Comparison of the aggregation properties, secondary structure and apoptotic effects of wild‐type, Flemish and Dutch N‐terminally truncated amyloid β peptides

Abstract

The Dutch (E22Q) and Flemish (A21G) mutations in the betaAPP region of the amyloid precursor protein (APP) are associated with familial forms of Alzheimer dementia. However, patients with these mutations express substantially different clinical phenotypes. Therefore, secondary structure and cytotoxic effects of the three Abeta(12-42) variants [wild-type (WT), Dutch and Flemish] were tested. At a concentration of 5 microM the aggregation of these peptides followed the order: Abeta(1-42) WT > Abeta(12-42) WT > Abeta(12-42) Flemish > Abeta(12-42) Dutch. The stability of the secondary structure of these peptides upon decreasing the trifluoroethanol (TFE) concentration in the buffer was followed by circular dichroism measurements. WT peptides progressively lost their alpha-helical structure; this change occurred faster for both the Flemish and Dutch peptides, and at higher percentages of TFE in the buffer, and was accompanied by an increase in beta-sheet and random coil content. Apoptosis was induced in neuronal cells by the Abeta(12-42) WT and Flemish peptides at concentrations as low as 1-5 microM, as evidenced by propidium iodide (PI) staining, DNA laddering and caspase-3 activity measurements. Even when longer incubation times and higher peptide concentrations were applied the N-truncated Dutch peptide did not induce apoptosis. Apoptosis induced by the full length Abeta(1-42) peptide was weaker than that induced by its N-truncated variant. These data suggest that N-truncation enhanced the cytotoxic effects of Abeta WT and Flemish peptides, which may play a role in the accelerated progression of dementia.

Polymorphic Triple β-Sheet Structures Contribute to Amide Hydrogen/Deuterium (H/D) Exchange Protection in the Alzheimer Amyloid β42 Peptide

“…3) The N-terminal truncated A␤(12-42) E22Q aggregates less (44), which could relate to the absence of a triple ␤-sheet. These experimental observations and the triple ␤-sheet fibril model highlight recent findings of the N-terminal role in the formation of the tubular A␤ fibril (32,45).…”

Oligomeric and Fibrillar Species of Amyloid-β Peptides Differentially Affect Neuronal Viability

“…Familial AD mutations within the APP gene induce an increase in either the total amount of A␤-(1-42) (Swedish) (34) or the ratio of A␤(1-42)/A␤(1-40) (London) (35) by affecting the activity of ␤-and ␥-secretase. In contrast, the 19 -25 region of the A␤ peptide is critical to several properties of the peptide (36), including proteolysis by ␣-secretase (33,37), aggregation (38,39), and neurotoxicity (40). The Dutch and Arctic mutations are of particular interest for investigating the effect of the A␤-(1-42) oligomer-and fibril-forming conditions on structure and neuronal viability, because these mutations appear to change the aggregation of the peptide in the absence of an increase in either the total amount of A␤ or the ratio of A␤( 41,42).…”

Staining of Amyloid Beta (Abeta) Using (Immuno) Histochemical Techniques and Abeta42 Specific Peptides

“…It should be noted that none of the D-peptides showed any binding to A deposits in the brains of mice which express the APPswe/dutch/iowa mutation van Groen et al, 2009). This is to be expected since the structure of the A peptide with these mutations (i.e., the Dutch and Iowa mutations) is predicted to be different from the "normal" A peptide (Demeester et al, 2001;Kumar-Singh et al, 2002;Tsubuki et al, 2003;Watson et al, 1999). It should be noted that these mutations are in the A peptide sequence of APP, in contrast to the Swedish mutation (Selkoe, 2001).…”