T-cell factor 4 and β-catenin chromatin occupancies pattern zonal liver metabolism in mice

Hepatic stellate cells: balancing homeostasis, hepatoprotection and fibrogenesis in health and disease

In the past decades, the pathogenic role of hepatic stellate cells (HSCs) in the development of liver fibrosis and its complications has been deeply characterized, rendering HSCs a primary target for antifibrotic therapies. By contrast, the beneficial roles of HSCs in liver homeostasis and liver disease are only beginning to emerge, revealing critical regulatory and fibrosis-independent functions in hepatic zonation, metabolism, injury, regeneration and non-parenchymal cell identity. Here, we review how HSC mediators, such as R-spondin 3, hepatocyte growth factor and bone morphogenetic proteins, regulate critical and homeostatic liver functions in health and disease via cognate receptors in hepatocytes, Kupffer cells and endothelial cells. We highlight how the balance shifts from protective towards fibropathogenic HSC mediators during the progression of chronic liver disease (CLD) and the impact of this shifted balance on patient outcomes. Notably, the protective roles of HSCs are not accounted for in current therapeutic concepts for CLD. We discuss the concept that reverting the HSC balance from fibrogenesis towards hepatoprotection might represent a novel holistic treatment approach to inhibit fibrogenesis and restore epithelial health in CLD simultaneously.

Unraveling the Role of the Wnt Pathway in Hepatocellular Carcinoma: From Molecular Mechanisms to Therapeutic Implications

Hepatocellular carcinoma (HCC) is one of the deadliest malignant tumors in the world, and its incidence and mortality have increased year by year. HCC research has increasingly focused on understanding its pathogenesis and developing treatments.The Wnt signaling pathway, a complex and evolutionarily conserved signal transduction system, has been extensively studied in the genesis and treatment of several malignant tumors. Recent investigations suggest that the pathogenesis of HCC may be significantly influenced by dysregulated Wnt/β-catenin signaling. This article aimed to examine the pathway that controls Wnt signaling in HCC and its mechanisms. In addition, we highlighted the role of this pathway in HCC etiology and targeted treatment.

The Diabetes Gene Tcf7l2 Organizes Gene Expression in the Liver and Regulates Amino Acid Metabolism

TCF7L2 harbors the strongest genetic association with diabetes identified thus far. However, its function in liver has remained unclear. Here, we find using mice with liver-specific deletion, that Tcf7l2 plays a central role in maintaining hepatic zonation. That is, in the normal liver, many genes show gradients of expression across the liver lobule; in the absence of Tcf7l2 , these gradients collapse. One major consequence is the disorganization of glutamine metabolism, with a loss of the glutamine production program, ectopic expression of the glutamine consumption program, and a decrease in glutamine levels. In parallel, metabolomic profiling shows glutamine to be the most significantly decreased metabolite in individuals harboring the rs7903146 variant in TCF7L2 . Taken together, these data indicate that hepatic TCF7L2 has a secondary role in glycemic control, but a primary role in maintaining transcriptional architecture and glutamine homeostasis.

Tetrahedral framework nucleic acids ameliorate cholestatic liver disease by activating Wnt/β-catenin signaling and promoting ERK1/2 phosphorylation

Cholestatic liver disease (CLD) is characterized by disruptions in bile formation, secretion and excretion, leading to progressive liver injury, inflammation and fibrosis. Effective treatments to halt or reverse the progression of CLD remain limited. The Wnt/β-catenin signaling pathway has been implicated in the regulation of bile acid homeostasis and liver regeneration, playing a complex role in CLD pathophysiology. Tetrahedral framework nucleic acids (TFNAs), a class of anti-inflammatory and antioxidant DNA nanomaterials, have shown potential in promoting mammalian cell proliferation through activation of cell cycle and proliferation-related signaling pathways. However, their therapeutic potential in CLD has not been fully explored. In this study, we investigated the effects of TFNAs in an α-naphthyl isothiocyanate (ANIT)-induced mouse model of CLD. TFNAs demonstrated the ability to enter hepatocytes, where they activated the Wnt/β-catenin signaling pathway and enhanced ERK1/2 phosphorylation. These molecular changes resulted in significant improvements in liver injury markers, bile acid metabolism and liver regeneration. Complementary in vitro experiments revealed that TFNAs reduced hepatocyte apoptosis and oxidative stress, while promoting cell viability and proliferation. Histological analysis confirmed that TFNAs treatment mitigated liver necrosis, reduced ductular reactions and decreased neutrophil infiltration, highlighting their anti-inflammatory and tissue-protective effects. These findings provide compelling evidence that TFNAs can ameliorate CLD by modulating key signaling pathways involved in hepatocyte survival, regeneration and bile acid homeostasis. Collectively, our findings highlight the therapeutic potential of TFNAs as a novel treatment for CLD and paves the way for further exploration of nanomaterials in liver disease therapy.

Toxin protein LukS-PV targeting complement receptor C5aR1 inhibits cell proliferation in hepatocellular carcinoma via the HDAC7-Wnt/β-catenin axis

Hepatocellular carcinoma (HCC) is one of the common malignant tumors. Complement system has become a new focus of cancer research by changing the biological behavior of cancer cells to influence the growth of cancer. Recent studies reported that the complement C5a-C5aR1 axis can promote the malignant phenotype of multiple tumors through various signaling pathways. LukS-PV (Panton-Valentine), the S component of Staphylococcus aureus-secreted PV leucocidin, can also bind C5aR1 specifically. This project aims to investigate the role of LukS-PV on HCC cell proliferation and explore underlying molecular mechanisms. Our findings revealed that LukS-PV targeting C5aR1 inhibited HCC cell proliferation in vitro and in vivo. Interestingly, we discovered that LukS-PV inhibited the proliferation of HCC cells by upregulating the acetylation level of β-catenin to promote its protein degradation. In addition, histone deacetylase (HDAC)7 identified as a regulator mediates the deacetylation of β-catenin. Furthermore, our results showed that LukS-PV inhibited proliferation in HCC cells by downregulating HDAC7 to promote the degradation of β-catenin through ubiquitin-proteasome system. Collectively, our findings revealed that LukS-PV targeting C5aR1 inhibits HCC cell proliferation through the HDAC7-Wnt/β-catenin axis. These results revealing a novel mechanism that LukS-PV as a bacterial toxin inhibits HCC cell proliferation through epigenetic remodeling by targeting complement receptor C5aR1, suggest the strong potential of LukS-PV as a promising candidate for HCC treatment.

Wnt/β-Catenin Signaling in Liver Pathobiology

The liver has a critical role in regulating host metabolism, immunity, detoxification, and homeostasis. Proper liver function is essential for host health, and dysregulation of hepatic signaling pathways can lead to the onset of disease. The Wnt/β-catenin signaling pathway is an important regulator of liver homeostasis and function. Throughout life, hepatic Wnt/β-catenin signaling contributes to liver development and growth, metabolic zonation, and regeneration. Extensive research has demonstrated that aberrant Wnt/β-catenin signaling drives liver pathologies, including cancers, steatohepatitis, and cholestasis. In this review, we discuss the Wnt/β-catenin pathway as it pertains to liver function and how disruptions in this pathway contribute to the onset and progression of liver diseases. Further, we discuss ongoing research that targets the Wnt/β-catenin pathway for the treatment of liver pathologies.

