A procedure called parabiosis was used in both studies, where the circulatory systems of two mice (one young and one old) are physically stitched together, allowing the blood flow between the young mouse and old mouse to commingle.
The first study, published in Nature Medicine, found that a number of genes important for brain health “turned on” in old mice infused with young blood, leading to neurogenesis, increased synaptic connections, and better cognitive performance. In particular, neurogenesis occurred in the hippocampus, a brain region important for memory and learning.
The second study, published in Science, found increased neural stem cell production along with new blood vessels surrounding the brain in old mice infused young blood.
So what is it about young blood that causes these healthy, rejuvenating changes in aging brains? Frankly, scientists don’t have a clear answer to that yet. There is some tantalizing evidence that a number of proteins in abundance in young mice provide the boost – growth differentiation factor 11 (GDF-11) is one of the proteins called out in these recent studies.
Human trials are probably still a few years away (without the need to surgically combine circulatory systems!) Longer term, it’s possible that the blood proteins responsible for boosting cognitive health can be manufactured for widespread use in older adults – the potential benefits for quality of life and healthcare savings would be substantial.