Regulation Of Liver Metabolism Research Articles

Epigenetic regulation of H3K27me3 in laying hens with fatty liver hemorrhagic syndrome induced by high-energy and low-protein diets

BackgroundFatty liver hemorrhagic syndrome (FLHS) in the modern poultry industry is primarily caused by nutrition. Despite encouraging progress on FLHS, the mechanism through which nutrition influences susceptibility to FLHS is still lacking in terms of epigenetics.ResultsIn this study, we analyzed the genome-wide patterns of trimethylated lysine residue 27 of histone H3 (H3K27me3) enrichment by chromatin immunoprecipitation-sequencing (ChIP-seq), and examined its association with transcriptomes in healthy and FLHS hens. The study results indicated that H3K27me3 levels were increased in the FLHS hens on a genome-wide scale. Additionally, H3K27me3 was found to occupy the entire gene and the distant intergenic region, which may function as silencer-like regulatory elements. The analysis of transcription factor (TF) motifs in hypermethylated peaks has demonstrated that 23 TFs are involved in the regulation of liver metabolism and development. Transcriptomic analysis indicated that differentially expressed genes (DEGs) were enriched in fatty acid metabolism, amino acid, and carbohydrate metabolism. The hub gene identified from PPI network is fatty acid synthase (FASN). Combined ChIP-seq and transcriptome analysis revealed that the increased H3K27me3 and down-regulated genes have significant enrichment in the ECM-receptor interaction, tight junction, cell adhesion molecules, adherens junction, and TGF-beta signaling pathways.ConclusionsOverall, the trimethylation modification of H3K27 has been shown to have significant regulatory function in FLHS, mediating the expression of crucial genes associated with the ECM-receptor interaction pathway. This highlights the epigenetic mechanisms of H3K27me3 and provides insights into exploring core regulatory targets and nutritional regulation strategies in FLHS.

Abstract IA06: Postpartum breast involution informs breast cancer metastasis to the liver

Abstract Young women with breast cancer have disproportionally higher rates of metastasis, and effective treatment strategies are lacking. Our lab has focused on investigating how normal reproductive changes in tissue biology interface with breast cancer metastasis in young patients. These studies identify weaning-induced involution of the breast as a tissue remodeling process similar to wound healing that promotes metastasis in rodent models. Relevance to women is suggested by the fact that a breast cancer diagnosis within 5 years of childbirth is a strong and independent risk factor for metastasis. Further, these studies find that up to 50% of all young onset breast cancer is diagnosed within this high risk postpartum window. This subset of common, young onset breast cancer is referred to as postpartum breast cancer (PPBC). We find that PPBC appears durably altered by involution, as PPBC tumors display involution, metastatic, and treatment resistant molecular signatures. PPBC also specifically associates with increased liver metastases, a metastatic site associated with very poor prognosis. In rodents, we identified a functional link between the mammary gland and the liver, including weaning-induced liver involution. Liver involution is characterized by hepatocyte cell death, fibroblast activation, ECM deposition, and an immune regulatory infiltrate similar to that found in the postpartum involuting breast. In rodent models of breast cancer liver metastasis (BCLM), the involuting liver supports outgrowth of circulating breast cancer cells more than the nulliparous host liver. Evidence for similar liver biology occurring in women is suggested by studies in healthy women, where we find liver volume increase during pregnancy and loss post wean, data consistent with liver involution. In our mouse models of BCLM, the involution metastatic advantage coincided with weaning-induced immune tolerance in the liver. We next targeted the pro-tumor, immune suppressed state of involution with the immune modulatory agent vitamin D. These studies revealed dramatic down regulation of liver metabolism with weaning, including liver cytochrome P450 enzymes, which effectively nullified the protective effect of vitamin D in involution hosts. Combined, these novel findings are anticipated to have implications for sex-specific liver diseases broadly, efficacy of pro-drugs in the postpartum window, and for breast cancer outcomes in young patients. Citation Format: Pepper Schedin. Postpartum breast involution informs breast cancer metastasis to the liver [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr IA06.

