Akt-mediated foxo1 inhibition is required for liver regeneration

Evidence for common mechanisms of pathology between SHANK3 and other genes of Phelan-McDermid syndrome

Chromosome 22q13.3 deletion (Phelan-McDermid) syndrome (PMS, OMIM 606232) is a rare genetic condition that impacts neurodevelopment. PMS most commonly results from heterozygous contiguous gene deletions that include the SHANK3 gene or likely pathogenic variants of SHANK3 (PMS-SHANK3 related). Rarely, chromosomal rearrangements that spare SHANK3 share the same general phenotype (PMS-SHANK3 unrelated). Very recent human and model system studies of genes that likely contribute to the PMS phenotype point to overlap in gene functions associated with neurodevelopment, synaptic formation, stress/inflammation and regulation of gene expression. In this review of recent findings, we describe the functional overlaps between SHANK3 and six partner genes of 22q13.3 (PLXNB2, BRD1, CELSR1, PHF21B, SULT4A1, and TCF20), which suggest a model that explains the commonality between PMS-SHANK3 related and PMS-SHANK3 unrelated classes of PMS. These genes are likely not the only contributors to neurodevelopmental impairments in the region, but they are the best documented to date. The review provides evidence for the overlapping and likely synergistic contributions of these genes to the PMS phenotype.

Identification of Dhx15 as a Major Regulator of Liver Development, Regeneration, and Tumor Growth in Zebrafish and Mice

RNA helicase DHX15 plays a significant role in vasculature development and lung metastasis in vertebrates. In addition, several studies have demonstrated the overexpression of DHX15 in the context of hepatocellular carcinoma. Therefore, we hypothesized that this helicase may play a significant role in liver regeneration, physiology, and pathology. Dhx15 gene deficiency was generated by CRISPR/Cas9 in zebrafish and by TALEN-RNA in mice. AUM Antisense-Oligonucleotides were used to silence Dhx15 in wild-type mice. The hepatocellular carcinoma tumor induction model was generated by subcutaneous injection of Hepa 1-6 cells. Homozygous Dhx15 gene deficiency was lethal in zebrafish and mouse embryos. Dhx15 gene deficiency impaired liver organogenesis in zebrafish embryos and liver regeneration after partial hepatectomy in mice. Also, heterozygous mice presented decreased number and size of liver metastasis after Hepa 1-6 cells injection compared to wild-type mice. Dhx15 gene silencing with AUM Antisense-Oligonucleotides in wild-type mice resulted in 80% reduced expression in the liver and a significant reduction in other major organs. In addition, Dhx15 gene silencing significantly hindered primary tumor growth in the hepatocellular carcinoma experimental model. Regarding the potential use of DHX15 as a diagnostic marker for liver disease, patients with hepatocellular carcinoma showed increased levels of DHX15 in blood samples compared with subjects without hepatic affectation. In conclusion, Dhx15 is a key regulator of liver physiology and organogenesis, is increased in the blood of cirrhotic and hepatocellular carcinoma patients, and plays a key role in controlling hepatocellular carcinoma tumor growth and expansion in experimental models.

Lipid droplet deposition in the regenerating liver: A promoter, inhibitor, or bystander?

Liver regeneration (LR) is a complex process involving intricate networks of cellular connections, cytokines, and growth factors. During the early stages of LR, hepatocytes accumulate lipids, primarily triacylglycerol, and cholesterol esters, in the lipid droplets. Although it is widely accepted that this phenomenon contributes to LR, the impact of lipid droplet deposition on LR remains a matter of debate. Some studies have suggested that lipid droplet deposition has no effect or may even be detrimental to LR. This review article focuses on transient regeneration-associated steatosis and its relationship with the liver regenerative response.

MDIG-mediated H3K9me3 demethylation upregulates Myc by activating OTX2 and facilitates liver regeneration

The mineral dust-induced gene (MDIG) comprises a conserved JmjC domain and has the ability to demethylate histone H3 lysine 9 trimethylation (H3K9me3). Previous studies have indicated the significance of MDIG in promoting cell proliferation by modulating cell-cycle transition. However, its involvement in liver regeneration has not been extensively investigated. In this study, we generated mice with liver-specific knockout of MDIG and applied partial hepatectomy or carbon tetrachloride mouse models to investigate the biological contribution of MDIG in liver regeneration. The MDIG levels showed initial upregulation followed by downregulation as the recovery progressed. Genetic MDIG deficiency resulted in dramatically impaired liver regeneration and delayed cell cycle progression. However, the MDIG-deleted liver was eventually restored over a long latency. RNA-seq analysis revealed Myc as a crucial effector downstream of MDIG. However, ATAC-seq identified the reduced chromatin accessibility of OTX2 locus in MDIG-ablated regenerating liver, with unaltered chromatin accessibility of Myc locus. Mechanistically, MDIG altered chromatin accessibility to allow transcription by demethylating H3K9me3 at the OTX2 promoter region. As a consequence, the transcription factor OTX2 binding at the Myc promoter region was decreased in MDIG-deficient hepatocytes, which in turn repressed Myc expression. Reciprocally, Myc enhanced MDIG expression by regulating MDIG promoter activity, forming a positive feedback loop to sustain hepatocyte proliferation. Altogether, our results prove the essential role of MDIG in facilitating liver regeneration via regulating histone methylation to alter chromatin accessibility and provide valuable insights into the epi-transcriptomic regulation during liver regeneration.

Hepatocyte FoxO1 Deficiency Protects From Liver Fibrosis via Reducing Inflammation and TGF-β1-mediated HSC Activation

BACKGROUND & AIMS

The O-class of the forkhead transcription factor FoxO1 is a crucial factor mediating insulin→PI3K→Akt signaling and governs diverse cellular processes. However, the role of hepatocyte FoxO1 in liver fibrosis has not been well-established. In his study, we investigated the role of hepatocyte FoxO1 in liver fibrosis and uncovered the underlying mechanisms.

METHODS

Liver fibrosis was established by carbon tetrachloride (CCL4) administration and compared between liver-specific deletion of FoxO1 deletion (F1KO) and control (CNTR) mice. Using genetic and bioinformatic strategies in vitro and in vivo, the role of hepatic FoxO1 in liver fibrosis and associated mechanisms was established.

RESULTS

Increased FoxO1 expression and FoxO1 signaling activation were observed in CCL4-induced fibrosis. Hepatic FoxO1 deletion largely attenuated CCL4-induced liver injury and fibrosis compared with CNTR mice. F1KO mice showed ameliorated CCL4-induced hepatic inflammation and decreased TGF-β1 mRNA and protein levels compared with those of CNTR mice. In primary hepatocytes, FoxO1 deficiency reduced TGF-β1 expression and secretion. Conditioned medium (CM) collected from wild-type hepatocytes treated with CCL4 activated human HSC cell line (LX-2); such effect was attenuated by FoxO1 deletion in primary hepatocytes or neutralization of TGF-β1 in the CM using TGF-β1 antibody. Hepatic FoxO1 overexpression in CNTR mice promoted CCL4-induced HSC activation; such effect was blocked in L-TGF-β1KO mice.

CONCLUSIONS

Hepatic FoxO1 mediates CCL4-inducled liver fibrosis via upregulating hepatocyte TGF-β1 expression, stimulating hepatic inflammation and TGF-β1-mediated HSC activation. Hepatic FoxO1 may be a therapeutic target for prevention and treatment of liver fibrosis.

Tcf20 deficiency is associated with increased liver fibrogenesis and alterations in mitochondrial metabolism in mice and humans

BACKGROUND & AIMS

Transcription co-activator factor 20 (TCF20) is a regulator of transcription factors involved in extracellular matrix remodelling. In addition, TCF20 genomic variants in humans have been associated with impaired intellectual disability. Therefore, we hypothesized that TCF20 has several functions beyond those described in neurogenesis, including the regulation of fibrogenesis.

METHODS

Tcf20 knock-out (Tcf20-/- ) and Tcf20 heterozygous mice were generated by homologous recombination. TCF20 gene genotyping and expression was assessed in patients with pathogenic variants in the TCF20 gene. Neural development was investigated by immufluorescense. Mitochondrial metabolic activity was evaluated with the Seahorse analyser. The proteome analysis was carried out by gas chromatography mass-spectrometry.

