Abstract

Hereditary cerebral haemorrhage with amyloidosis, Dutch type, is a cerebral amyloidosis characterized by prominent vascular deposits and fatal haemorrhages. The disorder is caused by a point mutation in codon 693 of the gene encoding the amyloid precursor protein, resulting in a Glu→Gln amino acid substitution at position 22 of the amyloid β-protein region. The pathogenetic mechanisms of HCHWA-D are unknown but could involve alterations in the proteolytic processing of APP and in amyloid fibril formation. We examined Aβ production and stability by using cultured human embryonic kidney 293 cells stably expressing wild-type or 'Dutch' APP. Radiosequencing and quantitative immunoprecipitation experiments showed that cells expressing Dutch APP secreted increased quantities of Aβ peptides beginning at Asp1, and of truncated peptides beginning at Val18 and Phe19. The ratio of levels of 4 kDa to 3 kDa peptides remained constant due to co-ordinate decreases in other peptide species. Novel truncated or elongated peptides were not observed. Pulse-chase experiments showed that the Dutch mutation did not affect the stability of the Aβ or p3 populations. These results are consistent with a disease process in which the Dutch mutation results in the production of Aβ peptides with enhanced propensities for fibrillogenesis, leading to accelerated vascular deposition and disease.