Role of Fibrinogen-Like Protein 2 Prothrombinase/Fibroleukin in Experimental and Human Allograft Rejection

The Maternal-Fetal Interface Fibrin Deposition and Expression of FGL2 in the Placenta of Preeclampsia and Fetal Growth Restriction

We aimed to assess fibrin deposition in placentas of patients with preeclampsia (PE) with fetal growth restriction (FGR) and the relationship with fibrinogen-like protein 2 (FGL2). In this case-control study, pregnant women with PE (n=48), PE with FGR (n=44), FGR (n=43), and healthy pregnant women (n=43) at term gestation were recruited. We compared the baseline characteristics, blood coagulation parameters, and placenta characteristics. Masson's trichrome staining was used to categorize 2 types of fibrinoid. FGL2 expression was examined by immunohistochemical staining. The PE+FGR placentas showed more obvious fetal and maternal vascular malperfusion and maternal-fetal interface fibrin deposition when compared with the others. Increased fibrin-type and matrix-type fibrinoids were found in the placenta of the PE+FGR group when compared with the controls. FGL2 was localized in the junction of these 2 types of fibrinoid, as well as extravillous trophoblastic layers and decidual stromal cells. The PE+FGR group had significantly lower FGL2 expression levels. Placental vascular malperfusion with massive maternal-fetal interface fibrin deposition was found in PE with FGR. We report the characteristic colocalization of 2 types of placental fibrinoid deposition and FGL2 immunoreactivity and, therefore, help in elucidating the mechanisms in the pathology of PE with FGR.

FGL2/FcγRIIB Signalling Mediates Arterial Shear Stress-Mediated Endothelial Cell Apoptosis: Implications for Coronary Artery Bypass Vein Graft Pathogenesis

The sudden exposure of venous endothelial cells (vECs) to arterial fluid shear stress (FSS) is thought to be a major contributor to coronary artery bypass vein graft failure (VGF). However, the effects of arterial FSS on the vEC secretome are poorly characterised. We propose that analysis of the vEC secretome may reveal potential therapeutic approaches to suppress VGF. Human umbilical vein endothelial cells (HUVECs) pre-conditioned to venous FSS (18 h; 1.5 dynes/cm2) were exposed to venous or arterial FSS (15 dynes/cm2) for 24 h. Tandem Mass Tagging proteomic analysis of the vEC secretome identified significantly increased fibroleukin (FGL2) in conditioned media from HUVECs exposed to arterial FSS. This increase was validated by Western blotting. Application of the NFκB inhibitor BAY 11-7085 (1 µM) following pre-conditioning reduced FGL2 release from vECs exposed to arterial FSS. Exposure of vECs to arterial FSS increased apoptosis, measured by active cleaved caspase-3 (CC3) immunocytochemistry, which was likewise elevated in HUVECs treated with recombinant FGL2 (20 ng/mL) for 24 h under static conditions. To determine the mechanism of FGL2-induced apoptosis, HUVECs were pre-treated with a blocking antibody to FcγRIIB, a receptor FGL2 is proposed to interact with, which reduced CC3 levels. In conclusion, our findings indicate that the exposure of vECs to arterial FSS results in increased release of FGL2 via NFκB signalling, which promotes endothelial apoptosis via FcγRIIB signalling. Therefore, the inhibition of FGL2/FcγRIIB signalling may provide a novel approach to reduce arterial FSS-induced vEC apoptosis in vein grafts and suppress VGF.

Biomarkers from subcutaneous engineered tissues predict acute rejection of organ allografts

Invasive graft biopsies assess the efficacy of immunosuppression through lagging indicators of transplant rejection. We report on a microporous scaffold implant as a minimally invasive immunological niche to assay rejection before graft injury. Adoptive transfer of T cells into Rag2-/- mice with mismatched allografts induced acute cellular allograft rejection (ACAR), with subsequent validation in wild-type animals. Following murine heart or skin transplantation, scaffold implants accumulate predominantly innate immune cells. The scaffold enables frequent biopsy, and gene expression analyses identified biomarkers of ACAR before clinical signs of graft injury. This gene signature distinguishes ACAR and immunodeficient respiratory infection before injury onset, indicating the specificity of the biomarkers to differentiate ACAR from other inflammatory insult. Overall, this implantable scaffold enables remote evaluation of the early risk of rejection, which could potentially be used to reduce the frequency of routine graft biopsy, reduce toxicities by personalizing immunosuppression, and prolong transplant life.

FGL2 promotes tumour growth and attenuates infiltration of activated immune cells in melanoma and ovarian cancer models

The tumour microenvironment is infiltrated by immunosuppressive cells, such as regulatory T cells (Tregs), which contribute to tumour escape and impede immunotherapy outcomes. Soluble fibrinogen-like protein 2 (sFGL2), a Treg effector protein, inhibits immune cell populations, via receptors FcγRIIB and FcγRIII, leading to downregulation of CD86 in antigen presenting cells and limiting T cell activation. Increased FGL2 expression is associated with tumour progression and poor survival in several different cancers, such as glioblastoma multiforme, lung, renal, liver, colorectal, and prostate cancer. Querying scRNA-seq human cancer data shows FGL2 is produced by cells in the tumour microenvironment (TME), particularly monocytes and macrophages as well as T cells and dendritic cells (DCs), while cancer cells have minimal expression of FGL2. We studied the role of FGL2 exclusively produced by cells in the TME, by leveraging Fgl2 knockout mice. We tested two murine models of cancer in which the role of FGL2 has not been previously studied: epithelial ovarian cancer and melanoma. We show that absence of FGL2 leads to a more activated TME, including activated DCs (CD86+, CD40+) and T cells (CD25+, TIGIT+), as well as demonstrating for the first time that the absence of FGL2 leads to more activated natural killer cells (DNAM-1+, NKG2D+) in the TME. Furthermore, the absence of FGL2 leads to prolonged survival in the B16F10 melanoma model, while the absence of FGL2 synergizes with oncolytic virus to prolong survival in the ID8-p53-/-Brca2-/- ovarian cancer model. In conclusion, targeting FGL2 is a promising cancer treatment strategy alone and in combination immunotherapies.

Chitotriose Enhanced Antitumor Activity of Doxorubicin through Egr1 Upregulation in MDA-MB-231 Cells

Dietary supplementation is proposed as a strategy to reduce the side effects of conventional chemotherapy for triple-negative breast cancer (TNBC). Chitosan oligosaccharides (COS), a functional carbohydrate, have been identified to potentially inhibit cancer cell proliferation. However, a detailed investigation is required to fully understand its exact influence, particularly in terms of COS composition. The antitumor activities of COS oligomers and its monomer of glucosamine, when combined with doxorubicin separately, were evaluated in MDA-MB-231 cells. Chitotriose was identified to have the most significant synergistic effect. Preincubation with chitotriose was observed to promote the entry of doxorubicin into the cell nuclei and induce morphological changes in the cells. Mechanism analysis at the transcriptional level revealed that the early growth response 1 (Egr1) gene was a key regulator in enhancing the suppressive effect. This gene was found to modulate the activity of its downstream gene, growth arrest, and DNA damage-inducible alpha (Gadd45a). The role of Egr1 was confirmed through a small interfering RNA test and function assay. These findings provide insight into the effect and underlying mechanism of chitotriose supplementation for TNBC therapy.

Fibrinogen-like protein 2 in inflammatory diseases: A future therapeutic target

Fibrinogen-like protein 2 (FGL2), a member of the fibrinogen family, exists as a membrane-bound protein with immune-associated coagulation activity and a soluble form possessing immunosuppressive functions. The immunomodulatory role of FGL2 is evident in fibrin deposition-associated inflammatory diseases and cancer, suggesting that FGL2 expression could be exploited as a disease biomarker and a therapeutic target. Recently, in vitro studies and knockout and transgenic animal FGL2 models have been used by us and others to reveal the involvement of FGL2 in the pathogenesis of various inflammatory diseases. This review summarizes our current knowledge of the immunomodulatory role of FGL2 in inflammatory diseases and examines the role of FGL2 as a potential therapeutic target.

