In the current study, Bu and colleagues found an aspect of cholesterol transport and metabolism in the brain was a link between early- and late-onset Alzheimer's disease. Both forms of the disease result in similar brain lesions and have the same symptoms, including difficulties communicating, learning, thinking and reasoning, which suggests they share underlying mechanisms. But until now, no one has been able to identify such a mechanism.
Early-onset Alzheimer's can be traced to mutations in one of three genes, and the gene coding for A-beta's precursor, APP, is one of these. People with mutations in APP nearly always develop Alzheimer's disease, usually at a relatively young age.
The genetic origins of late-onset Alzheimer's, which accounts for 95 percent of cases, have proven harder to pin down. However, studies have shown that people who have a particular mutation in the gene for a cholesterol carrier called apolipoprotein E are far more likely to develop Alzheimer's in old age than those who don't have the mutation.
Bu and colleagues demonstrated that APP and apolipoprotein E have a molecular connection. When APP is cleaved by a specific enzyme in the brain, it releases A-beta plus a small protein fragment. The fragment then can regulate apolipoprotein E, which moves cholesterol in the brain from support cells to neurons.
Past research by others implies that neural synapses, the junctions that nerves use to send impulses and communicate, are particularly sensitive to cholesterol levels and that interfering with cholesterol transport and metabolism could cause loss of synapses and degeneration of nerves.
|Contact: Gwen Ericson|
Washington University in St. Louis