Loss of TAZ after YAP deletion severely impairs foregut development and worsens cholestatic hepatocellular injury.

BACKGROUND: We previously showed that loss of yes-associated protein 1 (YAP) in early liver development (YAPKO) leads to an Alagille syndrome-like phenotype, with failure of intrahepatic bile duct development, severe cholestasis, and chronic hepatocyte adaptations to reduce liver injury. TAZ, a paralog of YAP, was significantly upregulated in YAPKO hepatocytes and interacted with TEA domain family member (TEAD) transcription factors, suggesting possible compensatory activity. METHODS: We deleted both Yap1 and Wwtr1 (which encodes TAZ) during early liver development using the Foxa3 promoter to drive Cre expression, similar to YAPKO mice, resulting in YAP/TAZ double knockout (DKO) and YAPKO with TAZ heterozygosity (YAPKO TAZHET). We evaluated these mice using immunohistochemistry, serum biochemistry, bile acid profiling, and RNA sequencing. RESULTS: DKO mice were embryonic lethal, but their livers were similar to YAPKO, suggesting an extrahepatic cause of death. Male YAPKO TAZHET mice were also embryonic lethal, with insufficient samples to determine the cause. However, YAPKO TAZHET females survived and were phenotypically similar to YAPKO mice, with increased bile acid hydrophilicity and similar global gene expression adaptations but worsened the hepatocellular injury. TAZ heterozygosity in YAPKO impacted the expression of canonical YAP targets Ctgf and Cyr61, and we found changes in pathways regulating cell division and inflammatory signaling correlating with an increase in hepatocyte cell death, cell cycling, and macrophage recruitment. CONCLUSIONS: YAP loss (with or without TAZ loss) aborts biliary development. YAP and TAZ play a codependent critical role in foregut endoderm development outside the liver, but they are not essential for hepatocyte development. TAZ heterozygosity in YAPKO livers increased cell cycling and inflammatory signaling in the setting of chronic injury, highlighting genes that are especially sensitive to TAZ regulation.

Hepatocyte ß-catenin loss is compensated by Insulin-mTORC1 activation to promote liver regeneration.

BACKGROUND AND AIMS: Liver regeneration (LR) following partial hepatectomy (PH) occurs via activation of various signaling pathways. Disruption of a single pathway can be compensated by activation of another pathway to continue LR. The Wnt-ß-catenin pathway is activated early during LR and conditional hepatocyte loss of ß-catenin delays LR. Here, we study mechanism of LR in the absence of hepatocyte-ß-catenin. APPROACH AND RESULTS: Eight-week-old hepatocyte-specific Ctnnb1 knockout mice (ß-catenin ΔHC ) were subjected to PH. These animals exhibited decreased hepatocyte proliferation at 40-120 h and decreased cumulative 14-day BrdU labeling of <40%, but all mice survived, suggesting compensation. Insulin-mediated mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) activation was uniquely identified in the ß-catenin ΔHC mice at 72-96 h after PH. Deletion of hepatocyte regulatory-associated protein of mTOR (Raptor), a critical mTORC1 partner, in the ß-catenin ΔHC mice led to progressive hepatic injury and mortality by 30 dys. PH on early stage nonmorbid Raptor ΔHC -ß-catenin ΔHC mice led to lethality by 12 h. Raptor ΔHC mice showed progressive hepatic injury and spontaneous LR with ß-catenin activation but died by 40 days. PH on early stage nonmorbid Raptor ΔHC mice was lethal by 48 h. Temporal inhibition of insulin receptor and mTORC1 in ß-catenin ΔHC or controls after PH was achieved by administration of linsitinib at 48 h or rapamycin at 60 h post-PH and completely prevented LR leading to lethality by 12-14 days. CONCLUSIONS: Insulin-mTORC1 activation compensates for ß-catenin loss to enable LR after PH. mTORC1 signaling in hepatocytes itself is critical to both homeostasis and LR and is only partially compensated by ß-catenin activation. Dual inhibition of ß-catenin and mTOR may have notable untoward hepatotoxic side effects.

Single-cell spatial transcriptomics reveals a dynamic control of metabolic zonation and liver regeneration by endothelial cell Wnt2 and Wnt9b.

The conclusive identity of Wnts regulating liver zonation (LZ) and regeneration (LR) remains unclear despite an undisputed role of ß-catenin. Using single-cell analysis, we identified a conserved Wnt2 and Wnt9b expression in endothelial cells (ECs) in zone 3. EC-elimination of Wnt2 and Wnt9b led to both loss of ß-catenin targets in zone 3, and re-appearance of zone 1 genes in zone 3, unraveling dynamicity in the LZ process. Impaired LR observed in the knockouts phenocopied models of defective hepatic Wnt signaling. Administration of a tetravalent antibody to activate Wnt signaling rescued LZ and LR in the knockouts and induced zone 3 gene expression and LR in controls. Administration of the agonist also promoted LR in acetaminophen overdose acute liver failure (ALF) fulfilling an unmet clinical need. Overall, we report an unequivocal role of EC-Wnt2 and Wnt9b in LZ and LR and show the role of Wnt activators as regenerative therapy for ALF.

