Altered hepatobiliary gene expressions in PFIC1: ATP8B1 gene defect is associated with CFTR downregulation

The macrocycle inhibitor landscape of SLC-transporter

In the past years the interest in Solute Carrier Transporters (SLC) has increased due to their potential as drug targets. At the same time, macrocycles demonstrated promising activities as therapeutic agents. However, the overall macrocycle/SLC-transporter interaction landscape has not been fully revealed yet. In this study, we present a statistical analysis of macrocycles with measured activity against SLC-transporter. Using a data mining pipeline based on KNIME retrieved in total 825 bioactivity data points of macrocycles interacting with SLC-transporter. For further analysis of the SLC inhibitor profiles we developed an interactive KNIME workflow as well as an interactive map of the chemical space coverage utilizing parametric t-SNE models. The parametric t-SNE models provide a good discrimination ability among several corresponding SLC subfamilies' targets. The KNIME workflow, the dataset, and the visualization tool are freely available to the community.

Genetic alterations and molecular mechanisms underlying hereditary intrahepatic cholestasis

Hereditary cholestatic liver disease caused by a class of autosomal gene mutations results in jaundice, which involves the abnormality of the synthesis, secretion, and other disorders of bile acids metabolism. Due to the existence of a variety of gene mutations, the clinical manifestations of children are also diverse. There is no unified standard for diagnosis and single detection method, which seriously hinders the development of clinical treatment. Therefore, the mutated genes of hereditary intrahepatic cholestasis were systematically described in this review.

Case Report: A Rare Heterozygous ATP8B1 Mutation in a BRIC1 Patient: Haploinsufficiency?

Benign recurrent intrahepatic cholestasis (BRIC) is an autosomal recessive disorder characterized by recurrent cholestasis. ATPase class I, type 8B, member 1 (ATP8B1) encodes familial intrahepatic cholestasis 1 (FIC1), which acts as a phosphatidylserine reversing enzyme in the tubule membrane of hepatocytes to mediate the inward translocation of phosphatidylserine (PS). At present, dozens of ATP8B1 pathogenic mutations have been identified that mainly cause BRIC1 and progressive familial intrahepatic cholestasis 1 (PFIC1). The diagnosis of BRIC1 is based on symptoms, laboratory tests, imaging, liver histology, and genetic testing. BRIC1 treatment seeks to prevent recurrence and reduce disease severity. At present, the main treatment methods include ursodeoxycholic acid (UDCA), rifampin, cholestyramine and haemofiltration, and endoscopic nasobiliary drainage (ENBD). Here, we report a 17-year-old patient with cholestasis who has a rare heterozygous ATP8B1 gene mutation (p.T888K). The patient was treated with UDCA, glucocorticoids and haemofiltration, after which bilirubin levels gradually returned to normal. This case was thought to be caused by an ATP8B1 heterozygous mutation, which may be related to haploinsufficiency (HI).

Biliary Atresia: A Complex Hepatobiliary Disease with Variable Gene Involvement, Diagnostic Procedures, and Prognosis

The diagnosis of biliary atresia is still terrifying at the 3rd decade of the 21st century. In a department of neonatal intensive care unit, parents and physicians face a challenge with a jaundiced baby, who may or may not have a surgically correctable hepatopathy. The approach has been systematically evaluated, but the etiology remains ambiguous. The study of families with recurrent biliary atresia has been undertaken at a molecular level. The primary interest with this disease is to identify the etiology and change the treatment from symptomatic to curative. The occurrence of this obstructive cholangio-hepatopathy in well-known genetic syndromes has suggested just coincidental finding, but the reality can be more intriguing because some of these diseases may have some interaction with the development of the intrahepatic biliary system. Several genes have been investigated thoroughly, including ADD3 and GPC1 shifting the interest from viruses to genetics. In this review, the intriguing complexities of this hepatobiliary disease are highlighted.

Impact of Genotype, Serum Bile Acids, and Surgical Biliary Diversion on Native Liver Survival in FIC1 Deficiency

BACKGROUND AND AIMS

Mutations in ATPase phospholipid transporting 8B1 (ATP8B1) can lead to familial intrahepatic cholestasis type 1 (FIC1) deficiency, or progressive familial intrahepatic cholestasis type 1. The rarity of FIC1 deficiency has largely prevented a detailed analysis of its natural history, effects of predicted protein truncating mutations (PPTMs), and possible associations of serum bile acid (sBA) concentrations and surgical biliary diversion (SBD) with long-term outcome. We aimed to provide insights by using the largest genetically defined cohort of patients with FIC1 deficiency to date.

APPROACH AND RESULTS

This multicenter, combined retrospective and prospective study included 130 patients with compound heterozygous or homozygous predicted pathogenic ATP8B1 variants. Patients were categorized according to the number of PPTMs (i.e., splice site, frameshift due to deletion or insertion, nonsense, duplication), FIC1-A (n = 67; no PPTMs), FIC1-B (n = 29; one PPTM), or FIC1-C (n = 34; two PPTMs). Survival analysis showed an overall native liver survival (NLS) of 44% at age 18 years. NLS was comparable among FIC1-A, FIC1-B, and FIC1-C (% NLS at age 10 years: 67%, 41%, and 59%, respectively; P = 0.12), despite FIC1-C undergoing SBD less often (% SBD at age 10 years: 65%, 57%, and 45%, respectively; P = 0.03). sBAs at presentation were negatively associated with NLS (NLS at age 10 years, sBAs < 194 µmol/L: 49% vs. sBAs ≥ 194 µmol/L: 15%; P = 0.03). SBD decreased sBAs (230 [125-282] to 74 [11-177] μmol/L; P = 0.005). SBD (HR 0.55, 95% CI 0.28-1.03, P = 0.06) and post-SBD sBA concentrations < 65 μmol/L (P = 0.05) tended to be associated with improved NLS.

CONCLUSIONS

Less than half of patients with FIC1 deficiency reach adulthood with native liver. The number of PPTMs did not associate with the natural history or prognosis of FIC1 deficiency. sBA concentrations at initial presentation and after SBD provide limited prognostic information on long-term NLS.

