Antagonizing Activin A/p15INK4b Signaling as Therapeutic Strategy for Liver Disease

BACKGROUND/AIM

Activin A is involved in the pathogenesis of human liver diseases, but its therapeutic targeting is not fully explored. Here, we tested the effect of novel, highly specific small-molecule-based activin A antagonists (NUCC-474/555) in improving liver regeneration following partial hepatectomy and halting fibrosis progression in models of chronic liver diseases (CLDs).

METHODS

Cell toxicity of antagonists was determined in rat hepatocytes and Huh-7 cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay. Hepatocytes and hepatic stellate cells (HSCs) were treated with activin A and NUCC-555 and analyzed by reverse transcription-polymerase chain reaction and immunohistochemistry. Partial hepatectomized Fisher (F)344 rats were treated with NUCC-555, and bromodeoxyuridine (BrdU) incorporation was determined at 18/24/36/120/240 h. NUCC-555 was administered into thioacetamide- or carbon tetrachloride-treated F344 rats or C57BL/6 mice, and the fibrosis progression was studied.

RESULTS

NUCC-474 showed higher cytotoxicity in cultured hepatic cells; therefore, NUCC-555 was used in subsequent studies. Activin A-stimulated overexpression of cell cycle-/senescence-related genes (e.g., p15INK4b, DEC1, Glb1) was near-completely reversed by NUCC-555 in hepatocytes. Activin A-mediated HSC activation was blocked by NUCC-555. In partial hepatectomized rats, antagonizing activin A signaling resulted in a 1.9-fold and 2.3-fold increase in BrdU+ cells at 18 and 24 h, respectively. Administration of NUCC-555 in rats and mice with progressing fibrosis significantly reduced collagen accumulation (7.9-fold), HSC activation indicated by reduced alpha smooth muscle actin+ and vimentin+ cells, and serum aminotransferase activity.

CONCLUSIONS

Our studies demonstrate that activin A antagonist NUCC-555 promotes liver regeneration and halts fibrosis progression in CLD models, suggesting that blocking activin A signaling may represent a new approach to treating people with CLD.

Mechanism and Effect of HNF4α Decrease in a Rat Model of Cirrhosis and Liver Failure

BACKGROUND & AIMS

HNF4α, a master regulator of liver development and the mature hepatocyte phenotype, is down-regulated in chronic and inflammatory liver disease. We used contemporary transcriptomics and epigenomics to study the cause and effects of this down-regulation and characterized a multicellular etiology.

METHODS

Progressive changes in the rat carbon tetrachloride model were studied by deep RNA sequencing and genome-wide chromatin immunoprecipitation sequencing analysis of transcription factor (TF) binding and chromatin modification. Studies compared decompensated cirrhosis with liver failure after 26 weeks of treatment with earlier compensated cirrhosis and with additional rat models of chronic fibrosis. Finally, to resolve cell-specific responses and intercellular signaling, we compared transcriptomes of liver, nonparenchymal, and inflammatory cells.

RESULTS

HNF4α was significantly lower in 26-week cirrhosis, part of a general reduction of TFs that regulate metabolism. Nevertheless, increased binding of HNF4α contributed to strong activation of major phenotypic genes, whereas reduced binding to other genes had a moderate phenotypic effect. Decreased Hnf4a expression was the combined effect of STAT3 and nuclear factor kappa B (NFκB) activation, which similarly reduced expression of other metabolic TFs. STAT/NFκB also induced de novo expression of Osmr by hepatocytes to complement induced expression of Osm by nonparenchymal cells.

CONCLUSIONS

Liver decompensation by inflammatory STAT3 and NFκB signaling was not a direct consequence of progressive cirrhosis. Despite significant reduction of Hnf4a expression, residual levels of this abundant TF still stimulated strong new gene expression. Reduction of HNF4α was part of a broad hepatocyte transcriptional response to inflammation.

Hepatocyte Smoothened Activity Controls Susceptibility to Insulin Resistance and Nonalcoholic Fatty Liver Disease

BACKGROUND & AIMS

Nonalcoholic steatohepatitis (NASH), a leading cause of cirrhosis, strongly associates with the metabolic syndrome, an insulin-resistant proinflammatory state that disrupts energy balance and promotes progressive liver degeneration. We aimed to define the role of Smoothened (Smo), an obligatory component of the Hedgehog signaling pathway, in controlling hepatocyte metabolic homeostasis and, thereby, susceptibility to NASH.

METHODS

We conditionally deleted Smo in hepatocytes of healthy chow-fed mice and performed metabolic phenotyping, coupled with single-cell RNA sequencing (RNA-seq), to characterize the role of hepatocyte Smo in regulating basal hepatic and systemic metabolic homeostasis. Liver RNA-seq datasets from 2 large human cohorts were also analyzed to define the relationship between Smo and NASH susceptibility in people.

