Effects of the amyloid precursor protein Glu(693) -> Gln 'Dutch' mutation on the production and stability of amyloid beta-protein

Hereditary cerebral haemorrhage with amyloidosis, Dutch type (HCHWA-D), is a cerebral amyloidosis characterized by prominent vascular deposits and fat al haemorrhages. The disorder is caused by a point mutation in codon 693 of the gene encoding the amyloid precursor protein (APP), resulting in a Glu --> Gln amino acid substitution at position 22 of the amyloid beta-protein (A beta) region. The pathogenetic mechanisms of HCHWA-D are unknown but cou ld involve alterations in the proteolytic processing of APP and in amyloid fibril formation. We examined A beta production and stability by using cult ured human embryonic kidney 293 cells stably expressing wild-type or 'Dutch ' APP. Radiosequencing and quantitative immunoprecipitation experiments sho wed that cells expressing Dutch APP secreted increased quantities of A beta peptides beginning at Asp(1), and of truncated peptides beginning at Val(1 8) and Phe(19). The ratio of levels of 4 kDa (AP) to 3 kDa (p3) peptides re mained constant due to co-ordinate decreases in other peptide species. Nove l truncated or elongated peptides were not observed. Pulse-chase experiment s showed that the Dutch mutation did not affect the stability of the A beta or p3 populations. These results are consistent with a disease process in which the Dutch mutation results in the production of A beta peptides with enhanced propensities for fibrillogenesis, leading to accelerated vascular deposition and disease.