New insights into the regulation of bile acids synthesis during the early stages of liver regeneration: A human and experimental study

BACKGROUND AND AIMS

Liver regeneration is essential for the preservation of homeostasis and survival. Bile acids (BAs)-mediated signaling is necessary for liver regeneration, but BAs levels need to be carefully controlled to avoid hepatotoxicity. We studied the early response of the BAs-fibroblast growth factor 19 (FGF19) axis in healthy individuals undergoing hepatectomy for living donor liver transplant. We also evaluated BAs synthesis in mice upon partial hepatectomy (PH) and acute inflammation, focusing on the regulation of cytochrome-7A1 (CYP7A1), a key enzyme in BAs synthesis from cholesterol.

METHODS

Serum was obtained from twelve human liver donors. Mice underwent 2/3-PH or sham-operation. Acute inflammation was induced with bacterial lipopolysaccharide (LPS) in mice fed control or antoxidant-supplemented diets. BAs and 7α-hydroxy-4-cholesten-3-one (C4) levels were measured by HPLC-MS/MS; serum FGF19 by ELISA. Gene expression and protein levels were analyzed by RT-qPCR and western-blot.

RESULTS

Serum BAs levels increased after PH. In patients with more pronounced hypercholanemia, FGF19 concentrations transiently rose, while C4 levels (a readout of CYP7A1 activity) dropped 2 h post-resection in all cases. Serum BAs and C4 followed the same pattern in mice 1 h after PH, but C4 levels also dropped in sham-operated and LPS-treated animals, without marked changes in CYP7A1 protein levels. LPS-induced serum C4 decline was attenuated in mice fed an antioxidant-supplemented diet.

CONCLUSIONS

In human liver regeneration FGF19 upregulation may constitute a protective response from BAs excess during liver regeneration. Our findings suggest the existence of post-translational mechanisms regulating CYP7A1 activity, and therefore BAs synthesis, independent from CYP7A1/Cyp7a1 gene transcription.

Prognostic value of ultra-low-pass whole-genome sequencing of circulating tumor DNA in hepatocellular carcinoma under systemic treatment

BACKGROUND/AIMS

New prognostic markers are needed to identify patients with hepatocellular carcinoma (HCC) who carry a worse prognosis. Ultra-low-pass whole-genome sequencing (ULP-WGS) (≤0.5× coverage) of cell-free DNA (cfDNA) has emerged as a low-cost promising tool to assess both circulating tumor DNA (ctDNA) fraction and large structural genomic alterations. Here, we studied the performance of ULP-WGS of plasma cfDNA to infer prognosis in patients with HCC.

METHODS

Plasma samples were obtained from patients with HCC prior to surgery, locoregional or systemic therapy, and were analyzed by ULP-WGS of cfDNA to an average genome-wide fold coverage of 0.3x. ctDNA and copy number alterations (CNA) were estimated using the software package ichorCNA.

RESULTS

Samples were obtained from 73 HCC patients at different BCLC stages (BCLC 0/A: n=37, 50.7%; BCLC B/C: n=36, 49.3%). ctDNA was detected in 18 out of 31 patients who received systemic treatment. Patients with detectable ctDNA showed significantly worse overall survival (median, 13.96 months vs not reached). ctDNA remained an independent predictor of prognosis after adjustment by clinical-pathologic features and type of systemic treatment (hazard ratio 7.69; 95%, CI 2.09-28.27). Among ctDNA-positive patients under systemic treatments, the loss of large genomic regions in 5q and 16q arms was associated with worse prognosis after multivariate analysis.

CONCLUSION

ULP-WGS of cfDNA provides clinically relevant information about the tumor biology. The presence of ctDNA and the loss of 5q and 16q arms in ctDNA-positive patients are independent predictors of worse prognosis in patients with advanced HCC receiving systemic therapy.

Comprehensive analysis of epigenetic and epitranscriptomic genes' expression in human NAFLD

Non-alcoholic fatty liver disease (NAFLD) is a multifactorial condition with a complex etiology. Its incidence is increasing globally in parallel with the obesity epidemic, and it is now considered the most common liver disease in Western countries. The precise mechanisms underlying the development and progression of NAFLD are complex and still poorly understood. The dysregulation of epigenetic and epitranscriptomic mechanisms is increasingly recognized to play pathogenic roles in multiple conditions, including chronic liver diseases. Here, we have performed a comprehensive analysis of the expression of epigenetic and epitranscriptomic genes in a total of 903 liver tissue samples corresponding to patients with normal liver, obese patients, and patients with non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH), advancing stages in NAFLD progression. We integrated ten transcriptomic datasets in an unbiased manner, enabling their robust analysis and comparison. We describe the complete landscape of epigenetic and epitranscriptomic genes' expression along the course of the disease. We identify signatures of genes significantly dysregulated in association with disease progression, particularly with liver fibrosis development. Most of these epigenetic and epitranscriptomic effectors have not been previously described in human NAFLD, and their altered expression may have pathogenic implications. We also performed a comprehensive analysis of the expression of enzymes involved in the metabolism of the substrates and cofactors of epigenetic and epitranscriptomic effectors. This study provides novel information on NAFLD pathogenesis and may also guide the identification of drug targets to treat this condition and its progression towards hepatocellular carcinoma.

Identification and experimental validation of druggable epigenetic targets in hepatoblastoma

BACKGROUND & AIMS

Hepatoblastoma (HB) is the most frequent childhood liver cancer. Patients with aggressive tumors have limited therapeutic options; therefore, a better understanding of HB pathogenesis is needed to improve treatment. HBs have a very low mutational burden; however, epigenetic alterations are increasingly recognized. We aimed to identify epigenetic regulators consistently dysregulated in HB and to evaluate the therapeutic efficacy of their targeting in clinically relevant models.

METHODS

We performed a comprehensive transcriptomic analysis of 180 epigenetic genes. Data from fetal, pediatric, adult, peritumoral (n = 72) and tumoral (n = 91) tissues were integrated. Selected epigenetic drugs were tested in HB cells. The most relevant epigenetic target identified was validated in primary HB cells, HB organoids, a patient-derived xenograft model, and a genetic mouse model. Transcriptomic, proteomic and metabolomic mechanistic analyses were performed.

RESULTS

Altered expression of genes regulating DNA methylation and histone modifications was consistently observed in association with molecular and clinical features of poor prognosis. The histone methyltransferase G9a was markedly upregulated in tumors with epigenetic and transcriptomic traits of increased malignancy. Pharmacological targeting of G9a significantly inhibited growth of HB cells, organoids and patient-derived xenografts. Development of HB induced by oncogenic forms of β-catenin and YAP1 was ablated in mice with hepatocyte-specific deletion of G9a. We observed that HBs undergo significant transcriptional rewiring in genes involved in amino acid metabolism and ribosomal biogenesis. G9a inhibition counteracted these pro-tumorigenic adaptations. Mechanistically, G9a targeting potently repressed the expression of c-MYC and ATF4, master regulators of HB metabolic reprogramming.

CONCLUSIONS

HBs display a profound dysregulation of the epigenetic machinery. Pharmacological targeting of key epigenetic effectors exposes metabolic vulnerabilities that can be leveraged to improve the treatment of these patients.

IMPACT AND IMPLICATIONS

In spite of recent advances in the management of hepatoblastoma (HB), treatment resistance and drug toxicity are still major concerns. This systematic study reveals the remarkable dysregulation in the expression of epigenetic genes in HB tissues. Through pharmacological and genetic experimental approaches, we demonstrate that the histone-lysine-methyltransferase G9a is an excellent drug target in HB, which can also be harnessed to enhance the efficacy of chemotherapy. Furthermore, our study highlights the profound pro-tumorigenic metabolic rewiring of HB cells orchestrated by G9a in coordination with the c-MYC oncogene. From a broader perspective, our findings suggest that anti-G9a therapies may also be effective in other c-MYC-dependent tumors.

