Project description:The liver is the central organ critically regulating the balance of the metabolically potent yet toxic bile acids in the body. While genomic association studies have pointed to hepatic Sel1L – a critical component of mammalian Hrd1 ER-associated degradation (ERAD) machinery – as an influencer of serum bile acid levels, physiological relevance and mechanistic insights of ERAD in bile homeostasis remain unexplored. Using hepatocyte-specific Sel1L-deficient mouse models, we report that hepatic Sel1L-Hrd1 ERAD critically manages bile homeostasis in the body. Mice with hepatocyte-specific Sel1L developed intrahepatic cholestasis, with significant overload of bile acids in the liver and circulation under basal condition, and were hypersensitive to dietary bile acid challenge. By contrast, biliary bile acid and phosphatidylcholine levels were reduced, pointing to an export defect from hepatocytes. Unbiased proteomics analysis followed by biochemical assays revealed significant accumulation of the bile-stabilizing phosphatidylcholine exporter ATP-binding cassette 4 (Abcb4) in the ER of Sel1L-deficient livers, a gene associated with Progressive Familial Intrahepatic Cholestasis type III. Indeed, Abcb4 was a substrate of Sel1L-Hrd1 ERAD. Hence, hepatic Sel1L-Hrd1 ERAD maintains bile equilibrium via quality control of Abcb4 maturation in the ER.
Project description:Hepatocytes are highly polarized epithelia. Loss of hepatocyte polarity is associated with various liver diseases, including cholestasis. However, the molecular underpinnings of hepatocyte polarization remain poorly understood. Previously, we have shown that loss of β-catenin at adherens junctions (AJs) is compensated by β-catenin and dual loss of both catenins in dual knockouts (DKO) in mice liver leads to progressive intrahepatic cholestasis. However, the clinical relevance of this observation, and further phenotypic characterization of the phenotype, is important. Here, we identify simultaneous loss of β- and γ-catenin in a subset of liver samples from patients of progressive familial intrahepatic cholestasis and primary sclerosing cholangitis. Hepatocytes in DKO mice exhibited defect in apical-basolateral localization of polarity proteins, impaired bile canaliculi formation, and loss of microvilli. Loss of polarity in DKO livers manifested as epithelial-to-mesenchymal transition, increased hepatocyte proliferation, and suppression of hepatocyte differentiation, which was associated with up-regulation of TGFβ signaling and repression of Hnf4α expression and activity. In conclusion, concomitant loss of the two catenins in the liver may be playing a pathogenic role in subsets of cholangiopathies. Our findings also support a previously unknown role β- and γ-catenin in the maintenance of hepatocyte polarity. Improved understanding of the regulation of hepatocyte polarization processes by β and γ-catenin could potentially benefit development of new therapies for cholestasis.
Project description:<p>This longitudinal observational study will investigate the natural history and progression of four genetic causes of intrahepatic cholestasis of childhood, including alpha-1 antitrypsin deficiency (α1-AT), Alagille syndrome (AGS), progressive familial intrahepatic cholestasis (PFIC), and bile acid synthesis defects (BAD). This study will be conducted as part of the Cholestatic Liver Disease Consortium (CLiC), an NIH-funded multi-centered Rare Disease Clinical Research Consortium. In this study, we will collect defined data elements in a uniform fashion at fixed intervals for five years over a relatively large number of patients with these rare disorders. In addition, a biobank of patient specimens and DNA samples will be established for use in ancillary studies to be performed in addition to this study. By comparing outcome measures between the four liver diseases (i.e., using each disorder as a disease-control for the other disorders), the full impact of each disorder can best be determined in comparison to the other liver diseases. Using the longitudinal database in this fashion, this study will provide an improved understanding of the effects of the cholestatic liver during childhood irrespective of the underlying etiology as well as to the pathophysiology, outcome, and complications of each of the disorders. This initial characterization will allow calculation of sample sizes for future therapeutic intervention clinical trials and provide the baseline to which interventions should be compared.</p>
Project description:Liver biopsy samples were obtained from 64 infants with biliary atresia at the time of intraoperative cholangiogram. Liver biopsy samples were obtained from 14 age-matched infants with other causes of intrahepatic cholestasis, and from 7 deceased-donor children. GeneChip® Human Gene 1.0 ST Array (Affymetrix, CA) were used to screen mRNAs whose expression was specifically regulated in the livers from patients with biliary atresia. Gene expression profiling: Liver biopsy samples obtained from infantas with other causes of intrahepatic cholestasis were served as diseased control. Liver tissue obtained from deceased-donor children were served as normal control. A molecular signataure of biliary atresia at the time of diagnosis was identified by comparing hepatic gene expression profile from biliary atresia to those from diseased and normal controls. This dataset is part of the TransQST collection.