Experimental Evidence of Liver Injury by BSEP-Inhibiting Drugs With a Bile Salt Supplementation in Rats

The bile salt export pump (BSEP, ABCB11) mediates bile acid efflux from hepatocytes into bile. Although the inhibition of BSEP has been implicated as an important mechanism of drug-induced liver injury (DILI), liver injury caused by BSEP-inhibiting drugs is rarely reproduced in experimental animals, probably due to species differences in bile acid composition between humans and rodents. In this study, we tested whether supplementation with chenodeoxycholic acid (CDCA) sodium, a hydrophobic bile salt, could sensitize rats to liver injury caused by a BSEP-inhibiting drug. A potent BSEP inhibitor, ketoconazole (KTZ), which is associated with clinical DILI, was intragastrically administered simultaneously with CDCA at a nontoxic dose once a day for 3 days. Plasma transaminase levels significantly increased in rats receiving CDCA+KTZ, whereas neither treatment with CDCA alone, KTZ alone nor a combination of CDCA and miconazole, a safe analog to KTZ, induced liver injury. In CDCA+KTZ-treated rats, most bile acid species in the liver significantly increased compared with treatment with vehicle or CDCA alone, suggesting that KTZ administration inhibited bile acid excretion. Furthermore, hepatic mRNA expression levels of a bile acid synthesis enzyme, Cyp7a1, and a basolateral bile salt influx transporter, Ntcp, decreased, whereas a canalicular phosphatidylcholine flippase, Mdr2, increased in the CDCA+KTZ group to compensate for hepatic bile acid accumulation. In conclusion, we found that oral CDCA supplementation predisposed rats to KTZ-induced liver injury due to the hepatic accumulation of bile acids. This method may be useful for assessing the potential of BSEP-inhibiting drugs inducing liver injury in vivo.

Transcriptomic Analysis of Cholestatic Compounds In Vitro

Drug-induced cholestasis is one of the most severe manifestations of drug-induced liver injury. Drug-induced cholestasis is characterized by an accumulation of endogenous metabolites normally excreted in the bile such as bile salts, cholesterol, bilirubin, or drug metabolites. The possibility to determine early in the drug development process whether a compound presents a risk of inducing drug-induced cholestasis is key information. Since preclinical repeated dose toxicity studies have limited predictive value, large efforts in identifying alternative in vitro models with improved prediction are being made. One of the best current models for in vitro human liver is primary human hepatocytes, and we recently reported that primary human hepatocytes can be kept as long-term cultures in 2D-sandwich configuration when regularly renewing the Matrigel overlay, thereby making the model useful for repeat exposure-related toxicities, as well as for the study of adaptive responses. This primary human hepatocyte culture system combined with transcriptomics carries the future promise to identify individual gene expression profiles predictive of increased drug-induced cholestasis risk.This chapter describes the various steps for culturing and exposing primary human hepatocytes to drugs during long-term 2D-sandwich culture, performing RNA extraction, gene chip assay and selecting hepatotoxic signature using the IPA software and highlighting genes involved in bile acid homeostasis.

Omics-based responses induced by bosentan in human hepatoma HepaRG cell cultures

Bosentan is well known to induce cholestatic liver toxicity in humans. The present study was set up to characterize the hepatotoxic effects of this drug at the transcriptomic, proteomic, and metabolomic levels. For this purpose, human hepatoma-derived HepaRG cells were exposed to a number of concentrations of bosentan during different periods of time. Bosentan was found to functionally and transcriptionally suppress the bile salt export pump as well as to alter bile acid levels. Pathway analysis of both transcriptomics and proteomics data identified cholestasis as a major toxicological event. Transcriptomics results further showed several gene changes related to the activation of the nuclear farnesoid X receptor. Induction of oxidative stress and inflammation were also observed. Metabolomics analysis indicated changes in the abundance of specific endogenous metabolites related to mitochondrial impairment. The outcome of this study may assist in the further optimization of adverse outcome pathway constructs that mechanistically describe the processes involved in cholestatic liver injury.

Living Donor Liver Transplantation for Progressive Familial Intrahepatic Cholestasis Type 1: Two Reported Cases

BACKGROUND

Progressive familial intrahepatic cholestasis type 1 (PFIC1) is an inherited disease characterized by cholestatic features. We report two patients with PFIC1 who underwent liver retransplantation.

CASE REPORT

One patient was a 3-year-old female who underwent liver transplantation for PFIC1. She presented with severe diarrhea and fatty liver, and went into liver failure. She therefore underwent liver retransplantation and external biliary diversion 8 years after the initial liver transplantation. The explanted liver was histologically diagnosed with chronic rejection. Her intractable diarrhea stopped after the retransplantation. She was diagnosed with a fatty liver 8 months after the retransplantation and died 4 years after retransplantation due to bleeding from an ileostomy. The other patient was a 3-year-old male. This patient underwent liver retransplantation due to liver cirrhosis caused by steatohepatitis 9 years after the initial liver transplantation. The biliary tract was not diverted. He also experienced severe diarrhea after the retransplantation and requires home parenteral nutrition due to an eating disorder.

CONCLUSIONS

Liver transplantation is the only treatment to resolve life-threatening issues due to PFIC1, but requires further improvement as a therapeutic modality.

Uptake of glucose-conjugated MGMT inhibitors in cancer cells: role of flippases and type IV P-type ATPases

The DNA repair protein O⁶-methylguanine-DNA-methyltransferase (MGMT) is a key determinant of cancer resistance. The MGMT inhibitors O⁶-benzylguanine (O⁶BG) and O⁶-(4-bromothenyl)guanine (O⁶BTG) failed to enhance the therapeutic response due to toxic side effects when applied in combination with alkylating chemotherapeutics, indicating a need of inhibitor targeting. We assessed MGMT targeting that relies on conjugating the inhibitors O⁶BG and O⁶BTG to ß-D-glucose, resulting in O⁶BG-Glu and O⁶BTG-Glu, respectively. This targeting strategy was selected by taking advantage of high demand of glucose in cancers. Contrary to our expectation, the uptake of O⁶BG-Glu and O⁶BTG-Glu was not dependent on glucose transporters. Instead, it seems that after membrane binding the conjugates are taken up via flippases, which normally transport phospholipids. This membrane binding is the consequence of the amphiphilic character of the conjugates, which at higher concentrations lead to the formation of micelle-like particles in aqueous solution. The unusual uptake mechanism of the conjugates highlights the importance of proper linker selection for a successful ligand-based drug delivery strategy. We also demonstrate that proteins of the P4-Type ATPase family are involved in the transport of the glucose conjugates. The findings are not only important for MGMT inhibitor targeting, but also for other amphiphilic drugs.

Expression patterns of nuclear receptors in parenchymal and non-parenchymal mouse liver cells and their modulation in cholestasis

Nuclear receptors (NR), the largest family of transcription factors, control many physiological and pathological processes. To gain insight into hepatic NR and their potential as therapeutic targets in cholestatis, we determined their expression in individual cell types of the mouse liver in normal and cholestatic conditions. Hepatocytes, cholangiocytes, hepatic stellate cells (HSC), sinusoidal endothelial cells (SEC) and Kupffer cells (KC) were isolated from the liver of mice with acute or chronic cholestasis (i.e. bile duct-ligated or Abcb4-/- mice, respectively) and healthy controls. The expression of 43 out of the 49 NR was evidenced by RT-qPCR in one or several liver cell types. Expression of four NR was restricted to non-parenchymal liver cells. In normal conditions, NR were expressed at higher levels in individual cell types when compared to total liver. Half of the NR expressed in the liver had maximal expression in non-parenchymal cells. After bile duct ligation, NR mRNA changes occurred mostly in non-parenchymal cells and mainly consisted in down-regulations. In Abcb4-/- mice, NR mRNA changes were equally frequent in hepatocytes and non-parenchymal cells. Essentially down-regulations were found in hepatocytes, HSC and cholangiocytes, as opposed to up-regulations in SEC and KC. While undetectable in total liver, Vdr expression was up-regulated in all non-parenchymal cells in Abcb4-/- mice. In conclusion, non-parenchymal liver cells are a major site of NR expression. During cholestasis, NR expression is markedly altered mainly by down-regulations, suggesting major changes in metabolic activity. Thus, non-parenchymal cells are important new targets to consider in NR-directed therapies.

