OBJECTIVETo investigate the effects of small interfering RNA targeting connective tissue growth factor (CTGF) on rat transforming growth factor beta (TGF beta)/Smads signal pathway.

METHODSChemically synthetic siRNA targeting CTGF was transfected into HSC T6 and then they were injected into rat livers through their intraportal veins. At the same time these rats also received CCl4 subcutaneously every three days for 6 consecutive weeks. Untreated HSC T6 or/and rats with random siRNA treatment served as controls. Total RNA or/and protein in HSC T6 and rat hepatic tissues were extracted. The expressions of CTGF and TGF beta 1, Smad2, 3 and 7 genes were detected by reverse transcription-polymerase chain reaction (RT-PCR) and/or Western blot.

RESULTSCTGF siRNA significantly reduced the expression of CTGF protein in HSC T6. At 48 h after CTGF siRNA treatment, the down-regulation of CTGF protein was the most significant, up to 94%+/-4% (t=46.196, P less than 0.01), but the expressions of TGF beta 1, Smad2, 3 and 7 mRNA showed no differences in HSC T6 compared with the blank controls. Six weeks after CCl4 injections, prominent up-regulations were observed in the gene expressions of CTGF and TGF beta 1 in saline control or siRNA-treated rat livers. Administering CTGF siRNA for six weeks markedly attenuated the induction of CTGF and TGF beta 1 genes; the expressions of CTGF and TGF beta 1 protein decreased by 95%+/-2% (F=21.234, P less than 0.01) and 74%+/-8% (F=13.464, P less than 0.05), respectively, whereas Smad2, 7 protein expressions were not affected.

CONCLUSIONSilencing the CTGF gene can suppress the TGF beta /Smads signal pathway in rat livers.