An interesting journal article
came out a week or so ago about the regenerative power of a growth-promoting molecule called sonic hedgehog, shh for short. And yes, it was named for the classic Sega video game featuring the spiky blue Sonic running and jumping, collecting rings and forming into a ball to destroy the enemies.
Shh is important in development, helping to differentiate the cells that form the spinal cord and brain. The molecule is important in the formation and guidance of motor neurons, the ones that affect our ability to activate muscle. Shh seems also to play a key role in the creation of myelin, the insulation on nerves that allows them to carry messages with high fidelity.
What’s especially cool about this paper is the delivery method: shh was infused in tiny biodegradable beads that release the molecule over several days. The results in two animal injury models (a cut in the cord, or hemisection; and contusion, using a weight drop) were very promising.
From the paper, "The effect of long-term release of Shh from implanted biodegradable microspheres on recovery from spinal cord injury in mice:"
We show for the first time that bioengineered delivery of Shh can promote significant behavioral recovery after SCI, and that the mechanism of Shh action is pleiotropic [multiple effects]. We have demonstrated that biodegradable microspheres are a suitable, minimally invasive approach for long-term modification of the injured environment. Given the conserved role of Shh in central nervous system (CNS) development, these findings encourage further translational studies of Shh microsphere treatment.
The new paper is from the lab of Sally Temple, Ph.D., who is scientific director for the Neural Stem Cell Institute
at the University at Albany. The work was funded by the Reeve Foundation and the New York State Spinal Cord Injury Research Program, supported since 1998 through surcharges on moving traffic violations. Alas, the state has redirected the surcharge money away from SCI research to cover shortfalls in the general budget.
Sally Temple received a B.A. (1982) from the University of Cambridge and a Ph.D. (1986) from University College London. She is active in The International Society for Stem Cell Research and currently serves as treasurer. In 2008 she was awarded one of the MacArthur Foundation
fellowships; this so-called genius award comes with half a million dollars, no strings attached.
Herewith is an interview with Dr. Temple.
You started out as a developmental neuroscientist…?
I started off trying to understand how the brain forms, specifically how the progenitor cells in the early embryo make the brain and spinal cord. It’s a really unbelievable process – it goes from a simple tube of cells to this incredibly rich and diverse array of interconnected neurons and glial cells. That is what captivated me as a grad student and has sustained my research for my whole career.
Did you imagine being scientist, say in high school?
In the U.K. students tend to specialize very early on. By the time you apply for college you’ve pretty much already decided, science or art. In high school I wanted to do art. But my father suggested that if I wanted to get a job I should do science. So I applied to Cambridge to study natural sciences and was accepted. Once I was immersed in biological science, developmental neurobiology was what I found the most exciting.
There seems to be a strong connection between art and discovery….
There’s a lot of art in science, surprisingly so. Images are our bread and butter. As biologists you have to produce images that convey a message so people reading a paper can understand the system and what you have done. So there is a strong artistic element to what we do as scientists. Of course technology has come a long way. Looking back at papers early on, in the 80s, there were papers in major journals with simple black and white images – nowadays its hard to get a paper accepted without stellar images.
Let’s hear about the work with sonic hedgehog …
Sonic hedgehog is a beautiful example of what is called a morphogen in biology. It’s a molecule that can instruct tissues how differentiate. Not only that, but the same molecule in different concentrations can produce different effects. If you have a very high concentration of sonic hedgehog it can dictate the tissue to produce one cell type and at a lower concentration it can produce a different cell type.
It is a really fascinating system and very powerful. Sonic hedgehog is a fundamental molecule in the spinal cord. There is a structure that runs along the ventral surface of the developing embryo called the notochord, a very primitive structure, that releases sonic hedgehog growth factor. At high concentration it induces the ventral side of the spinal cord to produce floorplate tissue and also to produce the motor neurons and oligodendrocytes. Then up at the top of the spinal cord, where you have low concentration of sonic hedgehog, the dorsal neurons are made.
So Sonic hedgehog is crucial to the formation of the spinal cord and its specialized cell types. I mentioned oligodendrocytes….these are one of the cell types that can be lost after spinal cord injury. In many cases, people with spinal cord injury will have axons remaining but the axons have lost their oligodendrocytes, which are the wrapping cells that help to insulate the axons. Without that covering, nerve impulses go much slower and peter out so they don’t get to the muscle to make it work.
