The enteric nervous system (ENS) is often referred to as the “second brain.” It can control the behavior of the gastrointestinal tract independently of the central nervous system (CNS). In fact, some review articles report that there are more neurons in the gut than there are in the spinal cord.

The physical and biochemical bidirectional connection between the nervous system, including the ENS, and the gut is called the gut-brain axis. Using multiple types of neurons, the ENS integrates various bits of information and controls gut function. Dr. Vanwalleghem explains:

Roughly speaking, you have enteric motor neurons that drive the peristalsis in the gut. You actually don't need the brain to do that. And there are sensory neurons that can sense nutrients in the gut and inform the body. Animal foraging behaviors can be guided, in part, by these neurons.

The gut microbiome has been examined in the context of numerous diseases and disorders over the past 10+ years, often raising more questions than answers. 

To shed light on the role of the microbiome in the gut-brain axis, Dr. Vanwalleghem and his team want to better understand how the gut microbiome, together with the nervous system, affects behavior and mental health disorders. In particular, they look at inflammation and immune responses in an interplay with neurons in regulating the microbiome. Dr. Vanwalleghem explains, 

The enteric nervous system regulates many gut functions, including immune system recruitment to the gut environment. Basically, if the gut microbiome goes bad, the immune system can get recruited. It’s this interplay and the complex interactions among the microbiome, ENS, and immune system that really interest me.

Chasing fundamental questions about the immune system, nervous system, gut inflammation, and autism

Interestingly, it seems that the ENS can turn down the immune system. And, a recent paper reported that neurons in the insular cortex, a region of the cerebral cortex in the brain, could sense the immune state of the gut [1]. Dr. Vanwalleghem explains:

Neurons in the insular cortex were activated when there was inflammation in the gut. And, if the gut bacteria triggering the inflammation were removed, these neurons could be re-activated, suggesting that the memory of the immune state was encoded in these neurons. Neurons can respond directly to bacterial factors, and to some bacterial metabolites. There are clearly strong interactions between the nervous system and the immune system.

But, how it actually happens and how much the ENS is involved are not yet known.

This is where Dr. Vanwalleghem and his team come in. With a research group established at the Danish Research Institute of Translational Neuroscience (DANDRITE) since autumn 2021, they are beginning to dig into fundamental questions about the immune and nervous systems in the gut: 

What are the molecular mechanisms by which the enteric nervous system can sense the bacteria? How can the enteric nervous system downregulate inflammation? – A lot of the gut microbiome is commensal, even beneficial to us. And, some gut bacteria are more inflammatory than others, so the mechanisms will depend on the balance of bacteria. Maintaining the regulation of the inflammatory state is very important.

These questions drive the research plans for the group:

One of my plans is to use bacteria that we can switch from being able to move very fast, a more inflammatory signal, because of increased expression of flagellar proteins to the same bacteria without the high motility. We can then stimulate different inflammatory states in the gut and relate these states to enteric nervous system activity. 

The second major area of Dr. Vanwalleghem’s research program opens up questions about autism and gastrointestinal disorders:

Autistic individuals have a lot of gastrointestinal disorders. There’s a very high prevalence of comorbidity. And there's a whole movement of linking changes in the microbiome to autism. It's highly controversial. And we’ve seen high impact papers that show completely contradictory results. What causes what is not yet clear, and I'm hoping that our zebrafish models can provide some clues.

To tackle his two major research program plans, Dr. Vanwalleghem utilizes the zebrafish model organism and light sheet microscopy. For a variety of reasons, zebrafish are a powerful research model for studying a wide array of questions (see recent Nordic EMBL Partnership article) In Dr. Vanwalleghem’s case, it’s because the animal is transparent and perfect for live imaging, using light sheet microscopy, of the gut that is virtually impossible in mice. “In zebrafish we can image the whole animal, all of the neurons, all of the cells, easily. We can manipulate them genetically, generating new lines of fish to ask very specific questions. And they have a lot of interesting behaviors to study”, explains Dr. Vanwalleghem. 

He continues, “we look at the activity of neurons, using a fluorescent calcium indicator, in vivo and in real time. Furthermore, we plan to manipulate the microbiome of the animal to study how the enteric nervous system’s activity changes, and how that can affect behavior.” 

An expanding research network

Setting up one’s first independent research program and group is no small task. Dr. Vanwalleghem chose the DANDRITE community for its expertise in neuroscience as well as scientific diversity, allowing for useful sparing and advice. In addition, the highly international environment provides support to team members, especially PhD students and postdocs, through Young DANDRITE, who may be coming from different corners of the world. 

In addition, local connections to scientists working on the microbiome are growing and expanding Dr. Vanwalleghem’s research network. For example, 

Per Borhammer, who is a clinician, has shown that in some cases, Parkinson disease could be starting in the gut. Some bacteria produce a protein, curli, that can misfold and thereby trigger the misfolding of alpha synuclein, which is then transported along the vagal nerve to the brain where it could trigger Parkinsons.

Dr. Vanwalleghem continues:

It was observed, 10-15 years ago, that vagus nerve cutting prevents the transmission of alpha synuclein into the brain resulting in a lower incidence of Parkinson disease. We may try some experiments in zebrafish to see if we can inject misfolded alpha synuclein in the gut and ask if it induces Parkinson’s disease, with the advantage of following its development in vivo.

New local scientific connections are not only related to human disease. Plant biologists in Aarhus are working on the soil microbiome and its interactions with the roots of the plants. Dr. Vanwalleghem and these scientists may join up, especially for the advanced imaging needed for microbiome studies. 

Furthermore, the Aarhus University zebrafish community and facility, initially started by Claus Oxvig, is growing, especially with the anticipated opening of a new and bigger infrastructure in the coming months. 

