COSTIMULATION OF FIBROBLAST COLLAGEN AND TRANSFORMING GROWTH-FACTOR BETA(1) GENE-EXPRESSION BY MONOCYTE CHEMOATTRACTANT PROTEIN-1 VIA SPECIFIC RECEPTORS

Recent studies indicate potential roles of monocyte chemotactic protei n-1 (MCP-1) in recruitment of monocytes to sites of inflammation, Howe ver, their increased expression does not always correlate with monocyt e influx, suggesting other possible biological activities for this mem ber of the C-C chemokine family. In view of its potential role in regu lating extracellular matrix expression in fibrotic disorders, the effe cts of MCP-1 on lung fibroblast collagen expression were evaluated. Is olated rat lung fibroblasts were treated with increasing doses of MCP- 1 for variable periods of time and examined for effects on collagen sy nthesis and expression of procollagen alpha(1)(I) mRNA expression, The results show that MCP-1 was able to stimulate collagen expression in these cells in a dose-dependent manner but required over 24 h for sign ificant elevation to occur, In view of this delayed time course, the p ossibility of mediation via endogenous transforming growth factor beta (TGF beta) was tested by the ability of anti-TGF beta antibody to inh ibit this MCP-1 stimulation of collagen expression. Significant but in complete inhibition by this antibody was observed. Pretreatment of the cells with antisense but not by sense or missense TGF beta(1) oligode oxyribonucleotides caused essentially complete inhibition of this MCP- 1 stimulatory effect. Furthermore, MCP-1 treatment was found to also s timulate TGF beta secretion and mRNA expression, which was also abolis hed by pretreatment with antisense TGF beta(1) oligodeoxyribonucleotid es. The kinetics of TGF beta expression indicates that significant inc rease preceded that for collagen expression. Binding studies using I-1 25-labeled MCP-1 indicated the presence of specific and saturable bind ing sites with a dissociation constant consistent with the dose respon se curves for stimulation of fibroblast collagen synthesis and TGF bet a activity by MCP-1. These results taken together suggest that MCP-1 s timulates fibroblast collagen expression via specific receptors and en dogenous up-regulation of TGF beta expression. The latter then results in autocrine and/or juxtacrine stimulation of collagen gene expressio n.