Enhanced matrix degradation after withdrawal of TGF-beta1 triggers hepatocytes from apoptosis to proliferation and regeneration

• Published in: Cell proliferation 2005-10, Vol.38 (5), p.287-299
• Main Authors: Arendt, E, Ueberham, U, Bittner, R, Gebhardt, R, Ueberham, E
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis - drug effects; Apoptosis - physiology; Cell Proliferation - drug effects; Collagenases - genetics; Collagenases - metabolism; Disease Models, Animal; Extracellular Matrix - metabolism; Gene Expression Regulation, Enzymologic; Hepatocytes - drug effects; Hepatocytes - metabolism; Hepatocytes - ultrastructure; Immunohistochemistry; Liver - metabolism; Liver - ultrastructure; Liver Cirrhosis - genetics; Liver Cirrhosis - metabolism; Liver Cirrhosis - pathology; Matrix Metalloproteinase 13; Matrix Metalloproteinase 2 - genetics; Matrix Metalloproteinase 2 - metabolism; Mice; Mice, Inbred C57BL; Mice, Inbred DBA; Mice, Transgenic; Regeneration - drug effects; Regeneration - physiology; RNA, Messenger - genetics; Tissue Inhibitor of Metalloproteinase-1 - genetics; Tissue Inhibitor of Metalloproteinase-1 - metabolism; Transforming Growth Factor beta - genetics; Transforming Growth Factor beta - metabolism; Transforming Growth Factor beta - pharmacology; Transforming Growth Factor beta1
• ISSN: 0960-7722

TGF-beta1 is a profibrogenic cytokine participating in deposition of extracellular matrix in fibrotic disorders. In liver, its anti-proliferative/apoptotic effect on hepatocytes promotes fibrosis. The tetracycline-controlled double-transgenic TA(LAP-2)/p(tet)TGF-beta1 mouse provides a model for reversible liver fibrosis. In livers of TGF-beta1-expressing mice, hepatocytes showed synchronous apoptosis detected by DNA laddering and active caspase-3 staining that disappeared when expression of transgenic TGF-beta1 was switched off. In these 'off' mice, perisinusoidal liver fibrosis resolved within 21 days accompanied by elevated proliferation of hepatocytes. Here, we have specified the intermediary stages (2-3 days off and 6 days off) in terms of (i) proliferation (by immunohistochemical staining of proliferating cell nuclear antigen and expression of cyclin D1 mRNA) and (ii) extracellular matrix remodelling processes (by measuring mRNA expression of matrix metalloproteinases-2 and -13 (mmp-2 and mmp-13) and tissue inhibitor of matrix metalloproteinases 1 (timp-1) and quantitative morphometric analysis. In summary, we show a rapidly declining timp-1 mRNA level together with lastingly high mmp-2 and mmp-13 mRNA levels after 2-3 days, suggesting that high matrix-degrading potential represents a prerequisite for the markedly enhanced proliferation of hepatocytes in the early stages after switching off transgenic TGF-beta1.