RESULTS

Characterization of Tcf20-/- newborn mice showed impaired neural development and death after birth. In contrast, heterozygous mice were viable but showed higher CCl4 -induced liver fibrosis and a differential expression of genes involved in extracellular matrix homeostasis compared to wild-type mice, along with abnormal behavioural patterns compatible with autism-like phenotypes. Tcf20-/- embryonic livers and mouse embryonic fibroblast (MEF) cells revealed differential expression of structural proteins involved in the mitochondrial oxidative phosphorylation chain, increased rates of mitochondrial metabolic activity and alterations in metabolites of the citric acid cycle. These results parallel to those found in patients with TCF20 pathogenic variants, including alterations of the fibrosis scores (ELF and APRI) and the elevation of succinate concentration in plasma.

CONCLUSIONS

We demonstrated a new role of Tcf20 in fibrogenesis and mitochondria metabolism in mice and showed the association of TCF20 deficiency with fibrosis and metabolic biomarkers in humans.

The Characteristic Function of Blood-Derived Exosomes and Exosomal circRNAs Isolated from Dairy Cattle during the Dry Period and Mid-Lactation

Exosomes are key mediators of intercellular communication. They are secreted by most cells and contain a cargo of protein-coding genes, long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), which modulate recipient cell behavior. Herein, we collected blood samples from Holstein cows at days 30 (mid-lactation) and 250 (dry period) of pregnancy. Prolactin, follicle-stimulating hormone, luteinizing hormone, estrogen, and progesterone levels showed an obvious increase during D250. We then extracted exosomes from bovine blood samples and found that their sizes generally ranged from 100 to 200 nm. Further, Western blotting validated that they contained CD9, CD63, and TSG101, but not calnexin. Blood-derived exosomes significantly promoted the proliferation of mammary epithelial cells, particularly from D250. This change was accompanied by increased expression levels of proliferation marker proteins PCNA, cyclin D, and cyclin E, as detected by EdU assay, cell counting kit-8 assay, and flow cytometric cell cycle analysis. Moreover, we treated mammary epithelial cells with blood-derived exosomes that were isolated from the D30 and D250 periods. And RNA-seq of two groups of cells led to the identification of 839 differentially expressed genes that were significantly enriched in KEGG signaling pathways associated with apoptosis, cell cycle and proliferation. In bovine blood-derived exosomes, we found 12,747 protein-coding genes, 31,181 lncRNAs, 9374 transcripts of uncertain coding potential (TUCP) candidates, and 460 circRNAs, and 32 protein-coding genes, 806 lncRNAs, 515 TUCP candidates, and 45 circRNAs that were differentially expressed between the D30 and D250 groups. We selected six highly expressed and four differentially expressed circRNAs to verify their head-to-tail splicing using PCR and Sanger sequencing. To summarize, our findings improve our understanding of the key roles of blood-derived exosomes and the characterization of exosomal circRNAs in mammary gland development.

Mitochondria-derived H2O2 triggers liver regeneration via FoxO3a signaling pathway after partial hepatectomy in mice

Reactive oxygen species (ROS) can induce oxidative injury and are generally regarded as toxic byproducts, although they are increasingly recognized for their signaling functions. Increased ROS often accompanies liver regeneration (LR) after liver injuries, however, their role in LR and the underlying mechanism remains unclear. Here, by employing a mouse LR model of partial hepatectomy (PHx), we found that PHx induced rapid increases of mitochondrial hydrogen peroxide (H2O2) and intracellular H2O2 at an early stage, using a mitochondria-specific probe. Scavenging mitochondrial H2O2 in mice with liver-specific overexpression of mitochondria-targeted catalase (mCAT) decreased intracellular H2O2 and compromised LR, while NADPH oxidases (NOXs) inhibition did not affect intracellular H2O2 or LR, indicating that mitochondria-derived H2O2 played an essential role in LR after PHx. Furthermore, pharmacological activation of FoxO3a impaired the H2O2-triggered LR, while liver-specific knockdown of FoxO3a by CRISPR-Cas9 technology almost abolished the inhibition of LR by overexpression of mCAT, demonstrating that FoxO3a signaling pathway mediated mitochondria-derived H2O2 triggered LR after PHx. Our findings uncover the beneficial roles of mitochondrial H2O2 and the redox-regulated underlying mechanisms during LR, which shed light on potential therapeutic interventions for LR-related liver injury. Importantly, these findings also indicate that improper antioxidative intervention might impair LR and delay the recovery of LR-related diseases in clinics.

Acute liver steatosis translationally controls the epigenetic regulator MIER1 to promote liver regeneration in a study with male mice

The early phase lipid accumulation is essential for liver regeneration. However, whether this acute lipid accumulation can serve as signals to direct liver regeneration rather than simply providing building blocks for cell proliferation remains unclear. Through in vivo CRISPR screening, we identify MIER1 (mesoderm induction early response 1) as a key epigenetic regulator that bridges the acute lipid accumulation and cell cycle gene expression during liver regeneration in male animals. Physiologically, liver acute lipid accumulation induces the phosphorylation of EIF2S1(eukaryotic translation initiation factor 2), which consequently attenuated Mier1 translation. MIER1 downregulation in turn promotes cell cycle gene expression and regeneration through chromatin remodeling. Importantly, the lipids-EIF2S1-MIER1 pathway is impaired in animals with chronic liver steatosis; whereas MIER1 depletion significantly improves regeneration in these animals. Taken together, our studies identify an epigenetic mechanism by which the early phase lipid redistribution from adipose tissue to liver during regeneration impacts hepatocyte proliferation, and suggest a potential strategy to boost liver regeneration.

Morin ameliorates methotrexate-induced hepatotoxicity via targeting Nrf2/HO-1 and Bax/Bcl2/Caspase-3 signaling pathways

BACKGROUND

Organ toxicity limits the therapeutic efficacy of methotrexate (MTX), an anti-metabolite therapeutic that is frequently used as an anti-cancer and immunosuppressive medicine. Hepatocellular toxicity is among the most severe side effects of long-term MTX use. The present study unveils new confirmations as regards the remedial effects of morin on MTX-induced hepatocellular injury through regulation of oxidative stress, apoptosis and MAPK signaling.

METHODS AND RESULTS

Rats were subjected to oral treatment of morin (50 and 100 mg/kg body weight) for 10 days. Hepatotoxicity was induced by single intraperitoneal injection of MTX (20 mg/kg body weight) on the 5th day. MTX related hepatic injury was associated with increased MDA while decreased GSH levels, the activities of endogen antioxidants (glutathione peroxidase, superoxide dismutase and catalase) and mRNA levels of HO-1 and Nrf2 in the hepatic tissue. MTX treatment also resulted in apoptosis in the liver tissue via increasing mRNA transcript levels of Bax, caspase-3, Apaf-1 and downregulation of Bcl-2. Conversely, treatment with morin at different doses (50 and 100 mg/kg) considerably mitigated MTX-induced oxidative stress and apoptosis in the liver tissue. Morin also mitigated MTX-induced increases of ALT, ALP and AST levels, downregulated mRNA expressions of matrix metalloproteinases (MMP-2 and MMP-9), MAPK14 and MAPK15, JNK, Akt2 and FOXO1 genes.

CONCLUSION

According to the findings of this study, morin may be a potential way to shield the liver tissue from the oxidative damage and apoptosis.

Exosomes derived from human adipose mesenchymal stem cells ameliorate hepatic fibrosis by inhibiting PI3K/Akt/mTOR pathway and remodeling choline metabolism

Liver fibrosis is a chronic liver disease with the presence of progressive wound healing response caused by liver injury. Currently, there are no approved therapies for liver fibrosis. Exosomes derived from human adipose mesenchymal stem cells (hADMSCs-Exo) have displayed a prominent therapeutic effect on liver diseases. However, few studies have evaluated therapeutic effect of hADMSCs-Exo in liver fibrosis and cirrhosis, and its precise mechanisms of action remain unclear. Herein, we investigated anti-fibrotic efficacy of hADMSCs-Exo in vitro and in vivo, and identified important metabolic changes and the detailed mechanism through transcriptomic and metabolomic profiling. We found hADMSCs-Exo could inhibit the proliferation of activated hepatic stellate cells through aggravating apoptosis and arresting G1 phase, effectively inhibiting the expression of profibrogenic proteins and epithelial-to-mesenchymal transition (EMT) in vitro. Moreover, it could significantly block collagen deposition and EMT process, improve liver function and reduce liver inflammation in liver cirrhosis mice model. The omics analysis revealed that the key mechanism of hADMSCs-Exo anti-hepatic fibrosis was the inhibition of PI3K/AKT/mTOR signaling pathway and affecting the changes of metabolites in lipid metabolism, and mainly regulating choline metabolism. CHPT1 activated by hADMSCs-Exo facilitated formation and maintenance of vesicular membranes. Thus, our study indicates that hADMSCs-Exo can attenuate hepatic stellate cell activation and suppress the progression of liver fibrosis, which holds the significant potential of hADMSCs-Exo for use as extracellular nanovesicles-based therapeutics in the treatment of liver fibrosis and possibly other intractable chronic liver diseases.