Mapping early serum proteome signatures of liver regeneration in living donor liver transplant cases

The liver is the only solid organ capable of regenerating itself to regain 100% of its mass and function after liver injury and/or partial hepatectomy (PH). This exceptional property represents a therapeutic opportunity for severe liver disease patients. However, liver regeneration (LR) might fail due to poorly understood causes. Here, we have investigated the regulation of liver proteome and phosphoproteome at a short time after PH (9 h), to depict a detailed mechanistic background of the early LR phase. Furthermore, we analyzed the dynamic changes of the serum proteome and metabolome of healthy living donor liver transplant (LDLT) donors at different time points after surgery. The molecular profiles from both analyses were then correlated. Insulin and FXR-FGF15/19 signaling were stimulated in mouse liver after PH, leading to the activation of the main intermediary kinases (AKT and ERK). Besides, inhibition of the hippo pathway led to an increased expression of its target genes and of one of its intermediary proteins (14-3-3 protein), contributing to cell proliferation. In association with these processes, metabolic reprogramming coupled to enhanced mitochondrial activity cope for the energy and biosynthetic requirements of LR. In human serum of LDLT donors, we identified 56 proteins and 13 metabolites statistically differential which recapitulate some of the main cellular processes orchestrating LR in its early phase. These results provide mechanisms and protein mediators of LR that might prove useful for the follow-up of the regenerative process in the liver after PH as well as preventing the occurrence of complications associated with liver resection.

Loss of liver function in chronic liver disease: An identity crisis

Adult hepatocyte identity is constructed throughout embryonic development and fine-tuned after birth. A multinodular network of transcription factors, along with pre-mRNA splicing regulators, define the transcriptome, which encodes the proteins needed to perform the complex metabolic and secretory functions of the mature liver. Transient hepatocellular dedifferentiation can occur as part of the regenerative mechanisms triggered in response to acute liver injury. However, persistent downregulation of key identity genes is now accepted as a strong determinant of organ dysfunction in chronic liver disease, a major global health burden. Therefore, the identification of core transcription factors and splicing regulators that preserve hepatocellular phenotype, and a thorough understanding of how these networks become disrupted in diseased hepatocytes, is of high clinical relevance. In this context, we review the key players in liver differentiation and discuss in detail critical factors, such as HNF4α, whose impairment mediates the breakdown of liver function. Moreover, we present compelling experimental evidence demonstrating that restoration of core transcription factor expression in a chronically injured liver can reset hepatocellular identity, improve function and ameliorate structural abnormalities. The possibility of correcting the phenotype of severely damaged and malfunctional livers may reveal new therapeutic opportunities for individuals with cirrhosis and advanced liver disease.

SLU7: A New Hub of Gene Expression Regulation—From Epigenetics to Protein Stability in Health and Disease

SLU7 (Splicing factor synergistic lethal with U5 snRNA 7) was first identified as a splicing factor necessary for the correct selection of 3′ splice sites, strongly impacting on the diversity of gene transcripts in a cell. More recent studies have uncovered new and non-redundant roles of SLU7 as an integrative hub of different levels of gene expression regulation, including epigenetic DNA remodeling, modulation of transcription and protein stability. Here we review those findings, the multiple factors and mechanisms implicated as well as the cellular functions affected. For instance, SLU7 is essential to secure liver differentiation, genome integrity acting at different levels and a correct cell cycle progression. Accordingly, the aberrant expression of SLU7 could be associated with human diseases including cancer, although strikingly, it is an essential survival factor for cancer cells. Finally, we discuss the implications of SLU7 in pathophysiology, with particular emphasis on the progression of liver disease and its possible role as a therapeutic target in human cancer.

Next-generation sequencing of bile cell-free DNA for the early detection of patients with malignant biliary strictures

OBJECTIVE

Despite significant progresses in imaging and pathological evaluation, early differentiation between benign and malignant biliary strictures remains challenging. Endoscopic retrograde cholangiopancreatography (ERCP) is used to investigate biliary strictures, enabling the collection of bile. We tested the diagnostic potential of next-generation sequencing (NGS) mutational analysis of bile cell-free DNA (cfDNA).

DESIGN

A prospective cohort of patients with suspicious biliary strictures (n=68) was studied. The performance of initial pathological diagnosis was compared with that of the mutational analysis of bile cfDNA collected at the time of first ERCP using an NGS panel open to clinical laboratory implementation, the Oncomine Pan-Cancer Cell-Free assay.

RESULTS

An initial pathological diagnosis classified these strictures as of benign (n=26), indeterminate (n=9) or malignant (n=33) origin. Sensitivity and specificity of this diagnosis were 60% and 100%, respectively, as on follow-up 14 of the 26 and eight of the nine initially benign or indeterminate strictures resulted malignant. Sensitivity and specificity for malignancy of our NGS assay, herein named Bilemut, were 96.4% and 69.2%, respectively. Importantly, one of the four Bilemut false positives developed pancreatic cancer after extended follow-up. Remarkably, the sensitivity for malignancy of Bilemut was 100% in patients with an initial diagnosis of benign or indeterminate strictures. Analysis of 30 paired bile and tissue samples also demonstrated the superior performance of Bilemut.

CONCLUSION

Implementation of Bilemut at the initial diagnostic stage for biliary strictures can significantly improve detection of malignancy, reduce delays in the clinical management of patients and assist in selecting patients for targeted therapies.

The Amphiregulin/EGFR axis protects from lupus nephritis via downregulation of pathogenic CD4+ T helper cell responses

Systemic lupus erythematosus (SLE) is a common autoimmune disorder with a complex and poorly understood immuno-pathogenesis. Lupus nephritis (LN) is a frequent and difficult to treat complication, which causes high morbidity and mortality. The multifunctional cytokine amphiregulin (AREG) has been implicated in SLE pathogenesis, but its function in LN currently remains unknown. We thus studied the model of pristane-induced LN and found increasing renal and systemic AREG expression during the course of disease. Importantly, renal injury was significantly aggravated in the absence of AREG, revealing a net anti-inflammatory role. Analyses of immune responses showed dual effects. On the one hand, AREG enhanced activation of pro-inflammatory myeloid cells, which however did not play a major role for the course of LN. More importantly, on the other hand, AREG strongly suppressed pathogenic cytokine production by T helper effector cells. This effect was more general in nature and could be reproduced in response to antigen immunization. Since AREG has been postulated to downregulate T cell responses via enhancing Treg suppressive capacity, we followed up on this aspect. Interestingly, however, in vitro studies revealed potential direct and Treg independent effects of AREG on T helper effector cells. In favor of this notion, we found significantly enhanced T cell responses and consecutive aggravation of LN, only if epidermal growth factor receptor (EGFR) signaling was abrogated in total T cells, but not if the EGFR was absent on Tregs alone. Finally, we also found enhanced AREG expression in plasma and renal biopsies of patients with LN, supporting the relevance of our findings for human disease. In summary, our data identify AREG as an anti-inflammatory mediator of LN via broad downregulation of pathogenic T cell immunity. These findings further highlight the AREG/EGFR axis as a potential therapeutic target.

DNA Methylation Regulates a Set of Long Non-Coding RNAs Compromising Hepatic Identity during Hepatocarcinogenesis

Simple Summary

Hepatocarcinogenesis is a long process which implies the loss of hepatic functions. Our effort is to understand the mechanisms implicated in this pathological process in order to contribute to the development of new diagnostic markers and therapeutic targets. In this study we have identified a set of lncRNAs significantly downregulated in hepatocellular carcinoma (HCC) in correlation with the grade of tumor dedifferentiation and patients’ worse prognosis. Mechanistically, our results show that they are related with hepatic differentiation and at least a subset of those lncRNAs are essential to ensure the expression of other hepato-specific genes required for liver function. Moreover, we demonstrate that the expression of these lncRNAs in HCC is silenced by DNA methylation. All in all, we uncover connected epigenetic alterations involved in the progression of liver cancer and identify potential new biomarkers.

Abstract

Background: Long noncoding RNAs (lncRNAs) are emerging as key players in cancer, including hepatocellular carcinoma (HCC). Here we identify the mechanism implicated in the HCC inhibition of a set of lncRNAs, and their contribution to the process of hepatocarcinogenesis. Methods and Results: The top-ranked 35 lncRNAs downregulated in HCC (Top35 LNDH) were validated in several human HCC cohorts. We demonstrate that their inhibition is associated with promoter hypermethylation in HCC compared to control tissue, and in HCC human cell lines compared to primary hepatocytes. Moreover, demethylating treatment of HCC human cell lines induced the expression of these lncRNAs. The Top35 LNDH were preferentially expressed in the adult healthy liver compared to other tissues and fetal liver and were induced in well-differentiated HepaRG cells. Remarkably, their knockdown compromised the expression of other hepato-specific genes. Finally, the expression of the Top35 LNDH positively correlates with the grade of tumor differentiation and, more importantly, with a better patient prognosis. Conclusions: Our results demonstrate that the selected Top35 LNDH are not only part of the genes that compose the hepatic differentiated signature but participate in its establishment. Moreover, their downregulation through DNA methylation occurs during the process of hepatocarcinogenesis compromising hepatocellular differentiation and HCC patients’ prognosis.

