A key role of toll-like receptor 3 in tissue factor activation through extracellular signal regulated kinase 1/2 pathway in a murine hypoxia model

Extracellular RNA Induces Neutrophil Recruitment Via Toll-Like Receptor 3 During Venous Thrombosis After Vascular Injury

BACKGROUND

Venous thromboembolism is associated with endothelial cell activation that contributes to the inflammation-dependent activation of the coagulation system. Cellular damage is associated with the release of different species of extracellular RNA (eRNA) involved in inflammation and coagulation. TLR3 (toll-like receptor 3), which recognizes (viral) single-stranded or double-stranded RNAs and self-RNA fragments, might be the receptor of these species of eRNA during venous thromboembolism. Here, we investigate how the TLR3/eRNA axis contributes to venous thromboembolism.

METHODS AND RESULTS

Thrombus formation and size in wild-type and TLR3 deficient (-/-) mice were monitored by ultrasonography after venous thrombosis induction using the ferric chloride and stasis models. Mice were treated with RNase I, with polyinosinic-polycytidylic acid, a TLR3 agonist, or with RNA extracted from murine endothelial cells. Gene expression and signaling pathway activation were analyzed in HEK293T cells overexpressing TLR3 in response to eRNA or in human umbilical vein endothelial cells transfected with a small interference RNA against TLR3. Plasma clot formation on treated human umbilical vein endothelial cells was analyzed. Thrombosis exacerbated eRNA release in vivo and increased eRNA content within the thrombus. RNase I treatment reduced thrombus size compared with vehicle-treated mice (P<0.05). Polyinosinic-polycytidylic acid and eRNA treatments increased thrombus size in wild-type mice (P<0.01 and P<0.05), but not in TLR3-/- mice, by reinforcing neutrophil recruitment (P<0.05). Mechanistically, TLR3 activation in endothelial cells promotes CXCL5 (C-X-C motif chemokine 5) secretion (P<0.001) and NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells) activation (P<0.05). Finally, eRNA triggered plasma clot formation in vitro (P<0.01).

CONCLUSIONS

We show that eRNA and TLR3 activation enhance venous thromboembolism through neutrophil recruitment possibly through secretion of CXCL5, a potent neutrophil chemoattractant.

VALPROIC ACID INHIBITS CLASSICAL MONOCYTE-DERIVED TISSUE FACTOR AND ALLEVIATES HEMORRHAGIC SHOCK-INDUCED ACUTE LUNG INJURY IN RATS

ABSTRACT

Background: Monocytes and monocyte-derived tissue factor (TF) promote the development of sepsis-induced acute lung injury (ALI). Classical monocytes (C-Mcs) can be induced to express TF. Valproic acid (VPA) alleviates hemorrhagic shock (HS)-induced ALI (HS/ALI) and inhibits TF expression in monocytes. We hypothesized that C-Mcs and C-Mc-derived TF promoted HS/ALI and that VPA could inhibit C-Mc-derived TF expression and attenuate HS/ALI. Methods: Wistar rats and THP-1 cells were used to evaluate our hypothesis. Monocyte subtypes were analyzed by flow cytometry; mRNA expression was measured by fluorescence quantitative polymerase chain reaction; protein expression was measured by Western blotting, immunofluorescence, or immunohistology; inflammatory cytokines levels were measured by enzyme-linked immunosorbent assay; and ALI scores were used to determine the degree of ALI. Results: The blood %C-Mcs and C-Mcs/non-C-Mcs ratios, monocyte TF levels, serum and/or lung inflammatory cytokine levels, and ALI scores of HS rats were significantly increased ( P < 0.05). After monocyte depletion and thrombin inhibition, the inflammatory cytokine levels and ALI scores were significantly decreased ( P < 0.05). VPA reduced the %C-Mcs and C-Mc/non-C-Mc ratios, TF expression, inflammatory cytokine levels, and ALI scores during HS ( P < 0.05) and inhibited HS-induced monocyte Egr-1 and p-ERK1/2 expression ( P < 0.05). VPA inhibited hypoxia-induced TF expression in THP-1 cells by regulating the p-ERK1/2-Egr-1 axis. Conclusion: C-Mcs and C-Mc-derived TF accelerate the development of HS/ALI by increasing thrombin production. VPA inhibits HS-induced C-Mc production of TF by regulating the p-ERK1/2-Egr-1 axis and alleviates HS/ALI.