We rationalized that after spinal cord injury we might want to put stem cells in to the site of injury, and then add a molecule to instruct the stem cells what to do. We thought that if we could increase the level of sonic hedgehog around implanted stem cells then perhaps they would produce cells like oligodendrocytes that would be valuable to the repair process. We also rationalized that if we were going to instruct stem cells we would have to do it over a long time period – stem cells take days to divide and differentiate into the cells you want. So that’s how we came to the idea of putting the sonic hedgehog into a sort of sustained release formulation. A little bit of it would dribble out over time, around the area of injury, to change the environment.
When we had that slow release concept we knew we needed to talk to engineers. So we went up to Rensselaer Polytechnic Institute, luckily just 20 minutes away from us. We talked to Dr. Ravi Kane and his group about making the biodegradable microspheres that we used in the paper. They did the work to encapsulate the sonic hedgehog, then show that it was bioactive and released in the right profile, and at the right concentration.
We chose PLGA [poly(lactide-coglycolide)] as the delivery material because we knew the material was approved by the FDA for other indications [for example, sutures and drug delivery]. Then we turned to neurosurgeons who were doing spinal cord injury surgeries to ask what sort of material would be compatible with treatment patients would be getting.
How big is a bead?
You need a microscope to see them; they are about the size of a cell -- 10 micrometers to 100 micrometers. Quite small.
In the paper you discuss stem cells too…
Our initial idea was to take stem cells and surround them with sonic hedgehog-loaded slow-release microbeads, put both in the spinal cord in animal models (mice) and see whether they would enhance recovery. We also took the sonic hedgehog loaded beads and put them into the injured cord just by themselves. Our big surprise was that the beads by themselves were beneficial. You didn’t have to put the stem cells in. You could just put the beads in. The combination of stem cells and sonic hedgehog was somewhat better but the beads alone were very good.
We were very excited about that finding; it said that the beads could be acting, somehow, on the injured cord to promote repair. That’s when we took a look at what it was doing. It seems that there were three effects. The shh beads reduced scar formation, and stimulated cells that are recognized as precursors for oligodendrocytes. The beads also stimulated axon outgrowth – there was enhanced nerve sprouting, which could potentially help axons to get around the area of injury.
When we contemplated putting both stem cells and sonic hedgehog beads into the spinal cord, we knew it would be a very complicated process. It’s something we would like to move towards but it is fraught with difficulty. So as a first process, if the sonic hedgehog beads can produce beneficial effects alone, that is a good place to start. We’re doing more preclinical studies and that’s what we are moving ahead with.
So the beads biodegrade after a few days?
Exactly, they are around for several days, maybe longer. We haven’t really tested how long they will live in the cord.
The beads ought to be useful to deliver lots of different molecules…
Yes, you see quite a bit of encapsulation now, with different kinds of factors. One possibility is to put chondroitinase [ch’ase] inside. This is an enzyme that can help chew up the scar. Or you could deliver a different type of growth factor. The nice thing about it is you can mix and match. You could put in some of the enzyme and some growth factor, the best combination for that individual. We have found that we could load the enzyme – we were not the first to do that, others have done this also. What we’d like to try is to put the two types of beads together.
Dr. Jerry Silver [who has helped with the ch’ase studies] was very important to our work. When we began we knew very little about spinal cord injury and he was the person who introduced us to the system and helped guide us as to what we needed to do.
He is always trying to keep the flame of hope alive…
You touch on such an important point, that flame of hope. When I began this study I was scared, I must say, to go into a field that was so difficult. It’s as if you have crystal vase and you break it and now you have a thousand little shards and you want to put it back together. It’s really, really difficult. I knew from being a neuroscientist that it would be hard, but around the time we were thinking about working on spinal cord injury my assistant Cindy Butler was in a car crash and her best friend Chris McMahon was driving. He is in a wheelchair now. Early on in the process Chris came and talked to us and he said some things that were very meaningful to me. He said how very important it is to begin. That struck home for me. Just because a problem is hard doesn’t mean you should stop trying to work on it. He said, you know you don’t have to get perfection. You could get an improvement that could be very meaningful to people’s lives. Then I began to think this is a problem we can approach. We can make steps. If we can make steps and other people can build on that, then we’re nearer the goal.
In the paper you note that sonic hedgehog, in certain quantities, can cause abnormal growth.
