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

Abstract

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.

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

“…IL-18 is a proinflammatory cytokine that has recently been implicated in the pathophysiology of obstructive renal injury (23). Interestingly, whereas increased TGF-␤1 production has long been regarded as the final common pathway for renal fibrotic injury, the profibrotic effect of IL-18 both in vivo and in tubular epithelial cells in vitro occurs independent of any alterations to TGF-␤1 activity.…”

“…Total RNA was extracted from the renal cortical tissue or cell lysates by homogenization in TRIzol (Invitrogen) and then isolated by precipitation with chloroform and isopropanol as previously described (23). Total RNA (0.5 g) was subjected to cDNA synthesis using iScript (Bio-Rad).…”

“…Recent studies have demonstrated a significant increase in renal tubular cell IL-18 production in response to obstruction, and an IL-18-mediated increase in collagen deposition, tubulointerstitial fibrosis, EMT, and tubular epithelial cell apoptosis independent of TNF-␣ or TGF-␤1 activity (23,26). We have recently demonstrated that IL-18 production localizes primarily to renal tubular cells, not infiltrating macrophage, during renal obstruction in mice (27), and studies have shown that circulating IL-18 levels and renal tubular cell IL-18 receptor expression is significantly increased in patients with chronic kidney disease (28).…”

“…EMT is characterized by a loss in epithelial cell markers (i.e., E-cadherin) and increased expression of the myofibroblast marker ␣-smooth muscle actin (␣-SMA). Although TGF-␤1 can induce renal fibrosis via stimulation of EMT, fibroblast proliferation (11)(12)(13)(14)(15)(16)(17), and extracellular matrix synthesis (1,(17)(18)(19)(20)(21)(22), IL-18 has recently been identified as an important mediator of obstruction-induced renal fibrosis and EMT independent of downstream TGF-␤1 production (23).…”

The pathological role of IL-18Rα in renal ischemia/reperfusion injury

“…8 Several reports indicate that Fas/Fas ligand (FasL) is involved in the pathogenesis of acute ischemic kidney injury via tubular apoptosis and necrosis. 9,10 FasL is a member of the TNF family that induces apoptosis by cross-linking its Fas receptor.…”