Overlooked peptide reveals clues to causes of Alzheimer disease

Jul 07, 2011

Researchers at the RIKEN Brain Science Institute (BSI) and their collaborators have shed light on the function of a little-studied amyloid peptide in promoting Alzheimer disease. Their surprising findings reveal that the peptide is more abundant, more neurotoxic, and exhibits a higher propensity to aggregate than amyloidogenic agents studied in earlier research, suggesting a potential role in new approaches for preventing Alzheimer disease-causing amyloidosis.

An irreversible, progressive brain disease affecting millions worldwide, Alzheimer disease is devastating for its victims, robbing them of their memory and cognitive skills and ultimately of their lives. Even after decades of research, however, the causes of Alzheimer disease remain elusive. Two features in the brain, abnormal clumps (senile plaques) and tangled bundles of fibers (neurofibrillary tangles), are known to characterize Alzheimer disease, but there is little consensus on the link between these features and the underlying roots of the disease.

One hypothesis that has attracted widespread support proposes that Alzheimer disease is caused by the buildup of the senile plaques, and in particular of their main constituent, amyloid-ß peptides (Aß). Two major forms of Aß, Aß40 and Aß42, have been associated with genetic mutations causing early-onset Alzheimer disease, and have thus received considerable research attention. The role of longer Aß species, in contrast, which also exist in the brains of patients with Alzheimer disease, has not yet been fully investigated.

In their current work, the researchers focused on Aß43, an amyloid-ß peptide found just as often in patient brains as Aß42, but about which relatively little is known. To study the peptide's role in Alzheimer disease, they generated mice with a mutation causing overproduction of Aß43, and used a highly sensitive system to distinguish between concentrations of Aß40, Aß42 and Aß43.

Their surprising results reveal that Aß43 is even more abundant in the brains of patients with Alzheimer disease than Aß40, and more neurotoxic than Aß42. Aß43 also exhibits the highest propensity to aggregate and considerably accelerates amyloid pathology. Moreover, unlike the other two Aß species, which exist in human and mouse brains at birth, Aß43 levels appear to increase with age, consistent with the pattern of Alzheimer disease onset.

Published in the journal Nature Neuroscience, the findings thus reveal the possible value of Aß43 as a biomarker for diagnosis of AD and suggest a potential role in new approaches for preventing Alzheimer disease-causing amyloidosis, promising hope to Alzheimer disease sufferers around the world.

Source: News Release
July 3, 2011