Connective tissue growth factor (CTGF) is one of the candidate factors mediating downstream events of
transforming growth factor-beta (
TGF-beta), but its role in fibrogenic properties of
TGF-beta and in tubulointerstitial
fibrosis has not yet been clarified. Using unilateral
ureteral obstruction (UUO) in rats, we analyzed gene expression of
TGF-beta1, CTGF, and
fibronectin. We further investigated the effect of blockade of endogenous CTGF on
TGF-beta-induced
fibronectin expression in cultured rat renal fibroblasts by antisense
oligodeoxynucleotide (ODN) treatment. After UUO, CTGF
mRNA expression in the obstructed kidney was significantly upregulated subsequent to
TGF-beta1, followed by marked induction of
fibronectin mRNA. By in situ hybridization, CTGF
mRNA was detected mainly in the interstitial fibrotic areas and tubular epithelial cells as well as in parietal glomerular epithelial cells in the obstructed kidney. The interstitial cells expressing CTGF
mRNA were also positive for alpha-smooth muscle actin. CTGF antisense ODN transfected into cultured renal fibroblasts significantly attenuated
TGF-beta-stimulated upregulation of
fibronectin mRNA and
protein compared with control ODN transfection, together with inhibited synthesis of
type I collagen. With the use of a reporter assay, rat
fibronectin promoter activity was increased by 2.5-fold with stimulation by
TGF-beta1, and this increase was abolished with antisense CTGF treatment. Thus CTGF plays a crucial role in
fibronectin synthesis induced by
TGF-beta, suggesting that CTGF blockade could be a possible therapeutic target against tubulointerstitial
fibrosis.