Summary: Why can’t the human spinal cord repair itself? Researchers have discovered a primary reason: a protein called the aryl hydrocarbon receptor (AHR). In a study, scientists revealed that AHR acts like a “biological brake” in neurons.
Following an injury, AHR forces the cell to focus entirely on surviving stress rather than regrowing damaged axons. By blocking this protein, the team was able to flip the switch from “survival mode” to “regeneration mode,” allowing nerve fibers to regrow and restoring movement in animal models.
Key Facts
- The Survival Trap: After an injury, neurons face a choice: protect their existing proteins (proteostasis) or build new ones to regrow. AHR pushes the cell toward protection, which inadvertently stops repair.
- Releasing the Brake: When researchers genetically removed or used drugs to block AHR, neurons began mass-producing the proteins needed for axon growth, significantly improving motor and sensory recovery.
- The Role of HIF-1α: The study found that once the AHR “brake” is released, a second factor called HIF-1α takes over, activating the metabolic genes necessary for rapid tissue repair.
- Environmental Sensor: Interestingly, AHR was originally known as a sensor for environmental toxins. This study proves it has a dual, “hidden” life as a master regulator of nerve regeneration.
- Clinical Potential: Because AHR-blocking drugs are already being tested for other diseases (like cancer), this discovery could be fast-tracked for human trials involving spinal cord injuries and stroke.
Source: Mount Sinai Hospital
Researchers from the Icahn School of Medicine at Mount Sinai have discovered a molecular switch in neurons that limits the regrowth of damaged axonal fibers.
The findings, published in the journal Nature, show that blocking a protein called the aryl hydrocarbon receptor (AHR) may help neural regeneration and restore function after injuries to the peripheral nerves or spinal cord.
Axons are the long fibers that carry signals between nerve cells, or neurons, in both central and peripheral nervous systems. Axons are essential for communication in the nervous system. When they are cut or damaged, recovery depends on the neuron’s ability to regrow these fibers.
But neurons in adult mammals have a limited ability to regrow their axonal connections so
injuries to the nerves or spinal cord often lead to long-lasting or permanent loss of movement or sensation. Scientists have long been trying to understand why this repair process is so restricted.
In the new study, investigators found that AHR acts as a key regulator that determines how neurons respond after injury.
“When neurons are injured, they must deal with stress while also trying to regrow their axons,” said Hongyan Zou, MD, PhD, Professor of Neurosurgery, and Neuroscience, at the Icahn School of Medicine at Mount Sinai and the study’s senior author. “We discovered that AHR functions like a brake that shifts neurons toward managing stress rather than rebuilding damaged connections.”
The research team showed that when AHR signaling is active, it slows down axon growth. But when the researchers removed AHR from neurons or blocked it with drugs, axonal fibers regrew more effectively. In mouse models of peripheral nerve injury and spinal cord injury, inhibiting AHR also improved recovery of motor and sensory function.
Further experiments revealed how this process works. After injury, AHR helps neurons protect themselves by maintaining protein quality control—a process known as proteostasis. While this protective response helps neurons cope with stress, it also reduces the production of new proteins needed for growth.
When AHR is turned off, neurons shift their strategy. They begin producing more new proteins and activate growth-related pathways that support axon regeneration. The researchers also found that this growth response depends on another factor called HIF-1α, which helps regulate genes involved in metabolism and tissue repair.
“This discovery shows that neurons use AHR to balance survival and regeneration,” Dr. Zou explained. “By releasing this brake, we can push neurons into a state that favors repair.”
AHR was originally identified as a sensor that detects environmental toxins and pollutants, termed xenobiotics. The new findings suggest that AHR also plays an unexpected role inside neurons by integrating environmental sensing and regenerative capability to regrow axons after injury.
The study is an early step toward possible treatments. Several drugs that block AHR are already being tested in clinical trials for other diseases, raising the possibility that they could eventually be studied for nerve or spinal cord injuries.
More research is needed before this approach can be used in patients. Future studies will examine how effective AHR inhibitors are in different types of neural damage, determine the best timing and dosage for treatment, and assess the impact on other cells after injury.
The Mount Sinai research team plans to test AHR-blocking drugs and gene-therapy strategies designed to reduce AHR activity in neurons. The goal of this next stage of research is to determine whether these approaches can further boost axon regrowth and improve recovery after spinal cord injury, stroke, or other neurological diseases.
Key Questions Answered:
A: It’s an evolutionary trade-off. After a traumatic injury, a neuron’s first priority is not dying. AHR ensures the cell stays stable by focusing on “quality control” (proteostasis). However, in adult mammals, this survival reflex is so strong that the cell never “remembers” to start rebuilding.
A: While it’s an early step, the implications are huge. Because AHR-inhibiting drugs are already in clinical trials for other conditions, we already know a lot about their safety. If these drugs can successfully “flip the switch” in humans as they did in mice, they could become a standard treatment alongside physical therapy for nerve damage.
A: Most research focuses on the environment around the nerve (like scar tissue). This study looks at the internal engine of the neuron itself. By changing the neuron’s internal strategy via AHR, we are essentially “reprogramming” the cell to want to grow again.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neurology research news
Author: Elizabeth Dowling
Source: Mount Sinai Hospital
Contact: Elizabeth Dowling – Mount Sinai Hospital
Image: The image is credited to Neuroscience News
Original Research: Open access.
“AhR inhibition promotes axon regeneration via a stress–growth switc” by Dalia Halawani, Yiqun Wang, Jiaxi Li, Daniel Halperin, Haofei Ni, Molly Estill, Aarthi Ramakrishnan, Li Shen, Arthur Sefiani, Cédric G. Geoffroy, Roland H. Friedel & Hongyan Zou. Nature
DOI:10.1038/s41586-026-10295-z
Abstract
AhR inhibition promotes axon regeneration via a stress–growth switc
Axon regeneration is limited in the mammalian central nervous system. Neurons must balance stress responses with regenerative demands after axonal injury, but the mechanisms remain unclear.
Here we identify aryl hydrocarbon receptor (AhR), a ligand-activated basic helix–loop–helix/PER-ARNT-SIM (bHLH-PAS) transcription factor, as a key regulator of this stress–growth switch. We show that ligand-mediated AhR signalling restrains axon growth, whereas neuronal deletion or pharmacological inhibition of AhR promotes axonal regeneration and functional recovery in both peripheral nerve and spinal cord injury models.
Mechanistic studies reveal that axotomy-induced AhR activation in dorsal root ganglion neurons enforces proteostasis and stress-response programs to preserve tissue integrity. By contrast, AhR ablation redirects the neuronal response towards elevated de novo translation and pro-growth signalling, enabling axon regeneration.
This growth-promoting effect requires HIF1α, with shared transcriptional targets enriched for metabolic and regenerative pathways. Single-cell and epigenomic analyses further revealed that the AhR regulon engages the integrated stress response and DNA hydroxymethylation to rewire neuronal injury-response programs.
Together, our findings establish AhR as a neuronal brake on axon regeneration, integrating environmental sensing, protein homeostasis and metabolic signalling to control the balance between stress adaptation and axonal repair.