A new animal model of atrophy-hypertrophy complex and liver damage following Yttrium-90 lobar selective internal radiation therapy in rabbits

Lobar selective internal radiation therapy (SIRT) is widely used to treat liver tumors inducing atrophy of the treated lobe and contralateral hypertrophy. The lack of animal model has precluded further investigations to improve this treatment. We developed an animal model of liver damage and atrophy–hypertrophy complex after SIRT. Three groups of 5–8 rabbits received transportal SIRT with Yttrium 90 resin microspheres of the cranial lobes with different activities (0.3, 0.6 and 1.2 GBq), corresponding to predicted absorbed radiation dose of 200, 400 and 800 Gy, respectively. Another group received non-loaded microspheres (sham group). Cranial and caudal lobes volumes were assessed using CT volumetry before, 15 and 30 days after SIRT. Liver biochemistry, histopathology and gene expression were evaluated. Four untreated rabbits were used as controls for gene expression studies. All animals receiving 1.2 GBq were euthanized due to clinical deterioration. Cranial SIRT with 0.6 GBq induced caudal lobe hypertrophy after 15 days (median increase 34% -ns-) but produced significant toxicity. Cranial SIRT with 0.3 GBq induced caudal lobe hypertrophy after 30 days (median increase 82%, p = 0.04). No volumetric changes were detected in sham group. Transient increase in serum transaminases was detected in all treated groups returning to normal values at 15 days. There was dose-dependent liver dysfunction with bilirubin elevation and albumin decrease. Histologically, 1.2 GBq group developed permanent severe liver damage with massive necrosis, 0.6 and 0.3 GBq groups developed moderate damage with inflammation and portal fibrosis at 15 days, partially recovering at 30 days. There was no difference in the expression of hepatocyte function and differentiation genes between 0.3 GBq and control groups. Cranial SIRT with 0.3 GBq of ⁹⁰Y resin microspheres in rabbits is a reliable animal model to analyse the atrophy–hypertrophy complex and liver damage without toxicity.

Activation of the Unfolded Protein Response (UPR) Is Associated with Cholangiocellular Injury, Fibrosis and Carcinogenesis in an Experimental Model of Fibropolycystic Liver Disease

Simple Summary

Polycystic liver disease (PLD) is a group of rare disorders that result from structural changes in the biliary tree development in the liver. In the present work, we studied alterations in molecular mechanisms and signaling pathways that might be responsible for these pathologies. We found that activation of the unfolded protein response, a process that occurs in response to an accumulation of unfolded or misfolded proteins in the lumen of the endoplasmic reticulum, as well as the scarring of the liver tissue, contribute to the pathogenesis of PLD and the development of cancer. As a preclinical animal model we have used mutant mice of a specific signaling pathway, the c-Jun N-terminal kinase 1/2 (Jnk1/2). These mice resemble a perfect model for the study of PLD and early cancer development.

Abstract

Fibropolycystic liver disease is characterized by hyperproliferation of the biliary epithelium and the formation of multiple dilated cysts, a process associated with unfolded protein response (UPR). In the present study, we aimed to understand the mechanisms of cyst formation and UPR activation in hepatocytic c-Jun N-terminal kinase 1/2 (Jnk1/2) knockout mice. Floxed JNK1/2 (Jnk^f/f) and Jnk^∆hepa animals were sacrificed at different time points during progression of liver disease. Histological examination of specimens evidenced the presence of collagen fiber deposition, increased α-smooth muscle actin (αSMA), infiltration of CD45, CD11b and F4/80 cells and proinflammatory cytokines (Tnf, Tgfβ1) and liver injury (e.g., ALT, apoptosis and Ki67-positive cells) in Jnk^∆hepa compared with Jnk^f/f livers from 32 weeks of age. This was associated with activation of effectors of the UPR, including BiP/GRP78, CHOP and spliced XBP1. Tunicamycin (TM) challenge strongly induced ER stress and fibrosis in Jnk^∆hepa animals compared with Jnk^f/f littermates. Finally, thioacetamide (TAA) administration to Jnk^∆hepa mice induced UPR activation, peribiliary fibrosis, liver injury and markers of biliary proliferation and cholangiocarcinoma (CCA). Orthoallografts of DEN/CCl₄-treated Jnk^∆hepa liver tissue triggered malignant CCA. Altogether, these results suggest that activation of the UPR in conjunction with fibrogenesis might trigger hepatic cystogenesis and early stages of CCA.

Splicing Factor SLU7 Prevents Oxidative Stress-Mediated Hepatocyte Nuclear Factor 4α Degradation, Preserving Hepatic Differentiation and Protecting From Liver Damage

BACKGROUND AND AIMS

Hepatocellular dedifferentiation is emerging as an important determinant in liver disease progression. Preservation of mature hepatocyte identity relies on a set of key genes, predominantly the transcription factor hepatocyte nuclear factor 4α (HNF4α) but also splicing factors like SLU7. How these factors interact and become dysregulated and the impact of their impairment in driving liver disease are not fully understood.

APPROACH AND RESULTS

Expression of SLU7 and that of the adult and oncofetal isoforms of HNF4α, driven by its promoter 1 (P1) and P2, respectively, was studied in diseased human and mouse livers. Hepatic function and damage response were analyzed in wild-type and Slu7-haploinsufficient/heterozygous (Slu7^+/- ) mice undergoing chronic (CCl₄ ) and acute (acetaminophen) injury. SLU7 expression was restored in CCl₄ -injured mice using SLU7-expressing adeno-associated viruses (AAV-SLU7). The hepatocellular SLU7 interactome was characterized by mass spectrometry. Reduced SLU7 expression in human and mouse diseased livers correlated with a switch in HNF4α P1 to P2 usage. This response was reproduced in Slu7^+/- mice, which displayed increased sensitivity to chronic and acute liver injury, enhanced oxidative stress, and marked impairment of hepatic functions. AAV-SLU7 infection prevented liver injury and hepatocellular dedifferentiation. Mechanistically we demonstrate a unique role for SLU7 in the preservation of HNF4α1 protein stability through its capacity to protect the liver against oxidative stress. SLU7 is herein identified as a key component of the stress granule proteome, an essential part of the cell's antioxidant machinery.

CONCLUSIONS

Our results place SLU7 at the highest level of hepatocellular identity control, identifying SLU7 as a link between stress-protective mechanisms and liver differentiation. These findings emphasize the importance of the preservation of hepatic functions in the protection from liver injury.

The splicing regulator SLU7 is required to preserve DNMT1 protein stability and DNA methylation

Gene expression is finely and dynamically controlled through the tightly coordinated and interconnected activity of epigenetic modulators, transcription and splicing factors and post-translational modifiers. We have recently identified the splicing factor SLU7 as essential for maintaining liver cell identity and genome integrity and for securing cell division both trough transcriptional and splicing mechanisms. Now we uncover a new function of SLU7 controlling gene expression at the epigenetic level. We show that SLU7 is required to secure DNMT1 protein stability and a correct DNA methylation. We demonstrate that SLU7 is part in the chromatome of the protein complex implicated in DNA methylation maintenance interacting with and controlling the integrity of DNMT1, its adaptor protein UHRF1 and the histone methyl-transferase G9a at the chromatin level. Mechanistically, we found that SLU7 assures DNMT1 stability preventing its acetylation and degradation by facilitating its interaction with HDAC1 and the desubiquitinase USP7. Importantly, we demonstrate that this DNMT1 dependency on SLU7 occurs in a large panel of proliferating cell lines of different origins and in in vivo models of liver proliferation. Overall, our results uncover a novel and non-redundant role of SLU7 in DNA methylation and present SLU7 as a holistic regulator of gene expression.

