α-Enolase Causes Proinflammatory Activation of Pulmonary Microvascular Endothelial Cells and Primes Neutrophils Through Plasmin Activation of Protease-Activated Receptor 2

Early posttraumatic brain injury tranexamic acid prevents blood-brain barrier hyperpermeability and improves surrogates of neuroclinical recovery

BACKGROUND

Tranexamic acid (TXA) given early, but not late, after traumatic brain injury (TBI) appears to improve survival. This may be partly related to TXA-driven profibrinolysis and increased leukocyte (LEU)-mediated inflammation when administered late post-injury. We hypothesized that early TXA (1 hour post-TBI), blunts penumbral, blood-brain barrier (BBB) leukocyte-endothelial cell (LEU-EC) interactions and microvascular permeability, in vivo when compared with late administration (24 hours post-TBI).

METHODS

CD1 male mice (n = 35) were randomized to severe TBI (injury by controlled cortical impact; injury: velocity, 6 m/s; depth, 1 mm; diameter, 3 mm) or sham craniotomy followed by intravenous saline (placebo) at 1 hour, or TXA (30 mg/kg) at 1 hour or 24 hours. At 48 hours, in vivo pial intravital microscopy visualized live penumbral LEU-EC interactions and BBB microvascular fluorescent albumin leakage. Neuroclinical recovery was assessed by the Garcia Neurological Test (motor, sensory, reflex, and balance assessments) and body weight loss recovery at 1 and 2 days after injury. Analysis of variance with Bonferroni correction assessed intergroup differences ( p < 0.05).

RESULTS

One-hour, but not 24-hour, TXA improved Garcia Neurological Test performance on day 1 post-TBI compared with placebo. Both 1 hour and 24 hours TXA similarly improved day 1 weight loss recovery, but only 1 hour TXA significantly improved weight loss recovery on day 2 compared with placebo ( p = 0.04). No intergroup differences were found in LEU rolling or adhesion between injured animal groups. Compared with untreated injured animals, only TXA at 1 hour reduced BBB permeability.

CONCLUSION

Only early post-TBI TXA consistently improves murine neurological recovery. Tranexamic acid preserves BBB integrity but only when administered early. This effect appears independent of LEU-EC interactions and demonstrates a time-sensitive effect that supports only early TXA administration.

Protease-activated receptor-2: Role in asthma pathogenesis and utility as a biomarker of disease severity

PAR₂, a receptor activated by serine proteases, has primarily pro-inflammatory roles in the airways and may play a role in asthma pathogenesis. PAR₂ exerts its effects in the lungs through activation of a variety of airway cells, but also activation of circulating immune cells. There is evidence that PAR₂ expression increases in asthma and other inflammatory diseases, although the regulation of PAR₂ expression is not fully understood. Here we review the available literature on the potential role of PAR₂ in asthma pathogenesis and propose a model of PAR₂-mediated development of allergic sensitization. We also propose, based on our previous work, that PAR₂ expression on peripheral blood monocyte subsets has the potential to serve as a biomarker of asthma severity and/or control.

The α-globin chain of hemoglobin potentiates tissue plasminogen activator induced hyperfibrinolysis in vitro

BACKGROUND

Severe injury predisposes patients to trauma-induced coagulopathy, which may be subdivided by the state of fibrinolysis. Systemic hyperfibrinolysis (HF) occurs in approximately 25% of these patients with mortality as high as 70%. Severe injury also causes the release of numerous intracellular proteins, which may affect coagulation, one of which is hemoglobin, and hemoglobin substitutes induce HF in vitro. We hypothesize that the α-globin chain of hemoglobin potentiates HF in vitro by augmenting plasmin activity.