RESULTS

Hepatocyte Smo deletion inhibited the Hedgehog pathway and promoted fatty liver, hyperinsulinemia, and insulin resistance. We identified a plausible mechanism whereby inactivation of Smo stimulated the mTORC1-SREBP1c signaling axis, which promoted lipogenesis while inhibiting the hepatic insulin cascade. Transcriptomics of bulk and single Smo-deficient hepatocytes supported suppression of insulin signaling and also revealed molecular abnormalities associated with oxidative stress and mitochondrial dysfunction. Analysis of human bulk RNA-seq data revealed that Smo expression was (1) highest in healthy livers, (2) lower in livers with NASH than in those with simple steatosis, (3) negatively correlated with markers of insulin resistance and liver injury, and (4) declined progressively as fibrosis severity worsened.

CONCLUSIONS

The Hedgehog pathway controls insulin sensitivity and energy homeostasis in adult livers. Loss of hepatocyte Hedgehog activity induces hepatic and systemic metabolic stress and enhances susceptibility to NASH by promoting hepatic lipoxicity and insulin resistance.

Dysregulation of Lipid and Glucose Homeostasis in Hepatocyte-Specific SLC25A34 Knockout Mice

Nonalcoholic fatty liver disease (NAFLD) is an epidemic affecting 30% of the US population. It is characterized by insulin resistance, and by defective lipid metabolism and mitochondrial dysfunction in the liver. SLC25A34 is a major repressive target of miR-122, a miR that has a central role in NAFLD and liver cancer. However, little is known about the function of SLC25A34. To investigate SLC25A34 in vitro, mitochondrial respiration and bioenergetics were examined using hepatocytes depleted of Slc25a34 or overexpressing Slc25a34. To test the function of SLC25A34 in vivo, a hepatocyte-specific knockout mouse was generated, and loss of SLC25A34 was assessed in mice maintained on a chow diet and a fast-food diet (FFD), a model for NAFLD. Hepatocytes depleted of Slc25a34 displayed increased mitochondrial biogenesis, lipid synthesis, and ADP/ATP ratio; Slc25a34 overexpression had the opposite effect. In the knockout model on chow diet, SLC25A34 loss modestly affected liver function (altered glucose metabolism was the most pronounced defect). RNA-sequencing revealed changes in metabolic processes, especially fatty acid metabolism. After 2 months on FFD, knockouts had a more severe phenotype, with increased lipid content and impaired glucose tolerance, which was attenuated after longer FFD feeding (6 months). This work thus presents a novel model for studying SLC25A34 in vivo in which SLC25A34 plays a role in mitochondrial respiration and bioenergetics during NAFLD.

Lymphocyte-Specific Protein-1 Suppresses Xenobiotic-Induced Constitutive Androstane Receptor and Subsequent Yes-Associated Protein-Activated Hepatocyte Proliferation

Activation of constitutive androstane receptor (CAR) transcription factor by xenobiotics promotes hepatocellular proliferation, promotes hypertrophy without liver injury, and induces drug metabolism genes. Previous work demonstrated that lymphocyte-specific protein-1 (LSP1), an F-actin binding protein and gene involved in human hepatocellular carcinoma, suppresses hepatocellular proliferation after partial hepatectomy. The current study investigated the role of LSP1 in liver enlargement induced by chemical mitogens, a regenerative process independent of tissue loss. 1,4-Bis [2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP), a direct CAR ligand and strong chemical mitogen, was administered to global Lsp1 knockout and hepatocyte-specific Lsp1 transgenic (TG) mice and measured cell proliferation, hypertrophy, and expression of CAR-dependent drug metabolism genes. TG livers displayed a significant decrease in Ki-67 labeling and liver/body weight ratios compared with wild type on day 2. Surprisingly, this was reversed by day 5, due to hepatocyte hypertrophy. There was no difference in CAR-regulated drug metabolism genes between wild type and TG. TG livers displayed increased Yes-associated protein (YAP) phosphorylation, decreased nuclear YAP, and direct interaction between LSP1 and YAP, suggesting LSP1 suppresses TCPOBOP-driven hepatocellular proliferation, but not hepatocyte volume, through YAP. Conversely, loss of LSP1 led to increased hepatocellular proliferation on days 2, 5, and 7. LSP1 selectively suppresses CAR-induced hepatocellular proliferation, but not drug metabolism, through the interaction of LSP1 with YAP, supporting the role of LSP1 as a selective growth suppressor.

Yes-Associated Protein Is Crucial for Constitutive Androstane Receptor-Driven Hepatocyte Proliferation But Not for Induction of Drug Metabolism Genes in Mice

BACKGROUND AND AIMS

Constitutive androstane receptor (CAR) agonists, such as 1,4-bis [2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP), are known to cause robust hepatocyte proliferation and hepatomegaly in mice along with induction of drug metabolism genes without any associated liver injury. Yes-associated protein (Yap) is a key transcription regulator that tightly controls organ size, including that of liver. Our and other previous studies suggested increased nuclear localization and activation of Yap after TCPOBOP treatment in mice and the potential role of Yap in CAR-driven proliferative response. Here, we investigated a direct role of Yap in CAR-driven hepatomegaly and hepatocyte proliferation using hepatocyte-specific Yap-knockout (KO) mice.