Dual Targeting of G9a and DNA Methyltransferase-1 for the Treatment of Experimental Cholangiocarcinoma

BACKGROUND AND AIMS

Cholangiocarcinoma (CCA) is a devastating disease often detected at advanced stages when surgery cannot be performed. Conventional and targeted systemic therapies perform poorly, and therefore effective drugs are urgently needed. Different epigenetic modifications occur in CCA and contribute to malignancy. Targeting epigenetic mechanisms may thus open therapeutic opportunities. However, modifications such as DNA and histone methylation often coexist and cooperate in carcinogenesis. We tested the therapeutic efficacy and mechanism of action of a class of dual G9a histone-methyltransferase and DNA-methyltransferase 1 (DNMT1) inhibitors.

APPROACH AND RESULTS

Expression of G9a, DNMT1, and their molecular adaptor, ubiquitin-like with PHD and RING finger domains-1 (UHRF1), was determined in human CCA. We evaluated the effect of individual and combined pharmacological inhibition of G9a and DNMT1 on CCA cell growth. Our lead G9a/DNMT1 inhibitor, CM272, was tested in human CCA cells, patient-derived tumoroids and xenograft, and a mouse model of cholangiocarcinogenesis with hepatocellular deletion of c-Jun-N-terminal-kinase (Jnk)-1/2 and diethyl-nitrosamine (DEN) plus CCl₄ treatment (Jnk^Δhepa + DEN + CCl₄ mice). We found an increased and correlative expression of G9a, DNMT1, and UHRF1 in CCAs. Cotreatment with independent pharmacological inhibitors G9a and DNMT1 synergistically inhibited CCA cell growth. CM272 markedly reduced CCA cell proliferation and synergized with Cisplatin and the ERBB-targeted inhibitor, Lapatinib. CM272 inhibited CCA tumoroids and xenograft growth and significantly antagonized CCA progression in Jnk^Δhepa + DEN + CCl₄ mice without apparent toxicity. Mechanistically, CM272 reprogrammed the tumoral metabolic transcriptome and phenotype toward a differentiated and quiescent status.

CONCLUSIONS

Dual targeting of G9a and DNMT1 with epigenetic small molecule inhibitors such as CM272 is a potential strategy to treat CCA and/or enhance the efficacy of other systemic therapies.

PHAROH lncRNA regulates Myc translation in hepatocellular carcinoma via sequestering TIAR

Hepatocellular carcinoma, the most common type of liver malignancy, is one of the most lethal forms of cancer. We identified a long non-coding RNA, Gm19705, that is overexpressed in hepatocellular carcinoma and mouse embryonic stem cells. We named this RNA Pluripotency and Hepatocyte Associated RNA Overexpressed in HCC, or PHAROH. Depletion of PHAROH impacts cell proliferation and migration, which can be rescued by ectopic expression of PHAROH. RNA-seq analysis of PHAROH knockouts revealed that a large number of genes with decreased expression contain a Myc motif in their promoter. MYC is decreased in knockout cells at the protein level, but not the mRNA level. RNA-antisense pulldown identified nucleolysin TIAR, a translational repressor, to bind to a 71-nt hairpin within PHAROH, sequestration of which increases MYC translation. In summary, our data suggest that PHAROH regulates MYC translation by sequestering TIAR and as such represents a potentially exciting diagnostic or therapeutic target in hepatocellular carcinoma.

Epigenetic Biomarkers for the Diagnosis and Treatment of Liver Disease

Research in the last decades has demonstrated the relevance of epigenetics in controlling gene expression to maintain cell homeostasis, and the important role played by epigenome alterations in disease development. Moreover, the reversibility of epigenetic marks can be harnessed as a therapeutic strategy, and epigenetic marks can be used as diagnosis biomarkers. Epigenetic alterations in DNA methylation, histone post-translational modifications (PTMs), and non-coding RNA (ncRNA) expression have been associated with the process of hepatocarcinogenesis. Here, we summarize epigenetic alterations involved in the pathogenesis of chronic liver disease (CLD), particularly focusing on DNA methylation. We also discuss their utility as epigenetic biomarkers in liquid biopsy for the diagnosis and prognosis of hepatocellular carcinoma (HCC). Finally, we discuss the potential of epigenetic therapeutic strategies for HCC treatment.

ARMCX3 Mediates Susceptibility to Hepatic Tumorigenesis Promoted by Dietary Lipotoxicity

Simple Summary

An excess fat in the liver enhances the susceptibility to hepatic cancer. We found that Armcx3, a protein only known to date to play a role in neural development, is strongly increased in mouse liver in response to lipid availability and proliferation-inducing insults. In patients, the levels of hepatic Armcx3 are also increased in conditions of high exposure of the liver to fat. We wanted to determine the role of Armcx3 in the hepatocarcinogenesis favored by a high-fat diet. We generated mice with genetically driven suppression of Armcx3, and we found that they were protected against experimentally induced hepatic cancer, especially in conditions of a high-fat diet. Armcx3 was also found to promote hepatic cell proliferation through the interaction with Sox9, a known proliferation factor in hepatocellular carcinoma. Armcx3 is identified as a novel factor in meditating propensity to liver cancer in conditions of high hepatic lipid insults.

Abstract

ARMCX3 is encoded by a member of the Armcx gene family and is known to be involved in nervous system development and function. We found that ARMCX3 is markedly upregulated in mouse liver in response to high lipid availability, and that hepatic ARMCX3 is upregulated in patients with NAFLD and hepatocellular carcinoma (HCC). Mice were subjected to ARMCX3 invalidation (inducible ARMCX3 knockout) and then exposed to a high-fat diet and diethylnitrosamine-induced hepatocarcinogenesis. The effects of experimental ARMCX3 knockdown or overexpression in HCC cell lines were also analyzed. ARMCX3 invalidation protected mice against high-fat-diet-induced NAFLD and chemically induced hepatocarcinogenesis. ARMCX3 invalidation promoted apoptotic cell death and macrophage infiltration in livers of diethylnitrosamine-treated mice maintained on a high-fat diet. ARMCX3 downregulation reduced the viability, clonality and migration of HCC cell lines, whereas ARMCX3 overexpression caused the reciprocal effects. SOX9 was found to mediate the effects of ARMCX3 in hepatic cells, with the SOX9 interaction required for the effects of ARMCX3 on hepatic cell proliferation. In conclusion, ARMCX3 is identified as a novel molecular actor in liver physiopathology and carcinogenesis. ARMCX3 downregulation appears to protect against hepatocarcinogenesis, especially under conditions of high dietary lipid-mediated hepatic insult.

Epigenetic mechanisms and metabolic reprogramming in fibrogenesis: dual targeting of G9a and DNMT1 for the inhibition of liver fibrosis

OBJECTIVE

Hepatic stellate cells (HSC) transdifferentiation into myofibroblasts is central to fibrogenesis. Epigenetic mechanisms, including histone and DNA methylation, play a key role in this process. Concerted action between histone and DNA-mehyltransferases like G9a and DNMT1 is a common theme in gene expression regulation. We aimed to study the efficacy of CM272, a first-in-class dual and reversible G9a/DNMT1 inhibitor, in halting fibrogenesis.

DESIGN

G9a and DNMT1 were analysed in cirrhotic human livers, mouse models of liver fibrosis and cultured mouse HSC. G9a and DNMT1 expression was knocked down or inhibited with CM272 in human HSC (hHSC), and transcriptomic responses to transforming growth factor-β1 (TGFβ1) were examined. Glycolytic metabolism and mitochondrial function were analysed with Seahorse-XF technology. Gene expression regulation was analysed by chromatin immunoprecipitation and methylation-specific PCR. Antifibrogenic activity and safety of CM272 were studied in mouse chronic CCl₄ administration and bile duct ligation (BDL), and in human precision-cut liver slices (PCLSs) in a new bioreactor technology.

RESULTS

G9a and DNMT1 were detected in stromal cells in areas of active fibrosis in human and mouse livers. G9a and DNMT1 expression was induced during mouse HSC activation, and TGFβ1 triggered their chromatin recruitment in hHSC. G9a/DNMT1 knockdown and CM272 inhibited TGFβ1 fibrogenic responses in hHSC. TGFβ1-mediated profibrogenic metabolic reprogramming was abrogated by CM272, which restored gluconeogenic gene expression and mitochondrial function through on-target epigenetic effects. CM272 inhibited fibrogenesis in mice and PCLSs without toxicity.

CONCLUSIONS

Dual G9a/DNMT1 inhibition by compounds like CM272 may be a novel therapeutic strategy for treating liver fibrosis.

