Variation of immunocytochemical expression of transforming growth factor (TGF)-β in hepatocytes in culture and liver slices

Abstract.

Transforming growth factor beta (TGF-β) is a major member of a cytokine family with pluripotent biological activity. In the liver, TGF-β has pathophysiological significance with respect to hepatic fibrogenesis, regulation of liver cell growth, tumor development, and induction of hepatocellular apoptosis. We show that the expression of immunocytochemically detectable TGF-β in cultured hepatocytes is strongly dependent on culture conditions and cellular microenvironment. Hepatocytes in situ and freshly isolated cells are TGF-β negative. In contrast, hepatocytes in incubated liver slices are stained with a patch-like pattern, whereas parenchymal cells cultured as a monolayer exhibit strong diffuse positive immunostaining for TGF-β within 2 h after seeding. The intensity of immunocytochemical staining is dependent on culture substrata, major expression being observed in cells maintained on glass or plastic surfaces. When collagen type-I and type-IV, or EHS-matrix are used as substrata, TGF-β is absent or only weakly immunocytochemically apparent in cultured hepatocytes, irrespective of the culture medium used. The positive immunocytochemical expression of TGF-β in hepatocytes arises neither by transcriptional and translational pathways nor by disturbed intracellular calcium homeostasis. However, calcium-dependent proteinases, such as calpain-I and -II, might be involved in the immunochemical presentation of intracellular TGF-β, because respective calpain inhibitors strongly reduce the appearance of TGF-β in cultured parenchymal liver cells. Thus, hepatocytes are a major cellular source of (latent) TGF-β in liver, as becomes evident during culture.