Albumin-Induced Epithelial Mesenchymal Transformation

Background: Progressive chronic kidney disease is often associated with albuminuria and renal fibrosis linked to the accumulation of myofibroblasts producing extracellular matrix. Renal myofibroblasts are derived from a number of cells including tubular epithelial cells (TECs) through epithelial mesenchymal transformation (EMT). This study explores the hypothesis that exposure of TECs to albumin induces EMT. Methods: Normal rat TECs (NRK52E) were exposed in culture to de-lipidated bovine serum albumin (dBSA; 10 mg/ml) for 2, 4 and 6 days. Binding/uptake of fluoresceined albumin by PTCs was evaluated. Transformation into myofibroblasts was assessed by light and electron microscopy, immunofluorescence and Western blotting for alpha-smooth muscle actin (alpha-SMA), E-cadherin and transforming growth factor-beta 1 (TGF-beta 1). We also investigated the expression of fibroblast-specific protein-1 (FSP-1) and collagens I, III and IV. TGF-beta 1 biological activity, mRNA and protein were measured. A neutralising anti-TGF-beta 1 antibody was used to analyse the role of TGF-beta 1 in albumin-induced EMT. Results: Exposure of TECs to dBSA led to binding/uptake of albumin as well as fibroblastic morphological changes. Incubation of TECs with dBSA caused a reduction of TEC marker E-cadherin (ANOVA p = 0.0002) and de novo expression of fibroblast markers alpha-SMA and FSP-1 (ANOVA p = 0.0001) in a time-dependent manner. It also increased expression and activity of TGF-beta 1. Neutralisation of TGF-beta 1 significantly reduced EMT (p<0.01). Conclusion: This study demonstrates that in vitro, albumin induces the transformation of TECs into cells with myofibroblast characteristics; a process that may be TGF-beta 1 dependent. Copyright (c) 2012 S. Karger AG, Basel