METHODS

Proteomic analysis was completed on a pilot study of 30 injured patients before blood component resuscitation, stratified by their state of fibrinolysis, plus 10 healthy controls. Different concentrations of intact hemoglobin A, the α- and β-globin chains, or normal saline (controls) were added to whole blood, and tissue plasminogen activator (tPA)-challenged thrombelastography was used to assess the degree of fibrinolysis. Interactions with plasminogen (PLG) were evaluated using surface plasmon resonance. Tissue plasminogen activator-induced plasmin activity was evaluated in the presence of the α-globin chain.

RESULTS

Only the α- and β-globin chains increased in HF patients (p < 0.01). The α-globin chain but not hemoglobin A or the β-globin chain decreased the reaction time and significantly increased lysis time 30 on citrated native thrombelastographies (p < 0.05). The PLG and α-globin chain had interaction kinetics similar to tPA:PLG, and the α-globin chain increased tPA-induced plasmin activity.

CONCLUSIONS

The α-globin chain caused HF in vitro by binding to PLG and augmenting plasmin activity and may represent a circulating "moonlighting" mediator released by the tissue damage and hemorrhagic shock inherent to severe injury.

LEVEL OF EVIDENCE

Prognostic, level III.

Plasminogen activator receptor assemblies in cell signaling, innate immunity, and inflammation

Tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) are serine proteases and major activators of fibrinolysis in mammalian systems. Because fibrinolysis is an essential component of the response to tissue injury, diverse cells, including cells that participate in the response to injury, have evolved receptor systems to detect tPA and uPA and initiate appropriate cell-signaling responses. Formation of functional receptor systems for the plasminogen activators requires assembly of diverse plasma membrane proteins, including but not limited to: the urokinase receptor (uPAR); integrins; N-formyl peptide receptor-2 (FPR2), receptor tyrosine kinases (RTKs), the N-methyl-d-aspartate receptor (NMDA-R), and low-density lipoprotein receptor-related protein-1 (LRP1). The cell-signaling responses elicited by tPA and uPA impact diverse aspects of cell physiology. This review describes rapidly evolving knowledge regarding the structure and function of plasminogen activator receptor assemblies. How these receptor assemblies regulate innate immunity and inflammation is then considered.

Plasmin improves blood-gas barrier function in oedematous lungs by cleaving epithelial sodium channels

BACKGROUND AND PURPOSE

Lung oedema in association with suppressed fibrinolysis is a hallmark of lung injury. Here, we have tested whether plasmin cleaves epithelial sodium channels (ENaC) to resolve lung oedema fluid.

EXPERIMENTAL APPROACH

Human lungs and airway acid-instilled mice were used for analysing fluid resolution. In silico prediction, mutagenesis, Xenopus oocytes, immunoblotting, voltage clamp, mass spectrometry, and protein docking were combined for identifying plasmin cleavage sites.

KEY RESULTS

Plasmin improved lung fluid resolution in both human lungs ex vivo and injured mice. Plasmin activated αβγENaC channels in oocytes in a time-dependent manner. Deletion of four consensus proteolysis tracts (αΔ432-444, γΔ131-138, γΔ178-193, and γΔ410-422) eliminated plasmin-induced activation significantly. Further, immunoblotting assays identified 7 cleavage sites (K126, R135, K136, R153, K168, R178, K179) for plasmin to trim both furin-cleaved C-terminal fragments and full-length human γENaC proteins. In addition, 9 new sites (R122, R137, R138, K150, K170, R172, R180, K181, K189) in synthesized peptides were found to be cleaved by plasmin. These cleavage sites were located in the finger and the thumb, particularly the GRIP domain of human ENaC 3D model composed of two proteolytic centres for plasmin. Novel uncleaved sites beyond the GRIP domain in both α and γ subunits were identified to interrupt the plasmin cleavage-induced conformational change in ENaC channel complexes. Additionally, plasmin could regulate ENaC activity via the G protein signal.

CONCLUSION AND IMPLICATIONS

Plasmin can cleave ENaC to improve blood-gas exchange by resolving oedema fluid and could be a potent therapy for oedematous lungs.

