Martin E. Schwab
Professor of Neuroscience em., Eidgenössische Technische Hochschule (ETH) Zürich, Chair of the Department of Neuromorphology, Brain Research Institute, University of Zürich, Switzerland
Breaking the Wall of Paraplegia. How Neuroscience Can Help Spinal- and Brain-Injured Patients.
Shortly after November 9th, I came to Berlin and walked through the former No Man’s Land.
We have heard about many types of walls today in this very unique and wonderful conference. The title of this session is Walls Around our Minds, however, I would also like to talk about walls in our minds: the prejudices that we have, the dogmas which we believe, often block us to see the right thing, block the progress in science, for instance. My little story that I am going to tell you in the next fifteen minutes or so will start with such an observation, where we were looking in the wrong direction for a long time and could not find the solution to something that seemed easy, as you will see.
Paraplegia is an almost biblical paradigm for severe disease, for being extremely limited by not having control over one’s body. In this first picture you see Christopher Reeve, former Superman, and you see Paralympics, even children, paraplegic patients or paraplegic people in the Olympic Games.
The brain, of course, controls all our movement, and it does so by controlling the spinal cord. The spinal cord has nerve cells, which give off nerve processes, which run to the muscles, and this is how we move. In essence, you have the control centres in the brain, you have the executive centres in the spinal cord, and these are connected by wires, which consist of millions of nerve fibres. The tract, which coordinates our fine movement when you are writing, for instance, or now that I am speaking, consists of a few million nerve fibres. This is our motor system.
The sensory system is very similar, the sensory information coming from the periphery of our skin, of the muscles, from the intestines and so on, sends information to the brain through nerve fibre bundles, with millions of nerve fibres.
Spinal cord injury, of course, interrupts these bundles of nerve fibres. This is what renders you paraplegic. Here you have an MR (magnetic resonance image) of a spinal cord injured patient: you see the brain, the spinal cord, and you see the injury site where the spinal cord is severely disrupted. We have about 2000 new spinal cord injury cases every year in Germany, and about ten times more, 20,000, severe brain injuries, which lead to neurological deficits- often extremely severe. Most of these patients are young people, because the accidents are traffic accidents, sport accidents, and work accidents.
Why is paraplegia, as I said, a biblical paradigm? Because it is life-long, because you are in the wheelchair forever, and destiny sort of strikes in a particularly devastating way. Why is it life-long? Why does it not repair itself?
If you look at our body in a very general way, skin repairs itself very well. Muscle repairs itself very well. Liver, as some of you may know, you can cut off half of it and it still regrows. You can take out one kidney; the other one grows and compensates. It is only the brain and the spinal cord, which have lost this capacity. Why is this?
On this slide you can see in an experimental animal the tract of the spinal cord, these one million nerve fibres, which run down from the motor centres of the forebrain into the spinal cord. Here they are interrupted by a section. .
We were teaching our students, medical and biology students, for 80 years, that there is no regrowth of these fibres. If they are interrupted here, they do not grow down the spinal cord to the former targets anymore. There is no regeneration and no repair; therefore, the deficits stay life long.
This was the situation. Now what can you do when you look at something like this- from an experimental point of view? Of course, every graduate student can tell you that if the fibres don’t grow, you just have to give them a growth factor, which makes them grow. So, this is the first thing we tried twenty years ago- at that time at the Max Planck Institute in Munich. We injected growth factors; there was no growth, so the system somehow didn’t work. The hypothesis, the theory, the dogma, that a lack of growth factorsis responsible for the absence of regeneration must have somehow been wrong. Astonishingly, the theory was formulated first in 1911, so it was in the literature for 80 years.
The second side remark that I would like to make after the walls in our minds, is a side remark on the value of basic science. We are talking about a very applied question here, however the solution came from a by chance observation in basic science. On this picture you see such an experiment.
The bright spots are nerve cells. They sit on a culture dish, and have been fed with growth factors. The culture dish has been coated before plating the cells with an extract of spinal cord or brain, or with an extract of a peripheral nerve of the rat, a nerve from the leg, actually. Now you see, that when you come back a day later, after you put the culture dish into the incubator, that these nerve cells have produced wonderful nerve fibres. They grow very beautifully if they can sit on a piece of peripheral nerve or an extract of peripheral nerve. However, if they sit on extracts from brain or spinal cord, they don’t grow.
The dogma, which we had to do away with, was the dogma that growth cannot take place, and, in fact, a new concept evolved, which was the concept of neurite growth inhibitory factors. It took us three years to publish this concept, because everybody says, “Nobody has seen an inhibitory factor so far. Why should we have an inhibitory factor for nerve fibre growth in the brain or spinal cord?” It is hard to overcome such walls- also in science. Nevertheless, in the end we could do it.
Again, in favour of basic science, in order to show and to prove that these factors actually exist, we had to use cell biology, biochemistry, molecular biology; we had to go through the entire purification procedure to show that these factors actually exist. Today we know about a dozen of them. One of them, which is called Nogo-A, is still the most potent one. Here you see a growing nerve fibre, which grows happily on the cell culture dish, and it has a sort of a hand with which it explores the territory. When you add a little bit of this purified protein called Nogo-A, the whole thing collapses within seconds. You end up with a very unhappy nerve fibre, which doesn’t grow anymore.