Total flavonoids extracted from Penthorum chinense Pursh mitigates CCl4-induced hepatic fibrosis in rats via inactivation of TLR4-MyD88-mediated NF-κB pathways and regulation of liver metabolism

Background:Penthorum chinense Pursh (PCP) is widely utilized in China to treat a variety of liver diseases. It has been shown that flavonoids inhibit inflammation and have the potential to attenuate tissue damage and fibrosis. However, the mechanisms underlying how total flavonoids isolated from PCP (TFPCP) exert their anti-fibrotic effects remain unclear.Methods: The chemical composition of TFPCP was determined using UHPLC–Q-Orbitrap HRMS. Subsequently, rats were randomly assigned to a control group (Control), a carbon tetrachloride (CCl4)-induced hepatic fibrosis model group (Model), a positive control group [0.2 mg/(kg∙day)] of Colchicine), and three TFPCP treatment groups [50, 100, and 150 mg/(kg∙day)]. All substances were administered by gavage and treatments lasted for 9 weeks. Simultaneously, rats were intraperitoneally injected with 10%–20% CCl4 for 9 weeks to induce liver fibrosis. At the end of the experiment, the liver ultrasound, liver histomorphological, biochemical indicators, and inflammatory cytokine levels were tested respectively. The underlying mechanisms were assessed using Western blot, immunohistochemistry, immunofluorescence, RT-qPCR, and metabolomics.Results: Fourteen flavonoids were identified in TFPCP. Compared with control animals, CCl4-treated rats demonstrated obvious liver injury and fibrosis, manifested as increases in gray values, distal diameter of portal vein (DDPV) and a decrease in blood flow velocity (VPV) in the ultrasound analysis; increased biochemical index values (serum levels of ALT, AST, TBIL, and ALP); marked increases in the contents of fibrotic markers (PC III, COL4, LN, HA) and inflammatory factors (serum TNF-α, IL-6, and IL-1β); and significant pathological changes. However, compared with the Model group, the ultrasound parameters were significantly improved and the serum levels of inflammatory cytokines were reduced in the TFPCP group. In contrast, the expression of TGF-β1, TLR4, and MyD88, as well as the p-P65/P65 and p-IκBα/IκBα ratios, were considerably reduced following TFPCP treatment. In addition, we identified 32 metabolites exhibiting differential abundance in the Model group. Interestingly, TFPCP treatment resulted in the restoration of the levels of 20 of these metabolites.Conclusion: Our findings indicated that TFPCP can ameliorate hepatic fibrosis by improving liver function and morphology via the inactivation of the TLR4/MyD88-mediated NF-κB pathway and the regulation of liver metabolism.

Protein phosphatase 2A regulates cytotoxicity and drug resistance by dephosphorylating AHR and MDR1

Protein phosphatase 2A (PP2A) is a serine/threonine dephosphorylating enzyme complex that plays numerous roles in biological processes, including cell growth and metabolism. However, its specific actions in many of these critical pathways are unclear. To explore mechanisms underlying metabolic enzyme regulation in the liver, we investigated the key pathways involved in regulation of xenobiotic-metabolizing enzymes in a mouse model with hepatocyte-specific deletion of Ppp2r1a, encoding the Aα subunit of PP2A. We performed transcriptome and phosphoproteome analysis in mouse livers at the age of 3 months and identified 2695 differentially expressed genes and 549 upregulated phosphoproteins in homozygous knockout mouse livers compared with WT littermates. In particular, the expression of metabolic enzymes Cyp2e1, Cyp1a1, Cyp1a2, Mdr1a, and Abcg2 was dramatically altered in homozygous knockout mouse livers. We also demonstrated that activation of PP2A reversed the decline of metabolic enzyme expression in primary mouse hepatocytes. We found that specific PP2A holoenzymes were involved in metabolic enzyme induction through dephosphorylation of transcription factors, nuclear receptors, or the target enzymes themselves, leading to dysregulation of xenobiotic metabolism or drug-induced hepatotoxicity. Notably, we confirmed that a regulatory axis, PP2A B56α–aryl hydrocarbon receptor–Cyp1a1, was involved in benzo(a)pyrene-induced cytotoxicity through dephosphorylation of the metabolic nuclear receptor, aryl hydrocarbon receptor, at serine 36. In addition, we showed that PP2A B56δ complexes directly dephosphorylated the multidrug efflux pump MDR1 (encoded by multi-drug resistance gene 1), contributing to drug resistance against the chemotherapeutic 5-fluorouracil. Taken together, these novel findings demonstrate the involvement of PP2A in the regulation of liver metabolism.

