July 4, 2011

Overlooked Peptide Reveals Clues To Causes Of Alzheimer’s Disease

Highly aggregative and neurotoxic amyloid peptide A-beta-43 points the way to new approaches for AD diagnosis and treatment

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's disease (AD). 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 AD-causing amyloidosis.

An irreversible, progressive brain disease affecting millions worldwide, Alzheimer's 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 AD remain elusive. Two features in the brain, abnormal clumps (senile plaques) and tangled bundles of fibers (neurofibrillary tangles), are known to characterize AD, 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 AD is caused by the buildup of the senile plaques, and in particular of their main constituent, amyloid-ÃŽ² peptides (AÃŽ²). Two major forms of AÃŽ², AÃŽ²40 and AÃŽ²42, have been associated with genetic mutations causing early-onset AD, and have thus received considerable research attention. The role of longer AÃŽ² species, in contrast, which also exist in the brains of Alzheimer's patients, has not yet been fully investigated.

In their current work, the researchers focused on AÃŽ²43, an amyloid-ÃŽ² peptide found just as often in patient brains as AÃŽ²42, but about which relatively little is known. To study the peptide's role in AD, they generated mice with a mutation causing overproduction of AÃŽ²43, and used a highly sensitive system to distinguish between concentrations of AÃŽ²40, AÃŽ²42 and AÃŽ²43.

Their surprising results reveal that AÃŽ²43 is even more abundant in the brains of AD patients than AÃŽ²40, and more neurotoxic than AÃŽ²42. AÃŽ²43 also exhibits the highest propensity to aggregate and considerably accelerates amyloid pathology. Moreover, unlike the other two AÃŽ² species, which exist in human and mouse brains at birth, AÃŽ²43 levels appear to increase with age, consistent with the pattern of AD onset.

Published in the journal Nature Neuroscience, the findings thus reveal the possible value of AÃŽ²43 as a biomarker for diagnosis of AD and suggest a potential role in new approaches for preventing AD-causing amyloidosis, promising hope to AD sufferers around the world.

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