APPROACH AND RESULTS

Adeno-associated virus 8-thyroxine binding globulin promoter-Cre recombinase vector was injected to Yap-floxed mice for achieving hepatocyte-specific Yap deletion followed by TCPOBOP treatment. Yap deletion did not decrease protein expression of CAR or CAR-driven induction of drug metabolism genes (including cytochrome P450 [Cyp] 2b10, Cyp2c55, and UDP-glucuronosyltransferase 1a1 [Ugt1a1]). However, Yap deletion substantially reduced TCPOBOP-induced hepatocyte proliferation. TCPOBOP-driven cell cycle activation was disrupted in Yap-KO mice because of delayed (and decreased) induction of cyclin D1 and higher expression of p21, resulting in decreased phosphorylation of retinoblastoma protein. Furthermore, the induction of other cyclins, which are sequentially involved in progression through cell cycle (including cyclin E1, A2, and B1), and important mitotic regulators (such as Aurora B kinase and polo-like kinase 1) was remarkably reduced in Yap-KO mice. Microarray analysis revealed that 26% of TCPOBOP-responsive genes that were mainly related to proliferation, but not to drug metabolism, were altered by Yap deletion. Yap regulated these proliferation genes through alerting expression of Myc and forkhead box protein M1, two critical transcriptional regulators of CAR-mediated hepatocyte proliferation.

CONCLUSIONS

Our study revealed an important role of Yap signaling in CAR-driven hepatocyte proliferation; however, CAR-driven induction of drug metabolism genes was independent of Yap.

Deletion of conserved non-coding sequences downstream from NKX2-1: A novel disease-causing mechanism for benign hereditary chorea

Background

Benign hereditary chorea (BHC) is an autosomal dominant disorder characterized by early‐onset non‐progressive involuntary movements. Although NKX2‐1 mutations or deletions are the cause of BHC, some BHC families do not have pathogenic alterations in the NKX2‐1 gene, indicating that mutations of non‐coding regulatory elements of NKX2‐1 may also play a role.

Methods and Results

By using whole‐genome microarray analysis, we identified a 117 Kb founder deletion in three apparently unrelated BHC families that were negative for NKX2‐1 sequence variants. Targeted next generation sequencing analysis confirmed the deletion and showed that it was part of a complex local genomic rearrangement. In addition, we also detected a 648 Kb de novo deletion in an isolated BHC case. Both deletions are located downstream from NKX2‐1 on chromosome 14q13.2‐q13.3 and share a 33 Kb smallest region of overlap with six previously reported cases. This region has no gene but contains multiple evolutionarily highly conserved non‐coding sequences.

Conclusion

We propose that the deletion of potential regulatory elements necessary for NKX2‐1 expression in this critical region is responsible for BHC phenotype in these patients, and this is a novel disease‐causing mechanism for BHC.

Targeted Inhibition of the E3 Ligase SCFSkp2/Cks1 Has Antitumor Activity in RB1-Deficient Human and Mouse Small-Cell Lung Cancer

The RB1 tumor suppressor gene is mutated in highly aggressive tumors including small-cell lung cancer (SCLC), where its loss, along with TP53, is required and sufficient for tumorigenesis. While RB1-mutant cells fail to arrest at G₁-S in response to cell-cycle restriction point signals, this information has not led to effective strategies to treat RB1-deficient tumors, as it is challenging to develop targeted drugs for tumors that are driven by the loss of gene function. Our group previously identified Skp2, a substrate recruiting subunit of the SCF-Skp2 E3 ubiquitin ligase, as an early repression target of pRb whose knockout blocked tumorigenesis in Rb1-deficient prostate and pituitary tumors. Here we used genetic mouse models to demonstrate that deletion of Skp2 completely blocked the formation of SCLC in Rb1/Trp53-knockout mice (RP mice). Skp2 KO caused an increased accumulation of the Skp2-degradation target p27, a cyclin-dependent kinase inhibitor, which was confirmed as the mechanism of protection by using knock-in of a mutant p27 that was unable to bind to Skp2. Building on the observed synthetic lethality between Rb1 and Skp2, we found that small molecules that bind/inhibit Skp2 have in vivo antitumor activity in mouse tumors and human patient-derived xenograft models of SCLC. Using genetic and pharmacologic approaches, antitumor activity was seen with Skp2 loss or inhibition in established SCLC primary lung tumors, in liver metastases, and in chemotherapy-resistant tumors. Our data highlight a downstream actionable target in RB1-deficient cancers, for which there are currently no targeted therapies available. SIGNIFICANCE: There are no effective therapies for SCLC. The identification of an actionable target downstream of RB1, inactivated in SCLC and other advanced tumors, could have a broad impact on its treatment.

Constitutive Activation of the Human Aryl Hydrocarbon Receptor in Mice Promotes Hepatocarcinogenesis Independent of Its Coactivator Gadd45b

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), or dioxin, is a potent liver cancer promoter through its sustained activation of the aryl hydrocarbon receptor (Ahr) in rodents. However, the carcinogenic effect of TCDD and AHR in humans has been controversial. It has been suggested that the inter-species difference in the carcinogenic activity of AhR is largely due to different ligand affinity in that TCDD has a 10-fold lower affinity for the human AHR compared with the mouse Ahr. It remains unclear whether the activation of human AHR is sufficient to promote hepatocellular carcinogenesis. The goal of this study is to clarify whether activation of human AHR can promote hepatocarcinogenesis. Here we reported the oncogenic activity of human AHR in promoting hepatocellular carcinogenesis. Constitutive activation of the human AHR in transgenic mice was as efficient as its mouse counterpart in promoting diethylnitrosamine (DEN)-initiated hepatocellular carcinogenesis. The growth arrest and DNA damage-inducible gene 45 β (Gadd45b), a signaling molecule inducible by external stress and UV irradiation, is highly induced upon AHR activation. Further analysis revealed that Gadd45b is a novel AHR target gene and a transcriptional coactivator of AHR. Interestingly, ablation of Gadd45b in mice did not abolish the tumor promoting effects of the human AHR. Collectively, our findings suggested that constitutive activation of human AHR was sufficient to promote hepatocarcinogenesis.