Key role of Extracellular RNA in hypoxic stress induced myocardial injury

Myocardial infarction (MI), atherosclerosis and other inflammatory and ischemic cardiovascular diseases (CVDs) have a very high mortality rate and limited therapeutic options. Although the diagnosis is based on markers such as cardiac Troponin-T (cTrop-T), the mechanism of cTrop-T upregulation and release is relatively obscure. In the present study, we have investigated the mechanism of cTrop-T release during acute hypoxia (AH) in a mice model by ELISA & immunohistochemistry. Our study showed that AH exposure significantly induces the expression and release of sterile inflammatory as well as MI markers in a time-dependent manner. We further demonstrated that activation of TLR3 (mediated by eRNA) by AH exposure in mice induced cTrop-T release and Poly I:C (TLR3 agonist) also induced cTrop-T release, but the pre-treatment of TLR3 immuno-neutralizing antibody or silencing of Tlr3 gene or RNaseA treatment two hrs before AH exposure, significantly abrogated AH-induced Caspase 3 activity as well as cTrop-T release. Our immunohistochemistry and Masson Trichrome (MT) staining studies further established the progression of myocardial injury by collagen accumulation, endothelial cell and leukocyte activation and adhesion in myocardial tissue which was abrogated significantly by pre-treatment of RNaseA 2 hrs before AH exposure. These data indicate that AH induced cTrop-T release is mediated via the eRNA-TLR3-Caspase 3 pathway.

An Integrated Approach of the Potential Underlying Molecular Mechanistic Paradigms of SARS-CoV-2-Mediated Coagulopathy

Coronavirus disease 2019 (Covid-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a pandemic disease which has affected more than 6.2 million people globally, with numbers mounting considerably daily. However, till date, no specific treatment modalities are available for Covid-19 and also not much information is known about this disease. Recent studies have revealed that SARS-CoV-2 infection is associated with the generation of thrombosis and coagulopathy. Fundamentally, it has been believed that a diverse array of signalling pathways might be responsible for the activation of coagulation cascade during SARS-CoV-2 infection. Henceforth, a detailed understanding of these probable underlying molecular mechanistic pathways causing thrombosis in Covid-19 disease deserves an urgent exploration. Therefore, in this review, the hypothetical crosstalk between distinct signalling pathways including apoptosis, inflammation, hypoxia and angiogenesis attributable for the commencement of thrombotic events during SARS-CoV-2 infection has been addressed which might further unravel promising therapeutic targets in Covid-19 disease.

Coagulation Disorders in COVID-19: Role of Toll-like Receptors

Coronavirus disease 2019 (COVID-19) has spread rapidly throughout the world. The range of the disease is broad but among hospitalized patients with COVID-19 are coagulation disorders, pneumonia, respiratory failure, and acute respiratory distress syndrome (ARDS). The excess production of early response proinflammatory cytokines results in what has been described as a cytokine storm, leading to an increased risk of thrombosis, inflammations, vascular hyperpermeability, multi-organ failure, and eventually death over time. As the pandemic is spreading and the whole picture is not yet clear, we highlight the importance of coagulation disorders in COVID-19 infected subjects and summarize it. COVID-19 infection could induce coagulation disorders leading to clot formation as well as pulmonary embolism with detrimental effects in patient recovery and survival. Coagulation and inflammation are closely related. In this review, we try to establish an association between virus infections associated with innate immune activation, inflammation and coagulation activation.

Hypoxia induced up-regulation of tissue factor is mediated through extracellular RNA activated Toll-like receptor 3-activated protein 1 signalling

Sterile Inflammation (SI), a condition where damage associated molecular patterns (DAMPs) released from dying cells, leads to TLR (Toll-like receptor) activation and triggers hypoxemia in circulation leading to venous thrombosis (VT) through tissue factor (TF) activation, but its importance under acute hypoxia (AH) remains unexplored. Thus, we hypothesized that eRNA released from dying cells under AH activates TF via the TLR3-ERK1/2-AP1 pathway, leading to VT. Animals were exposed to stimulate hypoxia for 0–24 h at standard temperature and humidity. RNaseA and DNase1 were injected immediately before exposure. TLR3 gene silencing was performed through in vivo injection of TLR3 siRNA. 80 μg/kg BW of isolated eRNA and eDNA were injected 6 h prior to sacrifice. Antigens of TF pathway were determined by ELISA and TF activity by a chromogenic assay. AH exposure significantly induced release of SI markers i.e. eRNA, eDNA, HMGB1 and upregulated TLR3, ERK1/2 (Extracellular signal-regulated kinases), AP1 (Activator Protein-1) and TF, whereas RNaseA pre-treatment diminished the effect of AH, thus inhibiting TF expression as well as activity during AH. Hence, we propose a possible mechanism of AH-induced TF activation and thrombosis where RNaseA can become the novel focal point in ameliorating therapy for AH induced thrombosis.

