Bile acid receptors regulate the metabolic and immune functions of circulating enterohepatic bile acids. This process is disrupted by administration of parenteral nutrition (PN), which may induce progressive hepatic injury for unclear reasons, especially in the newborn, leading to PN-associated liver disease. To explore the role of bile acid signaling on neonatal hepatic function, we initially observed that Takeda G protein receptor 5 (TGR5)-specific bile acids were negatively correlated with worsening clinical disease markers in the plasma of human newborns with prolonged PN exposure. To test our resulting hypothesis that TGR5 regulates critical liver functions to PN exposure, we used TGR5 receptor deficient mice (TGR5−/−). We observed PN significantly increased liver weight, cholestasis, and serum hepatic stress enzymes in TGR5−/− mice compared with controls. Mechanistically, PN reduced bile acid synthesis genes in TGR5−/−. Serum bile acid composition revealed that PN increased unconjugated primary bile acids and secondary bile acids in TGR5−/− mice, while increasing conjugated primary bile acid levels in TGR5-competent mice. Simultaneously, PN elevated hepatic IL-6 expression and infiltrating macrophages in TGR5−/− mice. However, the gut microbiota of TGR5−/− mice compared with WT mice following PN administration displayed highly elevated levels of Bacteroides and Parabacteroides, and possibly responsible for the elevated levels of secondary bile acids in TGR5−/− animals. Intestinal bile acid transporters expression was unchanged. Collectively, this suggests TGR5 signaling specifically regulates fundamental aspects of liver bile acid homeostasis during exposure to PN. Loss of TGR5 is associated with biochemical evidence of cholestasis in both humans and mice on PN. NEW & NOTEWORTHY Parenteral nutrition is associated with deleterious metabolic outcomes in patients with prolonged exposure. Here, we demonstrate that accelerated cholestasis and parental nutrition-associated liver disease (PNALD) may be associated with deficiency of Takeda G protein receptor 5 (TGR5) signaling. The microbiome is responsible for production of secondary bile acids that signal through TGR5. Therefore, collectively, these data support the hypothesis that a lack of established microbiome in early life or under prolonged parenteral nutrition may underpin disease development and PNALD.
Assessment of serum bile acid profiles as biomarkers of liver injury and liver disease in humans