Specific features of ß-catenin-mutated hepatocellular carcinomas

CTNNB1, encoding the ß-catenin protein, is a key oncogene contributing to liver carcinogenesis. Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer in adult, representing the third leading cause of cancer-related death. Aberrant activation of the Wnt/ß-catenin pathway, mainly due to mutations of the CTNNB1 gene, is observed in a significant subset of HCC. In this review, we first resume the major recent advances in HCC classification with a focus on CTNNB1-mutated HCC subclass. We present the regulatory mechanisms involved in β-catenin stabilisation, transcriptional activity and binding to partner proteins. We then describe specific phenotypic characteristics of CTNNB1-mutated HCC thanks to their unique gene expression patterns. CTNNB1-mutated HCC constitute a full-fledged subclass of HCC with distinct pathological features such as well-differentiated cells with low proliferation rate, association to cholestasis, metabolic alterations, immune exclusion and invasion. Finally, we discuss therapeutic approaches to target ß-catenin-mutated liver tumours and innovative perspectives for future drug developments.

Divergent WNT signaling and drug sensitivity profiles within hepatoblastoma tumors and organoids

Hepatoblastoma, the most prevalent pediatric liver cancer, almost always carries a WNT-activating CTNNB1 mutation, yet exhibits notable molecular heterogeneity. To characterize this heterogeneity and identify novel targeted therapies, we perform comprehensive analysis of hepatoblastomas and tumor-derived organoids using single-cell RNA-seq/ATAC-seq, spatial transcriptomics, and high-throughput drug profiling. We identify two distinct tumor epithelial signatures: hepatic 'fetal' and WNT-high 'embryonal', displaying divergent WNT signaling patterns. The fetal group is enriched for liver-specific WNT targets, while the embryonal group is enriched in canonical WNT target genes. Gene regulatory network analysis reveals enrichment of regulons related to hepatic functions such as bile acid, lipid and xenobiotic metabolism in the fetal subtype but not in the embryonal subtype. In addition, the dichotomous expression pattern of the transcription factors HNF4A and LEF1 allows for a clear distinction between the fetal and embryonal tumor cells. We also perform high-throughput drug screening using patient-derived tumor organoids and identify sensitivity to HDAC inhibitors. Intriguingly, embryonal and fetal tumor organoids are sensitive to FGFR and EGFR inhibitors, respectively, indicating a dependency on EGF/FGF signaling in hepatoblastoma tumorigenesis. In summary, our data uncover the molecular and drug sensitivity landscapes of hepatoblastoma and pave the way for the development of targeted therapies.

Getting in the zone: Metabolite transport across liver zones

The liver has many functions including the regulation of nutrient and metabolite levels in the systemic circulation through efficient transport into and out of hepatocytes. To sustain these functions, hepatocytes display large functional heterogeneity. This heterogeneity is reflected by zonation of metabolic processes that take place in different zones of the liver lobule, where nutrient-rich blood enters the liver in the periportal zone and flows through the mid-zone prior to drainage by a central vein in the pericentral zone. Metabolite transport plays a pivotal role in the division of labor across liver zones, being either transport into the hepatocyte or transport between hepatocytes through the blood. Signaling pathways that regulate zonation, such as Wnt/β-catenin, have been shown to play a causal role in the development of metabolic dysfunction-associated steatohepatitis (MASH) progression, but the (patho)physiological regulation of metabolite transport remains enigmatic. Despite the practical challenges to separately study individual liver zones, technological advancements in the recent years have greatly improved insight in spatially divided metabolite transport. This review summarizes the theories behind the regulation of zonation, diurnal rhythms and their effect on metabolic zonation, contemporary techniques used to study zonation and current technological challenges, and discusses the current view on spatial and temporal metabolite transport.

SLC13A3 is a major effector downstream of activated β-catenin in liver cancer pathogenesis

Activated Wnt/β-catenin pathway is a key genetic event in liver cancer development. Solute carrier (SLC) transporters are promising drug targets. Here, we identify SLC13A3 as a drug-targetable effector downstream of β-catenin in liver cancer. SLC13A3 expression is elevated in human liver cancer samples with gain of function (GOF) mutant CTNNB1, the gene encoding β-catenin. Activation of β-catenin up-regulates SLC13A3, leading to intracellular accumulation of endogenous SLC13A3 substrates. SLC13A3 is identified as a low-affinity transporter for glutathione (GSH). Silencing of SLC13A3 downregulates the leucine transporter SLC7A5 via c-MYC signaling, leading to leucine depletion and mTOR inactivation. Furthermore, silencing of SLC13A3 depletes GSH and induces autophagic ferroptosis in β-catenin-activated liver cancer cells. Importantly, both genetic inhibition of SLC13A3 and a small molecule SLC13A3 inhibitor suppress β-catenin-driven hepatocarcinogenesis in mice. Altogether, our study suggests that SLC13A3 could be a promising therapeutic target for treating human liver cancers with GOF CTNNB1 mutations.

Emerging role of oncogenic ß-catenin in exosome biogenesis as a driver of immune escape in hepatocellular carcinoma

Immune checkpoint inhibitors have produced encouraging results in cancer patients. However, the majority of ß-catenin-mutated tumors have been described as lacking immune infiltrates and resistant to immunotherapy. The mechanisms by which oncogenic ß-catenin affects immune surveillance remain unclear. Herein, we highlighted the involvement of ß-catenin in the regulation of the exosomal pathway and, by extension, in immune/cancer cell communication in hepatocellular carcinoma (HCC). We showed that mutated ß-catenin represses expression of SDC4 and RAB27A, two main actors in exosome biogenesis, in both liver cancer cell lines and HCC patient samples. Using nanoparticle tracking analysis and live-cell imaging, we further demonstrated that activated ß-catenin represses exosome release. Then, we demonstrated in 3D spheroid models that activation of β-catenin promotes a decrease in immune cell infiltration through a defect in exosome secretion. Taken together, our results provide the first evidence that oncogenic ß-catenin plays a key role in exosome biogenesis. Our study gives new insight into the impact of ß-catenin mutations on tumor microenvironment remodeling, which could lead to the development of new strategies to enhance immunotherapeutic response.

Loss of β-catenin reveals a role for glutathione in regulating oxidative stress during cholestatic liver disease

BACKGROUND

Cholestasis is an intractable liver disorder that results from impaired bile flow. We have previously shown that the Wnt/β-catenin signaling pathway regulates the progression of cholestatic liver disease through multiple mechanisms, including bile acid metabolism and hepatocyte proliferation. To further explore the impact of these functions during intrahepatic cholestasis, we exposed mice to a xenobiotic that causes selective biliary injury.

METHODS

α-naphthylisothiocyanate (ANIT) was administered to liver-specific knockout (KO) of β-catenin and wild-type mice in the diet. Mice were killed at 6 or 14 days to assess the severity of cholestatic liver disease, measure the expression of target genes, and perform biochemical analyses.

RESULTS

We found that the presence of β-catenin was protective against ANIT, as KO mice had a significantly lower survival rate than wild-type mice. Although serum markers of liver damage and total bile acid levels were similar between KO and wild-type mice, the KO had minor histological abnormalities, such as sinusoidal dilatation, concentric fibrosis around ducts, and decreased inflammation. Notably, both total glutathione levels and expression of glutathione-S-transferases, which catalyze the conjugation of ANIT to glutathione, were significantly decreased in KO after ANIT. Nuclear factor erythroid-derived 2-like 2, a master regulator of the antioxidant response, was activated in KO after ANIT as well as in a subset of patients with primary sclerosing cholangitis lacking activated β-catenin. Despite the activation of nuclear factor erythroid-derived 2-like 2, KO livers had increased lipid peroxidation and cell death, which likely contributed to mortality.

