Initiation of liver growth by tumor necrosis factor: deficient liver regeneration in mice lacking type I tumor necrosis factor receptor

HMGB1 neutralization is associated with bacterial translocation during acetaminophen hepatotoxicity

BACKGROUND

Acetaminophen (APAP) hepatotoxicity is associated with a high rate of gram-negative enteric bacterial infection; however, the underlying mechanism is still unknown. APAP overdose induces massive hepatocyte necrosis, necrotic tissue releases high mobility group B1 (HMGB1) and exogenous HMGB1 is able to induce gut bacterial translocation (BT) in normal mice; therefore, it is possible that HMGB1 mediates gut BT in APAP hepatotoxicity. This study aims to test this hypothesis by using anti-HMGB1 neutralizing antibody to treat APAP overdose for 24-48 hours.

METHODS

Male C57BL/6 mice were intraperitoneally (i.p.) injected with a single dose of APAP (350 mg/kg dissolved in 1 mL sterile saline). 2 hrs after APAP injection, the APAP challenged mice were randomized to receive treatment with either anti-HMGB1 antibody (400 μg per dose) or non-immune (sham) IgG every 24 h for a total of 2 doses.

RESULTS

24 and 48 hrs after APAP challenge, anti-HMGB1 treatment instead of sham IgG therapy significantly decreased serum HMGB1 concentrations and reduced BT by 85%; serum HMGB1 levels were positively correlated with the amount of BT; anti-HMGB1 therapy decreased hepatic BT at 48 h, which was associated with better recovered liver structure and better restored hepatic immune system that was shown by enhanced hepatic mRNA expression of TNF-α, IL-6 and extensive proliferation of inflammatory and reticuloendothelial cells; however, anti-HMGB1 treatment did not decrease gut mucosal permeability as compared to the sham IgG therapy at either 24 or 48 hrs.

CONCLUSION

HMGB1 neutralization is associated with bacterial translocation during APAP hepatotoxicity.

Liver regeneration

The liver is unique in its ability to regenerate in response to injury. A number of evolutionary safeguards have allowed the liver to continue to perform its complex functions despite significant injury. Increased understanding of the regenerative process has significant benefit in the treatment of liver failure. Furthermore, understanding of liver regeneration may shed light on the development of cancer within the cirrhotic liver. This review provides an overview of the models of study currently used in liver regeneration, the molecular basis of liver regeneration, and the role of liver progenitor cells in regeneration of the liver. Specific focus is placed on clinical applications of current knowledge in liver regeneration, including small-for-size liver transplant. Furthermore, cutting-edge topics in liver regeneration, including in vivo animal models for xenogeneic human hepatocyte expansion and the use of decellularized liver matrices as a 3-dimensional scaffold for liver repopulation, are proposed. Unfortunately, despite 50 years of intense study, many gaps remain in the scientific understanding of liver regeneration.

Signal transduction of platelet-induced liver regeneration and decrease of liver fibrosis

Platelets contain three types of granules: alpha granules, dense granules, and lysosomal granules. Each granule contains various growth factors, cytokines, and other physiological substances. Platelets trigger many kinds of biological responses, such as hemostasis, wound healing, and tissue regeneration. This review presents experimental evidence of platelets in accelerating liver regeneration and improving liver fibrosis. The regenerative effect of liver by platelets consists of three mechanisms; i.e., the direct effect on hepatocytes, the cooperative effect with liver sinusoidal endothelial cells, and the collaborative effect with Kupffer cells. Many signal transduction pathways are involved in hepatocyte proliferation. One is activation of Akt and extracellular signal-regulated kinase (ERK)1/2, which are derived from direct stimulation from growth factors in platelets. The other is signal transducer and activator of transcription-3 (STAT3) activation by interleukin (IL)-6 derived from liver sinusoidal endothelial cells and Kupffer cells, which are stimulated by contact with platelets during liver regeneration. Platelets also improve liver fibrosis in rodent models by inactivating hepatic stellate cells to decrease collagen production. The level of intracellular cyclic adenosine monophosphate (cyclic AMP) is increased by adenosine through its receptors on hepatic stellate cells, resulting in inactivation of these cells. Adenosine is produced by the degradation of adenine nucleotides such as adenosine diphosphate (ADP) and adenosine tri-phosphate (ATP), which are stored in abundance within the dense granules of platelets.

Genomics of liver transplant injury and regeneration

While improved surgical techniques, post-operative care, and immunosuppression regimens have reduced morbidity and mortality associated with orthotopic liver transplantation (OLT), further improvement of outcomes requires personalized treatment and a better understanding of genomic mechanisms involved. Gene expression profiles of ischemia/reperfusion (I/R) injury, regeneration, and rejection, may suggest mechanisms for development of better predictive tools and treatments. The liver is unique in its regenerative potential, recovering lost mass and function after injury from ischemia, resection, and rejection. I/R injury, an inevitable consequence of perfusion cessation, cold storage, and reperfusion, is regulated by the interaction of the immune system, inflammatory cytokines, and reduced microcirculatory blood flow in the liver. Rejection, a common post-operative complication, is mediated by the recipient's immune system through T-cell-dependent responses activating proinflammatory and apoptotic pathways. Characterizing distinctive gene expression signatures for these events can identify therapies to reduce injury, promote regeneration, and improve outcomes. While certain markers of liver injury and regeneration have been observed in animals, many of these are unverified in human studies. Further investigation of these genomic signatures and mechanisms through new technology offers promise, but continues to pose a significant challenge. An overview of the current fund of knowledge in this area is reviewed.

Serotonin modulation of macrophage polarization: inflammation and beyond

Macrophages display a ample plethora of effector functions whose acquisition is promoted by the surrounding cytokine and cellular environment. Depending on the stimulus, macrophages become specialized ("polarized") for either pathogen elimination, tissue repair and wound healing or immunosuppression. This "polarization" versatility allows macrophages to critically contribute to tissue homeostasis, as they promote initiation and resolution of inflammatory responses. As a consequence, deregulation of the tissue macrophage polarization balance is an etiological agent of chronic inflammation, autoimmune diseases, cancer and even obesity and insulin resistance. In the present review we describe current concepts on the molecular basis and the patho-physiological implications of macrophage polarization, and describe its modulation by serotonin (5-HT), a neurotransmitter that regulates inflammation and tissue repair via a large set of receptors (5-HTR1-7). 5-HT modulates the phenotypic and functional polarization of macrophages, and contributes to the maintenance of an anti-inflammatory state mainly via 5-HTR2B and 5-HTR7, whose activation has a great impact on macrophage gene expression profile. The identification of 5-HTR2B and 5-HTR7 as functionally-relevant polarization markers suggests their therapeutic value in inflammatory pathologies as well as their potential involvement in linking the immune and nervous systems.

Epigallocatechin gallate does not accelerate the early phase of liver regeneration after partial hepatectomy in rats

BACKGROUND

Two-thirds partial hepatectomy (PHx) is an established model for the study of liver regeneration after resection. This process is accompanied by oxidative stress.

AIMS

In our study, we tested the effect of epigallocatechin gallate (EGCG), a green tea antioxidant, on the early phase of liver regeneration after PHx.

METHODS

Male Wistar rats were divided into five groups: (I) laparotomy + water for intraperitoneal injections, (II) laparotomy + EGCG 50 mg/kg body weight, (III) PHx + water for injections, (IV) PHx + EGCG 20 mg/kg and (V) PHx + EGCG 50 mg/kg, for 3 consecutive days. The rats were killed 24 h after surgery. Biochemical analysis of rat sera was performed. Histological samples were stained with hematoxylin & eosin and bromodeoxyuridine (BrdU). In hepatectomized rats, we also measured plasma malondialdehyde, tissue malondialdehyde, glutathione and cytokines levels, the activity of caspases 3/7, expression of Nqo-1 and HO-1 genes at the mRNA level, and expression of p21, p-p27 and p-p53 genes at the protein level.

