Overexpression of the endothelial protein C receptor is detrimental during pneumonia-derived gram-negative sepsis (Melioidosis)

Endothelial Protein C Receptor: A Multifunctional Mediator in the Pathophysiology of Rheumatoid Arthritis

The endothelial protein C receptor (EPCR) is gaining recognition for its diverse functions that extend beyond its traditional role in the protein C anticoagulant pathway. This comprehensive review examines how EPCR contributes to the pathophysiology of rheumatoid arthritis (RA), an autoimmune disorder characterized by persistent inflammation and joint destruction. We explore how EPCR influences inflammatory responses and the coagulation cascade, affects endothelial function and vascular integrity, and regulates the characteristics of synovial fibroblasts in the context of RA. Furthermore, the review highlights the mechanisms by which EPCR affects disease progression, its potential use as a biomarker for disease activity, and the therapeutic implications of targeting EPCR in the treatment of RA. By synthesizing current research findings, this review aims to provide a detailed understanding of EPCR's role in RA, offering insights into innovative diagnostic and therapeutic strategies that could improve patient outcomes.

Endothelial Protein C Receptor and Its Impact on Rheumatic Disease

Endothelial Protein C Receptor (EPCR) is a key regulator of the activated protein C anti-coagulation pathway due to its role in the binding and activation of this protein. EPCR also binds to other ligands such as Factor VII and X, γδ T-cells, plasmodium falciparum erythrocyte membrane protein 1, and Secretory group V Phospholipases A2, facilitating ligand-specific functions. The functions of EPCR can also be regulated by soluble (s)EPCR that competes for the binding sites of membrane-bound (m)EPCR. sEPCR is created when mEPCR is shed from the cell surface. The propensity of shedding alters depending on the genetic haplotype of the EPCR gene that an individual may possess. EPCR plays an active role in normal homeostasis, anti-coagulation pathways, inflammation, and cell stemness. Due to these properties, EPCR is considered a potential effector/mediator of inflammatory diseases. Rheumatic diseases such as rheumatoid arthritis and systemic lupus erythematosus are autoimmune/inflammatory conditions that are associated with elevated EPCR levels and disease activity, potentially driven by EPCR. This review highlights the functions of EPCR and its contribution to rheumatic diseases.

EPCR deficiency ameliorates inflammatory arthritis in mice by suppressing the activation and migration of T cells and dendritic cells

OBJECTIVES

Endothelial protein C receptor (EPCR) is highly expressed in synovial tissues of patients with RA, but the function of this receptor remains unknown in RA. This study investigated the effect of EPCR on the onset and development of inflammatory arthritis and its underlying mechanisms.

METHODS

CIA was induced in EPCR gene knockout (KO) and matched wild-type (WT) mice. The onset and development of arthritis was monitored clinically and histologically. T cells, dendritic cells (DCs), EPCR and cytokines from EPCR KO and WT mice, RA patients and healthy controls (HCs) were detected by flow cytometry and ELISA.

RESULTS

EPCR KO mice displayed >40% lower arthritis incidence and 50% less disease severity than WT mice. EPCR KO mice also had significantly fewer Th1/Th17 cells in synovial tissues with more DCs in circulation. Lymph nodes and synovial CD4 T cells from EPCR KO mice expressed fewer chemokine receptors CXCR3, CXCR5 and CCR6 than WT mice. In vitro, EPCR KO spleen cells contained fewer Th1 and more Th2 and Th17 cells than WT and, in concordance, blocking EPCR in WT cells stimulated Th2 and Th17 cells. DCs generated from EPCR KO bone marrow were less mature and produced less MMP-9. Circulating T cells from RA patients expressed higher levels of EPCR than HC cells; blocking EPCR stimulated Th2 and Treg cells in vitro.

CONCLUSION

Deficiency of EPCR ameliorates arthritis in CIA via inhibition of the activation and migration of pathogenic Th cells and DCs. Targeting EPCR may constitute a novel strategy for future RA treatment.

