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Sofroniew Lab: SCI Scar And The Role Of Astrocytes

Neuroscientist Michael Sofroniew is a basic biologist whose work is focused on how the cellular anatomy of the spinal cord is affected by trauma. Some cells are wiped out; others change or adapt. In particular, Sofroniew looks at astrocytes and their relationship to scar formation; he hopes to manipulate these cells using molecules that might have therapeutic potential.

The following interview was held recently at Sofroniew’s office on the campus of UCLA. [tp:readmore]

What was your first exposure to working in a biology lab?

When I was a pre-med undergrad at nearby Loyola I volunteered at County General Hospital during the summer. One of the guys there ran a lab. When I visited the lab it was love at first sight. They were working on endocrinology – which has nothing to do with what I do now – and how steroids that are made in the adrenal gland might influence sexual differentiation. So every day I after I did my work at the hospital I ran over to the lab; they gave me a little project and – I still remember all this vividly, I was looking at the effect of maternal adrenal steroids on sexual development in the fetus. I spent all summer working very hard on that and it turned out very well. The next fall I was a senior and it was not possible to commute to County General from the Westside so I went through the directory at UCLA and I found a scientist who agreed to take me on. I was actually more interested in the neuro field by then. They actually gave me a paying job as a research assistant. I worked after class and on weekends a few days a week. The work went well; we even got some publications out of it, which was quite unusual for someone at my level for that time.

So you graduated and went on to medical school?

Yes. I applied to medical school in Munich and I got accepted. With the laboratory background I had from UCLA it was easy to find people to work with there; all along in school I was working in a lab on the side. The research was successful; we made some serendipitous observations and the publications did well. When I finished medical school I was offered a post-doc position at Oxford but I preferred to get a Ph.D. – getting an M.D./Ph.D. was better for an academic career. So I did that.

After my Ph.D. in Oxford, I had another major choice. Let me back track. When I was a medical student I became very much interested in neuroscience and neuroscience research, and that is where my first interest in neurodegenerative disease and trauma began. That’s what I worked on for my Ph.D. I had the intention of going into academic medicine, in particular, surgery, because I really liked it. From Oxford I went to Johns Hopkins to start a neurosurgery residency. I was there for a year, and that’s where reality set in….that you can’t do everything to the high standard you might want to. I thought about in a very simple way. I can do two things but not three. The three things I had to decide about were neurosurgery, the research and my family. I wasn’t going to let my family go. I stopped the neurosurgery residency and I went back to England where I was offered a faculty position at Cambridge. It was a good place to do science, and to raise children.

We lived there for the next 15 years. Things were going well, we were happy, I built up a good research program. Then we began to wonder, do we want to stay in England the rest of our lives? Is there enough money, for research and for personal life? So we looked around and really there were only two places to think about for us. Either Boston or California. But as an academic you don’t just decide that you want to move somewhere in particular….there has to be a position. They have to want you. UCLA turned out to be the best fit. Research here was and is really strong in trauma-related neuroscience, both in brain and spinal cord injury. A major draw for me was Reggie Edgerton and his group, one of the premier spinal cord injury groups globally.

My position is that of a scientist in neurobiology, as part of the medical school. The atmosphere here is of collegiality and collaboration. Collaborative work is becoming more and more prominent in basic biology, but it’s relatively new. Even scientists one generation older than me tended to be far more insular. For career advancement it used to be really frowned upon for you to collaborate with other people. It wasn’t clear who did the work, who got credit.

OK. Can you describe some of the work?

My main focus, which I started in Cambridge in the early 90s, has been to study astrocytes, which are scar forming cells in the brain and spinal cord, and to ask, why do they make scars? Scar formation is the most severe form of a process called reactive astrogliosis, which can exist in much milder forms, as well. Why does this happen, what regulates it, and what are its functions? Those are the main questions that have driven our research for the last 20 years. We use genetic tools that allow us to do loss-of-function studies in whole animals, in vivo. There’s only so much you can learn in cell culture when you are studying injury to the nervous system.