Abstract P158: Hepatic Trib1 Induces Proteosome-dependent Degradation Of C/ebpα In A Cop1- And Stk40- Dependent Manner

The gene tribbles pseudokinase 1 ( TRIB1 ) has been repeatedly linked to multiple human cardiometabolic traits through genome-wide association studies, including coronary artery disease, plasma cholesterol and triglycerides, and circulating liver transaminases, signaling that TRIB1 is a key regulator of liver metabolism and health. Studies in liver specific Trib1 KO mice have shown that hepatic TRIB1 regulates de novo lipogenesis and steatosis through the regulation of protein levels of the transcription factor C/EBPα, yet the mechanism governing this relationship in hepatocytes has not been investigated. We demonstrate here that human TRIB1 promotes the degradation of C/EBPα in both a COP1- and proteasome-dependent manner in human hepatoma cells. We also observe rapid degradation of TRIB1 protein in hepatoma cells, and find that this is also COP1- and proteasome-dependent. To identify hepatocyte-specific interacting partners of TRIB1 that regulate these processes, we performed tandem-affinity purification of TRIB1 in Huh7 cells and subsequent mass-spec analysis, and identified multiple novel TRIB1 binding partners including the pseudokinases serine/threonine kinase 38 (STK38) and 40 (STK40). We confirmed these interactions in vitro and found that STK40, but not STK38, is required for TRIB1-mediated proteasomal degradation of C/EBPα. Together, our results reveal that TRIB1 induces proteasomal degradation of CEBP/α in a COP1- and proteasome-dependent manner in human hepatocytes. Further, we identify the pseudokinase STK40 as a novel regulator of hepatic TRIB1 function, and ongoing work aims to investigate the role of STK40 in hepatic lipid metabolism. Finally, we show that TRIB1 is itself degraded by the proteosome in a COP1-dependent manner. As increased hepatic Trib1 confers a beneficial metabolic profile in mice, these findings could provide a novel avenue for therapeutic targeting of TRIB1 in the treatment of cardiometabolic disease. Overall, our findings add greater detail to the molecular mechanisms governing the regulation of metabolism by hepatic TRIB1, a gene which human genetics highlights as a crucial regulator of cardiometabolic traits in humans.

Effect of Liposome-Encapsulated Dextrazide on Local Regulation of Extracellular Matrix Metabolism in Liver and Lungs of Mice with during Chronic BCG-Induced Granulomatosis.

The liposomal form of isonicotinic acid hydrazide conjugate with oxidized dextran (liposomeencapsulated dextrazide, LEDZ) injected intraperitoneally for 3 months to BALB/c mice with chronic BCG-induced granulomatosis (6 month after infection) down-regulated activities of protease (MMP) and antiprotease (TIMP-1, TIMP-2, α2-macroglobulin) components of the regulation system, which indicates a drop of destructive and inflammatory potential of BCGinduced granulomatosis. The persistent enhanced hyaluronidase activity in the liver and its reduced (normalized to control level) activity in the lungs after administration of LEDZ indicates a greater hydrolysis of hyaluronan in the liver than in the lungs. LEDZ-induced changes in MMP/TIMP system in mouse liver and lungs are characterized with relative elevation of protease activity over that of antiprotease one.

