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

Abstract

Background: Besides regulating the 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 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 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.