Antisense oligonucleotides targeting microRNA binding sites in the GRN mRNA increase progranulin translation: potential therapeutic strategy for frontotemporal dementia

Abstract

Heterozygous GRN mutations cause frontotemporal dementia (FTD) due to haploinsufficiency of progranulin. The microRNA, miR-29b, negatively regulates progranulin protein levels. Antisense oligonucleotides (ASOs) are emerging as a promising therapeutic modality for neurological diseases, but strategies for increasing target protein levels are limited. Here, we tested if ASOs can increase progranulin levels by sterically blocking the miR-29b binding site in the 3' UTR of the human GRN mRNA. We found 16 ASOs that increase progranulin protein levels in a dose-dependent manner in neuroglioma cells. A subset of these ASOs also increased progranulin levels in iPSC-derived neurons and in a humanized GRN mouse model. While the ASOs did not increase GRN mRNA levels, polysome profiling experiments revealed that the ASOs increase progranulin translation. Consistent with this, ASO treatment increased levels of newly synthesized progranulin protein. In FRET-based assays, the ASOs effectively competed miR-29b from binding to the GRN 3' UTR RNA. Together, these studies establish the mechanism of action is that these ASOs displace miR-29b from its binding site and thereby de-repress translation, resulting in increased synthesis of progranulin protein. Our results demonstrate that ASOs can be used to effectively increase target protein levels by partially blocking miR binding sites; this ASO strategy may be therapeutically feasible for progranulin-deficient FTD as well as other conditions of haploinsufficiency.