ANTISENSE LONG NON-CODING RNA REPRESSES MAPT TRANSLATION THROUGH AN EMBEDDED MIR REPEAT

Abstract

Dysregulation of tau gene (MAPT) expression and splicing and tau protein aggregation directly cause neurodegenerative tauopathies. We investigated MAPT-AS1, an antisense long non-coding RNA (lncRNA) gene overlapping with the MAPT 5’-untranslated region. Antisense non-coding RNA genes can regulate transcription, epigenetic state, transcript stability or translation of their paired coding gene. Using RNA sequencing and qRT-PCR, we assessed expression of MAPT-AS1 and MAPT in brain and differentiating human induced pluripotent stem cells. In neuroblastoma cell lines, we either silenced or stably expressed MAPT-AS1 splice variants and targeted deletion mutants to identify the essential functional domains of MAPT-AS1 and characterized them by western blot, qRT-PCR, polysome profiling and luciferase reporter assays. Multiple splice variants of MAPT-AS1 specifically repress MAPT translation. This repression requires both the overlapping 5’ region of MAPT-AS1 complementary to the MAPT internal ribosome entry site (IRES) and a 3’ inverted mammalian-wide interspersed repeat (MIR) element. A truncated 94 nt MAPT-AS1 construct consisting of only the 5’ overlapping region and the MIR element, retained the capacity to repress MAPT translation. Furthermore, two 7-mer motifs within the MIR, complementary or identical to sequences within 18S ribosomal RNA, are essential for MAPT translational repression. Our data suggest that MAPT-AS1 lncRNA represses MAPT translation by interfering with ribosome recruitment to the MAPT mRNA. We identified 1,196 additional lncRNAs in the human transcriptome containing MIR elements (MIR-lncRNAs), forming sense-antisense pairs with 1,045 protein-coding genes and frequently overlapping with genes implicated in neurodegenerative diseases. These MIR-lncRNAs may establish an additional layer of translational regulation, with implications for proteostasis in neurodegeneration.