Reticulon 4B (Nogo‐B) is a novel regulator of hepatic fibrosis

Nogo‐B, also known as Reticulon 4B, plays important roles in vascular injuries. Its function in the liver is not understood. The aim of this study was to characterize Nogo‐B in liver fibrosis and cirrhosis. Nogo‐B distribution was assessed in normal and cirrhotic human liver sections. We also determined the levels of liver fibrosis in wild‐type (WT) and Nogo‐A/B knockout (NGB KO) mice after sham operation or bile duct ligation (BDL). To investigate the mechanisms of Nogo‐B's involvement in fibrosis, hepatic stellate cells were isolated from WT and NGB KO mice and transformed into myofibroblasts. Portal pressure was measured to test whether Nogo‐B gene deletion could ameliorate portal hypertension. In normal livers, Nogo‐B expression was found in nonparenchymal cells, whereas its expression in hepatocytes was minimal. Nogo‐B staining was significantly elevated in cirrhotic livers. Fibrosis was significantly increased in WT mice 4 weeks after BDL compared with NGB KO mice. The absence of Nogo‐B significantly reduced phosphorylation of Smad2 levels upon transforming growth factor β (TGF‐β) stimulation. Reconstitution of the Nogo‐B gene into NGB KO fibroblasts restored Smad2 phosphorylation. Four weeks after BDL, portal pressure was significantly increased in WT mice by 47%, compared with sham‐operated controls (P = 0.03), whereas such an increase in portal pressure was not observed in NGB KO mice (P = NS). Conclusion: Nogo‐B regulates liver fibrosis, at least in part, by facilitating the TGFβ/Smad2 signaling pathway in myofibroblasts. Because absence of Nogo‐B ameliorates liver fibrosis and portal hypertension, Nogo‐B blockade may be a potential therapeutic target in fibrosis/cirrhosis. (HEPATOLOGY 2011;)