August 28, 2013

expert reaction to brain organoids

A Nature paper described how human stem cells could be used to build a three dimensional tissue culture with the same structure as seen in the human brain. The ‘organoids’ open up new ways to study early human brain development.

Prof Paul Matthews, Professor of Clinical Neuroscience, Division of Brain Sciences, Imperial College London, said:

“Earlier work has shown how human stem cells can differentiate to form brain cells and, when together in a group of cells, how cells take on different characteristics depending on their immediate neighbors. 

“In this new study,  Lancaster and her colleagues show that stem cells suspended in droplets of  gel form brain cells that organize themselves spontaneously into highly structure spheres or “organoids”  mimicking –within a few mm diameter- the layered structure of the human brain. 

“What made the observations so particularly exciting is that cells from a patient with a severe disorder of brain development developed into an abnormal organoid with features analogous to many of those in the patient.  The investigators then showed that these abnormal features could be “cured” by replacing the defective gene. 

“This study offers the promise of a major new tool for understanding the causes of major developmental disorders of the brain such as autism and schizophrenia, as well as testing possible treatments.   Treatments are still a long way off, but this important study illuminates part of the pathway to them.”

Dr Zameel Cader, Principal Scientist, IMI StemBANCC at the University of Oxford and Consultant Neurologist at the John Radcliffe Hospital, said:

“This is a fascinating and exciting piece of research – extending the possibilities of stem cell technologies for understanding brain development, disease mechanistics and therapy discovery as well as hopes for regenerative medicine.

“The structure they have generated is a long way from a real brain and the challenges for creating even a primitive fetal brain remain daunting. Hopes to recreate a real brain therefore remain distant. The proper organisation and blood supply of the brain are not present in this model and are major limitations.

“However their model is audacious and the similarities with some of the features of a human brain are really quite astounding. For example – the fact that a considerable degree of the brain complexity and patterning is encoded and can arise from the DNA of the starting stem cells without additional external manipulations.

“This does have potential clinical applications including drug discovery. The technology could be used in the later stage testing of drug efficacy of candidate molecules in a more physiological system. This may reduce our reliance on rodents and other animal models which have proved poor predictors of drug success in human patients.

“The main caveats are that the techniques are likely to be costly, time consuming and the ability to recapitulate other disease processes needs to be demonstrated.”

Prof Zoltán Molnár, Professor of Developmental Neuroscience, University of Oxford, said:

“I find the use of the human cortical organoids extremely promising for basic brain developmental questions, especially at early stages of human brain development. There are stunning similarities between these organoids and an actual brain, e.g. the proportions, organisation and movement of various progenitor cells.  Moreover, the neurogenesis follows very similar overall patterns and sequence. Unfortunately there are time limitations.  After a particular stage the organoids no longer develop as a brain, probably due to the lack of circulation, meninges, vasculature etc.  Some organs, e.g. pituitary, eye could be also developed to relatively advanced stage with this method.

“These findings are extremely reassuring to finally establish the link between CDK5RAP2 and the development of human microcephaly and the model might be very useful for the study of other genes associated with human brain developmental abnormalities.  These models do not make the study of the rail human brain redundant, for the contrary.  They are only useful after careful validation and comparisons with the rail brain development.

“I would predict that a similar approach shall be very useful to study other brain developmental disorders (e.g. polymicrogyria, lissencephaly).  However, it is yet to be seen whether some aspects of more subtle brain developmental disorders as autism or schizophrenia could be modelled with similar methods. This in vitro system is particularly suited to test drugs and dissect molecular mechanisms.

“I doubt that we will be able to make a fully-working brain sometime in the not too distant future, although groups in Japan could produce a relatively mature pituitary gland and eye with similar methods.  The brain is a very complex organ with millions of cells, billions of connections established with trillions of specificity.  There are very complex interactions between the developing nervous system and the cerebrospinal fluid, vasculature, meninges, and the rest of the brain, sensory organs and the whole body. There are complex interactions through various barriers (blood brain barrier, maternal and foetal placental barriers) that this in vitro developed organoid shall not be able to model.   Nevertheless, these are early days.  The publication clearly indicates the utility of this model in the study of human brain developmental disorders during this early period.”

