Background : Exacerbations of asthma are most frequently attributed to upper and lower airway infections by respiratory viruses such as rhinovirus and influenza viruses. Host cells protect against these virus via innate and acquired immune responses. MicroRNAs act as key regulatory molecules in complicated interaction networks between viruses and hosts. However, a few studies have been performed on miRNA related with influenza infection. The aim of this study is to search for candidate miRNAs by in silico analysis, and validate the relation of the miRNAs in sputum with exacerbation of asthma.
Methods and Materials: Information on sequences of mature human miRNAs was obtained using miRBase (http://www.mirbase.org) and applied to the whole genome sequence of influenza viruses A (http://www.ncbi.nlm.nih.gov/) by searching complementarity. Viral RNA and miRNA were extracted from sputum of exacerbated asthmatics using Viral Gene-spinΆβ kit (iNtRON Biotechnology, Seoul, Korea) and miRNeasy kits (Qiagen, CA, USA), respectively. RT-PCR and Real-time PCR were applied to the discovery of 7 respiratory viruses (adenovirus, human metapneumovirus, parainfluenza virus 1/2/3, influenza A/B virus, respiratory syncytial virus A/B and rhinovirus A) and the measurement of miRNAs, respectively.
Results: Total 2578 human miRNAs were used for analysis. Among them, miR-23b-3p was predicted to match with 7 nucleotides in one location +1915-+1921 of polymerase basic protein 2 mRNA and to three locations +244-+251, +1446-+1453 and +1470-+1477 of haemagglutinin mRNA of influenza A. Respiratory viruses were identified in 21 patients out of total 37 patients and 5 patients were infected by influenza A virus. The levels of miR-23-3p were much lower in patients infected with influenza A and rhinovirus (n=9) than those of other virus-infected (n=7) or uninfected patients (n=16). The levels of miR-23b-3p in influenza A-infected patients were comparable with those in rhinovirus-infected subjects.
Conclusions: Down regulation of miR-23b-3p expression may be associated with infection with influenza A virus and might exert a negative regulatory activity on the influenza A virus replication.