APP mutations in the Aß coding region are associated with abundant cerebral deposition of Aß38.

ABSTRACT

Aß is the main component of amyloid deposits in Alzheimer disease (AD) and its aggregation into oligomers, protofibrils and fibrils is considered a seminal event in the pathogenesis of AD. Aß with C-terminus at residue 42 is the most abundant species in parenchymal deposits, whereas Aß with C-terminus at residue 40 predominates in the amyloid of the walls of large vessels. Aß peptides with other C-termini have not yet been thoroughly investigated. We analysed Aß38 in the brains of patients with Aß deposition linked to sporadic and familial AD, hereditary cerebral haemorrhage with amyloidosis, or Down syndrome. Immunohistochemistry, confocal microscopy, immunoelectron microscopy, immunoprecipitation and the electrophoresis separation of low molecular weight aggregates revealed that Aß38 accumulates consistently in the brains of patients carrying APP mutations in the Aß coding region, but was not detected in the patients with APP mutations outside the Aß domain, in the patients with presenilin mutations or in subjects with Down syndrome. In the patients with sporadic AD, Aß38 was absent in the senile plaques, but it was detected only in the vessel walls of a small subset of patients with severe cerebral amyloid angiopathy. Our results suggest that APP mutations in the Aß coding region favour Aß38 accumulation in the brain and that the molecular mechanisms of Aß deposition in these patients may be different from those active in patients with familial AD associated with other genetic defects and sporadic AD.