Tau gene polymorphism influences risk of sporadic tauopathy by allele-specific changes in transcription and alternative splicing

Abstract

Tauopathies, including Alzheimer's disease (AD) and progressive supranuclear palsy (PSP), are a group of neurodegenerative diseases characterised neuropathologically by brain lesions comprising aggregates of the microtubule associated protein, tau. Common variation in the gene encoding tau (MAPT) affects the production of tau protein and its six isoforms and has been shown to modulate disease risk. To study the activity of three common MAPT promoter variants (H1b, H1c and H2) in vitro in order to ascertain whether the genetic differences in disease risk are conferred by differences in MAPT expression and alternative splicing. Combinations of the allelic variants of three regions of the MAPT promoter - the minimal core promoter and an upstream and a downstream putative enhancer domain - were cloned into luciferase reporter plasmids. Reporter gene expression was analysed in vitro in SH-SY5Y and BE(2)-M17 neuroblastoma cell cultures. We have now extended this to studies of co-transcriptional regulation of splicing using MAPT minigenes. The H1c promoter variant had a 4.2-fold increase in transcriptional activity over the H2 variant (p < 0.0001). When only the core promoter and the downstream putative enhancer domain were included, the H1c variant had 2.7-fold greater transcriptional activity than the H1b variant (p < 0.01) and 4.2-fold greater than the H2 variant (p < 0.01). We also observed coincident H1c allele-specific changes in alternative splicing of MAPT exon 10 in vivo with increased 4R-tau transcripts. The H1c MAPT variant, previously associated with increased risk of neurodegenerative disease, has higher transcriptional activity in vitro than the neutral (H1b) and protective (H2) variants and this appears to be driven by the putative downstream enhancer. This is coupled with H1c-specific elevation of mRNAs coding for the more fibrillogenic 4R-tau variants. We are currently conducting an independent replication of this study, and also an investigation of other conserved putative regulatory promoter regions in order to obtain a better picture of the allele-specific differences in MAPT expression and the effect of promoter strength on alternative splicing. The results of this further work will also be presented.