Resolving the role of IL-6 in liver regeneration

Single nucleotide polymorphisms in interleukin-6 attenuates hepatocytes injury in hypoxia/re-oxygenation via STAT3 signal pathway mediated autophagy

Ischemia-reperfusion injury (IRI) is inevitable during liver surgery, and it is an important factor affecting the prognosis of patients. IL-6 rs1800796 single nucleotide polymorphisms (SNPs) can promote synthesis and secretion of IL-6 and protect hepatocytes from IRI. In this study, we investigated the mechanisms by which IL-6 alleviates hepatic IRI. We transfected lentivirus which carries IL-6 rs1800796 to L02 cells and constructed the cell line (L02-IL6) with a high expression of IL-6. The biological function of IL-6 SNPs was explored through a cell model of hypoxia-reoxygenation (H/R). Cell viability was evaluated by CCK8 and Real-Time Cell Analysis (RTCA), and found that the viability of the L02-IL6 cells was higher than that of the control group (P < 0.01). Flow cytometry assay showed that the rate of apoptosis was significantly decreased in L02-IL6 cells. Furthermore, in comparison with the control group, the level of cleaved-caspase3, which is an important marker of apoptosis, was dramatically decreased. These differences showed that the sequence variants at rs1800796 of the IL-6 gene could improve the resistance against H/R. Moreover, the levels of autophagy-related proteins, such as LC3 and Beclin-1, were upregulated in L02-IL6 group on H/R injury, which means IL-6 could alleviate apoptosis via activating the autophagy pathway. And we also found that the STAT3 signal pathway was activated. Next, we investigated whether the exogenous treatment with IL-6 affect hepatocytes and thus play a protective role. We pre-treated the L02 cells with recombinant human IL-6 for 12 h and then made H/R treatment. We found the treatment with 100 ng/ml IL-6 alleviated the damage of L02 cells and inhibited the apoptosis. And the further study revealed the pre-treatment with IL-6 activated the STAT3 signaling pathway in the L02 cells and then caused the activation of autophagy and apoptosis inhibition. IL-6 might play a critical role in alleviating hepatic IRI, through its modulation of the STAT3 signaling pathway, and activation of autophagy. Recombinant human IL-6 might be a potential therapeutic target in hepatic IRI.

Role of interleukin-6 in inhibiting hepatic autophagy markers in exercised mice

BACKGROUND

Based on the crosstalk of inflammation with apoptosis, autophagy, and endoplasmic reticulum (ER) stress, the main objective of this study was to explore the role of interleukin-6 (IL-6) on genes and proteins related to these phenomena in the livers of mice submitted to acute exhaustive exercise.

METHODS

Reverse transcription-quantitative polymerase chain reaction and immunoblotting technique were used to evaluate the livers of wild-type (WT) and IL-6 knockout (KO) mice at baseline (BL) and 3 h after the acute exhaustive physical exercise (EE).

RESULTS

Compared to the WT at baseline, the IL-6 KO had lower exhaustion velocity, mRNA levels of Mtor, Ulk1, Map1lc3b, and Mapk14, and protein contents of ATG5 and p-p70S6K/p70S6K. For the WT group, the EE decreased glycemia, mRNA levels of Casp3, Mtor, Ulk1, Foxo1a, Mapk14, and Ppargc1a, and protein contents of ATG5 and p-p70S6K/p70S6K, but increased mRNA levels of Sqstm1. For the IL-6 KO group, the EE decreased glycemia, mRNA levels of Casp3 and Foxo1a, and protein contents of pAkt/Akt and Mature/Pro IL-1beta, but increased mRNA levels of Sqstm1, and protein contents of p-AMPK/AMPK.

CONCLUSION

The inhibition of the hepatic autophagy markers induced by the acute EE was attenuated in IL-6 KO mice, highlighting a new function of this cytokine.