In one of our early projects on spinal cord injury, we found that if you prevent scar formation (using transgenic animals to completely prevent scar formation) the outcome is devastating, not beneficial. At that time there were still lots of people who thought that the main thing you needed to do after spinal cord injury is prevent the scar from forming. It turns out that the scar forms for a reason. It is essential for wound healing and without it, the wound is much bigger and tissue destruction is much worse; there is more dysfunction.

We read about experiments that are trying to bulldoze through the scar…

You can’t remove the scar completely. It makes things worse. I prefer to think about bridging across the scar, rather than bulldozing through it. The trick is to find ways around it that are not harmful.

How widely known is this?

It is becoming more widely known. Now, 12 years later our observations are holding up well and being replicated by others and people are starting to accept it.

What do we know about scar after spinal cord injury?

Reactive gliosis and scar formation were looked at as a single all-or-nothing phenomenon – it was either triggered or it was not. But looking at the molecular signaling pathways it has become clear that it is not an all-or-none process. It is composed of many, many different things that are regulated independently, and different injuries will trigger different things. That raises the possibility that you could control different aspects of scar formation with pharmacology, and perhaps improve outcome.

For example, if you inhibit one molecular signaling pathway, it always seems to make things worse. There’s another signaling pathway that if you inhibit it seems to reduce certain aspects of inflammation and can be associated with better outcome. We don’t think all aspects of gliosis are necessarily good.

Does this suggest a sort of neuroprotection kind of intervention, acutely?

Scar formation in animals takes at least two to four weeks. During that process, there is time to intervene – pharmacologically, or locally with a surgical intervention. And perhaps even the local delivery of a pharmacological agent. That is the basis of our current Roman Reed [California funding source] project – we use a surgically injected biomaterial to try and deliver molecules that might manipulate scar formation. It’s a synthetic hydrogel that is made by one of the bioengineers here at UCLA. You can inject as a liquid and it will then gel and have structure. You can use the gel for prolonged release of molecules.

This may lead to a treatment?

Perhaps in the long run, but the goal of our current research is not just “let’s try anything and see if the mouse gets better.” We also want to see what we can find out about the process of scar formation while we’re doing these experiments. We are trying to do two things. Yes, I am interested in applied research; but I have always tried to study basic biology. I try to study the biology of the response to injury. If you push forward with the biology you will be increasing knowledge and making a contribution, adding to the pool of useful information. If all you did was test potential interventions without advancing the biology, you’d run the risk of never understanding enough to develop something useful.

I’m also interested in the milder forms of astrogliosis which have the potential to alter the way nerve cells function, and we know hardly anything about that. In SCI you have the area where the scar forms immediately next to damaged tissue – and spreading away from the scar you have large areas of milder gliosis. We don’t really know what that does. The large areas of milder gliosis have the potential to have a strong impact on neural function.

What’s the scar for?

We have a working hypothesis based on our work – the reason the scar forms is so that inflammatory cells can get really active in areas of damaged tissue and clean up the lesion, but not spread into the neighboring healthy tissue. Every time we experimentally disrupt scar formation the inflammatory cells come out and make the lesion much bigger. That was a sort of serendipitous observation in our first paper that neither we nor anyone else expected.

Tell us about the paper you published with Reggie Edgerton and his group at UCLA….this got a lot of attention thee or four years ago.

It started with the question, what type of axon regeneration is going to be necessary to restore function? Twenty or 25 years ago, when people started thinking it might be possible to achieve axon regeneration, the tacit assumption was that the regenerating axons would have to grow back all the way to their target and re-establish connections precisely the way they had been before. To achieve this, you would need long distance axon regeneration, and most people assumed that this would be necessary. I was not convinced by this way of thinking and thought there was evidence to support alternatives. I challenged Reggie – what kind of axon regeneration do you think is needed? Is it really necessary to grow connections all the way down from brain to the bottom of the cord, or might local plasticity, local sprouting, and formation of new connections be an alternative?

We started looking at experimental models in which to test this idea. It’s well known, that if you have a cut on one side of the spinal cord only and wait, the animal will regain stepping on that side; that’s been known for 100 years. This kind of lesion is called a Brown Sequard lesion named after a 19th century neurologist. Brown Sequard patients, humans, recover stepping below the lesion in the absence of regrowing the original connections the way they were before. The hypothesis is that the other side of the cord takes over. Inside the spinal cord there are lots and lots of local neurons that form little networks up and down the spinal cord. They are not studied very much. It’s been shown in the last 20 years or so that you can have reorganization of other circuits, like after a stroke in the motor cortex. The stroke may kill an area but the areas around it are often able to take over a certain amount of function. So, we posed the question: Can this happen in the spinal cord?

