Lack of gp130 expression in hepatocytes promotes liver injury

The double-edged effects of IL-6 in liver regeneration, aging, inflammation, and diseases

Interleukin-6 (IL-6) is a pleiotropic cytokine and exerts its complex biological functions mainly through three different signal modes, called cis-, trans-, and cluster signaling. When IL-6 binds to its membrane or soluble receptors, the co-receptor gp130 is activated to initiate downstream signaling and induce the expression of target genes. In the liver, IL-6 can perform its anti-inflammatory activities to promote hepatocyte reprogramming and liver regeneration. On the contrary, IL-6 also exerts the pro-inflammatory functions to induce liver aging, fibrosis, steatosis, and carcinogenesis. However, understanding the roles and underlying mechanisms of IL-6 in liver physiological and pathological processes is still an ongoing process. So far, therapeutic agents against IL‑6, IL‑6 receptor (IL‑6R), IL-6-sIL-6R complex, or IL-6 downstream signal transducers have been developed, and determined to be effective in the intervention of inflammatory diseases and cancers. In this review, we summarized and highlighted the understanding of the double-edged effects of IL-6 in liver homeostasis, aging, inflammation, and chronic diseases, for better shifting the "negative" functions of IL-6 to the "beneficial" actions, and further discussed the potential therapeutic effects of targeting IL-6 signaling in the clinics.

Endotoxin Inflammatory Action on Cells by Dysregulated-Immunological-Barrier-Linked ROS-Apoptosis Mechanisms in Gut-Liver Axis

Our study highlighted the immune changes by pro-inflammatory biomarkers in the gut-liver-axis-linked ROS-cell death mechanisms in chronic and acute inflammations when gut cells are exposed to endotoxins in patients with hepatic cirrhosis or steatosis. In duodenal tissue samples, gut immune barrier dysfunction was analyzed by pro-inflammatory biomarker expressions, oxidative stress, and cell death by flow cytometry methods. A significant innate and adaptative immune system reaction was observed as result of persistent endotoxin action in gut cells in chronic inflammation tissue samples recovered from hepatic cirrhosis with the A-B child stage. Instead, in patients with C child stage of HC, the endotoxin tolerance was installed in cells, characterized by T lymphocyte silent activation and increased Th1 cytokines expression. Interesting mechanisms of ROS-cell death were observed in chronic and acute inflammation samples when gut cells were exposed to endotoxins and immune changes in the gut-liver axis. Late apoptosis represents the chronic response to injury induction by the gut immune barrier dysfunction, oxidative stress, and liver-dysregulated barrier. Meanwhile, necrosis represents an acute and severe reply to endotoxin action on gut cells when the immune system reacts to pro-inflammatory Th1 and Th2 cytokines releasing, offering protection against PAMPs/DAMPs by monocytes and T lymphocyte activation. Flow cytometric analysis of pro-inflammatory biomarkers linked to oxidative stress-cell death mechanisms shown in our study recommends laboratory techniques in diagnostic fields.

The gp130/STAT3-endoplasmic reticulum stress axis regulates hepatocyte necroptosis in acute liver injury

AIM

To investigate the effect of the gp130/STAT3-endoplasmic reticulum (ER) stress axis on hepatocyte necroptosis during acute liver injury.

METHODS

ER stress and liver injury in LO2 cells were induced with thapsigargin, and in BALB/c mice with tunicamycin and carbon tetrachloride (CCl4). Glycoprotein 130 (gp130) expression, the degrees of ER stress, and hepatocyte necroptosis were assessed.

RESULTS

ER stress significantly upregulated gp130 expression in LO2 cells and mouse livers. The silencing of activating transcription factor 6 (ATF6), but not of ATF4, increased hepatocyte necroptosis and mitigated gp130 expression in LO2 cells and mice. Gp130 silencing reduced the phosphorylation of CCl4-induced signal transducer and activator of transcription 3 (STAT3), and aggravated ER stress, necroptosis, and liver injury in mice.

CONCLUSION

ATF6/gp130/STAT3 signaling attenuates necroptosis in hepatocytes through the negative regulation of ER stress during liver injury. Hepatocyte ATF6/gp130/STAT3 signaling may be used as a therapeutic target in acute liver injury.

Targeting immunoregulation for cardiac regeneration

Inducing endogenous cardiomyocyte proliferation and heart regeneration is a promising strategy to treat ischemic heart failure. The immune response has recently been considered critical in cardiac regeneration. Thus, targeting the immune response is a potent strategy to improve cardiac regeneration and repair after myocardial infarction. Here we reviewed the characteristics of the relationship between the postinjury immune response and heart regenerative capacity and summarized the latest studies focusing on inflammation and heart regeneration to identify potent targets of the immune response and strategies in the immune response to promote cardiac regeneration.

Hepatocyte Specific gp130 Signalling Underlies APAP Induced Liver Injury

N-acetyl-p-aminophenol (APAP)-induced liver damage is associated with upregulation of Interleukin-11 (IL11), which is thought to stimulate IL6ST (gp130)-mediated STAT3 activity in hepatocytes, as a compensatory response. However, recent studies have found IL11/IL11RA/gp130 signaling to be hepatotoxic. To investigate further the role of IL11 and gp130 in APAP liver injury, we generated two new mouse strains with conditional knockout (CKO) of either Il11 (CKO^Il11) or gp130 (CKO^gp130) in adult hepatocytes. Following APAP, as compared to controls, CKO^gp130 mice had lesser liver damage with lower serum Alanine Transaminase (ALT) and Aspartate Aminotransferase (AST), greatly reduced serum IL11 levels (90% lower), and lesser centrilobular necrosis. Livers from APAP-injured CKO^gp130 mice had lesser ERK, JNK, NOX4 activation and increased markers of regeneration (PCNA, Cyclin D1, Ki67). Experiments were repeated in CKO^Il11 mice that, as compared to wild-type mice, had lower APAP-induced ALT/AST, reduced centrilobular necrosis and undetectable IL11 in serum. As seen with CKO^gp130 mice, APAP-treated CKO^Il11 mice had lesser ERK/JNK/NOX4 activation and greater features of regeneration. Both CKO^gp130 and CKO^Il11 mice had normal APAP metabolism. After APAP, CKO^gp130 and CKO^Il11 mice had reduced Il6, Ccl2, Ccl5, Il1β, and Tnfα expression. These studies exclude IL11 upregulation as compensatory and establish autocrine, self-amplifying, gp130-dependent IL11 secretion from damaged hepatocytes as toxic and anti-regenerative.

Interval-Based Secretomics Unravels Acute-Phase Response in Hepatocyte Model Systems

Mass spectrometry-based secretomics approaches frequently utilize serum-free culture conditions to circumvent serum-induced interference and to increase analytical depth. However, this can negatively affect a wide range of cellular functions and cell viability. These effects become particularly apparent when investigating transcriptionally regulated secretion events and feedback-loops in response to perturbations that require 48 h or more to fully manifest. We present an “interval-based” secretomics workflow, which determines protein secretion rates in short serum-free time windows. Relative quantification using tandem mass tags enables precise monitoring of time-dependent changes. We applied this approach to determine temporal profiles of protein secretion in the hepatocyte model cell lines HepG2 and HepaRG after stimulation of the acute-phase response (APR) by the cytokines IL1b and IL6. While the popular hepatocarcinoma cell line HepG2 showed an incomplete APR, secretion patterns derived from differentiated HepaRG cells recapitulated the expected APR more comprehensively. For several APR response proteins, substantial secretion was only observed after 72 h, a time window at which cell fitness is substantially impaired under serum-free cell culture conditions. The interval-based secretomics approach enabled the first comprehensive analysis of time-dependent secretion of liver cell models in response to these proinflammatory cytokines. The extended time range facilitated the observation of distinct chronological phases and cytokine-dependent secretion phenotypes of the APR. IL1b directed the APR toward pathogen defense over three distinct phases—chemotaxis, effector, clearance—while IL6 directed the APR toward regeneration. Protein shedding on the cell surface was pronounced upon IL1b stimulation, and small molecule inhibition of ADAM and matrix metalloproteases identified induced as well as constitutive shedding events. Inhibition of ADAM proteases with TAPI-0 resulted in reduced shedding of the sorting receptor SORT1, and an attenuated cytokine response suggesting a direct link between cell surface shedding and cytokine secretion rates.

