By Pat Anson, PNN Editor

An experimental injection therapy that uses synthetic nanofibers to stimulate nerve cells could be used someday to reverse paralysis and repair damaged spinal cord tissues, according to a new study by researchers at Northwestern University.

In experiments on laboratory animals, the therapy successfully regenerated spinal cord nerves, reduced scar tissue and triggered the formation of new blood vessels. After a single injection, paralyzed mice regained the ability to walk within four weeks.

“Our research aims to find a therapy that can prevent individuals from becoming paralyzed after major trauma or disease,” said lead author Samuel Stupp, PhD, an expert in regenerative medicine and founding director of the Simpson Querrey Institute for BioNanotechnology (SQI) at Northwestern.

“For decades, this has remained a major challenge for scientists because our body’s central nervous system, which includes the brain and spinal cord, does not have any significant capacity to repair itself after injury or after the onset of a degenerative disease. We are going straight to the FDA to start the process of getting this new therapy approved for use in human patients, who currently have very few treatment options.”

Stupp and his colleagues used nanotechnology to develop synthetic nanofibers that mimic the natural environment around the spinal cord. Intensifying the motion of molecules within the nanofibers promotes the repair and regeneration of myelin, the insulating layer of axons that help nerve cells transmit electrical signals.

Researchers say the nanofibers biodegrade into nutrients for nerve cells within 12 weeks and completely disappear from the body without noticeable side effects. Their study, published in the journal Science, is the first in which researchers controlled the motion of molecules through changes in chemical structure to increase a therapy’s efficacy.

Nearly 300,000 people are currently living with a spinal cord injury in the United States. About 30% are hospitalized at least once a year after the initial injury and less than 3% of those with a severe injury ever recover basic physical functions. Life expectancy for patients with spinal cord injuries is significantly lower than healthy people and has not improved since the 1980s.

“Currently, there are no therapeutics that trigger spinal cord regeneration,” Stupp said in a news release. “I wanted to make a difference on the outcomes of spinal cord injury and to tackle this problem, given the tremendous impact it could have on the lives of patients.” 

The key behind Stupp’s breakthrough therapy is fine tuning the motion of molecules so that they can find and constantly engage with moving cellular receptors with bioactive signals. Injected as a liquid, the “dancing molecules” immediately form a gel in a complex network of nanofibers that mimic the extracellular matrix of the spinal cord.

“Receptors in neurons and other cells constantly move around,” Stupp said. “The key innovation in our research, which has never been done before, is to control the collective motion of more than 100,000 molecules within our nanofibers. By making the molecules move, ‘dance’ or even leap temporarily out of these structures, known as supramolecular polymers, they are able to connect more effectively with receptors.”

Stupp and his team found that fine-tuning the molecules’ motion within the nanofibers makes them more agile and results in greater therapeutic effect in paralyzed mice. They also confirmed that formulations of their therapy performed successfully in vitro tests with human cells, indicating increased bioactivity and cellular signaling.

Once connected to the nerve receptors, the dancing molecules trigger two cascading signals, both of which are critical to spinal cord repair. One signal induces myelin to rebuild around axons, which improves how nerve cells communicate with the brain. The second signal helps neurons survive after injury by promoting the regrowth of lost blood vessels that feed neurons and other cells for tissue repair. The therapy also reduces glial scarring, which acts as a physical barrier that prevents the spinal cord from healing. 

“The signals used in the study mimic the natural proteins that are needed to induce the desired biological responses. However, proteins have extremely short half-lives and are expensive to produce,” said first author Zaida Álvarez, a former research assistant in Stupp’s laboratory who is now a researcher scholar at SQI. “Our synthetic signals are short, modified peptides that — when bonded together by the thousands — will survive for weeks to deliver bioactivity. The end result is a therapy that is less expensive to produce and lasts much longer.”

While the new therapy could be used to treat paralysis after a major spinal cord injury, Stupp believes it could also be used to as a therapy for neurodegenerative diseases and strokes.

“The central nervous system tissues we have successfully regenerated in the injured spinal cord are similar to those in the brain affected by stroke and neurodegenerative diseases, such as ALS, Parkinson’s disease and Alzheimer’s disease,” Stupp said. “Beyond that, our fundamental discovery about controlling the motion of molecular assemblies to enhance cell signaling could be applied universally across biomedical targets.”

You can learn more about Stupp’s research in this podcast and by watching this video:

Recent research at Yale University and Sapporo Medical University in Japan found that injections of mesenchymal stem cells (MSCs) in patients paralyzed by spinal cord injuries led to significant improvement in their motor functions. In a small study, more than half of the paralyzed patients showed substantial improvements in function within weeks of being injected with autologous MSCs derived from their own bone marrow.