Epigenetics in hepatocellular carcinoma development and therapy: The tip of the iceberg

Hepatocellular carcinoma (HCC) is a deadly tumour whose causative agents are generally well known, but whose pathogenesis remains poorly understood. Nevertheless, key genetic alterations are emerging from a heterogeneous molecular landscape, providing information on the tumorigenic process from initiation to progression. Among these molecular alterations, those that affect epigenetic processes are increasingly recognised as contributing to carcinogenesis from preneoplastic stages. The epigenetic machinery regulates gene expression through intertwined and partially characterised circuits involving chromatin remodelers, covalent DNA and histone modifications, and dedicated proteins reading these modifications. In this review, we summarise recent findings on HCC epigenetics, focusing mainly on changes in DNA and histone modifications and their carcinogenic implications. We also discuss the potential drugs that target epigenetic mechanisms for HCC treatment, either alone or in combination with current therapies, including immunotherapies.

FGF15/19 is required for adipose tissue plasticity in response to thermogenic adaptations

Objective

To determine the role of enterokine FGF15/19 in adipose tissue thermogenic adaptations.

Methods

Circulating FGF19 and gene expression (qRT-PCR) levels were assessed in subcutaneous adipose tissue from obese human patients. Effects of experimentally increased FGF15 and FGF19 levels in vivo were determined in mice using adenoviral and adeno-associated vectors. Adipose tissues were characterized in FGF15-null mice under distinct cold-related thermogenic challenges. The analyses spanned metabolic profiling, tissue characterization, histology, gene expression, and immunoblot assays.

Results

In humans, FGF19 levels are directly associated with UCP1 gene expression in subcutaneous adipose tissue. Experimental increases in FGF15 or FGF19 induced white fat browning in mice as demonstrated by the appearance of multilocular beige cells and markers indicative of a beige phenotype, including increased UCP1 protein levels. Mice lacking FGF15 showed markedly impaired white adipose tissue browning and a mild reduction in parameters indicative of BAT activity in response to cold-induced environmental thermogenic challenges. This was concomitant with signs of altered systemic metabolism, such as reduced glucose tolerance and impaired cold-induced insulin sensitization.

Conclusions

Enterokine FGF15/19 is a key factor required for adipose tissue plasticity in response to thermogenic adaptations.

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Circulating FGF19 levels correlate positively with signs of fat browning in humans.

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Adaptive adipose tissue browning in response to cold is impaired in mice lacking FGF15.

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Experimentally induced increase in FGF15 or FGF19 promotes fat browning in mice.

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FGF15/19 signaling is required for thermogenic challenge-induced plasticity of adipose tissue.

Epigenetics in Liver Fibrosis: Could HDACs be a Therapeutic Target?

Chronic liver diseases (CLD) represent a worldwide health problem. While CLDs may have diverse etiologies, a common pathogenic denominator is the presence of liver fibrosis. Cirrhosis, the end-stage of CLD, is characterized by extensive fibrosis and is markedly associated with the development of hepatocellular carcinoma. The most important event in hepatic fibrogenesis is the activation of hepatic stellate cells (HSC) following liver injury. Activated HSCs acquire a myofibroblast-like phenotype becoming proliferative, fibrogenic, and contractile cells. While transient activation of HSCs is part of the physiological mechanisms of tissue repair, protracted activation of a wound healing reaction leads to organ fibrosis. The phenotypic changes of activated HSCs involve epigenetic mechanisms mediated by non-coding RNAs (ncRNA) as well as by changes in DNA methylation and histone modifications. During CLD these epigenetic mechanisms become deregulated, with alterations in the expression and activity of epigenetic modulators. Here we provide an overview of the epigenetic alterations involved in fibrogenic HSCs transdifferentiation with particular focus on histones acetylation changes. We also discuss recent studies supporting the promising therapeutic potential of histone deacetylase inhibitors in liver fibrosis.

Liquid biopsy for cancer management: a revolutionary but still limited new tool for precision medicine

The term liquid biopsy is used in contraposition to the traditional "solid" tissue biopsy. In the oncology field it has opened a new plethora of clinical opportunities as tumor-derived material is shedded into the different biofluids from where it can be isolated and analyzed. Common biofluids include blood, urine, saliva, cerebrospinal fluid (CSF), pleural effusion or bile. Starting from these biological specimens several analytes can be isolated, among which we will review the most widely used: circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), circulating tumor RNA (ctRNA), proteins, metabolites, and exosomes. Regarding the nature of the biomarkers it will depend on the analyte, the type of tumor and the clinical application of the liquid biopsy and it includes, somatic point mutations, deletions, amplifications, gene-fusions, DNA-methylated marks, tumor-specific miRNAs, proteins or metabolites. Here we review the characteristics of the analytes and the methodologies used for their isolation. We also describe the applications of the liquid biopsy in the management of patients with cancer, from the early detection of cancers to treatment guidance in patients with advanced tumors. Finally, we also discuss some current limitations and still open questions.

Epigenetic Mechanisms in Gastric Cancer: Potential New Therapeutic Opportunities

Gastric cancer (GC) is one of the deadliest malignancies worldwide. Complex disease heterogeneity, late diagnosis, and suboptimal therapies result in the poor prognosis of patients. Besides genetic alterations and environmental factors, it has been demonstrated that alterations of the epigenetic machinery guide cancer onset and progression, representing a hallmark of gastric malignancies. Moreover, epigenetic mechanisms undergo an intricate crosstalk, and distinct epigenomic profiles can be shaped under different microenvironmental contexts. In this scenario, targeting epigenetic mechanisms could be an interesting therapeutic strategy to overcome gastric cancer heterogeneity, and the efforts conducted to date are delivering promising results. In this review, we summarize the key epigenetic events involved in gastric cancer development. We conclude with a discussion of new promising epigenetic strategies for gastric cancer treatment.

Amphiregulin Aggravates Glomerulonephritis via Recruitment and Activation of Myeloid Cells

BACKGROUND

Recent studies have identified the EGF receptor (EGFR) ligand amphiregulin (AREG) as an important mediator of inflammatory diseases. Both pro- and anti-inflammatory functions have been described, but the role of AREG in GN remains unknown.

METHODS

The nephrotoxic nephritis model of GN was studied in AREG^-/- mice after bone marrow transplantation, and in mice with myeloid cell-specific EGFR deficiency. Therapeutic utility of AREG neutralization was assessed. Furthermore, AREG's effects on renal cells and monocytes/macrophages (M/M) were analyzed. Finally, we evaluated AREG expression in human renal biopsies.

RESULTS

Renal AREG mRNA was strongly upregulated in murine GN. Renal resident cells were the most functionally relevant source of AREG. Importantly, the observation that knockout mice showed significant amelioration of disease indicates that AREG is pathogenic in GN. AREG enhanced myeloid cell responses via inducing chemokine and colony stimulating factor 2 (CSF2) expression in kidney resident cells. Furthermore, AREG directly skewed M/M to a proinflammatory M1 phenotype and protected them from apoptosis. Consequently, anti-AREG antibody treatment dose-dependently ameliorated GN. Notably, selective abrogation of EGFR signaling in myeloid cells was sufficient to protect against nephritis. Finally, strong upregulation of AREG expression was also detected in kidneys of patients with two forms of crescentic GN.

CONCLUSIONS

AREG is a proinflammatory mediator of GN via (1) enhancing renal pathogenic myeloid cell infiltration and (2) direct effects on M/M polarization, proliferation, and cytokine secretion. The AREG/EGFR axis is a potential therapeutic target for acute GN.

Pilot Multi-Omic Analysis of Human Bile from Benign and Malignant Biliary Strictures: A Machine-Learning Approach

Cholangiocarcinoma (CCA) and pancreatic adenocarcinoma (PDAC) may lead to the development of extrahepatic obstructive cholestasis. However, biliary stenoses can also be caused by benign conditions, and the identification of their etiology still remains a clinical challenge. We performed metabolomic and proteomic analyses of bile from patients with benign (n = 36) and malignant conditions, CCA (n = 36) or PDAC (n = 57), undergoing endoscopic retrograde cholangiopancreatography with the aim of characterizing bile composition in biliopancreatic disease and identifying biomarkers for the differential diagnosis of biliary strictures. Comprehensive analyses of lipids, bile acids and small molecules were carried out using mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (¹H-NMR) in all patients. MS analysis of bile proteome was performed in five patients per group. We implemented artificial intelligence tools for the selection of biomarkers and algorithms with predictive capacity. Our machine-learning pipeline included the generation of synthetic data with properties of real data, the selection of potential biomarkers (metabolites or proteins) and their analysis with neural networks (NN). Selected biomarkers were then validated with real data. We identified panels of lipids (n = 10) and proteins (n = 5) that when analyzed with NN algorithms discriminated between patients with and without cancer with an unprecedented accuracy.