Assessment of Fibrinogen-like 2 (FGL2) in Human Chronic Kidney Disease through Transcriptomics Data Analysis

Fibrinogen-like 2 (FGL2) was recently found to be associated with fibrosis in a mouse model of kidney damage and was proposed as a potential therapeutic target in chronic kidney disease (CKD). We assessed the association of renal FGL2 mRNA expression with the disease outcome in two independent CKD cohorts (NEPTUNE and Innsbruck CKD cohort) using Kaplan Meier survival analysis. The regulation of FGL2 in kidney biopsies of CKD patients as compared to healthy controls was further assessed in 13 human CKD transcriptomics datasets. The FGL2 protein expression in human renal tissue sections was determined via immunohistochemistry. The regulators of FGL2 mRNA expression in renal tissue were identified in the co-expression and upstream regulator analysis of FGL2-positive renal cells via the use of single-cell RNA sequencing data from the kidney precision medicine project (KPMP). Higher renal FGL2 mRNA expression was positively associated with kidney fibrosis and negatively associated with eGFR. Renal FGL2 mRNA expression was upregulated in CKD as compared with healthy controls and associated with CKD progression in the Innsbruck CKD cohort (p-value = 0.0036) and NEPTUNE cohort (p-value = 0.0048). The highest abundance of FGL2 protein in renal tissue was detected in the thick ascending limb of the loop of Henle and macula densa, proximal tubular cells, as well as in glomerular endothelial cells. The upstream regulator analysis identified TNF, IL1B, IFNG, NFKB1, and SP1 as factors potentially inducing FGL2-co-expressed genes, whereas factors counterbalancing FGL2-co-expressed genes included GLI1, HNF1B, or PPARGC1A. In conclusion, renal FGL2 mRNA expression is elevated in human CKD, and higher FGL2 levels are associated with fibrosis and worse outcomes.

FGL2-MCOLN3-Autophagy Axis-Triggered Neutrophil Extracellular Traps Exacerbate Liver Injury in Fulminant Viral Hepatitis

BACKGROUND & AIMS

Fulminant viral hepatitis (FVH) is a life-threatening disease, but its pathogenesis is not fully understood. Neutrophil extracellular traps (NETs) were an unrecognized link between inflammation and coagulation, which are 2 main features of FVH. Here, we investigated the role and mechanism of NETs in the pathogenesis of FVH.

METHODS

A mouse model of FVH was established by murine hepatitis virus strain-3 infection. Liver leukocytes of infected or uninfected mice were used for single-cell RNA sequencing and whole-transcriptome sequencing. NETs depletion was achieved using DNase 1. Acetaminophen was used to establish a mouse model of non-virus-caused acute liver failure. Clinically, NETs-related markers in liver, plasma, and peripheral neutrophils were assessed in patients with hepatitis B virus (HBV)-related acute liver injury.

RESULTS

Increased hepatic NETs formation was observed in murine hepatitis virus strain-3-infected mice, but not in acetaminophen-treated mice. NETs depletion improved the liver damage and survival rate in FVH by inhibiting hepatic fibrin deposition and inflammation. An adoptive transfer experiment showed that neutrophil-specific fibrinogen-like protein 2 (FGL2) promoted NETs formation. FGL2 was found to directly interact with mucolipin 3, which regulated calcium influx and initiated autophagy, leading to NETs formation. Clinically, increased plasma NETs level was associated with coagulation dysfunction in patients with HBV acute liver injury. Colocalization of FGL2, NETs, and fibrin in liver was observed in these patients.

CONCLUSIONS

NETs aggravated liver injury in FVH by promoting fibrin deposition and inflammation. NETs formation was regulated by the FGL2-mucolipin 3-autophagy axis. Targeting NETs may provide a new strategy for the treatment of FVH.

CFTR interactome mapping using the mammalian membrane two-hybrid high-throughput screening system

Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) is a chloride and bicarbonate channel in secretory epithelia with a critical role in maintaining fluid homeostasis. Mutations in CFTR are associated with Cystic Fibrosis (CF), the most common lethal autosomal recessive disorder in Caucasians. While remarkable treatment advances have been made recently in the form of modulator drugs directly rescuing CFTR dysfunction, there is still considerable scope for improvement of therapeutic effectiveness. Here, we report the application of a high-throughput screening variant of the Mammalian Membrane Two-Hybrid (MaMTH-HTS) to map the protein-protein interactions of wild-type (wt) and mutant CFTR (F508del), in an effort to better understand CF cellular effects and identify new drug targets for patient-specific treatments. Combined with functional validation in multiple disease models, we have uncovered candidate proteins with potential roles in CFTR function/CF pathophysiology, including Fibrinogen Like 2 (FGL2), which we demonstrate in patient-derived intestinal organoids has a significant effect on CFTR functional expression.

MAPK-mediated upregulation of fibrinogen-like protein 2 promotes proliferation, migration, and invasion of colorectal cancer cells

Fibrinogen-like protein 2 (FGL2) has been reported to play a key role in the development of human cancers. However, it is still unmasked whether FGL2 plays a potential role in colorectal carcinogenesis. In this study, the messenger RNA and protein expression levels were measured by quantitative real-time polymerase chain reaction and western blot. Cell counting kit-8 assay, transwell migration, and invasion assay were carried out to evaluate the proliferation, migration, and invasion of LOVO and SW620 cells. FGL2 was upregulated in colorectal cancer (CRC) tissues, as well as cell lines. Mitogen-activated protein kinase (MAPK) signaling was activated in CRC tissues and cell lines. FGL2 was confirmed to be downregulated by MAPK signaling inhibitor U0126. Further, we determined that knockdown of FGL2 caused a reduction of proliferation, migration, and invasion in LOVO and SW620 cells. Consistently, treatment of LOVO and SW620 cells with U0126 led to a decrease in cell proliferation, migration, and invasion. However, these changes initiated by U0126 were abolished by FGL2 overexpression. To conclude, MAPK-mediated upregulation of FGL2 promotes the proliferation, migration, and invasion of CRC cells.

Up-regulation of fibrinogen-like protein 2 in porcine endothelial cells by xenogeneic CD40 signal

Acute humoral xenograft rejection (AHXR), characterized by thrombin generation and endothelial cell activation, should be overcome for the success of xenotransplantation. Fibrinogen-like protein 2 (fgl2) expressed on endothelial cells can convert prothrombin to thrombin directly, which indicates that the induced fgl2 expression in activated endothelial cells can contribute to thrombosis. In xenotransplant condition, the interaction between human CD40L and porcine endothelial CD40 can activate endothelial cells. In this study, we investigated the effect of endothelial cell activation through the interaction between human CD40L and porcine CD40 on fgl2 expression and its function as a direct prothrombinase. We found that CD40 stimulation up-regulated fgl2 expression as well as its enzymatic activity in porcine endothelial cells. Moreover, functional studies using knock-down system showed that the major factor converting human prothrombin to thrombin is fgl2 protein expressed on porcine endothelial cells. Overall, this study demonstrates that fgl2 expression can be induced by xenogeneic CD40 signal on endothelial cells and contribute to thrombin generation.

Gene expression profiles of rat MMECs with different glucose levels and fgl2 gene silencing

BACKGROUND

Cardiac microvascular endothelial cells (MMECs) is one of the key factors in the process of diabetic cardiomyopathy, a common chronic complication of diabetes. Fibrinogen-like protein 2 (FGL2) is linked to apoptosis, angiogenesis, and inflammatory response, all of which also occur in diabetes. Thus, we investigate the role of FGL 2 and other genes in the pathology of diabetic cardiomyopathy.

METHODS

In the present study, we used high-throughput microarray to profile gene expression in rat myocardial MMECs with or without silencing the fgl2 gene and in different glucose environments. We use volcanic maps to isolate genes with significantly different expression levels between conditions, using the standard statistical criteria of fold changes ≥1.5 and P-values ≤0.05. From this list, we identified genes with the most signicant changes in RNA levels and confirmed their protein-level changes with Western blot. Furthermore, bioinformatic analysis predicts possible pathophysiology and clinical relevance of these proteins in diabetic cardiomyopathy.

RESULTS

We identified 17 upregulated and 15 downregulated genes caused by silencing fgl2 gene. Most of them are involved in metabolism, ion transport, cell membrane surface recognition signal modification, inflammatory response, and immune response. Using Western blot, we were able to confirm protein-level expression changes of three genes. Specifically, in both normal and high glucose conditions, silencing fgl2 significantly decreased the expression levels of CCL3 and PLAGL1 while increasing the expression level of CTSC. Significantly, bioinformatic analyses show that CCL3 is related to type 1 diabetes, PLAGL1 to cardiomyocytes, and CTSC to albuminuria in type 2 diabetes.

CONCLUSIONS

Our study provides clues for further studies on the mechanism of diabetic cardiomyopathy as well as function of FGL2 in this process, potentially offering new therapeutic strategies for treating diabetic cardiomyopathy.

