Cytosolic Sensors of Viral RNA Are Involved in the Production of Interleukin-6 Via Toll-Like Receptor 3 Signaling in Human Glomerular Endothelial Cells

BACKGROUND/AIMS:Dysregulation of interleukin-6 (IL-6) production in residual renal cells may play a pivotal role in the development of glomerulonephritis (GN). Given that Toll-like receptor 3 (TLR3) signaling has been implicated in the pathogenesis of some forms of GN, we examined activated TLR3-mediated IL-6 signaling in cultured normal human glomerular endothelial cells (GECs).METHODS:We treated GECs with polyinosinic-polycytidylic acid (poly IC), an authentic double-stranded RNA, and analyzed the expression of IL-6 and the cytosolic viral RNA sensors retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation associated gene 5 (MDA5) using reverse transcription quantitative real-time polymerase chain reaction, western blotting, and enzyme-linked immunosorbent assays. To further elucidate the effects of poly IC on this signaling pathway, we subjected the cells to small interfering RNA (siRNA) against TLR3, interferon (IFN)-β, RIG-I, and MDA5.RESULTS:We found that poly IC induced the expression of RIG-I, MDA5 and IL-6 via TLR3/IFN-β signaling in GECs. siRNA experiments revealed that both MDA5 and RIG-I were involved in the poly IC-induced expression of IL-6, with MDA5 being upstream of RIG-I.CONCLUSION:Interestingly, cytosolic sensors of viral RNA were found to be involved in IL-6 production via TLR3 signaling in GECs. Regional activation of TLR3/IFN-β/ MDA5/RIG-I/IL-6 axis due to viral and "pseudoviral" infections is involved in innate immunity and inflammatory reactions in GECs. We believe this signaling pathway also plays a pivotal role in the development of some forms of GN.