It’s a very powerful molecule. It can cause cells to proliferate and it can cause them to take on different fates. One of the diseases it is associated with is a childhood cancer called medulloblastoma, which affects the cerebellum, at the back of the head. One of the things we were concerned about was, could sonic hedgehog in the adult do anything detrimental like that. In other words, if we put it in to the cord, could it cause tumor formation? We know medulloblastoma happens in children in another part of the nervous system, not the spinal cord, but we did want to test it. So we looked carefully at the nervous tissue around the area where we are injecting the sonic hedgehog beads, but we didn’t see any proliferation that looked abnormal or indicated growths. We would want to do a lot more testing before putting this compound in humans, though.
Why did you use two animal models…hemisection and contusion?
This was part of our learning process. In the beginning we were using equipment that was available. We started with the hemisection because it is easy to do and it produces a very consistent injury. Then as we learned, we realized that a contusion injury was a more accepted model for human injury. So we had to purchase that equipment and be trained on it and then we did a larger range of experiments with that. The fact we got the same results, the same benefits in both models, because it adds strength to the findings.
The lead author for the paper is Natasha Lowry …
Yes, she is a fantastic scientist. She’s been in the lab now for about eight years. She is now an assistant professor at Albany Medical Center, but she comes here to the Neural Stem Cell Institute to continue her spinal cord work. Natasha is a physician, trained in Russia, then she came to the US and did a Ph.D. in molecular biology, and then retrained in spinal cord surgery work. This was the most intensive study that we’ve ever done. It required so much manpower, so much dedication.
Would sonic hedgehog have application in a chronic model of SCI?
It is hard to know because sonic hedgehog has multiple effects. If for example sonic hedgehog is able to stimulate the proliferation of oligodendrocyte progenitors that are there, it could increase myelination, and that is one possible beneficial effect. The other thing we might have to do is put in a scar-chewing enzyme along with the sonic hedgehog, maybe that is a way forward. It’s something we have to explore.
Besides funding from Reeve, you benefited by the New York program that put a surcharge on auto violations….
Yes. The Reeve Foundation funded the beginning of the bead work and we are very grateful. When we started to work in spinal cord injury we began from scratch. We got help from a New York state fund too. That program was started by Paul Richter, who was spinal cord injured [in 1973, working as a New York State Police trooper, he was shot in the neck]. Paul is from our local community and he came here to encourage us to work on this problem. He is such an inspiration. He has no ulterior motive other than to help people with spinal cord injury. The New York state funding [by way of the Spinal Cord Research Trust Fund] was so valuable to us. That state program allowed many people new to the field, including us, to begin to contribute. I don’t think many realize it, but to do a science experiment it’s up to the lab to raise the money, through grants or donations. The SCI trust fund program did so much good. Researchers showed that they were able to leverage that state funding and bring in more funding from other sources. For a small surcharge on moving violations, up to $8 million a year was set aside to fund spinal cord injury research. Unfortunately, none of that has been coming to research for the last couple of years. We would like it to be reestablished. A wonderful young man Keith Gurgui from Kingston NY who is a quadriplegic after a diving accident a couple of years ago is leading a new effort to do this. He is gaining support and we hope his voice is heard.
So the state took the trust fund money and put it in the general fund…
I realize the economy is bad but we need to recognize that this is an investment in health. The payback is enormous. It breaks new ground in therapeutics, in building biotech, in impacting lives in such a profound way.
Nancy Lieberman is an amazing example of the transformation this program allows. After she was spinal cord injured she was unable to move; her arms were locked to her chest. But after going to a robotic rehab program at the Burke Rehab Institute run by Dr. Raj Ratan, which was developed through funding from the New York State program, she has almost full movement of her arms. So she went back to work as a very accomplished lawyer in the city. So she went from someone who was dependent to being some who contributes, someone living a much fuller life, and being a taxpayer, back to work.
Just how strong is the flame of hope these days?
I have been in research a long time. And I am astonished at the speed we are moving now. It was as if for decades we moved very, very slowly and then suddenly in the last ten years things have picked up dramatically. Things like the human genome project. and recombinant DNA technology – it used to take six months to clone a gene, if you were lucky, and now you order it and it comes overnight in the mail. Things are moving at lightening speed in the lab and we can do things we could only dream of ten years ago. I see a burgeoning of biotech and biomedical advances in the lab that have not yet made it into the clinic. I think we are in the best position we have ever been in to make strides forward to treat spinal cord injury. I am very hopeful will see important steps forward in the next few years.