CONCLUSIONS

Loss of β-catenin leads to increased cellular injury and cell death during cholestasis through failure to neutralize oxidative stress, which may contribute to the pathology of this disease.

Perturbed liver gene zonation in a mouse model of non-alcoholic steatohepatitis

Liver zonation characterizes the separation of metabolic pathways along the lobules and is required for optimal hepatic function. Wnt signaling is a master regulator of spatial liver zonation. A perivenous-periportal Wnt activity gradient orchestrates metabolic zonation by activating gene expression in perivenous hepatocytes, while suppressing gene expression in their periportal counterparts. However, the understanding as to the liver gene zonation and zonation regulators in diseases is limited. Non-alcoholic steatohepatitis (NASH) is a chronic liver disease characterized by fat accumulation, inflammation, and fibrosis. Here, we investigated the perturbation of liver gene zonation in a mouse NASH model by combining spatial transcriptomics, bulk RNAseq and in situ hybridization. Wnt-target genes represented a major subset of genes showing altered spatial expression in the NASH liver. The altered Wnt-target gene expression levels and zonation spatial patterns were in line with the up regulation of Wnt regulators and the augmentation of Wnt signaling. Particularly, we found that the Wnt activator Rspo3 expression was restricted to the perivenous zone in control liver but expanded to the periportal zone in NASH liver. AAV8-mediated RSPO3 overexpression in controls resulted in zonation changes, and further amplified the disturbed zonation of Wnt-target genes in NASH, similarly Rspo3 knockdown in Rspo3+/- mice resulted in zonation changes of Wnt-target genes in both chow and HFD mouse. Interestingly, there were no impacts on steatosis, inflammation, or fibrosis NASH pathology from RSPO3 overexpression nor Rspo3 knockdown. In summary, our study demonstrated the alteration of Wnt signaling in a mouse NASH model, leading to perturbed liver zonation.

A spatiotemporal atlas of mouse liver homeostasis and regeneration

The mechanism by which mammalian liver cell responses are coordinated during tissue homeostasis and perturbation is poorly understood, representing a major obstacle in our understanding of many diseases. This knowledge gap is caused by the difficulty involved with studying multiple cell types in different states and locations, particularly when these are transient. We have combined Stereo-seq (spatiotemporal enhanced resolution omics-sequencing) with single-cell transcriptomic profiling of 473,290 cells to generate a high-definition spatiotemporal atlas of mouse liver homeostasis and regeneration at the whole-lobe scale. Our integrative study dissects in detail the molecular gradients controlling liver cell function, systematically defining how gene networks are dynamically modulated through intercellular communication to promote regeneration. Among other important regulators, we identified the transcriptional cofactor TBL1XR1 as a rheostat linking inflammation to Wnt/β-catenin signaling for facilitating hepatocyte proliferation. Our data and analytical pipelines lay the foundation for future high-definition tissue-scale atlases of organ physiology and malfunction.

Glutamine metabolism, a double agent combating or fuelling hepatocellular carcinoma

The reprogramming of glutamine metabolism is a key event in cancer more generally and in hepatocellular carcinoma (HCC) in particular. Glutamine consumption supplies tumours with ATP and metabolites through anaplerosis of the tricarboxylic acid cycle, while glutamine production can be enhanced by the overexpression of glutamine synthetase. In HCC, increased glutamine production is driven by activating mutations in the CTNNB1 gene encoding β-catenin. Increased glutamine synthesis or utilisation impacts tumour epigenetics, oxidative stress, autophagy, immunity and associated pathways, such as the mTOR (mammalian target of rapamycin) pathway. In this review, we will discuss studies which emphasise the pro-tumoral or tumour-suppressive effect of glutamine overproduction. It is clear that more comprehensive studies are needed as a foundation from which to develop suitable therapies targeting glutamine metabolic pathways, depending on the predicted pro- or anti-tumour role of dysregulated glutamine metabolism in distinct genetic contexts.

Wnt/β-catenin signaling pathway in liver biology and tumorigenesis

The Wnt/β-catenin pathway is an evolutionarily conserved signaling pathway that controls fundamental physiological and pathological processes by regulating cell proliferation and differentiation. The Wnt/β-catenin pathway enables liver homeostasis by inducing differentiation and contributes to liver-specific features such as metabolic zonation and regeneration. In contrast, abnormalities in the Wnt/β-catenin pathway promote the development and progression of hepatocellular carcinoma (HCC). Similarly, hepatoblastoma, the most common childhood liver cancer, is frequently associated with β-catenin mutations, which activate Wnt/β-catenin signaling. HCCs with activation of the Wnt/β-catenin pathway have unique gene expression patterns and pathological and clinical features. Accordingly, they are highly differentiated with retaining hepatocyte-like characteristics and tumorigenic. Activation of the Wnt/β-catenin pathway in HCC also alters the state of immune cells, causing "immune evasion" with inducing resistance to immune checkpoint inhibitors, which have recently become widely used to treat HCC. Activated Wnt/β-catenin signaling exhibits these phenomena in liver tumorigenesis through the expression of downstream target genes, and the molecular basis is still poorly understood. In this review, we describe the physiological roles of Wnt/b-catenin signaling and then discuss their characteristic changes by the abnormal activation of Wnt/b-catenin signaling. Clarification of the mechanism would contribute to the development of therapeutic agents in the future.

Spatial hepatocyte plasticity of gluconeogenesis during the metabolic transitions between fed, fasted and starvation states

The liver acts as a master regulator of metabolic homeostasis in part by performing gluconeogenesis. This process is dysregulated in type 2 diabetes, leading to elevated hepatic glucose output. The parenchymal cells of the liver (hepatocytes) are heterogeneous, existing on an axis between the portal triad and the central vein, and perform distinct functions depending on location in the lobule. Here, using single cell analysis of hepatocytes across the liver lobule, we demonstrate that gluconeogenic gene expression ( Pck1 and G6pc ) is relatively low in the fed state and gradually increases first in the periportal hepatocytes during the initial fasting period. As the time of fasting progresses, pericentral hepatocyte gluconeogenic gene expression increases, and following entry into the starvation state, the pericentral hepatocytes show similar gluconeogenic gene expression to the periportal hepatocytes. Similarly, pyruvate-dependent gluconeogenic activity is approximately 10-fold higher in the periportal hepatocytes during the initial fasting state but only 1.5-fold higher in the starvation state. In parallel, starvation suppresses canonical beta-catenin signaling and modulates expression of pericentral and periportal glutamine synthetase and glutaminase, resulting in an enhanced pericentral glutamine-dependent gluconeogenesis. These findings demonstrate that hepatocyte gluconeogenic gene expression and gluconeogenic activity are highly spatially and temporally plastic across the liver lobule, underscoring the critical importance of using well-defined feeding and fasting conditions to define the basis of hepatic insulin resistance and glucose production.