RESULTS

We observed lower accumulation of BrdU in group V when compared to groups III and IV. The activity of caspases 3/7 and expression of p-p53 were lower in group V than in groups III and IV. Tissue levels of IL-6 were lower in group V when compared to group III. Significant differences were not noted in other parameters.

CONCLUSIONS

Administration of EGCG did not stimulate early phase liver regeneration in rats after PHx. There was even lower DNA synthesis in the group treated with a high dose of EGCG.

Control of growth during regeneration

Regeneration is a process by which organisms replace damaged or amputated organs to restore normal body parts. Regeneration of many tissues or organs requires proliferation of stem cells or stem cell-like blastema cells. This regenerative growth is often initiated by cell death pathways induced by damage. The executors of regenerative growth are a group of growth-promoting signaling pathways, including JAK/STAT, EGFR, Hippo/YAP, and Wnt/β-catenin. These pathways are also essential to developmental growth, but in regeneration, they are activated in distinct ways and often at higher strengths, under the regulation by certain stress-responsive signaling pathways, including JNK signaling. Growth suppressors are important in termination of regeneration to prevent unlimited growth and also contribute to the loss of regenerative capacity in nonregenerative organs. Here, we review cellular and molecular growth regulation mechanisms induced by organ damage in several models with different regenerative capacities.

Differential Expression of Insulin-Like Growth Factor-I Receptor on Human Bone Marrow-Derived Mesenchymal Stem Cells Induced by Tumor Necrosis Factor-α

BACKGROUND

Cell-based therapy has been implicated in the treatment of liver diseases. Mesenchymal stem cells from various sources such as bone marrow are available. These cells are one of the major candidates in cell therapy. The production of insulin-like growth factor-I increases in the regenerating organ. The insulin-like growth factor-I in liver regeneration is effective after binding to insulin-like growth factor-I receptor.

OBJECTIVE

To test our hypothesis that tumor necrosis factor-α can stimulate mesenchymal stem cells to express insulin-like growth factor-I receptor.

METHODS

Bone marrow was aspirated from normal human donor after taking informed consent. Cells were isolated and cultured. Identification of cells was done by flowcytometry and functional tests. The fourth passage cells were treated with tumor necrosis factor-α at two doses of 1 and 10 ng/mL, and incubated for 2, 10, 24, and 48 hours. Insulin-like growth factor-I receptor gene expression was studied using real-time polymerase chain reaction.

RESULTS

Flowcytometry showed that the human bone marrow mesenchymal stem cells were positive for CD90 and negative for CD45 and CD80. The insulin-like growth factor-I receptor gene expression was increased in tumor necrosis factor-α treated in comparison with untreated cells.

CONCLUSION

Treatment of human bone marrow-derived mesenchymal stem cells with tumor necrosis factor-α increases gene expression of insulin-like growth factor-I receptor. This finding may be used for increasing the effectiveness of stem cell therapy in those with acute hepatic failure.

Mechanisms of Acute Liver Failure

Acute liver failure (ALF) is characterized by the sudden onset of liver failure in a patient without evidence of chronic liver disease. This definition is important, as it differentiates patients with ALF from patients who suffer from liver failure owing to end-stage chronic liver disease [1].

Delayed liver regeneration after partial hepatectomy in adipose differentiation related protein-null mice

BACKGROUND & AIMS

Adult hepatocytes undergo cell cycle progression and proliferation in response to partial hepatectomy (PH). Transient lipid accumulation within hepatocytes preceding the peak proliferative phase is a characteristic feature of regenerating livers. However, the molecular mediators and mechanisms responsible for lipid accumulation in regenerating livers are not well understood. Adipose differentiation related protein (ADRP; Plin2) regulates hepatic triglyceride storage and Plin2-deficient (Plin2(-/-)) mice have significantly reduced triglyceride (TG) content in the liver. We sought to determine the functional significance of PLIN2 in liver regeneration in response to PH and toxic liver injury and examined whether absence of Plin2 expression modulates hepatocyte proliferation and liver regeneration.

METHODS

We subjected wild-type (WT) and Plin2(-/-) mice to 70% PH or acute carbon tetrachloride (CCL4) treatment and examined the hepatic lipid content, the expression profile of lipid metabolism-related genes, the rate of cellular proliferation and the dynamics of liver regeneration in the treated animals.

RESULTS

In response to PH, Plin2(-/-) mice showed decreased hepatic triglyceride accumulation and delayed cell cycle progression, which was associated with impaired liver regeneration. Fatty acid (FA) synthesis and lipid transfer gene expression profile were comparable between Plin2(-/-) and wild-type mice, while VLDL secretion rate was higher in the Plin2(-/-) mice. Downregulated β-oxidation and reduced cytosolic FA level in Plin2(-/-) mice may have contributed to the attenuation of the liver regeneration capacity in these animals. In parallel experiments, we also observed attenuated hepatic lipid accumulation and proliferation in response to CCl4-mediated acute toxic liver injury in Plin2(-/-) mice.

CONCLUSIONS

We conclude that PLIN2-mediated lipid accumulation and utilization by the liver is important for efficient liver regeneration in response to PH and toxic liver injury.

Principles of liver regeneration and growth homeostasis

Liver regeneration is perhaps the most studied example of compensatory growth aimed to replace loss of tissue in an organ. Hepatocytes, the main functional cells of the liver, manage to proliferate to restore mass and to simultaneously deliver all functions hepatic functions necessary to maintain body homeostasis. They are the first cells to respond to regenerative stimuli triggered by mitogenic growth factor receptors MET (the hepatocyte growth factor receptor] and epidermal growth factor receptor and complemented by auxiliary mitogenic signals induced by other cytokines. Termination of liver regeneration is a complex process affected by integrin mediated signaling and it restores the organ to its original mass as determined by the needs of the body (hepatostat function). When hepatocytes cannot proliferate, progenitor cells derived from the biliary epithelium transdifferentiate to restore the hepatocyte compartment. In a reverse situation, hepatocytes can also transdifferentiate to restore the biliary compartment. Several hormones and xenobiotics alter the hepatostat directly and induce an increase in liver to body weight ratio (augmentative hepatomegaly). The complex challenges of the liver toward body homeostasis are thus always preserved by complex but unfailing responses involving orchestrated signaling and affecting growth and differentiation of all hepatic cell types.

Loss of caspase-8 in hepatocytes accelerates the onset of liver regeneration in mice through premature nuclear factor kappa B activation

The cytokine tumor necrosis factor alpha (TNF-α; TNF) plays a critical role early in liver regeneration following partial hepatectomy (PH). TNF stimulates at least three different pathways leading to nuclear factor kappa B (NF-κB) activation, apoptosis signaling by way of caspase-8 (Casp8), and activation of cJun N-terminal kinases (JNK). The present study aimed to better define the role of Casp8 during liver regeneration. We performed PH in mice lacking Casp8 specifically in hepatocytes (Casp8(Δhepa) ) and determined their liver regeneration capacity by measuring liver mass restoration and kinetics of cell cycle progression. Casp8(Δhepa) mice showed an accelerated onset of DNA synthesis after PH, delayed hepatocyte mitosis, but overall normal liver mass restoration. Analysis of immediate TNF-dependent signaling pathways revealed that loss of Casp8 prevents proteolytic cleavage of the receptor-interacting protein 1 (RIP1) in hepatocytes and subsequently triggers premature activation of NF-κB and JNK/cJun related signals. In order to define the role of NF-κB in this setting we blocked NF-κB activation in Casp8(Δhepa) mice by concomitant inactivation of the NF-κB essential modulator (NEMO) in hepatocytes. Lack of NEMO largely reverted aberrant DNA synthesis in Casp8(Δhepa) mice but resulted in incomplete termination of the regeneration process and hepatomegaly.

CONCLUSION

Casp8 comprises a nonapoptotic function during liver regeneration by balancing RIP1, NF-κB, and JNK activation. While loss of Casp8 triggers NF-κB activation and thus improves liver regeneration, combined loss of Casp8 and NEMO impairs a controlled regenerative response and drives hepatomegaly.

