Fibrotic scar 14d after spinal cord injury, red – Col1a1+ perivascular fibroblast derived cells Photo: Daniel Holl
New research has found that scar formation after spinal cord injuries is more complex than previously thought. Scientists at Karolinska Institutet have identified two types of perivascular cells as key contributors to scar tissue, which hinders nerve regeneration and functional recovery. These findings, published in Natural Neuroscience, are also relevant for other brain and spinal cord injuries and could lead to targeted therapies for reducing scarring and improving outcomes.
The central nervous system (CNS) has very limited healing abilities. Injuries or autoimmune diseases like multiple sclerosis often lead to permanent functional deficits.
Regardless of the injury’s cause, the body responds by forming a boundary around the damaged tissue, which eventually becomes permanent scar tissue.
Two contributing cell types
While scar tissue seals the damaged area, it also prevents functional repair. After spinal cord injuries, scar tissue blocks the regeneration of nerve fibers that connect the brain with the body, resulting in paralysis after severe injuries.
The research team led by Christian Göritz at Karolinska Institutet has made significant progress in understanding how scar tissue forms in the CNS. The group now identified two distinct types of perivascular cells, which line different parts of blood vessels, as the major contributors to fibrotic scar tissue after spinal cord injury. Depending on the lesion’s location, the two identified cell types contribute differently.
“We found that damage to the spinal cord activates perivascular cells close to the damaged area and induces the generation of myofibroblasts, which consequently form persistent scar tissue,” explains first author Daniel Holl, researcher at the Department of Cell and Molecular Biology.
By examining the process of scar formation in detail, the researchers hope to identify specific therapeutic targets to control fibrotic scarring.
Zebrafish have a remarkable ability to heal their spinal cord after injury. Now, researchers at Karolinska Institutet have uncovered an important mechanism behind this phenomenon – a finding that could have implications for the treatment of spinal cord injury in humans.
In a new study published in Nature Communications,researchers show that the neurons of adult zebrafish immediately start to cooperate after a spinal cord injury, keeping the cells alive and stimulating the healing process.
“We have shown that the neurons form small channels called gap junctions, which create a direct connection between the neurons and enable the exchange of important biochemical molecules, allowing the cells to communicate and protect each other,” explains Konstantinos Ampatzis, a researcher in the Department of Neuroscience at Karolinska Institutet, who led the study.
The researchers will further investigate the exact mechanisms behind this protective strategy in zebrafish and hope this knowledge will lead to new ways of treating spinal cord injury in humans.
“Spinal cord injuries are a major burden for sufferers and their families,” says Konstantinos Ampatzis. “What if we could get human neurons to adopt the same survival strategy and behave like zebrafish neurons after an injury? This could be the key to developing new effective treatments.”
Conditions such as diabetes, heart attack and vascular diseases commonly diagnosed in people with spinal cord injuries can be traced to abnormal post-injury neuronal activity that causes abdominal fat tissue compounds to leak and pool in the liver and other organs, a new animal study published in Cell Reports Medicine has found.
After discovering the connection between dysregulated neuron function and the breakdown of triglycerides in fat tissue in mice, researchers found that a short course of the drug gabapentin, commonly prescribed for nerve pain, prevented the damaging metabolic effects of the spinal cord injury – though not without side effects.
Gabapentin inhibits a neural protein that, after the nervous system is damaged, becomes overactive and causes communication problems – in this case, affecting sensory neurons and the abdominal fat tissue to which they’re sending signals.
“We believe there is maladaptive reorganisation of the sensory system that causes the fat to undergo changes, initiating a chain of reactions – triglycerides start breaking down into glycerol and free fatty acids that are released in circulation and taken up by the liver, the heart, the muscles, and accumulating, setting up conditions for insulin resistance,” said senior author Andrea Tedeschi, assistant professor of neuroscience in The Ohio State University College of Medicine.
