Secretin Treatment Promotes Hepatic Progenitor Cell Activation, Ductal‐Canalicular Junction Formation and Amelioration of Liver Damage in a Model of Late‐Stage Primary Biliary Cholangitis

Abstract

Introduction PBC is a cholestatic disease characterized by bile duct loss, ductular reaction and liver fibrosis. The canals of Hering (CoH) are the site of ductulo-canalicular junction (DCJ) that maintain proper bile drainage from the liver, and contain the hepatic progenitor cell (HPC) population. CoH loss is noted in PBC and correlates with scoring. Secretin binds to its receptor (SR, expressed by large cholangiocytes) to promote biliary proliferation during cholestasis; however, during large duct damage, small cholangiocytes acquire large cholangiocyte phenotypes including SR expression. Secretin/SR expression is downregulated in late-stage PBC; therefore, we aimed to understand the role of the secretin/SR axis during PBC. We hypothesized that secretin treatment restores DCJ through HPC activation and ameliorates liver phenotypes associated with late-stage PBC. Methods Female 34 wk old wild-type (WT) and dominant-negative transforming growth factor-β receptor II (dnTGFβRII, model of late-stage PBC) mice were treated with control or secretin (2.5 nmol/kg BW) for 8 wk by IP implanted minipumps. Cholangitis activity, hepatitis activity and bile duct loss were determined by the Nakanuma scoring system. Ductular reaction was measured by semi-quantitative CK-19 immunostaining. Liver fibrosis was evaluated by Sirius Red staining, collagen-1a immunostaining and qPCR for α-SMA. Hepatic stellate cell (HSC) presence was determined by desmin immunostaining. Cholestasis was indicated by hepatic total bile acid (TBA) levels using EIA. DCJ presence was evaluated by co-immunostaining for ABC transporter bile salt export pump (BSEP)/CK-19 and semi-quantification. HPC activation was assessed by Sox9 staining and semi-quantification. Results dnTGFβRII mice had an increase in cholangitis and hepatitis activity; however, 8 wks of secretin treatment significantly reduces cholangitis, but not hepatitis, activity. dnTGFβRII mice present with ductular reaction and significant bile duct loss, which was reversed with 8 wks secretin treatment. Hepatic TBA levels, liver fibrosis and HSC presence are increased in dnTGFβRII mice, but significantly reduced following 8 wks of secretin treatment. In line with human studies, dnTGFβRII mice have significant loss of DCJ and reduced HPC number; however, 8 wks of secretin treatment restores these parameters. Conclusion Long-term secretin treatment (i) reduces ductular reaction, (ii) reverses bile duct loss, (iii) decreases liver fibrosis, (iv) promotes HPC activity and (v) restores DCJ presence in a model of late-stage PBC. Secretin maintenance of the DCJ may be due to (i) the restoration of bile flow and release of toxic bile acids or (ii) secretin binding to SR acquired on small cholangiocytes/HPCs. Treatment with secretin may be a therapeutic option for late-stage PBC patients.