Summary: Spinal cord injuries are often permanent because nerve fibers have a limited ability to regrow. However, a new study offers a new strategy. Instead of trying to “regrow” severed fibers, researchers used a designer protein called hyper-interleukin-6 (hIL-6) to rewire existing, intact neural connections.
By turning the brain’s motor cortex into a “protein factory,” the team successfully restored coordinated walking in paralyzed mice by stimulating the sprouting of new collateral nerve branches.
Key Facts
- The “hIL-6” Messenger: Hyper-interleukin-6 is a potent signaling protein that can bind directly to nerve cells. In this study, it was delivered via a viral vector injected into the motor cortex, the brain’s movement control center.
- Transneuronal Transport: Once produced in the brain, the protein travels down existing nerve fibers to the brainstem. From there, it stimulates serotonergic neurons, which are crucial for controlling the rhythmic movements needed for walking.
- Plasticity over Regeneration: The treatment doesn’t shrink the injury site or replace dead cells. Instead, it triggers circuit plasticity, forcing healthy, intact nerve fibers to “sprout” new branches (collaterals) to bypass the damaged area.
- Restored Gait: While control groups remained largely paralyzed, the hIL-6 treated mice regained significantly improved walking ability and, crucially, coordinated gait patterns.
- The Serotonin Key: Researchers found that if they eliminated the serotonergic neurons in the brainstem, the recovery vanished. This proves these specific “descending” circuits are the primary drivers of functional restoration.
Source: University of Cologne
Spinal cord injuries typically result in permanent paralysis and loss of sensation, posing significant challenges for those affected and the healthcare system. In most cases, spinal cord injuries are contusion injuries, in which some of the fibers are damaged by compression while others remain intact.
Currently available treatment approaches can only improve functional recovery to a limited extent.
A research group led by Professor Dr Dietmar Fischer from the Institute of Pharmacology II at University Hospital Cologne is therefore pursuing a new approach to treating such contusion injuries.
The study “Transneuronal cytokine delivery promotes functional recovery across spinal cord contusion severities via descending circuit plasticity” will be published in the journal Neurobiology of Disease on 15 June 2026. It is already available online.
Using the protein hyper-interleukin-6 (hIL-6), which can bind directly to nerve cells, the researchers activated signaling pathways in both injured and uninjured nerve cells. What makes this approach unique is that hIL-6 is produced within the nerve cells themselves following the injection of a vector virus into the motor cortex.
The motor cortex is a region of the brain responsible for planning, controlling, and executing movements. From there, IL-6 is transported along existing neural pathways, reaching key motor areas in deeper brain regions (the brainstem) that can be stimulated.
“Instead of relying solely on the regrowth of severed nerve fibers, we also make use of neural connections that have remained intact. Through the sprouting of collateral branches, these connections were able to form new connections, resulting in a significant restoration of function,” says Fischer.
In various mouse models of spinal cord contusion of varying severity, the treatment showed consistent effects: animals treated with hIL-6 showed significantly improved walking ability after paralysis compared with untreated control groups. Particularly noteworthy was the restoration of coordinated gait patterns, which was not observed in the control groups.
The researchers also demonstrated that so-called serotonergic neurons, which originate in the brainstem, play a central role in the hIL-6-mediated restoration of function. When these cells were eliminated, the improvements achieved disappeared almost entirely.
“The treatment did not alter either the size of the injury or the extent of nerve cell loss. Rather, the functional improvements are due to new sprouting and a restructuring of existing neural networks,” said Fischer.
Although this new approach shows very promising results in mice with contusion injuries, the researchers emphasize that further steps and studies are necessary before it can be applied in humans. Questions that still need to be addressed include safety, optimal dosage, and potential side effects.
Key Questions Answered:
A: Think of it like a highway closure. Instead of rebuilding the collapsed bridge (the severed nerves), the hIL-6 protein encouraged the brain to build a series of “side streets” (collateral sprouts) using the existing roads that weren’t damaged. This creates a detour that carries the movement signals around the injury.
A: By injecting it into the motor cortex, the researchers turned the “source” of movement into a distribution hub. The nerve cells themselves transported the medicine deep into the brainstem and spinal cord, ensuring the treatment reached the exact circuits responsible for walking.
A: While the results in mice are “promising,” human application is several steps away. Researchers still need to verify the long-term safety of the viral vector, determine the correct dosage for a larger nervous system, and monitor for potential side effects before clinical trials can begin.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this spinal cord injury and genetics research news
Author: Eva Schissler
Source: University of Cologne
Contact: Eva Schissler – University of Cologne
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Transneuronal cytokine delivery promotes functional recovery across spinal cord contusion severities via descending circuit plasticity” by Marco Leibinger, Igor Moskaliov, Chinonso-John Ani, Dalia Halawani, and Dietmar Fischer. Neurobiology of Disease
DOI:10.1016/j.nbd.2026.107399
Abstract
Transneuronal cytokine delivery promotes functional recovery across spinal cord contusion severities via descending circuit plasticity
Spinal cord injury (SCI) frequently leads to permanent motor and sensory deficits, with complete injuries causing total loss of function below the lesion and incomplete injuries preserving only partial connectivity. Intracortical delivery of an AAV2 vector encoding the designer cytokine hyper-interleukin-6 (AAV2-hIL-6) enhances recovery after complete SCI by transneuronally stimulating raphe nuclei.
Here, we verified that AAV2-hIL-6 transneuronally activates subcortical neurons in the medulla and evaluated that this strategy enables recovery in clinically more relevant mouse models of mild, moderate, and severe contusion injury. Across all severities, AAV2-hIL-6 treatment significantly improved locomotor function compared to AAV2-GFP-treated controls.
Although lesion size and neuronal loss correlated with contusion severity and were unaffected by the AAV2-hIL-6 treatment, it robustly increased the number and length of descending serotonergic axons in the lumbar cord. Selective ablation of serotonergic neurons abolished these gains, confirming their essential role in functional sensorimotor recovery.
However, while AAV2-hIL-6 also reduced corticospinal tract (CST) axon retraction, it did not induce axon growth beyond the lesion, suggesting that CST regeneration was not required for recovery.
Thus, intracortical AAV2-hIL-6 delivery drives circuit remodeling and functional restoration across contusion severities, highlighting its promise as a regenerative therapy for SCI with spared pathways.
