Modulation of the Unfolded Protein Response by Tauroursodeoxycholic Acid Counteracts Apoptotic Cell Death and Fibrosis in a Mouse Model for Secondary Biliary Liver Fibrosis.

Annelies Paridaens,Sarah Raevens,Leo Van Grunsven,Isabelle Colle,Hans Van Vlierberghe,Anja Geerts,Eliene Bogaerts,Lindsey Devisscher,Anne Hoorens,Xavier Verhelst

doi:10.3390/ijms18010214

Abstract

The role of endoplasmic reticulum stress and the unfolded protein response (UPR) in cholestatic liver disease and fibrosis is not fully unraveled. Tauroursodeoxycholic acid (TUDCA), a hydrophilic bile acid, has been shown to reduce endoplasmic reticulum (ER) stress and counteract apoptosis in different pathologies. We aimed to investigate the therapeutic potential of TUDCA in experimental secondary biliary liver fibrosis in mice, induced by common bile duct ligation. The kinetics of the hepatic UPR and apoptosis during the development of biliary fibrosis was studied by measuring markers at six different timepoints post-surgery by qPCR and Western blot. Next, we investigated the therapeutic potential of TUDCA, 10 mg/kg/day in drinking water, on liver damage (AST/ALT levels) and fibrosis (Sirius red-staining), in both a preventive and therapeutic setting. Common bile duct ligation resulted in the increased protein expression of CCAAT/enhancer-binding protein homologous protein (CHOP) at all timepoints, along with upregulation of pro-apoptotic caspase 3 and 12, tumor necrosis factor receptor superfamily, member 1A (TNFRsf1a) and Fas-Associated protein with Death Domain (FADD) expression. Treatment with TUDCA led to a significant reduction of liver fibrosis, accompanied by a slight reduction of liver damage, decreased hepatic protein expression of CHOP and reduced gene and protein expression of pro-apoptotic markers. These data indicate that TUDCA exerts a beneficial effect on liver fibrosis in a model of cholestatic liver disease, and suggest that this effect might, at least in part, be attributed to decreased hepatic UPR signaling and apoptotic cell death.

Highlights

Cholestatic liver disease includes a spectrum of hepatobiliary pathologies and is characterized by impaired hepatobiliary production or excretion of bile, which causes biliary stasis and retention of bile acids [1]
We explored the hepatic unfolded protein response (UPR) and cell death signature in time during the initiation and progression of cholestasis-induced liver fibrosis in mice, and investigated whether modulating these processes with tauroursodeoxycholic acid (TUDCA) has a beneficial effect on liver damage and fibrosis
We found that the UPR response is activated after common bile duct ligation (CBDL) and that preventive and therapeutic treatment with TUDCA results in a significant reduction of liver fibrosis, which was associated with decreased expression of UPR and pro-apoptotic markers

Summary

Introduction

Cholestatic liver disease includes a spectrum of hepatobiliary pathologies and is characterized by impaired hepatobiliary production or excretion of bile, which causes biliary stasis and retention of bile acids [1]. Hydrophobic bile acids are cytotoxic due to their detergent action on lipid components and potential to induce oxidative stress and mitochondrial dysfunction which eventually results in hepatocyte and cholangiocyte death [3] This process, along with apoptotic debris and paracrine stimulation by neighboring cells, among many inducing factors, causes hepatic stellate cell activation, initiating progressive fibrosis [4,5]. The therapeutic potential to inhibit UPR-mediated liver damage following cholestasis in the evolution towards chronic liver disease and fibrosis has not been fully explored In this context, we were interested in the hydrophilic bile acid tauroursodeoxycholic acid (TUDCA), which is known for its ER stress-reducing and anti-apoptotic capacities [15,16,17,18,19,20,21,22,23,24,25,26,27]

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