Impaired liver regeneration in Ldlr-/- mice is associated with an altered hepatic profile of cytokines, growth factors, and lipids

BACKGROUND & AIMS

It is widely recognized that in the early stages of liver regeneration after partial hepatectomy, the hepatocytes accumulate a significant amount of lipids. The functional meaning of this transient steatosis and its effect on hepatocellular proliferation are not well defined. In addition, the basic mechanisms of this lipid accumulation are not well understood although some studies suggest the participation of the Low Density Lipoprotein Receptor (Ldlr).

METHODS

To address these questions, we studied the process of liver regeneration in Ldlr null mice and wild type mice following partial hepatectomy.

RESULTS

Ldlr deficiency was associated with a significant decrease in serum albumin concentration, during early stages of liver regeneration, and a delayed hepatic regeneration. Remnant livers of Ldlr(-)(/)(-) showed a time-shifted expression of interleukin-6 (IL6) and a defective activation of tumor necrosis factor-α (TNFα) and hepatocyte growth factor (HGF) expression in early phases of liver regeneration. Unexpectedly, Ldlr(-)(/)(-) showed no significant differences in the content of lipid droplets after partial hepatectomy compared to wild type mice. However, lipidomic analysis of the regenerating liver from Ldlr(-)(/)(-) revealed a lipid profile compatible with liver quiescence: high content of cholesterol esters and ceramide, and low levels of phosphatidylcholine.

CONCLUSIONS

Ldlr deficiency is associated with significant changes in the hepatic lipidome that affect cytokine-growth factor signaling and impair liver regeneration. These results suggest that the analysis of the hepatic lipidome may help predict the success of liver regeneration in the clinical environment, specifically in the context of pre-existing liver steatosis.

Tumor necrosis factor-α promotes bile ductular transdifferentiation of mature rat hepatocytes in vitro

We previously showed that mature hepatocytes could transdifferentiate into bile ductular cells when placed in a collagen-rich microenvironment. To explore the mechanism of transdifferentiation, we examined whether inflammatory cytokines affected the phenotype of hepatocytes in a three-dimensional culture system. Spheroidal aggregates of rat hepatocytes were embedded within a type I collagen gel matrix and cultured in the presence of various cytokines. In the control, hepatocytes gradually lost expression of albumin, tyrosine aminotransferase, and hepatocyte nuclear factor (HNF)-4α, while aberrantly expressed bile ductular markers, including cytokeratin 19 (CK 19) and spermatogenic immunoglobulin superfamily (SgIGSF). Among the cytokines examined, tumor necrosis factor (TNF)-α inhibited expression of albumin and HNF-4α, both at mRNA and protein levels. After culturing for 2 weeks with TNF-α, hepatocytic spheroids were transformed into extensively branching tubular structures composed of CK 19- and SgIGSF-positive small cuboidal cells. These cells responded to secretin with an increase in secretion and expressed functional bile duct markers. TNF-α also induced the phosphorylation of Jun N-terminal kinase (JNK) and c-Jun, and the morphogenesis was inhibited by SP600125, a specific JNK inhibitor. Furthermore, in chronic rat liver injury induced by CCl(4) , ductular reaction in the centrilobular area demonstrated strong nuclear staining of phosphorylated c-Jun. Our results demonstrate that TNF-α promotes the ductular transdifferentiation of hepatocytes and suggest a role of TNF-α in the pathogenesis of ductular reaction.

mTOR signaling in liver regeneration: Rapamycin combined with growth factor treatment

AIM: To investigate the effects of mammalian target of rapamycin (mTOR) inhibition on liver regeneration and autophagy in a surgical resection model.

METHODS: C57BL/6 mice were subjected to a 70% partial hepatectomy (PH) and treated intraperitoneally every 24 h with a combination of the mTOR inhibitor rapamycin (2.5 mg/kg per day) and the steroid dexamethasone (2.0 mg/kg per day) in phosphate buffered saline (PBS) or with PBS alone as vehicle control. In the immunosuppressant group, part of the group was treated subcutaneously 4 h prior to and 24 h after PH with a combination of human recombinant interleukin 6 (IL-6; 500 μg/kg per day) and hepatocyte growth factor (HGF; 100 μg/kg per day) in PBS. Animals were sacrificed 2, 3 or 5 d after PH and liver tissue and blood were collected for further analysis. Immunohistochemical staining for 5-Bromo-2’-deoxyuridine (BrdU) was used to quantify hepatocyte proliferation. Western blotting was used to detect hepatic microtubule-associated protein 1 light chain 3 (LC3)-II protein expression as a marker for autophagy. Hepatic gene expression levels of proliferation-, inflammation- and angiogenesis-related genes were examined by real-time reverse transcription-polymerase chain reaction and serum bilirubin and transaminase levels were analyzed at the clinical chemical core facility of the Erasmus MC-University Medical Center.

RESULTS: mTOR inhibition significantly suppressed regeneration, shown by decreased hepatocyte proliferation (2% vs 12% BrdU positive hepatocyte nuclei at day 2, P < 0.01; 0.8% vs 1.4% at day 5, P = 0.02) and liver weight reconstitution (63% vs 76% of initial total liver weight at day 3, P = 0.04), and furthermore increased serum transaminase levels (aspartate aminotransferase 641 U/L vs 185 U/L at day 2, P = 0.02). Expression of the autophagy marker LC3-II, which was reduced during normal liver regeneration, increased after mTOR inhibition (46% increase at day 2, P = 0.04). Hepatic gene expression showed an increased inflammation-related response [tumor necrosis factor (TNF)-α 3.2-fold upregulation at day 2, P = 0.03; IL-1Ra 6.0-fold upregulation at day 2 and 42.3-fold upregulation at day 5, P < 0.01] and a reduced expression of cell cycle progression and angiogenesis-related factors (HGF 40% reduction at day 2; vascular endothelial growth factor receptor 2 50% reduction at days 2 and 5; angiopoietin 1 60% reduction at day 2, all P≤ 0.01). Treatment with the regeneration stimulating cytokine IL-6 and growth factor HGF could overcome the inhibitory effect on liver weight (75% of initial total liver weight at day 3, P = 0.02 vs immunosuppression alone and P = 0.90 vs controls) and partially reversed gene expression changes caused by rapamycin (TNF-α and IL-1Ra levels at day 2 were restored to control levels). However, no significant changes in hepatocyte proliferation, serum injury markers or autophagy were found.

CONCLUSION: mTOR inhibition severely impairs liver regeneration and increases autophagy after PH. These effects are partly reversed by stimulation of the IL-6 and HGF pathways.

TNFR1 determines progression of chronic liver injury in the IKKγ/Nemo genetic model

Death receptor-mediated hepatocyte apoptosis is implicated in a wide range of liver diseases including viral and alcoholic hepatitis, ischemia/reperfusion injury, fulminant hepatic failure, cholestatic liver injury, as well as cancer. Deletion of NF-κB essential modulator in hepatocytes (IKKγ/Nemo) causes spontaneous progression of TNF-mediated chronic hepatitis to hepatocellular carcinoma (HCC). Thus, we analyzed the role of death receptors including TNFR1 and TRAIL in the regulation of cell death and the progression of liver injury in IKKγ/Nemo-deleted livers. We crossed hepatocyte-specific IKKγ/Nemo knockout mice (Nemo(Δhepa)) with constitutive TNFR1(-/-) and TRAIL(-/-) mice. Deletion of TNFR1, but not TRAIL, decreased apoptotic cell death, compensatory proliferation, liver fibrogenesis, infiltration of immune cells as well as pro-inflammatory cytokines, and indicators of tumor growth during the progression of chronic liver injury. These events were associated with diminished JNK activation. In contrast, deletion of TNFR1 in bone-marrow-derived cells promoted chronic liver injury. Our data demonstrate that TNF- and not TRAIL signaling determines the progression of IKKγ/Nemo-dependent chronic hepatitis. Additionally, we show that TNFR1 in hepatocytes and immune cells have different roles in chronic liver injury-a finding that has direct implications for treating chronic liver disease.

