Yannick Laperche

Gas6 deficiency prevents liver inflammation, steatohepatitis, and fibrosis in mice

The Gas6/Axl pathway has been increasingly implicated in regeneration and tissue repair and, recently, in the control of innate immunity. In liver, we have demonstrated that Gas6 and its receptor Axl are expressed in macrophages, progenitor cells, and myofibroblasts and that Gas6 deficiency reduced inflammation and myofibroblast activation, causing delayed liver repair in response to acute injury. All these data suggest a role of Gas6/Axl signaling in pathogenesis of chronic liver diseases. In the present study, we address the role of Gas6 in steatohepatitis and progression to liver fibrosis using Gas6-deficient mice fed a choline-deficient ethionine-supplemented diet (CDE) or receiving a chronic carbon tetrachloride (CCl(4)) treatment. Gas6 deficiency attenuated hepatic steatosis by limiting CDE-induced downregulation of genes involved in β-oxidation observed in wild-type animals. Moreover, Gas6-deficient mice displayed reduction of hepatic inflammation, revealed by limited F4/80-positive macrophage infiltration, decreased expression of IL-1β, TNF-α, lymphotoxin-β, and monocyte chemotactic protein-1, and attenuated hepatic progenitor cell response to CDE diet. Gas6 deficiency reduced CDE-induced fibrogenesis and hepatic myofibroblast activation and decreased expression of TGF-β and collagen 1 mRNAs. After chronic CCl(4) injury, Gas6-deficient mice also exhibited reduced liver fibrosis as a consequence of defective macrophage recruitment compared with wild-type animals. We conclude that improvement of steatohepatitis and fibrosis in Gas6(-/-) mice is linked to an inhibition of the inflammatory response that controls lipid metabolism and myofibroblast activation. This study highlights the deleterious effect of Gas6 in the progression of steatosis to steatohepatitis and fibrosis.

Differential Expression of the Rat γ-Glutamyl Transpeptidase Gene Promoters along with Differentiation of Hepatoblasts into Biliary or Hepatocytic Lineage

gamma-Glutamyl transpeptidase (GGT), a major enzyme of glutathione (GSH) homeostasis, is often used as a biliary marker to follow the differentiation of hepatic precursor cells. The expression of the GGT gene is driven by different promoters and yields multiple mRNAs, depending on the cell type or the stage of differentiation. In the present study, we analyzed the GGT mRNA expression pattern by quantitative reverse transcriptase-polymerase chain reaction or by in situ hybridization i) in the liver, in vivo, at early stages of development; ii) in oval cells, which proliferate and differentiate into hepatocytes in response to galactosamine injury in vivo; and finally, iii) during hepatoblast differentiation, in vitro. We show that GGT gene transcription originates from promoters P3, P4, and P5 in rat hepatic precursor cells. Differentiation of these cells induces profound alterations in GGT gene expression, leading to extinction of promoters P4 and P5, when they differentiate into the hepatocytic pathway, and to extinction of promoters P3 and P5 when they differentiate into the biliary pathway. This diversity in GGT mRNA expression provides unique molecular probes to follow hepatic precursor cell differentiation. Furthermore, the identification of factors governing GGT P5 and P4 promoter expression should provide further insight into the molecular events that occur as the liver precursor cell differentiates into the hepatic lineages.

Control of γ-Glutamyl Transpeptidase Expression by Glucocorticoids in the Rat Pancreas CORRELATION WITH GRANULE FORMATION

Glucocorticoids are known to promote the formation of zymogen granules in acinar cells of the exocrine pancreas in vivo as well as in vitro. To gain insight into the mechanism of this regulation, we studied the effects of glucocorticoids on the synthesis of two components of the secretory granule membrane, the glycoprotein 2 (GP-2) and the γ-glutamyl transpeptidase (GGT). It was demonstrated that following adrenalectomy, degranulation of pancreatic acinar cells is accompanied by a sharp decrease in GGT and GP-2 synthesis as measured by mRNA and protein accumulation. The decline of GGT synthesis was prevented by glucocorticoid replacement therapy, whereas GP-2 synthesis could be maintained with either glucocorticoid or estradiol treatment. These in vivo observations were corroborated and extended in an in vitro study using AR42J pancreatic cells. With this cell line, it was demonstrated that dexamethasone induces the formation of zymogen granules and the accumulation of a specific GGT transcript (mRNA III) by decreasing its degradation rate. At the same time, the GP-2 mRNA level was not modified by the hormonal treatment. These data demonstrate that glucocorticoids exert a positive control on the GGT expression in pancreatic cells at a post-transcriptional level. GGT, an enzyme of the glutathione metabolism, could play a significant role in protein packaging in secretory cells.

Toxic effects of indocyanine green on rat liver mitochondria

Abstract Indocyanine green (ICG) (68 to 171 nmol/mg of protein) inhibited the oxygen consumption of rat liver mitochondria in vitro . In state IV respiration, an acceleration of oxygen consumption occurred prior to this inhibition. ICG induced mitochondrial swelling in an isotonic KCl and K + acetate medium but not in a 0.27 m sucrose medium. The increase in the 42 K diffusion space of isolated mitochondria was significantly larger than that of the [ 14 C]sucrose diffusion space, indicating that ICG renders the mitochondrial membrane permeable to K + ions. At the same time, an efflux of H + ions from mitochondria was observed. It is concluded that the inhibition of mitochondrial oxygen consumption could be the result of a decrease in substrate penetration, as suggested by the diminution in NAD reduction by glutamate or isocitrate in the presence of ICG, without change in the activity of the corresponding dehydrogenases. A nigericin-like-mediated K + for H + antiport is proposed to account for the effects of ICG upon mitochondrial membrane permeability.

1284 Secretion of growth arrest-specific 6 protein by activated hepatic stellate cells and control of their survival in culture

1 2 8 4 SECRETION O F G R O W T H ARREST-SPECIFIC 6 PROTEIN B Y ACTIVATED HEPATIC STELLATE CELLS AND CONTROL OF THEIR SURVIVAL IN CULTURE. Fouad Lafdil-, INS~ RM U581, Cr~teil, France; Dominique Couchie, INS~ RM U581, Creteil, France; Marie N Chobert, INN RM U581, Cr~teil, France; Anne M Preaux, Liying Li, ~ lie S Zafrani, INN RM U581, Creteil, France; Philippe Mavier, Yannick Laperche, INS~ RM U581, Cr~teil, France