Understanding our most complex organ on a molecular level.
Organs-on-a-chip hold enormous promise – and pose an equal technological challenge. Of all organs, the brain is the most complex to model. Molecular biologist Joost Gribnau, psychiatrist Steven Kushner and neuroscientist Ype Elgersma of Erasmus University Medical Centre took up the challenge. A self-organising “minibrain” is still a dot on the horizon, but Kushner has already made the first discoveries on the cause of schizophrenia on the basis of living brain-cell systems.
“Until recently, it was not possible to investigate how the human brain develops,” says Professor Steven Kushner. “What gives rise to the nervous system? What role do genetic and environmental factors play? For other diseases such as cancer, where tissue can be taken from solid tumours, there were ways to unravel the molecular mechanisms. But for the brain there was just no way of finding out.”
There is hardly any living brain tissue available for research. But even if there were, the time window is too limited to draw conclusions. While cancer cells keep on dividing in vitro almost indefinitely, neurons in the brain cannot survive for more than a couple of hours after a biopsy is taken. “Now that we can develop living human brain tissue in vitro for the first time ever,” says Kushner, “we’ll not only be able to find answers to basic questions about the brain's functioning, but also – even more importantly – we’ll have a powerful new way of finding the causes of brain diseases and discovering better treatments.”
Skin cell to brain cell
Kushner has already been able to draw important conclusions on schizophrenia. First, he identified patients with schizophrenia and isolated their skin cells. Next, molecular biologist Dr Joost Gribnau converted these skin cells into induced Pluripotent Stem cells (iPSs). These iPS cells are manipulated into expansion, differentiation and finally maturation from embryonic cell to mature cell. All in all, it takes a year to grow the brain cells and to put various types of these together in a functioning tissue.
On the basis of the cells of schizophrenia patients turned into brain cells, Kushner was able to identify the cause of this disease in these specific patients. “The cause has to do with an abnormality in myelination. Myelin is a fatty substance that can be regarded as the insulation around the ‘electric wiring’ of the nervous system, just like the coating on electrical copper wires. If this insulation doesn’t function properly as a consequence of a genetic aberration, nerves don't work anymore and schizophrenia occurs. That’s what we found in our patients.”
The present process of making artificial brain tissue is time-consuming and costly, as it all depends on extensive and meticulous work. It is, however, worthwhile, says Gribnau. “In the model of a healthy person, mutations can be introduced to see what happens. Alternatively, as in the case of Kushner's schizophrenia research, the system from patients with brain diseases can be modelled to repair mutations. Both approaches lead to new insights into brain processes in general and into those of people with mental conditions, such as schizophrenia. The various models can be used to monitor the effects on neurons and glia, for instance.”
“Insight into the cellular mechanism of a brain disease is a first step,” says Gribnau. “Once you've found the phenotype, this insight can be used in screens. The next step is to develop intervention. Once you know what goes wrong, you can multiply the disease mechanism on chips to apply high-throughput screening to find the right molecules for effective drugs.”
Gribnau is excited about this approach. “We’re focusing on the brain, and other groups within hDMT are modelling tumours and the heart. So in ten years’ time – if other groups join us – we could model the entire body with its 300 different cell types and numerous physical processes that play a role in real-life tissue." He strongly believes that a “minibrain” is feasible and that costs will drop. “In the long run, more technology will become available – and later become cheaper – to automate the brain-on-a-chip process.”
Multidisciplinary collaboration between Delft and Rotterdam has proven to be very useful for this. “When you work in a team, you can solve a lot more than you thought possible beforehand. Aspects that we as biologists fear are hard to solve turn out to be no problem for engineers.” Kushner agrees: “We need doctors, biologists, electrophysiologists and engineers in the Medical Delta region to all collaborate. On the biology side we need a good interface to be able to measure, record, listen and manipulate our cells. For example, the group of Lino Sarro in Delft can help us to replace the present manual labour processes with efficient chip processes. In a glass capillary tube, the detailed electrical currents of individual neurons can be recorded one by one. With a chip this can be done much more efficiently. This will enable research into more brain diseases, and will bring quicker results for less money.”
When they started out there was a lot of scepticism, Kushner recalls. “Including from ourselves, to be honest! But now that we've proven it’s possible to standardise the derivation of 3D brain tissue in a format suitable for high-throughput screening, there’s a lot of enthusiasm. We’ve begun to scale up the approach with help of Delft and Leiden, and will expand to other brain diseases, with help of a Zwaartekracht grant, which we’re applying for through hDMT.”
The first results produced by a couple of pioneer groups, such as the one in Rotterdam, have already taught us a lot. “Although many groups have been trying, we were among the few worldwide to be successful,” Kushner concludes. “The 3D-structure looks, feels and acts like a mini brain. We’re still learning from it how the brain develops – for instance, the different ways brain cell-types can be ‘coached’.”
Imagine what larger scale, more complex models, automation and cost reductions could bring. “The Medical Delta region is among the best equipped in the world to bring that about,” says Kushner. “The diversity of expertise we need is all present in this one region – which is extremely rare. On top of that, there is also the willingness to collaborate: the key to solving the problems we face. That is what makes Medical Delta so exciting.”
Interview by: Leendert van der Ent