Construction and identification of recombinant replication-defective adenovirus vector Αd/CMV/V5-DEST-TNFα-scFv

AIM: To construct a recombinant replication-defective adenovirus vector carrying TNFα-scFv and to obtain high-purity virus solution by viral packaging, purification and titration.

METHODS: The TNFα-scFv gene was amplified from the PUC57-Αmp vector and cloned into the shuttle plasmid pDONR221. The resulting pDONR221-TNFα-scFv was identified by DNA sequencing and then co-transfected into bacteria carrying the adenoviral backbone plasmid pΑd-CMV-V5-DEST to generate an adenoviral plasmid carrying TNFα-scFv (pΑd/CMV/V5-DEST-TNFα-ScFv) by homologous recombination in bacteria. After the pΑd/CMV/V5-DEST-TNFα-ScFv vector was transfected into 293 cells, the transfected 293 cells were infected with adenoviruses. The expression of TNFα-ScFv was detected by cytopathic effect and Western blot.

RESULTS: PCR amplification, restriction analysis and DNA sequencing verified that both the recombinant shuttle plasmid pDONR221-TNFα -scFv and the recombinant adenovirus vector pΑd/CMV/V5-DEST-TNFα-scFv were correctly constructed. After amplification and purification, the titer of recombinant adenovirus was 2.5×10¹¹ TCID 50/mL after proliferation in 293 cells. Western blot analysis demonstrated that TNFα-scFv was expressed efficiently in 293 cells after infection.

CONCLUSION: The recombinant adenovirus vector Αd/CMV/V5-DEST-TNFα-scFv has been successfully constructed, which lays a foundation for further study of gene function and therapy.

Hepatitis B virus HBx protein impairs liver regeneration through enhanced expression of IL-6 in transgenic mice

BACKGROUND & AIMS

Conflicting results have been reported regarding the impact of hepatitis B virus X protein (HBx) expression on liver regeneration triggered by partial hepatectomy (PH). In the present report we investigated the mechanisms by which HBx protein alters hepatocyte proliferation after PH.

METHODS

PH was performed on a transgenic mouse model in which HBx expression is under the control of viral regulatory elements and liver regeneration was monitored. LPS, IL-6 neutralizing antibody, and SB203580 were injected after PH to evaluate IL-6 participation during liver regeneration.

RESULTS

Cell cycle progression of hepatocytes was delayed in HBx transgenic mice compared to WT animals. Moreover, HBx induced higher secretion of IL-6 soon after PH. Upregulation of IL-6 was associated with an elevation of STAT3 phosphorylation, SOCS3 transcript accumulation and a decrease in ERK1/2 phosphorylation in the livers of HBx transgenic mice. The involvement of IL-6 overexpression in cell cycle deregulation was confirmed by the inhibition of liver regeneration in control mice after the upregulation of IL-6 expression using LPS. In addition, IL-6 neutralization with antibodies was able to restore liver regeneration in HBx mice. Finally, the direct role of p38 in IL-6 secretion after PH was demonstrated using SB203580, a pharmacological inhibitor.

CONCLUSIONS

HBx is able to induce delayed hepatocyte proliferation after PH, and HBx-induced IL-6 overexpression is involved in delayed liver regeneration. By modulating IL-6 expression during liver proliferation induced by stimulation of the cellular microenvironment, HBx may participate in cell cycle deregulation and progression of liver disease.

A disintegrin and metalloproteinase 17 regulates TNF and TNFR1 levels in inflammation and liver regeneration in mice

A disintegrin and metalloproteinase 17 (ADAM17), or tumor necrosis factor (TNF)-α-converting enzyme, is a key metalloproteinase and physiological convertase for a number of putative targets that play critical roles in cytokine and growth factor signaling. These interdependent pathways are essential components of the signaling network that links liver function with the compensatory growth that occurs during liver regeneration following 2/3 partial hepatectomy (PH) or chemically induced hepatotoxicity. Despite identification of many soluble factors needed for efficient liver regeneration, very little is known about how such ligands are regulated in the liver. To directly study the role of ADAM17 in the liver, we employed two cell-specific ADAM17 knockout (KO) mouse models. Using lipopolysaccharide (LPS) as a robust stimulus for TNF release, we found attenuated levels of circulating TNF in myeloid-specific ADAM17 KO mice (ADAM17 m-KO) and, unexpectedly, in mice with hepatocyte-specific ADAM17 deletion (ADAM17 h-KO), indicating that ADAM17 expression in both cell types plays a role in TNF shedding. After 2/3 PH, induction of TNF, TNFR1, and amphiregulin (AR) was significantly attenuated in ADAM17 h-KO mice, implicating ADAM17 as the primary sheddase for these factors in the liver. Surprisingly, the extent and timing of hepatocyte proliferation were not affected after PH or carbon tetrachloride injection in ADAM17 h-KO or ADAM17 m-KO mice. We conclude that ADAM17 regulates TNF, TNFR1, and AR in the liver, and its expression in both hepatocytes and myeloid cells is important for TNF regulation after LPS injury or 2/3 PH, but is not required for liver regeneration.

Vitamin D3 up-regulated protein 1 controls the priming phase of liver regeneration

Vitamin D3 up-regulated protein 1 (VDUP1) is a potent growth suppressor that inhibits tumor cell proliferation and cell cycle progression when overexpressed. In a previous study, we showed that VDUP1 knockout (KO) mice exhibited accelerated liver regeneration because such animals could effectively control the expression of cell cycle regulators that drive the G1-to-S phase progression. In the present study, we further investigated the role played by VDUP1 in initial priming of liver regeneration. To accomplish this, VDUP1 KO and wild-type (WT) mice were subjected to 70% partial hepatectomy (PH) and sacrificed at different times after surgery. The hepatic levels of TNF-α and IL-6 increased after PH, but there were no significant differences between VDUP1 KO and WT mice. Nuclear factor-κB (NF-κB), c-Jun-N-terminal kinase (JNK), and signal transducer and activator of transcription 3 (STAT-3) were activated much earlier and to a greater extent in VDUP1 KO mice after PH. A single injection of TNF-α or IL-6 caused rapid activation of JNK and STAT-3 expression in both mice, but the responses were stronger and more sustained in VDUP1 KO mice. In conclusion, our findings provide evidence that VDUP1 plays a role in initiation of liver regeneration.

Tumor necrosis factor-α promotes cholestasis-induced liver fibrosis in the mouse through tissue inhibitor of metalloproteinase-1 production in hepatic stellate cells

Tumor necrosis factor (TNF)-α, which is a mediator of hepatotoxicity, has been implicated in liver fibrosis. However, the roles of TNF-α on hepatic stellate cell (HSC) activation and liver fibrosis are complicated and remain controversial. To explore this issue, the role of TNF-α in cholestasis-induced liver fibrosis was examined by comparing between TNF-α(-/-) mice and TNF-α(+/+) mice after bile duct ligation (BDL). Serum TNF-α levels in mice were increased by common BDL combined with cystic duct ligation (CBDL+CDL). TNF-α deficiency reduced liver fibrosis without affecting liver injury, inflammatory cell infiltration, and liver regeneration after CBDL+CDL. Increased expression levels of collagen α1(I) mRNA, transforming growth factor (TGF)-β mRNA, and α-smooth muscle actin (αSMA) protein by CBDL+CDL in the livers of TNF-α(-/-) mice were comparable to those in TNF-α(+/+) mice. Exogenous administration of TNF-α decreased collagen α1(I) mRNA expression in isolated rat HSCs. These results suggest that the reduced fibrosis in TNF-α(-/-) mice is regulated in post-transcriptional level. Tissue inhibitor of metalloproteinase (TIMP)-1 plays a crucial role in the pathogenesis of liver fibrosis. TIMP-1 expression in HSCs in the liver was increased by CBDL+CDL, and the induction was lower in TNF-α(-/-) mice than in TNF-α(+/+) mice. Fibrosis in the lobe of TIMP-1(-/-) mice with partial BDL was also reduced. These findings indicate that TNF-α produced by cholestasis can promote liver fibrosis via TIMP-1 production from HSCs. Thus, targeting TNF-α and TIMP-1 may become a new therapeutic strategy for treating liver fibrosis in cholestatic liver injury.