Scutellaria baicalensis in the Treatment of Hepatocellular Carcinoma: Network Pharmacology Analysis and Experimental Validation

Objective

The aim of the study was to use a network pharmacological method and experimental validation to examine the mechanism of Scutellaria baicalensis (SB) against hepatocellular carcinoma (HCC).

Methods

The traditional Chinese medicine systems pharmacology database and analysis platform (TCMSP) and GeneCards were used for screening of targets of SB for the treatment of HCC. Cytoscape (3.7.2) software was used to construct the "drug-compound-intersection target interaction" interaction network. The STING database was used to analyze the interactions of the previous intersecting targets. The results were visualized and processed by performing GO (Gene Ontology) enrichment analysis and KEGG (Kyoto Encyclopedia of Genes and Genomes) signaling pathway enrichment analysis at the target sites. The core targets were docked with the active components by AutoDockTools-1.5.6 software. We used cellular experiments to validate the bioinformatics predictions.

Results

A total of 92 chemical components and 3258 disease targets including 53 intersecting targets were discovered. The results showed that wogonin and baicalein, the main chemical components of SB, could inhibit the viability and proliferation of hepatocellular carcinoma cells, promote apoptosis through the mitochondrial apoptotic pathway, and effectively act on AKT1, RELA, and JUN targets.

Conclusion

SB has multiple components and targets in the treatment of HCC, providing possible potential targets for the treatment of HCC and providing a basis for further research.

mTORC2 Facilitates Liver Regeneration Through Sphingolipid-Induced PPAR-α-Fatty Acid Oxidation

BACKGROUND & AIMS

During liver regeneration after partial hepatectomy, the function and metabolic pathways governing transient lipid droplet accumulation in hepatocytes remain obscure. Mammalian target of rapamycin 2 (mTORC2) facilitates de novo synthesis of hepatic lipids. Under normal conditions and in tumorigenesis, decreased levels of triglyceride (TG) and fatty acids (FAs) are observed in the mTORC2-deficient liver. However, during liver regeneration, their levels increase in the absence of mTORC2.

METHODS

Rictor liver-specific knockout and control mice underwent partial hepatectomy, followed by measurement of TG and FA contents during liver regeneration. FA metabolism was evaluated by analyzing the expression of FA metabolism-related genes and proteins. Intraperitoneal injection of the peroxisome proliferator-activated receptor α (PPAR-α) agonist, p53 inhibitor, and protein kinase B (AKT) activator was performed to verify the regulatory pathways involved. Lipid mass spectrometry was performed to identify the potential PPAR-α activators.

RESULTS

The expression of FA metabolism-related genes and proteins suggested that FAs are mainly transported into hepatocytes during liver regeneration. The PPAR-α pathway is down-regulated significantly in the mTORC2-deficient liver, resulting in the accumulation of TGs. The PPAR-α agonist WY-14643 rescued deficient liver regeneration and survival in mTORC2-deficient mice. Furthermore, lipidomic analysis suggested that mTORC2 deficiency substantially reduced glucosylceramide (GluCer) content. GluCer activated PPAR-α. GluCer treatment in vivo restored the regenerative ability and survival rates in the mTORC2-deficient group.

CONCLUSIONS

Our data suggest that FAs are mainly transported into hepatocytes during liver regeneration, and their metabolism is facilitated by mTORC2 through the GluCer-PPAR-α pathway, thereby establishing a novel role for mTORC2 in lipid metabolism.

Distinctive molecular features of regenerative stem cells in the damaged male germline

Maintenance of male fertility requires spermatogonial stem cells (SSCs) that self-renew and generate differentiating germ cells for production of spermatozoa. Germline cells are sensitive to genotoxic drugs and patients receiving chemotherapy can become infertile. SSCs surviving treatment mediate germline recovery but pathways driving SSC regenerative responses remain poorly understood. Using models of chemotherapy-induced germline damage and recovery, here we identify unique molecular features of regenerative SSCs and characterise changes in composition of the undifferentiated spermatogonial pool during germline recovery by single-cell analysis. Increased mitotic activity of SSCs mediating regeneration is accompanied by alterations in growth factor signalling including PI3K/AKT and mTORC1 pathways. While sustained mTORC1 signalling is detrimental for SSC maintenance, transient mTORC1 activation is critical for the regenerative response. Concerted inhibition of growth factor signalling disrupts core features of the regenerative state and limits germline recovery. We also demonstrate that the FOXM1 transcription factor is a target of growth factor signalling in undifferentiated spermatogonia and provide evidence for a role in regeneration. Our data confirm dynamic changes in SSC functional properties following damage and support an essential role for microenvironmental growth factors in promoting a regenerative state.

Male germline regeneration after damage is dependent on spermatogonial stem cells (SSCs) but pathways mediating the regenerative response are unclear. Here the authors define roles for growth factor signalling and mTORC1 in SSC-driven regeneration.

Diverse MicroRNAs-mRNA networks regulate the priming phase of mouse liver regeneration and of direct hyperplasia

Objectives

Adult hepatocytes are quiescent cells that can be induced to proliferate in response to a reduction in liver mass (liver regeneration) or by agents endowed with mitogenic potency (primary hyperplasia). The latter condition is characterized by a more rapid entry of hepatocytes into the cell cycle, but the mechanisms responsible for the accelerated entry into the S phase are unknown.

Materials and methods

Next generation sequencing and Illumina microarray were used to profile microRNA and mRNA expression in CD‐1 mice livers 1, 3 and 6 h after 2/3 partial hepatectomy (PH) or a single dose of TCPOBOP, a ligand of the constitutive androstane receptor (CAR). Ingenuity pathway and DAVID analyses were performed to identify deregulated pathways. MultiMiR analysis was used to construct microRNA‐mRNA networks.

Results

Following PH or TCPOBOP we identified 810 and 527 genes, and 102 and 10 miRNAs, respectively, differentially expressed. Only 20 genes and 8 microRNAs were shared by the two conditions. Many miRNAs targeting negative regulators of cell cycle were downregulated early after PH, concomitantly with increased expression of their target genes. On the contrary, negative regulators were not modified after TCPOBOP, but Ccnd1 targeting miRNAs, such as miR‐106b‐5p, were downregulated.

Conclusions

While miRNAs targeting negative regulators of the cell cycle are downregulated after PH, TCPOBOP caused downregulation of miRNAs targeting genes required for cell cycle entry. The enhanced Ccnd1 expression may explain the more rapid entry into the S phase of mouse hepatocytes following TCPOBOP.

Genetic and Cellular Contributions to Liver Regeneration

The regenerative capabilities of the liver represent a paradigm for understanding tissue repair in solid organs. Regeneration after partial hepatectomy in rodent models is well understood, while regeneration in the context of clinically relevant chronic injuries is less studied. Given the growing incidence of fatty liver disease, cirrhosis, and liver cancer, interest in liver regeneration is increasing. Here, we will review the principles, genetics, and cell biology underlying liver regeneration, as well as new approaches being used to study heterogeneity in liver tissue maintenance and repair.