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Interval-based secretomics enables extended time course analysis.

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Time-resolved acute phase response in liver model systems HepG2 and HepaRG.

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IL1b response clusters in three phases.

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Cell surface shedding is amplified during acute-phase response.

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ADAM inhibition dampens secretion of inflammatory cytokines.

Omega‑3 polyunsaturated fatty acids inhibit IL‑11/STAT3 signaling in hepatocytes during acetaminophen hepatotoxicity

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) exert a negative effect on IL-6 production in several liver disorders, including cirrhosis, acute liver failure and fatty liver disease. However, its effect on the production of IL-11, another important IL-6 family cytokine, remains unclear. IL-11 was found to be significantly elevated in acetaminophen (APAP)-induced liver damage. The aim of the present study was to investigate whether and how n-3 PUFAs modulate IL-11 production during APAP-induced liver injury. For that purpose, wild-type (WT) and fat-1 transgenic mice were intraperitoneally injected with APAP to induce liver injury. Serum was collected for ELISA and alanine aminotransferase assay. The hepatocytes of APAP-injected mice were isolated for reverse transcription-quantitative PCR and western blot analyses. For the in vitro study, primary hepatocytes isolated from WT or fat-1 mice were stimulated with APAP. The results revealed that both endogenous and exogenous n-3 PUFAs significantly aggravated APAP-induced liver damage via the downregulation of STAT3 signaling. Notably, n-3 PUFAs inhibited IL-11 expression, but not IL-6 expression in hepatocytes during the APAP challenge. Furthermore, it was demonstrated that limited phosphorylation of ERK1/2 and Fos-like-1 (Fra-1) expression are responsible for the n-3 PUFA-mediated inhibitory effect on IL-11 production in APAP-treated hepatocytes. It was concluded that n-3 PUFAs inhibit IL-11 production and further STAT3 activation in hepatocytes during APAP-induced liver injury. Therefore, ERK1/2-mediated Fra-1 expression is responsible for the effect of n-3 PUFAs on IL-11 expression.

The two facets of gp130 signalling in liver tumorigenesis

The liver is a vital organ with multiple functions and a large regenerative capacity. Tumours of the liver are the second most frequently cause of cancer-related death and develop in chronically inflamed livers. IL-6-type cytokines are mediators of inflammation and almost all members signal via the receptor subunit gp130 and the downstream signalling molecule STAT3. We here summarize current knowledge on how gp130 signalling and STAT3 in tumour cells and cells of the tumour micro-environment drives hepatic tumorigenesis. We furthermore discuss very recent findings describing also anti-tumorigenic roles of gp130/STAT3 and important considerations for therapeutic interventions.

Pathophysiological Changes During Ischemia-reperfusion Injury in Rodent Hepatic Steatosis

BACKGROUND/AIM

Ischemia and reperfusion injuries may produce deleterious effects on hepatic tissue after liver surgery and transplantation. The impact of ischemia-reperfusion injury (IRI) on the liver depends on its substrate, the percentage of liver ischemic tissue subjected to IRI and the ischemia time. The consequences of IRI are more evident in pathologic liver substrates, such as steatotic livers. This review is the result of an extended bibliographic PubMed search focused on the last 20 years. It highlights basic differences encountered during IRI in lean and steatotic livers based on studies using rodent experimental models.

CONCLUSION

The main difference in cell death between lean and steatotic livers is the prevalence of apoptosis in the former and necrosis in the latter. There are also major changes in the effect of intracellular mediators, such as TNFα and IL-1β. Further experimental studies are needed in order to increase current knowledge of IRI effects and relevant mechanisms in both lean and steatotic livers, so that new preventive and therapeutic strategies maybe developed.

The Role of Fibrosis and Liver-Associated Fibroblasts in the Pathogenesis of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most aggressive types of cancer and lacks effective therapeutic approaches. Most HCC develops in the setting of chronic liver injury, hepatic inflammation, and fibrosis. Hepatic stellate cells (HSCs) and cancer-associated fibroblasts (CAFs) are key players in liver fibrogenesis and hepatocarcinogenesis, respectively. CAFs, which probably derive from HSCs, activate into extracellular matrix (ECM)-producing myofibroblasts and crosstalk with cancer cells to affect tumor growth and invasion. In this review, we describe the different components which form the HCC premalignant microenvironment (PME) and the tumor microenvironment (TME), focusing on the liver fibrosis process and the biology of CAFs. We will describe the CAF-dependent mechanisms which have been suggested to promote hepatocarcinogenesis, such as the alteration of ECM, CAF-dependent production of cytokines and angiogenic factors, CAF-dependent reduction of immuno-surveillance, and CAF-dependent promotion of epithelial-mesenchymal transition (EMT). New knowledge of the fibrosis process and the role of CAFs in HCC may pave the way for new therapeutic strategies for liver cancer.

The Role of Fibrosis and Liver-Associated Fibroblasts in the Pathogenesis of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most aggressive types of cancer and lacks effective therapeutic approaches. Most HCC develops in the setting of chronic liver injury, hepatic inflammation, and fibrosis. Hepatic stellate cells (HSCs) and cancer-associated fibroblasts (CAFs) are key players in liver fibrogenesis and hepatocarcinogenesis, respectively. CAFs, which probably derive from HSCs, activate into extracellular matrix (ECM)-producing myofibroblasts and crosstalk with cancer cells to affect tumor growth and invasion. In this review, we describe the different components which form the HCC premalignant microenvironment (PME) and the tumor microenvironment (TME), focusing on the liver fibrosis process and the biology of CAFs. We will describe the CAF-dependent mechanisms which have been suggested to promote hepatocarcinogenesis, such as the alteration of ECM, CAF-dependent production of cytokines and angiogenic factors, CAF-dependent reduction of immuno-surveillance, and CAF-dependent promotion of epithelial-mesenchymal transition (EMT). New knowledge of the fibrosis process and the role of CAFs in HCC may pave the way for new therapeutic strategies for liver cancer.

The Role of Cancer-Associated Fibroblasts and Fibrosis in Liver Cancer

Liver cancer is the second leading cause of cancer mortality worldwide, causing more than 700,000 deaths annually. Because of the wide landscape of genomic alterations and limited therapeutic success of targeting tumor cells, a recent focus has been on better understanding and possibly targeting the microenvironment in which liver tumors develop. A unique feature of liver cancer is its close association with liver fibrosis. More than 80% of hepatocellular carcinomas (HCCs) develop in fibrotic or cirrhotic livers, suggesting an important role of liver fibrosis in the premalignant environment (PME) of the liver. Cholangiocarcinoma (CCA), in contrast, is characterized by a strong desmoplasia that typically occurs in response to the tumor, suggesting a key role of cancer-associated fibroblasts (CAFs) and fibrosis in its tumor microenvironment (TME). Here, we discuss the functional contributions of myofibroblasts, CAFs, and fibrosis to the development of HCC and CCA in the hepatic PME and TME, focusing on myofibroblast- and extracellular matrix-associated growth factors, fibrosis-associated immunosuppressive pathways, as well as mechanosensitive signaling cascades that are activated by increased tissue stiffness. Better understanding of the role of myofibroblasts in HCC and CCA development and progression may provide the basis to target these cells for tumor prevention or therapy.

