Interleukin-1 induces tubular epithelial-myofibroblast transdifferentiation through a transforming growth factor-beta 1-dependent mechanism in vitro

Interleukin-1 (IL-1) has been shown to exert profibrotic activity in a numb er of disease models, including crescentic glomerulonephritis and pulmonary fibrosis, but the mechanisms by which this operates are poorly understood. Recent studies have identified a novel mechanism promoting renal fibrosis: tubular epithelial-myofibroblast transdifferentiation (TEMT). The present study examined whether IL-1 can stimulate TEMT in vitro. Cells of the norma l rat kidney tubular epithelial cell line (NRK52E) were grown to confluence on collagen-coated plates and cultured for 5 days in the presence 1 to 20 ng/mL of IL-1 alpha. Doses of 10 to 20 ng/mL of IL-1 caused transdifferenti ation of NRK52E cells into myofibroblast-like cells. Scanning electron micr oscopy identified IL-1-induced morphological changes as a loss of apical-ba sal polarity and microvilii, cell hypertrophy, and the development of an el ongated and invasive appearance. Phenotypically, IL-1-induced TEMT was char acterized by de novo messenger RNA and protein expression of the mesenchyma l marker alpha -smooth muscle actin, shown by Northern blotting, immunohist ochemistry, and Western blotting. This was accompanied by loss of the epith elial marker E-cadherin. The addition of an excess of IL-1-receptor antagon ist completely inhibited IL-1-induced TEMT. IL-1 was shown to stimulate the secretion of active transforming growth factor-beta1 (TGF-beta1) by NRK52E cells. Furthermore, the addition of a neutralizing anti-TGF-beta1 antibody inhibited IL-1-induced TEMT. In conclusion, IL-1 is a profibrogenic cytoki ne capable of inducing TEMT through a TGF-beta1-dependent mechanism. This m ay represent a novel mechanism by which IL-1 induces renal fibrosis in vivo . (C) 2001 by the National Kidney Foundation, Inc.