Project description:Ubiquitin-specific proteases (USPs) are the largest class of human deubiquitinases (DUBs) and comprise its phylogenetically most distant members USP53 and USP54, which are annotated as catalytically inactive pseudo-enzymes. Conspicuously, mutations in the USP domain of USP53 cause progressive familial intrahepatic cholestasis. Here we report the discovery that USP53 and USP54 are active DUBs with high specificity for K63-linked polyubiquitin. We demonstrate how USP53 patient mutations abrogate catalytic activity, implicating loss of DUB activity in USP53-mediated pathology. Depletion of USP53 increases K63-linked ubiquitination of tricellular junction components. Assays with substrate-bound polyubiquitin reveal that USP54 cleaves within K63-linked chains, whereas USP53 can en bloc deubiquitinate substrate proteins in a K63-linkage-dependent manner. Biochemical and structural analyses uncover underlying K63-specific S2-ubiquitin-binding sites within their catalytic domains. Collectively, our work revises the annotation of USP53 and USP54, provides reagents and a mechanistic framework to investigate K63-polyubiquitin decoding, and establishes K63-linkage-directed deubiquitination as novel DUB activity.
Project description:We used microarrays to provide a transcriptomic signature of different types of cholestasis evoked by 3 different drugs and obstructive surgery Adverse outcome pathways (AOPs) have been recently introduced as tools to map the mechanisms underlying toxic events relevant for chemical risk assessment. AOPs particularly depict the linkage between a molecular initiating event and an adverse outcome through a number of intermediate key events. An AOP has been previously introduced for cholestatic liver injury. The objective of this study was to test the robustness of this AOP for different types of cholestatic insult and the in vitro to in vivo extrapolation. For this purpose, in vitro samples from human hepatoma HepaRG cell cultures were exposed to cholestatic drugs (i.e. intrahepatic cholestasis), while in vivo samples were obtained from livers of cholestatic mice (i.e. extrahepatic cholestasis). The occurrence of cholestasis in vitro was confirmed through analysis of bile transporter functionality and bile acid analysis. Transcriptomic analysis revealed inflammation and oxidative stress as key events in both types of cholestatic liver injury. Major transcriptional differences between intrahepatic and extrahepatic cholestatic liver insults were observed at the level of cell death and metabolism. Novel key events identified by pathway analysis included endoplasmic reticulum stress in intrahepatic cholestasis, and autophagy and necroptosis in both intrahepatic as extrahepatic cholestasis. This study demonstrates that AOPs constitute dynamic tools that should be frequently updated with new input information.
Project description:Liver biopsy samples were obtained from 64 infants with biliary atresia at the time of intraoperative cholangiogram. Liver biopsy samples were obtained from 14 age-matched infants with other causes of intrahepatic cholestasis, and from 7 deceased-donor children. GeneChip® Human Gene 1.0 ST Array (Affymetrix, CA) were used to screen mRNAs whose expression was specifically regulated in the livers from patients with biliary atresia.
Project description:Cholelithiasis-induced cholestasis is one of the most common causes of hospitalization due to gastrointestinal disease, yet considerable knowledge gaps exist in the pathogenesis of this disease. This can partially be explained by inadequate characterization of experimental cholestasis models. Therefore, we compared the transcriptional profile of commonly used mouse models for obstructive cholestasis and benchmarked them to human disease to identify the model(s) best suited for cholelithiasis-induced cholestasis research and to uncover conserved mechanisms involved in human and murine cholestasis. Selected mouse models included bile duct ligation (BDL) surgery, 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet, associated with extra- and intrahepatic obstructive cholestasis, respectively, and a drug-induced cholestasis model relying on cyclosporin A (CsA), in an acute and chronic setting. Human samples were collected from patients with cholelithiasis-induced cholestasis of an acute and recurrent nature. RNA sequencing was performed on mouse and human liver tissue. Both the BDL and DDC models, but not the CsA model, were shown to be applicable for studying cholelithiasis-induced cholestasis, with transcriptomic profiles that highly correspond to acute cholestasis in human patients. In particular, the conservation of canonical pathways related to the inflammatory response and cytoskeleton organization, in which the Rho family GTPase is involved, were identified. This study furthermore revealed some promising mechanistic-based transcriptomic biomarkers relevant for murine and human cholestasis, which could potentially be useful for robust prediction and detection of diverse types of cholestatic liver disease.