AIM: To study the expression of cystatin C (CysC), its regulation by transforming growth factor-β1 (TGF-β1)and platelet-derived growth factor (PDGF) and the potential interference of CysC with TGF-β1 signaling in this special cell type.METHODS: We evaluated the CysC expression in cultured, profibrogenic hepatic stellate cells and transdifferentiated myofibroblasts by North and West blotting and confocal laser scanning microscopy.RESULTS: CysC was increased significantly in the course of trans-differentiation. Both TGF-β1 and PDGFBB suppressed CysC expression. Furthermore, CysC secretion was induced by the treatment with TGF-β1.Although CysC induced an increased binding affinity of TGF-β receptor type Ⅲ (beta-glycan) as assessed by chemical cross-linking with [125I]-TGF-β1, it did not modulate TGF-β1 signal transduction as shown by evaluating the Smad2/3 phosphorylation status and [CAGA]-MLP-luciferase reporter gene assay. Interestingly,the shedding of type Ⅲ TGF-β receptor beta-glycan was reduced in CysC-treated cells. Our data indicated that CysC expression was upregulated during transdifferentiation.CONCLUSION: Increased CysC levels in the serum of patients suffering from liver diseases are at least partially due to a higher expression in activated hepatic stellate cells. Furthermore, TGF-β1 influences the secretion of CysC, highlighting a potentially important role of cysteine proteases in the progression of hepatic fibrogenesis.