Hepatocytes as Immunological Agents

Hepatocytes are targeted for infection by a number of major human pathogens, including hepatitis B virus, hepatitis C virus, and malaria. However, hepatocytes are also immunological agents in their own right. In systemic immunity, they are central in the acute-phase response, which floods the circulation with defensive proteins during diverse stresses, including ischemia, physical trauma, and sepsis. Hepatocytes express a variety of innate immune receptors and, when challenged with pathogen- or damage-associated molecular patterns, can deliver cell-autonomous innate immune responses that may result in host defense or in immunopathology. Important human pathogens have evolved mechanisms to subvert these responses. Finally, hepatocytes talk directly to T cells, resulting in a bias toward immune tolerance.

Glycoprotein130 (Gp130)/interleukin-6 (IL-6) signalling in osteoclasts promotes bone formation in periosteal and trabecular bone

Interleukin-6 (IL-6) and interleukin-11 (IL-11) receptors (IL-6R and IL-11R, respectively) are both expressed in osteoclasts and transduce signal via the glycoprotein130 (gp130) co-receptor, but the physiological role of this pathway is unclear. To determine the critical roles of gp130 signalling in the osteoclast, we generated mice using cathepsin K Cre (CtskCre) to disrupt gp130 signalling in osteoclasts. Bone marrow macrophages from CtskCre.gp130(f/f) mice generated more osteoclasts in vitro than cells from CtskCre.gp130(w/w) mice; these osteoclasts were also larger and had more nuclei than controls. While no increase in osteoclast numbers was observed in vivo, osteoclasts on trabecular bone surfaces of CtskCre.gp130(f/f) mice were more spread out than in control mice, but had no functional defect detectable by serum CTX1 levels or trabecular bone cartilage remnants. However, trabecular osteoblast number and mineralising surfaces were significantly lower in male CtskCre.gp130(f/f) mice compared to controls, and this was associated with a significantly lower trabecular bone volume at 12 weeks of age. Furthermore, CtskCre.gp130(f/f) mice exhibited greatly suppressed periosteal bone formation at this age, indicated by significant reductions in both double-labelled surface and mineral apposition rate. By 26 weeks of age, CtskCre.gp130(f/f) mice exhibited narrower femora, with lower periosteal and endocortical perimeters than CtskCre.gp130(w/w) controls. Since IL-6 and IL-11R global knockout mice exhibited a similar reduction in femoral width, we also assessed periosteal bone formation in those strains, and found bone forming surfaces were also reduced in male IL-6 null mice. These data suggest that IL-6/gp130 signalling in the osteoclast is not essential for normal bone resorption in vivo, but maintains both trabecular and periosteal bone formation in male mice by promoting osteoblast activity through the stimulation of osteoclast-derived "coupling factors" and "osteotransmitters", respectively.

The Lung-Liver Axis: A Requirement for Maximal Innate Immunity and Hepatoprotection during Pneumonia

The hepatic acute-phase response (APR), stimulated by injury or inflammation, is characterized by significant changes in circulating acute-phase protein (APP) concentrations. Although individual functions of liver-derived APPs are known, the net consequence of APP changes is unclear. Pneumonia, which induces the APR, causes an inflammatory response within the airspaces that is coordinated largely by alveolar macrophages and is typified by cytokine production, leukocyte recruitment, and plasma extravasation, the latter of which may enable delivery of hepatocyte-derived APPs to the infection site. To determine the functional significance of the hepatic APR during pneumonia, we challenged APR-null mice lacking hepatocyte signal transducer and activator of transcription 3 (STAT3) and v-rel avian reticuloendotheliosis viral oncogene homolog A (RelA) with Escherichia coli in the airspaces. APR-null mice displayed ablated APP induction, significantly increased mortality, liver injury and apoptosis, and a trend toward increased bacterial burdens. TNF-α neutralization reversed hepatotoxicity, but not mortality, suggesting that APR-dependent survival is not solely due to hepatoprotection. After a milder (nonlethal) E. coli infection, hepatocyte-specific mutations decreased APP concentrations and pulmonary inflammation in bronchoalveolar lavage fluid. Cytokine expression in airspace macrophages, but not other airspace or circulating cells, was significantly dependent on APP extravasation into the alveoli. These data identify a novel signaling axis whereby the liver response enhances macrophage activation and pulmonary inflammation during pneumonia. Although hepatic acute-phase changes directly curb injury induced by TNF-α in the liver itself, APPs downstream of these same signals promote survival in association with innate immunity in the lungs, thus demonstrating a critical role for the lung-liver axis during pneumonia.

Lack of gp130 expression in hepatocytes attenuates tumor progression in the DEN model

Chronic liver inflammation is a crucial event in the development and growth of hepatocellular carcinoma (HCC). Compelling evidence has shown that interleukin-6 (IL-6)/gp130-dependent signaling has a fundamental role in liver carcinogenesis. Thus, in the present study we aimed to investigate the role of gp130 in hepatocytes for the initiation and progression of HCC. Hepatocyte-specific gp130 knockout mice (gp130(Δhepa)) and control animals (gp130(f/f)) were treated with diethylnitrosamine (DEN). The role of gp130 for acute injury (0-144 h post treatment), tumor initiation (24 weeks) and progression (40 weeks) was analyzed. After acute DEN-induced liver injury we observed a reduction in the inflammatory response in gp130(Δhepa) animals as reflected by decreased levels of IL-6 and oncostatin M. The loss of gp130 slightly attenuated the initiation of HCC 24 weeks after DEN treatment. In contrast, 40 weeks after DEN treatment, male and female gp130(Δhepa) mice showed smaller tumors and reduced tumor burden, indicating a role for hepatocyte-specific gp130 expression during HCC progression. Oxidative stress and DNA damage were substantially and similarly increased by DEN in both gp130(f/f) and gp130(Δhepa) animals. However, gp130(Δhepa) livers revealed aberrant STAT5 activation and decreased levels of transforming growth factor-β (TGFβ), pSMAD2/3 and SMAD2, whereas phosphorylation of STAT3 at Tyr705 and Ser727 was absent. Our results indicate that gp130 deletion in hepatocytes reduces progression, but not HCC initiation in the DEN model. Gp130 deletion resulted in STAT3 inhibition but increased STAT5 activation and diminished TGF-dependent signaling. Hence, blocking gp130 in hepatocytes might be an interesting therapeutic target to inhibit the growth of HCC.

Acute and chronic effects of IL-22 on acetaminophen-induced liver injury

Acetaminophen (APAP)-induced liver injury (AILI) accounts for half of the acute liver failure cases in the United States. A better understanding of the underlying mechanisms of AILI is necessary for the development of novel antidotes. We found that pretreatment with IL-22 protected mice from APAP-mediated hepatotoxicity. The protection was dependent on STAT3, as IL-22 failed to reduce APAP hepatotoxicity in liver-specific STAT3 knockout mice. In contrast to the acute exposure to IL-22, the endogenous chronic overexpression of IL-22 in IL-22 transgenic (TG) mice or IL-22 adenovirus treatment for 6 wk resulted in a markedly increased susceptibility to AILI. Furthermore, the hepatic expression levels of cytochrome 2E1 (Cyp2E1) and Cyp1A2 were much higher in IL-22TG mice. Ablation of Cyp2E1 but not hepatic STAT3 abolished AILI and protein-adduct formation in IL-22TG mice. Finally, hepatic expression of HNF-1α, a transcriptional factor that is known to control Cyp2E1 expression, was elevated in IL-22TG mice compared with wild-type mice. Upregulation of hepatic Cyp2E1 was only observed in mice with constitutive overexpression of IL-22 but not with short-term treatment with one dose of IL-22 or multiple doses of IL-22 for 2 wk. In conclusion, short-term acute IL-22 exposure protects mice against AILI through STAT3 activation; however, chronic constitutive overexpression of IL-22 exacerbates AILI by increasing Cyp2E1 and toxic reactive APAP metabolite production. These findings may not only enhance our understanding of the effects of chronic inflammation on AILI in patients with liver disease, but are also helpful to identify novel therapeutic targets for the treatment of AILI.

