Impaired liver regeneration in Nrf2 knockout mice caused by ROS-mediated insulin/IGF-1 resistance
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ABSTRACT: The liver is frequently challenged by surgery-induced metabolic overload, viruses, or toxins, which induce the formation of reactive oxygen species. To determine the effect of oxidative stress on liver regeneration and to identify the underlying signalling pathways, we studied liver repair in mice lacking the Nrf2 transcription factor. In these animals, expression of several cytoprotective enzymes was reduced in hepatocytes, resulting in oxidative stress. As a consequence, tissue damage was aggravated, and liver regeneration after partial hepatectomy was delayed. Using in vitro and in vivo studies we identified oxidative stress-induced insulin/insulin-like growth factor resistance as the underlying mechanism. This deficiency impaired the activation of p38 mitogen-activated kinase, Akt kinase, and downstream targets after hepatectomy, resulting in enhanced death and delayed proliferation of hepatocytes. Our results reveal novel roles of Nrf2 in the regulation of growth factor signalling and in tissue repair. In addition, they provide new insight into the mechanisms underlying oxidative stress-induced defects in liver regeneration and thus offer new avenues to improve regeneration in patients with acute or chronic liver damage. Keywords: genetic modification, wilde type (wt) vs. knock out (k.o.) liver samples
Project description:The liver is frequently challenged by surgery-induced metabolic overload, viruses, or toxins, which induce the formation of reactive oxygen species. To determine the effect of oxidative stress on liver regeneration and to identify the underlying signalling pathways, we studied liver repair in mice lacking the Nrf2 transcription factor. In these animals, expression of several cytoprotective enzymes was reduced in hepatocytes, resulting in oxidative stress. As a consequence, tissue damage was aggravated, and liver regeneration after partial hepatectomy was delayed. Using in vitro and in vivo studies we identified oxidative stress-induced insulin/insulin-like growth factor resistance as the underlying mechanism. This deficiency impaired the activation of p38 mitogen-activated kinase, Akt kinase, and downstream targets after hepatectomy, resulting in enhanced death and delayed proliferation of hepatocytes. Our results reveal novel roles of Nrf2 in the regulation of growth factor signalling and in tissue repair. In addition, they provide new insight into the mechanisms underlying oxidative stress-induced defects in liver regeneration and thus offer new avenues to improve regeneration in patients with acute or chronic liver damage. Experiment Overall Design: Livers from Nrf2 k.o. and wt mice; 3 hybridizations per genoype: RNA samples were pooled from 3 individual animals
Project description:The recovery of liver mass is mainly mediated by proliferation and enlargement of hepatocytes after partial hepatectomy. Studying the gene expression profiles of hepatocytes after partial hepatectomy will be helpful in exploring the mechanism of liver regeneration. We used microarrays to further highlight the regulatory role of hepatocyte in liver regeneration at gene transcription level.
Project description:The recovery of liver mass is mainly mediated by proliferation and enlargement of hepatocytes after partial hepatectomy. Studying the gene expression profiles of hepatocytes after partial hepatectomy will be helpful in exploring the mechanism of liver regeneration. We used microarrays to further highlight the regulatory role of hepatocyte in liver regeneration at gene transcription level. Rat liver regeneration after partial hepatectomy (PH) is a good model to study the regulation of cell proliferation. We isolated hepatocytes from regenerating liver at 9 time points (2, 6, 12,24, 30, 36, 72, 120, and 168h) after PH and measured gene expression profiles of hepatocytes from 2h to 168h with rat Genome 230 2.0 gene chip. Each sample corresponding to one time point was hybridized onto one array. The experiment was repeated 3 times for each time point. In total, 10 time points were measured and 0h was used control group. After careful quality control analyses of each chip, Affymetrix GCOS 2.0 software was used to analyze the data. The relevance of gene expression profiles and biological processes was analyzed by bioinformatics and systems biology.
Project description:The transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates an array of cytoprotective genes, yet studies in transgenic mice have led to conflicting reports on its role in liver regeneration. We aimed to test the hypothesis that pharmacological activation of Nrf2 would enhance liver regeneration. Wild type (WT) and Nrf2 null mice were administered bardoxolone methyl (CDDO-Me), a potent activator of Nrf2 that has entered clinical development, and then subjected to partial hepatectomy (PHx). CDDO-Me enhanced the rate of restoration of liver volume and improved liver function (multispectral optoacoustic imaging in wild type, but not Nrf2 null, mice following two-thirds partial hepatectomy. These effects were associated with an increase in hepatocyte hypertrophy and proliferation, the suppression of immune and inflammatory signals, and metabolic remodeling in the remnant liver tissue.