Proteomic profiling of proteins in the dorsal horn of the spinal cord in dairy cows with chronic lameness

Chronic lameness affects bovine welfare and has a negative economic impact in dairy industry. Moreover, due to the translational gap between traditional pain models and new drugs development for treating chronic pain states, naturally occurring painful diseases could be a potential translational tool for chronic pain research. We therefore employed liquid chromatography tandem mass spectrometry (LC-MS/MS) to stablish the proteomic profile of the spinal cord samples from lumbar segments (L2-L4) of chronic lame dairy cows. Data were validated and quantified through software tool (Scaffold® v 4.0) using output data from two search engines (SEQUEST® and X-Tandem®). Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) analysis was performed to detect proteins interactions. LC-MS/MS identified a total amount of 177 proteins; of which 129 proteins were able to be quantified. Lame cows showed a strong upregulation of interacting proteins with chaperone and stress functions such as Hsp70 (p < 0.006), Hsc70 (p < 0.0079), Hsp90 (p < 0.015), STIP (p > 0.0018) and Grp78 (p <0.0068), and interacting proteins associated to glycolytic pathway such as; γ-enolase (p < 0.0095), α-enolase (p < 0.013) and hexokinase-1 (p < 0.028). It was not possible to establish a clear network of interaction in several upregulated proteins in lame cows. Non-interacting proteins were mainly associated to redox process and cytoskeletal organization. The most relevant down regulated protein in lame cows was myelin basic protein (MBP) (p < 0.02). Chronic inflammatory lameness in cows is associated to increased expression of stress proteins with chaperone, metabolism, redox and structural functions. A state of endoplasmic reticulum stress and unfolded protein response (UPR) might explain the changes in protein expression in lame cows; however, further studies need to be performed in order to confirm these findings.

Fibrinolysis protease receptors promote activation of astrocytes to express pro-inflammatory cytokines

Background

Astrocytes contribute to the crosstalk that generates chronic neuro-inflammation in neurological diseases; however, compared with microglia, astrocytes respond to a more limited continuum of innate immune system stimulants. Recent studies suggest that the fibrinolysis system may regulate inflammation. The goal of this study was to test whether fibrinolysis system components activate astrocytes and if so, elucidate the responsible biochemical pathway.

Methods

Primary cultures of astrocytes and microglia were prepared from neonatal mouse brains. The ability of purified fibrinolysis system proteins to elicit a pro-inflammatory response was determined by measuring expression of the mRNAs encoding tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and chemokine (C-C motif) ligand 2 (CCL2). IκBα phosphorylation also was measured. Plasminogen activation in association with cells was detected by chromogenic substrate hydrolysis. The activity of specific receptors was tested using neutralizing antibodies and reagents.

Results

Astrocytes expressed pro-inflammatory cytokines when treated with plasminogen but not when treated with agonists for Toll-like Receptor-4 (TLR4), TLR2, or TLR9. Microglia also expressed pro-inflammatory cytokines in response to plasminogen; however, in these cells, the response was observed only when tissue-type plasminogen activator (tPA) was added to activate plasminogen. In astrocytes, endogenously produced urokinase-type plasminogen activator (uPA) converted plasminogen into plasmin in the absence of tPA. Plasminogen activation was dependent on the plasminogen receptor, α-enolase, and the uPA receptor, uPAR. Although uPAR is capable of directly activating cell-signaling, the receptor responsible for cytokine expression and IκBα phosphorylation response to plasmin was Protease-activated Receptor-1 (PAR-1). The pathway, by which plasminogen induced astrocyte activation, was blocked by inhibiting any one of the three receptors implicated in this pathway with reagents such as εACA, α-enolase-specific antibody, uPAR-specific antibody, the uPA amino terminal fragment, or a pharmacologic PAR-1 inhibitor.

Conclusions

Plasminogen may activate astrocytes for pro-inflammatory cytokine expression through the concerted action of at least three distinct fibrinolysis protease receptors. The pathway is dependent on uPA to activate plasminogen, which is expressed endogenously by astrocytes in culture but also may be provided by other cells in the astrocytic cell microenvironment in the CNS.