This is a new concept and a new protein family, which came up some fifteen years ago. The question now is: how does this relate to the question we were asking at the beginning? Is such a factor responsible for the lack of regeneration of nerve fibres in the brain or in the spinal cord of experimental animals and ultimately in humans? In order to look at this, you have to be able to do away with this factor, to neutralise it, or abolish it. One way to do this is to produce antibodies. You have heard wonderful antibody talks this morning. You can produce antibodies against viruses, or against bacteria, and the antibodies neutralise these viruses. You can also produce antibodies against proteins, proteins of the body. These antibodies block the action of these proteins. This is what this is. Here you have these nerve cells, stained in green this time, sitting on a culture dish, which is coated with extract- in this case of monkey brain. The nerve cells are unable to grow nerve fibres, although we stimulate them with goodies in the culture medium.
When you incubate such a culture dish with an antibody against this protein Nogo-A, the nerve cells produce fibres overnight, thus instantaneously. Now this is good news, because such an antibody can be produced in large amounts, and can be applied to, for instance, animals. Here you see rats with a partial spinal cord injury which disrupts the fine locomotor control, not locomotion in general, but the fine locomotor control of these animals. Now, you see the tract, which comes down from the brain and ends at the transection site here. You have a little bit of what we call regenerative sprouting, a few fibres, which form, but they don’t do very much.
Now you can implant these rats with a pump which leads the antibody into the fluid surrounding the spinal cord. These pumps are used already in humans for drugs, not for antibodies, against pain, for instance, or spastic cramps. When you infuse an inactive controlled antibody, which doesn’t do anything, you see only extremely limited spontaneous growth. When you infuse an antibody against this protein Nogo-A the fibres continue to grow. They grow around the scars; they grow down the spinal cord over long distances. They make nice arbors, and these arbors make connections to the nerve cells in the spinal cord, which have survived the injury. The injury is very local here; there are many nerve cells below the injury.
You can also manipulate a mouse genetically, and take this protein Nogo-A completely out (knockout mouse). You find that when you knockout Nogo that these nerve fibres can grow again down the spinal cord. This is again a basic science experiment, which is an interesting proof of principle, showing that these antibodies, or a completely different way of manipulating the mouse, actually works.
The key question is then: If we get these fibres growing after an injury over long distances what do these fibres do? They may be lost; they may not know where to go; they may not be able to link up with target cells in the spinal cord. After all, this system is very, very complex and millions of nerve fibres, millions of nerve cells are involved.
We do behaviour experiments, where we have the paraplegic rats running around in an open field, or trying to move in an open field , going over grids, narrow beams, swimming, and so on.
I will show you a single result here. This is the narrow beam walk; rats can very well walk over such beams. If you transect their motor command system in the spinal cord at a certain level, the rats are completely unable to walk over these beams. If you then treat them with anti-Nogo antibodies for two weeks, the rats learn to go over the beams again. They don’t do it very well; they slip off from time-to-time. Their motor control is not perfect. However, it is very good compared to these rats, which cannot do it at all.
These types of experiments then led us to the outlook that we could apply these antibody treatments one day in human patients. Because such a treatment has never been used so far, on the way to the human patient, , we used very small numbers of monkeys. The monkey, of course, is an animal, which is very close to humans, as we have heard this morning in the first talk of the conference. These are Macaque monkeys. They have a lateral transection here, which renders one hand and one arm paraplegic.
You see the command system from the brain, which is transected here. In a control antibody treated animal it sprouts a little bit, but it doesn’t do much. In an anti-Nogo-A antibody treated animal you see again this regeneration response. So, fibres grow around the injury site, around the scar; they grow down the spinal cord over long distances. They wind their ways down the spinal cord, they branch, and they find targets. In fact, you can see, the paraplegic hand of the control animal here, and the open hand, which will be able to catch this food pellet that is thrown at the animal very precisely and very efficiently. Also in a number of other tests we see recovery of function in a fantastic way.
This was the moment when drug companies, particularly Novartis, where clinicians heading big clinical centres all over the world, and also where the regulatory agencies, thought that we should really move on to human patients. This is where we are at the moment. In collaboration with Novartis and with the European and North American, US and Canada, clinical network, we are now applying these antibodies in freshly injured paraplegic patients, within two weeks after the accident in a way that is very similar to the way in the rats: a pump, or injections, which apply the antibody into the human being.
It is the first time that antibodies are applied towards the spinal cord and into the brain. The result so far is that this antibody is extremely well tolerated in close to 60 patients now, and that we start to see the first result of such a treatment in respect to functional improvements of the injury.
Of course, this is not only a story about hitting walls down, or about basic science moving towards applications; it is also a story about teamwork, teams of international cell biologists, molecular biologists, biochemists, and MDs, which work together, and from time to time gather somewhere in the Alps in Switzerland. It is also a story about the collaboration of public funding, like our University funding, and the public and EU networks, private funding, for instance private foundations, which fund research in the area of spinal cord injury or brain damage, and also pharma companies, which help us to bring this dream originally into application and into the patient.
Thank you very much for your attention.