Obstruction of the upper urinary tract induces a progressive loss in renal mass through apoptotic renal cell death. Although TNF-alpha has been implicated in ischemia-reperfusion-induced apoptotic renal cell death, its role in obstructive renal cell apoptosis remains unknown. To study this, male Sprague-Dawley rats were subjected to left unilateral ureteral obstruction vs. sham operation. Twenty-four hours before surgery and every 84 h thereafter, rats received either vehicle or a pegylated form of soluble TNF receptor type 1 (PEG-sTNFR1). The kidneys were harvested 1, 3, or 7 days postoperatively, and tissue samples were subsequently analyzed for TNF-alpha (ELISA, RT-PCR), Fas ligand (RT-PCR), apoptosis (TUNEL, ELISA), and caspase 8 and 3 activity (Western blot). Renal obstruction induced increased tissue TNF-alpha and Fas ligand mRNA levels, TNF-alpha protein production, apoptotic renal tubular cell death, and elevated caspase 8 and 3 activity, whereas treatment with PEG-sTNFR1 significantly reduced obstruction-induced TNF-alpha production, renal tubular cell apoptosis, and caspase activity. PEG-sTNFR1 did not significantly alter Fas ligand expression. These results demonstrate that TNF-alpha mediates obstruction-induced renal tubular cell apoptosis and proapoptotic signaling and identify TNF-alpha neutralization as a potential therapeutic option for the amelioration of obstruction-induced renal injury.

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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.

Upper urinary tract obstruction is a common cause of renal dysfunction in children and adults. While there is clinical evidence of an increased male incidence and mortality rate with acute renal failure, the effect of gender and testosterone on obstructive renal injury has not previously been evaluated. We hypothesized that testosterone exacerbates proinflammatory TNF-␣ production and proapoptotic and profibrotic signaling during renal obstruction, resulting in increased apoptotic cell death and tubulointerstitial fibrosis. To study this, male, female, castrated male, and testosterone-treated oophorectomized female rats were subjected to sham operation or 3 days of unilateral ureteral obstruction (UUO). Renal cortical tissue was then analyzed for TNF-␣ production; proapoptotic caspase-8, -9, and -3 activity; apoptotic cell death; profibrotic transforming growth factor-␤1 production; and ␣-smooth muscle actin expression. In a separate arm, glomerular filtration rate (inulin clearance) was measured in rats pre-and post-UUO. Male and testosterone-treated oophorectomized female rats demonstrated a significant increase in TNF-␣ production, caspase activity, apoptotic cell death, tubulointerstitial fibrosis, and renal dysfunction during UUO compared with castrated males and normal female rats subjected to the same time course of obstruction. These results demonstrate that endogenous testosterone production in normal male rats and testosterone exogenously administered to oophorectomized females significantly increases TNF production and proapoptotic and profibrotic signaling during renal obstruction, resulting in increased apoptotic cell death, tubulointerstitial fibrosis, and renal dysfunction.