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.

Bile Duct Ligation Induces ATZ Globule Clearance in a Mouse Model of α-1 Antitrypsin Deficiency.

α-1 Antitrypsin deficiency (A1ATD) can progress to cirrhosis and hepatocellular carcinoma; however, not all patients are susceptible to severe liver disease. In A1ATD, a toxic gain-of-function mutation generates insoluble ATZ "globules" in hepatocytes, overwhelming protein clearance mechanisms. The relationship between bile acids and hepatocytic autophagy is less clear but may involve altered gene expression pathways. Based on previous findings that bile duct ligation (BDL) induces autophagy, we hypothesized that retained bile acids may have hepatoprotective effects in PiZZ transgenic mice, which model A1ATD. We performed BDL and partial BDL (pBDL) in PiZZ mice, followed by analysis of liver tissues. PiZZ liver subjected to BDL showed up to 50% clearance of ATZ globules, with increased expression of autophagy proteins. Analysis of transcription factors revealed significant changes. Surprisingly nuclear TFEB, a master regulator of autophagy, remained unchanged. pBDL confirmed that ATZ globule clearance was induced by localized stimuli rather than diet or systemic effects. Several genes involved in bile metabolism were overexpressed in globule-devoid hepatocytes, compared to globule-containing cells. Retained bile acids led to a dramatic reduction of ATZ globules, with enhanced hepatocyte regeneration and autophagy. These findings support investigation of synthetic bile acids as potential autophagy-enhancing agents.

Genes inducing iPS phenotype play a role in hepatocyte survival and proliferation in vitro and liver regeneration in vivo.

UNLABELLED: Reprogramming factors have been used to induce pluripotent stem cells as an alternative to somatic cell nuclear transfer technology in studies targeting disease models and regenerative medicine. The neuronal repressor RE-1 silencing transcription factor (REST) maintains self-renewal and pluripotency in mouse embryonic stem cells by maintaining the expression of Oct3/4, Nanog, and cMyc. We report that primary hepatocytes express REST and most of the reprogramming factors in culture. Their expression is up-regulated by hepatocyte growth factor (HGF) and epidermal growth factor (EGF). REST inhibition results in down-regulation of reprogramming factor expression, increased apoptosis, decreased proliferation, and cell death. The reprogramming factors are also up-regulated after 70% partial hepatectomy in vivo. CONCLUSION: These findings show that genes inducing the iPS phenotype, even though expressed at lower levels than embryonic stem cells, nonetheless are associated with control of apoptosis and cell proliferation in hepatocytes in culture and may play a role in such processes during liver regeneration.

Hepatocyte proliferation and hepatomegaly induced by phenobarbital and 1,4-bis [2-(3,5-dichloropyridyloxy)] benzene is suppressed in hepatocyte-targeted glypican 3 transgenic mice.

UNLABELLED: Glypican 3 (GPC3) is a family of glycosylphosphatidylinositol-anchored, cell-surface heparan sulfate proteoglycans. Loss-of-function mutations of GPC3 cause Simpson-Golabi-Behmel syndrome characterized by overgrowth of multiple organs, including liver. Our previous study showed that in GPC3 transgenic (TG) mice, hepatocyte-targeted overexpression of GPC3 suppresses hepatocyte proliferation and liver regeneration after partial hepatectomy and alters gene expression profiles and potential cell cycle-related proteins. This study investigates the role of GPC3 in hepatocyte proliferation and hepatomegaly induced by the xenobiotic mitogens phenobarbital (PB) and TCPOBOP (1, 4-bis [2-(3, 5-dichloropyridyloxy)] benzene). Wildtype (WT) and GPC3 TG mice were given 0.1% PB in drinking water for 10 days or a single dose of TCPOBOP (3 mg/kg) by oral gavage. At day 5 the WT mice showed a 2.2- and 3.0-fold increase in liver weight, whereas the GPC3 TG mice showed a 1.3- and 1.6-fold increase in liver weight after PB and TCPOBOP administration, respectively. There was a significant suppression of proliferative response in the GPC3 TG mice, as assessed by percent of Ki67-positive hepatocyte nuclei. Moreover, gene array analysis showed a panel of changes in the gene expression profile of TG mice, both before and after administration of the xenobiotic mitogens. Expression of cell cycle-related genes in the TG mice was also decreased compared to the WT mice. CONCLUSION: Our results indicate that in GPC3 TG mice, hepatocyte-targeted overexpression of GPC3 plays an important role for regulation of liver size and termination of hepatocyte proliferation induced by the xenobiotic mitogens PB and TCPOBOP, comparable to the effects seen in the GPC3 TG mice during liver regeneration after partial hepatectomy.

