Development of RNA-based molecules for the inhibition of influenza A virus
University of Delaware
Avian influenza has always been a serious threat to the poultry industry and public health. Limitations in the effectiveness and possible adverse effects of vaccines and antiviral drugs demonstrate the need to develop new prophylactic and therapeutic approaches. RNA silencing, an evolutionarily conserved pathway in many eukaryotic cells, has been utilized as a powerful tool to reduce gene expression levels as an approach for potential therapeutic uses. Previous studies have shown that small interfering RNAs (siRNAs), synthetic 19-21nt double-stranded RNAs, can significantly inhibit influenza virus replication both in vitro and in vivo by targeting viral mRNAs for degradation. The studies herein focus on developing RNAi molecules and constructs as potential alternative methods to control avian influenza. With the restrictions of sequence complementarity for efficient siRNA targeting and yet the existence of high sequence variation within a dynamically changing influenza population, viral RNAi targets has to be selected within highly conserved regions of the influenza virus genome. However, not all the conserved regions were found to be optimal for siRNA design. To address these challenges, I first developed a system for the accurate and rapid quantitation of influenza infectious titer and for monitoring the antiviral activity of siRNAs. Influenza vRNA/cRNA promoter-controlled GFP/luciferase expression plasmids were developed and compared for their sensitivity and accuracy in determining influenza virus infectious titers. The vRNA-promoter driven luciferase expression reporter was selected for its high sensitivity and lower background. Secondly, siRNAs targeting highly conserved regions across different influenza A virus strains were designed and optimized with sequence, structural or size modifications. Several modifications were found to improve the selected siRNAs' antisense-strand targeting efficiency and antiviral activity. Furthermore, to extend the practical application of anti-influenza RNAi, an influenza infection-inducible microRNA expression cassette was developed and demonstrated to have strong inhibitory activity on influenza virus replication.