April 15, 2004

Gene technique targets memory loss

By Elizabeth Crown

Northwestern researchers have prevented learning and memory deficits in a model of Alzheimer’s disease using a gene-targeting approach to block production of beta-amyloid, or “senile,” plaques, one of the hallmarks of the disease.

Alzheimer’s disease is a neurodegenerative condition affecting over 15 million people worldwide that causes memory loss and, ultimately, dementia. Some research suggests that Alzheimer’s disease is caused by an increased amyloid burden in the brain — the so-called amyloid cascade hypothesis.

Results of the Northwestern study, published in the journal Neuron, provide compelling evidence for the therapeutic potential of inhibiting an enzyme, beta-secretase (BACE1), required for the production of beta-amyloid, to treat memory impairment in patients with Alzheimer’s disease.

The study also presents new evidence that beta-amyloid is directly responsible for causing the memory-robbing effects of Alzheimer’s disease, said Masuo Ohno, research assistant professor of physiology, Feinberg School of Medicine.

Ohno’s co-researchers on the project were John F. Disterhoft, professor of physiology, and Robert Vassar, associate professor of cell and molecular biology.

Ohno and colleagues used behavioral, biochemical and electrophysiologic methods to analyze BACE1 in mice bred to lack the enzyme but to also overproduce amyloid precursor protein, which BACE1 “clips” into fragments of beta-amyloid that eventually form the notorious plaques associated with Alzheimer’s disease.

The mice were healthy and had no serious neurological abnormalities, suggesting that BACE1 inhibition is a rational strategy for treating Alzheimer’s disease, Ohno said.

Importantly, the beneficial effects of BACE1 inhibition in the mice were seen well before beta-amyloid plaques formed, indicating that the soluble forms of the protein can disrupt learning and memory in early stages of the disease process.

“Potential compounds that block BACE1 should be useful in counteracting the Alzheimer’s disease process. We clearly show for the first time that genetic reduction of brain beta-amyloid levels prevents memory deficits and brain cell functional abnormalities in a laboratory model of Alzheimer’s disease,” Ohno said.