Tumor necrosis factor alpha suppresses the induction of connective tissue growth factor by transforming growth factor-beta in normal and scleroderma fibroblasts

Connective tissue growth factor (CTGF) is over-expressed in a variety of fi brotic disorders, presumably secondary to the activation and production of transforming growth factor-p (TGF-P), a key inducer of fibroblast prolifera tion and matrix synthesis. The CTGF gene promoter has a TGF-P response elem ent that regulates its expression in fibroblasts but not epithelial cells o r lymphocytes. Recent studies have shown that the macrophage-produced cytok ine tumor necrosis factor alpha (TNF alpha) is necessary to promote inflamm ation and to induce genes, such as matrix metalloproteinases, involved with the early stages of wound healing, In this study, we examined the ability of TNF alpha to modulate CTGF gene expression. TNF alpha was found to suppr ess the TGF-beta-induced expression of CTGF protein in cultured normal fibr oblasts. The activity of TNF alpha was blocked by NF-kappa B inhibitors. We showed that sequences between -244 and -166 of the CTGF promoter were nece ssary for both TGF-beta and TNF alpha to modulate CTGF expression. There wa s a constitutive expression of CTGF by scleroderma fibroblasts that was inc reased by TGF-beta treatment, Although TNF alpha was able to repress TGF-be ta-induced CTGF and collagen synthesis both in normal and scleroderma skin fibroblasts, fibroblasts cultured from scleroderma patients were more resis tant to TNF alpha as TNF alpha was unable to suppress the basal level of CT GF expression in scleroderma fibroblasts, Thus, we suspect that the high le vel of constitutive CTGF expression in scleroderma fibroblasts and its inab ility to respond to negative regulatory cytokines may contribute to the exc essive scarring of skin and internal organs in patients with scleroderma.