Submitted on June 11, 2007
Accepted on November 12, 2007
Wnt antagonism inhibits hepatic stellate cell activation and liver fibrosis
Jason H. Cheng1, Hongyun She1, Yuan-Ping Han2, Jiaohong Wang3, Shigang Xiong1, Kinji Asahina1, and Hidekazu Tsukamoto1*
1 Pathology, Keck SOM of USC, Los Angeles, California, United States
2 Surgery and Pathology, Keck SOM of USC, Los Angeles, California, United States
3 Los Angeles, California, United States; Pathology, Keck SOM of USC, Los Angeles, California, United States
* To whom correspondence should be addressed. E-mail: htsukamo{at}usc.edu.
Background & Aims. Activation of hepatic stellate cells (HSC), a key event in liver fibrosis, is caused by diminished adipogenic transcription. This study investigated whether Wnt signaling contributes to "anti-adipogenic" activation of HSC and liver fibrogenesis. Methods. Culture-activated HSC from normal rats and HSC from cholestatic rat livers were examined for expression of Wnt, Fzizzled receptors (Fz), and co-receptors by quantitative PCR. Wnt signaling was assessed by nuclear 
-catenin and Tcf promoter activity. Dickkopf-1 (Dkk-1), a Wnt co-receptor antagonist was transduced by an adenoviral vector to assess the effects of Wnt antagonism on culture-activation of HSC and cholestatic liver fibrosis in mice. Results. Messenger RNA for canonical (Wnt3a and 10b) and non-canonical (Wnt4 and5a) Wnt genes, Fz-1 and 2, and co-receptors (LRP6 and Ryk) are increased 3~12 fold in culture-activated HSC compared to quiescent HSC. The nuclear -catenin level and Tcf DNA binding are markedly increased in activated HSC. Tcf promoter activity is stimulated with Wnt1 but inhibited by Chibby, a protein that blocks -catenin interaction with Tcf, and by Dkk-1. Dkk-1 enhances PPAR
-driven PPRE promoter activity, a key adipogenic transcriptional parameter, abrogates agonst-stimulated contraction, and restores HSC quiescence in culture. High expression of Dkk-1 increases apoptosis of cultured HSC. Expression of Wnt and Fz genes are also induced in HSC isolated from experimental cholestatic liver fibrosis, and Dkk-1 expression ameliorates this form of liver fibrosis in mice. Conclusion. These results demonstrate anti-adipogenic Wnt signaling in HSC activation and therapeutic potential of Wnt antagonism for liver fibrosis.