A20 promotes liver regeneration by decreasing SOCS3 expression to enhance IL-6/STAT3 proliferative signals

Liver regeneration is of major clinical importance in the setting of liver injury, resection, and transplantation. A20, a potent antiinflammatory and nuclear factor kappa B (NF-κB) inhibitory protein, has established pro-proliferative properties in hepatocytes, in part through decreasing expression of the cyclin dependent kinase inhibitor, p21. Both C-terminal (7-zinc fingers; 7Zn) and N-terminal (Nter) domains of A20 were required to decrease p21 and inhibit NF-κB. However, both independently increased hepatocyte proliferation, suggesting that additional mechanisms contributed to the pro-proliferative function of A20 in hepatocytes. We ascribed one of A20's pro-proliferative mechanisms to increased and sustained interleukin (IL)-6-induced signal transducer and activator of transcription 3 (STAT3) phosphorylation, as a result of decreased hepatocyte expression of the negative regulator of IL-6 signaling, suppressor of cytokine signaling 3 (SOCS3). This novel A20 function segregates with its 7Zn not Nter domain. Conversely, total and partial loss of A20 in hepatocytes increased SOCS3 expression, hampering IL-6-induced STAT3 phosphorylation. Following liver resection in mice pro-proliferative targets downstream of IL-6/STAT3 signaling were increased by A20 overexpression and decreased by A20 knockdown. In contrast, IL-6/STAT3 proinflammatory targets were increased in A20-deficient livers, and decreased or unchanged in A20 overexpressing livers. Upstream of SOCS3, levels of its microRNA regulator miR203 were significantly decreased in A20-deficient livers.

CONCLUSION

A20 enhances IL-6/STAT3 pro-proliferative signals in hepatocytes by down-regulating SOCS3, likely through a miR203-dependent manner. This finding together with A20 reducing the levels of the potent cell cycle brake p21 establishes its pro-proliferative properties in hepatocytes and prompts the pursuit of A20-based therapies to promote liver regeneration and repair.

Nuclear receptors in regenerating liver and hepatocellular carcinoma

A comprehensive understanding of the pathways underlying hepatocyte turnover and liver regeneration is essential for the development of innovative and effective therapies in the management of chronic liver disease, and the prevention of hepatocellular carcinoma (HCC) in cirrhosis. Nuclear receptors (NRs) are master transcriptional regulators of liver development, differentiation and function. NRs have been implicated in the modulation of hepatocyte priming and proliferation in regenerating liver, chronic hepatitis and HCC development. In this review, we focus on NRs and their pathways regulating hepatocyte proliferation and liver regeneration, with a perspective view on NRs as candidate biomarkers and novel pharmacological targets in the management of liver disease and HCC.

Gene expression profiling of sense and antisense transcripts in liver regeneration by microarray analysis

Liver regeneration is a hyperplastic phenomenon induced by partial hepatectomy (PH) or hepatic damage. A large number of genes have been indicated to be involved in the process of liver regeneration. It was recently reported that natural antisense transcripts are involved in the regulation of gene expression. However, no antisense transcript expressions in liver regeneration have been reported thus far. Therefore, the present study aimed to comprehensively identify up- or downregulated sense and antisense transcripts in liver regeneration using PH mice and a sense/antisense custom-microarray. The results showed that 97 genes were upregulated and 7 genes were downregulated for sense transcripts, whereas 15 genes were upregulated and 2 genes were downregulated for antisense transcripts in regenerating livers as compared to normal livers (P<0.05 and fold change >2.0). Sense and antisense transcripts of the genes, Apoa4, Hp, Fgb and Fgg, exhibited concordant upregulation during the course of liver regeneration. Apoa4, Hp and Fgb transcripts were further investigated by strand-specific reverse transcription-quantitative polymerase chain reaction (RT-qPCR), revealing results consistent with those of the microarray. In conclusion, the up- or downregulated sense and antisense transcripts identified in the present study are suggested to be involved in liver regeneration.

Priming of hepatocytes enhances in vivo liver transduction with lentiviral vectors in adult mice

Lentiviral vectors are promising tools for liver disease gene therapy, because they can achieve protracted expression of transgenes in hepatocytes. However, the question as to whether cell division is required for optimal hepatocyte transduction has still not been completely answered. Liver gene-transfer efficiency after in vivo administration of recombinant lentiviral vectors carrying a green fluorescent protein reporter gene under the control of a liver-specific promoter in mice that were either hepatectomized or treated with cholic acid or phenobarbital was compared. Phenobarbital is known as a weak inducer of hepatocyte proliferation, whereas cholic acid has no direct effect on the cell cycle. This study shows that cholic acid is able to prime hepatocytes without mitosis induction. Both phenobarbital and cholic acid significantly increased hepatocyte transduction six- to ninefold, although cholic acid did not modify the mitotic index or cell-cycle entry. However, the effect of either compound was weaker than that observed after partial hepatectomy. In no cases was there a correlation between the expression of cell-cycle marker and transduction efficiency. We conclude that priming of hepatocytes should be considered a clinically applicable strategy to enhance in vivo liver gene therapy with lentiviral vectors.

Toll-like receptors in liver disease

Activation of inflammatory signaling pathways is of central importance in the pathogenesis of alcoholic liver disease (ALD) and nonalcoholic steatohepatitis (NASH). Recent studies demonstrated that Toll-like receptors, the sensors of microbial and endogenous danger signals, are expressed and activated in innate immune cells as well as in parenchymal cells in the liver and thereby contribute to ALD and NASH. In this review, we emphasize the importance of gut-derived endotoxin and its recognition by TLR4 in the liver. The significance of TLR-induced intracellular signaling pathways and cytokine production as well as the contribution of individual cell types to the inflammation is evaluated. The contribution of TLR signaling to the induction of liver fibrosis and to the progression of liver pathology mediated by viral pathogens is reviewed in the context of ALD and NASH.

Steatosis does not impair liver regeneration after partial hepatectomy

Hepatic steatosis is a key feature of non-alcoholic fatty liver disease (NAFLD). While storage of lipid droplet-bound triglycerides in simple steatosis is physiologically inert, non-alcoholic steatohepatitis (NASH) is associated with hepatocyte damage and apoptosis. Mitochondrial oxidation of free fatty acids (FFA), derived from lipid droplets and hepatocellular uptake, is a rapid and effective way of energy supply for proliferating cells and FFA esterification provides substrates for lipid synthesis and cell proliferation. Thus, we investigated whether simple steatosis induced by western diet (WD) improves liver regeneration after partial hepatectomy (PHx). WD feeding for 6 weeks caused simple steatosis with hepatic lipid droplet and triglyceride accumulation accompanied by induction of fatty acid transport proteins (FATP), death receptors (DR), pro- and anti-apoptotic genes, hepatocyte growth factor (Hgf) as well as increased serum leptin levels in a mouse model. After PHx, liver cell proliferation was higher in WD-fed mice and associated with FATP and Hgf induction. In addition, Erk1/2 (extracellular-related MAP kinase 1/2) dephosphorylation observed in standard diet (SD) mice was reduced in WD animals. PHx in steatotic livers did not affect hepatocyte apoptosis, despite DR upregulation. WD-induced steatosis enhances liver cell proliferation, which is accompanied by increased Hgf and leptin signaling as well as Erk1/2 phosphorylation. Induction of mild steatosis may therefore be beneficial for surgical outcome of hepatectomies.

