Characterization and regulation of insulin-like growth factor binding proteins in human hepatic stellate cells

Abstract

Cultured hepatic stellate cells (HSCs), the cell type primarily involved in the progression of liver fibrosis, secrete insulin-like growth factor-I (IGF-I) and IGF binding protein (IGFBP) activity. IGF-I exerts a mitogenic effect on HSCs, thus potentially contributing to the fibrogenic process in an autocrine fashion. However, IGF-I action is modulated by the presence of specific IGFBPs that may inhibit and/or enhance its biologic effects. Therefore, we examined IGFBP-1 through IGFBP-6 mRNA and protein expression in HSCs isolated from human liver and activated in culture. Regulation of IGFBPs in response to IGF-I and other polypeptide growth factors involved in the hepatic fibrogenic process was also assessed. RNase protection assays and ligand blot analysis demonstrated that HSCs express IGFBP-2 through IGFBP-6 mRNAs and release detectable levels of IGFBP-2 through IGFBP-5. Because IGF-I, platelet-derived growth factor-BB (PDGF-BB), and transforming growth factor-beta (TGF-beta) stimulate HSC proliferation and/or matrix production, we tested their effect on IGFBPs released by HSCs. IGF-I induced IGFBP-3 and IGFBP-5 proteins in a time-dependent manner without an increase in the corresponding mRNAs. IGFBP-4 protein levels decreased in response to IGF-I. TGF-beta stimulated IGFBP-3 mRNA and protein but decreased IGFBP-5 mRNA and protein. In contrast, PDGF-BB failed to regulate IGFBPs compared with controls. Recombinant human IGFBP-3 (rhIGFBP-3) was then tested for its effect on IGF-I-induced mitogenesis in HSCs. rhIGFBP-3 inhibited IGF-I-stimulated DNA synthesis in a dose-dependent manner, with a peak effect observed at 25 nM IGFBP-3. Because TGF-beta is highly expressed in cirrhotic liver tissue, we determined whether IGFBP-3 mRNA expression is increased in liver biopsies obtained from patients with an active fibroproliferative response due to viral-induced chronic active hepatitis. In the majority of these samples, IGFBP-3 mRNA was increased compared with normal controls. These findings indicate that human HSCs, in their activated phenotype, constitutively produce IGFBPs. IGF-I and TGF-beta differentially regulate IGFBP-3, IGFBP-4, and IGFBP-5 expression, which, in turn, may modulate the in vitro and in vivo action of IGF-I.

Expression of insulin‐like growth factor binding proteins in healing tendon lesions

“…This decrease is consistent with findings from previous binding protein studies in other tissues. 30,35 The changes in mRNA expression for IGFBP-5 and -6 may be correlated with decreased tissue levels of IGF-I; however, the changes occurred simultaneously rather than sequentially, suggesting the involvement of other cytokines. Addition of TGF-b1 to the culture medium decreased IGFBP-5 mRNA and protein expression in human hepatic stellate cells and IGFBP-6 expression in rat osteoblasts.…”

“…[23][24][25][26][27][28] These patterns vary according to individual tissue types and species. 29,30 Previous studies report that binding protein expression is upregulated in the synovial fluid of patients with rheumatoid arthritis and in osteoarthritic articular cartilage explants. 26,[31][32][33] From these reports, it is not unreasonable to assume that binding protein expression might also be upregulated in Figure 2.…”

IGF-I induces DNA synthesis and apoptosis in rat liver hepatic stellate cells (HSC) but DNA synthesis and proliferation in rat liver myofibroblasts (rMF)

“…[34][35][36][37][38][39][40][41] In most cases, however, enhanced DNA synthesis as measured by BrdU or 3 H-thymidine incorporation was taken to postulate the mitogenic effect of IGF-I. On the contrary, our data show that IGF-I Figure 4 Influence of IGF-I R and ERK1/2 receptor blockage on apoptosis of HSC (day 7) and rMF.…”

Transcriptional Profiling Reveals Novel Markers of Liver Fibrogenesis

“…A similar expression pattern of these IGFBPs has been reported for rat HSC (30). In activated human HSC, Gentilini et al (31) detected expression of IGFBP-1 through -6 using an RNase protection assay. These authors also reported excretion of IGFBP-2 through -6 to be differentially regulated by IGF-1 and TGF-␤.…”