The Stem Cell Connection
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Researchers in California are investigating whether stem cells can be integrated into and connected with the spinal cord’s tissue. Their goal: to lay the groundwork for a breakthrough therapy
It sounds like science fiction – at least a little. Where, until recently, all one could see was dead tissue, one can now see countless illuminated nerve cells that are sending impulses through the spinal cord. The man peering through the $100,000 microscope can’t stifle a smile, even though he has witnessed this spectacle before.
Steven Ceto, 28, is currently in the midst of his doctorate at the University of California in San Diego. His workplace is located in a modern, light-flooded building in the heart of the campus, and the Pacific Ocean is a mere few hundred metres away. These are perfect conditions for a young scientist who enjoys a spot of surfing before work. Initially, Ceto studied biochemistry, but he soon found himself focusing on spinal cord injuries. He’s tempted by the challenge – the “huge, complex problem” – and wants to help. He would like to help people such as Stephen Murray, an extreme-sports legend from his youth, now paralysed from the neck down; and Paul, a colleague who is in a wheelchair after a car accident. Ceto, who is from the Seattle area, is looking for a cure for them and the many others affected. “I want to do more than merely ease the symptoms,” he emphasises. “I want to get to the root of the problem. Mark has offered me an opportunity to do that.”
Stem cells: a new hope?
“Mark” is Professor Mark Tuszynski, Ceto’s boss and doctoral supervisor. The native Canadian is a luminary when it comes to recovering lost nerve functions. Tuszynski has received dozens of awards for his work, and has published more than a hundred articles. What Ceto appreciates most about the professor is that he’s very practice-oriented and demands that his teams search for new treatment approaches at high pressure. This also includes stem cells. Tuszynski and his team were able to demonstrate the potential of stem cells a few years ago. Back then, they injected neural stem cells into the spinal cord of a paraplegic rat.
Even though only a few cells of the graft survived, the survivors nevertheless started forming long nerve fibres called axons. This initial success encouraged the researchers to pursue this path further. They began looking for a way to fill the entire gap in the spinal cord caused by an injury. Finally, they utilised a protein to form a net-like structure that acts as an anchor for the stem cells. It worked. This time, almost all the stem cells survived and formed tens of thousands of new axons. It was a minor sensation.
Wanted: a right connection
Ceto’s current research is basically a continuation of the aforementioned research success. His work also focuses on stem cells. However, he is less interested in how many of the transplanted stem cells survive and form nerve fibres; he would rather discover how the graft integrates from a functional point of view. Do the cells dock properly? Do they become interconnected? And how do they communicate with nerve cells in the healthy tissue?
Generally speaking, the communication of nerves takes place via electrical and chemical signals. As soon as a nerve cell receives a signal, it processes it and passes it on.
This allows humans to feel, think, and act. The transmitting extension is called an axon, while the receiving counterparts are known as dendrites. The area in which an axon docks to a dendrite is known as a synapse. This structure allows a single nerve cell to connect with thousands of others. Ceto is attempting to find out whether and to what extent these synaptic connections also form after transplantation. “What happens within the graft is still a sort of ‘Black Box’ for us,” he explains. “We want to look into this box and examine how the nerve signals are relayed.”
Calcium, electricity and light
First and foremost, Ceto requires a copious amount of stem cells for his experiments. To be more precise, he needs up to one million cells for an injury that is shorter than a millimetre. He cultivates the cells in a petri dish until they have divided and proliferate accordingly. He then injects them directly into the lesion of a paralysed rat. The analysis usually commences six to eight weeks later. He uses a range of techniques to determine whether the cells have connected among each other and with the healthy tissue. One of these techniques is known as Calcium Imaging. This method exploits the fact that the calcium concentration in a cell increases as soon as it ‘fires’. By adding a certain fluorescent molecule, Ceto can make these invisible signals visible under a microscope. “The molecule attaches itself to the calcium and causes it to glow,” he explains.
The great advantage of this method is that Ceto can observe the activity of many hundreds of nerve cells simultaneously.
Another method is the so-called Patch-Clamp technique. This method allows Ceto to investigate whether a synaptic connection has been made; in other words, whether signals are being transferred from one cell to the other. He first forms a seal onto the cell membrane with a small glass pipette, and then gently opens it. He then applies a micro-electrode. Thus, he can measure whether there is any electric activity within the nerve cell.
Finally, Ceto also dips into the toolbox of brain researchers by using a method from the field of optogenetics. This technique allows him to control the activity of certain nerve cells precisely. A genetic trick renders the cells sensitive to light. He can then control them and cause them to fire electrical impulses with the help of light. Using Calcium Imaging and Patch- Clamp techniques, he can now track whether the impulses are actually passed on to other nerve cells via the synaptic connections. “Steven is fantastic,” Tuszynski says full of praise. “He has built this project up from the beginning, which wasn’t easy. He is a very accomplished researcher, and it’s a real pleasure to have him.”
The perfect formula
It’s still too early for concrete results. “We can see the first functional improvements in models. This means some connections have formed,” Ceto explains. “But we’re not where we would like to be just yet. We still need to gain a better understanding in terms of what happens within the graft.”
Ceto will be working on this task until at least 2018. The findings will one day help to refine the stem cell preparation, thus optimising the result for the patient. Until that time has come, there are still a few questions that need to be answered. Which stem cells are the most suitable? What is the perfect combination of stem cells, growth factors, molecules, and carrier materials? And how safe is the treatment for the patient? Ceto is already convinced that stem cells are the future in terms of treating patients with spinal cord injuries. “They have the potential to not only create the optimal environment for a regenerative healing process but also to restore the circuitry of nerve cells. This allows us to kill two birds with one stone.” In addition to this, they could also present a valid option for almost all types of spinal cord injuries, including – or even especially for – chronic and completely paralysed patients.
Ceto estimates it will take at least another five to 10 years before the exact formula that allows the use on patients is found. “We want to make absolutely sure that the treatment approach we are researching works perfectly before we start clinical studies. When the time comes, I’m convinced that the potential of this approach is greater than anything we have seen before,” he says. With a grin directed at Tuszynski, he adds, “After all, we are looking for a home run here.”
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