Inhibition of Rat Hepatic Lipocyte Activation in Culture by Interferon–γ

Abstract

Hepatic lipocytes (perisinusoidal, Ito cells) are the primary matrix–producing cells in liver fibrosis. During liver injury they undergo activation, a process characterized by cell proliferation and increased fibrogenesis. We and others have established a culture model in which in vivo features of lipocyte activation can be mimicked by cells grown on plastic. Additionally, we recently showed that activation is associated with new expression of smooth muscle-specific α–actin both in vivo and in culture. Although interferon–γ is known to inhibit collagen production in some systems, its action as a general modulator of lipocyte activation has not been examined; this issue forms the basis for our study. In culture–activated lipocytes, interferon–γ (1,000 U/ml) significantly inhibited lipocyte proliferation as assessed by [³H]thymidine incorporation assay and nuclear autoradiography. In time–course studies of activation, it also markedly reduced expression of smooth muscle-specific α–actin and its messenger RNA. In dose–response experiments, maximal inhibitory effects on smooth muscle-specific α–actin mRNA gene expression were achieved with as little as 10 U interferon–γ/ml. Inhibition of cellular activation was reversible; after interferon–γ withdrawal, messenger RNA levels of smooth muscle-specific α–actin returned to untreated control levels. The effect of interferon–γ extended to extracellular matrix gene expression, with reduction of type I collagen, type IV collagen and total fibronectin messenger RNAs to 3%, 24% and 15% of untreated control levels, respectively. In contrast to the marked effects on smooth muscle–specific α–actin and extracellular matrix gene expression, interferon–γ reduced total protein synthesis by only 17.7%. Moreover, maximal doses of interferon–γ had no effect on cell viability as determined by exclusion of propidium iodide. In summary, interferon–γ is a potent inhibitor of lipocyte activation and may prove useful in the treatment of fibrotic liver injury. (Hepatology 1992;16:776-784.)