The loss of DHX15 impairs endothelial energy metabolism, lymphatic drainage and tumor metastasis in mice

DHX15 is a downstream substrate for Akt1, which is involved in key cellular processes affecting vascular biology. Here, we explored the vascular regulatory function of DHX15. Homozygous DHX15 gene deficiency was lethal in mouse and zebrafish embryos. DHX15-/- zebrafish also showed downregulation of VEGF-C and reduced formation of lymphatic structures during development. DHX15+/- mice depicted lower vascular density and impaired lymphatic function postnatally. RNAseq and proteome analysis of DHX15 silenced endothelial cells revealed differential expression of genes involved in the metabolism of ATP biosynthesis. The validation of these results demonstrated a lower activity of the Complex I in the mitochondrial membrane of endothelial cells, resulting in lower intracellular ATP production and lower oxygen consumption. After injection of syngeneic LLC1 tumor cells, DHX15+/- mice showed partially inhibited primary tumor growth and reduced lung metastasis. Our results revealed an important role of DHX15 in vascular physiology and pave a new way to explore its potential use as a therapeutical target for metastasis treatment.

The Aging Liver: Redox Biology and Liver Regeneration

Significance: During aging, excessive production of reactive species in the liver leads to redox imbalance with consequent oxidative damage and impaired organ homeostasis. Nevertheless, slight amounts of reactive species may modulate several transcription factors, acting as second messengers and regulating specific signaling pathways. These redox-dependent alterations may impact the age-associated decline in liver regeneration. Recent Advances: In the last few decades, relevant findings related to redox alterations in the aging liver were investigated. Consistently, recent research broadened understanding of redox modifications and signaling related to liver regeneration. Other than reporting the effect of oxidative stress, epigenetic and post-translational modifications, as well as modulation of specific redox-sensitive cellular signaling, were described. Among them, the present review focuses on Wnt/β-catenin, the nuclear factor (erythroid-derived 2)-like 2 (NRF2), members of the Forkhead box O (FoxO) family, and the p53 tumor suppressor. Critical Issues: Even though alteration in redox homeostasis occurs both in aging and in impaired liver regeneration, the associative mechanisms are not clearly defined. Of note, antioxidants are not effective in slowing hepatic senescence, and do not clearly improve liver repopulation after hepatectomy or transplant in humans. Future Directions: Further investigations are needed to define mutual redox-dependent molecular pathways involved both in aging and in the decline of liver regeneration. Preclinical studies aimed at the characterization of these pathways would define possible therapeutic targets for human trials. Antioxid. Redox Signal. 35, 832-847.

Metabolic hallmarks of liver regeneration

Despite the crucial role of cell metabolism in biological processes, particularly cell division, metabolic aspects of liver regeneration are not well defined. Better understanding of the metabolic activity governing division of liver cells will provide powerful insights into mechanisms of physiological and pathological liver regeneration. Recent studies have provided evidence that metabolic response to liver failure might be a proximal signal to initiate cell proliferation in liver regeneration. In this review, we highlight how lipids, carbohydrates, and proteins dynamically change and orchestrate liver regeneration. In addition, we discuss translational studies in which metabolic intervention has been used to treat chronic liver diseases (CLDs).

Role of the Mammalian Target of Rapamycin Pathway in Liver Cancer: From Molecular Genetics to Targeted Therapies

Primary liver cancers, including hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA), are highly lethal tumors, with high worldwide frequency and few effective treatment options. The mammalian target of rapamycin (mTOR) complex is a central regulator of cell growth and metabolism that integrates inputs from amino acids, nutrients, and extracellular signals. The mTOR protein is incorporated into two distinct complexes: mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Specifically, mTORC1 regulates protein synthesis, glucose and lipid metabolism, and autophagy, whereas mTORC2 promotes liver tumorigenesis through modulating the adenine/cytosine/guanine family of serine/threonine kinases, especially the protein kinase B proteins. In human HCC and iCCA samples, genomics analyses have revealed the frequent deregulation of the mTOR complexes. Both in vitro and in vivo studies have demonstrated the key role of mTORC1 and mTORC2 in liver-tumor development and progression. The first-generation mTOR inhibitors have been evaluated for effectiveness in liver-tumor treatment and have provided unsatisfactory results. Current research efforts are devoted to generating more efficacious mTOR inhibitors and identifying biomarkers for patient selection as well as for combination therapies. Here, we provide a comprehensive review of the mechanisms leading to a deregulated mTOR signaling cascade in liver cancers, the mechanisms whereby the mTOR pathway contributes to HCC and iCCA molecular pathogenesis, the therapeutic strategies, and the challenges to effectively inhibit mTOR in liver-cancer treatment. Conclusion: Deregulated mTOR signaling significantly contributes to HCC and iCCA molecular pathogenesis. mTOR inhibitors, presumably administered in association with other drugs, might be effective against subsets of human liver tumors.

Global Phosphoproteomic Analysis Reveals Significant Metabolic Reprogramming in the Termination of Liver Regeneration in Mice

Phosphorylation is crucial in regulating various biological processes. However, comprehensive phosphoproteomic profiling in the termination of liver regeneration (LR) is still missing. Here, we used Tandem Mass Tag (TMT) labeling coupled with phosphopeptide enrichment and two-dimensional (2D) liquid chromatography-mass spectrometry (LC-MS)/MS analysis to establish a global phosphoproteomic map in the liver of mice at day 5 after partial hepatectomy (PH). Altogether, 9731 phosphosites from 3443 proteins were identified and 7802 phosphosites from 2980 proteins were quantified. Motif analysis of the identified phosphosites revealed a diverse array of consensus sequences, suggesting that multiple kinase families including ERK/MAPK, PKA/PKC, CaMK-II, CKII, and CDK may be involved in the termination of LR. Functional clustering analysis of proteins with dysregulated phosphosites showed that they mainly participate in metabolic pathways, DNA replication, and tight junction. More importantly, the deletion of PP2Acα in the liver remarkably changes the overall phosphorylation profile, indicating its critical role in regulating the termination of LR. Finally, several differentially phosphorylated sites were validated by co-immunoprecipitation and Western blot. Taken together, our data unravel the first comprehensive phosphoproteomic map in the termination of LR in mice, which greatly expands our knowledge in the complicated regulation of this process and provides new directions for the treatment of liver cancer using liver resection.

Up-Regulated CCDC34 Contributes to the Proliferation and Metastasis of Hepatocellular Carcinoma

Background

Coiled-coil domain-containing protein 34 (CCDC34), which belongs to the CCDCs family, has been recently reported to be up-regulated in various kinds of tumors. However, its role in the development of hepatocellular carcinoma (HCC) still remains unclear.

Materials and methods

In this study, real-time polymerase chain reaction (RT-PCR) and Western blot analysis were performed to measure the mRNA and protein levels of CCDC34 in clinical samples. Kaplan-Meier method was used to analyze the relationship between CCDC34 and the prognosis in HCC patients. CCK-8 and colony formation assays were conducted to investigate CCDC34's effect on the cell proliferation, and Transwell assays were used to detect CCDC34's effect on the cell metastasis. Moreover, subcutaneous xenograft tumor model and lung metastasis model were applied to confirm the impact of CCDC34 on the HCC development. Lastly, RNA sequencing and Western blot analysis were performed to probe the underlying mechanism of CCDC34's effect on HCC.

Results

CCDC34 was significantly induced in HCC tissues, and the overexpression of CCDC34 predicted the poor outcomes among HCC patients. It was verified by the in vitro and in vivo experiments that CCDC34-knockdown potently inhibited the proliferation and metastasis of HCC cells. Subsequent results indicated that CCDC34 inhibition can affect the activation of protein kinase B (PKB or AKT) as well as epithelial-mesenchymal transition (EMT) process.

Conclusion

CCDC34 is significantly associated with HCC. It will become a promising prognostic biomarker and therapeutic target against HCC.

mTORC2 Signaling Is Necessary for Timely Liver Regeneration after Partial Hepatectomy

Liver regeneration is a fundamental biological process required for sustaining body homeostasis and restoring liver function after injury. Emerging evidence demonstrates that cytokines, growth factors, and multiple signaling pathways contribute to liver regeneration. Mammalian target of rapamycin complex 2 (mTORC2) regulates cell metabolism, proliferation and survival. The major substrates for mTORC2 are the AGC family members of kinases, including AKT, SGK, and PKC-α. We investigated the functional roles of mTORC2 during liver regeneration. Partial hepatectomy (PHx) was performed in liver-specific Rictor (the pivotal unit of mTORC2 complex) knockout (Rictor^LKO) and wild-type (Rictor^fl/fl) mice. Rictor-deficient mice were found to be more intolerant to PHx and displayed higher mortality after PHx. Mechanistically, loss of Rictor resulted in decreased Akt phosphorylation, leading to a delay in hepatocyte proliferation and lipid droplets formation along liver regeneration. Overall, these results indicate an essential role of the mTORC2 signaling pathway during liver regeneration.