Pharmacologic Inhibition of Epidermal Growth Factor Receptor Suppresses Nonalcoholic Fatty Liver Disease in a Murine Fast-Food Diet Model

Epidermal growth factor receptor (EGFR) is a critical regulator of hepatocyte proliferation and liver regeneration. Our recent work indicated that EGFR can also regulate lipid metabolism during liver regeneration after partial hepatectomy. Based on these findings, we investigated the role of EGFR in a mouse model of nonalcoholic fatty liver disease (NAFLD) using a pharmacological inhibition strategy. C57BL6/J mice were fed a chow diet or a fast-food diet (FFD) with or without EGFR inhibitor (canertinib) for 2 months. EGFR inhibition completely prevented development of steatosis and liver injury in this model. In order to study if EGFR inhibition can reverse NAFLD progression, mice were fed the FFD for 5 months, with or without canertinib treatment for the last 5 weeks of the study. EGFR inhibition remarkably decreased steatosis, liver injury, and fibrosis and improved glucose tolerance. Microarray analysis revealed that ~40% of genes altered by the FFD were differentially expressed after EGFR inhibition and, thus, are potentially regulated by EGFR. Several genes and enzymes related to lipid metabolism (particularly fatty acid synthesis and lipolysis), which were disrupted by the FFD, were found to be modulated by EGFR. Several crucial transcription factors that play a central role in regulating these lipid metabolism genes during NAFLD, including peroxisome proliferator-activated receptor gamma (PPARγ), sterol regulatory element-binding transcription factor 1 (SREBF1), carbohydrate-responsive element-binding protein, and hepatocyte nuclear factor 4 alpha, were also found to be modulated by EGFR. In fact, chromatin immunoprecipitation analysis revealed that PPARγ binding to several crucial lipid metabolism genes (fatty acid synthase, stearoyl-coenzyme A desaturase 1, and perilipin 2) was drastically reduced by EGFR inhibition. Further upstream, EGFR inhibition suppressed AKT signaling, which is known to control these transcription factors, including PPARγ and SREBF1, in NAFLD models. Lastly, the effect of EGFR in FFD-induced fatty-liver phenotype was not shared by receptor tyrosine kinase MET, investigated using MET knockout mice. Conclusion: Our study revealed a role of EGFR in NAFLD and the potential of EGFR inhibition as a treatment strategy for NAFLD.

Biliary Obstruction Promotes Multilineage Differentiation of Hepatic Stem Cells

Because of their high regenerative potential, stem cells are an ideal resource for development of therapies that replace injured tissue mass and restore function in patients with end-stage liver diseases. Using a rat model of bile duct ligation (BDL) and biliary fibrosis, we investigated cell engraftment, liver repopulation, and ectopic tissue formation after intrasplenic transplantation of epithelial stem/progenitor cells. Fetal liver cells were infused into the spleens of Fisher 344 rats with progressing biliary fibrosis induced by common BDL or rats without BDL. Cell delivery was well tolerated. After migration to the liver, donor-derived stem/progenitor cells engrafted, differentiated into hepatocytes and cholangiocytes, and formed large cell clusters at 2 months in BDL rats but not controls. Substantial numbers of donor cells were also detected at the splenic injection site where they generated hepatic and nonhepatic tissue. Transplanted cells differentiated into phenotypes other than hepato/cholangiocytic cells only in rats that underwent BDL. Quantitative reverse-transcription polymerase chain reaction analyses demonstrated marked up-regulation of tissue-specific genes of nonhepatic endodermal lineages (e.g., caudal type homeobox 2 [Cdx2], pancreatic and duodenal homeobox 1 [Pdx1], keratin 13 [CK-13]), confirmed by immunohistochemistry. Conclusion: BDL and its induced fibrosis promote liver repopulation by ectopically transplanted fetal liver-derived cells. These cell fractions contain multipotent stem cells that colonize the spleen of BDL rats and differentiate into multiple gastrointestinal tissues, including liver, pancreas, intestine, and esophagus. The splenic microenvironment, therefore, represents an ideal niche to assess the differentiation of these stem cells, while BDL provides a stimulus that induces their differentiation.

Loss of hepatocyte β-catenin protects mice from experimental porphyria-associated liver injury

BACKGROUND & AIMS

Porphyrias result from anomalies of heme biosynthetic enzymes and can lead to cirrhosis and hepatocellular cancer. In mice, these diseases can be modeled by administration of a diet containing 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC), which causes accumulation of porphyrin intermediates, resulting in hepatobiliary injury. Wnt/β-catenin signaling has been shown to be a modulatable target in models of biliary injury; thus, we investigated its role in DDC-driven injury.