Model Based Targeting of IL-6-Induced Inflammatory Responses in Cultured Primary Hepatocytes to Improve Application of the JAK Inhibitor Ruxolitinib

IL-6 is a central mediator of the immediate induction of hepatic acute phase proteins (APP) in the liver during infection and after injury, but increased IL-6 activity has been associated with multiple pathological conditions. In hepatocytes, IL-6 activates JAK1-STAT3 signaling that induces the negative feedback regulator SOCS3 and expression of APPs. While different inhibitors of IL-6-induced JAK1-STAT3-signaling have been developed, understanding their precise impact on signaling dynamics requires a systems biology approach. Here we present a mathematical model of IL-6-induced JAK1-STAT3 signaling that quantitatively links physiological IL-6 concentrations to the dynamics of IL-6-induced signal transduction and expression of target genes in hepatocytes. The mathematical model consists of coupled ordinary differential equations (ODE) and the model parameters were estimated by a maximum likelihood approach, whereas identifiability of the dynamic model parameters was ensured by the Profile Likelihood. Using model simulations coupled with experimental validation we could optimize the long-term impact of the JAK-inhibitor Ruxolitinib, a therapeutic compound that is quickly metabolized. Model-predicted doses and timing of treatments helps to improve the reduction of inflammatory APP gene expression in primary mouse hepatocytes close to levels observed during regenerative conditions. The concept of improved efficacy of the inhibitor through multiple treatments at optimized time intervals was confirmed in primary human hepatocytes. Thus, combining quantitative data generation with mathematical modeling suggests that repetitive treatment with Ruxolitinib is required to effectively target excessive inflammatory responses without exceeding doses recommended by the clinical guidelines.

Epidermal growth factor receptor restoration rescues the fatty liver regeneration in mice

Hepatic steatosis is a common histological finding in obese patients. Even mild steatosis is associated with delayed hepatic regeneration and poor outcomes following liver resection or transplantation. We sought to identify and target molecular pathways that mediate this dysfunction. Lean mice and mice made obese through feeding of a high-fat, hypercaloric diet underwent 70 or 80% hepatectomy. After 70% resection, obese mice demonstrated 100% survival but experienced increased liver injury, reduced energy stores, reduced mitoses, increased necroapoptosis, and delayed recovery of liver mass. Increasing liver resection to 80% was associated with mortality of 40% in lean and 80% in obese mice (P < 0.05). Gene expression profiling showed decreased epidermal growth factor receptor (EGFR) in fatty liver. Meta-analysis of expression studies in mice, rats, and patients also demonstrated reduction of EGFR in fatty liver. In mice, both EGFR and phosphorylated EGFR decreased with increasing percent body fat. Hydrodynamic transfection of EGFR plasmids in mice corrected fatty liver regeneration, reducing liver injury, increasing proliferation, and improving survival after 80% resection. Loss of EGFR expression is rate limiting for liver regeneration in obesity. Therapies directed at increasing EGFR in steatosis might promote liver regeneration and survival following hepatic resection or transplantation.

A surgery trainee's guide to writing a manuscript

Publishing clinical and research work for dissemination is a critical part of the academic process. Learning how to write an effective manuscript should be a goal for medical students and residents who hope to participate in publishing. While there are a number of existing texts that address how to write a manuscript, there are fewer guides that are specifically targeted towards surgery trainees. This review aims to direct and hopefully encourage surgery trainees to successfully navigate the process of converting ideas into a publication that ultimately helps understanding and improves the care of patients.

Toll-like receptor 7 variations are associated with the susceptibility to HCV infection among Chinese females

Toll-like receptors 7 (TLR7) play a crucial role in provoking an immune response in HCV infection. We aimed to investigate whether single nucleotide polymorphisms (SNPs) of TLR7, including rs179009, rs179010 and rs179012, affect the outcomes of HCV infection among the Chinese population. A total of 1767 Chinese Han individuals were enrolled. The distribution of SNP frequencies among three groups with different outcomes of HCV infection was assessed, including healthy controls, cases with spontaneous clearance and cases with viral persistence. Then TLR7 mRNA expression and the production of IFN-α and IL-6 after TLR7 agonist Imiquimod stimulation in vitro were determined. Our results suggested that rs179009 GG genotype was significantly associated with a higher risk of the susceptibility to HCV infection among female subjects (OR=2.42, 95% CI=1.24-4.71, P=0.01). Haplotype GCG was significantly associated with a high risk for HCV susceptibility (OR=1.50, 95% CI=1.11-2.03, P=0.01) as compared with the reference haplotype ACG among females. In the functional research of rs179009, a lower IFN-α level was observed in GG genotype than in AA genotype (P=0.032). Our data indicate that TLR7 rs179009 GG genotype and haplotype GCG were associated with an increased risk of the susceptibility to HCV infection among Chinese females, which may be due to the impaired IFN-α response.