Increased expression of Fibrinogen-Like Protein 2 is associated with poor prognosis in patients with clear cell renal cell carcinoma

Fibrinogen-like protein 2 (FGL2) is highly expressed in various tumour tissues and plays a vital role in tumour initiation and progression. This study evaluated the clinical significance of FGL2 in patients with clear cell renal cell carcinoma (ccRCC). FGL2 expression in fresh and 170 archived paraffin-embedded ccRCC tissues was measured by quantitative RT-PCR, western blotting, and immunohistochemitry. FGL2 expression was significantly upregulated in ccRCC. Statistical analyses by using Kaplan-Meier method showed that high FGL2 expression was associated with poor overall survival (OS) and recurrence-free survival (RFS) of patients with ccRCC. Multivariate analyses indicated that FGL2 was as an independent prognostic factor of survivaland that tumoural FGL2 levels could significantly predict the prognosis of patients with early-stage ccRCC. Nomogram systems, which integrated FGL2 expression and other clinical parameters, were established and were found to be better than TNM staging in predicting the OS and RFS of patients with ccRCC. FGL2 silencing led to a significant reduction in cells viability and increase in cells apoptosis, accompanied with a reduced ERK1/2 and p38 MAPK activation, in ccRCC cells. Thus, our results suggest that high FGL2 expression is a novel, independent, and an adverse prognostic factor of clinical outcomes in patients with ccRCC.

Thrombalexins: Cell-Localized Inhibition of Thrombin and Its Effects in a Model of High-Risk Renal Transplantation

Allograft transplantation into sensitized recipients with antidonor antibodies results in accelerated antibody-mediated rejection (AMR), complement activation, and graft thrombosis. We have developed a membrane-localizing technology of wide applicability that enables therapeutic agents, including anticoagulants, to bind to cell surfaces and protect the donor endothelium. We describe here how this technology has been applied to thrombin inhibitors to generate a novel class of drugs termed thrombalexins (TLNs). Using a rat model of hyperacute rejection, we investigated the potential of one such inhibitor (thrombalexin-1 [TLN-1]) to prevent acute antibody-mediated thrombosis in the donor organ. TLN-1 alone was able to reduce intragraft thrombosis and significantly delay rejection. The results confirm a pivotal role for thrombin in AMR in vivo. This approach targets donor organs rather than the recipient and is intended to be directly translatable to clinical use.

Adenovirus-mediated artificial microRNA against human fibrinogen like protein 2 inhibits hepatocellular carcinoma growth

BACKGROUND

Human fibrinogen-like protein 2 (hFGL2) is overexpressed in various human solid tumors and is associated with tumor growth, invasion and angiogenesis of hepatocellular carcinoma (HCC) LM6 cells. In the present study, an adenoviral vector expressing an artificial microRNA (miRNA) against hfgl2 (Ad-hfgl2-miRNA) was used to evaluate the effect of FGL2 knockdown on cell proliferation and tumor growth of HCCLM6 xenografts.

METHODS

Ad-hfgl2-miRNA was constructed and its effect on hFGL2 expression and cell proliferation was analyzed. The xenograft tumor model was established in nude mice and this was accompanied by intratumoral injection of Ad-hfgl2-miRNA when the tumor volume had reached 100 mm(3) . The volume of the tumor xenograft was recorded and angiogenesis in the tumor xenograft was assessed.

RESULTS

Ad-hfgl2-miRNA significantly downregulated hFGL2 expression at both the mRNA and protein levels and exerted an inhibitory effect on proliferation in HCCLM6 cells. In HCCLM6 tumor-bearing mice, the tumor volume significantly decreased following the intratumoral injection of Ad-hfgl2-miRNA compared to that of control groups. Additionally, Ad-hfgl2-miRNA also exhibited potent anti-angiogenic effects.

CONCLUSIONS

HFGL2 might be a potential target for controlling angiogenesis in HCC and hfgl2 gene silencing via miRNA may be an alternative strategy for the management of HCC. Copyright © 2016 John Wiley & Sons, Ltd.

Association of Soluble Fibrinogen-like Protein 2 with the Severity of Coronary Artery Disease

Objective The purpose of this study was to investigate the relationship between circulating soluble fibrinogen-like protein 2 (sFGL2) concentrations and the severity of coronary artery disease (CAD) in patients who underwent first-time angiography for suspected CAD. Methods Serum sFGL2 concentrations were measured in 102 consecutive patients by an enzyme-linked immunosorbent assay (ELISA). The number of circulating CD4(+)CD25(+)CD127(low) T regulatory cells (Tregs) was determined by flow cytometry and effecter cytokines, including transforming growth factor-β1 and interleukin-10 (IL-10), were also evaluated by an ELISA. Associations between sFGL2 and Tregs with angiographic indexes of the severity of CAD (i.e., number of diseased vessels and the modified Gensini score) were estimated. Results The sFGL2 levels in patients with angiographically confirmed CAD were significantly lower than those in patients with normal coronary arteries (26.95±8.53 vs. 9.88±5.46 ng/mL, p<0.001). Significant correlations were observed between the serum sFGL2 level and number of diseased vessels (r=-0.860, p<0.001) and modified Gensini score (r=-0.833, p<0.001). Using a multivariate analysis, the serum sFGL2 level was independently associated with the presence and severity of CAD. Conclusion The serum sFGL2 levels are significantly lower in the presence of CAD and correlate with the severity of the disease. Further clinical studies are needed to confirm the use of sFGL2 as a biomarker for the detection and extent of CAD.

Actions of thrombin in the interstitium

Thrombin is a pleiotropic enzyme best known for its contribution to fibrin formation and platelet aggregation during vascular hemostasis. There is increasing evidence to suggest a role for thrombin in the development of interstitial fibrosis, but interstitial thrombin has not been demonstrated by the direct determination of activity. Rather its presence is inferred by products of thrombin action such as fibrin and activated fibroblasts. This review will focus on possible mechanisms of thrombin formation in the interstitial space, the possible actions of thrombin, processes regulating thrombin activity in the interstitial space, and evidence supporting a role for thrombin in fibrosis.

Sodium tanshinone IIA sulfonate ameliorates experimental coronary no-reflow phenomenon through down-regulation of FGL2

AIMS

The effects of sodium tanshinone IIA sulfonate (STS) on coronary no-reflow (CNR) relevant to microvascular obstruction (MVO) remain unknown. Studies had shown that fibrinogen-like protein 2 (FGL2) expressed in microvascular endothelial cells (MECs) is a key mediator in MVO. Thus, we aimed to elucidate the roles of STS in CNR and relations between STS and FGL2.

MAIN METHODS

Myocardial ischemia/reperfusion was selected to represent CNR model. The no-reflow zone and infarct area were assessed using Thioflavin S and TTC staining, and cardiac functional parameters were detected using echocardiography. Western blot was used to detected FGL2 level, fibrin level, protease-activated receptor-1 (PAR-1) activation and inflammation cells infiltration. FGL2 and inflammation cells were also identified by IHC. Microthrombus was detected by Carstairs' and MSB staining. We also detected the roles of STS on FGL2 expression, thrombin generation, phospho-Akt and NF-κB levels in MECs.

KEY FINDINGS

Upon treatment with STS in CNR model, the no-reflow and infarct areas decreased significantly and cardiac function improved. The FGL2 expression was inhibited by STS in vivo as well as in vitro with thrombin generation inhibition. In addition, STS up-regulates Akt phosphorylation and suppressed NF-κB expression in activated MECs. Furthermore, fibrin deposition, PAR-1 activation and inflammatory response were inhibited with STS administration in CNR model.

SIGNIFICANCE

Our results displayed a novel pharmacological action of STS on CNR. STS is able to ameliorate CNR through inhibition of FGL2 expression mediated by Akt and NF-κB pathways as well as prevention of MVO by suppressing fibrin deposition and inflammation.

Deletion of Fibrinogen-like Protein 2 (FGL-2), a Novel CD4+ CD25+ Treg Effector Molecule, Leads to Improved Control of Echinococcus multilocularis Infection in Mice

Background

The growth potential of the tumor-like Echinococcus multilocularis metacestode (causing alveolar echinococcosis, AE) is directly linked to the nature/function of the periparasitic host immune-mediated processes. We previously showed that Fibrinogen-like-protein 2 (FGL2), a novel CD4⁺CD25⁺ Treg effector molecule, was over-expressed in the liver of mice experimentally infected with E. multilocularis. However, little is known about its contribution to the control of this chronic helminth infection.

