Researchers have cracked part of the code for an important gene function in familial Alzheimer’s disease (FAD), an early-onset type of AD. Alzheimer’s disease is the most common cause of dementia. Working with cells in culture that had been altered to overexpress the amyloid precursor protein (APP), the researchers were able to document that expression of a mutant form of the presenilin-1 (PS-1) protein caused a significant reduction in the amount of amyloid formed. This continuing study of the mechanisms of plaque formation, researchers believe, moves them ever closer to the possible development of novel drugs to intervene in the processes leading up to Alzheimer’s dementia.
Naturally occurring mutations in PS-1 are found in about 40 percent of people with FAD. Previous studies have suggested that these inherited PS-1 gene mutations increase the amount of amyloid clipped out from the larger amyloid precursor protein, but no one could determine how that clipping occurred. Researchers named the elusive and not-well-understood enzyme that is involved in the clipping, gamma secretase. The current research suggests that either PS-1 may be the long sought gamma-secretase, or that PS-1 is essential for gamma secretase’s ability to clip amyloid.
The study of mutated PS-1 protein was published in the April 8, 1999 issue of Nature by Dr. Dennis J. Selkoe and his colleagues at Harvard Medical School and Brigham and Women’s Hospital, Boston, and the University of Tennessee, Memphis. Their work focuses on the chemical events that may lead to the development of brain damage and the symptoms of dementia. The National Institute on Aging (NIA), and the National Institute of Neurological Disorders and Stroke (NINDS), two components of the National Institutes of Health (NIH), funded the study.
In their search to explain why the amyloid fragments clump into plaques, which surround the brain cells of Alzheimer’s disease patients, Dr. Selkoe’s group gained an insight into the interaction of two key molecules involved in amyloid formation. When they altered the sequence of amino acids of the presenilin protein from the normal sequence in two critical locations, buried within the cell membrane, amyloid formation was reduced.
According to Dr. D. Stephen Snyder, who directs studies of the Etiology of Alzheimer’s Disease at NIA’s Neuroscience and Neuropsychology of Aging Program, “These studies have implications for the treatment of AD and related disorders of amyloid accumulation. If this gamma-secretase finding proves true, it could lead to significant advances in therapeutics research by showing us how to intervene before plaques form.”
Source: National Institute on Aging
Michael S. Wolfe, Weiming Xia, Beth L. Ostaszewski, Thekla S. Diehl, W. Taylor Kimberly, and Dennis J. Selkoe. Two transmembrane aspartates in presenilin-1 required for presenilin endoproteolysis and gamma-secretase activity. Nature, 398, (513-517).