Roles Of MiR-155 In Inflammatory Response Caused By Influenza Infection In Human Pulmonary Microvascular Endothelial Cells

Influenza virus is one of the most important pathogens causing acute respiratory infection.Because of its wide,strong infectious and mutable characteristics,it has been a major threat to human health.According to the WHO statistics,seasonal influenza causes annual epidemics with approximately 500 000 deaths worldwide per year.Occasionally,influenza virus of novel strains or subtypes can cause global pandemics,result in a substantial number of deaths and significant economic loss,such as the 1918-1919 H1N1 world pandemic killed about 40 million people;the 2009 H1N1 pandemic resulting in 21% people infected.The fatal complication of influenza virus infection is Acute Respiratory Distress Syndrome(ARDS).Recent studies have found that the excessive immune response caused by influenza virus infection,named “cytokine storm” is the main cause of ARDS,but the specific mechanism remains to be further studied.Pulmonary microvascular endothelial barrier disruption is an important pathological feature of ARDS.Recently,it has been revealed that pulmonary endothelial cells are central orchestrators of cytokine production and leukocyte recruitment in mice inoculated with 2009 pandemic H1N1 virus.Influenza-infected mice that received an S1PR1 specific agonist had significantly decreased early cytokine end chemokine levels as well as reduced inflammatory cell infiltrates in the lung,resulting in a 60% improvement in survival.Studies of highly pathogenic avian influenza viruses,such as H5N1 and H7N9,have also emphasized the importance of endothelial cells in the production of inflammatory cytokines.Therefore,immunomodulation of lung endothelium may serve as a potential strategy for the treatment of severe influenza infection.Micro RNA(miRNA)is a non-coding small RNA of about 22 nucleotides.It regulates gene expression through a post-transcriptional way and plays a role in biological process.miR-155 is a typical multi-functionmiRNA,many studies have confirmed that miR-155 is a key component of immune system and play a pro-inflammatory role in the pathogenesis of many autoimmune diseases.But the role of miR-155 in viral inflammation is not clear.Previous studies showed that the expression level of miR-155 in lungs of mice increased after influenza infection.Based on former research,we want to investigate the role of miR-155 in inflammation response caused by influenza infection in human pulmonarymicrovascular endothelial cells.After many experiments,we get the following results: 1.A/Nanjing/NJU-108/2009 can successfully infect primary human pulmonary microvascular endothelial cells and replicate in them.2.We observed that miR-155 was elevated in influenza infected HPMEC cells.3.Overexpression of miR-155 in HPMEC cells enhanced the inflammatory response against influenza infection,while inhibition of miR-155 decrease the inflammation.4.We predicted the possible binding site in3’-UTR of S1PR1 m RNA by bio-informatics method.5.The dual luciferase reporter assay was peformed in HPMEC cells to find out whether S1PR1 was a target gene of miR-155.6.The m RNA levels were significantly increased,but the protein levels did not change significantly in influenza infected HPMEC cells,suggesting that there may be a post-transcriptional regulation.7.The expression of S1PR1 was regulated by miR-155 at protein levels.8.The inhibitory effect of miR-155 inhibitor on the inflammatory response of HPMEC infected with influenza virus was not obvious after knocking down S1PR1.In conclusion,this study found that miR-155 can regulate the inflammatory response against influenza infection in HPMEC cells by regulating the expression of S1PR1,suggesting that miR-155/S1PR1 pathwaymay be one of the pathogenesis of ARDS caused by influenza infection,and it will provide a new target for clinical treatment of severe influenza.