Sex-specific association between X-linked Toll-like receptor 7 with the outcomes of hepatitis C virus infection

Toll-like receptor 7 (TLR7) senses hepatitis C virus (HCV) infection and drives the host specific innate and adaptive immune response. The aim of this study was to estimate the distributions of TLR7 single nucleotide polymorphisms (SNPs), including rs179019 and rs3853839, as well as the effect of TLR7 gene variants on TLR7 mRNA expression and cytokine production in response to TLR7 agonist in vitro. TLR7 SNP genotyping was performed among a Chinese sample population of 418 patients with persistent HCV infection, 317 patients with HCV spontaneous clearance, and 989 healthy controls. TLR7 mRNA expression and TLR7-specific IFN-α and IL-6 secretion in peripheral blood mononuclear cells, derived from 60 healthy individuals in vitro, were then quantified. We identified the association of TLR7 rs3853839C allele, haplotype CC and haplotype AC (rs179019/rs3853839) with protection against HCV persistence in Chinese females (OR=0.49, 95% CI=0.29-0.81, P=0.01 for rs3853839 GC; OR=0.29, 95% CI=0.11-0.75, P=0.01 for rs3853839 CC; OR=0.51, 95% CI=0.38-0.77, P<0.01 for haplotype CC; OR=0.29, 95% CI=0.10-0.88, P=0.03 for haplotype AC). In addition, the rs3853839 CC genotype among female carriers had significantly low TLR7 mRNA expression (P=0.006 for GG vs. CC, P=0.021 for GC vs. CC), along with decreased IFN-α (P=0.002 for GG vs. CC, P=0.021 for GC vs. CC) and increased antiviral IL-6 production (P=0.002 for GG vs. CC, P=0.030 for GC vs. CC), after treatment with Imiquimod in vitro. The cytokine profile among rs3853839 CC genotype female carriers may indicate a pronounced protective effect against persistent HCV infection. The functional polymorphism of TLR7 rs3853839C allele was found to be sex-specific and associated with protection against HCV persistence among Chinese females, which may be due to specific IFN-α and IL-6 secretion profiles.

Toll-like receptors in hepatitis C infection: implications for pathogenesis and treatment

Hepatitis C virus (HCV) infection is a significant global health problem, affecting over 150 million people worldwide. While the critical role of the adaptive immune system in HCV infection is well-established, the importance of the innate immune system in HCV infection has only been recognized in more recent years. Toll-like receptors form the cornerstone of the innate immune response, and there is considerable evidence for their crucial role in hepatitis C infection. This review outlines recent advances made in our understanding of the role of Toll-like receptor function in HCV infection, exploring how HCV manipulates host immunity to evade immune clearance and establish persistent infection despite leading to inflammatory hepatic damage.

Toll-like receptor 3 and 7/8 function is impaired in hepatitis C rapid fibrosis progression post-liver transplantation

Recurrence of hepatitis C (HCV) postliver transplant is universal, with a subgroup developing rapid hepatic fibrosis. Toll-like receptors (TLRs) are critical to innate antiviral responses and HCV alters TLR function to evade immune clearance. Whether TLRs play a role in rapid HCV recurrence posttransplant is unknown. We stimulated peripheral blood mononuclear cells (PBMCs) from 70 patients with HCV postliver transplant with TLR subclass-specific ligands and measured cytokine production, TLR expression and NK cell function. Rate of fibrosis progression was calculated using posttransplant liver biopsies graded by Metavir scoring (F0-4; R=fibrosis stage/year posttransplant; rapid fibrosis defined as >0.4 units/year). Thirty of 70 (43%) patients had rapid fibrosis progression. PBMCs from HCV rapid-fibrosers produced less IFNα with TLR7/8 stimulation (p=0.039), less IL-6 at baseline (p=0.027) and with TLR3 stimulation (p=0.008) and had lower TLR3-mediated monocyte IL-6 production (p=0.028) compared with HCV slow fibrosers. TLR7/8-mediated NKCD56 dim cell secretion of IFNγ was impaired in HCV rapid fibrosis (p=0.006) independently of IFNα secretion and TLR7/8 expression, while cytotoxicity remained preserved. Impaired TLR3 and TLR7/8-mediated cytokine responses may contribute to aggressive HCV recurrence postliver transplantation through impaired immune control of HCV and subsequent activation of fibrogenesis.

