Emerging roles of tyrosine kinases in hepatic inflammatory diseases and therapeutic opportunities

Inflammation has been convicted of causing and worsening many liver diseases like acute liver failure, fibrosis, cirrhosis, fatty liver and liver cancer. Pattern recognition receptors (PRRs) like TLRs 4 and 9 localized on resident or recruited immune cells are well known cellular detectors of pathogen and damage-associated molecular patterns (PAMPs/DAMPs). Stimulation of these receptors generates the sterile and non-sterile inflammatory responses in the liver. When these responses are repeated, there will be a sustained liver injury that may progress to fibrosis and its outcomes. Crosstalk between inflammatory/fibrogenic-dependent streams and certain tyrosine kinases (TKs) has recently evolved in the context of hepatic diseases. Because of TKs increasing importance, their role should be elucidated to highlight effective approaches to manage the diverse liver disorders. This review will give a brief overview of types and functions of some TKs like BTK, JAKs, Syk, PI3K, Src and c-Abl, as well as receptors for TAM, PDGF, EGF, VEGF and HGF. It will then move to discuss the roles of these TKs in the regulation of the proinflammatory, fibrogenic and tumorigenic responses in the liver. Lastly, the therapeutic opportunities for targeting TKs in hepatic inflammatory disorders will be addressed. Overall, this review sheds light on the diverse TKs that have substantial roles in hepatic disorders and potential therapeutics modulating their activity.

Effect of Epidermal Growth Factor Treatment and Polychlorinated Biphenyl Exposure in a Dietary-Exposure Mouse Model of Steatohepatitis

BACKGROUND

Polychlorinated biphenyls (PCBs) are signaling disrupting chemicals that exacerbate nonalcoholic steatohepatitis (NASH) in mice. They are epidermal growth factor receptor (EGFR) inhibitors that enhance hepatic inflammation and fibrosis in mice.

OBJECTIVES

This study tested the hypothesis that epidermal growth factor (EGF) administration can attenuate PCB-related NASH by increasing hepatic EGFR signaling in a mouse model.

METHODS

C57BL/6 male mice were fed a 42% milk fat diet and exposed to Aroclor 1260 (20 mg / kg ) or vehicle for 12 wk. EGF (0.2 μ g / g ) or vehicle were administered daily for 10 d starting at study week 10. Liver and metabolic phenotyping were performed. The EGF dose was selected based on results of an acute dose-finding study (30 min treatment of EGF at 0.2, 0.02, 0.002 μ g / g of via intraperitoneal injection). Hepatic phosphoproteomic analysis was performed using liver tissue from this acute study to understand EGFR's role in liver physiology.

RESULTS

Markers of EGFR signaling were higher in EGF-treated mice. EGF + PCB -exposed mice had lower hepatic free fatty acids, inflammation, and fibrosis relative to PCB-only exposed mice. EGF-treated mice had higher plasma lipids, with no improvement in hepatic steatosis, and an association with higher LXR target gene expression and de novo lipogenesis. EGF-treated mice showed more severe hyperglycemia associated with lower adiponectin levels and insulin sensitivity. EGF-treated mice had higher hepatic HNF 4 α , NRF2, and AhR target gene expression but lower constitutive androstane receptor and farnesoid X receptor target gene expression. The hepatic EGF-sensitive phosphoproteome demonstrated a role for EGFR signaling in liver homeostasis.

DISCUSSION

These results validated EGFR inhibition as a causal mode of action for PCB-related hepatic inflammation and fibrosis in a mouse model of NASH. However, observed adverse effects may limit the clinical translation of EGF therapy. More data are required to better understand EGFR's underinvestigated roles in liver and environmental health. https://doi.org/10.1289/EHP8222.

Role of epidermal growth factor receptor in liver injury and lipid metabolism: Emerging new roles for an old receptor

Epidermal growth factor receptor (EGFR) is conventionally known to play a crucial role in hepatocyte proliferation, liver regeneration and is also associated with hepatocellular carcinogenesis. In addition to these proliferative roles, EGFR has also implicated in apoptotic cell death signaling in various hepatic cells, mitochondrial dysfunction and acute liver necrosis in a clinically relevant murine model of acetaminophen overdose, warranting further comprehensive exploration of this paradoxical role of EGFR in hepatotoxicity. Apart from ligand dependent activation, EGFR can also be activated in ligand-independent manner, which is mainly associated to liver injury. Recent evidence has also emerged demonstrating important role of EGFR in lipid and fatty acid metabolism in quiescent and regenerating liver. Based on these findings, EGFR has also been shown to play an important role in steatosis in clinically relevant murine NAFLD models via regulating master transcription factors governing fatty acid synthesis and lipolysis. Moreover, several lines of evidences indicate that EGFR is also involved in hepatocellular injury, oxidative stress, inflammation, direct stellate cell activation and fibrosis in chronic liver injury models, including repeated CCl₄ exposure, high-fat diet and fast-food diet models. In addition to briefly summarizing role of EGFR in liver regeneration, this review comprehensively discusses all these non-conventional emerging roles of EGFR. Considering evidences of multi-facet role of EGFR at various levels in these pathophysiological process, EGFR can be a promising therapeutic target for various liver diseases, including acute liver failure and NAFLD, requiring further exploration. These roles of EGFR are relevant for alcoholic liver diseases (ALD) as well, thus providing a valid rationale for future investigations exploring a role of EGFR in ALD.