Wnt/β-catenin signaling regulates amino acid metabolism through the suppression of CEBPA and FOXA1 in liver cancer cells

Deregulation of the Wnt/β-catenin pathway is associated with the development of human cancer including colorectal and liver cancer. Although we previously showed that histidine ammonia lyase (HAL) was transcriptionally reduced by the β-catenin/TCF complex in liver cancer cells, the mechanism(s) of its down-regulation by the complex remain to be clarified. In this study, we search for the transcription factor(s) regulating HAL, and identify CEBPA and FOXA1, two factors whose expression is suppressed by the knockdown of β-catenin or TCF7L2. In addition, RNA-seq analysis coupled with genome-wide mapping of CEBPA- and FOXA1-binding regions reveals that these two factors also increase the expression of arginase 1 (ARG1) that catalyzes the hydrolysis of arginine. Metabolome analysis discloses that activated Wnt signaling augments intracellular concentrations of histidine and arginine, and that the signal also increases the level of lactic acid suggesting the induction of the Warburg effect in liver cancer cells. Further analysis reveals that the levels of metabolites of the urea cycle and genes coding its related enzymes are also modulated by the Wnt signaling. These findings shed light on the altered cellular metabolism in the liver by the Wnt/β-catenin pathway through the suppression of liver-enriched transcription factors including CEBPA and FOXA1.

Wnt, glucocorticoid and cellular prion protein cooperate to drive a mesenchymal phenotype with poor prognosis in colon cancer

BACKGROUND

The mesenchymal subtype of colorectal cancer (CRC), associated with poor prognosis, is characterized by abundant expression of the cellular prion protein PrPC, which represents a candidate therapeutic target. How PrPC is induced in CRC remains elusive. This study aims to elucidate the signaling pathways governing PrPC expression and to shed light on the gene regulatory networks linked to PrPC.

METHODS

We performed in silico analyses on diverse datasets of in vitro, ex vivo and in vivo models of mouse CRC and patient cohorts. We mined ChIPseq studies and performed promoter analysis. CRC cell lines were manipulated through genetic and pharmacological approaches. We created mice combining conditional inactivation of Apc in intestinal epithelial cells and overexpression of the human prion protein gene PRNP. Bio-informatic analyses were carried out in two randomized control trials totalizing over 3000 CRC patients.

RESULTS

In silico analyses combined with cell-based assays identified the Wnt-β-catenin and glucocorticoid pathways as upstream regulators of PRNP expression, with subtle differences between mouse and human. We uncover multiple feedback loops between PrPC and these two pathways, which translate into an aggravation of CRC pathogenesis in mouse. In stage III CRC patients, the signature defined by PRNP-CTNNB1-NR3C1, encoding PrPC, β-catenin and the glucocorticoid receptor respectively, is overrepresented in the poor-prognosis, mesenchymal subtype and associates with reduced time to recurrence.

CONCLUSIONS

An unleashed PrPC-dependent vicious circle is pathognomonic of poor prognosis, mesenchymal CRC. Patients from this aggressive subtype of CRC may benefit from therapies targeting the PRNP-CTNNB1-NR3C1 axis.

DLK1/DIO3 locus upregulation by a β-catenin-dependent enhancer drives cell proliferation and liver tumorigenesis

The CTNNB1 gene, encoding β-catenin, is frequently mutated in hepatocellular carcinoma (HCC, ∼30%) and in hepatoblastoma (HB, >80%), in which DLK1/DIO3 locus induction is correlated with CTNNB1 mutations. Here, we aim to decipher how sustained β-catenin activation regulates DLK1/DIO3 locus expression and the role this locus plays in HB and HCC development in mouse models deleted for Apc (ApcΔhep) or Ctnnb1-exon 3 (β-cateninΔExon3) and in human CTNNB1-mutated hepatic cancer cells. We identified an enhancer site bound by TCF-4/β-catenin complexes in an open conformation upon sustained β-catenin activation (DLK1-Wnt responsive element [WRE]) and increasing DLK1/DIO3 locus transcription in β-catenin-mutated human HB and mouse models. DLK1-WRE editing by CRISPR-Cas9 approach impaired DLK1/DIO3 locus expression and slowed tumor growth in subcutaneous CTNNB1-mutated tumor cell grafts, ApcΔhep HB and β-cateninΔExon3 HCC. Tumor growth inhibition resulted either from increased FADD expression and subsequent caspase-3 cleavage in the first case or from decreased expression of cell cycle actors regulated by FoxM1 in the others. Therefore, the DLK1/DIO3 locus is an essential determinant of FoxM1-dependent cell proliferation during β-catenin-driven liver tumorigenesis. Targeting the DLK1-WRE enhancer to silence the DLK1/DIO3 locus might thus represent an interesting therapeutic strategy to restrict tumor growth in primary liver cancers with CTNNB1 mutations.

A spatial map of hepatic mitochondria uncovers functional heterogeneity shaped by nutrient-sensing signaling

In the liver, mitochondria are exposed to different concentrations of nutrients due to their spatial positioning across the periportal and pericentral axis. How the mitochondria sense and integrate these signals to respond and maintain homeostasis is not known. Here, we combine intravital microscopy, spatial proteomics, and functional assessment to investigate mitochondrial heterogeneity in the context of liver zonation. We find that periportal and pericentral mitochondria are morphologically and functionally distinct; beta-oxidation is elevated in periportal regions, while lipid synthesis is predominant in the pericentral mitochondria. In addition, comparative phosphoproteomics reveals spatially distinct patterns of mitochondrial composition and potential regulation via phosphorylation. Acute pharmacological modulation of nutrient sensing through AMPK and mTOR shifts mitochondrial phenotypes in the periportal and pericentral regions, linking nutrient gradients across the lobule and mitochondrial heterogeneity. This study highlights the role of protein phosphorylation in mitochondrial structure, function, and overall homeostasis in hepatic metabolic zonation. These findings have important implications for liver physiology and disease.

Chromatin and DNA Dynamics in Mouse Models of Liver Cancers

In recent years, important efforts have been made to understand how the expression of a specific gene repertoire correlates with chromatin accessibility, histone mark deposition, as well as with chromatin looping establishing connectivity with regulatory regions. The emergence of new techniques for genome-wide analyses and their progressive optimization to work on low amounts of material allows the scientific community to obtain an integrated view of transcriptional landscapes in physiology and disease. Here, we describe our own experience aiming at correlating the TCF-4/β-catenin cistrome during liver tumorigenesis with chromatin remodeling, histone mark modifications, and long-distance DNA looping.

A spatial map of hepatic mitochondria uncovers functional heterogeneity shaped by nutrient-sensing signaling

In the liver, mitochondria are exposed to different concentrations of nutrients due to their spatial positioning across the periportal (PP) and pericentral (PC) axis. How these mitochondria sense and integrate these signals to respond and maintain homeostasis is not known. Here, we combined intravital microscopy, spatial proteomics, and functional assessment to investigate mitochondrial heterogeneity in the context of liver zonation. We found that PP and PC mitochondria are morphologically and functionally distinct; beta-oxidation was elevated in PP regions, while lipid synthesis was predominant in the PC mitochondria. In addition, comparative phosphoproteomics revealed spatially distinct patterns of mitochondrial composition and potential regulation via phosphorylation. Acute pharmacological modulation of nutrient sensing through AMPK and mTOR shifted mitochondrial phenotypes in the PP and PC regions, linking nutrient gradients across the lobule and mitochondrial heterogeneity. This study highlights the role of protein phosphorylation in mitochondrial structure, function, and overall homeostasis in hepatic metabolic zonation. These findings have important implications for liver physiology and disease.

Advances in Histological and Molecular Classification of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a primary liver cancer characterized by hepatocellular differentiation. HCC is molecularly heterogeneous with a wide spectrum of histopathology. The prognosis of patients with HCC is generally poor, especially in those with advanced stages. HCC remains a diagnostic challenge for pathologists because of its morphological and phenotypic diversity. However, recent advances have enhanced our understanding of the molecular genetics and histological subtypes of HCC. Accurate diagnosis of HCC is important for patient management and prognosis. This review provides an update on HCC pathology, focusing on molecular genetics, histological subtypes, and diagnostic approaches.