Inflammation, organomegaly, and muscle wasting despite hyperphagia in a mouse model of burn cachexia

BACKGROUND

Burn injury results in a chronic inflammatory, hypermetabolic, and hypercatabolic state persisting long after initial injury and wound healing. Burn survivors experience a profound and prolonged loss of lean body mass, fat mass, and bone mineral density, associated with significant morbidity and reduced quality of life. Understanding the mechanisms responsible is essential for developing therapies. A complete characterization of the pathophysiology of burn cachexia in a reproducible mouse model was lacking.

METHODS

Young adult (12-16 weeks of age) male C57BL/6J mice were given full thickness burns using heated brass plates or sham injury. Food and water intake, organ and muscle weights, and muscle fiber diameters were measured. Body composition was determined by Piximus. Plasma analyte levels were determined by bead array assay.

RESULTS

Survival and weight loss were dependent upon burn size. The body weight nadir in burned mice was 14 days, at which time we observed reductions in total body mass, lean carcass mass, individual muscle weights, and muscle fiber cross-sectional area. Muscle loss was associated with increased expression of the muscle ubiquitin ligase, MuRF1. Burned mice also exhibited reduced fat mass and bone mineral density, concomitant with increased liver, spleen, and heart mass. Recovery of initial body weight occurred at 35 days; however, burned mice exhibited hyperphagia and polydipsia out to 80 days. Burned mice had significant increases in serum cytokine, chemokine, and acute phase proteins, consistent with findings in human burn subjects.

CONCLUSIONS

This study describes a mouse model that largely mimics human pathophysiology following severe burn injury. These baseline data provide a framework for mouse-based pharmacological and genetic investigation of burn-injury-associated cachexia.

STAT3 activation in skeletal muscle links muscle wasting and the acute phase response in cancer cachexia

Background

Cachexia, or weight loss despite adequate nutrition, significantly impairs quality of life and response to therapy in cancer patients. In cancer patients, skeletal muscle wasting, weight loss and mortality are all positively associated with increased serum cytokines, particularly Interleukin-6 (IL-6), and the presence of the acute phase response. Acute phase proteins, including fibrinogen and serum amyloid A (SAA) are synthesized by hepatocytes in response to IL-6 as part of the innate immune response. To gain insight into the relationships among these observations, we studied mice with moderate and severe Colon-26 (C26)-carcinoma cachexia.

Methodology/Principal Findings

Moderate and severe C26 cachexia was associated with high serum IL-6 and IL-6 family cytokines and highly similar patterns of skeletal muscle gene expression. The top canonical pathways up-regulated in both were the complement/coagulation cascade, proteasome, MAPK signaling, and the IL-6 and STAT3 pathways. Cachexia was associated with increased muscle pY705-STAT3 and increased STAT3 localization in myonuclei. STAT3 target genes, including SOCS3 mRNA and acute phase response proteins, were highly induced in cachectic muscle. IL-6 treatment and STAT3 activation both also induced fibrinogen in cultured C2C12 myotubes. Quantitation of muscle versus liver fibrinogen and SAA protein levels indicates that muscle contributes a large fraction of serum acute phase proteins in cancer.

Conclusions/Significance

These results suggest that the STAT3 transcriptome is a major mechanism for wasting in cancer. Through IL-6/STAT3 activation, skeletal muscle is induced to synthesize acute phase proteins, thus establishing a molecular link between the observations of high IL-6, increased acute phase response proteins and muscle wasting in cancer. These results suggest a mechanism by which STAT3 might causally influence muscle wasting by altering the profile of genes expressed and translated in muscle such that amino acids liberated by increased proteolysis in cachexia are synthesized into acute phase proteins and exported into the blood.