Epidermal Growth Factor Receptor Signaling Disruption by Endocrine and Metabolic Disrupting Chemicals

The purpose of this study is to identify an environmentally relevant shared receptor target for endocrine and metabolism disrupting chemical pollutants. A feature of the tested chemicals was that they induced Cyp2b10 in vivo implicating activation of the constitutive androstane receptor (CAR). Recent studies suggest that these compounds could be indirect CAR activators via epidermal growth factor receptor (EGFR) inhibition. Assays included a CAR activity reporter assay, EGF endocytosis assay, and EGFR phosphorylation assay. Docking simulations were used to identify putative binding sites for environmental chemicals on the EGFR. Whole-weight and lipid-adjusted serum mean pollutant exposures were determined using data from the National Health and Examination Survey (NHANES) and compared with the IC50 values determined in vitro. Chlordane, trans-nonachlor, PCB-126, PCB-153, and atrazine were the most potent EGFR inhibitors tested. PCB-126, PCB-153, and trans-nonachlor appeared to be competitive EGFR antagonists as they displaced bound EGF from EGFR. However, atrazine acted through a different mechanism and could be an EGFR tyrosine kinase inhibitor. EGFR inhibition relative effect potencies were determined for these compounds. In NHANES, serum concentrations of trans-nonachlor, PCB-126, and PCB-153 greatly exceeded their calculated IC50 values. A common mechanism of action through EGFR inhibition for three diverse classes of metabolic disrupting chemicals was characterized by measuring inhibition of EGFR phosphorylation and EGF-EGFR endocytosis. Based on NHANES data, EGFR inhibition may be an environmentally relevant mode of action for some PCBs, pesticides, and herbicides.

Polychlorinated biphenyls disrupt hepatic epidermal growth factor receptor signaling

1. Polychlorinated biphenyls (PCBs) are persistent environmental pollutants that disrupt hepatic xenobiotic and intermediary metabolism, leading to metabolic syndrome and nonalcoholic steatohepatitis (NASH). 2. Since phenobarbital indirectly activates Constitutive Androstane Receptor (CAR) by antagonizing growth factor binding to the epidermal growth factor receptor (EGFR), we hypothesized that PCBs may also diminish EGFR signaling. 3. The effects of the PCB mixture Aroclor 1260 on the protein phosphorylation cascade triggered by EGFR activation were determined in murine (in vitro and in vivo) and human models (in vitro). EGFR tyrosine residue phosphorylation was decreased by PCBs in all models tested. 4. The IC₅₀ values for Aroclor 1260 concentrations that decreased Y1173 phosphorylation of EGFR were similar in murine AML-12 and human HepG2 cells (∼2-4 μg/mL). Both dioxin and non-dioxin-like PCB congeners decreased EGFR phosphorylation in cell culture. 5. PCB treatment reduced phosphorylation of downstream EGFR effectors including Akt and mTOR, as well as other phosphoprotein targets including STAT3 and c-RAF in vivo. 6. PCBs diminish EGFR signaling in human and murine hepatocyte models and may dysregulate critical phosphoprotein regulators of energy metabolism and nutrition, providing a new mechanism of action in environmental diseases.

Long-term influence of sialoadenectomy on the liver of male albino rat

Epidermal growth factor is an endocrine product of the submandibular gland; the liver is an important target of its action and is affected by sialoadenectomy. Thirty rats were used in this study and divided into group I (sham-operated animals), group II (sialoadenectomy after 4 weeks), and group III (sialoadenectomy after 10 weeks). Liver samples were processed for light and electron microscope examination. Sialoadenectomy induced mild-to-moderate liver damage which persists up to 10 weeks after the operation. This damage is manifested morphologically rather than functionally, affecting the general structure, hepatocytes, hepatic stellate cells, and hepatic sinusoids.

Amphiregulin suppresses epithelial cell apoptosis in lipopolysaccharide-induced lung injury in mice

BACKGROUND AND OBJECTIVE

As a member of the epidermal growth factor family, amphiregulin contributes to the regulation of cell proliferation. Amphiregulin was reported to be upregulated in damaged lung tissues in patients with chronic obstructive pulmonary disease and asthma and in lung epithelial cells in a ventilator-associated lung injury model. In this study, we investigated the effect of amphiregulin on lipopolysaccharide (LPS)-induced acute lung injury in mice.

