ATP11C targets basolateral bile salt transporter proteins in mouse central hepatocytes.

UNLABELLED: ATP11C is a homolog of ATP8B1, both of which catalyze the transport of phospholipids in biological membranes. Mutations in ATP8B1 cause progressive familial intrahepatic cholestasis type1 in humans, which is characterized by a canalicular cholestasis. Mice deficient in ATP11C are characterized by a conjugated hyperbilirubinemia and an unconjugated hypercholanemia. Here, we have studied the hypothesis that ATP11C deficiency interferes with basolateral uptake of unconjugated bile salts, a process mediated by organic anion-transporting polypeptide (OATP) 1B2. ATP11C localized to the basolateral membrane of central hepatocytes in the liver lobule of control mice. In ATP11C-deficient mice, plasma total bilirubin levels were 6-fold increased, compared to control, of which ∼65% was conjugated and ∼35% unconjugated. Plasma total bile salts were 10-fold increased and were mostly present as unconjugated species. Functional studies in ATP11C-deficient mice indicated that hepatic uptake of unconjugated bile salts was strongly impaired whereas uptake of conjugated bile salts was unaffected. Western blotting and immunofluorescence analysis demonstrated near absence of basolateral bile salt uptake transporters OATP1B2, OATP1A1, OATP1A4, and Na(+) -taurocholate-cotransporting polypeptide only in central hepatocytes of ATP11C-deficient liver. In vivo application of the proteasome inhibitor, bortezomib, partially restored expression of these proteins, but not their localization. Furthermore, we observed post-translational down-regulation of ATP11C protein in livers from cholestatic mice, which coincided with reduced OATP1B2 levels. CONCLUSIONS: ATP11C is essential for basolateral membrane localization of multiple bile salt transport proteins in central hepatocytes and may act as a gatekeeper to prevent hepatic bile salt overload. Conjugated hyperbilirubinemia and unconjugated hypercholanemia and loss of OATP expression in ATP11C-deficient liver strongly resemble the characteristics of Rotor syndrome, suggesting that mutations in ATP11C can predispose to Rotor syndrome. (Hepatology 2016;64:161-174).

[Risks of intrahepatic cholestasis of pregnancy]. / Intrahepatische zwangerschapscholestase: riskante jeuk.

Intrahepatic cholestasis of pregnancy (ICP) is defined as pruritus during pregnancy in the absence of primary skin lesions, combined with an increase in serum total bile salts and/or abnormal serum liver tests. This article provides an insight into the diagnostic and therapeutic considerations by presenting two cases. ICP usually presents around 34 weeks of gestation, but can be present early in pregnancy as described in a 32-year-old patient pregnant after in-vitro fertilization. DNA analysis showed a mutation in the ABCB4 gene, causing MDR3 deficiency. Ursodeoxycholic acid treatment seems to alleviate maternal pruritus and possibly reduces perinatal risks related to the severe form of ICP, defined as fasted serum bile salt levels of ≥ 40 µmol/l at any point during the pregnancy. Short-term rifampicin treatment can be considered in patients with persistent pruritus. Induction of labour is advised only after 37 weeks of gestation in patients with severe ICP.