Mexican Walking Fish may hold key to helping paralysed people walk again

Sarah Knapton
The axolotl, or Mexican salamander can regenerate limbs, lungs, the brain and spinal cord if injured  - Karen Echeverri, University of Minnesota. 

An endangered salamander may hold the key to helping paralysed people walk again, scientists believe.

The axolotl, or Mexican salamander has the astonishing ability to regenerate limbs and even spinal cord if it has been injured.

But now a new study by the University of Minnesota in the US has discovered how the animals achieve the feat, and how humans may be able to replicate the same process.

When an axolotl suffers a spinal cord injury, nearby cells called glial cells begin proliferating rapidly, repositioning themselves to rebuild the connections between nerves and reconnect the injured spinal cord.

By contrast, when a human suffers a spinal cord injury, the glial cells form scar tissue, which blocks nerves from ever reconnecting with each other.

The US team discovered that a particular protein called c-Fos - which is carried by both salamanders and humans - is crucial for the regeneration process. However in humans the protein is prevented from working by another family of proteins known as Juns, which trigger scar tissue formation.

An earlier Northeastern University study showing axolotl limbs growing back 

Scientists are hopeful that if they can now create a drug to switch off the Jun proteins, allowing the glial cells to grow back the spinal cord.

"Humans have very limited capacity for regeneration, while other species like salamanders have the remarkable ability to functionally regenerate limbs, heart tissue and even the spinal cord after injury," said lead researcher Dr Karen Echeverri, assistant professor in the department of genetics, cell biology and development at the University of Minnesota.

"We have discovered that despite this difference in response to injury, these animals share many of the same genes with humans. This knowledge could be used to design new therapeutic targets for treating spinal cord injury or other neurodegenerative diseases."

The spinal cord is a bundle of nerves and other tissue which extends from the brain’s base at the top of the neck down the length of the back. If it is damaged or injured, messages from the brain are disrupted, leading to partial or total loss of feeling or movement in limbs or internal organs below the injury.

Humans cannot regenerate their spinal cord and will lose movement below an injury  Credit: Alamy 

There are around 40,000 people living with spinal cord damage in Britain, and every year 1,000 new people suffer a life changing injury. Many need constant care to live.

The axolotl, which is also known as the Mexican Walking Fish, is native to lakes near Mexico City, and grows to around nine inches in length. It can grow back lost limbs in just a few weeks, and some even grow extra limbs. It can even replace its lungs and parts its brain if it suffers a head injury and heals without any scarring.

In the new study researchers compared gene expression in humans and salamanders to try and pinpoint where they were differing.

“Our approach allows us to identify not just the mechanisms necessary to drive regeneration in salamanders but what is happening differently in humans in responses to injury,” added Miss Echeverri, who also believes the breakthrough could help other injuries.

“In addition to spinal cord regeneration, our work also focuses on other forms of regeneration including scar-free wound healing and limb regeneration.”

The new research was presented at the 2018 Experimental Biology Meeting in San Diego.