Alternative splicing of exon 10 in the tau gene as a target for treatment of tauopathies

Abstract

Tau aggregation is one of the major features in Alzheimer's disease and in several other tauopathies, including frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17), and progressive supranuclear palsy (PSP). More than 35 mutations in the tau gene have been identified from FTDP-17 patients. A group of these mutations alters splicing of exon 10, resulting in an increase in exon 10 inclusion into tau mRNA. Abnormal splicing with inclusion of exon 10 into tau mRNA has also been observed in PSP and AD patients. These results indicate that abnormal splicing of exon 10, leading to the production of tau with exon 10, is probably one of the mechanisms by which tau accumulates and aggregates in tauopathic brains. Therefore, modulation of exon 10 splicing in the tau gene could potentially be targeted to prevent tauopathies. To identify small molecules or compounds that could potentially be developed into drugs to treat tauopathies, we established a cell-based high-throughput screening assay. In this review, we will discuss how realistic, specific biological molecules can be found to regulate exon 10 splicing in the tau gene for potential treatment of tauopathies.

Figure 1

The tau genomic structure and splicing products. The tau gene has 16 exons. Exons 4A, 6, and 8 are not expressed in the human brain. Exons 2, 3, and 10 are alternatively spliced, producing six different mRNAs. The mRNA with or without exon 10 encodes a tau protein with four repeats (4R) or three repeats (3R), respectively. Adapted from Lee et al. [28].

Figure 2

Validation of a cell-based luciferase system for measurement of exon 10 splicing in the tau gene (adapted from Yu et al. [91]). (A) The luciferase mini-gene construct. The firefly luciferase gene was fused downstream of exon 11 in frame with a SI9/LI10 mini-gene containing the M14 (G to T) mutation. A stop codon was introduced into exon 10 by mutagenizing position 73 in exon 10 (A to T). The nucleotide A of the initiation codon ATG in the luciferase gene was converted to T. (B) A control mini-gene with a fused Renilla luciferase to exon 11. (C) The firefly luciferase mini-gene (A) was co-transfected into SKN-MC cells with constructs of SRp40, SRp20, or SRp55. Relative firefly luciferase activities were normalized using the Renilla luciferase control (B). (D) RT-PCR from cells described in (C) was carried out to quantify exon 10 inclusion/exclusion.