Wnt/beta-catenin signaling and its modulators in nonalcoholic fatty liver diseases

Nonalcoholic fatty liver disease (NAFLD) is a global health concern associated with significant morbidity and mortality. NAFLD is a spectrum of diseases originating from simple steatosis, progressing through nonalcoholic steatohepatitis (NASH), fibrosis, and cirrhosis that may lead to hepatocellular carcinoma (HCC). The pathogenesis of NAFLD is mediated by the triglyceride accumulation followed by proinflammatory cytokines expression leading to inflammation, oxidative stress, and mitochondrial dysfunction denoted as "two-hit hypothesis", advancing with a "third hit" of insufficient hepatocyte proliferation, leading to the increase in hepatic progenitor cells contributing to fibrosis and HCC. Wnt/β-catenin signaling is responsible for normal liver development, regeneration, hepatic metabolic zonation, ammonia and drug detoxification, hepatobiliary development, etc., maintaining the overall liver homeostasis. The key regulators of canonical Wnt signaling such as LRP6, Wnt1, Wnt3a, β-catenin, GSK-3β, and APC are abnormally regulated in NAFLD. Many experimental studies have shown the aberrated Wnt/β-catenin signaling during the NAFLD progression and NASH to hepatic fibrosis and HCC. Therefore, in this review, we have emphasized the role of Wnt/β-catenin signaling and its modulators that can potentially aid in the inhibition of NAFLD.

Liver Regeneration in Acute on Chronic Liver Failure

Liver regeneration is a multifaceted process by which the organ regains its original size and histologic organization. In recent decades, substantial advances have been made in our understanding of the mechanisms underlying regeneration following loss of hepatic mass. Liver regeneration in acute liver failure possesses several classic pathways, while also exhibiting unique differences in key processes such as the roles of differentiated cells and stem cell analogs. Here we summarize these unique differences and new molecular mechanisms involving the gut-liver axis, immunomodulation, and microRNAs with an emphasis on applications to the patient population through stem cell therapies and prognostication.

Distinct hepatocyte identities in liver homeostasis and regeneration

The process of metabolic liver zonation is spontaneously established by assigning distributed tasks to hepatocytes along the porto-central blood flow. Hepatocytes fulfil critical metabolic functions, while also maintaining hepatocyte mass by replication when needed. Recent technological advances have enabled us to fine-tune our understanding of hepatocyte identity during homeostasis and regeneration. Subsets of hepatocytes have been identified to be more regenerative and some have even been proposed to function like stem cells, challenging the long-standing view that all hepatocytes are similarly capable of regeneration. The latest data show that hepatocyte renewal during homeostasis and regeneration after liver injury is not limited to rare hepatocytes; however, hepatocytes are not exactly the same. Herein, we review the known differences that give individual hepatocytes distinct identities, recent findings demonstrating how these distinct identities correspond to differences in hepatocyte regenerative capacity, and how the plasticity of hepatocyte identity allows for division of labour among hepatocytes. We further discuss how these distinct hepatocyte identities may play a role during liver disease.

Wnt Signaling Stimulates Cooperation between GREB1 and HNF4α to Promote Proliferation in Hepatocellular Carcinoma

Wnt signaling is known to maintain two cell states, hepatocyte differentiation and proliferation, in hepatocellular carcinoma (HCC). On the other hand, activation of Wnt signaling in colon cancer promotes uncontrollable stereotypic proliferation, whereas cells remain undifferentiated. To elucidate the unique mode of Wnt signaling in HCC, we comprehensively investigated HCC-specific Wnt pathway target genes and identified GREB1. Wnt signaling induced expression of GREB1 coupled with HNF4α and FOXA2, master transcription factors that maintain hepatic differentiation. Moreover, GREB1 was enriched at the regulatory region of atypical HNF4α target genes, including progrowth genes, thereby stimulating HCC proliferation. Therefore, GREB1 acts as a unique mediator of versatile Wnt signaling in HCC progression, bridging the roles of the Wnt pathway in differentiation and proliferation.

SIGNIFICANCE

GREB1 is a liver cancer-specific Wnt signaling target gene that induces an oncogenic shift of HNF4α, a putative tumor suppressor, and may represent a therapeutic target in Wnt-activated hepatocellular carcinoma.

Overexpression of POLA2 in hepatocellular carcinoma is involved in immune infiltration and predicts a poor prognosis

BACKGROUND

Hepatocellular carcinoma (HCC) is the second malignancy worldwide. POLA2 initiates DNA replication, regulates cell cycle and gene repair that promote tumorigenesis and disease progression. However, the prognostic and biological function roles of POLA2 in HCC had not been conclusively determined.

METHODS

The expression levels and prognosis role of POLA1 and POLA2 in HCC were analyzed based on TCGA-LIHC database and recruited 24 HCC patients. Gene mutations were analyzed using "maftools" package. POLA2 and immune cells correlations were analyzed by TIMER. POLA2 co-expressed genes functional enrichment were evaluated using Metascape. The mRNA and protein level of POLA2 was detected in HCC cells and tissues. Cell migration, invasion, proliferation, cell cycle and HCC cell lines derived xenograft model were performed to investigate POLA2 biological function.

RESULTS

POLA2 was significantly high expressed in HCC than in normal liver tissue in both TCGA-LIHC and our collected HCC samples. In validation cohort, POLA2 significantly related to tumor differentiation, tumor size and Ki-67 (p < 0.05). In TCGA-LIHC cohort, overexpression of POLA2 predicted a low OS and associated with different clinical stages. Multivariate Cox regression showed overexpression of POLA2 effectively distinguished the prognosis at different T, N, M, stages and grades of HCC. POLA2 expression correlated with mutation burden, immune cells infiltration and immune-associated genes expression of HCC. Functional enrichment revealed that POLA2 co-expressed genes were linked to cellular activity, plasma membrane protein complex and leukocyte activity, immune response-regulated cell surface receptor signaling pathway, and immune response-regulated signaling pathway. Moreover, POLA2 was also positively co-expressed with some immune checkpoints (CD274, CTL-4, HAVCR2, PDCD1, PDCD1LG2, TIGIT, and LAG3) (p < 0.001). Gene knockdown revealed that POLA2 promoted proliferation, migration, invasion, and cell cycle of SMMC-7721 and HepG2. The HCC xenograft tumor model also demonstrated remarkably tumor size inhibition, tumor proliferation inhibtion and tumor necrosis promotion when POLA2 knockdown.

CONCLUSIONS

POLA2 influenced immune microenvironment and tumor progression of HCC indicated that it might be a potential molecular marker for prognostic evaluation or a therapeutic target for HCC.

Hepatic stellate cells maintain liver homeostasis through paracrine neurotrophin-3 signaling that induces hepatocyte proliferation

Organ size is maintained by the controlled proliferation of distinct cell populations. In the mouse liver, hepatocytes in the midlobular zone that are positive for cyclin D1 (CCND1) repopulate the parenchyma at a constant rate to preserve liver mass. Here, we investigated how hepatocyte proliferation is supported by hepatic stellate cells (HSCs), pericytes that are in close proximity to hepatocytes. We used T cells to ablate nearly all HSCs in the murine liver, enabling the unbiased characterization of HSC functions. In the normal liver, complete loss of HSCs persisted for up to 10 weeks and caused a gradual reduction in liver mass and in the number of CCND1+ hepatocytes. We identified neurotrophin-3 (Ntf-3) as an HSC-produced factor that induced the proliferation of midlobular hepatocytes through the activation of tropomyosin receptor kinase B (TrkB). Treating HSC-depleted mice with Ntf-3 restored CCND1+ hepatocytes in the midlobular region and increased liver mass. These findings establish that HSCs form the mitogenic niche for midlobular hepatocytes and identify Ntf-3 as a hepatocyte growth factor.

