Tissue factor-deficiency and protease activated receptor-1-deficiency reduce inflammation elicited by diet-induced steatohepatitis in mice

Hepatocyte-independent PAR1-biased signaling controls liver pathology in experimental obesity

BACKGROUND

Protease-activated receptor-1 (PAR1) has emerged as an important link between coagulation and the complications of obesity including metabolic dysfunction-associated steatotic liver disease (MASLD). PAR1 is expressed by various cells and cleaved by different proteases to generate unique tethered agonists that activate distinct signaling pathways. Mice expressing PAR1 with an R41Q mutation have disabled canonical thrombin-mediated signaling, whereas R46Q mice express PAR1 resistant to noncanonical signaling by activated protein C.

METHODS

Mice with whole body and hepatocyte-selective PAR1 deficiency as well as PAR1 R41Q and R46Q mice were fed a high-fat diet (HFD) to induce MASLD.

RESULTS

HFD-fed R41Q mice displayed reduced hepatic steatosis and liver/body weight ratio. In contrast, HFD-fed R46Q mice displayed increased relative liver weight and hepatic steatosis alongside increased serum alanine aminotransferase activity. Surprisingly, despite the distinct impact of PAR1 mutations on steatosis, selective deletion of PAR1 in hepatocytes had no impact. To evaluate a viable PAR1-targeted approach, mice with HFD-induced obesity were treated with the allosteric PAR1 modulator NRD-21, which inhibits canonical PAR1 inflammatory signaling but promotes PAR1 protective, noncanonical anti-inflammatory signaling. NRD-21 treatment reduced plasma tumor necrosis factor-alpha, serum alanine aminotransferase activity, hepatic steatosis, and insulin resistance (Homeostatic Model Assessment for Insulin Resistance) but increased plasma active glucagon-like peptide-1.

CONCLUSION

The results suggest that nonhepatocellular canonical PAR1 cleavage drives MASLD in obese mice and provide translational proof-of-concept that selective pharmacologic modulation of PAR1 yields multiple metabolic benefits in experimental obesity.

Emerging roles of protease-activated receptors in cardiometabolic disorders

Cardiometabolic disorders, including obesity-related insulin resistance and atherosclerosis, share sterile chronic inflammation as a major cause; however, the precise underlying mechanisms of chronic inflammation in cardiometabolic disorders are not fully understood. Accumulating evidence suggests that several coagulation proteases, including thrombin and activated factor X (FXa), play an important role not only in the coagulation cascade but also in the proinflammatory responses through protease-activated receptors (PARs) in many cell types. Four members of the PAR family have been cloned (PAR 1-4). For instance, thrombin activates PAR-1, PAR-3, and PAR-4. FXa activates both PAR-1 and PAR-2, while it has no effect on PAR-3 or PAR-4. Previous studies demonstrated that PAR-1 and PAR-2 activated by thrombin or FXa promote gene expression of inflammatory molecules mainly via the NF-κB and ERK1/2 pathways. In obese adipose tissue and atherosclerotic vascular tissue, various stresses increase the expression of tissue factor and procoagulant activity. Recent studies indicated that the activation of PARs in adipocytes and vascular cells by coagulation proteases promotes inflammation in these tissues, which leads to the development of cardiometabolic diseases. This review briefly summarizes the role of PARs and coagulation proteases in the pathogenesis of inflammatory diseases and describes recent findings (including ours) on the potential participation of this system in the development of cardiometabolic disorders. New insights into PARs may ensure a better understanding of cardiometabolic disorders and suggest new therapeutic options for these major health threats.

Role of experimental periodontitis in inducing pulmonary inflammation in mice

OBJECTIVE

The aim of the study was to explore the potential role of experimental periodontitis in pulmonary inflammation in mice.

MATERIALS AND METHODS

Mice were divided into control, ligature-induced periodontitis (L) and ligature plus Porphyromonas gingivalis (P. gingivalis)-induced periodontitis (LPG) groups. Alveolar bone resorption, pulmonary function, lung tissue histology and cytokine expression were examined at 2, 4 and 8 weeks. Then cytokines and neutrophils in the peripheral blood and lung tissue were further assessed at 8 weeks to determine the role of cytokines induced by LPG periodontitis, and the effect of P. gingivalis was evaluated using P. gingivalis-IgG and P. gingivalis gingipain.

RESULTS

Alveolar bone resorption was more severe in the L and LPG groups. However, pulmonary inflammation was observed only in the LPG group at 8 weeks when cytokines and neutrophils in the peripheral blood and lung tissue were the most significant elevation, along with higher levels of P. gingivalis-IgG and P. gingivalis gingipain. Cytokine levels were also increased in the gingival tissue, peripheral blood and lung tissue in the L group, accompanied by elevated peripheral blood neutrophils, but not as significantly as that in the LPG group.

CONCLUSIONS

LPG periodontitis can trigger pulmonary inflammation over the long term, in which cytokines and P. gingivalis play an important role.

Antisense Tissue Factor Oligodeoxynucleotides Protected Diethyl Nitrosamine/Carbon Tetrachloride-Induced Liver Fibrosis Through Toll Like Receptor4-Tissue Factor-Protease Activated Receptor1 Pathway

Tissue factor (TF) is a blood coagulation factor that has several roles in many non-coagulant pathways involved in different pathological conditions such as angiogenesis, inflammation and fibrogenesis. Coagulation and inflammation are crosslinked with liver fibrosis where protease-activated receptor1 (PAR1) and toll-like receptor4 (TLR4) play a key role. Antisense oligodeoxynucleotides are strong modulators of gene expression. In the present study, antisense TF oligodeoxynucleotides (TFAS) was evaluated in treating liver fibrosis via suppression of TF gene expression. Liver fibrosis was induced in rats by a single administration of N-diethyl nitrosamine (DEN, 200 mg/kg; i. p.) followed by carbon tetrachloride (CCl4, 3 ml/kg; s. c.) once weekly for 6 weeks. Following fibrosis induction, liver TF expression was significantly upregulated along with liver enzymes activities and liver histopathological deterioration. Alpha smooth muscle actin (α-SMA) and transforming growth factor-1beta (TGF-1β) expression, tumor necrosis factor-alpha (TNF-α) and hydroxyproline content and collagen deposition were significantly elevated in the liver. Blocking of TF expression by TFAS injection (2.8 mg/kg; s. c.) once weekly for 6 weeks significantly restored liver enzymes activities and improved histopathological features along with decreasing the elevated α-SMA, TGF-1β, TNF-α, hydroxyproline and collagen. Moreover, TFAS decreased the expression of both PAR1 and TLR4 that were induced by liver fibrosis. In conclusion, we reported that blockage of TF expression by TFAS improved inflammatory and fibrotic changes associated with CCl4+DEN intoxication. In addition, we explored the potential crosslink between the TF, PAR1 and TLR4 in liver fibrogenesis. These findings offer a platform on which recovery from liver fibrosis could be mediated through targeting TF expression.