Splicing events in the control of genome integrity: role of SLU7 and truncated SRSF3 proteins

Genome instability is related to disease development and carcinogenesis. DNA lesions are caused by genotoxic compounds but also by the dysregulation of fundamental processes like transcription, DNA replication and mitosis. Recent evidence indicates that impaired expression of RNA-binding proteins results in mitotic aberrations and the formation of transcription-associated RNA-DNA hybrids (R-loops), events strongly associated with DNA injury. We identify the splicing regulator SLU7 as a key mediator of genome stability. SLU7 knockdown results in R-loops formation, DNA damage, cell-cycle arrest and severe mitotic derangements with loss of sister chromatid cohesion (SCC). We define a molecular pathway through which SLU7 keeps in check the generation of truncated forms of the splicing factor SRSF3 (SRp20) (SRSF3-TR). Behaving as dominant negative, or by gain-of-function, SRSF3-TR impair the correct splicing and expression of the splicing regulator SRSF1 (ASF/SF2) and the crucial SCC protein sororin. This unique function of SLU7 was found in cancer cells of different tissue origin and also in the normal mouse liver, demonstrating a conserved and fundamental role of SLU7 in the preservation of genome integrity. Therefore, the dowregulation of SLU7 and the alterations of this pathway that we observe in the cirrhotic liver could be involved in the process of hepatocarcinogenesis.

Defective HNF4alpha-dependent gene expression as a driver of hepatocellular failure in alcoholic hepatitis

Alcoholic hepatitis (AH) is a life-threatening condition characterized by profound hepatocellular dysfunction for which targeted treatments are urgently needed. Identification of molecular drivers is hampered by the lack of suitable animal models. By performing RNA sequencing in livers from patients with different phenotypes of alcohol-related liver disease (ALD), we show that development of AH is characterized by defective activity of liver-enriched transcription factors (LETFs). TGFβ1 is a key upstream transcriptome regulator in AH and induces the use of HNF4α P2 promoter in hepatocytes, which results in defective metabolic and synthetic functions. Gene polymorphisms in LETFs including HNF4α are not associated with the development of AH. In contrast, epigenetic studies show that AH livers have profound changes in DNA methylation state and chromatin remodeling, affecting HNF4α-dependent gene expression. We conclude that targeting TGFβ1 and epigenetic drivers that modulate HNF4α-dependent gene expression could be beneficial to improve hepatocellular function in patients with AH.

The Epidermal Growth Factor Receptor Ligand Amphiregulin Protects From Cholestatic Liver Injury and Regulates Bile Acids Synthesis

Intrahepatic accumulation of bile acids (BAs) causes hepatocellular injury. Upon liver damage, a potent protective response is mounted to restore the organ's function. Epidermal growth factor receptor (EGFR) signaling is essential for regeneration after most types of liver damage, including cholestatic injury. However, EGFR can be activated by a family of growth factors induced during liver injury and regeneration. We evaluated the role of the EGFR ligand, amphiregulin (AREG), during cholestatic liver injury and regulation of AREG expression by BAs. First, we demonstrated increased AREG levels in livers from patients with primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). In two murine models of cholestatic liver injury, bile duct ligation (BDL) and alpha-naphthyl-isothiocyanate (ANIT) gavage, hepatic AREG expression was markedly up-regulated. Importantly, Areg^-/- mice showed aggravated liver injury after BDL and ANIT administration compared to Areg^+/+ mice. Recombinant AREG protected from ANIT and BDL-induced liver injury and reduced BA-triggered apoptosis in liver cells. Oral BA administration induced ileal and hepatic Areg expression, and, interestingly, cholestyramine feeding reduced postprandial Areg up-regulation in both tissues. Most interestingly, Areg^-/- mice displayed high hepatic cholesterol 7 α-hydroxylase (CYP7A1) expression, reduced serum cholesterol, and high BA levels. Postprandial repression of Cyp7a1 was impaired in Areg^-/- mice, and recombinant AREG down-regulated Cyp7a1 mRNA in hepatocytes. On the other hand, BAs promoted AREG gene expression and protein shedding in hepatocytes. This effect was mediated through the farnesoid X receptor (FXR), as demonstrated in Fxr^-/- mice, and involved EGFR transactivation. Finally, we show that hepatic EGFR expression is indirectly induced by BA-FXR through activation of suppressor of cytokine signaling-3 (SOC3). Conclusion: AREG-EGFR signaling protects from cholestatic injury and participates in the physiological regulation of BA synthesis.

Dual Targeting of Histone Methyltransferase G9a and DNA-Methyltransferase 1 for the Treatment of Experimental Hepatocellular Carcinoma

Epigenetic modifications such as DNA and histone methylation functionally cooperate in fostering tumor growth, including that of hepatocellular carcinoma (HCC). Pharmacological targeting of these mechanisms may open new therapeutic avenues. We aimed to determine the therapeutic efficacy and potential mechanism of action of our dual G9a histone-methyltransferase and DNA-methyltransferase 1 (DNMT1) inhibitor in human HCC cells and their crosstalk with fibrogenic cells. The expression of G9a and DNMT1, along with that of their molecular adaptor ubiquitin-like with PHD and RING finger domains-1 (UHRF1), was measured in human HCCs (n = 268), peritumoral tissues (n = 154), and HCC cell lines (n = 32). We evaluated the effect of individual and combined inhibition of G9a and DNMT1 on HCC cell growth by pharmacological and genetic approaches. The activity of our lead compound, CM-272, was examined in HCC cells under normoxia and hypoxia, human hepatic stellate cells and LX2 cells, and xenograft tumors formed by HCC or combined HCC+LX2 cells. We found a significant and correlative overexpression of G9a, DNMT1, and UHRF1 in HCCs in association with poor prognosis. Independent G9a and DNMT1 pharmacological targeting synergistically inhibited HCC cell growth. CM-272 potently reduced HCC and LX2 cells proliferation and quelled tumor growth, particularly in HCC+LX2 xenografts. Mechanistically, CM-272 inhibited the metabolic adaptation of HCC cells to hypoxia and induced a differentiated phenotype in HCC and fibrogenic cells. The expression of the metabolic tumor suppressor gene fructose-1,6-bisphosphatase (FBP1), epigenetically repressed in HCC, was restored by CM-272. Conclusion: Combined targeting of G9a/DNMT1 with compounds such as CM-272 is a promising strategy for HCC treatment. Our findings also underscore the potential of differentiation therapy in HCC.

Splicing alterations contributing to cancer hallmarks in the liver: central role of dedifferentiation and genome instability

Hepatocellular carcinoma (HCC) is a major cause of cancer-related death worldwide. HCCs are molecularly heterogeneous tumors, and this complexity is to a great extent responsible for their poor response to conventional and targeted therapies. In this review we summarize recent evidence indicating that imbalanced expression of mRNA splicing factors can be a relevant source for this heterogeneity. We also discuss how these alterations may play a driver role in hepatocarcinogenesis by impinging on the general hallmarks of cancer. Considering the natural history of HCC, we focused on two pathogenic features that are characteristic of liver tumors: chromosomal instability and phenotypic de-differentiation. We highlight mechanisms connecting splicing derangement with these two processes and the enabling capacities acquired by liver cells along their neoplastic transformation. A thorough understanding of the alterations in the splicing machinery may also help to identify new HCC biomarkers and to design novel therapeutic strategies.

LKB1: Controlling Quiescence and Genomic Integrity at Home

The pleiotropic liver kinase B1 (LKB1) controls metabolism, cell polarity, and proliferation in an apparently cell- and context-specific manner. A recent study in Cell Reports has demonstrated that LKB1 is essential to maintain the characteristic quiescence of the liver and to secure genomic integrity during liver regeneration independently of AMPK.

