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 livers, including interleukin-1, interleukin-4 and interferon gamma, which are capable of regulating collagen production in human skin and lung fibroblasts.

METHODS

To investigate possible involvement of interleukin-1, interleukin-4 and interferon gamma in the regulation of collagen production in human liver fibrosis, we studied the effects of these cytokines on collagen synthesis by nonparenchymal human liver cells in vitro. The effects of interleukin-1, interleukin-4 and interferon gamma were compared with the effect of transforming growth factor-beta, a well-known stimulator of collagen synthesis in liver fibrosis. Using a Percoll gradient we isolated two types of fibroblast-like cells from human liver tissue: fat-storing cells, which transformed in culture into myofibroblasts co-expressing vimentin and alpha-smooth muscle actin (VA-cells), and fibroblasts expressing vimentin only (V-cells). Production of collagen was measured in confluent cell cultures by incorporation of 3H-proline into collagenase degradable proteins.

RESULTS

The cytokines studied had comparable effects on collagen synthesis in confluent cultures of VA-cells obtained from three different human livers and in confluent cultures of V-cells. Interleukin-1 beta and interleukin-4 enhanced collagen synthesis dose-dependently. 100 U/ml interleukin-1 beta stimulated collagen synthesis up to 174 +/- 25% (mean +/- sd, VA-cells) and 140 +/- 7% (V-cells) of control values. 1000 U/ml interleukin-4 enhanced collagen formation up to 195 +/- 58% (mean +/- sd, VA-cells) and 153 +/- 4% (V-cells) of control values after 48 h. These values were comparable to the stimulatory effects induced by transforming growth factor-beta (235 +/- 33% (mean +/- sd, VA-cells) and 150 +/- 18% of control values (V-cells) after incubation with 10 ng/ml transforming growth factor-beta for 48 h). Interferon gamma reduced both basal (36 +/- 29% (mean +/- sd) of control values in VA-cells, and 59 +/- 9% in V-cells) and transforming growth factor-beta induced collagen synthesis.

CONCLUSIONS

These results indicate that in addition to the well-known role of transformed fat-storing cells (VA-cells) in collagen synthesis, fibroblasts (V-cells) may contribute to collagen production in human liver tissue. Moreover, these data demonstrate that in addition to the extensively documented collagen-inducing mediator transforming growth factor-beta, other cytokines present in fibrotic liver tissue like interleukin-1 beta and interleukin-4 may contribute to the enhanced synthesis of collagen, whereas interferon gamma may reduce collagen formation during liver fibrosis in man.