Transforming growth factor-β-induced collagen synthesis by human liver myofibroblasts is inhibited by α2-macroglobulin

Background: Transforming growth factor-β (TGFβ) plays a central role in the stimulation of matrix production during liver fibrosis. The action of TGFβ in different systems has been shown to be influenced by α2-macroglubulin (α2M), a serum protein with strong protease-scavenging and cytokine-binding properties. Aims: In the present study, α2M derived from normal human plasma has been tested for its ability to modulate the TGFβ-induced collagen production by human liver fat-storing cells (FSC), which had transformed into α-smooth muscle actin-expressing myofibroblasts in culture. Methods: α2M has been tested after activation with methylamine (α2M-Me), an in vitro equivalent of protease activated α2M. The binding of 125I-TGFβ1 to activated forms of α2M was demonstrated by rate electrophoresis. Collagen synthesis was examined in human liver myofibroblast cultures obtained from three different human livers by incorporation of 3H-proline into TCA-precipitable, specific collagenase degradable proteins. Uptake of α2M was studied by means of immunofluorescence. Results: TGFβ (1 ng/ml) significantly stimulated collagen synthesis of controls in the absence of TGFβ. α2M-Me reduced this TGFβ-induced collagen synthesis dose-dependently, reaching significant inhibition from 10 μg/ml α2M-Me onward. Upon addition of 100 μg/ml α2M-Me the effect of TGFβ was reduced by 60% to 128±31% (mean±SD) of control values in the absence of TGFβ. Human liver myofibroblasts endocytosed α2M-Me added to the cultures as detected by immunofluorescence. Accordingly, reduction of TGFβ-activity by α2M-Me may be explained by receptor-mediated clearance of α2M-TGFβ complexes by the cells. Conclusions: TGFβ-induced collagen formation by human liver myofibroblasts obtained from three different livers is reduced in vitro by activated α2M. From these results, we hypothesize that α2M may have an antifibrogenic effect in vivo by interference with TGFβ-induced matrix synthesis during liver fibrosis.