Liver Metabolic Zonation Research Articles

Simulation of the crosstalk between glucose and acetaminophen metabolism in a liver zonation model.

The liver metabolizes a variety of substances that sometimes interact and regulate each other. The modeling of a single cell or a single metabolic pathway does not represent the complexity of the organ, including metabolic zonation (heterogeneity of functions) along with liver sinusoids. Here, we integrated multiple metabolic pathways into a single numerical liver zonation model, including drug and glucose metabolism. The model simulated the time-course of metabolite concentrations by the combination of dynamic simulation and metabolic flux analysis and successfully reproduced metabolic zonation and localized hepatotoxicity induced by acetaminophen (APAP). Drug metabolism was affected by nutritional status as the glucuronidation reaction rate changed. Moreover, sensitivity analysis suggested that the reported metabolic characteristics of obese adults and healthy infants in glucose metabolism could be associated with the metabolic features of those in drug metabolism. High activities of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphate phosphatase in obese adults led to increased APAP oxidation by cytochrome P450 2E1. In contrast, the high activity of glycogen synthase and low activities of PEPCK and glycogen phosphorylase in healthy infants led to low glucuronidation and high sulfation rates of APAP. In summary, this model showed the effects of glucose metabolism on drug metabolism by integrating multiple pathways into a single liver metabolic zonation model.

Hepatocyte β‐catenin is regulated by endothelial cell‐derived Wnt2 and Wnt9b to govern liver metabolic zonation and regeneration

BackgroundWnt/β‐catenin signaling pathway regulates hepatic metabolic zonation (MZ) and liver regeneration (LR) after surgical or toxicant injury. Central vein endothelial cells (CVECs) are the main source of Wnts regulating MZ, while liver sinusoidal ECs (LSECs) are the major source of Wnts regulating LR after 70% partial hepatectomy (PH). Of the 19 Wnt genes, Wnt2 and Wnt9b were reported to be expressed in CVECs and the same 2 Wnts were also upregulated in LSECs isolated from regenerating livers at 12h post PH. However, conclusive evidence of the specific roles of Wnt2 and Wnt9b in regulating MZ and LR, is lacking.MethodsHere, we report generation of Wnt2‐floxed mice and generation of Wnt2‐Wnt9b‐double‐floxed mice, which were then bred to lymphatic vessel endothelial hyaluronan receptor 1 (Lyve1)‐Cre mice to delete Wnt2, Wnt9b or both from both CVECs and LSECs referred to as EC knockouts (KO). We characterize EC‐Wnt2‐KO, EC‐Wnt9b‐KO, and EC‐Wnt2‐9b‐double KO (DKO), and assess for baseline phenotype, MZ, and LR after PH.ResultsUsing reporter mice, we first reaffirmed that Lyve1‐Cre induces recombination of floxed alleles in both CVECs and LSECs. Liver weight to body weight ratio (LW/BW) was lower in EC‐Wnt2‐9b‐DKO mice. Subsets of these mice showed an abnormal increase in one liver lobe size and mass at the expense of other lobes, along with mild periportal fibrosis. Male but not female EC‐Wnt2‐KO and EC‐Wnt9b‐KO mice had partial loss of pericentral expression of glutamine synthetase (GS), cytochrome P450 2e1 (Cyp2e1), and cytochrome P450 1a2 (Cyp1a2). Both male and female EC‐Wnt2‐9b‐DKOs lacked GS, Cyp2e1 and Cyp1a2, phenocopying EC‐Wntless‐KO mice in which all Wnts secretion from ECs were inhibited. After PH, EC‐Wnt2‐KO and EC‐Wnt9b‐KO mice showed decreased expression of Cyclin D1, Ki67 and incorporation of BrdU at 40h, which was even lower in EC‐Wnt2‐9b‐DKOs. The subset of EC‐Wnt2‐9b‐DKO mice with abnormal lobar morphology developed multiple necrotic foci infiltrated with immune cells, had a detrimental delay of LR and exhibited increased mortality after PH.ConclusionWnt2 and Wnt9b from CVECs play additive roles in controlling β‐catenin pericentral target gene expression. Additionally, Wnt2 and Wnt9b from LSECs play additive roles in regulating β‐catenin activation during LR after PH. Further studies are needed to address how and why ECs are the chief source of these two Wnts to regulate MZ and LR.

Liver Endothelial Heg Regulates Vascular/Biliary Network Patterning and Metabolic Zonation Via Wnt Signaling.

