REGULATION OF HUMAN LUNG FIBROBLAST C1Q-RECEPTORS BY TRANSFORMING GROWTH FACTOR-beta AND TUMOR NECROSIS FACTOR-alpha

Abstract

Transforming growth factor -beta (TGF -beta) and tumor necrosis factor -alpha (TNF -alpha) are two polypeptide mediators which are believed to play a role in the evolution of idiopathic pulmonary fibrosis (IPF) . We have evaluated the effect of these two substances on the expression of receptors for collagen (cC1q - R) and globular (gC1q - R) domains of C1q and on type I collagen in human lung fibroblasts. Two fibroblast subpopulations differing in C1q receptor expression were obtained by culturing human lung explants in medium containing fresh human serum and heated plasma - derived serum and separating them based on C1q binding [Narayanan, Lurton and Raghu: Am J Resp Cell Mol Biol. 1998;17:84]. The cells, referred to as HH and NL cells, respectively, were exposed to TGF -beta and TNF -alpha in serum - free conditions. The levels of mRNA were assessed by in situ hybridization and Northern analysis, and protein levels compared after SDS - polyacrylamide gel electrophoresis and Western blotting. NL cells exposed to TGF -beta and TNF -alpha contained 1. 4 and 1. 6 times as much cC1q - R mRNA, respectively, whereas in HH cells cC1q - R mRNA increased 2. 0 - and 2. 4 - fold. The gC1q - R mRNA levels increased to a lesser extent in both cells. These increases were not reflected in protein levels of CC1q - R and gC1q - R, which were similar to or less than controls. Both TGF -beta and TNF -alpha also increased procollagen [I] mRNA levels in both cells. Overall, TNF -alpha caused a greater increase and the degree of response by HH fibroblasts to both TGF -beta and TNF -alpha was higher than NL cells. These results indicated that TGF -beta and TNF -alpha upregulate the mRNA levels for cC1q - R and collagen and that they do not affect gC1q - R mRNA levels significantly. They also indicated different subsets of human lung fibroblasts respond differently to inflammatory mediators.