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Acute hypoxia exposure leads to systemic Sterile Inflammation.

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eRNA regulates upregulation of TF by activation of TLR3 pathway.

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RNase A pre-treatment ameliorates effect of acute hypoxia on coagulation.

HMGB1 facilitates hypoxia-induced vWF upregulation through TLR2-MYD88-SP1 pathway

Increased plasma level of von Willebrand Factor (vWF) is associated with major cardiovascular diseases. We previously reported that multimeric vWF binds to NO synthase and inhibits insulin-induced production of NO, thus promoting insulin resistance during acute hypoxia (AH). However, the transcriptional regulation of vWF during AH is not clearly understood. Here, we investigated the mechanisms underlying the upregulation of vwf in mice. AH significantly upregulates the tlr2, tlr3, myd88, and vwf expression and phosphorylation of specificity protein 1 (SP1). Furthermore, AH significantly upregulates high mobility group box-1 (HMGB1) in a time-dependent manner. Moreover, a TLR2 agonist upregulates vWF but a TLR3 agonist does not. Pretreatment with an HMGB1 inhibitor, TLR2-immunoneutralizing antibody, or SP1 inhibitor significantly inhibits vWF expression. Furthermore, Tlr2 silencing completely inhibited MYD88, vWF expression, and SP1 phosphorylation. However, pretreatment with glycyrrhizic acid or silencing of Tlr2 completely blocks binding of Sp1 to the Vwf promoter, thus inhibiting its expression, and enhances insulin resistance during AH. Patients with type 2 diabetes mellitus also showed significantly elevated levels of HMGB1, TLR2, SP1, and vWF, thereby supporting the results of the murine model of AH. Taken together, HMGB1 upregulates vWF in vivo through the TLR2-MYD88-SP1 pathway in mice.

Extracellular RNA facilitates hypoxia-induced leukocyte adhesion and infiltration in the lung through TLR3-IFN-γ-STAT1 signaling pathway

Endogenous ligands released from dying cells, including extracellular RNA (eRNA), cause TLR activation, which is associated with inflammation and vascular diseases. However, the importance of this response in acute hypoxia (AH) remains unexplored. Here, we observed eRNA-mediated TLR3 activation during exposure of mice to AH in the absence of exogenous viral stimuli. RNaseA treatment diminished AH-induced expression of IFN and cell adhesion molecules (CAMs) and myeloid cell infiltration in the lung, and TLR3 gene silencing or neutralization with antibodies markedly attenuated AH- or poly I:C-induced IFN and CAM expression and leukocyte adhesion (LA) and myeloid cell infiltration in the lung. However, RNaseA treatment or TLR3 gene silencing failed to alter AH-induced cell death and proliferation in lung vasculature. Furthermore, IFN-γ--but not IFN-α--regulated AH-induced CAM expression and LA. Treatment with RNaseA, TLR3 siRNA, neutralizing antibodies, or a STAT1 inhibitor substantially decreased AH- and poly I:C-induced STAT1 phosphorylation, CAM expression, and myeloid cell infiltration, suggesting a central role for STAT1 phosphorylation in AH-induced LA and infiltration. We conclude that eRNA activates TLR3 and facilitates, through in vivo IFN-γ-STAT1 signaling, AH-induced leukocyte infiltration in the lung. Thus, RNaseA might provide a therapeutic alternative for patients with lung diseases.

Particulate matter phagocytosis induces tissue factor in differentiating macrophages

