Gene expression during liver regeneration after partial hepatectomy in mice lacking type 1 tumor necrosis factor receptor

A transcriptomic biomarker predictive of cell proliferation for use in adverse outcome pathway-informed testing and assessment

High-throughput transcriptomics (HTTr) is increasingly being used to identify molecular targets of chemicals that can be linked to adverse outcomes. Cell proliferation (CP) is an important key event in chemical carcinogenesis. Here, we describe the construction and characterization of a gene expression biomarker that is predictive of the CP status in human and rodent tissues. The biomarker was constructed from 30 genes known to be increased in expression in prostate cancers relative to surrounding tissues and in cycling human MCF-7 cells after estrogen receptor (ER) agonist exposure. Using a large compendium of gene expression profiles to test utility, the biomarker could identify increases in CP in (i) 308 out of 367 tumor vs. normal surrounding tissue comparisons from 6 human organs, (ii) MCF-7 cells after activation of ER, (iii) after partial hepatectomy in mice and rats, and (iv) the livers of mice and rats after exposure to nongenotoxic hepatocarcinogens. The biomarker identified suppression of CP (i) under conditions of p53 activation by DNA damaging agents in human cells, (ii) in human A549 lung cells exposed to therapeutic anticancer kinase inhibitors (dasatinib, nilotnib), and (iii) in the mouse liver when comparing high levels of CP at birth to the low background levels in the adult. The responses using the biomarker were similar to those observed using conventional markers of CP including PCNA, Ki67, and BrdU labeling. The CP biomarker will be a useful tool for interpretation of HTTr data streams to identify CP status after exposure to chemicals in human cells or in rodent tissues.

Hepatocyte β-catenin loss is compensated by Insulin-mTORC1 activation to promote liver regeneration

BACKGROUND AND AIMS

Liver regeneration (LR) following partial hepatectomy (PH) occurs via activation of various signaling pathways. Disruption of a single pathway can be compensated by activation of another pathway to continue LR. The Wnt-β-catenin pathway is activated early during LR and conditional hepatocyte loss of β-catenin delays LR. Here, we study mechanism of LR in the absence of hepatocyte-β-catenin.

APPROACH AND RESULTS

Eight-week-old hepatocyte-specific Ctnnb1 knockout mice (β-catenin ΔHC ) were subjected to PH. These animals exhibited decreased hepatocyte proliferation at 40-120 h and decreased cumulative 14-day BrdU labeling of <40%, but all mice survived, suggesting compensation. Insulin-mediated mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) activation was uniquely identified in the β-catenin ΔHC mice at 72-96 h after PH. Deletion of hepatocyte regulatory-associated protein of mTOR (Raptor), a critical mTORC1 partner, in the β-catenin ΔHC mice led to progressive hepatic injury and mortality by 30 dys. PH on early stage nonmorbid Raptor ΔHC -β-catenin ΔHC mice led to lethality by 12 h. Raptor ΔHC mice showed progressive hepatic injury and spontaneous LR with β-catenin activation but died by 40 days. PH on early stage nonmorbid Raptor ΔHC mice was lethal by 48 h. Temporal inhibition of insulin receptor and mTORC1 in β-catenin ΔHC or controls after PH was achieved by administration of linsitinib at 48 h or rapamycin at 60 h post-PH and completely prevented LR leading to lethality by 12-14 days.

CONCLUSIONS

Insulin-mTORC1 activation compensates for β-catenin loss to enable LR after PH. mTORC1 signaling in hepatocytes itself is critical to both homeostasis and LR and is only partially compensated by β-catenin activation. Dual inhibition of β-catenin and mTOR may have notable untoward hepatotoxic side effects.

Angelica sinensis Polysaccharide and Astragalus membranaceus Polysaccharide Accelerate Liver Regeneration by Enhanced Glycolysis via Activation of JAK2/STAT3/HK2 Pathway

The promotion of liver regeneration is crucial to avoid liver failure after hepatectomy. Angelica sinensis polysaccharide (ASP) and Astragalus membranaceus polysaccharide (AMP) have been identified as being associated with hepatoprotective effects. However, their roles and specific mechanisms in liver regeneration remain to be elucidated. In the present study, it suggested that the respective use of ASP or AMP strikingly promoted hepatocyte proliferation in vitro with a wide range of concentrations (from 12.5 μg/mL to 3200 μg/mL), and a stronger promoting effect was observed in combined interventions. A significantly enhanced liver/body weight ratio (4.20%) on day 7 and reduced serum transaminase (ALT 243.53 IU/L and AST 423.74 IU/L) and total bilirubin (52.61 IU/L) levels on day 3 were achieved by means of ASP-AMP administration after partial hepatectomy in mice. Metabonomics showed that differential metabolites were enriched in glycolysis with high expression of beta-d-fructose 6-phosphate and lactate, followed by significantly strengthened lactate secretion in the supernatant (0.54) and serum (0.43) normalized to control. Upon ASP-AMP treatment, the knockdown of hexokinase 2 (HK2) or inhibited glycolysis caused by 2-deoxy-d-glucose decreased hepatocyte proliferation in vitro and in vivo. Furthermore, pathway analysis predicted the role of JAK2/STAT3 pathway in ASP-AMP-regulated liver regeneration, and phosphorylation of JAK2 and STAT3 was proven to be elevated in this promoting process. Finally, downregulated expression of HK2, an attenuated level of lactate secretion, and reduced hepatocyte proliferation were displayed when STAT3 was knocked out in vitro. Therefore, it can be concluded that ASP-AMP accelerated liver regeneration and exerted a hepatoprotective effect after hepatectomy, in which the JAK2/STAT3/HK2 pathway was actively involved in activating glycolysis.

