Healing properties (Image: Image: Baris Simse/Getty)

Young blood has once again shown its promise as an elixir of youth: blood from young mice helps bones of older animals heal.

Over the past few years, researchers have reversed muscle atrophy, memory loss, heart degradation and some of the effects of cognitive decline by pumping the blood of young mice into old mice. The results from these animal experiments were so intriguing that last year a team at Stanford University began the ultimate rejuvenation trial: giving blood plasma from under 30s to people with Alzheimer’s. Results are expected next year.

Now, Benjamin Alman, a professor of surgery at the Hospital for Sick Children in Toronto, Canada, and his colleagues have tested young blood’s ability to heal bones.


Two become one

The team surgically joined the circulatory systems of mice of various ages, in a procedure known as parabiosis. Fractured shin bones of old mice healed faster and better when the rodents were joined to young mice than to mice their own age.

In contrast, young mice that received blood from old mice had a slightly decreased ability to repair their fractured bones.

Older bones have higher levels of a protein called beta-catenin. This protein seems to makes bone marrow stem cells more likely to form cells that hold bone together than cells that make bone itself.

Beta-catenin levels were much lower in old mice that had received young blood, suggesting that a molecule present lowers beta-catenin and promotes healthier bone growth. “We’re honing in on that molecule,” says Alman.

What’s the secret?

However, it’s unlikely that any one molecule in youthful blood is responsible for all the rejuvenating effects seen so far. Pinpointing even one contender is proving difficult: work published this week called into question the rejuvenation power of the leading candidate, growth differentiation factor 11 (GDF11).

Over the past three years, a team at Harvard University, led by Amy Wagers, have had their eye on a GDF11, which they showed was more prevalent in young blood than old and seemed to have a restorative effect on mouse hearts and brains.

For example, when the protein was injected into middle-aged mice every day for a month, the volume of blood vessels in the brain and number of brain stem cells – both factors that improve brain function – significantly increased.

Muscle fibres in old mice injected with GDF11 also doubled in size to resemble that of 2-month-old mice.

But new work by a team at the Novartis Institutes for BioMedical Research in Cambridge, Massachusetts, contradicts Wagers’s results. They found that not only does GDF11 significantly inhibit muscle regeneration in mice, but levels of the protein slightly increase with age.

Hold the transfusion

Wagers says that there are lots of differences between the methods used in the Novartis work and her own. For example, Novartis used much higher concentrations of GDF11.

“We remain convinced that at least one form of GDF11 declines in blood with age and that maintaining GDF11 levels in an appropriate physiological range is essential for muscle health,” she says. “We look forward to addressing the differences in the studies with additional data very soon.”

As for the suggestion that young blood could help heal fractured bones – don’t go requesting a blood transfusion just yet. “I’m not sure if a blood transfusion would bring enough of the responsible cells,” says Alman.

“Our study suggests that as we age the cells in bone that heal don’t wear out, so they can be stimulated to still heal as if we were younger.” There are already drugs available that affect beta-catenin, says Alman, and these may be worth investigating as bone healing therapies.

Journal references: Nature Communications, DOI: 10.1038/ncomms8131 (Alman et al.); Cell Metabolism, DOI: 10.1016/j.cmet.2015.05.010 (Novartis)