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Transforming growth factor-beta1 increases albumin permeability of isolated rat glomeruli via hydroxyl radicals
1Division of Nephrology, Department of Medicine, Medical College of Wisconsin, Milwaukee 53226, USA.
Background:
Transforming growth factor-beta1 (TGF-beta1) is a multifunctional cytokine. Glomerular cells and tubular epithelial cells secrete and respond to TGF-beta1. A close association between elevated levels of TGF-beta1 and the development of glomerulonephritis, glomerulosclerosis, and tubular hypertrophy has been documented. The role of TGF-beta1 in proteinuria is not well understood.
Methods:
Isolated rat glomeruli were incubated in medium alone or with TGF-beta1 (1 to 10 ng/mL) and TGF-beta1 + 200 U/mL of superoxide dismutase (SOD) or 1 mmol/L of dimethylthiourea (DMTU) scavengers of superoxide and hydroxyl radicals, respectively, for up to 60 minutes at 37 degrees C. Glomerular albumin permeability (Palb) was calculated from the volumetric response of glomeruli to an oncotic gradient using videomicroscopy.
Results:
One or 2.5 ng/mL of TGF-beta1 had no effect on Palb (0.18 +/- 0.08, N = 17; 0.18 +/- 0. 079, N = 20 vs. control 0.00 +/- 0.06, N = 25), whereas 5 or 10 ng/mL of TGF-beta1 caused a significant increase in Palb (0.31 +/- 0. 09, N = 20; 0.33 +/- 0.06, N = 23) within 15 minutes. The effect of 10 ng/mL of TGF-beta1 on Palb increased further after 30, 45, or 60 minutes of incubation (0.43 +/- 0.06, N = 24; 0.53 +/- 0.06, N = 25; 0.74 +/- 0.075, N = 21). The TGF-beta1-induced increase in Palb (0. 75 +/- 0.065, N = 15) was blocked by SOD (0.07 +/- 0.14 N = 15) or by DMTU (0.04 +/- 0.13, N = 15). Incubation of glomeruli with the carrier medium (4N HCl) in which TGF-beta1 is dissolved and SOD or DMTU alone did not affect Palb.
Conclusion:
Elevated levels of TGF-beta1 derived from glomerular or extraglomerular sources are capable of increasing glomerular Palb via superoxide and hydroxyl radicals and may lead to proteinuria in vivo.