The Impact of Dabigatran Treatment on Sinusoidal Protection Against Hepatic Ischemia/Reperfusion Injury in Mice

Thrombin is a key player in the coagulation cascade, and it is attracting much attention as a promotor of cellular injured signaling. In ischemia/reperfusion injury (IRI), which is a severe complication of liver transplantation, thrombin may also promote tissue damage. The aim of this study is to reveal whether dabigatran, a direct thrombin inhibitor, can attenuate hepatic IRI with focusing on a protection of sinusoidal endothelial cells (SECs). Both clinical patients who underwent hepatectomy and in vivo mice model of 60-minute hepatic partial-warm IRII, thrombin generation was evaluated before and after IRI. In next study, IRI mice were treated with or without dabigatran. In addition, hepatic SECs and hepatocytes pretreated with or without dabigatran were incubated in hypoxia/reoxygenation (H-R) environment in vitro. Thrombin generation evaluated by thrombin-antithrombin complex (TAT) was significantly enhanced after IRI in the clinical study and in vivo study. Thrombin exacerbated lactate dehydrogenase cytotoxicity levels in a dose-dependent manner in vitro. In an IRI model of mice, dabigatran treatment significantly improved liver histological damage, induced sinusoidal protection, and provided both antiapoptotic and anti-inflammatory effects. Furthermore, dabigatran not only enhanced endogenous thrombomodulin (TM) but also reduced excessive serum high-mobility group box-1 (HMGB-1). In H-R models of SECs, not hepatocytes, pretreatment with dabigatran markedly attenuated H-R damage, enhanced TM expression in cell lysate, and decreased extracellular HMGB-1. The supernatant of SECs pretreated with dabigatran protected hepatocytes from H-R damage and cellular death. Thrombin exacerbated hepatic IRI, and excessive extracellular HMGB-1 caused severe inflammation-induced and apoptosis-induced liver damage. In this situation, dabigatran treatment improved vascular integrity via sinusoidal protection and degraded HMGB-1 by endogenous TM enhancement on SECs, greatly ameliorating hepatic IRI.

A high-fat diet delays plasmin generation in a thrombomodulin-dependent manner in mice

Obesity is a prevalent prothrombotic risk factor marked by enhanced fibrin formation and suppressed fibrinolysis. Fibrin both promotes thrombotic events and drives obesity pathophysiology, but a lack of essential analytical tools has left fibrinolytic mechanisms affected by obesity poorly defined. Using a plasmin-specific fluorogenic substrate, we developed a plasmin generation (PG) assay for mouse plasma that is sensitive to tissue plasminogen activator, α2-antiplasmin, active plasminogen activator inhibitor (PAI-1), and fibrin formation, but not fibrin crosslinking. Compared with plasmas from mice fed a control diet, plasmas from mice fed a high-fat diet (HFD) showed delayed PG and reduced PG velocity. Concurrent to impaired PG, HFD also enhanced thrombin generation (TG). The collective impact of abnormal TG and PG in HFD-fed mice produced normal fibrin formation kinetics but delayed fibrinolysis. Functional and proteomic analyses determined that delayed PG in HFD-fed mice was not due to altered levels of plasminogen, α2-antiplasmin, or fibrinogen. Changes in PG were also not explained by elevated PAI-1 because active PAI-1 concentrations required to inhibit the PG assay were 100-fold higher than circulating concentrations in mice. HFD-fed mice had increased circulating thrombomodulin, and inhibiting thrombomodulin or thrombin-activatable fibrinolysis inhibitor (TAFI) normalized PG, revealing a thrombomodulin- and TAFI-dependent antifibrinolytic mechanism. Integrating kinetic parameters to calculate the metric of TG/PG ratio revealed a quantifiable net shift toward a prothrombotic phenotype in HFD-fed mice. Integrating TG and PG measurements may define a prothrombotic risk factor in diet-induced obesity.

Characterizing the Role of HMG-CoA Reductase in Aryl Hydrocarbon Receptor-Mediated Liver Injury in C57BL/6 Mice

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor. The prototypical ligand of the AHR is an environmental contaminant called 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD exposure is associated with many adverse health outcomes in humans including non-alcoholic fatty liver disease (NAFLD). Previous studies suggest that AHR ligands alter cholesterol homeostasis in mice through repression of genes involved in cholesterol biosynthesis, such as Hmgcr, which encodes the rate-limiting enzyme of cholesterol biosynthesis called 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGCR). In this study, we sought to characterize the impact of HMGCR repression in TCDD-induced liver injury. C57BL/6 mice were exposed to TCDD in the presence or absence of simvastatin, a competitive inhibitor of HMGCR. Simvastatin exposure decreased TCDD-induced hepatic lipid accumulation in both sexes, but was most prominent in females. Simvastatin and TCDD (S + T) co-treatment increased hepatic AHR-battery gene expression and liver injury in male, but not female, mice. In addition, the S + T co-treatment led to an increase in hepatic glycogen content that coincides with heavier liver in female mice. Results from this study suggest that statins, which are amongst the most prescribed pharmaceuticals, may protect from AHR-mediated steatosis, but alter glycogen metabolism and increase the risk of TCDD-elicited liver damage in a sex-specific manner.

Caspase Inhibition Reduces Hepatic Tissue Factor-Driven Coagulation In Vitro and In Vivo

Tissue factor (TF) is the primary activator of the blood coagulation cascade. Liver parenchymal cells (ie, hepatocytes) express TF in a molecular state that lacks procoagulant activity. Hepatocyte apoptosis is an important feature of acute and chronic liver diseases, and Fas-induced apoptosis increases hepatocyte TF procoagulant activity in vitro. We determined the impact of a pan-caspase inhibitor, IDN-7314, on hepatocyte TF activity in vitro and TF-mediated coagulation in vivo. Treatment of primary mouse hepatocytes with the Fas death receptor ligand (Jo2, 0.5 μg/ml) for 8 h increased hepatocyte TF procoagulant activity and caused release of TF-positive microvesicles. Pretreatment with 100 nM IDN-7314 abolished Jo2-induced caspase-3/7 activity and significantly reduced hepatocyte TF procoagulant activity and release of TF-positive microvesicles. Treatment of wild-type C57BL/6 mice with a sublethal dose of Jo2 (0.35 mg/kg) for 4.5 h increased coagulation, measured by a significant increase in plasma thrombin-antithrombin and TF-positive microvesicles. Total plasma microvesicle-associated TF activity was reduced in mice lacking hepatocyte TF; suggesting TF-positive microvesicles are released from the apoptotic liver. Fibrin(ogen) deposition increased in livers of Jo2-treated wild-type mice and colocalized primarily with cleaved caspase-3-positive hepatocytes. Pretreatment with IDN-7314 reduced caspase-3 activation, prevented the procoagulant changes in Jo2-treated mice, and reduced hepatocellular injury. Overall, the results indicate a central role for caspase activity in TF-mediated activation of coagulation following apoptotic liver injury. Moreover, the results suggest that liver-selective caspase inhibition may be a putative strategy to limit procoagulant and prothrombotic changes in patients with chronic liver disease.

Roles of Coagulation Proteases and PARs (Protease-Activated Receptors) in Mouse Models of Inflammatory Diseases

Activation of the blood coagulation cascade leads to fibrin deposition and platelet activation that are required for hemostasis. However, aberrant activation of coagulation can lead to thrombosis. Thrombi can cause tissue ischemia, and fibrin degradation products and activated platelets can enhance inflammation. In addition, coagulation proteases activate cells by cleavage of PARs (protease-activated receptors), including PAR1 and PAR2. Direct oral anticoagulants have recently been developed to specifically inhibit the coagulation proteases FXa (factor Xa) and thrombin. Administration of these inhibitors to wild-type mice can be used to determine the roles of FXa and thrombin in different inflammatory diseases. These results can be compared with the phenotypes of mice with deficiencies of either Par1 (F2r) or Par2 (F2rl1). However, inhibition of coagulation proteases will have effects beyond reducing PAR signaling, and a deficiency of PARs will abolish signaling from all proteases that activate these receptors. We will summarize studies that examine the roles of coagulation proteases, particularly FXa and thrombin, and PARs in different mouse models of inflammatory disease. Targeting FXa and thrombin or PARs may reduce inflammatory diseases in humans.