NOTCH-YAP1/TEAD-DNMT1 Axis Drives Hepatocyte Reprogramming Into Intrahepatic Cholangiocarcinoma.

BACKGROUND & AIMS: Intrahepatic cholangiocarcinoma (ICC) is a devastating liver cancer with extremely high intra- and inter-tumoral molecular heterogeneity, partly due to its diverse cellular origins. We investigated clinical relevance and the molecular mechanisms underlying hepatocyte (HC)-driven ICC development. METHODS: Expression of ICC driver genes in human diseased livers at risk for ICC development were examined. The sleeping beauty and hydrodynamic tail vein injection based Akt-NICD/YAP1 ICC model was used to investigate pathogenetic roles of SRY-box transcription factor 9 (SOX9) and yes-associated protein 1 (YAP1) in HC-driven ICC. We identified DNA methyltransferase 1 (DNMT1) as a YAP1 target, which was validated by loss- and gain-of-function studies, and its mechanism addressed by chromatin immunoprecipitation sequencing. RESULTS: Co-expression of AKT and Notch intracellular domain (NICD)/YAP1 in HC yielded ICC that represents 13% to 29% of clinical ICC. NICD independently regulates SOX9 and YAP1 and deletion of either, significantly delays ICC development. Yap1 or TEAD inhibition, but not Sox9 deletion, impairs HC-to-biliary epithelial cell (BEC) reprogramming. DNMT1 was discovered as a novel downstream effector of YAP1-TEAD complex that directs HC-to-BEC/ICC fate switch through the repression of HC-specific genes regulated by master regulators for HC differentiation, including hepatocyte nuclear factor 4 alpha, hepatocyte nuclear factor 1 alpha, and CCAAT/enhancer-binding protein alpha/beta. DNMT1 loss prevented NOTCH/YAP1-dependent HC-driven cholangiocarcinogenesis, and DNMT1 re-expression restored ICC development following TEAD repression. Co-expression of DNMT1 with AKT was sufficient to induce tumor development including ICC. DNMT1 was detected in a subset of HCs and dysplastic BECs in cholestatic human livers prone to ICC development. CONCLUSION: We identified a novel NOTCH-YAP1/TEAD-DNMT1 axis essential for HC-to-BEC/ICC conversion, which may be relevant in cholestasis-to-ICC pathogenesis in the clinic.

ß-Catenin-NF-κB-CFTR interactions in cholangiocytes regulate inflammation and fibrosis during ductular reaction.

Expansion of biliary epithelial cells (BECs) during ductular reaction (DR) is observed in liver diseases including cystic fibrosis (CF), and associated with inflammation and fibrosis, albeit without complete understanding of underlying mechanism. Using two different genetic mouse knockouts of ß-catenin, one with ß-catenin loss is hepatocytes and BECs (KO1), and another with loss in only hepatocytes (KO2), we demonstrate disparate long-term repair after an initial injury by 2-week choline-deficient ethionine-supplemented diet. KO2 show gradual liver repopulation with BEC-derived ß-catenin-positive hepatocytes and resolution of injury. KO1 showed persistent loss of ß-catenin, NF-κB activation in BECs, progressive DR and fibrosis, reminiscent of CF histology. We identify interactions of ß-catenin, NFκB, and CF transmembranous conductance regulator (CFTR) in BECs. Loss of CFTR or ß-catenin led to NF-κB activation, DR, and inflammation. Thus, we report a novel ß-catenin-NFκB-CFTR interactome in BECs, and its disruption may contribute to hepatic pathology of CF.