Abstract 84: E2F8 tumor suppressive role in Non-Alcoholic Steatohepatitis

Abstract Non-Alcoholic Steatohepatitis (NASH) is the aggressive form of Non-Alcoholic Fatty Liver Disease (NAFLD). NAFLD is the accumulation of extra fat in liver cells, most commonly known as fatty liver. Some of the main conditions that distinguish NAFLD from NASH are severe liver inflammation, increased lipid accumulation and fibrosis. NASH is caused by an excess of fat in the liver which is linked to obesity and diet. Diets high in fats and sugars, typical of a Western diet, have been shown to induce NASH. Approximately 25% of NASH cases progress to Hepatocellular Carcinoma (HCC). Currently, there is no approved therapy for NASH and complications due to NASH is estimated to be the main reason for liver transplant. E2F8, a member of a family of transcription factors that are well known for regulating the cell cycle, has been shown to promote hepatic steatosis in a zebrafish model. Previous research from our lab has demonstrated that E2F8 has a tumor-suppressive role and loss of E2F8 leads to HCC in a carcinogen-induced model. Here, we use a mouse model to conditionally delete E2f8 in hepatocytes to sensitize to liver cancer and evaluate the effects of E2F8 on NASH development. Mice were fed with a low-fat diet (LFD), high-fat diet (HFD), choline-deficient high-fat diet (CDHFD) or Western diet (WD). Our results show that control mice in a LFD maintained a normal liver and E2F8 had a tumor-suppressive role for all diets including LF. However, a HFD induced NAFLD while a CDHFD and WD caused NASH by inflammation and fibrosis, respectively. We demonstrate that E2f8 ablation influences collagen deposition, lipid accumulation, and E-cadherin expression. Additionally, experimental mice fed a HFD had an incidence of less than 40% of spontaneous HCC, while experimental mice fed a WD had an incidence of more than 50% of spontaneous HCC; demonstrating that E2F8 tumor-suppressive role is essential to prevent progression to HCC in a NASH model. We hypothesize, that E2F8 has a role in the regulation of liver metabolism. Collectively, our study demonstrates that a WD and E2F8 hepatocyte deletion leads to an increase in lipid and collagen accumulation and HCC occurrence. Citation Format: Shaaron L. Ochoa-Rios, Lindsey N. Kent, Gustavo Leone. E2F8 tumor suppressive role in Non-Alcoholic Steatohepatitis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 84.

1721-P: In Vivo Effect of Perturbations in Hepatic Insulin Signaling on the Synthesis and Export of De Novo Synthesized Fatty Acids and Triglycerides

Hepatic lipid synthesis and Vldl production plays a major role in whole body lipid homeostasis. Insulin imposed regulation of liver metabolism is in large part executed on a transcriptional level. Several published studies focused on the effect of hepatic insulin resistance and the role of mTORC1 in liver lipid metabolism, sometimes with conflicting results. Here we used mouse genetic models with short-term liver specific removal of the insulin receptor (complete signaling pathway inactivation), Tsc1 (mTORC1 activation), Raptor (mTORC1 inactivation), Pten (simultaneous mTORC1 and Akt activation), and Raptor Pten (simultaneous mTORC1 inactivation and Akt activation) to precisely dissect the role of insulin signaling in the regulation of lipid metabolism. In vivo 2H2O administration, 1H and 2H NMR analyses revealed hepatic de novo fatty acid (FA) and triglyceride (TG) synthesis, export, as well as FA profiles both in liver and plasma. By direct examination of in vivo hepatic de novo lipogenesis (DNL), the direction and magnitude of changes observed in lipogenic gene expression did not correlate well with differences observed in DNL flux. For example, PtenLKO mice had a 3-fold increase in DNL flux with little effect on lipogenic gene expression. Our results suggest that in some contexts other factors, possibly including metabolite availability, TCA cycle metabolism, redox state or energy charge impose stronger control over DNL than regulation of gene expression. We also show that triglyceride synthesis and incorporation of de novo synthesized FA into triglycerides is regulated by mTORC1. While mTORC1 positively regulates export of newly synthesized TG it has a negative effect on export of de novo produced FA. Disclosure B. Kucejova: None. S. Deja: None. J. Duarte: None. X. Fu: None. S.C. Burgess: None. Funding National Institutes of Health (R01DK078184)

Compensatory Enzyme Expression In Response To Chronic Ethanol Intake And Partial Hepatectomy Disrupts Zone‐Specific Organization Of Lobular Metabolism In The Rat Liver

