Syndecan-1 inhibits early stages of liver fibrogenesis by interfering with TGFβ1 action and upregulating MMP14

Abstract

Increased expression of syndecan-1 is a characteristic feature of human liver cirrhosis. However, no data are available on the significance of this alteration. To address this question we designed a transgenic mouse strain that driven by albumin promoter, expresses human syndecan-1 in the hepatocytes. Liver cirrhosis was induced by thioacetamide in wild type and hSDC1^+/+ mice of the identical strain. The process of fibrogenesis, changes in signal transduction and proteoglycan expression were followed. In an in vitro experiment, the effect of syndecan-1 overexpression on the action of TGFβ1 was determined. Human syndecan-1 and TGFβ1 levels were measured by ELISA in the circulation. Without challenge, no morphological differences were observed between wild type and transgenic mice livers, although significant upregulation of phospho-Akt and FAK was observed in the latter. Fibrogenesis in the transgenic livers, characterized by picrosirius staining, collagen type I, and SMA levels, lagged behind that of control in the first and second months. Changes in signal transduction involved in the process of fibrogenesis, as SMAD, MAPK, Akt and GSK, pointed to the decreased effect of TGFβ1, and this was corroborated by the decreased mRNA expression of TIEG and the growth factor itself. In vitro experiments exposing the LX2 hepatic stellate cell line to conditioned media of wild type and syndecan-1 transfected Hep3B cell lines proved that medium with high syndecan-1 content inhibits TGFβ1-induced upregulation of SMA, TIEG, collagen type I and thrombospondin-1 expression. Detection of liver proteoglycans and heparan sulfate level revealed that their amounts are much higher in control transgenic liver, than that in the wild type. However, it decreases dramatically as a result of shedding after hepatic injury. Shedding is likely promoted by the upregulation of MMP14. As syndecan-1 can bind thrombospondin-1, and as our result demonstrated that the same is true for TGFβ1, shed syndecan-1 can remove the growth factor and its activator together into the systemic circulation.Taking together, our results indicate that the effect of syndecan-1 is accomplished on two levels: a, the shedded syndecan can bind, inhibit and remove TGFβ1; b, interferes with the activation of TGFβ1 by downregulation and binding thrombospondin-1, the activator of the growth factor. However, by the end of the fourth month the protective effect was lost, which is explained by the considerable decrease of syndecan-1 and the almost complete loss of heparan sulfate from the surface of hepatocytes.

Keywords: Heparan-sulfate; Liver fibrosis; MMP14; Syndecan-1; TGFβ1; Thrombospondin-1.