An Increased Percentage of Long Amyloid β Protein Secreted by Familial Amyloid β Protein Precursor (βApp ₇₁₇ ) Mutants

Abstract

Normal processing of the amyloid beta protein precursor (beta APP) results in secretion of a soluble 4-kilodalton protein essentially identical to the amyloid beta protein (A beta) that forms insoluble fibrillar deposits in Alzheimer's disease. Human neuroblastoma (M17) cells transfected with constructs expressing wild-type beta APP or the beta APP717 mutants linked to familial Alzheimer's disease were compared by (i) isolation of metabolically labeled 4-kilodalton A beta from conditioned medium, digestion with cyanogen bromide, and analysis of the carboxyl-terminal peptides released, or (ii) analysis of the A beta in conditioned medium with sandwich enzyme-linked immunosorbent assays that discriminate A beta 1-40 from the longer A beta 1-42. Both methods demonstrated that the 4-kilodalton A beta released from wild-type beta APP is primarily but not exclusively A beta 1-40. The beta APP717 mutations, which are located three residues carboxyl to A beta 43, consistently caused a 1.5- to 1.9-fold increase in the percentage of longer A beta generated. Long A beta (for example, A beta 1-42) forms insoluble amyloid fibrils more rapidly than A beta 1-40. Thus, the beta APP717 mutants may cause Alzheimer's disease because they secrete increased amounts of long A beta, thereby fostering amyloid deposition.

Observation of amyloid precursor protein cleavage and Aβ generation in living cells by using multiphoton laser scanning microscopy

“…For example, the Swedish double mutation (K670N/M671L) is immediately adjacent to the -secretase site and enhances the release of A [2] . There are three mutations at the APP residue 717 (APP717 mutations including V717I, V717F and V717G) near the -secretase site and all of them increase the production of the more amyloidgenic 42-aa form of A [A (1-42)] [3][4][5][6] . The biochemical mechanisms and cellular compartments involved in the A generation and deposition have not been fully elucidated.…”

“…Alzheimer's disease (AD) is a neurological degenerative disease and one of its characteristic pathological changes is senile plaque, the main component of which is Amyloid beta (A ) protein [1][2][3][4][5][6] . However, the biochemical mechanisms and the cellular compartments involved in A production have not been fully elucidated yet.…”

Nicotine Inhibits Amyloid Formation by the β-Peptide

“…On the basis of results from CD and NMR, we first proposed (Barrow & Zagorski, 1991) that the -peptide may normally exist in human biological fluids in a soluble form and that the longer 42-residue peptide results from an abnormal proteolysis. Subsequently, both of our propositions were shown to be correct using both in vivo and in vitro studies (Seubert et al, 1992;Shoji et al, 1992;Busciglio et al, 1993;Suzuki et al, 1994). There are currently no effective treatments for AD, and the current drug development process is often cumbersome, taking an average 8.8 years for approval (Cutler & Sramek, 1995).…”

All-D-Enantiomers of β-Amyloid Exhibit Similar Biological Properties to All-L-β-Amyloids

“…Evidence in support of a causative role for A␤ in neuropathology comes from genetic analysis of the APP gene where several autosomal dominant mutations have been linked with AD and hereditary cerebral hemorrhage with the Dutch type (2,3). In a recent in vitro study, the ␤-APP 717 mutation consistently caused a significant increase in the percentage of the longer and more amyloidogenic A␤ over the shorter A␤ (4). Incorporation of this same mutation into a transgenic mouse model yields A␤ deposition and neuropathology that closely parallels that observed in AD (5).…”