Measurement of altered AßPP isoform expression in frontal cortex of patients with Alzheimer's disease by absolute quantification real-time PCR.

ABSTRACT

Enzymatic cleavage of amyloid-ß protein precursor (AßPP) produces amyloid-ß (Aß) peptides which form the insoluble cortical plaques characteristic of Alzheimer's disease (AD). AßPP is post-transcriptionally processed into three major isoforms with differential cellular and tissue expression patterns. Changes in AßPP isoform expression may be indicative of disease pathogenesis in AD, but accurately measuring AßPP gene isoforms has been difficult to standardize, reproduce, and interpret. In light of this, we developed a set of isoform specific absolute quantification real time PCR standards that allow for quantification of transcript copy numbers for total AßPP and all three major isoforms (AßPP695, AßPP751, and AßPP770) in addition to glyceraldehyde-3-dehydrogenase (GAPDH) and examined expression patterns in superior frontal gyrus (SFG) and cerebellar samples from patients with (n = 12) and without AD (n = 10). Both total AßPP and AßPP695 transcripts were significantly decreased in SFG of patients with AD compared to control (p = 0.037 and p = 0.034, respectively). AßPP751 and AßPP770 transcripts numbers were not significantly different between AD and control (p > 0.15). There was trend for decreased percentage AßPP695 (p = 0.051) and increased percentage AßPP770 (p = 0.013) expression in SFG of patients with AD. GAPDH transcripts levels were also decreased significantly in the SFG of patients with AD compared to control (p = 0.005). Decreasing total AßPP and AßPP695 copy number was associated with increased plaque burden and decreased cognitive function. In this study we describe a simple procedure for measuring AßPP isoform transcripts by real-time PCR and confirm previous studies showing altered AßPP isoform expression patterns in AD.