Antagonism between wild-type and mutant β-catenin controls hepatoblastoma differentiation via fascin-1

Background & Aims

β-catenin is a well-known effector of the Wnt pathway, and a key player in cadherin-mediated cell adhesion. Oncogenic mutations of β-catenin are very frequent in paediatric liver primary tumours. Those mutations are mostly heterozygous, which allows the co-expression of wild-type (WT) and mutated β-catenins in tumour cells. We investigated the interplay between WT and mutated β-catenins in liver tumour cells, and searched for new actors of the β-catenin pathway.

Methods

Using an RNAi strategy in β-catenin-mutated hepatoblastoma (HB) cells, we dissociated the structural and transcriptional activities of β-catenin, which are carried mainly by WT and mutated proteins, respectively. Their impact was characterised using transcriptomic and functional analyses. We studied mice that develop liver tumours upon activation of β-catenin in hepatocytes (APC^KO and β-catenin^Δexon3 mice). We used transcriptomic data from mouse and human HB specimens, and used immunohistochemistry to analyse samples.

Results

We highlighted an antagonistic role of WT and mutated β-catenins with regard to hepatocyte differentiation, as attested by alterations in the expression of hepatocyte markers and the formation of bile canaliculi. We characterised fascin-1 as a transcriptional target of mutated β-catenin involved in tumour cell differentiation. Using mouse models, we found that fascin-1 is highly expressed in undifferentiated tumours. Finally, we found that fascin-1 is a specific marker of primitive cells including embryonal and blastemal cells in human HBs.

Conclusions

Fascin-1 expression is linked to a loss of differentiation and polarity of hepatocytes. We present fascin-1 as a previously unrecognised factor in the modulation of hepatocyte differentiation associated with β-catenin pathway alteration in the liver, and as a new potential target in HB.

Impact and implications

The FSCN1 gene, encoding fascin-1, was reported to be a metastasis-related gene in various cancers. Herein, we uncover its expression in poor-prognosis hepatoblastomas, a paediatric liver cancer. We show that fascin-1 expression is driven by the mutated beta-catenin in liver tumour cells. We provide new insights on the impact of fascin-1 expression on tumour cell differentiation. We highlight fascin-1 as a marker of immature cells in mouse and human hepatoblastomas.

CRISPR-induced exon skipping of β-catenin reveals tumorigenic mutants driving distinct subtypes of liver cancer

CRISPR/Cas9-driven cancer modeling studies are based on the disruption of tumor suppressor genes by small insertions or deletions (indels) that lead to frame-shift mutations. In addition, CRISPR/Cas9 is widely used to define the significance of cancer oncogenes and genetic dependencies in loss-of-function studies. However, how CRISPR/Cas9 influences gain-of-function oncogenic mutations is elusive. Here, we demonstrate that single guide RNA targeting exon 3 of Ctnnb1 (encoding β-catenin) results in exon skipping and generates gain-of-function isoforms in vivo. CRISPR/Cas9-mediated exon skipping of Ctnnb1 induces liver tumor formation in synergy with YAPS127A in mice. We define two distinct exon skipping-induced tumor subtypes with different histological and transcriptional features. Notably, ectopic expression of two exon-skipped β-catenin transcript isoforms together with YAPS127A phenocopies the two distinct subtypes of liver cancer. Moreover, we identify similar CTNNB1 exon-skipping events in patients with hepatocellular carcinoma. Collectively, our findings advance our understanding of β-catenin-related tumorigenesis and reveal that CRISPR/Cas9 can be repurposed, in vivo, to study gain-of-function mutations of oncogenes in cancer. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

WNT/β-catenin pathway is a key regulator of cardiac function and energetic metabolism

The WNT/β-catenin pathway is a master regulator of cardiac development and growth, and its activity is low in healthy adult hearts. However, even this low activity is essential for maintaining normal heart function. Acute activation of the WNT/β-catenin signaling cascade is considered to be cardioprotective after infarction through the upregulation of prosurvival genes and reprogramming of metabolism. Chronically high WNT/β-catenin pathway activity causes profibrotic and hypertrophic effects in the adult heart. New data suggest more complex functions of β-catenin in metabolic maturation of the perinatal heart, establishing an adult pattern of glucose and fatty acid utilization. Additionally, low basal activity of the WNT/β-catenin cascade maintains oxidative metabolism in the adult heart, and this pathway is reactivated by physiological or pathological stimuli to meet the higher energy needs of the heart. This review summarizes the current state of knowledge of the organization of canonical WNT signaling and its function in cardiogenesis, heart maturation, adult heart function, and remodeling. We also discuss the role of the WNT/β-catenin pathway in cardiac glucose, lipid metabolism, and mitochondrial physiology.

β-catenin/TCF4 inhibitors ICG-001 and LF3 alleviate BDL-induced liver fibrosis by suppressing LECT2 signaling

Liver fibrosis can be characterized by the over-deposition of extracellular matrix (ECM). It has been reported that β-catenin/TCF4 interaction was enhanced in bile duct ligation (BDL) model, which implicated the critical role of β-catenin/TCF4 interaction during the progression of fibrosis. However, whether inhibiting β-catenin/TCF4 signaling attenuates liver fibrosis remains unknown. In the current study, we used ICG-001, an inhibitor that disrupts the interaction between CREB binding protein (CBP) and β-catenin, to inhibit β-catenin/TCF4 transcriptional activity. We also used LF3, a small molecule antagonist, to inhibit β-catenin/TCF4 interaction. The antifibrotic effect of ICG-001 and LF3 was assessed on BDL-induced liver fibrosis model. The results indicated both ICG-001 and LF3 significantly reduced the positive staining area of Sirius Red and α-SMA. The protein expression levels of α-SMA, Collagen Ⅰ and CD31 were also significantly downregulated in BDL + ICG-001 and BDL + LF3 groups. Besides, ICG-001 and LF3 promoted portal angiogenesis and inhibited sinusoids capillarization in fibrotic livers. For mechanistic study, we measured the level of leukocyte cell-derived chemotaxin 2 (LECT2), a direct target of β-catenin/TCF4, which was recently reported to participate in hepatic fibrosis by regulating angiogenesis. The results showed that both ICG-001 and LF3 reduced LECT2 expression in BDL mice. LF3 also downregulated pSer 675 β-catenin and nuclear β-catenin. In conclusion, this study demonstrated that inhibiting β-catenin/TCF4 signaling by ICG-001 or LF3 mitigated liver fibrosis by downregulating LECT2, promoting portal angiogenesis and inhibiting sinusoids capillarization, which provided new evidence that β-catenin/TCF4 signaling might be a target for the treatment of liver fibrosis.