PDK4-Deficiency Reprograms Intrahepatic Glucose and Lipid Metabolism to Facilitate Liver Regeneration in Mice

Liver regeneration requires intrahepatic and extrahepatic metabolic reprogramming to meet the high hepatic bioenergy demand for liver cell repopulation. This study aims to elucidate how pyruvate dehydrogenase kinase 4 (PDK4), a critical regulator of glucose and lipid metabolism, coordinates metabolic regulation with efficient liver growth. We found that hepatic Pdk4 expression was elevated after two-thirds partial hepatectomy (PHx). In Pdk4 ^-/- PHx mice, the liver/body weight ratio was more rapidly restored, accompanied by more aggressive hepatic DNA replication; however, Pdk4 ^-/- mice developed more severe hypoglycemia. In Pdk4 ^-/- PHx livers, the pro-regenerative insulin signaling was potentiated, as demonstrated by early peaking of the phosphorylation of insulin receptor, more remarkable induction of the insulin receptor substrate proteins, IRS1 and IRS2, and more striking activation of Akt. The hepatic up-regulation of CD36 contributed to the enhanced transient regeneration-associated steatosis in Pdk4 ^-/- PHx mice. Notably, CD36 overexpression in mice promoted the recovery of liver/body weight ratio and elevated intrahepatic adenosine triphosphate after PHx. CD36 expression was transcriptionally suppressed by FOXO1 (forkhead box protein O1), which was stabilized and translocated to the nucleus following AMPK (adenosine monophosphate-activated protein kinase) activation. PHx remarkably induced AMPK activation, which became incompetent to respond in Pdk4 ^-/- livers. Moreover, we defined that PDK4-regulated AMPK activation directly depended on intracellular adenosine monophosphate in vitro and in regenerative livers. Conclusion: PDK4 inhibition reprograms glucose and lipid metabolism to promote liver regeneration by enhancing hepatic insulin/Akt signaling and activating an AMPK/FOXO1/CD36 regulatory axis of lipid. These findings may lead to potential therapeutic strategies to prevent hepatic insufficiency and liver failure.

Translationally controlled tumor protein promotes liver regeneration by activating mTORC2/AKT signaling

Translationally controlled tumor protein (TCTP), which is a protein characterized by its potent proliferation promoting activity, has been well studied in the area of growth and tumorigenesis. However, the specific role of TCTP in liver regeneration (LR) and its underlying mechanism remains unclear. In order to investigate the contribution of TCTP during LR, heterozygous TCTP mice were generated, and a mimic LR model was applied to TCTP-knockdown (KD) hepatic cell lines. The results revealed that TCTP-KD impaired LR in mice, and manifested as the following aspects: delayed proliferation of hepatocytes, accompanied by disruption of the mRNA expression of markers of the cell cycle, degenerated lipid metabolism, and abnormal immune response. Furthermore, it was found out that TCTP activated PI3K/AKT signaling by regulating mTORC2. Lastly, the increasing rate of serum TCTP positively correlated to the recovery of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) after liver resection in humans. In summary, the present study is the first to reveal the crucial role of intracellular TCTP in LR.

Akt1 signalling supports acinar proliferation and limits acinar-to-ductal metaplasia formation upon induction of acute pancreatitis

Molecular signalling mediated by the phosphatidylinositol-3-kinase (PI3K)-Akt axis is a key regulator of cellular functions. Importantly, alteration of the PI3K-Akt signalling underlies the development of different human diseases, thus prompting the investigation of the pathway as a molecular target for pharmacologic intervention. In this regard, recent studies showed that small molecule inhibitors of PI3K, the upstream regulator of the pathway, reduced the development of inflammation during acute pancreatitis, a highly debilitating and potentially lethal disease. Here we investigated whether a specific reduction of Akt activity, by using either pharmacologic Akt inhibition, or genetic inactivation of the Akt1 isoform selectively in pancreatic acinar cells, is effective in ameliorating the onset and progression of the disease. We discovered that systemic reduction of Akt activity did not protect the pancreas from initial damage and only transiently delayed leukocyte recruitment. However, reduction of Akt activity decreased acinar proliferation and exacerbated acinar-to-ductal metaplasia (ADM) formation, two critical events in the progression of pancreatitis. These phenotypes were recapitulated upon conditional inactivation of Akt1 in acinar cells, which resulted in reduced expression of 4E-BP1, a multifunctional protein of key importance in cell proliferation and metaplasia formation. Collectively, our results highlight the critical role played by Akt1 during the development of acute pancreatitis in the control of acinar cell proliferation and ADM formation. In addition, these results harbour important translational implications as they raise the concern that inhibitors of PI3K-Akt signalling pathways may negatively affect the regeneration of the pancreas. Finally, this work provides the basis for further investigating the potential of Akt1 activators to boost pancreatic regeneration following inflammatory insults. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The mTORC2-Akt1 Cascade Is Crucial for c-Myc to Promote Hepatocarcinogenesis in Mice and Humans

Hepatocellular carcinoma (HCC) is a deadly form of liver cancer with limited treatment options. The c-Myc transcription factor is a pivotal player in hepatocarcinogenesis, but the mechanisms underlying c-Myc oncogenic activity in the liver remain poorly delineated. Mammalian target of rapamycin complex 2 (mTORC2) has been implicated in cancer by regulating multiple AGC kinases, especially AKT proteins. In the liver, AKT1 and AKT2 are widely expressed. While AKT2 is the major isoform downstream of activated phosphoinositide 3-kinase and loss of phosphatase and tensin homolog-induced HCC, the precise function of AKT1 in hepatocarcinogenesis is largely unknown. In the present study, we demonstrate that mTORC2 is activated in c-Myc-driven mouse HCC, leading to phosphorylation/activation of Akt1 but not Akt2. Ablation of Rictor inhibited c-Myc-induced HCC formation in vivo. Mechanistically, we discovered that loss of Akt1, but not Akt2, completely prevented c-Myc HCC formation in mice. Silencing of Rictor or Akt1 in c-Myc HCC cell lines inhibited phosphorylated forkhead box o1 expression and strongly suppressed cell growth in vitro. In human HCC samples, c-MYC activation is strongly correlated with phosphorylated AKT1 expression. Higher expression of RICTOR and AKT1, but not AKT2, is associated with poor survival of patients with HCC. In c-Myc mice, while rapamycin, an mTORC1 inhibitor, had limited efficacy at preventing c-Myc-driven HCC progression, the dual mTORC1 and mTORC2 inhibitor MLN0128 effectively promoted tumor regression by inducing apoptosis and necrosis. Conclusion: Our study indicates the functional contribution of mTORC2/Akt1 along c-Myc-induced hepatocarcinogenesis, with AKT1 and AKT2 having distinct roles in HCC development and progression; targeting both mTORC1 and mTORC2 may be required for effective treatment of human HCC displaying c-Myc amplification or overexpression.

Hydrogen sulphide mitigates homocysteine-induced apoptosis and matrix remodelling in mesangial cells through Akt/FOXO1 signalling cascade

Cellular damage and accumulation of extracellular matrix (ECM) protein in the glomerulo-interstitial space are the signatures of chronic kidney disease (CKD). Hyperhomocysteinemia (HHcy), a high level of homocysteine (Hcy) is associated with CKD and further contributes to kidney damage. Despite a large number of studies, the signalling mechanism of Hcy-mediated cellular damage and ECM remodelling in kidney remains inconclusive. Hcy metabolizes to produce hydrogen sulphide (H2S), and a number of studies have shown that H2S mitigates the adverse effect of HHcy in a variety of diseases involving several signalling molecules, including forkhead box O (FOXO) protein. FOXO is a group of transcription factor that includes FOXO1, which plays important roles in cell growth and proliferation. On the other hand, a cell survival factor, Akt regulates FOXO under normal condition. However, the involvement of Akt/FOXO1 pathway in Hcy-induced mesangial cell damage remains elusive, and whether H2S plays any protective roles has yet to be clearly defined. We treated mouse mesangial cells with or without H2S donor, GYY4137 and FOXO1 inhibitor, AS1842856 in HHcy condition and determined the involvement of Akt/FOXO1 signalling cascades. Our results indicated that Hcy inactivated Akt and activated FOXO1 by dephosphorylating both the signalling molecules and induced FOXO1 nuclear translocation followed by activation of the FOXO1 transcription factor. These led to the induction of cellular apoptosis and synthesis of excessive ECM protein, in part, due to increased ROS production, loss of mitochondrial membrane potential (ΔΨm), reduction in intracellular ATP concentration, increased MMP-2, -9, -14 mRNA and protein expression, and Col I, IV and fibronectin protein expression. Interestingly, GYY4137 or AS1842856 treatment prevented these changes by modulating Akt/FOXO1 axis in HHcy. We conclude that GYY4137 and/or AS1842856 mitigates HHcy induced mesangial cell damage and ECM remodelling by regulating Akt/FOXO1 pathway.

