title: Profibrotic effect of interleukin-18 in HK-2 cells is dependent on stimulation of the Toll-like receptor 4 (TLR4) promoter and increased TLR4 expression.
abstract: BACKGROUND
  IL-18 induces profibrotic changes in TECs independent of TGF-β1 activity.
  
  
  RESULTS
  IL-18 stimulates the TLR4 promoter via AP-1 activation to increase TLR4 expression in TECs and stimulates profibrotic changes in TECs through increased TLR4 expression/signaling.
  
  
  CONCLUSIONS
  The profibrotic effect of IL-18 in TECs is mediated through stimulation of TLR4 expression via activation of AP-1.
  
  
  CONCLUSIONS
  This represents a novel fibrotic signaling pathway in TECs independent of TGF-β1. IL-18 is an important mediator of obstruction-induced renal fibrosis and tubular epithelial cell injury independent of TGF-β1 activity. We sought to determine whether the profibrotic effect of IL-18 is mediated through Toll-like receptor 4 (TLR4). Male C57BL6 wild type and mice transgenic for human IL-18-binding protein were subjected to left unilateral ureteral obstruction versus sham operation. The kidneys were harvested 1 week postoperatively and analyzed for IL-18 production and TLR4 expression. In a separate arm, renal tubular epithelial cells (HK-2) were directly stimulated with IL-18 in the presence or absence of a TLR4 agonist, TLR4 antagonist, or TLR4 siRNA knockdown. Cell lysates were analyzed for TLR4, α-smooth muscle actin, and E-cadherin expression. TLR4 promotor activity, as well as AP-1 activation and the effect of AP-1 knockdown on TLR4 expression, was evaluated in HK-2 cells in response to IL-18 stimulation. The results demonstrate that IL-18 induces TLR4 expression during unilateral ureteral obstruction and induces TLR4 expression in HK-2 cells via AP-1 activation. Inhibition of TLR4 or knockdown of TLR4 gene expression in turn prevents IL-18-induced profibrotic changes in HK-2 cells. These results suggest that IL-18 induces profibrotic changes in tubular epithelial cells via increased TLR4 expression/signaling.
authors.affiliation: Department of Urology, University of Florida, Gainesville, FL 32610, USA. Kirstan.Meldrum@urology.ufl.edu
authors.forename: Kirstan K
authors.initials: KK
authors.lastname: Meldrum
authors.forename: Hongji
authors.initials: H
authors.lastname: Zhang
authors.forename: Karen L
authors.initials: KL
authors.lastname: Hile
authors.forename: Lyle L
authors.initials: LL
authors.lastname: Moldower
authors.forename: Zizheng
authors.initials: Z
authors.lastname: Dong
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Meldrum
mesh_terms: D000818:Animals; D002460:Cell Line; D004847:Epithelial Cells / Q000378:metabolism; D005355:Fibrosis; D006801:Humans; D020382:Interleukin-18 / Q000378:metabolism*; D007674:Kidney Diseases / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D007684:Kidney Tubules / Q000166:cytology / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D011401:Promoter Regions, Genetic; D051197:Toll-Like Receptor 4 / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D020382:Interleukin-18; D051197:Toll-Like Receptor 4