Apobec-1 complementation factor modulates liver regeneration by post-transcriptional regulation of interleukin-6 mRNA stability

Apobec-1 complementation factor (ACF) is the RNA binding subunit of a core complex that mediates C to U RNA editing of apolipoprotein B (apoB) mRNA. Targeted deletion of the murine Acf gene is early embryonic lethal and Acf(-/-) blastocysts fail to implant and proliferate, suggesting that ACF plays a key role in cell growth and differentiation. Here we demonstrate that heterozygous Acf(+/-) mice exhibit decreased proliferation and impaired liver mass restitution following partial hepatectomy (PH). To pursue the mechanism of impaired liver regeneration we examined activation of interleukin-6 (IL-6) a key cytokine required for induction of hepatocyte proliferation following PH. Peak induction of hepatic IL-6 mRNA abundance post PH was attenuated >80% in heterozygous Acf(+/-) mice, along with decreased serum IL-6 levels. IL-6 secretion from isolated Kupffer cells (KC) was 2-fold greater in wild-type compared with heterozygous Acf(+/-) mice. Recombinant ACF bound an AU-rich region in the IL-6 3'-untranslated region with high affinity and IL-6 mRNA half-life was significantly shorter in KC isolated from Acf(+/-) mice compared with wild-type controls. These findings suggest that ACF regulates liver regeneration following PH at least in part by controlling the stability of IL-6 mRNA. The results further suggest a new RNA target and an unanticipated physiological function for ACF beyond apoB RNA editing.

Acute inhibition of myostatin-family proteins preserves skeletal muscle in mouse models of cancer cachexia

Cachexia, progressive loss of fat and muscle mass despite adequate nutrition, is a devastating complication of cancer associated with poor quality of life and increased mortality. Myostatin is a potent tonic muscle growth inhibitor. We tested how myostatin inhibition might influence cancer cachexia using genetic and pharmacological approaches. First, hypermuscular myostatin null mice were injected with Lewis lung carcinoma or B16F10 melanoma cells. Myostatin null mice were more sensitive to tumor-induced cachexia, losing more absolute mass and proportionately more muscle mass than wild-type mice. Because myostatin null mice lack expression from development, however, we also sought to manipulate myostatin acutely. The histone deacetylase inhibitor Trichostatin A has been shown to increase muscle mass in normal and dystrophic mice by inducing the myostatin inhibitor, follistatin. Although Trichostatin A administration induced muscle growth in normal mice, it failed to preserve muscle in colon-26 cancer cachexia. Finally we sought to inhibit myostatin and related ligands by administration of the Activin receptor extracellular domain/Fc fusion protein, ACVR2B-Fc. Systemic administration of ACVR2B-Fc potently inhibited muscle wasting and protected adipose stores in both colon-26 and Lewis lung carcinoma cachexia, without affecting tumor growth. Enhanced cachexia in myostatin knockouts indicates that host-derived myostatin is not the sole mediator of muscle wasting in cancer. More importantly, skeletal muscle preservation with ACVR2B-Fc establishes that targeting myostatin-family ligands using ACVR2B-Fc or related molecules is an important and potent therapeutic avenue in cancer cachexia.

Interleukin-6 inhibits oxidative injury and necrosis after extreme liver resection

Extreme hepatectomy or resection of more than 80% of liver mass often leads to liver failure and death and is a major limitation to therapeutic liver resection for patients with liver tumors. We sought to define the mechanisms leading to liver failure and to determine the utility of interleukin-6 (IL-6) administration to improve outcomes. Mice were injected with Chinese hamster ovary cells expressing human IL-6 or no recombinant protein, or were administered recombinant IL-6 or carrier by osmotic mini-pump. Mice were then subjected to 70% or 87% hepatectomy. Light and electron microscopy of liver sections after 87% hepatectomy showed ballooning hepatocytes, vacuolar changes, and mitochondrial abruption, with absence of anoikic nuclei. No significant activation of executor caspases or DNA laddering was observed, although a dramatic decrease in cellular adenosine triphosphate (ATP) stores was measured, suggesting cell death was by a necrotic pathway involving mitochondrial dysfunction. A large increase in protein oxidation was observed, indicative of significant oxidative stress. IL-6 treatment before 87% hepatectomy resulted in less biochemical and histological evidence of liver injury as well as earlier proliferating chain nuclear antigen (PCNA) expression and accelerated recovery of liver mass. IL-6 pretreatment induced the antioxidative injury proteins, ref-1 and GPX1, decreased protein oxidation, vacuolar changes and leakage of mitochondrial products, improved ATP stores, and maintained cellular ultrastructure after 87% hepatectomy.

CONCLUSION

Massive oxidative injury and mitochondrial dysfunction occurs in the liver after extreme hepatectomy. IL-6 improves recovery and survival from extreme liver resection by enhancing pro-growth pathways, reducing oxidative stress, and maintaining mitochondrial function.

