WASHINGTON - Neural stem cells can rescue memory in mice with advanced Alzheimer’s disease, opening the way to treating dementia that afflicts 5.3 million people in the US.

Mice genetically engineered to have Alzheimer’s performed markedly better on memory tests a month after mouse neural stem cells were injected into their brains. The stem cells secreted a protein that created more neural connections, improving cognitive function.

“Essentially, the cells were producing fertilizer for the brain,” said Frank LaFerla, director of the University of California Irvine (UCI) and co-author of the study.

Co-author Mathew Blurton-Jones, LaFerla and colleagues worked with older mice predisposed to develop brain lesions called plaques and tangles that are the hallmarks of Alzheimer’s.

The researchers found that the stem cells secreted a protein called brain-derived neurotrophic factor, or BDNF.

“If you look at Alzheimer’s, it’s not the plaques and tangles that correlate best with dementia; it’s the loss of synapses - connections between neurons,” Blurton-Jones said.

“The neural stem cells were helping the brain form new synapses and nursing the injured neurons (nerve cells) back to health.”

Diseased mice injected directly with BDNF also improved cognitively but not as much as with the neural stem cells, which provided a more long-term and consistent supply of the protein.

“This gives us a lot of hope that stem cells or a product from them, such as BDNF, will be a useful treatment for Alzheimer’s,” LaFerla said.

The study appeared online in the Proceedings of the National Academy of Sciences.