METHODS

Acute lung injury was induced by intranasal instillation of LPS in female C57BL/6 mice, and the mice were given intraperitoneal injections of recombinant amphiregulin or phosphate-buffered saline 6 and 0.5 h before and 3 h after LPS instillation. The effect of amphiregulin on apoptosis and apoptotic pathways in a murine lung alveolar type II epithelial cell line (LA-4 cells) were examined using flow cytometry and western blotting, respectively.

RESULTS

Recombinant amphiregulin suppressed epithelial cell apoptosis in LPS-induced lung injury in mice. Western blotting revealed that amphiregulin suppressed epithelial cell apoptosis by inhibiting caspase-8 activity.

CONCLUSION

Amphiregulin signaling may be a therapeutic target for LPS-induced lung injury treatment through its prevention of epithelial cell apoptosis.

Expression and Function of the Epidermal Growth Factor Receptor in Physiology and Disease

The epidermal growth factor receptor (EGFR) is the prototypical member of a family of membrane-associated intrinsic tyrosine kinase receptors, the ErbB family. EGFR is activated by multiple ligands, including EGF, transforming growth factor (TGF)-α, HB-EGF, betacellulin, amphiregulin, epiregulin, and epigen. EGFR is expressed in multiple organs and plays important roles in proliferation, survival, and differentiation in both development and normal physiology, as well as in pathophysiological conditions. In addition, EGFR transactivation underlies some important biologic consequences in response to many G protein-coupled receptor (GPCR) agonists. Aberrant EGFR activation is a significant factor in development and progression of multiple cancers, which has led to development of mechanism-based therapies with specific receptor antibodies and tyrosine kinase inhibitors. This review highlights the current knowledge about mechanisms and roles of EGFR in physiology and disease.

EGFR Signaling in Liver Diseases

The epidermal growth factor receptor (EGFR) is a transmembrane receptor tyrosine kinase that is activated by several ligands leading to the activation of diverse signaling pathways controlling mainly proliferation, differentiation, and survival. The EGFR signaling axis has been shown to play a key role during liver regeneration following acute and chronic liver damage, as well as in cirrhosis and hepatocellular carcinoma (HCC) highlighting the importance of the EGFR in the development of liver diseases. Despite the frequent overexpression of EGFR in human HCC, clinical studies with EGFR inhibitors have so far shown only modest results. Interestingly, a recent study has shown that in human HCC and in mouse HCC models the EGFR is upregulated in liver macrophages where it plays a tumor-promoting function. Thus, the role of EGFR in liver diseases appears to be more complex than what anticipated. Further studies are needed to improve the molecular understanding of the cell-specific signaling pathways that control disease development and progression to be able to develop better therapies targeting major components of the EGFR signaling network in selected cell types. In this review, we compiled the current knowledge of EGFR signaling in different models of liver damage and diseases, mainly derived from the analysis of HCC cell lines and genetically engineered mouse models (GEMMs).

White matter changes in chronic alcoholic liver disease: Hypothesized association and putative biochemical mechanisms

Advanced liver disease has long been associated with cerebral abnormalities. These abnormalities, termed acquired hepatocerebral degeneration, are typically visualized as T1 weighted hyperintensity on MRI in the deep gray matter of the basal ganglia. Recent reports, however, have demonstrated that a subset of patients with chronic alcoholic liver disease may also develop white matter abnormalities. Thus far, the morphology of these changes is not well characterized. Previous studies have described these changes as patchy, sporadic white matter abnormalities but have not posited localization of these changes to any particular white matter tracts. This paper hypothesizes that the white matter findings associated with advanced alcoholic liver disease localize to the corticocerebellar tracts. As an initial investigation of this hypothesis, 78 patients with a diagnosis of liver cirrhosis and an MRI showing clearly abnormal T1 weighted hyperintensity in the bilateral globus pallidus, characteristic of chronic liver disease, were examined for white matter signal abnormalities in the corticocerebellar tracts using FLAIR and T2 weighted images. The corticocerebellar tracts were subdivided into two regions: periventricular white matter (consisting of the sum of the centrum-semiovale and corona radiata), and lower white matter (consisting of the corona radiata, internal capsules, middle cerebral peduncles, middle cerebellar peduncles and cerebellum). As compared to matched controls, significantly greater signal abnormalities in both the periventricular white matter and lower white matter regions of the corticocerebellar tracts were observed in patients with known liver cirrhosis and abnormal T1 W hyperintensity in the globi pallidi. This difference was most pronounced in the lower white matter region of the corticocerebellar tract, with statistical significance of p<0.0005. Furthermore, the pathophysiologic mechanism underlying these changes remains unknown. This paper hypothesizes that the etiology of white matter changes associated with advanced liver disease may resemble that of white matter findings in subacute combined degeneration secondary to vitamin B12 deficiency. Specifically, significant evidence suggests that dysfunctional methionine metabolism as well as dysregulated cytokine production secondary to B12 deficiency play a major role in the development of subacute combined degeneration. Similar dysfunction of methionine metabolism and cytokine regulation is seen in alcoholic liver disease and is hypothesized in this paper to, at least in part, lead to white matter findings associated with alcoholic liver disease.