The liver has an incredible capacity to repair itself or 'regenerate' ­ that is, it has the ability to replace damaged tissue with new tissue. In order to do this, the organ relies on hepatocytes (the cells that form the liver) and bile duct cells (the cells that form the biliary ducts) dividing and transforming into each other to repair and replace damaged tissue, in case the insult is dire. During long-lasting or chronic liver injury, bile duct cells undergo a process called 'ductular reaction', which causes the cells to multiply and produce proteins that stimulate inflammation, and can lead to liver scarring (fibrosis). Ductular reaction is a hallmark of severe liver disease, and different diseases exhibit ductular reactions with distinct features. For example, in cystic fibrosis, a unique type of ductular reaction occurs at late stages, accompanied by both inflammation and fibrosis. Despite the role that ductular reaction plays in liver disease, it is not well understood how it works at the molecular level. Hu et al. set out to investigate how a protein called ß-catenin ­ which can cause many types of cells to proliferate ­ is involved in ductular reaction. They used three types of mice for their experiments: wild-type mice, which were not genetically modified; and two strains of genetically modified mice. One of these mutant mice did not produce ß-catenin in biliary duct cells, while the other lacked ß-catenin both in biliary duct cells and in hepatocytes. After a short liver injury ­ which Hu et al. caused by feeding the mice a specific diet ­ the wild-type mice were able to regenerate and repair the liver without exhibiting any ductular reaction. The mutant mice that lacked ß-catenin in hepatocytes showed a temporary ductular reaction, and ultimately repaired their livers by turning bile duct cells into hepatocytes. On the other hand, the mutant mice lacking ß-catenin in both hepatocytes and bile duct cells displayed sustained ductular reactions, inflammation and fibrosis, which looked like that seen in patients with liver disease associated to cystic fibrosis. Further probing showed that ß-catenin interacts with a protein called CTFR, which is involved in cystic fibrosis. When bile duct cells lack either of these proteins, another protein called NF-B gets activated, which causes the ductular reaction, leading to inflammation and fibrosis. The findings of Hu et al. shed light on the role of ß-catenin in ductular reaction. Further, the results show a previously unknown interaction between ß-catenin, CTFR and NF-B, which could lead to better treatments for cystic fibrosis in the future.

Compensatory hepatic adaptation accompanies permanent absence of intrahepatic biliary network due to YAP1 loss in liver progenitors.

Yes-associated protein 1 (YAP1) regulates cell plasticity during liver injury, regeneration, and cancer, but its role in liver development is unknown. We detect YAP1 activity in biliary cells and in cells at the hepatobiliary bifurcation in single-cell RNA sequencing analysis of developing livers. Deletion of Yap1 in hepatoblasts does not impair Notch-driven SOX9+ ductal plate formation but does prevent the formation of the abutting second layer of SOX9+ ductal cells, blocking the formation of a patent intrahepatic biliary tree. Intriguingly, these mice survive for 8 months with severe cholestatic injury and without hepatocyte-to-biliary transdifferentiation. Ductular reaction in the perihilar region suggests extrahepatic biliary proliferation, likely seeking the missing intrahepatic biliary network. Long-term survival of these mice occurs through hepatocyte adaptation via reduced metabolic and synthetic function, including altered bile acid metabolism and transport. Overall, we show YAP1 as a key regulator of bile duct development while highlighting a profound adaptive capability of hepatocytes.

Dual ß-Catenin and γ-Catenin Loss in Hepatocytes Impacts Their Polarity through Altered Transforming Growth Factor-ß and Hepatocyte Nuclear Factor 4α Signaling.

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. Loss of ß-catenin at adherens junctions is compensated by γ-catenin and dual loss of both catenins in double knockouts (DKOs) in mice liver leads to progressive intrahepatic cholestasis. However, the clinical relevance of this observation, and further phenotypic characterization of the phenotype, is important. Herein, simultaneous loss of ß-catenin and γ-catenin was identified in a subset of liver samples from patients of progressive familial intrahepatic cholestasis and primary sclerosing cholangitis. Hepatocytes in DKO mice exhibited defects in apical-basolateral localization of polarity proteins, impaired bile canaliculi formation, and loss of microvilli. Loss of polarity in DKO livers manifested as epithelial-mesenchymal transition, increased hepatocyte proliferation, and suppression of hepatocyte differentiation, which was associated with up-regulation of transforming growth factor-ß signaling and repression of hepatocyte nuclear factor 4α expression and activity. In conclusion, concomitant loss of the two catenins in the liver may play a pathogenic role in subsets of cholangiopathies. The findings also support a previously unknown role of ß-catenin and γ-catenin in the maintenance of hepatocyte polarity. Improved understanding of the regulation of hepatocyte polarization processes by ß-catenin and γ-catenin may potentially benefit development of new therapies for cholestasis.

Nuclear factor erythroid 2-related factor 2 and ß-Catenin Coactivation in Hepatocellular Cancer: Biological and Therapeutic Implications.