Thrombin promotes diet-induced obesity through fibrin-driven inflammation

Obesity promotes a chronic inflammatory and hypercoagulable state that drives cardiovascular disease, type 2 diabetes, fatty liver disease, and several cancers. Elevated thrombin activity underlies obesity-linked thromboembolic events, but the mechanistic links between the thrombin/fibrin(ogen) axis and obesity-associated pathologies are incompletely understood. In this work, immunohistochemical studies identified extravascular fibrin deposits within white adipose tissue and liver as distinct features of mice fed a high-fat diet (HFD) as well as obese patients. Fibγ390-396A mice carrying a mutant form of fibrinogen incapable of binding leukocyte αMβ2-integrin were protected from HFD-induced weight gain and elevated adiposity. Fibγ390-396A mice had markedly diminished systemic, adipose, and hepatic inflammation with reduced macrophage counts within white adipose tissue, as well as near-complete protection from development of fatty liver disease and glucose dysmetabolism. Homozygous thrombomodulin-mutant ThbdPro mice, which have elevated thrombin procoagulant function, gained more weight and developed exacerbated fatty liver disease when fed a HFD compared with WT mice. In contrast, treatment with dabigatran, a direct thrombin inhibitor, limited HFD-induced obesity development and suppressed progression of sequelae in mice with established obesity. Collectively, these data provide proof of concept that targeting thrombin or fibrin(ogen) may limit pathologies in obese patients.

From the Cover: Coagulation-Driven Hepatic Fibrosis Requires Protease Activated Receptor-1 (PAR-1) in a Mouse Model of TCDD-Elicited Steatohepatitis

Emerging evidence supports a role for environmental chemical exposure in the pathology of non-alcoholic fatty liver disease (NAFLD), a disease process tightly linked to increased activity of the blood coagulation cascade. Exposure of C57BL/6 mice to the persistent environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) recapitulates features of the NAFLD spectrum, including steatosis, hepatic injury, inflammation, and fibrosis. We assessed coagulation cascade activation, and determined the role of the thrombin receptor protease activated receptor-1 (PAR-1) in experimental TCDD-elicited NAFLD. Chronic exposure to TCDD (30 µg/kg every 4 days for 28 days) was associated with intrahepatic coagulation, indicated by increased plasma thrombin-antithrombin levels and hepatic fibrin(ogen) deposition. PAR-1 deficiency diminished TCDD-elicited body weight loss and relative liver weight was reduced in TCDD-exposed PAR-1^-/- mice compared with TCDD-exposed wild-type mice. PAR-1 deficiency did not affect TCDD-induced hepatic steatosis or hepatocellular injury, as indicated by serum alanine aminotransferase activity. Despite a lack of effect on these 2 features of NAFLD pathology, PAR-1 deficiency was associated with a reduction in hepatic inflammation evident in liver histopathology, and reflected by a reduction in serum levels of the proinflammatory cytokine interleukin-6. Moreover, TCDD-driven hepatic collagen deposition was markedly reduced in PAR-1-deficient mice. These results indicate that experimental TCDD-elicited steatohepatitis is associated with coagulation cascade activation and PAR-1-driven hepatic inflammation and fibrosis.

Role of hemostatic factors in hepatic injury and disease: animal models de-liver

Chronic liver damage is associated with unique changes in the hemostatic system. Patients with liver disease often show a precariously rebalanced hemostatic system, which is easily tipped towards bleeding or thrombotic complications by otherwise benign stimuli. In addition, some clinical studies have shown that hemostatic system components contribute to the progression of liver disease. There is a strong basic science foundation for clinical studies with this particular focus. Chronic and acute liver disease can be modeled in rodents and large animals with a variety of approaches, which span chronic exposure to toxic xenobiotics, diet-induced obesity, and surgical intervention. These experimental approaches have now provided strong evidence that, in addition to perturbations in hemostasis caused by liver disease, elements of the hemostatic system have powerful effects on the progression of experimental liver toxicity and disease. In this review, we cover the basis of the animal models that are most often utilized to assess the impact of the hemostatic system on liver disease, and highlight the role that coagulation proteases and their targets play in experimental liver toxicity and disease, emphasizing key similarities and differences between models. The need to characterize hemostatic changes in existing animal models and to develop novel animal models recapitulating the coagulopathy of chronic liver disease is highlighted. Finally, we emphasize the continued need to translate knowledge derived from highly applicable animal models to improve our understanding of the reciprocal interaction between liver disease and the hemostatic system in patients.

Role of Fibrin(ogen) in Progression of Liver Disease: Guilt by Association?

Strong experimental evidence indicates that components of the hemostatic system, including thrombin, exacerbate diverse features of experimental liver disease. Clinical studies have also begun to address this connection and some studies have suggested that anticoagulants can improve outcome in patients with liver disease. Among the evidence of coagulation cascade activation in models of liver injury and disease is the frequent observation of thrombin-driven hepatic fibrin(ogen) deposition. Indeed, hepatic fibrin(ogen) deposition has long been recognized as a consequence of hepatic injury. Although commonly inferred as pathologic due to protective effects of anticoagulants in mouse models, the role of fibrin(ogen) in acute liver injury and chronic liver disease may not be universally detrimental. The localization of hepatic fibrin(ogen) deposits within the liver is connected to the disease stimulus and in animal models of liver toxicity and chronic disease, fibrin(ogen) deposition may not always be synonymous with large vessel thrombosis. Here, we provide a balanced review of the experimental evidence supporting a direct connection between fibrin(ogen) and liver injury/disease pathogenesis, and suggest a path forward bridging experimental and clinical research to improve our knowledge on the nature and function of fibrin(ogen) in liver disease.

NF-κB-dependent increase in tissue factor expression is responsible for hypoxic podocyte injury

BACKGROUND

Fibrin deposition within glomeruli is commonly seen in kidney biopsy specimens, suggesting enhanced coagulant activity. Tissue factor (TF) is a coagulation factor which is also related to various biological effects, and TF is upregulated by hypoxia in cancer cells. Recently, hypoxic podocyte injury has been proposed, therefore, we investigated TF expression in hypoxia.

METHODS

Conditionally immortalized human podocytes were differentiated and treated under hypoxic or normoxic conditions. mRNA expressions of TF and tissue factor pathway inhibitor (TFPI) were analyzed by quantitative RT-PCR. Protein levels of TF and TFPI were tested by enzyme-linked immunosorbent assay. We employed small interfering RNA (siRNA) to temporary knockdown early growth response protein 1 (Egr-1), hypoxia-inducible factor-1α (HIF-1α) and TF. The expression of CD2-associated protein (CD2AP) mRNA and phalloidin staining was examined to assess podocyte injury.

RESULTS

Hypoxia increased mRNA expression of TF (6 h: 2.3 ± 0.05 fold, p < 0.001, 24 h: 5.6 ± 2.4 fold, p < 0.05) and suppressed TFPI (6 h: 0.54 ± 0.04 fold, p < 0.05, 24 h: 0.24 ± 0.06 fold, p < 0.001) compared with normoxia. Similarly, protein levels of TF were increased and TFPI were decreased. Egr-1 siRNA did not change TF mRNA expression. Pyrrolidine dithiocarbamate (PDTC), a nuclear factor kappa B (NF-κB) inhibitor, significantly reduced hypoxia induced TF expression, and HIF-1α knockdown further increased TF. Hypoxia resulted in decreased CD2AP and actin reorganization in podocytes, and these changes were attenuated by TF siRNA.

CONCLUSION

Hypoxia increased the expression of TF in human podocytes NF-κB dependently. TF may have a critical role in the hypoxic podocyte injury.