Spatiotemporal Metabolic Liver Zonation and Consequences on Pathophysiology

Hepatocytes are the main workers in the hepatic factory, managing metabolism of nutrients and xenobiotics, production and recycling of proteins, and glucose and lipid homeostasis. Division of labor between hepatocytes is critical to coordinate complex complementary or opposing multistep processes, similar to distributed tasks at an assembly line. This so-called metabolic zonation has both spatial and temporal components. Spatial distribution of metabolic function in hepatocytes of different lobular zones is necessary to perform complex sequential multistep metabolic processes and to assign metabolic tasks to the right environment. Moreover, temporal control of metabolic processes is critical to align required metabolic processes to the feeding and fasting cycles. Disruption of this complex spatiotemporal hepatic organization impairs key metabolic processes with both local and systemic consequences. Many metabolic diseases, such as nonalcoholic steatohepatitis and diabetes, are associated with impaired metabolic liver zonation. Recent technological advances shed new light on the spatiotemporal gene expression networks controlling liver function and how their deregulation may be involved in a large variety of diseases. We summarize the current knowledge about spatiotemporal metabolic liver zonation and consequences on liver pathobiology.

HNF4α Acts as Upstream Functional Regulator of Intestinal Wnt3 and Paneth Cell Fate

BACKGROUND & AIMS

The intestinal epithelium intrinsically renews itself ex vivo via the proliferation of Lgr5⁺ intestinal stem cells, which is sustained by the establishment of an epithelial stem cell niche. Differentiated Paneth cells are the main source of epithelial-derived niche factor supplies and produce Wnt3 as an essential factor in supporting Lgr5⁺ stem cell activity in the absence of redundant mesenchymal Wnts. Maturation of Paneth cells depends on canonical Wnt signaling, but few transcriptional regulators have been identified to this end. The role of HNF4α in intestinal epithelial cell differentiation is considered redundant with its paralog HNF4γ. However, it is unclear whether HNF4α alone controls intrinsic intestinal epithelial cell growth and fate in the absence of a mesenchymal niche.

METHODS

We used transcriptomic analyses to dissect the role of HNF4α in the maintenance of jejunal epithelial culture when cultured ex vivo as enteroids in the presence or absence of compensatory mesenchymal cells.

RESULTS

HNF4α plays a crucial role in supporting the growth and survival of jejunal enteroids. Transcriptomic analyses revealed an autonomous function of HNF4α in Wnt3 transcriptional regulation and Paneth cell differentiation. We showed that Wnt3a supplementation or co-culture with intestinal subepithelial mesenchymal cells reversed cell death and transcriptional changes caused by the deletion of Hnf4a in jejunal enteroids.

CONCLUSIONS

Our results support the intrinsic epithelial role of HNF4α in regulating Paneth cell homeostasis and intestinal epithelium renewal in the absence of compensatory Wnt signaling.

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 β-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 β-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.

Oncogenic β-catenin stimulation of AKT2-CAD-mediated pyrimidine synthesis is targetable vulnerability in liver cancer

CTNNB1, encoding β-catenin protein, is the most frequently altered proto-oncogene in hepatic neoplasms. In this study, we studied the significance and pathological mechanism of CTNNB1 gain-of-function mutations in hepatocarcinogenesis. Activated β-catenin not only triggered hepatic tumorigenesis but also exacerbated Tp53 deletion or hepatitis B virus infection-mediated liver cancer development in mouse models. Using untargeted metabolomic profiling, we identified boosted de novo pyrimidine synthesis as the major metabolic aberration in β-catenin mutant cell lines and livers. Oncogenic β-catenin transcriptionally stimulated AKT2, which then phosphorylated the rate-limiting de novo pyrimidine synthesis enzyme CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, dihydroorotase) on S1406 and S1859 to potentiate nucleotide synthesis. Moreover, inhibition of β-catenin/AKT2-stimulated pyrimidine synthesis axis preferentially repressed β-catenin mutant cell proliferation and tumor formation. Therefore, β-catenin active mutations are oncogenic in various preclinical liver cancer models. Stimulation of β-catenin/AKT2/CAD signaling cascade on pyrimidine synthesis is an essential and druggable vulnerability for β-catenin mutant liver cancer.

LKB1 acts as a critical brake for the glucagon-mediated fasting response

As important as the fasting response is for survival, an inability to shut it down once nutrients become available can lead to exacerbated disease and severe wasting. The liver is central to transitions between feeding and fasting states, with glucagon being a key initiator of the hepatic fasting response. However, the precise mechanisms controlling fasting are not well defined. One potential mediator of these transitions is liver kinase B1 (LKB1), given its role in nutrient sensing. Here, we show LKB1 knockout mice have a severe wasting and prolonged fasting phenotype despite increased food intake. By applying RNA sequencing and intravital microscopy, we show that loss of LKB1 leads to a dramatic reprogramming of the hepatic lobule through robust up-regulation of periportal genes and functions. This is likely mediated through the opposing effect that LKB1 has on glucagon pathways and gene expression. Conclusion: Our findings show that LKB1 acts as a brake to the glucagon-mediated fasting response, resulting in "periportalization" of the hepatic lobule and whole-body metabolic inefficiency. These findings reveal a mechanism by which hepatic metabolic compartmentalization is regulated by nutrient-sensing.

Deleting the β-catenin degradation domain in mouse hepatocytes drives hepatocellular carcinoma or hepatoblastoma-like tumor growth

BACKGROUND & AIMS

One-third of hepatocellular carcinomas (HCCs) harbor mutations activating the β-catenin pathway, predominantly via mutations in the CTNNB1 gene itself. Mouse models of Apc loss-of-function are widely used to mimic β-catenin-dependent tumorigenesis. Given the low prevalence of APC mutations in human HCCs, we aimed to generate liver tumors through CTNNB1 exon 3 deletion (βcatΔex3). We then compared βcatΔex3 liver tumors with liver tumors generated via frameshift in exon 15 of Apc (Apcfs-ex15).

METHODS

We used hepatocyte-specific and inducible mouse models generated through either a Cre-Lox or a CRISPR/Cas9 approach using adeno-associated virus vectors. Tumors generated by the Cre-Lox models were phenotypically analyzed using immunohistochemistry and were selected for transcriptomic analysis by RNA-sequencing (RNAseq). Mouse RNAseq data were compared to human RNAseq data (8 normal tissues, 48 HCCs, 9 hepatoblastomas) in an integrative analysis. Tumors generated via CRISPR were analyzed using DNA sequencing and immuno-histochemistry.

RESULTS

Mice with CTNNB1 exon 3 deletion in hepatocytes developed liver tumors indistinguishable from Apcfs-ex15 liver tumors. Both Apcfs-ex15 and βcatΔex3 mouse models induced growth of phenotypically distinct tumors (differentiated or undifferentiated). Integrative analysis of human and mouse tumors showed that differentiated mouse tumors cluster with well-differentiated human CTNNB1-mutated tumors. Conversely, undifferentiated mouse tumors cluster with human mesenchymal hepatoblastomas and harbor activated YAP signaling.

CONCLUSION

Apcfs-ex15 and βcatΔex3 mouse models both induce growth of tumors that are transcriptionally similar to either well-differentiated and β-catenin-activated human HCCs or mesenchymal hepatoblastomas.

LAY SUMMARY

New and easy-to-use transgenic mouse models of primary liver cancers have been generated, with mutations in the gene encoding beta-catenin, which are frequent in both adult and pediatric primary liver cancers. The mice develop both types of cancer, constituting a strong preclinical model.

Robust Colonic Epithelial Regeneration and Amelioration of Colitis via FZD-Specific Activation of Wnt Signaling

BACKGROUND AND AIMS

Current management of inflammatory bowel disease leaves a clear unmet need to treat the severe epithelial damage. Modulation of Wnt signaling might present an opportunity to achieve histological remission and mucosal healing when treating IBD. Exogenous R-spondin, which amplifies Wnt signals by maintaining cell surface expression of Frizzled (Fzd) and low-density lipoprotein receptor-related protein receptors, not only helps repair intestine epithelial damage, but also induces hyperplasia of normal epithelium. Wnt signaling may also be modulated with the recently developed Wnt mimetics, recombinant antibody-based molecules mimicking endogenous Wnts.

