5C). Although, after PH, hepatocytes adapted BA synthesis and transport in both genotypes, we found that bile composition in ions did not significantly adapt

Selleck Compound Library in TGR5 KO mice.[5] Because TGR5 is not significantly detected in hepatocytes,[12] TGR5-dependent biliary adaptation after PH most likely reflects processes occurring in cholangiocytes. Our data keep in line with the proposition that TGR5 would control CFTR-dependent Cl− secretion in cholangiocytes,[15] because TGR5 KO exhibited less Cl− secretion in bile than WT mice after PH or BDL. The underlying mechanisms may involve cAMP-dependent membrane targeting of apical sodium-dependent bile salt transporter and CFTR, as previously proposed,[23] although TGR5-dependent signaling pathway transcriptional control of CFTR mRNA remains possible (Supporting Fig. 7B,C). The post-PH increase in HCO3− biliary output, together with biliary pH regulation, may be part of a TGR5-dependent adaptive mechanism enhancing bile secretion and protecting the overloaded remnant liver from BA toxicity.[30, 31] In line with this idea, we observed a post-PH rise in bile viscosity in TGR5 KO mice that may be related to this deficient adaptive response impairing bile flow (Fig. 6D). In addition to the striking phenotype observed in TGR5 KO mice upon BA overload,

further work will be needed to understand how the lack of TGR5 affects basal liver homeostasis (Supporting Fig. 1). We finally found that TGR5 may contribute to BA elimination in urine, at least through the control of MRP2 and MRP4 gene expression in conditions of BA overload. Although nothing has been reported on yet about the role of TGR5 in the kidney,[7, 18] deficient urinary BA elimination worsens liver injury after BDL.[24, 32] In our study, because hepatic necrosis occurs very early on after PH, the default in urinary BA elimination, significantly observed in the days after PH, may more likely result in a worsening of BA overload, rather than in the initiation of liver injury. Interestingly, cAMP is reported as a crucial regulator for MRP2 targeting at

the bile canaliculus,[33] raising the possibility that TGR5-mediated (and cAMP-mediated) post-translational Bumetanide regulation of MRP2 may occur also in kidney epithelial cells. Further studies are needed to identify mechanisms involved in TGR5-mediated regulation of BA efflux in urine. In conclusion, we found that TGR5 protects the liver against BA overload after PH, thereby preserving its regeneration capacity. After PH, BDL, or upon CA-enriched feeding, intrahepatic stasis of abnormally hydrophobic bile may be one of the primary factors involved in liver injury observed in TGR5 KO mice. Moreover, in the setting of BA overload, excessive inflammation as well as impaired urinary BA efflux observed in the absence of TGR5 may worsen liver injury. The authors thank Patrick Pham, Nathalie Samson, Pascale Leblanc-Veyrac, and Noémie Dherbe for their technical help.