A Toll-like receptor 7 single nucleotide polymorphism protects from advanced inflammation and fibrosis in male patients with chronic HCV-infection

BACKGROUND/AIMS

HCV-infection leads to development of liver fibrosis, causing morbidity and mortality. Multiple factors influence the progression of fibrosis, including genetic factors. Since HCV is an RNA virus, a role for TLR7 in the immune response against HCV is likely. No systematic analysis of TLR7 single nucleotide polymorphisms (SNPs) has been published.

METHODS

We sequenced TLR7 in 52 women and investigated SNPs with an allele frequency >5% in 807 patients with chronic HCV-infection by melting curve analysis. We analyzed the effect of TLR7 SNPs on grade of inflammation and stage of fibrosis as determined by liver biopsy.

RESULTS

We detected five TLR7 SNPs, three of which showed a frequency >5%. One variant, c.1-120T>G, was more common in patients with no or little inflammation than in patients with grades 2-4 (10.7% vs. 6.1%; P=0.034). The variant was also enriched in patients with no or little fibrosis compared to those with higher stages (12.6% vs. 6.6%; P=0.005). The difference was fully attributable to male patients.

CONCLUSIONS

This is the first analysis of TLR7 SNPs in patients with chronic HCV-infection. Our data suggest that the c.1-120G TLR7 allele offers protection from the development of inflammation and fibrosis in male patients with chronic HCV-infection.

Molecular pathogenesis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common life-threatening malignancies in the world. This cancer generally arises within the boundaries of well-defined causal factors, of which viral hepatitis infection, aflatoxin exposure, chronic alcohol abuse, and nonalcoholic steatohepatitis are the major risk factors. Despite the identification of these etiological agents, hepatocarcinogenesis remains poorly understood. The molecular mechanisms leading to the development of HCC appear extremely complex and only recently have begun to be elucidated. Currently, surgical resection or liver transplantation offer the best chance of cure for the patient with HCC; however, these therapies are hindered by inability of many of these patients to undergo liver resection, by tumor recurrence and by donor shortages. A lack of suitable therapeutic strategies has led to a greater focus on prevention of HCC using antiviral agents and vaccination. Overall, the current outlook for patients with HCC is bleak; however, a better understanding of the molecular and genetic basis of this cancer should lead to the development of more efficacious therapies.

Matrix metalloproteinase-9 is an important factor in hepatic regeneration after partial hepatectomy in mice

Partial hepatectomy triggers hepatocyte proliferation, hepatic matrix remodeling, and hepatocyte apoptosis, all of which are important processes in the regenerating liver. Previous studies have shown an increase in the levels of matrix metalloproteinases gelatinase A (MMP-2) and gelatinase B (MMP-9) after partial hepatectomy. The goal of this study was to investigate the role of MMP-9 in liver regeneration after partial hepatectomy. A 70% hepatectomy or sham laparotomy was performed in wild-type or MMP-9-deficient (MMP-9-/-) mice. Hepatic regeneration was determined by liver weight/total body weight ratios and BrdU staining, which was used to a calculate mitotic index at several times postoperatively. Cytokine and growth factor expression was evaluated by Luminex bead-based ELISA and Western blots. Finally, the effect of MMP-9 on apoptosis was measured using TUNEL and caspase expression. The MMP-9-/- animals had a delayed hepatic regenerative response when compared with wild-type controls. The MMP-9-deficient animals expressed significantly less VEGF, HGF, and TNF-alpha between days 2 and 3 post-hepatectomy. Apoptosis, as measured by TUNEL staining and caspase expression, was decreased in the MMP-9-/-. In conclusion, MMP-9 plays an important role in liver regeneration after partial hepatectomy by affecting matrix remodeling, as well as cytokine, growth factor, and caspase expression.