Constitutive Expression of NRAS with Q61R Driver Mutation Activates Processes of Epithelial-Mesenchymal Transition and Leads to Substantial Transcriptome Change of Nthy-ori 3-1 Thyroid Epithelial Cells

The Q61R mutation of the NRAS gene is one of the most frequent driver mutations of thyroid cancer. Tumors with this mutation are characterized by invasion into blood vessels and formation of distant metastases. To study the role of this mutation in the growth of thyroid cancer, we developed a model system on the basis of thyroid epithelial cell line Nthy-ori 3-1 transduced by a lentiviral vector containing the NRAS gene with the Q61R mutation. It was found that the expression of NRAS(Q61R) in thyroid epithelial cells has a profound influence on groups of genes involved in the formation of intercellular contacts, as well as in processes of epithelial-mesenchymal transition and cell invasion. The alteration in the expression of these genes affects the phenotype of the model cells, which acquire traits of mesenchymal cells and demonstrate increased ability for survival and growth without attachment to the substrate. The key regulators of these processes are transcription factors belonging to families SNAIL, ZEB, and TWIST, and in different types of tumors the contribution of each individual factor can vary greatly. In our model system, phenotype change correlates with an increase in the expression of SNAIL2 and TWIST2 factors, which indicates their possible role in regulating invasive growth of thyroid cancer with the mutation of NRAS(Q61R).

miR-590-5p promotes liver cancer growth and chemotherapy resistance through directly targeting FOXO1

miR-590-5p functions as an onco-miR or an anti-onco-miR in various types of cancers. However, the exact role of miR-590-5p in liver cancer remains to be elucidated. In the present study, we explored the predictive role of miR-590-5p expression in liver cancer patients. In addition, CCK-8 assay, colony formation assay, and analysis of xenograft tumors were performed to investigate the biological effects of miR-590-5p in liver cancer. A direct target of miR-590-5p was identified based on a luciferase assay and further molecular experiments. Our results demonstrated that miR-590-5p was upregulated in malignant tissues of liver cancer patients and in liver cancer cell lines. miR-590-5p expression was found to be inversely correlated with disease-free survival of liver cancer patients. Furthermore, both in vitro and in vivo experiments showed that miR-590-5p knockdown inhibited the growth of HepG2 and Bel-7404 tumor cells by promoting apoptosis and cell cycle arrest. We also demonstrated that increasing of miR-590-5p in 5-Fu resistant patients and liver cancer cells, and knockdown of miR-590-5p enhances chemosensitivity to 5-Fu in liver cancer. FOXO1 was identified as a direct and necessary target of miR-590-5p during regulating liver cancer growth. Taken together, our findings provide insights into the role of miR-590-5p in liver cancer. Moreover, it is suggested that miR-590-5p can serve as a novel therapeutic target and predictive biomarker for liver cancer.

Hepatoprotective Activity of InlB321/15, the HGFR Ligand of Bacterial Origin, in CCI4-Induced Acute Liver Injury Mice

HGF (hepatocyte growth factor)/HGFR (HGF receptor) signaling pathway is a key pathway in liver protection and regeneration after acute toxic damage. Listeria monocytogenes toxin InlB contains a HGFR-interacting domain and is a functional analog of HGF. The aim of this work was to evaluate the hepatoprotective activity of the InlB HGFR-interacting domain. The recombinant HGFR-interacting domain InlB321/15 was purified from E. coli. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test was used to measure InlB321/15 mitogenic activity in HepG2 cells. Activation of MAPK- and PI3K/Akt-pathways was tracked with fluorescent microscopy, Western blotting, and ELISA. To evaluate hepatoprotective activity, InlB321/15 and recombinant human HGF (rhHGF) were intravenously injected at the same concentration of 2 ng·g⁻¹ to BALB/c mice 2 h before liver injury with CCl₄. InlB321/15 caused dose-dependent activation of MAPK- and PI3K/Akt-pathways and correspondent mitogenic effects. Both InlB321/15 and rhHGF improved macroscopic liver parameters (liver mass was 1.51, 1.27 and 1.15 g for the vehicle, InlB321/15 and rhHGF, respectively, p < 0.05), reduced necrosis (24.0%, 16.18% and 21.66% of the total area for the vehicle, InlB321/15 and rhHGF, respectively, p < 0.05). Obtained data suggest that InlB321/15 is a promising candidate for a tissue repair agent.

Liver-specific Sirtuin6 ablation impairs liver regeneration after 2/3 partial hepatectomy

Sirtuin 6 (Sirt6) is an NAD+-dependent deacetylase that regulates central metabolic functions such as glucose homeostasis, fat metabolism, and cell apoptosis. However, the tissue-specific function of Sirt6 in liver regeneration remains unknown. Here, we show that liver-specific Sirt6 knockout (Sirt6LKO) impaired liver reconstitution after 2/3 partial hepatectomy, which was attributed to an alteration of cell cycle progression. Sirt6 LKO delayed hepatocyte transition into S phase during liver regeneration, as shown by the analysis of cell cycle-related proteins and the immuno staining of Ki-67 and 5-bromo-2-deoxyuridine (BrdU). The delayed cell cycle in Sirt6 LKO mice was attributed to the disruption of m-TOR and Akt activity, which is an important pro-proliferation pathway in liver regeneration. Sirt6 LKO also reduced carbon tetrachloride (CCl₄ )-induced liver damage. Our results suggest that Sirt6 LKO impaired liver regeneration via delayed cell cycle and impaired m-TOR and Akt activity.

Schisandrin Attenuates Lipopolysaccharide-Induced Lung Injury by Regulating TLR-4 and Akt/FoxO1 Signaling Pathways

Objective: Acute lung injury is a severe clinic condition with limited therapeutic approaches. This study evaluated whether schisandrin (Sch), an ingredient of Schisandra chinensis, has preventive effects on endothelium and epithelium injury induced by lipopolysaccharide (LPS) and the underlying mechanisms.

Methods: Male Wistar rats were continuously infused with LPS (5 mg/kg/h) via the left jugular vein for 90 min. In some rats, Sch (2.5 mg/kg/h) was administrated through the left jugular vein 30 min before LPS infusion. Leukocyte recruitment, levels of inflammatory cytokines, lung histology and edema, vascular and alveolar barrier disruption and related proteins were evaluated at indicated time point after LPS challenge.

Results: LPS infusion for 90 min resulted in an increased leukocyte adhesion to pulmonary venules and overproduction of cytokine and chemokine in both serum and lung homogenate. At 8 h after termination of LPS infusion, obvious Evans blue extravasation and lung edema were observed, along with an increased apoptosis, a decreased expression of tight junction and adherent junction proteins, and a reduction in von Willebrand factor (vWF) and keratin, all of which were attenuated by Sch treatment. Meanwhile, the LPS-elicited activation of TLR-4/NF-κB/MAPK and FoxO1 signaling was inhibited by Sch.

Conclusion: The present study revealed that pretreatment with Sch alleviated lung endothelium and epithelium injury after LPS stimulation, which is attributable to inhibition of cell injury and activation of cell regeneration via regulation of TLR-4/NF-κB/MAPK and Akt/FoxO1 signaling pathway.

