Role of Connective Tissue Growth Factor in Oval Cell Response During Liver Regeneration After 2-AAF/PHx in Rats

Abstract

Recruitment and proliferation of Thy-1+ oval cells is a hallmark of liver regeneration after 2-acetylaminofluorene (2-AAF)/partial hepatectomy (PHx) in rats. To understand the molecular mechanism underlying this process, we investigated the role of connective tissue growth factor (CTGF), one of the candidate genes differentially expressed in Thy-1+ oval cells, in this liver injury model. Northern and Western analyses were performed to examine the induction of CTGF in total liver homogenate. Quantitative real-time polymerase chain reaction (PCR), immunofluorescent staining, and in situ hybridization were performed to confirm the expression and localization of CTGF in Thy-1+ oval cells. Finally, a known inhibitor of CTGF synthesis, Iloprost, was administered to 2-AAF/PHx treated rats to investigate the effect of Iloprost on oval cell response. CTGF was found to be up-regulated at both the RNA and protein levels and occurred concurrently with an up-regulation of transforming growth factor beta1 (TGF-beta1). Sorted Thy-1+ oval cells expressed a high level of CTGF gene in a quantitative PCR assay. Colocalization of Thy-1 antigen and ctgf signals by in situ hybridization further confirmed that Thy-1+ oval cells were a source of CTGF. Iloprost administration blocked CTGF induction in treated animals but did not affect TGF-beta1 expression. The inhibition of CTGF induction by Iloprost was associated with a significant decrease in oval cell proliferation and a lower level of alpha-fetoprotein expression as compared with control animals. These results show that CTGF induction is important for robust oval cell response after 2-AAF/PHx treatment in rats.