For centuries humans have anecdotally espoused the rejuvenating properties of young blood, however it is only in the past few years that scientists have begun to seriously explore the idea. Although previous experiments have revealed transfusing blood from young mice into older mice does seem to confer cognitive benefits it has never been clear what specifically could be causing these results. A new study has homed in on a potential hypothesis revealing young bone marrow transplants improved memory and learning in old mice.
Recent research has revealed that surgically connecting the circulatory systems of an older mouse with a young mouse results in incredible rejuvenation of the older animal while accelerating markers of aging in the younger animal. Similar effects have also been demonstrated by simply transfusing young mouse blood into an older animal, however these results have never been clinically validated or replicated in humans.
"While prior studies have shown that introducing blood from young mice can reverse cognitive decline in old mice, it is not well understood how this happens," says Helen Goodridge, co-senior author of the new study. "Our research suggests one answer lies in specific properties of youthful blood cells."
The experiments focused on bone marrow transplants. Bone marrow is the body's source of hematopoietic stem cells, the cells that give rise to all other kinds of blood cells. The hypothesis was that young hematopoietic cells may be what is behind the cognitive improvements seen in earlier young-to-old mouse experiments.
To test this, a group of 18-month old mice were administered bone marrow transplants from either mice their own age or four-month old mice. After six months all the animals were subjected to a barrage of cognitive tests and the results were undeniably compelling. The old mice with the young bone marrow performed better in most tests than older mice given old bone marrow.
Examining the brains of the animals the researchers discovered the young bone marrow transplants seemed to preserve a greater volume of synaptic connections in the hippocampus compared to the mice treated with old bone marrow. Alongside this, it was also discovered that the young bone marrow reduced the number of active microglia in the animal's brain. Overactive microglia are thought to play a role in neuronal degeneration so suppressing the activity of these brain immune cells could hypothetically play a role in maintaining long-term cognitive health.
This research appears at an interesting moment, literally a few days after the FDA released a statement slamming a burgeoning medical startup industry in the United States selling young blood transfusions to older consumers. Ambrosia, one of the key players in this new business, swiftly ceased operations following the FDA statement.
While this new study may seem to bolster the idea that young blood can confer anti-aging properties when transfused into older subjects, it also highlights a very specific form of transplant that may be effective. Ambrosia, for example, was previously trading in plasma transfusions only. Plasma is a single component of blood, left over after all blood cells have been removed. If the hypothesis generated by this new research is true, then a transfusion of young plasma would be ineffective in conferring any cognitive benefits.
"Our work indicates that cognitive decline in mice can be significantly reduced by simply providing young blood cells, which act on the brain to reduce the loss of synapses related to aging," explains Clive Svendsen, co-senior author on the new study.
A great deal more work is obviously needed before this research will deliver a clinical outcome, and the researchers suggest instead of literally taking young bone marrow from human subjects and administering it to older patients, the most realistic potential treatment would involve using modern stem cell technology to create youthful "personalized" blood cells.
Earlier this week a landmark study revealed a potential new method that uses CRISPR gene editing to create cheap and unlimited supplies of "universal" stem cells. This impressive technique could hypothetically be harnessed to produce pluripotent stem cells and used to prevent age-related cognitive decline.
The new research was published in the journal Communications Biology.
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