MYO5B mutations cause cholestasis with normal serum gamma-glutamyl transferase activity in children without microvillous inclusion disease

Some patients with microvillus inclusion disease due to myosin 5B (MYO5B) mutations may develop cholestasis characterized by a progressive familial intrahepatic cholestasis-like phenotype with normal serum gamma-glutamyl transferase activity. So far MYO5B deficiency has not been reported in patients with such a cholestasis phenotype in the absence of intestinal disease. Using a new-generation sequencing approach, we identified MYO5B mutations in five patients with progressive familial intrahepatic cholestasis-like phenotype with normal serum gamma-glutamyl transferase activity without intestinal disease.

CONCLUSION

These data show that MYO5B deficiency may lead to isolated cholestasis and that MYO5B should be considered as an additional progressive familial intrahepatic cholestasis gene. (Hepatology 2017;65:164-173).

Validation of precision-cut liver slices to study drug-induced cholestasis: a transcriptomics approach

Hepatotoxicity is one of the major reasons for withdrawal of drugs from the market. Therefore, there is a need to screen new drugs for hepatotoxicity in humans at an earlier stage. The aim of this study was to validate human precision-cut liver slices (PCLS) as an ex vivo model to predict drug-induced cholestasis and identify the possible mechanisms of cholestasis-induced toxicity using gene expression profiles. Five hepatotoxicants, which are known to induce cholestasis (alpha-naphthyl isothiocyanate, chlorpromazine, cyclosporine, ethinyl estradiol and methyl testosterone) were used at concentrations inducing low (<30 %) and medium (30-50 %) toxicity, based on ATP content. Human PCLS were incubated with the drugs in the presence of a non-toxic concentration (60 µM) of a bile acid mixture (portal vein concentration and composition) as model for bile acid-induced cholestasis. Regulated genes include bile acid transporters and cholesterol transporters. Pathway analysis revealed that hepatic cholestasis was among the top ten regulated pathways, and signaling pathways such as farnesoid X receptor- and liver X receptor-mediated responses, which are known to play a role in cholestasis, were significantly affected by all cholestatic compounds. Other significantly affected pathways include unfolded protein response and protein ubiquitination implicating the role of endoplasmic reticulum stress. This study shows that human PCLS incubated in the presence of a physiological bile acid mixture correctly reflect the pathways affected in drug-induced cholestasis in the human liver. In the future, this human PCLS model can be used to identify cholestatic adverse drug reactions of new chemical entities.

Functions of the Gallbladder

The gallbladder stores and concentrates bile between meals. Gallbladder motor function is regulated by bile acids via the membrane bile acid receptor, TGR5, and by neurohormonal signals linked to digestion, for example, cholecystokinin and FGF15/19 intestinal hormones, which trigger gallbladder emptying and refilling, respectively. The cycle of gallbladder filling and emptying controls the flow of bile into the intestine and thereby the enterohepatic circulation of bile acids. The gallbladder also largely contributes to the regulation of bile composition by unique absorptive and secretory capacities. The gallbladder epithelium secretes bicarbonate and mucins, which both provide cytoprotection against bile acids. The reversal of fluid transport from absorption to secretion occurs together with bicarbonate secretion after feeding, predominantly in response to an adenosine 3',5'-cyclic monophosphate (cAMP)-dependent pathway triggered by neurohormonal factors, such as vasoactive intestinal peptide. Mucin secretion in the gallbladder is stimulated predominantly by calcium-dependent pathways that are activated by ATP present in bile, and bile acids. The gallbladder epithelium has the capacity to absorb cholesterol and provides a cholecystohepatic shunt pathway for bile acids. Changes in gallbladder motor function not only can contribute to gallstone disease, but also subserve protective functions in multiple pathological settings through the sequestration of bile acids and changes in the bile acid composition. Cholecystectomy increases the enterohepatic recirculation rates of bile acids leading to metabolic effects and an increased risk of nonalcoholic fatty liver disease, cirrhosis, and small-intestine carcinoid, independently of cholelithiasis. Among subjects with gallstones, cholecystectomy remains a priority in those at risk of gallbladder cancer, while others could benefit from gallbladder-preserving strategies. © 2016 American Physiological Society. Compr Physiol 6:1549-1577, 2016.

Epithelial Anion Transport as Modulator of Chemokine Signaling

The pivotal role of epithelial cells is to secrete and absorb ions and water in order to allow the formation of a luminal fluid compartment that is fundamental for the epithelial function as a barrier against environmental factors. Importantly, epithelial cells also take part in the innate immune system. As a first line of defense they detect pathogens and react by secreting and responding to chemokines and cytokines, thus aggravating immune responses or resolving inflammatory states. Loss of epithelial anion transport is well documented in a variety of diseases including cystic fibrosis, chronic obstructive pulmonary disease, asthma, pancreatitis, and cholestatic liver disease. Here we review the effect of aberrant anion secretion with focus on the release of inflammatory mediators by epithelial cells and discuss putative mechanisms linking these transport defects to the augmented epithelial release of chemokines and cytokines. These mechanisms may contribute to the excessive and persistent inflammation in many respiratory and gastrointestinal diseases.

The phospholipid flippase ATP8B1 mediates apical localization of the cystic fibrosis transmembrane regulator

Progressive familial intrahepatic cholestasis type 1 (PFIC1) is caused by mutations in the gene encoding the phospholipid flippase ATP8B1. Apart from severe cholestatic liver disease, many PFIC1 patients develop extrahepatic symptoms characteristic of cystic fibrosis (CF), such as pulmonary infection, sweat gland dysfunction and failure to thrive. CF is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel essential for epithelial fluid transport. Previously it was shown that CFTR transcript levels were strongly reduced in livers of PFIC1 patients. Here we have investigated the hypothesis that ATP8B1 is important for proper CFTR expression and function. We analyzed CFTR expression in ATP8B1-depleted intestinal and pulmonary epithelial cell lines and assessed CFTR function by measuring short-circuit currents across transwell-grown ATP8B1-depleted intestinal T84 cells and by a genetically-encoded fluorescent chloride sensor. In addition, we studied CFTR surface expression upon induction of CFTR transcription. We show that CFTR protein levels are strongly reduced in the apical membrane of human ATP8B1-depleted intestinal and pulmonary epithelial cell lines, a phenotype that coincided with reduced CFTR activity. Apical membrane insertion upon induction of ectopically-expressed CFTR was strongly impaired in ATP8B1-depleted cells. We conclude that ATP8B1 is essential for correct apical localization of CFTR in human intestinal and pulmonary epithelial cells, and that impaired CFTR localization underlies some of the extrahepatic phenotypes observed in ATP8B1 deficiency.