“Through administration of gabapentin, we were able to normalise metabolic function.”
Previous research has found that cardiometabolic diseases are among the leading causes of death in people who have experienced a spinal cord injury. These often chronic disorders can be related to dysfunction in visceral white fat (or adipose tissue), which has a complex metabolic role of storing energy and releasing fatty acids as needed for fuel, but also helping keep blood sugar levels at an even keel.
Earlier investigations of these diseases in people with neuronal damage have focused on adipose tissue function and the role of the sympathetic nervous system, but also a regulator of adipose tissue that surrounds the abdominal organs.
Instead, Debasish Roy, a postdoctoral researcher in the Tedeschi lab and first author on the paper, decided to focus on sensory neurons in this context. Tedeschi and colleagues have previously shown that a neuronal receptor protein called alpha2delta1 is overexpressed after spinal cord injury, and its increased activation interferes with post-injury function of axons, the long, slender extensions of nerve cell bodies that transmit messages.
In this new work, researchers first observed how sensory neurons connect to adipose tissue under healthy conditions, and created a spinal cord injury mouse model that affected only those neurons – without interrupting the sympathetic nervous system.
Experiments revealed a cascade of abnormal activity within seven days after the injury in neurons – though only in their communication function, not their regrowth or structure – and in visceral fat tissue. Expression of the alpha2delta1 receptor in sensory neurons increased as they over-secreted a neuropeptide called CGRP, all while communicating through synaptic transmission to the fat tissue – which, in a state of dysregulation, drove up levels of a receptor protein that engaged with the CGRP.
“These are quite rapid changes. As soon as we disrupt sensory processing as a result of spinal cord injury, we see changes in the fat,” Tedeschi said. “A vicious cycle is established – it’s almost like you’re pressing the gas pedal so your car can run out of gas but someone else continues to refill the tank, so it never runs out.”
The result is the spillover of free fatty acids and glycerol from fat tissue, a process called lipolysis, that has gone out of control. Results also showed an increase in blood flow in fat tissue and recruitment of immune cells to the environment.
“The fat is responding to the presence of CGRP, and it’s activating lipolysis,” Tedeschi said. “CGRP is also a potent vasodilator, and we saw increased vascularisation of the fat – new blood vessels forming as a result of the spinal cord injury. And the recruitment of monocytes can help set up a chronic pro-inflammatory state.”
Silencing the genes that encode the alpha2delta1 receptor restored the fat tissue to normal function, indicating that gabapentin – which targets alpha2delta1 and its partner, alpha2delta2 – was a good treatment candidate. Tedeschi’s lab has previously shown in animal studies that gabapentin helped restore limb function after spinal cord injury and boosted functional recovery after stroke.
But in these experiments, Roy discovered something tricky about gabapentin: the drug prevented changes in abdominal fat tissue and lowered CGRP in the blood, in turn preventing spillover of fatty acids into the liver a month later, establishing normal metabolic conditions. But paradoxically, the mice developed insulin resistance, a known side effect of gabapentin.
The team instead tried starting with a high dose, tapering off and stopping after four weeks.
“This way, we were able to normalise metabolism to a condition much more similar to control mice,” Roy said. “This suggests that as we discontinue administration of the drug, we retain beneficial action and prevent spillover of lipids in the liver. That was really exciting.”
Finally, researchers examined how genes known to regulate white fat tissue were affected by targeting alpha2delta1 genetically or with gabapentin, and found both of these interventions after spinal cord injury suppress genes responsible for disrupting metabolic functions.
Tedeschi said the combined findings suggest starting gabapentin treatment early after a spinal cord injury may protect against detrimental conditions involving fat tissue that lead to cardiometabolic disease – and could enable discontinuing the drug while retaining its benefits and lowering the risk for side effects.
