Using well-established mouse models of Alzheimer's disease, the investigators examined how changing levels of the enzyme Fyn affects key aspects of the disease, including accumulation of large clumps of amyloid proteins in the brain (so-called plaques) and changes in the complex neuronal networks in which memories are formed and stored. Genetic engineering strategies were used to increase or decrease the expression of Fyn, which regulates many other proteins through the attachment of specific groups of atoms known as phosphate groups.
The researchers determined that changing levels of Fyn had no effect on plaque formation or aberrant sprouting (the abnormal growth of nerve terminals, in which neuchemical messages are stored), indicating that these pathologies involve discrete molecular mechanisms. However, they observed that blocking Fyn expression prevented amyloid proteins from damaging synapses, the specialized connections between brain cells, and improved the longevity of mice. (Experimental mice with Alzheimer's-like disease otherwise die prematurely.) In contrast, increasing Fyn in the brain worsened synaptic damage, and also increased the number of premature deaths in the mice.
Loss of synapses and abnormal outgrowth of nerve terminals occur both in people with Alzheimer's disease and in transgenic mice producing human amyloid proteins in the brain (the model used in the study). Humans with the disease, like mice, die prematurely.
"Synaptic degeneration in Alzheimer's disease is like electrical circuits in a computer becoming faulty -- signals can no longer be transmitted through broken connections," says senior author and GIND director Lennart Mucke, MD, who
Contact: John Watson
University of California - San Francisco