Regulation of liver metabolism is heterogeneous across lobular zones. In response to the acute metabolic challenge of partial hepatectomy (PHx), hepatocytes enact a global transcriptional program both to compensate for and replace lost tissue mass. Chronic ethanol intake has also been shown to rewire transcriptional programs in hepatocytes, with suppressive effects on hepatocyte proliferation and blunted regeneration post PHx. However, it is not clear how zone‐specific metabolism transiently adjusts to ensure PHx‐induced regeneration, or how zone‐specific metabolism is adapted due to chronic insult by ethanol intake.Male Sprague‐Dawley rats were fed a Lieber‐DeCarli liquid diet containing ethanol or carbohydrate for 5–6 weeks prior to 70% PHx in which left lateral and medial lobes were surgically removed. Liver tissue samples were collected at the time of surgery and after 24 hours of recovery. Laser‐capture microdissection was used to collect regions of tissue from eight distinct lobular zones between portal triads and central veins, and high throughput qPCR was used for transcriptional analysis.We show here that regrowth after PHx involves multiple patterns of compensatory gene expression of enzymes from most major metabolic pathways. Genes whose expression is normally restricted to a particular zone responded to PHx in a wide range of patterns, e.g., by increasing expression with no change of zone (e.g., Arg1), expanding expression to nearby zones (e.g., Glul), or transient uniform expression across the whole lobule (e.g., Ldha). We tested whether chronic ethanol intake dysregulates zonation patterns of gene expression by exaggerating, dampening, redistributing, or eliminating preexisting lobular heterogeneity. After PHx, chronic ethanol intake dysregulated zonation of expression patterns in a variety of ways, including a reversal of healthy adaptations (e.g., Pck1). Other ethanol‐induced patterns of expression seen were suppression of PHx‐induced expression (e.g., Ldha) and redistribution of expression (e.g., Arg1).The dysregulation of zonated metabolic gene expression patterns in chronic‐ethanol‐fed rats suggests that zone‐specific compensatory mechanisms may contribute to the ethanol‐impaired liver regeneration post‐PHx. Overall, this work shows the transient changes in zone‐specific transcriptional regulation in response to PHx, and identifies genes whose zone‐specific expression is affected early in ethanol‐induced disease progression. These heterogeneous changes within the hepatic lobule could be a marker of ethanol‐induced adaptation preceding more severe impairment.Support or Funding InformationSupported by NIH NIAAA R01 AA018873, T32 AA007463, and NIBIB U01 EB023224.

Transcriptomic analysis between Normal and high-intake feeding geese provides insight into adipose deposition and susceptibility to fatty liver in migratory birds

BackgroundDysregulation of adipogenesis causes metabolic diseases, like obesity and fatty liver. Migratory birds such as geese have a high tolerance of massive energy intake and exhibit little pathological development. Domesticated goose breeds, derivatives of the wild greyleg goose (Anser anser) or swan goose (Anser cygnoides), have high tolerance of energy intake resembling their ancestor species. Thus, goose is potentially a model species to study mechanisms associated with adipogenesis.ResultsPhenotypically, goose liver exhibited higher fat accumulation than adipose tissues during fattening (liver increased by 3.35 fold than 1.65 fold in adipose), showing a priority of fat accumulation in liver. We found the number of differentially expressed genes in liver (13.97%) was nearly twice the number of that in adipose (6.60%). These differentially expressed genes in liver function in several important lipid metabolism pathways, immune response, regulation of cancer, while in adipose, terms closely related to protein binding, gluconeogenesis were enriched. Typically, genes like MDH2 and SCD, which have key roles in glycolysis and fatty acids metabolism, had higher fold change in liver than in adipose tissues. Three hundred two differentially expressed long noncoding RNAs involved in regulation of metabolism in liver were also identified. For example, lncRNA XLOC_292762, which was 5.7 kb downstream of FERMT2, a gene involved phosphatidylinositol-3,4,5-trisphosphate binding, was significantly down-regulated after the high-intake feeding period. Further investigation of documented obesity-related orthologous genes in goose suggested that understanding the evolutionary split from mammals in adipogenesis will make goose fatty liver a better resource for future research.ConclusionsOur research reveals that goose uses liver as the major tissue to regulate a distinct lipid synthesis and degradation flux and the dynamic expression network analyses showed numerous layers of positive responses to both massive energy intake and possible pathological development. Our results offer insights into goose adipogenesis and provide a new perspective for research in human metabolic dysregulation.

Flux balance analysis predicts Warburg-like effects of mouse hepatocyte deficient in miR-122a.