Hyaladherins May be Implicated in Alcohol-Induced Susceptibility to Bacterial Pneumonia

Although the epidemiology of bacterial pneumonia and excessive alcohol use is well established, the mechanisms by which alcohol induces risk of pneumonia are less clear. Patterns of alcohol misuse, termed alcohol use disorders (AUD), affect about 15 million people in the United States. Compared to otherwise healthy individuals, AUD increase the risk of respiratory infections and acute respiratory distress syndrome (ARDS) by 2-4-fold. Levels and fragmentation of hyaluronic acid (HA), an extracellular glycosaminoglycan of variable molecular weight, are increased in chronic respiratory diseases, including ARDS. HA is largely involved in immune-assisted wound repair and cell migration. Levels of fragmented, low molecular weight HA are increased during inflammation and decrease concomitant with leukocyte levels following injury. In chronic respiratory diseases, levels of fragmented HA and leukocytes remain elevated, inflammation persists, and respiratory infections are not cleared efficiently, suggesting a possible pathological mechanism for prolonged bacterial pneumonia. However, the role of HA in alcohol-induced immune dysfunction is largely unknown. This mini literature review provides insights into understanding the role of HA signaling in host immune defense following excessive alcohol use. Potential therapeutic strategies to mitigate alcohol-induced immune suppression in bacterial pneumonia and HA dysregulation are also discussed.

Relationship between serum soluble endothelial protein C receptor level and COVID-19 findings

Coronavirus-related disease-2019 (COVID-19)-associated coagulopathy presents predominantly with thrombosis and leads to complications in close association with inflammatory process. Soluble endothelial protein C receptor (sEPCR), which is the soluble form of EPCR, reduces the anticoagulant and anti-inflammatory activity of activated protein C. The purpose of this study is to investigate the relationship between sEPCR and the laboratory parameters and thorax computed tomography (CT) findings in the course of COVID-19. Twenty-five laboratory-confirmed [reverse transcription-quantitative polimerase chain reaction (RT-qPCR) positive] and 24 clinically diagnosed (RT-qPCR negative) COVID-19 patients were enrolled in the study. Blood specimens were collected for sEPCR and haematological and biochemical parameter measurement. Thorax CT was performed to detect COVID-19 findings. These parameters from RT-qPCR positive and negative patients were then compared. Although there was no difference between the groups in terms of symptoms, the time between the onset of symptoms and the admission time was shorter in RT-qPCR positive group (P = 0.000). sEPCR levels were significantly higher in the RT-qPCR positive group (P = 0.011). Patients with ground-glass opacity and bilateral involvement on thorax CT have higher serum sEPCR levels (P = 0.012 and 0.043, respectively). This study has shown for the first time that serum sEPCR levels, which is a member of coagulation cascade and has also been reported to be associated with inflammation, is higher in patients with positive RT-qPCR test and patients with GGO or bilateral involvement on thorax CT regardless of the PCR result.

Endothelial Cell Protein C Receptor Deficiency Attenuates Streptococcus pneumoniae-induced Pleural Fibrosis

Streptococcus pneumoniae is the leading cause of hospital community-acquired pneumonia. Patients with pneumococcal pneumonia may develop complicated parapneumonic effusions or empyema that can lead to pleural organization and subsequent fibrosis. The pathogenesis of pleural organization and scarification involves complex interactions between the components of the immune system, coagulation, and fibrinolysis. EPCR (endothelial protein C receptor) is a critical component of the protein C anticoagulant pathway. The present study was performed to evaluate the role of EPCR in the pathogenesis of S. pneumoniae infection-induced pleural thickening and fibrosis. Our studies show that the pleural mesothelium expresses EPCR. Intrapleural instillation of S. pneumoniae impairs lung compliance and lung volume in wild-type and EPCR-overexpressing mice but not in EPCR-deficient mice. Intrapleural S. pneumoniae infection induces pleural thickening in wild-type mice. Pleural thickening is more pronounced in EPCR-overexpressing mice, whereas it is reduced in EPCR-deficient mice. Markers of mesomesenchymal transition are increased in the visceral pleura of S. pneumoniae-infected wild-type and EPCR-overexpressing mice but not in EPCR-deficient mice. The lungs of wild-type and EPCR-overexpressing mice administered intrapleural S. pneumoniae showed increased infiltration of macrophages and neutrophils, which was significantly reduced in EPCR-deficient mice. An analysis of bacterial burden in the pleural lavage, the lungs, and blood revealed a significantly lower bacterial burden in EPCR-deficient mice compared with wild-type and EPCR-overexpressing mice. Overall, our data provide strong evidence that EPCR deficiency protects against S. pneumoniae infection-induced impairment of lung function and pleural remodeling.

