Yellow fever virus infection alters mitochondrial network dynamics and trigger IFN-I response via TLR2 pathway

It has been emphasized that mitochondria play a fundamental role not only in cellular bioenergetics but also in the defense against infections. Here, we investigated mitochondrial network dynamics (MND) and IFN-Iβ signaling response in epithelial A549 cells after yellow fever virus (YFV) infection. We analyze the MND when only some cells are infected at 1 day post-infection (dpi) and after the spread of viral infection, at 3 dpi. Confocal microscopy and MiNA analysis showed that YFV infection leads to a decrease in the number of branches at 3 dpi and an increase in the length of branches at 1 and 3 dpi, suggesting that mitochondrial fission and fusion occur. Consistent with both processes, we found increased transcription of mitofusin 1 and Drp1 and increased colocalization of mitochondria with Drp1 at 3 dpi. In addition, mitochondrial membrane polarization decreased, mtROS production increased, p62 expression decreased, and LC3 expression increased, suggesting an increase in mitophagy flux. We found decreased expression of the IFN inducers RIG-I and MAVS sensors in YFV-infected A549 cells a t 3 dpi. Surprisingly, increased IFN-Iβ levels were observed at transcriptional and protein levels along with IRF7 induction at 1 and 3 dpi. Using the blocking antibody against TLR2, we showed that IFN-Iβ and IL-6 synthesis is maintained by TLR2 signaling. Mechanistically, infection led to activation of the NFκB pathway by degradation of IkBα, and increased phosphorylation of P65 and ERK MAPK signaling. Our results show that YFV infection induces altered MND in epithelial cells and triggers TLR2 signaling.