We devised an experiment with Reggie Edgerton and Gregoire Courtine, who was his post-doc at the time [Courtine now has his own lab at the University of Zurich]. After we made a lesion on one side of the cord, we made a second lesion on the other side, staggered so as to leave a bridge of intact tissue. We wanted to see if function can go through the intact local circuits in the tissue bridge without the long, direct projections from the brain that go all the way down the spinal cord. We found that indeed, there is information that can get though.

This is an important proof of concept study. We did it in mice; it’s been replicated in rats. But there’s a catch. If you make the two staggered lesions simultaneously, then the animals don’t recover; if you make the staggered lesions sequentially over time, and the animals are able to train between the first and second lesion, then they can recover some function.

So this paper came out in Nature Medicine and got into the newspapers as “animals walk again.” [See sidebar, below]. Some people thought we had done a “therapeutic” intervention, but we did not; we studied the biology of recovery. We showed that the spinal cord can reorganize to form relay circuits. This idea is important in providing a rationale for strong rehabilitation training to make maximal use of tissue and connections that are preserved after injuries, rather than just giving up because there is no hope, as has been the dogma told to many patients for a long time. Our observation also provides a rationale for trying to achieve short axon regeneration across lesions that might be able to form relay connections, rather than the previously assumed requirement for long distance regeneration that completely reconstructs what had been there before the injury.

How should people approach the idea of a cure…

I never talk about cure. I talk about incremental advances. I guess I have the surgeon’s mentality: If your wrist is broken you go and they fix it, then that’s a cure. Most people don’t notice the person’s wrist was broken. Or if you have a serious infection, you get the right antibiotics, and you are cured. It’s going to be a long time before we can say that with spinal cord injury. That doesn’t have to sound negative. Or that one is giving up. Cure is a difficult concept in spinal cord injury. But making it better – slowly and continually – is not at all unreasonable and has actually been going on for some time in terms of increased life expectancy and improvements in certain aspects of quality of life for spinal cord injured patients. I think we are now on the threshold where advances in experimental research will start leading to interventions that combined with rehabilitation training can improve the recovery of functions.

For the record, the paper Sofroniew mentions is “Recovery of supraspinal control of stepping via indirect propriospinal relay connections after spinal cord injury.” It was funded in part by the Reeve Foundation. This is from the abstract:
“Our findings show that pronounced functional recovery can occur after severe SCI without the maintenance or regeneration of direct projections from the brain past the lesion and can be mediated by the reorganization of descending and propriospinal connections. Targeting interventions toward augmenting the remodeling of relay connections may provide new therapeutic strategies to bypass lesions and restore function after SCI and in other conditions such as stroke and multiple sclerosis.”

This is what Sofroniew told a reporter:
“Imagine the long nerve fibers that run between the cells in the brain and lower spinal cord as major freeways. When there's a traffic accident on the freeway, what do drivers do? They take shorter surface streets. These detours aren't as fast or direct but still allow drivers to reach their destination. We saw something similar in our research. When spinal cord damage blocked direct signals from the brain, under certain conditions the messages were able to make detours around the injury. The message would follow a series of shorter connections to deliver the brain's command to move the legs.”

Two years later, Sofroniew was a co-author for another paper with Courtine and Edgerton, “Transformation of nonfunctional spinal circuits into functional states after the loss of brain input.”  See more here.

This paper, for which Edgerton answered to the press, showed that rats with completely severed spinal cords were able to walk on a treadmill with a near normal gait while bearing their full weight. This work, also funded in part by the Reeve Foundation, noted that the walking was facilitated not by restoring brain input but by tapping into the circuitry in the spinal cord itself. This was the basis for the epidural stimulation experiment reported last year wherein a human subject (Rob Summers) regained significant locomotor function after stimulation and training.

Posted by Sam Maddox on Apr 3, 2012 5:41 PM America/New_York