Interleukins in chronic liver disease: lessons learned from experimental mouse models

Interleukins represent a class of immunomodulatory cytokines, small intercellular signaling proteins, that are critically involved in the regulation of immune responses. They are produced in large amounts by various cell types during inflammatory reactions, and the balance of cytokines determines the outcome of an immune response. Therefore, cytokines are regarded as interesting therapeutic targets for the treatment of patients with liver diseases. Mouse models provide a good tool for in vivo studies on cytokine function, as human and mouse cytokines share many homologies. Sophisticated mouse models either mimicking distinct pathological conditions or targeting cytokines and cytokine-signaling pathways in the liver or even in distinct cellular compartments have provided enormous insight into the different functions of interleukins during hepatic inflammation. Interleukins may have pro- as well as anti-inflammatory functions in chronic liver diseases, some interleukins even both, dependent on the inflammatory stimulus, the producing and the responding cell type. IL-17, for example, promotes hepatic fibrogenesis through activation of hepatic stellate cells and facilitates development of liver cancer through recruitment of myeloid-derived suppressor cells. IL-22, on the other hand, protects from development of fibrosis or steatohepatitis. IL-12 balances T-helper (Th)-1 and Th2 cell responses in infectious disease models. IL-13 and IL-33, two cytokines related to Th2 cells and innate lymphoid cells, promote fibrotic responses in the liver. IL-10 is the prototypic anti-inflammatory interleukin with tissue-protective functions during chronic liver injury and fibrogenesis. Despite its critical role for inducing the acute-phase response in the liver, IL-6 signaling is protective during fibrosis progression, but promotes hepatocellular carcinoma. Experimental studies in mice help to define the exact influence of a specific cytokine on the outcome of chronic liver diseases and to identify useful therapeutic targets.

Gp130-dependent signaling in the podocyte

Renal inflammation, in particular glomerular, is often characterized by increased IL-6 levels. The in vivo relevance of IL-6 signaling in glomerular podocytes, which play central roles in most glomerular diseases, is unknown. Here, we show that in normal mice, podocytes express gp130, the common signal-transducing receptor subunit of the IL-6 family of cytokines. Following systemic IL-6 or LPS injection in mice, podocyte IL-6 signaling was evidenced by downstream STAT3 phosphorylation. Next, we generated mice deficient for gp130 in podocytes. Expectedly, these mice exhibited abrogated IL-6 downstream signaling in podocytes. At the age of 40 wk, they did not show spontaneous renal pathology or abnormal renal function. The mice were then challenged using two LPS injury models as well as nephrotoxic serum to induce crescentic nephritis. Under all conditions, circulating IL-6 levels increased markedly and the mice developed the pathological hallmarks of the corresponding injury models such as proteinuria and development of glomerular crescents, respectively. However, despite the capacity of normal podocytes to transduce IL-6 family signals downstream, there were no significant differences between mice bearing the podocyte-specific gp130 deletion and their control littermates in any of these models. In conclusion, under the different conditions tested, gp130 signaling was not a critical component of the (patho-)biology of the podocyte in vivo.

The primary function of gp130 signaling in osteoblasts is to maintain bone formation and strength, rather than promote osteoclast formation

Interleukin-6 (IL-6) family cytokines act via gp130 in the osteoblast lineage to stimulate the formation of osteoclasts (bone resorbing cells) and the activity of osteoblasts (bone forming cells), and to inhibit expression of the osteocyte protein, sclerostin. We report here that a profound reduction in trabecular bone mass occurs both when gp130 is deleted in the entire osteoblast lineage (Osx1Cre gp130 f/f) and when this deletion is restricted to osteocytes (DMP1Cre gp130 f/f). This was caused not by an alteration in osteoclastogenesis, but by a low level of bone formation specific to the trabecular compartment. In contrast, cortical diameter increased to maintain ultimate bone strength, despite a reduction in collagen type 1 production. We conclude that osteocytic gp130 signaling is required for normal trabecular bone mass and proper cortical bone composition.

Modeling progressive non-alcoholic fatty liver disease in the laboratory mouse

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the world and its prevalence is rising. In the absence of disease progression, fatty liver poses minimal risk of detrimental health outcomes. However, advancement to non-alcoholic steatohepatitis (NASH) confers a markedly increased likelihood of developing severe liver pathologies, including fibrosis, cirrhosis, organ failure, and cancer. Although a substantial percentage of NAFLD patients develop NASH, the genetic and molecular mechanisms driving this progression are poorly understood, making it difficult to predict which patients will ultimately develop advanced liver disease. Deficiencies in mechanistic understanding preclude the identification of beneficial prognostic indicators and the development of effective therapies. Mouse models of progressive NAFLD serve as a complementary approach to the direct analysis of human patients. By providing an easily manipulated experimental system that can be rigorously controlled, they facilitate an improved understanding of disease development and progression. In this review, we discuss genetically- and chemically-induced models of NAFLD that progress to NASH, fibrosis, and liver cancer in the context of the major signaling pathways whose disruption has been implicated as a driving force for their development. Additionally, an overview of nutritional models of progressive NAFLD is provided.

Optimization of upcyte® human hepatocytes for the in vitro micronucleus assay

"Upcyte(®) human hepatocytes" have the unique property of combining proliferation with the expression of drug metabolising activities. In our current study, we evaluated whether these cells would be suitable for early in vitro micronucleus (MN) tests. A treatment period of 96 h without a recovery period was most reliable for detecting MN formation in upcyte(®) hepatocytes from Donor 740. The basal MN rate in upcyte(®) hepatocytes varied considerably between donors (7-28%); therefore, modifications to the assay medium were tested to determine whether they could decrease inherent MN formation. Optimal medium supplements were 10 ng/ml oncostatin M for the pre-culture and recovery periods and 25 ng/ml epidermal growth factor and 10 ng/ml oncostatin M for the treatment period. Using the optimised conditions and outcome criteria, the upcyte(®) hepatocyte MN assay could correctly identify directly acting (e.g. mitomycin C, etoposide) and metabolically activated genotoxins (e.g. benzo[a]pyrene, cyclophosphamide). "True negative" and "false positive" compounds were also correctly identified as negative. The basal %MN in upcyte(®) hepatocytes from Donor 740 treated with DMSO, cyclophosphamide or MMC, was essentially unaffected by the growth stage ranging from population doublings of 14-61, suggesting that billions of cells could be produced from a single donor for standardised drug toxicity testing. In conclusion, we have established and optimised an in vitro MN test by using upcyte(®) hepatocytes to correctly identify known direct and metabolically activated genotoxicants as well as "false positives" and true negative compounds. The almost unlimited supply of cells from a single donor and optimised test conditions increase reproducibility in early and more predictive in vitro MN tests.

