The role of circRNAs on Amyloid-beta toxicity in C. elegans

Circular RNAs (circRNAs) are largely non-coding RNAs produced via back-splicing. We previously reported that hundreds of circRNAs accumulate during aging in C. elegans (Cortés-López et al. 2018). CircRNA expression is also associated with age-related diseases such as Alzheimer’s Disease (AD), suggesting that they may serve as therapeutic targets for AD. C. elegans, one of the most abundant circRNAs that accumulated during aging is circ-crh-1, which is a circRNA derived from the crh-1/CREB gene. Using a CRISPR-Cas9, we removed circ-crh-1 expression without disrupting the linearly-spliced crh-1 mRNA, and found that loss of circ-crh-1 extended the mean lifespan of C. elegans (Knupp et al. 2022). We hypothesized that loss of circ-crh-1 expression might alter the age-related onset of amyloid-b (Ab1-42) peptide in vivo and improve Ab-induced phenotypes. To test this hypothesis, we first analyzed where crh-1 circRNAs are expressed using published tissue-specific RNA-seq datasets (Kaletsky et al. 2018). We found that crh-1 circRNAs are widely expressed at different levels, i.e. intestine > neurons > muscle > hypodermis. Next, we used a well-characterized transgenic strain that expresses a full-length human Ab-peptide selectively in muscle cells (GMC101) or neurons of C. elegans (McColl et al. 2012; Fong et al. 2016). In this transgenic AD strains, Ab aggregate-mediated toxicity leads to an age-related onset of muscle paralysis and food-seeking behavior. We found that two independent circ-crh-1 mutations can significantly decrease Ab-induced muscle paralysis, suggesting that animals lacking circ-crh-1 improve Ab-induced paralysis phenotype. However, this was not the case in animals expressing Ab in all neurons. Using RT-PCR analysis, we did not observe significant differences in Ab mRNA levels between wild-type and circ-crh-1 mutants in aged Ab-muscle expressing animals, consistent with the idea that circ-crh-1 may promote the degradation of Ab-peptide. Future studies will determine whether and how loss of circ-crh-1 expression impacts Ab accumulation and content in muscles. Together, these results suggest that animals that lack circ-crh-1 expression delay the progression of Ab-induced paralysis and protect C. elegans against this age-related onset of Ab-mediated toxicity in muscles.