Rescue of defective ATP8B1 trafficking by CFTR correctors as a therapeutic strategy for familial intrahepatic cholestasis

BACKGROUND & AIMS

ATP8B1 deficiency is an autosomal recessive liver disease characterized by intrahepatic cholestasis. ATP8B1 mutation p.I661T, the most frequent mutation in European patients, results in protein misfolding and impaired targeting to the plasma membrane. Similarly, mutations in cystic fibrosis transmembrane conductance regulator (CFTR), associated with cystic fibrosis, impair protein folding and trafficking. The aim of this study was to investigate whether compounds that rescue CFTR F508del trafficking are capable of improving p.I661T-ATP8B1 plasma membrane expression.

METHODS

The effect of CFTR corrector compounds on plasma membrane expression of p.I661T-ATP8B1 was evaluated by cell surface biotinylation and immunofluorescence. ATPase activity was evaluated of a purified analogue protein carrying a mutation at the matching position (p.L622T-ATP8A2).

RESULTS

The clinically used compounds, 4-phenylbutyric acid (4-PBA), suberoylanilide hydroxamic acid (SAHA) and N-butyldeoxynojirimycin (NB-DNJ) improved p.I661T-ATP8B1 plasma membrane targeting. Compounds C4, C5, C13 and C17 also significantly increased plasma membrane expression of p.I661T-ATP8B1. SAHA and compound C17 upregulated ATP8B1 transcription. p.I661T-ATP8B1 was partly targeted to the canalicular membrane in polarized cells, which became more evident upon treatment with SAHA and/or C4. p.L622T-ATP8A2 showed phospholipid-induced ATPase activity, suggesting that mutations at a matching position in ATP8B1 do not block functionality. Combination therapy of SAHA and compound C4 resulted in an additional improvement of ATP8B1 cell surface abundance.

CONCLUSIONS

This study shows that several CFTR correctors can improve trafficking of p.I661T-ATP8B1 to the plasma membrane in vitro. Hence, these compounds may be suitable to be part of a future therapy for ATP8B1 deficiency and other genetic disorders associated with protein misfolding.

LAY SUMMARY

Compounds that improve the cellular machinery dealing with protein homeostasis (proteostasis) and allow for proper folding of proteins with (mild) missense mutations are called proteostasis regulators (Balch, Science 2008). Such compounds are potentially of high therapeutic value for many (liver) diseases. In this manuscript, we investigated whether compounds identified in screens as CFTR folding correctors are actually proteostasis regulators and thus have a broader application in other protein folding diseases. Using these compounds, we could indeed show improved trafficking to the (apical) plasma membrane of a mutated ATP8B1 protein, carrying the p.I661T missense mutation. This is the most frequently identified mutation in this rare cholestatic disorder. Importantly, ATP8B1 shows no similarity to CFTR. These data are important in providing support for the concept that rare, genetic liver diseases can potentially be treated using a generalized strategy.

Cholestasis and Hepatic Failure in a Neonate: A Case Report of Severe Pyruvate Kinase Deficiency

Unexpected severe cholestasis is part of the presentation in some neonates with hemolytic anemia but is usually self-resolving. Here we report the case of a neonate with pyruvate kinase deficiency (PKD) who presented severe hemolytic anemia at birth, characterized by a rapidly progressive and severe cholestasis with normal γ-glutamyl transpeptidase level associated with hepatic failure. After an extensive investigation to rule out contributing conditions explaining the severity of this patient's clinical presentation, PKD has remained the sole identified etiology. The patient abruptly died of sepsis at 3 months of age before a planned splenectomy and ongoing evaluation for liver transplantation. To the best of our knowledge, only a few similar cases of severe neonatal presentation of PKD complicated with severe hepatic failure and cholestasis have been reported.

Nuclear receptors in acute and chronic cholestasis

BACKGROUND

Nuclear receptors (NRs) form a family of 48 members. NRs control hepatic processes such as bile acid homeostasis, lipid metabolism and mechanisms involved in fibrosis and inflammation. Due to their central role in the regulation of hepatoprotective mechanisms, NRs are promising therapeutic targets in cholestatic disorders.

KEY MESSAGES

NRs can be classified into five different physiological clusters. NRs from the 'bile acids and xenobiotic metabolism' and from the 'lipid metabolism and energy homeostasis' clusters are strongly expressed in the liver. Furthermore, NRs from these clusters, such as farnesoid X receptor α (FXRα), pregnane X receptor (PXR) and peroxisome proliferator-activated receptors (PPARs), have been associated with the pathogenesis and the progression of cholestasis. The latter observation is also true for vitamin D receptor (VDR), which is barely detectable in the whole liver, but has been linked to cholestatic diseases. Involvement of VDR in cholestasis is ascribed to a strong expression in nonparenchymal liver cells, such as biliary epithelial cells, Kupffer cells and hepatic stellate cells. Likewise, NRs from other physiological clusters with low hepatic expression, such as estrogen receptor α (ERα) or reverse-Erb α/β (REV-ERB α/β), may also control pathophysiological processes in cholestasis.

CONCLUSIONS

In this review, we will describe the impact of individual NRs on cholestasis. We will then discuss the potential role of these transcription factors as therapeutic targets.

Cystic fibrosis related liver disease--another black box in hepatology

Due to improved medical care, life expectancy in patients with cystic fibrosis (CF) has veritably improved over the last decades. Importantly, cystic fibrosis related liver disease (CFLD) has become one of the leading causes of morbidity and mortality in CF patients. However, CFLD might be largely underdiagnosed and diagnostic criteria need to be refined. The underlying pathomechanisms are largely unknown, and treatment strategies with proven efficacy are lacking. This review focuses on current invasive and non-invasive diagnostic standards, the current knowledge on the pathophysiology of CFLD, treatment strategies, and possible future developments.

Transcriptomic hepatotoxicity signature of chlorpromazine after short- and long-term exposure in primary human sandwich cultures

Drug-induced liver injury is the most frequent reason for market withdrawal of approved drugs, and is difficult to predict in animal models. Here, we analyzed transcriptomic data derived from short- and long-term cultured primary human hepatocytes (PHH) exposed to the well known human hepatotoxin chlorpromazine (CPZ). Samples were collected from five PHH cultures after short-term (1 and 3 days) and long-term (14 days) repeat daily treatment with 0.1 or 0.2 µM CPZ, corresponding to C(max). Two PHH cultures were additionally treated with 1 µM CPZ, and the three others with 0.02 µM CPZ. Differences in the total number of gene changes were seen between donors and throughout treatment. Specific transcriptomic hepatotoxicity signatures were created for CPZ and consisted of inflammation/hepatitis, cholestasis, and liver proliferation in all five donors, as well as fibrosis and steatosis, which were observed in four of five donors. Necrosis was present in three of five donors, and an indicative signature of cirrhosis was observed after long-term 14-day repeat treatment, also in three of five donors. The inter-donor variability in the inflammatory response to CPZ treatment was associated with variability in the strength of the response of the transcriptomic hepatotoxicity signatures, suggesting that features of inflammation could be related to the idiosyncratic hepatotoxic effects of CPZ in humans.