Cyclin D1 and FADD as biomarkers in head and neck squamous cell carcinoma

OBJECTIVE

Cyclin D1 and FADD (Fas-associated protein with death domain) regulate the cell cycle and apoptosis, respectively, and are located on chromosome 11q13, which is frequently amplified in head and neck squamous cell carcinoma (HNSCC). This study evaluates these proteins as predictors of clinical outcomes for HNSCC.

STUDY DESIGN

Historical cohort study.

SETTING

Academic tertiary care center.

SUBJECTS

Two hundred twenty-two patients with upper aerodigestive HNSCC.

RESULTS

Patients with tumors that were strongly positive for cyclin D1 and FADD had reduced overall (OS; P = .003 and P < .001), disease-specific (DSS; P = .039 and P < .001), and disease-free (DFS; P = .026 and P < .001) survival, respectively. Together, the 2 markers effectively stratified OS (P < .001), DSS (P < .001), and DFS (P = .002). Strong FADD staining correlated with greater alcohol consumption and varied significantly with primary tumor site: 56% of hypopharynx tumors expressed high levels of FADD but only 7% of glottis tumors. Using Cox regression analysis, FADD and N stage were significant independent predictors of DSS and DFS, whereas cyclin D1, FADD, and N stage were independently significant for OS.

CONCLUSION

Cyclin D1 and FADD may have utility as predictors of long-term outcomes for patients with HNSCC. Further study is needed to determine if these proteins predict response to different treatment approaches or assist in selecting patients for multimodality therapy.

Impairment of long-term potentiation in the hippocampus of alcohol-treated OLETF rats

Type 2 diabetes and chronic heavy alcohol consumption each have been known to be associated with the impairment of hippocampus-dependent cognitive functions. Although both conditions often coexist clinically and there is accumulated evidence of a relationship between the two, the combined effect on hippocampal long-term potentiation (LTP) has not yet been investigated. We compared the effect of type 2 diabetes itself with that of type 2 diabetes with chronic heavy alcohol consumption on the hippocampal LTP using Otsuka Long-Evans Tokushima Fatty (OLETF) rat model, which resembles the characteristics of human type 2 diabetes. Ten of 16-week-old male OLETF rats were randomized into two treatment groups according to weight: the OLETF-Alcohol (O-A, n=5) and the OLETF-Control (O-C, n=5). The rats in the O-A group were fed Lieber-DeCarli Regular EtOH over a 10-week period and the amount of alcohol consumption was 8.42±2.52g/kg/day. To ensure the effect of poor glycemic control on LTP, intraperitoneal glucose tolerance test was performed after a 10-week treatment. The hippocampal LTP was measured by extracellular field excitatory post-synaptic potentials at Shaffer collateral (SC) synapses in the CA1 region. Although the O-A group showed significantly lower fasting and postprandial glucose (P<0.01 and P=0.02, respectively), the hippocampal LTP was more significantly attenuated in the O-A group than the O-C group (P=0.032). The results of this study suggested that chronic heavy alcohol consumption could potentiate the impairment of hippocampal LTP in individuals with impaired glucose tolerance or early type 2 diabetes, even though it did not aggravate, but did improve glycemic control. Clinical attention to chronic heavy drinking will be required in preventing cognitive impairment in individuals with type 2 diabetes.

Epidermal Growth Factor Receptor (EGFR) Crosstalks in Liver Cancer

Hepatocarcinogenesis is a complex multistep process in which many different molecular pathways have been implicated. Hepatocellular carcinoma (HCC) is refractory to conventional chemotherapeutic agents, and the new targeted therapies are meeting with limited success. Interreceptor crosstalk and the positive feedback between different signaling systems are emerging as mechanisms of targeted therapy resistance. The identification of such interactions is therefore of particular relevance to improve therapeutic efficacy. Among the different signaling pathways activated in hepatocarcinogenesis the epidermal growth factor receptor (EGFR) system plays a prominent role, being recognized as a “signaling hub” where different extracellular growth and survival signals converge. EGFR can be transactivated in response to multiple heterologous ligands through the physical interaction with multiple receptors, the activity of intracellular kinases or the shedding of EGFR-ligands. In this article we review the crosstalk between the EGFR and other signaling pathways that could be relevant to liver cancer development and treatment.

