequently peroxidated lipids, and we have shown that these can actually be released by neurons and taken up by glia to help reduce the burden on neurons. But the natural follow-up question is what happens to the glial cells? Can they process these peroxidated lipids or does it just shift the burden to the glia? Do those glia then become dysfunctional, and if so, what is the tipping point? So, these are the some of the questions that we are trying to address, but as I mentioned before, we will go where the data leads us, so who knows where this will take us in 5 or 10 years from now.

As you mentioned, a clear theme of your group is the use of live-cell imaging and super-resolution microscopy (SRM) – what are the benefits and/or limitations of these techniques and how do they help address your questions?

In terms of microscopy and science, seeing is believing. Biochemical techniques are very useful, but they can be static or lack compartmentalization, whereas watching something with your own eyes happening in real-time is very convincing and reveals a lot of new and exciting information. Right now, we're using SRM and live-cell imaging to monitor lipid transport between cells and organelles, which is an extremely valuable strategy. The major limitation of this, however, is that when you tag a lipid with a fluorophore you can potentially affect how it's incorporated into the cell and how it's metabolized. This is a general caveat to tagging proteins, and it definitely extends to lipids too. Therefore, biochemical techniques are still very important and complement the imaging work, and we try to do both. But the tools for studying lipid biology, especially for imaging, are really starting to ramp up; for example, the development of label-free lipid imaging methods and in vivo imaging. We have recently started trying to do two-photon imaging in live brains, and my dream is to be able to look at lipids in the brain in real-time in a live animal. So I think it's a really exciting time to be working at this interface of lipid biology and microscopy.

You recently published a paper showing that neurons release fatty acids to protect themselves against ferroptosis – how is this achieved and what are the implications of these findings?

Lysosomes are a major organelle responsible for both lipid and iron metabolism. When iron accumulates, the membranes can become peroxidated (damaged by reactive oxygen species). The cell then tries to compensate for this by using autophagy to degrade those membranes. If the oxidative stress is high enough, then the cell expels them by lysosomal exocytosis. In our paper (Ralhan et al., 2023), we demonstrate the presence of what we refer to as ‘lipid protein particles’. These are dense particles within autolysosomes that are released. We can detect them in the lysosomes by microscopy, but also by cryo-EM in the neuronal conditioned medium. We think that these are heavy particles of peroxidated lipids, iron and other proteins. We hypothesize that this is a precursor for lipofuscin, which is a membrane-bound granule comprising indigestible material, including peroxidated lipids and iron. Given that it cannot be degraded, lipofuscin accumulates with time and so is associated with ageing post-mitotic cells, such as neurons. If you prevent neurons from expelling these lipid particles, then that sensitizes them to death by ferroptosis. There is clearly a link between lipofuscin accumulation in aging cells, lysosomal exocytosis and susceptibility to ferroptosis. Thus, we hypothesize that the vulnerability of aged neurons to ferroptosis occurs when the neurons can't remove these damaged lipids and/or the glia have become overburdened with lipids and they have nowhere to go. This is a really interesting question in the context of ageing and neuronal degeneration.

I see from your website that your lab group regularly attends conferences – how important would you say conferences are for early-career researchers and what is your advice for getting the most out of them?

It may seem obvious, but I love conferences for the science; I always come back feeling inspired and motivated to do more experiments. As a young trainee, I particularly loved going to the smaller conferences as there are lots of opportunities to interact with new people, whereas in the big conferences it is easy to feel a bit lost. Being able to sit down at a table and have dinner with the senior PI on this big paper you just read last month – that's really exciting. You also get to meet a lot of people, learn about their different career paths and get advice on how they managed particular stages of their careers. So my advice would be to try and be as social as you can to establish connections. I realize that's not easy for everyone, but I think there is a lot of value in building a network with researchers in your field; some of my most productive collaborations that I have now are with researchers that I met at conferences when I was a trainee.

What is your approach to mentoring and what aspect(s) of mentoring do you find the most enjoyable or rewarding?

I love mentoring trainees. I like to keep my lab at a manageable size and not take on too many students, because I feel that it's important that I'm able to devote time and energy to each person. My mentoring approach is still a work in progress because I haven't had my lab for that long, but I've already learnt that you have to adapt your mentorship style to each different personality type. For example, I liked being independent when I was a trainee, but I also liked talking about my science all the time. So, I try to ensure everyone has the space to be independent, while making sure I have time to meet with them weekly – but I let them lead the meeting. I also try to make myself approachable; I want them to be excited about sharing their science with me. I especially love it when they're on the microscope and they come to my office and say, ‘do you want to see something?’ and then I can sit with them and observe the science in real-time, which is much more exciting than looking at still images.

The most rewarding part of mentoring students is watching how far they've come. Now that I'm about 4 years into running a lab, I'm seeing the first batch of students progress from beginning to near-end. I'm really proud to see how much they have developed as scientists and I think that is a great part of this job – it will be hard to let them go.

And finally, what do you like to get up to outside of the lab in your free time?

Outside of the lab, I spend as much time as I can with my family. I have a six-year-old and a two-and-a-half-year-old and they keep me very busy. When I do get some time to myself, though, I like to keep as active as I can. Not only does exercise keep you healthy, but for me it also provides mental clarity, and I think that I work better when I take time to be active. I often go on runs or take fitness classes at the university. Recently, I played my first (ice) hockey game in years! I played hockey competitively in my youth and intramurals when I was a PhD student and postdoc, but I stopped when I had young kids. I'm so excited to be back on the ice! I'm pretty rusty, but I managed to score a goal in my first game!

Maria Ioannou was interviewed by Daniel Routledge, Cross-title Reviews Editor for The Company of Biologists. This piece has been edited and condensed with approval from the interviewee.