Crosstalk Between Suppression of Tumorigenicity 2 and Transforming Growth Factor-13 Receptor Signaling Promotes Renal Fibrosis

IL-33, a member of the IL-1 family, acts as an alarmin in immune response. Epithelial-mesenchymal transition and transforming growth factor-b (TGF-b)-induced fibroblast activation are key events in the development of renal interstitial fibrosis. The current study found increased expression of IL-33 and suppression of tumorigenicity 2 (ST2), the receptor for IL-33, in human fibrotic renal tissues. In addition, IL-33- or ST2-deficient mice showed significantly reduced levels of fibronectin, a-smooth muscle actin, and vimentin, and increased E-cadherin levels. In HK-2 cells, IL-33 promotes the phosphorylation of the TGF-b receptor (TGF-bR), Smad2, and Smad3, and the production of extracellular matrix (ECM), with reduced expression of E-cadherin. Blocking TGF-bR signaling or suppressing ST2 expression impeded Smad2 and Smad3 phosphorylation, thereby reducing ECM production, suggesting that IL-33-induced ECM synthesis requires cooperation between the two pathways. Mechanistically, IL33 treatment induced a proximate interaction between ST2 and TGF-bRs, activating downstream Smad2 and Smad3 for ECM production in renal epithelial cells. Collectively, this study identified a novel and essential role for IL-33 in promoting TGF-b signaling and ECM production in the development of renal fibrosis. Therefore, targeting IL-33/ST2 signaling may be an effective therapeutic strategy for renal fibrosis. (Am J Pathol 2023, 193: 1029-1045; https://doi.org/10.1016/j.ajpath.2023.05.002)