title: IL-18 mediates proapoptotic signaling in renal tubular cells through a Fas ligand-dependent mechanism.
abstract: Renal tubular cell apoptosis is a significant component of obstruction-induced renal injury, and it results in a progressive loss in renal parenchymal mass during renal obstruction. Although IL-18 is an important mediator of inflammatory renal disease and renal fibrosis, its role in obstruction-induced renal tubular cell apoptosis remains unclear. To study this, male C57BL6 wild-type mice and C57BL6 mice transgenic for human IL-18-binding protein (IL-18BP Tg) were subjected to renal obstruction vs. sham operation. The kidneys were harvested after 1 or 2 wk and analyzed for IL-18 production, apoptosis, caspase activity, and Fas/Fas Ligand (FasL) expression. HK-2 cells were similarly analyzed for apoptosis and proapoptotic signaling following 3 days of direct exposure to IL-18 vs. control media. Renal obstruction induced a significant increase in IL-18 production, renal tubular cell apoptosis, caspase activation, and FasL expression. IL-18 neutralization, on the other hand, significantly reduced obstruction-induced apoptosis, caspase-8 and caspase-3 activity, and FasL expression. In vitro experiments similarly demonstrate that IL-18 stimulation induces apoptosis, FasL expression, and increases active caspase-8 and caspase-3 expression in a dose-dependent fashion. siRNA knockdown of FasL gene expression, however, significantly reduced IL-18-induced apoptosis. This study reveals that IL-18 is a significant mediator of obstruction-induced tubular cell apoptosis, and it demonstrates that IL-18 stimulates proapoptotic signaling through a FasL-dependent mechanism.
authors.affiliation: Department of Urology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Hongji
authors.initials: H
authors.lastname: Zhang
authors.forename: Karen L
authors.initials: KL
authors.lastname: Hile
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Asanuma
authors.forename: Brian
authors.initials: B
authors.lastname: Vanderbrink
authors.forename: Ethan I
authors.initials: EI
authors.lastname: Franke
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Campbell
authors.forename: Kirstan K
authors.initials: KK
authors.lastname: Meldrum
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D020169:Caspases / Q000096:biosynthesis; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D053222:Fas Ligand Protein / Q000096:biosynthesis / Q000502:physiology*; D005434:Flow Cytometry; D006801:Humans; D020287:In Situ Nick-End Labeling; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis / Q000235:genetics; D020382:Interleukin-18 / Q000235:genetics / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000187:drug effects / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects*; D014162:Transfection; D014517:Ureteral Obstruction / Q000378:metabolism / Q000473:pathology
chemical_list: D053222:Fas Ligand Protein; D036341:Intercellular Signaling Peptides and Proteins; D020382:Interleukin-18; D034741:RNA, Small Interfering; C118370:interleukin-18 binding protein; D020169:Caspases