Experimental and human liver fibrogenesis

In this work, we provide an overview of our results obtained by studying the role of transforming growth factor beta1 and proteoglycans in liver fibrogenesis. It has been found that transforming growth factor beta1 is one of the most important stimulators of extracellular matrix synthesis in the liver. In chronic liver injury, desmin-positive non-parenchymal liver cells expressed transforming growth factor beta1. The extracellular localization of the growth factor correlated well with types I, III and IV procollagen-alpha, which were detected in the fibrous septa of chronically injured livers. A similar distribution pattern was observed in human specimens. To identify the role of transforming growth factor beta1 in liver extracellular matrix protein synthesis, transforming growth factor beta1-positive transgenic mice were generated. Animals expressing the growth factor in their liver showed spontaneous liver fibrosis. Proteoglycans also participate in fibrogenesis. The majority of liver-specific heparan sulfate proteoglycans, such as syndecan-1 and fibroglycan, are produced by hepatocytes. The extracellular matrix proteoglycans decorin and perlecan are synthesized by non-parenchymal liver cells. The amount of the latter is very low in normal liver, but increases dramatically in liver fibrosis. The effect of regulatory factors on liver proteoglycans seems to be cell type-specific. In contrast to previous observations, elevated amounts of decorin did not inhibit the action of transforming growth factor beta1 in the liver.