Implication of glomerular endothelial expression of interferon-stimulated gene 20, an antiviral effector protein, in human kidney inflammation

Abstract Background: Besides regulating antiviral response, increased expression of Toll-like receptor 3 (TLR3) in resident renal cells plays a role in the development of some forms of glomerulonephritis. TLR3 activation leads to the production of type I interferon (IFN), which subsequently induces the expression of IFN-stimulated genes (ISGs). We previously reported that in glomerular resident cells, ISG20 expression is regulated via the TLR3/ IFN-β signaling, however, its detailed implications remain undetermined. Methods: Cultured normal human glomerular endothelial cells (GECs) were treated with polyinosinic-polycytidylic acid (poly IC), Escherichia coli lipopolysaccharide (LPS), R848, and CpG (TLR3, TLR4, TLR7, and TLR9 agonists). ISG20, CX3CL1/fractalkine and CXCL10/IP-10 mRNA levels were analyzed using quantitative reverse transcription-polymerase chain reaction (qRT-PCR). ISG20 protein expression was evaluated by western blotting. RNA interference (siRNA) was used to knockdown IFN-β and ISG20. CX3CL1 protein levels were evaluated by enzyme-linked immunosorbent assay (ELISA).Results: In GECs, the expression of ISG20 mRNA and protein was increased by poly IC but not by LPS, R848, or CpG treatment. siRNA-mediated knockdown of IFN-β inhibited the poly IC-induced ISG20 expression. Moreover, ISG20 knockdown prevented the poly IC-induced expression of CX3CL1, a representative chemokine that acts as a strong macrophage chemoattractant, whereas it had no effect on CXCL10 expression. Conclusion: In GECs, ISG20 is regulated via TLR3 but not via TLR4, TLR7, or TLR9 signaling, and ISG20 is involved in regulating CX3CL1 production. Besides regulating the antiviral innate immunity, ISG20 may act as a mediator of CX3CL1 production, thereby inducing glomerular inflammation. Thus, modulating ISG20 expression might be a possible therapeutic strategy for glomerulonephritis.