Activation of Slit2-Robo1 signaling promotes liver fibrosis

Background & Aims: The secretory protein Slit2 and its receptor Robo1 are believed to regulate cell growth and migration. Here, we aimed to determine whether Slit2-Robo1 signaling mediates the pathogenesis of liver fibrosis. Methods: Serum levels of Slit2 in patients with liver fibrosis were determined by ELISA. Liver fibrosis was induced in wild-type (WT), Slit2 transgenic (Slit2-Tg) and Robo1(+/-)Robo2(+/-) double heterozygotes (Robo1/2(+/-)) mice by carbon tetrachloride (CCl4). The functional contributions of Slit2-Robo1 signaling in liver fibrosis and activation of hepatic stellate cells (HSCs) were investigated using primary mouse HSCs and human HSC cell line LX-2. Results: Significantly increased serum Slit2 levels and hepatic expression of Slit2 and Robo1 were observed in patients with liver fibrosis. Compared to WT mice, Slit2-Tg mice were much more vulnerable to CCl4-induced liver injury and more readily develop liver fibrosis. Development of hepatic fibrosis in Slit2-Tg mice was associated with a stronger hepatic expression of collagen I and a-smooth muscle actin (alpha-SMA). However, liver injury and hepatic expression of collagen I and alpha-SMA were attenuated in CCl4-treated Robo1/2(+/-) mice in response to CCl4 exposure. In vitro, Robo1 neutralizing antibody R5 and Robo1 siRNA downregulated phosphorylation of Smad2, Smad3, PI3K, and AKT in HSCs independent of TGF-beta 1. R5 and Robo1 siRNA also inhibited the expression of a-SMA by HSCs. Finally, the protective effect of R5 on the CCl4-induced liver injury and fibrosis was further verified in mice. Conclusions: Slit2-Robo1 signaling promotes liver injury and fibrosis through activation of HSCs. (C) 2015 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.