Inspired early on by his mother’s healthcare career, Julen Sanz Serrano found his scientific home in toxicology — a path that eventually took him abroad as a postdoctoral researcher at the Vrije Universiteit Brussel. His work focuses on understanding liver toxicity and developing advanced in vitro models to support safer, animal-free chemical assessment. Within ONTOX — and as chair of the ASPIS Academy — he supports young researchers, fosters collaboration, and contributes to the shift toward non-animal testing. In this interview, Julen reflects on his journey, his achievements, and what it means to grow as a scientist in today’s rapidly evolving research landscape.
What inspired you to pursue a career in science?
I guess it comes from my mom, who is a nurse. Initially, I thought I wanted a career in health sciences to care for my family. I liked the scope, but I wasn’t sure which specific path to take, so I decided to try the a priori hardest career to get into: medical school. I didn’t reach the cutoff, but the university offered me alternatives like pharmacy and nutrition — and now I couldn’t be happier with my choice. During my studies and the summers in between, I explored various career paths, including work in laboratories, hospitals, and a pharmaceutical company. While doing my bachelor’s thesis, I realised that academia was the right fit for me. I completed my PhD in Toxicology in 2021, and one thing led to another, eventually bringing me abroad as a postdoc at the Vrije Universiteit Brussel.
What drew you to the Vrije Universiteit Brussel for your postdoctoral research?
A Belgian colleague knew I was looking for a postdoc in Europe and reached out to me about an opening in Mathieu Vinken’s team (editor’s note: Mathieu Vinken is the ONTOX coordinator). Sometimes, things can be that simple, I guess.
How would you describe your main scientific expertise or research focus?
It can be summarised as in vitro liver toxicology. Briefly, I am interested in the mechanisms of liver toxicity (particularly cholestatic and steatotic types) and in developing liver-based in vitro models for chemical toxicity testing. Within ONTOX, Adverse Outcome Pathways, which represent toxicity mechanisms, serve as the foundation for developing and optimising liver-based in vitro batteries. These are used to test chemicals from the pharmaceutical, cosmetics, food, and biocide sectors.
What motivated you to join the ONTOX project?
I initially applied for the ONTOX postdoctoral position in 2021, but I ended up working on another project within Mathieu Vinken’s team. After a couple of years and following the sudden departure of the postdoc from the ONTOX hepatotoxicity work package, I officially joined ONTOX in 2023 to fill that role. I already knew the team, really liked the project, and was collaborating with the researchers involved, so it was an easy choice for me.
“ONTOX has truly changed and shaped me as a researcher. I’ve grown in independence and confidence — no more impostor syndrome! I’ve become more focused on addressing the root problem and more efficient at multitasking without losing sight of the bigger picture.”
What are your main tasks and responsibilities within ONTOX?
I mainly provide initial support for the doctoral researchers in the work package. I assist with their daily work — initially in the lab (though they are now completely independent) — and now more with writing scientific outputs. I also help with presentations, reports, deliverables, and other related tasks.
As ONTOX moves toward its final stages in 2026, what have you found most valuable in this experience — scientifically or personally?
ONTOX has truly changed and shaped me as a researcher. I’ve grown in independence and confidence — no more impostor syndrome! I’ve also developed a much broader “helicopter view” of my work, and it has taught me everything I know about risk assessment. On a personal level, I’ve become more focused on addressing the root problem and more efficient at multitasking without losing sight of the bigger picture. It has definitely been a major step in both my professional and personal growth.
You are the chair of the ASPIS Academy, the network of Early-Stage Researchers in the ASPIS cluster. What do you find most valuable about this platform?
The people within ASPIS Academy are what make the platform most valuable. I am officially the chair, but honestly, I consider the whole core team as such. They are amazing, motivated researchers and genuinely good people whom I enjoy working with. I hope we can maintain the professional and personal bonds we’ve built over these past years.
You are also involved in other projects aimed at replacing animal testing. Could you tell us more about them?
In my postdoctoral project, I focus on improving in vitro models for predicting drug-induced liver injury and laying the foundation for further development. In addition, I co-supervise a PhD thesis on establishing and applying a liver-derived in vitro New Approach Methodology (NAM) for the safety evaluation of food ingredients, contaminants, and their mixtures.
What achievement in your career are you most proud of so far?
The first things that come to mind are securing a 10% position as an assistant professor at the Vrije Universiteit Brussel and being invited to serve on a PhD thesis jury at my hometown university (editor’s note: Universidad de Navarra, Spain).
What do you find most challenging about being a young scientist today?
Keeping up with the overwhelming amount of published data, finding a stable position in academia, and navigating the limbo between becoming a more senior researcher (writing grant proposals, supervising PhD students, etc.), while still being junior (spending time in the lab or writing articles as a first author).
What are your future research or career plans?
This one is simple: keep evolving as a researcher.
Outside the lab, what are your favourite hobbies or activities?
Tennis, I love playing and watching it. I also enjoy music in the same way, both playing and listening. I like reading fantasy and drawing as well.
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