Plasmin-mediated fibrinolysis enables macrophage migration in a murine model of inflammation

Efficient migration of macrophages to sites of inflammation requires cell surface-bound plasmin(ogen). Here, we investigated the mechanisms underlying the deficits of plasmin(ogen)-mediated macrophage migration in 2 models: murine thioglycollate-induced peritonitis and in vitro macrophage migration. As previously reported, macrophage migration into the peritoneal cavity of mice in response to thioglycollate was significantly impaired in the absence of plasminogen. Fibrin(ogen) deposition was noted in the peritoneal cavity in response to thioglycollate, with a significant increase in fibrin(ogen) in the plasminogen-deficient mice. Interestingly, macrophage migration was restored in plasminogen-deficient mice by simultaneous imposition of fibrinogen deficiency. Consistent with this in vivo finding, chemotactic migration of cultured macrophages through a fibrin matrix did not occur in the absence of plasminogen. The macrophage requirement for plasmin-mediated fibrinolysis, both in vivo and in vitro, was negated by deletion of the major myeloid integrin α_Mβ₂-binding motif on the γ chain of fibrin(ogen). The study identifies a critical role of fibrinolysis in macrophage migration, presumably through the alleviation of migratory constraints imposed by the interaction of leukocytes with fibrin(ogen) through the integrin α_Mβ₂ receptor.

Tissue-type plasminogen activator neutralizes LPS but not protease-activated receptor-mediated inflammatory responses to plasmin

Tissue-type plasminogen activator (tPA) activates fibrinolysis and also suppresses innate immune system responses to LPS in bone marrow-derived macrophages (BMDMs) and in vivo in mice. The objective of this study was to assess the activity of tPA as a regulator of macrophage physiology in the presence of plasmin. Enzymatically active and enzymatically inactive (EI) tPA appeared to comprehensively block the response to LPS in BMDMs, including expression of proinflammatory cytokines such as TNF-α and IL-1β and anti-inflammatory cytokines such as IL-10 and IL-1 receptor antagonist. The activity of EI-tPA as an LPS response modifier was conserved in the presence of plasminogen. By contrast, in BMDMs treated with tPA and plasminogen or preactivated plasmin, in the presence or absence of LPS, increased proinflammatory cytokine expression was observed and tPA failed to reverse the response. Plasmin independently activated NF-κB, ERK1/2, c-Jun N-terminal kinase, and p38 mitogen-activated protein kinase in BMDMs, which is characteristic of proinflammatory stimuli. Plasmin-induced cytokine expression was blocked by ε-aminocaproic acid, aprotinin, and inhibitors of the known plasmin substrate, Protease-activated receptor-1 (PAR-1), but not by N-methyl-d-aspartate receptor inhibitor, which blocks the effects of tPA on macrophages. Cytokine expression by BMDMs treated with the PAR-1 agonist, TFLLR, was not inhibited by EI-tPA, possibly explaining why EI-tPA does not inhibit macrophage responses to plasmin and providing evidence for specificity in the ability of tPA to oppose proinflammatory stimuli. Regulation of innate immunity by the fibrinolysis system may reflect the nature of the stimulus and a balance between the potentially opposing activities of tPA and plasmin.

Schistosoma "Eggs-Iting" the Host: Granuloma Formation and Egg Excretion

Schistosomiasis is a major cause of morbidity in humans invoked by chronic infection with parasitic trematodes of the genus Schistosoma. Schistosomes have a complex life-cycle involving infections of an aquatic snail intermediate host and a definitive mammalian host. In humans, adult male and female worms lie within the vasculature. Here, they propagate and eggs are laid. These eggs must then be released from the host to continue the life cycle. Schistosoma mansoni and Schistosoma japonicum reside in the mesenteric circulation of the intestines with egg excreted in the feces. In contrast, S. haematobium are present in the venus plexus of the bladder, expelling eggs in the urine. In an impressive case of exploitation of the host immune system, this process of Schistosome “eggs-iting” the host is immune dependent. In this article, we review the formation of the egg granuloma and explore how S. mansoni eggs laid in vasculature must usurp immunity to induce regulated inflammation, to facilitate extravasation through the intestinal wall and to be expelled in the feces. We highlight the roles of immune cell populations, stromal factors, and egg secretions in the process of egg excretion to provide a comprehensive overview of the current state of knowledge regarding a vastly unexplored mechanism.

