Could young blood revive memory in the aging brain?
The decline of these abilities is linked with many neurological disorders.
In this study, the scientists injected old mice with blood plasma - the fluid that carries blood cells - taken from human umbilical cords. There is also a startup called Ambrosia looking to see if transfusions of blood from young to older people can improve cognition. Moreover, as the biological and behavioral characteristics of mice closely resemble those of humans, the discovery increases the likelihood that younger plasma would benefit older people's cognitive ability.
Dr Pickett added: "As we age, cells in the brain's memory centre - the hippocampus - become less able to form strong connections with one another". This indicated enhanced activity in the mice's hippocampi, the memory and learning center of the brain.
The mice learned faster and their brains changed, producing more brain cells, Wyss-Coray and colleagues reported. Our capacity to learn and remember falters in lockstep with that physiological deterioration.
In this study, the team injected the plasma - the liquid that remains when blood cells are removed - into older mice whose immune systems were weakened so that their natural defenses would not attack the proteins.
The problem is, they didn't label the proteins in cord blood to see if TIMP2 was the key protein, according to Conboy.
In the meantime, a clinical trial created to test whether young human plasma can slow the cognitive decline of people with Alzheimer's disease is under way. Instead, they tested them in a maze to determine how long it took the mice to find their way to a dark and confined space they consider secure, Castellano said. (This activation did not happen in the hippocampi of young mice treated with cord blood.) After the injections, the aging animals also navigated a maze more quickly and performed better on other tests of learning and memory, Wyss-Coray's team reports today in Nature.
Although umbilical cord blood plasma seems to have the most TIMP2, studying it is logistically hard. The mice aged between 12 and 14 months old that is equivalent to being in the late 50s and 60s.
But researchers know little about how TIMP2 acts on the brain, Castellano said.
Researchers selected only subjects with a weak immunity as otherwise, the introduction of foreign plasma cells into the mice's body would have triggered an immune response and made the tests hard. It even restored these mice's nesting capacity: an instinctive penchant, largely lost in old age, for using available materials, such as cotton wads supplied by the researchers, to build nests in which mice typically prefer to sleep.
There are already several trials underway to inject elderly humans with plasma from the very young.
The researchers, however, voiced caution because most therapeutic approaches to disease that work in mice or other lab animals do not succeed in humans. "Because it has broad effects, we may actually have a more powerful factor". With injections of just that protein, the senior rodents again improved on memory and learning tests (though not quite to the extent that mice given whole plasma did). Electrophysiology of hippocampal slices from the infused mice revealed stronger long-term potentiation (LTP), a sign of improved neural plasticity, only in mice that had received cord plasma.
"Together our results argue that systemic factors present early in life may be beneficial for revitalization of aged tissue and that TIMP2, a protein enriched during development, represents such a restorative factor for the aged hippocampus", the authors conclude.