The effect of a methyl-deficient diet on the global DNA methylation and the DNA methylation regulatory pathways

Methyl-deficient diets are known to induce various liver disorders, in which DNA methylation changes are implicated. Recent studies have clarified the existence of the active DNA demethylation pathways that start with oxidization of 5-methylcytosine (5meC) to 5-hydroxymethylcytosine by ten-eleven translocation (Tet) enzymes, followed by the action of base-excision-repair pathways. Here, we investigated the effects of a methionine-choline-deficient (MCD) diet on the hepatic DNA methylation of mice by precisely quantifying 5meC using a liquid chromatography-electrospray ionization-mass spectrometry and by investigating the regulatory pathways, including DNA demethylation. Although feeding the MCD diet for 1 week induced hepatic steatosis and lower level of the methyl donor S-adenosylmethionine, it did not cause a significant reduction in the 5meC content. On the other hand, the MCD diet significantly upregulated the gene expression of the Tet enzymes, Tet2 and Tet3, and the base-excision-repair enzymes, thymine DNA glycosylase and apurinic/apyrimidinic-endonuclease 1. At the same time, the gene expression of DNA methyltransferase 1 and a, was also significantly increased by the MCD diet. These results suggest that the DNA methylation level is precisely regulated even when dietary methyl donors are restricted. Methyl-deficient diets are well known to induce oxidative stress and the oxidative-stress-induced DNA damage, 8-hydroxy-2'-deoxyguanosine (8OHdG), is reported to inhibit DNA methylation. In this study, we also clarified that the increase in 8OHdG number per DNA by the MCD diet is approximately 10 000 times smaller than the reduction in 5meC number, suggesting the contribution of 8OHdG formation to DNA methylation would not be significant.

Tissue factor pathways linking obesity and inflammation

Obesity is a major cause for a spectrum of metabolic syndrome-related diseases that include insulin resistance, type 2 diabetes, and steatosis of the liver. Inflammation elicited by macrophages and other immune cells contributes to the metabolic abnormalities in obesity. In addition, coagulation activation following tissue factor (TF) upregulation in adipose tissue is frequently found in obese patients and particularly associated with diabetic complications. Genetic and pharmacological evidence indicates that TF makes significant contributions to the development of the metabolic syndrome by signaling through G protein-coupled protease activated receptors (PARs). Adipocyte TF-PAR2 signaling contributes to diet-induced obesity by decreasing metabolism and energy expenditure, whereas hematopoietic TF-PAR2 signaling is a major cause for adipose tissue inflammation, hepatic steatosis and inflammation, as well as insulin resistance. In the liver of mice on a high fat diet, PAR2 signaling increases transcripts of key regulators of gluconeogenesis, lipogenesis and inflammatory cytokines. Increased markers of hepatic gluconeogenesis correlate with decreased activation of AMP-activated protein kinase (AMPK), a known regulator of these pathways and a target for PAR2 signaling. Clinical markers of a TF-induced prothrombotic state may thus indicate a risk in obese patient for developing complications of the metabolic syndrome.

Hematopoietic tissue factor-protease-activated receptor 2 signaling promotes hepatic inflammation and contributes to pathways of gluconeogenesis and steatosis in obese mice

Failure to inhibit hepatic gluconeogenesis is a major mechanism contributing to fasting hyperglycemia in type 2 diabetes and, along with steatosis, is the hallmark of hepatic insulin resistance. Obesity is associated with chronic inflammation in multiple tissues, and hepatic inflammation is mechanistically linked to both steatosis and hepatic insulin resistance. Here, we delineate a role for coagulation signaling via tissue factor (TF) and proteinase-activated receptor 2 (PAR2) in obesity-mediated hepatic inflammation, steatosis, and gluconeogenesis. In diet-induced obese mice, TF tail signaling independent of PAR2 drives CD11b(+)CD11c(+) hepatic macrophage recruitment, and TF-PAR2 signaling contributes to the accumulation of hepatic CD8(+) T cells. Transcripts of key pathways of gluconeogenesis, lipogenesis, and inflammatory cytokines were reduced in high-fat diet-fed mice that lack the cytoplasmic domain of TF (F3) (TF(ΔCT)) or that are deficient in PAR2 (F2rl1), as well as by pharmacological inhibition of TF-PAR2 signaling in diet-induced obese mice. These gluconeogenic, lipogenic, and inflammatory pathway transcripts were similarly reduced in response to genetic ablation or pharmacological inhibition of TF-PAR2 signaling in hematopoietic cells and were mechanistically associated with activation of AMP-activated protein kinase (AMPK). These findings indicate that hematopoietic TF-PAR2 signaling plays a pivotal role in the hepatic inflammatory responses, steatosis, and hepatic insulin resistance that lead to systemic insulin resistance and type 2 diabetes in obesity.

Coagulation in liver toxicity and disease: role of hepatocyte tissue factor

The liver is the primary source of a number of circulating coagulation factors, and acute liver injury and chronic liver disease are each associated with alterations in blood coagulation. Current views of the connection between liver injury and coagulation extend beyond the impact of liver disease on synthesis of coagulation factors to include a role for coagulation factor activity in the initiation and progression of liver disease. Mechanisms of coagulation initiation in liver disease are not completely understood. Compared to other tissues, liver expresses very low levels of tissue factor (TF). Recent studies indicate that expression of TF by hepatocytes comprises the majority of liver procoagulant activity, and that hepatocyte TF activates coagulation induced by liver injury. This review will briefly cover the expression and regulation of TF by hepatocytes, the role of TF in coagulation triggered by liver toxicity, and the contribution of coagulation activity to the progression of liver disease.

Thrombin inhibition with dabigatran protects against high-fat diet-induced fatty liver disease in mice

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of obesity and metabolic syndrome. Robust coagulation cascade activation is common in obese patients with NAFLD. We identified a critical temporal relationship between thrombin generation and the manifestation of hepatic steatosis, inflammation, and injury in C57BL/6J mice fed a high-fat diet (HFD) for 1, 2, and 3 months. Mice fed a HFD exhibited dramatic increases in hepatocellular injury and inflammation over time. Hepatic fibrin deposition preceded an increase in serum alanine aminotransferase, and the most dramatic changes in liver histopathology occurred in conjunction with a detectable increase in plasma thrombin-antithrombin levels at 3 months. To directly determine whether thrombin activity promotes NAFLD pathogenesis, mice were fed a HFD and simultaneously treated with the direct thrombin inhibitor dabigatran etexilate for 3 months. Notably, dabigatran treatment significantly reduced hepatic fibrin deposition, hepatic inflammation, hepatocellular injury, and steatosis in mice fed a HFD. Of interest, dabigatran treatment also significantly attenuated HFD-induced body weight gain. Gene expression analysis suggested that thrombin potentially drives NAFLD pathogenesis by altering the expression of genes associated with lipid metabolism and bile acid synthesis. Collectively, the results suggest that thrombin activity is central to HFD-induced body weight gain, liver injury, and inflammation and provide the proof-of-principle evidence that pharmacological thrombin inhibition could be effective in limiting NAFLD and associated pathologies.

Neonatal monosodium glutamate treatment causes obesity, diabetes, and macrovesicular steatohepatitis with liver nodules in DIAR mice

BACKGROUND AND AIM

Non-alcoholic steatohepatitis (NASH) is the hepatic manifestation of metabolic syndrome (MS). Monosodium glutamate (MSG)-treated ICR mice is a useful model of MS and NASH, but it shows the different patterns of steatosis from human NASH. Because inbred aged DIAR (ddY, Institute for Animal Reproduction) mice spontaneously show the similar pattern of steatosis as NASH, we analyzed their liver pathology after administering MSG.

