Interleukin-18 stimulates a positive feedback loop during renal obstruction via interleukin-18 receptor.

PURPOSE: Interleukin-18 is a proinflammatory cytokine that is an important mediator of obstruction induced renal tubulointerstitial fibrosis independent of tumor necrosis factor-α and ß1 activity. We hypothesized that interleukin-18 stimulates a positive feedback loop during obstruction via interleukin-18 receptor to increase interleukin-18 gene expression and protein production. MATERIALS AND METHODS: Male C57BL6 interleukin-18 receptor knockout (The Jackson Laboratory, Bar Harbor, Maine) and control wild-type mice underwent unilateral ureteral obstruction or sham operation and were sacrificed 1 week after surgery. Renal cortical tissue samples were harvested and analyzed for interleukin-18 protein by enzyme-linked immunosorbent assay, and for interleukin-18 and interleukin-18 receptor gene expression by quantitative polymerase chain reaction. The specific cellular localization of interleukin-18 and interleukin-18 receptor expression during obstruction was assessed using dual labeling immunofluorescence staining. RESULTS: Renal interleukin-18 receptor expression increased significantly in wild-type mice in response to obstruction but remained at sham operation levels in interleukin-18 receptor knockout mice. Similarly while interleukin-18 protein and gene expression were significantly increased in wild-type mice in response to obstruction, interleukin-18 levels and gene expression were significantly decreased during obstruction in knockout mice. Obstruction induced interleukin-18 and interleukin-18 receptor production were localized predominantly to tubular epithelial cells and to a lesser extent to the renal interstitium. CONCLUSIONS: Results reveal that interleukin-18 stimulates a positive feedback loop via interleukin-18 receptor during renal obstruction to stimulate interleukin-18 production and gene expression. The predominant cellular source of interleukin-18 production during renal obstruction appears to be tubular epithelial cells rather than infiltrating macrophages.

IL-18 neutralization ameliorates obstruction-induced epithelial-mesenchymal transition and renal fibrosis.

Ureteral obstruction results in renal fibrosis in part due to inflammatory injury. The role of interleukin-18 (IL-18), an important mediator of inflammation, in the genesis of renal fibrosis was studied using transgenic mice overexpressing human IL-18-binding protein. In addition, HK-2 cells were analyzed following direct exposure to IL-18 compared to control media. Two weeks after ureteral obstruction, the kidneys of wild-type mice had a significant increase in IL-18 production, collagen deposition, alpha-smooth muscle actin and RhoA expression, fibroblast and macrophage accumulation, chemokine expression, and transforming growth factor-beta1 (TGF-beta1) and tumor necrosis factor-alpha (TNF-alpha) production, whereas E-cadherin expression was simultaneously decreased. The transgenic mice with neutralized IL-18 activity exhibited significant reductions in these indicators of obstruction-induced renal fibrosis and epithelial- mesenchymal transition, without demonstrating alterations in TGF-beta1 or TNF-alpha activity. Similarly, the HK-2 cells exhibited increased alpha-smooth muscle actin expression and collagen production, and decreased E-cadherin expression in response to IL-18 stimulation without alterations in TNF-alpha or TGF-beta1 activity. Our study demonstrates that IL-18 is a significant mediator of obstruction-induced renal fibrosis and epithelial- mesenchymal transition independent of downstream TGF-beta1 or TNF-alpha production.