Familial Alzheimer's Disease Presenilin 1 Mutations Cause Alterations in the Conformation of Presenilin and Interactions with Amyloid Precursor Protein

Abstract

Presenilin 1 (PS1) is a critical component of the ␥-secretase complex, an enzymatic activity that cleaves amyloid ␤ (A␤) from the amyloid precursor protein (APP). More than 100 mutations spread throughout the PS1 molecule are linked to autosomal dominant familial Alzheimer's disease (FAD). All of these mutations lead to a similar phenotype: an increased ratio of A␤ 42 to A␤ 40, increased plaque deposition, and early age of onset. We use a recently developed microscopy approach, fluorescence lifetime imaging microscopy, to monitor the relative molecular distance between PS1 N and C termini in intact cells. We show that FAD-linked missense mutations located near the N and C termini, in the mid-region of PS1, and the exon 9 deletion mutation all change the spatial relationship between PS1 N and C termini in a similar way, increasing proximity of the two epitopes. This effect is opposite of that observed by treatment with A␤ 42 -lowering nonsteroidal anti-inflammatory drugs (NSAIDs) (Lleo et al., 2004b). Accordingly, treatment of M146L PS1-overexpressing neurons with high-dose NSAIDs somewhat offsets the conformational change associated with the mutation. Moreover, by monitoring the relative distance between a PS1 loop epitope and the APP C terminus, we demonstrate that the FAD PS1 mutations are also associated with a consistent change in the configuration of the PS1-APP complex. The nonpathogenic E318G PS1 polymorphism had no effect on PS1 N terminus-C terminus proximity or PS1-APP interactions. We propose that the conformational change we observed may therefore provide a shared molecular mechanism for FAD pathogenesis caused by a wide range of PS1 mutations.

Interrelationship between Changes in the Amyloid β 42/40 Ratio and Presenilin 1 Conformation

“…Neurons were fixed with 4% paraformaldehyde in phosphate-buffered saline (PBS), permeabilized with 0.1% Triton-X, and the nonspecific binding of antibodies was blocked by 1 h mutant PS1, favors γ-secretase cleavage site(s) on APP, producing longer Aβ species (13). Hence, we refer to this state as "closed," pathogenic PS1 conformation.…”

Presenilin Transmembrane Domain 8 Conserved AXXXAXXXG Motifs Are Required for the Activity of the γ-Secretase Complex

“…Additional mutants were generated: the PS1-AT (PS1 A409T), a FAD mutant (47), the corresponding engineered PS2-AT (PS2 A390T), and the inactive PS1-DA (PS1 D385A) and PS2-DA (PS2 D366A), where one catalytic Asp was substituted by Ala (16,60,61). Considering that PS1-dependent ␥-secretase is known as the major ␥-secretase complex responsible for A␤ production (62), we first analyzed the effects of those mutations on PS1 in CHO cells, a widely used cellular model for studying APP processing and ␥-secretase activity (34,60,63).…”

Familial Alzheimer Disease Presenilin-1 Mutations Alter the Active Site Conformation of γ-secretase

“…Furthermore, we have demonstrated that proteoliposomes containing PS1 mutants alone are sufficient to alter the specificity of ␥-secretase for the production of A␤40 and A␤42 (16). Fluorescence life-time imaging microscopy (19) and the substituted cysteine accessibility method (20) have been used to investigate the conformation of ␥-secretase and its catalytic core. However, both methods rely on the generation of artificial PS1 containing fluorescent epitopes or substituted cysteine residues.…”