ONE of the reasons why biologists set so much store by research into stem cells is that they hope to use them to repair damaged tissue. In part, that is because mammalian (and therefore human) tissues are bad at repairing themselves. That is in contrast to, say, the tissues of amphibians. As is well known, these animals can regenerate entire amputated limbs.
One mammal, however, can perform amphibian-like regeneration tricks. This is a laboratory-bred strain of mouse known as MRL. In 1998 Ellen Heber-Katz, a researcher at the Wistar Institute in Philadelphia, showed that these mice, instead of creating scar tissue in response to injury, effected seamless repairs to damaged organs (in this case ears with holes punched in them). Now, Dr Heber-Katz and her mice are back. A paper in this week's Proceedings of the National Academy of Sciences describes her work. And this time, the self-repairing organ in question is one more critical to survival—the heart.
To inflict non-lethal heart damage on their mice, Dr Heber-Katz and her colleagues opened each animal up and applied a cold instrument to the organ. This injured the muscle of the right ventricle, one of the chambers that pumps blood.
The team then waited several weeks to see whether the damaged muscle would recover in either the MRL mice or the ordinary mice that underwent the same treatment, and thus served as controls. To some extent, it did so in both—but about ten times as many new muscle cells formed in the right ventricles of the MRL mice as in those of the controls. Also, there was little or no scarring in the hearts of the MRL mice, and within two months or so their heart function had returned to normal.
Laboratory mice are one thing; ailing people are quite another. To make practical use of this discovery it will be necessary to find out how the mice do it, and then devise drugs that will stimulate a similar process in people.
To this end, Dr Heber-Katz and her colleagues have traced the regenerative capacity of the MRL animals to a number of genes on five different mouse chromosomes. Using this knowledge, they believe they are poised to make further discoveries on the molecular level which could point to new therapies.
That would have implications for many medical conditions. Tissue death and scarring are features shared by a lot of diseases. Stimulating self-repair would thus have wide application. And not a single stem cell need be sacrificed along the way.