Release of excess amyloid beta protein from a mutant amyloid beta protein precursor.

The 4-kilodalton amyloid beta protein (A beta), which forms fibrillar deposits in Alzheimer's disease (AD), is derived from a large protein referred to as the amyloid beta protein precursor (beta APP). Human neuroblastoma (M17) cells transfected with constructs expressing wild-type beta APP or a mutant, beta APP delta NL, recently linked to familial AD were compared. After continuous metabolic labeling for 8 hours, cells expressing beta APP delta NL had five times more of an A beta-bearing, carboxyl terminal, beta APP derivative than cells expressing wild-type beta APP and they released six times more A beta into the medium. Thus this mutant beta APP may cause AD because its processing is altered in a way that releases increased amounts of A beta.