The liver is a vital organ involving in various major metabolic functions in human body. MicroRNA-122 (miR-122) plays an important role in the regulation of liver metabolism, but its intrinsic physiological functions require further clarification. This study integrated the genome-scale metabolic model of hepatocytes and mouse experimental data with germline deletion of Mir122a (Mir122a–/–) to infer Warburg-like effects. Elevated expression of MiR-122a target genes in Mir122a–/–mice, especially those encoding for metabolic enzymes, was applied to analyze the flux distributions of the genome-scale metabolic model in normal and deficient states. By definition of the similarity ratio, we compared the flux fold change of the genome-scale metabolic model computational results and metabolomic profiling data measured through a liquid-chromatography with mass spectrometer, respectively, for hepatocytes of 2-month-old mice in normal and deficient states. The Ddc gene demonstrated the highest similarity ratio of 95% to the biological hypothesis of the Warburg effect, and similarity of 75% to the experimental observation. We also used 2, 6, and 11 months of mir-122 knockout mice liver cell to examined the expression pattern of DDC in the knockout mice livers to show upregulated profiles of DDC from the data. Furthermore, through a bioinformatics (LINCS program) prediction, BTK inhibitors and withaferin A could downregulate DDC expression, suggesting that such drugs could potentially alter the early events of metabolomics of liver cancer cells.

Retinoid X Receptors Intersect the Molecular Clockwork in the Regulation of Liver Metabolism.

Liver metabolic pathways are driven by the biological clock, and appropriate timing of 24-h patterns of metabolic gene expression as well as anabolic/catabolic processes with wake-related activity/feeding and sleep-related resting/fasting cycles preserves hepatic healthiness. The interplay among the liver metabolic pathways and the molecular clockwork is geared by the nuclear receptors, and ligand-dependent transcription factors that gauge the cellular nutritional status and redox balance, bind hormones and metabolites, and modulate the transcription of thousands target genes through their DNA-binding domain. Several nuclear receptors in the liver oscillate with circadian rhythmicity, and among these, the retinoid X receptors play a key role in metabolism regulation, intersecting with the cogs of the molecular clockwork.

Short communication: Free fatty acid receptors FFAR1 and FFAR2 during the peripartal period in liver of dairy cows grouped by their postpartum plasma β-hydroxybutyrate concentrations

Free fatty acid receptors (FFAR) play significant roles in various physiological processes, including energy metabolism, through interaction with their ligands, fatty acids. To determine whether the receptors FFAR1 and FFAR2 are involved in the regulation of liver metabolism during the peripartal period, we selected 13 German Holstein multiparous dairy cows and grouped them as high β-hydroxybutyrate (H-BHB; n = 8) or low β-hydroxybutyrate (L-BHB; n = 5) according to their individual maximum plasma BHB concentration observed within wk 2 or 3 postpartum (H-BHB: >1 mmol/L and L-BHB: <0.77 mmol/L). The selected cows had a milk yield of more than 10,000 kg/305 d during a previous lactation. The cows were fed a total mixed ration according to their requirements during the far-off dry period [5.9 MJ of net energy for lactation (NEL)/kg of dry matter (DM), crude protein (CP) 126 g/kg of DM], close-up dry period (6.5 MJ of NEL/kg of DM, CP 137 g/kg of DM), and lactation (7 MJ of NEL/kg of DM, CP 163 g/kg of DM). Blood samples were taken weekly, from d -34 to d 40 relative to parturition. Liver biopsies were taken on d -34, -17, 3, 18, and 30 relative to parturition and at slaughter (d 40). The protein abundance of FFAR1 was lower during the whole peripartal period in the H-BHB group. The abundance of FFAR2 increased over time and tended to be higher in H-BHB cows. The abundance of FFAR1 might be associated with imbalances of liver metabolism in peripartal dairy cows.

Hepatitis C virus alters metabolism of biogenic polyamines by affecting expression of key enzymes of their metabolism

Chronic infection with hepatitis C virus (HCV) induces liver fibrosis and cancer. In particular metabolic alterations and associated oxidative stress induced by the virus play a key role in disease progression. Albeit the pivotal role of biogenic polyamines spermine and spermidine in the regulation of liver metabolism and function and cellular control of redox homeostasis, their role in the viral life cycle has not been studied so far. Here we show that in cell lines expressing two viral proteins, capsid and the non-structural protein 5A, expression of the two key enzymes of polyamine biosynthesis and degradation, respectively, ornithine decarboxylase (ODC) and spermidine/spermine-N1-acetyl transferase (SSAT), increases transiently. In addition, both HCV core and NS5A induce sustained expression of spermine oxidase (SMO), an enzyme that catalyzes conversion of spermine into spermidine. Human hepatoma Huh7 cells harboring a full-length HCV replicon exhibited suppressed ODC and SSAT levels and elevated levels of SMO leading to decreased intracellular concentrations of spermine and spermidine. Thus, role of HCV-driven alterations of polyamine metabolism in virus replication and development of HCV-associated liver pathologies should be explored in future.

