COLLAGEN-SYNTHESIS BY HUMAN LIVER (MYO)FIBROBLASTS IN CULTURE - EVIDENCE FOR A REGULATORY ROLE OF IL-1-BETA, IL-4, TGF-BETA AND IFN-GAMMA

Background/Aims: Different cytokines have been described in fibrotic l ivers, including interleukin-1, interleukin-4 and interferon gamma, wh ich are capable of regulating collagen production in human skin and lu ng fibroblasts. Methods: To investigate possible involvement of interl eukin-1, interleukin-4 and interferon gamma in the regulation of colla gen production in human liver fibrosis, we studied the effects of thes e cytokines on collagen synthesis by nonparenchymal human liver cells in vitro. The effects of interleukin-1, interleukin-4 and interferon g amma were compared with the effect of transforming growth factor-beta, a web-known stimulator of collagen synthesis in liver fibrosis. Using a Percoll gradient we isolated two types of fibroblastlike cells from human liver tissue: fat-storing cells, which transformed in culture i nto myofibroblasts coexpressing vimentin and alpha-smooth muscle actin (VA-cells), and fibroblasts expressing vimentin only (V-cells). Produ ction of collagen was measured in confluent cell cultures by incorpora tion of H-3-proline into collagenase degradable proteins. Results: The cytokines studied had comparable effects on collagen synthesis in con fluent cultures of VA-cells obtained from three different human livers and in confluent cultures of V-cells. Interleukin-1 beta and interleu kin-4 enhanced collagen synthesis dose-dependently. 100 U/ml interleuk in-1 beta stimulated collagen synthesis up to 174+/-25% (mean+/-sd, VA -cells) and 140+/-7% (V-cells) of control values. 1000 U/ml interleuki n-4 enhanced collagen formation up to 195+/-58% (mean+/-sd, V-cells) a nd 153+/-4% (V-cells) of control values after 48 h. These values were comparable to the stimulatory effects induced by transforming growth f actor-beta (235+/-33% (mean+/-sd, VA-cells) and 150+/-18% of control v alues (V-cells) after incubation with 10 ng/ml transforming growth fac tor-beta for 48 h). Interferon gamma reduced both basal (36+/-29% (mea n+/-sd) of control values in VA-cells, and 59+/-9% in V-cells) and tra nsforming growth factor-beta induced collagen synthesis. Conclusions: These results indicate that in addition to the well-known role of tran sformed fat-storing cells (VA-cells) in collagen synthesis, fibroblast s CV-cells) may contribute to collagen production in human liver tissu e. Moreover, these data demonstrate that in addition to the extensivel y documented collagen-inducing mediator transforming growth factor-bet a, other cytokines present in fibrotic liver tissue like interleukin-1 beta and interleukin-4 may contribute to the enhanced synthesis of co llagen, whereas interferon gamma may reduce collagen formation during liver fibrosis in man.