Project description:The liver has an exceptional capacity for regeneration which is crucial for maintaining liver function. Since transcriptional regulation of genes controlling metabolism and cell division is a hallmark of liver regeneration (LR), we investigated the role of Zinc-finger and homeboxes 2 (ZHX2), a transcription factor critical for regulating liver postnatal gene expression and hepatic lipid hemostasis, in LR. Our results show that hepatocyte-specific Zhx2 knockout (Zhx2-KOhep) enhances LR after 2/3 partial hepatectomy in mice. Proteomics assays revealed higher mitochondrial oxidative phosphorylation (OXPHOS) in Zhx2-KOhep mouse livers. Oxygen consumption rate (OCR) and ATP generation assays confirmed the enhanced OXPHOS in Zhx2-KOhep mouse livers and human hepatocytes with ZHX2 knockdown.
Project description:Liver regeneration starting from hepatocyte proliferation was reported to be correlated with blood flow changes after partial hepatectomy (PHx). However, the regulatory effects of flow-induced shear stress on initiating hepatocyte proliferation have not been elucidated. Thus, the isolated hepatocytes were exposed to shear stress to identify their transcriptome changes.
Project description:The liver is the only organ in mammals, which fully regenerates after injury. To identify novel regulators of liver regeneration, we performed quantitative large-scale proteomics analysis of subcellular fractions from normal versus regenerating mouse liver. Proteins of the ubiquitin-proteasome pathway were rapidly regulated by partial hepatectomy, with the ubiquitin ligase Nedd4-1 being among the top hits. Knock-down of Nedd4-1 in hepatocytes in vivo through nanoparticle-mediated delivery of siRNA caused severe liver damage after partial hepatectomy and impaired regeneration, resulting in liver failure. Mechanistically, we demonstrate that Nedd4-1 is required for efficient activation of Erk1/2 signaling by receptor tyrosine kinases involved in liver regeneration through inhibition of receptor internalization, thus controlling a major pro-mitogenic and cytoprotective signaling pathway in the regenerating liver. These results highlight the power of large-scale proteomics to identify key players in liver regeneration and the importance of posttranslational regulation of growth factor signaling in this process.
Project description:After 70% partial hepatectomy (PHx), the metabolic pathways leading to hepatocyte lipid droplet accumulation during liver regeneration remain unclear. Aquaporin 5 (Aqp5) is an aquaporin and peroporin that facilitates the transport of both water and hydrogen peroxide (H2O2). In this study, we observed a delayed liver regeneration following PHx in Aqp5 knockout (Aqp5−/−) mice. Considering the role of Aqp5 in H2O2 transport, we hypothesized that deficiency in Aqp5 may induce oxidative stress and hepatocyte injury. Through the measurement of reactive oxygen species (ROS) and redox-related indices, we observed significant alterations in ROS levels as well as malondialdehyde (MDA), superoxide dismutase (SOD), and reduced glutathione (GSH) concentrations in regenerating livers lacking Aqp5 compared to wild-type controls. Oil Red O and 4-hydroxynonenal (4-HNE) staining results indicated that Aqp5 deficiency caused lipid accumulation during liver regeneration. The transcriptome sequencing results showed that the PPAR pathway is inhibited during the liver regeneration process in Aqp5 gene-knockout mice.The administration of the WY-14643 agonist, which targets the PPAR pathway, significantly mitigated delayed liver regeneration by enhancing hepatocyte proliferation and reducing lipid accumulation caused by Aqp5 deficiency. Our findings highlight the crucial role of Aqp5 in regulating H2O2 levels and lipid metabolism through the PPAR pathway during liver regeneration.
Project description:Deletion of the RPS6 gene in mouse liver results in the inhibition of 40S ribosome biogenesis and the failure of hepatocytes to enter S-phase following partial hepatectomy. This microarray experiment was designed to assess the effects of RPS6 deletion on the expression of genes involved in liver regeneration following partial hepatectomy. Keywords: time course, liver
Project description:Following partial hepatectomy, a coordinated series of molecular events occurs to regulate hepatocyte entry into the cell cycle to recover lost mass. In rats during the first six hours following resection, hepatocytes are primed by a tightly controlled cytokine response to prepare hepatocytes to begin replication. Although it appears to be a critical element driving regeneration, the cytokine response to resection has not yet been fully characterized. Specifically, the role of one of the key response elements to cytokine signaling (NF-κB) remains incompletely characterized. In this study, we present a novel, genome-wide, pattern-based analysis characterizing NF-κB binding during the priming phase of liver regeneration. We interrogated the dynamic regulation of priming by NF-κB through categorizing NF-κB binding in different temporal profiles: immediate sustained response, early transient response, and delayed response to partial hepatectomy. We then identified functional regulation of NF-κB binding by relating the temporal response profile to differential gene expression. We found that NF-κB bound genes govern negative regulation of cell growth and inflammatory response immediately following hepatectomy. NF-κB also transiently regulates genes responsible for lipid biosynthesis and transport as well as induction of apoptosis following hepatectomy. By the end of the priming phase, NF-κB regulation of genes involved in inflammatory response, negative regulation of cell death, and extracellular structure organization became prominent. These results suggest that the immediate, transient, and delayed NF-κB signaling serve different functional transitions that drive the onset of regeneration.