Dr. Vanwalleghem’s arrival in the Nordic region is also prompting interest from Nordic EMBL Partnership researchers, especially following the recent annual meeting hosted by DANDRITE. Funding from NordForsk for the Nordic EMBL Partnership research infrastructure hub, supports early career researcher mobility and will help to drive new collaborations, e.g., between DANDRITE and Swedish node, MIMS, The Laboratory for Molecular Infection Medicine. 

The Nordic zebrafish community is also expanding:

Florence Kermen, from Erme Yaksi’s [professor at the Kavli Institute for Systems Neuroscience of the NTNU in Norway] lab in Trondheim recently started a research group in Copenhagen, and Jan Kaslin from the Australian Regenerative Medicine Institute is setting up a group in Tampere, Finland.

says Dr. Vanwalleghem. A zebrafish neuroscience meeting in Trondheim this summer will bring together key people in the Nordics. 

Building bridges from neuroscience to immunity to computational biology

One of the great advantages of being a scientist is the ability to work in different fields and discover connections between them, opening up new interests and areas of research. Dr. Vanwalleghem is a perfect example, having studied molecular biology and neuroscience for his Master’s degree, moving into host-parasite interactions for his PhD degree and, thanks to an EMBO Fellowship, returning to neuroscience during his postdoc, ultimately linking the fields as he begins his independent career. 

During his postdoc with Ethan Scott in Australia, Dr. Vanwalleghem studied the cerebellum and how we sense our environment. And, with the power of technologies - the zebrafish model organism and optogenetics, in this case - he was able to start chipping away at key questions. Interest in the enteric nervous system arose in his last year in Australia. He explains:

I went back to the enteric nervous system through a collaboration with Jan Kaslin. Celia Vandestadt, a PhD student in Jan’s group at Monash University in Melbourne, Australia, and I were looking at regeneration in the spinal cord. We were doing live imaging of the spinal cord of the fish on its side. And at the same time, we could see the gut. I realized that this is a great model to study questions about the gut-brain axis that I've always been interested in. 

A challenge of rapidly developing research fields is the continual need to stay current, or even ahead of the curve, when it comes to approaches. Considering this challenge, along with shifting fields into neuroscience, Dr. Vanwalleghem has been driven to apply computational and data science approaches to his work:

We use lightsheet microscopy in zebrafish, which generates large amounts of functional data. Trying to make sense of all these data has really forced me to learn how to code, how to visualize data, and how to understand it. More and more I'm driven towards mathematical approaches.

And, he’s had to work up his knowledge base and network:

I'm not a mathematician, so I learn by myself through reading papers and talking with people. I was lucky to attend a workshop at Columbia University in 2019 where I met computational neuroscientists with whom I started collaborations. One of the large collaborations that I started, and Ethan is continuing through NIH grant support, is a collaboration with Prof. Dani Bassett at the University of Pennsylvania, doing topological data and advanced mathematical analyses. These are things that are at the edge of what I understand, so my collaboration with them is essential.

Curiosity and drive in basic science for the benefit of clinical application

Having always loved science and thanks to a great biology teacher during his university studies, Dr. Vanwalleghem found his curiosity in biology piqued for years onward:

My research has always been all about curiosity, and I think that leading a team now is so much about teaching. I built up teaching experience while in Australia, teaching part of a course on sensory neuroscience, and I really enjoyed it. Teaching new scientists is really one of the big aspects that speaks to me in terms of leading a team. And now I’m building the means to really answer the questions that we have about the gut-brain axis.

Dr. Vanwalleghem’s curiosity about the enteric nervous system can ultimately lead to implications for how inflammatory bowel disease and other gastrointestinal disorders are treated. For example:

A lot of the probiotic treatments that have been tested in animal models don't actually work well when translated to humans. And, in the past five or so years, there have been a lot of problems with the microbiome being linked to anything and everything, especially with findings being overhyped and giving way to very problematic treatments for certain conditions. 

What is needed to calm the hype and bring some clarity to the contradictory findings? Dr. Vanwalleghem gives his perspective:

Our fundamental knowledge is simply not there yet. By being able to better understand the basic science and workings of the gut-brain axis we’ll strengthen the core understanding and hopefully better target treatments that could at least alleviate some of the symptoms of gastrointestinal disorders. 

He continues:

The biomedical reproducibility crisis demonstrates the pressure to publish and the constant push to have translational output and clinical application in a very short time. This is a big problem in science at the moment. You need the basic knowledge before you're able to translate it and transfer it to actionable and applied science. So I think getting back to the basic questions is important. 

And, as a new team leader, getting back to basics and stimulating curiosity is exactly where Dr. Vanwalleghem is taking his team and research program. 

Brief career summary

Dr. Gilles Vanwalleghem completed an M.Sc. degree in molecular biology in 2005 at the Université libre de Bruxelles (ULB), Belgium. He then continued at ULB in research and completed his PhD degree in Trypanosoma brucei innate immunity adaptation in 2012. He then worked on programmed cell death and led the iGEM Premiere International Synthetic Biology Competition during 2009-2014 with Professor Laurence Van Melderen. In late 2014 and with a prestigious EMBO Fellowship, relocated to Brisbane, Australia for postdoctoral research in Professor Ethan Scott’s group at the University of Queensland using optogenetics to study the zebrafish brain. Since October 2021, Dr. Vanwalleghem is Team Leader at DANDRITE and assistant professor in neurobiology at the Department of Molecular Biology and Genetics at Aarhus University. He recently published a paper in Nature Communications on behavioral habituation, a form of learning in response to repeated stimuli. 

This article is published as part of the “Behind the Science'' profile series, taking an in-depth look at a scientist or group within the Nordic EMBL Partnership.