Hepatic NF-kB-inducing kinase (NIK) suppresses mouse liver regeneration in acute and chronic liver diseases

Reparative hepatocyte replication is impaired in chronic liver disease, contributing to disease progression; however, the underlying mechanism remains elusive. Here, we identify Map3k14 (also known as NIK) and its substrate Chuk (also called IKKα) as unrecognized suppressors of hepatocyte replication. Chronic liver disease is associated with aberrant activation of hepatic NIK pathways. We found that hepatocyte-specific deletion of Map3k14 or Chuk substantially accelerated mouse hepatocyte proliferation and liver regeneration following partial-hepatectomy. Hepatotoxin treatment or high fat diet feeding inhibited the ability of partial-hepatectomy to stimulate hepatocyte replication; remarkably, inactivation of hepatic NIK markedly increased reparative hepatocyte proliferation under these liver disease conditions. Mechanistically, NIK and IKKα suppressed the mitogenic JAK2/STAT3 pathway, thereby inhibiting cell cycle progression. Our data suggest that hepatic NIK and IKKα act as rheostats for liver regeneration by restraining overgrowth. Pathological activation of hepatic NIK or IKKα likely blocks hepatocyte replication, contributing to liver disease progression.

PPARβ/δ: Linking Metabolism to Regeneration

In contrast to the general belief that regeneration is a rare event, mainly occurring in simple organisms, the ability of regeneration is widely distributed in the animal kingdom. Yet, the efficiency and extent of regeneration varies greatly. Humans can recover from blood loss as well as damage to tissues like bone and liver. Yet damage to the heart and brain cannot be reversed, resulting in scaring. Thus, there is a great interest in understanding the molecular mechanisms of naturally occurring regeneration and to apply this knowledge to repair human organs. During regeneration, injury-activated immune cells induce wound healing, extracellular matrix remodeling, migration, dedifferentiation and/or proliferation with subsequent differentiation of somatic or stem cells. An anti-inflammatory response stops the regenerative process, which ends with tissue remodeling to achieve the original functional state. Notably, many of these processes are associated with enhanced glycolysis. Therefore, peroxisome proliferator-activated receptor (PPAR) β/δ—which is known to be involved for example in lipid catabolism, glucose homeostasis, inflammation, survival, proliferation, differentiation, as well as mammalian regeneration of the skin, bone and liver—appears to be a promising target to promote mammalian regeneration. This review summarizes our current knowledge of PPARβ/δ in processes associated with wound healing and regeneration.

CAR-mediated repression of Cdkn1a(p21) is accompanied by the Akt activation

It was shown that CAR participates in the regulation of many cell processes. Thus, the activation of CAR causes a proliferating effect in the liver, which provides grounds to consider CAR as a therapeutic target when having a partial resection of this organ. Even though a lot of work has been done on the function of CAR in regulating hepatocyte proliferation, very little has been done on its complex mediating mechanism. This study, therefore, showed that the liver growth resulting from CAR activation leads to the decline in the level of PTEN protein and subsequent Akt activation in mouse liver. The increase of Akt activation produced by CAR agonist was accompanied by a decrease in the level of Foxo1, which was correlated with decreased expression of Foxo1 target genes, including Cdkn1a(p21). Moreover, the study also demonstrated that there exists a negative regulatory impact of CAR on the relationship between Foxo1 and targeted Cdkn1a(p21) promoter. Therefore, the study results revealed an essential function of CAR-Akt-Foxo1 signalling pathway in controlling hepatocyte proliferation by repressing the cell cycle regulator Cdkn1a (p21).

Mesenchymal Stem Cells Enhance Liver Regeneration via Improving Lipid Accumulation and Hippo Signaling

The liver has the potential to regenerate after injury. It is a challenge to improve liver regeneration (LR) after liver resection in clinical practice. Bone morrow-derived mesenchymal stem cells (MSCs) have shown to have a role in various liver diseases. To explore the effects of MSCs on LR, we established a model of 70% partial hepatectomy (PHx). Results revealed that infusion of MSCs could improve LR through enhancing cell proliferation and cell growth during the first 2 days after PHx, and MSCs could also restore liver synthesis function. Infusion of MSCs also improved liver lipid accumulation partly via mechanistic target of rapamycin (mTOR) signaling and enhanced lipid β-oxidation support energy for LR. Rapamycin-induced inhibition of mTOR decreased liver lipid accumulation at 24 h after PHx, leading to impaired LR. And after infusion of MSCs, a proinflammatory environment formed in the liver, evidenced by increased expression of IL-6 and IL-1β, and thus the STAT3 and Hippo-YAP pathways were activated to improve cell proliferation. Our results demonstrated the function of MSCs on LR after PHx and provided new evidence for stem cell therapy of liver diseases.

Loss of Pten synergizes with c-Met to promote hepatocellular carcinoma development via mTORC2 pathway

Hepatocellular carcinoma (HCC) is a deadly malignancy with limited treatment options. Activation of the AKT/mTOR cascade is one of the most frequent events along hepatocarcinogenesis. mTOR is a serine/threonine kinase and presents in two distinct complexes: mTORC1 and mTORC2. While mTORC1 has been extensively studied in HCC, the functional contribution of mTORC2 during hepatocarcinogenesis has not been well characterized, especially in vivo. Pten expression is one of the major mechanisms leading to the aberrant activation of the AKT/mTOR signaling. Here, we show that concomitant downregulation of Pten and upregulation of c-Met occurs in a subset of human HCC, mainly characterized by poor prognosis. Using CRISPR-based gene editing in combination with hydrodynamic injection, Pten was deleted in a subset of mouse hepatocytes (sgPten). We found that loss of Pten synergizes with overexpression of c-Met to promote HCC development in mice (sgPten/c-Met). At the molecular level, sgPten/c-Met liver tumor tissues display increased AKT and mTOR signaling. Using Rictor conditional knockout mice, we demonstrate that sgPten/c-Met-driven HCC development strictly depends on an intact mTORC2 complex. Our findings therefore support the critical role of mTORC2 in hepatocarcinogenesis. sgPten/c-Met mouse model represents a novel valuable system that can be used for the development of targeted therapy against this deadly malignancy.

PTEN Down-Regulation Promotes β-Oxidation to Fuel Hypertrophic Liver Growth After Hepatectomy in Mice

In regenerating liver, hepatocytes accumulate lipids before the major wave of parenchymal growth. This transient, regeneration-associated steatosis (TRAS) is required for liver recovery, but its purpose is unclear. The tumor suppressor phosphatase and tensin homolog (PTEN) is a key inhibitor of the protein kinase B/mammalian target of rapamycin axis that regulates growth and metabolic adaptations after hepatectomy. In quiescent liver, PTEN causes pathological steatosis when lost, whereas its role in regenerating liver remains unknown. Here, we show that PTEN down-regulation promotes liver growth in a TRAS-dependent way. In wild-type mice, PTEN reduction occurred after TRAS formation, persisted during its disappearance, and correlated with up-regulated β-oxidation at the expense of lipogenesis. Pharmacological modulation revealed an association of PTEN with TRAS turnover and hypertrophic liver growth. In liver-specific Pten^-/- mice shortly after induction of knockout, hypertrophic regeneration was accelerated and led to hepatomegaly. The resulting surplus liver mass was functional, as demonstrated by raised survival in a lethal model of resection-induced liver failure. Indirect calorimetry revealed lipid oxidation as the primary energy source early after hepatectomy. The shift from glucose to lipid usage was pronounced in Pten^-/- mice and correlated with the disappearance of TRAS. Partial inhibition of β-oxidation led to persisting TRAS in Pten^-/- mice and abrogated hypertrophic liver growth. PTEN down-regulation may promote β-oxidation through β-catenin, whereas hypertrophy was dependent on mammalian target of rapamycin complex 1.

CONCLUSION

PTEN down-regulation after hepatectomy promotes the burning of TRAS-derived lipids to fuel hypertrophic liver regeneration. Therefore, the anabolic function of PTEN deficiency in resting liver is transformed into catabolic activities upon tissue loss. These findings portray PTEN as a node coordinating liver growth with its energy demands and emphasize the need of lipids for regeneration. (Hepatology 2017;66:908-921).