BACKGROUND AND AIMS: HCC remains a major unmet clinical need. Although activating catenin beta-1 (CTNNB1) mutations are observed in prominent subsets of HCC cases, these by themselves are insufficient for hepatocarcinogenesis. Coexpression of mutant CTNNB1 with clinically relevant co-occurrence has yielded HCCs. Here, we identify cooperation between ß-catenin and nuclear factor erythroid 2-related factor 2 (Nrf2) signaling in HCC. APPROACH AND RESULTS: Public HCC data sets were assessed for concomitant presence of CTNNB1 mutations and either mutations in nuclear factor erythroid-2-related factor-2 (NFE2L2) or Kelch like-ECH-associated protein 1 (KEAP1), or Nrf2 activation by gene signature. HCC development in mice and similarity to human HCC subsets was assessed following coexpression of T41A-CTNNB1 with either wild-type (WT)-, G31A-, or T80K-NFE2L2. Based on mammalian target of rapamycin complex 1 activation in CTNNB1-mutated HCCs, response of preclinical HCC to mammalian target of rapamycin (mTOR) inhibitor was investigated. Overall, 9% of HCC cases showed concomitant CTNNB1 mutations and Nrf2 activation, subsets of which were attributable to mutations in NFE2L2/KEAP1. Coexpression of mutated CTNNB1 with mutant NFE2L2, but not WT-NFE2L2, led to HCC development and mortality by 12-14 weeks. These HCCs were positive for ß-catenin targets, like glutamine synthetase and cyclin-D1, and Nrf2 targets, like NAD(P)H quinone dehydrogenase 1 and peroxiredoxin 1. RNA-sequencing and pathway analysis showed high concordance of preclinical HCC to human HCC subset showing activation of unique (iron homeostasis and glioblastoma multiforme signaling) and expected (glutamine metabolism) pathways. NFE2L2-CTNNB1 HCC mice were treated with mTOR inhibitor everolimus (5-mg/kg diet ad libitum), which led to >50% decrease in tumor burden. CONCLUSIONS: Coactivation of ß-catenin and Nrf2 is evident in 9% of all human HCCs. Coexpression of mutant NFE2L2 and mutant CTNNB1 led to clinically relevant HCC development in mice, which responded to mTOR inhibitors. Thus, this model has both biological and therapeutic implications.

Hepatic Stellate Cell-Specific Platelet-Derived Growth Factor Receptor-α Loss Reduces Fibrosis and Promotes Repair after Hepatocellular Injury.

Platelet-derived growth factor receptor (PDGFR)-α plays roles in cell survival, proliferation, and differentiation; however, its function in chronic liver injury sequelae, such as fibrosis, is unknown. Hepatic stellate cells (HSCs), the primary mediators of fibrosis, undergo activation, which entails differentiation to myofibroblasts, proliferation, migration, and collagen deposition, partially in response to PDGFs. To examine the role of PDGFR-α in HSCs, Lrat-Cre recombinase and Pdgfra-floxed mice were bred to generate Lrat-CrePdgfra-/- (knockout) animals, which were subjected to chronic liver injury through carbon tetrachloride treatment, bile duct ligation, and 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine. Although no major difference was observed after other types of liver injury, PDGFR-α loss in HSCs led to a significant albeit transient reduction in fibrosis after carbon tetrachloride injury, associated with increased HSC death and reduced migration. There was continued alleviation of hepatocellular injury in knockout mice despite ongoing carbon tetrachloride insult, associated with increased numbers of CD68 and F480 macrophages and increased clearance of damaged hepatocytes. Altogether our findings support a profibrotic role of PDGFR-α in HSCs during chronic liver injury in vivo via regulation of HSC survival and migration and affect the immune microenvironment, especially macrophages in clearing dying hepatocytes. Thus, our study provides a preclinical foundation for the future testing of therapeutic PDGFR-α inhibition in hepatic fibrosis, especially in combination with other therapies.

Inhibiting Glutamine-Dependent mTORC1 Activation Ameliorates Liver Cancers Driven by ß-Catenin Mutations.

Based on their lobule location, hepatocytes display differential gene expression, including pericentral hepatocytes that surround the central vein, which are marked by Wnt-ß-catenin signaling. Activating ß-catenin mutations occur in a variety of liver tumors, including hepatocellular carcinoma (HCC), but no specific therapies are available to treat these tumor subsets. Here, we identify a positive relationship between ß-catenin activation, its transcriptional target glutamine synthetase (GS), and p-mTOR-S2448, an indicator of mTORC1 activation. In normal livers of mice and humans, pericentral hepatocytes were simultaneously GS and p-mTOR-S2448 positive, as were ß-catenin-mutated liver tumors. Genetic disruption of ß-catenin signaling or GS prevented p-mTOR-S2448 expression, while its forced expression in ß-catenin-deficient livers led to ectopic p-mTOR-S2448 expression. Further, we found notable therapeutic benefit of mTORC1 inhibition in mutant-ß-catenin-driven HCC through suppression of cell proliferation and survival. Thus, mTORC1 inhibitors could be highly relevant in the treatment of liver tumors that are ß-catenin mutated and GS positive.

ß-Catenin and Yes-Associated Protein 1 Cooperate in Hepatoblastoma Pathogenesis.