Disodium gadoxetate uptake in progressive familial intrahepatic cholestasis type I: Enhancing our understanding of the cholestatic disease

Hepatocyte-specific magnetic resonance imaging (MRI) contrast agents are commonly used to depict anatomic hepatobiliary lesions and are also useful in characterizing the kinetics of hepatocyte uptake and excretion. We report a case of a 13-year old female with progressive familial intrahepatic cholestasis (PFIC) type 1 who demonstrated decreased uptake and excretion of gadoxetate disodium contrast material. This case illustrates the challenge of imaging children with cholestasis using hepatobiliary-specific contrast agents; we propose an alternative explanation for the delayed excretion that may be related to the underlying genetic defect of this child.

ATP8B1 gene expression is driven by a housekeeping-like promoter independent of bile acids and farnesoid X receptor

Background

Mutations in ATP8B1 gene were identified as a cause of low γ-glutamyltranspeptidase cholestasis with variable phenotype, ranging from Progressive Familial Intrahepatic Cholestasis to Benign Recurrent Intrahepatic Cholestasis. However, only the coding region of ATP8B1 has been described. The aim of this research was to explore the regulatory regions, promoter and 5′untranslated region, of the ATP8B1 gene.

Methodology/Principal Findings

5′Rapid Amplification of cDNA Ends using human liver and intestinal tissue was performed to identify the presence of 5′ untranslated exons. Expression levels of ATP8B1 transcripts were determined by quantitative reverse-transcription PCR and compared with the non-variable part of ATP8B1. Three putative promoters were examined in vitro using a reporter gene assay and the main promoter was stimulated with chenodeoxycholic acid. Four novel untranslated exons located up to 71 kb upstream of the previously published exon 1 and twelve different splicing variants were found both in the liver and the intestine. Multiple transcription start sites were identified within exon −3 and the proximal promoter upstream of this transcription start site cluster was proven to be an essential regulatory element responsible for 70% of total ATP8B1 transcriptional activity. In vitro analysis demonstrated that the main promoter drives constitutive ATP8B1 gene expression independent of bile acids.

Conclusions/Significance

The structure of the ATP8B1 gene is complex and the previously published transcription start site is not significant. The basal expression of ATP8B1 is driven by a housekeeping-like promoter located 71 kb upstream of the first protein coding exon.

Glucocorticoids promote hepatic cholestasis in mice by inhibiting the transcriptional activity of the farnesoid X receptor

BACKGROUND & AIMS

Glucocorticoids have potent anti-inflammatory effects, but also can cause insulin resistance, osteoporosis, and muscle wasting, preventing their long-term use. Glucocorticoids also have been associated with the development of hepatic cholestasis and gallstone disease, but little is known about their pathogenic mechanisms.

METHODS

We analyzed levels of bile acids (BAs) and glucocorticoids in serum samples from patients with Cushing disease and obese individuals (body mass index, >30). C57BL/6 mice were injected with dexamethasone and db/db obese mice were injected with glucocorticoid receptor (GR) antagonists or small hairpin RNAs. We analyzed farnesoid X receptor (FXR) signaling in HepG2 cells and cells from mice using immunoprecipitation, luciferase reporter, and glutathione-s-transferase and chromatin immunoprecipitation assays. We analyzed BA metabolism in FXR-/- mice and mice with reduced levels of the transcription factor C-terminal binding protein (CtBP).

RESULTS

Serum levels of BAs were higher in patients with Cushing disease or obesity than in individuals with normal levels of glucocorticoids. Administration of dexamethasone promoted cholestasis and overproduction of BAs in C57BL/6 mice, but not in FXR-/- mice. GR antagonists, or injection of an adenoviral small hairpin RNA against GR, reduced features of hepatic cholestasis in db/db mice. The GR interacted with FXR to reduce its transcriptional activity by recruiting CtBP co-repressor complexes. Mice with reduced levels of CtBP were resistant to induction of hepatic cholestasis by dexamethasone.

CONCLUSIONS

Glucocorticoids promote hepatic cholestasis in mice by recruiting CtBP co-repressor complexes to FXR and thereby blocking the transcriptional activity.

Intestinal synthesis and secretion of bile salts as an adaptation to developmental biliary atresia in the sea lamprey

Bile salt synthesis is a specialized liver function in vertebrates. Bile salts play diverse roles in digestion and signaling, and their homeostasis is maintained by controlling input (biosynthesis) and intestinal conservation. Patients with biliary atresia (i.e., obliteration of the biliary tree) suffer liver fibrosis and cirrhosis. In contrast, sea lamprey thrives despite developmental biliary atresia. We discovered that the sea lamprey adapts to biliary atresia through a unique mechanism of de novo synthesis and secretion of bile salts in intestine after developmental biliary atresia, in addition to known mechanisms, such as the reduction of bile salt synthesis in liver. During and after developmental biliary atresia, expression of cyp7a1 in intestine increased by more than 100-fold (P < 0.001), whereas in liver it decreased by the same magnitude (P < 0.001). Concurrently, bile salt pools changed in similar patterns and magnitudes in these two organs and the composition shifted from C24 bile alcohol sulfates to taurine-conjugated C24 bile acids. In addition, both in vivo and ex vivo experiments showed that aductular sea lamprey secreted taurocholic acid into its intestinal lumen. Our results indicate that the sea lamprey, a jawless vertebrate, may be in an evolutionarily transitional state where bile salt synthesis occurs in both liver and intestine. Understanding the molecular basis of these mechanisms may shed light on the evolution of bile salt synthesis and possible therapy for infant biliary atresia.

Living-donor liver transplantation for progressive familial intrahepatic cholestasis

BACKGROUND

Progressive familial intrahepatic cholestasis (PFIC) results in liver cirrhosis during the disease course, although the etiology includes unknown mechanisms. Some PFIC patients require liver transplantation (LT).

METHODS

In this study, 11 patients with PFIC type 1 (PFIC1) and 3 patients with PFIC type 2 (PFIC2) who underwent living-donor LT (LDLT) were evaluated.

RESULTS

Digestive symptoms after LDLT were confirmed in 10 PFIC1 recipients (90.9%); 8 PFIC1 recipients showed steatosis after LDLT (72.7%), which began during the early postoperative period (71.5±55.1 days). Seven of the eight steatosis-positive PFIC1 recipients (87.5%) showed a steatosis degree of ≥80%, which was complicated with steatohepatitis and resulted in fibrosis. Cirrhotic findings persisted in six PFIC1 recipients even after LDLT (54.5%), and three PFIC1 recipients finally died. The survival rates of the PFIC1 recipients at 5, 10, and 15 years were 90.9%, 72.7%, and 54.5%, respectively. In contrast, the PFIC2 recipients showed good courses and outcomes without any steatosis after LDLT.