Submandibular salivary glands: influence on growth rate and life span in mice

Submandibular glands accumulate a variety of growth factors, especially in male mice. Surgical excision of these glands (sialoadenectomy) results in alterations in several organs and systems including the liver, skin and reproductive system. We studied the life-long consequences of sialoadenectomy in male mice. Animals were operated at the age of 10 weeks. Thereafter, body weight and food and water intake were controlled until death. Few weeks after surgery, body weight was lower in sialoadenectomized than in control mice. The difference remained stable until the age of 80 weeks. In spite of the lower body weight, food intake was higher in sialoadenectomized mice than in controls. The first death of sialoadenectomized mice occurred 10 weeks earlier than that of the first control, and the initial death rate in sialoadenectomized mice was almost twice the rate in controls. After 100 weeks of life, the death rate increased in control mice, but suddenly decreased in sialoadenectomized mice. The consequence was that the mean life span of the last 25% surviving animals was 10 weeks longer in sialoadenectomized than in control mice. Autopsy examination suggests that the effect of sialoadenectomy on death rate may be the consequence of a contrasting effect on tumour growth. Our results indicate that submandibular glands, or rather the factors derived from these glands, have contrasting roles in tumour growth. At early ages they may be survival factors and protect tissues, whereas at later ages they may stimulate the growth of transformed cells.

Involvement and mechanism of DGAT2 upregulation in the pathogenesis of alcoholic fatty liver disease

The mechanisms involved in the development of alcoholic liver disease (ALD) are not well established. We investigated the involvement of acyl-CoA: diacylglycerol acyltransferase 2 (DGAT2) upregulation in mediating hepatic fat accumulation induced by chronic alcohol consumption. Chronic alcohol feeding caused fatty liver and increased hepatic DGAT2 gene and protein expression, concomitant with a significant suppression of hepatic MAPK/ERK kinase/extracellular regulated kinase 1/2 (MEK/ERK1/2) activation. In vitro studies demonstrated that specific inhibitors of the MEK/ERK1/2 pathway increased DGAT2 gene expression and triglyceride (TG) contents in HepG2 cells, whereas epidermal growth factor, a strong ERK1/2 activator, had the opposite effect. Moreover, chronic alcohol feeding decreased hepatic S-adenosylmethionine (SAM): S-adenosylhomocysteine (SAH) ratio, an indicator of disrupted transmethylation reactions. Mechanistic investigations revealed that N-acetyl-S-farnesyl-L-cysteine, a potent inhibitor of isoprenylcysteine carboxyl methyltransferase, suppressed ERK1/2 activation, followed by an enhanced DGAT2 expression and an elevated TG content in HepG2 cells. Lastly, we demonstrated that the beneficial effects of betaine supplementation in ALD were associated with improved SAM/SAH ratio, alleviated ERK1/2 inhibition, and attenuated DGAT2 upregulation. In conclusion, our data suggest that upregulation of DGAT2 plays an important role in the pathogenesis of ALD, and that abnormal methionine metabolism contributes, at least partially, to DGAT2 upregulation via suppression of MEK/ERK1/2 activation.

Protection of epidermal growth factor against clivorine-induced mitochondrial-mediated apoptosis in hepatocytes

Pyrrolizidine alkaloids (PAs) are well-known natural hepatotoxins. In this study, we investigated the protection of epidermal growth factor (EGF) against the hepatotoxicity of clivorine, which is an otonecine-type PA from traditional Chinese medicine Ligularia hodgsonii Hook. Cell viability assay and cell morphology observation showed that EGF (1 ng/mL) reversed clivorine-induced cytotoxicity on human normal liver L-02 cells. EGF (1 ng/mL) also inhibited clivorine-induced DNA fragmentation and caspase-3 cleavage. Our previous study has showed that antiapoptotic Bcl-xL degradation and mitochondrial-mediated apoptosis was involved in clivorine-induced hepatotoxicity. In this study, we found that EGF (1 ng/mL) inhibited clivorine-induced antiapoptotic Bcl-xL protein decrease, caspase-9 activation, and release of cytosolic cytochrome C. We further investigated the effects of vascular epidermal growth factor, basic fibroblast growth factor, and insulin-like growth factor-1 on clivorine-induced cytotoxicity, and there is no significant protection observed. Our results suggest that EGF exerts its protective effects against clivorine-induced hepatotoxicity probably by modulating mitochondrial-mediated apoptotic signal pathway.

MicroRNA expression profile in Lieber-DeCarli diet-induced alcoholic and methionine choline deficient diet-induced nonalcoholic steatohepatitis models in mice

BACKGROUND

Alcoholic and nonalcoholic steatohepatitis are leading causes of liver diseases worldwide. While of different etiology, these share common pathophysiological mechanisms and feature abnormal fat metabolism, inflammation and fibrosis. MicroRNAs (miRNA) are highly conserved noncoding RNAs that control gene expression at the post-transcriptional level either via the degradation of target mRNAs or the inhibition of translation. Each miRNA controls the expression of multiple targets; miRNAs have been linked to regulation of lipid metabolism and inflammation.

