Scientists Say Humans May be Able to Grow Another Limb

If you lose a limb, scientists suspect, you may someday be able to make a full recovery. Not with prosthetics, but by simply growing a new one.

A team of researchers studying the axolotl, a species of aquatic salamander, has taken one step closer to uncovering the mystery of limb regeneration in the creature by investigating the differences in molecular signature linked to regeneration in mice and axolotl, according to a recent study published in the journal American Association for Anatomy. The study also reveals how a mouse regenerates.

And, if we learn the secrets to limb regeneration in the axolotl, and adapt it for mammals like mice, then we'll be tremendously close to offering people who've lost limbs another option besides prosthetics.

Humans may have 'untapped potential' to regenerate lost limbs

The crucial difference comes down to an immunological cell known as a macrophage, and with this knowledge, the potential for human applications is closer than ever. When mammals are injured, they typically generate a scar at the site of damage. Since the scar becomes a physical barrier to regeneration, Godwin's team focused on learning why the axolotl doesn't scar over like mammals. Like us. "Our research shows that humans have untapped potential for regeneration," said James Godwin, researcher and lead study author of Mount Desert Island (MDI) Biological Laboratory, in a Phys.org report.

"If we can solve the problem of scar formation, we may be able to unlock our latent regenerative potential. Axolotls don't scar, which is what allows regeneration to take place. But once a scar has formed, it's game over in terms of regeneration. If we could prevent scarring in humans, we could enhance [the] quality of life for so many people," added Godwin in the report. The axolotl is a Mexican salamander that's nearly extinct in the wild, but its unique regenerative capabilities have provided a special status in scientific circles. Most salamanders possess some regenerative abilities, but the axolotl can rebuild nearly any body part, including its heart, lungs, jaws, limbs, spinal cord, ovaries, tail, skin, and much more. It can even regenerate its brain. A brain!

Mammals in their embryo or juvenile stages can regenerate, too. For example, human children can regenerate fingertips, and infants can regenerate heart tissue, which means adults, too, might retain the crucial genetic code for regeneration. This opens the door to potentially developing pharmaceutical therapies enabling humans to "grow" tissues and organs lost to injury or disease, instead of simply forming a permanent scar.

Salamander macrophages are key to regenerative capabilities

In his recent research, Godwin compared macrophages (a type of immune cell) in the axolotl to the same cells in mice, with aims to find the quality the former possesses that promotes regenerative capabilities. Godwin found these cells to be key in salamander's regeneration: When levels of macrophages were low, the axolotl formed a scar instead of new body parts, just like mammals. "We are getting closer to understanding how axolotl macrophages are primed for regeneration, which will bring us closer to being able to pull the levers of regeneration in humans," said Godwin in the report. "For instance, I envision being able to use a topical hydrogel at the site of a wound that is laced with a modulator that changes the behavior of human macrophages to be more like those of the axolotl."

If studies into the axolotl's macrophages, and how we can encourage their human counterparts progress — and they absolutely will — we could see the dawn of a new era in medicine, where everything from disease-related amputation to workplace injuries become far less serious, and as complex as a drug prescription and physical therapy. Of course, the issue of affordability could see early implementations of this advancement priced out of most people's range. But the possibility alone of regenerating lost limbs is too compelling to ignore.