The Amyloid Peptide and Its Precursor in Alzheimer's Disease

Alzheimer's disease, the most frequent cause of dementia, is characterized by the formation in the brain of neurofibrillary tangles and senile plaques. Neurofibrillary tangles are composed of bundles of paired helical filaments containing the microtubule-associated protein tau. In autopsy-derived brain samples from patients with Alzheimer's disease, tau is hyperphosphorylated and constitutes a promising disease marker. Senile plaques contain a small amyloid peptide derived from the amyloid precursor protein. Mutations of the amyloid precursor protein gene have been identified in rare cases of familial Alzheimer's disease, suggesting a causal role for amyloid peptide deposition in the disease. However, Alzheimer's disease has been demonstrated to be characterized by an important genetic heterogeneity. The identification of pathogenic DNA mutations, different from those of the amyloid precursor protein gene, will reveal whether the corresponding genes are involved in either an increased production of the amyloid peptide or a decrease of its removal, or in the fibrillogenic properties of the peptide, which seem to be related to its toxicity. Several mammalian cells are able to produce the amyloid peptide from its precursor. Understanding the cellular mechanisms that determine how cleavages occur in cells could help to identify new strategies for modulating amyloid peptide production. In attempts to produce animal models of Alzheimer's disease, investigators have used transgenic strategies. To date, these efforts have not been very successful. However, the expression in transgenic mice of both mutated amyloid peptide precursor and amyloid associated proteins should prove useful for examining the importance of putative etiological factors, and for testing novel therapies including anti-amyloidogenic strategies.