Zebra fish and salamanders have the awe-inspiring ability to regrow body parts, the secrets of which have proved the envy of many a medical practitioner. The master of regrowth is the axolotl, an aquatic salamander which takes this ability further than the rest by being able to regenerate its jaw, spine and even parts of the brain without long lasting damage. 

However, this is largely due to the fact that the axolotl has a very unusual life history. Instead of progressing through the salamander stages from the aquatic gilled larval stage into an adult salamander, the axolotl remains in the larval stage for the whole of its life. Growth hormones can be injected into the axolotl to force it to reach an artificial ‘mature’ stage which looks like most other adult salamanders, but this almost never happens in the wild. This life history explains its amazing regenerative skills. Remaining in this ‘larval’ stage means it has more hormones kicking about from when it was developing from an embryo, meaning all the building blocks for growing body parts are still present.

Humans have a much more straightforward life history than the axolotl. Although some would argue certain people never mature mentally, we all must face biological aging. Although humans may not be able to regrow amputated limbs, a new study has found that we can regenerate the cartilage in our joints in a similar way to salamanders and zebra fish. MicroRNA molecules are responsible for this regrowth and are more active in ankle joints than knees and hips. Coupled with the fact that the regrowth mechanism works better in ‘younger’ cartilage (cartilage age decreases as you radiate out from the core of the body, so extremities like ankles are younger), this explains why arthritis is less common in the ankles than in the hips and knees, where regeneration is slower. 

The belief used to be that humans could not recover from cumulative damage in the joints, but this study has profound implications for those who suffer with joint issues. MicroRNA could be injected into troublesome joints or developed into medicines which could then combat arthritis. Further research into these regeneration processes in salamanders and humans could even lead to finding new ways in which we could aid the human body regrow entire limbs. 

Nature is full of weird and wonderful creatures and mechanisms which inspire medical advances, but it is also extremely complex, meaning that becoming a real life Deadpool is probably still many decades away. Still, it’s amazing to see what studying the frail-looking axolotl has done and will continue to do for humanity.

image source: https://www.the-scientist.com/news-opinion/adult-humans-can-regenerate-cartilage–study-66558