METHODS

β-Catenin (Ctnnb1) knockout (KO) mice, Wnt co-receptor KO mice, and littermate controls were fed a DDC diet for 2 weeks. β-Catenin was exogenously inhibited in hepatocytes by administering β-catenin dicer-substrate RNA (DsiRNA), conjugated to a lipid nanoparticle, to mice after DDC diet and then weekly for 4 weeks. In all experiments, serum and livers were collected; livers were analyzed by histology, western blotting, and real-time PCR. Porphyrin was measured by fluorescence, quantification of polarized light images, and liquid chromatography-mass spectrometry.

RESULTS

DDC-fed mice lacking β-catenin or Wnt signaling had decreased liver injury compared to controls. Exogenous mice that underwent β-catenin suppression by DsiRNA during DDC feeding also showed less injury compared to control mice receiving lipid nanoparticles. Control livers contained extensive porphyrin deposits which were largely absent in mice lacking β-catenin signaling. Notably, we identified a network of key heme biosynthesis enzymes that are suppressed in the absence of β-catenin, preventing accumulation of toxic protoporphyrins. Additionally, mice lacking β-catenin exhibited fewer protein aggregates, improved proteasomal activity, and reduced induction of autophagy, all contributing to protection from injury.

CONCLUSIONS

β-Catenin inhibition, through its pleiotropic effects on metabolism, cell stress, and autophagy, represents a novel therapeutic approach for patients with porphyria.

LAY SUMMARY

Porphyrias are disorders resulting from abnormalities in the steps that lead to heme production, which cause build-up of toxic by-products called porphyrins. Liver is commonly either a source or a target of excess porphyrins, and complications can range from minor abnormalities to liver failure. In this report, we inhibited Wnt/β-catenin signaling in an experimental model of porphyria, which resulted in decreased liver injury. Targeting β-catenin affected multiple components of the heme biosynthesis pathway, thus preventing build-up of porphyrin intermediates. Our study suggests that drugs inhibiting β-catenin activity could reduce the amount of porphyrin accumulation and help alleviate symptoms in patients with porphyria.

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 β-catenin (Ctnnb1^flox/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 β-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.

Binding of Drug-Activated CAR/Nr1i3 Alters Metabolic Regulation in the Liver

The constitutive androstane receptor (CAR/Nr1i3) regulates detoxification of drugs and other xenobiotics by the liver. Binding of these compounds, activating ligands, causes CAR to translocate to the nucleus and stimulate genes of detoxification. However, CAR activation also changes metabolism and induces rapid liver growth. To explain this gene regulation, we characterized the genome-wide early binding of CAR; its binding partner, RXRα; and the acetylation that they induced on H4K5. CAR-linked genes showed either stimulation or inhibition and regulated lipid, carbohydrate, and energy metabolism, as well as detoxification. Stimulation of expression increased, but inhibition did not decrease, H4K5Ac. Transcriptional inhibition occurred when CAR bound with HNF4α, PPARα, or FXR on the same enhancers. Functional competition among these bound nuclear receptors normally coordinates transcriptional resources as metabolism shifts. However, binding of drug-activated CAR to the same enhancers adds a new competitor that constitutively alters the normal balance of metabolic gene regulation.

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CAR activation stimulates a massive liver transcriptional response

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Target genes control drug detoxification, general metabolism, and liver growth

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CAR stimulates genes through coactivation and histone acetylation

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CAR inhibits genes when it shares their enhancers with other nuclear receptors

β-Catenin regulation of farnesoid X receptor signaling and bile acid metabolism during murine cholestasis

Cholestatic liver diseases result from impaired bile flow and are characterized by inflammation, atypical ductular proliferation, and fibrosis. The Wnt/β-catenin pathway plays a role in bile duct development, yet its role in cholestatic injury remains indeterminate. Liver-specific β-catenin knockout mice and wild-type littermates were subjected to cholestatic injury through bile duct ligation or short-term exposure to 3,5-diethoxycarbonyl-1,4-dihydrocollidine diet. Intriguingly, knockout mice exhibit a dramatic protection from liver injury, fibrosis, and atypical ductular proliferation, which coincides with significantly decreased total hepatic bile acids (BAs). This led to the discovery of a role for β-catenin in regulating BA synthesis and transport through regulation of farnesoid X receptor (FXR) activation. We show that β-catenin functions as both an inhibitor of nuclear translocation and a nuclear corepressor through formation of a physical complex with FXR. Loss of β-catenin expedited FXR nuclear localization and FXR/retinoic X receptor alpha association, culminating in small heterodimer protein promoter occupancy and activation in response to BA or FXR agonist. Conversely, accumulation of β-catenin sequesters FXR, thus inhibiting its activation. Finally, exogenous suppression of β-catenin expression during cholestatic injury reduces β-catenin/FXR complex activation of FXR to decrease total BA and alleviate hepatic injury.

CONCLUSION

We have identified an FXR/β-catenin interaction whose modulation through β-catenin suppression promotes FXR activation and decreases hepatic BAs, which may provide unique therapeutic opportunities in cholestatic liver diseases. (Hepatology 2018;67:955-971).

