The bile acid receptor TGR5 and cholestasis

During liver injury and cholestasis, the mechanisms allowing the organ to protect itself with the aim of maintaining biliary homeostasis are not completely understood. Central to their biological roles, bile acids (BAs) and their receptors constitute a signaling network with multiple molecular and cellular impacts on both liver repair and protection from BA overload. BA signal through nuclear [mainly farnesoid X receptor (FXR)] and membrane [mainly G protein-coupled BA receptor 1 (GPBAR-1), aka Takeda G protein-coupled receptor 5 (TGR5)] receptors, in which activation elicits a wide array of biological responses. So far, most of the studies have been focused on FXR signaling as hepato-protective, TGR5 being less explored to this regard. While the liver faces massive and potentially harmful BA overload during cholestasis, it is crucial to understand that BAs induce also protective responses contributing not only to reduce the inflammatory burden, but also to spare liver cells and their repair capacities. Based on the available literature, the TGR5 BA receptor protects the liver in the cholestatic context and counteracts BA overload with the aim of restoring biliary homeostasis mainly through the control of inflammatory processes, biliary epithelial barrier permeability, and BA pool composition. Mouse experimental models of cholestasis reveal that the lack of TGR5 was associated with exacerbated inflammation and necrosis, leaky biliary epithelium, and excessive BA pool hydrophobicity, resulting in biliary cell and parenchymal insult, and compromising optimal restoration of biliary homeostasis and liver repair. There are thus widely opened translational perspectives with the aim of targeting TGR5-related signaling or biological responses to trigger protection of the cholestatic liver

Contrôle de la prolifération et de la polyploïdisation hépatique (rôles de l'insuline et de l'AMP-activated protein kinase)

Lors du développement post-natal du foie, ce tissu subit une polyploïdisation progressive qui débute au sevrage et aboutit à l émergence d hépatocytes tétraploïdes 4n et octoploïdes 8n, composés d un ou de deux noyaux (2x2n, 2x4n). Notre équipe a mis en évidence qu alors qu avant le sevrage tous les hépatocytes réalisent une cytodiérèse complète, après ce dernier, on observe des événements de cytodiérèse incomplète qui génèrent des hépatocytes binucléés. Durant ma thèse, nous avons démontré qu au sevrage, seules les modifications du signal insulinique jouent un rôle dans la mise en place de la polyploïdisation hépatocytaire. Nous démontrons que l inhibition de la voie PI3K/Akt (contrôlée par l insuline) se traduit par une diminution des événements de cytodiérèse incomplète dans les hépatocytes. Ces travaux représentent la 1ère démonstration que l insuline intervient dans le contrôle de la prolifération cellulaire en régulant les étapes tardives de la mitose. Récemment, les effets de l AMPK sur la polarité, la croissance et le contrôle de la ploïdie cellulaire ont été démontrés. Dans le foie, nous démontrons que la modulation de l activité AMPK n a pas d effet sur la mise en place de la ploïdie, mais qu elle entraîne une altération de la progression dans le cycle cellulaire. Des approches in vivo (Régénération Hépatique) et in vitro (Culture Primaire) révèlent que l absence d AMPK activée dans les hépatocytes en prolifération, entraîne un retard d entrée en phase S ainsi qu une inhibition de l expression de la cycline A. Nous démontrons un nouveau rôle de l AMPKa1 dans le contrôle de la prolifération hépatocytaire et ceci indépendamment du statut énergétique de la cellulePARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Engineered human liver based on pullulan-dextran hydrogel promotes mice survival after liver failure

International audienc

Hepatoprotective impact of the bile acid receptor TGR5

International audienceDuring liver repair after injury, bile secretion has to be tightly modulated in order to preserve liver parenchyma from bile acid (BA)-induced injury. The mechanisms allowing the liver to maintain biliary homeostasis during repair after injury are not completely understood. Besides their historical role in lipid digestion, bile acids (BA) and their receptors constitute a signalling network with multiple impacts on liver repair, both stimulating regeneration and protecting the liver from BA overload. BA signal through nuclear (mainly Farnesoid X Receptor, FXR) and membrane (mainly G Protein-coupled BA Receptor 1, GPBAR-1 or TGR5) receptors to elicit a wide array of biological responses. While a great number of studies have been dedicated to the hepato-protective impact of FXR signalling, TGR5 is by far less explored in this context. Because the liver has to face massive and potentially harmful BA overload after partial ablation or destruction, BA-induced protective responses crucially contribute to spare liver repair capacities. Based on the available literature, the TGR5 BA receptor protects the remnant liver and maintains biliary homeostasis, mainly through the control of inflammation, biliary epithelial barrier permeability, BA pool hydrophobicity and sinusoidal blood flow. Mouse experimental models of liver injury reveal that in the lack of TGR5, excessive inflammation, leaky biliary epithelium and hydrophobic BA overload result in parenchymal insult and compromise optimal restoration of a functional liver mass. Translational perspectives are thus opened to target TGR5 with the aim of protecting the liver in the context of injury and BA overload

The insulin/Akt pathway controls a specific cell division program that leads to generation of binucleated tetraploid liver cells in rodents

