The secretin receptor antagonist (SCT 5-27) reduces biliary hyperplasia and liver fibrosis in an animal model of primary sclerosing cholangitis

Secretin (SCT) is trophic and profibrotic hormone produced by the S cells of the duodenum as well as cholangiocytes. The SCT/secretin receptor (SR) axis stimulates biliary proliferation in normal and cholestatic mice following bile duct ligation (BDL). We have shown that SCT down-regulates the expression of the miRNAs, miR-125b and let-7a, which target the expression of VEGF-A and NGF, respectively, that are proliferative factors that stimulate biliary proliferation during cholestasis. The AIM of our study was to evaluate the effect of inhibition of the SCT/SR axis with Sec 5-27 on biliary proliferation and liver fibrosis in the Mdr2-/- mouse model of primary sclerosing cholangitis (PSC). PSC is a disease characterized by inflammation of cholangiocytes that leads to scar formation and duct obstruction with subsequent cirrhosis and liver failure. Methods: Our studies were performed in: (i) wild-type (WT) mice; and (ii) 12-wk old Mdr2-/- mice treated with saline or SCT 5-27 (10 μg/kg WT/day) by osmotic minipumps for 1 wk. Then, biliary proliferation and intrahepatic bile duct mass (IBDM) were evaluated by immunohistochemistry for PCNA and CK-19, respectively. Liver fibrosis was determined by: (i) Sirius red staining in liver sections; and (ii) qPCR for the profibrotic markers collagen 1, fibronectin, TGFβ1, alpha-SMA, MMP2, MMP9, TIMP- 1, TIMP-2 in total liver and purified cholangiocytes from the in vivo treatment groups. The expression levels of miR-125b, let-7a, VEGF-A and NGF in total liver and cholangiocytes were evaluated by qPCR. The serum levels of transaminases were evaluated. Serum and cholangiocyte supernatant levels of TGFβ1 (a key factor for the activation of hepatic stellate cells) were evaluated by ELISA. Results: In Mdr2-/- mice there enhanced biliary proliferation, IBDM and liver fibrosis compared to WT mice. There was a significant reduction in biliary proliferation, IBDM, liver fibrosis and mRNA expression of the aforementioned profibrotic markers in Mdr2-/- mice that were treated with SCT 5-27 compared to saline-treated Mdr2-/- mice. There was a significant reduction in the levels of serum transaminases as well as serum and cholangiocyte supernatant levels of TGFβ1 in Mdr2-/- mice treated with SCT 5-27 compared to controls. We also observed a significant increase in miR- 125b and let-7a in the Mdr2-/- mice treated with SCT 5-27 compared to control mice, which corresponded to decreased mRNA expression of the biliary proliferative factors VEGF-A and NGF. Conclusion: Inhibition of the SCT/SR axis with the SR antagonist may represent a novel therapeutic approach for modulating biliary proliferation and liver fibrosis during cholestasis.