In this study, spinal cords that associated limb position with an unpleasant experience learned to reposition the limb after only 10 minutes, and retained a memory the next day. Spinal cords that received random unpleasantness did not learn. Credit: RIKEN
Researchers in Japan have discovered the neural circuitry in the spinal cord that allows brain-independent motor learning. This study by Aya Takeoka at the RIKEN Center for Brain Science and colleagues found two critical groups of spinal cord neurons, one necessary for new adaptive learning, and another for recalling adaptations once they have been learned. The findings, published in Science, could help scientists develop ways to assist motor recovery after spinal cord injury.
It has been long been known that motor output from the spinal cord can be adjusted through practice even without a brain. This has been shown most dramatically in headless insects, whose legs can still be trained to avoid external cues. Until now, no one has figured out exactly how this is possible, and without this understanding, the phenomenon is not much more than a quirky fact. As Takeoka explains, “Gaining insights into the underlying mechanism is essential if we want to understand the foundations of movement automaticity in healthy people and use this knowledge to improve recovery after spinal cord injury.”
Before jumping into the neural circuitry, the researchers first developed an experimental setup that allowed them to study mouse spinal cord adaptation, both learning and recall, without input from the brain. Each test had an experimental mouse and a control mouse whose hindlegs dangled freely. If the experimental mouse’s hindleg drooped down too much it was electrically stimulated, emulating something a mouse would want to avoid. The control mouse received the same stimulation at the same time, but not linked to its own hindleg position.
After just 10 minutes, they observed motor learning only in the experimental mice; their legs remained high up, avoiding any electrical stimulation. This result showed that the spinal cord can associate an unpleasant feeling with leg position and adapt its motor output so that the leg avoids the unpleasant feeling, all without any need for a brain. Twenty-four hours later, they repeated the 10-minute test but reversed the experimental and control mice. The original experimental mice still kept their legs up, indicating that the spinal cord retained a memory of the past experience, which interfered with new learning.
Having thus established both immediate learning, as well as memory, in the spinal cord, the team then set out to examine the neural circuitry that makes both possible. They used six types of transgenic mice, each with a different set of spinal neurons disabled, and tested them for motor learning and learning reversal. They found that mice hindlimbs did not adapt to avoid the electrical shocks after neurons toward the top of the spinal cord were disabled, particularly those that express the gene Ptf1a.
When they examined the mice during learning reversal, they found that silencing the Ptf1a-expressing neurons had no effect. Instead, a group of neurons in the ventral part of the spinal cord that express the En1 gene was critical. When these neurons were silenced the day after learning avoidance, the spinal cords acted as if they had never learned anything. The researchers also assessed memory recall on the second day by repeating the initial learning conditions. They found that in wildtype mice, hindlimbs stabilised to reach the avoidance position faster than they did on the first day, indicating recall. Exciting the En1 neurons during recall increased this speed by 80%, indicating enhanced motor recall.
“Not only do these results challenge the prevailing notion that motor learning and memory are solely confined to brain circuits,” says Takeoka, “but we showed that we could manipulate spinal cord motor recall, which has implications for therapies designed to improve recovery after spinal cord damage.”
In a new study using mice, neuroscientists have uncovered a crucial component for restoring functional activity after spinal cord injury. In the study, published in Science, the researchers showed that re-growing specific neurons back to their natural target regions led to recovery, while random regrowth was not effective.
In a 2018 study in Nature, the team identified a treatment approach that triggers axons to regrow after spinal cord injury in rodents. But even as that approach successfully led to the regeneration of axons across severe spinal cord lesions, achieving functional recovery remained a significant challenge.
For the new study, the team of researchers from UCLA, the Swiss Federal Institute of Technology, and Harvard University aimed to determine whether directing the regeneration of axons from specific neuronal subpopulations to their natural target regions could lead to meaningful functional restoration after spinal cord injury in mice. They first used advanced genetic analysis to identify nerve cell groups that enable walking improvement after a partial spinal cord injury.