Hepatoblastoma (HB), the most common pediatric primary liver neoplasm, shows nuclear localization of ß-catenin and yes-associated protein 1 (YAP1) in almost 80% of the cases. Co-expression of constitutively active S127A-YAP1 and ΔN90 deletion-mutant ß-catenin (YAP1-ΔN90-ß-catenin) causes HB in mice. Because heterogeneity in downstream signaling is being identified owing to mutational differences even in the ß-catenin gene alone, we investigated if co-expression of point mutants of ß-catenin (S33Y or S45Y) with S127A-YAP1 led to similar tumors as YAP1-ΔN90-ß-catenin. Co-expression of S33Y/S45Y-ß-catenin and S127A-YAP1 led to activation of Yap and Wnt signaling and development of HB, with 100% mortality by 13 to 14 weeks. Co-expression with YAP1-S45Y/S33Y-ß-catenin of the dominant-negative T-cell factor 4 or dominant-negative transcriptional enhanced associate domain 2, the respective surrogate transcription factors, prevented HB development. Although histologically similar, HB in YAP1-S45Y/S33Y-ß-catenin, unlike YAP1-ΔN90-ß-catenin HB, was glutamine synthetase (GS) positive. However, both ΔN90-ß-catenin and point-mutant ß-catenin comparably induced GS-luciferase reporter in vitro. Finally, using a previously reported 16-gene signature, it was shown that YAP1-ΔN90-ß-catenin HB tumors exhibited genetic similarities with more proliferative, less differentiated, GS-negative HB patient tumors, whereas YAP1-S33Y/S45Y-ß-catenin HB exhibited heterogeneity and clustered with both well-differentiated GS-positive and proliferative GS-negative patient tumors. Thus, we demonstrate that ß-catenin point mutants can also collaborate with YAP1 in HB development, albeit with a distinct molecular profile from the deletion mutant, which may have implications in both biology and therapy.

Loss of Wnt Secretion by Macrophages Promotes Hepatobiliary Injury after Administration of 3,5-Diethoxycarbonyl-1, 4-Dihydrocollidine Diet.

Exposure of mice to a diet containing 3,5-diethoxycarbonyl-1, 4-dihydrocollidine (DDC) induces porphyrin accumulation, cholestasis, immune response, and hepatobiliary damage mimicking hepatic porphyria and sclerosing cholangitis. Although ß-catenin signaling promotes hepatocyte proliferation, and macrophages are a source of Wnts, the role of macrophage-derived Wnts in modulating hepatobiliary injury/repair remains unresolved. We investigated the effect of macrophage-specific deletion of Wntless, a cargo protein critical for cellular Wnt secretion, by feeding macrophage-Wntless-knockout (Mac-KO) and wild-type littermates a DDC diet for 14 days. DDC exposure induced Wnt11 up-regulation in macrophages. Mac-KO mice on DDC showed increased serum alkaline phosphatase, aspartate aminotransferase, direct bilirubin, and histologic evidence of more cell death, inflammation, and ductular reaction. There was impaired hepatocyte proliferation evidenced by Ki-67 immunostaining, which was associated with decreased hepatocyte ß-catenin activation and cyclin-D1 in Mac-KO. Mac-KO also showed increased CD45, F4/80, and neutrophil infiltration after DDC diet, along with increased expression of several proinflammatory cytokines and chemokines. Gene expression analyses of bone marrow-derived macrophages from Mac-KO mice and F4/80+ macrophages isolated from DDC-fed Mac-KO livers showed proinflammatory M1 polarization. In conclusion, this study shows that a lack of macrophage Wnt secretion leads to more DDC-induced hepatic injury due to impaired hepatocyte proliferation and increased M1 macrophages, which promotes immune-mediated cell injury.

Hepatocyte-Specific ß-Catenin Deletion During Severe Liver Injury Provokes Cholangiocytes to Differentiate Into Hepatocytes.

Liver regeneration after injury is normally mediated by proliferation of hepatocytes, although recent studies have suggested biliary epithelial cells (BECs) can differentiate into hepatocytes during severe liver injury when hepatocyte proliferation is impaired. We investigated the effect of hepatocyte-specific ß-catenin deletion in recovery from severe liver injury and BEC-to-hepatocyte differentiation. To induce liver injury, we administered choline-deficient, ethionine-supplemented (CDE) diet to three different mouse models, the first being mice with deletion of ß-catenin in both BECs and hepatocytes (Albumin-Cre; Ctnnb1flox/flox mice). In our second model, we performed hepatocyte lineage tracing by injecting Ctnnb1flox/flox ; Rosa-stopflox/flox -EYFP mice with the adeno-associated virus serotype 8 encoding Cre recombinase under the control of the thyroid binding globulin promoter, a virus that infects only hepatocytes. Finally, we performed BEC lineage tracing via Krt19-CreERT ; Rosa-stopflox/flox -tdTomato mice. To observe BEC-to-hepatocyte differentiation, mice were allowed to recover on normal diet following CDE diet-induced liver injury. Livers were collected from all mice and analyzed by quantitative real-time polymerase chain reaction, western blotting, immunohistochemistry, and immunofluorescence. We show that mice with lack of ß-catenin in hepatocytes placed on the CDE diet develop severe liver injury with impaired hepatocyte proliferation, creating a stimulus for BECs to differentiate into hepatocytes. In particular, we use both hepatocyte and BEC lineage tracing to show that BECs differentiate into hepatocytes, which go on to repopulate the liver during long-term recovery. Conclusion: ß-catenin is important for liver regeneration after CDE diet-induced liver injury, and BEC-derived hepatocytes can permanently incorporate into the liver parenchyma to mediate liver regeneration.