A Systems Biology Study on NFκB Signaling in Primary Mouse Hepatocytes

The cytokine tumor necrosis factor-alpha (TNFα) is one of the key factors during the priming phase of liver regeneration as well as in hepatocarcinogenesis. TNFα activates the nuclear factor κ-light-chain-enhancer of activated B cells (NFκB) signaling pathway and contributes to the conversion of quiescent hepatocytes to activated hepatocytes that are able to proliferate in response to growth factor stimulation. Different mathematical models have been previously established for TNFα/NFκB signaling in the context of tumor cells. Combining these mathematical models with time-resolved measurements of expression and phosphorylation of TNFα/NFκB pathway constituents in primary mouse hepatocytes revealed that an additional phosphorylation step of the NFκB isoform p65 has to be considered in the mathematical model in order to sufficiently describe the dynamics of pathway activation in the primary cells. Also, we addressed the role of basal protein turnover by experimentally measuring the degradation rate of pivotal players in the absence of TNFα and including this information in the model. To elucidate the impact of variations in the protein degradation rates on TNFα/NFκB signaling on the overall dynamic behavior we used global sensitivity analysis that accounts for parameter uncertainties and showed that degradation and translation of p65 had a major impact on the amplitude and the integral of p65 phosphorylation. Finally, our mathematical model of TNFα/NFκB signaling was able to predict the time-course of the complex formation of p65 and of the inhibitor of NFκB (IκB) in primary mouse hepatocytes, which was experimentally verified. Hence, we here present a mathematical model for TNFα/NFκB signaling in primary mouse hepatocytes that provides an important basis to quantitatively disentangle the complex interplay of multiple factors in liver regeneration and tumorigenesis.

IL-22 and IL-17 mRNA expression in PBMCs from patients with chronic hepatitis B virus infection

AIM: To detect the expression of IL-22 and IL-17 mRNAs in peripheral blood mononuclear cells (PBMCs) from patients with chronic hepatitis B (CHB) infection and to analyze their significance in the pathogenesis of CHB.

METHODS: Thirty-three patients with moderate CHB, 21 patients with severe CHB, 16 patients with liver failure, and 16 cirrhotic patients were enrolled in the study. Ten healthy volunteers were used as controls. RT-PCR method was used to detect the expression of IL-22 and IL-17 mRNAs in PBMCs from these subjects.

RESULTS: IL-22 expression in PBMCs from patients with moderate CHB, severe CHB, or cirrhosis was comparable, but all was higher than that from controls (P = 0.000). IL-22 expression in PBMCs from patients with liver failure was significantly lower than that from other three groups of patients (P = 0.000). IL-17 expression in PBMCs from four groups of patients was higher than that from controls (P = 0.000). IL-17 expression in PBMCs from patients with liver failure was slightly lower than that from other three groups of patients, although no statistical difference was found.

CONCLUSION: Down-regulation of IL-22 is unfavorable to repair of hepatic cells after liver injury. Up-regulation of IL-22 expression may be important in alleviating liver damage. IL-17 levels in patients infected with HBV are increased significantly. IL-17 may participate in the inflammatory process in chronic HBV infection and play an important role in development of liver fibrosis.

Human platelets promote liver regeneration with Kupffer cells in SCID mice

BACKGROUND

Platelets contain several growth factors, including vascular endothelial growth factor (VEGF) and insulin-like growth factor. We examined the role of human platelets in liver regeneration with a focus on Kupffer cells (KCs).

MATERIALS AND METHODS

Severe combined immunodeficiency mice were subjected to 70% hepatectomy and phosphate-buffered saline administration (PBS); 70% hepatectomy and human platelet transfusion (hPLT); 70% hepatectomy, KC depletion, and PBS administration (KD + PBS); 70% hepatectomy, KC depletion, and human platelet transfusion (KD + hPLT); or a sham operation and human platelet transfusion (sham). The groups were evaluated for liver regeneration, accumulation and activation of human platelets in the liver, and/or co-localization of platelets and KCs.

RESULTS

The liver-to-body weight ratio was significantly higher 48 h post-transfusion in the hPLT group compared with the PBS, KD + PBS, and KD + hPLT groups. Human VEGF concentrations were higher in liver tissues from the hPLT group, whereas VEGF was not detected in the other groups. Hepatic levels of KC-derived cytokines were elevated in the hPLT group compared with the PBS group. Molecules in signaling cascades downstream of these cytokines were phosphorylated earlier and more robustly in the hPLT group than in the PBS group. Activated human platelets accumulated in livers in the hPLT group, whereas fewer platelets accumulated and many were not activated in the sham and KD + hPLT groups. In the hPLT group, most human platelets were attached to KCs.

CONCLUSIONS

Human platelet transfusion promoted liver regeneration in severe combined immunodeficiency mice. Together, human platelets and KCs resulted in growth factor release and enhanced liver regeneration.

Novel therapy for liver regeneration by increasing the number of platelets

Platelets are the smallest blood constitutes which contain three types of granules; alpha granules, dense granules, and lysosomal granules. Each granule contains various biophysiological substances such as growth factors, cytokines, etc. Platelets have been conventionally viewed as a trigger of inflammatory responses and injury in the liver. Some studies revealed that platelets have strong effects on promoting liver regeneration. This review presents experimental evidence of platelets in accelerating liver regeneration and describes three different mechanisms involved; (1) the direct effect on hepatocytes, where platelets translocate to the space of Disse and release growth factors through direct contact with hepatocytes, (2) the cooperative effect with liver sinusoidal endothelial cells, where the dense concentration of sphingosine-1-phosphate in platelets induces excretion of interleukin-6 from liver sinusoidal endothelial cells, and (3) the collaborative effect with Kupffer cells, where the functions of Kupffer cells are enhanced by platelets.

TNF-dependent signaling pathways in liver cancer: promising targets for therapeutic strategies?

Liver cancer represents a growing health burden worldwide, and treatment options are still limited. Hepatocellular carcinoma (HCC), the most frequent primary hepatic malignancy, arises in most instances in chronically inflamed and fibrotic livers. However, current systemic molecular therapies against HCC are mainly focusing on tyrosine kinases involved in angiogenic and oncogenic signaling pathways, whereas the knowledge on the unique association between inflammation and carcinogenesis in the liver has not yet translated into preventive or therapeutic concepts against HCC. Tumor necrosis factor (TNF) is a cytokine derived from monocytes and various other immunological and parenchymal cells. Upon binding to its receptors, TNF activates different signaling cascades including the pro-apoptotic caspase cascade as well as inflammatory and stress-related pathways such as the NF-ĸB, p38MAPK, and Jun-(N)-terminal kinase (JNK) pathways. The role of TNF in cancer is controversial, since it was attributed both pro- and anti-carcinogenic functions. Its potential function in hepatocarcinogenesis has lately been investigated using genetically modified mouse models. These studies have highlighted that the various TNF-dependent signaling pathways withhold distinct functions in hepatocarcinogenesis, which are in part controversial and strongly depend on the experimental model system. Nevertheless, careful interpretation of findings in mouse models and critical consideration of their limitations might result in a new understanding of this complex pathway in hepatocarcinogenesis and thus might help identify the most promising targets in the TNF pathway and the appropriate clinical settings for future chemo-preventive or therapeutic strategies against HCC.

The NF-κB subunit RelA/p65 is dispensable for successful liver regeneration after partial hepatectomy in mice

BACKGROUND

The transcription factor NF-κB consisting of the subunits RelA/p65 and p50 is known to be quickly activated after partial hepatectomy (PH), the functional relevance of which is still a matter of debate. Current concepts suggest that activation of NF-κB is especially critical in non-parenchymal cells to produce cytokines (TNF, IL-6) to adequately prime hepatocytes to proliferate after PH, while NF-κB within hepatocytes mainly bears cytoprotective functions.

METHODS

To study the role of the NF-κB pathway in different liver cell compartments, we generated conditional knockout mice in which the transactivating NF-κB subunit RelA/p65 can be inactivated specifically in hepatocytes (Rela(F/F)AlbCre) or both in hepatocytes plus non-parenchymal cells including Kupffer cells (Rela(F/F)MxCre). 2/3 and 80% PH were performed in controls (Rela(F/F)) and conditional knockout mice (Rela(F/F)AlbCre and Rela(F/F)MxCre) and analyzed for regeneration.

