Scientists Identify Protein Required to Regrow Injured Nerves in Limbs
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Date posted: 22/06/2012
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 Augmenting Organics

A protein required to regrow injured peripheral nerves has been identified by researchers at Washington University School of Medicine in St. Louis.

The finding, in mice, has implications for improving recovery after nerve injury in the extremities. It also opens new avenues of investigation toward triggering nerve regeneration in the central nervous system, notorious for its inability to heal.

Peripheral nerves provide the sense of touch and drive the muscles that move arms and legs, hands and feet. Unlike nerves of the central nervous system, peripheral nerves can regenerate after they are cut or crushed. But the mechanisms behind the regeneration are not well understood.

In the new study, published online June 20 in Neuron, the scientists show that a protein called dual leucine zipper kinase (DLK) regulates signals that tell the nerve cell it has been injured -- often communicating over distances of several feet. The protein governs whether the neuron turns on its regeneration program.

"DLK is a key molecule linking an injury to the nerve's response to that injury, allowing the nerve to regenerate," says Aaron DiAntonio, MD, PhD, professor of developmental biology. "How does an injured nerve know that it is injured? How does it take that information and turn on a regenerative program and regrow connections? And why does only the peripheral nervous system respond this way, while the central nervous system does not? We think DLK is part of the answer."

The nerve cell body containing the nucleus or "brain" of a peripheral nerve resides in the spinal cord. During early development, these nerves send long, thin, branching wires, called axons, out to the tips of the fingers and toes. Once the axons reach their targets (a muscle, for example), they stop extending and remain mostly unchanged for the life of the organism. Unless they're damaged.

If an axon is severed somewhere between the cell body in the spinal cord and the muscle, the piece of axon that is no longer connected to the cell body begins to disintegrate. Earlier work showed that DLK helps regulate this axonal degeneration. And in worms and flies, DLK also is known to govern the formation of an axon's growth cone, the structure responsible for extending the tip of a growing axon whether after injury or during development.

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