METHODS

We fed Lieber-DeCarli alcohol or methionine-choline-deficient (MCD) diets to C57Bl6 and analyzed livers for histopathology, cytokines by ELISA, alanine aminotransferase (ALT) by biochemical assay, and microRNA profile by microarray.

RESULTS

Both Lieber-DeCarli and MCD diets lead to development of liver steatosis, liver injury, indicated by increased ALT, and elevated levels of serum TNFalpha, suggesting that animal models portray the pathophysiological features of alcoholic and nonalcoholic fatty liver, respectively. We identified that Lieber-deCarli diet up-regulated 1% and down-regulated 1% of known miRNA; MCD diet up-regulated 3% and down-regulated 1% of known miRNA, compared to controls. Of miRNAs that changed expression levels, 5 miRNAs were common in alcoholic and nonalcoholic fatty livers: the expression of both miR-705 and miR-1224 was increased after Lieber-DeCarli or MCD diet feeding. In contrast, miR-182, miR-183, and miR-199a-3p were down-regulated in Lieber-deCarli feeding, while MCD diet lead to their up-regulation, compared to corresponding controls.

CONCLUSIONS

Our findings indicate etiology-specific changes in miRNA expression profile during steatohepatitis models, which opens new avenues for research in the pathophysiology of alcoholic and nonalcoholic fatty liver disease.

Sialoadenectomy enhances hepatic injury induced by lipopolysaccharide/galactosamine in mice

BACKGROUND

Submandibular salivary glands (SMGs) synthesize, accumulate and secrete a large amount of epidermal growth factor (EGF) in mice. It is known that surgical removal of SMG (sialoadenectomy) alters cell turnover in the liver and exacerbates liver injury induced by lipopolysaccharide/galactosamine (LPS/GalN).

RESULTS

Here we show that such increased hepatotoxicity is not the consequence of the lack of EGF production from SMG. On the contrary, it appears to be the consequence of an inadequate cytokine production by the liver of sialoadenectomized mice. Thus, we found that the increase of plasma tumour necrosis factor-alpha and interleukin-6 was slower in sialoadenectomized than in sham-operated mice. This is because of a decreased rate of production of both cytokines by the liver. We found that the increase of plasma corticosterone (CS) concentration is lower in sialoadenectomized than that in sham-operated mice. Adrenalectomy exacerbated liver injury induced by LPS/GalN. In these animals, sialoadenectomy did not further increase the effect of LPS/GalN.

CONCLUSIONS

Our results suggest that the effect of sialoadenectomy on LPS/GalN-induced liver toxicity may be the consequence of an altered cytokine production by the liver and a reduced CS release from adrenal glands.

Distinct methylation patterns in histone H3 at Lys-4 and Lys-9 correlate with up- & down-regulation of genes by ethanol in hepatocytes

Ethanol induced liver injury is associated with a global change in gene expression but its mechanisms are not known. We studied whether alcohol-induced gene expression is associated with post-translational methylations of histone H3. Primary culture of rat hepatocytes was treated with ethanol (50 or 100 mM) for 24 h and the status of methylation of H3 at lys 4 (H3dimeK4) or lys 9 (H3dimeK9) was monitored by Western blotting using antibodies to dimethylated histone H3 at lys 4 or lys 9. The cells exposed to ethanol showed strikingly opposing behaviors in methylation patterns; H3dimeK9 methylation was decreased whereas H3dimeK4 increased. Similar results were obtained in the interphase nuclei. Their binding on the metaphase chromosomes exhibits distinct site specific pattern of accumulation. Next, chromatin immunoprecipitation of the ethanol treated samples with antibodies for methylated lys 4 or lys 9 histone H3 followed by amplification of the immunoprecipitated DNA, was used to determine their association with the promoters of genes up- or downregulated by ethanol. Lys4 methylation was associated with ethanol upregulated genes (Adh, GST-yc2) whereas lys 9 methylation with downregulated genes (Lsdh, cytP4502c11) demonstrating a difference between these two methylations. These results suggest that exposure of hepatocytes to ethanol changes the expression of several susceptible genes which are associated with site specific modification of dimethylated forms of histone H3 amino termini at their regulatory regions.