Differential regulation of hepatic organic cation transporter 1, organic anion-transporting polypeptide 1a4, bile-salt export pump, and multidrug resistance-associated protein 2 transporter expression in lymphocyte-deficient mice associates with interleukin-6 production

Cholestasis results from interrupted bile flow and is associated with immune-mediated liver diseases. It is unclear how inflammation contributes to cholestasis. The aim of this study was to determine whether T and B cells contribute to hepatic transporter expression under basal and inflammatory conditions. C57BL/6J wild-type mice or strains lacking T, B, or both T and B cells were exposed to lipopolysaccharide (LPS) or saline, and livers were collected 16 hours later. Branched DNA signal amplification was used to assess mRNA levels of organic anion-transporting polypeptides (Oatp) 1a1, 1a4, and 1b2; organic cation transporter (Oct) 1; canalicular bile-salt export pump (Bsep); multidrug resistance-associated proteins (Mrp) 2 and 3; and sodium-taurocholate cotransporting polypeptide (Ntcp). Real-time polymerase chain reaction analysis was used to correlate changes of transporter expression with interleukin-1b (IL-1b), IL-6, IL-17A, IL-17F, tumor necrosis factor-α (TNF-α), and interferon-γ expression in the liver. LPS treatment inhibited Bsep and Oct1 mRNA expression, and this was abrogated with a loss of T cells, but not B cells. In addition, the absence of T cells increased Mrp2 mRNA expression, whereas B cell deficiency attenuated Oatp1a4 mRNA in LPS-treated mice. Oatp1a1, Oatp1b2, Ntcp, and Mrp3 were largely unaffected by T or B cell deficiency. Lymphocyte deficiency altered basal and inflammatory IL-6, but not TNF-α or IL-1b, mRNA expression. Taken together, these data implicate lymphocytes as regulators of basal and inflammatory hepatic transporter expression and suggest that IL-6 signaling may play a critical role.

The regenerative activity of interleukin-6

Interleukin-6 (IL-6) is a cytokine which is involved in many inflammatory processes and in the development of cancer. In addition, IL-6 has been shown to be important for the induction of hepatic acute-phase proteins, for the regeneration of the liver and for the stimulation of B-cells. IL-6 binds to a transmembrane IL-6 receptor (IL-6R), which is present on hepatocytes and some leukocytes. The complex of IL-6 and IL-6R associates with a second protein, gp130, which is expressed on all cells of the body. Since neither IL-6 nor IL-6R has a measurable affinity for gp130, cells, which do not express IL-6R, are not responsive to the cytokine IL-6. It could be shown, however, that a naturally occurring soluble IL-6R (sIL-6R) in complex with IL-6 can bind to gp130 on cells with no IL-6R expression. Therefore, cells shedding the sIL-6R render cells, which only express gp130, responsive to the cytokine. This process has been called trans-signaling. In the present chapter, we summarize the known activities of IL-6 with a special emphasis on regenerative activities, which often depend on the sIL-6R. A designer cytokine called Hyper-IL-6, which is a fusion protein of IL-6 and the sIL-6R, can mimic IL-6 trans-signaling responses in vitro and in vivo with considerably higher efficacy than the combination of the natural proteins IL-6 and sIL-6R. We present recent examples from animal models in which the therapeutic potential of Hyper-IL-6 has been evaluated. We propose that Hyper-IL-6 can be used to induce potent regeneration responses in liver, kidney, and other tissues and therefore will be a novel therapeutic approach in regenerative medicine.

Lack of hepatic c-Met and gp130 expression is associated with an impaired antibacterial response and higher lethality after bile duct ligation

The prognosis of liver failure is often determined by infectious and cholestatic complications. As HGF/c-Met and interleukin (IL)-6/gp130 control hepatic cytoprotective pathways, we here investigated their cooperative role during the onset of cholestatic liver injury. Conditional hepatocyte-specific ((Δhepa)) c-Met, gp130 and c-Met/gp130 knockout mice (Cre-loxP system) were subjected to bile duct ligation (BDL) and lipopolysaccharide (LPS) stimulation. gp130(Δhepa) and c-Met/gp130(Δhepa) mice displayed increased lethality associated with severe bacteraemia early after BDL, whereas c-Met(Δhepa) and wild-type mice showed normal survival. Analysis of the innate immune response and the regulation of hepatic antibacterial pathways showed that the LPS-triggered hepatocellular response via the Toll-like receptor-4 pathway was regulated differentially by HGF/c-Met and IL-6/gp130. Activation of p38MAPK, c-Jun N-terminal kinase and signalling transducer and activator of transcription-3 was impaired in gp130(Δ) and c-Met(Δhepa) livers. In addition, the acute-phase response (APR) was reduced in c-Met(Δhepa) livers, whereas gp130(Δhepa) displayed a completely abolished APR. In contrast, TNF-α-dependent NF-κB activation was enhanced in gp130(Δhepa) and c-Met(Δhepa) mice and it was associated with a higher rate of apoptosis and inflammation. Moreover, expression of the neutrophil produced and secreted cathelin-related antimicrobial peptide and of genes related to the inflammasome complex correlated with the strength of the bacterial infection and with TNF-α expression. In conclusion, Gp130 and c-Met are involved in the hepatic antibacterial and innate immune response, control the APR and thus prevent sepsis and liver injury during cholestatic conditions.

Cell signals influencing hepatic fibrosis

Liver fibrosis is the result of the entire organism responding to a chronic injury. Every cell type in the liver contributes to the fibrosis. This paper first discusses key intracellular signaling pathways that are induced during liver fibrosis. The paper then examines the effects of these signaling pathways on the major cell types in the liver. This will provide insights into the molecular pathophysiology of liver fibrosis and should identify therapeutic targets.

Signal transducer and activator of transcription 3 in liver diseases: a novel therapeutic target

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that is activated by many cytokines and growth factors and plays a key role in cell survival, proliferation, and differentiation. STAT3 activation is detected virtually in all rodent models of liver injury and in human liver diseases. In this review, we highlight recent advances of STAT3 signaling in liver injury, steatosis, inflammation, regeneration, fibrosis, and hepatocarcinogenesis. The cytokines and small molecules that activate STAT3 in hepatocytes may have therapeutic benefits to treat acute liver injury, fatty liver disease, and alcoholic hepatitis, while blockage of STAT3 may have a therapeutic potential to prevent and treat liver cancer.

Nrf2 induces interleukin-6 (IL-6) expression via an antioxidant response element within the IL-6 promoter

IL-6 gene expression is controlled by a promoter region containing multiple regulatory elements such as NF-κB, NF-IL6, CRE, GRE, and TRE. In this study, we demonstrated that TRE, found within the IL-6 promoter, is embedded in a functional antioxidant response element (ARE) matching an entire ARE consensus sequence. Further, point mutations of the ARE consensus sequence in the IL-6 promoter construct selectively eliminate ARE but not TRE activity. Nrf2 is a redox-sensitive transcription factor which provides cytoprotection against electrophilic and oxidative stress and is the most potent activator of ARE-dependent transcription. Using Nrf2 knock-out mice we demonstrate that Nrf2 is a potent activator of IL-6 gene transcription in vivo. Moreover, we show evidence that Nrf2 is the transcription factor that activates IL6 expression in a cholestatic hepatitis mouse model. Our findings suggest a possible role of IL-6 in oxidative stress defense and also give indication about an important function for Nrf2 in the regulation of hematopoietic and inflammatory processes.

Hepatic progenitor cells: an update

Liver progenitor cells are activated in most human liver diseases. The dynamics, and therefore subpopulations, of progenitor cells are, however, different in acute versus chronic hepatocytic diseases and in biliary diseases. The role of Wnt and Notch signaling pathways in activation and differentiation of human hepatic progenitor cells holds great promise because they can be manipulated by drugs. Hepatocytic differentiation requires inhibition of Notch (numb switched on), whereas cholangiocytic differentiation requires Notch activation. In this way, the patients' own regenerative response could be supported, which could eventually even avoid the need for transplantation in several patients.

