Delivery and function of anti-viral miR-542-5p in vivo
MicroRNAs (miRNAs) have been identified as a key regulator in various biological processes and different diseases including cancer, heart disease, and viral infections. In the context of virus-host interactions, previous genome wide functional screen involving overexpression and inhibition of murine miRNAs in vitro identified several miRNAs that suppressed viral replication in diverse herpesviruses including herpes simplex virus 1 (HSV-1), murine cytomegalovirus (MCMV) and murine gamma herpesvirus 68 (MHV-68) (Santhakumar, D. et al, 2010). One of the top broad-spectrum anti-viral miRNAs, miR-542-5p, also suppressed human cytomegalovirus (HCMV) as well as a Semliki Forest virus (SFV) and two subtypes of influenza A virus (H1N1 & H3N2) in vitro. Following the previous study, this thesis focuses on generation of in vivo anti-viral efficacy data using miR-542-5p against two diverse viruses: MCMV and influenza (H1N1) in a pre-clinical model (mouse). One of the key challenges for generating in vivo efficacy data with miRNAs is the choice of delivery vehicle. To address this issue the first part of the project focused on optimising delivery conditions (dose, route of administration) for miR-542-5p mimic to target the lungs of mice (as both MCMV and H1N1 replicate in lungs). Initially, delivery was optimised using two cationic polymers: linear polyethylenimine (in vivo-JetPEI) and branched polyethylenimine (25KDa bPEI) that have been widely used previously to deliver nucleic acids in mouse. In parallel, two novel delivery systems were tested as an alternative delivery vehicle for miRNA mimics: biodegradable cationic lipids (Lifectin) and exosomes, natural vesicles produced by cells that can transport RNA. Results from in vivo delivery studies indicate that nebulisation of miR-542-5p mimic complexed with bPEI (25KDa) showed a more significant increase in the level of miRNA in the lung compared to other delivery systems and did not result in an immune response. Using bPEI as the delivery vehicle, the miR-542-5p mimic was administered to mouse lungs to test its anti-viral function against H1N1 and MCMV. Delivery of the miR-542-5p mimic resulted in 4.6 fold reduction of H1N1 virus titre in lungs (averaged across multiple experiments). The miR-542-5p mimic also had a 2 fold reduction in MCMV titre in the lungs. These data confirm the broad-spectrum anti-viral effect of miR-542-5p in mouse as observed in previous in vitro studies. Preliminary microarray analysis of genes regulated by miR-542-5p in vitro suggest this miRNA may target multiple genes required by diverse viruses during their life cycles and may modulate the PI3K-Akt signalling pathway.