The formation of polyploid cells is part of the developmental program of several tissues. During postnatal development, binucleated tetraploid cells arise in the liver, caused by failure in cytokinesis. In this report, we have shown that the initiation of cytokinesis failure events and the subsequent appearance of binucleated tetraploid cells are strictly controlled by the suckling-to-weaning transition in rodents. We found that daily light/dark rhythms and carbohydrate intake did not affect liver tetraploidy. In contrast, impairment of insulin signaling drastically reduced the formation of binucleated tetraploid cells, whereas repeated insulin injections promoted the generation of these liver cells. Furthermore, inhibition of Akt activity decreased the number of cytokinesis failure events, possibly through the mammalian target of rapamycin signaling complex 2 (mTORC2), which indicates that the PI3K/Akt pathway lies downstream of the insulin signal to regulate the tetraploidization process. To our knowledge, these results are the first demonstration in a physiological context that insulin signaling through Akt controls a specific cell division program and leads to the physiologic generation of binucleated tetraploid liver cells

Upregulation of Krebs cycle and anaerobic glycolysis activity early after onset of liver ischemia

<div><p>The liver is a highly vascularized organ receiving a dual input of oxygenated blood from the hepatic artery and portal vein. The impact of decreased blood flow on glucose metabolism and how hepatocytes could adapt to this restrictive environment are still unclear. Using the left portal vein ligation (LPVL) rat model, we found that cellular injury was delayed after the onset of liver ischemia. We hypothesized that a metabolic adaptation by hepatocytes to maintain energy homeostasis could account for this lag phase. Liver glucose metabolism was characterized by ¹³C- and ¹H-NMR spectroscopy and analysis of high-energy metabolites. ALT levels and caspase 3 activity in LPVL animals remained normal during the first 12 h following surgery (<i>P</i><0.05). Ischemia rapidly led to decreased intrahepatic tissue oxygen tension and blood flow (<i>P</i><0.05) and increased expression of Hypoxia-inducible factor 1-alpha. Intrahepatic glucose uptake, ATP/ADP ratio and energy charge level remained stable for up to 12 h after ligation. Entry of glucose in the Krebs cycle was impaired with lowered incorporation of ¹³C from [U^-13C]glucose into glutamate and succinate from 0.25 to 12 h after LPVL. However, total hepatic succinate and glutamate increased 6 and 12 h after ischemia (<i>P</i><0.05). Glycolysis was initially reduced (<i>P</i><0.05) but reached maximum ¹³C-lactate (<i>P</i><0.001) and ¹³C-alanine (<i>P</i><0.01) enrichments 12 h after LPVL. In conclusion, early liver homeostasis stems from an inherent ability of ischemic hepatocytes to metabolically adapt through increased Krebs cycle and glycolysis activity to preserve bioenergetics and cell viability. This metabolic plasticity of hepatocytes could be harnessed to develop novel metabolic strategies to prevent ischemic liver damage.</p></div

Time course of total and ¹³C-enriched hepatic lactate and alanine in the ligated lobe following LPVL.

<p>Unlabeled levels of hepatic (A) lactate and (B) alanine of sham-operated rats (open white squares) and LPVL-treated (filled grey squares) rats. ¹³C-enrichment of metabolites: lactate (A) and alanine (B) in sham (white patterned squares) and LPVL-treated (black patterned squares) rats. Values are expressed as the mean ± SEM of 3–5 animals per group. (**<i>P</i><0.01, ***<i>P</i><0.001 when total lactate and alanine levels were compared in (A-B)).</p

Time course of total and ¹³C glucose levels during hypoxia.

<p>(A) Total levels of hepatic glucose of sham-operated (filled white circles) and LPVL-treated (filled grey circles) rats. (B) Levels of ¹³C glucose in sham (filled white circles) versus LPVL-treated (filled grey circles) rats. [U^-13C] glucose was infused for 45 min after the indicated times. (C) Representative microphotographs of Hypoxia inducible factor 1-α (HIF 1-α) staining of the left liver lobe of LPVL-treated animals 12h after ischemia. Slides were stained with Mayer’s Hematoxylin and mouse-anti-HIF-1α. Values are expressed as the mean ± SEM of 3–10 animals per group.</p

Delayed hepatocyte injury after induction of ischemia.

<p>(A) Evaluation of ALT serum levels and (B) quantification of caspase 3 activity in sham and LPVL-treated rats over a period of up to 48 h following induction of ischemia. (C) Representative microphotographs of HPS staining of the left liver lobe of LPVL-operated rats over a period ranging from 6 to 48 h following ischemia. Liver injury was assessed by the histological evaluation of necrosis. Values are ±SEM of 3–8 different animals. (*<i>P</i><0.05, ***<i>P</i><0.001).</p

ATP/ADP ratio and energy charge levels in the left lateral lobe of sham and LPVL-treated rats.

<p>Hepatic (A) AMP, (B) ADP, (C) ATP, (D) ATP/ADP ratio and (E) energy charge of sham and LPVL-operated rats over a period ranging from 0.25 to 12 h following ischemia. Values are expressed as the mean ± SEM of 3–8 animals.</p