Increased β‐amyloid release and levels of amyloid precursor protein (APP) in fibroblast cell lines from family members with the Swedish Alzheimer's disease APP670/671 mutation

Abstract

Cell lines transfected with the Swedish Alzheimer's disease amyloid precursor protein APP6701671 mutation release significantly more B-amyloid than wild-type cells. Citron et al. [Proc. Natl. Acad. Sci. USA (1994) in press] have recently shown that fibroblasts carrying the APP670/671 mutation also release more /3-amyloid than control cells [l]. The present study confirms a ca. threefold increase in /3-amyloid release from mutation-bearing fibroblasts. APP mRNA levels did not differ between mutation-bearing and control cells, although mutation-bearing fibroblasts contained significantly more APP751/770 than controls. Mild stress decreased B-amyloid secretion and increased APP751/770 levels in all cell lines. In conclusion, the proportion of APP committed to amyloidogenic processing is increased in fibroblasts from family members with the APP670/671 mutation, and this mutation may also compromise the APP stress response.Key words: Alzheimer's disease; Amyloid precursor protein; APP mRNA; &4myloid; Fibroblast; Foetal calf serum IntioductionAlzheimer's disease is a progressive neurodegenerative disorder defined histopathologically by the excessive accumulation of extracellular proteinaceous deposits (amyloid plaques) and intraneuronal bundles of paired helical filaments (neurofibrillary tangles) throughout the hippocampus and neocortex. A 39-43 amino acid peptide, termed /3-amyloid, has been identified as the major constituent of plaque and cerebrovascular amyloid [2]. This peptide is a metabolite of the amyloid precursor protein (APP), encoded by a gene on chromosome 21 [3]. The identification of pathogenic APP gene mutations in some Alzheimer's disease families has firmly established the importance of APP and /3-amyloid in the aetiology of this disorder [4,51. APP RNA is alternatively spliced in a tissue-specific manner, giving rise to at least ten different mRNA species. These include APP770 with domains showing homology to a Kunitz type protease inhibitor (KPI) and the MRC OX-2 antigen; APP751 which includes the KPI region only; and APP695 which lacks both the KPI and the MRC OX-2 domains [3,&8].Two alternative APP processing routes utilising the as yet We have identified a double mutation in the APP gene resulting in amino acid substitutions of Lys to Asn (codon 670) and Met to Leu (671) in a large Swedish family where Alzheimer's disease is inherited in an autosomal dominant manner [5,16]. Subsequently, it was shown that human kidney 293 and neuroblastoma Ml7 cell lines transfected with this mutation released approximately 7 times more /?-amyloid into culture medium than their wild type counterparts [17,18]. Recently, Citron et al. have shown that /?-amyloid release is increased in fibroblast cell lines from Swedish APP670/671 mutation carriers, co'mpared to control family members [I].In the present study, we quantified B-amyloid release from primary fibroblast cell lines established from heterozygous APP670/671 mutation carriers and control family members using a sensitive ELISA assay [13]. In addi...

Unusual phenotypic alteration of β amyloid precursor protein (βAPP) maturation by a new Val-715 → Met βAPP-770 mutation responsible for probable early-onset Alzheimer’s disease

“…16). Several reports consistently indicated that the Swedish mutation leads to the exacerbation of the production of total A␤ (16)(17)(18)(19)(20)(21)(22)(23), by increasing both A␤40 and, to a lesser extent, A␤42 (24). This is accompanied by a decreased production of APP␣ (21) and corresponding Nterminally truncated A␤s (25).…”

Relative Increase in Alzheimer's Disease of Soluble Forms of Cerebral Aβ Amyloid Protein Precursor Containing the Kunitz Protease Inhibitory Domain

“…However, findings to date have been contradictory with data reporting a selective reduction in APP 695 (8, 29 -31), an increase in APP 695 (65,70), an increase in the ratio of APP 770 / APP 695 (25,27,34,35) or APP 751 /APP 695 (32,36,38), and no change in the relative message levels of different isoforms (57,58,(75)(76)(77)(78)(79)(80). Message levels for APP 751 and APP 770 are also reported to be increased in fibroblasts carrying the FAD Swedish APP 670/671 mutation and in normal fibroblasts in response to stress (81). While a consensus on APP transcripts levels in AD patients has yet to be reached, studies using animal models have convincingly demonstrated that a selective induction of mRNA for KPI ϩ isoforms occurs in response to acute neuronal insults.…”

Small heat-shock proteins: important players in regulating cellular proteostasis

“…Amyloid plaques are composed primarily of A peptides which are derived from the abnormal processing of -amyloid precursor protein by -secretase. In patients with familial AD, overproduction of A leads to early onset AD [182][183][184][185]. The level of Bc expression in brains of patients suffering AD is markedly increased compared to that in the normal human brain [105,186] presumably due to the cellular stress caused by disease.…”