Scientists identify protein brake blocking nerve repair, opening path to new treatments

For decades, neuroscientists have watched the same frustrating pattern repeat itself: when an adult's nerve or spinal cord gets damaged, the body struggles to rebuild what was broken. The axons—those long, delicate extensions that carry signals between neurons—simply don't regrow the way they do in children or in simpler organisms. A person suffers a spinal cord injury, and the damage often becomes permanent. A peripheral nerve gets crushed, and sensation or movement may never fully return. The question that has haunted the field is not whether repair is possible, but why the adult nervous system seems so reluctant to attempt it.

Researchers at the Icahn School of Medicine at Mount Sinai have now identified a specific culprit: a protein called AHR that acts as a cellular brake, forcing injured neurons to prioritize survival over reconstruction. When a neuron sustains damage, it faces an immediate crisis. The cell must stabilize itself, manage the stress of injury, and maintain the quality of its proteins—a process called proteostasis. This survival mode is protective in the short term, but it comes at a cost. While the neuron is focused on staying alive, it cannot simultaneously marshal the resources needed to rebuild its damaged axons. AHR, the researchers found, is the mechanism that enforces this tradeoff, locking neurons into a survival-first posture that prevents regeneration.

Hongyan Zou, the senior author of the study, describes AHR's function with deliberate simplicity: it shifts neurons toward managing stress rather than rebuilding damaged connections. When the research team removed AHR from neurons in laboratory settings or used drugs to block its activity, something unexpected happened. The damaged axonal fibers began to regrow. In mouse models of both peripheral nerve damage and spinal cord injury, suppressing AHR led to measurable improvements in movement and sensation. The brake had been released, and the neurons responded by changing their priorities entirely.

The mechanism underlying this shift reveals a deeper logic to how neurons make decisions after injury. Without active AHR, neurons increase production of new proteins and activate biological pathways associated with growth and regeneration. A second protein, called HIF-1α, plays a supporting role in this process, helping to control genes involved in metabolism and tissue repair. Together, these changes push the injured neuron away from mere survival and toward active reconstruction. The discovery suggests that neurons possess the capacity for robust regeneration all along—they simply need permission to use it. AHR has been holding that permission hostage.

What makes this finding particularly striking is that AHR was originally identified for an entirely different job. Scientists first discovered the protein because of its ability to detect environmental toxins and pollutants, a function that seemed narrow and specialized. The Mount Sinai team's work reveals that AHR's role is far broader. Inside neurons, it serves as a bridge between the cell's perception of its environment and the fundamental decision of whether to repair itself. This dual function—environmental sensing and regeneration control—suggests that AHR may have evolved to help organisms make strategic choices about when to invest energy in repair versus when to simply endure.

The path from laboratory discovery to clinical treatment remains long and uncertain, but the researchers have identified a potentially accelerating factor. Several drugs designed to inhibit AHR are already in clinical trials for other conditions, meaning the basic safety and pharmacology of AHR inhibition have begun to be established. This creates the possibility that existing compounds could eventually be tested as treatments for nerve and spinal cord injuries, though such human trials remain years away. Before that can happen, researchers must answer a series of practical questions: How do AHR inhibitors perform across different types of neural injury? What is the optimal timing and dosage? How does suppressing AHR affect the other cells involved in the injury response—immune cells, supporting glial cells, and others that may be essential to recovery?

The Mount Sinai team is already planning the next phase of investigation. They intend to test both pharmaceutical approaches and gene-therapy strategies that reduce AHR activity specifically within neurons, hoping to determine whether these methods can enhance axon regeneration and improve recovery following spinal cord injury, stroke, or other neurological diseases. The work remains preliminary, and the gap between mouse models and human patients is substantial. But for the first time, researchers have a clear molecular target and a mechanism they can manipulate. The brake has been identified. The question now is whether releasing it can restore movement and sensation to people whose nervous systems have stopped trying to heal themselves.