Excessive hepatomegaly of mice with hepatocyte-targeted elimination of integrin linked kinase following treatment with 1,4-bis [2-(3,5-dichaloropyridyloxy)] benzene.

UNLABELLED: TCBOPOP (1,4-bis [2-(3,5-dichaloropyridyloxy)] benzene) an agonist of the constitutive androstane receptor (CAR), produces rapid hepatocyte hyperplasia and hepatomegaly in the absence of hepatic injury. In this study we demonstrate that integrin-linked kinase (ILK), which is involved in transmission of the extracellular matrix (ECM) signaling by way of integrin receptors, plays an important role in regulating TCPOBOP-induced proliferation of hepatocytes and hepatomegaly. Hepatocyte-specific ILK knockout mice (ILK/liver-/- mice) and wildtype mice (WT) were given a single dose of TCPOBOP (3 mg/kg) by oral gavage. Mice were sacrificed at days 1, 2, 5, and 7 after TCPOBOP administration. WT mice showed maximum proliferation on days 1 and 2, which came back to baseline levels by days 5 and 7 after TCPOBOP administration. The ILK/liver-/- mice, on the other hand, showed a prolonged and a sustained proliferative response as evident by an increased number of proliferative cell nuclear antigen assay (PCNA)-positive cells even at days 5 and 7 after TCPOBOP administration. At day 7 the WT mice showed close to a 2.5-fold increase in liver weight, whereas the ILK/liver-/- mice showed a 3.7-fold increase in liver weight. The prolonged proliferative response in the ILK/liver-/- mice seems to be due to sustained induction of CAR leading to sustained induction of c-Myc, which is known to be a key mediator of TCPOPOP-CAR induced direct liver hyperplasia. CONCLUSION: The data indicate that ECM-mediated signaling by way of ILK is essential for adjustment of final liver size and proper termination of TCPOBOP-induced proliferation of hepatocytes.

Personalized Medicine for Liver Disease: From Molecular Mechanisms to Potential Targeted Therapies.

This Special Issue, entitled "Personalized Medicine for Liver Disease: From Molecular Mechanisms to Potential Targeted Therapies", includes 11 publications from colleagues working on various liver diseases including non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease (ALD), hepatocellular carcinoma (HCC), primary biliary cholangitis (PBC), as well as various treatment modalities including pharmacotherapies and liver transplantation [...].

Suppression of liver regeneration and hepatocyte proliferation in hepatocyte-targeted glypican 3 transgenic mice.