RESULTS

Hepatocyte-specific deletion of RelA/p65 in Rela(F/F)AlbCre mice resulted in an accelerated cell cycle progression without altering liver mass regeneration after 2/3 PH. Surprisingly, hepatocyte apoptosis or liver damage were not enhanced in Rela(F/F)AlbCre mice, even when performing 80% PH. The additional inactivation of RelA/p65 in non-parenchymal cells in Rela(F/F)MxCre mice reversed the small proliferative advantage observed after hepatocyte-specific deletion of RelA/p65 so that Rela(F/F)MxCre mice displayed normal cell cycle progression, DNA-synthesis and liver mass regeneration.

CONCLUSION

The NF-κB subunit RelA/p65 fulfills opposite functions in different liver cell compartments in liver regeneration after PH. However, the effects observed after conditional deletion of RelA/p65 are small and do not alter liver mass regeneration after PH. We therefore do not consider RelA/p65-containing canonical NF-κB signalling to be essential for successful liver regeneration after PH.

S-adenosylmethionine in liver health, injury, and cancer

S-adenosylmethionine (AdoMet, also known as SAM and SAMe) is the principal biological methyl donor synthesized in all mammalian cells but most abundantly in the liver. Biosynthesis of AdoMet requires the enzyme methionine adenosyltransferase (MAT). In mammals, two genes, MAT1A that is largely expressed by normal liver and MAT2A that is expressed by all extrahepatic tissues, encode MAT. Patients with chronic liver disease have reduced MAT activity and AdoMet levels. Mice lacking Mat1a have reduced hepatic AdoMet levels and develop oxidative stress, steatohepatitis, and hepatocellular carcinoma (HCC). In these mice, several signaling pathways are abnormal that can contribute to HCC formation. However, injury and HCC also occur if hepatic AdoMet level is excessive chronically. This can result from inactive mutation of the enzyme glycine N-methyltransferase (GNMT). Children with GNMT mutation have elevated liver transaminases, and Gnmt knockout mice develop liver injury, fibrosis, and HCC. Thus a normal hepatic AdoMet level is necessary to maintain liver health and prevent injury and HCC. AdoMet is effective in cholestasis of pregnancy, and its role in other human liver diseases remains to be better defined. In experimental models, it is effective as a chemopreventive agent in HCC and perhaps other forms of cancer as well.

Cell death biomarkers as early predictors for hepatic dysfunction in patients after orthotopic liver transplantation

BACKGROUND

Valid prognostic factors for early identification of a complicated course after orthotopic liver transplantation from deceased donors are rare. The aim of this study was to investigate the prognostic value of different cell death biomarkers and inflammatory markers in patients after orthotopic liver transplantation from deceased donors.

METHODS

In total, 100 patients were evaluated for short-term complications within 10 days after orthotopic liver transplantation from deceased donors. Blood samples were collected before surgery, immediately after the end of the surgical procedure, and 1 day and 3, 5, and 7 days later. Plasma levels of total keratin 18, keratin 18 fragments, interleukin 6, tumor necrosis factor α, and soluble intercellular adhesion molecule 1 were measured.

RESULTS

Total keratin 18 was demonstrated to be favorable in its prognostic value for early identification of a complicated course in comparison to routine markers of liver impairment (e.g., aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase). In contrast, inflammation markers (e.g., interleukin 6, tumor necrosis factor α and soluble intercellular adhesion molecule 1) were unsuitable for predicting early complications after liver transplantation from deceased donors.

CONCLUSIONS

For early identification of patients at high risk for complications, the implementation of total keratin 18 measurements in routine diagnostics after orthotopic liver transplantation from deceased donors should be taken into consideration.

Angiogenesis is crucial for liver regeneration after partial hepatectomy

BACKGROUND

Recent studies of hepatic regeneration have mainly focused on the growth of parenchymal cells. However, remodeling of liver vessels seems to be crucial during hepatic regeneration. In this study, we investigated the influence of antiangiogenesis on hepatic regeneration using sFlt-1, a soluble receptor for vascular endothelial growth factor that acts as a dominant negative receptor, and the hepatocyte growth factor antagonist NK4.

METHODS

A sFlt-1-expressing adenoviral vector, an NK4-expressing adenoviral vector, or both combined were infected into C57BL6 mice via the tail vein. A 70% partial hepatectomy was performed on all of the mice 48 hours after infection. The remnants of the liver were removed after the partial hepatectomy, and hepatic regeneration was assessed by measuring the remnant liver weight and hepatocyte mitosis, bromodeoxyuridine staining, immunohistochemical staining with anti-platelet endothelial cell adhesion molecule-1 antibodies, and real-time polymerase chain reaction studies for angiogenic factors.

RESULTS

The immunohistochemical staining for CD31 showed suppression of sinusoidal endothelial cells growth in sFlt-1-expressing adenoviral vector-and NK4-expressing adenoviral vector-infected mice. Increases in the remnant hepatic weight were significantly lower in the sFlt-1-expressing adenoviral vector-infected mice. The bromodeoxyuridine index and mitotic cell results revealed a significant decrease in hepatic regeneration in the sFlt-1-expressing adenoviral vector-and NK4-expressing adenoviral vector-infected mice. The suppressive effects on hepatic regeneration were significantly enhanced by combined sFlt-1-expressing adenoviral vector and NK4-expressing adenoviral vector infection. Real-time polymerase chain reaction results revealed the significant suppression of angiogenic growth factor receptors Tie-1 and Tie-2.

CONCLUSION

The angiogenesis inhibitor significantly suppressed hepatic regeneration. These results suggest that hepatic regeneration after hepatectomy closely correlates with angiogenesis.

Pentoxifylline improves liver regeneration through down-regulation of TNF-α synthesis and TGF-β1 gene expression

AIM: To investigate the mechanism of pentoxifylline (PTX) improvement in liver regeneration.

RESULTS: Rats were randomized into 4 groups: Control rats; Sham - sham-operation rats; Saline - 70% hepatectomy plus saline solution; PTX - 70% hepatectomy plus PTX. At 2 and 6 h after hepatectomy, aspartate aminotransferase, alanine aminotransferase, tumor necrosis factor (TNF)-α and interleukin-6 (IL-6) serum and hepatic tissue levels were determined. Tumor growth factor (TGF)-β1 gene expression in liver tissue was evaluated 24 h after hepatectomy by quantitative reverse transcriptase polymerase chain reaction analysis. Proliferation was analyzed by mitotic index and proliferating cell nuclear antigen (PCNA) staining 48 h after hepatectomy.

RESULTS: TNF-α and IL-6 serum levels increased at 2 and 6 h after hepatectomy. At 2 h after hepatectomy serum PTX was reduced but not hepatic levels of TNF-α and IL-6. A decrease in liver TGF-β1 gene expression and an increase in mitotic index and PCNA after hepatectomy were observed in the PTX treatment group in comparison to the saline group.

CONCLUSION: PTX improves liver regeneration by a mechanism related to down regulation of TNF-α production and TGF-β1 gene expression.

The zinc transporter Zip14 influences c-Met phosphorylation and hepatocyte proliferation during liver regeneration in mice

BACKGROUND & AIMS

Zinc homeostasis in cells is maintained through tight regulation of zinc influx, efflux, and distribution to intracellular organelles by zinc transporters. The Zrt-Irt-like protein (ZIP) transporters facilitate zinc influx to the cytosol. Expression of the ZIP family member Zip14 can be induced by inflammatory cytokines, which also initiate liver regeneration. Hepatocyte proliferation is required for liver regeneration. Zinc regulates cell proliferation, tissue growth, and many mitogenic signaling pathways; we investigated its role in hepatocytes.

METHODS

Wild-type and Zip14(-/-) mice that underwent partial hepatectomy (70% of liver removed) were used as models of liver regeneration. We also analyzed AML12 hepatocytes that overexpressed Zip14. Proliferation was assessed with proliferating cell nuclear antigen, CD1, and Ki67 markers and along with assays of zinc content was related to protein tyrosine phosphatase 1B (PTP1B) and extracellular signal-regulated kinase 1/2 signaling.