METHODS

MSG-treated DIAR mice (DIAR-MSG) and untreated DIAR mice (DIAR-controls) were sacrificed and assessed histopathologically at 29, 32, 40, 48, and 54 weeks of age. The NASH activity score, body mass index, blood glucose level, and oral glucose tolerance test were also assessed.

RESULTS

The body mass index and blood glucose levels of DIAR-MSG were significantly higher than controls. The oral glucose tolerance test revealed a type 2 diabetes pattern in DIAR-MSG. The livers of DIAR-MSG mice showed macrovesicular steatosis, lobular inflammation with neutrophils, and ballooning degeneration after 29 weeks. At 54 weeks, mild fibrosis was observed in 5/6 DIAR-MSG and 2/5 DIAR-control mice. In imaging mass spectrometry analysis, cholesterol as well as triglyceride accumulated in the liver of DIAR-MSG mice. Atypical liver nodules were also observed after 32 weeks in DIAR-MSG, some with cellular and structural atypia mimicking human hepatocellular carcinoma. The NASH activity score of DIAR-MSG after 29 weeks was higher than that of control mice, suggesting the development of NASH.

CONCLUSIONS

DIAR-MSG had NASH-like liver pathology and liver nodules typically associated with MS symptoms. DIAR-MSG provides a valuable animal model to analyze NASH pathogenesis and carcinogenesis.

Fas-induced apoptosis increases hepatocyte tissue factor procoagulant activity in vitro and in vivo

Hepatocyte (HPC) apoptosis occurs in association with hepatotoxic responses and chronic liver disease, and is coupled to activation of the blood coagulation cascade. HPCs have been shown to express tissue factor (TF), the primary activator of blood coagulation, in a form that lacks procoagulant activity. In this study, we determined the effect of inducing HPC apoptosis on the procoagulant activity of TF. Treatment of primary mouse HPCs with the Fas death receptor agonist (anti-CD95 antibody, Jo2) triggered apoptosis as shown by cleavage of caspase-3, increased caspase-3 proteolytic activity, and cell surface exposure of phosphatidylserine (PS). Jo2-induced apoptosis significantly increased TF-dependent factor Xa generation by HPCs. Moreover, Jo2 treatment was associated with increased levels of microparticle-associated TF procoagulant activity in the culture medium. Pretreatment with a caspase-3 inhibitor significantly reduced Jo2-induced HPC TF activity and prevented the increase in microparticle-associated TF procoagulant activity. Application of the high-affinity PS-binding protein lactadherin inhibited TF-dependent factor Xa generation by Jo2-treated HPCs and dramatically reduced microparticle-associated TF procoagulant activity. Treatment of wild-type mice with a sublethal dose of Jo2 was associated with a robust increase in the activation of coagulation as measured by plasma thrombin-antithrombin (TAT) levels; whereas mice with liver-specific TF deficiency had significantly lower TAT levels. Overall, the results indicate that Fas-initiated, caspase-3-dependent HPC apoptosis increases TF procoagulant activity through a mechanism involving PS externalization. This suggests that activation of liver TF likely contributes to the procoagulant state associated with HPC apoptosis in liver toxicity and disease.

Proteinase activated receptor 1 mediated fibrosis in a mouse model of liver injury: a role for bone marrow derived macrophages

Liver fibrosis results from the co-ordinated actions of myofibroblasts and macrophages, a proportion of which are of bone marrow origin. The functional effect of such bone marrow-derived cells on liver fibrosis is unclear. We examine whether changing bone marrow genotype can down-regulate the liver's fibrotic response to injury and investigate mechanisms involved. Proteinase activated receptor 1 (PAR1) is up-regulated in fibrotic liver disease in humans, and deficiency of PAR1 is associated with reduced liver fibrosis in rodent models. In this study, recipient mice received bone marrow transplantation from PAR1-deficient or wild-type donors prior to carbon tetrachloride-induced liver fibrosis. Bone marrow transplantation alone from PAR1-deficient mice was able to confer significant reductions in hepatic collagen content and activated myofibroblast expansion on wild-type recipients. This effect was associated with a decrease in hepatic scar-associated macrophages and a reduction in macrophage recruitment from the bone marrow. In vitro, PAR1 signalling on bone marrow-derived macrophages directly induced their chemotaxis but did not stimulate proliferation. These data suggest that the bone marrow can modulate the fibrotic response of the liver to recurrent injury. PAR1 signalling can contribute to this response by mechanisms that include the regulation of macrophage recruitment.

Polyphosphate suppresses complement via the terminal pathway

Polyphosphate, synthesized by all cells, is a linear polymer of inorganic phosphate. When released into the circulation, it exerts prothrombotic and proinflammatory activities by modulating steps in the coagulation cascade. We examined the role of polyphosphate in regulating the evolutionarily related proteolytic cascade complement. In erythrocyte lysis assays, polyphosphate comprising more than 1000 phosphate units suppressed total hemolytic activity with a concentration to reduce maximal lysis to 50% that was 10-fold lower than with monophosphate. In the ion- and enzyme-independent terminal pathway complement assay, polyphosphate suppressed complement in a concentration- and size-dependent manner. Phosphatase-treated polyphosphate lost its ability to suppress complement, confirming that polymer integrity is required. Sequential addition of polyphosphate to the terminal pathway assay showed that polyphosphate interferes with complement only when added before formation of the C5b-7 complex. Physicochemical analyses using native gels, gel filtration, and differential scanning fluorimetry revealed that polyphosphate binds to and destabilizes C5b,6, thereby reducing the capacity of the membrane attack complex to bind to and lyse the target cell. In summary, we have added another function to polyphosphate in blood, demonstrating that it dampens the innate immune response by suppressing complement. These findings further establish the complex relationship between coagulation and innate immunity.

Inflammation, obesity, and thrombosis

Clinical and epidemiological studies support a connection between obesity and thrombosis, involving elevated expression of the prothrombotic molecules plasminogen activator inhibitor-1 and tissue factor (TF) and increased platelet activation. Cardiovascular diseases and metabolic syndrome-associated disorders, including obesity, insulin resistance, type 2 diabetes, and hepatic steatosis, involve inflammation elicited by infiltration and activation of immune cells, particularly macrophages, into adipose tissue. Although TF has been clearly linked to a procoagulant state in obesity, emerging genetic and pharmacologic evidence indicate that TF signaling via G protein-coupled protease-activated receptors (PAR2, PAR1) additionally drives multiple aspects of the metabolic syndrome. TF-PAR2 signaling in adipocytes contributes to diet-induced obesity by decreasing metabolism and energy expenditure, whereas TF-PAR2 signaling in hematopoietic and myeloid cells drives adipose tissue inflammation, hepatic steatosis, and insulin resistance. TF-initiated coagulation leading to thrombin-PAR1 signaling also contributes to diet-induced hepatic steatosis and inflammation in certain models. Thus, in obese patients, clinical markers of a prothrombotic state may indicate a risk for the development of complications of the metabolic syndrome. Furthermore, TF-induced signaling could provide new therapeutic targets for drug development at the intersection between obesity, inflammation, and thrombosis.

Plasminogen controls inflammation and pathogenesis of influenza virus infections via fibrinolysis

Detrimental inflammation of the lungs is a hallmark of severe influenza virus infections. Endothelial cells are the source of cytokine amplification, although mechanisms underlying this process are unknown. Here, using combined pharmacological and gene-deletion approaches, we show that plasminogen controls lung inflammation and pathogenesis of infections with influenza A/PR/8/34, highly pathogenic H5N1 and 2009 pandemic H1N1 viruses. Reduction of virus replication was not responsible for the observed effect. However, pharmacological depletion of fibrinogen, the main target of plasminogen reversed disease resistance of plasminogen-deficient mice or mice treated with an inhibitor of plasminogen-mediated fibrinolysis. Therefore, plasminogen contributes to the deleterious inflammation of the lungs and local fibrin clot formation may be implicated in host defense against influenza virus infections. Our studies suggest that the hemostatic system might be explored for novel treatments against influenza.

