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Axolotl Salamander Could Hold the Key to Human Limb Regeneration

June 19, 2009 07:00 AM
by Denis Cummings
Scientists are studying a Mexican salamander to determine how it is able to regenerate body parts, hoping to develop a process to regrow human limbs.

Scientists Hope to Learn From Salamander Regeneration Process

A scientific team has received $6.25 million from the U.S. Department of Defense to study the axolotl, a Mexican salamander known for its ability to regenerate body parts, with the hope that the knowledge gained will help scientists one day induce the regeneration of a human limb.

Humans have the ability to regrow fingertips, reports Reuters, but lack the ability to regrow more complex body parts like the axolotl, which can regrow “limbs, jaws, skin, organs and parts of its brain and spinal chord.”
Tulane University cell and molecular biology professor Ken Muneoka, leader of the scientific team, told the New Orleans Times-Picayune that his team is attempting to map the genome of the axolotl and compare it to the genes of a mouse—which are similar to those of a human—to “deduce what is missing and what (genetic makeup) correlates with a non-regenerative response.”

The initial healing process after losing a limb is similar in both salamanders and humans, explained Muneoka, Manjong Han and David M. Gardiner in an April 2008 article in Scientific American. Fibroblasts at the scene of the wound produce an extracellular matrix; for humans and other mammals, “fibroblasts produce an excessive amount of matrix” that forms scar tissue. Salamander fibroblasts, on the other hand, stop “once the normal architecture has been restored.”

Salamanders then form a blastema, an “aggregation of stemlike cells” that will become a new limb. The cells in the blastema are similar to cells found in a salamander embryo, indicating that the regeneration process is “essentially a recapitulation of the limb formation that took place during the animal’s original development.”

Therefore, the key for scientists is to determine how to prevent the human body from forming scar tissue, and instead induce a blastema. Hope for human limb regeneration was raised last year when a 69-year-old man grew back half an inch of his finger using a extracellular matrix powder made from cells scraped from a pig’s bladder.

The powder was given to him by his brother, Dr. Stephen Badylak, who studies regeneration at the University of Pittsburgh. Badylak explained to the BBC, “We have taken out many of the stimuli for scar tissue formation and left those signals that were always there anyway for constructive remodeling.”

Muneoka, Han and Gardiner are optimistic about the prospect of human regeneration. “The surprising conclusion is that we may be only a decade or two away from a day when we can regenerate human body parts,” they wrote.

Background: Regeneration in animals

The ability to regenerate body parts is possessed by a small number of animals, mainly invertebrates. Sponges, hydra, planarian flatworms and starfish can regenerate entire bodies from just a small collections of cells, explains high school biology teacher and textbook author John Kimball.

Earthworms can regrow the back of their body if the organs to the front are unharmed, says the Internet Encyclopedia of Science. Crabs, lobsters and crayfish can regrow limbs, as can some insects.

Regeneration of limbs in vertebrate animals is far more rare. Lizards are known to grow back tails, though the new limbs are usually smaller than the original, according to the encyclopedia. Newts and salamanders can grow back legs, tails and even eyes, writes Kimball.

Humans and other mammals have not yet shown the ability to regenerate entire limbs, though humans can regrow fingertips and part of the liver. The University of California Irvine Regeneration Lab, headed by Drs. Gardiner and Susan V. Bryant, explains that mammals “do possess some regenerative abilities, and we should recognize that regeneration is a basic biological process exhibited in all animals. It is just that salamanders are exceptionally good at regeneration.”

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