Background & AimsThe liver has complex interconnecting blood vessel and biliary networks; however, how the vascular and biliary network form and regulate each other and liver function are not well-understood. We aimed to examine the role of Heg in mammalian liver development and functional maintenance.MethodsGlobal (Heg-/-) or liver endothelial cell (EC)-specific deletion of Heg (Lyve1-Cre;Hegfl/fl ) mice were used to study the in vivo function of Heg in the liver. Carbon-ink anterograde and retrograde injection were used to visualize the 3-dimensional patterning of liver portal and biliary networks, respectively. RNA sequencing, histology, and molecular and biochemical assays were used to assess liver gene expression, protein distribution, liver injury response, and function.ResultsHeg deficiency in liver ECs led to a sparse liver vascular and biliary network. This network paucity does not compromise liver function under baseline conditions but did alter liver zonation. Molecular analysis revealed that endothelial Heg deficiency decreased expression of Wnt ligands/agonists including Wnt2, Wnt9b, and Rspo3 in ECs, which limits Axin2 mediated canonical Wnt signaling and the expression of cytochrome P450 enzymes in hepatocytes. Under chemical-induced stressed conditions, Heg-deficiency in liver ECs protected mice from drug-induced liver injuries.ConclusionOur study found that endothelial Heg is essential for the 3-D patterning of the liver vascular and indirectly regulates biliary networks and proper liver zonation via its regulation of Wnt ligand production in liver endothelial cells. The endothelial Heg-initiated changes of the liver metabolic zonation and metabolic enzyme expression in hepatocytes was functionally relevant to xenobiotic metabolism and drug induced liver toxicity.

PS-099 - NAA25 and Tropomyosin regulate liver metabolic zonation, hepatocyte polarity and ploidy

PS-099 - NAA25 and Tropomyosin regulate liver metabolic zonation, hepatocyte polarity and ploidy

Upstream regulators of hepatic Wnt/β‐catenin activity control liver metabolic zonation, development, and regeneration

Upstream regulators of hepatic Wnt/β‐catenin activity control liver metabolic zonation, development, and regeneration

β-Catenin Links Hepatic Metabolic Zonation with Lipid Metabolism and Diet-Induced Obesity in Mice

β-catenin regulates the establishment of hepatic metabolic zonation. To elucidate the functional significance of liver metabolic zonation in the chronically overfed state invivo, we fed a high-fat diet (HFD) to hepatocyte-specific β-catenin transgenic (TG) and knockout (KO) mice. Chow-fed TG and KO mice had normal liver histologic findings and body weight. However, HFD-fed TG mice developed prominent perivenous steatosis with periportal sparing. In contrast, HFD-fed KO mice had increased lobular inflammation and hepatocyte apoptosis. HFD-fed TG mice rapidly developed diet-induced obesity and systemic insulin resistance, but KO mice were resistant to diet-induced obesity. However, β-catenin did not directly affect hepatic insulin signaling, suggesting that the metabolic effects of β-catenin occurred via a parallel pathway. Hepatic expression of key glycolytic and lipogenic genes was higher in HFD-fed TG and lower in KO mice compared with wild-type mice. KO mice also exhibited defective hepatic fatty acid oxidation and fasting ketogenesis. Hepatic levels of hypoxia inducible factor-1α, an oxygen-sensitive transcriptional regulator of glycolysis and a known β-catenin binding partner, were higher in HFD-fed TG and lower in KO mice. KO mice had attenuated perivenous hypoxia, suggesting disruption of the normal sinusoidal oxygen gradient, a major determinant of liver carbohydrate and liver metabolism. Canonical Wnt signaling in hepatocytes is essential for the development of diet-induced fatty liver and obesity.

Deciphering liver zonation: New insights into the β-catenin, Tcf4, and HNF4α triad

Deciphering liver zonation: New insights into the β-catenin, Tcf4, and HNF4α triad

Liver metabolic zonation and hepatic microcirculation in carbon tetrachloride-induced experimental cirrhosis.