Hdac1 Regulates Differentiation of Bipotent Liver Progenitor Cells During Regeneration via Sox9b and Cdk8.

BACKGROUND & AIMS: Upon liver injury in which hepatocyte proliferation is compromised, liver progenitor cells (LPCs), derived from biliary epithelial cells (BECs), differentiate into hepatocytes. Little is known about the mechanisms of LPC differentiation. We used zebrafish and mouse models of liver injury to study the mechanisms. METHODS: We used transgenic zebrafish, Tg(fabp10a:CFP-NTR), to study the effects of compounds that alter epigenetic factors on BEC-mediated liver regeneration. We analyzed zebrafish with disruptions of the histone deacetylase 1 gene (hdac1) or exposed to MS-275 (an inhibitor of Hdac1, Hdac2, and Hdac3). We also analyzed zebrafish with mutations in sox9b, fbxw7, kdm1a, and notch3. Zebrafish larvae were collected and analyzed by whole-mount immunostaining and in situ hybridization; their liver tissues were collected for quantitative reverse transcription polymerase chain reaction. We studied mice in which hepatocyte-specific deletion of ß-catenin (Ctnnb1flox/flox mice injected with Adeno-associated virus serotype 8 [AAV8]-TBG-Cre) induces differentiation of LPCs into hepatocytes after a choline-deficient, ethionine-supplemented (CDE) diet. Liver tissues were collected and analyzed by immunohistochemistry and immunoblots. We performed immunohistochemical analyses of liver tissues from patients with compensated or decompensated cirrhosis or acute on chronic liver failure (n = 15). RESULTS: Loss of Hdac1 activity in zebrafish blocked differentiation of LPCs into hepatocytes by increasing levels of sox9b mRNA and reduced differentiation of LPCs into BECs by increasing levels of cdk8 mRNA, which encodes a negative regulator gene of Notch signaling. We identified Notch3 as the receptor that regulates differentiation of LPCs into BECs. Loss of activity of Kdm1a, a lysine demethylase that forms repressive complexes with Hdac1, produced the same defects in differentiation of LPCs into hepatocytes and BECs as observed in zebrafish with loss of Hdac1 activity. Administration of MS-275 to mice with hepatocyte-specific loss of ß-catenin impaired differentiation of LPCs into hepatocytes after the CDE diet. HDAC1 was expressed in reactive ducts and hepatocyte buds of liver tissues from patients with cirrhosis. CONCLUSIONS: Hdac1 regulates differentiation of LPCs into hepatocytes via Sox9b and differentiation of LPCs into BECs via Cdk8, Fbxw7, and Notch3 in zebrafish with severe hepatocyte loss. HDAC1 activity was also required for differentiation of LPCs into hepatocytes in mice with liver injury after the CDE diet. These pathways might be manipulated to induce LPC differentiation for treatment of patients with advanced liver diseases.

Elimination of Wnt Secretion From Stellate Cells Is Dispensable for Zonation and Development of Liver Fibrosis Following Hepatobiliary Injury.

Alterations in the Wnt signaling pathway including those impacting hepatic stellate cells (HSCs) have been implicated in liver fibrosis. In the current study, we first examined the expression of Wnt genes in human HSC (HHSCs) after treatment with a profibrogenic factor TGF-ß1. Next, we generated HSC-specific Wntless (Wls) knockout (KO) using the Lrat-cre and Wls-floxed mice. KO and littermate controls (CON) were characterized for any basal phenotype and subjected to two liver fibrosis protocols. In vitro, TGF-ß1 induced expression of Wnt2, 5a and 9a while decreasing Wnt2b, 3a, 4, and 11 in HHSC. In vivo, KO and CON mice were born at normal Mendelian ratio and lacked any overt phenotype. Loss of Wnt secretion from HSCs had no effect on liver weight and did not impact ß-catenin activation in the pericentral hepatocytes. After 7 days of bile duct ligation (BDL), KO and CON showed comparable levels of serum alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, total and direct bilirubin. Comparable histology, Sirius red staining, and immunohistochemistry for α-SMA, desmin, Ki-67, F4/80, and CD45 indicated similar proliferation, inflammation, and portal fibrosis in both groups. Biweekly administration of carbon tetrachloride for 4 or 8 weeks also led to comparable serum biochemistry, inflammation, and fibrosis in KO and CON. Specific Wnt genes were altered in HHSCs in response to TGF-ß1; however, eliminating Wnt secretion from HSC did not impact basal ß-catenin activation in normal liver nor did it alter the injury-repair response during development of liver fibrosis.

