Regulation of endothelin-1 and transforming growth factor-β1 production in cultured proximal tubular cells by albumin and heparan sulphate glycosaminoglycans

Background. Both endothelin-1 (ET-1) and transforming growth factor beta 1 (TGF-beta1) have been implicated in the progression of interstitial fibrosis. In the present study we enquired if albumin influences the production of these factors in cultured human proximal tubular epithelial cells (PTEC) and if heparan sulphate glycosaminoglycans (HS-GAG) can inhibit this production. Methods. ET-1 and TGF-beta1 production in supernatants of PTEC was measured by RIA and ELISA respectively. In addition semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) was performed to study differences in ET-1 and TGF-beta1 mRNA expression. To demonstrate ET-1 or TGF-beta1 binding to heparin or HS-GAG, binding studies by means of dot blot analysis were carried out. Results. TGF-beta1 and ET-1 were both produced in different concentrations, depending on the PTEC culture tested. Human serum albumin (HSA) up-regulated the production of both factors in a time and dose dependent fashion. The production of these factors was inhibited by heparin under basal and stimulatory conditions. ET-1 production was only inhibited by HS-GAG with a high degree of sulphation. For the inhibition of TGF-beta1 production, the sulphation of HS-GAG was less critical. TGF-beta1, but not ET-1 mRNA expression was inhibited by HS-GAG. Inhibition of sulphation of cell surface HS-GAG resulted in the inhibition of ET-1 but not TGF-beta1 production. Both factors were able to bind to HS-GAG, although this required different amounts of HS-GAG sulphation for each factor. Conclusions. Our data demonstrate that in PTEC the release of pro-fibrogenic factors can be inhibited by HS-GAG. This may explain to some extent the beneficial effect of heparin in the treatment of interstitial fibrosis.