Connective tissue growth factor mediates transforming growth factor β‐induced collagen synthesis: down‐regulation by cAMP

Abstract

Connective tissue growth factor (CTGF) is a cysteine‐rich peptide synthesized and secreted by fibroblastic cells after activation with transforming growth factor beta (TGF‐β) that acts as a downstream mediator of TGF‐β‐induced fibroblast proliferation. We performed in vitro and in vivo studies to determine whether CTGF is also essential for TGF‐β‐induced fibroblast collagen synthesis. In vitro studies with normal rat kidney (NRK) fibroblasts demonstrated CTGF potently induces collagen synthesis and transfection with an antisense CTGF gene blocked TGF‐β stimulated collagen synthesis. Moreover, TGF‐β‐induced collagen synthesis in both NRK and human foreskin fibroblasts was effectively blocked with specific anti‐CTGF antibodies and by suppressing TGF‐β‐induced CTGF gene expression by elevating intracellular cAMP levels with either membrane‐permeable 8‐Br‐cAMP or an adenylyl cyclase activator, cholera toxin (CTX). cAMP also inhibited collagen synthesis induced by CTGF itself, in contrast to its previously reported lack of effect on CTGF‐induced DNA synthesis. In animal assays, CTX injected intradermally in transgenic mice suppressed TGF‐β activation of a human CTGF promoter/lacZ reporter transgene. Both 8‐Br‐cAMP and CTX blocked TGF‐β‐induced collagen deposition in a wound chamber model of fibrosis in rats. CTX also reduced dermal granulation tissue fibroblast population increases induced by TGF‐β in neonatal mice, but not increases induced by CTGF or TGF‐β combined with CTGF. Our data indicate that CTGF mediates TGF‐β‐induced fibroblast collagen synthesis and that in vivo blockade of CTGF synthesis or action reduces TGF‐β‐induced granulation tissue formation by inhibiting both collagen synthesis and fibroblast accumulation.—Duncan, M. R., Frazier, K. S. Abramson, S., Williams, S., Klapper, H., Huang, X., Grotendorst, G. R. Connective tissue growth factor mediates transforming growth factor β‐induced collagen synthesis: down‐regulation by cAMP. FASEB J . 13, 1774–1786 (1999)