Young Blood

Young Blood

A basketball team might look for "young blood" to pep up its starting lineup. Now, scientists are using young blood—literally—to revive aging muscles.


Making muscles think young. I'm Bob Hirshon and this is Science Update.

Old muscles heal faster when they're exposed to young blood. That's the conclusion of a recent experiment in mice, led by Stanford University neurologist Thomas Rando.

His team found that blood from younger mice stimulated stem cells in the muscles and livers of older mice. Those are the cells that generate new tissue.


The old stem cells, once they had been exposed to this young serum, behaved much more like young stem cells. They replaced the tissue better, they repaired the tissue better, and they proliferated more rapidly.

Conversely, he says old blood seems to inhibit the activity of the stem cells.

It's not clear what part of the young blood makes the difference, but Dr. Rando suspects it's a combination of factors. If scientists can solve the mystery, they may be able to develop new ways to help injuries and broken bones heal more quickly. I'm Bob Hirshon for AAAS, the Science Society.

Making Sense of the Research

You've probably heard the term "stem cell" in social studies class or on political advertisements. Politicians are currently debating the use of stem cells from human embryos in medical research. However, the body has many kinds of stem cells, including the ones studied in this experiment.

Muscle and liver are two tissues in the body that fix themselves pretty quickly after an injury. Stem cells are the supply centers for new tissue. They create new, healthy tissue to replace the dead or damaged material.

This doesn't work as well in older animals. It's easy to assume that the stem cells simply get older and weaker just like people do. However, Rando's team found that older muscle and liver tissue has the potential to repair itself just as well as young tissue—provided it's bathed in young blood.

The question is, what is it in the young blood that kicks healing back into high gear? Figuring that out will be a big challenge, because blood is a very complex substance. It's interesting that older blood actually makes younger animals heal more slowly; that suggests that the stem cells truly need something from the blood to work as well as they can.

The researchers also found a clue in something called delta-proteins. Delta-proteins serve as a kind of molecular switch that seems to enhance healing and tissue repair. Normally, delta-proteins switch on in young tissue, but not in older tissue. In Rando's experiment, however, the young blood made delta-proteins switch on in older animals. So it's possible that delta-proteins are like receivers that take their orders from the bloodstream.

What happens if scientists figure out how it all works? You might think that somewhere in young blood lies a Fountain of Youth, but Dr. Rando says that's unrealistic. First of all, while some tissues regenerate constantly, like blood and skin, and others repair themselves fairly quickly, like liver, muscle, and bone, many other tissues don't regenerate so well, even after an injury. The heart and the brain are two key examples. These organs probably would be fairly insensitive to any young-blood-based treatment.

Furthermore, the effect of the young blood lasts only as long as the tissue is bathed in it. So, for example, it wouldn't help a 70-year-old to a full blood transfusion from a 20-year-old – since his or her body would immediately start replacing the young blood with its own "old" blood. Dr. Rando says that if they do find the active chemicals in young blood that promote healing, it would have to be delivered directly to the tissue you wanted to fix, possibly several times a day. So, it's much more likely that this eventually could be used to help that 70-year-old's broken leg heal faster after a nasty fall.

Now try and answer these questions:

  1. How did the "young blood" benefit old muscles?
  2. What are stem cells? What role do they play in this research?
  3. Why wouldn't a single blood transfusion from a young person help an older person?
  4. Suppose the study found that young blood did NOT benefit old muscles, but that older blood did slow the healing of younger muscle tissue. What kinds of treatments and therapies might arise from this discovery?

For Educators

Tissues of Life, from the Science Museum of Minnesota, focuses on the tissues of the human body. Users can play tissue-related games; view tissue slides, scars, and more; read articles by healthcare professionals; and much more.

The two-part Science Netlinks lesson The Science of Aging, for advanced middle-school students, helps students understand factors that may affect aging.

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