Concerted functions of Gab1 and Shp2 in liver regeneration and hepatoprotection

Liver regeneration is a rapid and concerted response to injury, in which growth factor-generated intracellular signals result in activation of transcription factors, DNA synthesis, and hepatocyte proliferation. However, the link between cytoplasmic signals resulting in proliferative response to liver injury remains to be elucidated. We show here that association of Gab1 adaptor protein and Shp2 tyrosine phosphatase is a critical event at the early phase of liver regeneration. Partial hepatectomy (PH) rapidly and transiently induced assembly of a complex comprising Shp2 and tyrosine-phosphorylated Gab1 in wild-type hepatocytes. Consistently, liver-specific Shp2 knockout (LSKO) and liver-specific Gab1 knockout (LGKO) mice displayed very similar phenotypes of defective liver regeneration triggered by PH, including blunted extracellular signal-regulated kinase 1/2 (Erk1/2) activation, decreased expression of immediate-early genes, and reduced levels of cyclins A, E, and B1, as well as suppression of hepatocyte proliferation. In contrast, the Akt and interleukin-6/Stat3 pathways were up-regulated posthepatectomy in LSKO and LGKO mice, accompanied by improved hepatoprotection. Collectively, this study establishes the physiological significance of the Gab1/Shp2 link in promoting mitogenic signaling through the Erk pathway in mammalian liver regeneration.

Paradoxical effects of short- and long-term interleukin-6 exposure on liver injury and repair

Interleukin-6 (IL-6) is an important mediator of liver regeneration and repair that is also elevated in chronic liver diseases, including fatty liver of obesity and cirrhosis. IL-6 has been reported both to delay and accelerate liver regeneration. We examined the effects on liver injury and regeneration of a continuous administration of exogenous IL-6 to mice by injection of an IL-6-expressing CHO-cell line in athymic nude mice and by osmotic mini-pump delivery of recombinant murine IL-6. Short-term IL-6 administration (1-2 days) accelerated early recovery of liver mass, whereas more long-term administration (5-7 days) markedly impaired liver regeneration. Similarly, short-term IL-6 treatment increased hepatic resistance to the lethal effects of the Fas agonist Jo-2, but on more prolonged IL-6 exposure the Jo-2 resistance vanished. IL-6 administration initially induced expression of the anti-apoptotic proteins Bcl-2 and Bcl-xL, correlating with protection against Fas-mediated cell death. More prolonged IL-6 administration, however, resulted in marked induction of the pro-apoptotic protein Bax. This result coincided with increased activation of the type II or intrinsic, mitochondrial path to cell death, manifested by increased caspase-9 activation and increased cytochrome c release after Jo-2 exposure. These data demonstrate that IL-6 can function acutely to improve hepatic regeneration and repair, but that more chronic exposure not only abolishes the protective effects of IL-6, but actually sensitizes the liver to injury and death. In conclusion, elevated IL-6 in certain chronic liver diseases contributes to an increased likelihood of liver failure after injury.

Acute liver failure: from bench to bedside

Acute liver failure constitutes a challenge to clinicians and scientists alike. The course of the disease, usually unpredictable and polarizing, is associated with a high mortality unless liver transplantation is feasible, but can end in a spontaneous restitution. It poses many scientific questions regarding the mechanisms of liver cell damage and regeneration and the possibility of new therapeutic approaches. However, the performance of clinical studies in patients in acute liver failure presents problems because of the varied etiology, the small number of cases, and furthermore due to ethical and logistical difficulties. For this reason experimental investigations have gained a special importance. Arising from the improved understanding of the mechanisms of liver cell damage in acute liver failure, which may be primarily due not to the initial noxious agent alone but may also be triggered secondarily by the release of proinflammatory mediators, there are numerous options for liver cell protection, some of which have already proved successful in experimental studies. New insights into the mechanisms of regulation of liver regeneration and the physiological liver mass, gathered in particular from experimental models of partial hepatectomy and by the use of gene-manipulated animals, have contributed to the development of new therapeutic approaches for the stimulation of liver cell regeneration. Temporary liver support systems have already been successfully employed in some cases under clinical conditions. Although the systematic experimental investigation of many of the questions of acute liver failure has significantly contributed to a better understanding of liver cell damage and regeneration, the application of this new knowledge to clinical practice is to some extent made difficult by the artificial simplification that experimental studies inevitably entail and needs to be validated by controlled clinical studies.

Identification of expressed genes in regenerating rat liver in 0-4-8-12 h short interval successive partial hepatectomy

AIM: To identify the genes differentially expressed in the regenerating rat liver of 0-4-8-12 h short interval successive partial hepatectomy (SISPH) and to analyze their expression profiles.

METHODS: Five hundred and fifty-one elements screened from subtractive cDNA libraries were made into a cDNA microarray (cDNA chip). Extensive gene expression analysis following 0-4-8-12 h SISPH was conducted by microarray.

