TRANSFORMING GROWTH FACTOR-BETA-INDUCED COLLAGEN-SYNTHESIS BY HUMAN LIVER MYOFIBROBLASTS IS INHIBITED BY ALPHA(2)-MACROGLOBULIN

Background: Transforming growth factor-beta (TGF beta) plays a central role in the stimulation of matrix production during liver fibrosis. T he action of TGF beta in different systems has been shown to be influe nced by alpha(2)-macroglobulin (alpha(2)M), a serum protein with stron g protease-scavenging and cytokine-binding properties, Aims: In the pr esent study alpha(2)M derived from normal human plasma has been tested for its ability to modulate the TGF beta-induced collagen production by human liver fat-storing cells (FSC), which had transformed into alp ha-smooth muscle actin-expressing myofibroblasts in culture. Methods: alpha(2)M has been tested after activation with methylamine (alpha(2)M -Me), an in vitro equivalent of protease activated alpha(2)M. The bind ing of I-125-TGF beta 1 to activated forms of alpha(2)M was demonstrat ed by rate electrophoresis, Collagen synthesis was examined in human l iver myofibroblast cultures obtained from three different human livers by incorporation of H-3-proline into TCA-precipitable, specific colla genase degradable proteins, Uptake of alpha(2)M was studied by means o f immunofluorescence. Results: TGF beta (1 ng/ml) significantly stimul ated collagen synthesis of controls in the absence of TGF beta. alpha( 2)M-Me reduced this TGF beta-induced collagen synthesis dose-dependent ly, reaching significant inhibition from 10 mu g/ml alpha(2)M-Me onwar d. Upon addition of 100 mu g/ml alpha(2)M-Me the effect of TGF beta wa s reduced by 60% to 128 +/- 31% (mean +/- SD) of control values in the absence of TGF beta, Human liver myofibroblasts endocytosed alpha(2)M -Me added to the cultures as detected by immunofluorescence, According ly, reduction of TGF beta-activity by alpha(2)M-Me may be explained by receptor-mediated clearance of alpha(2)M-TGF beta complexes by the ce lls. Conclusions: TGF beta-induced collagen formation by human liver m yofibroblasts obtained from three different livers is reduced in vitro by activated alpha(2)M. From these results, we hypothesize that alpha (2)M may have an antifibrogenic effect in vivo by interference with TG F beta-induced matrix synthesis during liver fibrosis.