Liver injury after an aggressive encounter in male mice

Acute and intense psychological stressors induce cell damage in several organs, including the heart and the liver. Much less is known about social stress. In male mice, aggressive behavior is the most common social stressor. It is remarkable that upon fighting, submandibular salivary glands release a number of peptides into the bloodstream including epidermal growth factor (EGF). We showed previously that released EGF protects the heart from cell damage in this particular stressful situation. Here, we studied the effect of an aggressive encounter on the liver and whether EGF has a similar effect on this organ. An aggressive encounter in male mice caused inflammatory response and a transient increase in plasma alanine and aspartate transaminase activities. At 3 h, focal infiltration of neutrophils was observed in liver parenchyma. These cells accumulate on eosinophilic hepatocytes, which may correspond to dying cells. A few hours later, evidence of necrotic lesion was observed. Surgical excision of submandibular glands, sialoadenectomy, did not prevent the rise in plasma EGF concentration and did not affect the increase in plasma transaminase activities. Neither did the administration of tyrphostin AG-1478 (inhibitor of EGF receptor kinase) alter the increase in plasma alanine transaminase activity. However, it did enhance the rise in both aspartate transaminase and creatine kinase activity, suggesting heart damage. We conclude that an aggressive encounter causes mild liver damage and that released EGF does not protect this organ, in contrast to its effect on the heart.

Rheumatoid factor induction in murine models of liver injury

Alcoholic liver disease and hepatitis C are associated with the production of autoantibodies such as rheumatoid factors (RF), which bind to IgG and can aid in host defence, but are also associated with pathological conditions such as rheumatoid arthritis. Because little is known about the role of RF in liver disease, we characterized the RF production that either occurred spontaneously in response to alcohol consumption or was induced by injection of an Escherichia coli glycolipoprotein in C57Bl/6 mice. Whereas severe liver damage was induced by carbon tetrachloride (CCl(4)), minimal damage was caused by chronic alcohol consumption. Liver damage was monitored by measurements of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Circulating RF was induced in response to chronic alcohol consumption; the latter probably involved Toll-like receptor ligation. In contrast, CCl(4)-induced damage was not associated with RF induction. However, concurrent treatment with an E. coli glycolipoprotein macromolecule that induced RF, protected against CCL(4)-induced liver damage as measured by a highly significant decrease (P = 0.008) at 4 weeks in AST and ALT. RF induced by E. coli glycolipoprotein correlated with 'protection' from liver damage, indicating that the RF autoimmune response does not necessarily exacerbate liver disease.

New molecular targets for hepatocellular carcinoma: the ErbB1 signaling system

Hepatocellular carcinoma (HCC) is a major cause of cancer-related deaths. This malignancy is often diagnosed at an advanced state, when most potentially curative therapies are of limited efficacy. In addition, HCC is a type of tumor highly resistant to available chemotherapeutic agents, which leaves HCC patients with no effective therapeutic options and a poor prognosis. From a molecular perspective, HCC is a heterogeneous type of tumor. However, in most cases, HCC emerges on a background of persistent liver injury, inflammation and hepatocellular proliferation, which is characteristic of chronic hepatitis and cirrhosis. Recent studies have revealed that dysregulation of a limited number of growth and survival-related pathways can play a key role in HCC development. The epidermal growth factor receptor (ErbB1) can be bound and activated by a broad family of ligands, and can also engage in extensive cross talk with other signaling pathways. This system is considered as an important defense mechanism for the liver during acute tissue injury; however, accumulating evidences suggest that its chronic stimulation can participate in the neoplastic conversion of the liver. Agents that target the ErbB1 receptor have shown antineoplastic activity in other types of tumors, but their efficacy either alone or in combination with other compounds has just started to be tested in experimental and human HCC. Here, we review the evidences that support the involvement of the ErbB1 in HCC development and that provide a rationale for ErbB1 targeting in HCC prevention and treatment.

Novel Role for Amphiregulin in Protection from Liver Injury

Clinically, the Fas and Fas ligand system plays a central role in the development of hepatocyte apoptosis, a process contributing to a broad spectrum of liver diseases. Therefore, the development of therapies aimed at the inhibition of hepatocyte apoptosis is a major issue. Activation of the epidermal growth factor receptor has been shown to convey survival signals to the hepatocyte. To learn about the endogenous response of epidermal growth factor receptor ligands during Fas-mediated liver injury we investigated the expression of epidermal growth factor, transforming growth factor alpha, heparin-binding epidermal growth factor-like growth factor, betacellulin, epiregulin, and amphiregulin in the liver of mice challenged with Fas-agonist antibody. Amphiregulin expression, barely detectable in healthy liver, was significantly up-regulated. Amphiregulin administration abrogated Fas-mediated liver injury in mice and showed direct anti-apoptotic effects in primary hepatocytes. Amphiregulin activated the Akt and signal transducer and activator of transcription-3 survival pathways, and up-regulated Bcl-xL expression. Amphiregulin knock-out mice showed signs of chronic liver damage in the absence of any noxious treatment, and died faster than wild type mice in response to lethal doses of Fas-agonist antibody. In contrast, these mice were more resistant against sublethal liver damage, supporting the hypothesis that chronic liver injury can precondition hepatocytes inducing resistance to subsequent cell death. These results show that amphiregulin is a protective factor induced in response to liver damage and that it may be therapeutic in liver diseases.

