The blood of young people

Two teams of scientists published studies on Sunday showing that blood from young mice reverses aging in old mice, rejuvenating their muscles and brains. As ghoulish as the research may sound, experts said that it could lead to treatments for disorders like Alzheimer’s disease and heart disease.

“I am extremely excited,” said Rudolph Tanzi, a professor of neurology at Harvard Medical School, who was not involved in the research. “These findings could be a game changer.”

The research builds on centuries of speculation that the blood of young people contains substances that might rejuvenate older adults…

There was not enough known at the time about how the body rejuvenates itself.

It later became clear that stem cells are essential for keeping tissues vital. When tissues are damaged, stem cells move in and produce new cells to replace the dying ones. As people get older, their stem cells gradually falter.

In the early 2000s, scientists realized that stem cells were not dying off in aging tissues.

“There were plenty of stem cells there,” recalled Thomas A. Rando, a professor of neurology at Stanford University School of Medicine. “They just don’t get the right signals.”

Dr. Rando and his colleagues wondered what signals the old stem cells would receive if they were bathed in young blood. To find out, they revived Dr. McCay’s experiments.

The scientists joined old and young mice for a period of five weeks and then examined them. The muscles of the old mice healed about as quickly as those of the young mice, the scientists reported in 2005. In addition, the old mice grew new liver cells at a youthful rate.

The young mice, on the other hand, had effectively grown prematurely old. Their muscles healed more slowly, and their stem cells did not turn into new cells as quickly as before the procedure.

The experiment indicated that there were compounds in the blood of the young mice that could awaken old stem cells and rejuvenate aging tissue. Likewise, the blood of the old mice had compounds that dampened the resilience of the young mice.

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