Hepatic acute-phase proteins control innate immune responses during infection by promoting myeloid-derived suppressor cell function

Acute-phase proteins (APPs) are an evolutionarily conserved family of proteins produced mainly in the liver in response to infection and inflammation. Despite vast pro- and antiinflammatory properties ascribed to individual APPs, their collective function during infections remains poorly defined. Using a mouse model of polymicrobial sepsis, we show that abrogation of APP production by hepatocyte-specific gp130 deletion, the signaling receptor shared by IL-6 family cytokines, strongly increased mortality despite normal bacterial clearance. Hepatic gp130 signaling through STAT3 was required to control systemic inflammation. Notably, hepatic gp130-STAT3 activation was also essential for mobilization and tissue accumulation of myeloid-derived suppressor cells (MDSCs), a cell population mainly known for antiinflammatory properties in cancer. MDSCs were critical to regulate innate inflammation, and their adoptive transfer efficiently protected gp130-deficient mice from sepsis-associated mortality. The hepatic APPs serum amyloid A and Cxcl1/KC cooperatively promoted MDSC mobilization, accumulation, and survival, and reversed dysregulated inflammation and restored survival of gp130-deficient mice. Thus, gp130-dependent communication between the liver and MDSCs through APPs controls inflammatory responses during infection.

Lack of glycoprotein 130/signal transducer and activator of transcription 3-mediated signaling in hepatocytes enhances chronic liver injury and fibrosis progression in a model of sclerosing cholangitis

The 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) model leads to chronic cholestatic liver injury and therefore resembles human diseases such as sclerosing cholangitis and forms of metabolic liver diseases. The role of the interleukin-6/glycoprotein 130 (gp130) system in this context is still undefined. Therefore, conditional gp130 knockout and knockin mice were used to achieve hepatocyte-specific deletions of gp130 (gp130(Deltahepa)), gp130-dependent ras (gp130(DeltahepaRas)), and signal transducer and activator of transcription (STAT) (gp130(DeltahepaSTAT)) activation. These mice were treated with a DDC-containing diet and analyzed over time. Mice deficient in hepatic gp130 and STAT signaling showed increased and earlier mortality than wild-type and gp130(DeltahepaRas) animals. Over time, significantly more apoptosis and cholestasis became evident in gp130(Deltahepa) and gp130(DeltahepaSTAT) mice. These mice also displayed increased tumor necrosis factor-alpha expression, a diminished acute-phase response (lack of STAT3 and serum amyloid A activation), and enhanced immune cell infiltration in the liver. These were associated with stronger periportal oval cell activation. In addition, DDC treatment in gp130(Deltahepa) and gp130(DeltahepaSTAT) mice resulted in significantly stronger hepatic stellate cell activation. Long-term analysis revealed the development of severe liver fibrosis in gp130(Deltahepa) and gp130(DeltahepaSTAT) animals, as evidenced by increased collagen accumulation. Here we demonstrate that gp130/STAT signaling in hepatocytes provides protection in a cholestatic hepatitis mouse model. STAT3-dependent signaling pathways in hepatocytes protect from apoptosis and tissue injury, which subsequently reduce oval cell activation and prevent fibrosis progression.

Lack of interleukin-6/glycoprotein 130/signal transducers and activators of transcription-3 signaling in hepatocytes predisposes to liver steatosis and injury in mice

A deregulated cytokine balance is involved in triggering the sequence from steatosis to nonalcoholic steatohepatitis, ultimately leading to liver fibrosis and cancer. To better define the role of proinflammatory interleukin-6 (IL-6)-type cytokines in hepatocytes we investigated the role of IL-6 and its shared receptor, glycoprotein 130 (gp130), in a mouse model of steatohepatitis. IL-6(-/-) mice were fed a choline-deficient, ethionine-supplemented (CDE) diet. Conditional gp130 knockout and knockin mice were used to achieve hepatocyte-specific deletion of gp130 (gp130(Deltahepa)), gp130-dependent rat sarcoma (Ras)-(gp130(DeltahepaRas)), and signal transducers and activators of transcription (STAT)-(gp130(DeltahepaSTAT)) activation. CDE-treated IL-6(-/-) mice showed a significant hepatic steatosis at 2 weeks after feeding. The mice rapidly developed elevated fasting blood glucose, insulin serum levels, and transaminases. To better define IL-6-dependent intracellular pathways, specifically in hepatocytes, we next treated gp130(Deltahepa) mice with a CDE diet. These animals also developed a marked steatosis with hyperglycemia and displayed elevated insulin serum levels. Additionally, gp130(Deltahepa) animals showed an imbalanced inflammatory response with increased hepatic tumor necrosis factor-alpha and decreased adiponectin messenger RNA levels. Dissecting the hepatocyte-specific gp130-dependent pathways revealed a similar disease phenotype in gp130(DeltahepaSTAT) mice, whereas gp130(DeltahepaRas) animals were protected. In CDE-treated mice lack of gp130-STAT3 signaling was associated with immune-cell-infiltration, jun kinase-activation, a blunted acute-phase-response, and elevated transaminases. Furthermore, gp130(Deltahepa) and gp130(DeltahepaSTAT) mice showed beginning signs of liver fibrosis compared to gp130(DeltahepaRas) mice and controls.

CONCLUSION

During CDE treatment mice lacking IL-6 and gp130-STAT signaling in hepatocytes are prone to hepatic metabolic changes and inflammation. This ultimately leads to progressive steatohepatitis with signs of liver remodeling. Thus, the presented model allows one to further dissect the role of IL-6/gp130-type signaling in hepatocytes during fatty liver degeneration to define new therapeutic targets in metabolic liver diseases.

Arcuate nucleus proopiomelanocortin neurons mediate the acute anorectic actions of leukemia inhibitory factor via gp130

The proinflammatory cytokine leukemia inhibitory factor (LIF) is induced in disease states and is known to inhibit food intake when administered centrally. However, the neural pathways underlying this effect are not well understood. We demonstrate that LIF acutely inhibits food intake by directly activating pro-opiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus. We show that arcuate POMC neurons express the LIF-R, and that LIF stimulates the release of the anorexigenic peptide, alpha-MSH from ex vivo hypothalami. Transgenic mice lacking gp130, the signal transducing subunit of the LIF-R complex, specifically in POMC neurons fail to respond to LIF. Furthermore, LIF does not stimulate the release of alpha-MSH from the transgenic hypothalamic explants. These findings indicate that POMC neurons mediate the acute anorectic actions of central LIF administration and provide a mechanistic link between inflammation and food intake.

The protective role of pregnane X receptor in lipopolysaccharide/D-galactosamine-induced acute liver injury

The pregnane X receptor (PXR) is a nuclear receptor transcription factor regulating drug-metabolizing enzymes and transporters that facilitate xenobiotic and endobiotic detoxification. Recent studies show that PXR is important in abrogating intestinal tissue damage. This study examines the role of PXR in lipopolysaccharide (LPS)/D-galactosamine (GalN)-induced acute liver injury using wild-type and PXR-null mice. LPS/GalN-treated PXR-null mice had greater increases of alanine transaminase (ALT), hepatocyte apoptosis, necrosis, and hemorrhagic liver injury than wild-type mice. LPS/GalN-mediated phosphorylation of JNK1/2 and ERK1/2 was differentially regulated in wild-type and PXR-null mice. Importantly, LPS/GalN-induced hepatic Stat3 survival signaling was impaired and early activation of Jak2 was delayed in PXR-null mice. Expression levels of pro-survival proteins Bcl-xL and heme oxygenase-1 (HO-1), which are downstream of Stat3, were substantially lower in PXR-null than wild-type mouse livers after LPS/GalN treatment. Autophagy is also involved in LPS/GalN-induced liver injury. Lack of PXR resulted in a significant reduction of LC3B-I, -II as well as Beclin-1 protein levels after LPS/GalN treatment. In addition, PXR is implicated in hepatocytes homeostasis. Taken together, PXR is a critical hepatoprotective factor. Increases of LPS/GalN-induced hepatocyte apoptosis and liver injury in PXR-null mice are due to deregulated mitogen-activated protein (MAP) kinase activation as well as delayed Jak2/Stat3 activation, which lead to a compromise in defense mechanisms that involve Bcl-xL-, HO-1, and autophagy-mediated pathways.