CONCLUSIONS

The clinical courses and outcomes after LDLT are still not sufficient in PFIC1 recipients owing to steatosis/steatohepatitis and subsequent fibrosis, in contrast to PFIC2 recipients. PFIC2 is good indication for LDLT. PFIC1 patients require LT during the disease course; therefore, we suggest that the therapeutic strategies for PFIC1 patients, including the timing of LDLT, under the donor limitation should be reconsidered. The establishment of more advanced treatments for PFIC1 patients is required to improve the long-term prognosis of these patients.

Combined deletion of Fxr and Shp in mice induces Cyp17a1 and results in juvenile onset cholestasis

Bile acid homeostasis is tightly regulated via a feedback loop operated by the nuclear receptors farnesoid X receptor (FXR) and small heterodimer partner (SHP). Contrary to current models, which place FXR upstream of SHP in a linear regulatory pathway, here we show that the phenotypic consequences in mice of the combined loss of both receptors are much more severe than the relatively modest impact of the loss of either Fxr or Shp alone. Fxr-/-Shp-/- mice exhibited cholestasis and liver injury as early as 3 weeks of age, and this was linked to the dysregulation of bile acid homeostatic genes, particularly cytochrome P450, family 7, subfamily a, polypeptide 1 (Cyp7a1). In addition, double-knockout mice showed misregulation of genes in the C21 steroid biosynthesis pathway, with strong induction of cytochrome P450, family 17, subfamily a, polypeptide 1 (Cyp17a1), resulting in elevated serum levels of its enzymatic product 17-hydroxyprogesterone (17-OHP). Treatment of WT mice with 17-OHP was sufficient to induce liver injury that reproduced many of the histopathological features observed in the double-knockout mice. Therefore, our data indicate a pathologic role for increased production of 17-hydroxy steroid metabolites in liver injury and suggest that Fxr-/-Shp-/- mice could provide a model for juvenile onset cholestasis.

Progressive familial intrahepatic cholestasis: a single-center experience of living-donor liver transplantation during two decades in Japan

BACKGROUND

Progressive familial intrahepatic cholestasis (PFIC) results in liver cirrhosis. Therefore, some PFIC patients require liver transplantation (LT). Although three types of PFIC have been identified, their etiologies include unknown mechanisms.

PATIENTS

A total of 717 recipients who underwent living-donor LT (LDLT) at <20 yr old were enrolled in this study. Among these recipients, 14 PFIC recipients comprising 11 PFIC type 1 (PFIC1) and three PFIC type 2 (PFIC2) were evaluated.

RESULTS

Three of 11 PFIC1 recipients died, while all three PFIC2 recipients survived. Eight of 11 PFIC1 recipients showed steatosis after LDLT. Among the eight steatosis-positive PFIC1 recipients, seven showed severe steatosis and seven were complicated with steatohepatitis. Nine of 11 PFIC1 recipients showed fibrosis after LDLT, and eight of the nine fibrosis-positive PFIC1 recipients showed severe fibrosis. In contrast to the PFIC1 recipients, the PFIC2 recipients did not show any steatosis or fibrosis after LDLT.

CONCLUSIONS

The clinical courses and outcomes of PFIC1 recipients after LDLT are still not sufficient owing to steatosis/fibrosis, unlike the case for PFIC2 recipients. As PFIC1 patients will require LT during the long-term progression of the disease, further strategy improvements are required for PFIC1 patients.

Regulation of hepatic ABCC transporters by xenobiotics and in disease states

The subfamily of ABCC transporters consists of 13 members in mammals, including the multidrug resistance-associated proteins (MRPs), sulfonylurea receptors (SURs), and the cystic fibrosis transmembrane conductance regulator (CFTR). These proteins play roles in chemical detoxification, disposition, and normal cell physiology. ABCC transporters are expressed differentially in the liver and are regulated at the transcription and translation level. Their expression and function are also controlled by post-translational modification and membrane-trafficking events. These processes are tightly regulated. Information about alterations in the expression of hepatobiliary ABCC transporters could provide important insights into the pathogenesis of diseases and disposition of xenobiotics. In this review, we describe the regulation of hepatic ABCC transporters in humans and rodents by a variety of xenobiotics, under disease states and in genetically modified animal models deficient in transcription factors, transporters, and cell-signaling molecules.

ATPase Class I Type 8B Member 1 and protein kinase C zeta induce the expression of the canalicular bile salt export pump in human hepatocytes

The exact molecular mechanism(s) of the disease that results from defects in the ATPase Class I Type 8B Member 1 gene remains controversial. Prior investigations of human ileum and in intestinal and ovarian cell lines have suggested that familial intrahepatic cholestasis 1 (FIC1) activates the farnesoid X-receptor (FXR) via a pathway involving protein kinase C zeta (PKCzeta). Translational investigations of human liver from individuals with FIC1 disease have been confounded by secondary affects of progressive cholestatic liver disease and limited numbers of samples for analysis. These studies, performed in primarily derived human hepatocytes, circumvent this issue. The canalicular bile salt export pump (BSEP) served as a downstream target of FXR. The siRNA-mediated silencing of FIC1 in human hepatocytes led to a reduction in both human BSEP promoter activity and BSEP protein expression, which correlated with a reduction in FXR expression and redistribution of its localization from the nucleus to the cytoplasm. These changes in BSEP expression could be reproduced by altering the expression of PKCzeta, with a positive correlation of PKCzeta activity and BSEP expression. Overall, these findings support the hypothesis that FIC1 enhances FXR signaling via a PKCzeta-dependent signaling pathway.

Liver disease associated with canalicular transport defects: current and future therapies

Bile formation at the canalicular membrane is a delicate process. This is illustrated by inherited liver diseases due to mutations in ATP8B1, ABCB11, ABCB4, ABCC2 and ABCG5/8, all encoding hepatocanalicular transporters. Effective treatment of these canalicular transport defects is a clinical and scientific challenge that is still ongoing. Current evidence indicates that ursodeoxycholic acid (UDCA) can be effective in selected patients with PFIC3 (ABCB4 deficiency), while rifampicin reduces pruritus in patients with PFIC1 (ATP8B1 deficiency) and PFIC2 (ABCB11 deficiency), and might abort cholestatic episodes in BRIC (mild ATP8B1 or ABCB11 deficiency). Cholestyramine is essential in the treatment of sitosterolemia (ABCG5/8 deficiency). Most patients with PFIC1 and PFIC2 will benefit from partial biliary drainage. Nevertheless liver transplantation is needed in a substantial proportion of these patients, as it is in PFIC3 patients. New developments in the treatment of canalicular transport defects by using nuclear receptors as a target, enhancing the expression of the mutated transporter protein by employing chaperones, or by mutation specific therapy show substantial promise. This review will focus on the therapy that is currently available as well as on those developments that are likely to influence clinical practice in the near future.

