Small nuclear RNA-mediated modulation of splicing reveals a therapeutic strategy for a TREM2 mutation and its post-transcriptional regulation.

Loss-of-function mutations in TREM2 cause Nasu-Hakola disease (NHD), a rare genetic disease characterized by early-onset dementia with leukoencephalopathy and bone cysts. An NHD-associated mutation, c.482 + 2 T > C, disrupts the splice donor site of intron 3 and causes aberrant skipping of exon 3, resulting in the loss of full-length TREM2 protein. Here, we examined the efficacy of artificial U1 and U7 small nuclear RNAs (snRNAs) designed to enhance exon 3 inclusion. Using mutant TREM2 minigenes, we found that some modified U1, but not U7, snRNAs enhanced exon 3 inclusion and restored TREM2 protein expression. Unexpectedly, we found that exon 3 of wild-type TREM2 is an alternative exon, whose skipping leads to reduced expression of the full-length protein. Indeed, TREM2 protein levels were modulated by modified snRNAs that either promoted or repressed exon 3 inclusion. The splice donor site flanking exon 3 was predicted to be weak, which may explain both the alternative splicing of exon 3 under normal conditions and complete exon skipping when the c.482 + 2 T > C mutation was present. Collectively, our snRNA-based approaches provide a potential therapeutic strategy for NHD-associated mis-splicing and novel insights into the post-transcriptional regulation of TREM2.