Methods/Findings

Key parameters for infection outcome in E. multilocularis-infected fgl2^-/- (AE-fgl2^-/-) and wild type (AE-WT) mice at 1 and 4 month(s) post-infection were (i) parasite load (i. e. wet weight of parasitic metacestode tissue), and (ii) parasite cell proliferation as assessed by determining E. multilocularis 14-3-3 gene expression levels. Serum FGL2 levels were measured by ELISA. Spleen cells cultured with ConA for 48h or with E. multilocularis Vesicle Fluid (VF) for 96h were analyzed ex-vivo and in-vitro. In addition, spleen cells from non-infected WT mice were cultured with rFGL2/anti-FGL2 or rIL-17A/anti-IL-17A for further functional studies. For Treg-immune-suppression-assays, purified CD4⁺CD25⁺ Treg suspensions were incubated with CD4⁺ effector T cells in the presence of ConA and irradiated spleen cells as APCs. Flow cytometry and qRT-PCR were used to assess Treg, Th17-, Th1-, Th2-type immune responses and maturation of dendritic cells. We showed that AE-fgl2^-/- mice exhibited (as compared to AE-WT-animals) (a) a significantly lower parasite load with reduced proliferation activity, (b) an increased T cell proliferative response to ConA, (c) reduced Treg numbers and function, and (d) a persistent capacity of Th1 polarization and DC maturation.

Conclusions

FGL2 appears as one of the key players in immune regulatory processes favoring metacestode survival by promoting Treg cell activity and IL-17A production that contributes to FGL2-regulation. Prospectively, targeting FGL2 could be an option to develop an immunotherapy against AE and other chronic parasitic diseases.

In larval E. multilocularis infection causing alveolar echinococcosis (AE) in humans as well as mice, immune tolerance and/or down-regulation of protective immunity is a marked characteristic of this chronic disease. Our study provides a comprehensive evidence for a major involvement of the recently identified CD4⁺ CD25⁺ Regulatory T Cell Effector Molecule FGL2 to the outcome of AE. Our major findings are as follows: 1) FGL2 is mostly secreted by Tregs and partly contributes to their functions; 2) FGL2 can down-regulate the maturation of DCs, suppress Th1 and Th17 immune responses, and support Th2 and Treg immune responses, and finally 3) IL-17A contributes to FGL2 secretion. Based on the present findings in mice, we will investigate FGL2 as a potential marker of progression of AE in human patients, or as a potential immunotherapeutical target. Early prediction of parasite regression (currently not yet possible) would allow clinicians to plan for withdrawing benzimidazole treatment, which is currently administered for life. Then, FGL2 should be investigated as a target for an anticipated immunomodulatory treatment of patients with progressive AE, especially of those who are non- or low-responders to benzimidazole treatment, or who suffer from side-effects due to chemotherapy.

Neuroprotective effects of activated protein C on intrauterine inflammation-induced neonatal white matter injury are associated with the downregulation of fibrinogen-like protein 2/fibroleukin prothrombinase and the inhibition of pro-inflammatory cytokine expression

Maternal intrauterine inflammation or infection is an important risk factor for neonatal cerebral white matter injury (WMI) and future neurological deficits. Activated protein C (APC), a natural anticoagulant, has been shown to exhibit anti-inflammatory, anti-apoptotic, profibrinolytic and cytoprotective activities. Recent studies have demonstrated that the novel prothrombinase, fibrinogen-like protein 2 (fgl2), contributes to the pathogenesis of a number of inflammatory diseases through the generation of fibrin. Thus, we hypothesized that APC may regulate coagulant and inflammatory processes and improve brain injury in an experimental rat model of intrauterine inflammation-induced WMI. The animal model was established by the administration of an intraperitoneal injection of lipopolysaccharide (LPS) to pregnant Sprague-Dawley rats on embryonic day (E)17 and E18. APC was administered intraperitoneally 30 min after the second LPS injection. The expression of fgl2 and the pro-inflammatory cytokines, tumor necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-1β expression in the placentas and fetal brains was determined on E19. Nerve cell death, the brain water content and protease-activated receptor 1 (PAR1) and nuclear factor κB (NF-κB) p65 expression was detected in the fetal brains. WMI in the neonatal rat brains was evaluated by hematoxylin and eosin (H&E) staining and immunohistochemistry for myelin basic protein (MBP). The results revealed that APC markedly reduced the LPS-induced increase in fgl2 expression and fibrin deposition, as well as the production of the pro-inflammatory cytokines, TNF-α, IL-6 and IL-1β, in the placentas and fetal brains. In addition, APC attenuated cerebral apoptosis and brain edema, downregulated PAR1 and NF-κB p65 expression in the fetal brains, and improved hypomyelination and structural disturbances in the periventricular area of the neonatal rat brains. Our observations provide evidence that APC attenuates fetal neuroinflammation and the associated secondary WMI in the developing brain by inhibiting the expression of fgl2 and pro-inflammatory mediators, suggesting that APC may be a potential therapeutic approach for intrauterine inflammation-induced neonatal brain injury.

Fibrinogen-like protein 2/fibroleukin induces long-term allograft survival in a rat model through regulatory B cells

We previously described that in a rat model of heart transplantation tolerance was dependent on CD8+CD45RClow Tregs that over-expressed fibrinogen-like protein 2 (FGL2)/fibroleukin. Little is known on the immunoregulatory properties of FGL2. Here we analyzed the transplantation tolerance mechanisms that are present in Lewis 1A rats treated with FGL2. Over-expression of FGL2 in vivo through adenovirus associated virus -mediated gene transfer without any further treatment resulted in inhibition of cardiac allograft rejection. Adoptive cell transfer of splenocytes from FGL2-treated rats with long-term graft survival (> 80 days) in animals that were transplanted with cardiac allografts inhibited acute and chronic organ rejection in a donor-specific and transferable tolerance manner, since iterative adoptive transfer up to a sixth consecutive recipient resulted in transplantation tolerance. Adoptive cell transfer also efficiently inhibited anti-donor antibody production. Analysis of all possible cell populations among splenocytes revealed that B lymphocytes were sufficient for this adoptive cell tolerance. These B cells were also capable of inhibiting the proliferation of CD4+ T cells in response to allogeneic stimuli. Moreover, gene transfer of FGL2 in B cell deficient rats did not prolong graft survival. Thus, this is the first description of FGL2 resulting in long-term allograft survival. Furthermore, allograft tolerance was transferable and B cells were the main cells responsible for this effect.

The cell-membrane prothrombinase, fibrinogen-like protein 2, promotes angiogenesis and tumor development

The aim of the study was to further investigate the role of fibrinogen-like protein 2 (FGL-2), a transmembrane prothrombinase that directly cleaves prothrombin to thrombin, in angiogenesis and tumor development and the mechanism(s) underlying these processes. To study angiogenesis HUVEC clones with decreased fgl-2 mRNA were generated by specific siRNA. To study tumorigenesis SCID mice were implanted with intact (wild type) and fgl-2-silenced PC-3 clones. IFN-γ treated HUVEC expressing increased fgl-2 mRNA exhibited significant capillary sprouting that was not inhibited by hirudin, whereas fgl-2 silencing completely inhibited blood-vessel formation. Tumors (poorly differentiated carcinoma) developed in all 12 mice injected with wild type PC-3 compared with 8/12 mice injected with the fgl-2-silenced PC-3 clone. The tumors developed by fgl-2-silenced PC-3 clones were smaller and less aggressive and contained significantly fewer blood vessels (p<0.05). All tumors' sections were negative for thrombin staining, indicating that FGL-2-induced tumorigenesis was not mediated by thrombin. In fgl-2-silenced tumors there was a decrease in fgl-2 mRNA (p=0.02) and ERK1/2 phosphorylation (p<0.05) by 80% and a 20%, respectively. The mechanism underlying these processes, studied in PC-3 clones, revealed that fgl-2 silencing was associated with a 65% decrease in FGF-2 mRNA (p<0.01) and a 30% down regulation of ERK1/2 phosphorylation (p<0.05). Together, these results suggest that FGL-2 mediates angiogenesis and tumorigenesis not by thrombin-mediated mechanism but rather through FGF-2/ERK signaling pathway. FGL-2 may serve as a valuable therapeutic target in the future.

