Ambc. Tiggelman et al., TRANSFORMING GROWTH FACTOR-BETA-INDUCED COLLAGEN-SYNTHESIS BY HUMAN LIVER MYOFIBROBLASTS IS INHIBITED BY ALPHA(2)-MACROGLOBULIN, Journal of hepatology, 26(6), 1997, pp. 1220-1228
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.