Endothelial Wnts regulate ß-catenin signaling in murine liver zonation and regeneration: A sequel to the Wnt-Wnt situation.

ß-Catenin in hepatocytes, under the control of Wnts, regulates pericentral gene expression. It also contributes to liver regeneration (LR) after partial hepatectomy (PH) by regulating cyclin-D1 gene expression as shown in the ß-catenin and Wnt coreceptors low-density lipoprotein receptor-related protein 5/6 conditional knockouts (KO). However, conditional deletion of Wntless (Wls), required for Wnt secretion, in hepatocytes, cholangiocytes, or macrophages lacked any impact on zonation, while Wls deletion in macrophages only marginally affected LR. Here, we address the contribution of hepatic endothelial cells (ECs) in zonation and LR by characterizing EC-Wls-KO generated by interbreeding Wls-floxed and lymphatic vessel endothelial hyaluronan receptor (Lyve1)-cre mice. These mice were also used to study LR after PH. While Lyve1 expression in adult liver is limited to sinusoidal ECs only, Lyve1-cre mice bred to ROSA26-Stopflox/flox-enhanced yellow fluorescent protein (EYFP) mice showed EYFP labeling in sinusoidal and central vein ECs. EC-Wls-KO mice showed decreased liver weights; lacked glutamine synthetase, cytochrome P450 2e1, and cytochrome P450 1a2; and were resistant to acetaminophen-induced liver injury. After PH, EC-Wls-KO showed quantitative and qualitative differences in cyclin-D1 expression at 24-72 hours, which led to a lower hepatocyte proliferation at 40 hours but a rebound increase by 72 hours. ECs and macrophages isolated from regenerating livers at 12 hours showed significant up-regulation of Wnt2 and Wnt9b messenger RNA; these are the same two Wnts involved in baseline ß-catenin activity in pericentral hepatocytes. Conclusion: At baseline, ECs secrete Wnt proteins essential for ß-catenin activation in pericentral hepatocytes. During LR, sinusoidal and central vein ECs and secondarily macrophages secrete Wnt2, while predominantly central vein ECs and secondarily macrophages are the likely source of Wnt9b. This process spatiotemporally regulates ß-catenin activation in hepatocytes to induce cell proliferation. (Hepatology Communications 2018;2:845-860).

Dysregulated Bile Transporters and Impaired Tight Junctions During Chronic Liver Injury in Mice.

BACKGROUND & AIMS: Liver fibrosis, hepatocellular necrosis, inflammation, and proliferation of liver progenitor cells are features of chronic liver injury. Mouse models have been used to study the end-stage pathophysiology of chronic liver injury. However, little is known about differences in the mechanisms of liver injury among different mouse models because of our inability to visualize the progression of liver injury in vivo in mice. We developed a method to visualize bile transport and blood-bile barrier (BBlB) integrity in live mice. METHODS: C57BL/6 mice were fed a choline-deficient, ethionine-supplemented (CDE) diet or a diet containing 0.1% 3,5-diethoxycarbonyl-1, 4-dihydrocollidine (DDC) for up to 4 weeks to induce chronic liver injury. We used quantitative liver intravital microscopy (qLIM) for real-time assessment of bile transport and BBlB integrity in the intact livers of the live mice fed the CDE, DDC, or chow (control) diets. Liver tissues were collected from mice and analyzed by histology, immunohistochemistry, real-time polymerase chain reaction, and immunoblots. RESULTS: Mice with liver injury induced by a CDE or a DDC diet had breaches in the BBlB and impaired bile secretion, observed by qLIM compared with control mice. Impaired bile secretion was associated with reduced expression of several tight-junction proteins (claudins 3, 5, and 7) and bile transporters (NTCP, OATP1, BSEP, ABCG5, and ABCG8). A prolonged (2-week) CDE, but not DDC, diet led to re-expression of tight junction proteins and bile transporters, concomitant with the reestablishment of BBlB integrity and bile secretion. CONCLUSIONS: We used qLIM to study chronic liver injury, induced by a choline-deficient or DDC diet, in mice. Progression of chronic liver injury was accompanied by loss of bile transporters and tight junction proteins.