The exact cause of the hepatic failure in liver cirrhosis is currently unclear, and two main theories have been proposed: the first is based on the altered hepatocyte function (sick hepatocyte hypothesis); the second on the abnormal hepatic architecture (intact hepatocyte hypothesis). Moreover, the microcirculation, a fundamental component in liver structure, shows dramatic changes in cirrhosis that would heavily influence the development of the disease. In order to determine the importance of the microvascular alterations on liver morphofunctional features in experimentally induced cirrhosis, their relationships with structural, ultrastructural, and histoenzymological hepatocyte modifications were investigated. Experimental cirrhosis was induced with controlled intragastric CCl4 administration. Scanning electron microscopy of the vascular corrosion cast technique, associated with light microscopy, transmission electron microscopy, and histoenzymology techniques were employed. The results demonstrated a characteristic micronodular cirrhosis in all the livers studied; the microcirculation displayed the presence of newly formed perinodular plexus. Inside the nodule, areas with two or more hepatocyte-thick laminae were present. Moreover, a rearrangement of the hepatocyte quantitative ultrastructure without real pathological changes and a loss of normal metabolic lobular zonation were noted in the liver parenchyma. These findings support the concept that the progressive modifications of the microcirculation during experimental CC14 cirrhosis modify not only the normal blood flow direction, but also the normal hepatic metabolic gradient with a loss of the normal hepatocytic zonation.

Liver metabolic zonation in rat biliary cirrhosis: distribution is reverse of that in toxic cirrhosis.

Liver cell functional heterogeneity has been shown to persist in toxic CCl4 cirrhosis in growing rats, but the zonation observed in cirrhotic nodules may be different in other types of cirrhosis. To investigate this possibility, we looked at the zonal activities of two microsomal enzymes, glucose-6-phosphatase and NADPH dehydrogenase, in cirrhotic nodules from growing rats with chronic cholestasis. Zonal activities were measured by quantitative cytochemistry and microdensitometry. Liver cell heterogeneity was demonstrated, and we confirmed that the metabolic zonation is the mirror image of that observed in toxic cirrhosis, with periportal activity at the nodule periphery and perivenular activity at the nodule centers. Glucose-6-phosphatase activity was 2.06 times higher at the peripheries of the nodules than at the centers, whereas NADPH dehydrogenase activity at the nodule periphery was 72% of the nodule center activity. We conclude that a liver cell functional heterogeneity persists in biliary rat cirrhosis, with zonation the reverse of that previously found in toxic CCl4 cirrhosis.

Persistence of a liver metabolic zonation in extra-hepatic biliary atresia cirrhotic livers.

To evaluate whether liver metabolic zonation persists in human biliary cirrhosis, we used quantitative cytochemistry to measure activities of glucose 6 phosphatase (G6P) and NADPH dehydrogenase (ND) in hepatocytes situated in different zones of liver cirrhotic nodules. Liver specimens were obtained from 13 children with extrahepatic biliary atresia with compensated cirrhosis. Activity and distribution were compared with zonal activities measured in 17 control human liver specimens obtained during reduction hepatectomies for orthotopic liver transplantation. In normal human liver, G6P was 1.86 times more active in the periportal than in the perivenular zone. On the contrary, ND activity was lower in the periportal zone (63% of perivenular activity). A metabolic zonation persisted in extra-hepatic biliary atresia with compensated cirrhosis. G6P activity was 1.56 times greater at the nodule periphery than at the nodule center, whereas ND activity was lower at the periphery (75% of nodule center activity). This metabolic zonation is the opposite of that observed in animal toxic (CCl4) cirrhosis, in which greater G6P activity is observed at the nodule center and greater ND activity at its periphery. This confirms our previous hypothesis that the type of cirrhotic metabolic zonation may depend on the site of initial liver damage.

Adaptative changes of metabolic zonation during the development of cirrhosis in growing rats

To evaluate changes in liver metabolic zonation during development of juvenile cirrhosis, zonal activities of succinate dehydrogenase, glutamate dehydrogenase, glucose-6-phosphatase, and nicotinamide adenine dinucleotide phosphate (NADPH) dehydrogenase were measured by quantitative cytochemistry in the liver of developing rats intoxicated with carbon tetrachloride and phenobarbitone. During treatment, activities were most decreased in perivenular zones and subsequently at the periphery of the cirrhotic nodules for succinate dehydrogenase and glucose-6-phosphatase, whereas glutamate dehydrogenase and NADPH dehydrogenase were less affected. In the periportal zones, enzyme activities decreased less. After stopping intoxication, the rats remained cirrhotic, but enzyme activities returned to control perivenular levels at the periphery of the cirrhotic nodule and to control periportal levels at its center. It is concluded that a metabolic zonation persists in carbontetrachloride/phenobarbitone-induced juvenile cirrhosis and that enzyme activities can recover despite persisting cirrhosis. In this model, afferent vessels seem to be located at the center of the cirrhotic nodules, and efferent vessels, at their periphery. A different metabolic zonation may exist in other human and animal liver cirrhosis that could be related to the site of initial liver damage.