Increased activity of cell membrane-associated prothrombinase, fibrinogen-like protein 2, in peripheral blood mononuclear cells of B-cell lymphoma patients

Fibrinogen-like protein 2, FGL-2, was reported to be overexpressed in various cancer tissues, where it acts as a transmembrane prothrombinase. This study aims to determine the prothrombinase activity of FGL-2 in peripheral blood mononuclear cells (PBMC) of patients with B-cell lymphoma. FGL-2 activity was determined in patients with B-cell lymphoma (n = 53), and healthy controls (n = 145). FGL-2 activity in patients at diagnosis increased 3±0.3 fold (p<0.001). Sensitivity and specificity of the test was established at 73.6% and 80.7%, respectively, using a cutoff of 150% activity over control. Moreover, FGL-2 activity in 10 of 11 patients in remission decreased by 76%. In contrast, no significant difference was observed in expression levels of fgl-2 gene in patients and controls. Taken together, our study indicates that FGL-2 prothrombinase activity in PBMC of lymphoma patients is increased in active disease and normalizes during remission, thus being a potential marker for follow up of lymphoma patients.

The Duality of Fgl2 - Secreted Immune Checkpoint Regulator Versus Membrane-Associated Procoagulant: Therapeutic Potential and Implications

Fibrinogen-like protein 2 (Fgl2), a member of the fibrinogen family, can be expressed as a membrane-associated protein with coagulation activity or in a secreted form possessing unique immune suppressive functions. The biological importance of Fgl2 is evident within viral-induced fibrin depositing inflammatory diseases and malignancies and provides a compelling rationale for Fgl2 expression to not only be considered as a disease biomarker but also as a therapeutic target. This article will provide a comprehensive review of the currently known biological properties of Fgl2 and clarifies future scientific directives.

The role of soluble fibrinogen-like protein 2 in transplantation: protection or damage

Soluble fibrinogen-like protein 2 (sFGL2) is the soluble form of fibrinogen like protein 2. As a novel immunoregulatory molecule, sFGL2 is secreted mainly by T cells, especially regulatory T cells, and exerts an immunoregulatory property rather than a prothrombinase function in the immune system. sFGL2 changes not only the proliferation and differentiation of T cells but also the maturation of antigen presenting cells. Besides its innate and adaptive immunoregulatory functions, sFGL2 also induces apoptosis in cells including renal tubular epithelial cells through Fcγ receptors (FcγRs). It may affect transplantation via regulation of immunity and induction of apoptosis of different cells in a spatiotemporal manner. Here, we review the research progresses on sFGL2 including its structure, functions, and molecular mechanisms via which sFGL2 might affect organ transplantation, as well as discuss its characteristics and potential of becoming a therapeutic target in patients with rejection.

Novel antibody against a glutamic acid-rich human fibrinogen-like protein 2-derived peptide near Ser91 inhibits hfgl2 prothrombinase activity

Fibrinogen-like protein 2 (fgl2) is highly expressed in microvascular endothelial cells in diseases associated with microcirculatory disturbances and plays a crucial role in microthrombosis. Previous studies have demonstrated that the Ser89 residue is a critical site for mouse fgl2 prothrombinase activity. The aim of this study was to investigate the prothrombinase inhibitory ability of antibodies against an hfgl2-derived peptide. The peptide was termed NPG-12 because it is located at the N-terminus of membrane-bound hfgl2, contains 12 amino acid residues (corresponding to residues 76 to 87), and is rich in Glu. This peptide was selected as an antigenic determinant to produce antibodies in immunized rabbits using the DNAStar and HomoloGene software program. Abundant hfgl2 expression was induced in human umbilical vein endothelial cells through treatment with TNF-α. The generated anti-NPG-12 antibodies specifically recognize fgl2, as determined by ELISA, Western Blot and immunostaining. Moreover, one-stage clotting and thrombin generation tests provide evidence that the antibodies can reduce the hfgl2 prothrombinase activity without affecting the platelet-poor plasma prothrombin time (PT) or the activated partial thromboplastin time (APTT). In addition, the antibodies exerted undetectable influence on the proliferation or activation of bulk T cell populations. In conclusion, the selected peptide sequence NPG-12 may be a critical domain for hfgl2 prothrombinase activity, and the development of inhibitors against this sequence may be promising for research or management of hfgl2-associated microcirculatory disturbances.

TNF-α upregulates Fgl2 expression in rat myocardial ischemia/reperfusion injury

OBJECTIVE

Proinflammatory cytokine TNF-α during MI/R injury has been studied extensively. However, how TNF-α induces microvascular dysfunction in MI/R is still unclear. This study investigates whether TNF-α regulates fibrinogen-like protein 2 (fgl2) expression, a procoagulant resulting in the formation of fibrin-rich microthrombus in MI/R injury.

METHODS AND RESULTS

Microthrombosis, TNF-α and fgl2 expression were assessed in rats with MI/R injury. The effect of TNF-α on fgl2 expression and fgl2 prothrombinase activity was investigated in CMECs, then CMECs were pretreated with selective inhibitors of NF-κB and p38 MAPK pathways. TNF-α and fgl2 expression were both upregulated in MI/R group. When neutralization of TNF-α, fgl2 expression was decreased in vivo. Fgl2 expression was upregulated in CMECs exposed to TNF-α. Accordingly, the ability of thrombin generation was increased in CMECs. Besides, TNF-α-induced fgl2 expression in the cells was suppressed by NF-κB inhibitor PDTC and/or p38 MAPK inhibitor SB203580.

CONCLUSION

TNF-α upregulates fgl2 expression via activation of NF-kB and p38 MAPK in CMECs. TNF-α-induced flg2 in CMECs mediates the formation of fibrin-rich microthrombus, which may be one of the mechanisms of microvascular dysfunction or obstruction due to MI/R injury.

Cloning and expression analysis of the gene encoding fibrinogen-like protein A, a novel regeneration-related protein from Apostichopus japonicus

Fibrinogen-like protein A (FGLA), a member of the fibrinogen-related protein superfamily, exists in different tissues of vertebrates and invertebrates. FGLA plays crucial roles including innate immune response, blood clotting and regeneration. In this study, the fibrinogen-like protein A (fglA) was cloned from Apostichopus japonicus using rapid amplification of cDNA ends PCR techniques. The cDNA sequence of fglA is 1,524 bp with a 849 bp open reading frame encoding a polypeptide of 282 amino acids, with an N-terminal signal peptide and a conserved C-terminal domain. Bioinformatic analysis revealed that the predicted molecular weight of the whole protein is 31.9 kDa and it has an isoelectric point of 5.64. In-situ hybridization demonstrated that fglA is widely distributed in body wall, intestines, longitudinal muscles and respiratory tree. The expression levels of fglA during different regeneration stages in the body wall, intestine and respiratory trees were analyzed by real-time PCR. The expression of fglA gradually increased within 1 h in body wall, and reached a plateau before decreasing to the basal level. This indicates that fglA is associated with the regeneration of Apostichopus japonicus.

Correlation of fibrinogen-like protein 2 with disease progression in patients with severe acute pancreatitis

It has recently been demonstrated that fibrinogen-like protein 2 (fgl2) is expressed on the surface of macrophages, T cells and endothelial cells and directly cleaves prothrombin to thrombin. The present study was designed to examine fgl2 expression in patients with severe acute pancreatitis (SAP) and its correlation with disease progression. Peripheral blood mononuclear cells (PBMCs) were isolated from 25 patients with SAP, 37 patients with mild acute pancreatitis (MAP) and 20 healthy volunteers as controls. Paraffin sections of pancreas were obtained from 18 postoperative patients with SAP between 2003 and 2012. Human fgl2 (hfgl2) gene expression was determined in the PBMCs by real-time PCR. A monoclonal antibody against hfgl2 was applied to detect hfgl2 protein expression in the pancreatic tissues as well as in the PBMCs by immunohistochemical staining. The levels of hfgl2 expression in the PBMCs from the 25 patients with SAP were markedly upregulated compared with the other groups, whereas no significant difference between the MAP group and healthy controls was observed. hfgl2 expression in the PBMCs and pancreatic tissues was detectable through using immunohistochemistry and was demonstrated to be specifically localized to the endothelium of microvessels and inflammatory infiltrative cells in the areas of acute focal, confluent necrosis. There were positive correlations between hfgl2 expression in the PBMCs and the severity of SAP, as indicated by scores of Ranson and Acute Physiology and Chronic Health Evaluation II. The results suggest that hfgl2 is involved in the pathogenesis of SAP and hfgl2 levels may serve as a biomarker during disease progression.

Serum level of soluble fibrinogen-like protein 2 in renal allograft recipients with acute rejection: a preliminary study

BACKGROUND

Soluble fibrinogen-like protein 2 (sfgl2), which is mainly secreted by T cells, is a novel effector of regulatory T cells with immunosuppressive functions. The aim of this study was to investigate serum levels of sfgl2 among renal allograft recipients.