UNLABELLED: Glypican 3 (GPC3) belongs to a family of glycosylphosphatidylinositol-anchored, cell-surface heparan sulfate proteoglycans. GPC3 is overexpressed in hepatocellular carcinoma. Loss-of-function mutations of GPC3 result in Simpson-Golabi-Behmel syndrome, an X-linked disorder characterized by overgrowth of multiple organs, including the liver. Our previous study showed that GPC3 plays a negative regulatory role in hepatocyte proliferation, and this effect may involve CD81, a cell membrane tetraspanin. To further investigate GPC3 in vivo, we engineered transgenic (TG) mice overexpressing GPC3 in the liver under the control of the albumin promoter. GPC3 TG mice with hepatocyte-targeted, overexpressed GPC3 developed normally in comparison with their nontransgenic littermates but had a suppressed rate of hepatocyte proliferation and liver regeneration after partial hepatectomy. Moreover, gene array analysis revealed a series of changes in the gene expression profiles in TG mice (both in normal mice and during liver regeneration). In unoperated GPC3 TG mice, there was overexpression of runt related transcription factor 3 (7.6-fold), CCAAT/enhancer binding protein alpha (2.5-fold), GABA A receptor (2.9-fold), and wingless-related MMTV integration site 7B (2.8-fold). There was down-regulation of insulin-like growth factor binding protein 1 (8.4-fold), Rab2 (5.6-fold), beta-catenin (1.7-fold), transforming growth factor beta type I (3.1-fold), nodal (1.8-fold), and yes-associated protein (1.4-fold). Changes after hepatectomy included decreased expression in several cell cycle-related genes. CONCLUSION: Our results indicate that in GPC3 TG mice, hepatocyte overexpression of GPC3 suppresses hepatocyte proliferation and liver regeneration and alters gene expression profiles, and potential cell cycle-related proteins and multiple other pathways are involved and affected.

Investigation of the role of glypican 3 in liver regeneration and hepatocyte proliferation.

Glypicans are heparan sulfate proteoglycans that are bound to the cell surface by glycosylphosphatidylinositol. While six members of the glypican family are known in mammals, our study focused on glypican 3 (GPC3). Loss-of-function mutations of GPC3 result in the Simpson-Golabi-Behmel syndrome, an X-linked disorder characterized by pre- and postnatal liver and other organ overgrowth. GPC3 is overexpressed in human hepatocellular carcinoma; however, its role in normal liver regeneration and hepatocyte proliferation is unknown. Here we investigated the role of GPC3 in hepatocyte proliferation. GPC3 mRNA and protein levels begin to increase 2 days after hepatectomy with peak expression levels by day 5. In hepatocyte cultures, GPC3 reaches a plateau when hepatocyte proliferation decreases. In vitro studies using Morpholino oligonucleotides showed that blocking GPC3 expression promoted hepatocyte growth. Yeast two-hybrid assays revealed that GPC3 interacts with CD81, a member of the tetraspanin family that is reported to be involved in hepatitis C virus infection and cell proliferation. We found that CD81 levels also increased 2 days after partial hepatectomy and toward the end of regeneration. Immunofluorescence showed that CD81 and GPC3 colocalize by 2 and 6 days after hepatectomy. Co-immunoprecipitation validated the interaction of GPC3 and CD81. Our results indicate that GPC3 may be a negative regulator of liver regeneration and hepatocyte proliferation, and that this regulation may involve CD81.

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.

Cell cycle effects resulting from inhibition of hepatocyte growth factor and its receptor c-Met in regenerating rat livers by RNA interference.

UNLABELLED: Hepatocyte growth factor (HGF) and its receptor c-Met are involved in liver regeneration. The role of HGF and c-Met in liver regeneration in rat following two-thirds partial hepatectomy (PHx) was investigated using RNA interference to silence HGF and c-Met in separate experiments. A mixture of 2 c-Met-specific short hairpin RNA (ShRNA) sequences, ShM1 and ShM2, and 3 HGF-specific ShRNA, ShH1, ShH3, and ShH4, were complexed with linear polyethylenimine. Rats were injected with the ShRNA/PEI complex 24 hours before and at the time of PHx. A mismatch and a scrambled ShRNA served as negative controls. ShRNA treatment resulted in suppression of c-Met and HGF mRNA and protein compared with that in controls. The regenerative response was assessed by PCNA, mitotic index, and BrdU labeling. Treatment with the ShHGF mixture resulted in moderate suppression of hepatocyte proliferation. Immunohistochemical analysis revealed severe suppression of incorporation of BrdU and complete absence of mitosis in rats treated with ShMet 24 hours after PHx compared with that in controls. Gene array analyses indicated abnormal expression patterns in many cell-cycle- and apoptosis-related genes. The active form of caspase 3 was seen to increase in ShMet-treated rats. The TUNEL assay indicated a slight increase in apoptosis in ShMet-treated rats compared with that in controls. CONCLUSION: The data indicated that in vivo silencing of c-Met and HGF mRNA by RNA interference in normal rats results in suppression of mRNA and protein, which had a measurable effect on proliferation kinetics associated with liver regeneration.

