Indoxyl Sulfate Enhances p53-TGF-β1-Smad3 Pathway in Proximal Tubular Cells

Background/Aim: Indoxyl sulfate-induced activation of nuclear factor (NF)-kappa B promotes transforming growth factor (TGF)-beta(1) in human proximal tubular cells (HK-2 cells). The present study aimed to elucidate the cross talk among indoxyl sulfate, p53 and TGF-beta(1)-Smad3 signaling in proximal tubular cells. Methods: The effects of indoxyl sulfate on the expression of TGF-beta(1), Smad3, and alpha-smooth muscle actin (alpha-SMA) were determined using HK-2 cells. As for in vivo experiments the following animals were used: Dahl salt-resistant normotensive rats (DN) and indoxyl sulfate-administered Dahl salt-resistant normotensive rats (DN+IS). Results: Both indoxyl sulfate and nutlin-3, a specific p53 inducer, stimulated TGF-beta(1) expression, which was suppressed by pifithrin-alpha, p-nitro, a p53 inhibitor. Further, indoxyl sulfate stimulated TGF-beta(1)-induced expression of alpha-SMA by enhancing Smad3 expression and TGF-beta(1)-induced Smad3 phosphorylation. Indoxyl sulfate induced phosphorylation of extracellular signal-regulated kinase (ERK). U0126, an inhibitor of ERK pathway, prevented indoxyl sulfate-induced upregulation of Smad3 expression. Immunohistochennistry demonstrated that TGF-beta(1) and Smad3 were localized in renal tubular cells, and that indoxyl sulfate increased the TGF-beta(1) and Smad3-positive area in the kidney. Conclusion: Indoxyl sulfate stimulates p53-induced TGF-beta(1) expression and TGF-beta(1)-induced alpha-SMA expression in proximal tubular cells. Indoxyl sulfate-induced Smad3 accelerates TGF-beta(1)-induced alpha-SMA expression through ERK activation. Thus, indoxyl sulfate enhances p53-TGF-beta(1)-Smad3 pathway in proximal tubular cells. copyright (C) 2013 S. Karger AG, Basel