title: IL-18 activation is dependent on Toll-like receptor 4 during renal obstruction.
abstract: OBJECTIVE
  Interleukin 18 (IL-18) is a critical mediator of obstruction-induced renal injury. Although previous studies have demonstrated that IL-18 participates in a positive feedback loop via the IL-18 receptor (IL-18R) and localized renal IL-18 and IL-18R production to tubular epithelial cells (TEC), the mechanism of IL-18 activation during obstruction remains unclear. We hypothesized that IL-18 activation is dependent on Toll-like receptor 4 (TLR4) signaling during renal obstruction.
  
  
  METHODS
  Male C57BL6 TLR4 knockout (TLR4KO) and wild-type (WT) mice were subjected to unilateral ureteral obstruction versus sham operation for 1 wk. The animals were sacrificed, and renal cortical tissue was harvested and analyzed for TLR4 expression (Western blot), active IL-18 production (enzyme-linked immunosorbent assay, real-time polymerase chain reaction), IL-18 receptor expression (real-time polymerase chain reaction), and TLR4/IL-18 versus IL-18R cellular localization (dual immunofluorescent staining).
  
  
  RESULTS
  Renal TLR4 expression increased significantly in WT mice in response to obstruction, but remained at sham treatment levels in TLR4KO mice. IL-18 and IL-18R gene expression and active IL-18 production were similarly increased in WT mice in response to obstruction, but decreased significantly to sham treatment levels in the absence of TLR4. Dual immunofluorescent staining revealed co-localization of TLR4 and IL-18 to renal TEC during obstruction.
  
  
  CONCLUSIONS
  IL-18 production and activation during renal obstruction is dependent on intact TLR4 signaling. Co-localization of IL-18 and TLR4 production to TEC during obstruction suggests that TEC are the primary site of IL-18 production and activation. Further characterization of the pathway may be necessary to develop targeted therapy in obstruction-induced renal injury.
authors.affiliation: Department of Urology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Audrey C
authors.initials: AC
authors.lastname: Rhee
authors.forename: Alexandra L
authors.initials: AL
authors.lastname: Cain
authors.forename: Karen L
authors.initials: KL
authors.lastname: Hile
authors.forename: Hongji
authors.initials: H
authors.lastname: Zhang
authors.forename: Futoshi
authors.initials: F
authors.lastname: Matsui
authors.forename: Kirstan K
authors.initials: KK
authors.lastname: Meldrum
mesh_terms: D000818:Animals; D020170:Caspase 1 / Q000378:metabolism; D020382:Interleukin-18 / Q000378:metabolism*; D007672:Kidney Cortex / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053724:Receptors, Interleukin-18 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D014517:Ureteral Obstruction / Q000378:metabolism*
chemical_list: D020382:Interleukin-18; D053724:Receptors, Interleukin-18; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D020170:Caspase 1