Hepatocyte proliferation is the possible mechanism for the transient decrease in liver injury during steatosis stage of alcoholic liver disease

Steatosis is a frequent pathologic stage in alcoholic liver disease (ALD). Although the mechanisms for increased susceptibility of steatotic liver to injury have been postulated, the ability of these hepatocytes to proliferate and withstand injury is unknown. There are conflicting reports on the status of hepatocyte regeneration following chronic alcohol ingestion. Hence, the objective of this study was to investigate the temporal dynamics between the pattern of liver injury and hepatocyte proliferation during the steatosis stage of ALD. Alcoholic steatosis was induced in male Sprague-Dawley rats by feeding an ethanol (EtOH)-containing Lieber-DeCarli liquid diet for a period of 5 weeks. Microvesicular steatosis was evident in H&E sections by three weeks in the EtOH-treated rats, which further developed into panlobular macrovesicular steatosis by 5 weeks. Plasma transaminase activities indicated progressive increase in liver injury peaking at 3 weeks with significant but mild decrease at 4 and 5 weeks. CYP2E1 protein and activity was significantly increased in EtOH-fed rats as measured by Western blot and pNP hydroxylation assay. PCNA analysis of liver sections indicated that EtOH-treated rats had a significantly higher number of cells in S phase of cell division at weeks 1 (3.20 +/- 0.19), 2 (7.03 +/- 0.92), and 3 (4.23 +/- 1.41) when compared to controls (1.5 +/- 0.22). NF-kappaB DNA binding and Cyclin D1 proteins increased significantly in the EtOH-treated rats corresponding with enhanced hepatic proliferation. These data suggest the transient decline in liver injury during alcoholic steatosis is due to enhanced NF-kappaB-dependent hepatocyte proliferation.

Large-scale gene profiling of the liver in a mouse model of chronic, intragastric ethanol infusion

BACKGROUND/AIMS

The mechanisms underlying alcohol-induced liver injury are not fully elucidated. An approach in this direction would consist of an all-inclusive assessment of gene expression in the liver. The purpose of this study was to perform a comprehensive analysis of gene expression in the livers of mice treated with ethanol by means of intragastric infusion.

METHODS

An ethanol- or glucose-enriched liquid diet was fed to animals for 4 weeks via a long-term gastrostomy catheter. The animals were killed and plasma alanine:2-oxoglutarate aminotransferase (ALT) assay, liver histology and total RNA analysis by microarray gene technology were performed.

RESULTS

Alcohol increased ALT, induced steatosis, necrosis and inflammation. A total of 12,423 genes were analyzed for expression out of which 4867 were expressed by the liver. Alcohol repressed expression of 11 genes, induced expression of 13 genes, and up- or down-regulated expression of 44 and 42 genes >2-fold, respectively. Gene expression analysis identified several genes that have not previously been tested for alcohol effects.

CONCLUSIONS

This study: (i) expands the knowledge of mechanism(s) of action of ethanol; (ii) indicates novel pathways of ethanol action on the liver, and (iii) illustrates the utility of microarray gene analysis in hepatology research.

Sialoadenectomy alters liver cell turn-over and function in mice

In rodents, submandibular salivary glands accumulate a number of biologically active peptides, and release some of them to both saliva and the bloodstream. Surgical removal of these glands (sialoadenectomy) alters the ability of the liver to regenerate after partial hepatectomy. We show here that 5 weeks after surgery, the liver of sialoadenectomized mice contained 40% fewer hepatocytes than the liver of sham-operated mice. We did not obtain evidence of necrotic cell death after surgery. In contrast, sialoadenectomy transiently increased apoptotic hepatocyte death, as revealed by terminal deoxynucleotidyl transferase(TdT)-mediated dUTP nick-end labeling (TUNEL) assay. DNA synthesis was determined in vivo by the incorporation of bromo-deoxyuridine (BrdU) into hepatocyte nuclei. BrdU-labeling progressively increased after sialoadenectomy. We conclude that sialoadenectomy induced a transient wave of apoptotic cell death followed by a rise in DNA synthesis but not by cell division. This reduced cell number but increased mean cell volume. In spite of these alterations in cellularity, the liver responded adequately to several stressful conditions, as judged by the lack of any differential effect of sialoadenectomy on liver glycogen and plasma glucose concentration after immobilization, aggressive encounter, or fasting. However, the liver of sialoadenectomized mice was more sensitive to the effect of a non-lethal dose of bacterial lipopolysaccharide (LPS) combined with d-galactosamine, as shown by the enhanced rise in plasma alanine aminotransferase and aspartate aminotransferase, and liver myeloperoxidase (MPO) activities. All these results indicate that a submandibular salivary glands-liver axis is involved in the maintenance of liver structure in mice. A disturbance of this axis induces an adaptive response that preserves the metabolic function of the liver but renders it more sensitive to bacterial endotoxins.