The Mechanism Of FGF2 In Acute Lung Injury Induced By Influenza A(H1N1) Virus Infection

Influenza A(H1N1) virus, a high-risk infectious pathogen, can cause severe acute lung injury leading to significant morbidity and mortality. Increased basic fibroblast growth factor(FGF2) has been observed in several models of tissue injury and inflammation. However, the role of FGF2 in influenza-induced acute lung injury is still not clear. FGF2 is a pleiotropic factor involved in many biological processes, including cel cell proliferation, angiogenesis, injury repair, embryonic development, an so on. In this study, we try to investigate the mechanism of FGF2 on influenza A(H1N1) virus-induced lung injury.We first test FGF2 levels of patient serum with influenza A(H1N1) virus infection and mouse bronchoalveolar lavage fluid(BALF). The results showed that FGF2 levels of patient and mouse with H1N1 infection were both increased. Both FGF2-deficienct mice and FGF2-blocking mice by using FGF2 neutralizing antibodies in vivo were more susceptible to influenza infection. In contrast, administration of murine recombinant FGF2 proteins protected mice against lethal H1N1 infection. The results demonstrated that FGF2 serves a protective role against influenza A(H1N1) virus infection in mice. We further found that FGF2 deficiency reduced leukocyte recruitment such as neutrophil and macrophage, accompanied by lower levels of cytokines in mouse bronchoalveolar lavage fluid(BALF) during the early phase of infection. FGF2 deficiency impared effective immune response against infection. In addition, FGF2 knockout boosted viral loads in mouse lung tissues. Contrastly, FGF2 proteins administration could decrease viral loads. Collecting above results, we speculate those non-increased leukocyte and cytokines induced by FGF2 deficiency most likely play an important protective function in the early stages of influenza infections in mice.In recent years, the effect of mi RNA on inflammatory response has become a hot research focus, while the mechanism by which mi RNA paticipates influenza A(H1N1) virus infection remains unclear. Whether mi RNA play an important role in virus infection needs to be confimed. We investigated the expression profile of mi RNA in A549 cells with BJ501 strain infection, and found that H1N1 infection induced mi RNA expression disorders. The significantly reduced mi RNA by H1N1 were predicted to target gene of FGF2, and then identified the effect of these mi RNA candidates on FGF2 expression in A549 cells. We found that mi R-194-5p, mi R-25-3p, mi R-92b-3p, mi R-361-5p, mi R-15b-5p, mi R-22-3p, mi R-17-5p, mi R-503-5p and mi R-16-5p could downregulate FGF2 expression. Further, we identified the interaction between mi RNA and FGF2 3’UTR, and found that mi R-194-5p 、mi R-361-5p、mi R-92b-3p、mi R-25a-3p、mi R-16-5p、mi R-15a-5p、mi R-15b-5p and mi R-503-5p inhibit FGF2 3’UTR reporter activity, while after replacement of corresponding binding sites, these mi RNA completely lose their ability to interact with FGF2 3’UTR. Moreover, we examined mi RNA expression in mice with BJ501 infection, then confirmed the effect of mi RNA on FGF2 expression. Finally, we figured out that antagonists of mi RNA exhibited protective role in lung injury in mice. Our mi RNA study provides a new strategy for influenza A(H1N1) influenza virus n induced acute lung injury therapy.Secreted FGF2 binds to high affinity receptor(FGFR), then promotes FGFR dimerization, and activates downstream signaling pathways. FGFR consists of four members: FGFR1-4, which belongs to tyrosine kinase receptor subfamily. Here, we investigated four members of the fibroblast growth factor receptor(FGFR) family; FGFR1 to 4, and examined their expression patterns in human lung epithelial cells A549 with influenza A virus infection. We identified a functional role of FGFR1 in influenza A/Puerto Rico/8/1934(PR8) and A/Anhui/01/2005(H5N1) virus replication. Our results showed that FGFR1 silencing by si RNA interference promoted influenza A/PR8 and H5N1 virus replication in A549 cells, while lentivirus-mediated exogenous FGFR1 expression significantly suppressed influenza A virus replication; however, FGFR4 did not have the same effects. Moreover, FGFR1 phosphorylation levels were downregulated in A549 cells by influenza A virus infection, while the repression of FGFR1 kinase using PD173074, a potent and selective FGFR1 inhibitor, could enhance virus replication. Furthermore, we found that FGFR1 inhibits influenza virus internalization, but not binding, during viral entry. These results suggested that FGFR1 specifically antagonizes influenza A virus replication, probably by blocking viral entry.