Researchers have designed a structure-specific microRNA inhibitor that selectively represses a microRNA family member, which may in turn reverse the diabetes phenotype.
microRNAs (miRNAs) play a critical role in a number of biological processes. They achieve this through post-transcriptional regulation of gene expression. More specifically, they pair with specific mRNA targets to repress their expression. Abnormal miRNA expression has been implicated in many human diseases, including cancer and type 2 diabetes.
Targeting miRNAs provides an opportunity to study their biological function and exploit them for the development of therapeutics. The most common approach involves designing complementary oligonucleotides that bind and inhibit a target miRNA.
However, miRNA family members often share sequence homology, rendering the oligonucleotide-based targeting of individual members difficult. On the other hand, the pri-miRNA and pre-miRNA precursors of individual members may adopt unique secondary structures. Leveraging the distinct secondary structures of miRNA precursors is thus a viable method to selectively target one member of a family.
Structure-specific microRNA inhibitor
In a recent study, published in Cell Chemical Biology, researchers at the Scripps Research Institute in Florida designed a structure-binding ligand that selectively inhibits miR-200c, a member of the miR-200 family. The miR-200 family is associated with type 2 diabetes (T2D), specifically inducing pancreatic β-cell apoptosis. However, the overlapping sequences within the family have previously made it difficult to dissect the role of each member in T2D.
The researchers observed significant differences in the structures of the precursors of each of the five miR-200 members. Their analysis revealed a region in the miR-200c precursor that is unique across the family. Specifically, the region is a Dicer processing site, where the Dicer endoribonuclease cleaves pre-miRNAs to generate functionally mature miRNAs.
Using Inforna, a database of experimentally derived interactions between RNA structural elements and small molecules, the researchers identified a ligand that binds strongly to the pre-miR-200 functional site. After optimisation, the small molecule TGP-200c inhibited Dicer processing, and thus impeded miR-200c biogenesis in a T2D cellular model. It resulted in a dose-dependent decrease in mature miR-200c levels and a corresponding increase in miR-200c target mRNAs. TGP-200c had no effect on other miR-200 family members even at high doses.
Reversal of type 2 diabetes phenotypes
TGP-200c also exerted specific global effects on the transcriptome, proteome and phenotype of the T2D cellular model. TGP-200c significantly affected expression levels of 23 mRNA transcripts and 13 proteins, some of which were direct miR-200c targets. In contrast, an oligonucleotide-based inhibitor targeting all miR-200 members affected 45 mRNAs and 29 proteins. Among them, only 5 mRNAs and no proteins overlapped with those affected by TGP-200c, demonstrating that TGP-200c is selective for miR-200c.
Furthermore, the TGP-200c-modulated proteins were involved in pathways related to T2D, including insulin signalling and metabolism. Consistent with the observed reduction of β-cell apoptosis, there was also an upregulation of negative regulators of cell death.
These observations suggest that by selectively inhibiting miR-200c biogenesis, TGP-200c can repress pro-cell death factors and promote β-cell survival. As such, TGP-200c is an attractive candidate for further preclinical development as a potential novel treatment against T2D. Targeting miRNA precursor structures with small molecules may also represent a new avenue to dissect the individual functions of miRNA family members and reveal their role in health and disease.
Image credit: kjpargeter – Freepik