Airborne exposure to particulate matter with diameter < 10 mcM (PM10) has been linked to an increased risk of thromboembolic events, but the mechanisms are not completely understood. The aim of this study was to evaluate the effect of PM10 phagocytosis on the release of procoagulant molecules in human differentiating macrophages, and that of PM10 inhalation in an experimental model in rats. Human monocytes were separated from the peripheral blood by the lymphoprep method, differentiated in vitro and treated with standard PM10 or vehicle. Sprague-Dawley rats were instilled intratracheally with PM10 or vehicle alone. The outcome was expression of proinflammatory genes and of tissue factor (TF). In human differentiating macrophages, PM10 exposure upregulated inflammatory genes, but most consistently induced TF mRNA and protein levels, but not TF protein inhibitor, resulting in increased TF membrane expression and a procoagulant phenotype. Differentiation towards the anti-inflammatory M2 phenotype inhibited PM10 -mediated TF expression. TF induction required phagocytosis of PM10 , whereas phagocytosis of inert particles was less effective. PM10 phagocytosis was associated with a gene expression profile consistent with intracellular retention of iron, inducing oxidative stress. Both PM10 and iron activated the stress kinases ERK1/2 pathway, involved in the induction of TF expression. In rats, alveolar exposure to PM10 was associated with pulmonary recruitment of inflammatory cells and resulted in local, but not systemic, induction of TF expression, which was sufficient to increase circulating TF levels. In conclusion, TF induction by differentiating lung macrophages, activated following phagocytosis, contributes to the increased risk of thromboembolic complications associated with PM10 exposure.

MUC18 Differentially Regulates Pro-Inflammatory and Anti-Viral Responses in Human Airway Epithelial Cells

OBJECTIVE

MUC18 or CD146, a transmembrane glycoprotein, is mainly expressed by endothelial cells and smooth muscle cells where it serves as a cell-cell adhesion molecule. We have found MUC18 up-regulation in airway epithelial cells of patients with asthma and chronic obstructive pulmonary disease (COPD). However, the function of MUC18 in airway epithelial cells remains unclear. In the present study, we tested the hypothesis that MUC18 exerts a pro-inflammatory function during stimulation with a viral mimic polyI:C or human rhinovirus infection.

METHODS

Normal human primary airway epithelial cells were transduced with lentivirus encoding MUC18 cDNA to over-express MUC18 or with GFP (control), and treated with polyI:C or HRV for detection of pro-inflammatory cytokine IL-8 and anti-viral gene IFN-β. Additionally, we performed cell culture of human lung epithelial cell line NCIH292 cells to determine the mechanisms of MUC18 function.

RESULTS

We found that MUC18 over-expression promoted IL-8 production, while it inhibited IFN-β expression following polyI:C stimulation or HRV infection. Increased phosphorylation of MUC18 serines was observed in MUC18 over-expressing cells. Reduction of MUC18 serine phosphorylation by inhibiting ERK activity was associated with less production of IL-8 following polyI:C stimulation.

CONCLUSIONS

Our results for the first time demonstrate MUC18's pro-inflammatory and anti-viral function in human airway epithelial cells.

IL-12 secretion by Langerhans cells stimulated with Candida skin test reagent is mediated by dectin-1 in some healthy individuals

OBJECTIVE

Our group and others have shown that serial intra-lesional injections of common warts with skin testing reagents such as Candida, mumps and Trichophyton are effective in regressing injected and non-injected warts. Anti-HPV T-cell responses appear to be induced. The goal of this study was to understand the mechanisms of how Candida skin testing reagent enhances immune responses.

METHODS

The following immunological features were studied to understand how Candida induces immune responses in healthy subjects: (1) proliferative capacity of T-cells upon exposure to Candida through monocyte-derived human Langerhans cells (LCs) measured using alamarBlue, (2) cytokine (IL-1β, IL-6, IL-8, IL-10, IL-12p40, IL-23Ap19, IFN-γ, and TNF- expression upon Candida stimulation of LCs by quantitative reverse transcription (qRT)-PCR and cytokine secretion by ELISA, (3) expression of pattern recognition receptors (PRRs) known to associate with Candida albicans (DC-SIGN, dectin-1, dectin-2, galectin-3, mincle, mannose receptor, Toll-like receptors 1, 2, 4, 6, and 9) on LCs by qRT-PCR, (4) role of dectin-1 in IL-12 production by antibody blocking, and (5) induction of Th1, Th2, and/or Th17 responses by intracellular cytokine staining of CD4 cells exposed to Candida pulsed LCs for IFN-γ, IL-4, and IL-17A.

RESULTS

T-cell proliferation upon stimulation with Candida-pulsed LCs was significantly higher compared to proliferation in the absence of Candida (p=0.004). The most frequently expressed cytokine in stimulated LCs was IL-12p40 mRNA, and IL-12p40 and IL-12p70 were also detected at protein levels. All other cytokine mRNAs examined were detected in the following order of decreasing frequency: IL23Ap19, IFN-γ, IL-1β, IL-6, IL-8, and IL-10. LCs expressed all PRRs examined. Anti-dectin-1 inhibited IL-12p40 mRNA production upon Candida stimulation of LCs from some healthy subjects. IFN-γ secretion was increased and IL-4 secretion was decreased in CD4 cells of a few healthy subjects, but IL-17A was essentially unchanged upon Candida treatment.

