RNA interference mediates RNA toxicity with parent-of-origin effects inC. elegansexpressing CTG repeats

Abstract

Nucleotide repeat expansions are a hallmark of over 40 neurodegenerative diseases. These repeats cause RNA toxicity and trigger multisystemic symptoms that worsen with age. RNA toxicity can trigger, through an unclear mechanism, severe disease manifestation in infants that inherited repeats from their mothers. Here we show in Caenorhabditis elegans how RNA interference machinery causes intergenerational toxicity through inheritance of siRNAs derived from CUG repeats. The maternal repeat-derived small RNAs cause transcriptomic changes in the offspring, reduce motility and shorten lifespan. However, the toxicity phenotypes in the offspring can be rescued by perturbing the RNAi machinery in affected mothers. This points to a novel mechanism linking maternal bias and the RNAi machinery and suggests that toxic RNA is transmitted to offspring and causes disease phenotypes through intergenerational epigenetic inheritance.

Aurintricarboxylic Acid Decreases RNA Toxicity in a C. elegans Model of Repeat Expansions

“…Note that the highest dose of 2 mg/mL had a significant rescue effect on the 123CUG nematodes; however, it was attenuated and did not reach the fluorescence levels of their matched controls, or those treated with lower doses. As we previously showed, the repeat-derived siRNAs induce silencing of genes bearing complementary sequences through an RISC [6,7]. As ATA inhibits RNA binding to Argonaute and disrupts the assembly of the RISC, we anticipated a rescue of the gene silencing phenotype following its administration.…”

“…The RNAi pathway plays a key role in pathogenesis of repeat expansion disorders (Figure 1) [6][7][8]. Accordingly, to identify drug repurposing candidates for this group of disorders, we focused on targeting the RNAi machinery.…”

“…We utilized a C. elegans experimental system of expanded repeats. The C. elegans strains express green fluorescent proteins (GFP) bearing 0 or 123 repeats of CTG (0CUG and 123CUG, respectively) in the 3′ UTR, under the regulation of the myo-3 muscle-specific promotor [6,7,10]. Phenotypically, the toxicity induced by the expanded repeats manifests itself in motility impairment, expressed as slower crawling speeds in affected nematodes.…”

“…In our previous work, we revealed the key role of the RNA interference (RNAi) machinery in mediating RNA toxicity in a Caenorhabditis elegans DM1 model [6,7]. The long RNAs transcribed from the expanded repeats are targeted by Dicer and processed to shortinterfering RNAs (siRNAs).…”

“…The long RNAs transcribed from the expanded repeats are targeted by Dicer and processed to shortinterfering RNAs (siRNAs). These siRNAs bind to Argonaute enzymes, recruit an RNAinduced silencing complex (RISC), and induce silencing of genes bearing complementary sequences [6][7][8]. In the human genome, endogenous 6 CTG repeats occur in over 900 genes, marking them as potential targets for RNAi-mediated silencing.…”