Influenza viruses, including H5N1 bird influenza viruses continue to form a major threat for public health. Available antiviral drugs for the treatment of influenza are effective to a limited extent and the emergence of resistant viruses may further undermine their use. The symptoms associated with influenza are caused by replication of the virus in the respiratory tract and the host immune response. Here, we report that a molecule of the fibrinolytic system, plasminogen, contributes to inflammation caused by influenza. Inhibiting the action of plasminogen protected mice from severe influenza infections, including those caused by H5N1 and H1N1 pandemic 2009 viruses and may be a promising novel strategy to treat influenza.

Stimulation of fat accumulation in hepatocytes by PGE₂-dependent repression of hepatic lipolysis, β-oxidation and VLDL-synthesis

Hepatic steatosis is recognized as hepatic presentation of the metabolic syndrome. Hyperinsulinaemia, which shifts fatty acid oxidation to de novo lipogenesis and lipid storage in the liver, appears to be a principal elicitor particularly in the early stages of disease development. The impact of PGE₂, which has previously been shown to attenuate insulin signaling and hence might reduce insulin-dependent lipid accumulation, on insulin-induced steatosis of hepatocytes was studied. The PGE₂-generating capacity was enhanced in various obese mouse models by the induction of cyclooxygenase 2 and microsomal prostaglandin E-synthases (mPGES1, mPGES2). PGE₂ attenuated the insulin-dependent induction of SREBP-1c and its target genes glucokinase and fatty acid synthase. Nevertheless, PGE₂ enhanced incorporation of glucose into hepatic triglycerides synergistically with insulin. This was most likely due to a combination of a PGE₂-dependent repression of (1) the key lipolytic enzyme adipose triglyceride lipase, (2) carnitine-palmitoyltransferase 1, a key regulator of mitochondrial β-oxidation, and (3) microsomal transfer protein, as well as (4) apolipoprotein B, key components of the VLDL synthesis. Repression of PGC1α, a common upstream regulator of these genes, was identified as a possible cause. In support of this hypothesis, overexpression of PGC1α completely blunted the PGE₂-dependent fat accumulation. PGE₂ enhanced lipid accumulation synergistically with insulin, despite attenuating insulin signaling and might thus contribute to the development of hepatic steatosis. Induction of enzymes involved in PGE₂ synthesis in in vivo models of obesity imply a potential role of prostanoids in the development of NAFLD and NASH.

Anti-inflammatory potential of allyl-isothiocyanate--role of Nrf2, NF-(κ) B and microRNA-155

In this study, the underlying mechanisms of the potential anti-inflammatory properties of allyl-isothiocyanate (AITC) were analysed in vitro and in vivo. Murine RAW264.7 macrophages stimulated with lipopolysaccharide (LPS) were supplemented with increasing concentrations of AITC. In addition, C57BL/6 mice (n= 10 per group) were fed a pro-inflammatory high-fat diet and AITC was administered orally via gavage for 7 days. Biomarkers of inflammation were determined both in cultured cells and in mice. AITC significantly decreased tumour necrosis factor α mRNA levels and its secretion in LPS stimulated RAW264.7 macrophages. Furthermore, gene expression of other pro-inflammatory markers including interleukin-1β and inducible nitric oxide synthase were down-regulated following AITC treatment. AITC decreased nuclear p65 protein levels, a subunit of the transcription factor NF-κB. Importantly, our data indicate that AITC significantly attenuated microRNA-155 levels in LPS-stimulated RAW264.7 macrophages in a dose-dependent manner. The anti-inflammatory effects of AITC were accompanied by an increase in Nrf2 nuclear translocation and consequently by an increase of mRNA and protein levels of the Nrf2 target gene heme-oxygenase 1. AITC was slightly less potent than sulforaphane (used as a positive control) in down-regulating inflammation in LPS-stimulated macrophages. A significant increase in nuclear Nrf2 and heme-oxygenase 1 gene expression and only a moderate down-regulation of interleukin-1β and microRNA-155 levels due to AITC was found in mouse liver. Present data suggest that AITC exhibits potent anti-inflammatory activity in cultured macrophages in vitro but has only little anti-inflammatory activity in mice in vivo.

Therapeutic administration of the direct thrombin inhibitor argatroban reduces hepatic inflammation in mice with established fatty liver disease

Thrombin generation is increased in patients with nonalcoholic fatty liver disease (NAFLD) and in mouse models of diet-induced obesity. Deficiency in the thrombin receptor protease activated receptor-1 reduces hepatic inflammation and steatosis in mice fed a Western diet. However, it is currently unclear whether thrombin inhibitors can modify the pathogenesis of established NAFLD. We tested the hypothesis that thrombin inhibition could reverse hepatic steatosis and inflammation in mice with established diet-induced NAFLD. Low-density lipoprotein receptor-deficient LDLr(-/-) mice were fed a control diet or a Western diet for 19 weeks. Mice were given the direct thrombin inhibitor argatroban ∼15 mg/kg/day or its vehicle via a miniosmotic pump for the final 4 weeks of the study. Argatroban administration significantly reduced hepatic proinflammatory cytokine expression and reduced macrophage and neutrophil accumulation in livers of mice fed a Western diet. Argatroban did not significantly impact hepatic steatosis, as indicated by histopathology, Oil Red O staining, and hepatic triglyceride levels. Argatroban reduced serum triglyceride and cholesterol levels in mice fed a Western diet. Argatroban reduced both α-smooth muscle actin expression and Type 1 collagen mRNA levels in livers of mice fed a Western diet, indicating reduced activation of hepatic stellate cells. This study indicates that therapeutic intervention with a thrombin inhibitor attenuates hepatic inflammation and several profibrogenic changes in mice fed a Western diet.

Coagulation in hepatobiliary disease

OBJECTIVE

To review the pathogenesis and clinical consequences of coagulation abnormalities accompanying hepatobiliary disorders and to highlight the need for further studies to characterize these derangements and their treatment options in small animal patients.

DATA SOURCES

Veterinary and human medical literature: original research articles, scientific reviews, consensus statements, and recent texts.

SUMMARY

The liver plays an important role in the production and clearance of many components of coagulation. A wide range of hemostatic derangements can occur in patients with hepatobiliary disease including alterations in platelet number and function, coagulation factor levels, anticoagulants, vascular endothelial function, and fibrinolysis. As these hemostatic alterations include both pro- and anticoagulation pathways, the net result is often a rebalanced hemostatic system that can be easily disrupted by concurrent conditions resulting in either clinical bleeding or thrombosis. Conventional coagulation tests are inadequate at identifying the spectrum of coagulation alterations occurring in patients with hepatobiliary disease, but their evaluation is necessary to assess bleeding risk and provide prognostic information. A paucity of information exists regarding the treatment of the coagulation derangements in small animals with hepatobiliary disease. Extrapolation from human studies provides some information about potential treatment options, but further studies are warranted in this area to elucidate the best management for coagulation abnormalities in dogs and cats with hepatobiliary disease.

CONCLUSION

Hepatobiliary disease can have profound effects on coagulation function leading to hypercoagulable or hypocoagulable states. Overall coagulation status with hepatobiliary disease depends on both the type and severity of disease and the presence of associated complications.