The researchers then found that merely regenerating axons from these nerve cells across the spinal cord lesion without specific guidance had no impact on functional recovery. However, when the strategy was refined to include using chemical signals to attract and guide the regeneration of these axons to their natural target region in the lumbar spinal cord, significant improvements in walking ability were observed in a mouse model of complete spinal cord injury.
“Our study provides crucial insights into the intricacies of axon regeneration and requirements for functional recovery after spinal cord injuries,” said Michael Sofroniew, MD, PhD, professor of neurobiology at the David Geffen School of Medicine at UCLA and a senior author of the new study. “It highlights the necessity of not only regenerating axons across lesions but also of actively guiding them to reach their natural target regions to achieve meaningful neurological restoration.”
The authors say understanding that re-establishing the projections of specific neuronal subpopulations to their natural target regions holds significant promise for the development of therapies aimed at restoring neurological functions in larger animals and humans. However, the researchers also acknowledge the complexity of promoting regeneration over longer distances in non-rodents, necessitating strategies with intricate spatial and temporal features. Still, they conclude that applying the principles laid out in their work “will unlock the framework to achieve meaningful repair of the injured spinal cord and may expedite repair after other forms of central nervous system injury and disease.”
Researchers in the UK have evaluated a potential drug for the treatment of spinal cord injury (SCI), which could potentially regrow damaged nerves, and found it to be safe and tolerable. The results of their Phase 1 clinical trial were published in British Journal of Clinical Pharmacology and evaluated the KCL-286 drug, which activates retinoic acid receptor beta (RARb) in the spine to promote recovery.
There are no licensed drugs that can fix the adult central nervous system’s inability to regenerate. Implants have been able to restore some function, but for most, spinal cord injuries are life-changing.
Previous studies have shown that nerve growth can be stimulated by activating the RARb2 receptor, but no drug suitable for humans has been developed. KCL-286, an RARb2 agonist, was developed by Professor Corcoran and team and used in a first in man study to test its safety in humans.
The study by the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King’s College London, recruited 109 healthy males in a single ascending dose (SAD) adaptive design with a food interaction (FI) arm, and multiple ascending dose (MAD) arm. Participants in each arm were further divided into different dose treatments.
SAD studies are designed to establish the safe dosage range of a medicine by providing participants with small doses before gradually increasing the dose provided. Researchers look for any side effects, and measure how the medicine is processed within the body. MAD studies explore how the body interacts with repeated administration of the drug, and investigate the potential for a drug to accumulate within the body.
Researchers found that participants were able to safely take 100mg doses of KCL-286, with no severe adverse events.
Professor Jonathan Corcoran, Professor of Neuroscience and Director of the Neuroscience Drug Discovery Unit, at King’s IoPPN and the study’s senior author said, “This represents an important first step in demonstrating the viability of KCL-286 in treating spinal cord injuries. This first-in-human study has shown that a 100mg dose delivered via a pill can be safely taken by humans. Furthermore, we have also shown evidence that it engages with the correct receptor.
“Our focus can hopefully now turn to researching the effects of this intervention in people with spinal cord injuries.”
Dr Bia Goncalves, a senior scientist and project manager of the study, and the study’s first author from King’s IoPPN said, “Spinal Cord Injuries are a life changing condition that can have a huge impact on a person’s ability to carry out the most basic of tasks, and the knock-on effects on their physical and mental health are significant.
“The outcomes of this study demonstrate the potential for therapeutic interventions for SCI, and I am hopeful for what our future research will find.”
The researchers are now seeking funding for a Phase 2a trial studying the safety and tolerability of the drug in those with SCI.
Researchers screening more than 1000 potential drugs for spinal cord injury treatment identified an existing one – cimetidine – that improved spinal repair in zebrafish. The results, published in the journal Theranostics, showed that the drug also helped improve recovery of movement and reduce the extent of spinal cord damage when tested in spinal-injured mice.