Impact of thrombosis on pulmonary endothelial injury and repair following sepsis

The prevailing morbidity and mortality in sepsis are largely due to multiple organ dysfunction (MOD), most commonly lung injury, as well as renal and cardiac dysfunction. Despite recent advances in defining many aspects of the pathogenesis of sepsis-related MOD, including acute respiratory distress syndrome (ARDS), there are currently no effective pharmacological or cell-based treatments for the disease. Human and animal studies have shown that pulmonary thrombosis is common in sepsis-induced ARDS, and preclinical studies have shown that anticoagulation may improve outcome following sepsis challenge. The potential beneficial effect of anticoagulation on outcome is unconvincing in clinical studies, however, and these discrepancies may arise from the multiple and sometimes opposing actions of thrombosis on the pulmonary endothelium following sepsis. It has been suggested, for example, that mild pulmonary thrombosis prevents escape of bacterial infection into the circulation, while severe thrombosis causes hypoxia and results in pulmonary endothelial damage. Evidence from both human and animal studies has demonstrated the key role of microvascular leakage in determining the outcome of sepsis. In this review, we describe thrombosis-dependent mechanisms that regulate pulmonary endothelial injury and repair following sepsis, including activation of the coagulation cascade by tissue factor and stimulation of vascular repair by hypoxia-inducible factors. Targeting such mechanisms through anticoagulant, anti-inflammatory, and reparative methods may represent a novel approach for the treatment of septic patients.

Increased Von Willebrand factor, decreased ADAMTS13 and thrombocytopenia in melioidosis

BACKGROUND

Melioidosis, caused by bioterror treat agent Burkholderia pseudomallei, is an important cause of community-acquired Gram-negative sepsis in Southeast Asia and Northern Australia. New insights into the pathogenesis of melioidosis may help improve treatment and decrease mortality rates from this dreadful disease. We hypothesized that changes in Von Willebrand factor (VWF) function should occur in melioidosis, based on the presence of endothelial stimulation by endotoxin, pro-inflammatory cytokines and thrombin in melioidosis, and investigated whether this impacted on outcome.

METHODS/PRINCIPAL FINDINGS

We recruited 52 controls and 34 culture-confirmed melioidosis patients at Sappasithiprasong Hospital in Ubon Ratchathani, Thailand. All subjects were diabetic. Platelet counts in melioidosis patients were lower compared to controls (p = 0.0001) and correlated with mortality (p = 0.02). VWF antigen levels were higher in patients (geometric mean, 478 U/dl) compared to controls (166 U/dL, p<0.0001). The high levels of VWF in melioidosis appeared to be due to increased endothelial stimulation (VWF propeptide levels were elevated, p<0.0001) and reduced clearance (ADAMTS13 reduction, p<0.0001). However, VWF antigen levels did not correlate with platelet counts implying that thrombocytopenia in acute melioidosis has an alternative cause.

CONCLUSIONS/SIGNIFICANCE

Thrombocytopenia is a key feature of melioidosis and is correlated with mortality. Additionally, excess VWF and ADAMTS13 deficiency are features of acute melioidosis, but are not the primary drivers of thrombocytopenia in melioidosis. Further studies on the role of thrombocytopenia in B. pseudomallei infection are needed.