Tissue factor antisense deoxyoligonucleotide prevents monocrotaline/LPS hepatotoxicity in mice

Tissue factor (TF) is a membranous glycoprotein that functions as a receptor for coagulation factor VII/VIIa and activates the coagulation system when blood vessels or tissues are damaged. TF was upregulated in our monocrotaline (MCT)/lipopolysaccharide (LPS) hepatotoxicity model. We tested the hypothesis that TF-dependent fibrin deposition and lipid peroxidation in the form of oxidized low-density-lipoprotein (ox-LDL) accumulation contribute to liver inflammation induced by MCT/LPS in mice. In the present study, we blocked TF using antisense oligodeoxynucleotides against mouse TF (TF-ASO). TF-ASO (5.6 mg kg(-1) ) was given i.v. to ND4 male mice 30 min after administration of MCT (200 mg kg(-1) ) p.o. followed after 3.5 h by LPS i.p. (6 mg kg(-1) ). Blood alanine aminotransferase (ALT), TF, ox-LDL, platelets, hematocrit and keratinocyte-derived chemokine (KC) levels were evaluated in different treatment groups. Fibrin deposition and ox-LDL accumulation were also analyzed in the liver sections using immunofluorescent staining. The results showed that TF-ASO significantly restored blood ALT, hematocrit and KC levels, distorted after MCT/LPS co-treatment, as well as preventing the accumulation of ox-LDL and the deposition of fibrin in the liver tissues, and thereby inhibited liver injury caused by MCT/LPS. In a separate experiment, TF-ASO administration significantly prolonged animal survival. The current study demonstrates that TF is associated with MCT/LPS-induced liver injury. Administration of TF-ASO successfully prevented this type of liver injury.

Insulin immuno-neutralization in fed chickens: effects on liver and muscle transcriptome

Chickens mimic an insulin-resistance state by exhibiting several peculiarities with regard to plasma glucose level and its control by insulin. To gain insight into the role of insulin in the control of chicken transcriptome, liver and leg muscle transcriptomes were compared in fed controls and "diabetic" chickens, at 5 h after insulin immuno-neutralization, using 20.7K-chicken oligo-microarrays. At a level of false discovery rate <0.01, 1,573 and 1,225 signals were significantly modified by insulin privation in liver and muscle, respectively. Microarray data agreed reasonably well with qRT-PCR and some protein level measurements. Differentially expressed mRNAs with human ID were classified using Biorag analysis and Ingenuity Pathway Analysis. Multiple metabolic pathways, structural proteins, transporters and proteins of intracellular trafficking, major signaling pathways, and elements of the transcriptional control machinery were largely represented in both tissues. At least 42 mRNAs have already been associated with diabetes, insulin resistance, obesity, energy expenditure, or identified as sensors of metabolism in mice or humans. The contribution of the pathways presently identified to chicken physiology (particularly those not yet related to insulin) needs to be evaluated in future studies. Other challenges include the characterization of "unknown" mRNAs and the identification of the steps or networks, which disturbed tissue transcriptome so extensively, quickly after the turning off of the insulin signal. In conclusion, pleiotropic effects of insulin in chickens are further evidenced; major pathways controlled by insulin in mammals have been conserved despite the presence of unique features of insulin signaling in chicken muscle.

Early growth response factor-1 limits biliary fibrosis in a model of xenobiotic-induced cholestasis in mice

Hepatic expression of the transcription factor early growth response-1 (Egr-1) is increased in livers of patients with cholestatic liver disease. Bile acid induction of inflammatory genes in hepatocytes is Egr-1 dependent, and Egr-1 expression is increased in livers of mice after bile duct ligation. Of importance, Egr-1 deficiency reduces liver inflammation and injury in that model. However, it is not known whether Egr-1 promotes inflammation in other models of cholestasis. We tested the hypothesis that Egr-1 contributes to liver inflammation in mice exposed chronically to the bile duct epithelial cell (BDEC) toxicant alpha-naphthylisothiocyanate (ANIT). Egr-1-knockout (Egr-1(-/-)) mice and wild-type mice were fed a diet containing 0.025% ANIT for 2 weeks. Expression of Egr-1 mRNA and protein was significantly increased in livers of mice fed ANIT diet. Egr-1 deficiency did not significantly affect ANIT diet-induced hepatocellular injury, inflammatory gene induction, BDEC hyperplasia, or hepatic neutrophil accumulation. In contrast, the deposition of Type 1 collagen was significantly increased in livers of Egr-1(-/-) mice fed ANIT diet compared with wild-type mice fed ANIT diet. Interestingly, this increase in liver fibrosis occurred in association with elevated expression of the β6 integrin (Itgb6) gene, suggesting the potential for increased local activation of transforming growth factor beta. Taken together, the results indicate that Egr-1 does not contribute to liver injury or inflammation in mice fed a diet containing ANIT. Rather, these studies indicate that Egr-1 deficiency worsens liver fibrosis in conjunction with enhanced expression of the profibrogenic Itgb6 gene.

Differential roles of unsaturated and saturated fatty acids on autophagy and apoptosis in hepatocytes

Fatty acid-induced lipotoxicity plays a critical role in the pathogenesis of nonalcoholic liver disease. Saturated fatty acids and unsaturated fatty acids have differential effects on cell death and steatosis, but the mechanisms responsible for these differences are not known. Using cultured HepG2 cells and primary mouse hepatocytes, we found that unsaturated and saturated fatty acids differentially regulate autophagy and apoptosis. The unsaturated fatty acid, oleic acid, promoted the formation of triglyceride-enriched lipid droplets and induced autophagy but had a minimal effect on apoptosis. In contrast, the saturated fatty acid, palmitic acid, was poorly converted into triglyceride-enriched lipid droplets, suppressed autophagy, and significantly induced apoptosis. Subsequent studies revealed that palmitic acid-induced apoptosis suppressed autophagy by inducing caspase-dependent Beclin 1 cleavage, indicating cross-talk between apoptosis and autophagy. Moreover, our data suggest that the formation of triglyceride-enriched lipid droplets and induction of autophagy are protective mechanisms against fatty acid-induced lipotoxicity. In line with our in vitro findings, we found that high-fat diet-induced hepatic steatosis was associated with autophagy in the mouse liver. Potential modulation of autophagy may be a novel approach that has therapeutic benefits for obesity-induced steatosis and liver injury.

Tissue factor, blood coagulation, and beyond: an overview

Emerging evidence shows a broad spectrum of biological functions of tissue factor (TF). TF classical role in initiating the extrinsic blood coagulation and its direct thrombotic action in close relation to cardiovascular risks have long been established. TF overexpression/hypercoagulability often observed in many clinical conditions certainly expands its role in proinflammation, diabetes, obesity, cardiovascular diseases, angiogenesis, tumor metastasis, wound repairs, embryonic development, cell adhesion/migration, innate immunity, infection, pregnancy loss, and many others. This paper broadly covers seminal observations to discuss TF pathogenic roles in relation to diverse disease development or manifestation. Biochemically, extracellular TF signaling interfaced through protease-activated receptors (PARs) elicits cellular activation and inflammatory responses. TF diverse biological roles are associated with either coagulation-dependent or noncoagulation-mediated actions. Apparently, TF hypercoagulability refuels a coagulation-inflammation-thrombosis circuit in “autocrine” or “paracrine” fashions, which triggers a wide spectrum of pathophysiology. Accordingly, TF suppression, anticoagulation, PAR blockade, or general anti-inflammation offers an array of therapeutical benefits for easing diverse pathological conditions.