The glucagon-like peptide-1 analogue exendin-4 reverses impaired intracellular Ca2 + signalling in steatotic hepatocytes

The release of Ca2+ from the endoplasmic reticulum (ER) and subsequent replenishment of ER Ca2+ by Ca2+ entry through store-operated Ca2+ channels (SOCE) play critical roles in the regulation of liver metabolism by adrenaline, glucagon and other hormones. Both ER Ca2+ release and Ca2+ entry are severely inhibited in steatotic hepatocytes. Exendin-4, a slowly-metabolised glucagon-like peptide-1 (GLP-1) analogue, is known to reduce liver glucose output and liver lipid, but the mechanisms involved are not well understood. The aim of this study was to determine whether exendin-4 alters intracellular Ca2+ homeostasis in steatotic hepatocytes, and to evaluate the mechanisms involved. Exendin-4 completely reversed lipid-induced inhibition of SOCE in steatotic liver cells, but did not reverse lipid-induced inhibition of ER Ca2+ release. The action of exendin-4 on Ca2+ entry was rapid in onset and was mimicked by GLP-1 or dibutyryl cyclic AMP. In steatotic liver cells, exendin-4 caused a rapid decrease in lipid (half time 6.5min), inhibited the accumulation of lipid in liver cells incubated in the presence of palmitate plus the SOCE inhibitor BTP-2, and enhanced the formation of cyclic AMP. Hormone-stimulated accumulation of extracellular glucose in glycogen replete steatotic liver cells was inhibited compared to that in non-steatotic cells, and this effect of lipid was reversed by exendin-4. It is concluded that, in steatotic hepatocytes, exendin-4 reverses the lipid-induced inhibition of SOCE leading to restoration of hormone-regulated cytoplasmic Ca2+ signalling. The mechanism may involve GLP-1 receptors, cyclic AMP, lipolysis, decreased diacylglycerol and decreased activity of protein kinase C.

Skeletal muscle IL-6 and regulation of liver metabolism during high-fat diet and exercise training.

Interleukin (IL)‐6 is released from skeletal muscle (SkM) during exercise and has been shown to affect hepatic metabolism. It is, however, unknown whether SkM IL‐6 is involved in the regulation of exercise training‐induced counteraction of changes in carbohydrate and lipid metabolism in the liver in response to high‐fat diet (HFD) feeding. Male SkM‐specific IL‐6 KO (MKO) and Floxed mice were subjected to Chow diet, HFD or HFD combined with exercise training (HFD ExTr) for 16 weeks. Hepatic phosphoenolpyruvate carboxykinase (PEPCK) protein content decreased with both HFD and HFD ExTr in Floxed mice, but increased in IL‐6 MKO mice on HFD. In addition, the intrahepatic glucose concentration was in IL‐6 MKO mice higher in HFD than chow. Within HFD ExTr mice, hepatic glucose‐6‐phosphatase (G6Pase) 36 kDa protein content was higher in IL‐6 MKO than Floxed mice. Hepatic pyruvate dehydrogenase kinase (PDK) 4 and PDK2 protein content was in Floxed mice lower in HFD ExTr than Chow. In addition, hepatic ACC1‐phosphorylation was higher and ACC1 protein lower in HFD. Together this suggests that SkM IL‐6 regulates hepatic glucose metabolism, but does not seem to be of major importance for the regulation of oxidative capacity or lipogenesis in liver during HFD or HFD combined with exercise training.

Regulation of liver metabolism by the endosomal GTPase Rab5.

The liver maintains glucose and lipid homeostasis by adapting its metabolic activity to the energy needs of the organism. Communication between hepatocytes and extracellular environment via endocytosis is key to such homeostasis. Here, we addressed the question of whether endosomes are required for gluconeogenic gene expression. We took advantage of the loss of endosomes in the mouse liver upon Rab5 silencing. Strikingly, we found hepatomegaly and severe metabolic defects such as hypoglycemia, hypercholesterolemia, hyperlipidemia, and glycogen accumulation that phenocopied those found in von Gierke's disease, a glucose-6-phosphatase (G6Pase) deficiency. G6Pase deficiency alone can account for the reduction in hepatic glucose output and glycogen accumulation as determined by mathematical modeling. Interestingly, we uncovered functional alterations in the transcription factors, which regulate G6Pase expression. Our data highlight a requirement of Rab5 and the endosomal system for the regulation of gluconeogenic gene expression that has important implications for metabolic diseases.