Hemorrhagic shock and tissue injury drive distinct plasma metabolome derangements in swine

BACKGROUND

Tissue injury and hemorrhagic shock induce significant systemic metabolic reprogramming in animal models and critically injured patients. Recent expansions of the classic concepts of metabolomic aberrations in tissue injury and hemorrhage opened the way for novel resuscitative interventions based on the observed abnormal metabolic demands. We hypothesize that metabolic demands and resulting metabolic signatures in pig plasma will vary in response to isolated or combined tissue injury and hemorrhagic shock.

METHODS

A total of 20 pigs underwent either isolated tissue injury, hemorrhagic shock, or combined tissue injury and hemorrhagic shock referenced to a sham protocol (n = 5/group). Plasma samples were analyzed by UHPLC-MS.

RESULTS

Hemorrhagic shock promoted a hypermetabolic state. Tissue injury alone dampened metabolic responses in comparison to sham and hemorrhagic shock, and attenuated the hypermetabolic state triggered by shock with respect to energy metabolism (glycolysis, glutaminolysis, and Krebs cycle). Tissue injury and hemorrhagic shock had a more pronounced effect on nitrogen metabolism (arginine, polyamines, and purine metabolism) than hemorrhagic shock alone.

CONCLUSION

Isolated or combined tissue injury and hemorrhagic shock result in distinct plasma metabolic signatures. These findings indicate that optimized resuscitative interventions in critically ill patients are possible based on identifying the severity of tissue injury and hemorrhage.

Supernatants and lipids from stored red blood cells activate pulmonary microvascular endothelium through the BLT2 receptor and protein kinase C activation

BACKGROUND

Although transfusion is a lifesaving intervention, it may be associated with significant morbidity in injured patients. We hypothesize that stored red blood cells (RBCs) induce proinflammatory activation of human pulmonary microvascular endothelial cells (HMVECs) resulting in neutrophil (PMN) adhesion and predisposition to acute lung injury (ALI).

STUDY DESIGN AND METHODS

Ten units of RBCs were collected; 50% (by weight) were leukoreduced (LR-RBCs) and the remainder was unmodified and stored in additive solution-5 (AS-5). An additional 10 units of RBCs were collected, leukoreduced, and stored in AS-3. HMVECs were incubated with [10%-40%]_FINAL of the supernatants on Day (D)1 to D42 of storage, lipid extracts, and purified lipids. Endothelial surface expression of intercellular adhesion molecule-1 (ICAM-1), interleukin (IL)-8 release, and PMN adhesion to HMVECs were measured. HMVEC signaling via the BLT2 receptor was evaluated. Supernatants and lipids were also employed as the first event in a two-event model of ALI.

RESULTS

The supernatants [10%-40%]_FINAL from D21 LR-RBCs and D42 RBCs and LR-RBCs and the lipids from D42 stored in AS-5 induced increased ICAM-1 surface expression on endothelium, IL-8 release, and PMN adhesion. In addition, the supernatants [20%-40%]_FINAL from D21 and D42 RBCs in AS-5 also increased endothelial surface expression of ICAM-1. D42 supernatants and lipids also caused coprecipitation of β-arrestin-1 with BLT2, protein kinase C (PKC)β_I , and PKCδ and served as the first event in a two-event rodent model of ALI.

CONCLUSION

Lipids that accumulate during RBC storage activate endothelium and predispose to ALI, which may explain some of the adverse events associated with the transfusion of critically injured patients.