Hepatocyte-Derived Lipocalin 2 Is a Potential Serum Biomarker Reflecting Tumor Burden in Hepatoblastoma.

Hepatoblastoma (HB) is the most common pediatric liver malignant tumor. Previously, we reported co-activation of ß-catenin and Yes-associated protein-1 (YAP1) in 80% of HB. Hepatic co-expression of active ß-catenin and YAP1 via sleeping beauty transposon/transposase and hydrodynamic tail vein injection led to HB development in mice. Here, we identify lipocalin 2 (Lcn2) as a target of ß-catenin and YAP1 in HB and show that serum Lcn2 values positively correlated with tumor burden. Lcn2 was strongly expressed in HB tumor cells in our mouse model. A tissue array of 62 HB cases showed highest LCN2 expression in embryonal and lowest in fetal, blastemal, and small cell undifferentiated forms of HB. Knockdown of LCN2 in HB cells had no effect on cell proliferation but reduced NF-κB reporter activity. Next, liver-specific Lcn2 knockout (KO) mice were generated. No difference in tumor burden was observed between Lcn2 KO mice and wild-type littermate controls after sleeping beauty transposon/transposase and hydrodynamic tail vein injection delivery of active YAP1 and ß-catenin, although Lcn2 KO mice with HB lacked any serum Lcn2 elevation, demonstrating that transformed hepatocytes are the source of serum Lcn2. More blastemal areas and inflammation were observed within HB in Lcn2 KO compared with wild-type tumors. In conclusion, Lcn2 expressed in hepatocytes appears to be dispensable for the pathogenesis of HB. However, transformed hepatocytes secrete serum Lcn2, making Lcn2 a valuable biomarker for HB.

Bromodomain and Extraterminal (BET) Proteins Regulate Hepatocyte Proliferation in Hepatocyte-Driven Liver Regeneration.

Bromodomain and extraterminal (BET) proteins recruit key components of basic transcriptional machinery to promote gene expression. Aberrant expression and mutations in BET genes have been identified in many malignancies. Small molecule inhibitors of BET proteins such as JQ1 have shown efficacy in preclinical cancer models, including affecting growth of hepatocellular carcinoma. BET proteins also regulate cell proliferation in nontumor settings. We recently showed that BET proteins regulate cholangiocyte-driven liver regeneration. Here, we studied the role of BET proteins in hepatocyte-driven liver regeneration in partial hepatectomy (PHx) and acetaminophen-induced liver injury models in mice and zebrafish. JQ1 was injected 2 or 16 hours after PHx in mice to determine effect on hepatic injury, regeneration, and signaling. Mice treated with JQ1 after PHx displayed increased liver injury and a near-complete inhibition of hepatocyte proliferation. Levels of Ccnd1 mRNA and Cyclin D1 protein were reduced in animals injected with JQ1 16 hours after PHx and were even further reduced in animals injected with JQ1 2 hours after PHx. JQ1-treated zebrafish larvae after acetaminophen-induced injury also displayed notably impaired hepatocyte proliferation. In both models, Wnt signaling was prominently suppressed by JQ1. Our results show that BET proteins regulate hepatocyte proliferation-driven liver regeneration, and Wnt signaling is particularly sensitive to BET protein inhibition.

Hepatocyte Wnts Are Dispensable During Diethylnitrosamine and Carbon Tetrachloride-Induced Injury and Hepatocellular Cancer.

Activation of the Wnt/ß-catenin signaling is reported in large subsets of hepatocellular carcinoma (HCC). Upregulation of Wnt genes is one contributing mechanism. In the current study, we sought to address the role of hepatocyte-derived Wnts in a model of hepatic injury, fibrosis, and carcinogenesis. We subjected hepatocyte-specific Wntless knockout mice (HP-KO), unable to secrete Wnts from hepatocytes, and littermate controls (HP-CON) to diethylnitrosamine and carbon tetrachloride (DEN/CCl4) and harvested at 3, 5, and 6 months for histological and molecular analysis. Analysis at 5 months displayed increased hepatic expression of several Wnts and upregulation of some, but not all, ß-catenin targets, without mutations in Ctnnb1. At 5 months, HP-CON and HP-KO had comparable tumor burden and injury; however, HP-KO uniquely showed small CK19+ foci within tumors. At 6 months, both groups were moribund with comparable tumor burden and CK19 positivity. While HCC histology was indistinguishable between the groups, HP-KO exhibited increased active ß-catenin and decreased c-Myc, Brd4, E-cadherin, and others. Hepatic injury, inflammation, and fibrosis were also indistinguishable at 3 months between both groups. Thus, lack of Wnt secretion from hepatocytes did not affect overall injury, fibrosis, or HCC burden, although there were protein expression differences in the tumors occurring in the two groups.