Production of Amyloid β Protein from Normal Amyloid β‐Protein Precursor (βAPP) and the Mutated βAPPS Linked to Familial Alzheimer's Diseasea

Abstract

The approximately 4 kD (39-43 amino acid) polypeptide (amyloid beta protein, A beta) deposited as amyloid in Alzheimer's disease (AD) is derived from a set of 695-770 residue precursor proteins collectively referred to as the amyloid beta-protein precursor (beta APP). Using immunoblotting techniques, metabolic labeling, and sequencing we have analyzed beta APP derivatives in medium conditioned by: (1) human mononuclear leukemic (K562) cells expressing a model beta AP-bearing carboxyl-terminal beta APP derivative (2) human neuroblastoma (M17) cells transfected with constructs expressing full length beta APP and (3) M17 cells expressing only endogenous beta APP. In each case, we observed the release of a approximately 4 kD beta APP derivative essentially identical to the A beta found in AD amyloid. A similar, if not identical, beta APP fragment was readily detected in CSF from both Alzheimer's disease patients and controls. These observations indicate that the A beta is produced and released by normal processing of the beta APP. To determine if the production of A beta or A beta-tearing COOH-terminal beta APP derivatives is altered in cells expressing the mutant beta APPs linked to familial AD, we have compared M17 cells expressing wild type beta APP with those expressing mutant beta APPs (beta APP delta I or beta APP delta NL). After continuous metabolic labeling for 8 hours, cells expressing the beta APP delta NL mutant showed a 5-fold increase in the relative amount of an approximately 11.4 kD A beta-bearing carboxyl-terminal beta APP derivative, and they released 6-fold more 4 kD A beta into the medium. These observations provide strong evidence that: (1) the pathway producing A beta in cultured cells is highly relevant to AD and (2) the beta APP delta NL mutant causes AD because its processing is altered in a way that releases increased amounts of A beta.

An Etiological Role of Amyloidogenic Carboxyl‐Terminal Fragments of the β‐Amyloid Precursor Protein in Alzheimer's Disease

“…It has been clearly shown that transfection of human neuroblastoma with a /IAPP cDNA bearing the KM-NL double mutation leads to overproduction of A/I and A/I-bearing CT products (Citron et al, 1992;Cai et al, 1993;Golde et al, 1993;Felsenstein et al, 1994). However, lizuka et al (1991) reported that the KM-NL double mutation promoted the production of intracellular A/I and its release with no increase in level of CT fragment.…”

“…They suggested that amyloidogenic CT fragments can be produced by secretory cleavage of /IAPP, which is antegradely transported through axons in human brain. Recent work has shown that there is rapid processing of /IAPP in the optic nerve to generate a I 4-kDa terminal membrane-associated fragment that contains the A/I sequence (Amaratunga and Fine, 1995).CT 100 amyloidogenic fragments were produced by transgenic mice and rats with full-length human /IAPP containing native and genetic mutations linked to FAD and hereditary cerebral hemorrhage with amyloidosis of the Dutch type (Howland et al, 1995).It has been clearly shown that transfection of human neuroblastoma with a /IAPP cDNA bearing the KM-NL double mutation leads to overproduction of A/I and A/I-bearing CT products (Citron et al, 1992;Cai et al, 1993;Golde et al, 1993;Felsenstein et al, 1994). However, lizuka et al (1991) reported that the KM-NL double mutation promoted the production of intracellular A/I and its release with no increase in level of CT fragment.…”

Luteinizing Hormone, a Reproductive Regulator That Modulates the Processing of Amyloid-β Precursor Protein and Amyloid-β Deposition

“…Because FSH receptors are primarily located in reproductive tissues, and others and we have not detected FSH receptors in neuronal cell types, we focused our efforts on biochemical changes modulated by LH. To test whether LH impacts A␤ generation we used the M17 neuroblastoma cell line (widely used for studying A␤PP processing (1,3,45,46)) to examine whether LH altered A␤PP expression and/or processing. Immunoblot analysis using polyclonal (Fig.…”

In situ atomic force microscopy study of Alzheimer’s β-amyloid peptide on different substrates: New insights into mechanism of β-sheet formation

“…A␤ is found in body fluids in a soluble form (16), which is partially ␣-helical (12,17). In Alzheimer's disease, A␤ undergoes conformational change and deposits in the extracellular space of the brain and in walls of cerebral blood vessels as amyloid plaques (1).…”