Down-regulation of endothelin receptors by transforming growth factor β1 in hepatic stellate cells

Abstract

Background/Aims: Hepatic endothelin-1 (ET-1) receptor density as well as the levels of both ET-1 and transforming growth factor β1 (TGF-β1) increase in liver cirrhosis. Considering their potent contractile (ET-1) and fibrogenic (TGF-β1) actions on myofibro-blastic stellate cells found in the fibrotic/cirrhotic liver, we aimed to investigate the effects of TGF-β1 on ET-1 receptors and ET-1 synthesis in these cells. Methods: Stellate cells isolated from rat liver by enzymatic digestion were cultured and subjected to TGF-β1 treatment. Cellular ET-1 receptors and ET-1 released in the medium were determined. Results: TGF-β1 treatment produced time- and dose-dependent decrease in ET-1 binding sites, but did not affect the affinity of the receptors for ET-1. TGF-β1 also stimulated the release of ET-1 from stellate cells. The extent of TGF-β1-induced inhibition of [ 125I]ET-1 binding was much greater for ET B subtype (73±18% inhibition), which comprised a major portion (78±12%) of the total ET-1 receptors, than for ET A subtype (35±11% inhibition). The mRNA expression of the ET-1 receptors also was reduced by TGF-β1 treatment. TGF-β1-induced reduction in ET-1 receptor density was coupled to the inhibition of ET-1-stimulated release of [ 3H]arachidonic acid from the prelabeled cells. The effects of TGF-β1 were inhibited by a TGF-β1 neutralizing monoclonal antibody. Conclusions: These results suggest thatthe TGF-β1-induced decrease in ET-1 receptor density may be an important mechanism in limiting the pathologic actions of ET-1 on stellate cells in chronic liver disease.