IL-33/ST2 axis mediates hyperplasia of intrarenal urothelium in obstructive renal injury

Abstract

The monolayered intrarenal urothelium covers the renal papilla and ureteropelvic junction (UPJ). In response to increased renal pressure during obstruction or ischemic injuries, intrarenal urothelial cells begin to proliferate and form a multilayered urothelium. Little is known regarding the mechanism and pathophysiological role of urothelium hyperplasia during renal obstruction. In this study, we investigated the expression of interleukin (IL)-33, an IL-1 family cytokine, in kidneys with unilateral ureteral obstruction (UUO)-induced obstructive injury. IL-33 levels in hydronephrotic urine and serum were upregulated 2 days after UUO. The number of ST2-expressing immune cells was increased in the UUO kidney. We found that IL-33 was upregulated in vimentin-positive cells in the cortical and medullar layers and the UPJ stroma. Moreover, IL-33 expression was predominantly induced in multilayered keratin 5-positive urothelial cells in the UPJ. IL-33 was not detected in terminally differentiated superficial umbrella cells expressing uroplakin 3a. In vivo, we confirmed that deficiency of IL33 or its receptor ST2 attenuated UUO-induced hyperplasia of the UPJ urothelium. Deficiency of IL33 attenuated the expression of UUO-induced type 2 inflammatory cytokines and upregulated uroplakins and urothelial differentiation signaling in UPJ tissues. Our results collectively suggest that the IL-33/ST2 axis mediates the activation of innate immune responses and contributes to urothelial hyperplasia by regulating urothelial differentiation in obstructive kidney injury. An inflammatory signaling protein may play an important role in kidney damage associated with urinary tract blockage. Untreated obstructive nephropathy can lead to kidney injury, particularly in younger patients. Taiwanese researchers led by Wei-Yu Chen at the Kaohsiung Chang Gung Memorial Hospital and Ya-Jen Chang at the Academia Sinica, Taipei, homed in on a signaling pathway that apparently contributes to the pathology of this condition. Using an animal model of surgically induced obstructive nephropathy, the researchers observed a post-injury spike in production of an immunity-activating protein called interleukin (IL)-33. This protein subsequently activates a host of immune cell types, and also stimulates abnormal growth in a subset of urinary tract epithelial cells. This excessive growth may directly contribute to subsequent damage and functional impairment of the kidney, although more research will be needed to confirm this.