Healing of spinal cord injuries can be inefficient due to inflammation caused by an overreaction of the immune system. Anti-inflammatories that suppress the whole immune response also inhibit the immune cells which promote repair.
The University of Edinburgh-led study tested multiple drugs in zebrafish larvae for their ability to prevent excessive inflammation during an immune response. Scientists discovered that cimetidine acts by helping to regulate histamine levels.
The findings have enabled the team to pinpoint a specific signalling pathway that moderates the immune response after spinal injury to support repair.
The investigators say that other drugs that work in a similar way could also be tested for their ability to support recovery from spinal injury. They caution that further studies are needed to investigate their impact in human clinical trials. The researchers add that the study highlights the usefulness of zebrafish in the drug discovery process.
The research team included scientists from the University of Edinburgh, the Research Institute of the McGill University Health Centre and Technische Universität Dresden.
Study participant Gert-Jan Oskam walking with the brain-spine interface. Credit: Swiss Federal Institute of Technology in Lausanne
A 40 year-old man, Gert-Jan Oskam, has regained the ability to walk independently after being paralysed from a spinal cord injury with the use of a new brain-spine interface. The ‘digital bridging’ technology, developed at the Swiss Federal Institute of Technology in Lausanne and described in Nature, consists of implants and a computer to translate brain signals of the intention to move into stimulations that move the legs accordingly..
This BSI system could be calibrated in minutes, and remained stable for one year, including use at home. The BSI enabled the participant to exert natural control over the movements of his legs to stand, walk, climb stairs and even traverse complex terrains.
In addition to the digital bridging, neurorehabilitation supported by the BSI improved neurological recovery. The participant regained the ability to walk with crutches overground even when the BSI was switched off. This digital bridge establishes a framework to restore natural control of movement after paralysis.
The system consists of a pair cortical of sensors, each an array with 64 electrodes housed in 5cm-diameter titanium discs. These discs are implanted snugly in the skull to pick up brain activity. They transmit the data wirelessly to a personalised headset, which also provides power for the sensors. The headset then sends the data to a portable processing unit (which may be carried in a backpack). Using specialised software, it uses this brain signal data to generates real-time predictions of motor intentions. These decoded intentions are translated into stimulation commands and sent on to another implant, a paddle array of 16 electrodes implanted next to the spinal cord, delivering current to the targeted dorsal root entry zones.
Neurosurgical implantation procedure
Oskam had sustained an incomplete cervical (C5/C6) spinal cord injury during a biking accident 10 years previously. He had already participated in a neurological recovery programme, the STIMO trial, which had used neurostimulation to get him to the stage where he could walk with the aid of a front-wheel walker. The neurorehabilitation from the trial also enabled him to use his hip flexors and lift his legs against gravity, but recovery had plateaued for the three years prior to his participation in the present study.
For the BSI to function, the researchers needed to locate neural features related to the intention to move the legs. To pinpoint the cortical regions associated with the intention to move, they used CT scans and magnetoencephalography. Taking into account anatomical restraints, they then decided on the positions of the implants.
Under general anaesthesia, surgeons performed a bicoronal incision of the scalp to allow two circular-shaped craniotomies over the planned locations of the left and right hemispheres. They then replaced the bone flaps with the two implantable recording devices, before closing the scalp.
The paddle lead had already been emplaced over the dorsal root entry zones of the lumbar spinal cord during the STIMO clinical trial. Its optimal positioning was identified using high-resolution structural imaging of the spine, and its final position was decided during the surgery based on electrophysiological recordings. The implantable pulse generator was inserted subcutaneously in the abdomen. Oskam was able to return home 24 hours after each procedure.
For people with paralysis caused by neurologic injury or disease, brain-computer interfaces (BCIs) can potentially restore mobility and function by transmitting neural data to external devices such as mobility aids, which have already shown promise in trials.
Although implanted brain sensors, the core component of many brain-computer interfaces, have been used in neuroscientific studies with animals for decades and have been approved for short term use (< 30 days) in humans, the long-term safety of this technology in humans is unknown.