Analysis of Gene Expression in 4,4'-Methylenedianiline-induced Acute Hepatotoxicity

4,4′-Methylenedianiline (MDA) is an aromatic amine that is widely used in the industrial synthetic process. Genotoxic MDA forms DNA adducts in the liver and is known to induce liver damage in human and rats. To elucidate the molecular mechanisms associated with MDA-induced hepatotoxicity, we have identified genes differentially expressed by microarray approach. BALB/c male mice were treated once daily with MDA (20 mg/kg) up to 7 days via intraperitoneal injection (i.p.) and hepatic damages were revealed by histopathological observation and elevation of serum marker enzymes such as AST, ALT, ALP, cholesterol, DBIL, and TBIL. Microarray analysis showed that 952 genes were differentially expressed in the liver of MDA-treated mice and their biological functions and canonical pathways were further analyzed using Ingenuity Pathways Analysis (IPA). Toxicological functional analysis showed that genes related to hepatotoxicity such hyperplasia/hyperproliferation (Timpl), necrosis/cell death (Cd14, Mt1f, Timpl, and Pmaipl), hemorrhaging (Mt1f), cholestasis (Akr1c3, Hpx, and Slc10a2), and inflammation (Cd14 and Hpx) were differentially expressed in MDA-treated group. This gene expression profiling should be useful for elucidating the genetic events associated with aromatic amine-induced hepatotoxicity and for discovering the potential biomarkers for hepatotoxicity.

Knockdown of ATP8B1 expression leads to specific downregulation of the bile acid sensor FXR in HepG2 cells: effect of the FXR agonist GW4064

Farnesoid X receptor (FXR) is a bile acid-sensing nuclear receptor that controls bile acid homeostasis. It has been suggested that downregulation of FXR contributes to the pathogenesis of an inherited disorder of bile secretion caused by mutations in ATP8B1. We have investigated the relationship between ATP8B1 knockdown and FXR downregulation in the human hepatoblastoma cell line HepG2. Transfection of HepG2 cells with ATP8B1 small interfering RNA (siRNA) duplexes led to a 60% reduction in the endogenous levels of ATP8B1 mRNA and protein and a concomitant decrease in FXR mRNA and protein content, as well as in FXR phosphorylation. This decrease was accompanied by a marked reduction in mRNA levels of a subset of FXR targets, such as bile salt export pump (ABCB11), small heterodimer partner, and uridine 5'-diphosphate-glucuronosyltransferase. ATP8B1 inhibition specifically targeted FXR since mRNA expression of other prominent nuclear receptors, such as pregnane X receptor and constitutive androstane receptor, or liver-enriched transcription factors, such as hepatocyte nuclear factor 1alpha (HNF-1alpha) and HNF-4alpha, was not altered. The expression of other key genes involved in bile acid synthesis, detoxification, and transport also remained unchanged upon ATP8B1 knockdown. Supporting the specificity of the effect, siRNA-mediated silencing of ABCB11, whose defect is associated with another inherited disorder of bile secretion, did not affect FXR expression. Treatment with the synthetic FXR agonist GW4064 was able to partially neutralize ATP8B1 siRNA-mediated FXR downregulation and fully counteract inhibition of FXR target genes. Collectively these findings indicate that ATP8B1 knockdown specifically downregulates FXR, and this action can be circumvented by treatment with FXR agonists.

ATP8B1 deficiency disrupts the bile canalicular membrane bilayer structure in hepatocytes, but FXR expression and activity are maintained

BACKGROUND & AIMS

Progressive familial intrahepatic cholestasis 1 (PFIC1) results from mutations in ATP8B1, a putative aminophospholipid flippase. Conflicting hypotheses have been proposed for the pathogenesis of PFIC1. The aim of this study was to determine whether ATP8B1 deficiency produces cholestasis by altering the activity of the farnesoid X receptor (FXR) or by impairing the structure of the canalicular membrane.

METHODS

ATP8B1/Atp8b1 was knocked down in human and rat hepatocytes and Caco2 cells using adenoviral and oligonucleotide small interfering RNAs.

RESULTS

ATP8B1 messenger RNA and protein expression was greatly reduced in human and rat cells. In contrast, FXR expression and several FXR-dependent membrane transporters (bile salt export pump [BSEP], multidrug resistance-associated protein [MRP] 2) were unchanged at messenger RNA or protein levels in ATP8B1-deficient cells, whereas Mrp3 and Mrp4 were up-regulated in rat hepatocytes. FXR activity remained intact in these cells, as evidenced by 6alpha-ethyl chenodeoxycholic acid-mediated induction of small heterodimer partner, BSEP, and multidrug-resistant protein (MDR) 3/Mdr2. Fluorescent substrate excretion assays indicate that Bsep function was significantly reduced in Atp8b1-deficient rat hepatocytes, although Bsep remained localized to the canalicular membrane. Exposure to the hydrophobic bile acid CDCA resulted in focal areas of canalicular membrane disruption by electron microscopy and luminal accumulation of NBD-phosphatidylserine, consistent with the function of Atp8b1 as an aminophospholipid flippase.

CONCLUSIONS

ATP8B1 deficiency predisposes to cholestasis by favoring bile acid-induced injury in the canalicular membrane but does not directly affect FXR expression, which may occur in PFIC1 as a secondary phenomenon associated with cholestasis.

P4 ATPases - lipid flippases and their role in disease

P4 ATPases (type 4 P-type ATPases) are multispan transmembrane proteins that have been implicated in phospholipid translocation from the exoplasmic to the cytoplasmic leaflet of biological membranes. Studies in Saccharomyces cerevisiae have indicated that P4 ATPases are important in vesicle biogenesis and are required for vesicular trafficking along several intracellular vesicular transport routes. Although little is known about mammalian P4 ATPases, some members of this subfamily appear to be associated with human disease or mouse pathophysiology. ATP8B1, a phosphatidylserine translocase, is the most extensively studied mammalian P4 ATPase. This protein is important for maintaining the detergent resistant properties of the apical membrane of the hepatocyte. Mutations in ATP8B1 give rise to severe liver disease. Furthermore, a role for Atp8b3 in mouse sperm cell capacitation has been suggested, whereas deficiency of Atp10a and Atp10d leads to insulin resistance and obesity in mice. Here we review the present status on the pathophysiological consequences of P4 ATPase deficiency.

Progressive familial intrahepatic cholestasis

Progressive familial intrahepatic cholestasis (PFIC) refers to heterogeneous group of autosomal recessive disorders of childhood that disrupt bile formation and present with cholestasis of hepatocellular origin. The exact prevalence remains unknown, but the estimated incidence varies between 1/50,000 and 1/100,000 births.

