Mammalian antiviral RNAi is on the move

Design of antiviral AGO2-dependent short hairpin RNAs

The increasing emergence and re-emergence of RNA virus outbreaks underlines the urgent need to develop effective antivirals. RNA interference (RNAi) is a sequence-specific gene silencing mechanism that is triggered by small interfering RNAs (siRNAs) or short hairpin RNAs (shRNAs), which exhibits significant promise for antiviral therapy. AGO2-dependent shRNA (agshRNA) generates a single-stranded guide RNA and presents significant advantages over traditional siRNA and shRNA. In this study, we applied a logistic regression algorithm to a previously published chemically siRNA efficacy dataset and built a machine learning-based model with high predictive power. Using this model, we designed siRNA sequences targeting diverse RNA viruses, including human enterovirus A71 (EV71), Zika virus (ZIKV), dengue virus 2 (DENV2), mouse hepatitis virus (MHV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and transformed them into agshRNAs. We validated the performance of our agshRNA design by evaluating antiviral efficacies of agshRNAs in cells infected with different viruses. Using the agshRNA targeting EV71 as an example, we showed that the anti-EV71 effect of agshRNA was more potent compared with the corresponding siRNA and shRNA. Moreover, the antiviral effect of agshRNA is dependent on AGO2-processed guide RNA, which can load into the RNA-induced silencing complex (RISC). We also confirmed the antiviral effect of agshRNA in vivo. Together, this work develops a novel antiviral strategy that combines machine learning-based algorithm with agshRNA design to custom design antiviral agshRNAs with high efficiency.

Current advances in antiviral RNA interference in mammals

Mammals have potent innate immune systems that work together to fight against a variety of distinct viruses. In addition to interferon (IFN) response, which has been intensively studied, antiviral RNA interference (RNAi) is gradually being studied. However, previous studies indicated low Dicer activity on double-stranded RNA (dsRNA) substrates in vitro and that IFN response masks or inhibits antiviral RNAi in mammals. Therefore, whether or not the RNAi is functional for antiviral response in mammalian somatic cells is still an ongoing area of research. In this review, we will present the current advances in antiviral RNAi in mammals and focus on three fundamental questions critical to the intense debate about whether RNAi can function as an innate antiviral immunity in mammals.