Activin A is a prominent autocrine regulator of hepatocyte growth arrest

Activin A, a multifunctional cytokine, plays an important role in hepatocyte growth suppression and is involved in liver size control. The present study was aimed to determine the cell location of activin A in the normal rat liver microenvironment and the contribution of activin A signaling to the hepatocyte phenotype to obtain insight into molecular mechanisms. Immunohistochemical and in situ hybridization analyses identified hepatocytes as the major activin A‐positive cell population in normal liver and identified mast cells as an additional activin A source. To investigate paracrine and autocrine activin A‐stimulated effects, hepatocytes were cocultured with engineered activin A‐secreting cell lines (RF1, TL8) or transduced with an adeno‐associated virus vector encoding activin βA, which led to strikingly altered expression of cell cycle‐related genes (Ki‐67, E2F transcription factor 1 [E2F1], minichromosome maintenance complex component 2 [Mcm2], forkhead box M1 [FoxM1]) and senescence‐related genes (cyclin‐dependent kinase inhibitor 2B [p15^INK4b/CDKN2B], differentiated embryo‐chondrocyte expressed gene 1 [DEC1]) and reduced proliferation and induction of senescence. Microarray analyses identified 453 differentially expressed genes, many of which were not yet recognized as activin A downstream targets (e.g., ADAM metallopeptidase domain 12 [Adam12], semaphorin 7A [Sema7a], LIM and cysteine‐rich domains‐1 [Lmcd1], DAB2, clathrin adaptor protein [Dab2]). Among the main activin A‐mediated molecular/cellular functions are cellular growth/proliferation and movement, molecular transport, and metabolic processes containing highly down‐regulated genes, such as cytochrome P450, subfamily 2, polypeptide 11 (Cyp2C11), sulfotransferase family 1A, member 1 (Sult1a1), glycine‐N‐acyltransferase (Glyat), and bile acid‐CoA:amino acid N‐acyltransferase (Baat). Moreover, Ingenuity Pathway Analyses identified particular gene networks regulated by hepatocyte nuclear factor (HNF)‐4α and peroxisome proliferator‐activated receptor gamma (PPARγ) as key targets of activin A signaling. Conclusion: Our in vitro models demonstrated that activin A‐stimulated growth inhibition and cellular senescence is mediated through p15^INK4b/CDKN2B and is associated with up‐ and down‐regulation of numerous target genes involved in multiple biological processes performed by hepatocytes, suggesting that activin A fulfills a critical role in normal liver function. (Hepatology Communications 2017;1:852‐870)

p27T187A knockin identifies Skp2/Cks1 pocket inhibitors for advanced prostate cancer

SCFSkp2/Cks1 ubiquitinates Thr187-phosphorylated p27 for degradation. Overexpression of Skp2 coupled with underexpression of p27 are frequent characteristics of cancer cells. When the role of SCFSkp2/Cks1-mediated p27 ubiquitination in cancer was specifically tested by p27 Thr187-to-Ala knockin (p27T187A KI), it was found dispensable for KrasG12D-induced lung tumorigenesis but essential for Rb1-deficient pituitary tumorigenesis. Here we identify pRb and p53 doubly deficient (DKO) prostate tumorigenesis as a context in which p27 ubiquitination by SCFSkp2/Cks1 is required for p27 downregulation. p27 protein accumulated in prostate when p27T187A KI mice underwent DKO prostate tumorigenesis. p27T187A KI or Skp2 knockdown (KD) induced similar degrees of p27 protein accumulation in DKO prostate cells, and Skp2 KD did not further increase p27 protein in DKO prostate cells that contained p27T187A KI (AADKO prostate cells). p27T187A KI activated an E2F1-p73-apoptosis axis in DKO prostate tumorigenesis, slowed disease progression and significantly extended survival. Querying co-occurrence relationships among RB1, TP53, PTEN, NKX3-1 and MYC in TCGA of prostate cancer identified co-inactivation of RB1 and TP53 as the only statistically significant co-occurrences in metastatic castration-resistant prostate cancer (mCRPC). Together, our study identifies Skp2/Cks1 pocket inhibitors as potential therapeutics for mCRPC. Procedures for establishing mCRPC organoid cultures from contemporary patients were recently established. An Skp2/Cks1 pocket inhibitor preferentially collapsed DKO prostate tumor organoids over AADKO organoids, which spontaneously disintegrated over time when DKO prostate tumor organoids grew larger, setting the stage to translate mouse model findings to precision medicine in the clinic on the organoid platform.

