For the first time, a mammalian organ has been persuaded to renew itself
REGENERATIVE medicine—the idea that it is possible to renew old, worn-out tissue and thus keep a body going beyond the point when its organs start to fail—is an attractive idea. To that end, much effort has been put into creating and nurturing so-called pluripotent stem cells. These, when appropriately nudged, can be induced to turn into cells of any other type. They might thus be used for all sorts of repairs. Pluripotent cells, which once had to be extracted from embryos, can now be made routinely from body cells (skin cells, for example). Experiments are therefore going on to see if, when made from the cells of a particular individual, they might be used to repair damage to that person’s organs without (as a transplant from someone else would) attracting the attention of his immune system.
This approach is promising. It would be even better, though, if rather than having stem cells transplanted into it, a degenerate organ could be persuaded to repair itself. Until now, no one has managed to do this. But Clare Blackburn of Edinburgh University, in Britain, and her colleagues have succeeded. As they report in Development, they have treated, in mice, an organ called the thymus, which is a part of the immune system that runs down in old age. Instead of adding stem cells they have stimulated their animals’ thymuses to make more of a protein called FOXN1. This is a transcription factor (a molecular switch that activates genes), and for the thymus it turns out to be an elixir of life.
The thymus is the place where the immune system’s T-cells mature. T-cells have various jobs, such as destroying body cells infected with viruses. As an animal grows older, its thymus shrinks and the organ’s internal structure changes. As a result, the supply of new T-cells diminishes. That is why elderly people are more subject than the young to infection.
Dr Blackburn knew from earlier experiments that FOXN1 is important for the embryonic development of the thymus, so she wondered if it might be used to rejuvenate the organ in older animals. To this end, she and her colleagues bred a special strain of mice whose FOXN1 production could be stimulated specifically in the thymus by tamoxifen, a drug more familiar as a treatment for breast cancer.
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