Glycoprotein 130-dependent pathways in host hepatocytes are important for liver repopulation in mice

Hepatocyte transplantation (HT) is still restricted by the limited amount of transplantable cells. Therefore, a better understanding of the mechanisms involved in cellular engraftment, proliferation, and in vivo selection is important. Here we aimed to evaluate the role of the interleukin 6 (IL-6)/glycoprotein 130 (gp130) system for liver repopulation. Mice carrying a conditional hepatocyte-specific deletion of the common IL-6 signal transducer gp130 (gp130(Deltahepa)) were used for HT. First, we compared bone marrow transplantation (BMT), partial hepatectomy (PH), and retrorsine treatment of recipient mice to optimize the in vivo selection of transplanted hepatocytes. BMT combined with PH was sufficient to induce a 30-fold increase in the number of transplanted donor hepatocytes, whereas additional retrorsine pretreatment led to an up to 40-fold increase. Next, the influence of gp130 signaling in hepatocytes on cell selection was evaluated. Wild-type (WT) hepatocytes repopulated WT recipients at the same rate as gp130(Deltahepa) cells. In contrast, liver repopulation by transplanted cells was enhanced in gp130(Deltahepa) recipient mice. This was associated with higher proliferation of donor hepatocytes and enhanced apoptosis in gp130(Deltahepa) recipient livers. Additionally, the acute phase response was strongly induced after HT in WT recipients but blunted in gp130(Deltahepa) recipients. As a result, significantly more liver remodeling, evidenced by stronger hepatic stellate cell activation and collagen accumulation, was found in gp130(Deltahepa) mice after HT. In conclusion, the HT model established here can be efficiently applied to investigate cell-specific mechanisms in liver repopulation. Moreover, we have shown that gp130-dependent pathways in host hepatocytes are important for controlling liver repopulation.

Rapamycin prevents concanavalin A-induced liver injury by inhibiting lymphocyte activation

BACKGROUND AND AIMS

Liver injury induced by concanavalin A (Con A) is often used as a model to study the pathophysiology of immune mediated liver injury. Rapamycin (Rapa) is an effective immunosuppressant widely used for preventing immune activation and transplant rejection. However, the effect of Rapa on liver injury caused by Con A has not been carefully examined. In the present study, we examined the effect of Rapa on liver injury caused by Con A.

METHODS

Mice received intraperitoneal Rapa injection before Con A intravenous administration. The liver injury was examined by measuring serum transaminase and pathology, and the level of cytokines was detected by enzyme linked immunosorbent assay (ELISA).

RESULTS

In the present study, we examined the effect of Rapa on liver injury after Con A injection in mice. We found that the treatment of mice with Rapa protected the liver from Con A-induced injury. Pretreatment with Rapa dramatically ameliorated Con A-induced mortality. This protection was associated with reduced transaminase levels in the blood and further confirmed by liver histology. ELISA showed that Rapa suppressed pro-inflammatory cytokines IFN-gamma and TNF-alpha production as compared with the untreated controls. Furthermore, intrahepatic lymphocyte proliferation was significantly inhibited.

CONCLUSION

These findings suggested that Rapa has the therapeutic potential for treatment of immune-mediated liver injury in the clinic.

c-Met confers protection against chronic liver tissue damage and fibrosis progression after bile duct ligation in mice

BACKGROUND & AIMS

The hepatocyte growth factor (HGF)/mesenchymal-epithelial transition factor (c-Met) system is an essential inducer of hepatocyte growth and proliferation. Although a fundamental role for the HGF receptor c-Met has been shown in acute liver regeneration, its cell-specific role in hepatocytes during chronic liver injury and fibrosis progression has not been determined.

METHODS

Hepatocyte-specific c-Met knockout mice (c-Met(Delta hepa)) using the Cre-loxP system were studied in a bile duct ligation (BDL) model. Microarray analyses were performed to define HGF/c-Met-dependent gene expression.

RESULTS

Two strategies for c-Met deletion in hepatocytes to generate hepatocyte-specific c-Met knockout mice were tested. Early deletion during embryonic development was lethal, whereas post-natal Cre expression was successful, leading to the generation of viable c-Met(Delta hepa) mice. BDL in these mice resulted in extensive necrosis and lower proliferation rates of hepatocytes. Gene array analysis of c-Met(Delta hepa) mice revealed a significant reduction of anti-apoptotic genes in c-Met-deleted hepatocytes. These findings could be tested functionally because c-Met(Delta hepa) mice showed a stronger apoptotic response after BDL and Jo-2 stimulation. The phenotype was associated with increased expression of proinflammatory cytokines (tumor necrosis factor-alpha and interleukin-6) and an enhanced recruitment of neutrophils. Activation of these mechanisms triggered a stronger profibrogenic response as evidenced by increased transforming growth factor-beta(1), alpha-smooth muscle actin, collagen-1alpha messenger RNA expression, and enhanced collagen-fiber staining in c-Met(Delta hepa) mice.

CONCLUSIONS

Our results show that deletion of c-Met in hepatocytes leads to more liver cell damage and fibrosis in a chronic cholestatic liver injury model because c-Met triggers survival signals important for hepatocyte recovery.

Population-based discovery of toxicogenomics biomarkers for hepatotoxicity using a laboratory strain diversity panel

Toxicogenomic studies are increasingly used to uncover potential biomarkers of adverse health events, enrich chemical risk assessment, and to facilitate proper identification and treatment of persons susceptible to toxicity. Current approaches to biomarker discovery through gene expression profiling usually utilize a single or few strains of rodents, limiting the ability to detect biomarkers that may represent the wide range of toxicity responses typically observed in genetically heterogeneous human populations. To enhance the utility of animal models to detect response biomarkers for genetically diverse populations, we used a laboratory mouse strain diversity panel. Specifically, mice from 36 inbred strains derived from Mus mus musculus, Mus mus castaneous, and Mus mus domesticus origins were treated with a model hepatotoxic agent, acetaminophen (300 mg/kg, ig). Gene expression profiling was performed on liver tissue collected at 24 h after dosing. We identified 26 population-wide biomarkers of response to acetaminophen hepatotoxicity in which the changes in gene expression were significant across treatment and liver necrosis score but not significant for individual mouse strains. Importantly, most of these biomarker genes are part of the intracellular signaling involved in hepatocyte death and include genes previously associated with acetaminophen-induced hepatotoxicity, such as cyclin-dependent kinase inhibitor 1A (p21) and interleukin 6 signal transducer (Il6st), and genes not previously associated with acetaminophen, such as oncostatin M receptor (Osmr) and MLX interacting protein like (Mlxipl). Our data demonstrate that a multistrain approach may provide utility for understanding genotype-independent toxicity responses and facilitate identification of novel targets of therapeutic intervention.

