Expression of interferon-stimulated gene 20 (ISG20), an antiviral effector protein, in glomerular endothelial cells: possible involvement of ISG20 in lupus nephritis

Abstract

Background In addition to regulating the antiviral response, increased expression of Toll-like receptor 3 (TLR3) in resident renal cells plays a role in developing some forms of glomerulonephritis. TLR3 activation leads to type I interferon (IFN) production, which induces the expression of IFN-stimulated genes (ISGs). However, the role of ISG20 expression in resident renal cells remains unclear. 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, respectively). The mRNA levels of ISG20, CX3CL1/fractalkine, and CXCL10/IP-10 were measured by quantitative reverse transcription-polymerase chain reaction. ISG20 protein expression was assessed by Western blotting. RNA interference was used to knockdown IFN-β and ISG20 expression. CX3CL1 protein levels were assessed by enzyme-linked immunosorbent assay. We performed immunofluorescence to examine endothelial ISG20 expression in biopsy specimens from patients with lupus nephritis (LN). Results In GECs, the expression of ISG20 mRNA and protein was increased by polyIC, not by LPS, R848, or CpG treatment. Moreover, ISG20 knockdown prevented poly IC-induced CX3CL1 expression but had no effect on CXCL10 expression. Intense endothelial ISG20 immunoreactivity was observed in biopsy specimens obtained from patients with proliferative LN. Conclusion In GECs, ISG20 was regulated via TLR3 but not via TLR4, TLR7, or TLR9 signaling. Moreover, ISG20 was involved in regulating CX3CL1 production. In addition to regulating antiviral innate immunity, ISG20 may act as a mediator of CX3CL1 production, thereby inducing glomerular inflammation, particularly in patients with LN.

Type I IFN in Glomerular Disease: Scarring beyond the STING

“…Only the involvement of TLR3 in GECs has been reported. A number of publications originating from the same group using cultured human cells showed that the in vitro activation of TLR3 elicits the expression of IFN-I, RLRs, chemokines, and plasminogen activator inhibitor-1 (PAI-1), a negative regulator of fibrinolysis [ 111 , 112 , 113 , 114 , 115 , 116 ]. Taken together, this body of work suggests that the activation of TLR3 in GECs may contribute to inflammatory and fibrotic responses, events that could also be a result of a secondary response to the IFN-I pathway signaling.…”

“…There is little direct evidence of what effect IFN-I has on glomerular endothelial cells. A series of publications from Hiroshi Tanaka’s group using cultured human GECs identified a set of ISGs with the potential to be used as biomarkers for LN [ 111 , 141 , 142 ]. Instead, we might draw on work accomplished using other types of endothelial cells to extrapolate IFN-I signaling effects on GECs.…”