[Molecular biology of beta A4 protein and Alzheimer disease]

Senile plaques, neurofibrillary tangles and neuronal loss are the major histopathologic hallmarks of Alzheimer's disease. A prominent component of the senile plaques is a polypeptide (beta A4) of about 40 amino acids derived via proteolytic cleavage from a set of larger protein isoforms collectively referred to as the amyloid precursor protein (APP). The protein APP is a widely distributed transmembrane glycoprotein structurally related to a cell surface receptor. APP is encoded by a single gene on chromosome 21 in which missense mutations have been demonstrated in several cases of familial Alzheimer's disease. It is thought that various factors fostering the APP-processing pathway by which the polypeptide beta A4 is generated might be pathogenic. Thus the mechanisms that govern the rate of transcription of the APP gene, the differential splicing of the precursor messenger and the proteolytic processing of APP are current subjects of intensive investigation. Theoretically, each of these events represents a potential target for a therapeutic intervention. However, the relationships between amyloidogenesis and the formation of the neurofibrillary tangles associated to the neuronal loss remain to be elucidated.