Inflammatory pathways in liver homeostasis and liver injury

The liver is a unique organ with respect to its anatomical location, allowing continuous blood flow from the gastrointestinal tract through the sinusoids, and its cellular composition, comprising metabolically active hepatocytes, nonhepatocytic parenchymal cells, and various immune cell populations. Cytokines are key mediators within the complex interplay of intrahepatic immune cells and hepatocytes, as they can activate effector functions of immune cells, as well as hepatocytic intracellular signaling pathways controlling cellular homeostasis. Kupffer cells and liver-infiltrating monocyte-derived macrophages are primary sources of cytokines such as tumor-necrosis factor-alpha (TNF-alpha) and interleukin-6. The liver is also enriched in natural killer (NK) and NK T cells, which fulfill functions in pathogen defense, T cell recruitment, and modulation of liver injury. TNF-alpha can activate specific intracellular pathways in hepatocytes that influence cell fate in different manners, e.g., proapoptotic signals via the caspase cascade, but also survival pathways, namely the nuclear factor (NF)-kappaB pathway. NF-kappaB regulates important functions in liver physiology and pathology. Recent experiments with genetically modified mice demonstrated important and partly controversial functions of this pathway, e.g., in cytokine-mediated hepatocyte apoptosis or ischemia-reperfusion injury. The exact dissection of the contribution of recruited and resident immune cells, their soluble cytokine and chemokine mediators, and the intracellular hepatocytic response in liver homeostasis and injury could potentially identify novel targets for the treatment of acute and chronic liver disease, liver fibrosis, or cirrhosis.

Astrocyte gp130 expression is critical for the control of Toxoplasma encephalitis

Toxoplasma gondii infects astrocytes, neurons and microglia cells in the CNS and, after acute encephalitis, persists within neurons. Robust astrocyte activation is a hallmark of Toxoplasma encephalitis (TE); however, the in vivo function of astrocytes is largely unknown. To study their role in TE we generated C57BL/6 GFAP-Cre gp130(fl/fl) mice (where GFAP is glial fibrillary acid protein), which lack gp130, the signal-transducing receptor for IL-6 family cytokines, in their astrocytes. In the TE of wild-type mice, the gp130 ligands IL-6, IL-11, IL-27, LIF, oncostatin M, ciliary neurotrophic factor, B cell stimulating factor, and cardiotrophin-1 were up-regulated. In addition, GFAP(+) astrocytes of gp130(fl/fl) control mice were activated, increased in number, and efficiently restricted inflammatory lesions and parasites, thereby contributing to survival from TE. In contrast, T. gondii- infected GFAP-Cre gp130(fl/fl) mice lost GFAP(+) astrocytes in inflammatory lesions resulting in an inefficient containment of inflammatory lesions, impaired parasite control, and, ultimately, a lethal necrotizing TE. Production of IFN-gamma and the IFN-gamma-induced GTPase (IGTP), which mediate parasite control in astrocytes, was even increased in GFAP-Cre gp130(fl/fl) mice, indicating that instead of the direct antiparasitic effect the immunoregulatory function of GFAP-Cre gp130(fl/fl) astrocytes was disturbed. Correspondingly, in vitro infected GFAP-Cre gp130(fl/fl) astrocytes inhibited the growth of T. gondii efficiently after stimulation with IFN-gamma, whereas neighboring noninfected and TNF-stimulated GFAP-Cre gp130(fl/fl) astrocytes became apoptotic. Collectively, these are the first experiments demonstrating a crucial function of astrocytes in CNS infection.

IL-6 Promotes compensatory liver regeneration in cirrhotic rat after partial hepatectomy

Major hepatic resection in cirrhotic patients is associated with impaired liver regeneration and failure, leading to high peri-operative mortality. In this work, the causes of defective regeneration in cirrhotic liver and the utility of IL-6 treatment were investigated in an experimental model combining cirrhosis and partial hepatectomy in the rat. Relative to normal controls, decompensated cirrhotic animals showed decreased survival, while compensated cirrhotic animals showed similar survival but reduced hepatic DNA synthesis and newly regenerated liver mass amount. Defective liver regeneration was associated with a decrease in STAT3 and NF-kB activation, consistent with an increased accumulation of their respective inhibitors PIAS3 and IkBalpha, and with a decreased induction of Bcl-xL. Treatment with recombinant IL-6 enhanced survival of decompensated cirrhotic animals, while it did not affect survival of compensated cirrhotic animals but sustained liver regeneration, by restoring STAT3 and NF-kB activation and Bcl-xL induction to the levels found in normal controls. The pro-growth effects exerted by IL-6 treatment in cirrhotic liver were attained also at low, pharmacologically acceptable doses. In conclusion, our results suggest that IL-6 treatment may be therapeutic in major resection of cirrhotic liver.

Cell type-dependent pro- and anti-inflammatory role of signal transducer and activator of transcription 3 in alcoholic liver injury

BACKGROUND & AIMS

Signal transducer and activator of transcription 3 (STAT3) is known to be activated in human alcoholic liver disease, but its role in the pathogenesis of alcoholic liver injury remains obscure.

METHODS

The role of STAT3 in alcoholic liver injury was investigated in hepatocyte-specific STAT3 knockout (H-STAT3KO) mice and macrophage/neutrophil-specific STAT3 KO (M/N-STAT3KO) mice. Alcoholic liver injury was achieved by feeding mice a liquid diet containing 5% ethanol for up to 8 weeks.

RESULTS

Compared with wild-type mice, feeding H-STAT3KO mice with an ethanol-containing diet induced greater hepatic steatosis, hypertriglyceridemia, and hepatic expression of lipogenic genes (sterol regulatory element-binding protein, fatty acid synthase, acetyl-CoA carboxylase-1, and stearoyl-CoA desaturase 1), but less inflammation and lower expression of hepatic proinflammatory cytokines. In contrast, ethanol-fed M/N-STAT3KO mice showed more hepatic inflammation, worse injury, and increased hepatic expression of proinflammatory cytokines compared with wild-type mice. Kupffer cells isolated from ethanol-fed H-STAT3KO mice produced similar amounts of reactive oxygen species and tumor necrosis factor alpha, whereas Kupffer cells from M/N-STAT3KO mice produced more reactive oxygen species and tumor necrosis factor alpha compared with wild-type controls.

CONCLUSIONS

These findings suggest that STAT3 regulates hepatic inflammation in a cell type-dependent manner during alcoholic liver injury: STAT3 in hepatocytes promotes whereas STAT3 in macrophages/Kupffer cells suppresses inflammation. In addition, activation of hepatocellular STAT3 ameliorates alcoholic fatty liver via inhibition of sterol regulatory element-binding protein 1c expression.

Mao (Ephedra sinica Stapf) protects against D-galactosamine and lipopolysaccharide-induced hepatic failure

Mao is one component of various traditional herbal medicines. We examined the effects of Mao on an acute liver failure model treated with d-galactosamine (GalN) and lipopolysaccharide (LPS). The lethality of mice administrated Mao with GalN/LPS was significantly decreased compared with that in mice without Mao. Hepatic apoptosis and inflammatory cell infiltration were slight in Mao-treated mice. Serum alanine aminotransferase (ALT) and total bilirubin (T.Bil) activity, tumor necrosis factor alpha (TNF-alpha) levels and caspase 8, 9, and 3 activity in the liver were significantly lower in mice administrated Mao. But, Serum interleukin-6 (IL-6), IL-10 levels and signal transducers and activators of transcription 3 (STAT3) activity in the liver were significantly higher in mice administrated Mao. To investigate the effect of STAT3, we used AG490, which selectively inhibits the activation of Janus kinase (JAK) family tyrosine kinase and inhibits the constitutive activation of STAT3. There was significant aggravation in hepatic apoptosis treated with Mao and AG490 compared with Mao alone. In conclusions, Mao significantly suppressed hepatic apoptosis by inhibition of TNF-alpha production and caspase activity. Furthermore, it is also suggested that Mao, which activates STAT3 induced by IL-6, may be a useful therapeutic tool for fulminant hepatic failure.