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 protein-1 (MCP-1) in recruitment of monocytes to sites of inflammation, However, their increased expression does not always correlate with monocyte influx, suggesting other possible biological activities for this member of the C-C chemokine family. In view of its potential role in regulating extracellular matrix expression in fibrotic disorders, the effects of MCP-1 on lung fibroblast collagen expression were evaluated. Isolated rat lung fibroblasts were treated with increasing doses of MCP-1 for variable periods of time and examined for effects on collagen synthesis 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 significant elevation to occur, In view of this delayed time course, the possibility of mediation via endogenous transforming growth factor beta (TGF beta) was tested by the ability of anti-TGF beta antibody to inhibit this MCP-1 stimulation of collagen expression. Significant but incomplete inhibition by this antibody was observed. Pretreatment of the cells with antisense but not by sense or missense TGF beta(1) oligodeoxyribonucleotides caused essentially complete inhibition of this MCP-1 stimulatory effect. Furthermore, MCP-1 treatment was found to also stimulate TGF beta secretion and mRNA expression, which was also abolished by pretreatment with antisense TGF beta(1) oligodeoxyribonucleotides. The kinetics of TGF beta expression indicates that significant increase preceded that for collagen expression. Binding studies using I-125-labeled MCP-1 indicated the presence of specific and saturable binding sites with a dissociation constant consistent with the dose response curves for stimulation of fibroblast collagen synthesis and TGF beta activity by MCP-1. These results taken together suggest that MCP-1 stimulates fibroblast collagen expression via specific receptors and endogenous up-regulation of TGF beta expression. The latter then results in autocrine and/or juxtacrine stimulation of collagen gene expression.