MiR-873-5p acts as an epigenetic regulator in early stages of liver fibrosis and cirrhosis

Glycine N-methyltransferase (GNMT) is the most abundant methyltransferase in the liver and a master regulator of the transmethylation flux. GNMT downregulation leads to loss of liver function progressing to fibrosis, cirrhosis, and hepatocellular carcinoma. Moreover, GNMT deficiency aggravates cholestasis-induced fibrogenesis. To date, little is known about the mechanisms underlying downregulation of GNMT levels in hepatic fibrosis and cirrhosis. On this basis, microRNAs are epigenetic regulatory elements that play important roles in liver pathology. In this work, we aim to study the regulation of GNMT by microRNAs during liver fibrosis and cirrhosis. Luciferase assay on the 3ʹUTR-Gnmt was used to confirm in silico analysis showing that GNMT is potentially targeted by the microRNA miR-873-5p. Correlation between GNMT and miR-873-5p in human cholestasis and cirrhosis together with miR-873-5p inhibition in vivo in different mouse models of liver cholestasis and fibrosis [bile duct ligation and Mdr2 (Abcb4)^-/- mouse] were then assessed. The analysis of liver tissue from cirrhotic and cholestatic patients, as well as from the animal models, showed that miR-873-5p inversely correlated with the expression of GNMT. Importantly, high circulating miR-873-5p was also detected in cholestastic and cirrhotic patients. Preclinical studies with anti-miR-873-5p treatment in bile duct ligation and Mdr2^-/- mice recovered GNMT levels in association with ameliorated inflammation and fibrosis mainly by counteracting hepatocyte apoptosis and cholangiocyte proliferation. In conclusion, miR-873-5p emerges as a novel marker for liver fibrosis, cholestasis, and cirrhosis and therapeutic approaches based on anti-miR-873-5p may be effective treatments for liver fibrosis and cholestatic liver disease.

Fibroblast growth factors 19 and 21 in acute liver damage

Currently there are very few pharmacological options available to treat acute liver injury. Because its natural exposure to noxious stimuli the liver has developed a strong endogenous hepatoprotective capacity. Indeed, experimental evidence exposed a variety of endogenous hepatic and systemic responses naturally activated to protect the hepatic parenchyma and to foster liver regeneration, therefore preserving individual's survival. The fibroblast growth factor (FGF) family encompasses a range of polypeptides with important effects on cellular differentiation, growth survival and metabolic regulation in adult organisms. Among these FGFs, FGF19 and FGF21 are endocrine hormones that profoundly influence systemic metabolism but also exert important hepatoprotective activities. In this review, we revisit the biology of these factors and highlight their potential application for the clinical management of acute liver injury.

Engineered fibroblast growth factor 19 protects from acetaminophen-induced liver injury and stimulates aged liver regeneration in mice

The liver displays a remarkable regenerative capacity triggered upon tissue injury or resection. However, liver regeneration can be overwhelmed by excessive parenchymal destruction or diminished by pre-existing conditions hampering repair. Fibroblast growth factor 19 (FGF19, rodent FGF15) is an enterokine that regulates liver bile acid and lipid metabolism, and stimulates hepatocellular protein synthesis and proliferation. FGF19/15 is also important for liver regeneration after partial hepatectomy (PH). Therefore recombinant FGF19 would be an ideal molecule to stimulate liver regeneration, but its applicability may be curtailed by its short half-life. We developed a chimaeric molecule termed Fibapo in which FGF19 is covalently coupled to apolipoprotein A-I. Fibapo retains FGF19 biological activities but has significantly increased half-life and hepatotropism. Here we evaluated the pro-regenerative activity of Fibapo in two clinically relevant models where liver regeneration may be impaired: acetaminophen (APAP) poisoning, and PH in aged mice. The only approved therapy for APAP intoxication is N-acetylcysteine (NAC) and no drugs are available to stimulate liver regeneration. We demonstrate that Fibapo reduced liver injury and boosted regeneration in APAP-intoxicated mice. Fibapo improved survival of APAP-poisoned mice when given at later time points, when NAC is ineffective. Mechanistically, Fibapo accelerated recovery of hepatic glutathione levels, potentiated cell growth-related pathways and increased functional liver mass. When Fibapo was administered to old mice prior to PH, liver regeneration was markedly increased. The exacerbated injury developing in these mice upon PH was attenuated, and the hepatic biosynthetic capacity was enhanced. Fibapo reversed metabolic and molecular alterations that impede regeneration in aged livers. It reduced liver steatosis and downregulated p21 and hepatocyte nuclear factor 4 α (Hnf4α) levels, whereas it stimulated Foxm1b gene expression. Together our findings indicate that FGF19 variants retaining the metabolic and growth-promoting effects of this enterokine may be valuable for the stimulation of liver regeneration.

Fibroblast growth factor 15/19 (FGF15/19) protects from diet-induced hepatic steatosis: development of an FGF19-based chimeric molecule to promote fatty liver regeneration

OBJECTIVE

Fibroblast growth factor 15/19 (FGF15/19), an enterokine that regulates synthesis of hepatic bile acids (BA), has been proposed to influence fat metabolism. Without FGF15/19, mouse liver regeneration after partial hepatectomy (PH) is severely impaired. We studied the role of FGF15/19 in response to a high fat diet (HFD) and its regulation by saturated fatty acids. We developed a fusion molecule encompassing FGF19 and apolipoprotein A-I, termed Fibapo, and evaluated its pharmacological properties in fatty liver regeneration.

DESIGN

Fgf15^-/- mice were fed a HFD. Liver fat and the expression of fat metabolism and endoplasmic reticulum (ER) stress-related genes were measured. Influence of palmitic acid (PA) on FGF15/19 expression was determined in mice and in human liver cell lines. In vivo half-life and biological activity of Fibapo and FGF19 were compared. Hepatoprotective and proregenerative activities of Fibapo were evaluated in obese db/db mice undergoing PH.

RESULTS

Hepatosteatosis and ER stress were exacerbated in HFD-fed Fgf15^-/- mice. Hepatic expression of Pparγ2 was elevated in Fgf15^-/- mice, being reversed by FGF19 treatment. PA induced FGF15/19 expression in mouse ileum and human liver cells, and FGF19 protected from PA-mediated ER stress and cytotoxicity. Fibapo reduced liver BA and lipid accumulation, inhibited ER stress and showed enhanced half-life. Fibapo provided increased db/db mice survival and improved regeneration upon PH.

CONCLUSIONS

FGF15/19 is essential for hepatic metabolic adaptation to dietary fat being a physiological regulator of Pparγ2 expression. Perioperative administration of Fibapo improves fatty liver regeneration.

Bile acids, FGF15/19 and liver regeneration: From mechanisms to clinical applications

The liver has an extraordinary regenerative capacity rapidly triggered upon injury or resection. This response is intrinsically adjusted in its initiation and termination, a property termed the "hepatostat". Several molecules have been involved in liver regeneration, and among them bile acids may play a central role. Intrahepatic levels of bile acids rapidly increase after resection. Through the activation of farnesoid X receptor (FXR), bile acids regulate their hepatic metabolism and also promote hepatocellular proliferation. FXR is also expressed in enterocytes, where bile acids stimulate the expression of fibroblast growth factor 15/19 (FGF15/19), which is released to the portal blood. Through the activation of FGFR4 on hepatocytes FGF15/19 regulates bile acids synthesis and finely tunes liver regeneration as part of the "hepatostat". Here we review the experimental evidences supporting the relevance of the FXR-FGF15/19-FGFR4 axis in liver regeneration and discuss potential therapeutic applications of FGF15/19 in the prevention of liver failure. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Fibroblast Growth Factor 15/19 in Hepatocarcinogenesis

BACKGROUND

Advanced hepatocellular carcinoma (HCC) is a neoplastic disease with a very bad prognosis and increasing worldwide incidence. HCCs are resistant to conventional chemotherapy and the multikinase inhibitor sorafenib is the only agent that has shown some clinical efficacy. It is therefore important to identify key molecular mechanisms driving hepatocarcinogenesis for the development of more efficacious therapies. However, HCCs are heterogeneous tumors and different molecular subclasses have been characterized. This heterogeneity may underlie the poor performance of most of the targeted therapies so far tested in HCC patients. The fibroblast growth factor 15/19 (FGF15/19), FGF receptor 4 (FGFR4) and beta-Klotho (KLB) correceptor signaling system, a key regulator of bile acids (BA) synthesis and intermediary metabolism, is emerging as an important player in hepatocarcinogenesis. Key Messages: Aberrant signaling through the FGF15/19-FGFR4 pathway participates in the neoplastic behavior of HCC cells, promotes HCC development in mice and its overexpression has been characterized in a subset of HCC tumors from patients with poorer prognosis. Pharmacological interference with FGF15/19-FGFR4 signaling inhibits experimental hepatocarcinogenesis, and specific FGFR4 inhibitors are currently being tested in selected HCC patients with tumoral FGF19-FGFR4/KLB expression.