Triple Staining Including FOXA2 Identifies Stem Cell Lineages Undergoing Hepatic and Biliary Differentiation in Cirrhotic Human Liver

Recent investigations have reported many markers associated with human liver stem/progenitor cells, "oval cells," and identified "niches" in diseased livers where stem cells occur. However, there has remained a need to identify entire lineages of stem cells as they differentiate into bile ducts or hepatocytes. We have used combined immunohistochemical staining for a marker of hepatic commitment and specification (FOXA2 [Forkhead box A2]), hepatocyte maturation (Albumin and HepPar1), and features of bile ducts (CK19 [cytokeratin 19]) to identify lineages of stem cells differentiating toward the hepatocytic or bile ductular compartments of end-stage cirrhotic human liver. We identified large clusters of disorganized, FOXA2 expressing, oval cells in localized liver regions surrounded by fibrotic matrix, designated as "micro-niches." Specific FOXA2-positive cells within the micro-niches organize into primitive duct structures that support both hepatocytic and bile ductular differentiation enabling identification of entire lineages of cells forming the two types of structures. We also detected expression of hsa-miR-122 in primitive ductular reactions expected for hepatocytic differentiation and hsa-miR-23b cluster expression that drives liver cell fate decisions in cells undergoing lineage commitment. Our data establish the foundation for a mechanistic hypothesis on how stem cell lineages progress in specialized micro-niches in cirrhotic end-stage liver disease.

Biliary fibrosis drives liver repopulation and phenotype transition of transplanted hepatocytes

BACKGROUND & AIMS

Current research focuses on developing alternative strategies to restore decreased liver mass prior to the onset of end-stage liver disease. Cell engraftment/repopulation requires regeneration in normal liver, but we have shown that severe liver injury stimulates repopulation without partial hepatectomy (PH). We have now investigated whether a less severe injury, secondary biliary fibrosis, would drive engraftment/repopulation of ectopically transplanted mature hepatocytes.

METHODS

Ductular proliferation and progressive fibrosis in dipeptidyl-peptidase IV (DPPIV)(-) F344 rats was induced by common bile duct ligation (BDL). Purified DPPIV(+)/green fluorescent protein (GFP)(+) hepatocytes were infused without PH into the spleen of BDL rats and compared to rats without BDL.

RESULTS

Within one week, transplanted hepatocytes were detected in hepatic portal areas and at the periphery of expanding portal regions. DPPIV(+)/GFP(+) repopulating cell clusters of different sizes were observed in BDL rats but not untreated normal recipients. Surprisingly, some engrafted hepatocytes formed CK-19/claudin-7 expressing epithelial cells resembling cholangiocytes within repopulating clusters. In addition, substantial numbers of hepatocytes engrafted at the intrasplenic injection site assembled into multicellular groups. These also showed biliary "transdifferentiation" in the majority of intrasplenic injection sites of rats that received BDL but not in untreated recipients. PCR array analysis showed upregulation of osteopontin (SPP1). Cell culture studies demonstrated increased Itgβ4, HNF1β, HNF6, Sox-9, and CK-19 mRNA expression in hepatocytes incubated with osteopontin, suggesting that this secreted protein promotes dedifferentiation of hepatocytes.

CONCLUSIONS

Our studies show that biliary fibrosis stimulates liver repopulation by ectopically transplanted hepatocytes and also stimulates hepatocyte transition towards a biliary epithelial phenotype.

Precise let-7 expression levels balance organ regeneration against tumor suppression

The in vivo roles for even the most intensely studied microRNAs remain poorly defined. Here, analysis of mouse models revealed that let-7, a large and ancient microRNA family, performs tumor suppressive roles at the expense of regeneration. Too little or too much let-7 resulted in compromised protection against cancer or tissue damage, respectively. Modest let-7 overexpression abrogated MYC-driven liver cancer by antagonizing multiple let-7 sensitive oncogenes. However, the same level of overexpression blocked liver regeneration, while let-7 deletion enhanced it, demonstrating that distinct let-7 levels can mediate desirable phenotypes. let-7 dependent regeneration phenotypes resulted from influences on the insulin-PI3K-mTOR pathway. We found that chronic high-dose let-7 overexpression caused liver damage and degeneration, paradoxically leading to tumorigenesis. These dose-dependent roles for let-7 in tissue repair and tumorigenesis rationalize the tight regulation of this microRNA in development, and have important implications for let-7 based therapeutics.

DOI:http://dx.doi.org/10.7554/eLife.09431.001

The development of animals is guided by the expression of certain genes at critical moments. Many different mechanisms control development; in one of them, the expression of genes can be decreased by molecules called microRNAs. In particular, the group of microRNAs called let-7 has been intensively studied in roundworms and fruit flies. Although mammals have extremely similar let-7 microRNAs they seem to be more important during adulthood.

Previous studies using cells grown in the laboratory have shown that mammalian let-7 microRNAs decrease cell proliferation and cell growth. Furthermore, in mouse models of various cancers, let-7 microRNAs often reduce tumour growth when they are supplied to adult mice. Therefore, overall the let-7 group has been classified as genes that act to suppress tumors, and thus protect mice (and most likely humans too) from cancers. However, in-depth analysis of let-7 microRNAs was still missing.

Wu and Nguyen et al. have now studied mice with liver cancer using strains where they were able to regulate the levels of let-7. These mice overproduce a strong cancer-inducing gene in the liver; half were used as controls and the other half were further engineered to have moderately elevated levels of let-7 expression. Most of the control mice got large cancerous tumors, but only a few mice in the other group developed cancers and the tumors were smaller. This confirmed that let-7 hinders tumor formation.

