Stem cell therapy has long captured the limelight as a way to the goal of regenerative medicine, that of repairing the body with its own natural systems. But a few scientists, working in a relatively obscure field, believe another path to regenerative medicine may be as likely to succeed. The less illustrious approach is promising, in their view, because it is the solution that nature itself has developed for repairing damaged limbs or organs in a wide variety of animals.
Many species, notably amphibians and certain fish, can regenerate a wide variety of their body parts. The salamander can regenerate its limbs, its tail, its upper and lower jaws, the lens and the retina of its eye, and its intestine. The zebra fish will regrow fins, scales, spinal cord and part of its heart.
Mammals, too, can renew damaged parts of their body. All can regenerate the liver. Deer regrow their antlers, some at the rate of 2 centimeters a day, said to be the fastest rate of organ growth in animals. In many of these cases, regeneration begins when the mature cells at the site of a wound start to revert to an immature state. The clump of immature cells, known as a blastema, then regrows the missing part, perhaps by tapping into the embryogenesis program that first formed the animal.
There are reports that the tip of the finger can occasionally be regenerated, if the cut is above the last joint. And people can vigorously repair damage to the liver. Even after 75 percent has been removed in surgery, the liver regains its original mass in two to three weeks. It is not certain why other organs and limbs have lost this useful capacity, but perhaps only the liver was damaged often enough during its owner's lifetime to make a repair system worth the cost. "I believe that the reason is the extensive and recurring injury that the liver was exposed to in evolution: rotten food, plant toxins, viruses," says Markus Grompe, a liver expert at the Oregon Health and Science University.
Regeneration and stem cell therapy are promising aspects of regenerative medicine but both are still at the research stage. "I'm very bullish on regenerative medicine," said Dr. Keating, alluding to both types. "I think it's going to happen and it will be a revolution, but it will take time. It would be a mistake to oversell it and promise too much too early."
Stem cells aren't the only way we might regenerate lost limbs and organs. The body seems to have the capability to regrow much all by itself, it's just that the genes responsible for it are shut off. Future drugs might activate the genes again, thereby giving us back our regenerative capabilities.
Also see the Super Renegerative Mouse.