Abstract
Background: Retinoic acid-inducible gene-I (RIG-I) is a putative RNA helicase involved in immune reactions against RNA viruses and various inflammatory and autoimmune diseases. The purpose of the present study was to investigate the role of RIG-I in glomerular diseases.
Methods: We treated human mesangial cells (MC) in culture with interferon-γ (IFN-γ), a potent Th1 type cytokine, and polyinosinic-polycytidylic acid (poly IC), which is an authentic double-stranded RNA and analyzed the expression of RIG-I, interferon regulatory factors (IRF) 1 and 7, CC chemokine ligand 5 (CCL5) and IFN-β by western blotting, reverse transcriptase-polymerase chain reaction (RT-PCR), or enzyme-linked immunosorbent assay (ELISA). To elucidate the RIG-I-mediated signaling pathway, we subjected the cells to RNA interference (RNAi) against RIG-I, nuclear factor-κB p65, IFN-β or toll-like receptor (TLR) 3. Further, we studied the effects of IFN-β receptor blocking.
Results: IFN-γ was found to induce the expression of RIG-I in human mesangial cells in culture. Knockdown of RIG-I inhibited the IFN-γ-induced upregulation of IRF7, a transcriptional factor involved in immune and inflammatory reactions. Poly IC induced the expression of RIG-I and CCL5 in human mesangial cells, and RNAi against RIG-I inhibited this poly IC-induced CCL5 expression. Poly IC-induced RIG-I expression was also inhibited by RNAi against IFN-β and by an antibody against the IFN-β receptor. The knockdown of TLR3 abolished poly IC-induced RIG-I expression.
Conclusions: The IFN-γ/RIG-I/IRF7 and TLR3/IFN-β/RIG-I/CCL5 signaling pathways may be involved in the pathogenesis of glomerulonephritis, and also suggesting the role of this pathway in the aggravation of glomerulonephritis due to viral infection.