Steatosis inhibits liver cell store-operated Ca²⁺ entry and reduces ER Ca²⁺ through a protein kinase C-dependent mechanism.

Lipid accumulation in hepatocytes can lead to non-alcoholic fatty liver disease (NAFLD), which can progress to non-alcoholic steatohepatitis (NASH) and Type 2 diabetes (T2D). Hormone-initiated release of Ca²⁺ from the endoplasmic reticulum (ER) stores and subsequent replenishment of these stores by Ca²⁺ entry through SOCs (store-operated Ca²⁺ channels; SOCE) plays a critical role in the regulation of liver metabolism. ER Ca²⁺ homoeostasis is known to be altered in steatotic hepatocytes. Whether store-operated Ca²⁺ entry is altered in steatotic hepatocytes and the mechanisms involved were investigated. Lipid accumulation in vitro was induced in cultured liver cells by amiodarone or palmitate and in vivo in hepatocytes isolated from obese Zucker rats. Rates of Ca²⁺ entry and release were substantially reduced in lipid-loaded cells. Inhibition of Ca²⁺ entry was associated with reduced hormone-initiated intracellular Ca²⁺ signalling and enhanced lipid accumulation. Impaired Ca²⁺ entry was not associated with altered expression of stromal interaction molecule 1 (STIM1) or Orai1. Inhibition of protein kinase C (PKC) reversed the impairment of Ca²⁺ entry in lipid-loaded cells. It is concluded that steatosis leads to a substantial inhibition of SOCE through a PKC-dependent mechanism. This enhances lipid accumulation by positive feedback and may contribute to the development of NASH and insulin resistance.

Emerging roles of Notch signaling in liver disease.

This review critically discusses the most recent advances in the role of Notch signaling in liver development, homeostasis, and disease. It is now clear that the significance of Notch in determining mammalian cell fates and functions extends beyond development, and Notch is a major regular of organ homeostasis. Moreover, Notch signaling is reactivated upon injury and regulates the complex interactions between the distinct liver cell types involved in the repair process. Notch is also involved in the regulation of liver metabolism, inflammation, and cancer. The net effects of Notch signaling are highly variable and finely regulated at multiple levels, but also depend on the specific cellular context in which Notch is activated. Persistent activation of Notch signaling is associated with liver malignancies, such as hepatocellular carcinoma with stem cell features and intrahepatic cholangiocarcinoma. The complexity of the pathway provides several possible targets for agents able to inhibit Notch. However, further cell- and context-specific in-depth understanding of Notch signaling in liver homeostasis and disease will be essential to translate these concepts into clinical practice and be able to predict benefits and risks of evolving therapies.

Bile acid signaling in metabolic disease and drug therapy.

Bile acids are the end products of cholesterol catabolism. Hepatic bile acid synthesis accounts for a major fraction of daily cholesterol turnover in humans. Biliary secretion of bile acids generates bile flow and facilitates hepatobiliary secretion of lipids, lipophilic metabolites, and xenobiotics. In the intestine, bile acids are essential for the absorption, transport, and metabolism of dietary fats and lipid-soluble vitamins. Extensive research in the last 2 decades has unveiled new functions of bile acids as signaling molecules and metabolic integrators. The bile acid-activated nuclear receptors farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, vitamin D receptor, and G protein-coupled bile acid receptor play critical roles in the regulation of lipid, glucose, and energy metabolism, inflammation, and drug metabolism and detoxification. Bile acid synthesis exhibits a strong diurnal rhythm, which is entrained by fasting and refeeding as well as nutrient status and plays an important role for maintaining metabolic homeostasis. Recent research revealed an interaction of liver bile acids and gut microbiota in the regulation of liver metabolism. Circadian disturbance and altered gut microbiota contribute to the pathogenesis of liver diseases, inflammatory bowel diseases, nonalcoholic fatty liver disease, diabetes, and obesity. Bile acids and their derivatives are potential therapeutic agents for treating metabolic diseases of the liver.