METHODS

We first compared the epithelial healing effects of RSPO2 and a Wnt mimetic with broad Fzd specificity in an acute dextran sulfate sodium mouse colitis model. Guided by Fzd expression patterns in the colon epithelium, we also examined the effects of Wnt mimetics with subfamily Fzd specificities.

RESULTS

In the DSS model, Wnt mimetics repaired damaged colon epithelium and reduced disease activity and inflammation and had no apparent effect on uninjured tissue. We further identified that the FZD5/8 and LRP6 receptor-specific Wnt mimetic, SZN-1326-p, was associated with the robust repair effect. Through a range of approaches including single-cell transcriptome analyses, we demonstrated that SZN-1326-p directly impacted epithelial cells, driving transient expansion of stem and progenitor cells, promoting differentiation of epithelial cells, histologically restoring the damaged epithelium, and secondarily to epithelial repair, reducing inflammation.

CONCLUSIONS

It is feasible to design Wnt mimetics such as SZN-1326-p that impact damaged intestine epithelium specifically and restore its physiological functions, an approach that holds promise for treating epithelial damage in inflammatory bowel disease.

The Role of Liver Zonation in Physiology, Regeneration, and Disease

As blood flows from the portal triad to the central vein, cell-mediated depletion establishes gradients of soluble factors such as oxygen, nutrients, and hormones, which act through molecular pathways (e.g., Wnt/β-catenin, hedgehog) to spatially regulate hepatocyte functions along the sinusoid. Such "zonation" can lead to the compartmentalized initiation of several liver diseases, including alcoholic/non-alcoholic fatty liver diseases, chemical/drug-induced toxicity, and hepatocellular carcinoma, and can also modulate liver regeneration. Transgenic rodent models provide valuable information on the key molecular regulators of zonation, while in vitro models allow for subjecting cells to precisely controlled factor gradients and elucidating species-specific differences in zonation. Here, we discuss the latest advances in both in vivo and in vitro models of liver zonation and pending questions to be addressed moving forward. Ultimately, obtaining a deeper understanding of zonation can lead to the development of more effective therapeutics for liver diseases, microphysiological systems, and scalable cell-based therapies.

Changes in beta-catenin expression and activation during progression of primary sclerosing cholangitis predict disease recurrence

Primary sclerosing cholangitis (PSC) is a rare, chronic, cholestatic liver disease characterized by progressive inflammation and fibrosis of the bile ducts. We have previously demonstrated the importance of Wnt/β-catenin signaling in mouse models of PSC. In this study, we wished to determine the clinical relevance of β-catenin localization in patient samples. In livers explanted from patients diagnosed with PSC, the majority (12/16; 75%) lacked β-catenin protein expression. Biopsies from patients post-transplant were classified as recurrent or non-recurrent based on pathology reports and then scored for β-catenin activation as a function of immunohistochemical localization. Despite lack of statistical significance, patients with recurrent primary disease (n = 11) had a greater percentage of samples with nuclear, transcriptionally active β-catenin (average 58.8%) than those with no recurrence (n = 10; 40.53%), while non-recurrence is correlated with β-catenin staining at the cell surface (average 52.63% for non-recurrent vs. 27.34% for recurrent), as determined by three different methods of analysis. β-catenin score and years-to-endpoint are both strongly associated with recurrence status (p = 0.017 and p = 0.00063, respectively). Finally, there was significant association between higher β-catenin score and increased alkaline phosphatase, a marker of biliary injury and disease progression. Thus, β-catenin expression and activation changes during the progression of PSC, and its localization may be a useful prognostic tool for predicting recurrence of this disease.

Role and Regulation of Wnt/β-Catenin in Hepatic Perivenous Zonation and Physiological Homeostasis

Metabolic heterogeneity or functional zonation is a key characteristic of the liver that allows different metabolic pathways to be spatially regulated within the hepatic system and together contribute to whole body homeostasis. These metabolic pathways are segregated along the portocentral axis of the liver lobule into three hepatic zones: periportal, intermediate or midzonal, and perivenous. The liver performs complementary or opposing metabolic functions within different hepatic zones while synergistic functions are regulated by overlapping zones, thereby maintaining the overall physiological stability. The Wnt/β-catenin signaling pathway is well known for its role in liver growth, development, and regeneration. In addition, the Wnt/β-catenin pathway plays a fundamental and dominant role in hepatic zonation and signals to orchestrate various functions of liver metabolism and pathophysiology. The β-catenin protein is the central player in the Wnt/β-catenin signaling cascade, and its activation is crucial for metabolic patterning of the liver. However, dysregulation of Wnt/β-catenin signaling is also implicated in different liver pathologies, including those associated with metabolic syndrome. β-Catenin is preferentially localized in the central region of the hepatic lobule surrounding the central vein and regulates multiple functions of this region. This review outlines the role of Wnt/β-catenin signaling pathway in controlling the different metabolic processes surrounding the central vein and its relation to liver homeostasis and dysfunction.

[Up-to-date Knowledge on the Pathological Diagnosis of Hepatocellular Carcinoma]

Hepatocellular carcinoma (HCC) has heterogeneous molecular and pathological features and biological behavior. Large-scale genetic studies of HCC were accumulated, and a pathological-molecular classification of HCC was proposed. Approximately 35% of HCCs can be classified into distinct histopathological subtypes according to their molecular characteristics. Among recently identified subtypes, macrotrabecular massive HCC, neutrophil-rich HCC, vessels encapsulating tumor clusters HCC, and progenitor phenotype HCC (HCC with CK19 expression) are associated with a poor prognosis, whereas the lymphocyte-rich HCC subtype is related to a better prognosis. This review provides up-to-date knowledge on the pathological diagnosis of HCC according to the updated World Health Organization Classification of Digestive System Tumors 5th ed.

The protein kinase activity of NME7 activates Wnt/β-Catenin signaling to promote one-carbon metabolism in hepatocellular carcinoma

Metabolic reprogramming by oncogenic signaling is a hallmark of cancer. Hyperactivation of Wnt/β-catenin signaling has been reported in hepatocellular carcinoma (HCC). However, the mechanisms inducing hyperactivation of Wnt/β-catenin signaling and strategies for targeting this pathway are incompletely understood. In this study, we find nucleoside diphosphate kinase 7 (NME7) to be a positive regulator of Wnt/β-catenin signaling. Upregulation of NME7 positively correlated with the clinical features of HCC. Knockdown of NME7 inhibited HCC growth in vitro and in vivo, while overexpression of NME7 cooperated with c-Myc to drive tumorigenesis in a mouse model and promote the growth of tumor-derived organoids. Mechanistically, NME7 bound and phosphorylated serine 9 of GSK3β to promote β-catenin activation. Furthermore, MTHFD2, the key enzyme in one-carbon metabolism, was a target gene of β-catenin and mediated the effects of NME7. Tumor-derived organoids with NME7 overexpression exhibited increased sensitivity to MTHFD2 inhibition. Additionally, expression levels of NME7, β-catenin and MTHFD2 correlated with each other and with poor prognosis in HCC patients. Collectively, this study emphasizes the crucial roles of NME7 protein kinase activity in promoting Wnt/β-catenin signaling and one-carbon metabolism, suggesting NME7 and MTHFD2 as potential therapeutic targets for HCC.