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

Enzymatic cleavage of amyloid-β protein precursor (AβPP) produces amyloid-β (Aβ) peptides which form the insoluble cortical plaques characteristic of Alzheimer's disease (AD). AβPP is post-transcriptionally processed into three major isoforms with differential cellular and tissue expression patterns. Changes in AβPP isoform expression may be indicative of disease pathogenesis in AD, but accurately measuring AβPP 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 AβPP and all three major isoforms (AβPP695, AβPP751, and AβPP770) 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 AβPP and AβPP695 transcripts were significantly decreased in SFG of patients with AD compared to control (p = 0.037 and p = 0.034, respectively). AβPP751 and AβPP770 transcripts numbers were not significantly different between AD and control (p > 0.15). There was trend for decreased percentage AβPP695 (p = 0.051) and increased percentage AβPP770 (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 AβPP and AβPP695 copy number was associated with increased plaque burden and decreased cognitive function. In this study we describe a simple procedure for measuring AβPP isoform transcripts by real-time PCR and confirm previous studies showing altered AβPP isoform expression patterns in AD.