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Characterization of the IGF axis components in isolated rat hepatic stellate cells
Author(s) -
Scharf JensGerd,
Knittel Thomas,
Dombrowski Frank,
Müller Lars,
Saile Bernhard,
Braulke Thomas,
Hartmann Heinz,
Ramadori Giuliano
Publication year - 1998
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.510270513
Subject(s) - hepatic stellate cell , characterization (materials science) , chemistry , medicine , physics , optics
Abstract The insulin‐like growth factors I and II (IGF‐I, ‐II) are circulating peptides known to participate in the regulation of metabolism, growth, and cellular differentiation. In the present study, “early cultured” (days 2‐3 of culture) and “culture‐activated” (days 6‐7 of culture) rat hepatic stellate cells (HSCs) were analyzed for expression of individual components of the IGF axis. Northern blot analysis of IGF‐I messenger RNA (mRNA) revealed transcripts of 7.5, 4, 2, and 1.0 to 1.5 kb in culture‐activated HSCs, while early cultured HSCs did not express IGF‐I mRNA. In culture‐activated HSCs, an IGF‐I secretion of 8.3 ± 2.5 ng/10 6 cells per 24 hours was determined radioimmunologically. In media from early cultured HSCs, IGF‐I was not detectable. The IGF‐I receptor (IGF‐I‐R) mRNA expression was threefold higher in early cultured HSCs than in culture‐activated HSCs. By immunohistochemistry, a decrease of IGF‐I‐R expression of HSCs in vivo following CCl 4 ‐induced liver damage was noted as well. IGF binding proteins (IGFBPs) were detected in conditioned media from HSCs by 125 I–IGF‐I ligand blotting at apparent molecular masses of 24 and 41 to 45 kd that were immunologically identified as IGFBP‐4 and ‐3, respectively. Synthesis of these IGFBPs increased with time of culture. At neutral pH, no IGFBP proteolysis was observed in conditioned media of early cultured and culture‐activated HSCs, whereas at acidic pH, protease activities against IGFBP‐3 and ‐4 were detectable. IGFBP protease activities were completely abolished by inhibitors of aspartyl and cysteine proteases. Addition of 100 nmol/L IGF‐I stimulated cell proliferation of early cultured HSCs 5.6 ± 1.1‐ and 4.6 ± 0.2‐fold as measured by [ 3 H]thymidine and 5‐bromo‐2′‐deoxyuridine incorporation, respectively. In culture‐activated HSCs, proliferation was increased 1.2 ± 0.1‐fold in the presence of 100 nmol/L IGF‐I in both proliferation assays. It can be concluded that due to a higher expression of the IGF‐I‐R and lower levels of IGFBPs, early cultured HSCs are more susceptible to the mitogenic actions of IGFs than the culture‐activated HSCs. The present data suggest a role for the IGF axis components in the initiation rather than the perpetuation of HSC proliferation during hepatic fibrogenesis