Endothelial protein C receptor polymorphisms and risk of sepsis in a Chinese population

Objective

To examine the potential relationship of EPCR polymorphisms and the risk of sepsis in a Chinese population.

Methods

Snapshot SNP genotyping assays and DNA sequencing methods were used to detect polymorphisms of the EPCR gene, rs2069948C/T (2532C/T) and rs867186A/G (6936A/G), in 64 patients with sepsis and in 113 controls. Soluble EPCR (sEPCR) was measured by ELISA.

Results

There were significant differences in the allele and genotype frequencies of EPCR gene rs2069948C/T and allele frequencies of rs867186A/G between male and female patients and controls. Females carrying rs2069948 C/T genotype or T allele and males carrying rs867186 A allele were associated with a significantly increased risk of sepsis. Plasma sEPCR levels of sepsis patients were higher than controls and showed no correlation with EPCR gene polymorphisms.

Conclusions

EPCR polymorphisms may be associated with increased risk of sepsis, but this has no effect on the release of sEPCR in patients with sepsis.

The endothelial protein C receptor rs867186-GG genotype is associated with increased soluble EPCR and could mediate protection against severe malaria

The endothelial protein C receptor (EPCR) appears to play an important role in Plasmodium falciparum endothelial cell binding in severe malaria (SM). Despite consistent findings of elevated soluble EPCR (sEPCR) in other infectious diseases, field studies to date have provided conflicting data about the role of EPCR in SM. To better define this role, we performed genotyping for the rs867186-G variant, associated with increased sEPCR levels, and measured sEPCR levels in two prospective studies of Ugandan children designed to understand immunologic and genetic factors associated with neurocognitive deficits in SM including 551 SM children, 71 uncomplicated malaria (UM) and 172 healthy community children (CC). The rs867186-GG genotype was more frequent in CC (4.1%) than SM (0.6%, P = 0.002). The rs867186-G variant was associated with increased sEPCR levels and sEPCR was lower in children with SM than CC (P < 0.001). Among SM children, those who had a second SM episode showed a trend toward lower plasma sEPCR both at initial admission and at 6-month follow-up compared to those without repeated SM (P = 0.06 for both). The study findings support a role for sEPCR in severe malaria pathogenesis and emphasize a distinct role of sEPCR in malaria as compared to other infectious diseases.

Causes and consequences of coagulation activation in sepsis: an evolutionary medicine perspective

BACKGROUND

Coagulation and innate immunity have been linked together for at least 450 million years of evolution. Sepsis, one of the world's leading causes of death, is probably the condition in which this evolutionary link is more evident. However, the biological and the clinical relevance of this association have only recently gained the attention of the scientific community.

DISCUSSION

During sepsis, the host response to a pathogen is invariably associated with coagulation activation. For several years, coagulation activation has been solely regarded as a mechanism of tissue damage, a concept that led to several clinical trials of anticoagulant agents for sepsis. More recently, this paradigm has been challenged by the failure of these clinical trials, and by a growing bulk of evidence supporting the concept that coagulation activation is beneficial for pathogen clearance. In this article we discuss recent basic and clinical data that point to a more balanced view of the detrimental and beneficial consequences of coagulation activation in sepsis. Reappraisal of the association between coagulation and immune activation from an evolutionary medicine perspective offers a unique opportunity to gain new insights about the pathogenesis of sepsis, paving the way to more successful approaches in both basic and clinical research in this field.

The effect of plasma-derived activated protein C on leukocyte cell-death and vascular endothelial damage

INTRODUCTION

The role of leukocyte and its death in the progression in inflammation attracts attention nowadays. The purpose of this study is to examine the effects of activated protein C (APC) on leucocyte cell death and vascular endothelial damage in sepsis.