RESULTS

Zip14 was up-regulated and hepatic zinc content increased during liver regeneration. Increased hepatic zinc inhibited activity of the phosphatase PTP1B and increased phosphorylation of c-Met, which promoted hepatocyte proliferation. AML12 cells that overexpressed Zip14 increased in zinc content and proliferation; PTP1B was inhibited and phosphorylation of c-Met increased. The increases in hepatic levels of zinc and hepatocyte proliferation that occurred following partial hepatectomy were not observed in Zip14(-/-) mice.

CONCLUSIONS

The transporter Zip14 mediates hepatic uptake of zinc during liver regeneration and for hepatocyte proliferation. These findings indicate that zinc transporter activity regulates liver tissue growth by sequestering zinc. Reagents that regulate ZIP14 activity might be developed as therapeutics to promote liver regeneration in patients with chronic liver disease.

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.

Impaired hepatocellular regeneration in murine sepsis is dependent on regulatory protein levels

Sepsis is a poorly understood syndrome. Therefore, we examined the mechanisms underlying failed regeneration in sham-operated (SO), mildly septic (cecal ligation and single puncture [CLP]), and severely septic (cecal ligation with two punctures [2CLP]) C57Bl6 mice. Relative to no operation (T0) or SO, CLP, but not 2CLP, increased the number of cells staining for proliferating cell nuclear antigen, a marker for cell division. Levels of the retinoblastoma protein (pRb) were detected at T0 and after SO. CLP increased pRb abundance, whereas 2CLP decreased it. Changes in phosphorylated pRb were similar but more profound. The abundance of the transcription factor E2F was unaltered by SO, CLP, or 2CLP. However, E2F DNA binding activity, although unchanged after SO, increased after CLP and decreased after 2CLP. The abundance of cyclin D1 in nuclear fractions increased following CLP but decreased after 2CLP. Neither SO nor 2CLP altered the abundance of the cyclin-dependent kinase (cdk) 4. However, cdk-4 abundance increased after CLP. Finally, CLP increased the steady-state abundance of the mRNAs encoding thymidine kinase, DNA polymerase α, and dihydrofolate reductase, all required for DNA replication. No changes were noted after 2CLP. We conclude that 2CLP impaired hepatocyte proliferation following 2CLP in part via impaired cyclin D1/cdk-4-induced phosphorylation of pRb, maintaining the association between pRb and E2F and inhibited E2F transcriptional activity.

Secreted factors of human liver-derived mesenchymal stem cells promote liver regeneration early after partial hepatectomy

Rapid liver regeneration is required after living-donor liver transplantation and oncologic liver resections to warrant sufficient liver function and prevent small-for-size syndrome. Recent evidence highlights the therapeutic potential of mesenchymal stem cells (MSC) for treatment of toxic liver injury, but whether MSC and their secreted factors stimulate liver regeneration after surgical injury remains unknown. Therefore, the aim of this study is to investigate the effect of human liver-derived MSC-secreted factors in an experimental liver resection model. C57BL/6 mice were subjected to a 70% partial hepatectomy and treated with either concentrated MSC-conditioned culture medium (MSC-CM) or vehicle control. Animals were analyzed for liver and body weight, hepatocyte proliferation, and hepatic gene expression. Effects of MSC-CM on gene expression in a human hepatocyte-like cell line (Huh7 cells) were analyzed using genome-wide gene expression arrays. Liver regeneration was significantly stimulated by MSC-CM as shown by an increase in liver to body weight ratio and hepatocyte proliferation. MSC-CM upregulated hepatic gene expression of cytokines and growth factors relevant for cell proliferation, angiogenesis, and anti-inflammatory responses. In vitro, treatment of Huh7 cells with MSC-CM significantly altered expression levels of ~3,000 genes. Functional analysis revealed strong effects on networks associated with protein synthesis, cell survival, and cell proliferation. This study shows that treatment with MSC-derived factors can promote hepatocyte proliferation and regenerative responses in the early phase after surgical resection. MSC-CM may represent a feasible new strategy to promote liver regeneration in patients undergoing extensive liver resection or after transplantation of small liver grafts.

Molecular mechanisms of liver injury and hepatocarcinogenesis: focusing on the role of stress-activated MAPK

Hepatocellular carcinoma (HCC) is the third most common cause of cancer mortality. Short-term prognosis of patients with HCC has improved recently due to advances in early diagnosis and treatment, but long-term prognosis is still unsatisfactory. Therefore, obtaining a further understanding of the molecular carcinogenic mechanisms and the unique pathogenic biology of HCC is important. The most characteristic process in hepatocarcinogenesis is underlying chronic liver injury, which leads to repeated cycles of hepatocyte death, inflammation, and compensatory proliferation and subsequently provides a mitogenic and mutagenic environment leading to the development of HCC. Recent in vivo studies have shown that the stress-activated mitogen-activated protein kinase (MAPK) cascade converging on c-Jun NH(2)-terminal kinase (JNK) and p38 plays a central role in these processes, and it has attracted considerable attention as a therapeutic target. However, JNK and p38 have complex functions and a wide range of cellular effects. In addition, crosstalk with each other and the nuclear factor-kappaB pathway further complicate these functions. A full understanding is essential to bring these observations into clinical settings. In this paper, we discuss the latest findings regarding the mechanisms of liver injury and hepatocarcinogenesis focusing on the role of the stress-activated MAPK pathway.

Liver regeneration after liver transplantation

BACKGROUND/PURPOSE

The liver has a remarkable capacity to regenerate after injury or resection. The aim of this review is to outline the mechanisms and factors affecting liver regeneration after liver transplantation.

METHODS

Relevant studies were reviewed using Medline, PubMed and Springer databases.

RESULTS

A variety of cytokines (such as interleukin-6 and tumor necrosis factor-α), growth factors (like hepatocyte growth factor and transforming growth factor-α) and cells are involved in liver regeneration. Several factors affect liver regeneration after transplantation such as ischemic injury, graft size, immunosuppression, steatosis, donor age and viral hepatitis.

CONCLUSION

Liver regeneration has been studied for many years. However, further research is essential to reveal the complex processes affecting liver regeneration, which may provide novel strategies in the management of liver transplantation recipients and donors.

High mobility group B1 impairs hepatocyte regeneration in acetaminophen hepatotoxicity

Background

Acetaminophen (APAP) overdose induces massive hepatocyte necrosis. Necrotic tissue releases high mobility group B1 (HMGB1), and HMGB1 contributes to liver injury. Even though blockade of HMGB1 does not protect against APAP-induced acute liver injury (ALI) at 9 h time point, the later time points are not studied and the role of HMGB1 in APAP overdose is unknown, it is possible that neutralization of HMGB1 might improve hepatocyte regeneration. This study aims to test whether blockade of HMGB1 improves hepatocyte regeneration after APAP overdose.

Methods

Male C57BL/6 mice were treated with a single dose of APAP (350 mg/kg). 2 hrs after APAP administration, the APAP challenged mice were randomized to receive treatment with either anti-HMGB1 antibody (400 μg per dose) or non-immune (sham) IgG every 24 hours for a total of 2 doses.

Results

24 hrs after APAP injection, anti-HMGB1 therapy instead of sham IgG therapy significantly improved hepatocyte regeneration microscopically; 48 hrs after APAP challenge, the sham IgG treated mice showed 14.6% hepatic necrosis; in contrast, blockade of HMGB1 significantly decreased serum transaminases (ALT and AST), markedly reduced the number of hepatic inflammatory cells infiltration and restored liver structure to nearly normal; this beneficial effect was associated with enhanced hepatic NF-κB DNA binding and increased the expression of cyclin D1, two important factors related to hepatocyte regeneration.

Conclusion

HMGB1 impairs hepatocyte regeneration after APAP overdose; Blockade of HMGB1 enhances liver recovery and may present a novel therapy to treat APAP overdose.