CONCLUSIONS

Proliferation of T-cells in a substantial majority of healthy subjects can be demonstrated with Candida stimulation. We show Th1 promotion and dectin-1 stimulation of LCs as potential mechanisms in some healthy subjects.

Candida skin test reagent as a novel adjuvant for a human papillomavirus peptide-based therapeutic vaccine

A vaccine adjuvant that can effectively promote cell-mediated immunity is currently not available. Because of the ability of a Candida skin test reagent injection to induce common wart regression, our group is using it as a novel adjuvant in a clinical trial of a peptide-based human papillomavirus therapeutic vaccine. The goal of this current study was to investigate the mechanisms of how Candida enhances the vaccine immune responses. Maturation effects on Langerhans cells, capacity to proliferate T-cells, expression of cytokines and pattern recognition receptors by Langerhans cells, and ability to induce Th1, Th2, and Th17 responses were investigated in healthy subjects. The vaccine, human papillomavirus peptides with Candida, demonstrated partial maturation effects on Langerhans cells indicated by significantly up-regulated CD40 (p=0.00007) and CD80 (p<0.00001) levels, and showed T-cell proliferative capacity (p<0.00001) when presented by Langerhans cells in vitro. Interestingly, the maturation effects were due to the peptides while Candida was responsible for the T-cell proliferation. The cytokine profile (IL-1β, IL-6, IL-8, IL-10, IL-12p40, IL-23Ap19, IFN-γ and TNF-α) of Langerhans cells treated with the vaccine or Candida alone showed that IL-12p40 mRNA was most frequently induced, and IL-12p70 protein was detected in the supernatants. The presence of pattern recognition receptors known to associate with Candida albicans (DC-SIGN, dectin-1, dectin-2, galectin-3, mincle, mannose receptor, Toll-like receptors-1, 2, 4, 6 and 9) were demonstrated in all subjects. On the other hand, the induction of Th1 response demonstrated by IFN-γ secretion by CD4 cells stimulated with the vaccine or Candida pulsed Langerhans cells was demonstrated only in one subject. In summary, the Langerhans cell maturation effects of the vaccine were due to the peptides while the T-cell proliferative capacity was derived from Candida, and the most frequently induced cytokine was IL-12.

CXCR7 silencing attenuates cell adaptive response to stromal cell derived factor 1α after hypoxia

Previous studies have shown that chemotactic factor stromal-cell derived factor 1α (SDF1α) promotes cell recovery from hypoxic injury via its main receptor C-X-C chemokine receptor type (CXCR) 4. However, the role of its new receptor CXCR7 on cell repair against hypoxia and cell response to SDF1α remains largely unknown. In this study, neurons induced from hippocampal progenitor cells were pre-conditioned in hypoxia for 4 h and subsequently monitored to investigate the function of SDF1α on cell repair after hypoxia. Neurons were assessed for their cell morphology, actin filament polymerization and migration capability. SDF1α protein levels increased significantly 1 h after hypoxia compared to control (P<0.01), and it reached a peak at 24 h after hypoxia. Moreover, addition of SDF1α promoted neurite outgrowth and actin filament polymerization both in normoxic and hypoxic cells compared to untreated cells. Cell migration showed a time-dependent increase with SDF1α stimulation in both groups, and hypoxic cells illustrated a significant augment at 0.5 h, 1 h and 12 h after SDF1α application compared to normoxic cells (P<0.01). CXCR7 expression also increased with time dependence after hypoxia and demonstrated a two-fold upregulation compared to control at 24 h after hypoxia. With CXCR7 silencing, axon elongation and actin filament polymerization induced by SDF1α were inhibited sharply both in normoxic and hypoxic cells. CXCR7 silencing also leads to reduced hypoxic cell migration at 0.5 h, 1 h, 12 h, 24 h and 36 h after SDF1α application (P<0.01), but it failed to reduce normoxic cell migration induced by SDF1α at 0.5 h, 1 h and 12 h (P>0.05). 24 h SDF1α stimulation led to higher ERK1/2 phosphorylation compared to control, and ERK1/2 phosphorylation increased more in hypoxic cells than that in normoxic cells. This study suggested that CXCR7 plays an important role on cell repair processing induced by SDF1α, and CXCR7 silencing attenuates cell adaptive response to acute SDF1α stimulation (≤12 h) after hypoxia.