Expressions Profiles of the Proteins Associated with Carbohydrate Metabolism in Rat Liver Regeneration

Liver has a very amazing ability to regenerate from the remnant liver after injury or partial hepatectomy (PH). Carbohydrate metabolism plays a critical role in regeneration. Many signaling pathways are involved in the metabolism process. We analyzed the changes of proteins at 0–36 h after PH in rats using isobaric tags for relative and absolute quantitation (iTRAQ) coupled with LC-MS/MS-based quantitative proteomics strategy. The results showed that 110 proteins and 5 signaling pathways related to carbohydrate metabolism in rat LR changed significantly. Based on a motif discovery method performed by iRegulon, we identified for the first time that the transcription factor SPIB whose motif was enriched among the differentiated genes associated with carbohydrate metabolism may play an important role in liver regeneration for the first time. The findings of this research provide a molecular basis for further unrevealing the mechanism of regeneration at priming stage (0–6 h) and proliferation stage (6–36 h) of LR in rats. At the same time, our studies provide more novel evidence for the signaling pathways which regulate carbohydrate metabolism from proteomics level. This study can provide some new thinking of liver regeneration and treatment of diseases associated with glucose metabolism.

Proliferation‑inhibiting pathways in liver regeneration (Review)

Liver regeneration, an orchestrated process, is the primary compensatory mechanism following liver injury caused by various factors. The process of liver regeneration consists of three stages: Initiation, proliferation and termination. Proliferation‑promoting factors, which stimulate the recovery of mitosis in quiescent hepatocytes, are essential in the initiation and proliferation steps of liver regeneration. Proliferation‑promoting factors act as the 'motor' of liver regeneration, whereas proliferation inhibitors arrest cell proliferation when the remnant liver reaches a suitable size. Certain proliferation inhibitors are also expressed and activated in the first two steps of liver regeneration. Anti‑proliferation factors, acting as a 'brake', control the speed of proliferation and determine the terminal point of liver regeneration. Furthermore, anti‑proliferation factors function as a 'steering‑wheel', ensuring that the regeneration process proceeds in the right direction by preventing proliferation in the wrong direction, as occurs in oncogenesis. Therefore, proliferation inhibitors to ensure safe and stable liver regeneration are as important as proliferation‑promoting factors. Cytokines, including transforming growth factor‑β and interleukin‑1, and tumor suppressor genes, including p53 and p21, are important members of the proliferation inhibitor family in liver regeneration. Certain anti‑proliferation factors are involved in the process of gene expression and protein modification. The suppression of liver regeneration led by metabolism, hormone activity and pathological performance have been reviewed previously. However, less is known regarding the proliferation inhibitors of liver regeneration and further investigations are required. Detailed information regarding the majority of known anti‑proliferation signaling pathways also remains fragmented. The present review aimed to understand the signalling pathways that inhbit proliferation in the process of liver regeneration.

Nicotinamide adenine dinucleotide biosynthesis promotes liver regeneration

The regenerative capacity of the liver is essential for recovery from surgical resection or injuries induced by trauma or toxins. During liver regeneration, the concentration of nicotinamide adenine dinucleotide (NAD) falls, at least in part due to metabolic competition for precursors. To test whether NAD availability restricts the rate of liver regeneration, we supplied nicotinamide riboside (NR), an NAD precursor, in the drinking water of mice subjected to partial hepatectomy. NR increased DNA synthesis, mitotic index, and mass restoration in the regenerating livers. Intriguingly, NR also ameliorated the steatosis that normally accompanies liver regeneration. To distinguish the role of hepatocyte NAD levels from any systemic effects of NR, we generated mice overexpressing nicotinamide phosphoribosyltransferase, a rate-limiting enzyme for NAD synthesis, specifically in the liver. Nicotinamide phosphoribosyltransferase overexpressing mice were mildly hyperglycemic at baseline and, similar to mice treated with NR, exhibited enhanced liver regeneration and reduced steatosis following partial hepatectomy. Conversely, mice lacking nicotinamide phosphoribosyltransferase in hepatocytes exhibited impaired regenerative capacity that was completely rescued by administering NR.

CONCLUSION

NAD availability is limiting during liver regeneration, and supplementation with precursors such as NR may be therapeutic in settings of acute liver injury. (Hepatology 2017;65:616-630).

Combined systemic elimination of MET and epidermal growth factor receptor signaling completely abolishes liver regeneration and leads to liver decompensation

Receptor tyrosine kinases MET and epidermal growth factor receptor (EGFR) are critically involved in initiation of liver regeneration. Other cytokines and signaling molecules also participate in the early part of the process. Regeneration employs effective redundancy schemes to compensate for the missing signals. Elimination of any single extracellular signaling pathway only delays but does not abolish the process. Our present study, however, shows that combined systemic elimination of MET and EGFR signaling (MET knockout + EGFR-inhibited mice) abolishes liver regeneration, prevents restoration of liver mass, and leads to liver decompensation. MET knockout or simply EGFR-inhibited mice had distinct and signaling-specific alterations in Ser/Thr phosphorylation of mammalian target of rapamycin, AKT, extracellular signal-regulated kinases 1/2, phosphatase and tensin homolog, adenosine monophosphate-activated protein kinase α, etc. In the combined MET and EGFR signaling elimination of MET knockout + EGFR-inhibited mice, however, alterations dependent on either MET or EGFR combined to create shutdown of many programs vital to hepatocytes. These included decrease in expression of enzymes related to fatty acid metabolism, urea cycle, cell replication, and mitochondrial functions and increase in expression of glycolysis enzymes. There was, however, increased expression of genes of plasma proteins. Hepatocyte average volume decreased to 35% of control, with a proportional decrease in the dimensions of the hepatic lobules. Mice died at 15-18 days after hepatectomy with ascites, increased plasma ammonia, and very small livers.

CONCLUSION

MET and EGFR separately control many nonoverlapping signaling endpoints, allowing for compensation when only one of the signals is blocked, though the combined elimination of the signals is not tolerated; the results provide critical new information on interactive MET and EGFR signaling and the contribution of their combined absence to regeneration arrest and liver decompensation. (Hepatology 2016;64:1711-1724).

The oncoprotein HBXIP suppresses gluconeogenesis through modulating PCK1 to enhance the growth of hepatoma cells

Hepatitis B X-interacting protein (HBXIP) as an oncoprotein plays crucial roles in the development of cancer, involving glucose metabolism reprogramming. In this study, we are interested in whether the oncoprotein HBXIP is involved in the modulation of gluconeogenesis in liver cancer. Here, we showed that the expression level of phosphoenolpyruvate carboxykinase (PCK1), a key enzyme of gluconeogenesis, was lower in clinical hepatocellular carcinoma (HCC) tissues than that in normal tissues. Mechanistically, HBXIP inhibited the expression of PCK1 through down-regulating transcription factor FOXO1 in hepatoma cells, and up-regulated miR-135a targeting the 3'UTR of FOXO1 mRNA in the cells. In addition, HBXIP increased the phosphorylation levels of FOXO1 protein by activating PI3K/Akt pathway, leading to the export of FOXO1 from nucleus to cytoplasm. Strikingly, over-expression of PCK1 could abolish the HBXIP-promoted growth of hepatoma cells in vitro and in vivo. Thus, we conclude that the oncoprotein HBXIP is able to depress the gluconeogenesis through suppressing PCK1 to promote hepatocarcinogenesis, involving miR-135a/FOXO1 axis and PI3K/Akt/p-FOXO1 pathway. Our finding provides new insights into the mechanism by which oncoprotein HBXIP modulates glucose metabolism reprogramming in HCC.

Regenerating the liver: not so simple after all?

Under normal homeostatic conditions, hepatocyte renewal is a slow process and complete turnover likely takes at least a year. Studies of hepatocyte regeneration after a two-thirds partial hepatectomy (2/3 PH) have strongly suggested that periportal hepatocytes are the driving force behind regenerative re-population, but recent murine studies have brought greater complexity to the issue. Although periportal hepatocytes are still considered pre-eminent in the response to 2/3 PH, new studies suggest that normal homeostatic renewal is driven by pericentral hepatocytes under the control of Wnts, while pericentral injury provokes the clonal expansion of a subpopulation of periportal hepatocytes expressing low levels of biliary duct genes such as Sox9 and osteopontin. Furthermore, some clarity has been given to the debate on the ability of biliary-derived hepatic progenitor cells to generate physiologically meaningful numbers of hepatocytes in injury models, demonstrating that under appropriate circumstances these cells can re-populate the whole liver.