Further information: “The methods of growing human embryonic stem (ES) cells and iPS are now well established and several other systems have been studied previously (e.g. pituitary, retina, intestine etc).  Even human cortical development has been modelled by several groups (Yale, Cambridge, Brussels, Tokyo etc) and it has been demonstrated that the various progenitors (apical radial progenitors, outer radial progenitors, intermediate progenitors) are all present in these cultures and the tissue self organise into layers that show similarities to the cerebral cortex.  What is new about this paper is that the model (3D matrigel cultured human cerebral organoids) has been exploited for the study of the role of CDK5RAP2 protein in brains size determination.

“This protein has been suspected to regulate brain size in humans by increasing progenitor numbers (through proliferative divisions) and delaying neurogenic non-proliferative divisions, but this particular issue could not be studied in mice, since they have relatively little proliferative divisions to expand brain size compared to human.  In fact, mouse brain has very small outer radial progenitor population compared to human brain. The study developed 3D culture methods to generate small neuroepithelium vesicles (called human organoids) that were generated from iPCs derived from normal and CDK5RAP2 mutant patients and showed that the organoids developed differentially.   The organoid bodies from the patients were much smaller than normal. This result is very exciting, because it produced an in vitro human cortical developmental model where the mechanisms could be further studied.

“There are two main lines of evidence for their conclusions:

(1) The authors could reduce the proliferative divisions and kick start the premature neurogenic divisions in organoids where the CDK5RAP2 has been reduced (by application of specific siRNA agains CDK5RAP2).

(2)  The authors could rescue the growth of the CDK5RAP2 mutant organoids prepared from iPCs generated from fibroblasts of human patients by reintroducing CDK5RAP2 protein in vitro.”

Dr Dean Burnett, Lecturer in Psychiatry, School of Medicine, Cardiff University, said:

“This development certainly sounds like it has potential. Any facility for replicating the complexity of the human brain (or other organs) for study in the lab without the practical and ethical issues surrounding direct experimentation on humans or animals should be met with enthusiasm and supported where possible. However, the human brain is the most complex thing in the known universe, and has a frighteningly elaborate number of connections and interactions, both between its numerous subdivisions and the body in general. Saying you can replicate the workings of the brain with some tissue in a dish in the lab is like inventing the first abacus and saying you can use it to run the latest version of Microsoft Windows; there is a connection there, but we’re a long way from that sort of application yet.”

Dr Martin Coath, Outreach Research Fellow, Cognition Institute, Plymouth University, said:

“Any technique that gives us ‘something like a brain’ that we can modify, work on, and watch as it develops, just has to be exciting.  We can now create, in a ‘test tube’, colonies of cells that shuffle themselves around into vaguely recognizable patterns and begin to talk to one another in a brain-like way. This is exciting, but how exciting will only be clear after loads of good results.

“A lot of work has already gone in to making this possible, but this paper represents the next step because they have spotted a pattern in their mini-brain that has also been spotted in human brains that do not develop in the usual way.

“How this differs from an actual brain depends on your point of view. For me, anything that might reasonably be called a real brain is going to have to pass more tests than simply being made of brain cells and looking a bit like a brain under a microscope.  Of course in some ways this is more like a real brain than the computers that control robots.  But it doesn’t yet control anything, and it doesn’t yet learn anything, and there is no evidence yet that it could.

“If the authors are right – that their “brain in a bottle” develops in ways that mimic human brain development – then the potential for studying developmental diseases is clear. But the applicability to other types of disease is not so clear – but it has potential. There is no reason to suppose, for example, at this stage that the brain will eventually fail in ways that are similar to human brains.

“Testing drugs is, also, much more problematic.  Most drugs that affect the brain act on things like mood, perception, control of your body, pain, and a whole bunch of other things.  This brain-like-tissue has no trouble with any of these things yet.

Does this mean we will be able to make a fully-working real brain sometime in the not too distant future?

“Are we sure we want to? A human brain that was ‘fully working’ would be conscious, have hopes, dreams, feel pain, and would ask questions about what we were doing to it!  Something we have grown in the lab, but on a much simpler level than a human brain, might be hooked up to electronic eyes, ears, and hands and be taught to do something – maybe something that is as sophisticated as many simple living creatures.  That doesn’t seem so far off to me.”

‘Cerebral organoids model human brain development and microcephaly’ by Lancaster et al., published in Nature on Wednesday 28th August.