Wu and Nguyen et al. also observed that the protected mice were less able to regenerate their liver tissues. Further experiments showed that deleting just two out of ten let-7 microRNAs enhanced the mice’s ability to regenerate liver tissue after injury. These findings indicate that let-7 microRNAs slow down the growth of both cancerous and normal cells. Lastly, when let-7 levels were raised to very high levels for a prolonged amount of time this actually led to liver damage and subsequent tumor formation.

This last observation may have important consequences for possible cancer therapies. Some scientists have shown that providing extra let-7 can slow or even reverse tumour growth, but the findings here clearly point out that too much let-7 could actually worsen the situation. Since the let-7 family comprises a handful of microRNAs in mammals, in the future it will also be important to find out to what extent these molecules play overlapping roles and how much they differ.

DOI:http://dx.doi.org/10.7554/eLife.09431.002

Resetting the transcription factor network reverses terminal chronic hepatic failure

The cause of organ failure is enigmatic for many degenerative diseases, including end-stage liver disease. Here, using a CCl4-induced rat model of irreversible and fatal hepatic failure, which also exhibits terminal changes in the extracellular matrix, we demonstrated that chronic injury stably reprograms the critical balance of transcription factors and that diseased and dedifferentiated cells can be returned to normal function by re-expression of critical transcription factors, a process similar to the type of reprogramming that induces somatic cells to become pluripotent or to change their cell lineage. Forced re-expression of the transcription factor HNF4α induced expression of the other hepatocyte-expressed transcription factors; restored functionality in terminally diseased hepatocytes isolated from CCl4-treated rats; and rapidly reversed fatal liver failure in CCl4-treated animals by restoring diseased hepatocytes rather than replacing them with new hepatocytes or stem cells. Together, the results of our study indicate that disruption of the transcription factor network and cellular dedifferentiation likely mediate terminal liver failure and suggest reinstatement of this network has therapeutic potential for correcting organ failure without cell replacement.

Femoral nerve infusion after primary total knee arthroplasty: a prospective, double-blind, randomised and placebo-controlled trial

Objectives

Effective analgesia after total knee arthroplasty (TKA) improves patient satisfaction, mobility and expedites discharge. This study assessed whether continuous femoral nerve infusion (CFNI) was superior to a single-shot femoral nerve block in primary TKA surgery completed under subarachnoid blockade including morphine.

Methods

We performed an adequately powered, prospective, randomised, placebo-controlled trial comparing CFNI of 0.125% bupivacaine versus normal saline following a single-shot femoral nerve block and subarachnoid anaesthesia with intrathecal morphine for primary TKA. Patients were randomised to either treatment (CFNI 0 ml to 10 ml/h 0.125% bupivacaine) or placebo (CFNI 0 ml to 10 ml/h normal saline). Both groups received a single-shot femoral nerve block (0.25% 20 ml bupivacaine) prior to placement of femoral nerve catheter and subarachnoid anaesthesia with intrathecal morphine. All patients had a standardised analgesic protocol. The primary end point was post-operative visual analogue scale (VAS) pain score over 72 hours post-surgery. Secondary outcomes were morphine equivalent dose, range of movement, side effects, and length of stay.

Results

A total of 86 patients were recruited. Treatment and placebo groups were comparable. No significant difference was found in VAS pain scores, total morphine equivalent requirements, side effects, range of movement, motor block, or length of hospital stay.

Conclusion

No significant advantage was found for CFNI over a single-shot femoral block and subarachnoid anaesthesia after TKA.

Cite this article: Bone Joint Res 2015;4:11–16.

Antibacterial validation of electrogenerated hypochlorite using carbon-based electrodes

This proof-of-concept study explores the novel use of carbon-based electrodes for the electrochemical generation of hypochlorite and compares the antimicrobial efficacy against commercial hypochlorite solution. Antimicrobial concentrations of hypochlorite were generated using pad-printed carbon and carbon fibre electrodes, yielding up to 0·027% hypochlorite in 60 min and 0·1% hypochlorite in 15 min, respectively, in a nondivided assembly. The minimum inhibitory concentration (MIC) of the electrogenerated hypochlorite produced using carbon fibre electrodes was established for four medically important bacteria (Pseudomonas aeruginosa and Staphylococcus aureus approx. 0·025%, Escherichia coli and Enterococcus faecalis approx. 0·012%) and found to be in agreement with those determined using commercial hypochlorite solution. Therefore, carbon-based electrodes, particularly carbon fibre, have proven effective for the generation of antimicrobial concentrations of hypochlorite. The similarity of the MIC values to commercial hypochlorite solutions suggests that the antimicrobial efficacy is derived from the quantified hypochlorite generated and not due to marked cogeneration of reactive oxygen species, as identified for other assemblies. As such, the application of carbon electrodes may be suitable for the local production of hypochlorite for healthcare antisepsis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Carbon fibre electrodes can rapidly generate antimicrobial concentrations of hypochlorite; as such, these cheap and commercially available electrodes are proposed for the local production of hypochlorite for healthcare antisepsis. Importantly, the antimicrobial properties of the electrochemically generated hypochlorite mirror those of commercial hypochlorite, suggesting this is not enhanced by the cogeneration of reactive oxygen species. This illustrates the potential use of disposable carbon electrodes for localized small-volume production of hypochlorite for surface and skin cleansing, and opens a broader scope of research into the exploitation of carbon electrodes for this application.