Targeting Enolase in Reducing Secondary Damage in Acute Spinal Cord Injury in Rats

Spinal cord injury (SCI) is a complex debilitating condition leading to permanent life-long neurological deficits. The complexity of SCI suggests that a concerted multi-targeted therapeutic approach is warranted to optimally improve function. Damage to spinal cord is complicated by an increased detrimental response from secondary injury factors mediated by activated glial cells and infiltrating macrophages. While elevation of enolase especially neuron specific enolase (NSE) in glial and neuronal cells is believed to trigger inflammatory cascades in acute SCI, alteration of NSE and its subsequent effects in acute SCI remains unknown. This study measured NSE expression levels and key inflammatory mediators after acute SCI and investigated the role of ENOblock, a novel small molecule inhibitor of enolase, in a male Sprague-Dawley (SD) rat SCI model. Serum NSE levels as well as cytokines/chemokines and metabolic factors were evaluated in injured animals following treatment with vehicle alone or ENOblock using Discovery assay. Spinal cord samples were also analyzed for NSE and MMPs 2 and 9 as well as glial markers by Western blotting. The results indicated a significant decrease in serum inflammatory cytokines/chemokines and NSE, alterations of metabolic factors and expression of MMPs in spinal cord tissues after treatment with ENOblock (100 µg/kg, twice). These results support the hypothesis that activation of glial cells and inflammation status can be modulated by regulation of NSE expression and activity. Analysis of SCI tissue samples by immunohistochemistry confirmed that ENOblock decreased gliosis which may have occurred through reduction of elevated NSE in rats. Overall, elevation of NSE is deleterious as it promotes extracellular degradation and production of inflammatory cytokines/chemokines and metabolic factors which activates glia and damages neurons. Thus, reduction of NSE by ENOblock may have potential therapeutic implications in acute SCI.

The accumulation of lipids and proteins during red blood cell storage: the roles of leucoreduction and experimental filtration

Pre-storage leucoreduction has been universally adopted in most developed countries in Asia, Europe and the Americas. It decreases febrile transfusion reactions, alloimmunisation to HLA antigens, cytomegalovirus exposure, the accumulation of a number of pro-inflammatory mediators in the supernatant, including the accumulation of platelet-and leucocyte-derived proteins and metabolites during routine storage. This review will highlight the lipids and proteins, biological response modifiers (BRMs) that accumulate, their clinical effects in transfused hosts, and methods of mitigation.

Neuron specific enolase: a promising therapeutic target in acute spinal cord injury

Enolase is a multifunctional protein, which is expressed abundantly in the cytosol. Upon stimulatory signals, enolase can traffic to cell surface and contribute to different pathologies including injury, autoimmunity, infection, inflammation, and cancer. Cell-surface expression of enolase is often detected on activated macrophages, microglia/macrophages, microglia, and astrocytes, promoting extracellular matrix degradation, production of pro-inflammatory cytokines/chemokines, and invasion of inflammatory cells in the sites of injury and inflammation. Inflammatory stimulation also induces translocation of enolase from the cytosolic pool to the cell surface where it can act as a plasminogen receptor and promote extracellular matrix degradation and tissue damage. Spinal cord injury (SCI) is a devastating debilitating condition characterized by progressive pathological changes including complex and evolving molecular cascades, and insights into the role of enolase in multiple inflammatory events have not yet been fully elucidated. Neuronal damage following SCI is associated with an elevation of neuron specific enolase (NSE), which is also known to play a role in the pathogenesis of hypoxic-ischemic brain injury. Thus, NSE is now considered as a biomarker in ischemic brain damage, and it has recently been suggested to be a biomarker in traumatic brain injury (TBI), stroke and anoxic encephalopathy after cardiac arrest and acute SCI as well. This review article gives an overview of the current basic research and clinical studies on the role of multifunctional enolase in neurotrauma, with a special emphasis on NSE in acute SCI.