Differential effects of transforming growth factor-beta1, a fibrogenic factor, on macrophage-like cells (HS-P) and myofibroblastic cells (MT-9) in vitro.

Transforming growth factor-beta1 (TGF-beta1) produced by infiltrating macrophages plays a role in fibrotic disorders through the induction of myofibroblasts. To explore possible mechanisms by which TGF-beta1 may act in this context, we investigated effects of TGF-beta1 on macrophage-like (HS-P) and myofibroblastic (MT-9) cells, two novel cell lines developed by us. Immunocytochemically, the addition of TGF-beta1 (0, 0.1, 0.5, and 1.0 ng/ml) dose-dependently suppressed the expressions of antigens recognized by macrophage/histiocyte-specific antibodies (ED1 and ED2) in HS-P cells, whereas the addition concomitantly increased the number of anti-alpha-smooth muscle actin antibody-positive myofibroblastic cells, suggesting a possible phenotypical modulation of macrophages into myofibroblasts in the fibrotic lesions. By contrast, MT-9 cells did not show such immunophenotypical changes following TGF-beta1 addition. DNA synthesis, measured by tritiated thymidine-incorporation, was inhibited in a dose-dependent manner in MT-9 cells by TGF-beta1 addition (0, 0.1, 0.2, 0.5, 1.0, 5, and 10 ng/ml), but that in HS-P cells was unchanged. Northern blot analysis revealed that expressions of cell cycle-related early genes, c-jun and c-myc, were increased in HS-P cells after TGF-beta1 (1 ng/ml) addition, with c-jun showing peak expression prior to c-myc. By contrast, the peak expressions of c-jun and c-myc were delayed in TGF-beta1 (1 ng/ml)-added MT-9 cells, and their levels were less in MT-9 cells than in HS-P cells. Furthermore, TGF-beta1 (1 and 10 ng/ml) induced DNA laddering in MT-9 cells, but did not in HS-P cells. Based on these findings, it was speculated that TGF-beta1 could have induced G1 arrest in cell cycle and apoptosis in MT-9 cells. The present study showed that there were significant differences in the effects of TGF-beta1 between macrophage-like HS-P cells and myofibroblastic MT-9 cells, presumably depending on divergent susceptibilities to TGF-beta1 between both cell types. Because such cell types are key cells in the fibrogenesis, HS-P and MT-9 might be useful models for investigating the pathogenesis of fibrosis in vitro.