METHODS

From November 2010 to August 2011 we retrospectively divided 47 renal allograft recipients into an acute rejection (n = 19) versus a stable group (n = 28) according to allograft biopsy results, using the Banff 2007 classification. The acute rejection group was subdivided into grade I (n = 8) versus grade II T-cell-mediated (n = 6) or antibody-mediated rejection episodes (n = 5). Peripheral blood samples were collected at the time of biopsy. Fourteen healthy volunteers were included as normal group controls. Serum levels of sfgl2 were analyzed by enzyme-linked immunosorbent assay.

RESULTS

Serum levels of sfgl2 were increased among renal allograft recipients suffering from biopsy-proven acute rejection episodes (61.91 ± 45.68 ng/mL), versus those with stable allografts (38.59 ± 19.92 ng/mL, P < .05) or healthy volunteers (29.10 ± 18.08 ng/mL, P < .05). The sfgl2 level was significantly higher among patients with antibody-mediated (118.48 ± 55.54 ng/mL) than T-cell-mediated acute rejection episodes (41.71 ± 16.44 ng/mL, P < .01). Serum sfgl2 levels were remarkably elevated in patients with grade II (51.87 ± 19.13 ng/mL) versus grade I T-cell-mediated rejection (34.10 ± 9.26 ng/mL, P < .05).

CONCLUSIONS

Serum sfgl2 levels were increased among renal allograft recipients with acute rejection episodes to an extent dependent upon the pathological type and severity of the response.

Soluble FGL2 induced by tumor necrosis factor-α and interferon-γ in CD4+ T cells through MAPK pathway in human renal allograft acute rejection

BACKGROUND

Acute rejection (AR), initiated by alloreactive CD4(+) T cells, hampers allograft survival. Soluble fibrinogen-like protein 2 (sFGL2) is a novel effector of CD4(+) T cells. We previously found that serum sFGL2 significantly increased in renal allograft recipients with AR. In this study, sFGL2 secretion by CD4(+) T cells and its mechanism were further explored both in vivo and in vitro.

MATERIALS AND METHODS

Forty cases of living-related renal transplant recipients with biopsy-proven AR or stable renal function were collected and detected serum sFGL2, tumor necrosis factor (TNF)-α and interferon (IFN)-γ, and peripheral CD4(+) T cells. In vitro, the isolated human CD4(+) T cells were stimulated by TNF-α or IFN-γ. sFGL2 in the supernatant and mitogen-activated protein kinase (MAPK) proteins in the CD4(+) T cells were investigated. Approval for this study was obtained from the Ethics Committee of Fudan University.

RESULTS

sFGL2, TNF-α, IFN-γ, and CD4(+) T cells were significantly increased in the peripheral blood of renal allograft recipients with AR. Stimulation with 1000 U/mL TNF-α or 62.5 U/mL IFN-γ for 48 h provided an optimal condition for CD4(+) T cells to secrete sFGL2 in vitro. Phosphorylated (p-) c-Jun N-terminal kinase was remarkably upregulated in the activated CD4(+) T cells, whereas no significant changes were found in p-p38 MAPK or p-ERK1/2 expression. Furthermore, inhibition of c-Jun N-terminal kinase significantly reduced sFGL2 secretion by CD4(+) T cells.

CONCLUSIONS

sFGL2 secretion by CD4(+) T cells can be induced with TNF-α and IFN-γ stimulation through MAPK signaling in renal allograft AR. Our study suggests that sFGL2 is a potential mediator in the pathogenesis of allograft rejection.

Fibrinogen-like protein 2 expression correlates with microthrombosis in rats with type 2 diabetic nephropathy

Fibrinogen-like protein 2 (fgl2), a novel prothrombinase, is involved in microthrombosis. We examined fgl2 expression in the glomerular and tubulointerstitial capillaries and its correlation with microthromsis in rats with streptozocin-induced type 2 diabetic nephropathy. Our RT-PCR and immunoblotting analysis showed that fgl2 mRNA and protein levels were increased in microvascular endothelial cells of the glomeruli and renal interstitia at week 19 and became significantly elevated with the development of diabetic nephropathy (P < 0.01). Fgl2 was not or only weakly expressed in the renal tissues of normal rats. Furthermore, a direct significant correlation (r = 0.543, P < 0.01) was found between fgl2 expression and microthrombotic capillaries in the renal tissues. Enzyme linked immunosorbent assays (ELISA) additionally showed that circulating TNF-α levels in rats with type 2 diabetes were significantly elevated and closely correlated with fgl2 expression (r = 0.871, P < 0.01). Our results suggest that fgl2 may activate renal microthrombosis, thus contributing to glomerular hypertension and renal ischemia.

Toll-like receptor 4 in experimental kidney transplantation: early mediator of endogenous danger signals

The role of toll-like receptors (TLRs) has been described in the pathogenesis of renal ischemia/reperfusion injury, but data on the expression and function of TLR4 during renal allograft damage are still scarce. We analyzed the expression of TLR4 in an experimental rat model 6 and 28 days after allogeneic kidney transplantation in comparison to control rats and rats after syngeneic transplantation. On day 6, a significant induction in TLR4 expression--restricted to the glomerular compartment--was found in acute rejecting allografts only. TLR4 expression strongly correlated with renal function, and TLR4 induction was accompanied by a significant increase in CC chemokine expression within the graft as well as in urinary CC chemokine excretion. TLR4 induction may be caused by an influx of macrophages as well as TLR4-expressing intrinsic renal cells. Fibrinogen deposition in renal allografts correlated with renal TLR4 expression and may act as a potent stimulator of chemokine release via TLR4 activation. This study provides, for the first time, data about the precise intrarenal localization and TLR4 induction after experimental kidney transplantation. It supports the hypothesis that local TLR4 activation by endogenous ligands may be one pathological link from unspecific primary allograft damage to subsequent chemokine release, infiltration and activation of immune cells leading to deterioration of renal function and induction of renal fibrosis.

Characterization of fibrinogen-like protein 2 (FGL2): monomeric FGL2 has enhanced immunosuppressive activity in comparison to oligomeric FGL2

Fibrinogen-like protein 2 (FGL2), a novel effector molecule of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg), mediates its suppressive activity through binding to low affinity Fcγ receptors expressed on antigen presenting cells (APCs). FGL2 has been implicated in the pathogenesis of viral hepatitis, xeno- and allotransplant rejection, and rheumatoid arthritis. Here we fully analyzed the structure-function relationships of recombinant murine FGL2 generated in COS-7 cells and identified the receptor binding domains. Native FGL2 exists as an oligomer with a molecular weight of approximately 260 kDa, while under reducing conditions, FGL2 has a molecular weight of 65 kDa suggesting that native FGL2 is composed of four monomers. By site-directed mutation, cysteines at positions 94, 97, 184 and 187, found in the coiled-coil domain were shown to be crucial for FGL2 oligomerization. Monomeric FGL2 had a lower affinity binding to APCs, but increased immunosuppressive activity compared to oligomeric FGL2. Deglycosylation demonstrated that sugar moieties are critical for maintaining solubility of FGL2. SWISS-MODEL analysis suggested that FGL2 has a similar tertiary structure with other members of the fibrinogen family such as fibrinogen and tachylectin. Mutational analysis of cysteine residues and Western blots suggested an asymmetric bouquet-shaped quaternary structure for oligomeric FGL2, resembling many pattern-recognition molecules in the lectin pathway of innate immunity. The functional motifs of FGL2 were mapped to the C terminal globular domain, using a peptide blockade assay. These results collectively define the biochemical and immunological determinants of FGL2, an important immunosuppressive molecule of Treg providing important insights for designing FGL2-related therapeutics.

Downregulation of FGL2/prothrombinase delays HCCLM6 xenograft tumour growth and decreases tumour angiogenesis

BACKGROUND

Fibrinogen-like protein 2 (FGL2), which directly generates thrombin from prothrombin without activation of the conventional coagulation cascade, was shown to be overexpressed in various human malignant tumours.

AIMS

Herein, we aimed to investigate its expression pattern, biological function and mechanism of action in hepatocellular carcinoma (HCC).

METHODS

FGL2 expression and colocalization with fibrin was examined in 15 HCC tissues. FGL2 downregulation was performed by targeting microRNA in a HCCLM6 cell line in which FGL2 was highly expressed in xenografts of nude mice. The effects of FGL2 knockdown on tumour growth and angiogenesis were evaluated in vitro and in vivo. Cytometric bead arrays were employed to identify FGL2-regulated signalling pathways.

