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The alpha-secretase is an endogenous enzyme that is present in the nerve cells of the brain, where it is responsible for the cleavage of a specific protein. The result is a soluble protein fragment that promotes the growth of nerve cells and thus prevents the development of cerebral deterioration. However, if the enzyme beta-secretase is active, a chain reaction is initiated that subsequently results in the development of Alzheimer's disease and, in most cases, in the complete loss of memory capacity. "You could say that alpha-secretase is the good enzyme and that beta-secretase is the bad enzyme," Fahrenholz comments. "We now want to find out how to activate this 'good' enzyme or increase its concentrations in the brain as a way of combating this disease." With this in view, the collaborating partners have been investigating whether the positive effects of alpha-secretase are attributable to its enzymatic activity or whether the protective effect is due to other properties of the enzyme. Enzymes play an important role in the metabolism as they control, regulate, and catalyze numerous biochemical processes. "The alpha-secretase enzyme is a highly complex one, with many other functions. For example, it also relays signals from the intercellular space into cells and interacts with molecules on other cells." Following investigations in a transgenic mouse model, Fahrenholz and his colleagues have now established that it is the enzymatic activity alone that guarantees the protective effects. If this activity is neutralized, the laboratory mice exhibit the symptoms that are characteristic of Alzheimer's disease: impaired learning ability, poor memory capacity, and the build-up of plaques. It is thus possible that the enzymatic activity of alpha-secretase could represent the starting point for the development of future treatments. At the same time, the researchers were able to confirm with their experiments that it is not the plaque build-up itself that is responsible for the loss of memory capacity. The cytotoxic substances that accumulate in plaques only destroy neuron synapses when they are still in solution. Professor Fahrenholz concludes: "It is important to consider other aspects in addition to the plaques themselves, particularly their precursors, which are a real cause of the disease."
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