Amyloid precursor protein mRNA levels in Alzheimer's disease brain

Abstract

Insoluble β-amyloid deposits in Alzheimer's disease (AD) brain are proteolytically derived from the membrane bound amyloid precursor protein (APP). The APP gene is differentially spliced to produce isoforms that can be classified into those containing a Kunitz-type serine protease inhibitor domain (K +, APP 751, APP 770, APRP 365 and APRP 563), and those without (K −, APP 695 and APP 714,). Given the hypothesis that Aβ is a result of aberrant catabolism of APP, differential expression of mRNA isoforms containing protease inhibitors might play an active role in the pathology of AD. We took 513 cerebral cortex samples from 90 AD and 81 control brains and quantified the mRNA isoforms of APP with TaqMan™ real-time RT-PCR. After adjustment for age at death, brain pH and gender we found a change in the ratio of KPI+ to KPI− mRNA isoforms of APP. Three separate probes, designed to recognise only KPI+ mRNA species, gave increases of between 28% and 50% in AD brains relative to controls ( p=0.002). There was no change in the mRNA levels of KPI-(APP 695) ( p=0.898). Therefore, whilst KPI-mRNA levels remained stable the KPI+species increased specifically in the AD brains.