New results published in Neurology from the BrainGate feasibility study, the largest and longest-running clinical trial of an implanted BCI, suggest that these sensors’ safety is similar to other chronically implanted neurologic devices, with skin irritation around the implant interface.
This new report from a Massachusetts General Hospital (MGH)-led team, examined data from 14 adults with quadriparesis from spinal cord injury, brainstem stroke, or ALS who were enrolled in the BrainGate trial from 2004 to 2021 through seven clinical sites in the United States.
Participants underwent surgical implantation of one or two microelectrode arrays in a part of the brain responsible for generating the electrical signals that control limb movement. With these “Utah” microelectrode arrays, the brain signals associated with the intent to move a limb can then be sent to a nearby computer that decodes the signal in real-time and allows the user to control an external device simply by thinking about moving a part of their body.
The authors of the study report that across the 14 enrolled research participants, the average duration of device implantation was 872 days, yielding a total of 12 203 days for safety analyses. There were 68 device-related adverse events, including 6 device-related serious adverse events.
The most common device-related adverse event was skin irritation around the portion of the device that connects the implanted sensor to the external computer system. Importantly, they report that there were no safety events that required removal of the device, no infections of the brain or nervous system, and no adverse events resulting in permanently increased disability related to the investigational device.
“This interim report demonstrates that the investigational BrainGate Neural Interface system, which is still in ongoing clinical trials, thus far has a safety profile comparable to that of many approved implanted neurologic devices, such as deep brain stimulators and responsive neurostimulators,” says lead author Daniel Rubin, MD, PhD.
“Given the rapid recent advances in this technology and continued performance gains, these data suggest a favorable risk/benefit ratio in appropriately selected individuals to support ongoing research and development,.” said Rubin.
Leigh Hochberg, MD, PhD, director of the BrainGate consortium and clinical trials and the article’s senior author emphasised the importance of ongoing safety analyses as surgically placed brain-computer interfaces advance through clinical studies.
“While our consortium has published more than 60 articles detailing the ever-advancing ability to harness neural signals for the intuitive control of devices for communication and mobility, safety is the sine qua non of any potentially useful medical technology,” says Hochberg.
“The extraordinary people who enroll in our ongoing BrainGate clinical trials, and in early trials of any neurotechnology, deserve tremendous credit. They are enrolling not to gain personal benefit, but because they want to help,” said Hochberg.
Severed axons are unable to regenerate, which means that central nervous system (CNS) injuries such as to the spinal cord, can result in permanent loss of sensory and motor function. Presently, there are very limited options to help these patients regain their motor abilities. In mice, researchers have found that deleting a certain gene can cause axons to regrow. The results have recently been published in the scientific journal Neuron.
In a study using mice, a research team led by Associate Professor Kai Liu found that the deletion of PTPN2, a phosphatase-coding gene, in neurons can prompt axons to regrow. Combination with the type II interferon IFNγ, can accelerate the process and increase the number of axons regenerated.
Unlike the CNS, peripheral nerves have a greater ability to regrow and repair by themselves after injury. Scientists have yet to fully understand the relationship between this self-repair and the intrinsic immune mechanism of the nervous system. Thus, the team aimed to resolve how immune-related signalling pathways affected neurons after injury, and whether they could enhance axonal regeneration directly.
This study investigated whether the signalling pathway IFNγ-cGAS-STING had any role in the regeneration process of peripheral nerves. Researchers found that peripheral axons could directly modulate the immune response in their injured environment to promote self-repair after injury.
In previous research, Prof Liu’s team had already demonstrated that elevating the neuronal activity and regulating the neuronal glycerolipid metabolism pathway could boost axon regenerative capacity. The current study is providing further insights into the search of treatment solutions for challenging conditions such as spinal cord injuries, with one possible option being the joining of several types of different signalling pathways.