Protease-activated receptor 1 and hematopoietic cell tissue factor are required for hepatic steatosis in mice fed a Western diet

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of obesity and metabolic syndrome and contributes to increased risk of cardiovascular disease and liver-related morbidity and mortality. Indeed, obese patients with metabolic syndrome generate greater amounts of thrombin, an indication of coagulation cascade activation. However, the role of the coagulation cascade in Western diet-induced NAFLD has not been investigated. Using an established mouse model of Western diet-induced NAFLD, we tested whether the thrombin receptor protease-activated receptor 1 (PAR-1) and hematopoietic cell-derived tissue factor (TF) contribute to hepatic steatosis. In association with hepatic steatosis, plasma thrombin-antithrombin levels and hepatic fibrin deposition increased significantly in C57Bl/6J mice fed a Western diet for 3 months. PAR-1 deficiency reduced hepatic inflammation, particularly monocyte chemoattractant protein-1 expression and macrophage accumulation. In addition, PAR-1 deficiency was associated with reduced steatosis in mice fed a Western diet, including reduced liver triglyceride accumulation and CD36 expression. Similar to PAR-1 deficiency, hematopoietic cell TF deficiency was associated with reduced inflammation and reduced steatosis in livers of low-density lipoprotein receptor-deficient mice fed a Western diet. Moreover, hematopoietic cell TF deficiency reduced hepatic fibrin deposition. These studies indicate that PAR-1 and hematopoietic cell TF are required for liver inflammation and steatosis in mice fed a Western diet.

The roles of thrombin and protease-activated receptors in inflammation

Inflammation and coagulation constitute two host defence systems with complementary physiological roles in limiting tissue damage, restoring homeostasis and eliminating invading pathogens, functions reliant on effective regulation of both processes at a variety of levels. Dysfunctional activation or regulation of either pathway may lead to pathology and contribute to human diseases as diverse as myocardial infarction and septic shock. The serine protease thrombin, a key protein in the coagulation pathway, can activate cellular signalling directly via proteolytic cleavage of the N-terminal domain of a family of G protein-coupled receptors or indirectly through the generation of molecules such as activated protein C. These events transmit signals to many cell types and can elicit the production of various pro-inflammatory mediators such as cytokines, chemokines and growth factors, thereby influencing cell activation, differentiation, survival and migration. This review discusses recent progress in understanding how thrombin and protease-activated receptors influence biological processes, highlighting the detrimental and protective cellular effects of thrombin and its signalling pathways.

Fibrinogen deficiency increases liver injury and early growth response-1 (Egr-1) expression in a model of chronic xenobiotic-induced cholestasis

Chronic cholestatic liver injury induced by cholestasis in rodents is associated with hepatic fibrin deposition, and we found evidence of fibrin deposition in livers of patients with cholestasis. Key components of the fibrinolytic pathway modulate cholestatic liver injury by regulating activation of hepatocyte growth factor. However, the exact role of hepatic fibrin deposition in chronic cholestasis is not known. We tested the hypothesis that fibrinogen (Fbg) deficiency worsens liver injury induced by cholestasis. Fbg-deficient mice (Fbgα(-/-) mice) and heterozygous control mice (Fbgα(+/-) mice) were fed either the control diet or a diet containing 0.025% α-naphthylisothiocyanate (ANIT), which selectively injures bile duct epithelial cells in the liver, for 2 weeks. Hepatic fibrin and collagen deposits were evident in livers of heterozygous control mice fed the ANIT diet. Complete Fbg deficiency was associated with elevated serum bile acids, periportal necrosis, and increased serum alanine aminotransferase activity in mice fed the ANIT diet. Fbg deficiency was associated with enhanced hepatic expression of the transcription factor early growth response-1 (Egr-1) and enhanced induction of genes encoding the Egr-1-regulated proinflammatory chemokines monocyte chemotactic protein-1, KC growth-regulated protein, and macrophage inflammatory protein-2. Interestingly, peribiliary collagen deposition was not evident near necrotic areas in Fbg-deficient mice. The results suggest that in this model of chronic cholestasis, fibrin constrains the release of bile constituents from injured intrahepatic bile ducts, thereby limiting the progression of hepatic inflammation and hepatocellular injury.

Structure, function and pathophysiology of protease activated receptors

Discovered in the 1990s, protease activated receptors(1) (PARs) are membrane-spanning cell surface proteins that belong to the G protein coupled receptor (GPCR) family. A defining feature of these receptors is their irreversible activation by proteases; mainly serine. Proteolytic agonists remove the PAR extracellular amino terminal pro-domain to expose a new amino terminus, or tethered ligand, that binds intramolecularly to induce intracellular signal transduction via a number of molecular pathways that regulate a variety of cellular responses. By these mechanisms PARs function as cell surface sensors of extracellular and cell surface associated proteases, contributing extensively to regulation of homeostasis, as well as to dysfunctional responses required for progression of a number of diseases. This review examines common and distinguishing structural features of PARs, mechanisms of receptor activation, trafficking and signal termination, and discusses the physiological and pathological roles of these receptors and emerging approaches for modulating PAR-mediated signaling in disease.

Monocyte chemoattractant protein-1 deficiency does not affect steatosis or inflammation in livers of mice fed a methionine-choline-deficient diet

Monocyte chemoattractant protein-1 (MCP-1, Ccl2) expression is increased in livers of patients with nonalcoholic steatohepatitis and in murine models of steatohepatitis. Several studies in rodents indicate that MCP-1 contributes to liver steatosis induced by feeding a high-fat diet. However, the extent of MCP-1 involvement in the widely utilized methionine-choline-deficient (MCD) diet model of steatohepatitis has not been determined. We tested the hypothesis that MCP-1 contributes to steatohepatitis in mice fed the MCD diet. MCP-1-deficient mice on a C57Bl/6J background and age-matched C57Bl/6J mice were fed either MCD diet or control diet for 4 weeks. MCP-1 deficiency did not affect steatohepatitis, as indicated by liver histopathology, nor did it affect serum alanine aminotransferase activity, hepatic triglyceride levels, hepatic inflammatory gene induction, or macrophage accumulation in mice fed the MCD diet. MCP-1 deficiency reduced the expression of the profibrogenic genes, pro-collagen 1a1, connective tissue growth factor, and transforming growth factor-β, in mice fed the MCD diet. MCP-1 deficiency significantly reduced collagen deposition and α-smooth muscle actin protein levels in the livers of mice fed the MCD diet. The results indicate that MCP-1 does not contribute to liver steatosis or inflammation in the MCD diet model of steatohepatitis. Rather, the data suggest that MCP-1 contributes to fibrosis in mice fed the MCD diet, independent of effects on steatosis and inflammation.

The long term immunological response of swine after two exposures to a salmon thrombin and fibrinogen hemostatic bandage

Experimental salmon thrombin/fibrinogen dressings have been shown to provide effective hemostasis in severe hemorrhage situations. The hypothesis for this study was that swine would still remain healthy without coagulopathy six months after exposure to salmon thrombin/fibrinogen dressings. Initial exposure was by insertion of the salmon dressing into the peritoneal cavity. Three months after the initial exposure, the same animals were subjected to two full thickness dermal wounds on the dorsal surface. One wound was bandaged with the salmon thrombin/fibrinogen bandage and the other wound was dressed with a standard bandage. The animals were monitored for an additional three months. Blood was drawn every 14 days over the six months for immunological and coagulation function analysis. All of the animals (8 pigs) remained healthy during the six month period and the dermal wounds healed without incidence. Lymph nodes and spleen showed signs of normal immune response and Western blots showed development of antibodies against salmon fibrinogen, but none of the animals made antibodies that recognized any species of thrombin. Coagulation parameters (fibrinogen concentration, thrombin time, PT and aPTT) and hematological parameters remained normal over the course of the study when compared to initial values of the subject swine.