Three types of PFIC have been identified and related to mutations in hepatocellular transport system genes involved in bile formation. PFIC1 and PFIC2 usually appear in the first months of life, whereas onset of PFIC3 may also occur later in infancy, in childhood or even during young adulthood. Main clinical manifestations include cholestasis, pruritus and jaundice. PFIC patients usually develop fibrosis and end-stage liver disease before adulthood. Serum gamma-glutamyltransferase (GGT) activity is normal in PFIC1 and PFIC2 patients, but is elevated in PFIC3 patients. Both PFIC1 and PFIC2 are caused by impaired bile salt secretion due respectively to defects in ATP8B1 encoding the FIC1 protein, and in ABCB11 encoding the bile salt export pump protein (BSEP). Defects in ABCB4, encoding the multi-drug resistant 3 protein (MDR3), impair biliary phospholipid secretion resulting in PFIC3.

Diagnosis is based on clinical manifestations, liver ultrasonography, cholangiography and liver histology, as well as on specific tests for excluding other causes of childhood cholestasis. MDR3 and BSEP liver immunostaining, and analysis of biliary lipid composition should help to select PFIC candidates in whom genotyping could be proposed to confirm the diagnosis. Antenatal diagnosis can be proposed for affected families in which a mutation has been identified. Ursodeoxycholic acid (UDCA) therapy should be initiated in all patients to prevent liver damage. In some PFIC1 or PFIC2 patients, biliary diversion can also relieve pruritus and slow disease progression. However, most PFIC patients are ultimately candidates for liver transplantation. Monitoring of hepatocellular carcinoma, especially in PFIC2 patients, should be offered from the first year of life. Hepatocyte transplantation, gene therapy or specific targeted pharmacotherapy may represent alternative treatments in the future.

The membrane protein ATPase class I type 8B member 1 signals through protein kinase C zeta to activate the farnesoid X receptor

Prior loss-of-function analyses revealed that ATPase class I type 8B member 1 [familial intrahepatic cholestasis 1 (FIC1)] posttranslationally activated the farnesoid X receptor (FXR). Mechanisms underlying this regulation were examined by gain-of-function studies in UPS cells, which lack endogenous FIC1 expression. FXR function was assayed in response to wild-type and mutated FIC1 expression constructs with a human bile salt export pump (BSEP) promoter and a variety of cellular localization techniques. FIC1 overexpression led to enhanced phosphorylation and nuclear localization of FXR that was associated with FXR-dependent activation of the BSEP promoter. The FIC1 effect was lost after mutation of the FXR response element in the BSEP promoter. Despite similar levels of FIC1 protein expression, Byler disease FIC1 mutants did not activate BSEP, whereas benign recurrent intrahepatic cholestasis mutants partially activated BSEP. The FIC1 effect was dependent on the presence of the FXR ligand, chenodeoxycholic acid. The effect of FIC1 on FXR phosphorylation and nuclear localization and its effects on BSEP promoter activity could be blocked with protein kinase C zeta (PKC zeta) inhibitors (pseudosubstrate or small interfering RNA silencing). Recombinant PKC zeta directly phosphorylated immunoprecipitated FXR. The mutation of threonine 442 of FXR to alanine yielded a dominant negative protein, whereas the phosphomimetic conversion to glutamate resulted in FXR with enhanced activity and nuclear localization. Inhibition of PKC zeta in Caco-2 cells resulted in activation of the human apical sodium-dependent bile acid transporter promoter.

CONCLUSION

These results demonstrate that FIC1 signals to FXR via PKC zeta. FIC1-related liver disease is likely related to downstream effects of FXR on bile acid homeostasis. Benign recurrent intrahepatic cholestasis emanates from a partially functional FIC1 protein. Phosphorylation of FXR is an important mechanism for regulating its activity.

Update on progressive familial intrahepatic cholestasis

Three distinct forms of familial intrahepatic cholestasis are the result of mutations in the ATP8B1, ABCB11, and ABCB4 genes. The pathophysiologies of the latter 2 of these diseases are well characterized and are the result of abnormalities in canalicular excretion of bile acids and phospholipids, respectively. The molecular pathophysiology of the systemic disease associated with mutations in ATP8B1 remains unclear. In all of these diseases, wide variations in clinical phenotypes have been observed. The variability can be ascribed at least in part to predicted genotype:phenotype correlations. Disease- and genotype-specific prognoses and therapeutic approaches may exist, although much more information needs to be ascertained before clinicians can confidently make decisions based on genetic information.

Intestinal bile salt absorption in Atp8b1 deficient mice

BACKGROUND/AIMS

Mutations in the ATP8B1 gene can cause Progressive Familial Intrahepatic Cholestasis type 1. We have previously reported that Atp8b1(G308V/G308V) mice, a model for PFIC1, have slightly, but significantly, higher baseline serum bile salt (BS) concentrations compared to wt mice. Upon BS feeding, serum BS concentrations strongly increased in Atp8b1-deficient mice. Despite these findings, we observed only mildly impaired canalicular BS transport. In the present report we tested the hypothesis that Atp8b1(G308V/G308V) mice hyperabsorb BS in the intestine during BS feeding.

METHODS

Intestinal BS absorption was measured in intestinal perfusion and in intestinal explants. In addition, we measured BS concentrations in portal blood. Ileal expression of the Fxr-targets Asbt, Ilbp and Shp was assessed.

RESULTS

In wt and Atp8b1(G308V/G308V) mice, intestinal taurocholate absorption is primarily mediated by the ileal bile salt transporter Asbt. Neither of the experimental systems revealed enhanced absorption of BS in Atp8b1(G308V/G308V) mice compared to wt mice. In line with these observations, we found no difference in the ileal protein expression of Asbt. Induction of Shp expression during BS feeding also demonstrated that Fxr signalling is intact in Atp8b1(G308V/G308V) mice.

CONCLUSIONS

The accumulation of BS in plasma of Atp8b1(G308V/G308V) mice during BS feeding is not caused by increased intestinal BS absorption.

Cholestasis and cholestatic syndromes

PURPOSE OF REVIEW

This review focuses on the recent advances in cholestatic liver diseases. While there is an emphasis placed on translational and treatment-focused studies, basic science studies with the greatest impact on the field are also covered.

RECENT FINDINGS

Highlights include new discoveries for the role of the farsenoid X receptor and sodium-dependent taurocholate cotransporting polypeptide; new insights into the pathogenesis of progressive familial intrahepatic cholestasis type 1, biliary atresia, intrahepatic cholestasis of pregnancy, and primary biliary cirrhosis; new information for assessing prognosis in biliary atresia and primary biliary cirrhosis; and important clinical trials in intrahepatic cholestasis of pregnancy, primary biliary cirrhosis and primary sclerosing cholangitis.

SUMMARY

The studies of 2006 have furthered our understanding of cholestasis and cholestatic syndromes. While we continue to add to our knowledge of pathogenesis and treatment for many of these diseases, much work remains.