The research with rats proved to be surprisingly successful.
However, new stem cell research by Ashok K. Shetty and his team at the Texas A&M Health Science Center College of Medicine may have a silver lining — we may one day be able to replace brain cells and restore memory with neural stem cells.
The research, which appears in the journal Stem Cells Translational Medicine, took place over the course of three months in the hippocampi of both young and old animals — 344 rats were obtained for the study. The scientists implanted neural stem cells into the hippocampus, which is a brain region involved in making new memories and connecting them to emotions.
"We chose the hippocampus because it's so important in learning, memory and mood function," Shetty, who is a professor in the Department of Molecular and Cellular Medicine, said in a press release. "We're interested in understanding aging in the brain, especially in the hippocampus, which seems particularly vulnerable to age-related changes."
The volume of the hippocampus appears to decrease during the aging process, and this decrease might be related to the memory deficits that some older people experience.
In the study, the team found that the neural stem cells successfully engrafted onto the hippocampus in the young rats, which was expected, but the researchers were pleased to see that they also engrafted well in the older ones, which would be about 70 years old in human terms.
In fact, the implanted cells did more than simply survive — they divided several times to make new cells.
"They had at least three divisions after transplantation," Shetty said. "So the total yield of graft-derived neurons and glia (a type of brain cell that supports neurons) were much higher than the number of implanted cells, and we found that in both the young and aged hippocampus, without much difference between the two."
The research was conducted with donor cells from the sub-ventricular zone of the brain, dubbed the “brain marrow” due to its ability to hold neural cells that persist throughout life and continuously produce new neurons that travel to the olfactory system.
"What was really exciting is that in both old and young brains, a small percentage of the grafted cells retained their 'stemness' feature and continuously produced new neurons," said Bharathi Hattiangady, assistant professor at the Texas A&M College of Medicine and co-first author of the study.
He explains that this creates a new “niche” of neural stem cells, and they appear to be functioning well.
"They are still producing new neurons at least three months after implantation, and these neurons are capable of migrating to different parts of the brain,” Hattiangady said.
Although the success of the grafted cells is exciting, there’s still a lot of work to be done to conclude whether the extra grey matter actually improves cognition. As this work was done with animal models, we can’t yet say whether the stem cells would thrive in the same way in a human brain.
"Next, we want to test what impact, if any, the implanted cells have on behavior and determine if implanting neural stem cells can actually reverse age-related learning and memory deficits," Shetty said.