Dokument: Molecular remodeling of hepatic metabolism in different stages of fatty liver disease and their impact on hepatocyte secretome

Titel:	Molecular remodeling of hepatic metabolism in different stages of fatty liver disease and their impact on hepatocyte secretome
URL für Lesezeichen:	https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=49891
URN (NBN):	urn:nbn:de:hbz:061-20190617-110238-1
Kollektion:	Dissertationen
Sprache:	Englisch
Dokumententyp:	Wissenschaftliche Abschlussarbeiten » Dissertation
Medientyp:	Text
Autor:	Fahlbusch, Pia [Autor]
Dateien:	[Dateien anzeigen] Adobe PDF [Details] 9,75 MB in einer Datei [ZIP-Datei erzeugen] Dateien vom 13.06.2019 / geändert 13.06.2019
Beitragende:	Prof. Dr. Al-Hasani, Hadi [Betreuer/Doktorvater] Prof. Dr. Feldbrügge, Michael [Gutachter]
Dewey Dezimal-Klassifikation:	500 Naturwissenschaften und Mathematik » 540 Chemie
Beschreibung:	In the western civilization excessive hepatic lipid accumulation is the most common cause of chronic fatty liver disease. An increased systemic lipid load either by dietary intake or by increased adipose tissue lipolysis as well as an imbalance of intrahepatic lipid metabolism contribute to the development of fatty liver. Although single aspects of disease development and progression are subjected to numerous studies, the complex interplay of metabolic changes within the liver and the fatty liver associated changes in protein secretion patterns still remain unclear. The objective of this study was to characterize different stages of fatty liver using two different mouse models. One model (alb-SREBP-1c) exhibited genetically induced lipogenic lipid accumulation while in the second model (aP2-SREBP-1c) hepatic steatosis was induced by absent adipose tissue (generalized lipodystrophy) which lead to increased systemic lipid load and consequently ectopic hepatic lipid accumulation. In bioinformatic analyses of the transcriptome, the differential liver gene expression of each phenotype was set in relation to the molecular changes in hepatic metabolism. The most pronounced differences were annotated to lipid and carbohydrate metabolism as well as mitochondrial function. However, direct comparison of differentially expressed genes showed highly specific gene expression patterns for each fatty liver phenotype for identical pathways. The results from the bioinformatical analyses could be verified in ex vivo studies using enzyme activity-based assays. Thus, although functional annotation provided similar pathways of changed hepatic metabolism in the fatty liver transcriptomes functional consequences were fundamentally different. Thus, alb-SREBP-1c mice presented increased de novo lipogenesis (DNL) by transgene-mediated overrepresentation of the transcription factor sterol regulatory element-binding protein (SREBP)-1c. In addition, an increased mitochondrial potential as well as increased glycolysis could be determined, which indicated an adaption to metabolic stress. In hepatocytes from the aP2-SREBP-1c mice, however, only a slightly increased DNL was determined, while mitochondrial β-oxidation was decreased. Transcriptional analysis suggests a shift in lipid metabolism to increased cholesterol homeostasis in this phenotype. Transcriptome analyses also indicated fundamental changes in liver transcriptome towards an adipocyte-like transcriptome, which in particular forces the storage of lipids. Although gluconeogenesis was similar in all phenotypes, glycogen formation was reduced in the metabolic model. In summary, the lipogenic mouse model presents the phenotype of a mild hepatic steatosis while the metabolic phenotype indicates progressive fatty liver. Bioinformatics analyses of the secretome showed that the metabolic status of hepatocytes from the different phenotypes is reflected there. In line with transcriptome analysis, a unique pattern of secreted proteins (hepatokines) was identified for each phenotype not only compared to control but also between the two fatty liver models. A top candidate was the insulin-like growth factor binding protein (IGFBP) 2, a soluble binding protein for the insulin-like growth factor (IGF)-I. Bioinformatical processing of the transcriptome data identified that the IGF-I/IGFBP2 system, as top score upstream regulatory network, can differentiate between the metabolic and the lipogenic liver phenotype. Consistent with this, IGFBP2 was reduced in the secreted proteome of the primary hepatocytes from the metabolic phenotypes compared to the other phenotypes. Ex vivo experiments identified IGFBP2 not to have an immediate signaling effect, but to modulate IGF-I signaling. Further analyses showed that expression and secretion of IGFBP2 to be directly linked to fatty liver status. Consequently, IGFBP2 could serve a marker for the gradual fatty liver progression and might indicate the status at which changes in liver metabolism severely impact the whole organism. In humans, analyses of plasma from a cohort of NAFLD patients showed IGFBP2 levels to negatively correlate with hepatic steatosis status. In this cohort, two years follow-up post bariatric intervention showed increased IGFBP2 plasma levels in direct relation to a reduction of hepatic steatosis. In conclusion, this thesis showed for the first time a comprehensive insight on the pathogenesis and progression of fatty liver from transcriptome, to functional, up to the secretory level of liver metabolism. The data obtained in this thesis suggest that the evolutionary adaptation of the organism to periods of hunger ultimately leads to the progression of fatty liver disease, with a disturbed DNL in the center. In conjunction with the pathogenesis of fatty liver, changes in hepatocyte secretion could be detected, with IGFBP2 being a promising candidate for the non-invasive classification of fatty liver.
Lizenz:	Urheberrechtsschutz
Fachbereich / Einrichtung:	Sonstige Einrichtungen/Externe » An-Institute » Deutsches Diabetes-Zentrum
Dokument erstellt am:	17.06.2019
Dateien geändert am:	17.06.2019
Promotionsantrag am:	04.12.2018
Datum der Promotion:	04.04.2019