METHODS

Wistar rats were infused with lipopolysaccharide (8.0mg/kg) concomitantly with either a low dose (0.5mg/kg), a high dose (5.0mg/kg) of plasma-derived APC or albumin. One and 3hours after the injections, the mesenteric microcirculation was observed by intravital microscopy. The serum levels of nucleosome and High Mobility Group Box 1 (HMGB1) were measured in each group. In another series, cultured leukocyte cell-death in the medium supplemented with serum obtained from each group was examined in vitro.

RESULTS

Microcirculatory disturbance was significantly suppressed in both the high-dose and low-dose groups compared to the control group (P<0.01, 0.05, respectively). The bleeding area was significantly increased in the control and high-dose groups (P<0.05, 0.01, respectively). Serum levels of cell death markers such as nucleosome and HMGB1 were significantly decreased in the treatment groups (P<0.01), and the protective effect was more pronounced in high-dose group. Cell death suppression was most prominent in high-dose group and the formation of neutrophil extracellular traps (NETs) was significantly suppressed in the treatment groups.

CONCLUSION

Low-dose plasma-derived APC exerted protective effects on the microcirculation without increasing the risk of bleeding. The protective effect against leukocyte cell death and the suppressive effect on NETs formation of APC might be related to its beneficial effects.

The coagulation system in melioidosis: from pathogenesis to new treatment strategies

Melioidosis, caused by the Gram-negative bacterium Burkholderia pseudomallei, is a dreadful disease common in South-East Asia and Northern Australia and is characterized by chronic suppurative lesions and pneumonia. Melioidosis may evolve into severe sepsis with multi-organ failure with high mortalities, despite proper antibiotic therapy. Besides activation of a strong pro-inflammatory host response, the coagulation system plays an important role during melioidosis, which is thought to be host-protective. In particular, a procoagulant state together with downregulation of anticoagulant pathways and activation of fibrinolysis are present, all closely interrelated with parameters of inflammation. This review presents an overview of recent studies in which the role of coagulation, anti-coagulation and fibrinolysis during melioidosis was investigated both in patients and in experimental settings.

The coagulation system and its function in early immune defense

Blood coagulation has a Janus-faced role in infectious diseases. When systemically activated, it can cause serious complications associated with high morbidity and mortality. However, coagulation is also part of the innate immune system and its local activation has been found to play an important role in the early host response to infection. Though the latter aspect has been less investigated, phylogenetic studies have shown that many factors involved in coagulation have ancestral origins which are often combined with anti-microbial features. This review gives a general overview about the most recent advances in this area of research also referred to as immunothrombosis.

The endothelial protein C receptor impairs the antibacterial response in murine pneumococcal pneumonia and sepsis

Pneumococcal pneumonia is a frequent cause of gram-positive sepsis and has a high mortality. The endothelial protein C receptor (EPCR) has been implicated in both the activation of protein C (PC) and the anti-inflammatory actions of activated (A)PC. The aim of this study was to determine the role of the EPCR in murine pneumococcal pneumonia and sepsis. Wild-type (WT), EPCR knockout (KO) and Tie2-EPCR mice, which overexpress EPCR on the endothelium, were infected intranasally (pneumonia) or intravenously (sepsis) with viable Streptococcus pneumoniae and euthanised at 24 or 48 hours after initiation of the infection for analyses. Pneumonia did not alter constitutive EPCR expression on pulmonary endothelium but was associated with an influx of EPCR positive neutrophils into lung tissue. In pneumococcal pneumonia EPCR KO mice demonstrated diminished bacterial growth in the lungs and dissemination to spleen and liver, reduced neutrophil recruitment to the lungs and a mitigated inflammatory response. Moreover, EPCR KO mice displayed enhanced activation of coagulation in the early phase of disease. Correspondingly, in pneumococcal sepsis EPCR KO mice showed reduced bacterial growth in lung and liver and attenuated cytokine release. Conversely, EPCR-overexpressing mice displayed higher bacterial outgrowth in lung, blood, spleen and liver in pneumococcal sepsis. In conclusion, EPCR impairs antibacterial defense in both pneumococcal pneumonia and sepsis, which is associated with an enhanced pro-inflammatory response.