RESULTS

FGL2 was overexpressed in HCC tissues and colocalized with fibrin deposition. Knockdown of FGL2 expression in HCCLM6 cells (hFGL2(low) HCCLM6) resulted in delayed xenografts tumour growth within an observation period of 42 days and decreased vascularization, which was accompanied by decreased phosphorylation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK). In vitro hFGL2(low) HCCLM6 cells exhibited decreased proliferation without significant induction of apoptosis. Overexpression of FGL2 in HCCLM6 cells or addition of recombinant hFGL2 protein induced phosphorylation of p38-MAPK and ERK1/2 involving protease-activated receptors (PARs).activation.

CONCLUSIONS

FGL2 contributes to HCC tumour growth and angiogenesis in a thrombin-dependent manner, and downregulation of its expression might be of therapeutic significance in HCC.

Increased circulating fibrinogen-like protein 2 in patients with systemic sclerosis

Fibrinogen-like protein 2 (FGL2), a member of the fibrinogen-related superfamily of proteins, is expressed on the surface of macrophages, T cells, and endothelial cells and directly cleaves prothrombin to thrombin. The aim of this study is to determine the serum FGL2 level and its association with clinical parameters in patients with systemic sclerosis (SSc). Serum FGL2 level was examined by enzyme-linked immunosorbent assay in 61 patients with SSc, 24 patients with systemic lupus erythematosus, and 24 healthy individuals. In a retrospective longitudinal study, sera from 13 patients with SSc were analyzed. The serum FGL2 level was increased in patients with SSc compared with healthy individuals (P < 0.001) and patients with systemic lupus erythematosus (P < 0.01). Among patients with SSc, there were no differences in serum FGL2 level between limited cutaneous SSc and diffuse cutaneous SSc. In the longitudinal study, the FGL2 level was generally unchanged at follow-up. The results show that the serum FGL2 level was increased in patients with SSc but not in patients with systemic lupus erythematosus or healthy individuals. Therefore, FGL2 possibly contribute to the development of SSc.

Inhibitory function of Tregs via soluble FGL2 in chronic hepatitis B

CD4(+)CD25(+)CD127(dim/-) regulatory T cells (Tregs) have been implicated in suppressing T cell immune responses to hepatitis B virus (HBV), but the inhibition mechanism has not being clear yet. This study investigated the effects of soluble FGL2 (sFGL2) secreted by Tregs on immune suppression in chronic HBV-infected patients. We verified that sFGL2 protein and mRNA were highly expressed in Tregs. The separated Tregs by using magnetic beads from peripheral blood mononuclear cells (PBMCs) in 20 patients with chronic hepatitis B were co-cultured with PBMCs at a ratio of 1:3 with anti-CD3 stimulating antibody or FGL2 blocking antibody. The proliferation index of CD8(+)T cells after blocking FGL2 was higher than that in blank group (3.58±0.18 vs. 3.28±0.17, P=0.034) in 18 of 20 samples, and lower than that in CD3 stimulation group (3.82±0.19, P=0.026) in 16 of 20 samples. The IFN-γ secreted in the mixed culture in the absence of Tregs was higher than that in the culture in the presence of Tregs, but it could be abolished by FGL2 blocking antibody. These results suggest that sFGL2 protein secreted by Tregs suppresses the proliferation and function of CD8(+) T cells in chronic hepatitis B.

Antiviral resistance mutations potentiate HBV surface antigen-induced transcription of hfgl2 prothrombinase gene

Antiviral resistance mutations in the hepatitis B virus (HBV) polymerase (pol) gene have been demonstrated to play an important role in the progression of liver disease and the development of hepatocellular carcinoma. The HBV pol gene overlaps the S gene encoding surface antigen (HBsAg). Previous studies from our laboratory have shown that HBV core protein (HBc) and X protein (HBx), but not HBV S protein (HBs), promote hfgl2 prothrombinase transcription. To investigate whether the nucleotide (nucleoside)-induced resistant mutations of HBs potentiate transcription of hfgl2 prothrombinase gene, we generated two mutant HB expression constructs harboring rtM204V/sI195M or rtM204I/sW196L mutations. Two mutant expression plasmids were co-transfected with hfgl2 promoter luciferase-reporter plasmids and β-galactosidase plasmid in CHO cells and HepG2 cells, respectively. Luciferase assay showed that the rtM204I/V mutant HBs could activate the transcription of hfgl2 promoter compared with the wild type HBs. Site-directed mutagenesis and further experiment (co-transfection) demonstrated that transcription factor Ets translocated to its cognate cis-element in the hfgl2 promoter. The results show that mutated HBs caused by antiviral drug resistance induce transcription of the hfgl2 gene dependent on the transcription factor Ets.

Pathogenesis of murine coronavirus in the central nervous system

Murine coronavirus (mouse hepatitis virus, MHV) is a collection of strains that induce disease in several organ systems of mice. Infection with neurotropic strains JHM and A59 causes acute encephalitis, and in survivors, chronic demyelination, the latter of which serves as an animal model for multiple sclerosis. The MHV receptor is a carcinoembryonic antigen-related cell adhesion molecule, CEACAM1a; paradoxically, CEACAM1a is poorly expressed in the central nervous system (CNS), leading to speculation of an additional receptor. Comparison of highly neurovirulent JHM isolates with less virulent variants and the weakly neurovirulent A59 strain, combined with the use of reverse genetics, has allowed mapping of pathogenic properties to individual viral genes. The spike protein, responsible for viral entry, is a major determinant of tropism and virulence. Other viral proteins, both structural and nonstructural, also contribute to pathogenesis in the CNS. Studies of host responses to MHV indicate that both innate and adaptive responses are crucial to antiviral defense. Type I interferon is essential to prevent very early mortality after infection. CD8 T cells, with the help of CD4 T cells, are crucial for viral clearance during acute disease and persist in the CNS during chronic disease. B cells are necessary to prevent reactivation of virus in the CNS following clearance of acute infection. Despite advances in understanding of coronavirus pathogenesis, questions remain regarding the mechanisms of viral entry and spread in cell types expressing low levels of receptor, as well as the unique interplay between virus and the host immune system during acute and chronic disease.

The FGL2/fibroleukin prothrombinase is involved in alveolar macrophage activation in COPD through the MAPK pathway

Fibrinogen-like protein 2 (FGL2)/fibroleukin has been reported to play a vital role in the pathogenesis of some critical inflammatory diseases by possessing immunomodulatory activity through the mediation of "immune coagulation" and the regulation of maturation and proliferation of immune cells. We observed upregulated FGL2 expression in alveolar macrophages from peripheral lungs of chronic obstructive pulmonary disease (COPD) patients and found a correlation between FGL2 expression and increased macrophage activation markers (CD11b and CD14). The role of FGL2 in the activation of macrophages was confirmed by the detection of significantly decreased macrophage activation marker (CD11b, CD11c, and CD71) expression as well as the inhibition of cell migration and inflammatory cytokine (IL-8 and MMP-9) production in an LPS-induced FGL2 knockdown human monocytic leukemia cell line (THP-1). Increased FGL2 expression co-localized with upregulated phosphorylated p38 mitogen-activated protein kinase (p38-MAPK) in the lung tissues from COPD patients. Moreover, FGL2 knockdown in THP-1 cells significantly downregulated LPS-induced phosphorylation of p38-MAPK while upregulating phosphorylation of c-Jun N-terminal kinase (JNK). Thus, we demonstrate that FGL2 plays an important role in macrophage activation in the lungs of COPD patients through MAPK pathway modulation.

Construction of plasmids expressing Sars-CoV encoding proteins and their effects on transcription of hfgl2 prothrombinase

SARS coronavirus (SARS-CoV) is the etiologic agent of severe acute respiratory syndrome. The aim of this study was to construct Sars-CoV membrane (M), nucleocapsid (N) and spike 2 (S2) gene eukaryotic expression plasmids, and identify their expression in vitro. Gene fragments encoding N protein, M protein and S2 protein of SARS-CoV were amplified by PCR using cDNA obtained from lung samples of SARS patients as template, and subcloned into pcDNA3.1 vector to form eukaryotic expression plasmids. SARS-CoV protein eukaryotic expression plasmids were transfected respectively into CHO cells. Immunohistochemistry was employed to detect the expression of the structural proteins of SARS-CoV in transfected cells. SARS-CoV protein eukaryotic expression plasmids were successfully constructed by identification with digestion of restriction enzymes and sequencing. M, N and S2 proteins of SARS-CoV were detected in the cytoplasm of transfected CHO cells. It was concluded that these recombinant eukaryotic expression plasmids were constructed successfully, and SARS-CoV encoding proteins could activate transcription and expression of hfgl2 gene.