Lymphotoxin-β-receptor (LTβR) signaling on hepatocytes is required for liver regeneration after partial hepatectomy

Lymphotoxin-β-receptor deficient (LTβR-/-) and Tumor Necrosis Factor Receptor p55 deficient (TNFRp55-/-) mice show defects in liver regeneration (LR) after partial hepatectomy (PHx) with significantly increased mortality. LTβR and TNFRp55 belong to the core members of the TNF/TNFR superfamily. Interestingly, combined failure of LTβR and TNFRp55 signaling after PHx leads to a complete defect in LR. Here, we first addressed the question which liver cell population crucially requires LTβR signaling for efficient LR. To this end, mice with a conditionally targeted LTβR allele (LTβRfl/fl) were crossed to AlbuminCre and LysozymeMCre mouse lines to unravel the function of the LTβR on hepatocytes and monocytes/macrophages/Kupffer cells, respectively. Analysis of these mouse lines clearly reveals that LTβR is required on hepatocytes for efficient LR while no deficit in LR was found in LTβRfl/fl × LysMCre mice. Second, the molecular basis for the cooperating role of LTβR and TNFRp55 signaling pathways in LR was investigated by transcriptome analysis of etanercept treated LTβR-/- (LTβR-/-/ET) mice. Bioinformatic analysis and subsequent verification by qRT-PCR identified novel target genes (Cyclin-L2, Fas-Binding factor 1, interferon-related developmental regulator 1, Leucyl-tRNA Synthetase 2, and galectin-4) that are upregulated by LTβR/TNFRp55 signaling after PHx and fail to be upregulated after PHx in LTβR-/-/ET mice.

The Effect of Geraniol on Liver Regeneration After Hepatectomy in Rats

Geraniol is a monoterpenoid alcohol that has a hepatoprotective effect. We investigated the regenerative effects of geraniol in rats after a 70% partial hepatectomy (PH). Using Wistar albino rats, nine groups were created: Group I was the control group, while the remaining groups received a single intraperitoneal dose of saline, Silymarin, or geraniol after PH. A 70% PH was performed on all groups except for groups II and III. Blood serum samples were obtained for alanine amino transferase (ALT) analysis. Then liver tissues were harvested for histological and real-time polymerase chain reaction (PCR) analyses. Tumor necrosis factor-α (TNFα) and interleukin 6 (IL6) gene expression were examined 24 and 48 h after PH. ALT levels were found to be statistically significantly increased in all PH-treated groups. TNFα and IL6 gene expression levels were elevated in geraniol-treated groups. Histological evaluation revealed a hepatoprotective effect for geraniol-treated groups. Our results suggest that geraniol plays a significant role during liver regeneration, which involves the elevated expression of TNFα and IL6 48 h after PH.

The lipid raft-bound alkaline phosphatase activity increases and the level of transcripts remains unaffected in liver of merosin-deficient LAMA2dy mouse

Alkaline phosphatase (AP) and other proteins add glycosylphosphatidylinositol (GPI) before addressing to raft domains of the cell membrane. Our previous report showing an increased density of lipid rafts in muscle of dystrophic Lama2dy mice prompted us to compare livers of normal (NL) and dystrophic mice (DL) for their levels of rafts. With this aim, hepatic rafts were isolated as Triton X-100 resistant membranes, and identified by their abundance of flotillin-2, alkaline phosphatase (AP) and other raft markers. The comparable abundance of cholesterol and flotillin-2 in rafts of NL and DL contrasted with the double AP activity both in rafts of DL and whole DL. The AP mRNA level was the same in NL and DL. Sedimentation analysis profiles revealed AP activity of NL distributed between dimeric (dAP) and monomeric AP (mAP), whose proportions and lectin-binding extent changed in DL. The increased AP activity and changed AP glycosylation in DL, the prevalence of mAP in NL and the enhanced stability of dAP in DL demonstrated the critical role that glycosylation and oligomerization play for AP catalysis. The higher AP activity of DL probably arises from dystrophy-associated changes in glycosyl transferases, which alter AP glycosylation and subunit folding with profitable effects for AP stability and catalysis.

Lipocalin-2 gene expression during liver regeneration after partial hepatectomy in rats

BACKGROUND

Lipocalin-2 (Lcn2) is related to cell proliferation. We studied Lcn2 gene expression during liver regeneration after partial hepatectomy (PH).