Phenobarbital regulates nuclear expression of HNF-4alpha in mouse and rat hepatocytes independent of CAR and PXR.

Phenobarbital is a lipophilic molecule used as a sedative and antiepileptic drug that elicits a multitude of effects in the liver, including gross liver enlargement, hepatocyte hypertrophy, and induced expression of drug-metabolizing enzymes and other liver-specific genes. The constitutive androstane receptor (CAR; NR1I3) and to a lesser extent the pregnane X receptor (PXR; NR1I2) are responsible for mediating induction of many phenobarbital-responsive genes. However, CAR-mediated transcriptional control of some genes is critically dependent on hepatocyte nuclear factor 4 alpha (HNF-4alpha; NR2A1), which itself regulates multiple liver-specific genes involved in hepatic growth, metabolism, and differentiation. We studied the effects of phenobarbital on HNF-4alpha expression in hepatocytes and provide evidence that HNF-4alpha nuclear expression is regulated in response to phenobarbital. Real-time polymerase chain reaction analyses revealed that HNF-4alpha mRNA is modestly up-regulated by phenobarbital. In addition, nuclear expression of HNF-4alpha protein is significantly elevated 3 hours after the administration of phenobarbital in wild-type, CAR-/-, and CAR-/-/PXR-/- mice. In vitro analysis revealed that phenobarbital-induced HNF-4alpha expression is both time- and dose dependent. In addition, the phosphatase inhibitor okadaic acid and the Ca2+/calmodulin-dependent protein kinase II inhibitor KN62 block nuclear induction of HNF-4alpha by phenobarbital. Furthermore, HNF-4alpha nuclear expression is enhanced by inhibition of cyclic AMP-dependent protein kinase A. In conclusion, induced nuclear expression of HNF-4alpha and CAR is an integral part of the phenobarbital response, aimed at coordinated regulation of genes involved in drug metabolism and detoxification as well as maintenance of liver function.

Expression of Notch-1 and its ligand Jagged-1 in rat liver during liver regeneration.

The Notch/Jagged signaling pathway is important for cellular differentiation and proliferation. Its dysfunction is associated with human pathologies in several tissues including liver. Point mutations in Jagged-1 gene are the cause for Alagille syndrome, associated with paucity of intrahepatic bile ducts. To determine the putative role of the trans-membrane receptor Notch and its ligand Jagged-1 in liver regeneration, we investigated the expression of Notch and Jagged-1 in rat liver following 2/3 partial hepatectomy. Immunohistochemical staining of normal rat liver showed that Notch was expressed in hepatocytes, bile duct cells and endothelial cells, whereas Jagged-1 was expressed in bile duct cells and hepatocytes. Both Notch-1 and Jagged-1 proteins were upregulated in hepatocytes after partial hepatectomy up to day 4. After partial hepatectomy, nuclear translocation of the intracellular cytoplasmic domain of Notch (NICD) increased and peaked within 15 minutes, indicating the activation of Notch. Expression of the Notch-dependent target gene (HES-1) expression increased within 30-60 minutes. Addition of recombinant Jagged-1 protein to primary cultures of hepatocytes stimulated hepatocyte DNA synthesis. Furthermore, injection of silencing RNA for Notch and Jagged-1 to livers 2 days before partial hepatectomy significantly suppressed proliferation of hepatocytes at days 2 to 4 of the regenerative response. In conclusion, Notch/Jagged signaling pathway is activated during liver regeneration and is potentially contributing to signals affecting cell growth and differentiation.