CONCLUSIONS

Interference with FGF19-FGFR4 signaling represents a novel strategy in HCC therapy. Selection of candidate patients based on tumoral FGF19-FGFR4/KLB levels as biomarkers may result in increased efficacy of FGFR4-targeted drugs. Nevertheless, attention should be paid to the potential on target toxic effects of FGFR4 inhibitors due to the key role of this signaling system in BA metabolism.

ACOX2 deficiency: An inborn error of bile acid synthesis identified in an adolescent with persistent hypertransaminasemia

BACKGROUND & AIMS

Acyl-CoA oxidase (ACOX2) is involved in the shortening of C27 cholesterol derivatives to generate C24 bile acids. Inborn errors affecting the rest of peroxisomal enzymes involved in bile acid biosynthesis have been described. Here we aimed at investigating the case of an adolescent boy with persistent hypertransaminasemia of unknown origin and suspected dysfunction in bile acid metabolism.

METHODS

Serum and urine samples were taken from the patient, his sister and parents and underwent HPLC-MS/MS and HPLC-TOF analyses. Coding exons in genes of interest were amplified by high-fidelity PCR and sequenced. Wild-type or mutated (mutACOX2) variants were overexpressed in human hepatoblastoma HepG2 cells to determine ACOX2 enzymatic activity, expression and subcellular location.

RESULTS

The patient's serum and urine showed negligible amounts of C24 bile acids, but augmented levels of C27 intermediates, mainly tauroconjugated trihydroxycholestanoic acid (THCA). Genetic analysis of enzymes potentially involved revealed a homozygous missense mutation (c.673C>T; R225W) in ACOX2. His only sister was also homozygous for this mutation and exhibited similar alterations in bile acid profiles. Both parents were heterozygous and presented normal C24 and C27 bile acid levels. Immunofluorescence studies showed similar protein size and peroxisomal localization for both normal and mutated variants. THCA biotransformation into cholic acid was enhanced in cells overexpressing ACOX2, but not in those overexpressing mutACOX2. Both cell types showed similar sensitivity to oxidative stress caused by C24 bile acids. In contrast, THCA-induced oxidative stress and cell death were reduced by overexpressing ACOX2, but not mutACOX2.

CONCLUSION

ACOX2 deficiency, a condition characterized by accumulation of toxic C27 bile acid intermediates, is a novel cause of isolated persistent hypertransaminasemia.

LAY SUMMARY

Elevation of serum transaminases is a biochemical sign of liver damage due to multiplicity of causes (viruses, toxins, autoimmunity, metabolic disorders). In rare cases the origin of this alteration remains unknown. We have identified by the first time in a young patient and his only sister a familiar genetic defect of an enzyme called ACOX2, which participates in the transformation of cholesterol into bile acids as a cause of increased serum transaminases in the absence of any other symptomatology. This treatable condition should be considered in the diagnosis of those patients where the cause of elevated transaminases remains obscure.

Post-translational deregulation of YAP1 is genetically controlled in rat liver cancer and determines the fate and stem-like behavior of the human disease

Previous studies showed that YAP1 is over-expressed in hepatocellular carcinoma (HCC). Here we observed higher expression of Yap1/Ctgf axis in dysplastic nodules and HCC chemically-induced in F344 rats, genetically susceptible to hepatocarcinogenesis, than in lesions induced in resistant BN rats. In BN rats, highest increase in Yap1-tyr357, p73 phosphorylation and Caspase 3 cleavage occurred. In human HCCs with poorer prognosis (< 3 years survival after partial liver resection, HCCP), levels of YAP1, CTGF, 14-3-3, and TEAD proteins, and YAP1-14-3-3 and YAP1-TEAD complexes were higher than in HCCs with better outcome (> 3 years survival; HCCB). In the latter, higher levels of phosphorylated YAP1-ser127, YAP1-tyr357 and p73, YAP1 ubiquitination, and Caspase 3 cleavage occurred. Expression of stemness markers NANOG, OCT-3/4, and CD133 were highest in HCCP and correlated with YAP1 and YAP1-TEAD levels. In HepG2, Huh7, and Hep3B cells, forced YAP1 over-expression led to stem cell markers expression and increased cell viability, whereas inhibition of YAP1 expression by specific siRNA, or transfection of mutant YAP1 which does not bind to TEAD, induced opposite alterations. These changes were associated, in Huh7 cells transfected with YAP1 or YAP1 siRNA, with stimulation or inhibition of cell migration and invasivity, respectively. Furthermore, transcriptome analysis showed that YAP1 transfection in Huh7 cells induces over-expression of genes involved in tumor stemness. In conclusion, Yap1 post-translational modifications favoring its ubiquitination and apoptosis characterize HCC with better prognosis, whereas conditions favoring the formation of YAP1-TEAD complexes are associated with aggressiveness and acquisition of stemness features by HCC cells.

Matrix metalloproteinase 10 contributes to hepatocarcinogenesis in a novel crosstalk with the stromal derived factor 1/C-X-C chemokine receptor 4 axis

Matrix metalloproteinases (MMPs) participate in tissue repair after acute injury, but also participate in cancer by promoting a protumorigenic microenvironment. Previously, we reported on a key role for MMP10 in mouse liver regeneration. Herein, we investigated MMP10 expression and function in human hepatocellular carcinoma (HCC) and diethylnitrosamine (DEN)-induced mouse hepatocarcinogenesis. MMP10 was induced in human and murine HCC tissues and cells. MMP10-deficient mice showed less HCC incidence, smaller histological lesions, reduced tumor vascularization, and less lung metastases. Importantly, expression of the protumorigenic, C-X-C chemokine receptor-4 (CXCR4), was reduced in DEN-induced MMP10-deficient mice livers. Human HCC cells stably expressing MMP10 had increased CXCR4 expression and migratory capacity. Pharmacological inhibition of CXCR4 significantly reduced MMP10-stimulated HCC cell migration. Furthermore, MMP10 expression in HCC cells was induced by hypoxia and the CXCR4 ligand, stromal-derived factor-1 (SDF1), through the extracellular signal-regulated kinase 1/2 pathway, involving an activator protein 1 site in MMP10 gene promoter.

CONCLUSION

MMP10 contributes to HCC development, participating in tumor angiogenesis, growth, and dissemination. We identified a new reciprocal crosstalk between MMP10 and the CXCR4/SDF1 axis contributing to HCC progression and metastasis. To our knowledge, this is the first report addressing the role of a MMP in hepatocarcinogenesis in the corresponding genetic mouse model.

Radioembolization of hepatocellular carcinoma activates liver regeneration, induces inflammation and endothelial stress and activates coagulation

BACKGROUND & AIMS

Radioembolization may rarely induce liver disease resulting in a syndrome that is similar to veno-occlusive disease complicating bone marrow transplantation where inflammation, endothelial cell activation and thrombosis are likely involved. We hypothesized that similar mechanisms could be implicated in radioembolization-induced liver disease (REILD). Moreover, lobar radioembolization may induce hypertrophy of the non-treated hemiliver most probably by inducing liver regeneration.

METHODS

In patients with hepatocellular carcinoma, we prospectively studied serum levels of markers of liver regeneration, oxidative stress, pro-inflammatory pathways, endothelial activation and coagulation parameters over 2 months after radioembolization.

RESULTS

Although REILD did not occur among 14 treated patients, a decrease in effective liver blood flow was observed. Radioembolization was followed by a persistent increase in pro-inflammatory (interleukin 6 and 8) and oxidative stress (malondyaldehide) markers, an induction of endothelial injury markers (vW factor and PAI-1) and an activation of the coagulation cascade (factor VIII, PAI-1, D-Dimer) as well as a significant increase in factors related to liver regeneration (FGF-19 and HGF).

CONCLUSION

Radioembolization activates liver regeneration, produces oxidative stress, activates inflammatory cytokines and induces endothelial injury with partial activation of the coagulation cascade. These findings may have implications in the pathogenesis, prevention and therapy of REILD and in the development of new therapies to enhance hypertrophy with a surgical perspective.