METHODS

Male Wistar rats were sacrificed before and 2, 4, 6, 12, 24, 72 h, 7 days after 70% or 40% PH. The remnant liver weight/body weight (RLW/BW) ratio, Lcn2 gene and mRNA expression in the remnant livers were measured. Hepatocytes and nonparenchymal cells were isolated from the remnant livers. Expression of Lcn2 related protein was detected by Western blot.

RESULTS

The RLW/BW ratio increased to nearly 90% of the original liver 72 h after PH. Lcn2 gene expression showed upward curves from 4 to 72 h after PH in both 70% and 40% PH rats and peaked at 12 h (8 times vs 0 h). Lcn2 mRNA expression showed parallel upward curves from 2 to 72 h. The peak was significantly higher in 70% PH rats (2(7) times vs 0 h) than in 40% PH rats (2(5) times vs 0 h) 12 h after PH (p < 0.05). Lcn2 related protein in the isolated liver cells was markedly enhanced 24 h after PH, more in hepatocytes than in nonparenchymal cells.

CONCLUSION

The expressions of Lcn2 gene and mRNA, and its related protein increased markedly after PH. Lcn2 might be important in the genetic regulation of liver regeneration after PH.

High-throughput analysis of tumor necrosis factor signaling pathways in eight cell types during rat hepatic regeneration

This study aims to clarify the relevance of tumor necrosis factor (TNFs) signaling pathways and liver regeneration (LR) at the cellular level. Eight liver cell types were isolated using Percoll density gradient centrifugation and immunomagnetic beads methods. Expressions of TNF signaling pathway-involved genes in each cell type after 2/3 hepatectomy (PH) were detected using gene chip. Results show the following: gene TNFα was upregulated in most cell types, especially in Kupffer cells (KC); TNFβ expression was insignificantly changed in eight liver cell types; the majority of genes involved in four TNFα signaling pathways showed increased expression during LR in hepatocytes (HC); TNFα-induced NFκB pathway-involved genes were upregulated preferentially between 2 and 24 h during LR in biliary epithelial cells (BECs); and TNFα-induced apoptotic pathway genes were downregulated preferentially at progressing phase of LR in dendritic cells (DCs). Referring to the above results, TNFα-mediated signaling pathways, in contrast to TNFβ, play the more proactive role in LR, and four TNFα-mediated signaling pathways seem helpful to regulate biological events in HC; BEC proliferation was partly controlled by TNFα-mediated NFκB pathway; and the impaired TNFα-mediated apoptotic pathway in DCs might contribute to the restoration of DC mass after PH. Briefly, the comparative analysis of genomewide expression profiles of TNF signaling pathways between different cell types is helpful in understanding the implication of TNF signaling in LR at the cellular level.

Partial hepatectomy in mice: current status of research and implications for clinical practice

The classic model of partial hepatectomy was first established in the 1930s and played a key role in the research of liver regeneration and liver disease in mammals. Rats and mice are the most commonly used animals for research, but surgery is usually performed in rats. Considering many differences between rats and mice, this paper aims to summarize the crucial points in the surgical procedure for mice and the principles and methods of partial hepatectomy.

Potential role of caveolin-1 in acetaminophen-induced hepatotoxicity

Caveolin-1 (Cav-1) is a membrane scaffolding protein, which functions to regulate intracellular compartmentalization of various signaling molecules. In the present studies, transgenic mice with a targeted disruption of the Cav-1 gene (Cav-1(-/-)) were used to assess the role of Cav-1 in acetaminophen-induced hepatotoxicity. Treatment of wild-type mice with acetaminophen (300 mg/kg) resulted in centrilobular hepatic necrosis and increases in serum transaminases. This was correlated with decreased expression of Cav-1 in the liver. Acetaminophen-induced hepatotoxicity was significantly attenuated in Cav-1(-/-) mice, an effect that was independent of acetaminophen metabolism. Acetaminophen administration resulted in increased hepatic expression of the oxidative stress marker, lipocalin 24p3, as well as hemeoxygenase-1, but decreased glutathione and superoxide dismutase-1; no differences were noted between the genotypes suggesting that reduced toxicity in Cav-1(-/-) mice is not due to alterations in antioxidant defense. In wild-type mice, acetaminophen increased mRNA expression of the pro-inflammatory cytokines, interleukin-1beta, and monocyte chemoattractant protein-1 (MCP-1), as well as cyclooxygenase-2, while 15-lipoxygenase (15-LOX), which generates anti-inflammatory lipoxins, decreased. Acetaminophen-induced changes in MCP-1 and 15-LOX expression were greater in Cav-1(-/-) mice. Although expression of tumor necrosis factor-alpha, a potent hepatocyte mitogen, was up-regulated in the liver of Cav-1(-/-) mice after acetaminophen, expression of proliferating cell nuclear antigen and survivin, markers of cellular proliferation, were delayed, which may reflect the reduced need for tissue repair. Taken together, these data demonstrate that Cav-1 plays a role in promoting inflammation and toxicity during the pathogenesis of acetaminophen-induced injury.