Generation and characterization of a mouse model for bile salt export pump deficiency with the p.E297G mutation.

Abstract

BACKGROUND & AIMS: Bile Salt Export Pump (BSEP) deficiency is a rare genetic cholestatic liver disease, often necessitating liver transplantation. The p.E297G missense mutation is associated with residual BSEP function in vitro and delayed need for transplantation in patients. We aimed to generate a p.E297G BSEP knock-in (BSEP) mouse model to evaluate interventions to improve residual BSEP function. METHODS: We generated BSEPmice by CRISPR-Cas9 technology. BSEPmice and wild type (WT) littermates were characterized for BSEP expression and liver pathology at 14&#xa0;weeks of age. Maximal BSEP transport capacity without and after 4-phenylbutyrate (4-PB) treatment were determined in vivo by quantification of biliary bile acid secretion during intravenous infusion of increasing dosages of tauroursodeoxycholic acid (TUDCA) in WT, BSEPand BSEPmice. RESULTS: Western blot analysis showed immature BSEP protein in BSEPlivers. Median plasma AST was three-fold higher in BSEPmice (Males: 198 vs. 60&#xa0;U/L; Females: 188 vs. 50&#xa0;U/L; each p&#xa0;<&#xa0;0.001) while plasma bile acid levels were higher in female BSEPmice compared to WT (Females: 36 vs. 6&#xa0;&#x3bc;M, p&#xa0;<&#xa0;0.001; Males: 11 vs. 3&#xa0;&#x3bc;M, p&#xa0;=&#xa0;0.07). Histological analysis revealed features of cholestatic liver pathology in BSEPmice. TUDCA infusion strongly increased biliary bile acid secretion in WT but not in BSEPand BSEPmice. 4-PB treatment did not enhance bile acid transport capacity in BSEPmice. CONCLUSIONS: BSEPmice display a BSEP deficiency phenotype with a strongly reduced hepatobiliary bile acid transport capacity. The expression of immature BSEP protein suggests the potential to assess correctors of the BSEP functionality in vivo.