The novel CD4+CD25+ regulatory T cell effector molecule fibrinogen-like protein 2 contributes to the outcome of murine fulminant viral hepatitis

Fulminant viral hepatitis (FH) remains an important clinical problem in which the underlying pathogenesis is not well understood. Here, we present insight into the immunological mechanisms involved in FH caused by murine hepatitis virus strain 3 (MHV-3), indicating a critical role for CD4(+)CD25(+) regulatory T cells (Tregs) and production of the novel Treg effector molecule FGL2. Before infection with MHV-3, susceptible BALB/cJ mice had increased numbers of Tregs and expression of fgl2 messenger RNA (mRNA) and FGL2 protein compared with resistant A/J mice. After MHV-3 infection, plasma levels of FGL2 in BALB/cJ mice were significantly increased, correlating with increased percentage of Tregs. Treatment with anti-FGL2 antibody completely inhibited Treg activity and protected susceptible BALB/cJ mice against MHV-3-liver injury and mortality. Adoptive transfer of wild-type Tregs into resistant fgl2(-/-) mice increased their mortality caused by MHV-3 infection, whereas transfer of peritoneal exudate macrophages had no adverse effect.

CONCLUSION

This study demonstrates that FGL2 is an important effector cytokine of Tregs that contributes to susceptibility to MHV-3-induced FH. The results further suggest that targeting FGL2 may lead to the development of novel treatment approaches for acute viral hepatitis infection.

Interaction of notochord-derived fibrinogen-like protein with Notch regulates the patterning of the central nervous system of Ciona intestinalis embryos

The midline organ the notochord and its overlying dorsal neural tube are the most prominent features of the chordate body plan. Although the molecular mechanisms involved in the formation of the central nervous system (CNS) have been studied extensively in vertebrate embryos, none of the genes that are expressed exclusively in notochord cells has been shown to function in this process. Here, we report a gene in the urochordate Ciona intestinalis encoding a fibrinogen-like protein that plays a pivotal role in the notochord-dependent positioning of neuronal cells. While this gene (Ci-fibrn) is expressed exclusively in notochord cells, its protein product is not confined to these cells but is distributed underneath the CNS as fibril-like protrusions. We demonstrated that Ci-fibrn interacts physically and functionally with Ci-Notch that is expressed in the central nervous system, and that the correct distribution of Ci-fibrn protein is dependent on Notch signaling. Disturbance of the Ci-fibrn distribution caused an abnormal positioning of neuronal cells and an abnormal track of axon extension. Therefore, it is highly likely that the interaction between the notochord-based fibrinogen-like protein and the neural tube-based Notch signaling plays an essential role in the proper patterning of CNS.

The FGL2-FcgammaRIIB pathway: a novel mechanism leading to immunosuppression

Fibrinogen-like protein 2 (FGL2) is a multifunctional protein, which has been implicated in the pathogenesis of allograft and xenograft rejection. Previously, FGL2 was shown to inhibit maturation of BM-derived DC and T-cell proliferation. The mechanism of the immunosuppressive activity of FGL2 remains poorly elucidated. Here, we focus on identification of FGL2-specific receptor(s) and their ability to modulate APC activity and allograft survival. Using flow cytometry and surface plasmon resonance analysis, we show that FGL2 binds specifically to Fc gamma receptor (FcgammaR)IIB and FcgammaRIII receptors, which are expressed on the surface of APC, including B lymphocytes, macrophages and DC. Antibody to FcgammaRIIB and FcgammaRIII, or deficiency of these receptors, abrogated FGL2 binding. FGL2 inhibited the maturation of BMDC from FcgammaRIIB+/+ mice but not from FcgammaRIIB(-/-) mice and induced apoptosis in the FcgammaRIIB+ mouse B-cell line (A20) but not the A20IIA1.6 cell line that does not express FcgammaRIIB. Recombinant FGL2 infused into FcgammaRIIB+/+ (C57BL/6J, H-2b) mice but not FcgammaRIIB(-/-) mice inhibited rejection of fully mismatched BALB/cJ (H-2d) skin allografts. The identification of specific receptor binding has important implications for the pathogenesis of immune-mediated disease and suggests a potential for targeted FGL2 therapy.

Hepatitis B virus-induced hFGL2 transcription is dependent on c-Ets-2 and MAPK signal pathway

Fibrinogen-like protein 2 (FGL2)/fibroleukin plays a pivotal role in the pathogenesis of experimental and human fulminant and chronic viral hepatitis. To define the transcription factor(s) and upstream signal transduction pathways involved in the transcription of human FGL2 (hFGL2) in response to hepatitis B (HB) virus, hepatitis B core (HBc), hepatitis B virus S protein (HBs), or hepatitis B virus X protein (HBx) protein, expression plasmids were cotransfected with an hFGL2 promoter luciferase reporter construct into Chinese hamster ovary and HepG2 cells, respectively. HBc and HBx proteins, but not HBs protein, enhanced hFGL2 transcription in both cell lines. A strong regulatory region from -712 to -568 (relative to the transcriptional starting site) was shown to be responsible for hFGL2 gene transcription in response to both HBc and HBx proteins. c-Ets-2 was shown to be translocated to the nucleus in association with hFGL2 expression in response to both HBc and HBx proteins. Short hairpin RNA (shRNA) interference of c-Ets-2 expression inhibited hFGL2 gene transcription by 64.8 and 60.0% in response to HBc and HBx, respectively. c-Ets-2 protein was highly expressed in peripheral blood mononuclear cells from patients with severe chronic hepatitis B (CHB) in contrast to patients with mild CHB. Increased phosphorylation of ERK and JNK was detected in peripheral blood mononuclear cells from patients with severe CHB. ERK inhibitor PD098059 or ERK shRNA abolished the nuclear c-Ets-2 DNA binding activity and hFGL2 induction in response to HBc, whereas JNK inhibitor SP600125 or JNK shRNA abolished the nuclear c-Ets-2 DNA binding activity and hFGL2 induction in response to HBx. In conclusion, HBc and HBx proteins enhance transcription of hFGL2 through c-Ets-2 dependent on MAPK signal pathways.

A quantitative proteomic approach for identification of potential biomarkers in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide. In this study, our objective was to identify differentially regulated proteins in HCC through a quantitative proteomic approach using iTRAQ. More than 600 proteins were quantitated of which 59 proteins were overexpressed and 92 proteins were underexpressed in HCC as compared to adjacent normal tissue. Several differentially expressed proteins were not implicated previously in HCC. A subset of these proteins (six each from upregulated and downregulated groups) was further validated using immunoblotting and immunohistochemical labeling. Some of the overexpressed proteins with no previous description in the context of HCC include fibroleukin, interferon induced 56 kDa protein, milk fat globule-EGF factor 8, and myeloid-associated differentiation marker. Interestingly, all the enzymes of urea metabolic pathway were dramatically downregulated. Immunohistochemical labeling confirmed differential expression of fibroleukin, myeloid associated differentiation marker and ornithine carbamoyl transferase in majority of HCC samples analyzed. Our results demonstrate quantitative proteomics as a robust discovery tool for the identification of differentially regulated proteins in cancers.

The nucleocapsid protein of SARS-CoV induces transcription of hfgl2 prothrombinase gene dependent on C/EBP alpha

Fibrin deposition was universal in the lungs of SARS patients and fgl2 prothrombinase gene, a novel procoagulant, was demonstrated to express highly in a clinically relevant SARS model. To investigate whether and which structural protein of SARS-CoV induced transcription of hfgl2 prothrombinase gene, three eukaryotic expression plasmids expressing nucleocapsid protein (N), membrane protein (M) and spike protein 2 (S2) of SARS-CoV were co-transfected with hfgl2 promoter luciferase-reporter plasmids and beta-galactosidase plasmid in CHO cells, respectively. M, N and S2 protein of SARS-CoV were detected by western blotting and immunohistochemistry analysis. Further assays demonstrated that expression of hfgl2 gene was related with N protein, but not with M or S2 protein in THP-1 cells and Vero cells. N protein significantly induced functional procoagulant activity in comparison with control group. Luciferase assay showed that N protein of SARS-CoV could activate the transcription of hfgl2 promoter compared with the pcDNA3.1 empty vector. Site-directed mutagenesis and EMSA assay further demonstrated that transcription factor C/EBP alpha band with its cognate cis-element in hfgl2 promoter. The results showed that N protein of SARS-CoV induced hfgl2 gene transcription dependent on the transcription factor C/EBP alpha, which maybe contribute to the development of thrombosis in SARS.