RESULTS: One hundred and eighty-three elements were selected, which were either up- or down-regulated more than 2-fold at one or more time points after SISPH. Cluster analysis and generalization analysis showed that there were five distinct temporal patterns of gene expression. Eighty-six genes were unreported, associated with liver regeneration (LR).

CONCLUSION: Microarray analysis shows that the down regulated genes are much more than the up-regulated ones in SISPH; the numbers of genes expressed consistently are fewer than that expressed immediately; the genes expressed in high abundance are much fewer than that increased 2-5-fold. The comparison of SISPH with partial hepatectomy (PH) shows that the expression trends of most genes in SISPH and in PH are similar, but the expression of 43 genes is specifically altered in SISPH.

Gene expression profile of liver regeneration induced by monosodium L-glutamate in rat

AIM: By analyzing the gene expression profile in the regenerated liver tissue, to study the molecular mechanism of liver regeneration disturbance induced by monosodium L-glutamate (MSG) in rat.

METHODS: Both rats (control group) and MSG-rats (model group) were operated to excise the left and middle lobes of liver (about 68% of all the liver) 6 weeks after birth. The rats were executed at 5th day after operation, and the regenerated liver tissues were frozen by liquid nitrogen. A gene chip with 1176 genes was used to detect the differentially expressed genes in the regenerated liver tissue. mRNAs were extracted from the regenerated liver tissue and 33P labeled cDNA probes were prepared by RT-PCR. The probes were hybridized with the gene chip. The data were analyzed with Microsoft Access and Excel to determine the differentially expressed genes.

RESULTS: In the 1176 examined genes, there were 256 differentially expressed genes in model group in contrast with control group, with 40 genes up-regulated and 216 gene down-regulated. Among them, there were 10 genes associated with cell receptors, 15 genes associated with transcription, 9 genes associated with cell adhesion receptor, 98 genes associated with metabolism, 9 genes associated with post-translational modification/protein folding, and 11 genes associated with protein turnover.

CONCLUSION: The gene expression profile of the MSG-indcued liver regeneration is significantly different from partial hepatectomy-induced liver regeneration in rat.

Negative regulation of liver regeneration by innate immunity (natural killer cells/interferon-gamma)

BACKGROUND AND AIMS

Hepatic lymphocytes are composed mainly of natural killer (NK) cells and NKT cells, which play key roles in innate immune responses against pathogens and tumors in the liver. This report analyzes the effects of activation of innate immunity by viral infection or the toll-like receptor 3 (TLR3) ligand on liver regeneration.

METHODS

The partial hepatectomy (PHx) method was used as a model of liver regeneration. Murine cytomegalovirus (MCMV) infection and the TLR3 ligand polyinosinic-polycytidylic acid [poly(I:C)] were used to activate innate immunity.

RESULTS

NK cells are activated after PHx, as evidenced by producing interferon (IFN)-gamma. Infection with MCMV or injection of poly(I:C) further activates NK cells to produce IFN-gamma and attenuates liver regeneration in the PHx model. Depletion of NK cells or disruption of either the IFN-gamma gene or the IFN-gamma receptor gene enhances liver regeneration and partially abolishes the negative effects of MCMV and polyI:C on liver regeneration, whereas NKT cells may only play a minor role in suppression of liver regeneration. Adoptive transfer of IFN-gamma +/+ NK cells, but not IFN-gamma -/- NK cells, restores the ability of polyI:C to attenuate liver regeneration in NK-depleted mice. Finally, administration of polyI:C or IFN-gamma enhances expression of several antiproliferative proteins, including STAT1, IRF-1, and p21cip1/waf1 in the livers of partially hepatectomized mice.

CONCLUSIONS

Our findings suggest that viral infection and the TLR3 ligand negatively regulate liver regeneration via activation of innate immunity (NK/IFN-gamma), which may play an important role in the pathogenesis of viral hepatitis.

Liver regeneration: from myth to mechanism

The unusual regenerative properties of the liver are a logical adaptation by organisms, as the liver is the main detoxifying organ of the body and is likely to be injured by ingested toxins. The numerous cytokine- and growth-factor-mediated pathways that are involved in regulating liver regeneration are being successfully dissected using molecular and genetic approaches. So what is known about this process at present and which questions remain?